Abstract:
A C-clip retainer is provided in a groove of a piston, such as for an engine hydraulic valve lash adjuster, to allow installation and removably retain the piston in a cylinder of an associated assembly. The groove has a novel shape including an inner surface that is angled relative to a longitudinal axis of the piston to provide a larger groove diameter at a first axial end surface and a smaller diameter at an opposite second axial end surface of the groove. Upon installation, the clip is urged into the smaller diameter, allowing easier installation, but upon removal the clip is expanded by forcing it to the larger diameter, thereby increasing the retention force on the piston. The first axial end surface may also be formed with a back angle that reduces forces of the associated cylinder edge that tend to compress the retainer into the groove, thus further increasing the piston retention force.

Description:
TECHNICAL FIELD 
     This invention relates to piston retention, especially for engine valve train lash adjusters. 
     BACKGROUND OF THE INVENTION 
     It is known in the art to retain the piston or body of an engine valve train lash adjuster by means of a C-clip positioned in a groove of the piston and engaging an abutment in the periphery of the cylinder in which the lash adjuster is installed. For example, a hydraulic element assembly or lash adjuster may be retained in a cylinder baffle of a direct acting cam follower; or a hydraulic lash adjuster by having a swivel foot for engaging a valve or other component may be retained in a cylinder recess of an associated rocker arm. 
     Typically in such arrangements, the C-clip is formed of resilient spring wire biased to spring outward against a bore or abutment in which the piston is reciprocably retained. The C-clip is retained in a groove on the exterior of the piston The groove has a depth such that, when added to the diametral clearance be een the piston and cylinder, the total exceeds the diameter of the spring wire of the C-clip. This is necessary to allow installation of the piston into a closed end cylinder without scratching or otherwise damaging the associated cylinder wall. The retaining groove typically has a cylindrical er surface and opposed upper and lower end surfaces, which are generally radial but may be sloped slightly outward for tool clearance. 
     To allow installation of the piston or body in a cylinder, the entry opening of the cylind r is generally angled to provide a lead-in cone angle. The cone angle com resses the C-clip into the piston groove and allows the piston with clip installed to be slid into the closed end cylinder and past a retaining abutment into operating position. The retaining abutment may be, for example, the upper edge of a baffle tube of a direct acting cam follower and its configuration is important in determining the ability of the C-clip to retain the hydraulic element assembly (HEA) in the cam follower cylinder. 
     For example, if the upper edge of the baffle tube is formed with a surface normal to the axis of the cylinder, that is horizontal when the cylinder axis is vertical, the retention of the piston in the cylinder by the expanded C-clip will be at a maximum since the horizontal or normal surface will not provide a substantial radial force for compressing the C-clip into the groove. Thus, if removal of the HEA is desired, it may be necessary to shear off the retaining parts of the C-clip in order to disassemble the assembly. 
     Since disassembly is sometimes required for inspection or replacement, the inner edge or abutment of the cylinder or baffle tube is generally sloped or angled downward and inward to provide a conical surface that engages the C-clip when retention or removal is desired. This angle may be varied as desired in order to maintain a sufficient force to retain the piston in place under anticipated operating conditions, while having a sufficient slope to allow removal of the lash adjuster or HEA from the cylinder when desired, without damaging the cylinder or HEA surface. The selection of the installation and retention angles on the cylinder edges is determined in part by the actual configuration of the C-clip and the diameter of wire from which it is made, as well as the depth of the retaining groove in which it is installed. These factors then, as well as the resilient force applied in expansion of the C-clip, all have a bearing on the selection of angles for accomplishing the various desired purposes of retention and ability to remove the HEA or lash adjuster when desired. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved lash adjuster assembly in a retaining cylinder based upon a piston having an improved cross-sectional configuration of the retaining groove in which the C-clip retainer is installed. 
     In a first feature of the invention, the retaining groove is made axially longer than is conventional so that the retainer clip may be slid between spaced upper and lower positions along the groove. The inner diameter of the groove is angled with the desired slope, referred to as the clip diameter assembly angle, which may be ten degrees more or less within a suitable operating range as conditions may require. For example, angles of five to fifteen or twenty degrees may be found useful in particular operating environments. The clip diameter assembly angle allows the clip to be compressed further during assembly of the piston within its cylinder than is permitted in the retention or removal condition of the assembly. 
