PHASE CHANGE MECHANISM

Abstract: A phase change mechanism is described for varying the phase of an engine camshaft relative to the engine crankshaft. The mechanism comprises a drive member (10) to be connected to the camshaft drive, a driven member (14) to be connected to the camshaft, an eccentric (20) mounted for rotation about the axis of the camshaft, a coupling element (18) mounted about the eccentric and acting to transmit torque from the drive member to the driven member, and drive means (22) for rotating the eccentric to move the coupling element (18) relative to the drive and driven members (10, 14) and thereby vary the phase between the drive and driven members. To reduce noise caused by chattering of the coupling element (18) about the eccentric (20), means such as springs (19, 19') are provided for applying a constant additional force to the coupling element while the phase change mechanism is in rotation, the force acting in a direction transverse to the line of action of the reaction force reversals acting on the eccentric (20).

Description: PHASE CHANGE MECHANISM Technical Field The invention relates to a phase change mechanism for varying the phase of an engine camshaft relative the engine crankshaft, comprising a drive member to be connected to the camshaft drive, a driven member to be connected to the camshaft, an eccentric mounted for rotation about the axis of the camshaft, a coupling element mounted about the eccentric and acting to transmit torque from the drive member to the driven member, and means for rotating the eccentric to move the coupling element relative to the drive and driven members and thereby vary the phase between the drive and driven members. Background of the invention The optimum times for opening and closing the inlet and exhaust valves in an internal combustion engine vary with operating parameters such as engine load and speed. In any engine with fixed angles for opening and closing the valves for all engine operating conditions, the valve timing is a compromise which detracts from the engine efficiency in all but a limited range of operating conditions. For this reason, control systems have been proposed which vary the valve timing during engine operation. Numerous phase change mechanisms are described in the prior art using a wide variety of techniques and principles. A mechanism which bears a close resemblance to that of the present invention is that described in the Applicants' own earlier PCT Patent Publication No. O90/10788. This publication discloses a phase change mechanism for a camshaft of an internal combustion engine, which comprises a drive member to be connected by a toothed belt to the crankshaft, a driven member to be connected to the camshaft and a coupling element for transmitting torque from the drive member to the driven member. The coupling element is connected for rotation with the drive and driven members in such a manner that the phase of the driven member relative to the drive member depend on the position of the coupling element. An inertial member is connected to the coupling element by an eccentric crank that causes the coupling element to move between two end positions when the inertial member rotates relative to the drive and driven members. A further development of the invention in the latter PCT application is described in copending British Patent Application No. 9213210.9 filed on 20 June, 1992. This application describes and claims a phase change mechanism for varying the phase of an engine camshaft relative the engine crankshaft, comprising a drive member to be connected to the camshaft drive, a driven member to be connected to the camshaft, a coupling element for transmitting torque from the drive member to the driven member and movable relative to the drive and driven members to vary the phase between the drive and driven members, an inertial member coupled by means of a one-way clutch for rotation with the drive and driven members and having an eccentric crank thereon acting on the coupling element to vary the position of the coupling element in dependence of the angular position of the inertial member, and latching means for arresting rotation of the inertial member at predetermined angular positions, characterised in that the latching means comprise an abutment surface projecting radially from the inertial member, a latch member mounted on one of the drive and driven members for transverse sliding movement relative to the axis of the inertial member between two end positions, a pair of opposed abutment surfaces on the latch member disposed one on each side of the inertial member and each engaging the abutment surface on the inertial member in a respective one of the end positions of the latch member and means for switching the latch member between the end positions while the phase change mechanism is rotating. The present invention is concerned with reducing noise in phase change mechanisms of the types described above in which a coupling element connecting the drive member to the driven member is moved by an eccentric in order to vary the phase of the drive between the drive and driven members . Summary of the invention According to the present invention, there is provided a phase change mechanism for varying the phase of an engine camshaft relative the engine crankshaft, comprising a drive member to be connected to the