Abstract:
A push rod is constructed with a self-contained lash take-up spring and auxiliary oil pumping assembly inserted at an end of the rod body and includes an end part slidably mounted relative to the rod body and a biasing spring that urges the end part axially to extend the push rod length to take up the play of normal lash in a valve actuator of an internal combustion engine. Axial movement of the end part is constrained between a yielding maximum extension of the push rod under spring bias and a non-yielding minimal working rod length in which the end part movement is stopped against an end of the rod body for pushing open the engine valve in reaction to cam and tappet movements. Reciprocation of the end piece relative to the rod body causes localized oil pumping action that delivers enhanced oiling through the rod body to the valve actuator parts.

Description:
This is a continuation-in-part of application Ser. No. 08/388,248, filed Feb. 14, 1995, now abandoned. 
    
    
     BACKGROUND 
     The invention concerns an improvement in push rods used in valve actuators for internal combustion engines. 
     The conventional push rod is a rigid member acting in compression between a tappet reciprocated by a rotating cam and one end of a rocker arm that forces a valve open against a valve spring. In the assemblage of these components, a closed valve clearance or play, called lash, is initially set by a gap gauge or the like to ensure complete valve closure at the proper cycle of the engine piston usually corresponding to an off lobe cam position at the tappet. As the cam lobe rotates to drive the tappet, the push rod is forced along its axis, in compression driving one end of the rocker arm which in turn opens the valve against the valve spring at the opposite end of the rocker arm. 
     As the engine rpm is increased, the reciprocation and acceleration and deceleration forces on the valve actuator parts and specifically on the push rod attain high force levels. The lash that exists in the valve closed condition causes cycling metal to metal contact which is associated with valve actuator noise such as clatter, increased wear due to friction, metal to metal wear and diminished engine efficiency. The amount of lash initially set for the valve actuator will typically vary with wear, often increasing so that the problems of noise, increased friction and wear and still further lowering of actuator efficiency results. 
     SUMMARY OF THE INVENTION 
     A push rod is constructed with a lash take-up spring and oil pump assembly, mounted so as to be contained within at least one end of the rod body. This assembly includes an end part slidably inserted into a coaxial bore of the rod body and a biasing spring that urges the end part axially away from the mounting end of the rod body so as to create a spring biased slight axial extension of the overall rod length. In the preferred embodiment, the end assembly includes an oil pumping chamber accommodating the lash take-up spring and forming a cylinder-piston pump in communication with a coaxial oil duct in the rod that delivers oil to engine parts at the opposite end of the rod, such as to the rocker arm assembly. Means such as an internal clip mounted on a shank of the end part limit the axial movement of the part between a spring biased extension of the push rod length and a non-yielding minimal working rod length in which the end part movement is stopped against the mounting end of the rod body allowing the rod to act in full force compression to drive the rocker arm against the valve spring assembly to open the valve in reaction to the cam and tappet or lifter movements. 
     Further in another embodiment, the end assembly has a retainer insert fixed to one end of a hollow or tubular rod body. The insert, which may be generally cup-shaped, has an open-flanged end that seats against an axial end of the tubular rod body and has a closed recessed end. The movable end piece has a rounded head that fits against a pocket in the rocker arm or tappet lifter and a shank that slidably fits in a shank opening formed in the closed end of the cup-shaped insert. A lash take-up compression spring fits coaxially about the end piece shank and acts in compression between the recessed closed end of the insert and the underside of the head of the end part. Spring clip means is preferably used to retain the shank of the end part in the insert opening and limit the amount of axial extension or travel of the end part under the spring bias. The underside of the head forms a structure that moves down against a stop at the flange of the retainer insert and thus in effect against the axial end of the tubular rod body to transmit the compression force from the rounded head end to the rod body to accommodate the high compression force needed to operate the valve spring under the variable revolutions per minute required. 
     Further in the preferred embodiment, the end part has an oil bore provided along the end part axis through its shank and opening at the rounded head which communicates with the internal pump chamber and an inner axial duct in the tubular rod body for ducting oil to lubricate the corresponding end of the push rod where it engages the rocker arm or tappet. The spring biased axial movement of the end part is at least sufficient to take up the initial specified clearance or lash in the valve actuator assemblage and is preferably about 200% of the specified lash in order to continue to take up play as the parts wear between service adjustments in the valve actuator. Thus when properly and initially adjusted, the push rod has its end part slightly depressed against the lash take-up spring to approximately one half of the maximum extension. The lash take-up spring force is selected to be substantially less than the predetermined valve spring force to ensure that the rod end assembly does not deflect and thus does not partially open the valve during the valve closed portion of the camming cycle. 
     These and other features, advantages and aspects of the invention will become better understood by reference to the following detailed description and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged axial section view of the push rod shown shortened from its true length by broken lines mid-body of the push rod. 
     FIG. 2 is a further enlarged vertical cross sectional view of an end of the push rod of FIG. 1, showing in better detail the end assembly. 
     FIG. 3 is a diagrammatic view, partly in section with areas broken away, to illustrate the positioning and operation of the push rod in a valve actuator of an internal combustion engine. 
