GB2105403A - I.C. engine intake and exhaust valve stem seals - Google Patents

Abstract

Valve stem seal 26 comprises a P.T.F.E. element 29 having, in the stem contact area, helical ribs which define oil lubrication grooves. Lip seal 27 which need not necessarily be provided, allows passage of oil downwards but prevents manifold pressure leakage. Embodiments are disclosed which consist of the P.T.F.E. seal alone (Fig. 2 not shown) and a combination of the P.T.F.E. seal and glass fibre reinforced rubber and P.T.F.E. washers (Fig. 3, not shown). <IMAGE>

Description

SPECIFICATION Valve stem seals This invention relates to valve stem seals for use especially but not exclusively on air and exhaust valves.

With the development of higher mean effective pressures in internal combustion engines the exhaust valve stem is exposed to increasing pressure and corrosive elements. For example, in diesel engines burning heavy fuel oil, weak sulphuric acids are produced and in petrol engines hydrobomic acid is a result of the use of tetraethyl lead and in all cases steam condensate accelerates the corrosive effects of the above chemicals.

Gas pressures can vary on inlet and exhaust valves from high negative to positive pressures.

These gas pressures have a marked effect on the lubrication of the valve stems and a satisfactory solution of providing lubricants in metered quantities to the valve stems is not satisfactorily achieved with the customary elastomeric and plastics seal elements presently employed since they cannot be designed to meter sufficient oil predictably to control the amount of wear on the valve stem.

It is therefore an object of the present invention to obviate or mitigate this drawback of existing valve stem seals.

According to the present invention there is provided a valve stem seal incorporating a lubricant-metering collar for contact with a valve stem and constituted by a film of polytetrafluorethylene (PTFE) of frusto-conical shape and having on its stem-adjacent surface a series of ribs defining lubricant control passages.

Preferably the ribs are helical.

These helical ribs preferably extend around the whole of the inner surface of the frusto-conical collar to define the lubricant control passages which tests have shown predictably meter sufficient oil to control the amount of wear on a valve stem.

The helical ribs may extend from the edge of the frusto-conical collar in contact with the valve stem for part or all of the axial length of the collar, or alternatively they may stop short of said edge.

The helical ribs are preferably formed intaglio on the surface of the frusto-conical collar in contact with the valve stem.

It will be manifest that the greater the depth of the passages between adjacent helical ribs, the greater the amount of oil metered down the valve stem.

The metered oil is, of course, pumped down between the valve stem and the valve guide due to the reciprocation of the former in the latter.

Due to the presence of negative and positive pressures in the engine, the valve stem seal of the present invention is preferably provided with a secondary seal arrangement which provides a duplex sealing system having an annular oil chamber.

The presence of this secondary sealing arrangement restricts gas pressures from the engine exhaust system while still permitting passage of lubricating oil due to cycle pulsation, negative pressures being similarly controlled on inlet valves.

Possible secondary seal elements are, inter alia, a synthetic rubber fibre glass reinforced gasket in conjunction with a PTFE washer, or a rubber covered lip seal.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a fragmentary side view of a valve of an internal combustion engine incorporating a valve stem seal according to the present invention; Fig. 2 is a part-sectional view, to an enlarged scale, of the valve stem seal of Fig. 1; Figs. 3 and 4 are views similar to Fig. 2 of two alternative designs of valve stem seals incorporating secondary seal arrangements; and Fig. 5 is an underneath plan view of a frustoconical collar of a valve stem seal of the present invention.

Referring to Figs. 1, 2 and 5, there is shown a valve stem 10 reciprocable in a tubular valve guide 11, a valve spring return arrangement being generally indicated at 12.

The valve stem seal 1 3 shown is satisfactory for negative pressures as a vacuum would exist between the bore of the valve guide 11 and the valve stem 10.

The seal 13 comprises a frusto-conical collar 14 of PTFE film which on its inner surface for part of its length has embossed helical ribs 1 5 defining metering passages 1 6 therebetween to control the amount of lubricating oil pumped down the valve stem 10 due to its reciprocation in the valve guide 11.

The collar 14 is sandwiched between angled tubular sleeves 1 7 and 1 8 which are press-fitted onto the valve guide 11.

This seal 13 has less capability for lateral movement caused by the valve stem 10 due to the sandwiching of the collar 14 between the angled tubular sleeves 1 7 and 1 8.

Referring now to Fig. 3, the valve stem seal 19 illustrated will provide the required metered amount of lubricating oil to the valve stem 10 and will control exhaust pressures in the seal chamber 20 defined by the seal collar 21 of PTFE film and a secondary seal arrangement provided in this seal 19.

Seal collar 21 is of the same construction as seal collar 14 and, in this instance, there is provided a synthetic rubber fibre glass reinforced gasket 22 positively to seal the base circle of the collar 21 without restricting the function of the seal 19 when the valve stem 10 and valve guide 11 are worn. A pressure element in the form of a washer 23 of PTFE and synthetic fibre glass abuts the gasket 22.

The collar 21, gasket 22 and washer 23 are secured in an outer angled tubular sleeve 24 by an inner L-section metal pressing 25 which is an interference fit in the bore of the sleeve 24.

The seal 1 9 is press-fitted over the valve guide 11.

In Fig. 4, the seal 26 has a secondary seal in the form of a conventional rubber covered lip seal 27 with a spring 28, which serves to retain the frustoconical collar 29 (identical with collar 14) in the angled tubular sleeve 30 which again is a press fit over the valve guide 1 As the seal 27 is intended to pass fluid, it is fitted so that the spring 28 is on the opposite side of the seal 27 than would usually be the case. In order to permit the passage of lubricant the seal 27 is provided with a frustoconical surface 31 making an angle a of between 1 50 and 250 to the longitudinal axis of the stem 10.

The valve stem seals of Figs. 3 and 4 are capable of dealing with both negative and positive pressures on both inlet and exhaust valve stems particularly but not exclusively in the case of turbo-charged internal combustion engines.

Claims (9)

1. A valve stem seal incorporating a lubricantmetering collar for contact with a valve stem and constituted by a film of polytetrafluorethylene (PTFE) of frusto-conical shape and having on its stem-adjacent surface a series of ribs defining lubricant control passages.

2. A valve stem seal as claimed in Claim 1, in which the ribs are helical.

3. A valve stem seal as claimed in Claim 1 or 2, in which the ribs extend around the whole of the surface of the frusto-conical coilar.

4. A valve stem seal as claimed in any one of Claims 1 to 3, in which the ribs extend from the edge of the frusto-conical collar in contact with the valve stem for part or all of the axial length of the collar, or alternatively they may stop short of said edge.

5. A valve stem seal as claimed in any one of Claims 1 to 4, in which the ribs are formed intaglio on the surface of the frusto-conical collar in contact with the valve stem.

6. A valve stem seal as claimed in any one of Claims 1 to 5 comprising a secondary seal arrangement which provides a duplex sealing system having an annular oil chamber.

7. A valve stem seal as claimed in Claim 6, in which the secondary seal arrangement comprises a synthetic rubber fibre glass reinforced gasket in conjunction with a PTFE washer.

8. A valve stem seal as claimed in Claim 6 in which the secondary seal arrangement is a rubber covered lip seal.

9. A valve stem seal, substantially as hereinbefore described with reference to Figs. 1, 2 and 5 or Fig. 3 or Fig. 4 of the accompanying drawings.