GB2481462A

GB2481462A - Engine for an air hybrid vehicle

Info

Publication number: GB2481462A
Application number: GB1011903.0A
Authority: GB
Inventors: Thomas Tsoi Hei Ma; Hua Zhao
Original assignee: Brunel University London
Current assignee: Brunel University London
Priority date: 2010-06-24
Filing date: 2010-07-15
Publication date: 2011-12-28
Anticipated expiration: 2030-07-15
Also published as: GB2481462B; GB201011903D0; GB201010649D0

Abstract

A four-stroke engine cylinder 10 has two separate intake ports 20a, 20b controlled by respective port throttles 22a, 22b and leading to respective intake valves 18a, 18b which are arranged in close proximity to the associated intake valves. A compressed air storage tank 30 is connected by respective lines 24, 32 to the intake ports 20a, 20b, each line 24, 32 incorporating a control valve 26, 32 and being connected to the associated intake port 20a, 20b at a point lying between the port throttle 22a, 2b and the intake valve 18a, 18b. In addition to a normal mode of operation in which fuel is burnt to generate power, the engine is operable in an air driven motor mode in which compressed air is supplied to the engine cylinder 10 from the compressed air storage tank 30 during the intake stroke of the engine by way of one of the intake ports 20a, 20b and is discharged from the engine cylinder during the ensuing compression stroke of the engine by way of the other intake port. Each port throttle valves 22a, 22b may be pivotally mounted (figs. 7,8).

Description

ENGINE FOR AN AIR HYBRID VEHICLE

Field of the invention

The present invention relates to an engine for an air hybrid vehicle.

Background of the invention

It has previously been proposed to use energy that would be wasted when braking a vehicle to generate compressed air. The compressed air can be used either to operate auxiliary equipment or to crank the engine for starting. In order to achieve this, it is known to operate an engine in a compressor mode in which it is driven by the momentum of the vehicle and used to produce compressed air that is stored in a tank for later use. It is also known to operate the engine in an air driven motor mode so that it can be cranked using the compressed air stored in the tank.

In previous proposals, to enable a four-stroke engine to operate as a compressor has required the cam timing of the intake valve to be modified so that the intake valve remains open both during the intake stroke and the compression stroke of the piston. Furthermore, a non-return valve was used in the intake port to allow air to be admitted into the engine cylinder during the intake stroke but to prevent it from flowing back into the intake manifold during the compression stroke so that this air could be compressed and diverted to a compressed air storage tank.

It is also difficult to modify a four-stroke engine so that it may operate as an air driven motor. If compressed air is introduced into the engine cylinder during the intake stroke to crank the engine, the resistance encountered during the compression stroke is sufficient to prevent further turning of the crankshaft. To introduce the compressed air during the power or expansion stroke of the four-stroke cycle, on the other hand, would require yet another set of cam timing for the intake valve.

As a consequence, modifying existing four-stroke engines to enable them to function both as a compressor and as an air driven motor within a hybrid vehicle has only been achievable by extensive modification of the engine cam operated valve train as well is the incorporation of non-return valves.

Summary of the invention

With a view to mitigating at least some of the foregoing disadvantages, the present invention provides a four-stroke engine having two intake valves per cylinder and two separate intake ports leading to the respective intake valves each controlled by a respective port throttle arranged in close proximity to the intake valve, and a compressed air storage tank connected by way of respective lines to the intake ports, each line incorporating a respective control valve and being connected to the associated intake port at a point lying between the port throttle and the intake valve, wherein, in addition to a normal mode of operation in which fuel is burnt to generate power, the engine is operable in an air driven motor mode in which compressed air is supplied to the engine cylinder from the compressed air storage tank during the intake stroke of the engine by way of one of the intake ports and is discharged from the engine cylinder during the ensuing compression stroke of the engine by way of the other intake port.

The two intake valves are preferably cam actuated, a first intake valve being operated with a normal intake event during both modes of operation of the engine and the second intake valve being operated with a first valve event during the normal mode of operation of the engine and with a second valve event during the air driven motor mode operation of the engine. Both port throttles are open during normal mode operation of the engine, and the throttle of the first intake port is closed while the throttle of the second intake port is opened during the air driven motor mode operation of the engine.

If desired, the engine may be further operable in a compressor mode in which air is drawn into the cylinder during the intake stroke by way of one of the intake ports and is compressed and supplied to the compressed air storage tank during the ensuing compression stroke by way of the other intake port. In this case, the first intake valve may be operated with a normal intake event while the second intake valve may be operated with the same second valve event as that used in the air driven motor mode. The throttle of the first intake port is opened while the throttle of the second intake port is closed during the compressor mode operation of the engine.

Conveniently, the valve train driving the second intake valve comprises switchable cams, one cam setting the valve event during normal mode operation of the engine and the second cam setting the valve event during the air driven motor mode and the compressor mode operations of the engine.

