Patent Application
20110220051
The present disclosure is directed to overhead valve engines, and more in particular to overhead valve engines having retainers for holding elements of a valve actuator subassembly, such as a rocker arm and a push rod, in proximity of each other.
Overhead valve engines are internal combustion engines wherein the intake and exhaust valves are located in the cylinder head while the camshaft is placed in the cylinder block. The valves may be actuated by the camshaft through the intermediation of lifters, push rods and rocker arms, in that order. Lifters, also known as tappets or lash adjusters, are often hydraulic in nature and serve to maintain zero valve clearance. A hydraulic lifter is able to take up valve train slack due to for example low engine temperatures, wear or incorrect adjustment, thereby eliminating tappet valve train noise. Typically, a hydraulic lifter comprises a pressure chamber that is intermittently filled with engine oil from an oil gallery via a small drilling. When a valve associated with the lifter is closed, the lifter is free to fill with oil. When the valve is opening and the lifter is being operated by the camshaft, the oil feed is blocked. The blockage substantially seals the pressure chamber, and the lifter acts much like a solid one would, oil being virtually incompressible.
When an engine remains unused for a relatively long period of time, on the order of days or weeks, there is the possibility that the pressure chamber will become emptied or pumped down. This condition may arise because when the engine is stopped, one or more cylinders may have valves in their open positions. As an open valve corresponds to a pressurized hydraulic lifter, the pressure chamber of the lifter may leak down over a prolonged period. A pumped down lifter may cause serious problems on startup. When the camshaft starts to turn while starting the engine, and the compressive load—or what is left thereof—is abruptly removed from the hydraulic lifter, the lifter may not be able to recover from its compressed length fast enough to eliminate the atypically large amount of clearance in the valve train that just arose. Consequently, the push rod, which is positioned in between the lifter and rocker arm, may detach from the rocker arm and topple sideways. When it does, it has become not only a dysfunctional component, but also an uncontrollable one that may for example be driven into other engine components by motion imparted to it by the revolving camshaft. This may obviously cause serious damage to the engine.
To prevent a push rod from toppling due to a relatively large play between the rocker end of the push rod and the rocker arm, either because of a pumped down hydraulic lifter or an other malfunctioning engine component, a push rod retainer may be used. Such a push rod retainer is known from WO 90/02249. The retainer disclosed therein cradles the cupped rocker end of a push rod in a pre-established proximity to a rocker arm provided with a ball pivot, and thus prevents the push rod from tipping or falling to one side.
Although the push rod retainer disclosed in WO 90/02249 may work largely satisfactorily, it embodies a number of drawbacks. For example, the push rod retainer is pre-assembled to the rocker arm: the ball pivot, which is larger than a hole in the retainer wall, is provided with a shank that goes through the hole in the retainer wall and is press fitted into a bore in the rocker arm. As a result, the retainer is troublesome to replace during servicing. Secondly, the push rod retainer is mounted immovably relative to the rocker arm. It is not supposed to touch the push rod, except when a malfunction of the engine occurs. Clearance relative to the push rod is provided for by tailoring the dimensions of the retainer to the dimensions of the push rod. Due to the repetitive angular movement of the push rod, the maximum amount of clearance between the retainer and the push rod will vary periodically. The amount of clearance is thus not constant, and at some points in time greater than desirable. After all, the larger the clearance between the push rod and the wall of the push rod retainer, the greater the possibility that the push rod will escape from the confines of the retainer cup.
The present disclosure is directed, at least in part, to improving or overcoming some aspects of known push rod retainers.
In one aspect a push rod retainer may be provided for retaining an extremity of a push rod and a first end of a rocker arm in proximity of each other. The push rod retainer may include a base section that may accommodate at least a part of a junction space wherein the extremity of the push rod and a connection member of the rocker arm may be joinable. It may also include at least two resilient projections. The projections may extend from the base section and may at least partly extend in a direction towards each other. The resilient projections may bound a first entrance to the junction space.
Another aspect of the present disclosure may be directed to a rocker arm. The rocker arm may have a connection member that is provided with a circumferential constriction configured for engagement by the resilient projections of a disclosed push rod retainer. The circumferential constriction may be provided behind an at least partly spheroidally shaped pivot head that is arranged on one end of the connection member, and in between a substantially square shoulder and a smooth and concave tapering that defines a transition between the pivot head and the constriction.