     FIGS. 4a and 4b are a diagrammatic view and an enlarged fragmentary, cross-section view of the currently preferred push rod assembly shown in a valve closed phase of the engine cycle. 
     FIGS. 5a and 5b are views corresponding to FIGS. 4a and 4b showing the push rod assembly in a valve opened phase. 
    
    
     DETAILED DESCRIPTION 
     With reference to FIGS. 1 and 2, the push rod 10 in accordance with one embodiment, is constructed of a substantially rigid metal tubular rod body 12. To one end of the rod body 12, an end assembly 14 is mounted and is shown to include an end piece 16, a cup-shaped retainer 18, a lash take-up spring 20, and a retainer clip 22. End piece 16 is generally elongated axially with an enlarged rounded head portion 16a, a smaller diameter shank portion 16b, a mid-body portion 16c of intermediate diameter, and a central axially extending oil duct 16d appearing in dotted lines in the drawings. Retainer insert 18 is of generally hat or cup shape, with a cylindrical main body portion 18a, an end 18b that has a radial flange, and a closed end 18c. Retainer insert 18 is press-fitted into a counter bore 12a of tubular rod body 12 and forced inwardly into the open tubular end of the counter bore until a lip of flange 18b rests against the rim or axial end of rod body 12 as shown in FIGS. 1 and 2. Counter bore 12a forms a slight shoulder or lip 13 against which the closed axial end of insert 18 seats when press fitted into tubular rod body 12 to further ensure transmission of adequate push rod force between head portion 16a of the movable end part 16 and the rod body through insert 18. Alternatively, a different insert configuration or elimination of insert 18 would provide an alternative embodiment in which end piece 16 is forced directly against the end of rod body 12 to provide the full valve opening force required. 
     The intermediate diameter mid-body portion 16c of end part 16 is of generally cylindrical shape and has a sliding clearance fit into the inner diameter 18d as best illustrated in FIG. 2. The free end of shank 16b slides axially freely in an opening 18e (see FIG. 2) and clip 22 held in a circumferential recess of shank portion 16b retains it and end piece 16 in retainer insert 18, yet allows axial movement of the end piece. 
     An opposite end of rod body 12 may also be fitted with a like or similar end assembly so that both ends have anti-lash extensions, but usually one end piece is sufficient. Here the opposite end of the push rod is provided with a fixed end piece 15 press fitted into that end of the rod body 12. An oil duct 15a is formed in the axial center of fixed end part 15. 
     With reference to FIGS. 2 and 3, during operation, the push rod 10 is installed in the valve actuator assemblage such as illustrated in FIG. 3 and the amount of lash specified for a closed valve condition is set by depressing rocker arm 30 against anti-lash push rod 10 to depress the head 16a of end piece 16 down into insert 18 against lash take-up spring 20. Although not shown in FIG. 2, this setup procedure causes a lower face 17 underlying head portion 16a of the end piece 16 to stop against the upwardly confronting shoulder surface 19 of insert flange 18b. By limiting the travel of end piece 16 in this manner, the amount of nominal lash in the valve actuator assemblage is set such as with a feeler gauge between rocker arm 30, shown in FIG. 3, and end 32 of the valve spring and adjacent valve stem 34 and 36, respectively. Then the rocker arm 30 is released, allowing lash take-up spring 20 to urge end piece 16 of the push rod to extend, taking up the preset lash in the valve actuator assembly. The amount of yielding extension provided by lash take-up spring 20 is pre-selected to be a fraction of the spring rate force of valve spring 34 to ensure that the valve head 38 remains closed during the off lobe position of the valve actuator. In other words, the anti-lash spring and anti-lash head assembly take up lash but do not override or force open the intended closed valve condition. 
     When the valve actuator cam 40 rotates or otherwise moves to cause the cam lobe to drive lifter or tappet 42 toward a valve opening position, the push rod end part is fully depressed, closing the lash gap as shown in FIG. 2 between head 16a and insert shoulder 19. The lash take-up spring 20 is now effectively removed from the actuator system and end part 16 acts as a non-yielding stiff unit with insert 18 and rigid rod body 12 transmitting the full cam actuating force against the spring valve and valve components 34 and 36 to force open valve head 38. The cycle continues until the valve head 38 closes and the compression force on the push rod 14 is relieved, allowing lash take-up spring 20 to take up the play by forcing head portion 16a of the end part axially outwardly of rod body 12. 
     By way of example, one embodiment of push rod 14 used an end part 16 of hardened 41-40 or 30 heat treated steel. A 50 thousands maximum gap is provided between face 17 of head portion 16a and shoulder 19 of insert 18, however this dimension can vary with engine design and required performance. Lash take-up spring 20 is a standard heat treated spring steel and is selected in this example to have a force of about 25 pounds over the operating deflection. Tubular rod body 12 is titanium to reduce the amount of inertia, and hence energy cost and drag, especially during high rpms. 
     With reference to FIGS. 4a and 4b and 5a and 5b, another and now preferred embodiment of the push rod assembly is illustrated in which lash take-up end assembly 14&#39; is shaped and mounted at one end of rod body 12&#39; and has an internal localized oil pumping cylinder and spring retaining chamber 50 behind the reciprocating shank of end piece 16&#39;. 
     More particularly, the end piece 16&#39; has a shank 16c&#39; that is sized to slidably fit into a coaxial counterbore 12a&#39; of the rod body 12&#39;. An internal coaxial oil duct 12b&#39; of diameter less than counterbore 12a&#39; in rod body 12&#39; communicates with spring and pumping chamber 50 and continues henceforth upwardly away from the pumping chamber along the length of the rod body opening at the opposite end of the push rod where it seats into rocker arm 30&#39; as illustrated in FIG. 4a. A lash take-up compression spring 20&#39; is mounted between the end face 16e&#39; of shank 16b&#39; and the opposed bottom wall 20&#39; of the pumping cylinder chamber 50 to bias end piece 16 away from seating against rod body 12. Thus the underside of head 16a&#39; of end piece 16&#39; is pushed off seated contact with the rim 13&#39; of push rod body 12&#39; as illustrated in FIG. 4b. 
     A retainer clip 22&#39; of the spring C-type is mounted in a circumferential recess on the shank 16c&#39; of end piece 16&#39; about mid-position of its length with a protruding edge portion of the clip 22&#39; projecting outwardly to be retained in a recess 52 formed circumferentially in the interior wall of the counterbore 12a&#39;. The axial extent of recess 52 limits reciprocation of end piece 16&#39; but is sufficient to accommodate the intended movement, such as 50 thousandths, between its extended spring-biased lash take-up position as shown in FIG. 4b, and its valve opening retracted condition. The latter condition is shown in FIG. 5b when the underside 17&#39; of the head 16a&#39; is shouldered against the end 13&#39; of the push rod body for forced opening of the valve against the heavier valve spring as illustrated in the companion FIG. 5a. 
     As the engine operates, rapid reciprocation of the push rod including the back and forth movement of the end piece 16 between its spring-biased lash take-up position as shown in FIG. 4b, and its closed retracted position shown in FIG. 5b causes a localized oil pumping action in chamber 50 of push rod 12&#39;. Flow of oil that normally would occur under the nominal oil pressure of the engine through a lifter 56, conventional or hydraulic, into the coaxial oiler duct 12b&#39; of the push rod is augmented by this localized pumping action. 
     The pumping action is due to the reciprocation of shank 16b&#39; in chamber 50. Oil from lifter 56 passes up from the lifter seat, into duct 16d&#39; of end piece 16&#39; filling the pumping chamber 50 when head 16a&#39; is extended. As the chamber constricts in volume due to the inward movement of the end piece shank 16b&#39;, oil is forced and hence pumped, as in a piston cylinder hydraulic pump, upwardly into the relatively smaller diameter rod body duct 12b&#39; where it is then discharged either at the contact seat with the rocker arm 30&#39; or preferably through an arm dispersal port 58 provided for that purpose in the rocker arm extremity in line with or in communication with the opening of the oil duct 12b&#39; at the upper end of the push rod body 12&#39;. 
     The amount of pumping action and its effectiveness increases along with the increase in the reciprocation rate of the end piece 16&#39; in rod body 12&#39; such that at higher engine RPM with more rapid reciprocation of the push rod and end piece 16, greater local pumping action and thus increased lubrication results. Furthermore, the lash take-up spring 20&#39; holds head 16a&#39; in seated contact with lifter seat 56a, minimizing the amount of oil bleed at this coupling point and hence enhancing the delivery of oil to the push rod upper end at the rocker arm. 
     Preferably the size and hence volume of the pumping chamber 50 and the shank of the end piece 16&#39; is selected so that a 50 to 100 thousandths axial movement of end piece 16&#39; causes a volume displacement sufficient for the engine size and lubrication requirements. In relation, the size of the internal coaxial oiling duct 12b&#39; in the main body of the push rod is preferably 1/2 or less than the diameter of the chamber 50. 
     With these considerations, this now preferred embodiment of the push rod lash take-up spring and oil pump assembly produces a highly effective mechanism for oiling the contact points at the ends of the push rod, the rocker arm and the various parts adjacent to the rocker arm as a result of oil being forced through duct 12b&#39; under this augmented, localized pumping action. The invention not only minimizes the amount of free play noise and vibration that exists in the conventional push rod without the lash take-up spring-biased end piece, but also enhances the oiling of the associated parts of the engine by directing the oil to the most critical wear components and at a flow rate that increases with engine speed. Furthermore, the disclosed construction of the push rod 10&#39; with its self-contained lash take-up end piece and auxiliary oil pump assembly being fully contained in the geometry of a typical conventional push rod allows the push rod 10&#39; to be used as a replacement part to quiet an engine, reduce its valve actuator wear and enhance oil delivery to the related parts. 
     While only particular embodiments have been disclosed herein, it will be readily apparent to persons skilled in the art that numerous changes and modifications can be made thereto, including the use of equivalent means, devices, and method steps without departing from the spirit of the invention.