GB2102065A

GB2102065A - An inlet or exhaust valve assembly for an internal combustion engine

Info

Publication number: GB2102065A
Application number: GB08218794A
Authority: GB
Inventors: Alois Bitterli
Original assignee: Sulzer AG; Gebrueder Sulzer AG
Current assignee: Sulzer AG
Priority date: 1981-07-07
Filing date: 1982-06-29
Publication date: 1983-01-26
Also published as: DK225982A; IT1152258B; IT8221957A0; JPS5815707A

Abstract

A pneumatic biasing arrangement comprises a volume (12) of gas which is compressed as a result of the valve opening. The compressed gas volume (12) acts on a cap (5) fixed to the valve stem (1) to exert a force longitudinally of the valve stem (1) to bias the valve to its closure position in which a valve head (8) is pressed against a valve seat (15). Leakage from the gas volume (12) is replenished from a source (9) of compressed gas through a compressed gas line (10). A vacuum is created within the cover (18) due to cap movement and connection of the cover space to atmosphere through the non-return valve 25. The valve is opened by the periodic application of fluid pressure to the piston 7. <IMAGE>

Description

SPECIFICATION Inlet or exhaust valve assembly for an internal combustion engine The present invention relates to an inlet or an exhaust valve assembly for the cylinder head of an internal combustion engine, which valve can be opened by a controlled drive and closed by resilient biasing means exerting a constant restoring force.

Conventionally, valves of this kind are resiliently biased to the closed position by springs, usually coil springs, and valve opening is achieved in a variety of ways using mechanical, hydraulic, electrical or pneumatic means, such as rockers, plungers or electromagnets. It has been found that, more particularly in circumstances where valve bounce occurs, the return springs tend to vibrate in operation with a consequent risk of spring breakages.

The present invention seeks therefore to provide a valve which does not need a mechanical spring to return the valve to its closed position.

According to the invention, therefore, there is provided an inlet or exhaust valve assembly for the cylinder head of an internal combustion engine, in which the valve is biased to a closed position by biasing means in the form of a closed volume of gas under pressure the volume of which is varied by the valve movement.

The arrangement of the invention provides additional advantages over mechanical return springs, since it is simpler to manufacture than the latter, more particularly for large valves, and no high-grade spring material is required. Moreover, the restoring force exerted on the valve is more readily controllable. In particular the restoring force can be adapted to meet requirements of individual engines, for instance, by adjustment of the pressure of the volume of gas.

As an example of an advantageous construction of such a valve, the gas volume is contained in a cylindrical chamber surrounding the valve stem of a mushroom-headed valve, which chamber is bounded at the end remote from the valve head by a cap fixed to the valve stem.

Conveniently, there are provided means for maintaining the gas within the said closed volume at a greater pressure than the pressure existing, during operation of the engine, in the port closed by the valve. In the case of exhaust valves, this latter feature ensures that exhaust gases cannot flow up along the valve stem and possibly soil or corrode the valve stem or valve guide surfaces. As a simple means of compensating for loss of the gas, which would generally be air, due to the escape of the pressurized gas, the enclosed gas volume may be connected to a source of pressurized gas, for example a pressurized gas cylinder such as are used in large engines for starting; in the case of supercharged engines, such a pressure gas source can be the turbine generating the compressed air.

Preferably, as a means of considerably reducing the risk of disturbances in operation, the gas volume is large in relation to its variation in volume. Also, it is a very simple matter for a valve having the restoring means of the invention to be provided with a valve rotating device since no additional axial bearings are required for this purpose.

As a means of further improving the effect of the new restoring means, the chamber housing the closed volume and the cap are located within a gastight hood whose interior communicates, via a unidirectional valve, with the atmosphere.

Consequently, a variable reduced pressure which boosts the restoring force is produced in the chamber below the hood in which the cap moves.

This feature also helps to reduce noise.

The invention may be carried into practice in various ways, but one specific embodiment will now be described in greater detail by way of example with reference to the accompanying drawings the single Figure of which is a longitudinal section of an exhaust valve assembly taken on the axis of the valve.

