GB1602542A

GB1602542A - Friction elements

Info

Publication number: GB1602542A
Application number: GB20388/78A
Authority: GB
Original assignee: Societe Europeenne de Propulsion SEP SA
Current assignee: Societe Europeenne de Propulsion SEP SA
Priority date: 1977-05-25
Filing date: 1978-05-18
Publication date: 1981-11-11
Also published as: ES249532Y; DE2822386A1; CA1090720A; JPS53146075A; IT1095530B; BR7803347A; SE7805380L; ES249532U; CH630155A5; SE441615B; FR2392280A1; NL7805580A; FR2392280B1; BE867393A; IT7823768A0

Abstract

The friction shoe, in particular for a disc brake, comprises at least two stratified layers (11, 12) having their outer faces (13, 14) constituting opposed friction surfaces of the friction shoe. Each layer is formed by an assembly of leaves (15) with a rosette shape in the opposite direction with respect to the other layer, each leaf (15) of one layer (11, 12) extending from the friction surface (13, 14) over the entire thickness of the layer while being inclined with respect to the friction surface. The leaves are produced from a friction material having high thermal conductivity, especially carbon. <IMAGE>

Description

(54) IMPROVEMENTS IN OR RELATING TO FRICTION ELEMENTS (71) We, SOCIETE EUROPEENE DE PROPULSION, a French Body Corporate, of 3 avenue du General de Gaulle, 92800 Puteaux, France, 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 relates to a friction element and, more particularly, to an element which is constituted by an assembly of strata of a heat conductive friction material.

Friction elements of the construction outlined above have been proposed for use with multiple disc brakes for aircraft and are in this case generally formed by a stack of annular flat strata. In previously proposed friction elements, the strata are oriented perpendicularly to the axis of the discs and the one located at one or each end of the stack defines a rubbing surface of the friction element. This arrangement presents several drawbacks.

Firstly, if whole strata cut out in one piece from a reinforcing sheet or carbon fibres are used, the unusable waste material resulting therefrom is considerable, this increasing the cost price due to the high cost of the material used. Furthermore, the stack of strata in planes parallel to the rubbing surface does not promote the effective conduction of heat which is necessary in order to dissipate the heat produced by the friction as rapidly and uniformly as possible. Heat stresses may therefore be produced and promote the occurrence of cleavages. Moreover the risks of irregularities occurring on the rubbing surfaces, due to an irregular wear, are not negligible. This may result in a decohesion of the strata near the rubbing surfaces. Moreover, the passage from one stratum to the other during the wear of the friction element provokes a discontinuity of the rubbing characteristics.

Finally, in the case of discs requiring manufacturing treatments in which the materials emit gases, or gases or liquids are required to penetrate in the materials for their densification, the arrangement of the strata one above the other perpendicularly to the axis of the disc is the least favourable as the evacuation or penetration of these fluids which is generally effected parallel to the strata, can then be made only through the side faces of the stack.

This promotes the occurrence of cleavages in the course of treatment, if the evacuation of the gases is rendered difficult, and may lead to an insufficient or heterogeneous densification if the penetration is not able to be effected completely or uniformly from the cylindrical side faces of the stack.

According to the invention there is provided a friction element comprising at least two fric tion layers having their outer faces constituting opposite rubbing surfaces of the friction element, each layer being formed by a respec tive assembly of strata with a rosette type arrangement (as herein defined) in the opposite direction with respect to the other layer, said strata being made of a frictional heat conducting material and each stratum of each layer extending from the rubbing surface over the whole thickness of the layer by being inclined with respect to the rubbing surface.

Preferably, the heat conducting material is carbon.

The term rosette type arrangement" as used herein means that all the strata of the same friction layer extend from the rubbing surface towards the inner surface of the friction layer in the same clockwise or anticlockwise direction with respect to the central axis of the friction element.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a schematic view in perspective of an embodiment of a friction element according to the invention; Figure 2 is a schematic view in perspective, partly cut away, illustrating a layer of the friction element shown in Figure 1; Figure 3 is a schematic view in perspective illustrating another embodiment of a friction element according to the invention; Figure 4 is a schematic view in perspective illustrating the use as a brake of a friction element according to the invention; and Figures 5 and 6 are two schematic views in perspective illustrating two modes of using friction elements according to the invention for producing a multiple disc brake.

