GB2271614A

GB2271614A - A supercharged four-stroke engine

Info

Publication number: GB2271614A
Application number: GB9221871A
Authority: GB
Inventors: William Noel Hutton
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-10-19
Filing date: 1992-10-19
Publication date: 1994-04-20
Also published as: GB9221871D0

Abstract

Air compressed in the crankcase 10 on the exhaust stroke is transferred to the chamber 27 to be supplied to the combustion chamber with air compressed on the intake stroke when the valve 30 is opened. An injector 14 which supplies fuel is controlled in response to the pressure in the chamber 27. <IMAGE>

Description

A SUPERCHARGED ENGINE This invention relates to a supercharged engine.

Attempts to supercharge engines have in the past been based on systems, for example pressure wave reactors (PWRs), which attempt to apply by external means an overpressure to the air/fuel mixture compressed above a piston in the cylinder head. Problems have arisen in relation to the extra mechanical parts required to implement the application of this overpressure.

In GB 649016, a different approach is adopted. In that patent, an attempt is made to return mixture put under pressure by the downstroke of the piston to the space above the piston through a rotary valve timed to be synchronised with the piston stroke. The rotary valve is bidirectional and is open on the downstroke of the piston so that there is no increase in pressure and hence no true supercharging effect.

Another proposal in GB 1433182 relates not to supercharging but to the transfer of mixture between at least two cylinders of a multicylinder engine, with a view to reducing toxic waste in fuel emissions.

There have been other proposals which have relied on transfer of compressed mixture from beneath the piston to the space above the piston but none have been satisfactorily implemented. One system which is being satisfactorily implemented is described in my earlier British Patent Application No. 9108241.2, the contents of which are herein incorporated by reference. That application describes an engine in which supercharging is accomplished by transferring compressed mixture to the space above the piston through a reed valve and a pressure chamber.

While this system provides an efficiently supercharged engine, fuel entering the crankcase as a mixture can wash away lubricant in the crankcase. The mixture thus includes oil to replace this lubricant. The earlier system also results in exhaust emission rich with CO waste.

The present invention provides a supercharged four stroke engine comprising a piston reciprocally mounted in a cylinder; first unidirectional valve means for introducing air below the piston, the unidirectional valve means being opened in response to pressure upstream of the valve means exceeding that downstream of the valve means; a chamber extending from an inlet below the piston to an outlet above the piston; a second unidirectional valve means arranged at said inlet so that air enters the chamber in response to the pressure below the piston exceeding that in the chamber, the arrangement being such that a first charge of air introduced below the piston as the piston moves up is transferred into the pressure chamber on the subsequent downstroke of the piston and a second charge of air introduced below the piston as the piston again moves up is transferred into the pressure chamber on the next downstroke; a controllable valve at the outlet of the chamber operable to control the ingress of air to a zone above the piston whereat ignition occurs, and a fuel injection device for injecting fuel into said zone, said controllable valve being controlled by timing means in dependence on the reciprocation of said piston so that the controllable valve opens to permit air under pressure in said chamber to enter the zone above the piston, after both said first and second charges have been transferred to the chamber.

The supercharging effect arises as a result of using the working downstroke of the piston to transfer an extra charge of air to the pressure chamber and thence to the zone above the piston before ignition. Even allowing for considerable losses, an increase in pressure of around 50% is achievable if the chamber is comparable in volume to the stroke displacement of the engine.

The invention has the advantage of requiring no driving parts and no timing means to control the flow of air into the crankcase and to the pressure chamber, since the unidirectional valves are pressure responsive. In the preferred embodiment, reed valves are used.

The present invention differs from the system described in my earlier Application No. 9108241.2 by being applied to a fuel injection system where fuel is injected into the ignition zone in a controlled manner and timed to the ingress of pressurised air from the chamber. This reduces the quantity of CO in the exhaust emissions. Furthermore, the crankcase can be more easily lubricated.

The system also has a particular advantage that it is possible to control injection of fuel by the fuel injection device in response to the pressure in the pressure chamber so that the quantity of fuel can be adapted to the load and speed of the engine.

For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a diagrammatic view of a four stroke single cylinder engine.

Figure 1 shows a cylinder 2 in which is reciprocally mounted a piston 4 on a crankshaft 6. As is well known, the crankshaft 6 is mounted to a rotatable flywheel 8 so that rotation of the flywheel 8 causes the piston 4 to slide up and down within the cylinder 2. The precise details of the piston mounting arrangement are well known in the art and are not material to the invention so they will not be described further herein.

The crankshaft and flywheel are mounted in a crank case 10.

The crank case 10 has an inlet 12 for receiving ambient air.

A reed valve 16 is arranged between the inlet 12 and the crankcase 10 and opens to allow the air to pass through when there is a sufficient pressure difference across it to cause the valve to open. With the piston at top dead centre as shown in Figure 1 the pressure in the cylinder is less than the pressure at the outlet of the inlet tract 12 so the reed valve 16 opens automatically. It will also be noted that a reed valve is essentially a one way valve permitting air to pass in one direction but not in the reverse direction. At the top of the cylinder 2 there is an exhaust port 18 opening into an exhaust conduit 20. The exhaust port 18 is closed by an exhaust valve 22 which is timed to open to release waste mixture from the cylinder in synchronism with the firing stroke of the piston as will later be described.

