GB2260366A - I.c. engine piston valve gear - Google Patents

Abstract

Combustion chamber exhaust and inlet ports 11, 19 are control lad by respective valve pistons 8, 14. The piston 14 may act as a charge pump during movement to open the port 19. The valve pistons may be circular or oval and the engine may be turbocharged. The counterweight 23 may act as a charge pump. <IMAGE>

Description

VALVE MECHANISM The present invention relates to a valve mechanism for an internal combustion engine.

The cylinder head of an OHV internal combustion engine incorporates valves which allow air into, and exhaust gases out of, the combustion chamber. The use of poppet valves to provide such inlet and outlet valves is well known. The head of each poppet valve is positioned to move within the combustion chamber, the valve being closed when the head is seated against a seat provided on the cylinder head. The stem of each valve extends from the head thereof through the cylinder head, and is operated by means exterior to the combustion chamber to open and close the poppet valve. The operating means are usually provided by cam-driven rocker arms or tappets which depress the valve stem and lift the poppet valve from its seat. A spring is then usually employed to return the valve to its seat.

In order to ensure that the valve is close quickly enough to match the rotational speed of the engine a strong valve spring, or even a double spring, is required. A number of disadvantages result from the use of such a strong spring. Firstly, energy is lost in overcoming the spring force to open the poppet valve; secondly, the valve may be returned to the closed position with such force that "valve bounce" results; and finally, the effort of overcoming the spring force exerts significant torsional stress on the cam shaft.

One way to avoid these disadvantages is to use dual cams and mechanical restraints instead of springs; that is, to close as well as open the valve positively by means of cams. However, this requires that the parts are precisely machined and fitted and are carefully and frequently checked in use, all of which adds to the expense of the engine. Furthermore, if there is any inaccuracy, such that the valve is not completely closed, the flow of hot combustion products past the valve quickly makes the valve white-hot, and susceptible to serious damage.

It would therefore be desirable to provide a cylinder head valve mechanism which would allow air/fuel into and exhaust gases out of the cylinder, but wherein no part of the valve mechanism lies in the flow path of the air or exhaust gas, and wherein the mechanism only requires minimal power to operate: preferably, the power is just sufficient to overcome friction.

According to one aspect of the present invention there is provided a valve mechanism for an internal combustion engine, the valve mechanism comprising a piston working in a cylinder, the cylinder having a port the wall thereof and being in communication with the combustion chamber, and the piston being operable as it reciprocates in its cylinder to open and close the port.

Thus, when the valve is open, no part of the valve lies in the flow path of fluid entering or leaving the cylinder via the valve port.

In accordance with another aspect of the invention there is provided an internal combustion engine having at least one of the aforementioned valve mechanisms.

Preferably, each combustion chamber of the engine has at least one inlet port, and at least one exhaust port, a valve mechanism according to the invention being associated with each inlet and each outlet port. The, or each, inlet port valve mechanism may include means whereby the combustion chamber may be supercharged. The supercharging means may be an air pump, a supercharger or a turbocharger.

The present invention will now be described in more detail by way of example with reference to the accompanying drawings, in which: Figure 1 shows a first arrangement of a valve mechanism in accordance with the present invention; Figure 2 shows a second arrangement of a valve mechanism in accordance with the present invention; Figure 3 shows a further arrangement of a valve mechanism in accordance with the invention; Figure 4 shows a variation on the embodiment shown in Figure 2; and Figure 5 shows a detail of the Figure 4 embodiment taken on line V-V of Figure 4.

Figure 1 shows a section through a cylinder head 1 of an engine having a combustion chamber 2. The cylinder head has an air inlet 3 and an exhaust outlet 4. Air flowing in through the inlet 3 passes through a throttle 5 and a reed or membrane valve 6 which acts to prevent reverse flow of the air out of the inlet. The exhaust outlet 4 will be connected to the main exhaust manifold (not shown).

A cylinder 7 is provided in the cylinder head and accommodates a valve piston 8, which is connected by a piston rod 9 to a crank shaft 10. The cylinder 7 opens at one end into the combustion chamber 2 and the exhaust outlet 4 leads into the side of the cylinder 7 at exhaust port 11. The piston 8 is slidably moveable between a first, extended position (as shown) in which the piston obstructs the exhaust port 11 and prevents any flow of gases from the combustion chamber to the exhaust outlet, and a second, retracted position (not shown) in which the combustion chamber communicates directly with the exhaust outlet, and no part of the piston or piston operating mechanism lies in the flow path of the exhaust gases.

Sealing rings 12 may be provided in grooves on the piston, and because the piston moves transversely across the exhaust port 11 to seal the exhaust port from the combustion chamber, there is no requirement for the piston to be precisely machined.

Similarly, a second cylinder 13 is provided which houses an inlet valve piston 14 connected by a piston rod 15 to a crank shaft 16. Cylinder 13 is formed beside the cylinder 7 in the cylinder head, and the cylinder 13 also opens at one end into the combustion- chamber 2. The other end of cylinder 13 communicates with the air inlet 3, via the throttle 5 and valve 6. A passage 17 is provided which has a first end 18 opening into the upper end of cylinder 13, and a second end opening into the lower end of cylinder 13 and providing an air inlet port 19 into the combustion chamber 2.The piston 14 is slidably moveable in the cylinder 13 between-a first, extended position (as shown) in which the piston'obstructs the air inlet port 19 and prevents the flow of air into the combustion chamber, and a second retracted position (not shown) in which the air inlet 3 communicates with the combustion chamber via passage 17, and no part of the piston lies in the flow path of the incoming air.

Sealing rings 20 may be provided in grooves on the piston. Cooling liquid may be supplied to galleries 21 around the main cylinder and cylinder head.

