VARIABLE VALVE LIFT/TIMING MECHANISM

Abstract: A variable valve lift and timing valve train mechanism includes a rocker arm (23) having one end thereof operatively engaging a valve (12) and its opposite end being engaged by a valve actuator (20), the upper surface of the rocker arm intermediate its ends having a predetermined cam surface profile (26) which is adapted to co-operate with a working surface (61d) of an angularly-movable reaction member (60) used to provide a fulcrum to thereby effect pivotal movement of the rocker arm (23) in a valve-opening direction. The point of line contact between the cam surface (26) of the rocker arm (23) against the working surface (61d) of the upper reaction member (60) and the geometry of the upper surface of the rocker arm (23) co-operate to control the amount of valve lift and the timing thereof. The angular position of the reaction member (60) used to control valve lift is controlled by a pivoted eccentric cam (43a) engaging an axially-­ movable slide pin (45) interposed between the pivoted eccentric cam (43a) and the reaction member (60).

Description: Field of the Invention This invention relates to valve train mechanisms for internal combustion engines and, in particular, to a variable valve lift and variable timing valve train mechanism as specified in the preamble of claim 1, for example as disclosed in US-A-4,638,773. Description of the Prior Art Various variable valve lift valve train mechanisms are well-known. For example, in United States patents 4,498,432 and 4,526,142 both entitled "Variable Valve Timing Arrangement for an Internal Combustion Engine or the Like", issued February 12, 1985 and July 2, 1985, respectively, in the names of Seinosuke Hara, Schunichi Aoyama and Kazuyuki Miisho, and in United States patent 4,638,773 entitled "Variable Valve Lift/Timing Mechanism", issued January 27, 1987 to Duane J. Bonvallet, there is disclosed a type of variable lift valve train mechanism in which a rocker arm is positioned so that one end thereof is adapted to be actuated either directly by a cam or by a cam-actuated push rod while its other, opposite end operatively engages a free stem end of a poppet valve, such as an intake valve or exhaust valve. The upper surface of the rocker arm has a contoured portion which is adapted to abut against an upper reaction member such as a lever, with the contact point between the rocker arm and the lever serving as the pivot, i.e., the fulcrum point of the rocker arm. The lever itself is adapted to have its angular position changed, as desired, by means of a second eccentric cam so as to, in effect, vary the effective pivotable movement of the rocker arm to thereby vary both valve lift and the timing thereof. In the U.S. patent 4,638,773 mechanism, either the rocker arm or the reaction member has a predetermined reaction cam contour profile thereon whereby the lift-off and landing profiles of the poppet valve actuated thereby are unchanged by the amount of lost motion introduced between the rocker arm and the reaction member. Summary of the Invention A variable lift valve train according to the present invention is characterised by the features specified in the characterising portion of claim 1. The present invention concerns an improved variable valve lift and timing valve train mechanism that includes a rocker arm having one end thereof adapted to be operatively associated with a valve actuator, such as a push rod associated with a cam on a rotatable camshaft, the opposite end of the rocker arm being pivotably and operatively engaged with a ball-shaped free stem end of a poppet valve; an upper reaction member having one end thereof pivotable about a centre on the axis of the stem of the poppet valve when the poppet valve is in a valve-closed position. The upper reaction member is normally biased towards the free stem end of the poppet valve by means of a suitable lash adjuster, and the opposite end of the upper reaction member is adapted to be engaged by an L-shaped slidable guide pin which in turn is engaged by a rotatable eccentric mechanism whereby valve lift and timing can be varied as desired, with the upper surface of the rocker arm or reaction member intermediate its ends having a predetermined contour shaped, as desired, to produce a desired lift-off and landing motion profile of the poppet valve. A spring mechanism operatively interconnects the rocker arm with the push rod and maintains the latter in biased engagement with the cam. It is therefore a primary object of this invention to provide an improved variable valve lift and timing valve train mechanism of the type having a