Abstract:
A plate ( 1 ) for a multiple-plate clutch has at least one friction surface ( 4 ) for transmitting a torque, in particular for a wet-running switchable multiple disk clutch. The plate ( 1 ) has at least one friction surface ( 4 ) which has grooves ( 7.1, 7.2, 10.1, 10.2 ) with an inside bordering edge ( 6 ) and an outside bordering edge ( 5 ), and at least one groove ( 7.1, 7.2, 10.1, 10.2 ) that runs from the inside bordering edge ( 6 ) to the outside bordering edge ( 5 ). The at least one groove ( 7.1, 7.2, 10.1, 10.2 ) has at least one bending point ( 8.1, 8.2, 9.1, 9.2, 11.1, 11.2, 12.1, 12.2 ) at which the at least one groove ( 7.1, 7.2, 10.1, 10.2 ) is bent at an angle (α 1 , α 2 , α 3 , α 4 ).

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to a plate having at least one friction surface for a multiple-plate clutch, in particular for a wet-running switchable multiple-plate clutch. Multiple-plate clutches on which the present invention is based are known in general in a variety of modifications. For example, reference may be made to the variants of the embodiments described in German Patent 28 54 051 A1, U.S. Pat. No. 4,280,609 or German Patent 35 32 759 C1. 
   Accordingly, the essential components of such multiple-plate clutches to which reference is made below include two or more plates having an essentially ring-shaped shape. If the multiple-plate clutch includes a plurality of plates, as is the case in the majority of such multiple plate clutches, then a first group of plates, the so-called outer plates, are arranged on an outer plate carrier, called the drive ring, which is connected to a shaft, e.g., a drive shaft, and a second group of plates, the so-called inner plates, are arranged on an inner plate carrier which is connected to a shaft, e.g., an output shaft. The plates of the two groups engage in the manner of gears to form a plate package, with one outer plate being adjacent to an inner plate. Outer plates and inner plates are displaceable relative to one another in the axial direction and can be brought into or out of frictional engagement with their adjacent end faces in pairs, i.e., transmitting torque from the drive shaft to the output shaft. 
   The plates on which the present invention is based are known from the state of the art in a plurality of modifications. For example, there are known plates which have a friction lining, which is usually made of a fibrous material or the like, on one or both essentially ring-shaped end faces of a preferably metallic carrier. There are also those made of a single material in one piece, in particular those made of a friction material of the aforementioned type. Reference is gain made to the discussions and citations in the aforementioned publications as examples. 
   As a rule, at least one of the two end faces—the so-called friction surfaces—which can be brought into frictional connection with one another, of adjacent plates is provided with a specially designed surface structuring and/or with a pattern grooves. 
   For example, International Patent WO 97/32678 describes surface structuring of so-called steel plates, where this structuring causes an increase in the coefficient of friction of the steel and friction coating surfaces of adjacent plates which are in contact with one another. 
   On the other hand, the clutch plate illustrated in FIG. 2 of U.S. Pat. No. 4,280,609 as well as the clutch plate illustrated in FIG. 4 of German Patent 28 54 051 A1 both have a so-called waffle pattern of grooves on their friction surfaces, where a plurality of parallel linear grooves are intersected by a plurality of parallel linear grooves running at right angles to the former. The reason for such a groove structure lies in the necessity of cooling the surfaces which rub one against one another, this cooling being implemented by a stream of coolant passing through these grooves. 
   Although plates have been developed for a wide variety of equipment transmitting a torque, e.g., clutches, brakes and the like, and the plates have been adapted to the different stresses accordingly, there are still unwanted problems for many applications. Namely, there is still certain frictional contact between adjacent plates for a variety of reasons even when the equipment is not being operated, i.e., when no torque is to be transmitted but there is, nevertheless, a torque, the so-called drag torque, which is transmitted from the drive shaft to the output shaft or vice-versa. 
   SUMMARY OF THE INVENTION 
   Thus, the object of this invention is to design friction plates for multiple plate clutches and improve upon the friction plates so that the drag torque is reduced. 
