Patent Publication Number: US-2005126878-A1

Title: Segmented clutch plate for automatic transmission

Description:
TECHNICAL FIELD  
      This invention relates to a wet disc clutch pack for a friction-launch automatic transmission.  
     BACKGROUND OF THE INVENTION  
      Wet disc clutches are used in automatic transmissions to facilitate power transfer and gear shifting from one gear to another. Forward input clutch plates and reverse input clutch plates are known in prior transmissions. With such transmissions, both clutches embody a piston, wave plate, apply plate, friction plates, reaction plates, backing plate, return spring and snap rings. The number of friction plates is calculated based on the torque capacity and durability requirements for the transmission. The reaction plates used for most automatic transmission applications are steel and about 2 mm thick which is sufficient for shift energy absorption and dissipation.  
      For a friction-launch application using wet disc clutches, the torque converter of such prior automatic transmissions is replaced with an isolator assembly having input clutches which are used as the launching devices. The number of friction plates may be reduced by 1-2 plates because there is no longer a torque converter multiplication. In such prior friction-launch applications, 4-6 mm thick steel reaction plates are required for heat sink and to absorb the vehicle launch energy. Using thicker reaction plates will not normally enhance the clutch cooling capability and therefore a greater cooling lubricant flow rate is required to cool the clutch pack. This greater flow rate requires a bigger transmission oil pump. Thus higher parasitic losses due to plates running on oil and lower efficiency may be the result.  
     SUMMARY OF THE INVENTION  
      The improvement of this invention is to increase the cooling performance of a clutch pack using one or more segmented steel reaction plates. One side of the steel plate has a segmented configuration, which allows cooling flow to enter when it is placed against a conventional or unsegemented steel plate. While friction launch applications normally require thicker reaction plates for heat sink, this invention suggests using the thinner conventional plates in combination with segmented reaction plates. This will increase the convective heat transfer area. For example, for a wet disc clutch pack normally requiring thicker reaction plates (i.e., 6 mm), one thinner conventional plate (i.e., 2 mm) and two of the segmented plates of this invention when used in combination results in 400% improvement in convective area.  
      Many different designs may be used for the segmented pattern with various depths. This invention teaches using 25-50% of plate thickness to be used as a guideline for the depth of the triangular-shape grooves. This kind of groove (flow inlet area much larger than outlet area) will trap or impede the centrifugally-induced outward flow of cooling lubricant and cause the cooling fluid to wash over the entire surface of the adjacent plates and therefore increase cooling performance.  
      The ideal application for this invention is to utilize it as a starting device for input forward and reverse clutches, e.g., in the friction launch of a 6-speed automatic transmission. Prior clutches for such friction launch applications have used thicker reaction plates and a reduced number of friction plates. With this invention, however, the clutch when used in a 6-speed rear wheel drive (RWD) automatic transmission includes forward and reverse input clutches which are modified with the improved reaction plates of this invention. The torque converter is replaced with a flywheel and the isolator assembly, and vehicle launch is carried out with the improved clutch for forward and reverse directions.  
      The technical advantages of this invention, inter alia, include improvement in clutch cooling and therefore transmission durability in addition to fuel economy improvement due to use of a smaller transmission oil pump; and avoidance of thick (4-6 mm) reaction plates which would require a much higher cooling flow rate and a larger pump.  
      Accordingly, it is an object of this invention to provide a liquid flow cooled wet disc clutch pack for a friction launch transmission which comprises a sufficient number of friction plates to meet the torque capacity and durability requirements of the clutch pack; a first reaction plate adjacent to at least one of the friction plates and having one side sufficiently configured in convective heat exchange relation with the liquid flow to absorb at least a portion of the energy of the friction launch for at least partially cooling the clutch pack; and a second reaction plate having one side adjacent to the one side of the first reaction plate. The second reaction plate has on the one side thereof segments sufficiently configured in cooperation with the one side of the first reaction plate to control the flow of the liquid by increasing the convective surface area of a reaction plate side so that the flow washes over the one side of the first reaction plate in a manner to increase the cooling of the clutch pack.  
      With respect to the foregoing object and a normally needed plurality of first reaction plates, it is also an object of the invention to provide the second reaction plate with a predetermined thickness and with segments which protrude substantially 25-50% of the predetermined thickness, and form a triangular-shaped channel or groove so that when a first reaction plate is combined with a second reaction plate, the convective heat transfer area is sufficiently increased to reduce the number of first reaction plates needed.  
      Still another object of this invention is a segmented reaction plate for use in a wet disc clutch pack comprising an annular ring of predetermined thickness and having an inner periphery and an outer periphery connected on opposite sides of the predetermined thickness by opposed first and second surfaces, said first surface being substantially flat and said second surface being segmented into protruding configurations extending around the annular ring.  
