GB2367859A

GB2367859A - Methods of operating i.c. engines having electrically controlled actuators for the inlet and/or exhaust valves

Info

Publication number: GB2367859A
Application number: GB0025049A
Authority: GB
Inventors: Donald Law
Original assignee: Lotus Cars Ltd
Current assignee: Lotus Cars Ltd
Priority date: 2000-10-12
Filing date: 2000-10-12
Publication date: 2002-04-17
Also published as: GB0025049D0

Abstract

In the methods one or more electrically controlled actuator(s) eg electro-hydraulic actuators (18,19; 21,22 - see Figure 1) is/are used to open and close an inlet and/or exhaust valve. In a first method the valves are controlled such that the compression ratio is lower than normal when the engine is cold. In a second method the exhaust valve is opened earlier than normal when a catalytic converter is cold. In a third method the valves are operated to reduce exhaust temperature when a catalytic converter overheats. In a fourth method a knock sensor is used and valve overlap is varied when knock is sensed to reduce pre-ignition. In a fifth aspect the inlet valve is used to throttle the engine. In a sixth method the valve operation is varied to suit driving style. In a seventh method a cylinder is deactivated by closing the valves with combusted gases trapped. In an eighth method, swirl and tumble of in-cylinder gases is varied by varying the valve operations. In a ninth method, the valve operation is controlled to provide engine braking.

Description

NOVEL METHODS OF OPERATING INTERNAL COMBUSTION ENGINES The present invention relates to novel methods of operating internal combustion engines.

In a conventional four-stroke internal combustion engine the combustion chamber is provided by a variable volume chamber defined between a piston and a cylinder in which the piston reciprocates. A flow of fuel/air mixture into the chamber is controlled typically by a poppet valve which is spring-biassed into its valve seat. Typically a cam on a rotating cam shaft engages a tappet which in turn engages the poppet valve and the opening and closing of the valve and the lift of the valve is controlled by the profile of the cam. The flow of combusted gases from the chamber is also typically controlled by an exhaust valve which is a poppet valve actuated by a cam on the rotating cam shaft.

The use of rotating cams to control valve motion has limitations. Very little flexibility is given and whilst it may be possible to vary valve motion by switching between different cams on the cam shaft, the degree of variation is limited. This has been recognised in the past and proposals have been made to replace cam actuated inlet and exhaust valves with inlet and exhaust valves actuated by electric actuators or electro-hydraulic actuators. The present invention takes this further by recognising that with valves actuated either electrically or electrohydraulically novel methods of operating internal combustion engines can be achieved.

The present invention provides in a first aspect a method of operating an internal combustion engine comprising : using a first electrically controlled actuator to open and close an inlet valve which controls admission of fresh charge into a variable volume combustion chamber; using a second electrically controlled actuator to open and close an exhaust valve which controls exhaust of combusted gases from the variable volume combustion chamber; and when the internal combustion engine is operating at a temperature below a normal engine operating temperature range in a period following starting of the engine, using the first and second electrically controlled actuators to open and close the inlet and exhaust valves in such a manner that charge compressed in the variable volume combustion chamber has a peak pressure which is less than peak pressures of charge compressed in the variable volume combustion chamber when the engine is operating in the normal temperature range.

In a first aspect of the invention the valve train is controlled to reduce the compression ratio in cold start conditions to minimise peak pressure so that the crevice volume containment of hydrocarbons is minimised and the pollutant levels drop. It is important in cold start conditions to ensure that the level of hydrocarbons exiting the combustion chamber is kept to a minimum, because any catalytic converter used with the engine will not be at operating temperature in cold start conditions.

Preferably the engine is operated using a four

stroke cycle and at engine temperatures below the normal operating temperature range the method comprises opening the exhaust valve during an initial part of the compression stroke. This is preferred when the engine uses gasoline direct injection so that the charge in the combustion chamber at the beginning of the compression stroke comprises purely air (or a mixture of air and retained exhaust gases). The fuel is not injected into the combustion chamber until later on in the compression stroke. In the method put forward by the invention the opening of the exhaust valve in the earlier part of the compression stroke would lead to part of the charge air being exhausted before compression of the remaining charge air is commenced. This would limit the peak pressure in the cylinder.

Alternatively a method is proposed in which the engine is operated using a four-stroke cycle and at temperatures below the normal operating temperature the method comprises the steps of closing the inlet valve at a point in the engine cycle delayed in comparison with the closing of the inlet valve at normal operating temperatures and keeping the inlet valve open in the initial part of the compression stroke. Again, this is a technique designed to limit the pressure in the cylinder. However, this technique is more suited to conditions where the charge admitted to the combustion chamber is a mixture of fuel and air and the engine does not have gasoline direct injection. In the proposed method some of the inducted charge of fuel/air mixture is expelled from the combustion chamber back into the inlet passage, so that the total mass of fuel and air compressed is reduced and thereby the peak pressure is reduced (in

comparison with normal operating conditions).

Another possibility is to operate the engine using a four-stroke cycle and at engine temperatures below the normal operating temperature range taking the step of closing the inlet valve earlier in the induction stroke than would be usual at normal operating temperatures. Once the inlet valve is closed the inducted charge will be expanded before it is subsequently compressed. The initial expansion of the inducted charge leads to a pressure at the commencement of the compression stroke which is lower than would be the case in normal operating conditions.

The reduced initial pressure at the start of the compression stroke leads to a reduced peak pressure.

In any of the methods of operation described above it is also preferable to open the exhaust valve earlier in the engine cycle than the exhaust valve would be opened when the engine is operating in its normal operating temperature range. Preferably the exhaust valve is opened before the end of the expansion stroke. By taking this step the combusted gas mixture which is exhausted during low engine temperature operating conditions is hotter than it would be if the exhaust valve did not open until the end of the expansion stroke. The hotter exhaust temperature facilitates catalyst light-off and therefore reduces pollutant release.

In a second aspect the present invention provides a method of operating an internal combustion engine comprising using an electrically controlled actuator to open and close an exhaust valve which controls exhaust of combusted gases from a variable volume

combustion chamber and passing the exhausted combusted gases through a catalytic converter before the exhausted combusted gases are passed to atmosphere wherein when the internal combustion engine is operating at a temperature below a normal engine operating temperature range in a period following starting of the engine, the method comprises the step of opening the exhaust valve to allow flow of combusted gases from the combustion chamber earlier in the cycle of the engine than allowed by the opening of the exhaust valve when the engine is operating at normal engine operating temperatures.

Preferably in the second aspect of the invention the engine is operated using a four-stroke cycle and at engine temperatures below the normal engine operating temperature range the method comprises the step of opening the exhaust valve prior to the end of the expansion stroke to allow hot combusted gases to be expelled to the catalytic converter to warm the catalytic converter.

In normal operating conditions, it is generally desired to keep the expansion stroke as long as possible to take maximum work out of the expanding gases. However, the applicant has realised that in cold start conditions this need can be outweighed by the need to receive catalyst light-off and this can be achieved by ensuring that the temperature of the gases exhausted from the combustion chamber is raised by an earlier opening of the exhaust valve.

Preferably in both aspects of the invention mentioned above the methods comprise additionally the steps of measuring the engine temperature using a

temperature sensor which generates an electrical signal indicative of sensed temperature ; using an electrical sensor to monitor progression of the engine through the combustion cycle thereof and to produce an electrical signal indicative of the position of the engine in the engine cycle; and using an electrical controller to process the engine position signal and the temperature signal to produce control signals for controlling each electrically controlled actuator in dependence on the engine position signal and the temperature signal.

In the preferred embodiment the timing of the opening of the inlet and exhaust valves is controlled by an electrical controller which takes notice of the temperature of the engine and varies the operating regime of the engine accordingly. The term"engine temperature"mentioned above should be taken to indicate temperature of the engine as a whole (e. g. by measuring temperature of oil or water in the engine) or as indicating temperature of a catalytic converter attached to the exhaust of the engine.

In a third aspect the present invention provides a method of operating an internal combustion engine comprising: using a first electrically actuator to open and close an inlet valve which controls admission of fresh charge into a variable volume combustion chamber; using a second electrically controlled actuator to open and close an exhaust valve which controls exhaust of combusted gases from the variable volume combustion chamber ; passing the exhausted combusted gases through a catalytic converter before the exhausted combusted

gases are passed to atmosphere ; monitoring temperature of the catalytic converter; and when the temperature of the catalytic converter reaches or exceeds a catalytic converter temperature threshold, varying opening and closing of the inlet and/or exhaust valve to reduce temperature of the exhausted combusted gases flowing from the variable volume combustion chamber.

The present invention has recognised that electrically operated valves give an opportunity for protection of catalytic converters which was not foreseen before. In order to protect the catalytic converter the engine operation is changed to reduce the temperature of the exhausted gases and thereby to lower the temperature of the catalytic converter.

Preferably in the method of the third aspect of the invention, the engine is operated using a fourstroke cycle and when the temperature of the catalytic converter reaches or exceeds the temperature threshold then the method comprises retarding opening of the exhaust valve to delay exhaust of combusted gases from the combustion chamber, the exhaust valve being opened later in the exhaust stroke than in normal operation of the engine. A later opening of the exhaust valve permits a longer period of cooling of the combusted gases before they are exhausted.

Alternatively in the method of the third aspect of the invention the engine is operated using a fourstroke cycle and when the temperature of the catalytic converter reaches or exceeds the temperature threshold then the method comprises retarding the closing of the

inlet valve and closing the inlet valve during an initial phase of the compression stroke and expelling previously inducted charge out of the combustion chamber past the inlet valve to an inlet passage. By doing this the total mass of fuel and air in the combustion chamber prior to ignition is reduced and therefore the temperature of the combusted gases is reduced.

