Patent Application
20060016405
The present invention relates to hydraulic lash adjusters for combustion valves of internal combustion engines; more particularly, to a hydraulic lash adjuster (HLA) wherein a plunger is operative within an HLA body; and most particularly, to an improved hydraulic lash adjuster having a simplified long plunger assembly having the side-loading capability of a one-piece plunger, with reduced manufacturing complexity and cost.
An HLA generally comprises a plunger slidably disposed within a cup-shaped body for fixed mounting in an internal combustion engine, which plunger may be hydraulically extended from the body to take up mechanical lash in an engine valve train. The HLA is supplied with low-pressure engine oil for conventional lubrication and for lash adjustment. A spring in a high-pressure chamber formed between the plunger and the body urges the plunger out of the body to take up mechanical lash in the valve train, thereby expanding the high-pressure chamber. A ball check valve between the low-pressure reservoir and the high-pressure chamber allows that chamber to fill with oil, thereby making the HLA hydraulically rigid. As oil escapes from the high-pressure chamber by leakage around the plunger, the lost oil is replenished through the check valve. If the effective length of the valve train shortens during the engine's cam operating cycle, positive lash is created and the HLA extends, moving the plunger to a higher position at the end of the cycle than at the beginning. Inversely, if the effective length of the valve train lengthens during the cam cycle, negative lash is created and the lash adjuster contracts, moving the plunger to a lower position at the end of the cycle than at the beginning. The latter condition typically occurs when valve train components lengthen in response to increased temperature.
A problem exists in some prior art HLA assemblies. A prior art one-piece plunger has a ball surface at its outer end with a central opening for supplying oil from the low-pressure reservoir to the socket end of an associated rocker arm assembly, the reservoir being supplied via a radial port in a sidewall of the reservoir. The inner end of the plunger comprises a seat for the ball check valve. See, for example, FIG. 2 in U.S. Pat. No. 5,642,694.
Although a one-piece plunger is desirable because it provides a long bearing surface within the body and hence excellent stability against side-load forces, forming such a single element plunger in the prior art is known to be costly and difficult. The manufacture requires a large investment in equipment such as cold-forming equipment, making the cost of small production volume applications prohibitive. Additionally, due to the forming process required, the resulting plunger tends to have a thin wall section at its outer ball surface end, a region where thicker walls are desirable.
It is more common in the recent prior art to provide an HLA plunger formed as two shorter sections, each of which may be formed by relatively inexpensive methods such as boring, turning, screw-machining, powdered metal forming, and/or metal injection molding. See, for example, FIG. 1 in U.S. Pat. No. 5,622,147.
Forming the plunger as upper and lower halves reduces the cost but at a sacrifice in side-loading stability. Further, the surfaces forming the joint between the upper and lower halves benefit from precision grinding to ensure a leak-proof juncture, again at additional manufacturing cost. In either prior art example, the seat for the ball check valve is integrally formed in the lower end of the plunger, a process that adds cost to the manufacture of the plunger, and a potential source of leakage across the seated check valve since fine finishing of the seating surface is difficult to achieve in an integral seat.
It is a principal object of the present invention to provide a hydraulic lash adjuster including a plunger that is easier to manufacture and has a long bearing surface equivalent to the bearing surface of a prior art one-piece plunger.
Briefly described, a hydraulic lash adjuster in accordance with the invention comprises a hollow adjuster body for fixed mounting onto an engine, and a plunger assembly disposed within the hollow body. A plunger body includes a stepped axial bore extending from an inner end thereof to a central oil passage opening onto a conventional hemispherical pivot head. A valve seat for a check valve is disposed against the step, defining thereby a low-pressure oil reservoir in the axial bore. The plunger body is provided with an annular collector groove and entrance port for supplying lash-adjusting oil to the low-pressure reservoir. A check ball and lash adjustment spring are disposed against the seat in a high-pressure chamber formed conventionally between the valve seat the adjuster body. The plunger body may be formed to any desired length, to provide an outer bearing surface equivalent to that of a prior art one-piece plunger to resist torsional side loads which may be imposed on the HLA in use. It is understood that the plunger body may be formed of induction hardenable steels, nonferrous metals, or ceramics. The plunger body is readily formed by inexpensive processes.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring to
A plunger return spring 26 is interposed between the bottom 28 of the cup-shaped body 12 and the lower end 30 of plunger 16 and acts to bias plunger 16 such that contact is maintained with the spherically concave portion of the rocker arm, thereby eliminating mechanical lash in the associated valve train. Fluid for the dash pot of lash adjuster 10 is in the form of oil supplied from the engine lubricating system to a gallery 32. An external annular groove 34 in body 12 communicates through port 36 to deliver oil to annular space 38 defined by inner wall 40 of body 12 and an annular groove 42 in the outer surface of tubular plunger 16. A second port 46 extends through the plunger wall and provides a means for fluid communication between annular space 38 and low pressure chamber 48 of plunger 16.
