GB2164711A - Brake linings and lined brake shoes for drum brakes, in particular for the drum brakes of vehicles - Google Patents

Abstract

A brake lining is provided in which reinforcing fibres/elements (4, 5) are embedded in a base material (9). At least 60% of the fibres/ elements (based on the length of such), in a projection onto a plane lying normal to the axis of the frictional surface (8) of the lining (as shown), form an angle ( alpha , beta ) between 20 DEG and 70 DEG with a normal (n) to the frictional surface (8). The fibres (4, 5) e.g. of copper alloy diverse materials have a modulus of elasticity at least an order of magnitude greater than the base material (9) which is a synthetic base mixed with fillers. Various arrangement of fibres' elements are described and shown e.g. in Fig. 2 fibres (4) and (5) form on angle of alpha + beta = 120 DEG with each other. The fibres may form web-sheets (Fig. 3); and may be folded in various ways (Figs. 4, 5, 6). Perforated sheet may be used. In Fig. 7 reinforcing fibres (20) in a disordered state and straight reinforcing fibres (21) to form angle of approximately 2=45 DEG with (n) are utilised. <IMAGE>

Description

SPECIFICATION Brake linings and lined brake shoes for drum brakes, in particular for the drum brakes of vehicles The invention relates to a brake lining and lined brake shoes for drum brakes, in particular for drum brakes of vehicles, which show advantageous heat conductivity properties due to the inner structural design and accordingly their useful life is longer, and brake squeal and noises can be avoided.

Aspects of ecology necessitate a reduction in braking noises of vehicles, in particular elimination of brake squeal. At the same time we are confronted with the problem of the insufficient useful life of brake lines; in particular, with heavy vehicles the main problem lies in that, in comparison to the other structural elements, the useful life of brake linings is three times shorter, i.e. they are quickly worn, and exchange is costly. Simultaneously, due to the disadvantageous heat conductivity of the brake lining, the operation of connected structural elements, mainly of brake drums, are impaired, resulting in frequent repairs and exchange.

Known solutions and proposals have tried to reduce the phenomenon of brake squeal in two ways. Firstly, the brake drums are designed so that they are not liable to vibration.

The tendency to vibration is reduced by rings or coils with a high inner damping pressed onto the outer surface of the brake drum, or linings exerting a damping effect are arranged in a channei formed in a flange of the brake drum. Secondly, there have been efforts to reduce brake squeal by the expedient composition of brake shoes and the brake linings.

According to a known solution brake linings of different hardness, e.g. made of different materials, are used on the same brake shoe or on single brake shoes within the same brake construction.

A brake lining is also known that shows different moduli of elasticity along the generatrix of the friction surface, i.e. th extent of deformation is different under the influence of compressive force, for example, along the generatrix of the lining. Thus, the thickness of different parts of the brake lining may be different or the thickness may be constant and inserts with moduli of elasticity differing from the modulus of elasticity of the brake linings are embedded. These solutions require a more costly technological process and are different from th presently used productional technology of brake linings, accordingly their use with vehicles cannot be considered as economical.

Taking said circumstances into consideration, the aim of our invention is to eliminate brake squeal resulting from drum brakes, particularly those of heavy vehicles, without changing the shape and size of the brake linings and to increase the useful life of the presently used brake linings which presently can be very short.

From the aim set, we have tried to solve the problem by the proper formation of the inner structure of the brake lining in such a manner that the brake lining could be produced by applying the presently used technological methods (or similar methods) with the resulting low costs of production. The cost of the production of brake linings is considerably influenced by the method of positioning the reinforcing fibres or the fabric. In general, reinforcing fibres with a relatively short fibrelength are admixed-in an irregular orientation-with the mass from which brake linings are produced, and linings are produced either individually in an arched finished form or in band, by pressing, baking or rolling. Although irregular orientation of the fibres cannot be considered as advantageous, it represents the simplest technology.Brake linings with regular fibre orientation have also been proposed.

Decades ago, it was recognized that in the course of wear of brake linings, the fibres exposed along their full length to the friction surface are torn out from the lining in a short time and accordingly their reinforcing and heat conducting role cannot be fulfilled.

