Abstract:
A hydraulic lash adjuster ( 11 ) for an internal combustion engine, and an improved method of assembly of such a lash adjuster. The lash adjuster ( 11 ) is of the type having a body ( 13 ), a plunger ( 15 ), and a check valve assembly ( 17 ). In accordance with one aspect of the invention, the check valve assembly comprises a cartridge ( 17 A; 17 B) comprising a member ( 27;41 ) separate from the plunger ( 15 ) and defining a valve seat ( 27 S; 41 S). The check valve cartridge is capable of being assembled and tested for compliance with a predetermined relationship of flow versus pressure differential, prior to assembly into the plunger ( 15 ). In accordance with the improved method of assembly, a plurality of different bodies ( 13 A; 13 B) and plungers ( 15 A; 15 B; 15 C; 15 D) is provided, as well as a plurality of different, interchangeable check valve cartridges ( 17 A; 17 B), and the assembly operator selects a body, a plunger, and a cartridge to provide an assembled lash adjuster having the predetermined, desired operating parameters.

Description:
BACKGROUND OF THE DISCLOSURE 
   The present invention relates to hydraulic lash adjusters for internal combustion engines, and more particularly, to an improved check valve assembly for use in such lash adjusters, and to an improved method of assembling such lash adjusters. 
   In a conventional hydraulic lash adjuster (HLA) of the type to which the present invention relates, there is an outer body, which is typically disposed within a mating bore in the engine cylinder head, and disposed within the body is an output plunger assembly engaging a rocker arm. The output plunger assembly may be of either a one-piece or a two-piece construction, and typically, includes a ball plunger element which engages a socket formed in an “underside” surface of the rocker arm. A blind bore formed within the body cooperates with the plunger assembly to define a high pressure chamber, as is well known to those skilled in the art. There is normally a biasing spring seated within the high pressure chamber, biasing the plunger “outward” of the body bore (toward the rocker arm), as is also well known in the HLA art. 
   Most HLA&#39;s which are sold commercially are of the “conventional leakdown” type, in which the radial clearance space between the outer diameter of the plunger and the inner diameter of the body bore forms a leakdown path. This leakdown path (or clearance) permits communication of fluid from the high pressure chamber, through the leakdown clearance, and into the reservoir (or “low pressure” chamber) of the HLA whenever an axial force is transmitted from the rocker arm to the ball plunger. 
   As is well known to those skilled in the art, one of the key performance criteria of an HLA is the “leakdown” performance of the HLA, i.e., the leakdown flow and resulting plunger assembly travel, as a function of time, for a given force applied to the plunger assembly. For any given engine application, the HLA must provide a leakdown performance which is within a predetermined, specified tolerance range, in order for the HLA to be acceptable for assembly into the engine cylinder head, and in order for the engine valve gear train to operate in a manner which is satisfactory. 
   In a typical HLA, there is included a check valve assembly, disposed between the high pressure chamber and the low pressure (reservoir) chamber, and operable to control (either to block or to permit) fluid communication between those two chambers, in response to the instantaneous pressure differential between the chambers. Therefore, in the typical HLA, the lower end of the plunger assembly defines a check valve seat, and prior to insertion of the plunger assembly into the HLA body, the check valve assembly (typically consisting of a check ball, a spring, and some sort of retainer) is assembled to the lower end of the plunger assembly. 
   As is also well known to those skilled in the art, another of the key performance criteria for an HLA is the check valve assembly performance, in terms of the rate of fluid flow from the low pressure chamber into the high pressure chamber (or vice versa), in response to a particular pressure differential between the chambers. Again, for any given engine application, the HLA must provide a check valve assembly performance which is within a predetermined, specified tolerance range, in order for the HLA to be acceptable for assembly into the engine cylinder head, and in order for the engine valve gear train to operate in manner which is satisfactory. 
   Unfortunately, it occurs periodically that after the HLA is completely assembled, performance testing of the HLA shows that, either the leakdown performance or the check valve assembly performance is not within the specified, permissible limits. When such unacceptable performance occurs, the entire HLA is then either scrapped, (thus wasting several parts of the HLA which, individually, may have been acceptable parts, and therefore, wasting the material, labor and machining costs associated with those parts), or the HLA is sent through some sort of rework process, wherein parts are disassembled, re-inspected, re-sized, and re-assembled. Such a rework process is not only time-consuming, but is also quite expensive. 
