Abstract:
A DHLA including a hydraulic lash adjustment mechanism disposed within a plunger slidably disposed within a pin housing that is slidably disposed within an axial bore in an adjuster body. A lash ring disposed in a groove near the outer end of the DHLA body includes a portion extending into the bore to limit travel of the pin housing and thereby set the internal mechanical lash in the DHLA. The lash ring has a thickness selected to provided a predetermined amount of mechanical lash in the assembled lifter, which thickness varies from assembly to assembly to compensate for manufacturing variation in the components. A biasing means such as a wave ring, a Belleville washer or a beveled retaining ring is also installed in the annular groove to urge the lash ring against the lower surface of the groove under all DHLA operating conditions.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to valve train members such as hydraulic lash adjusters (HLAs) for supporting roller finger followers in overhead-camshaft valvetrains in internal combustion engines; more particularly, to such HLAs having means for selectively engaging and disengaging activation of valves in valvetrains; and most particularly, to apparatus and method for setting internal mechanical lash in a deactivating hydraulic lash adjuster (DHLA). 
       BACKGROUND OF THE INVENTION 
       [0002]    It is well known that overall fuel efficiency in a multiple-cylinder internal combustion engine can be increased by selective deactivation of one or more of the engine valves, under certain engine load conditions. For example, for an overhead-cam engine, a known approach to providing selective deactivation is to equip a valvetrain member such as the hydraulic lash adjusters for the overhead-cam engine valvetrains with means whereby the roller finger followers (RFFs) may be rendered incapable of transferring the cyclic motion of engine cams into reciprocal motion of the associated valves. Typically, a DHLA includes, in addition to the conventional hydraulic lash adjuster, a concentric inner pin housing and outer HLA body which are mechanically responsive to the force of the RFF as exerted by the cam lobe, and which may be selectively latched and unlatched hydromechanically to each other, typically by the selective engagement of pressurized engine oil on locking pins. 
         [0003]    An important consideration in a DHLA is the amount of internal mechanical lash deliberately incorporated into the DHLA. In prior art DHLAs, a transverse bore in the pin housing contains the two opposed locking pins which are urged outwards of the pin housing by a pin-locking spring disposed in compression therebetween to engage a first annular groove including a locking surface (also referred to herein as “pin shelf”) in the inner wall of the HLA body whereby the HLA body and the pin housing are locked together to produce reciprocal motion of an RFF disposed on the DHLA. When valve deactivation is desired, the pins are withdrawn from the DHLA body by application of hydraulic fluid such as engine oil to the outer ends of the pins at pressure sufficient to overcome the force of the pin-locking spring. 
         [0004]    Prior art DHLAs also are assembled from a top end of the DHLA body (which is closed at its bottom end) by insertion of components through the open top end and securing the components with one or more retaining rings into a second annular groove formed in the inner wall of the DHLA body near the open end thereof. The rings used to secure the components also serve to set internal mechanical lash in the DHLA by the selection of rings of appropriate thickness during assembly of the DHLA. Thus, the rings act as a mechanical stop to limit the outward motion of the pin housing prior to engagement and disengagement of the locking pins. With the lost motion springs applying an upward force on the pin housing to force the top surface of the ring against the top of the annular groove, the lash rings permit the pin housing to travel to a position wherein the locking pins can clear the bottom surface, or pin shelf, of the locking groove in the DHLA body by a small amount, typically about 0.005 inches or less. Excess clearance or internal mechanical lash results in clatter and wear of the DHLA during engine operation. Variations in internal mechanical lash can also adversely affect the opening and/or closing timing of the associated valve. Thus, the axial position of the underside of the retaining rings with respect to the locking groove pin shelf is of critical importance. 
         [0005]    Typically, because of variation in manufacturing tolerances of the body, pin housing, and pins, the correct lash is obtained only by iterative trial and measurement using lash-adjusting rings of differing thicknesses. Setting the lash in this fashion is difficult and complicated. Moreover, since setting lash in this fashion relies on the machined integrity of the top surface of the annular groove, machining difficulties inherent in forming the top surface of the groove can result in unnecessary variances in mechanical lash settings. 
         [0006]    What is needed in the art is an improved DHLA wherein components are easily assembled and wherein mechanical lash is easily set in a single, simple procedure. 
         [0007]    It is a principal object of the present invention to reduce the cost and complexity of an improved DHLA, and to improve the ease and reliability of assembly thereof. 
       SUMMARY OF THE INVENTION 
       [0008]    Briefly described, a DHLA in accordance with the present invention comprises a conventional hydraulic lash adjustment mechanism within a plunger slidably disposed within a pin housing that is slidably disposed within an axial bore in an adjuster body. A transverse bore in the pin housing contains two opposed, selectively-retractable locking pins that engage a lower annular groove including a locking surface in the adjuster body whereby the lash adjuster body and the pin housing are locked together for mutual actuation by rotary motion of the cam lobe to produce reciprocal motion of an engine RFF pivotably disposed on a domed head of the plunger. 
         [0009]    A lash ring disposed in an annular groove near the outer end of the DHLA body includes a first portion extending into the bore in the DHLA body to engage the pin housing. The lash ring thus functions to limit the travel of the pin housing within the DHLA body and thereby sets the internal mechanical lash in the deactivation mechanism. The first portion of the lash ring has a thickness selected to provide a predetermined amount of mechanical lash in the assembled lifter to ensure facile engagement and disengagement of the locking pins in the lifter body. Preferably, the lash ring is provided as a single ring having a first portion of a desired thickness, which thickness varies from assembly to assembly to compensate for manufacturing variation in the components. A biasing means is also installed in the second annular groove to urge the lash ring against the lower face of the groove under all DHLA operating conditions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0011]      FIG. 1  is an elevational cross-sectional view of an upper portion of a prior art valve-deactivating hydraulic lash adjuster for use in an overhead-camshaft internal combustion engine, showing the pin housing retained by a lash clip disposed in an annular groove in the inner wall of the DHLA body; 
           [0012]      FIG. 2  is an elevational cross-sectional view of a portion of a DHLA body in accordance with the present invention; 
           [0013]      FIG. 3  is an elevational cross-sectional view showing the DHLA body portion shown in  FIG. 2  with the addition of an operational lash ring and a wave spring in an annular groove in accordance with the present invention; 
           [0014]      FIG. 4  is an elevational cross-sectional view of a complete DHLA in accordance with the present invention; 
           [0015]      FIG. 5  is a partially exploded isometric view of the complete DHLA shown in  FIG. 4 ; and 
           [0016]      FIG. 6   a  is a top view of an exemplar gage tool, in accordance with the invention, superimposed on a profile of the offset lash ring shown in  FIGS. 3-5 ; 
           [0017]      FIGS. 6   b  and  6   c  are enlarged cross-sections of two exemplar gage tools, in accordance with the invention, taken along line  6 B/ 6 C- 6 B/ 6 C of  FIG. 6   a ; and 
           [0018]      FIG. 7  is a partial view of an upper portion of a body and pin housing showing a lash ring and a biasing member of a second embodiment, in accordance with the invention. 
       
    
    
       [0019]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    Referring to  FIG. 1 , a prior art DHLA  10  has a generally cylindrical adjuster body  12 . A pin housing  14  is slidably disposed within a first axial bore  16  in adjuster body  12 . Pin housing  14  itself has a second axial bore  18  for slidably receiving a plunger  20  having a domed end  22  for receiving a socket end (not shown) of a roller finger follower (not shown) in an overhead-cam engine valve train (not shown). Pin housing  14  has a transverse bore  24  slidably receivable of two opposed locking pins  26  separated by a pin-locking spring  28  disposed in compression therebetween. First axial bore  16  in is adjuster body  12  is provided with an annular groove  30  for receiving the outer ends of locking pins  26 , thrust outwards by spring  28  when pins  26  are axially aligned with groove  30 . In such configuration, DHLA  10  is in valve-activation mode. (As shown in  FIG. 1 , DHLA  10  is in valve-deactivation mode.) A loss-of-motion (LM) return spring  34  is disposed within a chamber  35  below pin housing for absorbing lost motion of pin housing  14  within bore  16  when DHLA  10  is in deactivation mode. 
         [0021]    Groove  30  further defines a reservoir for providing high pressure oil against the outer ends  36  of locking pins  26  to overcome spring  28  and retract the locking pins into bore  24 , thereby unlocking the pin housing from the adjuster body to deactivate the DHLA. In use, groove  30  is in communication via at least one port  38  with an oil gallery (not shown) in an engine  40 , which in turn is supplied with high pressure oil by an engine control module (not shown) under predetermined engine parameters in which deactivation of valves is desired. 
         [0022]    Plunger  20  includes a hydraulic element assembly (HEA)  42  lodged at an inner end thereof. The arrangement of components and operation of hydraulic lash adjuster elements such as HEA  42  has been well known in the prior art for many years. HEA  42  comprises a spring loaded check ball  44  lodged against a seat  46  formed in plunger  20  separating a low-pressure oil reservoir  48  from a high-pressure chamber  50  formed between HEA  42  and pin housing  14 . Oil is supplied to annular chamber  51  from an engine oil gallery (not shown) via port  54  in adjuster body  12 . Chamber  51  is also in communication with reservoir  48  via port  56  and annular groove  58  in pin housing  14  and port  62  in plunger  20 . Oil may be supplied from reservoir  48  to an associated roller finger follower (not shown) via port  52  in the end  22  of plunger  20 . 
         [0023]    In operation, prior art DHLA  10  is disposed in a bore in engine  40  such that housing  12  remains stationary. When the associated cam and RFF (not shown) exert force on plunger end  22 , in lost motion (valve-deactivation) mode, plunger  20  and pin housing  14  are forced into adjuster body  12  in a lost-motion stroke, compressing spring  34 . 
         [0024]    Of particular interest to the present invention is the means by which the outward stroke of pin housing  14  is limited in prior art body  12 . An annular groove  64  formed in bore  16  near the outer end thereof receives a retaining clip  66  that extends into bore  66  to engage shoulder  68  of pin housing  14 . The axial thickness  70  of clip  16  is selected from a family of such clips having differing thicknesses to set the amount of axial mechanical lash  72  in DHLA  10 . As described above, the amount of lash  72  is an important manufacturing parameter which must be calibrated for each DHLA assembly because of manufacturing variability in the length  74  from shoulder  68  to the lower edge  76  of pins  26 , and length  78  from the upper face  80  of groove  64  to the lower face  82  of groove  30 . (Lower face  82  is also known in the art as a “pin shelf” for lock pins  26 .) The trial-and-error method of assembly, measurement, disassembly, reassembly, and re-measurement is time-consuming, costly, and difficult when using prior art groove  64  and clip  66 . 
         [0025]    Referring to  FIGS. 2 through 5 , an improved DHLA  110  in accordance with the present invention is formed substantially like prior art having similar components except as follows. 
         [0026]    As described above, the amount of mechanical lash  172  (also referred herein as desired mechanical lash) is an important manufacturing parameter which must be calibrated for each DHLA assembly because of manufacturing variability in the length  174  from shoulder  168  of pin housing  114  to the lower edge  176  of locking pins  126 . 
         [0027]    A lash ring  166 , of a selectable size, is retained in groove  164  in body  112  by a resilient biasing member  165  such as a Belleville washer, or preferably a wave ring. Lash ring  166  includes a first portion such a collar  169  having a length  171 , and first and second surfaces  175 ,  177 . 
         [0028]    After pin housing  114  is installed in body  112  as in the prior art, a method for setting mechanical lash in an individual DHLA  110  consists in the following steps. 
         [0029]    First, a gage tool  173 ,  173 ′ ( FIG. 6   a ), designed to simulate at least a portion of lash ring  166  (shown as dashed lines in  FIG. 6   a ), and having exemplary cross sections as shown in  FIGS. 6   b  and  6   c , is positioned in first annular groove  164  with its first surface  175 ′ positioned against the bottom surface  167  of annular groove  164  and its second surface  177 ′ in abutting contact with shoulder  168  of pin housing  114 , thereby establishing a known, fixed axial relationship between bottom face  167  of groove  164  and shoulder  168  of pin housing  114 . (When using gage tool  173  in which surfaces  175 ′ and  177 ′ are collinear, bottom face  167  and shoulder  168  will be collinear as well). Pin housing  114  is then depressed into body  112  until locking pins  126  engage lower face  182  of groove  130  with a specified force. A longitudinal distance D in which pin housing  114  travels from its starting position of being in contact with second surface  177 ′ to its ending position of wherein locking pins  126  engage lower face  182  is observed. Then, desired lash  172  is subtracted from observed distance D. The numerical remainder (D−172) is used to determine length  171  of first portion  169  of lash ring  166  that will result in the desired lash  172 . After gage tool  173 ,  173 ′ is removed from groove  164 , a lash ring  166  having a selected length  171  of first portion  169  as determined above is installed in groove  164  with second surface  177  facing shoulder  168  of pin housing  114 . Finally, wave ring  165  is installed on top of lash ring  166  to retain ring  166  in annular groove  164  and to preload lash ring  166  against bottom surface  167  of annular groove  164 . 
         [0030]    Wave ring  165  is selected to preload lash ring  166  and to apply a clamping force on lash ring  166  that is greater than the installed load of the lost motion spring(s)  134  to keep lash ring  166  seated against bottom surface  167  of groove  164  during use of DHLA  110 . Suitable wave rings are commercially available from, for example, Smalley Steel Ring Co, Inc., Lake Zurich, Ill., USA. Alternatively, a Belleville washer may be used, such as is available from Mubea Inc., Florence, Ky., USA. 
         [0031]    The improved arrangement in accordance with the present invention changes the precision feature of ring groove  164  to bottom surface  167  rather than the top face  180  as in the prior art ( FIG. 1 ). This represents an important manufacturing improvement; top face  180  is difficult to grind as it requires a grind relief in the upper corner of the groove. Also, top face  180  cannot be machined simultaneously with lower face  182  so tolerances cannot be controlled as precisely. In improved DHLA  110 , bottom surface  167  is the key surface and can be machined with tooling similar to that used for lower face/pin shelf  182 . Also, bottom surface  167  may be machined simultaneously with pin shelf  182  to precisely establish length  178  ( FIG. 2 ) thereby reducing the variation that the lash ring thickness must accommodate. 
         [0032]    Note also that preferably, the outer diameter  181  of lash ring  166  is less than the inner diameter  183  of the opening of body  112  ( FIG. 2 ). Thus, ring  166  need not be radially compressed to fit into second groove  164  thereby avoiding the risk of distorting the flatness of ring  166  and introducing error in the resulting mechanical lash  172 . Also, preferably, outside diameter  185  of second surface  177  of lash ring  166  pilots on the inside diameter  187  of body  112 . 
         [0033]    In an alternate embodiment, wave ring  165  may be substituted with internal split beveled retaining ring  265  as shown in  FIG. 7 , commercially available from Rotor Clip Company, Inc. of Somerset, N.J. 08873. In this embodiment, surface  263  of split ring  265  is formed with a 15° bevel for mating with a 15° bevel formed in the upper face  261  of groove  264 . After lash ring  166  having a selected length  171  as determined above is installed in groove  264 , split ring  265  is radially compressed so that its outer diameter fits inside inner diameter  283  of the opening of body  212 . Then, split ring  265  is allowed to radially expand into groove  264  so that surface  263  of split ring  265  wedges against upper face  261  of groove  264  thereby firmly pre-loading and seating first surface  175  of lash ring  166  against bottom surface  167  of groove  264 . 
         [0034]    While the invention described herein relates to setting of the mechanical lash of a DHLA, it is understood that the invention may be used in any deactivating valvetrain member such as, for example, a deactivating valve lifter. 
         [0035]    While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.