In a further variant of the method of the third aspect of the invention the engine is again operated using a four-stroke cycle, but when the temperature of the catalytic converter reaches or exceeds the temperature threshold then the method comprises advancing of closing of the inlet valve and closing the inlet valve before the end of the induction stroke; and thereafter expanding the inducted charge before subsequent compression thereof in the compression stroke. The early closing of the inlet valve in the induction stroke leads to the inducted charge being expanded in the latter part of the induction stroke so that the pressure of the inducted gas at the beginning of the compression stroke is reduced from that of normal operating conditions and therefore the peak pressure of the combustion is reduced and the temperature of the exhausted gases is also reduced. Furthermore, the mass of charge available for ignition is reduced and this reduces the temperature of the combusted gases.

In a fourth aspect the present invention provides a method of operating a four-stroke spark ignition internal combustion engine comprising using a first electrically controlled actuator to open and close an inlet valve which controls admission of fresh charge

into a variable volume combustion chamber ; and using a second electrically controlled actuator to open and close an exhaust valve which controls exhaust of combusted gases from the variable volume combustion chamber; wherein the method also comprises: operating the engine in at least one operating regime such that in an engine cycle the inlet valve is opened before the exhaust valve is closed, whereby both the inlet and the exhaust valve are simultaneously opened for an overlap period; using a knock sensor to sense undesired preignition in the combustion chamber; and when the knock sensor senses undesired preignition, varying the duration of the overlap period during which both the inlet and exhaust valves are open in order to prevent further undesired preignition.

The applicant has realised that the use of electrically controlled actuators to open and close the inlet and exhaust valves permits control of preignition by the variation of the valve overlap period.

It is envisaged that the valve overlap period would be adjusted incrementally until such time as pre-ignition was no longer sensed by the knock sensor.

In a fifth aspect of the present invention there is provided a method of operating a four-stroke internal combustion engine comprising the steps of: using a first electrically controlled actuator to open and close an inlet valve which controls admission of fresh charge into a variable volume combustion chamber; and throttling the engine by controlling the opening

and closing of the inlet valve, wherein : the engine is throttled by limiting the mass of charge inducted into the cylinder by closing the inlet valve during an induction stroke prior to the end of the induction stroke; throttling is varied by varying how early in the induction stroke the inlet valve is closed, with throttling being increased by advancing the closure of the inlet valve and with throttling being reduced by retarding the closing of the inlet valve; and once the inlet valve is closed prior to the end of the induction stroke thereafter expanding the inducted charge prior to subsequent compression of the inducted charge during a compression stroke.

The present invention in a sixth aspect provides a method of operating a four-stroke internal combustion engine comprising: using a first electrically controlled actuator to open and close an inlet valve which controls admission of fresh charge into a variable volume combustion chamber; and throttling the engine by controlling the opening and closing of the inlet valve; wherein: the engine is throttled by allowing previously inducted charge to flow out of the combustion chamber during the compression stroke by keeping the inlet valve open during a part of the compression stroke; throttling is varied by varying how late in the compression stroke the inlet valve is closed, with throttling increased by retarding the closing of the inlet valve and throttling reduced by advancing the closing of the inlet valve; and charge expelled from the combustion chamber during the compression stroke flows out of the

combustion chamber past the inlet valve into an inlet passage for subsequent redelivery to the combustion chamber.

In a sixth aspect of the present invention the mass of charge in the combustion chamber at the time of ignition is reduced by keeping the inlet valve open longer than usual and allowing some charge to flow back out to the inlet passage.

Preferably the methods of the fifth and sixth aspects of the invention allow throttling of the engine to be achieved without use of a throttle to restrict flow of charge into the variable volume combustion chamber. It is envisaged that the throttling provided by control of the motion of the inlet valve will be more efficient than the throttling using, e. g. a butterfly valve in an inlet passage.

The main objective of throttle-less engine operation is to reduce engine fuel consumption and emissions through reduction in the pumping losses associated with an engine operating under part load. The conventional use of e. g. a butterfly valve to throttle flow of air into the induction system operates to the detriment of engine efficiency. Using control of inlet valve operation to control the output of the engine can provide a reduction in pumping losses.

In a seventh aspect the present invention provides a method of operating an internal combustion engine comprising: using a first electrically controlled actuator to open and close an inlet valve which controls admission of fresh charge into a variable volume combustion chamber;

using a second electrically controlled actuator to open and close an exhaust valve which controls exhaust of combusted gases from the variable volume combustion chamber; sensing a plurality of engine operating parameters and producing electrical signals indicative thereof; controlling operation of the first and second actuators using a controller to produce electrical control signals in dependence upon the electrical signals indicative of the sensed engine operating parameters; monitoring use of a throttle control by a driver of the vehicle and recording the history of manner of use of the throttle control; and adapting the operation of the first and second electrically controlled actuators to alter operation of the engine to optimise performance and/or efficiency of the engine having regard to the recorded history of manner of use of the throttle control.

The present invention provides a method in which the engine's performance characteristics are tuned to match the driver's style. This is achieved by monitoring the use of a throttle control by the driver, e. g. use of an accelerator pedal. The timing of the opening and closing of the inlet and exhaust valves in each engine cycle is controlled by an electrical controller and therefore the electrical controller has the ability to vary the valve timing throughout operation of the engine in order to optimise the efficiency of the engine.

In an eighth aspect, the present invention provides a method of controlling a four-stroke multi

cylinder internal combustion engine comprising : using electrically controlled actuator means to open and close all of the inlet and exhaust valves of at least one cylinder; when the engine is only part loaded de-activating the cylinder by using the electrically controlled actuator means to close all the inlet and exhaust valves of the said cylinder; and when loading of the engine is subsequently increased, re-activating the previously de-activated cylinder by recommencing cyclically opening and closing of the inlet and exhaust valves; wherein the said cylinder is only de-activated when full of combusted gases at the end of the expansion stroke, whereby the trapped combusted gases subsequently function as a gas spring; and the said cylinder is subsequently re-activated by opening of the exhaust valve (s) to allow flow of the trapped combusted gases from the combustion chamber during an exhaust stroke.

Preferably the method of the eighth aspect of the invention is used as part of a method in which combusted gases exhausted from the combustion chamber are passed through a catalytic converter before they are expelled to atmosphere and preferably one or more cylinders are deactivated when the engine is only partly loaded in order to make the activated cylinders run at higher loads so as to keep the temperature of the combusted gases high enough to ensure good operation of the catalytic converter.

The combusted gases trapped in the combustion chamber are compressed in each compression stroke, but the work put in to compressing the combusted gases is

largely returned during the subsequent expansion stroke. This method of deactivation is preferable to keeping the inlet and exhaust valves open or to opening and closing of the exhaust valves in a normal manner without introduction of fuel for combustion. In the latter case there will be pumping losses associated with deactivation, which are not present with the method of the present invention.

With the activated cylinders running at a much higher load (for a given total engine power) the tolerance of the active cylinders to exhaust gas recirculation is increased and the mean temperatures produced in the cylinder are higher. The higher temperatures have the effect of reducing hydrocarbon emissions by up to 16%, whilst the ability to continue running with high rates of exhaust gas recirculation permits greater dilution rates and therefore NO., reductions.

Preferably the method of the eighth aspect of the invention uses electrically controlled activation means which do not require power to keep the inlet and exhaust valves in their closed positions.

With the cylinder deactivation being achieved by commanding both valves not to open and with the actuators not requiring any power to keep the inlet and exhaust valves closed, the power consumption of the valve system is reduced, reducing parasitic demands on the engine in part-load conditions.

In a ninth aspect the present invention provides a method of operating an internal combustion engine comprising:

using a pair of electrically controlled actuators to open and close a pair of inlet valves which control admission of fresh charge into a single variable volume combustion chamber defined by a piston reciprocating in a cylinder, the charge being admitted to the combustion chamber via a pair of ports provided in a head of the cylinder and each inlet valve controlling admission of charge through one port; opening both inlet valves in a first engine cycle to cause the charge to be inducted through both ports in the cylinder head with the charge being given a first degree of swirl and a first degree of tumble; and opening only one of the inlet valves in a second engine cycle to force all of the charge to be inducted through only one inlet port with the charge being given a second degree of swirl higher than said first degree and with the charge being given a second degree of tumble lower than said first degree.

Swirl generation investigations involving direct injection compression ignition engines have shown that swirl is essential for adequate mixture formation within the combustion chamber. It is responsible for a marked effect on the reduction of smoke and particulate emissions along with improvements in fuel consumption. Through modification of in-cylinder swirl using valve port activation reductions in soot level, Nox emissions and fuel consumption are all possible.

Investigations involving four-stroke fuelinjected gasoline engines have led to the conclusion that fuel consumption and emissions can be reduced by increasing swirl generation in part-load conditions.

Swirl generation increases levels of turbulence within the combustion chamber resulting in increase in the rate of combustion and reduction in the delay period.

Preferably in the ninth aspect of the invention the length and duration of the opening of the inlet valves is varied with variations in engine speed and/or load in order to provide varying degrees of swirl and tumble of the charge in the combustion chamber.

The applicant has realised that the use of electrically controlled actuators to open and close the inlet and exhaust valves permits control of the levels of swirl and tumble so that the levels of swirl and tumble in the combustion chamber can be controlled to best suit the needs of the engine for particular speeds and loads.