   Although an HLA manufacturer normally produces several different, standard HLA models, each in relatively large volume, it is quite common for an engine manufacturer to request or need an HLA which is nearly identical to one of the standard models, but differs in respect to perhaps only one of the performance criteria, such as the leakdown performance, or the check valve performance, or the plunger travel. When the HLA manufacturer has the opportunity to make and sell such a non-standard HLA, it is then necessary for the HLA manufacturer to design (and provide tooling for) the non-standard part of the HLA, and design and test what then is effectively a whole new HLA design, and a different part number, even though the resulting HLA may have much commonality with an existing model. This approach to designing and manufacturing new HLA models adds substantially to the overall cost of manufacture of the HLA and the lead time to produce the required, non-standard HLA. 
   BRIEF SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide an improved hydraulic lash adjuster, and an improved method for assembling such a lash adjuster, which makes it possible to verify the proper performance of the check valve assembly prior to assembly of the entire HLA. 
   It is another object of the present invention to provide an improved HLA, and an improved method of assembly thereof, in which the performance of the check valve assembly and the leakdown performance each may be changed, independently of the other, without designing and tooling an entirely new HLA. 
   It is another, related object of the present invention to provide an improved HLA, and a method of assembly thereof, which greatly facilitates the design and production of an HLA which varies, in perhaps only one aspect or performance criteria, from a standard HLA model already designed and tooled and, possibly in production. 
   The above and other objects of the invention are accomplished by an improved hydraulic lash adjuster for an internal combustion engine, the lash adjuster comprising a body defining a bore therein, a plunger slidingly received within the bore and defining a fluid chamber, the plunger and the bore cooperating to define a pressure chamber, and biasing means normally urging the plunger outward of the bore. The body and the plunger cooperate to define a leakdown clearance providing fluid communication between the pressure chamber and the fluid chamber. A check valve assembly is operably associated with the plunger for permitting or blocking fluid communication between the fluid chamber and the pressure chamber in response to changes in the pressure difference between the chambers. The check valve assembly has a predetermined relationship of permitted fluid communication versus pressure difference. 
   The improved hydraulic lash adjuster is characterized by the check valve assembly comprising a member, separate from the plunger, the member defining a valve seat. The check valve assembly further comprises a valve member, a spring disposed to bias the valve member toward its normal position, and a retaining member to retain the valve member. The check valve assembly is capable of being assembled and tested for compliance with the predetermined relationship of permitted fluid communication versus pressure difference, prior to installation of the check valve assembly within the plunger. 
   In accordance with another aspect of the invention, an improved method of assembling a hydraulic lash adjuster is provided, the lash adjuster comprising a body defining a bore therein, a plunger slidingly received within the bore, and defining a fluid chamber. The plunger and the bore cooperate to define a pressure chamber, and biasing means normally urges the plunger outward of the bore. The body and the plunger cooperate to define a leakdown clearance providing fluid communication between the pressure chamber and the fluid chamber. A check valve assembly is operably associated with the plunger for permitting or blocking fluid communication between the fluid chamber and the pressure chamber in response to changes in pressure difference between the chambers. 
   The improved method of assembly is characterized by (a) providing the body defining the bore; (b) providing a plurality of check valve assemblies, including a first check valve assembly and a second check valve assembly, the first and second check valve assemblies having substantially the same exterior configuration, but differing from each other in some performance criteria; (c) providing a plurality of plungers including a first plunger having a first characteristic and a second plunger having a second characteristic; (d) selecting one of the first and second check valve assemblies; (e) selecting one of the first and second plungers and installing therein the selected check valve assembly; and (f) inserting within the bore of the body the selected plunger and check valve assembly combination. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an axial cross-section of one particular embodiment of hydraulic lash adjuster, made in accordance with the present invention. 
       FIG. 2A  is an enlarged, axial cross-section of a check valve cartridge of the normally biased-open type, which comprises one aspect of the present invention. 
       FIG. 2B  is an enlarged, axial cross-section of a check valve cartridge of the normally biased-closed type, and on the same scale as  FIG. 1 . 
       FIG. 3  is an axial cross-section of a hydraulic lash adjuster body, on a substantially smaller scale than  FIGS. 2A and 2B . 
       FIGS. 3A and 3B  are axial cross-sections of lash adjuster plungers useable with the body of  FIG. 3 , and on the same scale as  FIG. 3 . 
       FIG. 4  is an axial cross-section of a hydraulic lash adjuster body which is different than that shown in  FIG. 3 , but on the same scale. 
