WO1996001940A1

WO1996001940A1 - Internal combustion engine

Info

Publication number: WO1996001940A1
Application number: PCT/GB1995/001633
Authority: WO
Inventors: Allan Oades
Original assignee: Allan Oades
Priority date: 1994-07-12
Filing date: 1995-07-11
Publication date: 1996-01-25
Also published as: AU2894795A

Abstract

An internal combustion engine having at least one cylinder (2) with a primary piston (3) slidable therein, the primary piston (3) being linked to a crankshaft (4) to provide power output from the engine, is characterised in that the upper part of the cylinder (2) has a secondary piston (5) slidable therein, the secondary piston being driven by cam means (9) which are in turn driven by said crankshaft (4) and being arranged to move at least to maintain the compression of the charge after the primary piston passes top dead centre, whereby ignition of the charge can take place when the primary piston has passed top dead centre.

Description

INTERNAL COMBUSTION ENGINE Field of the Invention

This invention relates to an internal combustion engine having a movable cylinder head. Background to the Invention

In a conventional internal combustion engine, during the compression stroke when induced air (or air and fuel mixture) is compressed, the compressed fuel/air charge is ignited before the piston reaches top dead centre (TDC). This means that part of the force developed by the expanding gases is -directed at the piston when the crank is still near to a position in which it is aligned with the cyl¬ inder longitudinal axis and therefore the turning moment is very small. It is desir¬ able to be able to unleash the energy of the explosion when the piston has already passed TDC, but unfortunately this would mean that the position of maximum compression is also passed, reducing the efficiency of the engine. Summary of the Invention

According to the invention there is provided an internal combustion en¬ gine having at least one cylinder with a primary piston slidable therein, the pri¬ mary piston being linked to a crankshaft to provide power output from the engine, the upper part of the cylinder having a secondary piston slidable therein, the sec- ondary piston being driven by cam means which are in turn driven by said crank¬ shaft and being arranged to move at least to maintain the compression of the charge after the primary piston passes top dead centre, whereby ignition of the charge can take place when the primary piston has passed top dead centre.

Preferably, the secondary piston contains at least one valve, for example a poppet valve operable by said cam means, to open a chamber in said secondary pis¬ ton which in turn selectively communicates with an outlet and an inlet port in the wall of the cylinder as the secondary piston moves up and down. A single valve may be used for both induction and exhaust and may be made large to maximise gas flow. Advantageously, an exhaust suction device is provided to purge the ex¬

haust gases from the cylinder after the power stroke. The engine suitably operates

on a four-stroke cycle.

The secondary piston is preferably spring-biased upwardly, and is moved

downwardly by the direct action of a rotary cam. It is preferably arranged to in¬

crease the compression of the charge after the primary piston passes TDC.

It is expected that the increased power output on the crankshaft as a result of this arrangement will significantly exceed the additional power absorbed in the

cam drive means. The invention will drastically reduce machining costs, because only one block has to be cast and machined; a separately machined cylinder head is not required. Problems resulting from failure of the gasket between the cylinder head and block are obviated. Brief Description of the Drawings

In the drawings, which illustrate diagrammatically the functioning of an en¬ gine according to an exemplary embodiment of the invention:

Figures 1 to 6 are sectional elevations of the upper part of one cylinder of the engine at various stages of a four-stroke internal combustion cycle; Figure 7 is an elevation at right angles to the views of Figures 1 to 6 of the secondary piston and its associated cam;

Figure 8 is a horizontal sectional view through the engine; and

Figure 9 is an enlarged side elevation of a preferred form of inlet valve for use in the engine. Detailed Description of the Illustrated Embodiment

Referring to the drawings, the engine block 1 has a cylinder bore 2 in which a primary piston 3 reciprocates. The primary piston 3 is coupled by a connecting rod to a crankshaft 4 in conventional manner. In place of the cylinder head with the inlet and exhaust valves of a conventional engine, a secondary piston 5 is slida- bly mounted in an upper extension of the bore 2. The secondary piston 5 has a helical compression spring 6 seated in a recess 7 in an insert 8 in the upper end of the bore 2 to bias it upwardly away from the primary piston 3, while a rotary over¬ head cam 9, driven from the engine crankshaft, causes the secondary piston 5 to move down against the spring bias. The cam 9 is carried by a driven shaft extend¬ ing along the engine block.

