GB2362691A

GB2362691A - Vehicle brake cam roller having a ceramic sleeve

Info

Publication number: GB2362691A
Application number: GB0012759A
Authority: GB
Inventors: Keith John Chapman
Original assignee: Meritor Heavy Vehicle Systems Ltd
Current assignee: Meritor Heavy Vehicle Systems Ltd
Priority date: 2000-05-26
Filing date: 2000-05-26
Publication date: 2001-11-28
Anticipated expiration: 2020-05-26
Also published as: GB2362691B; GB0012759D0

Abstract

A cam roller 1 for a vehicle drum brake has a sleeve 2 of a ceramic material. The cam roller may also have a ceramic pin, or the pin 3 may be nitro carburised steel coated 8 with a ceramic material. The ceramic material avoids corrosion and a need for lubrication, which substantially increases the useful working life of the cam roller. Preferably the ceramic sleeve 2 has its external surface bevelled 4, with slight convexity, at the opposite ends so as to reduce stress at the ends. Opposite ends of the internal circumferential surface may also be bevelled 5, the pin 3 being a close rotatable fit in the sleeve 2.

Description

2362691 1 VEHICLE BRAKE CAM ROLLER This invention relates to a vehicle

brake cam roller such as used in a brake assembly of the kind in which brake shoes of an internal shoe drum brake are operated by rotation of a brake cam, the brake shoes being relatively pivoted on cam rollers between their inoperative and operative positions.

Cam rollers have conventionally comprised a metal sleeve on a metal pin. The sleeve has usually been made of steel such as C117 which has been case hardened and chromium plated, and the pin has also been of a hard chromium plated steel such as EN16T. A problem has been that these cam rollers have been prone to corrosion, the rate of corrosion depending upon the climatic conditions in which the vehicles operate. For example, in Scandinavian countries, because of adverse weather conditions for driving, vehicles may be laid-up for long periods during winter months and cam rollers can become solid with rust within about three months. Under the weather conditions of the United Kingdom cam rollers may corrode within as little as six months. Only in warmer, drier countries, such as Mediterranean countries, may a significantly longer useful working life, of say up to three years, be expected for cam rollers. Corroded cam rollers may be made serviceable again by de-corroding and greasing them but even so they can still only have a relatively short useful life, and during the servicing work the vehicles are out of commission, which is undesirable.

In an attempt to increase their useful working life, cam rollers have been made which have a hardened steel sleeve and pin with a phosphor bronze bush in the sleeve in which the pin is located. Typically the sleeve is 2 made of 708 M40T steel which is vacuum hardened and then nitrocarbourised to final working hardness, and the pin is made of 605M36T steel which is also nitro-carbourised to final working hardness. Such cam rollers can have a substantially longer useful working life than the conventional cam rollers described. However, these cam rollers do also suffer from corrosion.

The aim of the present invention is to provide a cam roller which avoids the corrosion problems of the known cam rollers.

According to a first aspect the present invention consists in a vehicle brake cam roller having a sleeve of a ceramic material.

The cam roller may also have a pin of a ceramic material or at least 15 coated with a ceramic material. The pin may be made of metal, for example a steel, to which a ceramic coating is applied.

Use of the ceramic material avoids corrosion and a need for lubrication of the cam roller.

Ceramic materials are available of which the sleeve may be made, and the pin made or coated, which will co-operate satisfactorily with minimal wear.

Ceramic materials which may be used may, for example, comprise: alumina, including toughened aluminas, alumina silicate, magnesium silicate, zirconia, silicon nitride, silicon carbide, plastic and polymer ceramics. Suitable polymer ceramic materials are made by Rauschert GmbH & Co.KG under the registered trade marks CERMOPOL and CERMASIL.

t 3 In one embodiment the cam roller has a ceramic sleeve on a steel pin coated with ceramic material. The ceramic material is Rapal 200 AZ made by Rauschert GmbH & Co. KG and the pin is 605M 36T steel.

The ceramic sleeve may be moulded to its required finished form for use so that it can be produced in one operation. No heat treatment is required subsequently. It is possible, therefore, for a cam roller in accordance with the present invention to be made more cheaply than a known cam roller having a steel sleeve which has needed heat treatment to attain a suitable hardness for use.

