Abstract:
A method for the production of a friction lining. The friction lining is produced in alternating layers wound in a helical shape and a star shape.

Description:
This application is a continuation application of PCT/DE2008/000474 filed Mar. 18, 2008, which in turn claims the priority of DE 10 2007 026 657.1, filed Jun. 8, 2007, the priority of both applications is hereby claimed and both applications are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a friction lining and to a method for producing a friction lining, in particular for clutch disks, brakes or the like, according to the preamble of claims  1  and  12 . 
     BACKGROUND OF THE INVENTION 
     Clutch linings of this type are used particularly for friction clutches in motor vehicles, in which they are riveted to a metallic carrier plate or clutch disk, in order to enable, in conjunction with a counterelement, a force transmission between an engine and a transmission in the coupled state and, with the clutch open, to decouple said force transmission. 
     In this case, the clutch linings have to satisfy stringent requirements because they should fulfill many requirements which cannot readily be achieved in the same way. In particular, the clutch lining should have a high burst rotational speed, so as not to be destroyed by centrifugal forces, should have a high coefficient of friction by means of which a high torque can be transferred, and should at the same time have low wear and be resistant to deforming distortion due to heat and/or force influences. Nevertheless, the clutch linings should be capable of being produced in as uncomplicated a way as possible and therefore economically. 
     To increase the bursting strength, that is to say the strength of the clutch lining in the circumferential direction, it is already known to deposit a binder-impregnated yarn material in a plurality of flat plies in a wavy manner in the circumferential direction, the turns of this strand material having radially inner and radially outer reversal regions which lie on concentric circles (DE 44 20 291 B4). In particular, the reversal regions of the turns may in each case be distributed to a plurality of concentric circles having different diameters, the radii of the circles differing from one another sufficiently to avoid thickenings at the margins of the clutch lining or lining body which may otherwise lead to pressure damage to the yarn material. The fraction of yarn material in the overall composition of the lining body material can consequently be increased. 
     Winding mostly takes place with the aid of a winding machine, one ply being wound in a circumferential direction per revolution, as defined. 
     Such yarn material wound in the form of an annular disk, as shown, for example, in  FIG. 1 , is also designated as a winding or preform. The imaginary circle with an outside diameter of the friction part in the form of an annular disk is itself also designated as the outside diameter of the winding, and the same applies to the inside diameter. The radially inner and radially outer reversal regions of the turns on the yarn material wound in the form of an annular disk are tangent to the inside and the outside diameter of the winding. 
     The winding ratio indicates how often the yarn in each case is tangent to an imaginary circle with an outside diameter of the friction part in the form of an annular disk or of the dimensionally similar reinforcing part, or, in other words, how often the yarn is tangent to the outside diameter during one revolution of an annular part. A winding ratio of 1:2.6 states that the yarn touches the outside diameter 2.6 times during one revolution on account of the turns. A winding ratio of 1:4 is in this case lower than a winding ratio of 1:5 and is not to be interpreted in the sense of a division. 
     When a spiral is wound, winding may be carried out from the inside diameter to the outside diameter, or vice versa. In order to wind such a spiral, the winding machine requires a plurality of revolutions from tangent to the inside diameter as far as tangent to the outside diameter, or vice versa. This required number of revolutions corresponds to the number of turns of the spiral. 
     SUMMARY OF THE INVENTION 
     The object on which the invention is based is to propose a friction lining, the set-up of which allows a further improvement in terms of rotational speed strength and of dimensional stability. 
     The solution according to the invention is obtained by means of a method for producing a friction lining. According to this method, the friction lining is produced from at least one winding. The winding consists of a plurality of plies of at least one impregnated yarn and a plurality of layers. The winding is wound from a predetermined number of two alternately successive layers. In this case, one layer is wound from a first predetermined number of spirals which each have a predetermined number of turns. The other layer is wound from a second predetermined number of plies wound in a star-shaped manner. 
     In a preferred embodiment, the two layers are wound from different yarn material. 
     In a preferred embodiment, a spiral is wound from 2 to 100, particularly preferably 5 turns. 
     In a further preferred embodiment, the first number amounts to 1 to 100 spirals. 
     In a further preferred embodiment, the second number amounts to 1 to 100 plies, preferably 5 plies with a winding ratio between 1:1.0 and 1:6.0, preferably of between 1:2.0 and 1:5.0. 
     In a preferred embodiment, there is provision for the number of two alternately successive layers to lie between 1 and 100. 
     In a further embodiment, there is provision for the winding to be wound from an additional layer continuing the alternating layer sequence, so that the two outer faces or outer layers of the winding have the same layer type. 
     In further preferred embodiments, there is provision for the ply wound in a star-shaped manner to be implemented in involute form or the form of an arc of a circle or in an S-form or polygonal form. 
     According to the method described above, a friction lining can be produced with the corresponding specifications, resulting from the method, with regard to layering, to the number of plies and turns and to the form of the laying pattern of the yarn or yarns and also to the yarn type. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and advantageous refinements of the invention are the subject matter of the following figures and their description parts. In the figures, in particular, 
         FIG. 1  shows a winding according to the prior art; 
         FIG. 2  shows a two-layer winding schematically; 
         FIG. 3  shows an S-shaped winding pattern schematically; 
         FIG. 4  shows an involute winding pattern schematically; 
         FIG. 5  shows a polygonal winding pattern schematically; and 
         FIG. 6  shows a winding pattern in the form of an arc of a circle schematically. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a winding according to the prior art. 
