GB2263152A

GB2263152A - Variable valve timing apparatus for an engine

Info

Publication number: GB2263152A
Application number: GB9300015A
Authority: GB
Inventors: Edgar Hoyle
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-01-08
Filing date: 1993-01-04
Publication date: 1993-07-14
Anticipated expiration: 2013-01-04
Also published as: GB9225911D0; GB9300015D0; GB9200277D0; GB2263152B

Abstract

Variable valve timing apparatus (2) for an engine, which apparatus (2) comprises a crankshaft, a camshaft (4), a first member (6) attached to the camshaft (4), a second member (12) which is for being driven by the engine, a roller member (14), a track (16) which is for the roller member (14) and which is formed by a pair of opposed grooves (18, 20) in opposed first faces (22, 24) of the first and the second members (6, 12), and biasing means (26) against which the roller member (14) moves when the roller member (14) moves outwardly under centrifugal force caused by the first and the second members (6, 12) rotating during operation of the apparatus (2), whereby the apparatus (2) operates such as to vary the timing of the camshaft (4) with engine speed as related to the speed of rotation of the crankshaft. <IMAGE>

Description

VARIABLE VALVE TIMING APPARATUS FOR AN ENGINE This invention relates to variable valve timing apparatus for an engine. This invention also relates to an engine when provided with the variable valve timing apparatus.

Variable valve timing apparatus for engines is well known. The existing types of variable valve timing apparatus are complex and expensive.

It is an aim of the present invention to provide variable valve timing apparatus which is simpler to produce and operate and which is able to be produced at lower cost, when compared with known types of variable valve timing apparatus.

Accordingly, the present invention provides variable valve timing apparatus for an engine, which apparatus comprises a crankshaft, a camshaft, a first member attached to the camshaft, a second member which is for being driven by the engine, a roller member, a track which is for the roller member and which is formed by a pair of opposed grooves in opposed first faces of the first and the second members, and biasing means against which the roller member moves when the roller member moves outwardly under centrifugal force caused by the first and the second members rotating during operation of the apparatus, whereby the apparatus operates such as to vary the timing of the camshaft with engine speed as related to the speed of rotation of the crankshaft.

Preferably the apparatus is one in which the first member is a disc member, and in which the second member is a disc member. Other types of first and second members may however be employed.

Usually, the roller member will be a ball member.

Other types of roller member may however be employed.

In one embodiment of the invention, the apparatus is one in which the grooves in the pair of opposed grooves are such that they are both straight. In another embodiment of the invention, the apparatus is one in which the grooves in the pair of opposed grooves are such that one groove is straight and the other groove is non-linear, for example curved. In a further embodiment of the invention, the apparatus is one in which the grooves in the pair of opposed grooves are such that both grooves are non-linear, for example curved.

The biasing means may be a closed loop spring. The biasing means may alternatively be a compression spring positioned in the track. Still further, the biasing means may be a compression spring which is positioned on the camshaft, in which case the groove in the second member has an inclined base which forms a ramp over which the roller member rolls.

The apparatus of the invention may include a drive train, the apparatus then being one in which the drive train drives the second member. The part of the drive train that drives the second member will usually be a toothed belt.

The apparatus may be one in which there are more than one of the tracks and more than one of the roller members, there being one roller member for each track.

Preferably, there are four of the tracks and four of the roller members.

Preferably the apparatus is one in which there are at least two of the camshafts. One camshaft will usually be used to operate inlet valves of the engine, and another camshaft will usually be used to operate exhaust valves of the engine.

Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 is a side sectional view of first variable valve timing apparatus for an engine; Figure 2 is a section on line X-X shown in Figure 1; Figure 3 is a view similar to Figure 2 but shows an alternative track construction; and Figure 4 is a view similar to Figure 1 and shows a further alternative track construction.

Referring to Figures 1 and 2, there is shown variable valve timing apparatus 2 for an engine (not shown). The apparatus 2 comprises a crankshaft (not shown), a camshaft 4, and a first member 6 attached to a reduced diameter end portion 8 of the camshaft 4 by a fixing device 10. The fixing device 10 may be any suitable and appropriate fixing device.

The apparatus 2 also comprises a second member 12 which is for being driven by the engine. The apparatus 2 still further comprises four roller members which are each in the form of a ball member 14, and a track 16 for each ball member 14. Each track 16 is formed by a pair of opposed grooves 18, 20. As can be seen from Figure 1, the grooves 18, 20 are in opposed first faces 22, 24 of the first and the second members 6, 12 respectively.

The apparatus 2 still further comprises biasing means in the form of a closed loop spring 26 against which the ball members 14 move outwardly under centrifugal force caused by the first and the second members 6, 12 rotating during operation of the apparatus 2. The apparatus 2 operates such as to vary the timing of the camshaft 4 with engine speed as related to the speed of rotation of the crackshaft.

As can be seen from Figure 1, the first and the second members 6, 12 are each disc members. As can be seen from Figure 2, the grooves 18, 20 are such that they are both straight grooves.

As can be seen from Figure 1, the apparatus 2 includes a toothed belt 28 which forms part of a drive train which is driven by the engine. Thus the engine is able to drive the second member 12 via the toothed belt.

During operation of the apparatus 2 as shown in Figures 1 and 2, as the speed of rotation of the camshaft 4 increases, the ball members 14 move radially outwardly under centrigugal force caused by the rotation of the first and the second members 6, 12. As the ball members 14 move radially outwardly along their tracks 16, they act against the spring 26. The radially outward movement of the ball members 14 along their tracks 16 alters the overlapping relationship of the grooves 18, 20. This in turn causes a change in the angular relationship between the first and the second members 6, 12, which in turn causes a change in the valve timing. Thus the valve timing is able to be altered in a simple and effective manner by apparatus which is simply constructed and is thus able to be produced at relatively low cost.