       FIGS. 4A and 4B  are axial cross-sections of plungers useable with the body of  FIG. 4 , and on the same scale as  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawings, which are not intended to limit the invention,  FIG. 1  is an axial cross-section of one particular embodiment of HLA, by way of example only, made in accordance with the present invention. Therefore,  FIG. 1  shows an hydraulic lash adjuster, generally designated  11 , which may be of the general type illustrated and described in U.S. Pat. No. 5,855,191, assigned to the assignee of the present invention and incorporated herein by reference. However, those skilled in the art will understand that the present invention, in each of its aspects, is not limited to the particular type of or configuration of HLA shown in  FIG. 1 , as will be explained in greater detail subsequently. 
   The HLA  11 , as shown in  FIG. 1 , may be of a general type and configuration well known to those skilled in the art (except where noted otherwise hereinafter), and will be described only briefly at this point. The HLA  11  includes a body  13  which, as noted previously, would typically be disposed within a mating bore in the engine cylinder head (not shown herein). Disposed within the body  13  is a plunger  15 , including a check valve assembly, generally designated  17 , with the combination of the plunger  15  and the check valve assembly  17  being biased in an “outward” direction (upward in  FIG. 1 ), relative to the body  13 , by means of a plunger spring  19 . It should be noted that certain reference numerals  13 ,  15 ,  17 ,  19 , and others to be introduced (with no “A” or “B”, etc., attached) will be used at various times hereinafter, and in the appended claims, to refer to the particular element, but in only a generic sense. For example, the generic body in  FIG. 1  bears the reference numeral “ 13 ”, but in  FIGS. 3 and 4 , there will be illustrated and described two specific bodies  13 A and  13 B, respectively. 
   Disposed within the plunger  15  is a fluid chamber  21  (also referred to hereinafter as a “reservoir” or a “low pressure chamber”). The body  13  and the lower end of the plunger  15  cooperate to define a high pressure chamber  23  (also referred to hereinafter, and in the appended claims, as simply the “pressure chamber”). As was mentioned previously, and as is well known to those skilled in the HLA art, the function of the check valve assembly  17  is either to permit fluid communication, or to block fluid communication, between the low pressure chamber  21  and the high pressure chamber  23 , in response to the pressure differential between the chambers  21  and  23 . 
   Disposed about the upper end of the body  13  is a cap member  25 , the function of which is to retain the plunger  15 , and limit outward movement thereof relative to the body  13 . It should be understood that the particular configuration of the cap member  25 , or even the presence of any cap member, is not an essential feature of the invention, and all that is essential to the invention (as is essential to any HLA) is that there be provided some suitable means for retaining the plunger  15  within the body  13 . 
   Referring now primarily to  FIGS. 2A and 2B , and in accordance with one important aspect of the present invention, the check valve assembly  17  shown in  FIG. 1  comprises a check valve cartridge. In accordance with a further aspect of the invention, there are multiple check valve cartridges provided, from among which one may be selected as part of the method of assembly of the HLA  11 . Therefore, but by way of example only,  FIG. 2A  illustrates a check valve cartridge  17 A, while  FIG. 2B  illustrates a check valve cartridge  17 B, it being understood that in accordance with one aspect of the invention, the check valve cartridges  17 A and  17 B are designed and produced to be “interchangeable” as that term will be explained in greater detail subsequently. One aspect of the check valve cartridges  17 A and  17 B being interchangeable is that they both have the same exterior configuration which, as may be seen by comparing  FIGS. 2A and 2B , means that the cartridges  17 A and  17 B have the same outside diameters, but clearly not the same overall lengths, at least in the subject embodiment. 
   Referring now primarily to  FIG. 2A , the check valve cartridge  17 A comprises a generally cylindrical seat member  27 , defining a check valve seat surface  27 S. Disposed about the seat member  27 , at the upper end thereof, is a seal member  29  which may comprise any of the materials now conventionally used for HLA seals. The seal member  29  is retained in place as shown in  FIG. 2A  by means of a retention and seat member  31  which, preferably, has an interference fit with the upper portion of the inside diameter of the seat member  27 . 