rocker arm pivotable on an upper reaction member wherein the control of the opening and closing of a poppet valve is, in effect, transferred from the usual cam on a camshaft to the rocker arm by providing a predetermined contour on either of the opposed working surfaces of the rocker arm or on the upper reaction member, the other surface being a flat surface, and having the pivotable position of the reaction member controlled by a guide pin engaged by an eccentric. A further object of the invention is to provide an improved variable lift and timing valve train mechanism of the type introducing lost motion between a cam-actuated rocker arm and an associated upper reaction member, wherein one of the elements has a predetermined reaction cam contour profile thereon whereby the lift-off and landing profiles of an associated poppet valve actuated thereby are unchanged by the amount of lost motion and wherein an eccentric cam lobe on an actuating shaft is used to control the angular position of the reaction member via a slidable slide pin and a spring mechanism interconnects the rocker arm with a cam-actuated push rod. A further object of this invention is to provide an improved variable lift and timing valve train mechanism of the type introducing lost motion between a cam-actuated rocker arm and an associated upper reaction member, wherein pivotal motion of the upper reaction member to change valve lift does not in itself cause valve lift and wherein a spring mechanism connects the rocker arm to a push rod, the arrangement being such that the rocker arm is operatively connected to the push rod which in turn is biased into operative engagement with a cam on an engine-driven camshaft. For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings. Description of the Drawings Figure 1 is a top view of a portion of a bank of cylinders of an internal combustion engine with a variable valve lift and timing valve train mechanism in accordance with the invention incorporated therein, with parts such as a valve cover, etc., partially or completely removed therefrom; Figure 2 is an elevational view, partially in section and taken approximately along line 2-2 of Figure 1 to show a portion of an internal combustion engine with a variable valve lift and timing valve train mechanism in accordance with the invention incorporated therein, with a poppet valve shown in a closed position and an upper reaction member of the mechanism positioned to obtain maximum valve lift; Figure 3 is a sectional view taken along line 3-3 of Figure 2 showing the operational relationship between a lash adjuster in an eccentric shaft housing, the upper reaction member and an end of a rocker arm engaging a free stem end of an associated poppet valve to illustrate how the upper reaction member can be pivoted about a centre on the longitudinal axis of the poppet valve; Figure 4 is a view similar to that of Figure 1 but with the rocker arm rotated fully in a valve-­ opening direction; and Figures 5 and 6 are views corresponding to those of Figures 2 and 4, respectively, but showing the upper reaction member pivotably moved to a position to effect zero lift of the poppet valve. Description of the Preferred Embodiment Referring first to Figure 1, for purpose of illustration only, there is shown a portion of one bank of aligned cylinders of a V-6 type internal combustion engine, of the overhead valve type, having an exhaust valve and an inlet valve, only one being shown, per engine cylinder. There is an exhaust valve and an intake valve for each cylinder, not shown in Figure 1. However, since the valve train mechanism of the present invention is the same for both an inlet valve and an exhaust valve, this valve train mechanism will be described as it relates to one poppet valve, either intake or exhaust. Referring now in particular to Figure 2, there is shown a portion of one cylinder bank of an internal combustion engine having an engine body that includes a cylinder head 10 fixed to a cylinder block 11 having a plurality of in-line cylinders 11a therein and in which a valve 12, in the form of a poppet valve, either intake or exhaust, is operatively mounted to control fluid flow through a passage 14 having at one end a port 14a encircled by a conventional valve seat 15, with a variable lift and timing valve train mechanism, in accordance with the invention, operatively associated with the valve 12. As is conventional, the valve 12 is guided for axial reciprocation in a valve stem guide bore 16, with an upper stem end, in the shape of a ball end 12a, of the valve projecting above the cylinder head 10. In a conventional manner, the