Abstract:
A friction plate for a wet type multiplate clutch has a substantially ring-shaped core plate and a friction member attached to the core plate. The friction member has a surface which includes a passage formed on a surface of the friction member, the passage extending from an inner peripheral edge of the friction member to an outer peripheral edge of the friction member, and a groove having an opened end which opens to the inner peripheral edge of the friction member and a closed end which is closed at a middle of the surface of the friction member. A width of the groove decreases towards a direction to the outer peripheral edge from the inner peripheral edge of the friction member.

Description:
[0001]     The present invention claims foreign priority to Japanese patent application no. P.2003-308212, filed on Sep. 1, 2003, the contents of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a friction plate for a wet type multiplate clutch, which can reduce drag torque and improve frictional properties between the friction plate and a separator plate of the clutch.  
         [0004]     2. Description of the Related Art  
         [0005]      FIG. 1  is a cross-sectional side view showing abasic structure of a wet type multiplate clutch  10 . In  FIG. 1 , the wet type multiplate clutch  10  includes a clutch case  20 , a piston  30 , a center shaft  40 , a separator plate  50  and a friction plate  60 . A spline groove  21  is formed on the clutch case  20  and is spline-engaged with the separator plate  50 . Also, spline teeth  22  are formed on the clutch case  20  and are spline-engaged with the center shaft  40 . The separator plate  50  and the friction plate  60  are arranged alternately so that they can be engaged or disengaged with each other, and the friction plate  60  is spline-engaged with a hub (not shown). When the clutch is engaged, hydraulic fluid enters an operating chamber  25  via an oil hole  41  of the center shaft  40  and an oil hole  23  of the clutch case  20  to thereby press the piston  30  to the right direction in  FIG. 1 . A piston head  31  of the piston  30  presses the separator plate  50  and friction plate  60  towards a stopper ring  24  to thereby engage the clutch. Line X-X indicates a center axis of the center shaft  40 .  
         [0006]     When the clutch is disengaged by releasing the hydraulic fluid from the operating chamber  25 , the piston  30  returns to the left direction in  FIG. 1  due to the return force of a return spring  34 . The return spring  34  is supported by spring support  35  and a stopper ring  36  is attached to the clutch case  30  as a stopper for the spring support  35 . O-rings  32 ,  33  are provided between the clutch case  20  and the piston  30 , respectively. Further, seal members  42 ,  43  are provided between the clutch case  20  and the center shaft  40 .  
         [0007]      FIG. 10  shows the first conventional example of the friction plate used for the wet type multiplate clutch. In the friction plate  60 , a friction member  62  is attached to a surface of a core plate  61 . It is required for the friction plate  60  to reduce the drag torque and to improve cooling capability. Accordingly, an oil passage  63  and an oil groove  64  are formed on the friction plate so that they are arranged alternately as shown in  FIG. 10 . Note that the oil passage  63  extends outwardly in a direction from an inner peripheral edge  73  to an outer peripheral edge  74  of the friction member  62  with a constant width. The oil groove  64  opens to the inner peripheral edge  73  and closes at a middle of a surface of the friction member  62 , and a width thereof is constant. Spline teeth  75  are formed on an inner puerperal edge of the core plate  61 .  
         [0008]     In the second conventional example as shown in  FIG. 11 , the oil groove  64  is formed so that its width is larger than that of the oil groove  64  of the first conventional example. Further, U.S. Pat. No. 5,094,331, Japanese Utility Model Unexamined Publications JP-UM-A-1-146019 and JP-UM-A-50-30145 show that the width of the oil passage is formed so as to be decreased towards a direction of an outer peripheral edge to an outer peripheral edge.  
         [0009]     It has been carried out to reduce the drag torque by forming oil passages or oil grooves, however, it is required further reduction of the drag torque. In addition, in the friction member having oil passages on its surface, it could reduce the drag torque, however, it tends to have high friction coefficient at an initial stage of a frictional engaging, accordingly, there occurs a problem of biting between the friction plate and the separator plate. Also, this biting depends on engaging pressure at the frictional engaging.  
       SUMMARY OF THE INVENTION  
       [0010]     An object of the present invention is to provide a friction plate for a wet type multiplate clutch which can reduce the drag torque and improve the frictional properties between the friction plate and the separator plate of the clutch.  
         [0011]     To achieve the above-mentioned object, according to a first aspect of the present invention, there is provided a friction plate for a wet type multiplate clutch, comprising: 
        a substantially ring-shaped core plate; and     a friction member attached to the core plate, the friction member having a surface including; 
            a passage extending from an inner peripheral edge of the friction member to an outer peripheral edge of the friction member; and     a groove having an opened end which opens to the inner peripheral edge of the friction member and a closed end which is closed at a middle thereof,    
            wherein a width of the groove decreases towards a direction to the outer peripheral edge from the inner peripheral edge of the friction member.        
 
