GB2057596A

GB2057596A - Rubber or Rubber-like Material Gasket

Info

Publication number: GB2057596A
Application number: GB8023459A
Authority: GB
Original assignee: IAO Industrie Riunite SpA
Current assignee: IAO Industrie Riunite SpA
Priority date: 1979-07-25
Filing date: 1980-07-17
Publication date: 1981-04-01
Also published as: ES252253U; FR2462627A1; ES252253Y; DE3027213A1; IT1118813B; FR2462627B3; IT7968542A0

Abstract

A gasket (22) of rubber or of a rubber-like material for sealing about a tachometer shaft in a gearbox, consists of an inner sealing bush (28) supported coaxially within one end of an annular support body (24), the radially inner surface of the bush being formed with helical dynamic sealing ridges. The radially inner surface of the bush may be cylindrical or conical in which case the half-apex angle is no more than 5 DEG . <IMAGE>

Description

SPECIFICATION Rubber or Rubber-like Material Gasket This invention relates to a sealing gasket for a tachometer drive shaft taken from a motor vehicle gearbox.

The present trend among automobile manufacturers is to make such drive shafts from suitable plastics material, in particular, polyamide resins (nylon), rather than steel, mainly for economic reasons. However, the sealing gaskets previously successfully used, on steel drive shafts are unsuitable for avoiding long-term oil leakage outwards along the shaft. Our tests have shown that these gaskets, even those with a thin lip, in time, erode the nylon shaft, which thus requires replacement.

An object of the present invention is to provide a gasket which avoids the aforesaid disadvantage.

According to the invention there is provided a sealing gasket of rubber or a rubber-like material for a tachometer drive shaft taken from a motor vehicle gearbox, which comprises an annular sealing bush supported coaxially, and in a floating manner, within one end of an annular support body, the radially inner surface of the bush being formed with helical dynamic sealing ridges. The principle of "dynamic sealing" by helical ridges is known and is not considered in detail (except insofar as it may concern a particular aspect of the present invention).

An embodiment of the invention will now be described with reference to the accompanying drawing, in which Figure 1 is a part-sectioned end view of a gear boxy including a gasket embodying the invention; Figure 2 is a partial view, in axial section, of the gasket and Figure 3 is a section, on an enlarged scale, of some ridges of the gasket.

Figure 1 shows a motor vehicle gearbox 10 having an output shaft 12, with a helical gear 14.

The approximate oil level in the gear box is indicated L. The gear 14 drives, in known manner, a helically-toothed pinion 16, fixed to a tachometer drive shaft 18. The shaft 18 is rotatable in a support 20 which can be removed or unscrewed from the gearbox, and its outer end 18' is housed in a cylindrical cavity 20' in the support 20. Leakage of oil outwards along the shaft 1 8 is prevented by a gasket 22, according to the invention, inserted with reasonable force into the cavity 20'. The shaft 18 may be inclined (as illustrated), vertical or horizontal, but in each case the cavity 20' and the gasket 22 are located above the oil level L. The shaft 1 8 can be made from nylon in one piece with the pinion 1 6.

The gasket 22, Figure 2, has an annular rubber body 24 of circular cross-section, having an enlarged end 24' stiffened by a metal reinforcing ring 26. When in use, this end faces towards the outside of the gearbox 1 0, and the ring 26 acts as a bearing for the tool which inserts the gasket into the cavity 20'. The opposite end of the body 24 faces towards the inside of the gearbox 10, that is, towards the flow of the oil leakage, and hence is termed the "wet end." A bush, shown as 28, is internally located relative to the body 24, and is coaxial therewith.

This bush 28 extends from an axially intermediate part of the body 24 towards the wet end of the body 24, and is supported at one end by an annular portion 30 of reduced thickness (relative to that of the bush and the body) so that the bush "floats" in relation to the body.