camshaft drive, a driven member to be connected to the camshaft, an eccentric mounted for rotation about the axis of the camshaft, a coupling element mounted about the eccentric and acting to transmit torque from the drive member to the driven member, and drive means for rotating the eccentric to move the coupling element relative to the drive and driven members and thereby vary the phase between the drive and driven members, characterised by means for applying a constant additional force to the coupling element while the phase change mechanism is in rotation, the force acting in a direction transverse to the line of action of the force exerted by said drive means on the eccentric. Conveniently, the drive means for rotating the eccentric may comprise a one-way clutch acting to permit rotation of the eccentric in only one direction, the forces causing the rotation of the eccentric being derived from the torque reversals acting on the camshaft. The torque reversals would normally cause the eccentric to oscillate but in the presence of a one-way clutch they cause rotation of the eccentric in one direction. - A - Regardless of whether or not the torque reversals are used as the means for driving the eccentric, they are always present and as a clearance is unavoidable between the coupling element and the eccentric there is a tendency for the coupling element to chatter about the eccentric. The forces tending to cause the coupling element to chatter always act along the same line. If one were to use a spring force acting along this same line of action, it would prevent operation of the mechanism as it would neutralise the effect of the force reversals. In the present invention, a force is applied at an angle, preferably 90°, to the line of action of the force reversals and it acts to maintain the coupling element in permanent contact with the eccentric at one point of its circumferences. The force reversals in the presence of such a force do not cause the coupling element to chatter but instead the two components remain in contact and only the point of contact moves silently about its central position. Preferred features of the invention It is preferred to use a spring to bias the coupling element but it is alternatively possible to rely on centrifugal force if the centre of gravity of the coupling element is designed to lie to one side of the axis of the camshaft. The latter is not preferred as the mechanism is then unbalanced. The coupling element, if made as a single rigid component, must slide as well as pivot relative to the drive and driven members. To enable this movement to take place, it has been proposed to use a slider block which is journalled on a pin on one of these members and moves along a slot formed in the coupling element. Clearance between the slider block and the slots in the coupling element will again cause chatter on account of the reversal of the reaction forces. In order to prevent the slider blocks from acting as a noise source, it is preferred that the faces of the slider blocks in contact with the coupling element be tapered and that the sides of the slots should taper in the opposite sense so that by moving the slider blocks parallel to the tapering axis, the clearances between the slider blocks and the slots may be taken up. Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a transverse section through a phase change mechanism of the invention, taken along the section line I-I in Figure 2, Figure 2 is an axial section through the phase change mechanism of Figure 1, and Figure 3 is a schematic detailed view drawn to an enlarged scale and taken along the plane III-III in Figure 1. Detailed description of the preferred embodiment The phase change mechanism in the drawings is formed as a drive pulley for the camshaft of an engine. The pulley has an outer toothed drive member 10 which is engaged by a toothed belt passing around the crankshaft pulley. The drive member 10 is journalled for rotation about a driven member 14 which has a central hub 14' for connection to the engine camshaft. The drive member 10 has a radial extension on which is mounted a pin 12 and a second pin 16 is mounted on the driven member 14. Torque is transmitted from the drive member 10 to the driven member 14 through the pins 12 and 16 which engage a coupling element 18 in the form of a yoke with two diametrically opposed slots in which the pins engage. The coupling element 18, as will be described below, can move relative to the drive member 10 and the driven member 14 and such movement result in a change in the phase between these two members. The coupling element 18 carries slider blocks 13, 15 at its opposite ends, in which blocks the pins 12 and 16 are journalled. The slider blocks can slide relative to the coupling element 18 and for this purpose they are received in parallel sided open slots in the ends of the coupling element 18. The sides of the slider blocks 13, 15 and the slots in the coupling element 18 taper in opposite directions, as shown in Figure 3 and retainers or leaf springs 32 held by bolts 30 on the coupling element 18 urge the slider blocks 13, 15 in the direction to take up lateral play between the slider blocks and the sides of the slots in the coupling element 18. The coupling element 18 has a central circular aperture which is journalled about an eccentric crank 20 which projects axially from