Abstract:
A hydraulic valve lifter assembly including a lifter body and a cam follower. The cam follower is mounted to an end of the lifter body wherein the lifter body has a first diameter over a first body portion for engaging a wall of an engine bore. The lifter body also including a second diameter smaller than the first diameter over a second body portion supportive of the cam follower. The hydraulic valve lifter assembly further including a contiguous annular transitional chamfer between the first and second diameter portions of the lifter body.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. application Ser. No. 10/977,071, which was filed on Oct. 29, 2004. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to hydraulic lifters for activating valves in response to rotation of a camshaft in an internal combustion engine; more particularly, to the body of such lifters including a chamfered relief and a reduced body diameter with respect to a main body diameter of the lifter body to eliminate the need to remove a residual burr contained within the reduced body diameter portion after a wheel groove is cut for a cam follower.  
       BACKGROUND OF THE INVENTION  
       [0003]     Hydraulic lifter assemblies for actuating intake and exhaust valves in internal combustion engines are well known. A typical lifter assembly includes a lifter body supportive of cam follower such as a roller. In use, the body is disposed for reciprocal motion in a bore in an engine block for translating rotary motion of a cam lobe into reciprocal motion of a pushrod. A piston within a well in the lifter body defines a high-pressure chamber in the well between the piston and the bottom of the well. The piston includes a low-pressure reservoir supplied with engine oil, from which the high-pressure chamber is replenished via a check valve. A pushrod seat closes the low-pressure chamber and receives the pushrod. A spring within the high-pressure chamber urges the piston outwards, thus removing mechanical lash in the valve train. The low-pressure chamber is provided with oil via an axial passage in the pushrod in communication with an oil gallery in the engine rocker arm assembly, such that there are no air voids in the oil supply system during engine operation.  
         [0004]     It is necessary to completely purge air from an engine oil supply system after assembly of the engine and before the first starting. Of necessity, when the rocker arm assembly is bolted to the engine head, some of the intake and exhaust valves are placed in an open position. In a relatively short time, those lifter assemblies associated with the open valves will leak oil from their high-pressure chambers in response to force exerted by the valve springs. When this happens during normal operation of an engine, as during periods of inoperation, it is of little consequence, as the lifter automatically refills from the low-pressure reservoir through the check valve as soon as the engine is re-started and the force is relieved from the lifter. However, upon first starting an engine after assembly, it is essential that the low-pressure reservoir have sufficient oil to refill the high-pressure chamber immediately. A failure to provide oil for filling of the high-pressure chamber immediately results in a noisy lifter, a false indication of lifter failure, a failure of the first-start-after-assembly engine test, and substantial engine rework costs.  
         [0005]     To guard against this problem in the prior art, lifters are carefully filled with oil after assembly of the lifter and are shipped in a vertical position. However, engine assembly can require a lifter to be placed in an orientation wherein oil can drain from the lifter. In addition, some engines have normal lifter positions wherein oil can drain from the low-pressure reservoir during and after engine assembly.  
         [0006]     Prior to starting a newly-assembled engine, oil is forced through the oil distribution system under pressure for a predetermined time period, typically on the order of one minute, to purge air from the system. A large amount of air is initially present in galleries in the rocker arm shaft, rocker arms, and pushrods, which air must be expelled from the pushrods at or through the hydraulic valve lifters. Because there is no lash between elements in the valve-open valve trains, air purging is difficult and frequently incomplete, resulting in a noisy lifter upon initial starting. Further, any lifter with residual air trapped in the low-pressure reservoir may suck that air into the high-pressure chamber upon start-up, producing a void therein resulting in prolonged lifter noise and test failure.  
         [0007]     Another known problem in prior art hydraulic valve lifters is that a burr is formed at a lower edge of the lifter body when machining the lifter body to form a wheel groove for the cam follower. If not removed, the burr is known to cause undesirable scratching and wear of the surface of the engine bore during use. In the prior art, the burr is typically removed in a separate deburring operation, adding to the cost of manufacture of prior art hydraulic valve assemblies.  
         [0008]     What is needed in the art of hydraulic valve lifters is an improvement that eliminates the need to remove a residual burr contained in a lifter body after a wheel groove is cut therein.  
         [0009]     It is a principal object of the present invention to provide a lifter body that eliminates the need to remove a residual burr from the lifter body after a wheel groove is cut.  
       SUMMARY OF THE INVENTION  
       [0010]     Briefly described, a hydraulic valve lifter assembly in accordance with the invention includes a lifter body and a cam follower. The cam follower is mounted to an end of the lifter body wherein the lifter body has a first diameter over a first body portion for engaging a wall of an engine bore. The lifter body also includes a second diameter smaller than the first diameter over a second body portion supportive of the cam follower. The hydraulic valve lifter assembly further includes a contiguous annular transitional chamfer between the first and second diameter portions of the lifter body.  
