Self-contained hydraulic lash-adjuster with pressurizing diaphragm

Abstract: A self-contained lash-adjuster (10) includes a closed end cylinder body (11) and a plunger (15) in the cylinder (12) defining a pressure chamber (23) at the closed end (14) of the cylinder (12) and an internal reservoir (39) connected with the chamber (23) by a one-way passage (27) in the plunger (15). A diaphragm (35) sealing the reservoir (39) is loaded by a spring piston (51) to pressurize the reservoir (39) and apply a differential pressure-extending force to the plunger (15). The plunger (15) is preferably made in two parts (16,18) with the diaphragm (35) in the lower part (18) defining the chamber (23) and with the piston (51) in the upper part (16) remote from the chamber (23). The two-part construction permits leakdown testing before final installation of the diaphragm (35). A seal (43) in the lower part (18) beyond a return port (40) seals the plunger walls (19) to the cylinder (12). Installation during assembly of excess fluid for make-up is controlled by positioning of the lower part (18) of the plunger (15) during filling in a hyper-extended position beyond the fully-extended position to which the plunger (15) is limited after full assembly of the lash-adjuster (10).

Description: This invention relates to lash-adjusters for use in the valve-actuating gear of internal combustion engines and the like. More particularly the invention relates to self-contained hydraulic lash-adjusters wherein all of the hydraulic fluid for actuating the valve lash-adjusting means is sealed within the lash-adjuster as specified in the preamble of claim 1, for example as disclosed in US-A-4,402,285. In this connection, the term "lash-adjuster" as used herein is, unless otherwise indicated, intended to include, for example, stationary finger-followers (commonly called lash-adjusters) which may be used as pivots or reaction members for rocker levers or arms and also other lash-adjusting devices such as hydraulic valve lifters or tappets which are usually located in valve trains between the valves and their respective actuating cams. It is known in the art relating to self-contained hydraulic lash-adjusters to pressurize a sealed reservoir which supplies hydraulic actuating fluid to a pressure chamber of the lash-adjuster. This can aid the flow of fluid to the pressure chamber upon its expansion for taking up valve-lash. Application of the pressure to differential areas of the plunger can also provide additional restoring force for lash take-up. Known means for pressurizing the reservoir have included spring-loaded pistons and gas-filled bellows which define a movable wall of the variable reservoir volume. Low or ambient pressure reservoir arrangements are also known using various forms of movable wall elements including, for example, collapsible bag diaphragms and rolling diaphragms. The form and mounting of such diaphragms is the subject of a number of patent disclosures in the recent art. A hydraulic lash-adjuster according to the present invention is characterised by the features specified in the characterising portion of claim 1. The present invention provides a self-contained hydraulic lash-adjuster featuring a flexible diaphragm defining a movable wall of a reservoir and engaged by a spring-loaded piston to pressurize the reservoir fluid. The plunger is conveniently formed from separate upper and lower members for ease of assembly and manufacture. The lower portion preferably carries a check-valve, recirculation port, side seal and a diaphragm defining the reservoir. The upper portion carries a diaphragm-loading piston and biasing spring. Close tolerances are made unnecessary between the piston and upper plunger member by reason of the diaphragm and side seal which control sealing and leakdown-functions being mounted in the lower portion. By shaping the reservoir cavity to conform with the shape of the diaphragm, the reservoir volume is minimized so that thermal expansion of the contained fluid is limited. Mounting of the diaphragm inwards from the outer edge of the plunger provides a differential pressure action on the lower plunger member that urges it against the upper member, supplementing the action of the plunger spring. These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings, in which: Figure 1 is an axial cross-sectional view of a finger-follower incorporating a self-contained hydraulic lash-adjuster with diaphragm means according to the invention, the adjuster and pressurizing piston being shown in their fully-extended positions; Figure 2 is a view of a fragmentary portion of the adjuster of Figure 1 shown fully-extended but with excess fluid fill for loss compensation maintaining the piston at less than full extension. Figure 