GB2219635A - Sliding stem seal for valve stems - Google Patents

Description

SLIDING STEM SEAL, PARTICULARLY FOR VALVE STEMS The present invention

relates to a sliding stem seal, particularly for the stem of an intertia 1 combustion engine intake or exhaust valve.

Seals of the aforementioned type are employed for preventing the tappet Lubricating oil from seeping along the valve stem into the engine, and comprise a first cylindrical portion fitted on to a cylindrical portion of IU a bush supporting the stem and fitted inside the cylinder head; and a second cylindrical portion inside which is formed an annular lip cooperating with the valve stem. The tappet lubricating oil aLso lubricates the contact surface between the valve stem and sea 1 ing lip for reducing friction between the same.

Iffien the engine is left idle for some tinie, the Lubricating oil seeps out of the cylinder head, thus resulting CI in the -sealing lip drying up and sticking to the valve stem when the engine is started again, the disadvantages 20 of which are obvious.

1 1 f The aim of the present invention is to provide a seal designed to overcome the aforementioned drawback, i.e. to prevent the sealing lip from sticking to the val.ve stem when the engine is Left idle for prolonged periods 5 of t ime.

With this aim in view, according to the present invention, there is provided a sliding stem seal, particularl.y for the stem of an internal combustion engine valve en Y characterised by the fact that it comprises a first portion fitted integral with an element supporting said stem; and a second portion inside which are formed a top and bottom annular lip cooperating in contacting manner with said stem and defining, together and with said stem, a fiuidtight annular chamber designed to permanently trap lubricating oil when said stem is idle.

A preferred embodiment of the present invention will be described by way of a non-limiting example with reference to the accompanying drawing, in which number 1 indicates a sea] for a sliding stem 2, in the example shown, the stem of a known type of internal combustion engine intake or exhaust valve (not shown).

Said seal 1 is substantially formed from elastomeric material, and comprises a bottom portion ^j in the form of a cyLindrical sleeve designed to fit on to a cylindrical portion 4 of a bush 5 supporting stem 2; a center portion 6 substantially in the form of a truncatedcone sleeve; and a top portion 7 in the form of a cylindrical sleeve having a smaller outside diameter than portion 3. Said portion 3 presents an integraL outer Strengthening s I c eve 8 preferably of metal, having a top edge 11 in the form of an annular flange covered by a peripheral annular appendix 12 projecting radially from center portion 6. Sleeve 8 is conceniently bonded on to portions 4 and 6 at the curing stage, and bush 5, which Ls of known type and shown only partially, is fitted into the cylinder head on the ellgille.

Inside top portion 7 of seal 1, there are formed a radially-projecting top arid bottom annular lip 13 arid 14 designed to cooperate in sliding manner with stem 2, which extends through and slides axia 1 Ly inside seal 1 by virtue of a known hydraulic tappet (not shown). Between lips 13 and 14, and closer to lip 13, there. is fitted, oil outer lateral surface 9 of portion 7, 1 - dfl annular spring 10, the function of which is to exert predetermined radial pressure 011 lips 1 ^5 and 14 and so press them or) to the outer lateral surface of stem 2. Lips 13 and 14 present a triangular radial section, the rounded, radially-innermost free apex cooperating with stem 2. Ill particular, top 1 ill 13 presents an inner edge 15 defining a more rounded apex than that defined by the corresponding inner edge 16 of bottom lip 14, thus providiiig for greater contact wit.h stem. 2. Moreover, lips 13 arid 14 are designed to cooperate C.5 differentially with stem 2, by virtue Of top liP 13 being higher than bottom lip 14 and so cooperating f= to a greater extent with stem 2.

In actual use, lips 13 and 14 define, together and with the outer surface of stem 2, a fluidtight annular chamber 18 designed, when stem 2 is idle, to permanently 4 trap part of the oil usua l ly present in the cylinder head on the engine for lubricating the, tappets controlling stem 2.

When the engine is running, i.e. with stem 2 sliding axially inside seal 1, the lubricating oil out side seal 1 is allowed to seep inside chamber 18 by virtue of the softly rounded shape of edge 15 on lip 13, and despite liP 13 cooperating with stem 2. Due to the sharper edge 16 on lip 14, however, the oil entering chamber 18 is prevented from seeping out, and so gradually cl fills up chamber 18. When stem 2 is idle, on the other hand, the aforementioned design of liPs. 13 arid 14 results in total sealing by both top Lip 13 and bottom lip 14 on stem 2, thus preventing both upward and downward leakage. When stem 2 is idle, therefore, the oil inside chamber 18 is trapped for ensuring lips 13 and 14 are adequately lubricated when stem 2 is next operated. The advantages of the present invention will be clear from the foregoing description. In particular, even when the engine is idle, sufficient lubricating oil is trapped between lips 13 and 14 for preventing these from sticking to stem 2, and for ensuring they are kept lubricated even over prolonged periods, thu s enabling smooth, troublefree start-up of the engine.

To those-skilled in the art it will be clear that changes may be made to seal 1 its described and illustrated herein without, however, departing from the scope of the present invention.

Claims (1)

1 A sliding stem seal, particularly for the stem of all internal combustion engine valve, charac- terised by the fact that it comprises a first portion f itt ted integra 1 with an c lement supporting said stelll and a second portion inside which are formed a top anti bottom annular lip cooper- ating in contacting mariner with said stem and def in- ing, together and with said stem, a fluidtight annular chamber designed to permanently trap lubri- cating oil when said stem is idle.

2) - A seal its claimed in Claim 1, characterised by the fact that said lips present a triangular radial section, and cooperate with said stem via respective rounded edges defining respective t!' free apexes; said edge of said top lip being more rounded than that of said bottom lip 3) - A seal as claimed in Claitn 2, characterised by the fact that said lips are designed to cooper ate differentially with said stem; said top lip being higher than said bottom lip 4) - A seal as claimed in one of the foregoing Claims, characterised by the fact that, on the outer surface of said second portion. spring means are pro- vided for pressing said lips on to said stem; said spring means being fitted between said lips and closer to said top lip 5) - A seal as claimed in one of the foregoing Claims, 30 characterised by the fact that said first portion i.-, in tile form of a cyLindrical sleeve, and is designied to fit Oil to a cylindrical portion of said element support ing said stein arid by the fact that said first portion presents all integral outer metal sleeve having. an edge in tile form of an annular f lange and covered by a peripheral annular appendix of a portion corinectin- said first and 91 said second seal portions.

6) - A seal as claimed in one of the foregoing Claims, characterised by the fact that said first arid said second portions are formed from clastomeric material.

7) - A sliding stem seal, particularly for valve stems, CS substantially as described and illustrated herein with reference to the accompanying drawing.

Published 1989 at The Patent Office, State House, 66171 High Holborn. London WC1R 4TR Further copies may be obtained from The Patent office, Sales Branch, St Mary Cray, Orpington. Kent BR5 3RD. Printed by Multiplex techniques ltd. St Mary Cray, Kent, Con. 1/87