GB2085963A - Crankcase compression four stroke engine with piston controlled parts - Google Patents

Abstract

In addition to the normal inlet valves (7) inlet ports (22) are uncovered by the pistons towards the end of the induction strokes to admit air or mixture compressed behind the pistons 3a, 3b). The inlet ports (22) are angled in the wall of the cylinders to provide a substantial tangential component of motion to the incoming charge and possibly also a substantial axial component Figs. 3 and 4 (not shown). A rotary valve (13) is provided to feed the compressed mixture from the crank case (1) to the cylinder in which the induction stroke has just been completed. <IMAGE>

Description

SPECIFICATION Engine This invention relates to reciprocating internal combustion engines.

While the present invention is primarily described in connection in its application to spark ignition or petrol engines, it will be understood that the invention is also applicable to compression ignition or diesel engines.

A conventional four stroke spark ignition engine has the or each cylinder operating with an induction stroke during which the inlet valve is open and an air/fuel mixture is drawn into the cylinder as the piston travels away from the cylinder head. The inlet valve then closes and as the piston travels towards the cylinder head the induced mixture is compressed. Approaching top dead centre on the compression stroke the mixture is ignited by a spark and, as it burns, expansion forces the piston down on the power stroke. On the next return of the piston the exhaust valve is open for the exhaust stroke. The cycle then repeats.

Multicylinder engines are arranged so that the cylinders are at different phases.

Much effort has been devoted over many years for improvement of the efficiency of combustion in internal combustion engines with a view both to improving the power output from a given amount of fuel of a given grade and to improving the cleanliness of the exhaust gases.

In order to increase the amount of fuel/air mixture introduced into the cylinders of a spark ignition engine, recourse has been had in the past to the use of a supercharger, which is effectively a fan or blower to boost the flow of mixture during the induction stroke. This increases the effective power for a given size of engine.

One idea which has been proposed on various occasions, but has not had any marked commercial success, is the use of the power and/or induction strokes of a four stroke cycle to compress a supplementary change of air or fuel/air mixture behind the piston, and especially in the crank case, and then to admit this supplementary change to the combustion chamber at the conclusion of the induction stroke.

According to the present invention, there is provided a reciprocating internal combustion engine wherein the or each cylinder has valve controlled inlet exhaust ports and at least one additional inlet port which is uncovered by the piston on the induction stroke to admit additional air or air/fuel mixture compressed behind the piston, in which the or each said additional inlet port is arranged obliquely in the cylinder wall to provide a substantial tangential component to the motion of the additional air or mixture admitted.

Preferably, the or each said additional inlet port is also angled to impart to the additional air or mixture a substantial component of motion axially of the cylinder.

This axial component may be towards or away from the cylinder head and in the latter case, the piston may be provided with a bowl or other formation to improves the mixing characteristics.

The introduction of a tangential component, and also where appropriate of an axial component, to the motion of the additional air or mixture improves the mixing and hence the combustion efficiency.

This may enable a lower grade or quality of fuel to be used. Alternatively, it may enable a higher energy output to be achieved from a given quantity of fuel.

Preferably, the engine has one or more pairs of opposed pistons, the or each pair being associated with a common sealed crank case or crank case zone, the pistons operating 180 out of phase so that air or mixture is compressed in the crank case or zone during the power stroke of each piston (and induction stroke of the other), and valve means is provided to control the flow of the compressed air or mixture to the inlet port uncovered by the piston completing its induction stroke.

The said valve means may be a rotary valve driven at half engine speed and is preferably associated with a valve means controlling admission of gas or mixture to the crank case or zone during the compression and exhaust strokes of the pistons.

The invention will be further described with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a section through a pair of cylinders of a preferred form of engine according to the invention, showing the piston at bottom dead centre; Figure 2 is a section taken across a cylinder at the level of additional inlets; Figure 3 is a partial axial section showing axial applying of an additional inlet; and Figure 4 is an axial section showing a variation.

Fig. 1 shows one pair of cylinders, and the preferred embodiment of the invention will be described as being a twin cylinder engine, but it will be appreciated that by arranging two or more pairs of cylinders side-by-side and connecting them to a common crank shaft, engines of larger size may be built. In such a case, it is envisaged that each pair of cylinders will have associated with it a sealed zone of a common crank case and in the description of the two cylinder engine which follows, reference will be made to the zone associated with the two cylinders illustrated as the crank case.

Fig. 1 illustrates a crank case 1 and a pair of opposed cylinders 2a and 2b each of which has an associated piston 3a or 3b respectively. A fly wheel 4 is located in the crank case 1 and carries a pair of crank pins 5a and 5b connected to the corresponding pistons 3a and 3b by connecting rods 6a, 6b. Each cylinder is also provided with an inlet port controlled by an inlet valve 7 and connected to a carburettor 8, and with an exhaust port controlled by an exhaust valve 9. Also shown are spark plugs 10.

As described thus far, and details of cam shafts and similar items have been omitted as being generally conventional, the engine will operate as a generally conventional opposed two cylinder four stroke spark ignition engine.

As illustrated, the pistons are both at bottom dead centre with the exhaust valve 9 in the cylinder 2b shown open to indicate that the exhaust stroke is about to commence and that the power stroke has finished. The piston 3a has just finished its induction stroke and is about to commence the compression stroke.

In order to provide for additional air/fuel mixture to be admitted to the cylinder at the end of the induction stroke, i.e. cylinder 2a as illustrated, means is provided for admitting mixture from a carburettor 1 2 into the crank case 1, compressing it and then transferring it to the cylinder as the piston completes the induction stroke. For this purpose, a rotary valve 1 3 is mounted in a housing 1 3a and is driven at half engine speed.