In order to avoid this phenomenon it was proposed to arrange and fix the reinforcing fibres in such a manner that, after the space between the fibres has been filled with lining mass, the fibres, or at least the majority of them, lie perpendicularly to the frictional surface of the finished brake lining. Fibre orientation of this character can be achieved with a fabric lining too, if the fibres lying normal to the frictional surface are stronger (thicker) than the cross fibres, which hold the fibres lying normal to the frictional surface.

With another known solution the fabric is arranged essentially parallel with the frictional surface, but the fibres are arranged at an acute angle to each other and in this case fibres are not torn out in long pieces when contacting the frictional surface. Fibres of different materials, mixed with each other or forming a fabric web, function differently in the material of the brake lining. Depending on the temperature, asbestos fibres reduce the drop of mechanical strength and admixed metal fibres also increase mechanical strength and perform the function of heat conducting within the brake lining. Hitherto, mechanical strength has been increased by different inserts, e.g. by inserting a perforated sheet, which was arranged parallel with the frictional surface.

In spite of these proposals aimed at the elimination of brake squeal or at a defined line or fibre orientation brake squeal could not be eliminated in heavy vehicles.

However, by using the brake lining accord ing to our invention, brake squeal can be reduced or fully eliminated; the invention is based on the recognition that the stiffness of brake linings with respect to compressive forces and the stiffness against frictional shearing forces affecting the frictional surfaces can be made independent of each other by increasing the latter and simultaneously the dependence on temperature can be decreased by using reinforcing elements in the lining material and by the special orientation thereof.

When the reinforcing elements are good heat conductors, heat conductivity normal to the frictional surface of the brake lining can be also increased.

Accordingly, our invention relates to a brake and lined brake shoe, in particular primary (leading) and secondary (trailing) brake shoes for drum brakes of vehicles, which have a frictional surface matching to the surface of rotation of the brake drum and a supporting surface on the opposite side for fixing to a carrying member and in the material of the frictional brake lining in which a base consisting of oriented fibres and/or reinforcing elements are embeded in a filament-rod-like formation, the modulus of elasticity of the materials the reinforcing fibres and/or rod-like elements are made of, is iarger by at least one order of magnitude than modulus of elasticity of the material of the brake lining, and according to their length at least 60% of the reinforcing fibres and/or rod-like elements in a projection onto the plane normal to the axis of rotation of the frictional surface form an acute angle in the range between 20 and 70" (a) with the normal of the frictional surface, and more than 50% falling onto one side of the normal on said plane form an angle of 90"-rr with the frictional motion vector.

With a preferred embodiment of the invention, fibres of the base material and/or reinforcing elements are made of diverse materials within one brake lining, formed of continuous or discontinuous fibres, which are united expediently into woven or glued fabric and which are arranged in the brake lining in several layers being perpendicular to the axis of the frictional surface, or they form a lining consisting of several webs made of different materials that are folded in a wavy line or sawtooth-like pattern and are arranged in one or more layers lying above one another in the brake lining, while the position and direction of the folded sections correspond to the requirements defined in claim 1.

By the orientation of the fibres of the base material and/or the reinforcing elements the stiffness of the brake lining with respect to compressive forces and frictional shearing forces can be made independent of each other, while this latter stiffness can be considerably increased compared to the stiffness of the matrix material of the brake lining and since modulus of elasticity of the reinforcing elements is higher by at least one order of magnitude, dependence on temperature is less than that of the brake lining material; thus temperature dependence of the entire brake lining can be positively influenced.

Since the lining has independent stiffness against compressive forces and stiffness against frictional shearing forces affecting the frictional surface of the brake lining, within certain limits, it becomes possible to produce a brake lining--according to our inventionwhich deforms under the influence of the compressive forces, whereby it is able to bear up against the whole frictional surface on the inner surface of the brake drum having been deformed under load; simultaneously it should show considerable stiffness against arising shearing forces with a possibly less elastic deformation in this direction. Changing shearing stresses arising under the influence of changing deformation result in the generation of brake squeal causing longitudinal and connected beinding vibrations in the brake drum.

These vibrations cause a considerable radiation of airborne sound manifesting itself in brake squeal. Earlier mentioned vibrations of the brake lining result in fluctuation of the relative slip velocity (v) between the brake lining and the brake drum and fluctuation of the shearing stress (T). As a consequence, on the brake drum, extremely large longitudinal oscillations will arise if the frequencies fs of the brake lining coincide with the natural frequency foci of the brake drum.