Preferably in the method of the ninth aspect of the invention the method comprises additionally the steps of: using one or more electrically controlled actuators to open and close an exhaust valve or valves which control (s) exhaust of combusted gases from the variable volume combustion chamber; closing the exhaust valve or valves before the end of the exhaust stroke to trap combusted gases in the combustion chamber; and mixing the fresh charge with the trapped combusted gases prior to combustion.

Generation of high degrees of swirl in part load conditions can increase the tolerance of the combustion process to exhaust gas recirculation. This

improved toleration can be exploited in a reduction of NOx emissions through the increased dilution of the fuel/air charge with exhaust gases.

In a tenth aspect the present invention provides a method of operating a four-stroke internal combustion engine to provide engine braking comprising: using one or more electrically controlled actuators to open and close an exhaust valve or valves which control (s) exhaust of combusted gases from a variable volume combustion chamber; and interrupting normal operation of the engine during engine braking to operate the engine without ignition of fuel with the engine functioning as a compressor requiring input of power by taking steps including: opening the exhaust valve or valves at the end of what would be, in normal operation of the engine, a compression stroke or at the beginning of what would be, in normal operation of the engine, an expansion stroke, in order to release to atmosphere gases previously compressed in the combustion chamber during the compression stroke.

In a method of the invention, the engine is turned into a compressor and kinetic energy of e. g. a vehicle using the engine is input to the engine in order to compress gases in the compression stroke, this energy being released at the end of the compression stroke or at the beginning of the subsequent stroke by venting the compressed gases to atmosphere, so that the energy in the compressed gases is not returned to the engine.

Preferably in the tenth aspect of the invention the method comprises additionally using an electrically controlled actuator to open and close an inlet valve or valves which control (s) induction of fresh charge into the combustion chamber; and controlling lift of the inlet valve during an induction stroke to throttle induction of fresh charge into the combustion chamber whilst allowing sufficient mass of charge to be inducted for subsequent compression.

The use of an inlet valve controlled by an actuator provides an inlet valve which can function in a similar manner to e. g. a butterfly valve and throttle the charge inducted into the combustion chamber.

Preferably the method also comprises additionally opening the inlet valve during what would, in normal operation of the engine, be an expansion stroke to allow charge to be drawn into the combustion chamber; and delaying opening of the exhaust valve or valves to the end of what would, in normal operation of the engine, be an exhaust stroke whereby charge previously inducted into the combustion chamber is compressed during the stroke and then exhausted to atmosphere.

In the preferred method of operation, in every 3600 rotation of the engine, air is inducted into the combustion chamber, compressed and then the compressed gas released to atmosphere.

The applicant has realised that the use of exhaust valves which are opened and closed by electrically controlled actuators permits engine

braking to be achieved without the need for a throttle valve.

In an eleventh aspect the invention provides a method of operating a four-stroke internal combustion engine to provide engine braking comprising: using one or more electrically controlled actuators to open and close an inlet valve or valves which control (s) induction of fresh charge into the combustion chamber; interrupting normal operation of the engine during normal engine braking to operate the engine without additional fuel, with the engine functioning as a compressor requiring input of power, by taking steps including: opening the inlet valve or valves during what would, in normal operation of the engine, be an expansion stroke of the engine to allow charge to be drawn into the combustion chamber; and delaying opening of the exhaust valve or valves to the end of what would be, in normal operation of the engine, an exhaust stroke whereby charge previously inducted into the combustion chamber is compressed during the stroke and then exhausted to atmosphere.

Preferably the method in every aspect uses electrically controlled actuators, each of which is an electro-hydraulic actuator comprising an actuator piston movable in an actuator cylinder, the actuator piston defining with the actuator cylinder a pair of variable volume actuator chambers, each of the actuator chambers being connected by an individual conduit to electrically operated valve means which regulates flow of hydraulic fluid to and from each

actuator chamber respectively from a source of pressurised fluid or to a reservoir of fluid.

In each aspect of the invention the charge inducted into the combustion chamber can comprise a mixture of fuel and air. Alternatively, the charge inducted to the combustion chamber can comprise a charge of just air and the method comprises additionally the step of delivering the fuel to the combustion chamber independently of the charged air.

In a further aspect the present invention provides an internal combustion engine operated according to any one of the methods described above.

The present invention also provides an automobile comprising such an internal combustion engine.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic illustration of a first embodiment of a single-cylinder four-stroke internal combustion engine according to the present invention; Figure 2 is a schematic illustration of a first variant of the single-cylinder four-stroke internal combustion engine of Figure 1; Figure 3 is a schematic illustration of a second variant of the single-cylinder four-stroke internal combustion engine of Figure 1; Figure 4 is a schematic illustration of a third variant of the single-cylinder four-stroke internal combustion engine of Figure 1; Figure 5 is a schematic illustration of a fourth variant of the single-cylinder four-stroke internal combustion engine of Figure 1;

Figure 6a is a valve timing diagram showing operation of an exhaust valve of an internal combustion engine as shown in Figures 1 to 5 in a first mode of operation; Figure 6b is a valve timing diagram showing operation of an inlet valve of an internal combustion engine as shown in Figures 1 to 5 according to a second mode of operation; Figure 6c is a valve timing diagram showing operation of an inlet valve of an internal combustion engines as shown in Figures 1 to 5 in a third mode of operation; Figure 6d is a valve timing diagram showing operation of an exhaust valve of an internal combustion engine as shown in Figures 1 to 5 in a fourth mode of operation; Figure 7a is a valve timing diagram for an exhaust valve of an internal combustion engine as shown in Figures 1 to 5 showing a fifth method of operation; Figure 7b is a valve timing diagram for an inlet valve of an internal combustion engine as shown Figures 1 to 5 showing a sixth method of operation ; Figure 7c is a valve timing diagram of an inlet valve of an internal combustion engine as shown in Figures 1 to 5 showing a seventh method of operation; Figure 8 is a valve timing diagram for inlet and exhaust valves of an internal combustion engine as shown in Figures 1 to 5 showing an eighth method of operation; Figure 9a is a valve timing diagram for an inlet valve of an internal combustion engine as shown in Figures 1 to 5 showing a ninth method of operation; Figure 9b is a valve timing diagram for an inlet valve of an internal combustion engine as shown in

Figures 1 to 5 showing a tenth method of operation ; Figures 10aa, lab, lac, lad and 10e are figures showing the piston and cylinder arrangement of an internal combustion engine as shown in Figures 1 to 5 in different stages of an engine cycle, with the engine operating according to an eleventh method of operation; and Figure lla shows a cylinder head of a variant of an internal combustion engine shown in Figures 1 to 5 and Figures llb and lie show tumble and swirl in a cylinder of an internal combustion engine as shown in Figures 1 to 5.

For simplicity, the detailed description following will address the methods of the present invention with their application to a single-cylinder four-stroke internal combustion engine, although it should be appreciated that the present invention is equally applicable to a multi-cylinder four-stroke internal combustion engine or indeed to singlecylinder or multi-cylinder two-stroke internal combustion engines. Furthermore, the methods of the present invention can be used for gasoline engines, diesel engines and engines which use compressed gas or other alternative fuels. The methods of the present invention are most applicable to a four-stroke internal combustion engine.

A schematic representation of a first embodiment of a single-cylinder four-stroke internal combustion engine is given in Figure 1. In Figure 1 a piston 10 is movable in a cylinder 11 and defines with the cylinder 11 a variable volume combustion chamber 12.

An inlet passage 13 is used to supply fuel/air

mixture to the combustion chamber 12. The flow of a charge comprising fuel/air mixture into the combustion chamber 12 is controlled by an inlet valve 15.

Combusted gases can flow from the combustion chamber 12 via an exhaust passage 14 to atmosphere.

Flow of combusted gases out of the combustion chamber 12 is controlled by an exhaust valve 16. The combusted gases pass through a catalytic converter 38 before being exhausted to atmosphere.

The inlet valve 15 and the exhaust valve 16 are hydraulically actuated. It can be seen in Figure 1 that the stem 17 of the inlet valve 15 has provided thereon a piston 18 which is movable in a cylinder 19.

Similarly the stem 20 of the exhaust valve 16 has a piston 21 provided thereon which is movable in a cylinder 22.

The flow of hydraulic fluid to the cylinder 19 is controlled by a servo-valve 23. The servo-valve 23 is electrically controlled. The servo-valve 23 is controlled by a control signal generated by a controller 24. The servo-valve 23 can control flow of hydraulic fluid into an upper chamber 25 of an arrangement of piston 18 and cylinder 19 whilst controlling flow of fluid out of a lower chamber 26.

The servo-valve 23 can also control flow of hydraulic fluid to and from the cylinder 19 such that hydraulic fluid is delivered to the bottom chamber 26 whilst hydraulic fluid is expelled from the upper chamber 25.

The fluid supplied to and expelled from the cylinder 19 is metered so as to control exactly the position and/or the velocity of the inlet valve 15.

In a similar fashion, a servo-valve 27 is provided to control flow of hydraulic fluid to and from the cylinder 22. The servo-valve 27 is controlled electrically by the controller 24. The servo-valve 27 can operate to supply hydraulic fluid under pressure to an upper chamber 28 of the cylinder 22 whilst allowing hydraulic fluid to be expelled from a lower chamber 29 of the cylinder 22. Conversely, the servovalve 27 can allow pressurised hydraulic fluid to be supplied to the lower chamber 29 whilst allowing hydraulic fluid to be expelled from the upper chamber 28. The servo-valve 27 meters the flow of hydraulic fluid to and from the cylinder 22 in order to control the position and/or the velocity of the exhaust valve 16.