3 is a view of a fragmentary portion of the adjuster of Figure 1 shown in a partially-extended position; and Figure 4 is a view similar to Figure 2 showing the adjuster in a fully-collapsed position. Referring now to the drawings in detail, numeral 10 generally indicates a self-contained hydraulic lash-adjuster having the form of a finger-follower of a type used, for example, for supporting the pivot point of a rocker lever in the valve gear of an overhead cam engine, not shown. The hydraulic lash-adjuster 10 has a cylindrical body 11 internally defining a cylinder 12 having a closed end 14. A hollow plunger 15 is reciprocably received in the cylinder 12 and is formed of two separate elements, an upper member 16 and a lower member 18. The lower member 18 has side walls in the form of a cylindrical outer wall 19 fitted with controlled clearance within the cylinder 12. A lower end wall 20 has a small recess 22 and opposes the closed end 14 of the cylinder to define a pressure chamber 23 therebetween. An upper end 24 of member 18 abuts the upper member 16 and has a deep central recess 26 forming a hollow interior portion of the plunger 15 and connected by an axially-extending port 27 with the small recess 22. A ball-check valve 28 in the pressure chamber 23 is biased by a valve spring 30 towards the port 27 to permit flow of fluid therethrough only into the chamber 23. A ball-retainer cage 31 containing the ball 28 and spring 30 is seated in the recess 22 and is engaged by a plunger spring 32. The spring 32 also engages a spring recess 34 in the closed end 14 of the cylinder to bias the plunger 15 away from the cylinder end 14. In accordance with the invention, a rolling flexible diaphragm 35 is held in sealing engagement with an annular seat 36 by a retaining ring 38 near the upper end 24 of the lower member 18 of the plunger. The diaphragm 35 extends across the opening of the central recess 26 to form therewith a closed reservoir 39. A bleed port 40 connects the reservoir with the close clearance between the cylinder 12 and the outer wall 19. An annular groove 42 around the lower member 18 between the port 40 and the upper end 24 contains a seal ring 43 to prevent the escape of fluid from the sealed hydraulic system including the reservoir 39 and pressure chamber 23. The shape of the lower plunger recess 26 is preferably contoured to surround closely the shape of the diaphragm in its fully-extended position as shown in Figure 1. This minimizes the non-functional volume of fluid in the reservoir 39 and the total volume of trapped fluid in the sealed hydraulic system. The change of volume and resulting diaphragm displacement caused by thermal expansion of the fluid is thus limited. The upper member 16 of the plunger comprises a hollow body 44 reciprocably movable in the cylinder 12 and having a rocker pivot 46 at the upper, outer end 47. The hollow interior forms an inner cylinder 48 open through a lower end 50 of member 16 which abuts the upper end 24 of the lower member 18. A piston 51 slidable in the inner cylinder 48 is biased by a pressure spring 52 into engagement with the diaphragm 35. The diaphragm is contacted by a protruding portion 54 of the piston 51 which is shaped in tapered fashion to guide the rolling motion of the diaphragm and to support it against fluid pressure in the reservoir 39. The spring 52 seats against shoulders 55, 56 of recesses 58, 59 in the piston 51 and upper member 16, respectively. The inner cylinder 48 is vented through openings 60 in the upper member 16 and the piston 51 also has a vent 61 in its nose, which is hollow to minimize weight. The plunger 15 is retained in the cylinder 12 by a retainer 62 which snaps on the open end of the body 11 and engages a shoulder 63 of the upper member 16. Since all of the sealing components and leakdown-control tolerances are connected with the lower member 18 of the plunger 15, the dimensional tolerances of the upper member 16 are not as critical and its manufacturing and assembly costs are thus minimized. During assembly, prior to seating of the diaphragm 35 and installation of the upper member 16, the volume in and surrounding the lower member 18 of the plunger, including the pressure chamber 23 and the reservoir 39, is filled with hydraulic oil fluid suitable for use in a self-contained, sealed lash-adjuster. The partially-assembled unit can at that time be checked for leakdown of fluid past the plunger 15 under load before final assembly. In this way, unsatisfactory components can be detected and replaced or re-worked without destruction of any of the assembled components, such as the diaphragm 35 and its retaining ring 38, which are not yet installed. The amount of fluid supplied is preferably slightly more (for example ten