Backing plate for a clutch disc
BACKGROUND OF THE INVENTION 
     This invention relates to an improvement in attaching friction material to a clutch disc. 
     Clutch discs are used in clutch assemblies to transmit drive forces from a prime mover to an output shaft. Prior art clutch discs often have a plurality of backing plates each of which has friction material disposed on an outwardly facing surface. The backing plates are spaced circumferentially about the clutch disc, and are selectively engaged with a drive disc to transmit a rotational force drive to an output shaft. In the prior art, the friction material is typically attached to the backing plate, and the backing plate is riveted to the clutch disc. 
     One problem with the prior art backing plates is that, due primarily to unequal heat distribution, they often pull away from the clutch disc at a central location. Further, the center of the friction material tends to bear the greatest friction and forces. Thus, the friction material at the center of the backing plate heats to a higher temperature then other portions of the friction material. The coefficient of friction at the center of the friction material is then different than at the remainder of the friction material. This may cause the clutch facings to grab upon engagement producing &#34;jerky&#34; vehicular operation, particularly in heavy trucks. These problems are particularly acute with ceramic friction materials which may experience warpage or bowing distortion. 
     The prior art teaches spacing friction material portions to create air channels therebetween which cool select areas of the friction material. The prior art clutch discs have thus included large spaces between friction material portions. It would be desirable to increase the area covered by the friction material. These prior art structures have also not overcome the aforementioned bowing problem. Thus, it is desirable to improve the prior art backing plates. 
     SUMMARY OF THE INVENTION 
     In a disclosed embodiment of the present invention a backing plate is secured to a clutch disc by a plurality of securing members. The backing plate includes a friction material having a radially innermost edge and a radially outermost edge. At least one central securing member is positioned at a radially central location spaced between the radially innermost and radially outermost edges of the friction material, and also at a circumferentially central portion between the two circumferential edges of the friction material. The central securing member prevents the center of the backing plate from bowing away from the clutch disc. 
     In a preferred embodiment of the present invention a channel extends radially through the entirety of the friction material defining a channel such that cooling air passes over the center of the friction material. A pair of central securing members are positioned at a radially inner and a radially outer location in the channel. 
     These and other features of the present invention will be best understood from the following specification and drawings, a brief description of which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the inventive backing plate of the present invention for use with a clutch disc. 
     FIG. 2 is a front view of the backing plate shown in FIG. 1. 
     FIG. 3 is an end view of a clutch disc including the inventive backing plate. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     FIG. 1 shows a backing plate 20 consisting of a pair of pads 22 and 24 composed of friction material. Backing plate 20 is connected to a clutch disc 48, see FIG. 2, by end rivets 26, a central radially outer rivet 28 and a central radially inner rivet 29. Each pad 22 and 24 has a radially outer edge 30, a radially inner edge 31, a circumferentially outer edge 32, and a circumferentially inner edge 33. Circumferentially inner edge 33 includes a radially outer edge portion 34 extending radially inwardly and towards the opposed pad to a central edge portion 35. The opposed radially outer edge portions 34 define a radially outer gap 36 through which is received the central radially outer rivet 28. The opposed central edge portions 35 define a central gap 37. Radially inner edge portions 38 extend radially inwardly and away from the opposed pad to define a gap 39 which receives central radially inner rivet 29. Gaps 36 and 39 are triangular to maximize the area covered by friction material, while still providing room for rivets 28 and 29. 
     Central rivets 28 and 29 ensure that backing plate 20 is firmly secured to a clutch disc 48 and will not pull away therefrom. The gaps 36, 37 and 39 define a channel that ensures that the center of the friction material is adequately cooled. In a preferred embodiment, radially outer edge portions 34 each extend at an angle of 30 degrees relative to central edge portions 35. Preferably, radially inner edge portions 38 each extend at an angle of 20 degrees relative to central edge portion 35. 
     The rivets are omitted in FIG. 2 to show holes or apertures 44 for passage of the central rivets 28 and 29 and apertures 46 for receiving end rivets 26. Rivets 28 and 29 secure backing plate 20 to radially outer portion 47 and radially inner portion 49, respectively, of clutch disc 48. The dimensions are defined about a central axis R of clutch disc 48. Rivets 26 secure the respective circumferentially outer edges of the backing plate 20 to disc 48. Radially outer and radially inner gaps 36 and 39 are both generally triangular. 
     The radial dimension of clutch disc 48 may be defined as a lateral dimension of backing plate 20, while the circumferential dimension of clutch disc 48 may be defined as a longitudinal dimension of backing plate 20. 
     Referring to FIG. 3, clutch disc 48 preferably includes a backing plate 20 on each face, with rivets 26 and 28 extending through both backing plates 20 for rigid securement of the plates to clutch disc 48. Clutch disc 48 may be a driven disc in a clutch. The teaching of this invention, however, extends to any type of clutch disc used in any environment. 
     Friction material sections 22 and 24 are preferably formed of ceramics and bonded to backing plate 20 using known methods. Other known friction materials may be used for this invention. 
     A preferred embodiment of the present invention has been disclosed. One of ordinary skill in the art, however, would recognize that certain modifications may fall within the spirit and scope of this invention. For that reason the subject matter afforded protection should extend to the subject matter defined in the claims including all fair equivalents thereof.