valve 12 is normally maintained in a closed position, the position shown in Figure 2, by a valve return spring 17, of a predetermined bias force as described in detail hereinafter, with one end of the spring 17 engaging a surface 10a of the cylinder head 10 and the other end of the spring engaging a conventional spring retainer assembly 18 secured to the stem of the valve 12 in a conventional manner. A conventional valve stem seal 19 is operatively positioned so as to sealingly engage an upper stem portion of the valve 12. In the engine construction illustrated, a hollow push rod 20, which is reciprocably disposed in the cylinder head 10 laterally of the valve 12, has an upper semi-spherical ball end projecting above the cylinder head 10. As would be conventional, a lower end of the push rod 20 is operatively associated with a conventional roller follower type hydraulic tappet 22 engaging a cam 21a of a camshaft 21 in a conventional manner, whereby the push rod 20 and tappet 22 are caused to reciprocate as determined by the profile of the cam. Motion of the push rod 20 is imparted to the valve 12 by means of a rocker arm 23 that is adapted to engage an upper reaction member 60 that can be positioned in a manner to be described whereby it can operate as a fulcrum about which the rocker arm 23 can pivot to effect opening and closing movement of the valve 12, as desired, in a manner to be described hereinafter. In the construction illustrated, the rocker arm 23 is provided at opposite ends thereof with semi-spherical sockets 24 and 25 to socketably receive the upper semi-spherical ball ends 12a of the valve 12 and the push rod 20, respectively, the rocker arm 23 thus being adapted to pivot about a pivot axis X on the reciprocating axis of the valve 12 for a purpose to be described, as determined by the pre-selected radius of the ball end 12a of the valve 12 and the complementary radius of socket 24. Thus in a given engine application, these driven and drive ends of the rocker arm, corresponding to the push rod 20 and valve 12-engaging ends, respectively, are laterally spaced apart by a predetermined distance. For this purpose, each rocker arm 23, at its socket end 24, is provided on opposite sides thereof with outwardly extending bearing arms 23a, each of which is of semi-circular external configuration and predetermined radius and is formed concentric with the socket 24 as seen from the side as shown in Figures 4-6. In addition, in the construction shown, the upper surface of the rocker arm 23 is provided with a contoured working, cam surface 26 having a profile of generally convex configuration, which extends from a point B next adjacent to the socket 24 end (right-hand end with reference to Figures 2, 4, 5 and 6) of the rocker arm for a predetermined extent to a point A, as shown in these Figures, so as to merge into a downwardly-extending surface 27, which, in effect, can be referred to as a non-working surface of the rocker arm 23 as will become apparent hereinafter from an operational description of the valve train mechanism of the invention. The profile of the cam surface 26 is preferably calculated for each degree of rotation of the cam lobe 21a in a manner as disclosed in the aforesaid United States Patent 4,638,773, the disclosure of which is incorporated herein by reference thereto. Referring again in particular to Figure 2 and as shown therein, a longitudinally-extending base plate 30 is suitably secured as by spaced-apart socket screws 31, only one being shown in this Figure, to the top of the cylinder head 10. In addition, an actuator shaft housing 40, having a stepped bottom, is suitably fixed to the base plate 30 and to the cylinder head 10 outboard of the base plate 30 as by elongated laterally and longitudinally spaced-apart socket-head cap screws 5, shown in Figure 1, threaded into the cylinder head 10. The actuator shaft housing 40, at each intake and exhaust valve 12 position, is provided on its lower side with a suitably sized, stepped, through slot 41 to receive an associated rocker arm 23, reaction member 60 and a slide pin 45, both of the latter being described hereinafter. Now in accordance with a feature of the present invention, both the cylinder head 10 and base plate 30 are bored or otherwise formed so as to define a spring cavity 32, for each poppet valve 12, that is sized so as to loosely receive an associated spring 33 therein. As shown, one end of each spring 33 abuts against an associated shoulder 30a of the base plate 30, whilst its opposite end engages an associated ring-like retainer 34 that loosely encircles the associated push rod 20 and