      The above objects, and other objects, features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of a segmented steel reaction plate in accordance with this invention for use in the forward clutch portion of a wet disc clutch pack in a friction launch transmission;  
       FIG. 2  is a perspective view of a segmented steel reaction plate in accordance with this invention for use in the reverse clutch portion of a wet disc clutch pack in a friction launch transmission;  
       FIG. 3  is a fragmentary cross-section of the input clutches in a wet disc clutch pack improved by this invention for use in a 6-speed automatic transmission; and  
       FIG. 4  is a fragmentary cross-section of the input clutches in a wet disc clutch pack similar to  FIG. 3  but with the normally required thicker reaction plates for heat sink when used as friction launch clutches in a 6-speed automatic transmission. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      With reference to  FIG. 3  (improved) and  FIG. 4  (normal), wet disc clutch packs  10 ,  10 ′ are used in automatic transmissions  12  to facilitate power transfer and gear shifting from one gear to another. Forward input clutches  20 ,  20 ′ [C1234] and reverse input clutches  60 ,  60 ′ [C35R] of the transmission  12  are shown in  FIGS. 3 and 4 . As seen there, both clutches  20 ,  20 ′,  60 ,  60 ′ embody pistons  96 ,  100 , wave plates  22 ,  22 ′, 62 ,  62 ′ apply plates adjacent a wave plate not shown in clutches  10 ,  10 ′ for transmission  12 , friction plates  40 - 54  in clutch pack  10  and  40 ′- 54 ′ in clutch pack  10 ′, and reaction plates  24 - 32  in clutch pack  10  and  29 ′- 32 ′ in clutch pack  10 ′, backing plates  56 ,  92  in clutch pack  10 , and  56 ′,  92 ′ in clutch pack  10 ′, and return springs such as  98 , 102  and snap rings  120 ,  122  in  FIG. 3  which would also be included in the normal clutch pack of  FIG. 4 . The number of friction plates such as  40 - 54  and  40 ′- 54 ′ are calculated based on the torque capacity and durability requirements. The steel reaction plates such as  24 ′- 32 ′ in  FIG. 3  are used for most automatic transmission applications and are each about 2 mm thick which is sufficient for shift energy absorption and dissipation.  
      The wet disc clutch  10 ′ in  FIG. 3  is cooled by circulating lubricant such as oil. For this purpose, the transmission  12  has a pump  14  in oil-flow communication with the clutch pack  10 ′ by way of a passageway  16  (arrows A). Oil flowing through the passageway terminates in a centrifugally-induced oil spray or turbulence (arrows B) due to the rotation of clutch pack  10 ′. A similar oil flow (not shown) would exist in the normal wet disc clutch  10  of  FIG. 4 , but the oil pump  14  would necessarily be larger.  
      For friction-launch application of wet disc clutches ( FIGS. 3 and 4 ), the torque converter is replaced with an isolator assembly or clutch pack  10 ,  10 ′ and input clutches  20 ,  60  ( FIG. 4 ) and  20 ′,  60 ′ ( FIG. 3 ) are used as the launching devices. The number of friction plates  40 - 46  and  50 - 54  may be reduced by 1-2 plates in such clutches because there is no longer any converter multiplication. In the normal wet disc clutch of  FIG. 4 , 4-6 mm thick steel reaction plates  24 - 32  are required for heat sink and to absorb the vehicle launch energy. But using thicker reaction plates  24 - 32  will not enhance the clutch cooling capability and therefore more cooling lubricant flow rate is required to cool the clutch pack  10 . This means a larger capacity transmission oil pump is needed than that shown as  14  in  FIG. 3  in the improved clutch pack of this invention. Thus, higher parasitic losses and lower efficiency may be expected.  
      The forward input clutch  20 ′ and the reverse input clutch  60 ′ of wet disc clutch packs  10 ′ are packaged in a rotatable housing  108  having an outer housing portion  110 , an inner housing portion  112 , a forward piston dam  114  and a rearward piston dam  116 . The dams  114 ,  116  are fixed in place with respect to the inner and outer housings by snap rings  120 ,  122 . Snap ring  120  holds the dam  116  in place with O-rings  136 ,  138  providing seals that divide the housing into a reverse apply chamber  142  having an oil supply passage  194  and a return chamber  146  having an oil supply passage  148 . The return of piston  100  is aided by the reverse return spring  102 .  
      Piston  100  has a plurality of piston fingers  150  which extend through notches or openings  152  in the forward clutch plates  20 . The fingers serve to bias the wave plates  62 ′ of the reverse input clutches  60 ′.  
      The forward input clutch piston  96  cooperates with O-rings  130  and  132  and the dams  114 ,  116  to divide the housing  108  into a forward clutch apply chamber  154  having an oil supply passage  156  and a forward return chamber  158  having oil release passage  160 . Piston  96  biases wave plates  22 ′ of the forward input clutch  20 ′. The return of piston  96  is aided by the forward return spring  98 .  