percent greater) than needed to fill the volume below the diaphragm when it is fully extended as shown in Figure 1. Thus, after assembly, when the lash-adjuster 10 is fully extended, the excess fluid will maintain a slight upward positioning of the diaphragm 35 with an equivalent slightly-retracted position of the piston 51 as shown in Figure 2. This allows for some small loss of fluid from the sealed unit without any loss of reservoir pressure over the complete range of travel of the lash-adjuster plunger 15. Figure 3 shows the assembled lash-adjuster and its piston 51 and diaphragm 35 in intermediate, partially-extended positions and Figure 4 shows the lash-adjuster 10 in the fully-collapsed position with the diaphragm 35 and piston 51 retracted to their upper positions as might occur at elevated operating temperatures. At lower temperatures, the contraction in volume of the hydraulic fluid in the lash-adjuster will be accommodated by a corresponding extension downwards of the piston and diaphragm positions. Providing the desired excess of hydraulic fluid in the lash-adjuster is preferably performed whilst the lower member 18 of the plunger is in a hyper-extended position sufficiently above the fully-extended position to allow the desired volume of excess fluid to enter the pressure chamber 23. The diaphragm 35 and sealing ring 38 are then installed and seated, sealing the charge of fluid in the system with the diaphragm in its fully-extended position as in Figure 1 but with the lower member 18 hyper-extended. Subsequent assembly of the upper member 16 forces the lower member 18 to its normal extended position as shown in Figures 1 and 2, displacing the excess fluid from the pressure chamber 23 into the reservoir 39 and raising the diaphragm and piston slightly to their Figure 2 positions. In use, the lash-adjuster body 11 is fixedly received in an engine component, such as a cylinder head. The upper member 16 of the plunger 15 extends from the body 11 with the pivot 46 in engagement with a seat in a lever or rocker arm of an engine valve train. The lever may, for example, also be engaged by a cam and contact a valve for actuation of the valve by the cam with the lever reacting against the pivot 46. When the valve is closed and the lever rides on the cam base circle, the lash-adjuster is unloaded and acts to take up lash in the valve train. This is accomplished in part because the spring 32 urges the plunger 15 upwards in the body 11 until the lash is taken up. This normally occurs before the plunger reaches the end of its travel and contacts the retainer 62 as shown in Figure 1, otherwise the lash may not be fully taken-up. In addition, the force of the pressure spring 52 against the piston 51 forces the diaphragm 35 against the sealed charge of fluid partially contained in the reservoir 39. This raises the reservoir pressure above ambient and assists in unseating the ball-valve 28 from its seat and forcing fluid through the port 27 into the pressure chamber 23. Since the transverse projected area of the lower end wall 20 of the plunger and the attached valve assembly exposed to the pressure chamber 23 is greater than the transverse projected area of the plunger exposed to the reservoir 39, a differential pressure force is developed as the pressure in the pressure chamber 23 approaches that in the reservoir 39. This force adds to that of the spring 32 in urging the plunger 15 upwards to take up the valve train lash. When the cam rotates to force the lever to move in a valve-opening direction, the reaction force against the pivot 46 is carried through the upper and lower members 16, 18 of the plunger 15 to the fluid in the pressure chamber 23, raising its pressure above that in the reservoir 39. This forces the ball valve 28 to seat firmly and trap the fluid in the pressure chamber, allowing the lash adjuster to act as a nearly solid member in the valve train during the valve opening event. However, during each valve lift event, a small amount of fluid passes from the pressure chamber 23 through a controlled close clearance between the cylinder 12 and the lower member 18 of the plunger. This leakdown fluid is returned to the reservoir 39 through the bleed port 40. Thus a controlled leakdown occurs which introduces a small amount of lash in the valve train when the valve is again closed. This lash is then taken up in the manner previously described. The hydraulic system including the reservoir 39 and pressure chamber 23 is sealed by the seal ring 43 against significant loss of the hydraulic fluid provided during assembly of the lash-adjuster. However, the provision of excess fluid during assembly permits a loss of the excess fluid to occur without limiting the full lash-adjustment travel of the plunger 15.