   This object is achieved according to this invention with a plate having at least one groove that extends from an inner bordering edge to an outer bordering edge where the at least one groove has at least one bending point at which the at least one groove is bent at an angle. 
   Advantageous embodiments and refinements of this invention are characterized in the subclaims. 
   This invention is based in general on a plate having at least one friction surface for a multiple-plate clutch for transmitting a torque, e.g., for a wet-running switchable multiple-plate clutch which has a friction surface having at least one groove. In the case of at least one groove running from the inner bordering edge of the friction surface to its outer bordering edge, it is provided according to this invention that this groove will have at least one bending point at which it is bent at an angle. The coolant, such as oil or the like, passes by this bending point, where it creates a spot increase in the static pressure according to the law of conservation of pressure as discovered by Bernoulli, according to which for any streamline, the sum of the static pressure and the dynamic pressure (as well as the geodetic pressure) is constant. This spot increase in pressure results in adjacent plates being pressed apart and thus not being in friction engagement when the torque transmission device (clutch) is not being actuated. The result is ultimately a reduction in the drag torque. 
   Model calculations and empirical experiments have shown that an especially great reduction in drag torque occurs with grooves having one or two bending points if an angle (deflection angle or bending angle) at the bending point or points is selected to be between about 75° and about 115°. Furthermore, it has been found to especially advantageous if the grooves in question have at least two successive bending points at which these grooves are diverted in opposite directions. The grooves of an essentially ring-shaped plate therefore preferably form an S shape or Z shape. There are no restrictions with regard to the width or depth of the groove. The groove channels outside of the S or Z shape may have the same or different width and may also be offset radially, with approximately one groove width preferably being set as the minimum offset distance. 
   It has been found to be advantageous if at least two adjacent grooves have a mutually opposing course. It is also advantageous if at least two adjacent grooves run in the same direction a symmetrical arrangement of grooves in groups or pairs over the surface of a ring-shaped plate, for example. The groove may be arranged according to the direction of rotation or with (radial) symmetry. 
   In the case of plates having a friction lining, the grooves of the aforementioned type are preferably incorporated into the friction lining. The depth of the groove (and, in certain embodiments, also the width of the groove) may be coordinated with the particular application case. The depth of the groove may also include the total friction lining thickness. A combination of different groove depths and groove width is also possible. In addition, other grooves may also be provided, aimed, for example, at a certain loading or switching performance of the clutch. 
   Furthermore, it is also provided according to this invention that plates, which are designed in the manner of disks and have friction surfaces on their two end faces, have identical grooves, i.e., identical patterns of grooves on both of their end faces. The groove patterns on the front and rear sides may be oriented according to the direction of rotation, with (radial) symmetry or in opposition. The grooves on the front side and the grooves on the rear side may also be designed to be identical, and in addition they may be offset mutually by a certain angle. 
   Finally, this invention also provides for a portion of the grooves to be designed optionally as blind grooves. 
   According to another variant of this invention, the width of the groove in the case of the grooves in question varies over its longitudinal extent. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various exemplary embodiments of the present invention are illustrated in the drawings and are described in greater detail below. They show: 
     FIG.  1 —various groove patterns according to this invention on a ring-shaped friction plate (detail)
         a) s-shaped grooves running in the same direction   b) s-shaped grooves running in the opposite direction   c) grooves with a single bending point running in the same direction       

     FIG.  2 —details of various annual friction plates having friction linings, which exhibit the groove patterns according to this invention
         a) s-shaped grooves running in the opposite direction   b) s-shaped grooves running in the same direction, type spacing, angle (of curvature) &lt;90°   c) s-shaped grooves running in the same direction, greater spacing between grooves   d) s-shaped grooves running in the same direction, type spacing, angle (of curvature) &gt;90°   e) s-shaped grooves running in the same direction, type spacing, curvature offset radially toward the outside   f) s-shaped grooves running in the same direction, wide distance between adjacent grooves, curvature offset radially toward the outside   g) a groove pattern corresponding to that in  FIG. 2   b ) but with different groove widths at the inflow and outflow sides.       

   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a selection of grooves according to this invention in a ring-shaped plate  1 . 