Both of the servo-valves 23 and 27 are connected to a pump 30 and a sump 31. Hydraulic fluid under pressure is supplied by the pump 30 and when hydraulic fluid is expelled from either or both of the cylinders 19 and 22 it is expelled to the sump 31. The pump 30 will in practice draw fluid from the sump 31 to pressurise the fluid and will then supply the pressurised fluid to the servo-valves 23 and 27.

The electronic controller 24 will control the movement of the inlet valve 15 and exhaust valve 16 having regard to the position of the inlet and exhaust valves 15 and 16 as measured by two position transducers 32 and 33. The controller 24 will also have regard to the position of the engine, which will be measured by a rotation sensor 34 which is connected to a crankshaft 35 of the internal combustion engine, the crankshaft 35 being connected by a connecting rod 36 to a piston 10 reciprocal in the cylinder 11.

The engine of the present invention has a hydraulically controlled valve train which is controlled by a controller 24 which is programmable and controls the opening and closing of both the inlet 15 and exhaust 16 valves. The controller 24 controls motion of the inlet 15 and the exhaust 16 valves and in particular the time (in terms of the engine cycle) when the inlet 15 and exhaust 16 valves open and the duration of time for which they are open.

Also shown in Figure 1 is an engine throttle control in the form of an accelerator pedal 70 and a sensor 71 which senses displacement of the pedal 70 and produces a signal indicative thereof which is relayed to the controller 24. This signal is used in some methods of the invention described below.

Additionally shown in Figure 1 is a sensor 72 which measures temperature of the engine (e. g. by measuring coolant temperature) and/or temperature of the catalytic converter 38. Furthermore, shown in Figure 1 is a knock sensor 73 which senses preignition in the combustion chamber 12 and provides an electrical signal to the controller 24.

The engine of Figure 2 is identical in all respects to the engine of Figure 1 save that a restrictor 40 is present in the exhaust passage 14 to restrict flow of exhaust gases. The restrictor 40 provides an orifice 41 of a cross-section smaller than the cross-section of the exhaust passage 14.

The engine of Figure 3 is identical in all respects to the engine of Figure 1 save that a variable throttle 50 is provided in the exhaust

passage 14 which can throttle the flow of exhaust gases to a variable degree. The throttle 50 is a butterfly valve mounted on a spindle which is connected to an electric motor 51. The electric motor 51 is controlled by the controller 24. The controller 24 receives a signal from a pressure sensor 52 present in the exhaust passage 14 and controls the electric motor to control the position of the throttle valve 50 to throttle the combusted gases to achieve a desired back pressure behind the exhaust valve 16. This is a preferred feature in some of the engine operating methods which will be described later.

The engine of Figure 4 is identical to the engine of Figure 1 save that the engine has additionally a gasoline direct injector 60 which is controlled by the controller 24. The'inlet valve 15 of the Figure 4 engine is used to control the flow of a charge of pure air into the combustion chamber 12, rather than flow of a charge of fuel/air mixture. The gasoline injector 60 is used to inject fuel directly into the combustion chamber 12, independently from the charge of pure air delivered by the inlet passage 13.

Figure 5 shows a variant of the Figure 4 engine, the Figure 5 engine differing from the Figure 4 engine in the use of a piston 10 which has an asymmetric crown. The piston 10 has a recess 61 in the crown, which defines a region in which a compressed mixture is concentrated during the compression stroke.

The injector 60 can inject LPG, diesel or natural gas as well as the more usual gasoline.

In each of the engines shown in Figure 1 to 5 a

spark plug 37 is provided which will generate a spark to cause ignition of gasoline in the combustion chamber 12. In the Figure 5 embodiment, the spark plug 37 is located to provide a spark in the region of the recess 61, when the piston 10 is at its top dead centre position. Whilst use of the spark plug 37 is preferred, it is not strictly necessary. The spark plug 37 will not be needed for diesel engines operating according to the methods to be described and may be replaced, e. g. by a glo plug. Also, it is known that gasoline engines can be operated using autoignition rather than spark ignition and this is possible within the realms of the present invention.

It should also be mentioned that whilst above it is shown that the inlet valve 15 and exhaust valve 16 are both actuated by electro-hydraulic actuators, the actuators could be replaced by actuators which function purely electrically without the need for hydraulics. Furthermore, some of the methods described above require only that an inlet valve is operated by an actuator or only that an exhaust valve is operated by an actuator and it would be possible for such methods to have the other valve operated by a normal mechanical cam shaft.

The present invention in a first aspect recognises that the hydraulically actuated valves of the engines illustrated in Figures 1 to 5 can be used to deal with the problem that 80% of the emissions produced by modern engines of vehicles occur during a cold start period of the first 2/3 minutes of engine performance. The applicant has realised that a considerable gain can be made to engine performance and to pollutant reduction by the use of an advanced

valve control strategy for the cold start and early period of engine and valve operation. In normal engines with fixed cam profiles or with switchable cam profiles the formation of pollutants is governed by the degree of over-fuelling required to provide stable running of the engine, to deliver power and to preheat the catalyst. In its first aspect, the present invention aims to provide valve control strategies to meet the requirements of cold start drivability and catalyst light-off. Since these account for 80% of the pollutant formation they will have a significant impact on emissions in general.

A temperature sensor 72 shown in Figures 1 to 5 will provide the controller 24 with an electrical signal indicative of the temperature of the engine.

When the controller 24 realises that the temperature of the engine is below a threshold temperature, e. g. in cold start up conditions, the controller 24 will recognise that a valve motion is required which is different from the valve motion used for the engine in normal operating temperature conditions. The controller 24 will act to control the motion of the inlet valve 15 and/or exhaust valve 16 such that the compression ratio of the engine is reduced from that of normal operation. The reduction of compression ratio on cold start up conditions is advantageous so that the crevice volume containment of hydrocarbons is minimised and therefore pollutant levels drop.

The compression ratio of the engine can be reduced in several ways. The first is shown in Figure 6a. Figure 6a is a valve timing diagram showing motion of the exhaust valve 16. The 00 position shown in this Figure is the position of the engine at the

commencement of the expansion (sometimes called "power") stroke. In the Figure it can be seen that the exhaust valve opens at roughly 1800 i. e. at the end of the expansion stroke, and then remains open until roughly 360 , i. e. at the end of the exhaust stroke.

This motion is conventional. However, in order to reduce the compression ratio of the engine the exhaust

valve is also opened at 5400 for a short period until 6000. The period of 540'to 720'of rotation forms the compression stroke of the engine. Therefore, the exhaust valve 16 is opened at the beginning of the compression stroke. Thus, the length of the compression stroke is reduced and the peak pressure in the combustion chamber 12 is reduced.

The method of Figure 6a is applicable only in the engine shown in Figures 4 and 5. In the engines shown in Figures 4 and 5 pure air is introduced into the combustion chamber 12 via the inlet passage 13 and fuel is directly injected into the combustion chamber 12 by a direct injector 60. At the beginning of the compression stroke the combustion chamber 12 will be full of pure air and it is only at the latter part of the compression stroke that fuel is injected. With the exhaust valve motion shown in Figure 6a the upward motion of the piston 10 in the cylinder 11 at the beginning of the compression stroke acts to force pure air out of the combustion chamber into the exhaust 14.

Then when the exhaust valve 16 is closed at 6000 the remaining air is compressed, fuel is injected by the injector 60 and ignition occurs.

It should be appreciated that the exhaust valve motion shown in Figure 6a will be maintained by the controller 24 only whilst the temperature of the

engine is below the temperature threshold and once the temperature of the engine has exceeded the temperature threshold then the second opening of the exhaust valve 16 in the cycle (between 540and 600 ) will no longer occur.

A second way of reducing the compression ratio in cold start conditions involves a variation on inlet valve motion. This is illustrated by Figure 6b. When the controller 24 recognises that the temperature of the engine (as sensed by the temperature sensor 72) is below a threshold temperature then the controller 24 can vary the motion of the inlet valve 15. In Figure 6b the varied inlet valve motion is shown by a solid line and this can be compared with the inlet valve motion in normal operating conditions which is shown by the first part of the solid line and then by a dotted line. In normal operating conditions, the inlet valve is opened at roughly 360 , at the commencement of the induction stroke. The inlet valve then remains open until 5400 approximately, the end of the intake stroke. However, to reduce the compression ratio at low temperatures the controller 24 commands the inlet valve 15 to remain open for a longer period, until roughly 6000. Thus, the inlet valve 15 will be open at the commencement of the compression stroke.

Therefore charge previously introduced into the combustion chamber 12 will be expelled out of the combustion chamber 12 back to the inlet passage 13.

Once the inlet valve 15 closes at roughly 6000 then the remainder of the charge will be compressed and then subsequently ignited by a spark generated by the spark plug 37.

The variation of the inlet valve motion reduces

the volume to be compressed and also reduces the mass of fuel and air to be ignited. This reduces the compression ratio.

The inlet valve motion illustrated in Figure 6b is suitable for the engines of Figures 1 and 2 and 3, because it does not matter that fuel/air is expelled to the inlet passage 13, because the expelled fuel and air will be subsequently reintroduced into the combustion chamber 12.

Once the controller 24 recognises that the engine has reached its temperature threshold then the inlet valve motion will be brought back to a normal operation so that the inlet valve no longer remains open at the commencement of the compression stroke.