an inertial member which is mounted on the hub of the driven member 14 through a one-way or overrunning clutch 22. In this way the inertial member can rotate freely about the hub but in only one direction. Because of the inertia of the inertial member 20, it cannot follow the torsional vibrations of the camshaft which are caused by the torque fluctuations on the camshaft. In the absence of the one-way clutch 22 these torque fluctuations would cause the inertial member 20 to oscillate relative to the hub of the driven member 14 but because the one-way clutch 22 prevents movement in one direction, the net effect of the torque fluctuations is to make the inertial member 20 rotate always in the other direction about the hub. As the inertial member 20 rotates, its eccentric crank 20 moves from one side of the axis of the driven member 14 to the other and causes a similar movement of the coupling element 18, which therefore moves to advance then retard the phase of the driven member 14 relative to the drive member 10 with each complete revolution of the inertial member 20. All that is required to achieve a phase changing mechanism is to be able to arrest the rotation of the inertial member at the position corresponding to the desired phase between the drive and the driven member. The design of the stops for inhibiting rotation of the eccentric crank 20 is not material to the present invention and will not therefore be described in detail. Reference is however made in this context to copending application No. 9213210.9 filed on 20 June, 1992, which describes a convenient latch mechanism for this purpose. In Figure 1, an exaggerated clearance has been drawn between the coupling element 18 and the eccentric crank 20 to demonstrate that at any one time, there is only contact at one point between these two. When torque reversals act on the coupling element 18, this point of contact jumps in Figure 1 between the 12 O'clock and the 6 O'clock positions, as the coupling element chatters relative to the eccentric and this is a serious source of noise. To mitigate this problem, the invention proposes the application of an additional constant force as represented by the arrows 19 and 19 ' which tends to keep the coupling element 18 and the eccentric 20 in contact at or near the 3 O'clock position. The effect of the torque reversals will then be to cause the point of contact to oscillate quietly about this 3 O'clock position but without jumping from one side of the coupling element 18 to the other. The arrows in Figure 1 are intended to represent springs acting between the opposite sides of the coupling element 18 and anchoring points 11, 11' on the driven member 14. It is not however essential to use springs in that if the coupling element 18 is designed such that its centre of gravity is offset to one side of the axis of the camshaft, then the centrifugal force acting on the coupling element 18 will achieve the same objective. Springs are however preferred as the balance of the camshaft drive pulley is not then disturbed.

Claims: Claims 1. A phase change mechanism for varying the phase of an engine camshaft relative the engine crankshaft, comprising a drive member (10) to be connected to the camshaft drive, a driven member (14) to be connected to the camshaft, an eccentric (20) mounted for rotation about the axis of the camshaft, a coupling element (18) mounted about the eccentric (20) and acting to transmit torque from the drive member to the driven member, and drive means (22) for rotating the eccentric to move the coupling element (18) relative to the drive and driven members (10,14) and thereby vary the phase between the drive and driven members, characterised by noise suppression means (19) for applying a constant additional force to the coupling element while the phase change mechanism is in rotation, the force acting in a direction transverse to the line of action of the force exerted by said drive means on the eccentric (20 " ) . 2. A phase change mechanism as claimed in claim 1, wherein the drive means for rotating the eccentric may comprise a one-way clutch acting to permit rotation of the eccentric in only one direction, the forces causing the rotation of the eccentric being derived from the torque reversals acting on the camshaft. 3. A phase change mechanism as claimed in claim 1 or 2, wherein a spring is used to bias the coupling element. 4. A phase change mechanism as claimed in claim 1 or 2, wherein the centrifugal force acting on the coupling element is used to bias the coupling element, the centre of gravity of the latter being offset to one side of the axis of the camshaft . 5. A phase change mechanism as claimed in any preceding claims, wherein the coupling element is made as a single rigid component carrying slider blocks each of which is journalled on a pin on a respective one of the drive and driven members and moves along a slot formed in the coupling element . 6. A phase change mechanism as claimed in claim 5, wherein the faces of the slider blocks in contact with the coupling element taper and the sides of the slots taper in the opposite sense.

Inventors: MA THOMAS TSOI-HEI, MA, THOMAS, TSOI-HEI
Applicants: FORD FRANCE, FORD MOTOR CO, FORD WERKE AG, MA THOMAS TSOI HEI, FORD FRANCE S.A., FORD MOTOR COMPANY, FORD MOTOR COMPANY LIMITED
Application year: 1993
Main classification: F01L1
IPC codes: F01L1