         [0017]     According to a second aspect of the present invention according to the first aspect of the present invention, it is preferable that a width of the passage decreases towards the direction to the outer peripheral edge from the inner peripheral edge of the friction member.  
         [0018]     According to a third aspect of the present invention, there is provided a friction plate for a wet type multiplate clutch, comprising: 
        a substantially ring-shaped core plate;     a friction member attached to the core plate; and     a plurality of pairs of two passages formed on a friction surface of the friction member, the passage extending from an inner peripheral edge of the friction member to an outer peripheral edge of the friction member,     wherein the two passages have bent portions at a middle portion of the friction member, respectively, and     the two passages extend from the inner peripheral edge of the friction member to the bent portion at the middle portion of the friction member so as to approach each other and extend from the bent portion to the outer peripheral edge of the friction member so as to apart from each other.        
 
         [0024]     According to a fourth aspect of the present invention according to the third aspect of the present invention, it is preferable that at least one pair of two passages has extended portions at the bent portions, respectively, and the extended portions extend from the bent portions so as to approach each other.  
         [0025]     According to a fifth aspect of the present invention according to the third aspect of the present invention, it is more preferable that at least one pair of passages has a circumferential groove communicating bent portions.  
         [0026]     According to a sixth aspect of the present invention according to the third aspect of the present invention, it is further suitable that the friction plate further includes: 
        a groove having an open end which opens to the inner peripheral edge of the friction member, and     wherein a width of the groove decreases towards a direction to the outer peripheral edge from the inner peripheral edge of the friction member.        
 
         [0029]     According to a seventh aspect of the present invention, there is provided a friction plate for a wet type multiplate clutch, comprising: 
        a substantially ring-shaped core plate; and     a friction member attached to the core plate, the friction member having a surface including; 
            a passage formed on a surface of the friction member, the passage extending from an inner peripheral edge to an outer peripheral edge of the friction member; and     a groove shaped into substantially triangle with three vertexes,    
            wherein the two vertexes of the groove are disposed on an inner peripheral edge of the friction member and the other vertex is disposed at a middle portion of the friction member.        
 
