Abstract:
A switchable valve train device including a pin housing slidably disposed in a body and having a transverse bore. A stepped plug in the transverse bore extends beyond the pin housing to engage a slot in the body to prevent rotation of the pin housing. The upper end of the slot limits travel of the pin housing. The plug is a seat for a compression spring. A locking pin is disposed in the transverse bore against the spring to selectively engage a locking port in the body, the locking pin and the locking port have mating flats to distribute the load. Mechanical lash is set by use of a gage tool during assembly, allowing selection of a locking pin of appropriate thickness. The device may be, for example, a switchable hydraulic lash adjuster or a switchable valve lifter.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to switchable valve train members for internal combustion engines for supporting a roller finger follower or a pushrod in a combustion valve train; more particularly, to a switchable hydraulic lash adjuster or a switchable valve lifter that is switchable between a first mode wherein valve actuation is permitted and a second mode wherein valve actuation is prevented; and most particularly, to a sub-assembly for a switchable member wherein a latchable pin housing is selectively latched to a sub-assembly body by a single transverse locking pin, and wherein the pin housing is prevented from rotation within the adjuster body, and wherein axial mechanical lash in the sub-assembly is easily set during assembly thereof without requiring repeated assembly and disassembly of the sub-assembly. 
       BACKGROUND OF THE INVENTION 
       [0002]    Switchable valve train devices are well known in the engine arts for selectively permitting or preventing the opening of an associated engine combustion valve. See, for example, U.S. Pat. No. 7,263,956 B1 (“the &#39;956 patent”) wherein a pin housing of a switchable valve lifter (SVL) is slidably disposed within an outer body bore. Opposing dual, flatted locking pins having a compression spring therebetween are disposed in a transverse bore in the pin housing for extending radially to engage an annular locking shelf in the body bore. Pressurized oil is applied selectively to the outer ends of the pins to retract the pins into the pin housing, allowing the pin housing to slide in the body bore in lost motion. The dual locking pin concept, as disclosed in the &#39;956 patent, offers several benefits over the prior art single locking pin concept. For example, the valve train load that is transferred through the switchable device during valve lift is supported by two locking pins instead of one and the overall diameter of the device may be reduced since load bearing lengths may be shared by both sides of the body and pin housing. This dual flatted locking pin construction disclosed in the &#39;956 patent has been adapted to other valve train members such as switchable hydraulic lash adjusters (SHLA). 
         [0003]    An additional known problem in prior art SHLAs having dual locking pins is that side-loading of the pin housing with respect to the body is significantly greater than in prior art SVLs wherein forces are nearly parallel to the axis of the SVL. This is because a hydraulic lash adjuster supports and is a pivot point for a roller finger follower (RFF), and force vectors imposed on the RFF by an associated cam lobe during opening and closing of such a valve are not entirely parallel to the axis of the SHLA. Because the pin housing of a prior art SHLA is not constrained from rotation within the SHLA body, there are orientations of the pin housing with respect to the sideloading wherein the entire axial load is carried by a single locking pin during certain periods during the valve lift event. 
         [0004]    A separate issue in prior art SHLAs is the need for a precise setting of the internal axial lash (mechanical lash) between the pin housing and adjuster body with the pin in locked position. It is important that the locking pin be given sufficient clearance to engage reliably and securely; however, if too much clearance is permitted, the SHLA will be noisy and will experience excessive wear. Also, too much clearance will adversely effect the opening timing of the associated valve since, in the valve opening direction, the pin housing must first traverse the mechanical lash before the switchable valve train can even begin to open the associated valve. Because the stack-up of manufacturing tolerances of the individual lash adjuster components cannot provide a consistent, as-built mechanical lash, a means for adjusting the mechanical lash of each SHLA must be provided. Typically, in the prior art, each SHLA is at least partially assembled and the gross axial lash is measured. The required clearance is then subtracted from the gross axial lash and a graded shim of the resulting thickness is inserted into the SHLA, typically after first disassembling the partially-assembled device. 
         [0005]    What is needed in the art is an improved SHLA wherein the axial load is reliably carried by a single locking pin and wherein the gross mechanical lash may be easily measured and a desired mechanical lash may be set without disassembly of the device. 