which is operatively secured to an associated rocker arm 23 by a U-shaped wire yoke 35. The wire yoke 35 is suitably secured at its open ends to the retainer 34. As illustrated, the closed loop end of the yoke 35 is pivotably engaged in a notched portion 27a at the socket end 25 of the associated rocker arm 23, the rocker arm 23 at the notched portion 27a being shaped in cross-section so as to conform to the arcuate shape of the closed end of the yoke 35. Thus with this arrangement, the spring force on the valve train mechanism of the present invention is divided between the poppet valve 12 and the push rod 20. As is well-known, in a conventional push rod type valve train, the conventional valve return spring is always compressed when the cam lobe raises the push rod, that is, the valve always opens per cam revolution. In addition, as is well-known in the art, the bias force of a valve return spring is pre-selected so that the valve train is, in effect, a substantially balanced spring/mass system. However, in a variable valve lift mechanism, as disclosed in the aforesaid U.S. Patent 4,638,773, by design, the valve does not always open and sometimes only opens slightly. Therefore, in such a variable valve lift mechanism, the valve return spring, at no lift or lower lift operation, is not compressed or compressed sufficiently so as to produce a force to keep the push rod riding on the cam lobe. Accordingly, in the valve train mechanism shown in the drawings, the spring 33, when compressed by the rise portion of the cam 21a, is used to ensure a sufficient return force on the push rod 20 and tappet 22 against the cam 21a and to retain the rocker arm 23 and push rod 20 in operative relationship with each other. Accordingly, in a particular engine embodiment, the force of each spring 17 and 33 is selected to equal one-half the force of a conventional valve return spring for the valve train balanced spring/mass system for that engine application. However, if desired, the respective force of the springs 17 and 33 can vary from 40%-60% to 60%-40% relative to the force of a conventional valve return spring or, alternatively, the total forces of the springs 17 and 33 can be slightly greater than that of a conventional valve return spring for a given engine application whilst still providing for a substantially balanced spring/mass valve train system. Referring now to the actuator shaft housing 40, it is provided on one side (the left-hand side thereof, with reference to Figures 2, 4, 5 and 6), with a pair of spaced-apart, longitudinally-extending actuator shaft bores 42, each of these bores having an actuator shaft 43 rotatably journalled therein whereby each of said actuator shafts can be selectively rotated by a suitable drive mechanism, not shown, for a purpose to be described, only the right-hand actuator shaft 43 being shown. One of these actuator shafts can be referred to as an exhaust actuator shaft, and the other then can be referred to as an inlet actuator shaft. Each of these actuator shafts 43 is provided with a plurality of axially spaced-apart eccentric cam lobes 43a thereon corresponding in number to the number of cylinders in the bank of cylinders. Thus three such cam lobes 43a would be used in one bank of three cylinders in a V-6 engine, although, preferably, each actuator shaft 43 is provided with six such cam lobes so as to allow these actuator shafts to be interchanged with each other. In the particular embodiment shown, the profile of each cam lobe 43a is selected to produce a desired linear travel of from 0 to 8.97 mm (0 to 0.353 inches) between the position shown in Figures 5 and 6 and the position shown in Figures 2 and 4 during 238 degrees of rotation of the respective actuator shaft. The actuator shaft housing 40 is also provided with an in-line plurality of vertical bores 44, one for each of the poppet valves 12, intake and exhaust, in the bank of cylinders. Each bore 44 is located so as to extend down between the actuator shaft bores 42 so that the vertical axis thereof is located substantially mid-way between a pair of spaced-apart guide surfaces 41a defining the sides of a respective slot 41 in the actuator shaft housing 40, and each bore 44 is sized so as to slidably receive an annular upright leg 45a of the L-shaped slide pin 45, while a base 45b of this slide pin 45 extends to one side in a position to be engaged by an associated cam lobe 43a on an actuator shaft 43. Thus with reference to Figure 2 and as an example, if the right-hand actuator shaft 43 shown is the inlet actuator shaft, then all of the slide pins 45 for the inlet valves 12 would be positioned