The engine may additionally have a temporary boost, fuel burning mode operation. In this mode, both port throttles are kept closed and pressurised air is supplied to the first intake port from the compressed air storage tank while both intake valves are operated with the valve events for normal mode operation of the engine.

Brief description of the drawings

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of one cylinder of an internal combustion engine embodying the present invention, Figures 2, 3 and 4 show the same engine as in figure 1 but with the port throttles positioned for different operating modes, Figure 5 is a valve timing diagram showing the valve events of both intake valves when the engine is operating in its normal power generating mode, Figure 6 is a valve timing diagram showing the valve events of the two intake valves when the engine is operating in an air driven motor mode or in a compressor mode, Figures 7 and 8 show the closed and open position, respectively, of a port throttle designed to withstand a high back pressure and provide good sealing.

Detailed description of the preferred embodiment

Figure 1 shows one cylinder 10 of a four-stroke internal combustion engine. The piston 12 which is connected to the crankshaft by a connecting rod 14 reciprocates within the cylinder 10 to define a variable volume working chamber 16. The working chamber has two intake valves 18a and 18b.

It also has one or more exhaust valves which are not shown in the drawing. The exhaust valves are not of importance to the present invention and may be assumed to operate in a conventional manner.

Separate intake ports 20a and 20b lead to the respective intake valves 18a and 18b. Each of the intake ports has a respective port throttle 22a and 22b. The intake port 20a is connected at a point between the port throttle 22a and the intake valve 18a to a line 24 which contains an on-off valve 26 and a pressure regulator 28, and leads to a compressed air storage tank 30. The intake port 20b is connected at a point between the port throttle 22b and the intake valve 18b to a line 32 which contains a one-way valve 34 and leads to the compressed air storage tank 30.

The valves 18a and 18b are operated by respective cams 36a and 36b. The cam 36b is a switchable cam that can allow one of two different cam profiles to be used to operate the valve 18b depending on the operating mode of the engine. The different cam profiles for 36b are shown in Figures 5 and 6 and are discussed in further detail below.

The primary mode of operation of the engine is the normal mode in which fuel is burnt to generate power.

During such operation, the two port throttles 22a and 22b are kept open as shown in Figure 1 and the valves 18a and 18b are operated in unison in accordance with the valve events 36a & 36b shown in Figure 5. This is the conventional way of operating a four-stroke engine. Essentially, both intake valves 18a and 18b are open during the intake stroke to admit an air charge into the cylinder. The charge is compressed in the following stroke and ignited when the piston approaches top dead centre. The burning charge expands during the power stroke imparting energy to the crankshaft and the burnt gases are discharged during the following exhaust stroke through the open exhaust valve (s) The valve events 36a & 36b during normal mode operation can be adjusted in phase and/or duration, as is well known, to optimise the combustion process according to the prevailing operating conditions, such as load, speed, temperature, etc. The engine configuration shown in Figure 1 also allows the engine to be operated in different modes as will now be described. The aim of these alternative modes is to allow the engine to capture energy in the form of compressed air while the vehicle is being braked and to use that compressed air during cranking to restart the engine after it has been temporarily switched off or to boost the engine for a short period to counteract the undesirable effect of turbo lag.

For convenience, the strokes of the piston have been given their conventional names for four-stroke operation and these names do not correctly reflect what occurs in the engine cylinder when operating in the alternative modes.

Figure 2 shows the position of the port throttles 22a and 22b during operation of the engine in an air driven motor mode. The valves 18a and 18b are operated with the valve events designated 36a and 36b respectively shown in Figure 6. In this mode, the fuel supply is discontinued as no charge is burnt in the combustion chamber 16.

After closing of the port throttle 22a, the on/off valve 26 is opened to pressurise the intake port between the throttle 22a and the intake valve 18a. This on/off valve 26 may be kept open for the duration of operation in the air driven motor mode. The pressure regulator 28 ensures that the air supply pressure is below the level that can be withstood by the valve spring of the intake valve 18a so that the valve 18a controls the admission of air into the cylinder according to the valve event 36a shown in Figure 6.

When the valve 18a is opened at the commencement of the intake stroke according to the valve event 36a, air is admitted into the engine cylinder 10 under pressure and forces the piston 12 downwards to crank the engine. After the valve 18a is closed at the end of the cranking stroke, the other valve 18b is opened according to the second valve event 36b shown in Figure 6 and air is allowed to escape through the other intake port.

During the following power stroke and exhaust stroke, ambient air is free to enter and leave the cylinder so that no negative work will be done on the piston 12 during these two strokes and the crankshaft accelerates under the cranking power of the four-stroke air driven motor which operates at a high efficiency.