The insert 8 is suitably held in place by screws or bolts passing through an outwardly-directed flange on the top of the cylinder block 1. By removing the screws or bolts, the insert can be lifted out with the secondary piston 5, permitting the secondary piston to be overhauled without the need for a major dismantling of the engine.

A spring-biased poppet valve 10 is mounted in the secondary piston and can be opened under the action of a central portion of the cam 9, as explained hereinafter with reference to Figure 7, to expose a chamber 11 within the piston 5. The chamber 11 has a series of outwardly-facing openings 12 which can communi¬ cate with an inlet port 13 in the cylinder wall as the piston 5 slides up and down.

The inlet port 13 is supplied by an air filter/carburettor through an external inlet manifold in conventional manner. These components are omitted from the drawings for the sake of clarity; their construction and configuration are well- known and do not require illustration. An exhaust port 14 communicates through a series of circumferentially- spaced apertures 15 (Figures 4 and 5) in the wall of the bore 2 with the combustion space in the cylinder. The apertures are closed by the secondary piston 5 during the induction, compression and power strokes, as hereinafter described. Externally of the cylinder, the port 14 leads to a manifold and thence to a silencer system, with the option of a suction device to assist purging of the cylinder. Again, these well-known components are omitted from the drawings for clarity.

Figures 1 to 6 illustrate the sequence of actions in a four-stroke cycle. In Figure 1 , the primary piston 3 is at the top dead centre position prior to the power stroke. The secondary piston 5 is at a position wherein the exhaust apertures 15 are sealed from the combustion chamber by the rings 16 on the lowermost part thereof, while the sparking plug 17 projecting through the side wall of the cylinder is exposed to the combustion chamber. As the primary piston 3 starts to move downwardly in the cylinder again, the cam rotates towards the position shown in Figure 2, causing the secondary piston to follow the primary piston and thus main¬ tain the compression of the mixture in the combustion chamber. When the pri¬ mary piston reaches a position corresponding to an angle of approximately 20° after TDC, the sparking plug is operated to ignite the mixture. The secondary pis¬ ton continues to follow the primary piston for a short distance down the bore, maintaining compression of the ignited gases until the secondary piston reaches the full extent of its downward movement, as illustrated in Figure 3.

The power stroke of the primary piston then continues, driving the crank¬ shaft round, while the secondary piston is then moved upwardly, so that as the Bottom Dead Centre position of the primary piston is reached, the exhaust aper- tures 15 are exposed to permit the exhaust stroke to start, as shown in Figure 4, and the inlet valve is closed. During the exhaust stroke, the primary piston 3 moves upwardly until it again reaches top dead centre, as shown in Figure 5. The cam is arranged so that the secondary piston remains substantially stationary dur¬ ing the exhaust stroke.

When the exhaust stroke is completed, if necessary with the aid of a suction device, the secondary piston 5 is caused by the cam 9 to move downwards in the bore 2 until the exhaust apertures 15 are closed off from the combustion chamber. The inlet valve 10 then opens, permitting the fresh fuel/air charge (in the case of a petrol (gasoline) carburettor engine) to be drawn in by the downward movement of the primary piston 3, through the inlet port 13, the annular space 18 surrounding the secondary piston, through the circumferential inlet apertures 12 in the piston 5, and thence through the inlet valve 10 to the chamber. When the primary pis¬ ton 3 reaches bottom dead centre, as illustrated in Figure 6, the cam 9 causes the valve 10 to close and, with the secondary piston 5 still held stationary by the cam 9, the primary piston 3 then commences its upward compression stroke, until it reaches its top dead centre position as illustrated in Figure 1. Figure 7 shows the cam 9 and the secondary piston 5 in enlarged form re¬ moved from the cylinder block. The upper part of the secondary piston is pro¬ vided with a pair of rails 20 while a part of the circumference of the cam 9 is provided with flanges 21 which are engageable with the rails to prevent downward movement of the secondary piston. The portion of the circumference of the flange 9 over which the flanges 21 extend are represented in each of Figures 1 to 6 by the thick black line. While the piston 5 is held by the flanges 21 on the cam 9, the central cam surface 22 can then push downwardly on the stem 23 of the poppet valve 10 to open the valve without the risk of the whole piston tending to follow the valve in its downward movement, against the force of the restoring spring 6. It will be seen that the upper end of the secondary piston has a series of sealing rings 24 mounted therein, in addition to the rings 16 at its lower end, to ensure that the air/fuel mixture drawn in is not diluted by leakage in of air from the camshaft casing.

