WO1996005449A1

WO1996005449A1 - Brake pad without metallic backplate

Info

Publication number: WO1996005449A1
Application number: PCT/GB1995/001832
Authority: WO
Inventors: Franck Pierre-Jean Basille; Michel René DEPERROIS
Original assignee: Ferodo Abex Sa; T & N Plc
Priority date: 1994-08-08
Filing date: 1995-08-02
Publication date: 1996-02-22
Also published as: FR2723411B1; FR2723411A1

Abstract

This invention relates to a brake pad (6) for a vehicle brake, of the type comprising a friction lining (12) intended to mate with a rotary component which is part of the brake, and a support member (11) intended to work with a brake calliper to counteract braking torque. This brake pad (6) is characterised by the fact that the friction lining and the support member (11) are made together in one piece by moulding from essentially the same material.

Description

Brake Pad Without Metallic Backplate

The present invention relates to a brake pad for a vehicle brake, comprising a friction lining intended to mate with a rotary component which is part of the brake and a support member intended to co-operate with a brake calliper to counteract forces developed when the brake is in use. These forces include, for example, the torque or shearing force in the lining and between the lining and the support member.

Generally, the support member is made from metal, as it must fulfil different functions. It acts as mechanical reinforcement at the back of the brake pad in order to resist the pressure of the associated brake piston and it reinforces the brake pad to better counteract the braking torque; it allows the used brake pad to be taken out of the calliper; it allows indelible marking, for example by engraving information which ensures the identification of the product and finally, by virtue of its shape adapted to that of the calliper and by various drilled holes for the passage of pins, it ensures retention of the brake pad in the calliper without too much play.

Disc brake pads provided with a metallic support member (herein also referred to as a backplate) have some drawbacks.

It is possible to have problems of partial or total detachment between the backplate and the friction lining material, both during production of the brake pads and in certain cases of severe use. This detachment may be due to a poor metal/friction material compatibility, or it may be brought about by corrosion of the support member in service, despite use of protective coatings.

It is possible to have noise problems caused by vibration during braking at least partly due to friction between the metal of the backplate and the metal of the brake piston.

A metal backplate has great thermal conductivity and may cause volatilisation of the brake fluid when the friction lining material reaches very high temperatures in use. This may bring about a total loss of brake efficiency.

Furthermore, too great a difference between the thermal properties of the metal support member and the friction lining can sometimes result in deformation of the pad by virtue of differential expansion. This may lead to a lack of flatness of the friction surface, cases of jamming in the calliper and cases of slanting (uneven) wear.

Finally, a metal backplate has a considerable weight which increases the weight of the vehicle.

FR-A-2,406,128 has already suggested a brake pad in which the support member or backplate is made of an organic material which may contain asbestos. This type of material has high thermal insulation, but it can produce problems in use because of too great a difference between the thermal properties of the support member and the friction lining.

This last document represents the state of the art closest to the present invention.

According to the present invention, a friction pad or lining and support member for it are made together in one piece by moulding from essentially the same material. "Essentially the same material" in this present context includes both the use of exactly the same formulation for both components and also the use of a slightly modified formulation for the support member, as will be apparent from the following description of preferred aspects of the invention. It has been found that by using what is essentially a friction material formulation with no, or relatively minor, changes to modify its physical characteristics, it is possible to produce a one-piece article comprising a friction facing together with an underlayer which serves as a backplate, without the disadvantages thereof.

The invention further comprises friction linings and brake pads made by moulding in this way.

It is preferred that the material is made up of a mix in powder form which comprises 10 to 60% of fibres, from 0 to 15% resins, from 0 to 15% rubbers, from 1 to 8% accelerators, from 25 to 70% metals and alloys, from 10 to 30£ metal derivatives, from 0 to 10% organic friction modifying agents, from 0 to 6% inorganic friction modifying agents, from 5 to 30% fillers, from 0 to 10% solvents.

In order that the invention is better understood, it will now be described by way of example with reference to the attached drawings, in which:

Figure 1 shows a section of a mould used for manufacturing a brake pad according to the invention,

Figure 2 is a view of the front face of a brake pad according to the invention,

Figure 3 is a side view of the brake pad in Figure 2, and

Figure 4 is a plan view of the brake pad in Figure 2.

In Figure 1, a mould 1 has a die 2 supporting an anvil 2a and of which the internal cavity 3 is adapted to the shape of the brake pad required, together with a piston 4 intended to compress a friction material mix in powder form 5 introduced into the internal cavity 3. The mix 5 is subjected to a hot-pressing operation in appropriate conditions of temperatures, pressure and time, as a function of its composition.

The die 2, the anvil 2a and the piston 4 supply heat to cure the mix. The piston 4 is used both for moulding and for extraction of the brake pad 6, the anvil being removable.

It will be appreciated that the mould described above is similar to the moulds used for the manufacture of friction linings for brake pads with conventional metal backplates.

The back of the pad 6 obtained may be moulded in such a manner that it has, when worn to a thickness lower than or equal to the projected thickness at the end of its service life, (as defined by the position of the wear indicator) , protuberances 7 which allow easy extraction of the brake pad 6 from the brake calliper without having to use a special tool.

These protuberances 7 may be designed in such a manner that they ensure by their shape the same role of holding in the brake calliper as the metal support member or the member made of organic material of the previous kind. In order to facilitate removal of the pad 6 from the mould, the protuberances 7 may have a substantial relief angle relative to the plane of the back surface of the pad.

To ensure a better mechanical resistance to the force developed whilst counteracting braking torque, the pad 6 may be moulded in such a manner that it does not have a relief angle in that region of the back of the pad having a thickness e equal to that of the pad at the end of its projected service life. There is therefore a better distribution of forces over one relatively large surface and the phenomenon of localised material bruising is reduced.

The dimensions of the mould 1 are calculated so that the sides of the finished brake pad 6 are in accordance with the drawing provided and that the brake pad 6 is lodged perfectly in the brake calliper intended to hold it. The formulation of the mix 5 has been designed so that, in service on a vehicle, modification of the working surfaces due to thermal expansion is less than that required for good functioning of the brake.

Figures 2 to 4 show a brake pad 6 according to the invention, provided with protuberances 7. The brake pad 6 has on its rear face some optional dummy holes 8 to facilitate its extraction from the calliper, as well as a recess 9 intended to receive a wear indicator in a known manner. The service life thickness e may be between a third and a quarter of the total thickness E of the brake pad 6, this thickness E being, for example between 25mm and 30mm.

The recess 9 may alternatively be provided in the friction surface 10.

The material of which the brake pad 6 is made up is preferably uniform through the whole thickness of the pad, but the material of the underlayer 11 which does not take part in the friction may be different from the material of the friction lining 12, whilst still being of the same nature, with an essentially similar composition, in order to ensure better cohesion than with a metal backplate, this underlayer 11 being modified in comparison with the friction material, with the aim of improving its mechanical characteristics, such as resistance to the piston pressure and to braking torque, as well as to localised bruising due to all the shocks suffered by the brake pad 6 when in use.

The modified composition of this underlayer 12 is formulated such that it has thermal characteristics which make it possible to minimise heating of the brake fluid, because it is a better insulator than a metal backplate, yet still to ensure sufficient dissipation of heat to prevent the friction material itself from heating up too much, which could alter its frictional properties and/or cause other defects.

For the brake pads 6 described above, the mixes 5 preferably have the following compositions. Friction Rednfccced Basic Constituents Material Uτ3erlayer

Fibres

Asbestos: grades 7D, 5K, 5R

Glass, carbon, boron, ceramic silicon, mineral, graphite fibres 10-60 10-60

Metallic fibres (Fe, Cu, Al, Zn, steel ...)

Textile fibres (natural of synthetic)

Organic fibres

Resins

Phenol-formaldehyde, unmodified or modified organic (oils, rubber ...) 0-15 0-50 or inorganic (boron, silane, aluminium ...) on a base of ordinary phenol or of sub¬ stituted phenols (cresols, xylenols ...) Urea-formaldehyde, elamine, other nitrogenous derivatives.

Resins on a base of aldehydes other than formaldehyde (furfural, benzaldehyde, croton-aldehyde ...)

Thermostable resins other than phenolic resins (polyimides, polyesterimides, polyamide-imide, polybenzimidazole, polycarbonates, polyphenyl- sulphide, polyamides, polyester ...)

Rubbers

Natural rubbers

Mixture of 30% styrene

+ 70% butadiene

Nitriles and acrylonitriles

Butyl

Polychloroprene 0-15 0-30

Chlorobutyl

Ethylene propylene terpolymer Friction ReinfoxoBd Material Underlayer

Rubbers (Cont ' d)

Polyolefin Regenerated Pulverised wastes

Accelerators. Vulcanising Agents

Sulphur Zinc oxide Magnesium oxide Mercaptobenzothiazole sulphide 1-8 5-10 Cumates Altax etc ... Cobalt naphthenate Hexamethylene tetramine

Metals and Allovs

Copper, zinc aluminium, brass, bronze

Antimony, tin 25-70 25-70

Bismuth

Iron powder, cast-iron powder

Steel wool

Metal Derivatives 10-30 10-30

Litharge, galena Copper sulphides Copper oxide Antimony sulphide Molybdenum sulphide Iron oxides Iron sulphide Zinc sulphide Titanium oxides Friction Reinforced Material IJnderlaver Friction Modifying Agents

Organic: resins based on modified cashew 0-10 0-10 nut shell oil or non-graphitic

Inorganic: silicon cyanites rottenstone chromium oxides 0-6 0-6 slag glass globules zirconium silicate

Various Fillers

Calcium aluminate

Antioxidants (agerite ...)

Carbon black

Wood dust 5-30 5-30

Petrol coke

Lime; Barium sulphate

Coal; Mica; Vermiculite

Chalk, kaolin, marble powder

Clays

Talk

Solvents

Water

Aromatics

Aliphatics 0-10 0-10

Chlorinated

Alcohols

Ketones

Claims

1. A brake pad for a vehicle brake, comprising a friction pad or lining intended to mate with a rotary component which is part of the brake, and a support member for said pad or lining, intended to work together with a brake calliper to counteract the forces developed when the brake is in use, characterised in that the friction lining and the support member for it are made together in one piece by moulding from essentially the same material.

2. A brake pad according to claim 1, characterised in that the material is made up of a mix in powder form which contains 10 to 60% fibres, from 0 to 15% resins, from 0 to 15% rubbers, from 1 to 8% accelerators, from 25 to 70% metals and alloys, from 1- to 30% metal derivatives, from 0 to 10% organic friction modifying agents, from 0 to 6% inorganic friction modifying agents, from 5 to 30% fillers, from 0 to 10% solvents.

3. A brake pad according to claim 1 or claim 2 characterised in that the mix composition of that part of the one-piece moulding which in use constitutes the support member is modified to enhance its strength and thermal conductivity in relation to that of the working part of the pad or lining.

4. A method of making a brake pad for a vehicle brake characterised by the step of moulding as a unitary article a friction element and a support element for it, from essentially the same material.