By considerably increasing the value of the modulus of slip elasticity G of the brake lining material and by considerably decreasing the dependence on temperature, brake squeals can be efficiently reduced or even fully eliminated. In this case the natural frequencies of the brake lining are shifted to the ultrasonic range in the whole range of operative temperatures. An advantageous effect of the increased G value could prevail in practice but to a certain limit up to now, geometric inaccuracies of the brake construction have resulted in variations of local bearing pressure p and simultaneously of breaking moment and a higher modulus of elasticity E of the brake lining, which changes proportionally-as it is well known-with the value G. Such local pressure variations result in unequal temperature distribution and shortened useful life of the brake lining.

Accordingly, reduction of brake squeal and prolongation of useful life require the application of non-isotropic materials, with which close correlation between values G and E-characteristic for homogeneous and isotropic materials-does not prevail.

The invention will be described in detail by means of some preferred embodiments serving as examples, with the aid of the accompanying drawings, wherein: Figure 1 is a schematic illustration of a brake shoe provided with a brake lining and fitted in the brake drum; Figure 2 illustrates the arrangement of the reinforcing elements in a brake lining according to the invention and shows the geometric arrangement of the elements in particular; Figures 3 to 7 show further single embodiments with differently oriented elements.

Fig. 1 shows a brake shoe 1 of a drum brake provided with a brake lining 2 in the brake drum 3. The shape of the outer cylindrical frictional surface 8 of the brake lining 2 is matched with the inner cylindrical surface with R radius of the brake drum 3. The brake lining 2 is fixed by gluing to the brake shoe 1 forming the carrying member, that is to say lining 2 is glued to the inner cylindrical bearing surface 6, which runs parallel with the frictional surface 8.

When the drum rotates in rotational direction A, the brake shoe 1 is a primary (leading) one, while for rotational direction B the brake shoe 1 is a secondary (trailing) one.

Fig. 2 shows a first embodiment of the brake lining 2. The left part of the figure shows the arrangement of a multitude of reinforcing elements as projected onto a plane lying normal to the axis of rotation, while the right part shows the same projection of two reinforcing elements only for the sake of clarity. Reinforcing elements 6 are formed by reinforcing fibres 4 and 5 made of copper alloy.

Reinforcing fibres 5 form an angle a=60 with the normal n of the frictional surface 8 of the brake ling 2 in a projection onto a plane normal to the axis of the frictional surface 8.

Reinforcing fibres 4 form an angle ss=60 with the normal n of the frictional surface 8 of the brake lining 2 in a projection onto the plane normal to the axis of the frictional surface 8.

Thus, the reinforcing fibres 4 and 5 form an angle of a+ss=120 with each other.

In the brake lining material 9 embedding the reinforcing fibres 4 and 5, reinforcing fibres 4, i.e. the fibres forming an angle ss with the normal n, constitute about the half of all the embedded reinforcing fibres, while reinforcing fibres 5 forming angle a with the normal constitute the remaining half. The majority of the reinforcing fibres 4, 5 lie in planes normal to the axis of the frictional surface 8 and they form an approximately logarithmic helical shape, and fibres not lying in such a plane form an angle a or ss with the normal when projected onto the plane.The material 9 of the brake lining is a material having a synthetic base mixed with fillers, while its modulus of elasticity is lower than the modulus of elasticity of the reinforcing fibres 4 and 5, which are partly elementary fibres and partly twists consisting of a plurality of elementary fibres.

Compared to known brake linings, the brake lining 2 shows similar stiffness against the compressive forces acting in direction of the normal n, however, compared to known brake linings, it displays an increased stiffness against frictional forces acting in the direction tangential to the frictional surface 8, because, under the influence of the shearing forces, slippage of the equidistant layers of the brake lining 2 is reduced by several orders of magnitude. As a consequence of applying reinforcing fibres 4, 5 with a high modulus of elasticity that are affected only to a small extent by temperature, the stiffness of the brake lining 2 against the frictional forces depends relatively little on the temperature since reinforcing fibres 4 and 5 form a strong skeleton in the material of the brake lining, which latter material softens under the influence of temperature rise.

