Abstract:
An improved dual feed hydraulic lash adjuster (HLA), for use in an internal combustion engine, comprising a hollow body and a plunger assembly disposed in a bore of the engine. A one-piece plunger body includes a first chamber for forming a low-pressure oil reservoir and receiving a lash adjustment mechanism, and a second chamber open at one end and partially closed hemispherically for supporting a rocker arm and providing valve deactivating oil thereto for an auxiliary valve actuation system. The first and second chambers are separated by a transverse web, optionally having a small-diameter passage therethrough for air evacuation. The one-piece plunger body provides a high degree of resistance to side loads which may be imposed on the HLA in use.

Description:
TECHNICAL FIELD 
   The present invention relates to hydraulic lash adjusters for combustion valves of internal combustion engines; more particularly, to a dual feed hydraulic lash adjuster for controlling the action of an auxiliary valve actuation system such as a variable lift valve mechanism; and most particularly, to an improved dual feed hydraulic lash adjuster having a one-piece plunger body for increased side-loading capability. 
   BACKGROUND OF THE INVENTION 
   Variable lift valve mechanisms for internal combustion engines are well known. In one example of such engines, a two-step roller finger follower rocker arm is known to pivot on a hydraulic lash adjuster (HLA) disposed on the engine block. An HLA generally comprises a slidable plunger that may be hydraulically extended to take up mechanical lash in a valve train. In an example where a valve lift change is accomplished by increasing oil pressure to the associated variable lift valve mechanism, the HLA is supplied with low pressure engine oil for conventional lubrication and lash adjustment. When a valve lift change is desired, oil pressure in the HLA is increased, and high-pressure oil flows through the same circuit in HLA to actuate the variable lift valve mechanism. To reverse the change the oil pressure is again reduced. 
   A problem exists in some prior art HLA assemblies having a single oil feed wherein the oil pressure is varied between the two modes. Because a minimum lash-adjusting oil pressure is present in the HLA at all times, the minimum required switching pressure must include the HLA minimum pressure. That is, the minimum required switching pressure must be higher than in other known systems wherein the lash adjuster and the switching element are independently supplied. Thus, providing dual independent oil supplies to a hydraulic lash adjuster represents an advance in the art. 
   Prior art HLAs receptive of such dual independent oil supplies comprise upper and lower plunger elements disposed within a body and defining a low pressure chamber or reservoir therebetween. The upper portion is dedicated to the auxiliary valve actuation function, and the lower portion to the hydraulic lash adjustment function. Because each of the elements is axially relatively short, the overall plunger may exhibit inferior side-load capability, resulting in relatively short working lifetimes and premature wear of such HLAs. 
   It is a principal object of the present invention to provide a dual feed hydraulic lash adjuster having superior side-load capability. 
   SUMMARY OF THE INVENTION 
   Briefly described, a dual feed hydraulic lash adjuster in accordance with the invention comprises a plunger assembly disposed within an engine bore. A one-piece plunger body includes a first chamber for forming a low-pressure oil reservoir and receiving a lash adjustment mechanism, and a second chamber open at one end and partially closed hemispherically for supporting a rocker arm and providing valve oil thereto for an auxiliary valve actuation system. The first and second chambers are separated by a transverse web, optionally having a small-diameter passage therethrough for purging of air from the lash adjustment mechanism. The plunger body is provided with a first annular collector groove and entrance port for supplying lash-adjusting oil to the first chamber, and a second annular collector groove and entrance port for supplying oil for the auxiliary valve actuation system to the second chamber. The one-piece plunger body is substantially longer than the upper section of a prior art two-piece plunger body and therefore provides a much higher resistance to torsional side loads which may be imposed on the HLA in use. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is an elevational cross-sectional view of a prior art two-step hydraulic lash adjuster, showing the plunger assembly comprising upper and lower plunger body portions; 
       FIG. 2  is an elevational view of an improved plunger in accordance with the invention for a two-step hydraulic lash adjuster; 
       FIG. 3  is an exploded isometric view of the improved plunger shown in  FIG. 2 ; and 
       FIG. 4  is an elevational cross-sectional view of the improved plunger shown in  FIG. 2 , taken along line  4 — 4  therein, installed for use in a two-step hydraulic lash adjuster in accordance with the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , a prior art dual feed hydraulic lash adjuster  10  includes a lash adjuster body  12  and a plunger assembly, generally designated as  14 , which is slidingly disposed within body  12 . Plunger assembly  14  includes an upper plunger element  16  and a lower plunger element  18  meeting at an interface  19 , and further includes a hydraulic element assembly  21  (HEA). The plunger elements are received within body  12  in a close-fitting relationship within a bore  20  of body  12 . As elements of HEA  21 , upper and lower plunger elements  16 , 18  define a low pressure chamber  22  (reservoir) therebetween. The bottom of lower plunger element  18  forms, in cooperation with the end of a reduced diameter portion  24  of body bore  20 , a high pressure chamber  26 . A check valve  28  is disposed in the end of a passage  30  which connects high pressure chamber  26  and low pressure chamber  22 . Check valve  28  is retained in a cage  32  which is in an interference fit within a counterbore  34  formed in lower plunger element  18 . Cage  32  provides a seat for a lash adjuster plunger spring  36 . A bias spring  38  biases check valve  28  into a normally closed position. A first oil entry port  40  in body  12  opens into bore  20  and intersects a first annular collector groove  42  which, in turn, intersects a first radial port  44  in upper plunger element  16  to supply hydraulic fluid from a first source (not shown) to low pressure chamber  22 . A second oil entry port  46  opens into bore  20  of body  12  and intersects a second collector groove  48  which, in turn, intersects a second radial port  50  in upper plunger element  16  to provide hydraulic fluid from a second source (not shown) to an axial passage  52  for an auxiliary valve actuation system (not shown). Typically, the surface of the rocker arm engages a hemispherical element  54  formed on the upper end of plunger assembly  14 , hydraulic fluid being passable through central opening  55 . 
   Because plunger assembly  14  is formed in two parts as upper and lower plunger elements  16 , 18  meeting at interface  19 , the engagement length  56  of upper element  18  within bore  20  is relatively short, making prior art HLA  10  relatively vulnerable to displacement or distortion by side-load forces on upper element  16  during use. Such forces may cause lash adjuster body  12  to fail structurally, allowing escape of hydraulic fluid past upper element  16  and causing failure of the HLA. 
   Referring to  FIGS. 2 through 4 , where like numbers (primed) are used for like elements in prior art HLA  10 , an improved plunger assembly  14 ′ for an improved dual feed hydraulic lash adjuster  10 ′ is shown. In assembly  14 ′, lash adjuster body  12  of the prior art is eliminated. Instead, assembly  14 ′ is inserted directly into close-fitting bore  20 ′ formed in casting  12 ′ of an internal combustion engine  13 . One-piece plunger body  11  extends virtually the full length of bore  20 ′ and, because of its one-piece design, provides a greatly increased engagement length  56 ′, a significant benefit of an improved plunger assembly, and, when installed in bore  20 ′, forming an improved HLA  10 ′, in accordance with the invention. 
   All elements of a dual feed HLA plunger assembly  14 ′ are contained within one-piece plunger body  11 . A modified HEA  21 ′ resides in an appropriately-sized counterbored chamber  70  formed in one end of plunger body  11 ′. HEA  21 ′ includes a cylindrical first element  74  having well  73  and closed bottom  75 , and a low-pressure reservoir  22 ′ contained in a cylindrical second element  72  slidably disposed in and cooperating with first element  74  to form a high-pressure chamber  26 ′. A check valve  28 ′ is disposed in the end of a passage  30 ′ which connects high pressure chamber  26 ′ and low pressure chamber  22 ′. Check valve  28 ′ is retained in a cage  32 ′ which is in an interference fit within a counterbore  34 ′ formed in second element  72 . Cage  32 ′ provides a seat for a lash adjuster plunger spring  36 ′. A bias spring  38 ′ biases check valve  28 ′ into a normally closed position. However, it should be understood that various other check ball biasing arrangements are known, and the present invention is not limited to any particular check valve configuration or arrangement for biasing the check valve. Furthermore, the check valve may be positioned to be “free” and not be biased in any direction. 
   The entry to low-pressure chamber  22 ′ is covered by a fixed web  78 . Preferably, a small-diameter passage  80  is provided through web  78  to permit air to bleed out of the HEA. 
   A first entry port  40 ′ in casting  12 ′ opens into bore  20 ′ and intersects a first annular collector groove  42 ′ which, in turn, intersects a first radial port  44 ′ in plunger body  11 ′ to supply hydraulic fluid from a first source (not shown) to an annular reservoir  76  and thence to low pressure chamber  22 ′. Thus the lash-adjusting mechanism is supplied from a first hydraulic fluid source, for example an engine oil pump, and functions conventionally to eliminate lash in the valve train. 
   A second entry port  46 ′ in casting  12 ′ opens into bore  20 ′ and intersects a second collector groove  48 ′ which, in turn, intersects a second radial port  50 ′ in plunger body  11 ′ to provide hydraulic fluid from a second source (not shown) to axial second chamber  52 ′ for engaging an associated auxiliary valve actuation system such as, for example, a variable valve deactivation rocker arm assembly (not shown). The surface of the rocker arm engages a hemispherical element  54 ′ formed on the upper end of plunger assembly  14 ′, hydraulic fluid being passable through central opening  55 ′. Thus the axial chamber  52 ′ is supplied from a second hydraulic fluid source, for example, a controlled split of flow from an engine oil pump, and functions conventionally to activate or deactivate the auxiliary valve actuation system. 
   First element  74  is provided with an annular groove  77  which is positioned axially to overlap annular reservoir  76  after assembly of plunger assembly  14 ′. A compressible expansion ring  79  in groove  77  snaps into reservoir  76 , locking HEA  21 ′ into plunger body  11 . 
   In operation, hydraulic fluid for lash adjustment is provided from a first source at a first pressure to low-pressure chamber  22 ′ via port  40 ′, annular collector groove  42 ′, and reservoir  70 . Preferably, this fluid pressure is continuously available during operation of the associated engine. Lash adjustment spring  36 ′ urges second element  72  away from bottom  75  and thereby urges plunger body  11  axially of lifter body  12 ′ until mechanical lash is removed from the valve train. The pressure of hydraulic fluid in chamber  22 ′ overcomes bias spring  38 ′ and fills high-pressure chamber  26 ′, conventionally making lash adjuster  10 ′ hydraulically rigid. When the engine control module signals the need to engage the auxiliary valve actuation system, hydraulic fluid is provided from a second source, which may be at a higher pressure than fluid from the first source, through port  46 ′, annular collector groove  48 ′, port  50 ′, chamber  52 ′, and opening  55 ′ to the auxiliary valve actuation system. When engagement of the auxiliary valve actuation system is no longer required, the second source is shut off from HLA  10 ′, and pressure is relieved via leakage at mechanical joints in the valve train, such as at surface  54 ′, and hydraulic fluid drains to a sump (not shown). 
   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.