GB2069041A - Crankcase compression four- stroke engine - Google Patents

Abstract

In order to increase the amount of air or fuel/air mixture introduced into the cylinders there is provided, in addition to the normal inlet valve (7) to the combustion chamber (2a or 2b), and inlet (14a or 14b) uncovered by the piston towards the end of the induction stroke and fed at that time with air or mixture compressed behind the piston (3a and 3b). As illustrated two opposed pistons (3a and 3b) work 360 DEG out of phase and a rotary valve (13) is provided to direct the compressed mixture from the crank case to the combustion chamber in which the induction stroke has just been completed. <IMAGE>

Description

SPECIFICATION Internal combustion 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 this compressor 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.

In order to increase the amount of fuel for 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.

According to the present invention, there 5 provided a reciprocating internal combustion engine in which the or each cylinder has valve controlled inlet exhaust ports and an additional inlet port which is uncovered by the piston on the induction stroke to admit air or air/fuel mixture compressed behind the piston.

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 1800 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 drive 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 drawings, in which: Figure 1 is a diagrammatic 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 plan view of a form of housing for a rotary valve; Figure 3 is a side elevation of the housing of Figure 2; and Figure 4 is an elevation of the valve member cooperable with the housing o Figures 2 and 3.

Figure 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.

Figure 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 o, crank pins 5a and Sb 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 12 into the crank case 1, compressing it and then transferring it to the cylinder as the piston complete 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. The housing 1 3a and valve 13 are better illustrated in figure 2 to 4.

It will be appreciated that the valve 13 connects the interior of the crank case 1 with the carburettor 12 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 13 opens communication between the interior of the crank case 1 and the relevant one of two transfer pipes 1 4a, 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 13 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 3D 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.

Turning now to figures 2 to 4, the housing 1 3a is shown as having an axial bore 21 in which the valve 13 is received for rotation with a substantially sealing fit. The carburettor 12 is to be secured to the top of the housing 1 3a using a pair of threaded holes 22 so that the carburettor communicates with a vertical bore 23 itself communicating with the axial bore 21 and aligned with a channel 25 leading to an inlet port to the crank case 1. Communication between the bore 23 and channel 25 is controlled by a cross bore 26 in the valve 13. The housing 1 3a is also shown as having a pair of cross bores 27 communicating with the bore 23. These may be used to connect the carburettor 12 with the inlet ports for the cylinders 2a and 2b, thus obviating the need for separate carburettors 8.

The crank case 1 has an outlet port communicating with a channel 28 leading to the bore 21 and communicating between this channel 28 and ducts 29a and 29b leading to the transfer pipes 1 4a and 1 4b is controlled by a diametral bore 30 in the valve 13. This bore 30 communicates with an axial bore 31 and a radial bore 32 which alternatively communicates with the ducts 29a and 29b.

The valve 13 rotates at half engine speed and is timed to admit mixture from carburettor 12 to the crank case during the outward movement of the pistons 3a and 3b, thus giving an induction, and to pass the compressed mixture for the crank case to the appropriate transfer pipes 1 3a or 1 3b, when the pistons are approximately at bottom dead centre and to close the transfer pipes as the pistons move away from bottom dead centre as illustrated in Figure 1.

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 12 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 12. It is also possible to have a single carburettor supplying mixture to both pistons and the crank case, e.g. as described above.

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 twin-lead head 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 20C 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 13 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 by injected and will ignite as is normal in a compression ignition engine. In this case, the carburettors 8 and 12 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 will 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.

Various other modifications may be made within the scope of the invention.

Claims (6)

1. A reciprocating internal combustion engine in which the or each cylinder has valve controlled inlet exhaust ports and an additional inlet port which is uncovered by the piston on the induction, stroke to admit air or air/fuel mixture compressed behind the piston.

2. An engine as claimed in claim 1, 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 1 800 out of phase so that air or mixture is compressed in the crank case 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.

3. A engine as claimed in claim 2, in which the said valve means is a rotary valve driven at half engine speed.

4. An engine as claimed in claim 3, 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.

5. 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).

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