SELF-CONTAINED HYDRAULIC BUCKET LIFTER

Abstract: A hydraulic lash adjusting tappet (l0) for use in engine valve gear of the direct-acting type having one end of the tappet contacting the end (26) of the combustion chamber valve stem (22) and the other end contacting the camshaft lobe (l6). The tappet has a body (34) formed with a tubular wall portion (36) having one end thereof closed by an end wall (38) and with a tubular hub (40) therewithin formed integrally with the end wall and extending axially therefrom. A lash adjuster assembly (44) is slidingly received in the tubular hub which defines a reaction surface (50) remote from the cam face reaction surface (l8) defined by the end wall. A seal (88) defines an expansible closed fluid reservoir (ll4) in combination with the body and includes a compliant diaphragm (90) carried about the outer circumferential portion (92) thereof by said body and a sleeve cap (52) insert-molded within the inner circumferential portion (ll0) of the diaphragm to provide a central portion (l04) wear surface interposed, in application, between the lash adjuster reaction surface and the valve stem. In the preferred embodiment the compliant diaphragm has a plurality of circumferentially spaced accumulators (118) for absorbing by flexure thereof, pressure transients in the reservoir and has stiffening ribs integrally formed between the accumulators.

Description: SELF-CONTAINED HYDRAULIC BUCKET LIFTER The present invention relates generally to hydraulic lash adjusters or lifters as they are sometimes referred to and the like for maintaining substantially zero lash in motion-transmitting mechanisms such as, for example, cam-operated valves of internal combustion engines, and particularly to hydraulic valve lifters of the bucket-type which directly interconnect the cam and valve stem of an overhead cam and valve engine. More specifically the present invention relates to hydraulic valve lifters of the self-contained type within direct-acting valve gear. Self-contained lash adjusters overcome many of the shortcomings of conventional lash adjuster arrangements. Because no external source of hydraulic fluid is required, self-contained lash adjusters are easily applied to engines since no oil galleries are required. Furthermore, because no fluid is supplied to the outside diameter of the adjuster, leakage therefrom will not collect within the engine block and head as has been heretofore experienced. Because self-contained lash adjusters do not communicate with their host engine's hydraulic (lubrication) system, they do not become subject to the contaminants and air bubbles contained therein. The presence of air-free hydraulic fluid within a lash adjuster is desirable, particularly in reducing cold-start cavitation which, in the worst case, can cause collapse of the lash adjuster. Additionally, by containing its own reservoir of hydraulic fluid, a self-contained lash adjuster provides improved control over leakdown by permitting use of hydraulic fluid having a viscosity differing from that of the host engine fluid. A still further advantage of self-contained lash adjusters is their independence from engine fluid pressure which tends to be high during cold-start conditions and low at hot idle. Although having many advantages over conventional lash adjuster arrangements, prior art self-contained lash adjusters have a number of shortcomings. Because self-contained lash adjusters, by definition, have no outside source of hydraulic fluid, the fluid contained therein at the time of manufacture must remain intact for the life of the lash adjuster. Accordingly, a virtually perfect seal is required to prevent any self-contained lash adjuster hydraulic fluid from escaping. Providing such a seal has been a difficult problem and an area of weakness in virtually all prior art commercial self-contained lash adjusters. The prior art patent literature has recognized this problem and has acknowledged that some leakage is inevitable by providing arrangements for compensating for limited amounts of hydraulic fluid loss. More specifically the sealing problems in self contained lash adjusters have been described as having two distinct aspects. First, all such lash adjusters require an absorption chamber to account for differential volumes of reservoir fluid. The shortcomings of prior art absorption chambers has been the difficulty encountered in establishing and maintaining a seal between two reciprocating elements. Such motion tends to substantially reduce the life of the seal through fatigue embrittlement and the like. The second aspect is the sealing function of the high-pressure portion of the lash adjuster. Prior art approaches have employed a dynamic or sliding seal which, by its nature, is susceptible to mechanical wear from sliding contact against less-than-perfect surface finishes. Known hydraulic tappets for self-contained direct acting valve gear have employed a body or bucket, formed as an integral unit having a reservoir defined by the closed end of the body and an annular diaphragm. One such tappet is that shown and described in U.S. Patent 3,521,608 to Scheibe, wherein the diaphragm is sealed about the outer circumference thereof to the body and engages the plunger portion of the lash adjuster at the inner circumference thereof. Although providing a relatively small tappet profile, seal arrangements such as that shown in the Scheibe patent can have shortcomings when the device is applied to certain applications, particularly those requiring long life and minimal hydraulic fluid leakage. Although the Scheibe device may overcome some of the above-described shortcomings of other prior art devices by eliminating need for a dynamic seal, the