Internal-combustion engines – Poppet valve operating mechanism – Rocker
Patent
1990-05-29
1991-01-01
Myhre, Charles J.
Internal-combustion engines
Poppet valve operating mechanism
Rocker
123 9054, F01L 122
Patent
active
049811177
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a mechanical automatic clearance adjuster as may be used as a clearance adjuster for a valve operating mechanism in an internal combustion engine or compressor or the like. A mechanical automatic clearance adjuster comprising an internally threaded female member, a male member within said female member having an external thread form generally complimentary to the internal thread form of the female member, the thread form 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, spring means acting on the male member to bias it in the said opposite direction of axial loading and thus to urge the male member in a direction to advance axially of the female member with the thread form being configured to provide co-operating running flanks and locking flanks whereby the male member will rotate and advance axially of the female member under the axial thrust of the spring means on the said running flanks is referred to throughout this specification as "a mechanical automatic adjuster of the kind specified".
Mechanical automatic adjusters of the kind specified used as valve clearance adjusters are disclosed in GB No. A-2033472 and EP No. A-0032284. In one such adjuster described and illustrated in the above patent specifications, an externally threaded screw member runs within a complimentarily 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 complimentarily internally threaded bush in a bucket type tappet; such arrangement being particularly applicable to an overhead cam valve operating mechanism.
In GB No. A-2160945 there is described and illustrated a self-contained mechanical automatic adjuster of the kind specified comprising a pre-assembly of a housing having an internal buttress thread form, a screw member having a co-operating external buttress thread form and a compression spring within the housing acting to bias the screw member to rotate and advance axially out of the housing.
In all of the above mentioned disclosures, the buttress thread form exhibits a relatively high friction in that direction of axial loading of the male member relative to the female member which is opposed to the direction of the spring loaded axial bias. Conversely, the thread form exhibits a relatively low friction in that direction of axial loading in which the spring means biases the male member whereby the male member may rotate and advance axially of the female member upon the running flanks of the co-operating threads under the axial spring bias. The aforesaid relatively high friction is exhibited between the locking flanks of the co-operating threads which are designed in a manner intended to prevent any substantial degree of rotation of the male member relative to the female member in that said direction of axial loading of the male member which is opposed to the direction of the spring loaded axial bias.
In GB No. A-2160945 it is disclosed that, despite the wedging/locking engagement which is obtainable between the locking flanks of the male and female members in the high friction direction of axial loading, a condition can sometimes arise in use when, for a short period of time, friction conditions on the co-operating locking flanks are very low as a result of the oil film and that axial loading produces "back off" rotation of the male member relative to the female member. The existence of an oil film between the locking flanks can lead to an excessive degree of such back-off rotation and it is an object of the present invention to provide an improved mechanical automatic adjuster of the kind specified wherein the co-operating thread forms of the male and female members are configured to mitigate against an undesi
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patent: 4867112 (1989-09-01), Ishii
Gill Peter J.
McRobert Stewart C.
GKN Technology Limited
Lo Weilun
Myhre Charles J.
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