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1. (WO1991018189) TAPPETS
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CLAIMS

1. A tappet (10; 43; 100; 160) comprising a generally cylindrical body (12), characterised in that the
body (12) has discrete bearing portions (14; 90; 1 6,128; 162,164,166) formed thereon, each discrete bearing portion having a maximum radial dimension greater than that of the surrounding surface of the body
(12) adjacent to the bearing portion, and in that each bearing portion is provided with means (26,28;
50,58;60;70,74;92;132,134,136,138) to form a convergent gap (angle b) with a co-operating bore (30) in which the tappet is guided for the formation of a hydrodynamic oil lubrication film (150).

2. A tappet according to Claim 1, characterised in that the bearing portions are distributed substantially evenly ci r cumf erent i a I ly of the tappet.

3. A tappet according to either one of Claims
1 and 2, characterised in that the bearing portions themselves have a geometry (52,54,56;60;74) which
forms the convergent gap.

4. A tappet according either one of Claims 1
and 2, characterised in that the bearing portions
are in the form of plateaux (14; 54;72; 90; 126,128;
162,164,166) lying substantially in a cylindrical
surface and said means to form a convergent gap is provided by inclined ramps (26,28;50,58;70;92;
133,134,136,138) associated with the plateaux.

5. A tappet according to Claim 4, characterised in that the angle of the inclined ramps is at least
0.1 milliradians greater than the maximum misalignment (angle a) between the tappet axis (40) and the axis
(42) of the co-operating guide bore (30).

6. A tappet according to either one of Claims
4 and 5, characterised in that the angle of the inclined ramps (26,28; 50, 58;70; 92; 132,134,1 6,138) to the tappet axis (40) lies in the range from 0.3 to 1.5 milliradians.

7. A tappet according to any one of Claims 1 to 6, characterised in that the bearing portions are in the form of raised lands (14;90) distributed on the body (12) both axially and ci rcumf erenti al ly.

8. A tappet according to Claim 7, characterised in that the lands (14;90) are ci rcumferent i a L ly overlapping when viewed axially of the tappet.

9. A tappet accord ng to either one of Claims
7 and 8, characterised in that the raised lands (90) are arranged helically on the tappet body (12).

10. A tappet according to Claim 9, characterised in that the helices formed by the raised lands (90) form an angle of between 15 and 25 degrees with the axis (40) of the tappet.

11. A tappet according to any one of Claims 1 to 6, characterised in that the discrete bearing portions comprise two ci rcumf erenti a I ly extending portions (126,128;162,166) adjacent opposite ends of the body (12).

12. A tappet according to Claim 11, characterised in that the bearing portions (126,1 8; 162,166) are of cylindrical form.

13. A tappet according to either one of Claims
11 and 12, characterised in that a further circumferent-ially extending portion (164) s disposed centrally of the body (12) .

14. A tappet according to any one of Claims 11 to 13, characterised in that the axial length of
each ci rcumf erent i al ly extending portion (126,128;
162,164,166) is between 2 per cent and 25 per cent of the axial length of the tappet.

15. A tappet according to any one of Claims 11 to 14, characterised in that the body (12) of the tappet is hollow and ha.s apertures ( 1 0; 168) therethrough between the ci rcumf erenti a I ly extending portions (126,128;162,164,166) .