GB2062795A - Internal combustion engine camshaft - Google Patents

Abstract

An internal combustion engine has a camshaft (1) which carries cams (2). Each cam is engaged by a roller to which is attached one end of a rod (4) whose other cam is attached to a rocker arm (5) for opening a valve (7). Each cam has a main valve-actuating portion and a preliminary bulge before the main portion which serves to take up tolerance in the valve-controlling system while the valve (7) is still resting on its seat. <IMAGE>

Description

SPECIFICATION Internal combustion engines The invention relates to internal combustion engines, and in particular, but not exclusively, high pressure combustion engines such as diesel engines.

In the customary internal combustion engines one of the drawbacks is that the valves of the engine do not close and open at the exactly required moment, and may hit their seat too hard.

This latter phenomenon may result in excitation of the valve spring. When a valve closes too late, a part of the fuel supplied wil be lost, causing a loss of potential energy, and when the valve is opened too early, a part of the energy created will also get lost. Furthermore, excessive force or vibration while closing the valves will result in excessive mechanical wear.

Accordngly it would be desirable to be able to avoid the abovementioned deviations from the ideal functioning of valves, especially with a view to reducing fuel consumption.

The invention provides a way of compensating the tolerance, which is present in a customary valve-controlling system. Thus, it is possible to avoid e.g. in diesel engines, deviations between the closing of the valves on the one hand and the ignition on the other hand. Also, the invention makes it possible to avoid, at least to a large extent, mechanical wear of the valves when they hit their seats.

According to the invention there is provided an internal combustion engine comprising at least one valve controlling system and camshaft with one or more cams corresponding with the number of valves to be actuated, wherein each cam is provided with a perliminary bulge (or pre-cam) on its actuating side, causing compensation of the tolerance of the valve controlling system while the valve is still resting on its seat, followed by the main valve-actuating came portion, the release side of the cam being of such a shape as to provide quick valve release. The preliminary bulge, or "pre-cam", compensates for the tolerance in the valve controlling system, thus ensuring that the valve remain pressed against its seat.This avoids the valve hitting its seat too hard or vibrating as a consequence of the impact, and thus avoids undue mechanical wear and ensures proper closing of the valve at the proper moment.

As is known, the valve controlling systems, i.e.

the transmitting system between cam and valve, in a customary engine will have some tolerance at the moment that the valve is released from its seat, thus causing the valve to be opened slightly too early or slightly too late and consequently having an adverse effect on the economy of the engine concerned.

In a preferred embodiment of the invention the cams are generally pearshaped and are mounted in such as way, that the narrower part thereof extends as actuating part for the corresponding valves respectively, and show a dimple at the actuating side of the cam.

Though the invention provides improved results for internal combustion engines in general, it is of special advantage with diesel engines. Thus, in diesel engines constructed in accordance with the invention, the injected fuel is used more completely, resulting, in a substantial saving in fuel for a given output. This saving in fuel may easily reach 5% under otherwise identical conditions of operation, and may even be as high as 10% or more.

The invention will now be further explained with reference to the accompanying drawings, in which: Fig. 1 is a schematic cross-section of an engine, with the relevant cam and drive mechanism of a valve turned through 900 in order to obtain a clear view of the essential parts thereof, and Fig. 2 shows a cam, such as the one shown in Fig. 1, in more detail as an illustration of the effect of the cam on the functioning of the valve.

Fig. 1 shows a camshaft 1 with a plurality of cams, of which one cam 2 is shown turned through 900 in order to demonstrate clearly the functioning of the valve control system. On rotating the camshaft 1 the cam 2 will cause roller 3 to move upwards and downwards in accordance with the surface of the cam as it rotates past the roller. Roller 3 is connected to an actuating rod 4, which in turn actuates a rocker arm 5 which causes valve 7 to open and to close, assisted by a valve spring 6, depending on the position of the roller 3 on the cam 2. The cam has a preliminary bulge, or pre-cam, which compensate, for the tolerance existing in the valve controlling system, thus avoiding the occurrence of harsh movements which could result from kinetic energy first being used for absorbing remaining tolerance before starting the motion of the valve.Thus, rod 4 will be lifted to a limited extent, leaving the valve 7 still resting on its seat, while the pre-cam passes the roller, and the valve 7 will be released from its seat only once the main part of the cam reaches the roller directly following movement of the rocker arm 5 and rod 4 without any delay as would be caused by conventional cams in absorbing any tolerance. Consequently any jolting of the valve is avoided with the accompanying advantages of reducing energy consumption and mechanical wear.

As is shown in Fig. 2 in more detail, the cam 2 is provided with a pre-cam 12, preceding the main actuating part (11), of the cam 11, on the actuating side of the relevant cam, thus causing a dimple to be formed on the actuating surface.

Though not an absolute necessity, it will be clear that a similar post-cam on the "returning" surface of the cam will provide the advantage, that the valve is released up to exactly the position where it fits to its seat again, whereas the tolerance is only released when "post-cam" passes the roller.

In conventional cams the change of direction of the curvature is constantly clockwise, but nowhere counterclockwise, whereas with the cams used in the present invention the change of direction of the curvature is predominantly clockwise, but is at least at one point counterclockwise. This latter change of direction occurs at the transition from the pre-cam to the main cam, and simultaneously this may occur on the returning side of the cam, though a symmetrical shape of the cam is not a primary requirement. From the above it will appear, that each cam compensates the tolerance in the valve controlling mechanism prior to or at the moment of opening of the valve. In addition the release of the tolerance on return of the valve to its seat may be postponed until after the valve has returned to its seat. In the latter case the shape of the relevant cam will be substantially symmetrical.

Claims (7)

1. An internal combustion engine comprising at least one valve controlling system and a camshaft with one or more cams corresponding with the number of valves to be actuated, wherein each cam is provided with a preliminary bulge (or precam) on its actuating side, causing compensation of the tolerance of the valve controlling system while the valve is stiil resting on its seat, followed by the main valve-actuating cam portion, the release side of the cam being of such a shape as to provide quick valve release.

2. An'internal combustion engine according to Claim 1, wherein the or each cam is generally pearshaped with a dimple at at least the actuating side of the cam, the narrower part serving as the main valve-actuating cam portion.

3. An internal combustion engine according to claim 1 or 2, wherein the engine is a diesel engine.

4. A combustion engine according to any preceding claim, wherein the or each cam is substantially symmetrical about its longitudinal axis.

5. An internal combustion engine according to any preceding claim, wherein the or each cam is arranged to compensate the tolerance in the valve controlling system prior to or at the moment of opening of the valve.

6. An internal combustion engine according to claim 5, wherein the or each valve-controlling system comprises a roller which bears on the cam a rod connected at one end to the roller, a rocker arm connected to the other end of the rod, and a spring urging the valve into engagement with a valve seat.

7. An internal combustion engine, substantially as herein described with reference to the accompanying drawings.