The lower end of plunger 16 is provided with an outlet port 50 through which oil, stored within low-pressure chamber 48, may flow into high-pressure chamber 52 defined between the lower end 30 of the plunger 16 and the bottom, closed end 28 of cup-shaped body 12. Flow through outlet port 50 is controlled by a check valve in the form of a ball 54 which closes against a seat 56 encircling the lower end of the outlet port 50. A suitable valve cage 58 and valve return spring 60 limit open travel of valve ball 54 to the amount necessary to accomplish replenishment of high-pressure chamber 52 with oil which normally escapes therefrom between the sliding surfaces of tubular plunger 16 and cup-shaped body 12 as “leak-down”. As shown, valve cage 58 is held against plunger 16 by plunger spring 26.
Low-pressure chamber 48 of plunger 16 extends substantially the length of the plunger, from adjacent the outlet port 50 to the semi-spherical thrust end 20. An opening 62 extends through the thrust end 20 of plunger 16 to enable oil within low pressure chamber 48 to lubricate the end of the rocker arm. An integral baffle 64 is disposed within the low-pressure chamber 48 intermediate the ends of the chamber. The baffle 64 is configured as an annular shelf which extends radially inwardly from the inner wall 66 of the low-pressure chamber 48 to define a central opening 68 for the passage of oil from the oil supply port 46 to the outlet port 50.
Prior art one-piece plunger 16 thus enjoys an outer bearing surface length 70 extending virtually the entire depth of bore 18 in HLA body 12.
Referring to
An oil entry port 130, in communication with engine lubricating system oil gallery (not shown), opens into the body bore and intersects a collector groove 132 which intersects a radial port 134 in the upper plunger element to supply hydraulic fluid to the chamber 110. A second collector groove 136 and port 138 in the upper plunger element provides metered hydraulic fluid to an axial bore 140 to supply lubricant to a rocker arm (not shown) which engages a modified ball end 142 formed on the end of the upper plunger element, metering being provided by means of a controlled clearance between the plunger and the bore in the area of the land between the port 130 and the collector groove 136. The plunger is retained within the body by means of a cap 144.
As noted above, dividing the plunger into an upper half 106 and a lower half 108, for the sake of manufacturing ease and economy, yields a plunger which either a) has an undesirably short bearing length 170 of the upper half, or b) requires welding together and machining of the upper and lower halves to provide a non-divided plunger having a desirably long bearing length, but at increased manufacturing cost.
Referring to
An axial bore 222 extends the length of plunger 216, preferably having a reduced diameter portion 224 extending through upper thrust end 220 for providing oil to the rocker arm. Bore 222 is preferably stepped near the lower end thereof for receiving a check valve seat element 226 to close bore 222 and form thereby a low-pressure chamber 228 within plunger 216.
Seat element 226, in conjunction with tubular plunger 216 to form plunger assembly 227, is sized for a close fit within bore 222 and may be secured and sealed against bypass leakage as by welding to plunger 216. Seat element 226 includes an annular beveled seat 230 for receiving a check ball 232 to regulate flow from chamber 228 across seat 230. In a currently preferred embodiment, element 226 is provided with identical beveled seats 230 on opposite sides thereof such that element 226 does not require specific orientation for installation into plunger 216. Seat element 226 forms, in cooperation with the end of a reduced diameter portion 214 of the body bore, a high pressure chamber 217.
Check ball 232 is retained by a cage 234 which provides a seat for the lash adjuster plunger spring 236. A bias spring 238 acting between the bottom of the cage 234 and the check ball 232 biases the check valve into a normally closed position. Valve cage 234 and bias spring 238 limit open travel of valve ball 232 to the amount necessary to accomplish replenishment of high-pressure chamber 217 with oil which normally escapes therefrom between the sliding surfaces of tubular plunger 216 and cup-shaped body 212 as “leak-down”.
Fluid for the dash pot of lash adjuster 200 is in the form of oil supplied from the engine lubricating system to a gallery 240, similar to that shown as numeral 32 in
Simplified and improved plunger 216 thus enjoys an outer bearing surface length 270 extending virtually the entire depth of bore 218 in HLA body 212, equivalent at least to the length 70 of bearing surface in prior art one-piece plunger 16 (
In the embodiment shown of an HLA, having a separate seat element 226 allows for, among other things, improved manufacturability of seat element 226 and the axial bore 222 of plunger 216. However, it is understood that separate seat element 226, with an associated check ball 232 and cage 234, may be alternately incorporated into other valve train members having a lash adjustment feature such as, for example, a hydraulic valve lifter, thereby allowing for similar improvements in the manufacturability of the axial bore of the valve train member as well.
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.