Referring now to Figure 3, similar parts as in Figures 1 and 2 have been given the same reference numerals for ease of comparison and understanding. In Figure 3, the groove 18 is curved whilst the groove 20 is straight.

With the apparatus 2 shown in Figure 3, the spring 26 is dispensed with and it is replaced by a separate compression spring 30 positioned in each track formed by the grooves 18, 20.

The arrangement of the grooves 18, 20 shown in Figure 2 is for engines requiring a linear characteristic. Figure 3 generally illustrates the versatility of the apparatus of the invention in that the apparatus can be arranged to provide any suitable and appropriate pattern of change in valve timing characteristic. Thus the arrangement of the grooves 18, 20 shown in Figure 3 is for engines requiring a more sophisticated valve timing characteristic than a linear characteristic.

As will be seen from the grooves 18, 20 in Figure 3, the grooves 18, 20 overlap at a maximum at the inner and outer ends 32, 34 of the grooves 18, 20. At the mid-position 36, only approximately 50% of the grooves 18, 20 overlaps. The overlapping position shown at the inner end 32 occurs at engine idling where the engine is operating at minimum revolutions. The overlapping position shown at end 34 occurs at maximum engine operating revolutions. The overlapping positions shown at the mid-position 36 occurs when the engine is operating at a point part-way in its speed range. The overlap position shown at the ends 32, 34 is such as to give minimum inlet and exhaust valve overlap. If there were valve overlap, then the exhaust valves might Just be finishing closing as the inlet valves Just started opening.

In ideal engine operating conditions, there is minimum valve overlap when the engine is operating at idling speed or at maximum speed. It is widely recognised that some valve overlap at engine idling conditions tends to cause the engine to idle unstably. Also, valve overlap when some engines are operating at maximum revolutions may cause the engines to be uneconomical on fuel because the fuel is able to pass directly from the inlet valve to the exhaust valve and thus be wasted.

The grooves used in the apparatus of the invention can be arranged in any suitable and appropriate shape or manner to have the contours required to meet a required valve timing characteristic.

Referring now to Figure 4, it will be seen that the illustrated apparatus 2 has a spring 38 which is positioned around the end portion 8 of the camshaft 4. One end of the spring 38 is located in a recess 40 formed in the second member 12, and the other end of the spring 38 is held in position by an abutment member 42 and a circlip 44 locating in a groove 46 in the end portion 8.

In Figure 4, the groove 20 is such that it has an inclined base which forms a ramp over which the ball member 14 rolls as it is moved radially inwardly and outwardly under centrifugal action. As the ball member 14 moved radially outwardly, it pushes the second member 12 against the spring 38, due to the ball member 14 moving up the ramp formed by the inclined base 48.

The apparatus of the invention is thus simple to produce and operate. Also, the apparatus of the invention includes its own means for sensing engine speed by the nature of its construction. Further, the apparatus of the invention provides its own power to change the valve timing.

It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications may be effected. Thus, for example, the springs 26, 30, 38 may be replaced by other types of biasing means. The apparatus 2 preferably has two camshafts 4 so that the engines will then be a twin cam engine. More or less than the illustrated four ball members 14 and tracks 16 may be employed. The apparatus 2 can be fitted to one or more camshafts 4 of an engine.

Claims

1. Variable valve timing apparatus for an engine, which apparatus comprises a crankshaft, a camshaft, a first member attached to the camshaft, a second member which is for being driven by the engine, a roller member, a track which is for the roller member and which is formed by a pair of opposed grooves in opposed first faces of the first and the second members, and biasing means against which the roller member moves when the roller member moves outwardly under centrifugal force caused by the first and the second members rotating during operation of the apparatus, whereby the apparatus operates such as to vary the timing of the camshaft with engine speed as related to the speed of rotation of the crankshaft.

2. Apparatus according to claim 1 in which the first member is a disc member, and in which the second member is a disc member.

3. Apparatus according to claim 1 or claim 2 in which the roller member is a ball member.

4. Apparatus according to any one of the preceding claims in which the grooves in the pair of opposed grooves are such that they are both straight.

5. Apparatus according to any one of claims 1 to 3 in which the grooves in the pair of opposed grooves are such that one groove is straight and the other groove is non-linear.

6. Apparatus according to any one of claims 1 to 3 in which the grooves in the pair of opposed grooves are such that both grooves are non-linear.

7. Apparatus according to any one of the preceding claims in which the biasing means is a closed loop spring.

8. Apparatus according to any one of claims 1 to 6 in which the biasing means in a compression spring positioned in the track.

9. Apparatus according to any one of claims 1 to 6 in which the biasing means is a compression spring which is positioned on the camshaft, and in which the groove in second member has an inclined based which forms a ramp over which the roller member rolls.

10. Apparatus according to any one of the preceding claims and including a drive train, and in which a part of the drive train drives the second member.

11. Apparatus according to claim 10 in which the part of the drive train that drives the second member is a toothed belt.

12. Apparatus according to any one of the preceding claims in which there are more than one of the tracks and more than one of the roller members, there being one roller member for each track.

13. Apparatus according to claim 12 in which there are four of the tracks and four of the roller members.

14. Apparatus according to any one of the preceding claims in which there are at least two of the camshafts.

15. Variable valve timing apparatus for an engine, substantially as herein described with reference to the accompanying drawings.

16. An engine when provided with variable valve timing apparatus according to any one of the preceding claims.