Referring now to the drawing, the valve assembly shown comprises an annular valve seat 1 5 which is located against a step or shoulder 14 in a bore in a cylinder head 13 and is retained in place by a valve cage 2 disposed outside and on top of cylinder head 1 3 in the orientation shown in the drawing. References herein to the orientation of the valve assembly and components thereof will be understood to relate to the orientation illustrated in the drawing and not to be limitative.

Extending through the annular valve seat 1 5 and the cage 2 is a valve port 11 through which the combustion product gases pass from a combustion chamber 1 6 (the valve of the present example being an exhaust valve).

The port 11 is opened and closed by a mushroom-shape valve head 8 which is of conventional shape and merges into a valve stem 1 guided for longitudinal reciprocation in a valve guide bush 3 secured in the cage 2. Extending annularly around the valve stem 1 is a hollow casing member 1 7 which is mounted on the cage 2 and which in turn is covered by a hood 18.

A supply line 10 from a cylinder 9 containing a pressurized gas, preferably compressed air, is connected by means of a flange 1 9 to the casing member 17 the central part of the latter of which is in the form of a stationary hollow cylinder 4 over the upper end of which is fitted a cylindrical cap 5 separated from the atmosphere by the hood 1 8 covering the casing member 1 7. Two O-ring seals 20 are provided between the cylinder 4 and the cap 5 to provide a sliding gastight seal between them.

The cap 5 is fixedly mounted to the top end of the valve stem 1, and serves as a movable cover for the volume of air 12 trapped inside the casing member 17. When the valve is displaced axially to move the valve head 8 away from the valve seat the volume 12 is reduced by a downward movement of the cap 5 which is connected to the valve head 8 by the valve stem 1; consequently, the air volume 12 is compressed by this movement. This compressed air acts as a stressed return spring tending to return the valve to its original position with the valve head 8 in contact with the valve seat.

In the example shown the valve is opened by means of a piston 7 which, to facilitate assembly and manufacture, acts via an intermediate member 21 on the cap 5 and through this on the valve stem 1. The piston 7 is movable within a cylinder 23, which is connected to a line 22 leading to a fluid pressure source (not shown) which periodically increases in pressure to cause the required periodic opening of the valve.

The hollow space below the hood 1 8 is formed with a vent orifice 6 to which is connected a vent line 24 which is shown only diagrammatically in the drawing and in which there is a unidirectional valve 25 adapted to allow a flow of fluid away from the volume enclosed by the hood 1 8. The presence of this valve 25 makes it possible to boost the restoring force exerted by the compressed air within the volume 12 by creating a reduced pressure in the space enclosed by the hood 1 8 when the valvehead 8 is open due to the increase in the volume of this space caused by the movement of the cap 5. This also helps to reduce the noise of operation.

The air within the volume 12 is topped up with compressed air from the cylinder 9 to compensate for any losses occurring as a result of air escape along the valve stem 1 which arises because the pressure in the volume 12 is higher than the pressure in the exhaust port 11.

Claims

1. An inlet or exhaust valve assembly for the cylinder head of an internal combustion engine, in which the valve is biased to a closed position by biasing means in the form of a closed volume of gas under pressure the volume of which is varied by the valve movement.

2. A valve assembly as claimed in Claim 1, in which the gas volume is contained in a cylindrical chamber surrounding the valve stem of a mushroom-headed valve, which chamber is bounded at the end remote from the valve head by a cap fixed to the valve stem.

3. A valve assembly as claimed in Claim 1 or Claim 2, in which there are provided means for maintaining the gas within the said closed volume at a greater pressure than the pressure existing, during operation of the engine, in the port closed by the valve.

4. A valve assembly as claimed in any preceding Claim, in which the said closed volume of gas is large in relation to its variation in volume.

5. A valve assembly as claimed in any of Claims 1 to 4, in which the said closed volume is connected to a source of gas under pressure.

6. A valve assembly as claimed in any of Claims 2 to 5, in which the said cylindrical chamber and cap are disposed below a gastight hood the interior of which communicates with the atmosphere via a unidirectional valve allowing gas to flow out of the space enclosed by the hood.

7. An inlet or exhaust valve assembly substantially as hereinbefore described with reference to the accompanying drawings.