as shown in Figure 2, whilst the slide pins 45 for the exhaust valves 12 would be rotated through 180° from the position of the slide pin 45 shown in Figure 2 so that the bases 45b thereof would be positioned to be actuated by the left-hand actuator shaft, not shown, that is thus the exhaust actuator shaft in this example. As shown, each leg 45a of a respective slide pin 45 is provided with a through bore 45c having internal threads in a portion thereof so as to adjustably threadingly receive an adjusting screw 46 therein that is adapted to be locked in position therein by a lock nut 47 for a purpose to be described hereinafter. The actuator shaft housing 40, as shown in Figures 2-6, is provided with a number of blind bores 48, each one laterally aligned in spaced-apart relationship to an associated bore 44 at a location so as to be substantially co-axial with the reciprocating axis of an associated poppet valve 12, with said blind bore 48 intersecting a longitudinally-extending oil supply passage 49 adapted to be supplied with pressurized engine lubricating oil in a conventional manner. Each blind bore 48 is sized so as to slidably receive a cup-shaped cylinder member 50a of a conventional hydraulic lash adjuster generally designated 50. Since the construction of such a hydraulic lash adjuster 50 is well-known, it is not deemed necessary to describe such a hydraulic lash adjuster, as shown, in detail herein. However, as is well-known and as is shown in Figure 2, in a conventional hydraulic lash adjuster of the type illustrated, so-called "pump-up" or axial extension of the cylinder member 50a relative to a plunger 50b can be rapidly accomplished by pressurized hydraulic fluid, such as engine lubricating oil, flowing into a pressure chamber 50c of the unit, whereas axial retraction of the cylinder member 50a relative to the plunger 50b is relatively slow because such retraction is effected as a result of the controlled leak-down of hydraulic fluid from the pressure chamber 50c in a manner well-known in the art. The actuator shaft housing 40 on the side thereof opposite to the actuator shaft bores 42, the right-hand side with reference to Figures 2, 4, 5 and 6, is provided with a plurality of longitudinally spaced-apart internally-threaded bores for receiving socket-head cap screws 51 used to secure a reaction lever hold- down bracket 52. As shown, for example in Figure 2, the reaction lever hold-down bracket 52 adjacent to each poppet valve 12 is provided with a tubular plunger guide 52a, each of which is secured, as by welding, to bracket 52. Each plunger guide 52a is adapted to slidably receive an associated hold-down plunger 53 which is biased axially downwards, with reference to Figures 2, 4, 5 and 6, by a spring 54 operatively engaging an annular, radially outwardly-extending flange 53a of the associated hold-down plunger 53 for a purpose to be described hereinafter. Referring now to the reaction member 60, it is in the form of a lever arm which, intermediate its ends, is of inverted U-shape, and thus includes a base 61 with depending, spaced-apart side walls 62. As is best seen in Figures 2 and 4-6, one end, the eccentric-­ engaging end, 61a of the base 61 of reaction member 60, the left-hand end with reference to these Figures, is positioned so as to be engaged by the screw 46 carried by the slide pin 45, whilst the opposite, right-hand end 61b of the base is located so as to be engaged by the hold-down plunger 53. Base 61 of the reaction member 60 is provided with a semi-circular boss 61c upstanding from the upper surface of the base 61 at a predetermined location adjacent to the end 61b, so that this boss 61c will be engaged by the closed end of cylinder member 50a of hydraulic lash adjuster 50, as seen in Figures 2-6. As will now be apparent, screw 46 can be adjusted to provide for the proper angular original orientation of the reaction member 60, as desired. In addition, the side walls 62 are each provided with an outwardly-extending bearing arm 62a, which is also of semi-circular external configuration and is formed concentric to boss 61c. These bearing arms 62a are sized so as to be pivotable in spaced-apart, arcuately-ended slots 40a provided for this purpose in the right hand end, with reference to Figures 2 and 4-6, of the actuator shaft housing 40, and also as shown in Figure 3. These side walls 62, on their inboard surfaces, are each provided with a semi-circular groove 62b, which, at its upper end, blends into the lower surface of base 61 so as to define a slotted end opening of a size to guidingly receive a respective bearing arm 23a of rocker arm 23, as