problem of a fluid-tight absorption chamber requiring life-long seal integrity has remained. Pressure transients in the fluid reservoir of known self-contained hydraulic lash adjusters can have damaging effects on the seal diaphragm. European Patent Application No. EP-A2-0 145 445 in the name of the present applicants describes a self-contained hydraulic lash adjuster comprising: (a) a generally cup-shaped body having a closed end and a cylindrical wall extending therefrom, the closed end thereof defining a face adapted to contact an engine cam, the inner side of said closed end defining a precision guide surface; (b) hydraulic lash adjusting means including one-way valve means slidably received against said guide surface and defining a force transmitting surface, said lash adjusting means operative to adjust and hold the distance of said transmitting surface from said cam face; (c) a flexible diaphragm disposed to close the open end of said cup over said lash adjustment means, said flexible diaphragm having the outer periphery thereof sealed about the inner periphery of the cylindrical wall of said cup to form a hydraulic fluid reservoir for said one way valve means, said flexible diaphragm having, a rigid central portion operative to receive and transmit forces from said force transmitting surface; and a plurality of accumulator means formed therein and disposed in circumferentially spaced arrangement about said rigid central portion. The flexible diaphragm provided with a plurality of accumulator means circumferentially spaced around a rigid central portion is intended to absorb reservoir fluid pressure transients by localised bending deformation. This reduces shock-stressing on the seal diaphragm and thereby enhances the seal life. However, in some applications, and over prolonged periods of use, these prior art devices have sometimes been known to fail particularly in the region of the inner peripheral portion of the diaphragm seal where it adjoins the rigid central portion and around the outer rim of the diaphragm which seals within the cylindrical body of the lash adjuster. The present invention in one of its aspects relates to a diaphragm subassembly for such a lash adjuster, comprising: a flexible diaphragm having an outer periphery adapted for sealing engagement with the body of a lash adjuster, said flexible diaphragm having, (i) a rigid central portion operative to receive and transmit forces in the valve train of an engine. (ii) a plurality of accumulator means formed therein and disposed in circumferentially spaced arrangement about said rigid central portion; characterised by the provision of (iii) a plurality of stiffening rib portions formed integrally therein, with one of said rib portions disposed between adjacent ones of said accumulator means wherein the wall of each of said accumulator means is more flexible than said rib portions thereby allowing said accumulator means to absorb pressure transients by localized flexing thereof. According to a preferred embodiment of the present invention there is provided a self-contained hydraulic adjuster including such a diaphragm subassembly, the lash adjuster comprising: (a) a generally cup-shaped body having a closed end and a cylindrical wall extending therefrom, the closed end thereof defining a face adapted to contact an engine cam, the inner side of said closed end defining a precision guide surface; and (b) hydraulic lash adjusting means including one-way valve means slidably received against said guide surface and defining a force transmitting surface, said lash adjusting means operative to adjust and hold the distance of said transmitting surface from said cam face; (c) the flexible diaphragm of said subassembly being disposed to close the open end of said cup over said lash adjustment means, said flexible diaphragm having the outer periphery thereof sealed about the inner periphery of the cylindrical wall of said cup to form a hydraulic fluid reservoir for said one way valve means, and (d) said rigid central portion being positioned to receive and transmit forces from said force transmitting surface. The provision of a stiffening rib between adjacent accumulator means provides the diaphragm with improved flexural strength the increased thickness of the ribs enables the accumulators to preferentially absorb transient pressure fluctuations by flexing and displacement rather than cause unwanted sudden flexing of the reminder of the diaphragm. Preferably the accumulator means is defined by one or more displacement pockets integrally formed, such as by molding, with the seal diaphragm and extending within the fluid reservoir at a point radially intermediate the outer wall of the body structure and the hub. The pockets have the outer surfaces thereof normally communicating with fluid in the reservoir and the inner surfaces normally communicating with ambient pressure, typically the atmosphere. A plurality of such displacement pockets are formed in the diaphragm and are circumferentially arranged within the fluid reservoir and interspaced by generally radially extending web portions, which add rigidity to the overall diaphragm assembly. The outer peripheral rim is axially offset from the inner peripheral portion; and, axially extending stiffening ribs are provided in the spaces between the accumulator pockets. This arrangement provides the advantage of an extremely strong seal diaphragm, which has one or more accumulators provided therein whereby hydraulic fluid pressure transients from operation of the tappet are absorbed by the accumulators through flexing and displacement thereof rather than compression or tension loading of the diaphragm itself. Other aspects and advantages