Fig. 3 shows another embodiment of the brake lining 2, giving a sectional view in the plane normal to the axis of the frictional surface 8, i.e. in cross-section. In material 9 of the brake lining, the fibres forming web-sheets 10 form the reinforcing elements. Web-sheets 10 are arranged in parallel planes lying normal to the frictional surface 8. Web-sheets 10 are similarly built up, as shown in Fig. 2, that means that reinforcing fibres 5 form an angle a=600 with the normal n of the frictional surface 8 of the brake line 2 in a projection onto a plane normal to the axis of the frictional surface 8.Reinforcing fibres 4 form an angle ss-60 with the normal n of the frictional surface 8 of the brake lining 2 in a projection onto a plane normal to the axis of the frictional surface 8 and in such a manner that reinforcing fibres 4 and 5 form an angle a+/J=1200 with one another.

Reinforcing fibres 4 form about the half of all the reinforcing fibres in the material 9 of the brake lining embedding the reinforcing fibres 4 and 5 and form an angle ss with the normal n, while reinforcing fibres 5-forming the remaining half-form the angle a with the normal n.

Fig. 4 shows a third embodiment of the brake lining according to the invention in which fibres have been projected onto a plane normal to the axis of rotation of the frictional surface 8. In the material 9 of the brake lining, continuous fibre 11 is folded and lies in a plane normal to said axis of rotation. The part containing the reinforcing fibres 12 forms an angle a50 with the normal n of the frictional surface 8, while reinforcing fibres 13 form an angle of 10 with the normal n.All continuous fibres 11 are folded and positioned and embedded similarly in the material 9 of the brake lining, and as the part constituting the reinforcing fibres 12 is longer than that constituting the reinforcing fibres 13, this arrangement meets the requirements of the present invention according to which more than 60% of the reinforcing fibres (according to length) form an angle in the range between 20 and 70" with the normal n-in a projec tion onto a plane normal to the axis of rotation since the reinforcing fibres 12 form an angle a"50".

A fourth embodiment of the brake lining according to the invention is to be seen in Fig.

5 in a projection onto a plane normal to the axis of the frictional surface 8. In the material 9 of the brake lining the fibres of a folded web-sheet 14 form the reinforcing elements.

Warp and weft fibres of the web-sheets 14 are perpendicular to each other and the web has a square mesh. The sheets are folded along the diagonals of the square and are arranged in a folded state in the material 9 of the brake lining. Both foldings 15 and 16 form an angle 45" with the normal of the frictional surface 8, while the foldings 15 and 16 form an angle of 90" with one another. In the material 9 of the brake lining three web-sheets 14 lie above one another, with folded edges of adjacent sheets being juxtaposed. In a cross-section taken normal to the axis of rota tion of the frictional surface 8, fibres of the web-sheet 14 i.e. all the reinforcing fibres, form an angle ap;45" with the normal n.

Instead of the web-sheet 14, a perforated sheet with similar openings can be used.

A fifth embodiment of the brake lining 2 according to the invention is to be seen in Fig. 6, in a projection onto a plane normal to the axis of the frictional surface 8. In the material 9 of the brake lining, mats 17 with fibres oriented at random form the reinforcing elements. Mats 17 are arranged in a folded state in the material 9 of the brake lining.

Both foldings 18 and 19 form an approximate 60 angle with the normal n of the frictional surface 8, while foldings 18 and 19 form an angle of 1200 with one another. In the material 9 of the brake lining, a plurality of mats 17 lie above one another; said mats are fitted into each other, folded edges are matched and run essentially parallel with the generatrix of the frictional surface 8. In a projection falling onto the plane normal to the frictional surface 8, elementary fibres are unoriented in the mats 17, however, their longitu dinal extension is parallel with the plane of the mat-layer, accordingly statically they occupy the same position as the foldings 18 and 19, that means that reinforcing elements form an angle aj3;60" with the normal n.

A sixth embodiment of the brake lining 2 according to the invention can be seen in Fig.