It will be appreciated that the valve 1 3 connects the interior of the crank case 1 with the carburettor 1 2 during the outward i.e.

exhaust and compression strokes of the pistons 3a and 3b so that mixture is induced into the crank case and the zone of the cylinders behind the pistons. This communication is then closed so that during the succeeding inward, i.e. power and induction stroke, this mixture is compressed within the crank case and zone of the cylinders behind the pistons, and at that stage the rotary valve 1 3 opens communication between the interior of the crank case 1 and the relevant one of two transfer pipes 14a, 1 4b which open into the cylinders 2a and 2b just above the tops of the pistons when in bottom dead centre position.

The valve 1 3 is arranged to divert the mixture into the transfer pipe 1 4a when the piston 3a has reached the end of the induction stroke, and into the transfer pipe 1 4b when the piston 3b has ended its induction stroke. The compressed mixture is thus at least partially admitted into the appropriate cylinder to increase the charge of mixture therein. As the compression stroke starts. the port forming the end of the transfer pipe 1 4a or 1 4b is closed by the piston.

In order to create swirl within the combustion chamber, and thereby improve mixing and subsequently combustion of the mixture within the combustion chamber, the inlets from the transfer pipes 1 4a and 1 4b are angled to produce substantial tangential and axial components of motion of the incoming mixture. Referring particularly to Fig. 2, it will be seen that the mixture is fed from the transfer pipe to manifolds 21 and then through angled ports 22 in the cylinder wall.

These ports are shown as being very substantially inclined to the radial direction so as to impart a substantial tangential component of motion, and Fig. 3 shows how the ports 22 may also be angled to give a substantial axial component of motion. As illustrated in Fig. 3, this axial component of motion is towards the cylinder head, and in an alternative shown in Fig. 4, the ports 22 are directed towards the piston, when the latter is in its bottom dead centre position so that the incoming additional charge impinges on the piston to introduce further swirl or turbulence. In order to control and possibly improve this, the crown of the piston is shown as being provided with a bowl 24.

By having the cylinders operating out of phase, i.e. one piston on the power stroke while the other is on induction, not only is the flow of power to the fly wheel 4 improved, but also the amount of additional mixture which may be admitted to the cylinders is increased, since it is a result of compression behind both pistons at each stroke.

It is envisaged that each of the carburettors 8 and 1 2 would normally be controlled by a single throttle control, but it is of course possible to have a different throttle control for throttle for the carburettor 1 2. It is also possible to have a single carburettor supplying mixture to both pistons and the crank case. It is also possible for the carburettoi- 8 to be omitted and all the fuel to be introduced via the transfer ports 14a and 14b.

It is envisaged that the described horizontally opposed twin cylinder engine will be fitted with a gear train to drive a cam shaft at half engine speed, and will have an overhead valve mechanism to operate the illustrated normal inlet and exhaust poppet type valve.

Ignition will be by a battery powering a twinlead high tension coil wired through one set of contact points operated by a two lobe cam driven from the crank shaft gear train and running at half engine speed.

It will be understood that the engine operates normally as a conventional four stroke engine with the addition that the additional mixture is compressed in the crank case 1 and behind the pistons and admitted to the appropriate cylinder at the conclusion of the induction stroke. It is envisaged that the transfer ports 1 4a and 1 4b will be uncovered at approximately 20 from bottom dead centre so that the compressed mixture will start to flow at that time and the inlet valve 7 will close at approximately bottom dead centre and also the rotary valve 1 3 will close communication between the crank case and transfer pipe at approximately bottom dead centre to retain the maximum amount of mixture in the cylinder.

As so far described, the invention is applied to a spark ignition engine, but will also be appreciated that it is applicable to a compression ignition engine in which the fuel is injected at high pressure into the already compressed air which has been induced into the cylinder. In this case, the compression in the crank case and behind the pistons will be used to force extra air into the cylinders which will then be compressed during the compression stroke and the appropriate amount of fuel for the increased amount of air will then be injected and will ignite as is normal in a compression ignition engine. In this case, the carburettors 8 and 1 2 will be omitted, as will the spark plugs and will be replaced by fuel injection devices.

It is also of course possible to use the invention with fuel injection used in conjunction with a spark ignition engine.

By using the arrangement according to the invention it has been found possible to generate more power from an engine of given size so that the power weight ratio of the engine is thus increased. It has also been found possible to operate with a comparatively low compression ratio and with a comparatively low grade fuel Various other modifications may be made within the scope of the invention.

Claims (7)

1. A reciprocating internal combustion engine wherein the or each cylinder has valve controlled inlet and exhaust ports and at least one additional inlet port which is uncovered by the piston on the induction stroke to admit additional air or air/fuel mixture compressed behind the piston, in which the or each said additional inlet port is arranged obliquely in the cylinder wall to provide a substantial tangential component to the motion of the additional air mixture admitted.

2. An engine as claimed in claim 1, in which the or each said additional inlet port is also angled to impart to the additional air or mixture a substantial component of motion axially of the cylinder.

3. A engine as claimed in claim 1 or 2, having one or more pairs of opposed pistons, the or each pair being associated with a common sealed crank case or crank case zone, the pistons operating 180 out of phase so that air or mixture is compressed in the crank case or zone during the power stroke or each piston (and induction stroke of the other), and valve means is provided to control the flow of the compressed air or mixture to the inlet port uncovered by the piston completing its induction stroke.

4. A engine as claimed in claim 3, in which the said valve means is a rotary valve driven at half engine speed.

5. An engine as claimed in claim 4, in which said rotary valve is associated with a valve means controlling admission of gas or mixture to the crank case or zone during the compression and exhaust strokes of the pistons.

6. An engine as claimed in any of the preceding claims, in which a separate carburettor or other mixture controlling device is provided to control the admission of mixture to be compressed behind the piston(s).

7. A reciprocating internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings.