Abstract:
A hydraulic lash adjuster ( 17;61;81 ) in which the body ( 19 ) defines a body bore ( 39 ) extending over substantially the entire axial length of the body, thus making it possible to finish the bore ( 39 ) by a more accurate process, such as honing. In the FIG.  2  embodiment, there is a cylindrical member ( 71 ) disposed in the lower portion of the body bore ( 39 ) cooperating to define a leakdown clearance ( 39,71  S), to isolate side load on the plunger ( 25 ) the leakdown. In the FIG.  3  embodiment, there is both the leakdown clearance ( 23 S, 39 ) between the body bore and the plunger ( 23 ) and the leakdown clearance ( 39,71  S) between the body bore and the cylindrical member ( 71 ), the leakdown flow rate of FIG.  3  being variable if the body and the cylindrical member ( 71 ) comprise dissimilar metals, having different coefficients of thermal expansion.

Description:
BACKGROUND OF THE DISCLOSURE 
   The present invention relates generally to hydraulic lash adjusters, and more particularly, to a hydraulic lash adjuster (HLA) of the type in which there is both a high pressure chamber and a low pressure (reservoir) chamber. 
   Hydraulic lash adjusters (also sometimes referred to as “lifters” or “lash compensation devices”) for internal combustion engines have been in use for many years, and serve to eliminate the clearance (or lash) between engine valve train components under varying operating conditions, in order to maintain efficiency and to reduce noise and wear in the valve train. An HLA operates on the principal of transmitting the energy of the valve actuating cam through hydraulic fluid, trapped in a high pressure chamber under a plunger. During each operating cycle of the cam, as the length of the valve actuating components varies, as a result of temperature changes and wear, small quantities of hydraulic fluid are permitted to enter the pressure chamber, or escape therefrom, thus effecting an adjustment of the position of the plunger, and consequently adjusting the effective total length of the valve train. 
   The typical, prior art HLA comprises a generally cylindrical, cup-shaped body member which is disposed within a cylindrical bore defined by the engine cylinder head. Disposed within the body is a plunger assembly which is slidingly received within a blind bore defined by the body member. The lower end of the plunger assembly cooperates with the blind bore to define the high pressure chamber. In the conventional HLA, when a load is applied to the plunger assembly (from the cam profile, by means of a rocker arm), the load increases the pressure of the hydraulic fluid within the high pressure chamber, and fluid escapes the high pressure chamber through a cylindrical clearance defined between the blind bore and the outer cylindrical surface of the plunger. An HLA of the type described is referred to as a “conventional leakdown” lash adjuster. Although the present invention could be utilized in conjunction with various other types of HLA, it is especially adapted for use in an HLA of the conventional leak-down type, and will be described in connection therewith. 
   In a conventional leakdown HLA, in which the leakdown clearance is defined between the body bore and the plunger outer surface, it is understood by those skilled in the art that the diameter of the blind bore defined by the body must be maintained within a very tight tolerance range. Typically, the final step in machining/sizing the body bore is a grinding operation which, as is well known to those skilled in the art, tends to be a fairly expensive operation, in part because of the cup-shape of the body. Even after such an expensive grinding operation on the body bore, it is typical in the HLA art that the bodies and plungers are “sized and sorted” with regard to the body bore inner diameter and the plunger outer diameter, in order that, after assembly, each body-and-plunger pair has a leakdown clearance within the desire tolerance range. Even after the size and sort operation, and the match fitting of the plunger and body, it is fairly common to have leakdown performance outside of the tolerance range. When such unacceptable performance is identified, subsequent to assembly, it is then necessary to dis-assemble the HLA, and re-assemble the body and plunger from that HLA with other components, in an attempt to achieve HLA performance within the tolerance range. All of that type of “re-work” is time consuming and expensive, and should be avoided to the extent possible. 
   Those skilled in the art of hydraulic lash adjusters understand that, even though the rocker arm imposes a generally axial load on the plunger of an HLA, there is typically also a side load component applied to the plunger. As is also now well known, any such side load imposed on the plunger will effectively change the leakdown clearance between the body and the plunger, thus resulting in undesirable variations in the leakdown performance of the HLA. 
   BRIEF SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide an improved hydraulic lash adjuster which makes it possible to substantially reduce the cost of machining and sizing the body bore, and substantially eliminates, or at least reduces, the need for the above-described size-and-sort operation. 
   It is a more specific object of the present invention to provide an improved hydraulic lash adjuster which accomplishes the above-stated objects, and which makes it possible, if desirable, to separate the leakdown function of the HLA from the side load imposed on the plunger assembly. 
   It is another object of the present invention to provide an improved hydraulic lash adjuster which accomplishes the above-stated objects, and also makes it feasible to provide a leakdown rate which varies, such as with changes in the temperature of the engine oil. 
   The above and other objects of the invention are accomplished by the provision of an improved hydraulic lash adjuster adapted to be disposed within a bore defined in an internal combustion engine, the lash adjuster comprising a body disposed within the bore defined in the engine, the body defining a generally cylindrical body bore, and a fluid port in communication with a source of fluid pressure. A plunger assembly includes a plunger member slidingly received within the body bore, and cooperating therewith to define a pressure chamber, the plunger assembly including a reservoir chamber in fluid communication with the fluid port. A biasing means normally urges the plunger assembly outward of the body bore, the plunger assembly including a portion adapted for engagement with an adjacent surface of a valve train component. A generally cylindrical member is disposed within a lower end of the body bore, the biasing means having a lower end thereof seated relative to the cylindrical member. The plunger assembly includes check valve means operable to control fluid communication between the reservoir chamber and the pressure chamber in response to the pressure difference therebetween. 
   The improved hydraulic lash adjuster is characterized by the body bore extending over the entire axial length of the body. The body bore and one of the plunger member and the cylindrical member cooperate to define a leakdown clearance, permitting fluid communication from the pressure chamber to the reservoir chamber, in response to movement of the plunger assembly inward of the body bore. 
   In accordance with a more limited aspect of the present invention, the body bore and the generally cylindrical member cooperate to define the leakdown clearance, the plunger member defining a radial fluid passage permitting fluid flow from between the bore defined in the engine and the body, through the fluid port, then through the radial fluid passage into the reservoir chamber. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a fragmentary, axial cross-section through one embodiment of the present invention. 
       FIG. 2  is a fragmentary, axial cross-section, on a slightly larger scale than  FIG. 1 , showing an alternative embodiment of the present invention. 
       FIG. 3  is a fragmentary, axial cross-section, on approximately the same scale as  FIG. 2 , showing another alternative embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawings, which are not intended to limit the present invention,  FIG. 1  is a fragmentary, axial cross-section through a cylinder head  11  which defines a generally cylindrical bore  13 . The bore  13  is referred to hereinafter in the appended claims as the “bore defined within the engine”, it being understood that the bore  13  would typically, but not necessarily, be defined by the cylinder head  11 . The cylinder head  11  defines a fluid passage  15  which intersects the bore  13  and comprises, for purposes of the subsequent description of the invention and the appended claims, a “source of fluid pressure”. As is known in the art, the fluid passage  15  would typically be in fluid communication with the engine lubrication circuit. 
   Disposed within the bore  13  defined within the engine is a hydraulic lash adjuster, generally designated  17 , which comprises a body  19  and a plunger assembly, generally designated  21 . It should be noted that, for ease of illustration, there appears to be a radial gap between the cylindrical bore  13  and an outer cylindrical surface of the body  19 , whereas, in reality, there would be a fairly close, sliding fit between the bore  13  and the body  19 , as is already well known to those skilled in the HLA art. 
   The plunger assembly  21  includes a generally cylindrical plunger member  23 , which is slidingly received within the body  19 , as was mentioned previously. The plunger member  23  includes, at its upper end in  FIG. 1 , a ball plunger portion  25  which would typically be in engagement with a mating surface of a valve train component, such as a rocker arm (not shown herein) in a manner well known to those skilled in the art, and which forms no part of the present invention. Disposed within the plunger member  23  is a low pressure reservoir chamber  27 . 
   Disposed within a lower end of the plunger member  23 , and comprising part of the plunger assembly  21 , is a check valve assembly, generally designated  29 , which includes a seat member  31 , against which is seated a check ball  33 . Beneath the check ball  33  is a retainer member  35 , against which is seated a compression spring  37 , biasing the check ball  33  toward engagement with the seat member  31 . Although it is conventional for an HLA to include a check valve assembly, it should be understood that the present invention is not limited to any particular type or configuration of check valve assembly. For example, although the check valve assembly  29  shown in  FIG. 1  is of the “normally biased closed” type, it would also be within the scope of the invention to utilize a check valve assembly of the “normally biased open” type or of the “free ball” type in which there is no spring biasing the check ball, toward either a closed position or toward an open position. 
   Referring still primarily to  FIG. 1 , and in accordance with one important aspect of the invention, the body  19  defines a body bore  39  which is substantially cylindrical, and extends over substantially the entire axial length of the body  19 , i.e., the diameter of the body bore  39  is the same over the entire axial length of the body bore  39 . It should be noted in  FIG. 1  that the body bore  39  is slightly shorter, axially, than the body  19  because, at the upper axial end of the body  19  is a retainer  41 , seated within an annular groove defined by the body  19 . Similarly, at the lower axial end of the body  19  there is a C-clip  43  disposed within an annular groove defined by the body  19 , for reasons which will be explained subsequently. However, for purposes of the present invention and the appended claims, the body bore  39  shown in  FIG. 1  extends “over substantially the entire axial length” of the body  19 . 
   It is one important advantage of the present invention that, because the body  19  is not cup-shaped as in the prior art, but instead, is tubular and open from both ends, it is possible to finish machining and sizing the body bore  39  by means of a honing operation. As was mentioned in the BACKGROUND OF THE DISCLOSURE, in the case of the typical, prior art, cup-shaped HLA body, it was necessary to perform a relatively more expensive grinding operation in order to finish machine the body bore. The ability to utilize a finishing process such as honing, in accordance with the present invention, provides a substantial improvement in the overall manufacturing process for making high quality, cost-effective (closer tolerance) hydraulic lash adjusters. 
   In a manner which is now well known to those skilled in the HLA art, but is not essential to the invention, the body  19  defines, about its outer periphery, a cylindrical recess  45  which is positioned to be in continuous, open fluid communication with the fluid passage  15 . The body  19  also defines a radial fluid port  47 , in communication with the recess  45 , and similarly, the plunger member  23  defines a radial fluid port  49 , such that the reservoir chamber  27  is in continuous fluid communication with the source of the fluid pressure, i.e., the fluid passage  15 . 
   Disposed within a lower axial end of the body bore  39  of the body  19  is a generally cylindrical member  51  which, in the subject embodiment, is somewhat cup-shaped and has disposed therein a stamped retainer member  53 , which serves several purposes. One purpose for the retainer  53  is to maintain a seal member  55  in engagement with the axially upper portion of the cylindrical member  51 , and in sealing engagement with the body bore  39 . In addition, the retainer  53  serves as a seat, against which is disposed the lower axial end of a compression spring  57  (also referred to as a “plunger spring”), the upper end of which is seated against the retainer member  35 . As is well known to those skilled in the art, the primary function of the compression spring  57  is to normally bias the plunger assembly  21  “outward” of the body bore  39 , i.e., in an upward direction in  FIG. 1 . The region within the body bore  39 , disposed axially between the plunger assembly  21  and the cylindrical member  51  (i.e., the region surrounding the spring  57 ) comprises a pressure chamber  59 , such that the check ball  33  controls fluid flow between the low pressure reservoir chamber  27  and the pressure chamber  59 , in response to the pressure differential therebetween, in a manner which is typical and is now well known to those skilled in the HLA art. 
   As was mentioned previously, the seal member  55  engages, and seals against, the body bore  39 , thus preventing any substantial flow or leakage of fluid from the pressure chamber  59 , past the cylindrical member  51  into the cylindrical bore  13  surrounding the HLA  17 . Instead, in the embodiment of  FIG. 1 , the body bore  39  and an outer cylindrical surface  23 S, of the plunger member  23 , cooperate to define a conventional leakdown path which will be referred to by the reference numerals of the surfaces which define the leakdown path, such that the leakdown path is hereinafter referenced as “ 23 S, 39 ”. Therefore, the embodiment of  FIG. 1  is fairly conventional in its operation, but, as was explained previously, would be substantially more cost-effective to manufacture, because of the ability to finish machine and size the body bore  39  by means of an operation such as honing. Thus, after the size and sort operation involving the body  19  and the plunger member  23 , there should be substantially less re-work, utilizing the present invention, than was previously required. 
   Referring now primarily to  FIG. 2 , there is illustrated an alternative embodiment of the present invention, in which like elements bear like numerals, and new, or substantially modified elements bear reference numerals in excess of “ 60 ”. Therefore,  FIG. 2  illustrates a modified HLA, generally designated  61 , having a plunger assembly  63 , including a plunger member  65  which defines the ball plunger portion  25 . Disposed at the lower end of the plunger member  65  is the check valve assembly  29  which, in the embodiment of  FIG. 2 , merely has a different configuration of a seat member  67 . One reason for the difference in the configuration of the seat member  67  is that, trapped between the lower end of the plunger member  65  and a shoulder defined by the seat member  67  is a seal member  69 , the function of which is to prevent any substantial flow of fluid from the pressure chamber  59  upward in  FIG. 2  between the body bore  39  and the outer cylindrical surface of the plunger member  65 , for reasons which will be explained subsequently. 
   Referring still primarily to  FIG. 2 , it may be seen that the body  19  may be substantially identical to the body  19  of the  FIG. 1  embodiment although, as shown in  FIG. 2 , the body  19  does not include the annular groove in which is disposed the retainer  41  of the  FIG. 1  embodiment. However, as will be understood by those skilled in the art, the presence or absence of the retainer  41  in either of the embodiments is not in any way essential to the practice of the present invention. 
   Disposed within the lower end of the body bore  39  is a generally cylindrical member  71  which includes, toward its upper end, a generally cup-shaped portion in which is disposed the lower end of the compression spring  57 , in the same general manner as in the  FIG. 1  embodiment. As was described in connection with the  FIG. 1  embodiment, the body bore  39  in the  FIG. 2  embodiment may be machined and finished in a more cost-effective manner, such as by honing, for reasons which were described previously. One difference in the  FIG. 2  embodiment is that, because the plunger member  65  does not cooperate with the body bore  39  to define a leakdown clearance (but instead, such flow is prevented by the seal member  69 ), there can be a much looser tolerance associated with the outer surface of the plunger member  65 . Furthermore, any side load applied to the plunger member  65  as a result of the engagement of components such as a rocker arm with the ball plunger portion  25 , will not affect the leakdown clearance, and therefore, will not affect the leakdown rate. In accordance with one important aspect of the  FIG. 2  embodiment, the part of the HLA  61  which is subjected to side loading is separated from that portion which defines the leakdown clearance. 
   Therefore, in accordance with another important aspect of the  FIG. 2  embodiment, the generally cylindrical member  71  defines a cylindrical outer surface  71 S, and the body bore  39  and the outer cylindrical surface  71 S cooperate to define a leakdown path, which will hereinafter be referred to as “ 39 , 71 S”. During operation of the engine, when the rocker arm or other engine component applies an axial loading to the ball plunger portion  25 , causing an increase in fluid pressure in the pressure chamber  59 , there will be a controlled flow of leakage fluid from the pressure chamber  59  through the leakdown path  39 , 71 S into the lower portion of the cylindrical bore  13 . Fluid exiting the leakdown path will then flow between bore  13  and the body  19 , in an upward direction in  FIG. 2 , then will flow radially inward through the fluid ports  47  and  49  into the low pressure reservoir chamber  27 . 
   Referring now primarily to  FIG. 3 , there is illustrated another alternative embodiment of the present invention, in which like elements bear like numerals, and new, or substantially modified elements bear reference numerals in excess of “ 80 ”.  FIG. 3  illustrates a modified HLA, generally designated  81 , in which the body  19  may be substantially the same as in either of the earlier embodiments, and the plunger assembly  21  of the first embodiment is included, including the check valve assembly  29  shown in  FIG. 1 . Therefore, in the  FIG. 3  version, there is a conventional leakdown clearance  23 S, 39 , as described previously in connection with the  FIG. 1  embodiment. 
   In the  FIG. 3  alternative embodiment, instead of the generally cylindrical member  51  of the  FIG. 1  version, the generally cylindrical member  71  of the  FIG. 2  embodiment is included. As a result, there is also a leakdown clearance  39 , 71 S defined between the lower portion of the body  19  and the cylindrical member  71 , as in the  FIG. 2  embodiment. 
   However, in accordance with a further aspect of the present invention, in the  FIG. 3  embodiment, the cylindrical member  71  comprises a different material than does the body  19 . By means of example only, the body  19  typically comprises a low carbon steel, and in the subject embodiment, the cylindrical member  71  of  FIG. 3  comprises a material such as bronze, having a substantially different coefficient of thermal expansion than the steel body  19 . Those skilled in the art will understand that none of the embodiments of the invention are limited to any particular material, except as specifically otherwise recited in the appended claims. 
   Specifically, in the  FIG. 3  embodiment, the materials utilized for the body  19  and the cylindrical member  71  are selected such that the cylindrical member  71  has at least a somewhat greater coefficient of thermal expansion. As a result, and by way of example only, the dimension of the body bore  39  and the cylindrical member  71  are selected such that, when the engine oil is cold (room temperature), the leakdown clearance  39 , 71 S is about two-thirds of the total leakdown clearance, with the leakdown clearance  23 S, 39  comprising the other one-third. Then, as the engine begins to operate, and the engine oil gets warmer, the cylindrical member  71  of the  FIG. 3  version begins to grow at a faster rate than does the body  19 . Thus, the leakdown clearance  39 , 71 S begins to decrease, and that process continues until the engine oil achieves its maximum (normal) operating temperature. The material and dimensions for the cylindrical member  71  may be selected such that, at maximum oil temperature, the leakdown clearance  39 , 71 S decreases, approaching (and possibly even reaching) a zero clearance condition. When that occurs, only the leakdown clearance  23 S, 39  remains open and in effect, such that (in accordance with the example above), the total leakdown flow at maximum oil temperature is only about one-third of the leakdown flow at cold (start-up) temperature. It is believed that the  FIG. 3  version may therefore be of benefit in dealing with situations such as CSSR (“cold start spark retard”). 
   Thus, it may be seen that the present invention provides a series of benefits, and a hydraulic lash adjuster may, in accordance with the present invention, be designed to take advantage of only some of the benefits, such as more accurate finishing of the body bore  39  and less re-work ( FIG. 1  embodiment), or the HLA may be designed also to take advantage of the ability to separate the side load on the ball plunger from the leakdown clearance ( FIG. 2  embodiment). Finally, the HLA may be designed to take advantage of the benefit of less re-work while also having the capability of total leakdown flow being variable, in response to variations in the temperature of the engine oil ( FIG. 3  embodiment). 
   The invention has been described in great detail in the foregoing specification, and it is believed that various alterations and modifications of the invention will become apparent to those skilled in the art from a reading and understanding of the specification. It is intended that all such alterations and modifications are included in the invention, insofar as they come within the scope of the appended claims.