The radially inner surface 28' of the bush 28 has a succession of closely spaced helical ridges 32. This surface may be cylindrical as shown, or it may be conical, narrowing towards the wet end of body 24 with a half-apex angle of not more than 50. The ridges 32 effect, together with cylindrical surface 18" of the end 18' of the shaft 18, the dynamic sealing mentioned previously. These are therefore inclined either in the clockwise or anticlockwise sense depending on the direction of rotation of the shaft 18, and are so chosen that, in use, any oil which tends to leak is forced back by the ridges. Preferably, in such a gasket, the angle of inclination of helix of each ridge 32 is 450, and the length of the ridged surface 28' of the bush 28 is such that each ridge extends for at least 1/8 (450 of arc) of the inner circumference of the bush.Note that it is not necessary for each ridge to form a complete spiral around the hole of the bush. An unnecessarily long bush would result.

Preferably, each ridge (Figure 3) has a concave, circular arc profile, the profile of two adjoining ridges forming a cusp 34; the width A of each ridge being 0.3 to 0.4 mm, and the depth B of each ridge being 0.05 to 0.09 mm.

In the assembled state, the bush 28 surrounds the portion 18' of the shaft 1 8 without interference: in fact, see Figure 2, a slight radial clearance is preferred, which, measured against the cusps 34, does not exceed about 0.1 mm (so as not to prejudice the dynamic sealing).

It should be pointed out, contrary to what may appear from the drawings, that the gasket according to the invention is very small, owing to the small diameter of the end 18'. For example, for a diameter of 8 mm, the length of the body 24 of the gasket is in the region of 4-5 mm, while the length of the sealing surface 28' of the bush 28 is about 1.5-2 mm, this surface being formed with 68 ridges inclined at 450 and having the dimensions given above.

Claims

1. A sealing gasket of rubber or a rubber-like material for a tachometer drive shaft taken from a motor vehicle gearbox, which comprises an annular sealing bush supported coaxially, and in a floating manner, within one end of an annular support body, the radially inner surface of the bush being formed with helical dynamic sealing ridges.

2. A gasket according to Claim 1, in which said inner surface is cylindrical.

3. A gasket according to Claim 1, in which said inner surface is conical, narrowing towards the free end of the bush at a halfapex angle of no more than 5 .

