GB2186057A

GB2186057A - Internal combustion engine valve assemblies

Info

Publication number: GB2186057A
Application number: GB08602400A
Authority: GB
Inventors: Robert Anthony Furnivall
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-01-31
Filing date: 1986-01-31
Publication date: 1987-08-05
Also published as: GB8602400D0

Abstract

In a valve assembly comprising a valve closure member (1) having an elongate stem (5) with at least two gripping members (15) which partially define a cavity (19) which is open at one axial end (21), an end (13) of the valve stem (5) extends through the open end (21) of the cavity (19) and is gripped by sections of the respective gripping members (15) which define the open end (21) of the cavity (19), the gripping members (15) defining an outer tapered surface which is engaged by an annular clamp member (31). Preferably the cavity (19) is closed at its other end by a shim (17) and is biassed by a valve spring (9). If a piston (39) should hit the valve closure member (1), the grip of the gripping members (15) is overcome and the stem (13) moves within the cavity (19), reducing the likelihood of damage; the valve spring (9) subsequently resets the assembly. <IMAGE>

Description

SPECIFICATION Improvements relating to internal combustion engine valve assemblies The present invention relates to a valve assembly for an internal combustion engine.

In an internal combustion engine at least one inlet valve assembly and at least one exhaust valve assembly is provided for each cylinder of the engine. As the pistons reciprocate in their respective cylinders, so the valves are opened and closed as required by a cam arrangement. The cam arrangement is driven by a timing chain or belt which connects with a crankshaft on which the pistons are mounted.

As will be appreciated, the relative positions of the crankshaft and cam arrangement are critical for the desired engine performance.

However, it is known for the timing chain or belt to break so that the engine ceases to function as required. When this occurs, the inertia of the cam arrangement causes the cam arrangement to continue opening and closing the valve assemblies, though the cam arrangement will gradually slow. Further, piston movement will continue through the vehicle still being in gear or just through crankshaft and flywheel inertia.

In certain engines, for example, the Rover (Trade Mark) 2300 and 2600 engines, the top dead centre position of the pistons is extremely close to the closed valves, the cyiinder then being ready for firing, and should the timing chain or belt snap on such engines, so that the valve assembly movement becomes out of the required phase with the piston movement, the pistons can and do actually hit the valves, causing a large amount of damage.

Such damage is expensive to repair, if in fact repair is possible.

The aim of the present invention is to provide a valve assembly wherein damage is at least reduced should a piston hit a valve.

According to the present invention there is provided a valve assembly for an internal combustion engine, said assembly comprising a valve closure member having an elongate stem, at least two gripping members being arranged to partially define a cavity which is open at one end and closed at the other end, an end region of the valve stem extending through said open end of the cavity and being gripped by the sections of the respective gripping members which define said open end of the cavity, the gripping members defining an outer tapered surface which is gripped by an annular clamp member.

In use, a cam arrangement engages either directly or indirectly with the closed end of the cavity and a standard spring arrangement engages the annular clamp member to bias the valve towards a closed position, the spring causing the gripping members to firmly grip the end region of the valve stem. During normal engine operation the gripping members firmly grip the valve stem so that the valve closure member and gripping members are moved as a unitary construction under the action of the cam arrangement. If, however, the valves and piston should become out of phase, e.g. when the timing chain or belt breaks, and a piston should hit a valve closure member, then the end region of the valve stem breaks the frictional grip of the gripping members and moves back into the said cavity.

Damage is thus kept to a minimum, if in fact damage occurs. During continued engine movement the springs acting on the annular clamp members and thus on the respective gripping members, move the gripping members along the valve stem to the original position, so that the engine can continue normal operation when the timing chain or belt has been replaced, without further repair being required.

In a preferred embodiment of the present invention the said end region of the valve stem has a neck-down region which is engaged by two arcuate gripping members. The closed end of said cavity is formed by a shim which engages said gripping members, the shim being engaged directly or indirectly by the cam arrangement.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of part of one embodiment of a valve assembly constructed according to the present invention; Figure 2 is an enlarged partial cross-sectional view of part of the valve assembly of Fig. 1; and Figure 3 is an exploded perspective view of the detail of Fig. 2.