         [0011]     Therefore, when a wheel groove is cut for the cam follower, any residual burr is contained within the reduced diameter portion, cannot interface with an engine bore surface, and need not be removed.  
     
    
     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 prior art non-valve-deactivating hydraulic lifter assembly;  
         [0014]      FIG. 2  is an elevational cross-sectional view of a first prior art valve-deactivating lifter assembly;  
         [0015]      FIG. 3  is an elevational cross-sectional view of a second prior art valve-deactivating lifter assembly;  
         [0016]      FIG. 4  is an elevational cross-sectional view of a third prior art valve-deactivating lifter assembly;  
         [0017]      FIG. 5  is a detailed elevational cross-sectional view of the upper end of the lifter assembly shown in  FIG. 4 , showing modifications thereto in accordance with the invention;  
         [0018]      FIGS. 6 through 12  are plan views of the mating surfaces of the push rod socket, piston and/or, seat, showing seven exemplary surface patternings in accordance with the invention;  
         [0019]      FIG. 13  is an elevational view of a lower end of a lifter assembly in accordance with the invention, showing a reduced diameter portion to reduce chafing and galling in an associated engine bore; and  
         [0020]      FIG. 14  is an elevational cross-sectional view of the lifter shown in  FIG. 13 , taken along line  14 - 14  therein. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     Referring to  FIGS. 1 through 4 , prior art hydraulic valve lifter assemblies  10   a,   10   b,   10   c,   10   d,  respectively, for moving reciprocally in a bore  11  to actuate a valve (not shown) in an internal combustion engine  13  comprise a generally cylindrical lifter body  12  supporting at a lower end  14  a cam follower roller  16  rotatably attached to body  12  by an axle  18  for following a cam lobe  20 .  
         [0022]     Lifter assembly  10   a  is substantially identical to non-valve-deactivating hydraulic valve lifter assemblies, as are well known in the prior art of internal combustion engines.  
         [0023]     Lifter assembly  10   b  is a valve-deactivating lifter assembly substantially as disclosed in U.S. Pat. No. 6,595,174 issued Jul. 22, 2003 to Schnell.  
         [0024]     Lifter assembly  10   c  is a valve-deactivating lifter assembly substantially as disclosed in U.S. Pat. No. 6,606,972 issued Aug. 19, 2003 to Wenisch et al.  
         [0025]     Lifter assembly  10   d  is a valve-deactivating lifter assembly substantially as disclosed in U.S. Pat. No. 6,578,535 issued Jun. 17, 2003 to Spath et al., the relevant disclosure of which is incorporated herein by reference.  
         [0026]     Lifter assemblies  10   b , 10   c , 10   d  differ significantly from lifter assembly  10   a  only in their respective deactivating mechanisms  22   b , 22   c , 22   d  which are not immediately relevant to the present invention and need not be discussed in detail further. The purpose in showing a prior art non-valve-deactivating lifter assembly  10   a  along with three representative prior art valve-deactivating lifter assemblies  10   b , 10   c , 10   d  is to show that the upper end hydraulic valve lifter means  24   a , 24   b , 24   c , 24   d  is substantially identical, functionally, in both non-valve-deactivating and valve-deactivating prior art lifter assemblies. As is shown below, the invention is useful when incorporated into either type of hydraulic valve lifter assembly.  
         [0027]     Referring to  FIGS. 2 through 4 , in a valve-deactivating lifter assembly, a pin housing  26  is slidably disposed within a first axial bore  28  in lifter body  12 . Pin housing  26  itself has a second axial bore  30  for receiving a conventional hydraulic lash adjuster (HLA) mechanism generally designated  24  which may be of a type well known to those  25  skilled in the art. HLA  24  includes a pushrod seat  32  having a spherical socket surface  34  for receiving a ball end  36  of a conventional engine valve pushrod  38 . HLA  24  further includes a piston  40  slidably disposed in bore  30  and defining a high-pressure chamber  42  containing a lash elimination spring  44 . A bottom surface of piston  40  defines, in part, a low-pressure reservoir  46  communicating with high-pressure chamber  42  via a check valve  48 . Reservoir  46  is in fluid communication with and therefore is supplied with engine oil by passage  50  through pushrod seat  32  and supply passage  54  within pushrod  38 . Reservoir  46  is closed by an interface between first and second mating surfaces  56 , 58  of seat  32  and piston  40 , respectively.  
         [0028]     The HLA  24  as just described is common ( 24   a , 24   b , 24   c , 24   d ) to all four exemplary lifter assemblies  10   a , 10   b,   10   c,   10   d.    
         [0029]     Referring to  FIGS. 5 through 9 , in a hydraulic valve lifter  110  a first embodiment of venting means  152  in accordance with the invention comprises seat  132  having socket  134 , including socket surface  135  and/or first mating surface  156  and/or second mating surface  158  between the seat and socket, modified to provide a relief patterning to permit passage of air between pushrod ball end  36  and socket surface  135  and/or between first and second mating surfaces  156 , 158 . The relief patterning may take the form of a sacrificial layer  157 , formed, for example, of a heavy ink, wax, or other suitable polymer and featured with grooves or other features that serve to controllably disrupt the sealability of mating surfaces  156 / 158  and/or socket surface  135  to permit passage of air across the surface thereof. The layer may be applied by conventional means such as spraying, dipping, and the like. Being sacrificial, the layer is competent to readily vent air being purged from the engine oil galleries during initial engine start-up after assembly, permitting the topping up with engine oil of the low-pressure reservoir  46 , but is rapidly destroyed and flushed away during engine operation when such venting is no longer necessary.  
         [0030]     The relief patterning may also take the form of permanent patterns formed in socket surface  135  and/or mating surfaces  156 , 158 . Some exemplary patterns, which may be either temporary or permanent, are offered in  FIGS. 6 through 12 : radial grooves  200  ( FIG. 6 ); spiral grooves  300  ( FIG. 7 ); random roughness  400  ( FIG. 8 ); parallel grooves  500  ( FIG. 9 ); cross-hatched grooves  600  ( FIG. 10 ); and radial quadrant grooves  700  ( FIG. 11 ).  FIG. 12  shows one continuous spiral groove  800  formed in the face of the surface beginning at an inside edge and proceeding outward in an increasing radius spiral to its terminus approximately adjacent its beginning point at an outside edge.  
         [0031]     The patterns shown herein are only exemplary; obviously, other patterns as may be conceived of by one of ordinary skill in the art are fully comprehended by the invention. Further, as may be determined by one of ordinary skill in the art without undue experimentation, the grooves or roughness should be sized in dimension and number to permit ready venting of air during purging thereof from the engine galleries but to inhibit significant passage of engine oil during normal operation of the lifter.  
         [0032]     When air is vented across socket surface  135 , in accordance with the invention, air escapes generally into the engine cavity via the top of assembly  110 . When air is vented across either surface  156  or surface  158 , in accordance with the invention, air escapes generally into the engine cavity via vent space  162  formed in bore  130  between seat  132  and the pin housing (shown as  26  in  FIG. 2 ), or an analogous space in a non-deactivating lifter assembly such as  10   a.    
         [0033]     Referring again to  FIG. 5 , in a second embodiment of venting means in accordance with the invention, one or more vent passages  160 , and preferably a plurality, are provided in pushrod seat  132 , in a generally radial direction through seat  132  to recess  163 , thereby venting trapped air from push rod supply passage  54 , seat passage  150 , and/or reservoir  46  to recess  163 . As described above for the grooves and roughness, passages  160  should be sized in dimension and number to permit ready venting of air during purging thereof from the engine galleries but to inhibit significant passage of engine oil during normal operation of the lifter. Also, while this embodiment, as shown, provides venting of trapped air from the head space above low pressure reservoir  46  to seat recess  163 , it is understood that vent passages  160  may be disposed to provide a path for the venting of air to the outside of the lifter assembly from within push rod  38 , seat  132  or low pressure reservoir  46 . For example, within the scope of this invention, passages  160  may connect seat passage  150  to vent space  162 .  
         [0034]     Referring to  FIGS. 13 and 14 , an HLA in accordance with the invention preferably includes an additional improvement comprising a chamfered relief  170  and reduced body diameter  172  with respect to main body diameter  174 . A known problem in the prior art is a burr  80  ( FIG. 1 ) at lower edge  82  formed when machining body  12  to form wheel groove  84 . If not removed, burr  80  is known to cause undesirable scratching and wear of the surface of bore  11  during use. In the prior art, burr  80  typically is removed in a separate deburring operation, adding to the cost of manufacture of a prior art HLA.  
         [0035]     A less expensive solution to the problem is to add chamfered relief  170  and reduced body diameter as part of the machining operation of the outer surfaces of body  12 , adding little if any cost to manufacture. Thus, when wheel groove  84  is cut, any residual burr is contained within the reduced diameter portion, cannot interface with bore surface  11 , and need not be removed.  
         [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.