of the present invention will become apparent upon reading the following specification which, along with application drawings, describes and discloses a preferred embodiment of the invention in detail. Figure 1 is a cross-section of a portion of the direct-acting valve gear of an internal combustion engine illustrating the tappet as installed in the engine; Figure 2 is a plan view of a tappet inverted with respect to Figure 1 illustrating an embodiment of the invention. Figure 3 is a section view taken along section­ indicating lines 7-7 of Figure 2; and Figure 4 is a partial section view taken along section-indicating lines 8-8 of Figure 2. Referring to Figure 1, a bucket tappet indicated generally at 10 is slidably received in a guide bore 12 provided in the cylinder head 13 of the engine structure. A camshaft 14 having a cam lobe 16 contacts the upper end or cam face reaction surface 18 of the tappet. A typical combustion chamber valve 20 is shown seated on a valve seating surface formed in the cylinder head 13 with the stem portion 22 of the valve extending substantially vertically upward through a valve guide 24 formed in the cylinder head 13, with the upper end 26 of the valve stem contacting the lower end of the tappet. The valve is biased to the closed position by concentric valve springs 28, having their lower ends registered against the exterior of the upper portion of the valve guide 24 and their upper ends in contact with a retainer 30 secured to the valve stem adjacent its upper end and retained thereon in a suitable manner, as for example, by the use of a split keeper 32 which is well known in the art. Referring now to Figure 2, an embodiment of the invention is illustrated indicated generally by reference number 300 and has a generally cup-shaped body 302 having a diaphragm subassembly received in the open end thereof for defining a flexible closing wall for a fluid reservoir 303, which can best be seen in Figure 3. Referring to Figure 3, the diaphragm subassembly is indicated generally at 304 and is sealed about its periphery in the tappet body by a washer 306 retained therein by a suitable snap ring 308. A hydraulic lash adjusting plunger assembly, indicated generally at 310, is received in a guide bore 312 provided in the tappet body. With reference to Figures 2, 3 and 4, the diaphragm subassembly has an inner peripheral portion 314, an outer peripheral rim or flange portion 316, and an intermediate flexible web portion 318 which interconnects the inner portion 314 and the outer rim 316. The outer peripheral rim 316 preferably has an axially extending bead 320 provided thereon to facilitate engagement and sealing within the body 302. A rigid metal central force transmitting disc 322 is provided which has a plurality of axially extending retention surfaces comprising apertures 324 formed about the periphery thereof in circumferentially spaced arrangement, and the inner periphery of the diaphragm is preferably molded thereover such that the material of the diaphragm is received in the apertures 324 for providing positive retention of the inner portion 314 of the diaphragm onto the disc 322. It will be understood that the disc serves to transmit valve train forces from the hydraulic plunger assembly 310 to the end of the valve stem 26 (see Figure 1). The web portion 318 of the elastomeric flexible diaphragm has provided integrally thereon a plurality of flexible accumulators or pockets formed integrally therein in preferably circumferentially equally spaced arrangement as indicated in the drawings by the numerals 326, 328, 330 and 332. The accumulators or pockets extend in a direction axially with respect to the outer peripheral rim 316 and in a direction toward the closed end of the tappet body or into the fluid reservoir. In the presently preferred practice of the invention, the inner peripheral portion 314 is axially displaced from the outer peripheral rim 316 in a direction opposite that of the pockets to thus provide an axially offset configuration for the subassembly 304. The aforesaid offset configuration gives the radially inner faces of the pocket an axially extending elongated configuration to thereby provide improved flexibility therefor. The accumulator means functions to absorb, by localized flexing and displacement thereof, pressure transients in the fluid reservoir, which experience has taught are encountered during operation of the tappet in a firing engine. The portions of the web 318 comprising the spaces between the accumulator means or pockets are configured to have an increased thickness with respect to the wall of the pocket to thereby form a plurality of stiffening ribs, indicated in Figures 2 and 4 by the reference numerals 334, 336, 338 and 340, which extend axially between the inner peripheral portion 314 and the peripheral rim 316 to provide stiffness to the web 318. The employment of the ribs 334, 336, 338 and 340 has been found to provide improved flexural strength to the diaphragm subassembly 304 for preventing failure of the diaphragm in the region of the inner peripheral portion 314 and the outer rim 316. The increased peripheral portion 314 and the outer rim 316. The increased thickness of the ribs permits the accumulators to absorb transient pressure fluctuations rather than cause unwanted sudden flexing of the diaphragm web 318. It is to be understood that the invention has been described with reference to specific illustrated embodiments which provide the features and advantages previously described; and, that such specific embodiments are susceptible of modification as will be apparent to those skilled in the art. Accordingly, the invention is limited only by the scope of the following claims.

