GB2190156A

GB2190156A - Brake anchor pin assemblies

Info

Publication number: GB2190156A
Application number: GB08709941A
Authority: GB
Inventors: Edward Jackson Diggs
Original assignee: Rubery Owen Rockwell Ltd
Current assignee: Rubery Owen Rockwell Ltd
Priority date: 1986-05-02
Filing date: 1987-04-27
Publication date: 1987-11-11
Also published as: GB2190156B; GB8709941D0

Abstract

Brakes, particularly on commercial vehicles, are subject to frequent and severe use in all weather conditions whereby component parts are subjected to arduous working conditions. Successive heating and cooling cycles in use, allied with humidity, provide ideal conditions for promoting corrosion. This corrosion frequently makes it very difficult to remove brake anchor pins to enable maintenance or repair of brakes to be effected. An internal expanding shoe and drum type brake has a bearing bush 2 in a brake anchor bracket 1. The bush 2 receives an anchor pin 5 having a cylindrical bearing surface. Pin 5, with circlips in grooves 8, locates the gussets 9 of a brake shoe. The bore of bush 2 has indentations 4 distributed over its surface which serve as a lubricant reservoir. Grooves 6 on pin 5 receive sealing rings 7 which retain the lubricant and inhibit access of corrosion causing agents. Bush 2 may have a plain bore and the identations may be provided on pin 5, and the grooves for the sealing rings may be provided in the bush 2. Methods of assembling the pin and bush are disclosed. <IMAGE>

Description

SPECIFICATION Brake anchor pin assemblies This invention relates to anchor pin assemblies for use with brake shoes of vehicles fitted with brakes of the internal expanding shoe and drum type.

Brakes, particularly on commercial vehicles, are subject to frequent and severe use in all weather conditions whereby component parts are subjected to arduous operating conditions.

In operation, parts heat up when brakes are applied and are then subsequently cooled.

Successive heating and cooling cycles, allied with humidity, provide ideal conditions for promoting corrosion and this is accelerated by the presence of salt applied to roads in winter.

A long standing problem arising from this becomes apparent when a brake malfunction occurs or when the time comes to replace brake shoes due to their friction linings being worn. The corrosion which has occurred makes removal of the brake anchor pin from the anchorage, for example a brake anchor bracket, a difficult and time consuming operation. Various protective treatments have been tried but these break down within the useful life of the brake linings and corrosion sets in.

Generally the anchor pin is cylindrical and works in a bearing bush, for example of bronze, in the anchor bracket and the pin is hard chromium plated. The plating breaks down and flakes off initially in the high stress unbushed regions where the pin is engaged in holes in the brake shoe gussets. In severe cases the flaking can extend also over the central portion of the pin which is inside the bush. As the plating breaks down corrosion sets in and, once started, proceeds at an accelerating rate. The hard flakes of plating abrade the gussets and bush so that either the pin seizes up or rapid wear takes place promoting increased clearances which allow easier access of moisture and accelerated corrosion leading to seizure and malfunction of the brake.

According to one aspect of the present invention a brake anchor pin assembly comprises in combination a bearing bush having a generally cylindrical bore and adapted to be mounted in an anchorage, a brake anchor pin having a cylindrical bearing surface situated within the bore and co-operating therewith, a lubricant reservoir incorporated between the anchor pin and the bush, and sealing means acting between the anchor pin and the bush so as to retain lubricant between said anchor pin and bush and to inhibit access of corrosion causing agents thereto.

According to another aspect of the present invention a brake assembly of the internal expanding shoe and drum type comprises in combination an anchorage, at least one bearing bush having a generally cylindrical bore and mounted in the anchorage, a brake anchor pin having a cylindrical bearing surface situated within the or each bush and co-operating therewith, a lubricant reservoir incorporated between the or each anchor pin and bush, and sealing means acting between the or each anchor pin and bush so as to retain lubricant between each said anchor pin and bush and to inhibit access of corrosion causing agents thereto.

The anchorage may comprises, for example, a brake anchor bracket or a brake back plate.

The lubricant reservoir may comprise indented surfaces in the bore of the bush which provide little pockets in which lubricant, for example grease, is stored.

The anchor pin may be straight cylindrical.

In an alternative construction it may be stepped cylindrical.

The sealing means may comprise an annular groove at each end of the cylindrical bearing surface and a sealing ring therein, for example an 0 ring of rubber or like material.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a section through part of a brake anchor bracket and the gussets of a brake shoe and incorporating a brake anchor pin assembly according to this invention Figure 2 is a scrap view on the developed inner surface or bore of the bearing bush of Fig. 1, Figure 3 is a section on line A-A of Fig. 2, Figure 4 is similar to Fig. 1 incorporating a stepped cylindrical design of brake anchor pin, and Figure 5 is a view on one of the anchor pin of Fig. 4, Referring to the drawing Fig. 1, a brake anchor bracket 1 is bored to receive the bush 2 of a brake anchor pin assembly 3 with a push fit.The bush 2 may be formed from a flat strip of bearing material the inner surface of which bears a plurality of indentations 4, for example ball indentations, as illustrated in Figs. 2 and 3. The indentations 4 may be arranged in rows in a pattern in which successive rows are inclined at an angle to one another as indicated at B, and with the indentations of successive rows staggered axially of the bore of the bush with respect to the indentations of the adjacent rows. Each indentation 4 provides a small pocket for lubricant, for example grease, and the staggering of the indentations ensures availability of lubricant to the whole of the bearing surface of the anchor pin 5 which lies within the bush 2.

The anchor pin 5 is straight cylindrical. It has a cylindrical bearing surface which lies within the bush 2 and at each end of this surface an annular groove 6 is provided to receive a sealing ring, for example an 0 ring of rubber or like resilient material, shown sec tioned at 7.

Adjacent each end of the anchor pin 5 a further annual groove 8 is provided to receive a circlip or like locating and retaining member (not shown).

A brake shoe is represented by its two gussets 9, shown in section. These have aligned holes to receive the anchor pin 5.

The assembly is built up by pushing bush 2 into its mounting in anchor bracket 1, the inner surface of the bush being coated with lubricant.

A sealing ring 7 is fitted in one of the grooves 6 and, with the gusset holes in register with the bush, the anchor pin 5 is inserted so that the empty groove 6 enters first. The pin 5 is pushed through until the empty groove 6 is clear of the gusset so as to enable a sealing ring 7 to be fitted. The pin 5 is then centred so that both sealing rings lie within the bore and to enable circlips to be fitted in the grooves 8 to retain the asembly.

Referring now to Fig. 4, the anchor bracket 1 similarly provides a mounting for the bush 2 in which a stepped cylindrical anchor pin 11 is journalled.

The anchor pin 11 and brake shoe gussets 12 are generally as described and claimed in British Patents Nos. 1580963 and 1600535 of Rockwell International Corporation. Thus, the gussets 12 have slots 13 to facilitate removal of the brake shoe without removal of the anchor pin 11, and the reduced diameter ends of the anchor pin 11 allow it to be located and retained by the gussets 12.

The anchor pin 11 has a cylindrical bearing surface within the bush 2 and at each end an annular groove 14 is provided for a sealing ring 15 as has been described with reference to Fig. 1.

The assembly is built up by first assembling the anchor pin 11 to the bush 2. The anchor pin assembly is then fitted to the anchor bracket 1 by pushing the bush 2 into its mounting in bracket 1. The slotted ends of the brake shoe gussets are then passed over the reduced diameter ends of the anchor pin 11.

The pin 11, with a sealing ring 15 in one groove 14, is entered into the lubricated bush 2, the empty groove 14 entering first. When the latter has passed through the bush a sealing ring 15 is fitted and the pin 11 is then centred in the bush 2. This method of assembly assists in filling the indentations with lubricant and avoids expulsion of the lubricant which would occur if a sealing ring 15 passed through the bush 2 during assembly. An interference fit of the sealing rings lightly retains the anchor pin in the bush in both constructions described.

Fig. 5 is an end view on the anchor pin 11.

It will be appreciated that the lubricant reservoir provided by the indentations in the bush 2 could be provided in other ways, for example by slotting or grooving the inner surface of bush 2 or by indenting slotting or grooving the cylindrical bearing surface of the anchor pin 5, 11. Similarly the annular grooves and sealing rings could be provided in the bush 2 instead of in the pin 5, 11.

If the indentations are provided on the anchor pin the cylindrical bearing surface is lubricated before assembly, and the assembly method is otherwise preferably as has already been described.

If the sealing rings are provided in the bush 2 a modified method of assembly is preferred.

Namely, a sealing ring is fitted at one end of the bush, the indented surface is lubricated and the anchor pin is entered into the other end of the bush and passed through until access to the empty groove is available to enable the second sealing ring to be fitted. The anchor pin is then centred in the bush so that its cylindrical bearing surface is engaged by both sealing rings.

The anchor pin 5, 11, conventionally of steel, is preferably provided with a suitable corrosion resistant coating in accordance with normal practice.

Claims

1. A brake anchor pin assembly comprising in combination a bearing bush having a generally cylindrical bore and adapted to be mounted in an anchorage, a brake anchor pin having a cylindrical bearing surface situated within the bore and co-operating therewith, a lubricant reservoir incorporated between the anchor pin and the bush, and sealing means acting between the anchor pin and the bush so as to retain lubricant between said anchor pin and bush and to inhibit access of corrosion causing agents thereto.

2. A brake anchor pin assembly as claimed in Claim 1 wherein the reservoir comprises indented surfaces in the bore of the bush providing pockets in which lubricant is contained

3. A brake anchor pin assembly as claimed in Claim 2 wherein the indented surfaces are arranged in rows in a pattern in which successive rows are inclined at an angle to one another with the indentations of successive rows staggered axially of the bore of the bush with respect to the indentations of the adjacent rows.

4. A brake anchor pin assembly as claimed in Claim 1 wherein the reservoir comprises an indented surface or surfaces in the cylindrical bearing surface of the anchor pin in which lubricant is contained.

5. A brake anchor pin assembly as claimed in any preceding claim wherein the sealing means comprises an annular groove adjacent each end of one of the cylindrical bearing surface of the anchor pin or the bore of the bush and a sealing ring of rubber or like material in each groove providing a seal between the groove and the other of the bore of the bush or the cylindrical bearing surface of the anchor pin.

6. A brake assembly of the internal expanding shoe and drum type comprising in combination an anchorage, at least one mounting for a brake anchor pin assembly and a brake anchor pin assembly as claimed in any preceding claim in each said mounting.

7. A method of assembling a brake anchor pin assembly as claimed in Claim 5 comprising the steps of lubricating the indented surface, fitting a sealing ring to one groove and entering the anchor pin into the bush such that the sealing ring is not engaged between the anchor pin and the bush until the anchor pin is fully entered into the bush, passing the anchor pin through the bush to allow access to the other groove, fitting a sealing ring to said other groove and moving the anchor pin in the opposite direction until both sealing rings are engaged between the bush and the anchor pin.

8. A brake anchor pin assembly substantially as described herein with reference to the accompanying drawings Fig. 1 to 3 or Figs. 2 to 5.

9. A brake assembly of the internal expanding shoe and drum type substantially as described herein with reference to the accompanying drawings Figs. 1 to 3 or Figs. 2 to 5.