GB1592817A

GB1592817A - Disc brake apparatus

Info

Publication number: GB1592817A
Application number: GB10691/78A
Authority: GB
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1977-03-18
Filing date: 1978-03-17
Publication date: 1981-07-08
Also published as: CA1104953A; SE412101B; SE7703128L; DE2811848A1; JPS53134172A; IT1158668B; IT7821348A0; FR2384161A1

Description

(54) DISC BRAKE APPARATUS (71) We, E. I. DU PONT DE NEMOURS AND COMPANY, a Corporation organised and existing under the laws of the State of Delaware, United States of America, located at Wilmington, State of Delaware, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: The present invention concerns so-called disc brakes in which one or several discs attached to a wheel are arranged to effect braking with the help of brake pads mounted on the chassis of the vehicle.

In practice, disc brakes have been shown to have certain problems which, so far, have been difficult to correct. Because of economy in production, the choice of less suitable materials and the lack of precision during production, the brake discs can become more or less skew, or during rotation the pads may engage the brake discs unevenly. It can also happen that, following heavy braking, the brake disc may be damaged so that it becomes skew. When the brake pads engage these skew brake discs, the discs tend to transfer a sideways movement to the brake pads which in turn are mounted on the chassis of the vehicle. This movement causes the brake pads to move somewhat in their mounting units, the so-called brake seats.

Because of the frictional forces between the brake pads and the brake seats these movements are transferred to the chassis of the vehicle. This causes vibrations and abnormal wear of the brake pad linings and of the pads themselves and even causes wear on certain parts of the chassis of the vehicle. Squealing brakes can result from the movement between the brake pads and the brake seats.

It is desirable to eliminate these problems and to create a disc brake apparatus that prevents the transfer of at least a large part of the movement of the brake pads to the brake pad mounting unit. It is also desirable to prevent the squealing which arises from the movement of the brake pads in the brake seats.

Prior efforts to solve these problems are described in U.S. Patents 3,648,807 -- Lottridge et al. (1972), 3,684,061 - Ogawa et al.

(1972), 3,730,302 - Ogawa et al. (1973), 3,722,634 - Ogawa et al. (1973), and 3,998,296 - James (1976). Further improvements are still desirable.

The present invention provides a disc brake apparatus wherein at least one brake disc is fixed to a rotating body which is to be braked by means of brake pads moveably mounted in a housing and which are arranged to be urged towards opposite sides of the rotating body by urging means to cause braking, where in each brake pad is provided directly or via an intermediate member with coating of a self-lubricating solid polymer material, said antifriction coating being located both between said brake pad and said urging means and between the brake seat and the edge of the brake pad which is the trailing edge relative to the normal direction of rotation of the rotating body.

Preferably, the invention provides for restricted motion beween the intermediate member and the brake pad. The polymer material of the antifriction coating is preferably a fluoropolymer such as polytetrafluoroethylene. The antifriction coating can be integral with the brake pad, or it can be in the form of a thin sheet, and it is sometimes preferable to shape the intermediate member so that it is cut away in a portion between the brake pad and the urging means which is distant from the trailing edge.

The invention will now be described by way of example with reference to the accompanying drawings, wherein: Fig. 1 is an elevation, partially in section, schematically showing a disc brake apparatus of the invention; Fig. 2 is a similar elevation taken along section line 2-2 in Fig. 1, showing the face of a brake pad; Fig. 3 is a similar elevation taken along line 3-3 in Fig. 1 showing the antifriction member on the back of a brake pad; and Fig. 4 is a similar elevation taken along section line 4-4 in Fig. 3, showing a brake pad, an antifriction member and the brake seat on an enlarged scale.

It can be assumed that the main force that causes vibrations and brake squeal is transferred from the trailing edge of the brake pad in the normal direction of rotation of the brake disc. In a preferred embodiment of the invention, the disc with the lubricating polymeric coating is bent at an angle, such as about a right angle, and sits with its one portion between the brake pad and its hydraulic piston, and the other angularly bent limb between the above-mentioned forward edge of the brake pad and its holder.

The invention will now be described in more detail with reference to the attached drawings which show a preferred practical example of the invention.