Claims: 1. A diaphragm subassembly for a self-contained hydraulic lash adjuster for the valve gear of an engine comprising: a flexible diaphragm (318) having an outer periphery adapted for sealing engagement with the body of a lash adjuster, said flexible diaphragm having, (i) a rigid central portion (322) operative to receive and transmit forces in the valve train of an engine; (ii) a plurality of accumulator means (326, 328, 330, 332) formed therein and disposed in circumferentially spaced arrangement about said rigid central portion; characterised by the provision of (iii) a plurality of stiffening rib portions (334, 336, 338, 340) formed integrally therein, with one of said rib portions disposed between adjacent ones of said accumulator means wherein the wall of each of said accumulator means is more flexible than said rib portions thereby allowing said accumulator means to absorb pressure transients by localized flexing thereof. 2. A diaphragm subassembly as defined in claim 1, wherein said flexible diaphragm has an annular rim forming the outer periphery thereof and said rigid central portion is spaced from said annular rim in a direction extending axially thereof. 3. A diaphragm subassembly as defined in claim 1, wherein said rigid central portion includes a moulded­ in metal disc insert. 4. A diaphragm subassembly as defined in any one of claims 1 to 3, wherein each accumulator means comprises a pocket formed in said diaphragm. 5. A diaphragm subassembly as defined in claim 1 wherein: (a) said rigid central portion is a rigid plate member having a generally circular configuration; (b) said diaphragm has a generally annular portion which has, (i) an inner peripheral portion received over the periphery of said plate in fluid sealing engagement; (ii) an outer periphery in the form of an outer rim portion adapted for sealing engagement with the body of a lash adjuster (310), (iii) a web portion interconnecting said rim and inner peripheral portion, said web portion including said plurality of accumulator means (326, 328, 330, 332) formed therein disposed in circumferentially spaced arrangement; and (c) said stiffening rib portions (334, 336, 338, 340) are formed integrally with said web portion said accumulator means having the walls thereof configured to be more flexible than said rim, inner portion and stiffening rib portions. 6. The diaphragm subassembly defined in claim 5, wherein said rim and said plate and inner peripheral portion are axially offset and said ribs extend generally axially therebetween. 7. The diaphragm subassembly defined in claim 5, wherein said plate and inner peripheral portion are axially offset on one side of said rim portion and said accumulator means extend axially on the opposite side of said rim portion. 8. The diaphragm subassembly defined in claim 5, wherein said accumulator means have an elongated configuration in the circumferential direction. 9. The diaphragm subassembly defined in claim 5, wherein said accumulator means are circumferentially equally spaced and extend from said web portion in a generally axial direction with respect to the annulus of said diaphragm. 10. The diaphragm subassembly defined in claim 5, wherein said accumulator means each comprises a pocket formed in said diaphragm. 11. A self-contained hydraulic lash adjuster including a diaphragm subassembly as defined in any one of claims 1 to 4, the lash adjuster comprising: (a) a generally cup-shaped body (302) having a closed end and a cylindrical wall extending therefrom, the closed end thereof defining a face adapted to contact an engine cam, the inner side of said closed end defining a precision guide surface; and (b) hydraulic lash adjusting means (310) including one-way valve means slidably received against said guide surface and defining a force transmitting surface, said lash adjusting means operative to adjust and hold the distance of said transmitting surface from said cam face; (c) the flexible diaphragm of said subassembly being disposed to close the open end of said cup over said lash adjustment means, said flexible diaphragm having the outer periphery thereof sealed about the inner periphery of the cylindrical wall of said cup to form a hydraulic fluid reservoir (303) for said one way valve means, and (d) said rigid central portion being positioned to receive and transmit forces from said force transmitting surface. 12. The lash adjuster defined in claim 11, wherein said rib portions extend generally parallel to the cylindrical wall of said cup.

Inventors: BUENTE, STEPHEN M., HILLEBRAND, GEORGE A.
Applicants: EATON CORPORATION
Application year: 1986
Main classification: F01L1
IPC codes: F01L1