Preferably the ceramic sleeve has its external circumferential surface bevelled, desirably with slight convexity, at the opposite ends. The bevelling takes away from the ends of the sleeve loading exerted on the cam roller while it is in use, thereby reducing stresses at the ends which might cause the sleeve to split. The opposite ends of the internal circumferential surface of the sleeve may also be bevelled.

A cam roller in accordance with the present invention may have a useful working life in excess of 5 years.

The pin of the cam roller may be supported in known manner by a retaining clip of a known form. Eyes of the retaining clip which receive the opposite ends of the pin may have seals bonded into them.

According to a second aspect of the present invention there is provided a vehicle internal shoe drum brake which includes a cam roller in accordance with the foregoing first aspect of the invention.

4 An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a side view of a vehicle brake cam roller in accordance with the first aspect of the present invention; Figure 2 is an enlarged fragmentary sectional view of the part of the cam roller encircled at A in Figure 1, and Figure 3 is an exploded perspective view of part of an internal shoe drum brake assembly for a vehicle including cam rollers of the form shown in Figures 1 and 2.

Referring to Figures 1 and 2, a vehicle brake cam roller 1 is shown which comprises a sleeve 2 and an axial pin 3.

The sleeve 2 is a moulding of a ceramic material, for example Rapal 200 AZ as aforementioned. As shown, the sleeve is substantially cylindrical but its external circumferential surface has bevelling 4 at the opposite ends. The bevelling 4 has a slight convexity. The opposite ends of the internal circumferential surface of the sleeve 2 also have bevelling 5, Figure 2.

Pin 3 is longer than the sleeve 2 having a central portion 6 which rotatably locates in the sleeve and opposite end portions 7 of slightly smaller diameter which project from the sleeve. The pin is made of steel, for example 605M36T, which is nitro carburised and has a coating 8 of ceramic material applied to it similar to that of the sleeve. The coating 8 is applied to a thickness such that the coated central portion 6 of the pin 3 is a close rotatable fit in the sleeve.

For use the cam roller is located in a Ushaped retaining clip 9, Figure 3, of a known form having a pair of spaced parallel eyes 10 in which the end portions 7 of the pin are engaged with the sleeve 2 positioned between the eyes. The retaining clip 9 is mounted in known manner in an internal shoe drum brake assembly for the cam roller to provide a pivot for a cam actuated brake shoe 11.

6

Claims

1. A vehicle brake cam roller having a sleeve of a ceramic material.

2. A vehicle brake cam roller according to claim 1 further comprising a pin of a ceramic material.

3. A vehicle brake cam roller according to claim 1 further comprising 10 a pin coated with a ceramic material.

4. A vehicle brake cam roller according to claim 3 in which the pin made of metal.

5. A vehicle brake cam roller according to any preceding claim in which the ceramic material comprises at least one of the group of alumina, toughened aluminas, alumina silicate, magnesium silicate, zirconia, silicon nitride, silicon carbide, plastic and polymer ceramics.

6. A vehicle brake cam roller according to claim 1 having the sleeve of ceramic material on a steel pin coated in ceramic material.

7. A vehicle brake cam roller according to any preceding claim in which the sleeve is moulded to its required finished form.

8. A vehicle brake cam roller according to any preceding claim in which the external circumferential surface at the opposite ends of the sleeve is bevelled.

7

9. A vehicle brake cam roller according to claim 8 in which the bevelling has a convexity.

10. A vehicle brake cam roller according to claim 8 or claim 9 in which the opposite ends of the internal circumferential surface of the sleeve are bevelled.

11. A vehicle brake cam roller according to any preceding claim that in turn depends on claims 2, 3, 4 or 6 in which the pin is supported by a 10 retaining clip.

12. A vehicle brake cam roller according to claim 11 in which eyes of the retaining clip, which receive the opposite ends of the pin in use, have seals bonded into them.

13. A vehicle brake cam roller substantially as herein before described and as illustrated by the drawings.

14. A vehicle internal shoe drum brake comprising a brake cam roller 20 according to any preceding claim.