The arrangement shown in the drawings consists of brake disc 1, which is fixed on a rotating unit (not shown) that is to be braked, two brake pads 2, 3 and a holding unit in the form of housing or brake seat 4.

In case a brake disc normally rotates in either direction, it can be said to have two opposite normal directions of rotation.

Brake disc 1, which is normally made of cast iron or steel, is assumed to have the normal direction of rotation marked by arrow 5.

The disc and its associated rotating unit are arranged so that they can be braked by pressing brake pads 2, 3 against the disc.

Each brake pad consists of brake shoe 6, made of iron or other hard material, which is equipped with brake lining 7 made of a material having a known coefficient of friction.

The brake pads are essentially rectangular in shape and they are each mounted in their corresponding holder 8 in brake seat 4. The pads are prevented from falling out of the brake seat, and are held together despite any tendency toward internal sideways movement, by pins 9. The brake seats are normally equipped with pneumatic or hydraulic pistons 10 which are designed to press the brake pads toward one another and against brake disc 1.

It is clear that a skew brake disc, during braking, tends to displace the brake pads sideways in relation to the brake seat. Because of the friction between the brake pads and the brake seat this sideways movement cannot occur without some reaction. Thus a vibration is generated and transferred to the vehicle, partly via the brake pads and the brake seat and partly even via the brake disc itself. At the same time a squeal can be created. It has previously been assumed that the main transfer of vibration takes place via the large planar surface of the brake shoe 6. Attempts have been made to impregnate that surface with fat, oil, or similar types of materials. These efforts, however, have given fairly poor results and the fat or oil can, together with the dust and dirt which collects in the space behind the brake pads, further hinder the movement of the brake pads in relation to the brake seat.

The invention rests partly on the discovery that the main vibrational forces are transferred from the narrow trailing edge of the brake pad as seen from the direction of motion of the brake disc. The invention also depends on the idea that one can reduce the transfer of ,the brake pad motion to the brake seat to a minimum by reducing the friction between brake pad and brake seat, and by keeping the space in the holder 8 behind the brake pad as clean as possible.

A member 11, made of sheet metal or other suitable material, is placed on the far side of brake shoe 6 from brake disc 1, that is on the outside of brake shoe 6. This member has limited freedom of movement in relation to the brake pad and, like the pad, it is mounted by means of pins 9.

Member 11 is coated on at least one side and preferably on both sides with a selflubricating solid polymer of a type which can withstand the high temperatures, up to 2500C, which can occur during braking. This polymeric material should also be able to withstand pressures up to 50 kp/cm2 or more. This material should also repel grease and dirt and have the ability to remove the heat that is formed in the brake pad during braking. As examples of suitable lubricating solid polymers, can be mentioned fluoropolymers, especially the fluoroethane polymers, e.g. polychlorotrifluoroethylene (PCTFE) or polytetrafluoroethylene (PTFE). The latter has especially good properties for this purpose. These plastics have an unusually low coefficient of friction, they are for the most part chemically inert, they are very tough and withstand temperatures of up to 250 C or more. Their durability and load capacity is good enough so that an antifriction disc covered with tetrafluoroethylene should hold up at least as long as the friction lining on the brake pad.

During braking, a twisting movement arises in the brake disc. To compensate for this twisting, member 11 is preferably recessed or cut away as shown at 12 on the side distant from the trailing edge of the brake pad.

As mentioned earlier, a main part of the vibrational motion of the brake block seems to be transferred to the brake seat via the narrow trailing edge 13 on the brake shoe 6, i.e. the edge which is facing the normal direction of motion of the brake disc. In order to eliminate or at least reduce the transfer of vibration to the vehicle and the risk of brake squeal, the member 11 is constructed with edge 14 bent at an angle. This edge is situated between trailing edge 13 of brake shoe 6 and the corresponding part 15 of the brake seat. In certain cases, it is advantageous to place a thicker layer of polymeric material on the trailing edge 14 of the antifriction disc.

Most of the heat removal from the brake block takes place across the planar rear side of the brake shoe 6 and the corresponding part of the antifriction disc. For this reason, the layer of polymeric material 16 on that part of member 11 should be thin enough and of such a quality that it allows adequate transfer of heat to the brake seat.

In an alternative form of the invention, brake shoe 6 is coated with the same or similar material as the polymer layer used on the member 11. It is especially advantageous to coat trailing edge 13 of the brake shoe 6 with such a material in order to further reduce the friction between brake pads 2, 3 and brake seat 4. It is best to coat both the trailing edge and opposite edge and the side of the brake shoe which is away from the brake disc, with an antifriction material. The coating on the brake shoe can be used in conjunction with or in place of a separate intermediate member.

It is to be understood that the above description only constitutes an illustrative example and that many different modifications can exist within the scope of the patent claims given below. In particular, the invention is intended to include many different types of polymer coatings in addition to those already mentioned.

WHAT WE CLAIM IS:- 1. A disc brake apparatus wherein at least one brake disc is fixed to a rotating body which is to be braked by means of brake pads moveably mounted in a housing and which are arranged to be urged towards opposite sides of the brake disc by urging means to cause braking, wherein each brake pad is provided directly or via an intermediate member with an antifriction coating of a self-lubricating solid polymer material, said antifriction coating being located both between said brake pad and said urging means and between the brake seat and the edge of said brake pad which is the trailing edge relative to the normal direction of rotation of the rotating body.

2. The disc brake apparatus of Claim 1 wherein the polymer material is a fluoropolymer.

3. The disc brake apparatus of Claim 2 wherein the polymer material is polytetrafluoroethylene.

4. The disc brake apparatus of Claim 1, 2 or 3 wherein the urging means comprises a hydraulic piston.

5. The disc brake apparatus of any one of the preceding claims wherein the coating is provided on at least one side of an intermediate member.

6. The disc brake apparatus of Claim 5 wherein the intermediate member has restricted motion relative to the brake pad.

7. The disc brake apparatus of Claim 5 or 6 wherein the intermediate member comprises two portions in planes at about right angles to each other, one portion being between the brake pad and the urging means and the other portion being between the brake seat and the trailing edge of the brake pad.

8. The disc brake apparatus of Claim 5, 6 or 7 wherein the intermediate member is coated with a self-lubricating solid polymer material on two opposing sides.

9. The disc brake apparatus of Claim 5, 6, 7 or 8 wherein the polymer material is thicker on parts of the intermediate member that are closer to the trailing edge of the brake pad than on parts of the intermediate member which are further away from the trailing edge.

10. The disc brake apparatus of any one of Claims 5 to 9 wherein the intermediate member is shaped so that there is no intermediate member between part of the brake pad and the urging means distant from the trailing edge of the brake pad.

11. The disc brake apparatus of Claim 1, 2, 3 or 4 wherein the coating is integral with the brake pad on the side of the brake shoe facing the urging means and on the trailing edge of the brake shoe.

12. A disc brake substantially as hereinbefore described.

13. A disc brake substantially as hereinbefore described with reference to the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Most of the heat removal from the brake block takes place across the planar rear side of the brake shoe 6 and the corresponding part of the antifriction disc. For this reason, the layer of polymeric material 16 on that part of member 11 should be thin enough and of such a quality that it allows adequate transfer of heat to the brake seat. In an alternative form of the invention, brake shoe 6 is coated with the same or similar material as the polymer layer used on the member 11. It is especially advantageous to coat trailing edge 13 of the brake shoe 6 with such a material in order to further reduce the friction between brake pads 2, 3 and brake seat 4. It is best to coat both the trailing edge and opposite edge and the side of the brake shoe which is away from the brake disc, with an antifriction material. The coating on the brake shoe can be used in conjunction with or in place of a separate intermediate member. It is to be understood that the above description only constitutes an illustrative example and that many different modifications can exist within the scope of the patent claims given below. In particular, the invention is intended to include many different types of polymer coatings in addition to those already mentioned. WHAT WE CLAIM IS:-

1. A disc brake apparatus wherein at least one brake disc is fixed to a rotating body which is to be braked by means of brake pads moveably mounted in a housing and which are arranged to be urged towards opposite sides of the brake disc by urging means to cause braking, wherein each brake pad is provided directly or via an intermediate member with an antifriction coating of a self-lubricating solid polymer material, said antifriction coating being located both between said brake pad and said urging means and between the brake seat and the edge of said brake pad which is the trailing edge relative to the normal direction of rotation of the rotating body.

12. A disc brake substantially as hereinbefore described.