A third method of reducing the compression ratio in cold start conditions is shown in Figure 6c. In this diagram the motion of the inlet valve 15 is illustrated. The cold start motion of the inlet valve 15 is illustrated by the solid line and this can be compared with the conventional (normal operating temperature) motion of the inlet valve 15 which is shown by the first part of the solid line and then by the dotted line. In normal operation, the inlet valve will open at roughly 360 (at the commencement of the induction stroke) and will close at roughly 5400 (at the end of the induction stroke). In the cold start conditions the controller 24 still opens the inlet valve 15 at the commencement of the induction stroke, but closes the inlet valve 15 early, before the end of the induction stroke. Once the inlet valve 15 is closed then the previously inducted charge will be expanded by the further downward motion of the piston

10 within the cylinder 11. Therefore, the pressure of the charge in the combustion chamber 12 at the beginning of the compression stroke is reduced from the pressure which would be in the combustion chamber were the inlet valve to remain open until the end of the induction stroke. The reduction in initial pressure in the combustion chamber at the beginning of the compression stroke reduces the peak pressure in the combustion chamber 12.

The method illustrated in Figure 6c is suitable for all of the engines shown in Figures 1 to 5. It does not matter whether charge comprises purely air or fuel and air. However, it is preferable that the charge comprises just air and that the method is used with the engines of Figures 4 and 5. This is because the expansion of the charge at the end of the induction stroke does cause some cooling of the charge and this could lead to cylinder wall wetting if the charge comprises both fuel and air.

The method of control of the inlet valve 15 illustrated in Figure 6c could be used in conjunction with the method of control of the exhaust valve 16 shown in Figure 6a, in order to achieve the required reduction in peak pressure.

As well as reducing peak pressure in cold start conditions, it is advantageous to produce a hot exhaust gas mixture which facilitates early catalyst light-off and therefore reduces pollutant release.

This can be achieved by varying the motion of the exhaust valve 16 in cold start conditions. This is illustrated by Figure 6d.

In Figure 6d a solid line shows the motion of the exhaust valve 16 in cold start conditions, whilst the motion of the exhaust valve 16 in normal conditions is illustrated by a combination of a dotted line and a solid line. In normal operating conditions the exhaust valve 15 will not open until the end of the expansion stroke and the beginning of the exhaust stroke, i. e. at roughly 1800. This is because it is desired to maximise the work output from the engine and therefore it is advantageous to maximise the expansion stroke. However, in cold start conditions it is preferable to release to exhaust a hot mixture of combusted gases. The temperature of the combusted gases at the end of the expansion stroke is less than the temperature of the combusted gases before the end of the expansion stroke. Therefore in the Figure 6d method the exhaust valve 16 is opened early and is opened during the expansion stroke, in the latter phase of the expansion stroke. Therefore, whilst power is not maximised, the method provides for the release of combusted gases which would be hotter than if conventional valve timings were used and this achieves rapid catalyst light-off, so that normal operation can be achieved quicker than usual.

The method of Figure 6d can be used in conjunction with any of the methods shown in Figures 6a, 6b or 6c.

The methods of any of Figures 6a, 6b, 6c or 6d can be combined with fuelling strategies and spark timing events to create a hot carbon monoxide rich combustion mixture to facilitate catalyst light-off.

Another difficulty faced by engines which can be

addressed by novel operating methods is the problem of limiting the maximum temperature of a catalytic converter. It is typical for engine management systems to deploy specific spark and fuelling events to moderate and contain within a temperature threshold the temperatures that the catalytic converters are exposed to. This is usually accomplished through heavy fuelling resulting in catalyst cooling. This can have a detrimental effect in terms of emissions.

The present invention uses variations in the valve timing to achieve a reduction in temperature of the combusted gases expelled from the combustion chamber/12, in order to protect the catalytic converter 38.

Figure 7a illustrates motion of the exhaust valve 16. A solid line shows the modified valve motion and a combination of a dotted line and the solid line shows normal exhaust valve motion. In the modified method of operation the opening of the exhaust valve 15 is delayed until later in the exhaust stroke. The delay allows for a greater period of cooling of the combusted gases and therefore the combusted gases exiting the combustion chamber 12 are cooler than they would be if the exhaust valve 16 was opened, as normal, at the commencement of the exhaust stroke.

Figure 7b shows a variation in motion of the inlet valve 15 which can be used to reduce the temperature of the combusted gases leaving the combustion chamber 12. In Figure 7b a solid line shows modified motion of the inlet valve 15 and a combination of the solid line and a dotted line shows a more typical motion of inlet valve 15. It can be

seen from the Figure that whilst it is usual to close the inlet valve 15 at the end of the induction stroke, in the modified method the inlet valve 15 is kept open into the compression stroke. The delayed closing of the inlet valve 15 permits expulsion of the previously inducted charge from the combustion chamber 12 at the commencement of the compression stroke. The expelled charge is expelled back to the inlet passage 13.

Charge is expelled from the combustion chamber 12 until the inlet valve 15 closes, whereafter the remaining charge is compressed and then ignited by the spark plug 37. The delay in closing of the inlet valve 15 both reduces the total volume compressed and therefore reduces the peak pressure and also reduces the mass of fuel available for ignition and therefore reduces both peak pressure and peak temperature. The reduction in peak pressure and peak temperature leads to a reduction in temperature of the combusted gases at the end of the expansion stroke.

Figure 7c shows an alternative valve operation strategy. The Figure shows by a solid line modified motion of the inlet valve 15 and shows by a combination of a first part of the solid line and then a dotted line a more typical inlet valve motion. In the modified motion, the closing of the inlet valve 15 in the induction stroke is advanced, so that the inlet valve 15 is closed before the end of the induction stroke. After closure of the inlet valve 15 the previously inducted charge is then expanded, before subsequent compression in the compression stroke. The early closing of the inlet valve 15 reduces the mass of fuel and air available for ignition in the subsequent compression stroke and therefore limits peak temperature. Furthermore, the expansion of the

inducted charge at the end of the induction stroke reduces the pressure of the charge at the commencement of the compression stroke and therefore reduces the peak pressure obtained at the end of the compression stroke. These effects lead to a reduction in temperature of the combusted gases.

Either of the inlet valve strategies shown in Figure 7b and 7c can be used with the exhaust valve strategy of Figure 7a. All of the strategies can be used on any of the engines of Figures 1 to 5, because it does not matter whether the charge comprises air on its own or a mixture of fuel and air. However, it is likely that the strategy of Figure 7b will be preferred to the strategy of Figure 7c for the engines of Figures 1 to 3, because the expansion of the inducted charge at the end of the induction stroke does lead to a reduction in temperature which could lead to cylinder wall wetting if the charge comprises both fuel and air.

A further possibility provided by the use of electrically controlled inlet and exhaust valves is a possibility for control of pre-ignition.

Figure 8 is a valve timing diagram showing in solid line the motion of an exhaust valve 16 and in dashed line the motion of an inlet valve 15. In the Figure it can be seen that there is a degree of valve overlap, i. e. a period in which both the inlet valve 15 and the exhaust valve 16 are simultaneously open.

This period is denoted A in Figure 8.

It is a typical configuration to run an engine with some valve overlap, with the exhaust valve 16

closing slightly after the end of the exhaust stroke, at the beginning of the induction stroke and with the inlet valve 15 opening slightly before the beginning of the induction stroke at the end of the exhaust stroke.

Occasionally, the overlap of valves can cause problems of pre-ignition i. e. the fuel in the cylinder igniting at a time before generation of the spark by the spark plug 37. The pre-ignition can be sensed by a knock sensor 73. Once pre-ignition is sensed by the knock sensor 73, then a signal indicating pre-ignition is sent to the controller 24. The controller 24 then varies the duration of valve overlap until preignition is no longer sensed by the knock sensor 73.

Once this occurs, a normal valve timing regime is reestablished.

The applicant has also appreciated that with engines having valve trains configured as shown in Figures 1 to 5 it is possible to achieve throttle-less engine operation. The majority of engines are throttled by e. g. the use of a butterfly valve in the induction system and conventional part load operation of a homogeneous charge engine is achieved by throttling the flow of air (and thus fuel) into the induction system, thus reducing the engine power produced. This is, however, to the detriment of engine efficiency, with increases in pumping losses being produced.

It is possible to control motion of the inlet valve 15 to control the load of the engine, whilst achieving a reduction in pumping losses. The reduction in pumping losses reduces engine fuel

consumption and emissions in part load conditions.

The inlet valve 15 can be controlled to achieve throttling of the engine in part load conditions in two different ways.

Figure 9a is a valve timing diagram showing motion of the inlet valve 15. The inlet valve 15 is shown to open at roughly 3600, i. e at the beginning of the induction stroke. The timing of closing of the inlet valve 15 can take place anywhere between 500 and 5400, 5400 being the end of the induction stroke.

The range of possible closing times of the inlet valve 15 is shown by the range B shown in the Figure. The shaded part of the valve timing diagram shows the area of valve motion possible with the invention.

The inlet valve 15 will be closed right at the end of the induction stroke at 5400 in full load conditions. To achieve throttling of the engine in part load conditions, the inlet valve 15 is closed early in the induction stroke. By doing this, the mass of charge inducted into the cylinder may be limited. The charge may comprise fuel/air mixture in the engines of Figures 1,2 and 3 or pure air in the engines of Figures 4 and 5, where the fuel is separately delivered by the direct injector 60.

