Internal-combustion engines – Poppet valve operating mechanism – Tappet
Patent
1986-01-31
1987-11-17
Lazarus, Ira S.
Internal-combustion engines
Poppet valve operating mechanism
Tappet
123 9045, F01L 122
Patent
active
047066202
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a mechanical automatic clearance adjuster as may be used, for example, as a valve clearance adjuster for a valve operating mechanism as is described in British Pat. No. 2 033 472 and European Pat. No. 0 032 284. However the present invention is not limited to a clearance adjuster for use in a valve operating mechanism as it may find application in other fields, eg as a drive belt slack adjuster or as a levelling device.
The valve clearance adjuster describe in British Pat. No. 2 033 472 and European Pat. No. 0 032 284 comprises two complementarily screw threaded components exhibiting a higher friction in one direction of axial loading compared with the friction in the opposite direction of axial loading. In one embodiment of adjuster described and illustrated in the aforesaid patents, an externally threaded screw member runs within a complementarily internally threaded bush which bush comprises an integral part of one end of a rocker arm; the screw member being disposed between a spring, at one end, and a cam or cam-operated push-rod at the other end. In another embodiment, the screw member comprises an integral end part of a valve stem which part runs within a complementarily internally threaded bush in a bucket type tappet; such arrangement being particularly applciable to an overhead cam valve operating mechanism.
It has now been found that the types of valve clearance adjuster described above may be replaced in some applications by a self-contained clearance adjuster which, as stated in the opening paragraph above, may have uses outside those of valve operating mechanisms.
Hence it is a broad object of the present invention to provide an improved construction of mechanical automatic clearance adjuster. However, the clearance adjuster of the present invention will find particular application as a valve clearance adjuster particularly in situations where it may be located in the actual cylinder head of an internal combustion engine.
In accordance with the broadest aspect of the invention there is provided a mechanical automatic clearance adjuster comprising an internally threaded housing; a screw member within said housing having an external thread from complementary to the internal thread form of the housing, the thread from exhibiting a relatively high friction in one direction of axial loading of the screw threads compared with a relatively low friction in the opposite direction of axial loading; a compression spring within said housing acting between a reaction element on the housing at one end thereof and the screw member to bias the screw member in the said opposite direction of axial loading and thus to urge the screw member in a direction outwardly off the other end of the housing; the thread form being so configured that the screw member will rotate and advance axially of the housing solely under the axial thrust of the compression spring.
The reaction element conveniently comprises an end cap at said one end of the housing which may be secured to the housing by, for example, screw threaded engagement therewith or, alternatively, such end cap may be integral with said housing. The compression spring preferably comprises a coil compression spring which is conveniently located between a recess in the end cap and a bore formed centrally of the screw member.
The complementary threads of the housing and the screw member are preferably of buttress thread form and are preferably so configured to have a helix angle H, a first flank termed a running flank and having a flank angle G.sub.R and a second flank termed a locking flank and having a flank angle G.sub.L satisfying the conditions that: expected values of the coefficient of friction between the co-operating flanks of the threads of the housing and the screw member whereby the screw threads exhibit the said high friction between the locking flanks having said second flank angle G.sub.L under axial loads applied to either the housing or the screw member in the said one direction compared with the said low friction between th
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GKN Technology Limited
Lazarus Ira S.
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