It will be appreciated that, while a spark ignition engine is illustrated, the same principle could be employed in a compression ignition engine, with injection of the fuel being timed to occur after TDC of the primary piston.

It will also be appreciated that, while the drawings show helical compres¬ sion springs controlling the movement of the secondary piston and the valve, hy¬ draulic springs or other devices for applying a biasing force may be used for either or both of these components. Figure 8 is a section through the engine block at the level of the exhaust outlets 15 and the exhaust port 14. The four cylinder barrels 80 each have a plu¬ rality of outlets 15 to a chamber 81 substantially surrounding the barrels, and hav¬ ing four exhaust ports 14 through the engine block 1 which can communicate with an external manifold leading to an exhaust suction device (not shown). It will be seen, therefore, that the removal of exaust gases from the combustion chambers may therefore be effected rapidly and efficiently, with no unnecessary constrictions to impede flow. The engine block also contains coolant 82 and oil 83 passages therethrough in conventional manner. The positions of the sparking plugs 17 just below the level of the chamber 81 are indicated by shaded portions. Figure 9 shows one inlet valve 10 having a plurality of vanes 90 formed on the rear face thereof. The vanes 90 are arranged to cause the incoming fuel/air charge to swirl as it enters the combustion chamber, thus enhancing mixing and aiding efficient combustion. The provision of such vanes is relatively straightfor¬ ward in the engine of the invention, since only one large inlet valve is needed in each cylinder, with no separate exhaust valve to be accommodated. Achieving the desirable swirling action is much less easy in conventional engines having exhaust and inlet valves side-by-side.

Claims

1. An internal combustion engine having at least one cylinder with a primary piston slidable therein, the primary piston being linked to a crankshaft to provide power output from the engine, characterised in that the upper part of the cylinder has a secondary piston slidable therein, the secondary piston being driven by cam means which are in turn driven by said crankshaft and being arranged to move at least to maintain the compression of the charge after the primary piston passes top dead centre, whereby ignition of the charge can take place when the pri¬ mary piston has passed top dead centre.

2. An engine according to Claim 1, wherein the secondary piston con¬ tains at least one valve to open a chamber in said secondary piston which in turn selectively communicates with an inlet port in the wall of the cylinder as the secon¬ dary piston moves up and down.

3. An internal combustion engine according to Claim 2, wherein the chamber also selectively communicates with an exhaust port in the wall of the cyl¬ inder as the secondary piston moves up and down.

4. An internal combustion engine according to Claim 2, wherein an ex¬ haust port is provided in the wall of the cylinder, and the movement of the secon¬ dary cylinder opens or closes the port to the combustion space in the cylinder between the primary and secondary pistons.

5. An internal combustion engine according to Claim 2, 3 or 4, wherein the or each valve is a poppet valve operable by said cam means.

6. An internal combustion engine according to any preceding claim, wherein an exhaust suction device is provided to purge the exhaust gases from the cylinder after the power stroke.

7. An internal combustion engine according to any preceding claim, which is arranged to operate on a four-stroke cycle.

8. An internal combustion engine according to any preceding claim, wherein the secondary piston is spring-biased away from the primary piston, and is moved towards the primary piston by the direct action of a rotary cam.

9. An engine according to any preceding claim, wherein the secondary piston is arranged to increase the compression of the charge after the primary pis¬ ton passes the top dead centre position thereof.