   Referring still to  FIG. 2A , disposed at the lower end of the seat member  27  is a retainer  33 , which would normally be crimped in place, relative to the seat member  27 , as shown in  FIG. 2A . As is well known to those skilled in the art, one function of the retainer  33  is to retain, and limit axial travel of, a check ball  35  which is biased toward an open position (away from the seat surface  27 S) by a compression spring  37 . Thus, the check valve cartridge  17 A is of the type referred to as “normally biased open”, in accordance with the teachings of U.S. Pat. No. 5,758,613, assigned to the assignee of the present invention and incorporated herein by reference. 
   Referring now primarily to  FIG. 2B , the check valve cartridge  17 B includes a seat member  41 , defining a seat surface  41 S, and disposed around the seat member  41  is a seal member which, in the subject embodiment, and by way of example only, is (or at least, may be) the same seal member  29  used in the cartridge  17 A. The seal member  29  is retained in place by means of a retention member  43  which, on its inside diameter, has an interference fit with an adjacent outer surface of the seat member  41 . 
   A retainer  45  is in engagement, such as by crimping or any other suitable means, with a lower portion of the seat member  41 . Seated against the upper surface of the retainer  45  is a compression spring  47  which engages a check ball  49  and biases it toward the seat surface  41 S. Therefore, the check valve cartridge  17 B is of the type referred to as “normally biased closed”, as has been well known in the HLA art for many years. 
   In accordance with one important aspect of the present invention, as the check valve cartridges  17 A are produced, each one may be placed in an appropriate test fixture, and subjected to one or more predetermined pressure differentials, while the test fixture measures the permitted fluid flow past the check ball  35  to verify that, for any given pressure differential, the rate of fluid flow is within the predetermined tolerance range. Similarly, as each of the check valve cartridges  17 B is produced, it may be placed in its own test fixture, and subjected to one or more pressure differentials across the check ball  49 , while the fixture measures the rate of fluid flow, again to verify that for each pressure differential, the fluid flow is within the predetermined tolerance range. 
   After each check valve cartridge ( 17 A or  17 B) is tested, if it meets all of the check valve performance criteria specified for that particular cartridge, it then proceeds to the HLA assembly area. Those cartridges which do not meet all of the performance criteria are rejected (and possibly scrapped) at this stage of the process, rather than after the entire HLA is assembled and tested, as has been the case in connection with the prior art hydraulic lash adjusters and the prior art methods of assembly thereof. 
   Although the present invention is being illustrated and described in connection with an embodiment in which one of the available check valve assemblies is normally biased open, and the other is normally biased closed, those skilled in the HLA art will recognize that the invention is not so limited. In the broadest aspects of the method of assembling an HLA, all that is essential is that at least two different check valve assemblies be available, and that the two assemblies differ from each other in some performance criteria. For example, in the HLA assembly area, there could be provided two (or more) different types of check valve cartridge, wherein both are, for example, of the normally biased open type, but wherein the first cartridge ( 17 A) has one particular check ball size and/or travel, while the second cartridge (not shown herein) has a different check ball size and/or travel. Or, as another example, there could be provided two (or more) different types of check valve cartridge wherein both are of the normally biased-closed type, but wherein one ( 17 B) has one particular bias force for the spring  47 , while the other (not shown herein) has a different bias force for the spring  47 . 
   Referring now primarily to  FIGS. 3 and 4 , there is shown in  FIG. 3  a short HLA body  13 A and there is shown in  FIG. 4  a long HLA body  13 B. By way of example only, the short body  13 A and the long body  13 B may be substantially identical, except for the overall length, and therefore each defines a body bore  51 , and in the subject embodiment, and by way of example only, the body bores  51  of both of the bodies  13 A and  13 B are identical in diameter, the significance of which will be described subsequently. 
   Referring now primarily to  FIGS. 3A and 3B , there are illustrated short plungers  15 A and  15 B, respectively which, for purposes of the present invention, may be substantially identical in parameters such as overall length, outside diameter  55 , etc. However, in the subject embodiment, and by way of example only, the short plunger  15 A defines a cartridge recess  53 A which is adapted to receive therein the check valve cartridge  17 A, shown in  FIG. 2 , while the short plunger  15 B defines a relatively shorter cartridge recess  53 B adapted to receive therein the relatively shorter check valve cartridge  17 B, shown in  FIG. 2B . As noted above, the short plunger  15 A and the short plunger  15 B could have exactly the same outside diameters  55 , in which case, each would cooperate with the body bore  51  of the short body  13 A to provide the same leakdown clearance. 