Once the inlet valve 15 is closed early in the induction stroke then the inducted charge undergoes expansion through what remains of the induction stroke before compression in the following compression stroke. The energy expended in expanding the charge is, to a large extent, returned to the engine upon subsequent recompression.

Differing amounts of throttling can be achieved by varying the point of closing of the inlet valve 15.

The maximum level of throttling shown in Figure 9a is indicated by closing of the inlet valve 15 at 500 .

Throttling of the engine can also be achieved by closing the inlet valve 15 later in the engine cycle, as is illustrated in Figure 9b. In normal full load operation of the engine, the inlet valve 15 is closed at 5400, at the end of the induction stroke. To achieve throttling in part load conditions, the inlet valve 15 is closed later than normal, so that it closes in the compression stroke. The Figure shows a range of late closing of the inlet valve 15. The shaded region gives possible inlet valve motions to achieve throttling.

By closing the inlet valve 15 during a compression stroke, charge previously inducted in the induction stroke is expelled back out past the inlet valve 15 into the inlet passage 13. When the inlet valve 15 finally closes the remaining charge is trapped in the combustion chamber 12 and compressed ready for ignition. The inlet valve 15 is therefore used to control the charge mass in the combustion chamber 12 available for ignition. Control of the charge mass affects throttling of the engine.

The method illustrated in Figure 9a may not be ideal in engines such as those in Figures 1,2 and 3 where the charge comprises a mixture of fuel and air, because the expansion of the inducted charge may cause fuel condensation and excessive wall wetting.

The throttle-less control of the engine is

particular compatible with gasoline direct injection engines as illustrated in Figures 4 and 5. The technique can exploit the ability of gasoline direct injection to control precisely timing and amount of in-cylinder fuel delivery.

In tests the complete deletion of a conventional throttle and the use of inlet valve motion control to provide throttling has achieved a reduction in fuel consumption of approximately 14%. The omission of a throttle body also increases possibility for package space reduction and saves costs.

The control of the inlet valve 15 and the exhaust valve 16 by actuators also provides the possibility of cylinder de-activation. The main objective of cylinder de-activation is to reduce engine fuel consumption and emissions through a reduction in the pumping losses associated with an engine which operates under part load. The cylinder de-activation aims to achieve a controlled reduction in total engine power by de-activating individual engine cylinders.

This allows the power required to meet the driver's demands to be produced from a sub-set of the cylinders. The cylinders will run largely unthrottled and hence there will be a corresponding increase in pumping efficiency.

To achieve effective cylinder de-activation with a worthwhile reduction in pumping losses it is necessary to prevent gas flow into and out of the deactivated cylinders. This is achieved in the present invention by disabling both the inlet 15 and exhaust 16 valves of the cylinder 11.

The present invention proposes that the most effective method of cylinder de-activation is achieved by trapping the combusted gases present in the combustion chamber 12 at the end of the expansion stroke. This is accomplished through the deactivation of the inlet valve 15 and exhaust valve 16 at this point in the engine cycle. The trapped combusted gases within the combustion chamber 12 now behave in the manner of a gas spring. The pumping losses of the de-activated cylinder are all but eliminated and the majority of the work necessary in each cycle to compress the trapped combustion gases is returned to the engine with the expansion of the trapped combusted gases.

After deactivation, the cylinder is subsequently re-activated first by exhausting the trapped combusted gases on an exhaust stroke through re-activation of the exhaust valve 16. This is then followed as usual by a charge induction through a re-activated inlet valve 15. The use of a controller 24 to control motion of the valves 15 and 16 facilitates easy activation and de-activation of the inlet valve 15 and exhaust valve 16.

With cylinder de-activation applied to a fourcylinder spark ignition engine and with two of the four cylinders de-activated in part load conditions, it is believe that a 14-20% reduction in fuel consumption can be achieved.

There is also potential for emissions reduction through the use of cylinder de-activation. With two active cylinders firing at part load conditions, frequency of the combustion events is halved

giving inherent reductions in NO. and hydrocarbon emissions. Furthermore, with the activated cylinders running at a much higher load (for a given total engine power) their tolerance to exhaust gas recirculation is increased and the mean temperatures produced in the cylinder are necessarily higher.

These higher temperatures have the effect of reducing hydrocarbon emissions by up to 16% whilst the improved tolerance to exhaust gas recirculation permits greater dilution rates and therefore NOx reduction.

Exhaust gas recirculation in the activated cylinders can be achieved by early closing of the exhaust valve 16 in the exhaust stroke, in order to trap combusted gases in the combustion chamber 12 for mixing with the subsequently introduced fresh charge.

Alternatively, exhaust gas recirculation can be achieved by simultaneous opening of the inlet 15 and exhaust 16 valves for a part of the induction stroke so that combusted gases previously exhausted from the combustion chamber 12 are drawn back into the combustion chamber 12 from the exhaust passage 14. In this latter case, it will be advantageous to provide some throttling in the exhaust passage 14 so that suitable back pressure is maintained behind the exhaust valve 16 so that when the exhaust valve 16 is opened, combusted gases can be drawn in to the combustion chamber 12. Throttling is shown in the engines of Figures 2 and 3. In Figure 2 a fixed throttle 40 is shown having an orifice 41 which throttles the flow of exhaust gas through the exhaust passage 14. In Figure 3 a variable throttle 50 is shown which can provide a variable degree of throttling on the flow of exhaust gas through the exhaust passage 14. The degree of throttling is

controlled by rotating the throttle 50 using an electric motor 51 which is controlled by the electronic controller 24. The electronic controller 24 receives a pressure signal from the controller pressure sensor 52 indicating the back pressure behind the exhaust valve 16. Therefore, the controller 24 can control the throttling provided by the variable throttle 50 to provide the required back pressure.

The implementation of cylinder de-activation is simple when valves are controlled by electrically controlled actuators controlled by an electronic controller 24. It is simple to de-activate the individual valves in the time necessary to cleanly and efficiently trap combusted gases upon de-activation and to cleanly and efficiently exhaust trapped gases upon re-activation. With high speed microcontroller control the relative phasing of the cylinder during de-activation can be monitored such that when it is re-activated it is brought back into the correct fourstroke sequence.

It is preferred that the actuators will be constructed such that there is no power consumption when it is necessary to keep the valves 15 and 16 in their valve seats. Thus, when the cylinders are deactivated the power consumption of the valve train system will be reduced leading to lower parasitic demands on the engine.

The applicant has also appreciated that valve deactivation can facilitate control of swirl and tumble in a combustion chamber, as will now be described.

Figure lla shows the cylinder head of a four

valve per cylinder four-stroke engine. The two valves at the two ports 110 and 111 in the cylinder head are both inlet ports. The two ports 112 and 113 are both exhaust ports. The opening and closing of each port will be controlled by a poppet valve which is actuated by an electro-hydraulic actuator controlled by an electronic controller.

At full load conditions, both of the inlet valves will be opened in every engine cycle so that both of the inlet ports 110 and 111 are opened in each cycle to allow maximum flow area into the combustion chamber. In such a situation, the motion of the inducted charge in the combustion chamber is dominated by a tumble component, although there will be some swirl. The dominant tumble is indicated by the large arrow 114 in Figure lib and the minimal swirl is indicated by the small arrow 115 in Figure lib.

In part load conditions it is advantageous to increase the swirl in the combustion chamber. This is achieved by de-activating one of the two inlet valves in the induction stroke. This de-activation results in all of the inducted air being forced through one inlet port, e. g. 110. When the ports 110 and 111 are suitably arranged, the intensification of the flow through a single port increases the level of bulk swirl motion in the inducted charge. This can be seen in Figure lie where the large arrow 116 indicates a large degree of swirl and the smaller arrow 117 indicates a lesser degree of tumble.

Swirl generation investigations involving direct injection compression ignition engines have shown that swirl is essential for adequate mixture formation

within the combustion chamber. It is responsible for a marked effect on reduction of smoke and particulate emissions and also for an improvement in fuel consumption. Through modification of in-cylinder swirl using valve port de-activation reductions in soot levels in part load conditions can be achieved along with reductions in NO. and in fuel consumption.

Investigations involving four-stroke port injected gasoline engines have also demonstrated the advantages of the strategy increasing swirl at part loads in fuel consumption and for reduction of emissions. Swirl generation has been shown to increase the levels of turbulence within the combustion chamber resulting in an increase in the rate of combustion and in a reduction in the delay period. This has led to reductions in fuel consumption and an increase in the combustion chamber tolerance to exhaust gas recirculation. The improved tolerance can be exploited with a reduction in NO, emissions through an increased dilution of the inducted charge with recirculated exhaust gas. The exhaust gas can be recirculated, as mentioned above, either by trapping some combusted gases in the combustion chamber at the end of the exhaust stroke using early exhaust valve closing or by reintroducing previously exhausted combusted gases to the cylinder in an induction stroke by simultaneous opening of the inlet and exhaust valves. At high swirl rates, increases in exhaust gas recirculation can be seen to reduce hydrocarbon emissions by up to 40%.

Alternatively, the increase in bulk swirl can be used to run mixtures which are very lean whilst avoiding increased NO, emissions. Combustion stability is improved by the increased swirl down to idle. In twostroke engines the increased swirl can have benefits

in the scavenging process.

The implementation of de-activation of a single inlet valve in a pair of inlet valves is achieved by the valve train of the engine of Figures 1 to 5 with no difficulty. The systems shown not only make possible the de-activation of a particular inlet valve but also the modulation of the lift of the valve throughout the induction stroke. Thus it is possible to exercise precise control over the levels of bulk swirl and bulk tumble.