     During assembly of the piston, the clip is pushed axially downward in the groove to the smaller diameter or deeper end of the groove so that the clip may be compressed further into the groove and provide a reduced rubbing force on the associated cylinder, thereby reducing the possibility of damage to the parts during assembly. After the piston is installed, attempted removal of the piston, either by operating forces or by attempted disassembly with tools, the retaining clip is forced upwardly in the groove to the larger diameter or shallower end where the retaining clip is urged outwardly to increase its resistance to compression into the groove. This increases the retaining force of the clip so that the assembly does not come apart too easily during operations. 
     An additional feature of the invention is the provision at the upper or retaining end of the groove of a clip retention back angle having an outward or upward slope of a suitable amount such as, for example, twenty degrees. The back angle cooperates with the bore retention angle formed at the upper edge of the associated cylinder so that the two angles together control the compression force acting on the C-clip to retain or allow removal of the piston from the cylinder. 
     As the clip retention back angle is increased to approach the bore retention angle, the radial compression force exerted by the bore retention angle during attempted disassembly of the piston from the cylinder, is reduced toward zero. Thus, reducing the clip retention back angle provides more positive retention of the piston in the cylinder but also makes it harder to remove the piston without damaging the cylinder or clip. Accordingly, selection of the clip retention back angle and bore retention angle are important in accomplishing the desired amount of force retaining the piston within the cylinder at this connection. The spring force of the clip and the diameter of the clip also need to be taken into account in determining the proper angles for the assembly. 
     In some cases, the bore retention angle is fixed by prior manufacturing practices. In such cases, the clip retention back angle may be adjusted as desired to provide the proper degree of retaining force while allowing removal of the piston for inspection or replacement. 
     These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is an axial cross-sectional view through a direct acting hydraulic valve lifter forming an assembly according to the invention; 
     FIG. 2 is a plan view of a C-clip retainer shown schematically as confined in a piston retaining groove within a cylinder; 
     FIG. 3 is a cross-sectional view of a rocker arm and lash adjuster forming an alternative assembly according to the invention; 
     FIG. 4 is a schematic view showing associated features of an assembly according to the invention; 
     FIG. 5 is a schematic view illustrating a first embodiment of an assembly; 
     FIG. 6 is a schematic view illustrating a second embodiment of an assembly; 
     FIG. 7 is a schematic view illustrating a third embodiment of an assembly; and 
     FIG. 8 is a graph illustrating variations in compression and shear resistance retention loads over a range of clip groove diameters. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1 of the drawings, there is shown a direct acting hydraulic valve lifter (DAHVL), generally indicated by numeral  10 , and forming an assembly in accordance with the invention. Assembly  10  includes a housing in the form of a cam follower body  12  having a closed end  14  connected with an external cylindrical external wall  16 . A baffle  18  portion of housing  12  extends inwardly from the interior of wall  16  and upwardly to form an internal cylinder  20  in which a hydraulic element assembly (HEA)  22  is received. 
     HEA  22  conventionally includes an open-ended piston  24  having an axis  25 . Piston  24  is received within the cylinder  20  and internally receives a cylindrical plunger  26 . The plunger includes a lower wall with a check valve  28 , which together define a hydraulic chamber at the closed end of the piston. A spring  30  biases the plunger upward against the closed end of the follower body  12  when the DAHVL  10  is installed in an engine with the closed end of the piston  24  engaging an associated engine valve, not shown. In operation, oil pressure in the chamber leaks down slightly when the associated engine valve is opened and is replenished through the check valve when the engine valve is closed. 
     In order to retain the HEA  22  within the baffle cylinder  20 , a spring wire C-clip or retainer clip  32  is mounted within an associated groove  34  in the exterior of the piston  24  shown in assembly  10  with the clip  32  above an upper end  36  of the cylinder  20 . Conventionally, the assembly is completed by installing the retainer clip  32  in the clip groove  34  and inserting the assembled HEA  22  into the baffle cylinder  20  from the open end of the cam follower body  12 . During this installation, the retainer clip  32  is compressed into the groove  34  and it expands resiliently after entry into the chamber above the upper end  36  of the baffle cylinder to retain the plunger within the cylinder prior to installation in an engine, and thereafter if required by abnormal engine operation. 
     Referring now to FIG. 2, retainer C-clip  32  is shown as compressed within a piston groove indicated by the phantom line  34  and retained therein by the baffle cylinder  20  indicated by phantom line  20 . The C-clip  32  may be formed of round or ovalized spring wire or other suitable material having a diametral gap that allows installation of the C-clip on the piston. The C-clip  32  is preferably formed with three outwardly projecting radii or bumps  38 ,  40 ,  42  at spaced locations about its major diameter. When the retainer clip  32  is expanded as the ring is pushed through the cylinder  20  into the upper chamber of a DAHVL, the bumps  38 ,  40 ,  42  extend outward beyond the internal diameter of the cylinder  20  and provide a retention force which maintains the HEA  22  within the cam follower body  12  during handling and normal operating conditions. 
     Referring now to FIG. 3, there is shown an alternative assembly  44  of a rocker arm  46  having a closed end cylinder  48  in which a hydraulic lash adjuster or hydraulic element assembly (HEA)  50  is received. HEA  50  is generally similar in internal construction and operation to HEA  22  previously described; however, its piston  52 , formed on axis  25 , includes a pivotable foot  54  for directly engaging an engine valve. The HEA  50  is again retained by a C-clip retainer  56  like that of retainer clip  32 . Clip  56  is received in an external groove  58  around the upper end of the piston  52  and the clip is engagable with a conical surface  60  comprising a first angled abutment defining a bore retention angle at a stepped portion of the internal cylinder  48 . A conical surface  62  forming an entry angle is provided at the lower open edge of the cylinder  48  forming a second angled abutment that allows easy installation of the HEA  50  into the cylinder  48  of the rocker arm. 
     FIG. 4 represents schematically the retention elements of an assembly  64  according to the invention. The assembly  64  comprises a DAHVL including a baffle  66  defining a cylinder  68  having at its lower end a conical surface  70  forming an abutment with a conical entry angle A and at its upper end a conical surface  72  forming an abutment with a bore retention angle B. Within the cylinder  68  is a piston  74  of an HEA or other lash adjuster device, the piston including a cylindrical exterior  76  centered on an axis  25  (see FIG. 1) and containing a circular retainer groove  78 . Within the groove and expanded into position for engagement with the bore retention angle  72  is a C-clip retainer  80  of the type illustrated in FIG.  2 . 
     In accordance with the invention, the retainer groove  78  includes an inner surface  82  formed with an angle referred to as the clip diameter assembly angle C. Surface  82  extends between the inner edges of a first end surface  84  forming the upper edge of the groove  78 , as shown, and a second end surface  86  forming the lower edge of the groove, as shown. The upper or first end surface  84  forms a back angle D sloping axially away from the groove  78  relative to a plane normal to the axis  25 , (FIG. 1) and the exterior  76  of the piston  74  so as to widen the groove slightly on its open side. The second end surface  86  may be sloped slightly, as shown, or may be essentially horizontal as desired. The angle D of surface  84  is referred to as the clip retention back angle. 
     The function of the novel groove configuration and other associated surfaces in the installation and retention or removal of an HEA or lash adjuster in a housing defining a cylinder will now be described. To install the piston  74  in the baffle  66 , the retainer  80  is first slid into place on the groove  78  of the piston. The piston  74  is then inserted from the bottom of the baffle  66 , as shown in FIG. 4, so that, as the piston is raised, the retainer clip  80  first engages the entry angle A formed by surface  70  on the bottom edge of the baffle. The entry angle cams the C-clip  80  inwardly, compressing it into the groove  78 , while at the same time, the clip is forced downward to engagement with the lower or second end surface  86  of groove  78 . At this point, the diameter of the inner surface  82  is at a minimum due to the slope of the groove assembly angle C. Thus, the C-clip is easily compressed into the groove and allows upward motion of the piston with a minimum of C-clip force against the cylinder  68 . This reduces the possibility of scratching or otherwise damaging the cylinder surface. 
     When the piston is fully installed, as shown in FIG. 4, attempted removal of the piston from the baffle requires downward motion of the piston relative to the cylinder  68 . This causes the bore retention angle D formed by surface  84  to engage the retainer clip  80 , forcing it upward in the groove  78  toward engagement with the upper or first end surface  84 . By this motion, the retainer clip reaches the larger diameter end of the groove which creates greater resistance to compression of the C-clip  80  into the groove. Thus, the force of the clip is increased when it is in this position so that it provides a greater force tending to retain the piston within the baffle than was exerted by the clip during installation of the piston within the baffle. The increased retaining force provides increased resistance to accidental dislodgement of the piston from the baffle during handling prior to installation, as well as reducing the likelihood of separation of the components during abnormal operation of the engine after the assembly is installed therein. 
     FIGS. 5-7 schematically illustrate various combinations of angles, which may reasonably be applied in various embodiments of lash adjuster installations having the novel groove  78  feature of the invention. FIG. 5 approximates the embodiment of FIG.  4  and illustrates a bore retention angle B of 30 degrees, a clip retention back angle D of about 20 degrees, and a clip diameter assembly angle C of about 10 degrees, the related clip retention and assembly angles being variable within reasonable limits. 
     In this embodiment, the small difference of 10 degrees between the bore retention angle B and clip retention back angle D provides a minimum of radial force for urging the C-clip  80  outward into the piston groove  78  when removal of the piston from the baffle is desired. With such a small angular differential, removal of the piston might require shearing off of part of the C-clip material in order to get the piston out of the baffle. To avoid this, it might be preferable to increase the bore retention angle B to 45 degrees or so, in order to increase the outward force on the C-clip so that easier removal of the piston from the baffle may be obtained. 
     FIG. 6 represents the suggested solution for the embodiment of FIG. 5 to provide easier withdrawal or removal of the piston from the baffle while still providing adequate retention for most purposes. In FIG. 6, the bore retention angle B is 45 degrees, while the clip retention back angle D remains at 20 degrees, more or less, and the clip diameter assembly angle C remains 10 degrees, more or less. This combination provides increased expanding force against the C-clip when removal of the piston is desired, and thus permits removal to be accomplished more easily and generally without damage to the bore of the cylinder. 
     Referring now to FIG. 7, an embodiment similar to that shown in FIG. 3 is illustrated, wherein the bore retention angle B is increased to 60 degrees, while the clip retention back angle D and clip diameter assembly angle C remain as before, 20 and 10 degrees approximately. With this combination, as illustrated, the expanding force against the C-clip  80  is significantly increased so that removal of the piston  52  from the cylinder  48  becomes easier, possibly to the extent that the piston will come loose from the assembly when such removal is not desired. To prevent this possibility, the bore retention angle B may be reduced to 45 degrees as previously shown or, alternatively, the clip retention back angle D could be increased to reduce the difference between the bore retention and clip retention angles. 
     Either alternative would reduce the outward force effectively acting on the C-clip  80  tending toward its expansion upon attempted removal of the piston  52  from the cylinder  48 . Thus, if the bore retention angle B is fixed at some predetermined angle that is not advantageous with the piston angles usually provided, it is possible to vary the clip retention angle D or, in an alternative situation, the clip diameter assembly angle C to accomplish the desired forces on the assembly. Thus, the piston may be easily installed in the cylinder while the resistance to removal of the piston from the cylinder is increased to a level that is sufficient to maintain the parts in assembly without preventing their disassembly when and if desired. 
     FIG. 8 graphically illustrates the effects on piston retention force of varying clip groove diameter at two different bore retention angles B while wire diameter and bore diameter of the cylinder are held constant. As the groove diameter increases, the clip is increasingly expanded, increasing engagement with the bore retention angle and increasing retention load, as shown by lines  88 . When the clip, as expanded by the groove, exceeds the associated cylinder bore diameter, the clip wire must be sheared to remove the piston from the cylinder leading to a more rapid increase in retention force, as indicated by lines  90 . Further, the 45 degree bore retention angle B provides a lower retention force than the 30 degree bore retention angle B because the 45 degree angle applies a greater cam pressure force to the clip, urging it into the groove and reducing the retention force. 
     While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.