Patent Application
20110061615
The present invention relates to valve train members such as hydraulic lash adjusters (HLAs) for supporting roller finger followers in overhead-camshaft valvetrains in internal combustion engines; more particularly, to such HLAs having means for selectively engaging and disengaging activation of valves in valvetrains; and most particularly, to apparatus and method for setting internal mechanical lash in a deactivating hydraulic lash adjuster (DHLA).
It is well known that overall fuel efficiency in a multiple-cylinder internal combustion engine can be increased by selective deactivation of one or more of the engine valves, under certain engine load conditions. For example, for an overhead-cam engine, a known approach to providing selective deactivation is to equip a valvetrain member such as the hydraulic lash adjusters for the overhead-cam engine valvetrains with means whereby the roller finger followers (RFFs) may be rendered incapable of transferring the cyclic motion of engine cams into reciprocal motion of the associated valves. Typically, a DHLA includes, in addition to the conventional hydraulic lash adjuster, a concentric inner pin housing and outer HLA body which are mechanically responsive to the force of the RFF as exerted by the cam lobe, and which may be selectively latched and unlatched hydromechanically to each other, typically by the selective engagement of pressurized engine oil on locking pins.
An important consideration in a DHLA is the amount of internal mechanical lash deliberately incorporated into the DHLA. In prior art DHLAs, a transverse bore in the pin housing contains the two opposed locking pins which are urged outwards of the pin housing by a pin-locking spring disposed in compression therebetween to engage a first annular groove including a locking surface (also referred to herein as “pin shelf”) in the inner wall of the HLA body whereby the HLA body and the pin housing are locked together to produce reciprocal motion of an RFF disposed on the DHLA. When valve deactivation is desired, the pins are withdrawn from the DHLA body by application of hydraulic fluid such as engine oil to the outer ends of the pins at pressure sufficient to overcome the force of the pin-locking spring.
Prior art DHLAs also are assembled from a top end of the DHLA body (which is closed at its bottom end) by insertion of components through the open top end and securing the components with one or more retaining rings into a second annular groove formed in the inner wall of the DHLA body near the open end thereof. The rings used to secure the components also serve to set internal mechanical lash in the DHLA by the selection of rings of appropriate thickness during assembly of the DHLA. Thus, the rings act as a mechanical stop to limit the outward motion of the pin housing prior to engagement and disengagement of the locking pins. With the lost motion springs applying an upward force on the pin housing to force the top surface of the ring against the top of the annular groove, the lash rings permit the pin housing to travel to a position wherein the locking pins can clear the bottom surface, or pin shelf, of the locking groove in the DHLA body by a small amount, typically about 0.005 inches or less. Excess clearance or internal mechanical lash results in clatter and wear of the DHLA during engine operation. Variations in internal mechanical lash can also adversely affect the opening and/or closing timing of the associated valve. Thus, the axial position of the underside of the retaining rings with respect to the locking groove pin shelf is of critical importance.
Typically, because of variation in manufacturing tolerances of the body, pin housing, and pins, the correct lash is obtained only by iterative trial and measurement using lash-adjusting rings of differing thicknesses. Setting the lash in this fashion is difficult and complicated. Moreover, since setting lash in this fashion relies on the machined integrity of the top surface of the annular groove, machining difficulties inherent in forming the top surface of the groove can result in unnecessary variances in mechanical lash settings.
What is needed in the art is an improved DHLA wherein components are easily assembled and wherein mechanical lash is easily set in a single, simple procedure.
It is a principal object of the present invention to reduce the cost and complexity of an improved DHLA, and to improve the ease and reliability of assembly thereof.
Briefly described, a DHLA in accordance with the present invention comprises a conventional hydraulic lash adjustment mechanism within a plunger slidably disposed within a pin housing that is slidably disposed within an axial bore in an adjuster body. A transverse bore in the pin housing contains two opposed, selectively-retractable locking pins that engage a lower annular groove including a locking surface in the adjuster body whereby the lash adjuster body and the pin housing are locked together for mutual actuation by rotary motion of the cam lobe to produce reciprocal motion of an engine RFF pivotably disposed on a domed head of the plunger.
A lash ring disposed in an annular groove near the outer end of the DHLA body includes a first portion extending into the bore in the DHLA body to engage the pin housing. The lash ring thus functions to limit the travel of the pin housing within the DHLA body and thereby sets the internal mechanical lash in the deactivation mechanism. The first portion of the lash ring has a thickness selected to provide a predetermined amount of mechanical lash in the assembled lifter to ensure facile engagement and disengagement of the locking pins in the lifter body. Preferably, the lash ring is provided as a single ring having a first portion of a desired thickness, which thickness varies from assembly to assembly to compensate for manufacturing variation in the components. A biasing means is also installed in the second annular groove to urge the lash ring against the lower face of the groove under all DHLA operating conditions.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
a is a top view of an exemplar gage tool, in accordance with the invention, superimposed on a profile of the offset lash ring shown in
b and 6c are enlarged cross-sections of two exemplar gage tools, in accordance with the invention, taken along line 6B/6C-6B/6C of
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.