As an alternative to using a pressure regular, which has the effect of limiting the supply pressure of the compressed air and therefore the cranking torque, the on/off valve 26 may be cyclically operated to apply the full tank pressure to the engine cylinder 10, but only for a short period during the intake stroke of the engine after the valve 18a has opened and before the valve 18a is closed.

For the compressor mode operation, the port throttles 22a and 22b are placed in the positions shown in Figure 3.

The valves 18a and 18b are again operated in accordance with the respective valve events 36a and 36b shown in Figure 6.

Once again, the fuel supply is discontinued.

In this mode, during the intake stroke, air is admitted into the engine cylinder by way of the open port throttle 22a and the intake valve 18a. In the ensuing compression stroke, this air is compressed into the second intake port which is closed at this time by the port throttle 22b. The air then flows by way of the one-way valve 34 into the tank for storage at high pressure. Compressing the air into the storage tank 30 requires energy and this is derived from the engine acting as a vehicle brake.

During the following power stroke, the compressed air remaining in the second intake port expands to fill the engine cylinder 10 and it is duly discharged through an exhaust valve during the following exhaust stroke. These two strokes help to reduce the power consumption of the four-stroke air compressor and increase the compressed air production efficiency.

In the temporary boost mode operation of the engine represented by Figure 4, fuel is supplied to the engine and normal combustion takes place with the valve events shown in Figure 5. However, during this time both port throttles 22a and 22b are kept closed, the on/off valve 24 is opened, and all the intake air is supplied by the tank 30 pressurising the first intake port. The pressure regulator 28 is set at a safe boost pressure and this is available to counteract the effect of turbo lag at times when the turbocharger itself is unable to provide the required boost pressure during low load and low speed operation of the engine. As soon as the turbocharger reaches the desired boost pressure, this temporary boost mode will cease and the engine will revert back to its normal mode operation as shown in Figure 1 where both port throttles 22a and 22b are opened and the on-off valve 26 is closed.

In normal mode operation, the port throttles 22a and 22b can also be individually opened or closed for swirl control and load control.

In Figures 1, 2, 3 and 4, the two intake ports are shown diagrammatically as being on opposite sides of the engine but in practice they are on the same side while the exhaust ports, which are not shown in the drawings, are on the opposite side. In practice, a conventional engine with separate intake ports can be modified to implement the invention by the addition of a spacer plate located between the cylinder head and the intake manifold. The intake port throttles as well as the connectors for the lines 24 and 34 can be built into the spacer plate. The valves 26 and 34 may also be integrated into such a spacer plate.

It is important to note that when operating in the air driven motor mode, the opening events of the cams 36a and 36b must not overlap at any time as this would allow the compressed air in the tank to leak directly to atmosphere.

The second valve event 36b shown in Figure 6 has a reduced lift to avoid collision between the second intake valve 18b and the piston 12 near IDC so that phase shifting of a full lift cam for the second valve event is not recommended. It is therefore preferred to rely on cam switching and to select a different profile for the second cam 36b with a lesser lift. The duration of the second cam 36b is not critical and it can if desired extend further into the exhaust stroke for both the air driven motor mode and the compressor mode.

The port throttles 22a and 22b have been represented diagrammatically in Figures 1 to 4 by butterfly throttles but it will be appreciated that when then are closed, as in modes shown in Figures 2, 3 and 4 they are called upon to withstand a significant back pressure without leaking.

To meet these demands, it would be possible to design the port throttles as conventional poppet valves but accommodating such a design in the small space available would present packaging problems. A preferred compact design of the port throttle 22b is shown in Figures 7 and 8, but this design would be equally applicable to the port throttle 22a.

The port throttle 22b in Figures 7 and 8 has a valve head 50 that is shaped like the head of a conventional poppet valve. As with a convention poppet valve, the head seal against a conical valve seat 52 which, in this case, is cut into a body 54.

-10 -Instead of being connected rigidly to a straight valve stem, the valve head 50 is connected by a pivot joint 56 to an actuating linkage consist of a thin blade 58 which passes through a slot 60 formed in the housing 54 on the low pressure side of the valve seat 52 and is connected to a spindle 62. The spindle 62 is arranged within a chamber 64 that communicates with the low pressure side of the valve seat and is closed off from the ambient atmosphere by a cover 66.

When the throttle is closed, as shown in Figure 7, the valve head 50 is self aligning with valve seat 52 because of the mating conical surface and this enables an excellent seal to the achieved. Furthermore, the higher the pressure acting on the valve head 50, the more strongly it is urged against its valve seat 52. When, on the other hand, the throttle is open, as shown in Figure 8, the valve head 50 is stored out of the path of the intake air and does not obstruct the engine air intake system.

The linkage used to pull the valve head 50 into the closed position need not comprise rigid members pivotably connected to one another. A resilient arm fixed to the rear face of the valve head 50 is one alternative design that may be adopted to permit self alignment of the valve head 50 with the valve seat 52.