is best seen in Figure 6. In the construction shown, the base 61 of the reaction member 60 is provided with a lower flat working surface 61d of an extent so as to co operate with the cam surface 26 of the rocker arm 23 thereby to operate as a fulcrum for the rocker arm 23 so that the latter can, in effect, be operatively adjustably fixed for pivotable movement relative to the reaction member 60 so as to control the opening and closing movement of the associated valve 12. It will be appreciated by those skilled in the art that alternatively, if desired, the upper surface of the rocker arm 23 could be flat whilst the cam surface 26 could be provided on the lower surface of base 61 of reaction member 60. Also, in the construction shown and as illustrated in Figures 2 and 4-6, the valve train mechanism is preferably enclosed by a valve cover 70, the lower edge of which rests on a seal retainer 71, supporting a seal 72 engaged in a suitable slot provided for this purpose in the cylinder head 10. Also as shown, the actuator shaft housing 40 is provided with an upstanding externally-threaded boss 40c at each bore 44, with each boss 40c extending through an associated opening 70a in the valve cover 70. Each boss 40c is provided with a seal 73 encircling its lower end and a nut 74 is threaded thereon to effect axial retention of the valve cover 70. Preferably, as shown, a closed cap nut 75 is also threaded on each boss 40c to serve as both a lock for the associated nut 74 and to enclose the associated bore 44 at the boss 40c end of the actuator shaft housing 40. Also in the construction illustrated and as shown in Figure 2, each rocker arm 23 is provided with an internal oil passage 76 in flow communication at one end with socket 25 and, adjacent to its opposite end, in flow communication with a second oil passage 77 that is in communication with socket 24. In addition, a riser passage 78 extends upward from passage 76 so as to open out through the notched portion 27a of the rocker arm 23. With this arrangement, pressurized engine lubricating oil supplied via a conventional oil gallery 80 in the cylinder block 11 to the hydraulic tappet 22 can then flow up through the hollow push rod 20 and then via passages 76, 77 and 78 so as to provide lubrication to the operative surfaces of sockets 24 and 25 and to the notched portion 27a. Operation of the Valve Train Reference is now made to Figures 2 and 4-6. As shown in these figures, the rocker arm 23 is always urged into contact with the reaction member 60 by the bias force of the valve return spring 17 acting through valve 12 and of course by the previously described mechanical linkage of the rocker arm 23 to the push rod 20. At the same time, the spring-biased plunger 53 engages the right-hand end 61b, with reference to these Figures, of the reaction member 60 causing the reaction member 60 to pivot about the interface of its boss 61c and the lower closed end of the cylinder member 50a of the hydraulic lash adjuster 50 so that the opposite end 61a of the reaction member 60 engages adjusting screw 46, throughout any vertical up or down movement of the cylinder member 50a to effect lash adjustment. At the same time lateral movement of the reaction member 60 to either the left or right, with reference to Figures 2 and 4-6, is substantially prevented by the sliding engagement of the bearing arms 62a thereof in the slots 40a of the fixed actuator shaft housing 40. Reference is now made to Figures 2 and 4, with Figure 2 showing the position of the rocker arm 23 in the closed position of valve 12 and reaction member 60 positioned for full lift of valve 12, and Figure 4 being similar to Figure 2 but showing the rocker arm 23 having actuated the valve 12 to the full lift open position. During initial rotation of the cam 21a, the rocker arm 23 is launched on a pivotal cycle prior to valve 12 actuation, from the position shown in Figure 2, to acquire the desired necessary velocity, which is then nominally held constant during rotation of the cam 21a in degrees of rotation. During this initial pivoting movement of the rocker arm 23, it is free to pivot about the first axis X, and thus does not effect any axial movement of the valve 12. For maximum lift of valve 12, the eccentric cam 43a is, as described above, positioned as shown in Figures 2 and 4, with the reaction member 60 thus moved to its most counter-clockwise position about pivot axis Y at the closed end of the cylinder member 50a of the hydraulic lash adjuster 50, so that motion of valve 12 begins when point A, on rocker arm 23 pivots on reaction member 60 and the valve 12 begins to lift with