As shown in Figure 1 the pistons 8, 14 may be driven by rotation of the crank shaft 10, 16, which impart reciprocating motion to the pistons by way of the piston rods 9, 15. In this embodiment, when the piston 14 is being moved from its extended to its retracted position to open the air inlet port 19, because the reed valve 6 prevents any reverse flow of air, the air in the cylinder 13 is compressed as the piston is moved, thus increasing the pressure of the air entering the combustion chamber 2 through port 19. Thus the piston valve 14 acts as a sort of "supercharger" for the combustion chamber.

In Figure 1 counterweights 22, 23 are shown on the piston crank shaft 10, 16, respectively. The counterweight 23 can be used to force the incoming air through the passage 17 and into the combustion chamber to enhance the supercharging effect and increase the engine efficiency.

Although the pistons 8, 14 in Figure 1 are shown as each being driven by a continuous rotation of the crank shaft 10, it is possible to envisage that the reciprocating motion of the pistons may be provided by intermittent clockwise and anti-clockwise rotation of suitable driving means through a selected angle, or by direct linear movement of the piston rods 9, 15, or by any other suitable means.

Figure 2 shows a similar arrangement to that shown in Figure 1, but here the piston rods 9, 15 are driven by direct linear movement to impart the reciprocating motion to the pistons 8, 14. Furthermore, in the embodiment of Figure 2, the air inlet 3 flows directly into the side of the cylinder 13 at inlet port 19. Thus, the main cylinder head is only approximately half the height of the cylinder head shown in Figure 1 and other conventional cylinder heads, and is particularly useful for situations in which space is restricted.

Figure 3 shows a variation on the embodiment shown in Figure 2, and is particularly suitable for engines with a high compression ratio: diesel engines, and the like. In this Figure 3 embodiment the valve pistons 8, 14 reciprocate in a direction which is longitudinal to the combustion chamber 2, and parallel to the motion of an engine piston 24 within the combustion chamber. When the inlet port 19 and exhaust port 11 are sealed and the pistons 8, 14 are in their fully extended positions, the lower ends 25, 26 of pistons 8, 14 respectively protrude beyond the inner surface 27 of the cylinder head 1 into the combustion chamber 2. The crown or top surface 28 of the engine piston 24 is formed with two corresponding recesses 29, 30.When the valve pistons 8, 14 are in their fully extended position and the engine piston 24 is top dead centre, the lower ends 25, 26 of the valve pistons fit into recesses 29, 30 in the engine piston. This allows the compressed combustion chamber unswept volume to be very low, yielding a high compression ratio. Moreover, the action of the pistons entering the recesses 29, 30 creates squish and turbulence in the combustion chamber which promotes combustion and improves the engine performance.

The above embodiments have been described with respect to a cylinder head having two piston valves in accordance with the present invention. However, it is envisaged that any number of such piston valves may be used, as required. Moreover, the piston valves may be circular, oval or any other suitable cross-sectional shape, there may be any number of spark plugs in any suitable position, and the piston valves may be used in any size and for any number of cylinders per engine.

Preferably, the pistons 8, 14 are made from aluminium or ceramic, or aluminium with a ceramic coating.

In order to improve the volumetric efficiency of the engine an air pump could be arranged to supply air to the air inlet 3, and could be designed to produce a mild form of supercharging. This would only absorb a small amount of energy from the engine, to overcome friction in the pump itself. The air pump might be small, such that one such pump could be fitted to each individual air inlet or cylinder. Alternatively, one larger air pump might be used to pump air into a manifold to supply all the cylinders It is also envisaged that a conventional supercharger or turbocharger might be connected to the air inlet 3 to improve engine performance.

The embodiment of Figure 4 is similar to that shown in Figure 2 save for the addition of a steel liner 31 which is pressed into the cylinder 13 in the cylinder head 1. Such a steel liner may also be fitted in the cylinder 7 in Figure 4 and in the piston valve cylinders of any of the alternative embodiments of the invention.

A cross-section of the steel liner 31 is shown in Figure 5. The liner includes a number of slots 32 which align with the inlet port 19 when the liner is fitted into the cylinder 13, and allow air to flow into the combustion chamber when the piston 14 is retracted. The ribs 33 formed between the slots in the liner act to prevent the piston sealing ring or rings 20 from moving into the port 19.

Claims (11)

1. A valve mechanism for an internal combustion engine, the valve mechanism comprising a piston working in a cylinder, the cylinder having a port in the wall thereof and being in communication with the combustion chamber, and the piston being operable as it reciprocates in its cylinder to open and close the port.

2. A valve mechanism in accordance with Claim 1, wherein the piston is of circular cross-section.

3. A valve mechanism in accordance with Claim 1, wherein the piston is of oval cross-section.

4. A valve mechanism in accordance with any preceding claim, wherein the piston is moveable by means of a piston rod and driving means.

5. An internal combustion engine having at least one valve mechanism in accordance with any preceding claim.

6. An engine in accordance with Claim 5, wherein each combustion chamber of the engine has at least one inlet port, and at least one exhaust port, one said valve mechanism being associated with each inlet port and each exhaust port.

7. An engine in accordance with Claim 6, wherein the, or each, inlet port valve mechanism includes means whereby the combustion chamber may be supercharged.

8. An engine in accordance with Claim 7, wherein the supercharging means is an air pump.

9. An engine in accordance with Claim 7, wherein the supercharging means is a supercharger.

10. An engine in accordance with Claim 7, wherein the supercharging means is a turbocharger.

11. An engine in accordance with Claim 7, wherein an inlet communicates with one side of the piston in the, or each, inlet port valve mechanism, said inlet port communicating with the other side of said piston when the valve mechanism is open, and a through passage being provided between the inlet and the inlet port, such that said through passage acts as said supercharging means as the piston is moved from a closed to an open position.