GB2263307A

GB2263307A - Four-stroke engine with a charge pump.

Info

Publication number: GB2263307A
Application number: GB9200241A
Authority: GB
Inventors: Christopher John Mccann
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-01-07
Filing date: 1992-01-07
Publication date: 1993-07-21
Also published as: GB9200241D0

Abstract

The diaphragm 21 operated by crankcase pressure variations charges the inlet tract 15. In a multi-cylinder engine separate diaphragm pumps operated by pressure variations in respective crank chambers may supply respective inlet tracts or a common manifold. <IMAGE>

Description

Title: Four stroke internal combustion engine with inlet gas pressurisation DESCRIPTION The present invention relates to a four stroke internal reciprocating piston combustion engine with inlet gas pressurisation.

In a conventionally aspirated four stroke internal combustion engine, air from the inlet manifold is drawn into the combustion chamber by downward movement of the piston on its so-called inlet stroke when the inlet valve is open. With such an arrangement there is no compression of the inlet air. It is known to provide pressurisation of the inlet air in a four stroke engine utilising either an exhaust driven turbocharger or an engine driven supercharger.

Substantial boost pressures can be achieved by either of these means. However, in the case of the turbo charger there is an inevitable lag in generation of the boost whilst in the case of the supercharger there is a penalty to be paid in terms of requiring engine horse power to drive the supercharger. It is recognised that increased power output can be achieved by pressurising the inlet air since it gives rise to a denser charge in the combustion chamber. Even a small increase in inlet pressurisation across the rev range, especially at low revs, would be advantageous if it could be provided in a manner which did not drain engine power.

It is an aim of the present invention to provide inlet pressurisation without the use of turbocharger or a mechanical supercharger driven directly from the engine.

Accordingly, the present invention provides a four stroke internal reciprocating piston combustion engine comprising a reciprocal piston one end face of which is presented to a combustion chamber and its other end face serves to control pressurisation of inlet air in response to movement of the piston.

More particularly the invention comprises a compression chamber disposed in the inlet tract and in which air is pressurised in response to movement of the piston. The compression chamber has an inlet for induction air provided with a non-return valve to prevent reverse flow, and an outlet to the inlet manifold also provided with a non-return valve to preclude air being sucked from the inlet manifold into the compression chamber. In a preferred embodiment the compression chamber incorporates a flexible diaphragm one side of which is in communication with the crank case of the engine and subject to the fluctuating pressure of the crank case which is otherwise sealed whereby the diaphragm moves to compress air in the compression chamber on downward movement of the piston.

By means of the compression chamber the density of air can be increased up to two times that of a normally aspirator engine (assuming 100% efficiency) by virtue of the fact that there is compression of the air in the compression chamber during the firing stroke.

The present invention will now be described further by way of example only with reference to the accompanying drawings, in which Figures 1 to 4 are cross-sectional views illustrating diagrammatically the cycles of a four stroke internal combustion engine according to the invention.

An engine according to the invention comprises a cylinder block 1 having a cylinder 3 receiving reciprocally therein a piston 5 connected by way of connecting rod 7 to a rotatable crank 9 journalled in bearings (not shown). Fitted to the block is a cylinder head which in this instance is of double overhead cam type operating inlet valve 11 and exhaust valve 12. A combustion chamber is defined above the piston and an inlet manifold is shown at 15 and an exhaust port at 17.

The inlet tract includes a compression chamber 21 provided with a respective non-return valve 23;25 on the upstream and downstream sides. The non-return valve 23 on the upstream side allows air to flow from the inlet tract into the compression chamber but not in the reverse direction whilst the non-return valve 25 on the downstream side allows air to flow out of the compression chamber into the inlet manifold but not in the reverse direction. Read valves are envisaged for the non-return valves but any other suitable type may be employed. In contrast to a conventional four stroke internal combustion engine the crank case chamber is sealed so as to be subject to pressure fluctuations according to movement of the piston.