De-activation of single valves in pairs of valves also has the benefit of reducing the power consumption of the valve train system and therefore reduction in parasitic demands upon the engine.

Whilst above it is mentioned that one inlet valve of a pair of inlet valves is de-activated, it is also possible to de-activate one exhaust valve of the pair of exhaust valves in part-load conditions. This would halve the power consumption of the valve train system and could give substantial levels of swirl enhancement. This could be of particular use in cold start conditions. In such conditions, all of the cylinders of the engine could be run with only two valves operating, one inlet and one exhaust valve for each cylinder, allowing warm up of all cylinders initially whilst managing the power of the output of the engine at part load conditions by cylinder valve de-activation.

It has been mentioned above that the present invention allows removal of the need for a throttle body. Diesel engines and unthrottled gasoline direct

injection engines are also typically unthrottled. As a direct result of this there is little or no manifold depression in the intake system to be used in"engine braking". This can lead to problems with vehicle retardation, particularly with large commercial diesel-powered vehicles. These have traditionally used methods of compression release braking (or exhaust braking) to augment the operation of their conventional braking system.. This avoids the possibility of over-heating during long braking periods and allows for a possible downsize of brakes, thereby reducing the unsprung mass of the vehicle and aiding dynamics.

The applicant has realised that the use of exhaust valves opened and closed by hydraulic actuators can provide compression release engine braking. This will be illustrated with reference to Figures lOa to 10f.

At the commencement of engine braking, the controller 24 will de-activate the spark plug 37 and will de-activate the fuel system so that no fuel is introduced to the charge admitted to the combustion chamber in each cycle. Thereafter, the cycle of the engine will be as follows. First of all, as shown in Figure lofa, a full charge of air is inducted into the combustion chamber during the induction stroke. Then, as shown in Figure lab, the inducted air is subsequently compressed during the compression stroke using energy taken from the total kinetic energy of a vehicle driven by the engine. The piston 10 will be connected to a crankshaft 35 which in turn will be connected via a drive train to the wheels of the vehicle. Kinetic energy is transferred from the

wheels via the drive train and the crank shaft 35 to the piston 10. As shown in Figure 10c, as the piston reaches the top of the compression stroke, the exhaust valve 16 is opened and the compressed air is allowed to exhaust from the combustion chamber without returning any of the stored pressure energy during the expansion stroke.

Additionally during engine braking the movement of the inlet valve 15 can be varied so that the inlet valve 15 opens at the commencement of what would be, in normal operation of the engine, the expansion stroke. This is shown in Figure lad. Therefore, expansion stroke is turned into a second induction stroke. At the end of what would in normal operation be the expansion stroke, the piston 10 will then move upwardly for the exhaust stroke. However, the motion of the exhaust valve 16 will be varied from its normal operation so that the exhaust valve 16 will remain closed for the majority of the exhaust stroke so that the trapped air is compressed, removing kinetic energy from the vehicle. The compressed air will then be released at the end of the compression stroke as can be seen in Figure 10f.

The modified operation allows twice as many compression release events to take place compared to a conventional system. It is also possible to provide for some dissipation of energy through a degree of throttling of the air past the inlet valve 15. The controller 24 can control the motion of the inlet valve 15 so that the air flowing into the combustion chamber is throttled whilst ensuring that there is a sufficient mass of air in the combustion chamber for compression in the subsequent compression stroke.

The present invention also comprises a valve strategy which responds to behaviour of the driver.

As can be seen in Figures 1 to 5 a throttle control 70 in the form of an accelerator pedal is associated with a sensor 71 which generates electrical signals indicating the position of the throttle control. This is fed to the engine controller 24.

Initially, the engine controller 24 will contain default settings aimed at standard driving styles and will control the opening and closing of the inlet and exhaust valves 15 and 16 accordingly. During normal driving by an owner the controller 24 will record how the throttle control 70 is used by the driver. Once the history of use of the accelerator pedal by the driver is ascertained, then the controller 24 will adapt its control of the motion of the inlet valve 15 and exhaust valve 16 to the driver's behaviour and will respond to the nature of the driver in order to, e. g. improve fuel economy for touring, acceleration for fast driving etc. The adapted settings can be stored in the memory by the controller 24 so that an individual user can select his or her driver profile or driving mode before driving the vehicle.

Whilst above the engines and methods described have been described with reference to spark ignition or compression ignition engines it is also possible that the methods of the invention could be used with engines using auto-ignition. The methods of control of the inlet and exhaust valves needed to achieve autoignition are already described in the applicant's co pending United Kingdom patent application Nos. 0018225.3 and 9930380.2.

Claims

1. A method of operating an internal combustion engine comprising : using a first electrically controlled actuator to open and close an inlet valve which controls admission of fresh charge into a variable volume combustion chamber; using a second electrically controlled actuator to open and close an exhaust valve which controls exhaust of combusted gases from the variable volume combustion chamber; and when the internal combustion engine is operating at a temperature below a normal engine operating temperature range in a period following starting of the engine, using the first and second electrically controlled actuators to open and close the inlet and exhaust valves in such a manner that charge compressed in the variable volume combustion chamber has a peak pressure which is less than peak pressures of charge compressed in the variable volume combustion chamber when the engine is operating in the normal temperature range.

2. A method as claimed in claim 2 wherein in the method the engine is operated using a four-stroke cycle and at engine temperatures below the normal operating temperature range the method comprises opening the exhaust valve during an initial part of the compression stroke.

3. A method as claimed in claim 1 wherein in the method the engine is operated using a four-stroke cycle and at engine temperatures below the normal operating temperature range the method comprises the

steps of : closing of the inlet valve at a point in the engine cycle delayed in comparison with the closing of the inlet valve at normal operating temperatures; and keeping the inlet valve open in the initial part of the compression stroke.

4. A method as claimed in claim 1 wherein in the method the engine is operated using a four-stroke cycle and at engine temperatures below the normal operating temperature range the method comprises closing the inlet valve earlier in an induction stroke in comparison with the closing of the inlet valve at normal operating temperatures and thereafter expanding admitted charge and consequently reducing the pressure of the admitted charge reduced prior to subsequent compression of the charge during the compression stroke.

5. A method of operating an internal combustion engine as claimed in any one of claims 1 to 4 wherein at engine temperatures below the normal engine operating temperature range the method comprises opening the exhaust valve earlier in the engine cycle than the exhaust valve is opened whilst the engine is operating in the normal engine operating temperature range.

6. A method as claimed in claim 5 wherein in the method the engine is operated using a four-stroke cycle and at engine temperatures below the normal engine operating temperature range the method comprises opening the exhaust valve before the end of the expansion stroke.

7. A method of operating an internal combustion engine comprising : using an electrically controlled actuator to open an close an exhaust valve which controls exhaust of combusted gases from a variable volume combustion chamber; and passing the exhausted combusted gases through a catalytic converter before the exhausted combusted gases are passed to atmosphere; wherein when the internal combustion engine is operating at a temperature below a normal engine operating temperature range in a period following starting of the engine, the method comprises the step of: opening the exhaust valve to allow flow of combusted gases from the combustion chamber earlier in the cycle of the engine than allowed by the opening of the exhaust valve when the engine is operating at normal engine operating temperatures.

8. A method as claimed in claim 8 wherein in the method the engine is operated using a four-stroke cycle and at engine temperatures below the normal engine operating temperature range the method comprises the step of opening the exhaust valve prior to the end of the expansion stroke to allow hot combusted gases to be expelled to the catalytic converter to warm the catalytic converter.

9. A method of operating an engine as claimed in any one of the preceding claims comprising additionally the steps of: measuring the engine temperature using a temperature sensor which generates an electrical signal indicative of sensed temperature; using an electrical sensor to monitor progression

of the engine through the combustion cycle thereof and to produce an electrical signal indicative of position of the engine in the engine cycle; and using an electrical controller to process the engine position signal and the temperature signal and to produce control signals for controlling each electrically controlled actuator in dependence on the engine position signal and the temperature signal.

10. A method of operating an internal combustion engine comprising: using a first electrically controlled actuator to open and close an inlet valve which controls admission of fresh charge into a variable volume combustion chamber; using a second electrically controlled actuator to open and close an exhaust valve which controls exhaust of combusted gases from the variable volume combustion chamber; passing the exhausted combusted gases through a catalytic converter before the exhausted combusted gases are passed to atmosphere; monitoring temperature of the catalytic converter; and when the temperature of the catalytic converter reaches or exceeds a catalytic converter temperature threshold, varying opening and closing of the inlet and/or the exhaust valve to reduce temperature of the exhausted combusted gases flowing from the variable volume combustion chamber.

11. A method as claimed in claim 10 wherein in the method the engine is operated using a four-stroke cycle and when the temperature of the catalytic converter reaches or exceeds the temperature threshold

then the method comprises retarding opening of the exhaust valve to allow flow of combusted gases from the combustion chamber, the exhaust valve being open later in the exhaust stroke than in normal operation of the engine.

12. A method as claimed in claim 10 wherein in the method the engine is operated using a four-stroke cycle and when the temperature of the catalytic converter reaches or exceeds the temperature threshold then the method comprises retarding the closing of the inlet valve and closing the inlet valve during an initial phase of the compression stroke and expelling previously inducted charge out of the combustion chamber past the inlet valve to an inlet passage.

13. A method as claimed in claim 10 wherein in the method the engine is operated using a four-stroke cycle and when the temperature of the catalytic converter reaches or exceeds the temperature threshold then the method comprises: advancing of closing the inlet valve and closing the inlet valve before the end of the induction stroke; and thereafter expanding the inducted charge before subsequent compression thereof in the compression stroke.