The embodiment of the present invention illustrated in the accompanying drawings comprises a valve closure member 1 which has a valve head 3 and a valve stem 5. The valve head 3 is biassed against a valve seat 7 under the action of springs 9. The valve stem 5 passes through a valve guide 11 and has a necked-down or reduced diameter end region 13.

Two part-cylindrical gripping members 15, together with a shim 17 define a cavity 19 which is open at one end 21. Each part-cylindrical gripping members 15 has a radially inwardly directed gripping lip 23 which both partially defines said open one 21 and grips the reduced diameter end region 13 of the valve stem 5. Whilst the gripping members 15 are slightly spaced apart from each other for the majority of their length, they have circumferential extensions 25 which engage each other at the end engaged by the shim 17, the shim sitting snugly in a recess 27 defined by said gripping members 15. These circumferential extensions 25 are produced by applying pres sure to form V-shaped notches 29- (see Figs.

2 and 3), the material thus displaced being machined to form said circumferential extensions 25. A similar structure can be produced by forming the two gripping members as a unitary construction and then separating the gripping members, after hardening.

An annular clamping member 31 engages over the tapered surfaces 33 of the gripping members 15 and is engaged by springs 9.

The clamping member 31 has a tapered inside surface 35 which is complementary to the outer surfaces 33 of the gripping members so that the springs 9 cause the gripping lips 23 to firmly grip the reduced diameter portion 13 of the valve stem 5.

In normal operation the gripping lips 23 firmly grip the upper end region (as viewed in Fig. 1) of the reduced diameter portion 13 of the valve stem 5, and movement of the rocker assembly 37 under the action of a cam arrangement (not shown) compresses and releases the springs 9 and causes the shim 17, gripping members 15 and valve stem 5 to move as an integral unit.

If, however, the timing chain or belt (not shown) interconnecting the cam arrangement (not shown) and a crankshaft (not shown) on which piston 39 is mounted, should break, allowing the piston 39 to hit the valve head 3, the force on the valve stem 5 can break the frictional grip of the gripping lips 23 allowing the valve stem 5 to move further into the cavity 19. Thus, damage is avoided, or at least reduced, and the force of springs 9 can move the gripping members 15 back along the valve stem 5 to their original position so that solely the timing chain or belt requires repair.

To reduce any frictional forces which may exist between the piston 39 and the valve head 3 when the piston 39 hits the valve head 3, and thus reduce the possibility of bending the valve stem 5, the valve head can be provided with a rounded rather than a right angled, peripheral edge. This has the effect of reducing the contact area and thus reducing any frictional forces.

The present invention thus provides a simple but efficient valve assembly which avoids certain inherent problems in certain internal combustion engines.

It is to be noted that existing engines of the problem type can be modified with advantage by shortening the existing valve stem and installing gripping members 15 and a clamp member 31 as described hereabove.

Claims

1. A valve assembly for an internal combustion engine, said assembly comprising a valve closure member having an elongate stem, at least two gripping members being arranged to partially define a cavity which is open at one axial end, an end region of the valve stem extending through said open end of the cavity and being gripped by sections of the respective gripping members, which define said open end of the cavity, the gripping members defining an outer tapered surface which is gripped by an annular clamp member.

2. A valve assembly as claimed in claim 1, in which a shim closes the other axial end of the cavity.

3. A valve assembly as claimed in claim 2, in which the shim is engaged in a recess formed by the respective gripping members and, in use is engageable by a cam arrangement.

4. A valve assembly as claimed in any one of claims 1 to 3, in which the said end region of the valve stem has a necked-down region which is engaged by the respective gripping members.

5. A valve assembly as claimed in any one of claims 1 to 4, in which two part cylindrical gripping members define said cavity, the gripping members being slightly spaced apart from each other for the majority of their length and each having a radially inwardly gripping lip, which lips together define said open end at said one axial end of the cavity, circumferential extensions projecting from each gripping member in the region defining the other axial end of the cavity, interengaging to maintain the spacing between said gripping members.

6. A valve assembly as claimed in any one of the preceding claims, in which the annular clamp member is engaged by a valve spring.

7. A valve assembly as claimed in any one of the preceding claims, in which the valve closure member has a circular disc-shaped head which has a rounded edge.

8. A valve assembly for an internal combustion engine, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.