Referring to
Groove 30 further defines a reservoir for providing high pressure oil against the outer ends 36 of locking pins 26 to overcome spring 28 and retract the locking pins into bore 24, thereby unlocking the pin housing from the adjuster body to deactivate the DHLA. In use, groove 30 is in communication via at least one port 38 with an oil gallery (not shown) in an engine 40, which in turn is supplied with high pressure oil by an engine control module (not shown) under predetermined engine parameters in which deactivation of valves is desired.
Plunger 20 includes a hydraulic element assembly (HEA) 42 lodged at an inner end thereof. The arrangement of components and operation of hydraulic lash adjuster elements such as HEA 42 has been well known in the prior art for many years. HEA 42 comprises a spring loaded check ball 44 lodged against a seat 46 formed in plunger 20 separating a low-pressure oil reservoir 48 from a high-pressure chamber 50 formed between HEA 42 and pin housing 14. Oil is supplied to annular chamber 51 from an engine oil gallery (not shown) via port 54 in adjuster body 12. Chamber 51 is also in communication with reservoir 48 via port 56 and annular groove 58 in pin housing 14 and port 62 in plunger 20. Oil may be supplied from reservoir 48 to an associated roller finger follower (not shown) via port 52 in the end 22 of plunger 20.
In operation, prior art DHLA 10 is disposed in a bore in engine 40 such that housing 12 remains stationary. When the associated cam and RFF (not shown) exert force on plunger end 22, in lost motion (valve-deactivation) mode, plunger 20 and pin housing 14 are forced into adjuster body 12 in a lost-motion stroke, compressing spring 34.
Of particular interest to the present invention is the means by which the outward stroke of pin housing 14 is limited in prior art body 12. An annular groove 64 formed in bore 16 near the outer end thereof receives a retaining clip 66 that extends into bore 66 to engage shoulder 68 of pin housing 14. The axial thickness 70 of clip 16 is selected from a family of such clips having differing thicknesses to set the amount of axial mechanical lash 72 in DHLA 10. As described above, the amount of lash 72 is an important manufacturing parameter which must be calibrated for each DHLA assembly because of manufacturing variability in the length 74 from shoulder 68 to the lower edge 76 of pins 26, and length 78 from the upper face 80 of groove 64 to the lower face 82 of groove 30. (Lower face 82 is also known in the art as a “pin shelf” for lock pins 26.) The trial-and-error method of assembly, measurement, disassembly, reassembly, and re-measurement is time-consuming, costly, and difficult when using prior art groove 64 and clip 66.
Referring to
As described above, the amount of mechanical lash 172 (also referred herein as desired mechanical lash) is an important manufacturing parameter which must be calibrated for each DHLA assembly because of manufacturing variability in the length 174 from shoulder 168 of pin housing 114 to the lower edge 176 of locking pins 126.
A lash ring 166, of a selectable size, is retained in groove 164 in body 112 by a resilient biasing member 165 such as a Belleville washer, or preferably a wave ring. Lash ring 166 includes a first portion such a collar 169 having a length 171, and first and second surfaces 175, 177.
After pin housing 114 is installed in body 112 as in the prior art, a method for setting mechanical lash in an individual DHLA 110 consists in the following steps.
First, a gage tool 173, 173′ (
Wave ring 165 is selected to preload lash ring 166 and to apply a clamping force on lash ring 166 that is greater than the installed load of the lost motion spring(s) 134 to keep lash ring 166 seated against bottom surface 167 of groove 164 during use of DHLA 110. Suitable wave rings are commercially available from, for example, Smalley Steel Ring Co, Inc., Lake Zurich, Ill., USA. Alternatively, a Belleville washer may be used, such as is available from Mubea Inc., Florence, Ky., USA.
The improved arrangement in accordance with the present invention changes the precision feature of ring groove 164 to bottom surface 167 rather than the top face 180 as in the prior art (
Note also that preferably, the outer diameter 181 of lash ring 166 is less than the inner diameter 183 of the opening of body 112 (
In an alternate embodiment, wave ring 165 may be substituted with internal split beveled retaining ring 265 as shown in
While the invention described herein relates to setting of the mechanical lash of a DHLA, it is understood that the invention may be used in any deactivating valvetrain member such as, for example, a deactivating valve lifter.
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.