     Such a winding may be wound, for example, from an impregnated yarn. In this case, yarn optimized in terms of coefficient of friction and of wear is drawn through an impregnating solution and is brought to a constant weight ratio of yarn to impregnating solution. The yarn is subsequently dried. For example, a carded yarn consisting of aramid fibers, staple glass fibers, viscose fibers and PAN fibers and also brass wire may be used. Another example is a mixed filament yarn consisting of glass filament and metal wires. The various yarns may also be used as a combination. A dispersion consisting of polymeric components, fillers and solvents is suitable as an impregnating solution. The polymeric components may consist of thermosetting components, such as, for example, phenolic resin or melamine resin, and also elastomeric components, such as, for example, SBR or NBR rubber. Fillers are, for example, barium sulfate, kaolin or carbon black. The solvent used is usually water. The dried yarn is subsequently wound into a winding. 
     To improve the friction lining properties, a winding may also be constructed from a plurality of plies or layers of different types of impregnated yarn. First, for example, a lower layer and then, for example, with another yarn, a layer lying above it are wound. In this context, the winding ratios of the two layers may differ from one another. 
     Usually, a winding produced in this way is subsequently pressed under time and temperature control, then hardened and deburred and finally ground and drilled. 
       FIG. 2  illustrates schematically two layers  30  and  40  according to the invention. One is wound spirally  30  and the other in a star-shaped manner  40 . This results in a very close-meshed composite. The star-shaped composite structure  40  has, in contrast to a sinusoidal form, which places more material radially inward and outward than in the middle, an involute form  40 , as also illustrated in  FIG. 4 . The quantity of the yarn per unit area of the friction lining thereby becomes markedly more uniform. Other angular forms, such as polygons, as in  FIG. 5 , but also arcs of a circle, as in  FIG. 6 , which are similar to a sinusoidal profile, and also an S-form  50 ,  60 , as illustrated in  FIG. 3 , have also proved to be expedient with regard to a more uniform distribution of the yarn over the friction surface and therefore a reduction in undesirable thickenings, particularly on the inside and/or the outside diameter of the friction lining. 
     In order to produce the friction lining from a winding, as illustrated in  FIG. 2 , the method according to the invention, in a first preferred embodiment, provides for winding the two layers along the yarn from the same yarn material. 
     In a further preferred embodiment, there is in this case provision for the first layer to consist of a spiral with 10 turns and for the second layer to consist of 10 plies of yarn wound in a star-shaped manner, particularly preferably in involute form. 
     In a likewise preferred embodiment, there is in this case provision for the first layer to consist of a spiral with 5 turns and for the second layer to consist of 5 plies of yarn wound in a star-shaped manner. 
     In a further preferred embodiment, there is in this case provision for the first layer to consist of a spiral with 3 to 5 turns, for the second layer to consist of 3 to 5 plies of yarn wound in a star-shaped manner, for the third layer also to consist of a spiral with 3 to 5 turns and for the fourth layer to consist of 3 to 5 plies of yarn wound in a star-shaped manner. 
     In a further preferred embodiment, there is in this case provision for the first layer to consist of 2 spirals, each with 5 turns, and for the second layer to consist of 5 plies of yarn wound in a star-shaped manner, particularly preferably in involute form. 
     In a further preferred embodiment, there is in this case provision for a winding to be wound from a sequence of a first and a second layer which is repeated four times. Depending on the desired layer thickness, in this case, the first layer is formed from one or two spirals. 
     In a further preferred embodiment, a star-shaped layer is wound even before the start of the winding of the sequence which is repeated four times, so that the two outer faces or outer layers of the winding are then formed by a star-shaped layer. In another preferred embodiment, a spiral layer forms the uppermost and the lowermost layer of the winding in the axial direction. 
     In two further preferred embodiments, the winding is produced in three layers. In this case, the two layer combinations spiral/star-shaped/spiral and star-shaped/spiral/star-shaped are obtained. 
     In a further preferred embodiment, different yarn material is used for winding the various layers. In a preferred embodiment, the layers formed from spirals are wound from yarn optimized in terms of burst rotational speed, and the layers wound in a star-shaped manner are wound from yarn optimized in terms of friction and of wear. For special purposes, in another preferred embodiment, the layers formed from spirals are wound from yarn optimized in terms of friction and of wear and the layers wound in a star-shaped manner are wound from yarn optimized in terms of burst rotational speed. 
       FIG. 3  illustrates schematically a course of the yarn in an S-form, this being restricted in the illustration to a single course between the inside and/or the outside diameter. The complete schematic winding pattern for the S-shaped course in  FIG. 3  arises from the turn profile in involute form  40  in  FIG. 2  and  FIG. 4 . A yarn profile according to the laying pattern  50  increases the yarn fraction in favor of the middle between the inside and/or the outside diameter, as compared with a yarn profile according to the laying pattern  60 . Depending on purposes, both patterns constitute preferred embodiments. 
     LIST OF REFERENCE SYMBOLS 
     
         
           30  Spiral winding pattern 
           40  Involute winding pattern 
           50  S-shaped winding pattern 
           60  S-shaped winding pattern