Patent Application
20060266320
The present invention relates to hydraulic valve lifters for cams of push-rod internal combustion engines; and, more particularly, to a hydraulic valve lifter having an integral rocker arm hydraulic lash adjuster assembly replacing a prior art hydraulic plunger assembly having a solid plunger.
Internal combustion engines having hydraulic valve lifters are well known in the automotive arts. Hydraulic lifters, also known in the art as hydraulic tappets, are currently available in mass production and incorporate integral hydraulic components to provide a simple, inexpensive package for primarily automotive and truck engines. Ease of assembly and service provide significant benefits to a cam-in-block (CIB) engine, also known in the art as a “pushrod” engine, relative to more expensive and complex multiple valve overhead cam (OHC) engines.
Various non-automotive engine manufacturers, for example, some aircraft engine manufacturers, utilize CIB engines, which have evolved relatively little in many years. In some applications, conventional hydraulic lifter assemblies cannot be used as received from a lifter manufacturer because a typical hydraulic lifter lacks the total adjustment range necessary for a “net build” engine assembly, employing identical standard-length pushrods. Therefore, in manufacturing these engines with hydraulic lifters, some engine manufacturers require the capability in a lifter to disassemble the lifter and measure the solid height of each individual component. The heights are summed to establish a predetermined dry valve stem clearance; then a pushrod of predetermined length is selected for each cylinder from an array of pushrod lengths so that the lifter can operate within its desired operating range.
A serious problem exists in using prior art lifters in this manufacturing scheme because commercially-available lifters are self-contained, that is, the body and plunger are matched to achieve a nominal leakdown rate and are not well-suited for disassembly and reassembly after measurement. Disassembly requires removal of internal fluids supplied within the lifters by the manufacturer, but the fluids are trapped in a reservoir which is inaccessible except by disassembly of the lifter. Further, reassembly is vulnerable to potential quality issues associated with lifter mis-builds, including damaging of valve train dynamics and objectionable valve clatter resulting from lack of oil in the high-pressure chamber of a lifter at engine start-up. For these reasons, OEM manufacturers of hydraulic lifters do not recommend such disassembly and reassembly.
What is needed is means for providing a hydraulic lifter that may be readily drained and refilled to permit simple measurement of the “dry” height of a lifter without disassembly.
What is further needed is a simple, inexpensive, and drainable hydraulic lifter that may be assembled from prior art lifter and hydraulic lash adjuster components.
It is a principal object of the present invention to provide an improved hydraulic lifter that is readily drained and refilled to permit simple measurement of the “dry” height of a lifter without disassembly.
Briefly described, an improved roller hydraulic valve lifter (RHVL) comprises a prior art lifter body having a roller assembly at a first end for following a camshaft cam, a large internal oil chamber connectable to an engine oil gallery, and a pushrod seat slidably disposed in an open second end and having a socket for engaging the end of a valve pushrod. A commercially-available hydraulic lash adjuster (HLA), manufactured for use as a lash-adjusting pivot for a rocker arm in an overhead valve engine, is disposed within the internal chamber of the RHVL body in place of the originally-provided solid plunger, spring, and check valve. A socket-faced adapter, which may be an inverted prior art pushrod seat, is slidably disposed between the hemispherical head of the HLA and the RHVL pushrod seat to transfer motion of the HLA to the pushrod seat.
An important advantage of the combination of HLA within an RHVL body is that the HLA has an oil passage in the tip of the hemispherical head and the HLA check valve is inverted from the orientation of the original check valve in the RHVL. Thus, by inserting a pin through the pushrod socket and into the HLA assembly, oil can be readily drained from behind the check valve to permit easy measurement of overall dry length without requiring any disassembly and reassembly. Further, the HLA chamber is readily refilled after such measurement, and further, the HLA is completely bathed in engine oil during operation and therefore is immune to deflation and air embolism during periods of engine shutdown.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Hydraulic valve lifters as a class are intended to adapt in length to remove lash in a valve train of an internal combustion engine, thereby optimizing the opening and closing performance of the intake and exhaust valves and minimizing the clatter of valve stems against tappets. Early hydraulic lifters were so-called mushroom or slider lifters (SHVL) wherein the surface of a foot on the lifter slidingly followed a rotating cam lobe.
Although the foot was bathed in oil during engine operation, engines thus equipped suffered from frictional wear of the cam and lifter foot, which tended to occur especially upon starting of the engine when the interface was drained of oil. More recently, in hydraulic valve lifters a precision roller replaces the slider foot for following the cam lobe (RHVL), with reduced wear to the lifter and the cam lobe. It should be understood that an improved hydraulic valve lifter in accordance with the invention may be formed as either an SHVL or an RHVL, although for convenience only the RHVL version is exemplarily shown below.
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As further noted above, a serious problem exists in adapting lifter 10 for use in an engine having close valve train tolerances. To measure the net mechanical length of lifter 10 from foot 18 to socket 22 requires that high-pressure chamber 45 be completely compressed such that plunger 30 rests against cage 34. But oil can escape from chamber 45 only via a clearance between plunger 30 and bore 28 or through valve seat 40. Check ball 36 cannot be reached mechanically to relieve oil through the valve seat, so either the lifter must be disassembled and then reassembled, or the lifter must be subjected to high axial pressure for an extended period of time to force the oil in chamber 45 past plunger 30. Neither option is attractive from an engine manufacturing point of view.
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To measure the deflated length of lifter 110 that has been previously filled with oil in high pressure chamber 82, pin 98 is inserted through axial passage 58, through passages 258 and 80, and into valve seat passage 86. The pin is then used to move check ball 88 away from mating engagement with seat 84 thereby releasing the oil from high pressure chamber 82. Upon release of the oil, plunger 70, and seats 220 and 20′, move toward high pressure chamber 82 reducing the lifter assembly to its dry or mechanical length. In that state, the mechanical length of the lifter can be measured between any two reference points such as, for example, between a first body reference point 99 and a second plunger reference point 100.
Optionally, a flat disk 206 may be installed in space 204 which functions in known fashion as a metering valve for oil flow between passages 58 and 258. Of course, a disadvantage of incorporating disk 206 is that check ball 88 then is not directly accessible by a pin via passages 58,258,80,86 to relieve oil pressure in high-pressure chamber 82 and in order to measure directly the deflated length of lifter 110. Such measurement then requires partial disassembly of lifter 110, removing pushrod seat 20′ and disk 206, a minor inconvenience. Of course, if metering oil flow from lifter 110 is not needed, a unified pushrod seat (not shown) may be fabricated, combining sockets 22′ and 222 in a single element. However, an advantage of an RHVL in accordance with embodiment 110 as shown in
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.