         [0006]    It is a principal object of the present invention to provide a reliable single-pin SHLA or SVL. 
         [0007]    It is a further object of the invention to reduce the manufacturing complexity and cost of a SHLA or SVL. 
       SUMMARY OF THE INVENTION 
       [0008]    Briefly described, a sub-assembly for a switchable valve train device, which may be either a SHLA or a SVL, includes a pin housing slidably disposed in a body and having a transverse bore. A stepped plug has a major diameter portion that is full-fitting in the transverse bore and a minor diameter portion extending beyond the surface of the pin housing to engage a longitudinal slot in a wall of the body to prevent rotation of the pin housing within the body. The upper end of the slot limits axial travel of the pin housing and thus participates in setting mechanical lash in the device. 
         [0009]    The plug also acts as a seat for a compression spring. A locking pin is disposed in the transverse bore against the spring for extension beyond the pin housing to engage a locking port formed in a wall of the body opposite the longitudinal slot. Because the pin housing is prevented from rotation within the body, the orientation of the locking pin to the locking port is maintained. 
         [0010]    The locking pin and the locking port are provided with mating flats to distribute the locked load. The locking pin is prevented from rotation within the cross-bore by action of an anti-rotation cross pin to maintain the rotational orientation of the locking pin flat to the locking port flat. 
         [0011]    Mechanical lash is readily set by use of a gage tool during assembly via selection of a locking pin having an appropriate thickness. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0013]      FIG. 1  is an elevational cross-sectional view of a first prior art single locking pin SVL substantially as disclosed in U.S. Pat. No. 6,196,175 B1; 
           [0014]      FIG. 2  is an elevational cross-sectional view of a second prior art single locking pin SVL substantially as shown in U.S. Pat. No. 6,606,972 B2; 
           [0015]      FIG. 3  is an elevational cross-sectional view of a sub-assembly of a single locking pin SHLA in accordance with the present invention; 
           [0016]      FIG. 4  is an elevational view of a first side of the SHLA sub-assembly shown in  FIG. 3 ; 
           [0017]      FIG. 5  is an elevational view of a second and opposite side of the SHLA sub-assembly shown in  FIGS. 3 and 4 ; and 
           [0018]      FIGS. 6 through 12  are elevational cross-sectional views showing progressive steps in the assembling and lash-setting of the sub-assembly shown in  FIG. 3 . 
       
    
    
       [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]    As noted above, the construction and functionality of SVLs and SHLAs are very similar. Although the following presentation is directed to an improved single-pin SHLA, the disclosed principles of construction are equally applicable to an improved single-pin SVL. Prior art is found in two single-pin SVL disclosures. 
         [0021]    Referring to  FIG. 1 , a first prior art single-pin SVL  10  is shown substantially as disclosed in U.S. Pat. No. 6,196,175 B1 (“the &#39;175 patent”). SVL  10  is shown disposed in a bore  11  in engine  12  for selectively converting the eccentric motion of cam lobe  14  into linear motion of pushrod  16 . SVL  10  comprises a body  18  having a stepped bore  20  for receiving an annular spacer  22  and a stepped pin housing  24  slidably disposed in bore  20 . Pin housing  24  contains a conventional hydraulic lash-adjusting apparatus  26  for eliminating lash in a valve train. A lost motion spring  25  is disposed in an annular space  27  between body  18  and pin housing  24 . A transverse stepped bore  28  in pin housing  24  receives a press-fit plug  30  extending from pin housing  24  through a first longitudinal slot  32  in body  18  and into a second longitudinal slot  34  formed in bore  11  for preventing rotation of pin housing  24  in body  18  and rotation of body  18  in bore  11 . Plug  30  is axially slidable in slots  32  and  34 . The upper end  35  of slot  32  defines a stop for the axial travel of plug  30  and therefore the axial travel of pin housing  24  within body  18 . A single locking pin  36  having a circular cross-section is also disposed in stepped bore  28  for selective locking and unlocking with a circular locking port  38  formed through the wall of body  18 . When pressurized oil (not shown) is supplied to end  40  of pin  36 , return spring  42 , disposed in compression between plug  30  and pin  36 , is overcome and pin  36  is forced from locking port  38 . During engine operation, when the SVL is in unlocked mode, pin housing  24  is held motionless by pushrod  16  and body  18  is free to oscillate within bore  11  in lost motion of cam lobe  14 . When oil pressure is removed from pin end  40 , spring  42  returns pin  36  into locking engagement with locking port  38 . In locked mode, SVL  10  functions as a conventional valve lifter. 
         [0022]    The disclosed SVL  10  has at least the shortcomings that would exist if the locking arrangement were used in a single-pin SHLA. 
         [0023]    First, operating experience has shown that a round pin disposed in a round port suffers from undesirably rapid wear to the pin and/or port because of the relatively short bearing length of the mating bore and because the pin and port have essentially line contact as a result of a deliberate difference in diameters that allows the pin to enter the port reliably. The result is that, as the wear occurs, the internal mechanical lash between the pin housing and the body increases undesirably. The increased lash results in objectionably noisier operation of the engine, but more importantly, results in a later valve opening point and a progressively lower valve lift. 
         [0024]    Second, there is no apparent method for conveniently setting internal mechanical lash during assembly of SVL  10  as shown in the &#39;175 patent. 
         [0025]    Third, the axial positions of upper end  35  of slot  32  and locking port  38  define the amount of internal mechanical lash and are subject to variation in manufacturing tolerances of pin housing  24 , plug  30 , and body  18 , making the amount of lash in any given unit, and hence the precise point of opening and lift of an associated valve, unreliable. 
         [0026]    Referring to  FIG. 2 , a second prior art single-pin SVL  10 ′ is shown substantially as disclosed in U.S. Pat. No. 6,606,972 B2 (“the &#39;972 patent”). It is seen that the basic construction is very similar to that of first prior art SVL  10  except that return spring  25 ′ is disposed below pin housing  24 ′ rather than surrounding it. 
         [0027]    While a means has been provided in SVL  10 ′ for setting mechanical lash, SVL  10 ′ has the other shortcomings as SVL  10  recited above, especially since it utilizes a cylindrical locking pin  36 ′ having a circular cross-section that locks into a round locking port  38 ′ formed in bore  20 ′ of body  18 ′. As noted above, this shortcomings would also exist if the locking arrangement were used in a single-pin SHLA. 
         [0028]    As an improvement over a single locking pin design, switchable valve train members in the prior art employ dual opposing locking pins, as disclosed in the &#39;956 patent, which arrangement provides greater locking stability and reliability than a single-pin arrangement. Experience has shown, however, that a dual-pin arrangement can have a drawback in certain applications. As noted above, because the pin housing is free to rotate within the body of a prior art SHLA having dual locking pins for engagement with an annular locking shelf, there are orientations of the pin housing with respect to an associated RFF wherein the entire axial load is carried by only one of the two locking pins during periods of the valve lift event, the force balance within the SHLA prevents contact of the opposite pin with the locking shelf due to the component of force applied to the pin housing that is transverse to the axis of the body. Further, as the diameter of the pin housing is reduced for packaging purposes, the transverse length of the bore in the pin housing also becomes smaller, leading to shorter pins having a reduced length/diameter ratio, resulting in increased potential for cocking and wear of the pins, thereby reducing the stiffness of the locking mechanism. 
         [0029]    Referring now to  FIGS. 3 through 5 , a sub-assembly portion  100  of an improved single-pin SHLA or SVL  110  is shown. Sub-assembly  100  comprises body  118 ; pin housing  124  slidably disposed in body  118 ; and a stepped plug  130 , spring  142 , and locking pin  136  disposed in a transverse bore  128  in pin housing  124 . Stepped plug  130  extends into a slot  134  formed in body  118  for preventing rotation of the pin housing within the body as in the prior art. Also, as in the prior art, plug stop  135  limits the axial travel of pin housing  124  within body  118 . The shapes and relationships of these components is the subject of the present invention. 
         [0030]    In one aspect of the present invention, a locking port  138  formed in a wall of body  118  is provided with a locking ledge  150  for receiving a mating flat  152  on locking pin  136 . The use of a broad planar contact area between the pin and the body overcomes the prior art wear problem wherein a locking pin having a circular cross-section engages a circular bore of a slightly larger diameter as noted above. This arrangement requires that locking pin  136  be prevented from rotation about its own axis, which is readily accomplished in many ways by providing an additional flat (not visible) on the side of pin  136  and a mating flat-ended cross-pin (not visible) disposed in pin housing  124 , substantially as disclosed in U.S. Pat. No. 6,513,470 (“the &#39;470 patent”) directed to a SVL, the relevant disclosure of which is herein incorporated by reference. Note that if the rotational orientation of the body of a SHLA or SVL relative to the receiving bore in the engine is critical, such as, for example, for maintaining roller alignment with a cam lobe in the case of a roller SVL or for oil port alignment in either a SHLA or SVL, a means for locating the body in the receiving bore, as known in the art, may be provided. 
         [0031]    Further, locking port  138  is provided with an additional notch  154  to allow locking pin  136  to be installed through port  138  after pin housing  124  is inserted into body  118 , the benefits of which are described below. 
         [0032]    Referring now to  FIGS. 6 through 12 , a method will be described for assembling and setting the desired internal mechanical lash in a SHLA or SVL sub-assembly in accordance with the present invention. First, a flat-ended cross-pin (not visible) is mounted into a bore in pin housing  124 , as shown in the incorporated &#39;470 patent, and stepped plug  130  is inserted into transverse bore  128  (slidable therein). Then, after the lost motion springs such as shown in  FIG. 2  (numeral  25 ′) is installed in chamber  160 , the pin housing is installed into bore  120  in body  118 , as shown in  FIG. 6 , until transverse bore  128  is aligned with locking port  138 , as shown in  FIGS. 6 and 7 . 
         [0033]    Next, a gage tool  156  is inserted ( FIG. 7 ) through locking port  138  until a flat  158  on the gage tool is directly adjacent locking ledge  150  ( FIG. 8 ). The thickness  157  of gauge tool  156  at flat  158  is known and preferably is the nominal thickness of a locking pin  136  at pin flat  152 . Pin housing  124  is lowered into body  118  against the force of the lost motion springs until flat  158  makes contact with locking ledge  150 , defined as a first position A ( FIG. 9 ). Simultaneously, gage tool  156  is advanced to urge the minor diameter portion of plug  130  into slot  134 . Pin housing  124  is then released, and lost motion springs (not shown) in chamber  160  urge pin housing  124  upward until plug  130  is stopped by the upper end  135  of slot  134 , defined as a second position B. Thus, the measured lash  162  between position A and position B is the mechanical lash in subassembly  100  inherent when a locking pin of thickness  157  is used. The desired lash is then subtracted from the measured lash  162  to yield a lash correction which, when added to the gage tool of known thickness, yields a desired thickness for the actual locking pin  136  to be used. A locking pin  136  of the desired thickness is selected from the sorted family of locking pins having a suitable range of sizes. 
         [0034]    Plug  130  is then urged back into transverse bore  128  and pin housing  124  is raised a small distance, without disassembly, to permit gage tool  156  to be withdrawn ( FIG. 10 ). Then, return spring  142  and the selected locking pin  136  are inserted into transverse bore  128  ( FIG. 11 ). Pin housing  124  is again depressed within body  118  until stopped by pin flat  152  against locking ledge  150 . Simultaneously, pin  136  is urged by the locking pin spring further into transverse bore  128 , re-seating the minor portion of plug  130  into slot  134 . Pin housing  124  and locking pin  135  are released, again allowing the lost motion springs to urge pin housing  124  upwards until slot end  136  is engaged. A stopper such as a wire clip (not shown) may be installed in transverse bore  128  before plug  131  is inserted in the bore to prevent end face  131  of plug  130  ( FIG. 3 ) from rubbing against the inside bore of body  118  when locking pin  136  is retracted from locking port  138  and pin housing  124  is cycle in lost motion. 
         [0035]    Sub-assembly  100  is now fully assembled with the correct internal mechanical lash and is ready for subsequent insertion of a prior art lash adjusting mechanism  26  ( FIG. 1 ) to complete the assembly in accordance with the present invention. 
         [0036]    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.