An important advantage offered by the described preferred embodiment of the invention is that it allows four different modes of operation with just one cam switching device applied on one of the intake valves of each engine cylinder, and a set of control valves and port throttles which can be incorporated into a spacer plate mounted between the engine cylinder head and the intake manifold.

In the present invention, there is no need of a whole variety of valve timing schedules to achieve the various operating modes as was the case in earlier prior art -11 -proposals, but just two valve event schedules shown in Figures 5 and 6 will be sufficient, one when fuel is being burnt and the other during all other modes of operation of the engine.

Claims

-12 -CLPiIMS 1. A four-stroke engine having two intake valves per cylinder and two separate intake ports leading to the respective intake valves each controlled by a respective port throttle arranged in close proximity to the intake valve, and a compressed air storage tank connected by way of respective lines to the intake ports, each line incorporating a respective control valve and being connected to the associated intake port at a point lying between the port throttle and the intake valve, wherein, in addition to a normal mode of operation in which fuel is burnt to generate power, the engine is operable in an air driven motor mode in which compressed air is supplied to the engine cylinder from the compressed air storage tank during the intake stroke of the engine by way of one of the intake ports and is discharged from the engine cylinder during the ensuing compression stroke of the engine by way of the other intake port.
2. A four-stroke engine as claimed in claim 1, wherein both intake valves are cam actuated, a first intake valve being operated with a normal intake event during both modes of operation of the engine and a second intake valve being operated with a first valve event during the normal mode of operation of the engine and with a second valve event during the air motor mode operation of the engine, and wherein both port throttles are open during normal mode operation of the engine, and the throttle of the first intake port is closed while the throttle of the second intake port is opened during the air motor mode operation of the engine.
3. A four-stroke engine as claimed in claim 1 or claim 2, wherein the engine is further operable in a compressor mode in which air is drawn into the engine cylinder during the intake stroke by way of one of the -13 -intake ports and is compressed and supplied to the storage tank during the ensuing compression stroke by way of the other intake port.
4. A four-stroke engine as claimed in claims 2 and 3, wherein the first intake valve is operated with the a normal intake event during all modes of operation of the engine and the second intake valve is operated with the same second valve event during both the air motor mode operation and the compressor mode operation of the engine, and wherein the throttle of the first intake port is opened while the throttle of the second intake port is closed during the compressor mode operation of the engine.
5. An engine as claimed in any preceding claim, wherein the valve train driving the second intake valve comprises switchable cams, one cam setting the valve event during normal mode operation of the engine and the second cam setting the valve event during the air driven motor mode and the compressor mode operations of the engine.
6. An engine as claimed in any preceding claim, wherein the engine additionally has a temporary boost, fuel burning mode operation in which both port throttles are closed and pressurised air is supplied to the first intake port from the air storage tank while both intake valves are operated with the valve events for normal mode operation of the engine.
7. An air hybrid engine as claimed any preceding claim, wherein a pressure regulator is provided in the line leading from the air storage tank to the first intake port to limit the pressure in the first intake port to below the sealing limit of the first intake valve while the first control valve remains open.

-14 -
8. An air hybrid engine as claimed in any one of claims 1 to 6, wherein the first control valve is an on/off valve timed to open only during the intake stroke.
9. An air hybrid engine as claimed in any preceding claim, wherein the second control valve is a one-way valve which automatically opens only when the air pressure within the second intake port exceeds the pressure in the compressed air storage tank.
10. An air hybrid engine as claimed in any preceding claim, wherein each port throttle comprises a valve head shaped to seal against a conically tapering valve seat and an articulated or flexible linkage connecting the valve head to a spindle to enable the valve head to be pulled by rotation of the spindle in one direction into sealing engagement with the valve seat and to be moved by rotation of the spindle in the opposite direction to an open position in which the valve head is stored out of the flow path of the engine intake air.*::r: INTELLECTUAL . ... PROPERTY OFFICE 1 5 Application No: GB 1011903.0 Examiner: John Twin Claims searched: ito 10 Date of search: 1 November 2010 Patents Act 1977: Search Report under Section 17 Documents considered to be relevant: Category Relevant Identity of document and passage or figure of particular relevance to claims A -FR2833650A1 (Peugeot Citroen) A -GB 2430975 A (Ma) A -GB2402169A (Lotus Cars) Categories: X Document indicating lack of novelty or inventive A Document indicating technological background and/or state step of the art.Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of before the filing date of this invention.same category.& Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP. WO & US patent documents classified in the following areas of the UKCX Worldwide search of patent documents classified in the following areas of the IPC B6OK; FO2B; FO2M The following online and other databases have been used in the preparation of this search report EPODOC, WPI International Classification: Subclass Subgroup Valid From FO2B 002 1/00 Oi/Oi/2006 B6OK 0006/12 Oi/0l/2006 Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk