Patent Publication Number: US-4543920-A

Title: Hypocyclic rolling contact rocker arm and hydraulic lash adjuster pivot

Description:
This application is a continuation-in-part of copending U.S. patent application Ser. No. 531,269, filed Sept. 12, 1983, now U.S. Pat. No. 4,491,099, filed as a continuation-in-part of copending application Ser. No. 496,930, filed May 23, 1983, now U.S. Pat. No. 4,476,822, all being assigned to the same assignee. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to valve trains for internal combustion engines and, in particular, to a hypocyclic rolling contact rocker arm and hydraulic lash adjuster pivot assembly for use in such valve trains in conventional and also overhead cam engines. 
     DESCRIPTION OF THE PRIOR ART 
     Conventional rocker arm and pivot assemblies, as normally used in passenger vehicle type engine valve trains, for example, as used in an overhead valve push-rod type actuated valve train, include a pedestal mounted rocker arm which generally has a spherical or part cylindrical pivot or fulcrum that provide essentially large bearing surfaces. With such an arrangement, the rocker arm is actually in sliding engagement relative to its associate fulcrum and, thus even though these elements may be adequately lubricated, this type arrangement still provides a large area for frictional resistance so as to produce a heat build-up as a result of the loads being applied to the respective bearing surfaces. 
     The desirability to overcome the above problem has been recognized and, accordingly, various specially constructed or non-production, in terms of passenger vehicle usage, type rocker arm assemblies have been proposed. Such specially constructed or non-production type rocker arm assemblies have been used in special engine applications, as for example, in engines of race cars. Thus in such specialized engine applications, in order to reduce friction, roller bearing assemblies have been used to pivotally support a rocker arm. Such roller bearing assemblies are mounted, for example, on stub shafts secured to a fulcrum in a manner whereby to pivotably support an associate rocker arm in a manner similar to that shown, for example, in U.S. Pat. No. 3,621,823, entitled &#34;Frictionless Rocker Arm Fulcrum Assembly&#34;, issued Nov. 23, 1971 to John Lombardi 
     It is readily apparent that such a rocker arm and its associate pivot assembly which includes one or more roller bearing assemblies is far more complex and expensive, from a production standpoint, to use in conventional passenger vehicle engines. 
     It has also been proposed to provide a rocker arm and pivot arrangement such that the rocker arm is claimed to be movable about a support in rolling motion in a manner shown, for example, in U.S. Pat. No. 2,943,612 entitled &#34;Valve Gear&#34; which issued on July 5, 1960 to Alexander G. Middler as an improvement over the rocker arm pivot structure shown in U.S. Pat. No. 1,497,451 entitled &#34;Rocker Arm&#34; issued June 10, 1924 to John F. Kytlica. However, it will be apparent that the rolling contact between the rocker arm and pivot of this U.S. Pat. No. 2,943,612 teaching is comparable to that of a cylinder rolling on a flat or substantially flat surface. 
     As a further improvement there has been disclosed in U.S. Pat. No. 4,393,820, issued July 19, 1983 to Emil R. Maki, Ferdinand Freudenstein; Raymond L. Richard, Jr., and Meng-Sang Chew, a rolling contact rocker arm and pivot assembly that includes a rocker arm with a semi-cylindrical bearing surface intermediate its ends and an associate fixed pivot member having a semi-cylindrical fulcrum bearing surface, the ratio of the radii of these surfaces being on the order of 3:1 to 1.7:1 and preferably 2:1 to provide for cardanic motion. In this assembly, one of the bearing surfaces is provided with a guide recess or slot therein of a size and shape so as to receive in substantially rolling contact a raised retainer pin provided on the other bearing surface, the slot and retainer being located intermediate the arcuate ends of the respective bearing surface. 
     SUMMARY OF THE INVENTION 
     A primary object of the present invention is to provide an improved rocker arm and pivot assembly for an internal combution engine, wherein an otherwise conventional type rocker arm and its fixed fulcrum are provided with part circular convex and concave bearing surfaces respectively having, a radius relationship of substantially 1/2R and R, respectively, with these elements being provided with a retainer pin and slot arrangement whereby there is effected substantially rolling or walking contact between all parts relative to each other during pivotable movement of the rocker arm and wherein the center of revolution of the concave surface that is, its geometric center is located on the cross-sectional area of the stem of an associate valve. In accordance with a feature of the present invention, the fulcrum is the follower of a hydraulic lash adjuster that is operatively positioned in an adjuster socket provided in a lash adjuster retainer fixed to the cylinder head at a location between an associate valve and a valve actuator, such as, an overhead cam. The point of contact of the rocker arm against the stem of the valve is located as an arcuate extension of the convex bearing surface so that straight line motion will be imparted to the valve. Preferably the axis of rotation of a cam follower or the point of contact of the cam follower on the cam is also located on an arcuate extension of the convex bearing surface. In addition, as used in an overhead cam engine, the axis of rotation of the cam follower on the rocker and of the camshaft would preferably be in a plane that substantially intersects the center of revolution of the concave surface. 
     Accordingly, another object of this invention is to provide an improved rocker arm and pivot assembly that is operative so as to impart straight line motion to a valve, the pivot, provided as part of a hydraulic lash adjuster defining a rocker bearing support intermediate the length of the rocker arm, the pivot and the rocker arm defining a pair of cooperative outer and inner semi-cylindrical bearing surface contours carrying the reaction forces of the rocker arm pivotal movement, the radius of the outer conformation being substantially two times the radius of the inner conformation with the center of revolution of the outer conformation being located substantially on the operating axis of the valve, the inner conformation of the rocker arm being located such that an extension thereof will intersect the contact point at one end of the rocker arm on the stem of the valve at the free stem end thereof and preferably also intersecting the axis of rotation of a cam follower rotatably supported on the opposite end of the rocker arm. The pivot and rocker arm are provided with associate slot means and retainer means to insure substantially rolling contact between the rocker arm and pivot. 
     Still another object of this invention is to provide an improved rocker arm and pivot assembly for use in an overhead cam type internal combustion engine which, in operation, is characterized by minimum energy loss to thus maximize fuel efficiency. 
     A still further object of the present invention is to provide a rocker arm and pivot of the above type which is easy and inexpensive to manufacture, which is reliable in operation, and in other respects suitable for use on production motor vehicle engines. 
     For a better understanding of the invention, as well as other objects and further features thereof, reference is had to the following detailed description to be read in connection with the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a portion of an internal combustion engine, with the valve cover removed, having valve trains in accordance with the invention incorporated therein; 
     FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1 showing a valve train and associate valve, the rocker arm being shown in the valve closed position; 
     FIG. 3 is a cross-sectional view, taken along line 3--3 of FIG. 2, showing the rocker arm and fulcrum of the valve train assembly; 
     FIG. 4 is a pictorial view of the valve train of FIG. 2 showing the geometry of the valve train in accordance with the invention. 
     FIG. 5 is a transverse, vertical sectional view of a portion of an overhead cam type internal combustion engine, with the valve cover removed, having a valve train in accordance with the invention incorporated therein with this embodiment using a hydraulic valve lifter; 
     FIG. 6 is a cross-sectional view taken along line 6--6 of FIG. 5 showing th rocker arms and fulcrums for the inlet and exhaust valves for a cylinder of the engine; 
     FIG. 7 is a transverse, vertical sectional view similar to FIG. 5 but showing the valve train used with an alternate embodiment valve lifter; 
     FIG. 8 is a transverse, vertical sectional view of a portion of an overhead cam type internal comustion engine, with the valve cover removed, having a valve train in accordance with the invention incorporated therein, with this embodiment using the follower of an otherwise conventional hydraulic lash adjuster as the fulcrum pivot for the rocker arm; and, 
     FIG. 9 is a view similar to FIG. 8 but showing an alternate embodiment wherein the follower of an otherwise conventional hydraulic lash adjuster, used as the fulcrum pivot for the rocker arm, is arranged so that an extension of the axis of movement of the follower substantially intersects the geometric center of the fulcrum pivot surface for the rocker arm. 
    
    
     DESCRIPTION OF THE FIRST EMBODIMENT 
     Referring first to FIG. 1 there is shown a portion of an internal combustion engine, of the conventional overhead valve type, having a cylinder head 10 in which a pair of poppet valves 12 (intake and exhaust) are operatively mounted to control the ingress of a combustion mixture to a cylinder, not shown, of the engine and to control the egress of exhaust gases therefrom. A pair of valve trains, in accordance with the invention, are operatively associated with the valves 12 to effect their operation. 
     As best seen in FIG. 2, each poppet valve 12 is guided for axial reciprocation in a valve stem guide 14 that is received in a suitable bored opening 15 provided for this purpose in the cylinder head 10, with the upper portion of the poppet valve 12 projecting above the cylinder head. In a conventional manner, the poppet valve 12 is normally maintained in a closed position by a spring 16 encircling the upper portion of the stem of the valve 12, with one end of the spring 16 engaging a washer 17 on the cylinder head 10 and the other end operatively engaging a conventional spring retaining washer assembly 18 secured to the stem of the poppet valve 12 in a conventional manner. A conventional valve stem seal 19 is positioned so as to sealingly engage the stem of the poppet valve. 
     A push rod 20, which is reciprocably disposed in the cylinder head laterally of the poppet valve 12, has its upper end projecting above the cylinder head 10. As would be conventional, the lower end of the push rod 20 abuts against the upper end of a conventional hydraulic valve tappet, not shown, which operatively engages the cam of a camshaft, not shown, in a conventional manner whereby the push rod is caused to reciprocate, as determined by the profile of the cam on the camshaft, not shown. 
     Motion of the push rod 20 is imparted to the poppet valve 12 by means of a rocker arm 21 that is pivotably supported by means of a fulcrum 22 fixed to a support member 23 which is rigidly mounted, as by screws 24, to the top of the cylinder head 10 at a suitable location between an associate set of push rods 20 and poppet valves 12. 
     In the construction shown and as best seen in FIG. 1, the support member 23 is configured so as to support on opposite sides thereof a right hand and a left hand fulcrum 22, for the poppet valves 12 intake and exhaust, respectively associated with a cylinder, not shown, of the engine. In the construction illustrated and as best seen in FIG. 3, each side of the support member 23 is suitably formed so as to provide a vertical support surface 25 and a shoulder 26 at right angles to each other so as to recieve an associate fulcrum 22 in a manner whereby to prevent movement of the fulcrum, the right hand fulcrum being shown in FIGS. 2 and 3. Each fulcrum 22 is suitably secured to the support member 23 as by means of screws 28, each of which extends through a stepped bore 27 in the fulcrum so as to be threadingly received in the support member 23. 
     Since the fulcrums 22 are of similar construction but of opposite hand it is deemed necessary to describe only the right hand fulcrum. 
     As shown, the right hand fulcrum 22, of inverted U-shape, is provided with a lower semi-cylindrical concave bearing surface 30 of a suitable predetermined radius 2R in the central portion thereof and, in the construction illustrated, with retainer arms 31 depending downward from opposite sides of the bearing surface 30, all for a purpose to be described in detail hereinafter. As previously described, the left hand fulcrum 22 is of the same configuration as the right hand fulcrum 22 but of the opposite hand, that is, to accept the screws 28 in a manner to permit it to be mounted on the opposite side of the support member 23 from the right hand fulcrum. 
     Since the right hand and left hand rocker arms 21 are also of similar configuration, only the right hand rocker arm 21, illustrated in FIGS. 2 and 3, will be described. This rocker arm 21 is provided with arms 32 and 33 overlying and resting on the upper ends of the associate push rod 20 and poppet valve 12, respectively. As shown in FIG. 2, the bottom surface of the arm 32 is spherically dished as to 34 to socketably receive the upper ball end of the push rod 20. Between the arms 32 and 33, the rocker arm 21 is provided with an upper, intermediate, semi-cylindrical convex bearing surface 35 of a radius R. As best seen in FIG. 3, the width of this bearing surface 35 is formed complementary to the width of the bearing surface 30 for suitable engagement therewith. 
     Now in accordance with a feature of the invention, the bearing surface 30 of the fulcrum 22 with a radius 2R is positioned so that the center of revolution of this bearing surface is located on the operating axis of the associate poppet valve 12, as shown in FIG. 4. In addition, the bearing surface 35 of a radius R is located and the arm 33 is so configured, whereby an extension of the bearing surface 35, as shown in FIGS. 2 and 4, will intersect the contact point X of the lower surface of the arm 33 onto the axis of the associate poppet valve 12 at the upper free end thereof. 
     With this arrangement, wherein the bearing surface 30, of a radius 2R defines an outer conformation, the bearing surface 35 defines an inner conformation, during pivotal movement of the rocker arm 21, the bearing surface 35 of the rocker arm 21 will be in rolling contact with the bearing surface 30 of the associate fulcrum 22. The relative rolling contact between these bearing surfaces 30, 35 having a radii ratio of 2:1 is a special case hypocycloid often referred to as cardanic motion. Cardanic motion is the plane motion of a circle or cylinder rolling inside another circle or cylinder, respectively, twice its size without slippage at the contact point between these elements. Thus in the embodiment of the rocker arm and fulcrum shown, the cardanic motion is obtained by having the radii of curvature of these fixed and moving centrodes in the ratio of 2:1, with the centrodes lying on the same side of a common tangent. With this ratio of the radii of 2:1 to obtain cardanic motion, a point on the circumference of the rolling circle or cylinder will be in a straight line extending through the center of the outside circle or cylinder. Thus, the hypocycloid for this special case in which the inner circle or cylinder is one half the diameter of the outer circle or cylinder is a straight line passing through the center of the outer circle or cylinder. 
     Accordingly, since the point X on the rocker arm 21 is located, in effect, on the effective circumference of the rolling cylinder, that is, the bearing surface 35 of rocker arm 21, movement of this point X will be in a straight line extending through the center of the outer cylinder, that is the center of revolution defining the bearing surface 30 of fulcrum 22, which center, as described hereinabove, is located on the reciprocating axis of the associate poppet valve 12. Thus during engine operation, a straight line force is applied by the arm 33 on the associate poppet valve 12, a line which corresponds to the reciprocating axis of this valve. Thus the rocker arm 21 will produce straight line-zero scrub motion at the rocker arm-valve stem contact point X. 
     In order to insure substantial rolling contact of the rocker arm 21 on its associate fulcrum 22, the rocker arm 21 is provided with raised retainer pins or teeth 40 located on opposite sides of the bearing surfaces 35 thereof which are adapted to operate in tapered guide slots 41 provided in each of the retainer arms 31 of the fulcrum 22. 
     As best seen in FIG. 4, the centers of the slots 41 lie on a plane that extends from the center of revolution of the bearing surface 30 through the point of line contact of the bearing surface 35 on the bearing surface 30 at the mean position of the rocker arm 21, that is, in its travel from the valve closed position shown in FIGS. 2 and 4 to a full valve open position. 
     Now in accordance with another feature of the invention, the special straight line hypocycloid is utilized to simplify the shape and to thus reduce the manufacturing cost of the locating pin and slot and this construction is graphically illustrated in FIG. 4. By way of example, the configuration of each retainer pin and its associate slot will be described herein using the dimension of a rocker arm and pivot structure used in a particular internal combustion engine application. 
     Thus in this particular rocker arm and pivot application, the radius 2R of the bearing surface 30 on the fulcrum 22 was 88.9 millimeters and, accordingly, the radius R of the bearing surface 35 on the associate rocker arm 21 was 44.45 millimeters. 
     Referring now to the retainer pin 40 configuration, the opposed sides of the retainer pin are of semi-cylindrical configuration, that is, as shown in FIG. 4, they are segments on circles D and E of a radius CR of 25 millimeters, with the centers thereof located on the curved plane conforming to an extension of the bearing surface 35 of the rocker arm 21. 
     Accordingly, then the centers of these circles D and E will travel along straight lines through the center of the outer conformation, that is, through the center of the bearing surface 30. 
     It therefore follows that the tangents of the circles D and E that parallel the paths of the centers of these circles D and E are always the same straight lines, which thus permits the opposed sides of an associate guide slot 41 to be straight lines. 
     Thus the opposed surfaces of a guide pin 40 are semi-circular and the opposed sides of an associate slot 41 are straight lines as viewed in the construction illustrated in FIGS. 2 and 4, with these sides preferably being interconnected by a curved wall of suitable radius, as desired. As shown in FIG. 4, the opposed straight wall sides of each slot 41 are thus lined in planes that are tangent to a circle of a construction radius CR of 25 millimeters, the center of revolution of this circle corresponding to the center of revolution of the bearing surface 30 that is located on the reciprocating axis of the associate poppet valve 12. 
     As will be apparent to those skilled in the art, the centers of the circles D and E are located so as to provide a retainer pin of suitable width and thus of a suitable strength for a given application. Thus in the construction described, the centers of the circles D and E were located so as to provide for a width across the retainer pin 40, at the bearing surface 35 location of this pin, of approximately 5.60 mm. It will be apparent that the spacing between the set of retainer pins 40 on a rocker arm 21 is selected so as to be greater than the width of the bearing surface 30 of the associate fulcrum 22 so as to permit rolling contact engagement between the bearing surfaces 30 and 35 as shown in FIG. 3. 
     As should now be apparent, the retainer pins 40 and associate slots 41 will not only insure substantially rolling contact of the rocker arm 21 on its associate fulcrum 22 but will also maintain the correct alignment of these elements. 
     The advantages of the hypocyclic rolling contact rocker arm and pivot of the subject invention are as follows: 
     1. The rolling friction between the rocker arm and its stationary fulcrum is less than the sliding friction of conventional rocker shafts or ball pivots. 
     2. The zero scrub straight line actuation of the subject rocker arm effectively eliminates the scrub losses at the rocker arm-valve stem interface. 
     3. True straight line actuation of the valve eliminates the kinematic side loads on the valve guide. This has the following advantages: 
     a. Reduced friction losses in the valve guide. 
     b. This in turn permits use of smaller diameter valve stems further reducing valve guide losses, and proportionally lowering valve guide seal losses. 
     c. Smaller valve stems lower the valve mass, which permits lower valve return spring force, lowering the losses through the entire valve train. 
     FIGS. 5 and 7 are illustrations of an alternate embodiment of a hypocyclic rolling contact rocker arm and pivot, in accordance with a feature of the invention that is constructed for use in an overhead cam engine, with similar parts being designated by similar numerals but with the addition of a prime (&#39;) where appropriate. The rocker arm in the engine arrangement shown in FIG. 5 actuates an associate poppet valve via a hydraulic lifter whereas in the engine arrangement shown in FIG. 7, the rocker arm actuates the associate poppet valve via a mechanical lifter. 
     Referring now to FIG. 5, there is shown a portion of an overhead cam type internal combustion engine having a multiple piece cylinder head 10&#39;, which, in the construction shown, includes a lower cylinder head element 50 and an upper cylinder head element 51 suitably secured together as by screws 52, only one of which is shown. 
     In the construction shown in this embodiment, the upper cylinder head element 51 is provided with suitable bores 53, each of which is aligned coaxial with the reciprocating axis of a poppet valve 12 journaled in the lower cylinder head element 50. Each bore slidably receives a suitable, conventional type hydraulic lash adjuster or lifter 54 operatively positioned between the free end of the stem of an associate poppet valve 12 and the end of an associate rocker arm 21&#39; that is pivotably supported by means of an associate fulcrum 22&#39; on a pedestal portion 51a formed integral with the upper cylinder head element 51. As shown, the upper cylinder head 51 is also provided on opposite sides thereof with longitudinal extending oil galleries 55 for supplying hydraulic fluid, such as engine lubricating oil, to the hydraulic valve lifters 54 in a conventional manner known in the art. 
     With the V configuration of the inlet and exhaust poppet valve 12 in the engine construction shown in FIG. 5, these valves are operated from a single camshaft 56 that extends longitudinally of the engine above the associated cylinders, not shown, and that is located transversely between the stems of the inlet and exhaust poppet valves 12 with its axis of rotation preferably positioned, in accordance with a feature of the invention, in a manner to be described in detail hereinafter. 
     Camshaft 56 has suitable cam lobes 57 located and oriented to effect operation of the poppet valves 12 of the engine. As would be conventional, the camshaft 56 is rotatably supported by bearings, not shown, which are suitably supported on longitudinally spaced webs 58 formed integral with the upper cylinder head element 51 and is driven in timed relationship to the rotation of the engine crankshaft by conventional means, not shown. 
     As shown, each fulcrum 22&#39;, such as the left hand fulcrum for the inlet poppet valve 12 with reference to FIG. 5, is provided with a lower semi-cylindrical, concave bearing surface 30&#39; of a suitable predetermined radius 2R and, in the construction illustrated, with grooves 60 therein on opposite sides of a depending retainer pin or tooth 40&#39;. 
     Each rocker arm 21&#39;, such as the rocker arm for the inlet poppet valve 12, as best seen in FIG. 5, is provided with arms 32&#39; and 33&#39; overlying the camshaft 56 and associate poppet valve 12, respectively. Between the arms 32&#39; and 33&#39;, each rocker arm 21&#39; is provided with an upper, intermediate, semi-cylindrical convex bearing surface 35&#39; of a radius R and, with spaced apart teeth 61 to define therebetween a guide slot 41&#39;. 
     The width of the teeth 61 relative to the width of grooves 60 and, the width of the retainer tooth 40&#39; relative to the width of the guide slot 41&#39;, are preselected, as desired, whereby the teeth 61 and tooth 40&#39; are slidably received in the grooves 60 and guide slot 41&#39;, respectively, as best seen in FIG. 6. In addition, the widths of the bearing surfaces 30&#39; and 35&#39; are formed complementary to each other, as desired, to provide for suitable engagement therebetween for a particular engine application. 
     As should now be apparent from the structure shown in FIG. 6, each pedestal portion 51a can be provided with a set of fulcrums 21&#39; for the inlet and exhaust valves of a cylinder at opposite ends thereof and, that plural spaced apart pedestal portions 51a can be provided on the upper cylinder head 51 as desired for a given engine application. 
     In a manner and for the same purpose previously described with reference to the embodiment shown in FIGS. 1-4, the bearing surface 30&#39; of the fulcrum 22&#39; with a radius 2R is positioned so that the center of revolution of this bearing surface is located on the operating axis of the associate poppet valve 12. In addition, the rocker arm 21&#39; is configured whereby an extension of the bearing surface 35&#39; thereon, as shown in FIG. 5, will intersect the contact point X of the lower surface of the arm 33&#39; onto the upper end of the hydraulic valve lifter 54 at a point corresponding to the reciprocating axis of the associate poppet valve 12. 
     Now in accordance with another feature of the present invention, the opposite arm 32&#39; of the rocker arm 21&#39; is bifurcated and is provided with an aperture therethrough, as at 62 whereby to receive a roller cam follower 63 rotatably supported on a shaft 64 fixed in the aperture 62, with the axis of the shaft 64, and thus the axis Y of rotation of the cam follower 63, being also located, in effect, on an extension of the bearing surface 35&#39; as best seen in FIG. 5. 
     In addition, the axis Y of the shaft 64, and thus the axis of rotation of the cam follower 63 and, the axis of rotation of the camshaft 56 are preferably positioned so as to be in a plane that intersects the center of revolution of the bearing surface 30&#39;, as shown in FIG. 5, for a purpose to be described in detail hereinafter. 
     With this arrangement, wherein the bearing surface 30&#39;, of a radius 2R defines an outer conformation and the bearing surface 35&#39; defines an inner conformation of radius R during pivotal movement of the rocker arm 21&#39;, the bearing surface 35&#39; of the rocker arm 21&#39; will be in rolling contact with the bearing surface 30&#39; of the associate fulcrum 22&#39; in the same manner as previously described with reference to the embodiment of FIGS. 1-4. 
     Also as previously described, the relative rolling contact between these bearing surfaces 30&#39;, 35&#39; having a radii ratio of 2:1 is a special case hypocycloid often referred to as cardanic motion which is the plane motion of a circle or cylinder rolling inside another circle or cylinder, respectively, twice its size without slippage at the contact point between these elements. Thus in the embodiment of the rocker arm and fulcrum shown in FIG. 5, the cardanic motion is obtained by having the radii of curvature of these fixed and moving centrodes, 30&#39; and 35&#39;, respectively in the ratio of 2:1. 
     Thus as described, with this ratio of the radii of 2:1 to obtain cardanic motion, a point on the circumference of the rolling circle or cylinder will be in a straight line extending through the center of the outside circle or cylinder. Thus, the hypocycloid for this special case in which the inner circle or cylinder is one half the diameter of the outer circle or cylinder is a straight line passing through the center of the outer circle or cylinder, that is, through the center of revolution of the bearing surface 30&#39;. 
     Now, since the point X on the rocker arm 21&#39; is located, in effect, on the effective circumference of the rolling cylinder, that is, the bearing surface 35&#39; of rocker arm 21&#39;, movement of this point X will be in a straight line extending through the center of the outer cylinder, that is the center of revolution defining the bearing surface 30&#39; of fulcrum 22&#39;, which center, as described hereinabove, is located on the reciprocating axis of the associate poppet valve 12 and of the hydraulic lifter 54. Thus during engine operation, a straight line force is applied by the arm 33&#39; on the associate poppet valve 12 via the hydraulic lifter 54, a line which corresponds to the reciprocating axis of the poppet valve 12. Thus the rocker arm 21&#39; will produce straight line-zero scrub motion at the rocker arm-valve stem contact point X. 
     In addition, with the axis Y of rotation of the cam follower 63 also located, in effect, on an extension of the bearing surface 35&#39; of rocker arm 21&#39; and if, in effect, on a line passing through the axis of rotation of the camshaft 56 and the center of revolution defining the bearing surface 30&#39;, there will be substantially no skidding force on the rocker arm 21&#39; due to contact between its cam follower 63 and the associate lobe 57 on the camshaft 56. 
     In addition, the engagement of the tooth 40&#39; in the guide slot 41&#39; between teeth 111 on the rocker arm 21&#39; will ensure rolling contact of the bearing surface 35&#39; on the bearing surface 30&#39; and, in addition, this engagement of these elements and of the teeth 111 in groove 110 of the fulcrum 22&#39;, as best seen in FIG. 6, will prevent skewing of the associate rocker arm 21&#39;. 
     An alternate embodiment of an overhead cam engine with a hypocyclic rolling contact rocker arm and pivot, in accordance with the invention is shown in FIG. 7, wherein similar parts are designated by similar numerals but with the addition of a double prime (&#34;) where appropriate. 
     In this embodiment, the overhead cam engine has a cylinder head 10&#34; which, in the construction shown, includes a lower cylinder head element 50 with one or more upper cylinder head elements in the form of pedestals 51&#34; secured thereto as by screws 52. 
     Each pedestal 51&#34; is provided with at least one end thereof with a set of fulcrums 22&#34; rocker arms 21&#34; to effect actuation of the inlet and exhaust poppet valves for a cylinder, not shown, of the engine, only the inlet valve 12 and associate rocker arm 21&#34; being shown. Also, in order to simplify this drawing FIG. 7, only the cam lobe 57 for the inlet valve is shown on camshaft 56. 
     In this embodiment, a suitable, conventional mechanical lifter or mechanical expansion compensating device generally designated 70, is operatively positioned between the free end of an associate poppet valve 12 and arm 33&#34; of its associate rocker arm 21&#34;. 
     By way of an example, the mechanical expansion compensating device 70, in the construction shown, is of the type disclosed in U.S. Pat. No. 4,365,595, entitled &#34;Actuation of Valves of Internal Combustion Engines&#34;, issued Dec. 18, 1982, to Sanzio P. V. Piatti, and includes a metal spring disc 71 operatively positioned between a lower abutment member 72, an upper piston 73, and an elongated, cup-shaped, spring retainer 18&#34;. 
     As shown, the abutment member 72 has a head with a semi-spherical, convex upper surface 72a which abuts against the central lower surface of the spring disc 71 and a stem portion 72b which abuts the end of the stem of the associate poppet valve 12, with the head thereof loosely secured in the tubular shaped, spring retainer 18&#34;. 
     The piston 73, of inverted cup shape, is slidably journaled in the upper open end of the spring retainer 18&#34; and is provided at its lower end with an annular, radially inward inclined end surface 73a, which is preferably of generally concave shape formed complementary to convex upper surface 72a of the abutment member 72, so as to abut against the upper surface of the spring disc 71 adjacent to its outer peripheral edge. For purpose of illustration only, the spring disc 71 is shown flat, but it should be realized that at initial adjustment in an engine the spring disc 71 would be bent, as desired, to take up lash as necessary. 
     As shown, the piston 73 is also preferably provided with a central upstanding boss 73b on its upper or base end for engagement by the operating end of the arm 33&#39; of the rocker arm 21&#39;. 
     In this FIG. 7 engine embodiment, the rocker arm 21&#34; and fulcrums 22&#34; on the pedestal 51&#34; are similar to those of FIGS. 5 and 6, previously described hereinabove, and, accordingly it is not deemed necessary to again describe these elements in detail. 
     FIG. 8 is an illustration of a further alternate embodiment of a hypocyclic rolling contact rocker arm and pivot, in accordance with a feature of the invention wherein the pivot fulcrum for the rocker arm is provided as part of a hydraulic lash adjuster, with similar parts being designated by similar numerals but with the addition of a triple prime (&#39;&#34;) where appropriate. 
     Accordingly, there is shown in FIG. 8 a portion of an internal combustion engine, which in the construction illustrated, is of the overhead cam type having a multiple piece cylinder head 10&#39;&#34; which includes a lower cylinder head element 50&#39;&#34; and an upper cylinder head element 51&#39;&#34; suitably secured together as by screws 52 extending through upright pedestal post sections 51&#39;&#34;a of the latter element. 
     In the construction shown, the longitudinal extending raised beam portion 51&#39;&#34;b of the upper cylinder head element 51&#39;&#34; serves as a retainer means for hydraulic lash adjuster/pivots, hereinafter also referred to as lash adjusters generally designated 74, and, accordingly, the beam portion 51&#39;&#34;b is provided with spaced apart adjuster receiving sockets located above and between an associate poppet valve 12 and an associate valve actuator, such as the lobe 57 on a camshaft 56, only one such adjuster receiving socket being shown in FIG. 8. 
     Each such adjuster receiving socket is defined by a stepped blind bore that defines an adjuster receiving bore wall 75 extending upward from the lower surface of the beam portion 51&#39;&#34;b and an upper wall 76 of an internal diameter greater than that of the adjuster receiving bore wall 75, with these walls 75 and 76 being interconnected by a flat shoulder 77. 
     The enlarged diameter upper wall 76 defines a fluid reservoir 78 which is in communication with one end of a transverse passage 80, the opposite end of passage 80 being in flow communication with a longitudinal passage 81 that is in continuous communication with a pressurized hydraulic fluid supply, such as engine lubricant oil, during engine operation through suitable interconnecting passage means, not shown, in a manner known in the art. 
     The hydraulic lash adjuster/pivot or lash adjuster 74 includes an upwardly presenting, cup-shaped follower body 82 with a lower enlarged closed pivot or fulcrum end 83, which as will be described in detail hereinafter is provided on its lower surface with a bearing surface 30&#39;&#34; to serve as a fulcrum for the rocker arm 21&#39;&#34;. A cup-shaped plunger 84 has a close sliding fit for reciprocation within the follower body 82, and is normally biased upwardly therein by a plunger spring 85 so that its notched upper end, with reference to FIG. 8, normally abuts against the upper internal wall 79 of the adjuster receiving socket in the retainer beam portion 51&#39;&#34;b. The plunger spring 85 also acts against the closed end of the follower body 82 to maintain it in abutment with the rocker arm 21&#39;&#34;. 
     The lower end of the plunger 84 forms with the closed end of the follower body 82 a pressure chamber 86 while the upper open end of the plunger 84 defines a supply chamber 87 that is in continuous flow communication with the fluid reservoir 78 in the embodiment illustrated. The supply chamber 87 is in flow communication with the pressure chamber 86 via an axial port 88, flow through which is controlled by a one-way valve in the form of a ball 90 which closes against a seat of the plunger that encircles port 88. 
     A suitable valve cage 91 and valve return spring 92 limits open travel of the valve ball 90 to the amount necessary to accommodate replenishment of the pressure chamber 86 with oil which normally escapes therefrom between the sliding surfaces of the plunger 84 and follower body 82 as &#34;leak-down&#34; during cam induced opening movements of the poppet valve 12. As shown, the valve cage 91 is held in position against the plunger 84 by the plunger spring 85. 
     The hydraulic lash adjuster/pivot 74 is maintained in unit assembly within the adjuster receiving socket in the beam portion 51&#39;&#34;b by means of a retainer ring 93 operatively positioned in an annular groove provided for this purpose in the follower body 82 whereby the retainer ring can abut against the flat shoulder 77 to thereby limit outward travel of the follower body 82, which is the predetermined maximum extension of the lash adjuster, the position shown in FIG. 8 for purposes of illustration only. 
     Preferably, a suitable conventional type anti-rotation retainer means is also operatively associated with the follower body 82 to prevent rotation thereof within the adjuster receiving socket. For example, the exterior of the follower body 82 can be provided with a machined flat, not shown, of a suitable axial extent to be engaged by a cylindrical retainer pin, not shown, rotatably supported in the beam portion 51&#39;&#34;b of the upper cylinder head element 51&#39;&#34; for rolling contact with the flat in a manner well known in the art. 
     As shown in FIG. 8, the pivot or fulcrum end 83 of the follower body 82 of the hydraulic lash adjuster/pivot 74, is provided with a lower semi-cylindrical, concave bearing surface 30&#39;&#34; of a suitable predetermined radius 2R and, in the construction shown, with a guide slot 41&#39;&#34;. 
     The associate rocker arm 21&#39;&#34; is provided with arms 32&#39;&#34; and 33&#39;&#34; overlying the camshaft 56 and associate poppet valve 12 respectively and, between these arms the rocker arm 21&#39;&#34; is provided with an upper intermediate semi-cylindrical convex bearing surface 35&#39;&#34; of a radius R and with an upstanding retainer pin or tooth 40&#39;&#34; for operational engagement in the guide slot 41&#39;&#34; in the fulcrum end portion 83 of the follower body 82. 
     In a manner and for the same purpose as previously described with reference to the embodiments shown in FIGS. 1-4, 5-6 and 7, the bearing surface 30&#39;&#34; of the fulcrum end 83 of the follower body 82 with a radius 2R is positioned, in the construction shown in FIG. 8, so that the center of revolution, that is, the geometric center, of this bearing surface 30&#39;&#34; is located on the effective operating axis of the associate poppet valve 12. As in these prior embodiments, the rocker arm 21&#39;&#34; is configured so that an extension of the bearing surface 35&#39;&#34; thereon will intersect the contact point X on the lower surface of the arm 33&#39;&#34; onto the upper free stem end of the poppet valve 12. 
     Preferably, as shown in FIG. 8, the arm 33&#39;&#34; of rocker arm 21&#39;&#34; is provided with spaced apart retainer extensions 33&#39;&#34;a loosely received by the upper free stem end of the poppet valve 12 so as to assist in maintaining transverse non-rotative alignment of the rocker arm 21&#39;&#34;, it being realized that further non-rotative alignment of the rocker arm can be effected in a manner similar to that shown in the FIGS. 1-4 embodiment or in the FIGS. 5-7 embodiments, wherein the rocker arm and associated fulcrum are provided with means to effect alignment of the rocker arm relative to the associate poppet valve and the actuator means. 
     In the construction shown, each adjuster socket in the upper cylinder head element 51&#39;&#34; is located so that the reciprocating axis of the follower body 82 is parallel to the axis of the poppet valve 12. Thus during movement of the follower body 82 between its fully retracted position and its fully extended position, the position shown in FIG. 8, the geometric center of the upper bearing surface 30&#39;&#34; will be merely moved up or down on the central axis of reciprocation of the poppet valve 82. 
     However, it will be appreciated that in certain engine applications, because of allowable space limitations, this parallel movement of the follower body 82 relative to the axis of the poppet valve 12 would not be practical. Preferably, in such an application, it would then be desirable to have the axis of movement of the follower body 82 aligned so that this axis will intersect the geometric center of the upper bearing surface 30&#39;&#34;, so that during the predetermined maximum movement of the follower body 82 of the hydraulic lash adjuster 74, the geometric center of the upper bearing surface 30&#39;&#34; will remain within the stem diameter area of the poppet valve 12 whereby the force of the rocker arm 21&#39;&#34; acting on the poppet valve will always be in a direction parallel to the reciprocating axis of this valve. 
     As an example, in a particular engine application having an aluminum cylinder head 10&#39;&#34; with hardened valve inserts 11, as shown in FIG. 8, the hydraulic lash adjuster/pivot 74 was designed for a maximum travel of 0.060 inch for the follower body 82 within the adjuster socket in the upper cylinder head member 51&#39;&#34; between a bottomed out position, at which the upper end of the follower body 82 would abut against wall 79, and a fully extended position, the position shown, at which the retainer ring 93 abuts the shoulder 77. Accordingly, using this particular lash adjuster, if the geometric center of the upper bearing surface 30&#39;&#34; was located so as to be on the central axis of the poppet valve 12 as when the follower body 82 is in the mid-point in its predetermined range of travel, then, even if the axis of movement of the follower body 82 is located so as to be at a right angle to the central axis of the poppet valve 12, the geometric center of the bearing surface 30&#39;&#34; would only move approximately 0.030 inch either to the left or right of the central axis of the poppet valve 12 when moving between a fully extended position and a bottomed out position and thus this geometric axis would always be within the effective internal stem boundary area of the poppet valve. Accordingly, the contact point X of rocker arm 21&#39;&#34; against the stem of the poppet valve 12 will always be positioned so as to impart straight line motion to the poppet valve. 
     In the construction shown in FIG. 8, the axis of shaft 64 rotatably supporting the cam follower 63 on the rocker arm 21&#39;&#34; is located on a plane forming an extension of the inner conformation lower bearing surface 35&#39;&#34; of the rocker arm 21&#39;&#34;, in a manner similar to that described with reference to the FIG. 5 and FIG. 7 embodiments. However, because of the movement of the follower body 82 of the hydraulic lash adjuster 74 during engine operation so as to effect lash adjustment, a straight line extending from the axis of shaft 64 to the geometric axis of the upper bearing surface 30&#39;&#34; will not necessarily intersect the axis of rotation of the camshaft 56. However, since the follower 63 on the rocker arm 21&#39;&#34; is in the form of a roller type cam follower, friction loss will still be kept to a minimum. 
     Alternatively, in certain engine applications it may be desirable to configure the rocker arm 21&#39;&#34;  whereby the line contact of the cam follower 63 thereon against the cam lobe 57 be located in a plane forming an extension of the conformation of the inner bearing surface 35&#39;&#34;. Alternatively, it will also be appreciated that although in the FIG. 8 construction shown, the rocker arm 21&#39;&#34; is actuated by direct engagement with the camshaft via the cam follower 63, the rocker arm could be actuated by a push rod as shown in the FIGS. 1-4 embodiment. 
     It will be appreciated by those skilled in the art that during engine operation actual lash take-up by the hydraulic lash adjuster/pivot will occur as the cam follower rides on the base circle of the cam lobe 57. Thus, during an operating cycle of the valve, the hydraulic lash adjuster/pivot 74 will provide a fixed fulcrum pivot support for the rocker arm. 
     While the invention has been described with reference to the structures disclosed herein, it is not 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. This application is therefore intended to cover such modifications or changes as may come within the purposes of the improvements or scope of the following claims.