7, in a projection normal to the axis of the frictional surface 8. In the material 9 of the brake lining, reinforcing elementary fibres 20 are embedded in a disordered state. Straight reinforcing fibres 21 with a total length corresponding to the total length of the fibres 20 and having a higher modulus of elasticity than the fibres 20, are embedded so as to form an angle of approximately a;45" with the normal n of the frictional surface 8; fibres 21 run nearly parallel and normal to the generatrix of the cylindrical frictional surface 8. From this it becomes obvious that more than 60% of the reinforcing elements or fibres form an angle of 45" with the normal n in the plane perpendicular to the axis of rotation of the frictional surface 8.

Claims (12)

1. A brake lining for a drum brake, in particular for the drum brake of vehicles, which lining has a frictional surface matched to the surface of rotation of the brake drum and a supporting surface on the opposite side for fixing to a carrying member, wherein the material of the lining includes a base in which there is embedded oriented fibres and/or reinforcing elements in a filament-rod-like formation, the modulus of elasticity of the materials that the reinforcing fibres and/or rod-like elements are made of is larger by at least one order of magnitude, than modulus of elasticity of the base material of the brake lining, wherein according to their length at least 60% of the reinforcing fibres and/or rod-like elements in a projection onto a plane normal to the axis of rotation of the frictional surface form an acute angle in the range between 20 and 70" (a) with the normal of the frictional surface, and wherein more than 50% falling onto one side of the normal on said plane form an angle of 90"-rr with the frictional motion vector.

2. A brake lining as claimed in claim 1, characterised in that reinforcing elements within the same brake lining are made of diverse materials.

3. A brake lining as claimed in claim 1, characterised in that reinforc'ing elements and/or rod-like elements are formed by a perforated sheet or a pressed net.

4. A brake lining as claimed in claim 1, characterised in that reinforcing fibres are folded and a projection of the single foldings onto the plane normal to the axis of the frictional surface forms an acute angle (a) in the range between 20 and 70" with the normal of the frictional surface.

5. A brake lining as claimed in claim 4, characterised in that folded fibres are arranged in several layers above and/or next to each other in the material of the brake lining.

6. A brake lining as claimed in claim 1, characterised in that elementary reinforcing fibres are united into a mat, said mat is folded and a projection of the single foldings onto a plane normal to the axis of the frictional surface forms an acute angle (a) in the range between 20 and 70" with the normal of the frictional surface.

7. A brake lining as claimed in claim 1, characterised in that elementary reinforcing elements are arranged as independent, straight fibre-pieces in the base material of the brake lining.

8. Lined brake shoes for drum brakes, in particular primary (leading) and secondary (trailing) brake shoes for drum brakes of vehicles, which have a frictional surface matching to the surface of rotation of the brake drum and a supporting surface on the opposite side for fixing to a carrying member, wherein in a base material of the frictional brake lining, oriented fibres and/or like formation are embedded, wherein the modulus of elasticity of the materials that the reinforcing fibres and/or rod-like elements are made of is larger by at least one order of magnitude than modulus of elasticity of the base material of the brake lining, wherein according to their length at least 60% of the reinforcing fibres and/or rod-like elements in a projection onto a plane normal to the axis of rotation of the frictional surface form an acute angle in the range between 20 and 70 (a) with the normal of the frictional surface, and wherein more than 50% falling onto one side of the normal on said plane form an angle of 90"-a with the frictional motion vector.

9. A brake lining for drum brakes,which lining has outer and inner surfaces matched in shape to the shape of the drum brake and to the shape of a support respectively, wherein the lining is made of a base material in which there is embedded reinforcing fibres or elements, the fibres or elements having a modulus of elasticity that is greater by at least an order of magnitude than that of the base material, wherein at least 60% (calculated on the basis of the length of the fibres or elements) of the fibres or elements, when projected onto a plane lying normal to the axis of rotation of the outer surface, form an angle of between 20 and 70" (a) with a line normal to the frictional surface.

10. A brake lining as claimed in claim 9, wherein at least 50% of the fibres or elements, when projected onto a said plane, falling on one side of the normal on said projection plane form an angle of 900-a with the frictional motion vector of the outer surface.

11. A brake lining substantially as hereinbefore described in connection with, and as schematically iilustrated in, any one of Figs. 2 to 7 of the accompanying drawings.

12. A brake shoe incorporating a lining as claimed in any one of claims 1 to 7 or 9 to 11.