Apparatus and method for setting mechanical lash in a valve-deactivating hydraulic lash adjuster

A DHLA including a hydraulic lash adjustment mechanism disposed within a plunger slidably disposed within a pin housing that is slidably disposed within an axial bore in an adjuster body. A lash ring disposed in a groove near the outer end of the DHLA body includes a portion extending into the bore to limit travel of the pin housing and thereby set the internal mechanical lash in the DHLA. The lash ring has a thickness selected to provided a predetermined amount of mechanical lash in the assembled lifter, which thickness varies from assembly to assembly to compensate for manufacturing variation in the components. A biasing means such as a wave ring, a Belleville washer or a beveled retaining ring is also installed in the annular groove to urge the lash ring against the lower surface of the groove under all DHLA operating conditions.

TECHNICAL FIELD

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).

BACKGROUND OF THE INVENTION

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.

SUMMARY OF THE INVENTION

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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1, a prior art DHLA10has a generally cylindrical adjuster body12. A pin housing14is slidably disposed within a first axial bore16in adjuster body12. Pin housing14itself has a second axial bore18for slidably receiving a plunger20having a domed end22for receiving a socket end (not shown) of a roller finger follower (not shown) in an overhead-cam engine valve train (not shown). Pin housing14has a transverse bore24slidably receivable of two opposed locking pins26separated by a pin-locking spring28disposed in compression therebetween. First axial bore16in is adjuster body12is provided with an annular groove30for receiving the outer ends of locking pins26, thrust outwards by spring28when pins26are axially aligned with groove30. In such configuration, DHLA10is in valve-activation mode. (As shown inFIG. 1, DHLA10is in valve-deactivation mode.) A loss-of-motion (LM) return spring34is disposed within a chamber35below pin housing for absorbing lost motion of pin housing14within bore16when DHLA10is in deactivation mode.

Groove30further defines a reservoir for providing high pressure oil against the outer ends36of locking pins26to overcome spring28and retract the locking pins into bore24, thereby unlocking the pin housing from the adjuster body to deactivate the DHLA. In use, groove30is in communication via at least one port38with an oil gallery (not shown) in an engine40, 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.

Plunger20includes a hydraulic element assembly (HEA)42lodged at an inner end thereof. The arrangement of components and operation of hydraulic lash adjuster elements such as HEA42has been well known in the prior art for many years. HEA42comprises a spring loaded check ball44lodged against a seat46formed in plunger20separating a low-pressure oil reservoir48from a high-pressure chamber50formed between HEA42and pin housing14. Oil is supplied to annular chamber51from an engine oil gallery (not shown) via port54in adjuster body12. Chamber51is also in communication with reservoir48via port56and annular groove58in pin housing14and port62in plunger20. Oil may be supplied from reservoir48to an associated roller finger follower (not shown) via port52in the end22of plunger20.

In operation, prior art DHLA10is disposed in a bore in engine40such that housing12remains stationary. When the associated cam and RFF (not shown) exert force on plunger end22, in lost motion (valve-deactivation) mode, plunger20and pin housing14are forced into adjuster body12in a lost-motion stroke, compressing spring34.

Of particular interest to the present invention is the means by which the outward stroke of pin housing14is limited in prior art body12. An annular groove64formed in bore16near the outer end thereof receives a retaining clip66that extends into bore66to engage shoulder68of pin housing14. The axial thickness70of clip16is selected from a family of such clips having differing thicknesses to set the amount of axial mechanical lash72in DHLA10. As described above, the amount of lash72is an important manufacturing parameter which must be calibrated for each DHLA assembly because of manufacturing variability in the length74from shoulder68to the lower edge76of pins26, and length78from the upper face80of groove64to the lower face82of groove30. (Lower face82is also known in the art as a “pin shelf” for lock pins26.) The trial-and-error method of assembly, measurement, disassembly, reassembly, and re-measurement is time-consuming, costly, and difficult when using prior art groove64and clip66.

Referring toFIGS. 2 through 5, an improved DHLA110in accordance with the present invention is formed substantially like prior art having similar components except as follows.

As described above, the amount of mechanical lash172(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 length174from shoulder168of pin housing114to the lower edge176of locking pins126.

A lash ring166, of a selectable size, is retained in groove164in body112by a resilient biasing member165such as a Belleville washer, or preferably a wave ring. Lash ring166includes a first portion such a collar169having a length171, and first and second surfaces175,177.

After pin housing114is installed in body112as in the prior art, a method for setting mechanical lash in an individual DHLA110consists in the following steps.

First, a gage tool173,173′ (FIG. 6a), designed to simulate at least a portion of lash ring166(shown as dashed lines inFIG. 6a), and having exemplary cross sections as shown inFIGS. 6band6c, is positioned in first annular groove164with its first surface175′ positioned against the bottom surface167of annular groove164and its second surface177′ in abutting contact with shoulder168of pin housing114, thereby establishing a known, fixed axial relationship between bottom face167of groove164and shoulder168of pin housing114. (When using gage tool173in which surfaces175′ and177′ are collinear, bottom face167and shoulder168will be collinear as well). Pin housing114is then depressed into body112until locking pins126engage lower face182of groove130with a specified force. A longitudinal distance D in which pin housing114travels from its starting position of being in contact with second surface177′ to its ending position of wherein locking pins126engage lower face182is observed. Then, desired lash172is subtracted from observed distance D. The numerical remainder (D−172) is used to determine length171of first portion169of lash ring166that will result in the desired lash172. After gage tool173,173′ is removed from groove164, a lash ring166having a selected length171of first portion169as determined above is installed in groove164with second surface177facing shoulder168of pin housing114. Finally, wave ring165is installed on top of lash ring166to retain ring166in annular groove164and to preload lash ring166against bottom surface167of annular groove164.

Wave ring165is selected to preload lash ring166and to apply a clamping force on lash ring166that is greater than the installed load of the lost motion spring(s)134to keep lash ring166seated against bottom surface167of groove164during use of DHLA110. 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 groove164to bottom surface167rather than the top face180as in the prior art (FIG. 1). This represents an important manufacturing improvement; top face180is difficult to grind as it requires a grind relief in the upper corner of the groove. Also, top face180cannot be machined simultaneously with lower face182so tolerances cannot be controlled as precisely. In improved DHLA110, bottom surface167is the key surface and can be machined with tooling similar to that used for lower face/pin shelf182. Also, bottom surface167may be machined simultaneously with pin shelf182to precisely establish length178(FIG. 2) thereby reducing the variation that the lash ring thickness must accommodate.

Note also that preferably, the outer diameter181of lash ring166is less than the inner diameter183of the opening of body112(FIG. 2). Thus, ring166need not be radially compressed to fit into second groove164thereby avoiding the risk of distorting the flatness of ring166and introducing error in the resulting mechanical lash172. Also, preferably, outside diameter185of second surface177of lash ring166pilots on the inside diameter187of body112.

In an alternate embodiment, wave ring165may be substituted with internal split beveled retaining ring265as shown inFIG. 7, commercially available from Rotor Clip Company, Inc. of Somerset, N.J. 08873. In this embodiment, surface263of split ring265is formed with a 15° bevel for mating with a 15° bevel formed in the upper face261of groove264. After lash ring166having a selected length171as determined above is installed in groove264, split ring265is radially compressed so that its outer diameter fits inside inner diameter283of the opening of body212. Then, split ring265is allowed to radially expand into groove264so that surface263of split ring265wedges against upper face261of groove264thereby firmly pre-loading and seating first surface175of lash ring166against bottom surface167of groove264.

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.