EP0345252B1

EP0345252B1 - Variable lift cam follower

Info

Publication number: EP0345252B1
Application number: EP87906051A
Authority: EP
Inventors: Donald Charles Wride
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-09-09
Filing date: 1987-09-09
Publication date: 1992-03-25
Anticipated expiration: 2007-09-09
Also published as: EP0345252A4; EP0345252A1; WO1988002059A1

Abstract

A mechanism to vary the lift of a valve of an internal combustion engine, the valve (3) being operated by a cam lobe (2) on a cam shaft (1). A lever (7) is pivoted to a support (5) rotatable about the cam shaft (1), the cam lobe (2) acting on a shaped bearing area (10) on the lever, the other side (11) of the lever contacting the cam follower (8), so that by rotation of the support the timing of lift of the valve can be varied. Provision is also made for varying the degree of lift independently of the timing by means of a further lever pivoted to a sleeve rotatable about the cam shaft, the further lever contacting the first lever (7) on one side and the cam follower (8) on the other side. Rotation of the sleeve causes the effective lever arm of the first lever to be varied and thereby the degree of lift of the valve.

Description

The present invention relates to variable lift cam followers.
In patent application PCT/AU83/00003 there is described a mechanism for varying the valve timing and duration of lift of the valves of an internal combustion engine, the engine having a cam shaft and hydraulic cam followers, characterised in that the bleed of oil from the hydraulic cam follower is controlled through a secondary cam follower, the secondary cam follower in a housing adjustably rotatable about a secondary cam shaft. In an embodiment described in that specification the secondary cam shaft actuates the secondary cam follower through an intermediate lever which is pivoted to the housing about the secondary cam follower, this lever then being shaped to give a reduced lift to the secondary cam follower by virtue of the secondary cam follower being in contact with the lever between its pivot point and the point at which the cam operates.
US 4502426 discloses a mechanism for varying the lift of a valve of an internal combustion engine, the valve being controlled by means of a cam lobe on a rotatable cam shaft. This mechanism may be considered to include a support member, mounted for rotation about the axis of the said cam shaft, providing a pivot axis spaced radially from the said cam shaft. The mechanism may also be considered to include a first lever, mounted on the said support member for pivotal movement about the said pivot axis, having at one side thereof a first actuating surface, which bears against the said cam lobe when the mechanism is in use, and having at an opposite side thereof a second actuating surface, which surface serves to control displacement of a cam follower of the mechanism used to actuate the said valve, whereby such rotation of the said support member can bring about variation of the timing of lift of the valve relative to the rotation of the said cam shaft.
Thus, in the mechanism disclosed in US 4502426 a secondary cam (lever) is interposed between the primary cam of the cam shaft and the valve stem (cam follower) and is mounted for pivotal movement on a support shaft which is rotatable around the cam shaft. The secondary cam has a profile shaped such that as the secondary cam is varied in position the timing of opening/closing of the valve is varied and also the degree of lift of the valve is varied. However, this prior mechanism is such that variations in the timing of lift of the valve are inevitably accompanied by variations in the degree of lift.
It is desirable to provide a variable lift cam follower mechanism in which variations in the lift and timing of the valve are not so strongly linked to one another.
According to the present invention there is provided a mechanism for varying the lift of a valve, the valve being controlled by means of a cam lobe on a rotatable cam shaft, which mechanism includes:
a support member, mounted for rotation about the axis of the said cam shaft, providing a pivot axis spaced radially from the said cam shaft; and
a first lever, mounted on the said support member for pivotal movement about the said pivot axis, having at one side thereof a first actuating surface, which bears against the said cam lobe when the mechanism is in use, and having at an opposite side thereof a second actuating surface, which surface serves to control displacement of a cam follower of the mechanism used to actuate the said valve, whereby such rotation of the said support member can bring about variation of the timing of lift of the valve relative to the rotation of the said cam shaft;
characterised by a sleeve, coaxial with the cam shaft and rotatable thereabout, having pivotally connected thereto a second lever that has at a side thereof facing the cam shaft a contact abutment, which bears against the said second actuating surface when the mechanism is in use, and that extends between the said second actuating surface and the said cam follower so that such rotation of the said sleeve varies the effective lever arm of the said first lever, thereby bringing about variation of the degree of lift of the said valve.
Reference will now be made by way of example, to the accompanying drawings in which:-

Fig. 1 is a schematic sectional view of a control mechanism, connected hydraulically for varying the lift of a valve, not embodying the present invention;
Fig. 2 is a schematic sectional view of parts of a mechanism, for varying the lift of a valve, embodying the present invention;
Fig. 3 is a view corresponding to that of Fig. 2, but showing the mechanism in a different operating disposition; and
Fig. 4 is a view corresponding to that of Fig. 1 but showing a modified hydraulic system.

Figure 1 shows, by way of background information, a mechanism, for varying the lift of a valve, not embodying the present invention. Hydraulic arrangements shown in Fig. 1 (and in Fig. 4) are, however, also applicable to mechanisms embodying the present invention.
The mechanism of Fig. 1 includes a cam shaft 1 provided with a number of cam lobes 2 corresponding to the number of inlet and exhaust valves 3 (only one is shown in Fig. 1) of the internal combustion engine, the cam shaft operating in a housing 4. The housing 4 includes end plates 5 which are rotatable in the housing 4 about the cam shaft 1, a plurality of intermediate plates 5′ being mounted in the housing, these intermediate plates being spaced intermediate the adjacent cam lobes 2. The plates 5, 5′ are connected by a pair of diametrically opposed shafts 6 to support and add stability to the assembly to allow movement to be rigid and accurate, one of the shafts 6 having pivoted thereon cam levers 7 acting between the cam lobes 2 and the cam followers 8. A lever 9 is attached to one of the plates 5 so that the plates may be rotated about the cam shaft 1 so that in this way the timing of the opening of the inlet and exhaust valves of the engine can be varied.
The cam levers 7 can be of any desired shape, having a bearing area 10 to bear on the cam lobe 2, the body of the lever preferably being a thin flange-like construction which can be lightened by the incorporation of holes therein, and also having an upper bearing surface 11, for the cam follower 8, in the form of a flange or the like. The contour of the upper surface 11 is curved and is ground concentric with the cam shaft 1. The plates 5 are rotatable about the cam shaft with the cam levers contacting and moving relative to the cam shaft 1, and each cam lever 7 has its bearing surface 11 extended for contact with the cam follower.
As shown in Fig. 1, the valve 3 is operated by a rocker arm 12 which is actuated by a hydraulic piston 13, a spring 14 maintaining the piston 13 against a bearing member 15 on the rocker 12.
Hydraulic fluid is supplied through line 16 from a pump and pressure relief valve through a manifold block 17 which distributes fluid to all the valves of the engine, a line 18 connecting the manifold block to the piston chamber 19.
Line 20 connects the piston chamber 19 to the bore 21 in housing 4 in which the cam follower 8 moves, the cam follower at its inner end forming a cam follower piston 22, a spring 23′ acting on the piston 22 to maintain contact of the follower 8 with the lever 7.
An adjustable bleed valve 23 connects to the bore 21, the bleed valve being adjustable by lever 24 and control member 25 and a one way valve 26 is provided on the inlet to the block 17. A further one way valve (not shown) is provided in the outlet of the block.
Incidentally, US-4278233 discloses a hydraulic system for actuating gas-change valves in an internal combustion engine in which a cam lobe actuates an input piston formed integrally with the cam follower. In this system a control line leads from the input cylinder to the output cylinder which has an output piston adapted to actuate a gas-change valve. The system concerned includes infinitely adjustable throttle means for adjusting the specific lift of the valve but does not permit adjustment of the timing of the valves.
In an alternative hydraulic arrangement shown in Fig. 4, the supply of pressure fluid to line 16 can be provided by a further cam follower 27 operated by a further cam lobe 28 on a further cam shaft 29, and supplied by a pump 30 through line 31, and having a bleed line 32. Thus the pressure impulse by the further cam follower is controlled and modified by the first cam follower to either increase the lift or vary the timing as desired.
In Figs. 1 and 4, means are provided for the lubrication of the rocker assembly 12, this including a lubrication line 41 connected to the through passage 42.
Figs. 2 and 3 illustrate a mechanism embodying the present invention. In this mechanism the degree of lift of the opening of the valve can be varied, i.e. to give a greater opening of the valve, and the valve can be mechanically operated or have a hydraulic lift arrangement as in Fig. 1. As shown the lift is mechanical, by means of a through a cam follower 33 actuating a push rod 34. This cam follower can be a mechanical follower or a hydraulic cam follower.
Inside the casing 4 there is provided a rotatable sleeve 35 actuated by a control lever 36, the sleeve 35 having pivoted thereto a follower lever 37 by a pivot pin 38. The cam follower 33 bears on a follower lever 37, the follower lever 37 having a contact abutment 39 which bears on the cam lever 7. Thus, it will be seen that by adjustment of the sleeve 35, the effective lever arm of the cam lever 7 is varied, from a short lever arm to give a small lift to a large lever arm to give a larger lift to the valve, without varying the timing of the valve lift. Thus, as shown in Figs. 2 and 3, there is provision for varying the timing of the lift by adjustment of position of the cam lever 7, or for varying the degree of lift by adjustment of the position of the follower lever 37. Figs. 2 and 3 show the operation of the two levers in two positions of the cam shaft 1.
Incidentally, DE 2951361 also discloses a double lever arrangement for varying the degree of lift a valve wherein the effective lever arm of a primary cam lever is adjusted by means of a follower lever bearing thereagainst. However, in the arrangement concerned such adjustment is effected by a translational movement of the follower lever rather than by a purely rotational movement as described above. This prior arrangement is accordingly not so compact or so reliable in operation as the coaxial sleeve arrangement embodying the present invention.
The control for the timing of the opening of the valves by virtue of the end plates 5 can be any desired mechanism for turning the end plates. There could, for example, be provided on each end plate a gear or the like, a shaft with co-operation gear wheel interconnecting the end plates so that they move simultaneously. A further gear on the interconnecting shaft can thus be actuated by any suitable control mechanism.
The control for varying the angular position of the sleeve can be as desired, preferably by a lever arrangement. All mechanisms return to preset positive location for idle either by using a spring tensioned mechanism or a powered source.
The two controls can be manual, or can be automatic (hydraulic, pneumatic or electrical) dependent upon the speed and load requirements on the engine, or can be part automatic and part manual so that the driver can select himself the control for either economy or performance.
Also it is within the concept of the invention that the control can be computerised so that this is fully automatic depending upon the speed, throttle opening, load and other operating parameters of the engine.
A further mechanism embodying the invention (not shown) can be bolted to the head of the engine and there may be a direct mechanical action between the cam shaft and the valve stem, the follower lever bearing on an adjustable tappet which contacts the valve stem, and the valve stem having a spring retained by a collet. In such a case the cam lobe may be of flattened form to have a flat extended contact area so as to provide a longer duration of the valve opening.
One such mechanism and the cam shaft can be utilised by the inlet valves, while a second such mechanism and cam shaft can operate the outlet valves, whereby in effect the invention can be applied to a twin overhead cam shaft engine. Hence either or both of the sets of valves can be individually controlled, and, by controlling the inlet valves, speed variation can be obtained without recourse to varying the flow of the fuel/air mixture by a carburettor. Hence a constant fuel mixture can be delivered to the inlet valves eliminating the high vacuum in the inlet manifold which would be created by a carburettor, the speed control being attained by adjustment of the duration and timing of opening only of the inlet valves.
In all of the embodiments of the invention it will be realised that the sleeves, plates, rings and levers all have concentric movement about the cam shaft.
Furthermore, although it is possible to vary the inlet and exhaust valves of each of the cylinders simultaneously, it is within the concept of this invention to vary selected ones of the inlet valves so that a group of valves for a particular group of pistons and cylinders may be rendered ineffective while the engine continues to run on the remaining cylinders. Thus it is possible to render ineffective various cylinders, such as two or three or four cylinders from six or eight cylinder engines so that the valves are then effectively held open all the time or closed all the time, as desired, so that the engine would then operate on a reduced number of cylinders at low loads.
In an alternative arrangement each of the cam levers can be mounted on an independent spacer mounted in the housing, so that each cam lever can be moved independently of the others as desired, or alternatively a mechanism can be provided, externally of the housing, interconnecting each of the independent spacers controlling the cam levers.
It will be appreciated that, in an embodiment of the invention, one cam follower can be used to control or modify the action produced by another cam follower. The latter cam follower operates as a conventional solid cam follower, with a heat expansion gap, and has a closed hydraulic cylinder connected hydraulically to a valve lifter connected also with the said one cam follower. If the said one cam follower fails, in certain circumstances the said valve lifter can continue to function under the control of the other cam follower, so that although there may be some loss of efficiency the engine will continue to operate without causing undue problems.
Embodiments of the invention can be applied to engines when the hydraulic cam followers are provided on the cylinder head, and is also applicable to engines operating by push rods.

Claims

1. A mechanism for varying the lift of a valve, the valve (3) being controlled by means of a cam lobe (2) on a rotatable cam shaft (1), which mechanism includes:
a support member (6), mounted for rotation about the axis of the said cam shaft (1), providing a pivot axis spaced radially from the said cam shaft; and
a first lever (7), mounted on the said support member (6) for pivotal movement about the said pivot axis, having at one side thereof a first actuating surface (10), which bears against the said cam lobe (2) when the mechanism is in use, and having at an opposite side thereof a second actuating surface (11), which surface serves to control displacement of a cam follower (33, 8) of the mechanism used to actuate the said valve (3), whereby such rotation of the said support member (6) can bring about variation of the timing of lift of the valve relative to the rotation of the said cam shaft (1);
characterised by a sleeve (35), coaxial with the cam shaft (1) and rotatable thereabout, having pivotally connected thereto a second lever (37) that has at a side thereof facing the cam shaft a contact abutment (39), which bears against the said second actuating surface (11) when the mechanism is in use, and that extends between the said second actuating surface (11) and the said cam follower (33, 18) so that such rotation of the said sleeve (35) varies the effective lever arm of the said first lever (7), thereby bringing about variation of the degree of lift of the said valve (3).

2. A mechanism as claimed in claim 1, wherein the valve (3) is a valve of an internal combustion engine.

3. A mechanism as claimed in claim 1 or 2, wherein the said cam follower (33) actuates a push rod (34) to operate the valve (3).

4. A mechanism as claimed in claim 1 or 2, wherein the said cam follower is a hydraulic cam follower.

5. A mechanism as claimed in claim 4, wherein the said hydraulic cam follower comprises a piston (22) operating in a first chamber (21), there being a further piston (13) operating in a further chamber (19) connected to the said first chamber (21) by way of a hydraulic line (20), which further piston is connected by a linkage (12) to operate the said valve (3).

6. A mechanism as claimed in claim 5, wherein hydraulic fluid is supplied from a pump (P) through a pressure relief valve (PRV) to a distribution block (17), there being a non-return valve (26) arranged to prevent return of fluid to the pump, the hydraulic fluid being then supplied from the distribution block (17) by way of a further hydraulic line (18) to the said further chamber (19), and there being an adjustable relief valve (23) arranged for regulating bleed from the said hydraulic cam follower.

7. A mechanism as claimed in claim 5, wherein the hydraulic fluid for the said hydraulic cam follower, which is provided with fluid bleed means (23), is supplied from a pump (30) through a second hydraulic cam follower (27), whereby adjustment of the action of the hydraulic cam follower of claim 3 modifies the effects of the said second hydraulic cam follower (27) on the timing and lift of the said valve (3).