Claims: A hydraulic lash-adjuster (10) of the self-contained type including a body (11) defining a cylinder (12) with a closed end (14), a hollow plunger (15) internally defining a fluid reservoir (39), the plunger (15) having side walls (19) slidably fitted in the cylinder (12) and an end wall (20) co-operating with the closed end (14) of the cylinder (12) to define a chamber (23) for thrust-transmitting fluid between the cylinder (12) and the plunger (15), said end wall (20) of the plunger (15) having a one-way passage (27) therethrough for fluid flow from the reservoir (39) to the chamber (23), said side walls (19) of the plunger (15) having a port (40) extending therethrough intermediate their ends for returning to the reservoir (39) fluid which escapes from the chamber (23) externally of the plunger 15 during operation of the lash-adjuster (10), the side walls (19) of the plunger (15) being sealed to the cylinder (12) beyond the port (40) relative to the closed end (14) of the body (11), said plunger (15) further defining an inner cylinder (48) open towards the reservoir (39), a piston (51) slidable in the inner cylinder (48) and a spring (52) urging the piston (51) towards the reservoir (39) with a force effective to raise pressure within the reservoir (39) substantially above ambient pressure, characterised in that the lash-adjuster (10) includes a flexible diaphragm (35) extending across the hollow plunger (15) between the piston (51) and the reservoir (39), which diaphragm (35) is sealingly mounted in the side walls (19) to define a sealing wall with a central portion movable to vary the volume of the reservoir (39); and the piston (51) engages said central portion of the diaphragm (35) and is shaped to partially support the diaphragm (35) against the force of pressure in the reservoir (39). A hydraulic lash-adjuster (10) according to claim 1, in which said plunger (15) is formed with separate upper and lower members (16,18), said upper member (16) defining the inner cylinder (48) and supporting the piston (51) and spring (52). A hydraulic lash-adjuster (10) according to claim 2, in which said upper and lower members (16,18) further include open ends engageable with one another, an annular recess (36) in one of said open ends which receives an edge portion of the diaphragm (35), and retaining means (38) received in the annular recess (36) for sealingly retaining the diaphragm (35). A hydraulic lash-adjuster (10) according to claim 3, in which said diaphragm (35) is retained in said lower member (18). A hydraulic lash-adjuster (10) according to claim 4, in which said diaphragm (35) is a form of rolling diaphragm such that its contact with said piston (51) is such as to avoid any substantial relative sliding motion therebetween. A hydraulic lash-adjuster (10) according to claim 5, in which said upper member (16) includes a seat (46) for engaging a movable component of an engine valve train. A hydraulic lash-adjuster (10) according to claim 6, in which said seat is a rocker pivot (46). A hydraulic lash-adjuster (10) according to claim 2, in which said diaphragm (35) is retained in said lower member (18). A hydraulic lash-adjuster (10) according to claim 8, in which said piston (51) is carried by said upper member (16). A hydraulic lash-adjuster (10) according to claim 9, which includes seal means (43) between the cylinder (12) and said lower member (18) and between said port (40) and an outer end (24) of said lower member (18) remote from said pressure chamber (23) to seal the side walls (19) of the plunger (15) to the cylinder (12). A hydraulic lash-adjuster (10) according to claim 9, in which said lower member (18) contains a recess (26) into which said diaphragm (35) extends, the recess (26) conforming closely with the shape of the diaphragm (35) when fully-extended and having minimal clearance therewith to limit the volume of non-working fluid in the lash-adjuster (10). A hydraulic lash-adjuster (10) according to claim 9, in which the reservoir (39) contains a predetermined excess of fluid such that the piston (51) and diaphragm (35) are partially retracted when the lash-adjuster (10) is fully-extended. A method of making a lash-adjuster (10) according to claim 1, which method includes the steps of: providing a body (11) defining a cylinder (12) with a closed end (14); installing in the body (11) a hollow lower plunger member (18) internally defining a fluid reservoir (39) having an open end (24) adapted to receive a flexible sealing diaphragm (35), the plunger member (18) having side walls (19) slidably fitted in the cylinder (12) and an end wall (20) co-operating with the closed end (14) of the cylinder (12) to define a chamber (23) for thrust-transmitting fluid between the cylinder (12) and the plunger member (18), said end wall (20) of the plunger member (18) having a one-way passage (27) therethrough for fluid flow from the reservoir (39) to the chamber (23), said side walls (19) of the plunger member (18) having a port (40) extending therethrough intermediate their ends for returning to the reservoir (39) fluid which escapes from the chamber (23) externally of the plunger member (18) during operation of the lash-adjuster (10); providing seal means (43) between the side walls (19) of the plunger member (18) and the cylinder (12) beyond the port (40) relative to the closed end (20) of the plunger member (18); filling the chamber (23) and the reservoir (39) with a charge of hydraulic fluid; testing the leakdown characteristics of the partial assembly; thereafter installing the sealing diaphragm (35) to close the open end (24) of the reservoir (39); and providing a biased piston (51) engaging the sealing diaphragm (35) to raise the reservoir pressure. A method according to claim 13, in which the plunger member (18) has a fully-extended position in which it is spaced as far from the closed end (14) of the body (11) as is possible when the lash-adjuster (10) is fully assembled; and said step of filling is performed with said plunger member (18) hyper-extended beyond its fully-extended position such that an excess volume of fluid is installed in the chamber (23) to provide an excess in the reservoir (39) after assembly of the plunger member (18) in the fully-extended position.

Inventors: CUATT DANIEL RICHARD, SHOST MARK ANTHONY, CUATT, DANIEL RICHARD, SHOST, MARK ANTHONY
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1992
Main classification: F01L1
IPC codes: F01L1