Abstract:
An improved hydraulic lash adjuster including a cup-shaped adjuster body, and a plunger assembly disposed within the adjuster body. The plunger assembly includes a stepped axial bore extending from a body inner end to a central oil passage opening onto a hemispherical pivot head. A valve seat for a check valve is disposed against the step, defining a low-pressure oil chamber in the axial bore. A check ball and lash adjustment spring are disposed against the seat in a high-pressure chamber formed between the valve seat and adjuster body. The body of the plunger assembly may be formed by inexpensive processes to a length equivalent to that of a prior art one-piece plunger to resist torsional side loads which may be imposed on the HLA in use. The separately formed valve seat may also be used in other hydraulic lash adjusters such as incorporated in hydraulic valve lifters.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to hydraulic lash adjusters for combustion valves of internal combustion engines; more particularly, to a hydraulic lash adjuster (HLA) wherein a plunger is operative within an HLA body; and most particularly, to an improved hydraulic lash adjuster having a simplified long plunger assembly having the side-loading capability of a one-piece plunger, with reduced manufacturing complexity and cost.  
       BACKGROUND OF THE INVENTION  
       [0002]     An HLA generally comprises a plunger slidably disposed within a cup-shaped body for fixed mounting in an internal combustion engine, which plunger may be hydraulically extended from the body to take up mechanical lash in an engine valve train. The HLA is supplied with low-pressure engine oil for conventional lubrication and for lash adjustment. A spring in a high-pressure chamber formed between the plunger and the body urges the plunger out of the body to take up mechanical lash in the valve train, thereby expanding the high-pressure chamber. A ball check valve between the low-pressure reservoir and the high-pressure chamber allows that chamber to fill with oil, thereby making the HLA hydraulically rigid. As oil escapes from the high-pressure chamber by leakage around the plunger, the lost oil is replenished through the check valve. If the effective length of the valve train shortens during the engine&#39;s cam operating cycle, positive lash is created and the HLA extends, moving the plunger to a higher position at the end of the cycle than at the beginning. Inversely, if the effective length of the valve train lengthens during the cam cycle, negative lash is created and the lash adjuster contracts, moving the plunger to a lower position at the end of the cycle than at the beginning. The latter condition typically occurs when valve train components lengthen in response to increased temperature.  
         [0003]     A problem exists in some prior art HLA assemblies. A prior art one-piece plunger has a ball surface at its outer end with a central opening for supplying oil from the low-pressure reservoir to the socket end of an associated rocker arm assembly, the reservoir being supplied via a radial port in a sidewall of the reservoir. The inner end of the plunger comprises a seat for the ball check valve. See, for example, FIG. 2 in U.S. Pat. No. 5,642,694.  
         [0004]     Although a one-piece plunger is desirable because it provides a long bearing surface within the body and hence excellent stability against side-load forces, forming such a single element plunger in the prior art is known to be costly and difficult. The manufacture requires a large investment in equipment such as cold-forming equipment, making the cost of small production volume applications prohibitive. Additionally, due to the forming process required, the resulting plunger tends to have a thin wall section at its outer ball surface end, a region where thicker walls are desirable.  
         [0005]     It is more common in the recent prior art to provide an HLA plunger formed as two shorter sections, each of which may be formed by relatively inexpensive methods such as boring, turning, screw-machining, powdered metal forming, and/or metal injection molding. See, for example, FIG. 1 in U.S. Pat. No. 5,622,147.  
         [0006]     Forming the plunger as upper and lower halves reduces the cost but at a sacrifice in side-loading stability. Further, the surfaces forming the joint between the upper and lower halves benefit from precision grinding to ensure a leak-proof juncture, again at additional manufacturing cost. In either prior art example, the seat for the ball check valve is integrally formed in the lower end of the plunger, a process that adds cost to the manufacture of the plunger, and a potential source of leakage across the seated check valve since fine finishing of the seating surface is difficult to achieve in an integral seat.  
         [0007]     It is a principal object of the present invention to provide a hydraulic lash adjuster including a plunger that is easier to manufacture and has a long bearing surface equivalent to the bearing surface of a prior art one-piece plunger.  
       SUMMARY OF THE INVENTION  
       [0008]     Briefly described, a hydraulic lash adjuster in accordance with the invention comprises a hollow adjuster body for fixed mounting onto an engine, and a plunger assembly disposed within the hollow body. A plunger body includes a stepped axial bore extending from an inner end thereof to a central oil passage opening onto a conventional hemispherical pivot head. A valve seat for a check valve is disposed against the step, defining thereby a low-pressure oil reservoir in the axial bore. The plunger body is provided with an annular collector groove and entrance port for supplying lash-adjusting oil to the low-pressure reservoir. A check ball and lash adjustment spring are disposed against the seat in a high-pressure chamber formed conventionally between the valve seat the adjuster body. The plunger body may be formed to any desired length, to provide an outer bearing surface equivalent to that of a prior art one-piece plunger to resist torsional side loads which may be imposed on the HLA in use. It is understood that the plunger body may be formed of induction hardenable steels, nonferrous metals, or ceramics. The plunger body is readily formed by inexpensive processes. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0010]      FIG. 1  is an elevational cross-sectional view of a first prior art hydraulic lash adjuster having a one-piece plunger body;  
         [0011]      FIG. 2  is an elevational cross-sectional view of a second prior art hydraulic lash adjuster having a two .piece plunger body; and  
         [0012]      FIG. 3  is an elevational cross-sectional view of an improved hydraulic lash adjuster in accordance with the invention having a simplified two-piece plunger. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     Referring to  FIG. 1 , there is shown a prior art hydraulic lash adjuster, designated generally as  10 , which includes a generally cup-shaped cylindrical adjuster body  12  configured to be received in an engine cylinder head  14 , or other suitable installation location. The cup-shaped cylindrical body  12  forms a dash pot for a tubular one-piece plunger  16  configured for sliding disposition within the bore  18  of the body  12 . In the embodiment shown, the one-piece plunger body  16  includes a semispherically shaped, upper thrust end  20  which extends out from the body  12  for engagement with a corresponding, concave portion of a valve train rocker arm (not shown) in cylinder head  14 .  
         [0014]     A plunger return spring  26  is interposed between the bottom  28  of the cup-shaped body  12  and the lower end  30  of plunger  16  and acts to bias plunger  16  such that contact is maintained with the spherically concave portion of the rocker arm, thereby eliminating mechanical lash in the associated valve train. Fluid for the dash pot of lash adjuster  10  is in the form of oil supplied from the engine lubricating system to a gallery  32 . An external annular groove  34  in body  12  communicates through port  36  to deliver oil to annular space  38  defined by inner wall  40  of body  12  and an annular groove  42  in the outer surface of tubular plunger  16 . A second port  46  extends through the plunger wall and provides a means for fluid communication between annular space  38  and low pressure chamber  48  of plunger  16 .  
         [0015]     The lower end of plunger  16  is provided with an outlet port  50  through which oil, stored within low-pressure chamber  48 , may flow into high-pressure chamber  52  defined between the lower end  30  of the plunger  16  and the bottom, closed end  28  of cup-shaped body  12 . Flow through outlet port  50  is controlled by a check valve in the form of a ball  54  which closes against a seat  56  encircling the lower end of the outlet port  50 . A suitable valve cage  58  and valve return spring  60  limit open travel of valve ball  54  to the amount necessary to accomplish replenishment of high-pressure chamber  52  with oil which normally escapes therefrom between the sliding surfaces of tubular plunger  16  and cup-shaped body  12  as “leak-down”. As shown, valve cage  58  is held against plunger  16  by plunger spring  26 .  
         [0016]     Low-pressure chamber  48  of plunger  16  extends substantially the length of the plunger, from adjacent the outlet port  50  to the semi-spherical thrust end  20 . An opening  62  extends through the thrust end  20  of plunger  16  to enable oil within low pressure chamber  48  to lubricate the end of the rocker arm. An integral baffle  64  is disposed within the low-pressure chamber  48  intermediate the ends of the chamber. The baffle  64  is configured as an annular shelf which extends radially inwardly from the inner wall  66  of the low-pressure chamber  48  to define a central opening  68  for the passage of oil from the oil supply port  46  to the outlet port  50 .  
         [0017]     Prior art one-piece plunger  16  thus enjoys an outer bearing surface length  70  extending virtually the entire depth of bore  18  in HLA body  12 .  
         [0018]     Referring to  FIG. 2 , there is illustrated a prior art hydraulic lash adjuster  100  having a two-piece plunger, substantially as disclosed in U.S. Pat. No. 5,622,147 FIG. 1. Adjuster  100  has a body  102 , a plunger assembly  104  defined by an upper plunger element  106  and a lower plunger element  108  which are received within the body in close fitting relationship and which define a low-pressure chamber  110  between them. The bottom  112  of lower plunger element  108  forms, in cooperation with the end of a reduced diameter portion  114  of the body bore, a high pressure chamber  116 . A check valve  118  is provided in the end of a passage  120  which connects the high and low pressure chambers. The check valve, which is shown as a ball but which can be a flat disk or the like, is retained by a cage  122  which is in interference fit with a counterbore  124  formed in the lower plunger element and which provides a seat for the lash adjuster plunger spring  126 . In accordance with the most prevalent design practice, a bias spring  128  acting between the bottom of the cage  122  and the check valve  118  biases the check valve into a normally closed position.  
         [0019]     An oil entry port  130 , in communication with engine lubricating system oil gallery (not shown), opens into the body bore and intersects a collector groove  132  which intersects a radial port  134  in the upper plunger element to supply hydraulic fluid to the chamber  110 . A second collector groove  136  and port  138  in the upper plunger element provides metered hydraulic fluid to an axial bore  140  to supply lubricant to a rocker arm (not shown) which engages a modified ball end  142  formed on the end of the upper plunger element, metering being provided by means of a controlled clearance between the plunger and the bore in the area of the land between the port  130  and the collector groove  136 . The plunger is retained within the body by means of a cap  144 .  
         [0020]     As noted above, dividing the plunger into an upper half  106  and a lower half  108 , for the sake of manufacturing ease and economy, yields a plunger which either a) has an undesirably short bearing length  170  of the upper half, or b) requires welding together and machining of the upper and lower halves to provide a non-divided plunger having a desirably long bearing length, but at increased manufacturing cost.  
         [0021]     Referring to  FIG. 3 , a simplified and improved hydraulic lash adjuster  200  in accordance with the invention includes a generally cup-shaped cylindrical adjuster body  212  configured to be received in an engine cylinder head  14  of an internal combustion engine shown schematically as numeral  15 . The cup-shaped cylindrical body  212  forms a dash pot for a tubular plunger  216  configured for sliding disposition within the bore  218  of the body  212 . In the embodiment shown, the plunger  216  includes a semispherically shaped, upper thrust end  220  which extends out from the body  212  for engagement with a corresponding, concave portion of a rocker arm of valve train  213  in cylinder head  14 . It is understood that the plunger body may be formed of induction hardenable steels, nonferrous metals, or ceramics.  
         [0022]     An axial bore  222  extends the length of plunger  216 , preferably having a reduced diameter portion  224  extending through upper thrust end  220  for providing oil to the rocker arm. Bore  222  is preferably stepped near the lower end thereof for receiving a check valve seat element  226  to close bore  222  and form thereby a low-pressure chamber  228  within plunger  216 .  
         [0023]     Seat element  226 , in conjunction with tubular plunger  216  to form plunger assembly  227 , is sized for a close fit within bore  222  and may be secured and sealed against bypass leakage as by welding to plunger  216 . Seat element  226  includes an annular beveled seat  230  for receiving a check ball  232  to regulate flow from chamber  228  across seat  230 . In a currently preferred embodiment, element  226  is provided with identical beveled seats  230  on opposite sides thereof such that element  226  does not require specific orientation for installation into plunger  216 . Seat element  226  forms, in cooperation with the end of a reduced diameter portion  214  of the body bore, a high pressure chamber  217 .  
         [0024]     Check ball  232  is retained by a cage  234  which provides a seat for the lash adjuster plunger spring  236 . A bias spring  238  acting between the bottom of the cage  234  and the check ball  232  biases the check valve into a normally closed position. Valve cage  234  and bias spring  238  limit open travel of valve ball  232  to the amount necessary to accomplish replenishment of high-pressure chamber  217  with oil which normally escapes therefrom between the sliding surfaces of tubular plunger  216  and cup-shaped body  212  as “leak-down”.  
         [0025]     Fluid for the dash pot of lash adjuster  200  is in the form of oil supplied from the engine lubricating system to a gallery  240 , similar to that shown as numeral  32  in  FIG. 1 . An external annular groove  242  in body  212  communicates through port  244  to deliver oil to annular space  246  defined by inner wall  248  of body  212  and an annular groove  250  in the outer surface of tubular plunger  216 . A second port  252  extends through the plunger wall and provides a means for fluid communication between annular space  246  and low pressure chamber  228  of plunger  216 .  
         [0026]     Simplified and improved plunger  216  thus enjoys an outer bearing surface length  270  extending virtually the entire depth of bore  218  in HLA body  212 , equivalent at least to the length  70  of bearing surface in prior art one-piece plunger  16  ( FIG. 1 ), and far longer than the length  170  of bearing surface in prior art upper plunger element  106  ( FIG. 2 ).  
         [0027]     In the embodiment shown of an HLA, having a separate seat element  226  allows for, among other things, improved manufacturability of seat element  226  and the axial bore  222  of plunger  216 . However, it is understood that separate seat element  226 , with an associated check ball  232  and cage  234 , may be alternately incorporated into other valve train members having a lash adjustment feature such as, for example, a hydraulic valve lifter, thereby allowing for similar improvements in the manufacturability of the axial bore of the valve train member as well.  
         [0028]     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.