Another aspect of the present disclosure may be directed to an assembly. The assembly may include a disclosed push rod retainer, and a disclosed rocker arm. The resilient projections of the push rod retainer may engage the circumferential constriction of the connection member of the rocker arm.
In yet another aspect a method of retaining together a push rod and a rocker arm may be provided. The method may include attaching a resilient retainer to one of the push rod and the rocker arm such that the retainer cannot be removed therefrom without applying a removal force and such that relative movement of the retainer and the one of the push rod and the rocker arm is allowed. The method may further include enclosing an end of the other of the push rod and the rocker arm in a jacket-shaped portion of the retainer to prevent the push rod from falling sideways when the push rod and the rocker arm temporarily disengage.
Valve train 100 may include a camshaft 102 of a conventional design, having cam lobes 104. In total, the depicted camshaft 102 features eight cam lobes 104, two for each cylinder of the four-cylinder engine with which valve train 100 may be used. Lifters 106, such as hydraulic tappets, may abut camshaft 102 where cam lobes 104 are provided so that a rotating motion of the camshaft results in a periodical activation of the lifters. Each lifter 106 may support a first end of an elongate push rod 130. A second end 132 of the push rod 130 may normally be in contact with a first end 144 of an associated rocker arm 140. The operable connection between a push rod end 132 and a first end 144 of a rocker arm 140 may be secured by a push rod retainer 300 (see for more detail
A rocker arm 140 may be pivotably mounted on a rocker shaft 108 in a conventional manner. An actuation end 146 of a rocker arm 140—opposite the first end 144—may mechanically operate a valve 112. In the embodiment shown in
Push rod retainer 300 may include a base section 302 that bounds a passage 304 extending through the base section from a first end 322 to a second end 324. The passage 304 may form at least a (lower) part of a junction space 306 wherein an extremity 132 of a push rod 130 and a connection member 600 of a rocker arm 140 are joinable.
Passage 304 may be dimensioned to snugly receive the cupped end 132 of a push rod 130. Such a cupped end 132 may be substantially cylindrical for conventional push rods, but need not be. The cross-sectional shape of passage 304 may therefore vary for different embodiments of the disclosed push rod retainer 300, depending on the cross-sectional shape of the cupped end 132 for whose reception passage 304 is designed. It is noted, however, that even in case the cupped end 132 of a pushrod 130 has a circular cross-section, the passage 304 may have a cross-section that is not circular. It may, for example, have a polygonal cross-section with an inscribed circle that is slightly larger than the circular cross-section of the push rod's cupped end 132.
Though passage 304 is shown as having constant cross-sectional shape and area in
The outside shape of base section 302 may follow the contours of passage 304, so as to obtain a base section that is much like a sleeve. Accordingly, the base section 302 of the embodiment shown in
Attached to and extending from base section 302 may be a number of resilient projections 310. The embodiment depicted in
Though the exemplary embodiments of push rod retainer 300 depicted in
Push rod retainer 300 may be made in one piece, for example by injection moulding. In addition, push rod retainer 300 may be constructed from a plastic, such as engineering plastics including nylon.
Connection member 600 may include a shank 604 that allows it to be inserted into a bore provided through the first end 144 of the rocker arm 140. Shank 604 may be substantially cylindrical, though other shapes are conceivable as well. To enable a reliable connection, an upper portion of shank 604 may be provided with an outer thread that may engage an inner thread provided on a wall bounding the shank-receiving bore in end 144. A head 614 may be provided on a top end of the partly threaded shank 604, so as to allow the connection member 600 to be inserted and/or removed much like a screw or bolt. To this end, the head may define at least one of an angular circumferential edge for engagement by a spanner and a socket 616 for engagement by a socket head wrench, a screwdriver or the like. Alternatively, shank 604 may be press fitted into the bore, or the rocker arm 140 may be manufactured including the connection member 600 as one piece.
Connection member 600 may further include a pivot head 610 that is provided at a lower end of the shank 604. The pivot head 610 may be at least partly spheroidally shaped and configured to complement a cupped end 132 of the push rod 130.
Seen along a longitudinal dimension of connection member 600, the shank 604 may further include a constriction 608. The constriction 608 may have a diameter that approximately corresponds to the diameter of the first entrance 326 to the junction space 306, outlined by the resilient projections 310 of the push rod retainer 300, in particular by the end segments 316 thereof. The constriction may be provided in between a substantially square shoulder 606 and the pivot head 610. A tapering transition 618 between the (back of) of the pivot head 610 and the constriction 608 may be concave and smooth.
The relative dimensions of the portion of the shank 604 above the shoulder 606, which portion may have an outer diameter D2, and the pivot head 610, which may have an outer diameter D1, are preferably chosen such that D2>D1 (see
Rocker shaft 108, rocker arm 140 and connection member 600 may all be fitted with a lubricant channel for transporting a lubricant, such as oil, to the pivot head 610. The pivot head may in turn be fitted with a lubricant exit hole 612 to allow the lubricant to access a contact area between pivot head 610 and cupped end 132 of a push rod 130. The lubricant channels 110, 142, and 602 may be arranged in their respective host members 108, 140 and 600 such that at least an intermittent, pressurized flow of lubricant may be effected from rocker shaft 108 to pivot head 610 during operation of valve train 100.
Although this disclosure focuses on valve trains comprising a push rod-rocker arm linkage, push rod trains similar to the one shown in
Referring now to
In the background section of this text it is described how a temporarily malfunctioning hydraulic lash adjuster 106 may cause an uncontrolled motion of the push rod 130. Another example of a malfunction that could occur, and that might cause the first end 144 of the rocker arm 140 to remain in its elevated position—corresponding to an open valve—would be if the valve spring 118 was to seize or break, for example due to metal fatigue. Such valve spring failure may result in a situation wherein the upward force on the push rod 130 would be relieved, while the first end 144 of the rocker arm 140 would not be forced down. Consequently, the push rod 130 would become free of contact with the first end 144 of the rocker arm 140, resulting in the push rod 130 being free to topple sideways. When this would happen, the push rod 130 is no longer functional as it can no longer operate any valves. In addition, the rotating camshaft 102 may move the push rod 130 into contact with nearby components of an engine in which the valve train 100 is implemented, with sufficient force to seriously damage these components.
The disclosed push rod retainer 300 may prevent these effects of loss of contact between the push rod 130 and the rocker arm 140 by retaining the respective extremity 132 of the push rod 130 and a first end 144 of rocker arm 140 in proximity of each other. This can best be described with reference to
A pushrod retainer 300 may include a junction space 306 wherein the pivot head 610 of the connection member 600 of the rocker arm 140 and the cupped end 132 of the push rod 130 may be joinable. The push rod 130 and the connection member 600 may extend into the junction space 306 from opposite sides.
The cupped end 132 of the push rod 130 may extend into the junction space 306 through a second end 324 of a passage 304. Passage 304 may be dimensioned such that it may snugly receive the cupped end 132, at least at some points along its circumference. This would be to ensure that a central axis 320 of the push rod retainer 300 may remain substantially in alignment with a (longitudinal direction) of the push rod 130, despite the periodical angular movement of the push rod during valve train operation. The substantially constant and relatively small clearance between the circumference of the cupped end 132 of pushrod 130 and the wall bounding the passage 304 may reduce the chance that the cupped end 132 of the push rod 130 will escape from the confines of junction space 306 due to temporal variations in the amount of radial clearance during operation. In case the resilient projections 310 include segments 314, these segments 314 may provide for a stop against which a front face 134 of the cupped end 132 of the push rod 130 may abut.
Connection member 600 may be engaged by the resilient projections 310. The projections 310 may reach around the pivot head 610 to flexibly seize the connection member 600 at the constriction 608 that may be provided right behind it. This may position the pivot head 610 inside the junction space 306. Contact edges 318 of the resilient projections 310, which may be adapted to the circumferential shape of the connection member 600 at constriction 608, may provide for a fitting engagement that reliably locks the pivot head 610 inside the junction space 306. The engagement may preferably be such that push rod retainer 300 is somewhat moveable relative to the connection member 600, both pivotably and translationally in the longitudinal direction of the connection member 600. Such mobility relative to the connection member 600 enables the push rod retainer 300 to continuously adapt its orientation to the periodically changing mutual orientation of the pushrod 130 and the connection member 600. A gradual tapering 618 of the connection member 600 near the constriction 608, i.e. the smooth, concave contour flanking constriction 608, may assist in providing a flexible engagement. The gradual tapering 618 may also provide for a self-centering functionality of the push rod retainer 300 that may help to keep it in place. This may be because the extremum of constriction 608, relative to the gradually tapering flank 618, presents an energy minimum for the resilient projections 310. The resilient projections 310 may be guided naturally to this minimum as they may relieve internal tension that is inherent to any position on the flank 618.
To prevent the push rod retainer 300 from being pushed up too far along shank 604 of connection member 600, the constriction 608 may be bounded at an upper side thereof by a substantially square shoulder 606. The shoulder 606 does not facilitate the spreading apart of resilient projections 310 of the push rod retainer 300, and forms an effective barrier to any upward movement. Should, due to detrimental circumstances, the resilient projects 310 be forced apart anyway, then a relatively large diameter D2 of the upper part of the shank 604 may prevent the projections 310 from engaging the shank 604 at a position above the shoulder 606 that bounds the constriction 608.
Referring now in particular to
The overall dimensions of the push rod retainer 300 may be kept as small as possible, both to save space and manufacturing material. Though the proportions of the push rod retainer 300 may partly be dictated by the push rod 130 and the connection member 600 to be used, it is worth noting that for example the thickness of the wall bounding the passage 304 need not be greater than structurally necessary. A sleeve-like base section 302 requires relatively little material to manufacture, and may minimize the size of the cut-away 148 in rocker arm 140 provided to accommodate the push rod retainer 300 during its arcuate movements when in use.
The process and materials used to fabricate push rod retainer 300 may reduce its cost and improve its reliability. Specifically, a one-piece design may improve the inherent strength of the retainer 300. In addition, injection moulding, as a low cost manufacturing method, may enable it to be fabricated economically from a plastic such as for example nylon, which is a relatively inexpensive material that offers good wear resistance and low specific weight.
The process of mounting the push rod retainer 300 onto a rocker arm 140 has been described above with reference to
In brief, here is how a push rod retainer 300, mounted on the connection member 600 of a rocker arm 140, may be made to engage the cupped end 132 of a push rod 130. After a push rod retainer 300 has been mounted on a connection member 600, which connection member 600 has itself been inserted into a bore through the rocker arm 140 prior to mounting of the retainer 300, the connection member 600 may be partially backed out of the rocker arm 140. In this position, the push rod retainer 300 may not be down low enough for the push rod end 132 to be received in the junction space 306 when the rocker shaft 108 holding the rocker arm 140 is placed in the engine. To establish a secured connection, the push rod 130 may be aligned with the rocker arm 140, and the connection member 600 may be threaded further into the (bore in the) rocker arm 140 towards a working position, whereby the push rod retainer 300 may be moved down to capture the end 132 of the push rod 130 and to guide it to its seating position opposite the pivot head 610 of the connection member 600. Finally, the connection member may be torqued against the rocker arm 140 such that the head 614 at the top of the connection member 600 fixingly contacts a flat surface on the top of the rocker arm 140 to define the working position. The opposite procedure may, of course, be performed when disassembling an engine, for example to replace the push rod, the push rod retainer or the connection member.
It will be clear that a disclosed push rod retainer 300 can easily be detached from a rocker arm during maintenance. Removal of a push rod retainer 300 from a connection member 600 merely requires a modest separating force to be exerted that is large enough to spread the resilient projections 310 apart, such that the opening outlined by in particular segments 316 may become sufficiently wide to allow the pivot head 610 to pass through. Such a force may be exerted manually, but cannot be provided by either the rocker arm 140 or the push rod 130 during operation of the valve train 100.
The push rod retainer 300 according to this disclosure has been described above as having a number of resilient projections 310 that may engage a connection member 600 of a rocker arm 140. One skilled in the art will recognize, however, that a push rod and a rocker arm may be designed such, that it is the push rod that includes a circumferential construction and a pivot head on one end thereof, while it is the rocker arm's connection member that includes a cupped end. Clearly, the disclosed push rod retainer 300 may be used in this case as well. Its resilient projections 310 may engage the pushrod, and may thereby lock its pivot head inside the junction space 306, while the cupped end of the connection member may be inserted into the junction space through the second end 324 of the passage 304.
It will be apparent to those having ordinary skill in the art that various modifications and variations can be made to the push rod retainer and the rocker arm—in particular the connection member thereof—as disclosed herein. Other embodiments will be apparent to those having ordinary skill in the art from consideration of the specification. It is intended that the specification and examples are considered as exemplary only. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08169788.0 | Nov 2008 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/008257 | 11/19/2009 | WO | 00 | 5/19/2011 |