The compression chamber includes a flexible diaphragm 26 and the crank case chamber communicates with one side of the flexible diaphragm, the other side forming part of the compression chamber. The flexible diaphragm may be a plastics material such as silicone rubber.

In operation of the engine the conventional four strokes apply, namely induction of air on the downward stroke of the piston (see Figure 1) with the inlet valve being open during this stroke. Subsequent compression of the air and fuel mixture during an upward stroke of the piston with the inlet and exhaust valves being closed (see Figure 2). The combustion phase generating a downward stroke of the piston as seen in Figure 3 followed by the exhaust stroke, ie. an upward movement of the piston with the exhaust valve open as represented by Figure 4.

Movement of the flexible diaphragm separating the crank case and the compression chamber will be determined by the relative pressures to which the opposite sides are subjected. The volume of a sealed crank case will fluctuate in response to reciprocal movement of the piston and as a consequence these will be pressure fluctuations. However, in the present invention those pressure and volume fluctuations serve to move the flexible diaphragm. Thus on the induction stroke downward movement of the piston generates a movement of the flexible diaphragm into the compression chamber. This arises since the theoretical reduction in crank case volume generates an increase in pressure, relative to the pressure is the inlet tract where air is flowing in the inlet tract between the compression chamber and into the combustion chamber.On the subsequent compression stroke upward movement of the piston generates a reverse movement of the diaphragm, ie. suction on the diaphragm. In effect the volume in the crank case chamber attempts to remain the same and thus downward movement of the piston which would otherwise create a compression force must result in movement of the diaphragm. On the subsequent firing stroke the downward movement of the piston generates movement of the flexible diaphragm into the compression chamber and since the inlet valve is closed during this movement a pressure will be generated in the compression chamber and correspondingly passed through to the inlet manifold.During the final exhaust stroke upward movement of the piston causes the flexible diaphragm to return expanding the compression chamber whilst compressed air is retained in the inlet manifold since the inlet valve is closed and the non-return valve prevents reverse flow into the compression chamber.

By utilising read valves for the non-return valve negligible resistance to flow is created in the opening direction and the flexible diaphragm itself has little resistance to movement. This ensures that there is a cyclical action of the diaphragm rather than simply giving rise to pressurisation in the crank case.

The foregoing description has been made with reference to a single cylinder engine, but the arrangement can be applied to a multi-cylinder engine.

In such an application, the space below each piston will have to be isolated from one another to avoid cancelling out the effects of piston movement. Each piston and associated crank case volume drives a respective compression chamber. The outlets from the respective compression chamber may be direct to the associated inlet tract or lead to a plenum chamber from which inlet ports branch to more than one of the cylinders of the engine.

Claims

1. A four stroke reciprocating piston internal combustion engine comprising a reciprocal piston one end face of which is presented to a combustion chamber and its other end face serves to control pressurisation of inlet air in response to movement of the piston.

2. An engine as claimed in claim 1 comprising a compression chamber disposed in the inlet tract and in which air is pressurised in response to movement of the piston.

3. An engine as claimed in claim 2 in which the compression chamber has an inlet for induction air provided with a non-return valve to prevent reverse flow, and an outlet to the inlet manifold also provided with a non-return valve to preclude air being sucked from the inlet manifold into the compression chamber.

4. An engine as claimed in claim 2 or 3 in which the compression chamber incorporates a flexible diaphragm one side of which is in communication with the crank case of the engine and subject to the fluctuating pressure of the crank case which is otherwise sealed whereby the diaphragm moves to compress air in the compression chamber and hence the inlet manifold on downward movement of the piston at least during the firing stroke.

5. An engine as claimed in claim 2 in which other or both of the non-return valves are read valves.

6. An engine as claimed in any one of claims 2 to 5 when of multi-cylinder type in which there is a compression chamber for each piston.

7. An engine as claimed in claim 6 in which the respective compression chambers deliver compressed air to an inlet manifold communicating with all the cylinders.

8. A four stroke internal reciprocating piston combustion engine constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.