Figure 1 also illustrates a pressure chamber 27 having an inlet 24 at an outlet of the crankcase 10 at the base of the cylinder 2 and an outlet communicative with an inlet port 26 at the top of the cylinder 2. The inlet port is closed by a inlet valve 30 which is timed to open and close in a manner described hereinafter. There is a reed valve 32 located at the inlet 24 of the pressure chamber 27 which opens automatically when the pressure in the crankcase exceeds by a predetermined amount the pressure in the chamber 28. For maximum benefit to be derived from the present invention the volume of the pressure chamber should be comparable with the stroke displacement of the engine. The air in the chamber 28 is supplied to the top of the cylinder through the inlet port 26 with a timing described hereinafter so as to supercharge the engine. As one example, the pressure chamber can take the form of a circular metal tube having as an example an internal chamber of 38mm, a thickness of 2mm and a volume of 500cc.

When charged, the chamber will hold a volume of 750-800cc air under pressure. Of course, other implementations of the pressure chamber are possible.

A fuel injection device 14 is provided, again in a known manner, to inject fuel above the piston when a charge of air is received.

The operation of the engine will now be described.

The operation is similar to that described in my earlier Application No. 9108241.2 to which reference is made.

Figure 1 shows the piston 2 at top dead centre. As the pressure in the crankcase is less than the pressure of air entering the crankcase, the reed value 16 opens to permit air to enter the cylinder 2 and crankcase 10. The reed valve 32 remains closed. As ignition occurs, the piston 2 is forced downwards on its work stroke causing a rapid increase of pressure in the crankcase 10. The reed valve 16 hence closes and the reed valve 32 opens to permit a charge of air swept from the cylinder during the down stroke to enter the pressure chamber 27.

The piston next moves up with the exhaust port 18 opened to allow the release of waste gases from the cylinder head. The decrease of pressure in the crankcase causes the reed valve 16 to open to permit a second charge of air to enter the crankcase 10 while the reed valve 32 remains closed. At the down stroke of the piston 2, the inlet port 26 is opened to allow the air from the pressure chamber 27 to enter the cylinder above the piston, while the second charge of air is transferred from the crankcase to the pressure chamber 28.

At the work stroke of the next cycle, the charge of air transferred to the pressure chamber supplements the charge remaining there as a result of the compression stroke of the previous cycle. Hence there is, just prior to fuel injection and ignition, roughly two charges of air in the pressure chamber, less air lost through dead space remaining in the crankcase. Of course, it is important that fuel is injected at a pressure exceeding that in the pressure chamber, greater than 101b sq. in. Available fuel injectors satisfy this criteria. The pressure of this air is hence approximately twice that which it would normally be after the compression stroke so that the engine is supercharged. A practical assessment of "lost volume" around the flywheel, reed valves etc. lead to 11/2 atmospheres being attainable in the cylinder head which is a boost of about 71b. This gives a large increase in performance and should improve economy if correctly utilised.

Reference numeral 15 denotes a pressure sensor and reference numeral 17 denotes a release valve for safety purposes. The pressure sensor could be coupled to a control device which could monitor the pressure and control the injection of fuel in response thereto. This would increase the efficiency of the engine.

Claims

CLAIMS:

1. A supercharged four stroke engine comprising a piston reciprocally mounted in a cylinder; first unidirectional valve means for introducing air below the piston, the unidirectional valve means being opened in response to pressure upstream of the valve means exceeding that downstream of the valve means; a chamber extending from an inlet below the piston to an outlet above the piston; a second unidirectional valve means arranged at said inlet so that air enters the chamber in response to the pressure below the piston exceeding that in the chamber, the arrangement being such that a first charge of air introduced below the piston as the piston moves up is transferred into the pressure chamber on the subsequent downstroke of the piston and a second charge of air introduced below the piston as the piston again moves up is transferred into the pressure chamber on the next downstroke; a controllable valve at the outlet of the chamber operable to control the ingress of air to a zone above the piston whereat ignition occurs, and a fuel injection device for injecting fuel into said zone, said controllable valve being controlled by timing means in dependence on the reciprocation of said piston so that the controllable valve opens to permit air under pressure in said chamber to enter the zone above the piston, after both said first and second charges have been transferred to the chamber.

2. An engine as claimed in claim 1 wherein the chamber is comparable in volume to the stroke displacement of the engine.

3. An engine as claimed in claim 1 or 2 wherein the unidirectional valves are reed valves.

4. An engine as claimed in claim 1, 2 or 3 wherein injection of fuel by the fuel injection device is controlled in response to the pressure in the pressure chamber so that the quantity of fuel can be adapted to the load and speed of the engine.

5. A supercharged four stroke engine substantially as herein described with reference to or as shown in the accompanying drawings.