Patent Application
20050188938
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'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.
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.
Referring now to the drawings, which are not intended to limit the invention,
The HLA 11, as shown in
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
Referring now primarily to
Referring still to
Referring now primarily to
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 41S. Therefore, the check valve cartridge 17B 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 17A 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 17B 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 (17A or 17B) 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 (17A) 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 (17B) 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
Referring now primarily to
Referring now primarily to
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 15A and 15B, or both of the long plungers 15C and 15D. 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 15A and 15B 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 15C and 15D 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 13A and long bodies 13B would be formed and machined, etc., and sent to the HLA assembly area, and the short plungers 15A and 15B and the long plungers 15C and 15D would also be formed and machined, etc. and also sent to the HLA assembly area. After the check valve cartridges 17A and 17B 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
For example, the assembly operator would select one of the long bodies 13B, as shown in
Although, for ease and simplicity of illustration, only two bodies (13A and 13B) 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 17B could be assembled into a plurality of the short plungers 15B, and then these cartridge-plungers combinations installed in the bodies of deactivating HLA'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 17A or 17B, 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.