         [0035]     To achieve the object of the present invention, it is better to form the groove which gradually narrows its width towards the outer peripheral direction according to the first, second and sixth aspect of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]      FIG. 1  is a cross sectional view showing a basic structure of a multiplate clutch;  
         [0037]      FIG. 2  is a front view showing a first embodiment of the present invention;  
         [0038]      FIG. 3  is an enlarged view of part A in  FIG. 2 ;  
         [0039]      FIG. 4  is a view showing a second embodiment of the present invention;  
         [0040]      FIG. 5  is a view showing a third embodiment of the present invention;  
         [0041]      FIG. 6  is a view showing a fourth embodiment of the present invention;  
         [0042]      FIG. 7  is a view showing a fifth embodiment of the present invention;  
         [0043]      FIG. 8  is an enlarged view showing part B in  FIG. 7 ;  
         [0044]      FIG. 9  is a view showing a sixth embodiment of the present invention;  
         [0045]      FIG. 10  is a view showing the first conventional example;  
         [0046]      FIG. 11  is a view showing the second conventional example;  
         [0047]      FIG. 12  is a view showing a test result of the drag torque;  
         [0048]      FIG. 13  is a view showing another test result of the drag torque;  
         [0049]      FIG. 14  is a view showing a test result of the friction coefficient; and  
         [0050]      FIG. 15  is a view showing another test result of the friction coefficient. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0051]      FIG. 2  is a front view showing the first embodiment of a friction plate  60  of the present invention, and  FIG. 3  is an enlarged view showing part A in  FIG. 2 . The friction plate  60  is constituted in such a manner that a friction member  62  is attached on a substantially ring-shaped core plate  61 . Spline teeth  75  are formed on an inner peripheral edge of the core plate  61  and spline-engaged with an opposed member to transmit torque from the center shaft to the hub. An oil passage  63  and an oil groove  64  are formed on the friction member  62 . The oil passage  63  extends outwardly from an inner peripheral edge  73  to an outer peripheral edge  74  of the friction member  62 . The oil groove  64  has an opening end portion which opens to the inner peripheral edge  73  and has a closed end portion  65  on a friction surface of the friction member  62 . As shown in  FIG. 3  clearly, the oil groove  64  is formed in such a manner that a width  1  at the closed end portion  65  is smaller than a width L at the opening end portion, and the width gradually decreases towards a direction to the outer peripheral edge from the inner peripheral edge.  
         [0052]      FIG. 4  shows the second embodiment of the present invention. In the second embodiment of the present invention, in addition to the structure of the first embodiment, an oil passage  63  is also formed so as to gradually narrow its width towards the direction to the outer peripheral edge  74  from inner peripheral edge  73 . In both of the first and second embodiments, the oil passage  63  and the oil groove  64  are arranged alternately along a circumferential direction of the friction member  62 .  
         [0053]     Due to the above described structure, in the case where lubricating oil is subject to centrifugal force caused by the rotation of the friction plate, the force applied to the lubricating oil increases when the lubricating oil is pressed out from the groove, accordingly force for separating the separator plate from the friction plate increases. Especially, this effect is occurred by the oil groove which opens to the inner peripheral edge, has the closed end portion on the surface of the friction member and is formed so as to gradually narrow its width towards the direction to the outer peripheral edge from the inner peripheral edge as shown in the first and second embodiments of the present invention.  
         [0054]     In the third embodiment as shown in  FIG. 5 , the friction plate is structured in such a manner that a plurality of pairs of two oil passages are provided on the friction member  62 . Each of the pair of two oil passages has a bent portion at a middle portion of the friction surface of the friction member  62 , and the two oil passages approach each other fron the inner peripheral edge of the friction member  62  to the bent portion at the middle portion of the friction surface, and then apart from each other from the bent portion at the middle portion to the outer peripheral edge of the friction member  62 .  
         [0055]     In other words, in  FIG. 5 , portions  66 A,  66 B, which are defined between the inner peripheral edge  73  and the bent portion  68 A,  68 B at the middle portion of the friction surface of the two oil passages  63 A,  63 B, are extended so as to approach each other, and portions  67 A,  67 B which are defined between the bent portions  68 A,  68 B at the middle portion and the outer peripheral edge  74  are extended and inclined so as to apart from each other. That is, the two oil passages  63 A,  63 B are dogleg-shape such as “&lt;” and “&gt;”, respectively, and are provided so that the bent portions  68 A,  68 B approach each other so as to form “&gt;&lt;” shape. The two oil passages  63 A,  63 B form the pair  70  of oil passages.  
         [0056]      FIG. 6  shows the fourth embodiment of the present invention. In addition to the structure of the third embodiment, the two oil passages  63 A,  63 B have circumferential extended portions  71 A,  71 B which extend from the respective bent portions  68 A,  68 B in the circumferential direction of the friction member  62  in such a manner that they are opposed to each other.  
         [0057]      FIG. 7  shows the fifth embodiment of the present invention, and  FIG. 8  is an enlarged view showing part B in  FIG. 7 . In addition to the structure of the third embodiment shown in  FIG. 5 , the two oil passages  63 A,  63 B have a circumferential groove  72  which communicates with the bent portions  68 A,  68 B and extends in the circumferential direction of the friction member  62 .  
         [0058]      FIG. 9  shows the sixth embodiment of the present invention, in addition to the structure of the third embodiment, there is formed an oil groove  64  which opens to the inner peripheral edge of the friction member  62  and gradually narrow its width towards the direction to the outer peripheral edge.  
         [0059]     According to the dogleg-shaped oil passage as shown in  FIG. 5  to  FIG. 9 , the lubricating oil which is subject to the centrifugal force caused by the rotation of the friction plate hits the bent portion at the middle of the oil passage, and then the lubricating oil is pressed out from the oil passage in an axial direction of the center shaft, accordingly, an operation separating from the separator plate of the friction plate is occurred. This operation is increased by the combination of the circumferential extended portion, the circumferential groove or the oil groove which narrows its width gradually.  
         [0060]     Results of the comparative test of the drag torque and the initial friction coefficient among the comparative examples  1 ,  2  and embodiments of the present invention will be described below. Wherein the comparative example  1  represents the above-described conventional example  1  as shown in  FIG. 10 , and the comparative example  2  is the above-described conventional example  2  as shown in  FIG. 11 .  
         [0061]     Comparative Test of the Drag Torque a Test Condition is:  
                                                       oil temperature     40° C.           flow rate of the lubricant oil    0.4 l/min.           number of friction surface   8           clearance    0.2 mm/plate           inner diameter   Φ142           outer diameter   Φ159           friction area   40.19 cm 2  (in total)               about 32 cm 2  (except               groove area)                      
 