   Referring now primarily to  FIGS. 4A and 4B , there is shown a pair of long plungers  15 C and  15 D, respectively which, as was explained in connection with  FIGS. 3A and 3B , may be substantially identical to each other in terms of overall length and outside diameter  55 , but in the subject embodiment, and by way of example only, differ from each other at least in regard to the fact that the long plunger  15 C defines a cartridge recess  53 C whereas the long plunger  15 D defines a relatively shorter cartridge recess  53 D. In the subject embodiment, and by way of example only, the cartridge recess  53 C is substantially identical to the cartridge recess  53 A, and therefore, is configured to receive therein the check valve cartridge  17 A, whereas, the cartridge recess  53 D is substantially identical to the cartridge recess  53 B, and therefore, is configured to receive therein the relatively shorter check valve cartridge  17 B. 
   It should be understood by those skilled in the art that, within the scope of the invention, the different check valve cartridges could all be configured to have the same axial length, thus eliminating the need to provide both of the short plungers  15 A and  15 B, or both of the long plungers  15 C and  15 D. However, the invention is being described in connection with an embodiment in which the check valve cartridges are different (and require different plungers) to help illustrate the flexibility in design afforded by the invention. Also, and as is now well known in the HLA art, the shorter plungers  15 A and  15 B would typically be utilized in markets which require relatively less plunger travel, as is now the case normally in the European market. On the other hand, the longer plungers  15 C and  15 D would typically be utilized in markets which require relatively greater plunger travel, as is now the case normally in the North American market. 
   In accordance with another important aspect of the present invention, there is provided the ability to assemble a number of different HLA models, each being different from the others in at least one aspect of its configuration or its performance criteria, but without the cost required for each different model of HLA to be comprised of parts and components which are completely unique to that particular model. 
   Therefore, and by way of example only, the short bodies  13 A and long bodies  13 B would be formed and machined, etc., and sent to the HLA assembly area, and the short plungers  15 A and  15 B and the long plungers  15 C and  15 D would also be formed and machined, etc. and also sent to the HLA assembly area. After the check valve cartridges  17 A and  17 B are assembled and tested, those which successfully pass the performance test would be sent to the HLA assembly area as was mentioned previously. In the HLA assembly area, it is then possible to assemble a number of different HLA models utilizing those opponents shown in  FIGS. 2 through 4 . 
   For example, the assembly operator would select one of the long bodies  13 B, as shown in  FIG. 4 . The assembly operator would then select one of the check valve cartridges  17 A, and one of the long plungers which is suitable for use with the cartridge  17 A, i.e., one of the long plungers  15 C. The assembly operator would then install the selected check valve cartridge  17 A within the selected long plunger  15 C, and then install within the body  13 B the assembled cartridge-plunger sub-assembly or combination. As is well known to those skilled in the art, just prior to installing the cartridge-plunger combination, it is necessary to put in place the plunger spring  19  (shown only in  FIG. 1 ). In accordance with another aspect of this invention, there may be available to the assembly operator several different plunger springs ( 19 A and  19 B, not shown herein because both are represented generically by the spring  19  in  FIG. 1 ), each having a different biasing characteristic (for example, a different “curve” of biasing force as a function of axial compression). Thus, two different HLA models could be provided simply by having available two different plunger springs  19 . 
   Although, for ease and simplicity of illustration, only two bodies ( 13 A and  13 B) have been shown and described herein, in which the only difference between them is the length, those skilled in the art will understand that other body configurations could be utilized. For example, a plurality of the normally-closed check valve cartridges  17 B could be assembled into a plurality of the short plungers  15 B, and then these cartridge-plungers combinations installed in the bodies of deactivating HLA&#39;s of the type which are now well know to those skilled in the HLA art. 
   For each different HLA assembly to be designed and assembled, it is necessary to start by specifying the check valve cartridge type (normally-biased open; normally-biased closed, or “free ball”, as that term is understood in the art) and check valve performance. Based upon that determination, the next step is to select the appropriate check valve cartridge (either  17 A or  17 B, etc.) from among the multiple cartridge models available. Next, the designer must specify the desired leakdown performance, and based upon that, select the appropriate plunger which “accepts” the selected check valve cartridge and at the same time, cooperates with the body to be used to provide the desired leakdown performance. The invention has been illustrated and described based upon the assumption that the different desired leakdown clearances may be achieved by selecting from among several different plungers, having slightly different diameters. However, it should be apparent that the same result could be achieved by having available several different bodies, each having a slightly different body bore diameter. 
   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.