the actual lift profile of the valve 12 being determined by the cam surface contour 26 between points AB, which can be contoured in a manner as desired. As lift continues, the rocker arm 23 essentially pivots about line point A, as seen in Figure 4, and the valve 12 lift profile is determined by the high lift portion of the lobe of cam 21a. The landing or valve-seating profile is the reverse of the opening profile and is determined by the contour of the cam surface 26 between AB. Valve 12 lift can be reduced by angular movement of the actuator shaft 43 to move cam 43a, and thus slide pin 45, so that the upper reaction member 60 will pivot in a clockwise direction from the position shown in Figures 2 and 4 to the position shown in Figures 5 and 6. Thus if the upper reaction member 60 is pivoted in a clockwise direction to a position intermediate from that which is shown in Figures 2 and 4 and the position shown in Figures 5 and 6, additional lost motion is introduced so as to delay the point at which motion of valve 12 begins. In this example, rocker arm 23 essentially pivots between the flat working surface 61d of the reaction member 60 and the semi-spherical end of valve 12. When lift of valve 12 begins, the lift-off profile is the same as with maximum lift because this profile is still determined by the contour of cam surface 26 between AB and the high lift portion of the lobe of cam 21a. Thus, with the valve train mechanism of the present invention the lift-off and landing profiles of the valve 12 are unchanged by the amount of lost motion. Referring now to Figures 5 and 6, it will be seen that if the actuator shaft 43 is rotated to the position shown in these figures, the reaction member 60 will pivot about pivot axis Y in a clockwise direction to its maximum clockwise extent, the position illustrated in these Figures. In this position of the reaction member 60, during rotation of the operating cam 21a to effect upward movement of the push rod 20 to the position shown in Figure 6, it will merely cause the rocker arm 23 to pivot about the pivot axis X, resulting in zero lift of the valve 12, with the cam surface 26 between AB never coming into direct working engagement with the lower flat working surface 61d of the reaction member 60. Stated in a somewhat different manner, in this angular position of the reaction member 60, point B on the profile of the cam surface 26 is located, with reference to Figures 5 and 6, at a position slightly to the left of the reciprocating axis of the valve 12 and, thus, in effect, the reaction member 60 is angularly positioned so that it cannot serve as a fixed fulcrum for the contour of the cam surface 26 on the rocker arm 23. Accordingly, it will now be apparent that the valve train mechanism of the present invention can also be used to de-activate a valve. By locating point B of the cam surface 26 contour on the rocker arm 23 slightly to the left of the reciprocating axis of the valve 12, with reference to Figures 5 and 6, the rocker arm 23 during initial pivotal movement is thus free to pivot about axis point X to obtain a desired velocity before the contour of the cam surface 26 can possibly engage the opposed working surface of the upper reaction member 60. It will be apparent to those skilled in the art that there may be other ways by which the profile of the cam surface 26 may be obtained so as to provide for a desired lift-off and landing profile for the valve 12 in a particular engine application. However, it should also now be apparent that the lift-off and landing of the valve 12 should preferably occur during the nearly constant velocity portion of the profile of the pre-selected cam 21a, so that the lift-off and landing profiles for the valve 12 will be substantially the same. It will also be apparent that, as the valve 12 approaches maximum lift, for a particular angular position of the upper reaction member 60, the cam 21a lift velocity is slowing to zero and, of course, with this arrangement, the lift-off and landing profiles will be relatively gradual. The result is a smooth opening of the valve 12 and substantially no impact at closing of the valve 12 for all lifts at all engines speeds. Whilst the invention has been described with reference to the structure disclosed herein, it is not intended to be confined to the specific details set forth, since it is apparent that many modifications and changes can be made by those skilled in the art. For example, the same variable valve lift function can be achieved by forming the cam surface contour on the reaction member and using an opposed flat working surface on the rocker arm.

Claims: 1. A variable lift valve train for an internal combustion engine of the type having a body (10, 11) defining a cylinder (11a) with a port (14a), said valve train including a valve (12) with an axially-extending valve stem (12a) located for axial movement between a valve-closed position and a valve-open position relative to said port (14a) and normally biased to said valve-closed position; a valve actuator (20) spaced from said valve (12) and operable to effect reciprocation of said valve (12); a rocker arm (23) pivotably supported at one end on said valve stem (12a) and at its other end engaging said valve actuator (20); said body (10, 11) including a fixed overhead support housing (40) extending in part over said rocker arm (23) and spaced therefrom a predetermined distance; a lash adjuster (50) including a movable cylinder member (50a) operatively positioned in said overhead support housing (40) with said cylinder member (50a) having a closed end projecting towards said valve stem (12a) in substantially co-axial alignment therewith, an actuator shaft (43) including an angularly-movable eccentric cam (43a) operatively located in said overhead support housing (40) so as to substantially overlie said other end of said rocker arm (23), a reaction member (60) pivotably supported adjacent to one end (61b) thereof by said projecting end of said cylinder member (50a), the opposite end (61a) of said reaction member (60) being adapted to be engaged by said actuator shaft (43); and said reaction member (60) and said rocker arm (23) having opposed working surfaces (61d, 26), one (61d) of which is flat and the other (26) of which has a cam surface contour of a predetermined profile, characterised in that there are spring means (33, 34, 35) mechanically interconnecting said valve actuator (20) with said rocker arm (23), and a spring-biased plunger (53) is operatively supported by said overhead support housing (40) in a position to abut said one end (61b) of said reaction member (60) to bias said opposite end (61a) of said reaction member (60) into engagement with said actuator shaft (43); 2. A variable lift valve train according to claim 1, characterised in that a slidable pin (45) is operatively positioned in said overhead support housing in spaced-apart relationship to said lash adjuster (50) so as to substantially overlie said other end of said rocker arm (23), said spring-actuated plunger (53) operatively associated with said reaction member (60) biases said opposite end (61a) of said reaction member (60) into engagement with said slidable pin (45), and said eccentric cam (43a) of the actuator shaft (43) contacts said slidable pin (45) in such a manner that, after a predetermined pivotable movement of said rocker arm, said opposed working surfaces (61d, 26) are in operational contact with each other so that said working surface (61d) of said reaction member (60) can serve as a fulcrum for pivotable movement of said rocker arm (23) to effect opening movement of said valve (12), the amount of lift and timing of said valve (12) being controlled by the angular position of said eccentric cam (43a). 3. A variable lift valve train according to claim 1 or 2, characterised in that said valve is spring-biased to said valve-closed position by a first spring (17), and the spring means mechanically interconnecting said valve actuator (20) with said rocker arm (23) comprises a second spring (33), a ring-like spring retainer (34) and a U-shaped yoke (35) interconnecting said rocker arm (23) to said valve actuator (20). 4. A variable lift valve train according to Claim 3, characterised in that said first spring (17) has a bias force of from 40% to 60% and said second spring (33) has a bias force of from 60% to 40% of the total spring force required for said valve train to be a substantially balanced spring/mass system.

Inventors: GIAMPA, ROLAND D., MEHAFFEY, DOUGLAS K.
Applicants: GENERAL MOTORS CORPORATION
Application year: 1988
Main classification: F01L31
IPC codes: F01L13