         [0062]     Wherein the friction surface is a surface defined between the friction plate and the separator plate  50 , the clearance is defined between the friction plate  60  and the separator plate  50 , and inner and outer diameter are diameters of the friction plate.  
         [0063]      FIG. 12  is a graph which a vertical axis indicates torque (kgf-m) and a horizontal axis indicates number of rotations. Line A denotes comparative example  1 , line B denotes the fifth embodiment and line C denotes the sixth embodiment.  FIG. 13  shows another result of  FIG. 12 , line D denotes the comparative example  2 , line E denotes the second embodiment and the line F denotes the third embodiment. As a test result, a group of the third, fourth and fifth embodiments show similar common result and another group of the first, second and six embodiments show another similar common result.  
         [0064]     Comparative Test of the Initial Friction Coefficient a Test Condition is;  
                                                       number of rotations    3600 r.p.m.           inertial mass   0.294 kg-m 2             surface pressure (MPa)   0.1, 0.2, 0.41, and 0.82           oil temperature     40° C.           flow rate    0.3 l/min.           number of friction member     3           inner diameter   Φ142           outer diameter   Φ159           friction area   40.19 cm 2  (in total)               about 32 cm 2  (except               groove area)                      
 
         [0065]     Wherein the surface pressure is pressure applied to the surface of the friction plate  60 .  
         [0066]      FIG. 14  is a graph which a vertical axis indicates friction coefficient and a horizontal axis indicates surface pressure applied to the surface of the friction plate. Line A denotes comparative example  1 , line B denotes the fifth embodiment and line C denotes the sixth embodiment.  FIG. 15  shows another result of  FIG. 14 , line D denotes the comparative example  2 , line E denotes the second embodiment and the line F denotes the third embodiment. As a test result, a group of the third, fourth and fifth embodiments show similar common result and another group of the first, second and six embodiments show another similar common result.  
         [0067]     While there has been described in connection with the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modification may be made therein without departing from the present invention, and it is aimed, therefore, to cover in the appended claim all such changes and modifications as fall within the true spirit and scope of the present invention.  
         [0068]     According to the above-mentioned present invention, it is achieved to reduce the drag torque and to keep the low initial friction coefficient at frictional engaging and reduce the variation of the friction coefficient in accordance with the engaging pressure.