14. A method of operating a four-stroke spark ignition internal combustion engine comprising: using a first electrically controlled actuator to open and close an inlet valve which controls admission of fresh charge into a variable volume combustion chamber; and using a second electrically controlled actuator

to open and close an exhaust valve which controls exhaust of combusted gases from the variable volume combustion chamber; wherein the method also comprises: operating the engine in at least one operating regime such that in an engine cycle the inlet valve is opened before the exhaust valve is closed, whereby both the inlet valve and the exhaust valve are simultaneously open for an overlap period; using a knock sensor to sense undesired preignition in the combustion chamber; and when the knock sensor senses undesired preignition varying the duration of the overlap period during which both the inlet and exhaust valves are open in order to prevent further undesired preignition.

15. A method of operating a four-stroke internal combustion engine comprising the steps of: using a first electrically controlled actuator to open and close an inlet valve which controls admission of fresh charge into a variable volume combustion chamber; and throttling the engine by controlling the opening and closing of the inlet valve, wherein: the engine is throttled by limiting the mass of charge inducted into the cylinder by closing the inlet valve during an induction stroke prior to the end of the induction stroke; throttling is varied by varying how early in the induction stroke the inlet valve is closed, with throttling being increased by advancing the closing of the inlet valve and with throttling being reduced by retarding the closing of the inlet valve; and once the inlet valve is closed prior to the end of the induction stroke thereafter expanding the inducted charge prior to subsequent compression

thereof during a compression stroke.

16. A method of operating a four-stroke internal combustion engine comprising: using a first electrically controlled actuator to open and close an inlet valve which controls admission of fresh charge into a variable volume combustion chamber; and throttling the engine by controlling opening and closing of the inlet valve; wherein the engine is throttled by allowing previously inducted charge to flow out of the combustion chamber during the compression stroke by keeping the inlet valve open during a part of the compression stroke; throttling is varied by varying how late in the compression stroke the inlet valve is closed, with throttling increased by retarding the closing of the inlet valve and throttling reduced by advancing the closing of the inlet valve; and charge expelled from the combustion chamber during the compression stroke flows out of the combustion chamber past the inlet valve into an inlet passage for subsequent redelivery to the combustion chamber.

17. A method as claimed in claim 15 or claim 16 wherein: throttling of the engine is achieved without use of a throttle valve to restrict flow of charge into the variable volume combustion chamber.

18. A method of operating an internal combustion engine comprising: using a first electrically controlled actuator to open and close an inlet valve which controls admission

of fresh charge into a variable volume combustion chamber ; using a second electrically controlled actuator to open and close an exhaust valve which controls exhaust of combusted gases from the variable volume combustion chamber; sensing a plurality of engine operating parameters and producing electrical signals indicative thereof; controlling operation of the first and second actuators using a controller to produce electrical control signals in dependence on the electrical signals indicative of the sensed engine operating parameters; monitoring use of a throttle control by a driver of the vehicle and recording a history of manner of use of the throttle control; and adapting the operation of the first and second electrically controlled actuators to alter operation of the engine to optimise performance and/or efficiency of the engine having regard to the recorded history of manner of use of the throttle control.

19. A method of operating a four stroke multicylinder internal combustion engine comprising: using electrically controlled actuator means to open and close all of the inlet and exhaust valves of at least one cylinder; when the engine is only partly loaded deactivating the said cylinder by using the electrically controlled actuator means to close all of the inlet and exhaust valves of the said cylinder; and when loading of the engine is subsequently increased re-activating the previously de-activated cylinder by recommencing cyclical opening and closing

of the inlet and exhaust valves ; wherein the said cylinder is only de-activated when full of combusted gases at the end of the expansion stroke, whereby the trapped combusted gases subsequently function as a gas spring; and the said cylinder is subsequently reactivated by the opening of the exhaust valve (s) of the combustion chamber during an exhaust stroke.

20. A method of operating a four stroke multicylinder engine as claimed in claim 19 wherein combusted gases exhausted from the combustion chamber are passed through a catalytic converter before they are expelled to atmosphere and wherein one or more cylinders are de-activated when the engine is only partly loaded in order to make the activated cylinders run at higher loads so as to keep the temperature of the combusted gases high enough to ensure good operation of the catalyst converter.

21. A method of operating a four-stroke multicylinder engine as claimed in claim 19 or claim 20 wherein the electrically controlled activation means do not require power to keep the inlet and exhaust valves in their closed positions.

22. A method of operating an internal combustion engine comprising: using a pair of electrically controlled actuators to open and close a pair of inlet valves which control admission of fresh charge into a single variable volume combustion chamber defined by a piston reciprocating in a cylinder, the charge being admitted to the combustion chamber via a pair of ports provided in a head of the cylinder and each inlet valve controlling admission of charge through one port;

opening both inlet valves in each engine cycle to cause the charge to be inducted through both ports in the cylinder head with the charge being given a first degree of swirl and a first degree of tumble ; and opening only one of the inlet valves in a second engine cycle to force all of the charge to be inducted through only one inlet port with the charge being given a second degree of swirl higher than said first degree and with the charge being given a second degree of tumble lower than said first degree.

23. A method as claimed in claim 22 wherein the lift and duration of the opening of the inlet valves is varied with variations in engine speed and/or load in order to provide varying degrees of swirl and tumble of the charge in the combustion chamber.

24. A method as claimed in claim 22 or claim 23 comprising additionally the steps of: using one or more electrically controlled actuators to open and close an exhaust valve or valves which control exhaust of combusted gases from the variable volume combustion chamber; closing the exhaust valve or valves before the end of the exhaust stroke to trap combusted gases in the combustion chamber ; and mixing the fresh charge with the trapped combusted gases prior to combustion.

25. A method of operating a four-stroke internal combustion engine to provide engine braking comprising: using one or more electrically controlled actuators to open and close an exhaust valve or valves which control exhaust of combusted gases from a

variable volume combustion chamber ; and interrupting normal operation of the engine during engine braking to operate the engine without ignition of fuel, with the engine functioning as a compressor requiring input of power, by taking steps including: opening the exhaust valve or valves at the end of what would be in normal operation of the engine a compression stroke or at the beginning of what would in normal operation of the engine be the expansion stroke in order to release to atmosphere gases compressed in the combustion chamber during the compression stroke.

26. A method of operating a four-stroke internal combustion engine as claimed in claim 25 comprising additionally: using one or more electrically controlled actuators to open and close an inlet valve or valves which control (s) induction of fresh charge into the combustion chamber; and controlling lift of the inlet valve during an induction stroke to throttle induction of fresh charge into the combustion chamber whilst allowing sufficient mass of charge to be inducted for subsequent compression.

27. A method of operating a four-stroke internal combustion engine as claimed in claim 26 comprising additionally: opening the inlet valve or valves during what would in normal operation of the engine be an expansion stroke to allow charge to be drawn into the combustion chamber; and delaying opening of the exhaust valve or valves

to the end of what would in normal operation of the engine be the exhaust stroke whereby charge previously inducted into the combustion chamber is compressed during the stroke.

28. A method of operating a four-stroke internal combustion engine as claimed in claim 25 comprising additionally the step of: using one or more electrically controlled actuators to open and close an inlet valve or valves which control (s) induction of fresh charge into the combustion chamber; opening the inlet valve or valves during what would in normal operation of the engine be an expansion stroke of the engine to allow charge to be drawn into the combustion chamber; and delaying opening of the exhaust valve or valves to the end of what would in normal operation of the engine be an exhaust stroke whereby charge previously inducted into the combustion chamber is compressed during the stroke.

29. A method of operating a four stroke internal combustion engine to provide engine braking comprising: using one or more electrically controlled actuators to open and close an inlet valve or valves which control (s) induction of fresh charge into the combustion chamber; using one or more electrically controlled actuators to open and close an exhaust valve or valves which control (s) exhaust and combusted gases from the combustion chamber; interrupting normal operation of the engine during engine braking to operate the engine without

ignition of fuel, with the engine functioning as a compressor requiring input of power, by taking steps including: opening the inlet valve or valves during what would in normal operation of the engine be an expansion stroke of the engine to allow charge to be drawn into the combustion chamber; and delaying opening of the exhaust valve or valves to the end of what would in normal operation of the engine be an exhaust stroke whereby charge previously inducted into the combustion chamber is compressed during the stroke.

30. A method as claimed in any one of the preceding claims wherein each electrically controlled actuator used is an electro-hydraulic actuator comprising an actuator piston movable in an actuator cylinder, the actuator piston defining with the actuator cylinder a pair of variable volume actuator chambers, each of the actuator chambers being connected by an individual conduit to electrically operated valve means which regulates flow of hydraulic fluid to and from each actuator chamber respectively from a source of pressurised fluid or to a reservoir of fluid.

31. A method as claimed in any one of the preceding claims wherein the charge inducted to the combustion chamber comprises a mixture of fuel and air.

32. A method as claimed in any one of claims 1 to 30 wherein the charge inducted to the combustion chamber comprises a charge of air and the method comprises additionally the step of delivering fuel to the combustion chamber independently of the charged air.

33. An internal combustion engine operated according to the method of any one of the preceding claims.

34. An automobile comprising an internal combustion engine operating according to the method of any one of claims 1 to 32.

35. A method operating an internal combustion engine substantially hereinbefore described with reference to and as shown in the accompanying drawings.