   It should be pointed out in advance that the actual friction surface of a plate need not necessarily include the entire end face or even both end faces but instead, as in the present case, a ring-shaped section may be formed as the friction surfaces or as described in German Patent Application 28 54 051 A1, separate partial areas of the end faces may be designed as the friction surfaces. In addition, as already indicated in the introduction to the description, the “bare” end face of a plate or the end face provided with a friction coating or a combination of these two variants may also serve as the friction surface. 
   In the present case, the ring-shaped plate  1  is bordered in the radial direction by the outside circumference, which has been labeled as  2  in  FIG. 1 , and the inside circumference, which has been labeled as  3 . The friction surface  4  of plate  1  is bordered by the outside circumference  5 , which lies inside the outside circumference  2  of the ring-shaped plate  1 , and the inside circumference  6 , which lies inside the inside circumference  3  of plate  1 . Thus, in the present case the actual friction surface  4  is much smaller than the end side area of plate  1  shown here. 
     FIG. 1   a ) shows two s-shaped grooves  7 . 1  and  7 . 2  running in the same direction and arranged side-by-side. The grooves extend from the inside circumference  6  of the friction surface  4  to its outside circumference  5 . There are two bending points  8 . 1  and  8 . 2  or  9 . 1  and  9 . 2  according to this invention, situated essentially at the center between the inside circumference  6  and the outside circumference, where the grooves  7 . 1  and  7 . 2  at first run counterclockwise and then clockwise with a bend, starting from the inside circumference  6 . The angles (of bending) are represented by the symbols α 1  and α 2  in the figure. The minimum distance between adjacent grooves  7 . 1  and  7 . 2 , which should not be less than the width of one groove, is labeled as d 1  in the figure. 
     FIG. 1   b ) shows two s-shaped grooves  10 . 1  and  10 . 2  running in opposite directions side by side. Like grooves  7 . 1  and  7 . 2  in the exemplary embodiment described above, these grooves extend from the inside circumference  6  of the friction surface  4  to its outside circumference  5 . Again there are two bending points  11 . 1  and  11 . 2  or  12 . 1  and  12 . 2  according to this invention at which the grooves  10 . 1  and  10 . 2  run first counterclockwise with the bending points which run eccentrically and are offset radially in the direction of the outside circumference  5 . The angles (of bending) are labeled as α 3  and α 4  in the figure. The minimum distance between the adjacent grooves  10 . 1  and  10 . 2 , which in turn should be no less than one groove width, is labeled as d 2  in  FIG. 1   b ). 
     FIG. 1   c ) illustrates a third exemplary embodiment in which two identical grooves  13 . 1  and  13 . 2  adjacent to one another run from the inside circumference  6  of the friction surface  4  to its outside circumference  5 . Essentially at the center between the inside circumference  6  and the outside circumference  5  is their single bending point  14 . 1  and/or  15 . 1  at which the grooves  13 . 1  and/or  13 . 2  run clockwise with a kink, starting from the inside circumference  6 . The angle (of the kink) is represented by α 5  in the figure, and the minimum distance between adjacent grooves  13 . 1  and  13 . 2  is represented by the symbol d 3 . 
     FIG. 2  shows in general different ring-shaped friction linings with groove patterns according to this invention. 
   In the case of plate  19  shown in  FIG. 2   a ), the outside circumference is labeled as  20  and the inside circumference is labeled as  21 . The lining on plate  19  forming friction surface  22  is bordered by the outside circumference  23 , which coincides with the outside circumference  20  of the ring-shaped plate  19  and by the inside circumference  24  which is within the inside circumference  21  of plate  19 . The actual friction surface  22  in the present case is thus also smaller than the end side face of the plate  19  shown here, bordered by its outside circumference  20  and inside circumference  21 . 
   In the present case, s-shaped grooves  25  and  26  running essentially in opposite directions but with the same spacing are incorporated into the friction lining around the entire circumference of plate  19 . 