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Rubber or Rubber-like Material Gasket This invention relates to a sealing gasket for a tachometer drive shaft taken from a motor vehicle gearbox. The present trend among automobile manufacturers is to make such drive shafts from suitable plastics material, in particular, polyamide resins (nylon), rather than steel, mainly for economic reasons. However, the sealing gaskets previously successfully used, on steel drive shafts are unsuitable for avoiding long-term oil leakage outwards along the shaft. Our tests have shown that these gaskets, even those with a thin lip, in time, erode the nylon shaft, which thus requires replacement. An object of the present invention is to provide a gasket which avoids the aforesaid disadvantage. According to the invention there is provided a sealing gasket of rubber or a rubber-like material for a tachometer drive shaft taken from a motor vehicle gearbox, which comprises an annular sealing bush supported coaxially, and in a floating manner, within one end of an annular support body, the radially inner surface of the bush being formed with helical dynamic sealing ridges. The principle of "dynamic sealing" by helical ridges is known and is not considered in detail (except insofar as it may concern a particular aspect of the present invention). An embodiment of the invention will now be described with reference to the accompanying drawing, in which Figure 1 is a part-sectioned end view of a gear boxy including a gasket embodying the invention; Figure 2 is a partial view, in axial section, of the gasket and Figure 3 is a section, on an enlarged scale, of some ridges of the gasket. Figure 1 shows a motor vehicle gearbox 10 having an output shaft 12, with a helical gear 14. The approximate oil level in the gear box is indicated L. The gear 14 drives, in known manner, a helically-toothed pinion 16, fixed to a tachometer drive shaft 18. The shaft 18 is rotatable in a support 20 which can be removed or unscrewed from the gearbox, and its outer end 18' is housed in a cylindrical cavity 20' in the support 20. Leakage of oil outwards along the shaft 1 8 is prevented by a gasket 22, according to the invention, inserted with reasonable force into the cavity 20'. The shaft 18 may be inclined (as illustrated), vertical or horizontal, but in each case the cavity 20' and the gasket 22 are located above the oil level L. The shaft 1 8 can be made from nylon in one piece with the pinion 1 6. The gasket 22, Figure 2, has an annular rubber body 24 of circular cross-section, having an enlarged end 24' stiffened by a metal reinforcing ring 26. When in use, this end faces towards the outside of the gearbox 1 0, and the ring 26 acts as a bearing for the tool which inserts the gasket into the cavity 20'. The opposite end of the body 24 faces towards the inside of the gearbox 10, that is, towards the flow of the oil leakage, and hence is termed the "wet end." A bush, shown as 28, is internally located relative to the body 24, and is coaxial therewith. This bush 28 extends from an axially intermediate part of the body 24 towards the wet end of the body 24, and is supported at one end by an annular portion 30 of reduced thickness (relative to that of the bush and the body) so that the bush "floats" in relation to the body. The radially inner surface 28' of the bush 28 has a succession of closely spaced helical ridges 32. This surface may be cylindrical as shown, or it may be conical, narrowing towards the wet end of body 24 with a half-apex angle of not more than 50. The ridges 32 effect, together with cylindrical surface 18" of the end 18' of the shaft 18, the dynamic sealing mentioned previously. These are therefore inclined either in the clockwise or anticlockwise sense depending on the direction of rotation of the shaft 18, and are so chosen that, in use, any oil which tends to leak is forced back by the ridges. Preferably, in such a gasket, the angle of inclination of helix of each ridge 32 is 450, and the length of the ridged surface 28' of the bush 28 is such that each ridge extends for at least 1/8 (450 of arc) of the inner circumference of the bush.Note that it is not necessary for each ridge to form a complete spiral around the hole of the bush. An unnecessarily long bush would result. Preferably, each ridge (Figure 3) has a concave, circular arc profile, the profile of two adjoining ridges forming a cusp 34; the width A of each ridge being 0.3 to 0.4 mm, and the depth B of each ridge being 0.05 to 0.09 mm. In the assembled state, the bush 28 surrounds the portion 18' of the shaft 1 8 without interference: in fact, see Figure 2, a slight radial clearance is preferred, which, measured against the cusps 34, does not exceed about 0.1 mm (so as not to prejudice the dynamic sealing). It should be pointed out, contrary to what may appear from the drawings, that the gasket according to the invention is very small, owing to the small diameter of the end 18'. For example, for a diameter of 8 mm, the length of the body 24 of the gasket is in the region of 4-5 mm, while the length of the sealing surface 28' of the bush 28 is about 1.5-2 mm, this surface being formed with 68 ridges inclined at 450 and having the dimensions given above. Claims

2. A gasket according to Claim 1, in which said inner surface is cylindrical.

4. A gasket according to Claim 1,2 or 3, in which the angle of inclination of the helix of the ridges is substantially 450, and in which the length of the bush is such that each ridge extends for at least 1/8 of the inner circumference of the bush.

5. A gasket according to Claim 1, 2, 3, or 4 in which each ridge has a concave, arcuate profile, two adjoining ridges forming cusps, the width of each ridge being from 0.3 to 0.4 mm, and the depth of each ridge being from 0.5 to 0.9 mm.

6. A sealing gasket for a tachometer drive shaft taken from a motor vehicle gearbox, substantially as described and illustrated in the accompanying drawing.

7. A gearbox provided with a gasket according to any one of Claims 1 to 6, in which the shaft is made from a polyamide resin, and in which the bush of the gasket encloses the shaft without interference.

8. A gearbox according to Claim 7, in which the bush surrounds the shaft with a radial clearance no greater than 0.1 mm.

9. A gearboxy subsantially as described with reference to the accompanying drawing.