Referring now to the drawings, the friction element 10 shown in Figure 1 is an element of annular shape constituted by two annular friction layers 11, 12 which are superposed, coaxial and connected to each other. The outer fiat faces 13, 14 of the friction layers 11, 12 constitute the rubbing surfaces of the friction element 10.

Each layer 11, 12 is formed by an assembly of strata 15 disposed as a rosette. Each stratum 15 of a layer extends from the outer face of this layer, where it is flush substantially radially, up to the inner face where it is also flush substantially radially, by being inclined with respect to the rubbing face. The traces of each stratum 15 on the side faces of a layer therefore extend along a part of the periphery thereof.

By way of example the strata 15 of each layer are disposed on regulated surfaces each generated by a straight line which passes through the axis 16 of the element and which follows a helix (for example 17) traced on a side face 18 of this layer.

Figure 2 illustrates the arrangement of the strata 15 in the layer 11. These strata are disposed similarly in layer 12, but with an inclination, with respect to the rubbing surfaces, opposite that of the strata of layer 11. The arrangements of the strata of layers 11, 12 are preferably symmetrical one to the other with respect to the median radial plane of the element 10, the layers 11, 12 having the same thickness.

The layers 11, 12 may be contiguous (Figure 1) or, as a variant, may be separated by an intermediate layer 19 (Figure 3) made of a material identical to that of layers 11 and 12 or a different material, for example metal.

The strata 15 are for example cut out of reinforcing sheets constituted by carbon fibres which may or may not be impregnated. As these strata have substantially the shape of an annular sector, cutting out may be effected wih minimum waste, this being very important in view of the cost of such sheets. Thus, with respect to the cutting of annular strata, in one piece, the saving of material may be of the order of 30% or more, to form friction elements of the same dimensions.

After assembly of the strata of each layer by rosette arrangement on one another and superposition of the layers, the element 10 may be formed by a known process of rigidification by densification, for example by deposit of pyrocarbon. It will be noted that the rosette arrangement facilitates, during a densification treatment, the penetration of gas or liquids or the evacuation of gas since this may take place through all the faces of the element 10. This promotes, of course, the obtaining of a friction element with homogeneous physical characteristics, therefore with constant braking properties as it wears. On this subject, it will be noted that such wear is progressive and regular since the strata are not oriented perpendicularly to the axis 16.

When used as a brake disc (Figure 4), the friction element 10 is placed between two rings 21, 22 and is rotatable relative thereto.

Upon braking, the rings 21 and 22 are applied against the rubbing surfaces 13 and 14 of the element 10. The heat conductivity of the strata perpendicularly to the rubbing faces is improved in comparison with a stratification perpendicularly to the friction axis.

The regularity of wear and an improved evacuation of heat contribute, of course, to limiting the possibility of creation of mechanical or thermal stresses tending to the decohesion of the strata 15, well anchored within the friction element.

Due to the double-rosette arrangement, the rubbing surfaces 13, 14 of the friction element 10 are both urged in the same direction with respect to the inclination their strata, this direction being different according to whether the element 10 rotates with respect to the discs 21, 22, in the direction indicated by arrow 23 or in the direction indicated by arrow 24.

Figures 5 and 6 illustrate two relative arrangements of friction elements according to the invention, for producing a multiple disc brake of the type used for aircraft.

Figures 5 and 6 represent coaxial friction elements which are alternately fixed 31, 33, 35 (stators) and rotary 32, 34 (rotors). In the example illustrated, each intermediate element 32, 33 34 is constituted by a friction element of the type shown in Figure 1, with two coupled friction layers constituted by assemblies of strata in rosette arrangement with opposite directions for the two layers. The end friction elements 31, 35 may be of identical constitu tion to that of the intermediate elements or, as illustrated, may be friction elements comprising one friction layer only since these elements 31, 35 have only one rubbing surface.

Upon braking, the friction elements are pressed against one another.

In the case illustrated in Figure 5, the elements are disposed so that all the rubbing surfaces are subjected to the same stresses, either when the rotary elements 32, 34 rotate in the direction indicated by the arrows 36, or when the rotary elements rotate in the other direction as indicated (arrows 37).

In the case illustrated in Figure 6, the rubbing surfaces of each friction element are subjected to the same stresses but these stresses are opposite for two adjacent elements.

In the elements particularly described, due to the rosette arrangement, the heat is rapidly evacuated through the strata towards the inside of the friction element. Furthermore, the rubbing surfaces are constituted by the juxtaposed edges of the strata and not by end strata as in the case of an arrangement formed by stacking strata oriented perpendicularly to the axis of the discs, hence a more regular wear and the obtaining of rubbing surfaces with relatively constant characteristics.

The regularity of the wear and the better dissipation of the heat contribute to reducing the risks of decohesion. The arrangement of the strata promotes to a maximum the admission or evacuation of gases or liquid in the course of a heat treatment or a densification operation.

Furthermore, the sector shape of the strata enables them to be cut in one piece from a reinforcing sheet with a minimum of waste. The cost price of the friction element may therefore be considerably reduced. Their arrangement allows on the other hand a better penetration or an improved evacuation of fluids through all the faces of the friction element which they form, hence a clear reduction of the risks of manufacturing defects occurring.

Finally, due to the double-rosette arrangement, the friction element is subjected to the same stresses on each rubbing surface, for ex ample within the scope of its use as inter mediate element in a disc brake.

WHAT WE CLAIM IS: 1. A friction element comprising at least two friction layers having their outer faces constituting opposite rubbing surfaces of the friction element, each layer being formed by a respective assembly of strata with a rosette type arrangement (as herein defined) in the opposite direction with respect to the other layer, said strata being made of a frictional heat conducting material and each stratum of each layer extending from the rubbing surface over the whole thickness of the layer by being inclined with respect to the rubbing surface.

2. A friction element as claimed in claim 1, wherein said heat conducting material is carbon.

3. A friction element as claimed in claim 1 or claim 2, wherein the strata are each disposed substantially along a surface produced by a straight line which passes through the axis of the friction element and which follows a helix traced on its side face.

4. A friction element as claimed in any one of claims 1 to 3, wherein the element is of annular form.

5. A friction element as claimed in any one of claims 1 to 4, further comprising at least one intermediate layer between the two friction layers.

6. A friction element as claimed in any one of the preceding claims, wherein the arrangements of the strata of the friction layers are symmetrical one to the other with respect to the median plane of the friction element.

7. A multiple disc brake comprising alternately fixed and rotary annular friction elements, in which brake each intermediate friction element is an element according to any one of the preceding claims.

8. A friction element substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

9. A multiple disc brake substantially as hereinbefore described with reference to Figures 4 to 6 of the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. strata as in the case of an arrangement formed by stacking strata oriented perpendicularly to the axis of the discs, hence a more regular wear and the obtaining of rubbing surfaces with relatively constant characteristics. The regularity of the wear and the better dissipation of the heat contribute to reducing the risks of decohesion. The arrangement of the strata promotes to a maximum the admission or evacuation of gases or liquid in the course of a heat treatment or a densification operation. Furthermore, the sector shape of the strata enables them to be cut in one piece from a reinforcing sheet with a minimum of waste. The cost price of the friction element may therefore be considerably reduced. Their arrangement allows on the other hand a better penetration or an improved evacuation of fluids through all the faces of the friction element which they form, hence a clear reduction of the risks of manufacturing defects occurring. Finally, due to the double-rosette arrangement, the friction element is subjected to the same stresses on each rubbing surface, for ex ample within the scope of its use as inter mediate element in a disc brake. WHAT WE CLAIM IS:

1. A friction element comprising at least two friction layers having their outer faces constituting opposite rubbing surfaces of the friction element, each layer being formed by a respective assembly of strata with a rosette type arrangement (as herein defined) in the opposite direction with respect to the other layer, said strata being made of a frictional heat conducting material and each stratum of each layer extending from the rubbing surface over the whole thickness of the layer by being inclined with respect to the rubbing surface.