   In the case of plate  27  show in  FIG. 2   b ), the outside circumference and inside circumference are labeled as  28  and  29 , in accordance with the preceding exemplary embodiment. The lining on the plate  27 , which forms the friction surface  30 , is in turn bordered by the outside circumference  31 , which coincides with the outside circumference  28  of the ring-shaped plate  27 , and by the inside circumference  32 , which is within the inside circumference  29  of the plate  27 . 
   In the present exemplary embodiment, s-shaped grooves  33  running in the same direction according to this invention are incorporated into the friction lining. This variant of the embodiment is characterized by a comparatively tight distance between adjacent grooves  33  and an angle of bending of less than 90° at the respective bending points. 
   In the case of plate  34 , illustrated in  FIG. 2   c ), the outside circumference and the inside circumference are labeled as  35  and  36 , in accordance with the preceding exemplary embodiment. The lining on plate  34  forming friction surface  37  is bordered by the outside circumference  38 , which coincides with the outside circumference  35  of the ring-shaped (friction) plate  34  and by the inside circumference  39 , which is inside of the inside circumference  36  of the plate  34 . 
   Characteristics of this embodiment include the adjacent grooves  40  running in the same direction, the s-shaped grooves  40  and the radially central arrangement of the bending points of the grooves  40  between the outside circumference  38  and the inside circumference  39  of the friction surface  37 . 
   The exemplary embodiment according to  FIG. 2   d ) includes an essentially ring-shaped plate  41  with an outside circumference  42  and an inside circumference  43  in accordance with the three preceding exemplary embodiments. The friction surface  44  having the friction lining is also designed in a ring shape with an outside circumference  45  and an inside circumference  46  and extends on the end face of plate  41  up to its outside circumference  42  but not as far as its inside circumference  43 , 
   It is characteristic of this embodiment that the grooves  47  incorporated into the friction lining forming the friction surface  44  run in the same direction in the form of mirror-image S pattern over the entire circumference. The distance between adjacent grooves  47  is small in comparison with that of the variant described above according to sub figure 2   c ) but it is comparable to the distance between adjacent grooves  33  in the embodiment according to sub figure 2   b ). In contrast with the latter embodiment however, the angle (of curvature) at the bending point is much greater than 90° in the present case. 
   The embodiment according to  FIG. 2   e ) also includes an essentially ring-shaped plate  48  (outside circumference  49 , inside circumference  50 ) according to four preceding exemplary embodiments. The friction surface  51  which is also provided with a friction lining is likewise designed in a ring shape which only partially covers the end face of plate  48  (outside circumference  52 , inside circumference  53 ). 
   This friction lining also has s-shaped grooves  54  with a comparatively small distance between them running in the same direction. In the present case however the bending points are arranged with a radial offset toward the outside in comparison with the preceding embodiments of  FIG. 2 . 
   Plate  55  (outside circumference  56  and inside circumference  57  of the plate), illustrated in  FIG. 2   f ), has s-shaped grooves  61  running in the same direction cut in the friction lining/surface  58  (outside circumference  59  and inside circumference  60  of the friction surface  58 ), these grooves being designed in the manner of the preceding embodiment according to  FIG. 2   e ). However in this case, a greater distance between adjacent grooves  61  has been selected along with bending points that have been shifted further outward in the radial direction. 
   The point  62  shown in  FIG. 2   g ) having the outside circumference  63  and the inside circumference  64  is designed to be largely identical to the exemplary embodiment according to  FIG. 2   b ) in its friction lining/surface  65 , which is bordered by the outside circumference  66  and the inside circumference  67 . 
   In the present exemplary embodiment, s-shaped grooves  68  running in the same direction are incorporated into the friction lining. Here again the comparatively tight spacing of adjacent grooves  68  and an angle of bending of less 90° at the respective bending points are characteristic of this embodiment. 
   In addition, the widths of the grooves  68  at the inflow side  68 . 2  or different from the widths of the grooves  68  on the outflow side  68 . 1 . 
   INDUSTRIAL APPLICABILITY 
   The present invention is useful as a plate for multiple-part clutch plates and the like. The above descriptions of the preferred and alternative embodiments of the present invention are intended to be illustrative and are not intended to be limiting upon the scope and content of the following claims.