      The friction plates  40 ′- 54 ′ cooperate respectively with the reaction plates  24 ′- 28 ′ to launch the vehicle forward. In particular, the rotatable housing  108  cooperates through the forward and reverse clutches  20 ′ and  60 ′ to drive respectively the C1234 hub  170  and the C35R hub  172 . Hubs  170 ,  172  are relatively rotatable with respect to the housing  108 . When the forward input clutch  20 ′ is being biased by piston  96 , reaction plates  24 ′- 28 ′ frictionally bind with friction plates  40 ′- 46 ′ and hub  170  is locked up for rotation with housing  108 . The transmission is thus launched in the forward direction.  
      Similarly, the friction plates  50 ′- 54 ′ cooperate respectively with reaction plates and  30 ′- 32 ′ to launch the vehicle in reverse. In particular, the rotatable housing  108  cooperates through the reverse clutch  60 ′ to drive the C35R hub  172 . The transmission is thus launched in the reverse direction.  
      With reference to  FIGS. 1 and 2 , the improved liquid flow cooled wet disc clutch pack  10 ′ of this invention has segmented clutch plates  180 ,  182 . For use in the friction launch transmission shown in  FIG. 3 a  segmented clutch plate  180  and/or  182  is adapted to lay adjacent a respective normal 2 mm thick reaction plate  24 ′- 32 ′.  
      Forward clutch plate  180  ( FIG. 1 ) is configured as a circular ring  184  having an inner circumference  186 , an outer circumference or periphery  188  and a thickness  190  of about 2 mm. The outer circumference or periphery is notched at spaced points  192  to accommodate the projecting fingers  150  of the piston  100  and at spaced points  194  to accommodate guides  196  on outer housing  110  for the reciprocable movement of the plates  180 . Segments  200  are configured to protrude substantially 25-50% of the plate&#39;s thickness to abut the adjoining surface of a respective regular forward reaction plate  24 ′- 28 ′.  
      Reverse clutch plate  182  ( FIG. 2 ) is configured with a circular ring  184  having an inner circumference  186 ′, an outer circumference or periphery  188 ′ and a thickness  190 ′ of about 2 mm. Segments  200 ′ are configured to protrude substantially 25-50% of the plate&#39;s thickness to abut the adjoining surface of a respective normal reverse reaction plate  30 ′- 32 ′. The outer circumference or periphery is notched at spaced points  194 ′ to accommodate guides  196  on outer housing  110  for the reciprocable movement of the plates  182 . The improved clutch pack  10 ′ also has a sufficient number of friction plates  40 ′- 46 ′ (forward) and  50 ′- 54 ′ (reverse) selected to meet the torque capacity and durability requirements of the clutch pack.  
      The flat sides of forward reaction plates  24 ′- 28 ′ are respectively frictionally engageable with the friction plates  40 ′- 46 ′ and have the other side sufficiently configured in convective heat exchange relation with the liquid flow B moving radially outwardly between the normal reaction plates  24 ′- 28 ′ and the segmented reaction plates  180  to absorb at least a portion of the energy of the friction launch and for at least partially cooling the clutch pack  10 ′. In particular, each segmented reaction plate  180  has a flat side adjacent to a friction plate and a segmented side adjacent to a respective one of the reaction plates. On the segmented side thereof the segments are sufficiently configured into triangular protrusions which in cooperation with a flat side of an adjacent reaction plate impede radially the outward flow B of the cooling oil between a reaction plate and an adjacent segmented plate. The segments increase the convective surface area of at least the segmented plate so that the flow washes over one side of a normal thickness reaction plate in a manner to increase and improve the cooling of the clutch pack.  
      Each segmented plate has pairs of protruding triangular segments  200 ,  200 ′ which cooperate to form triangular-shaped grooves  201 ,  201 ′ which converge in the radially outward direction to impede the outward flow of cooling liquid or oil. The liquid flow is in a direction between the normal or regular plates and the segmented plates. Since the flow is retarded or impeded by the groove-like configurations of the protruding segments, the cooling is forced between the facing surfaces of the plates, whereby to improve the cooling with a smaller capacity pump  14 .  
      The combination of a regular or normal reaction plate with a segmented reaction plate increases the convective heat transfer area, so that the number of normal reaction plates needed in the clutch pack  10 ′ can be reduced.  
      In summary, the clutch pack is improved by a segmented reaction plate. The segmented reaction plate is a circular ring with two surfaces. The first surface is substantially flat, and the second surface is segmented by protruding or raised configurations which extend around the ring. The ring is steel, and the protruding configurations are spaced triangles. The space between each pair of triangles is configured as a channel or groove on the segmented surface. The groove converges from the inner periphery of the ring toward the outer periphery of the ring. The convergence of the channel impedes the flow of radially outwardly moving oil and causes the oil to spread over the increased convective area of the segmented plate to improve cooling of the clutch.  
      While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.