Slipping bypass clutch construction for a hydrokinetic torque converter

Abstract: A hydrokinetic torque converter and lockup clutch assembly comprising an impeller housing (80) and a clutch construction situated within the housing (80) comprising a clutch plate (86) in the form of a piston having formed thereon an annular friction surface (90), a friction disc (92) located between the friction surface (90) of the clutch plate (86) and an adjacent wall (82) of the impeller housing (80) and having an inner margin (94) secured to the impeller housing (80) at a location radially inward of the friction surface (90), friction material (100) formed on the friction disc (92) and flow passage means for establishing a circuitous cooling oil flow path across the dynamic friction surfaces of the clutch to establish cooling and for eliminating wear as the pressure in the clutch control pressure chamber is modulated to effect a continuous slipping of the clutch surfaces during operation of the converter, the friction disc (92) providing a shield that minimizes heat transfer to the impeller housing (80) and for providing maximum compliance of the face of the friction surface (90) with respect to the friction material (100) carried by the friction disc (92).

Description: A hydrokinetic torque converter transaxle of the kind as described in U.S. Patent US-A-4 509 389 and schematically shown in Fig. 1 of the appended drawing includes a torque converter having an impeller and a turbine. The housing for the impeller includes a lockup clutch assembly having a clutch plate that engages a friction surface on the impeller housing. The clutch plate carries friction material that establishes a frictional driving connection between the impeller and the turbine when the pressure differential across the clutch plate is sufficient to establish a clutch engaging force. The clutch plate is connected through a damper assembly to the hub of the turbine, thus establishing a mechanical torque transfer between an engine crankshaft and the turbine shaft which bypasses the hydrokinetic torque flow path through the torque converter. A related bypass or lockup clutch for a hydrokinetic torque converter is described in U.S. Patent US-A-4 469 206 which defines the features in accordance with the preamble of claim 1. U.S. Patents US-A-4 468 988 describe a bypass or lockup clutch which is actuated by the pressure in the torus circuit of the torque converter in such a manner that a continuous slip rather than an engagement of the clutch is allowed to establish a full lockup condition. In such instances a relatively large heat dissipation is necessary because of the heat energy that is developed by reason of the dynamic friction torque. This tends to cause instability of the clutch because the annular friction surfaces of the clutch tend to go out of flat. Further, heat spots develop in the impeller housing. Most of the heat that is generated because of the slipping condition of the friction surfaces is transferred directly into the cover for the impeller. Furthermore, the friction surface on the cover requires precise machining and polishing during manufacture. This makes it necessary to use metal stock thickness greater than otherwise would be needed. The prior art designs also are deficient with respect to the ability of the converter to transfer heat energy into the fluid within the torus circuit. Also the instability of the clutch due to heat distortion makes controlling of the clutch torque capacity difficult. The present invention comprising the features of claim 1 eliminates the disadvantages outlined in the preceding discussion with respect to the modulated, continuously-slipping bypass clutches for use in hydrokinetic torque converters. It includes a simple friction disc comprising a steel core with friction material bonded to one side of the steel core. The disc is secured to the inner wall of the converter housing so that it will rotate with the converter housing. The steel core and the friction material provide a shield that protects the housing and reduces significant heat transfer to the housing, which could cause distortion. The improved design also eliminates hot spots on the friction material and on the face of the clutch plate. Maximum compliance between the registering friction surfaces of the improved clutch construction eliminates the necessity for finish machining and polishing of the frictional surfaces on the housing. There is provided a circuitous oil flow passage in the friction material that is bonded to the steel disc. Grooves in the friction material establish a uniform flow distribution pattern across the friction surfaces without causing an excessive pressure drop, thereby making it possible to maintain a controlled clutch pressure in the clutch control pressure chamber. The groove pattern is designed to establish a relatively large cooling fluid flow across the friction surfaces while still maintaining a desired sealing action. That permits maintenance of a controlled pressure drop across the piston plate. The oil flow grooves have a pattern that includes a radial flow as well as a circumferential flow so that the entire friction surface is adequately fed with cooling oil. Cooling oil exits through radial grooves thus providing uniform temperature distribution across the friction surfaces. Figure 1 is a view of a prior art clutch construction of the kind shown in U.S. Patent US-A-4 509 389. Figure 2 is an enlarged cross-sectional view of a portion of the prior art construction of Figure 1. Figure 3A is a cross-sectional view corresponding to the cross-sectional view of Figure 2 showing a first embodiment of the invention. Figure 3B is a second embodiment of the invention wherein a static seal is added to the construction of Figure 3A and cooling grooves are added to the piston plate. Figure 4 is a view showing the friction disc as seen from the plane of section line 4-4 of Figure 3A. Figure 5 is a cross-sectional view showing a third embodiment of the invention wherein a continuous weld is used to secure the friction disc to the inner wall of the converter housing. Figure 6 is another embodiment of the invention wherein the friction disc is secured by rivets or the like to the inner wall of the torque converter housing and wherein frictional material is formed on each of the two faces of the friction disc. Figure 7 is another embodiment similar to the embodiment of Figure 6 wherein the friction disc is secured to the inner wall of the housing by welding rather than by rivets. Figure 8 is another embodiment of the invention similar to Figure 6 wherein the friction disc is secured to the inner wall of the housing by means of a splined connection. Figure 1 shows a torque converter 10 having an impeller shell 12. This shell is joined at its outer margin to an impeller cover 14, which is secured to the outer margin by weld 16. The impeller shell 12 has recesses 18 that receive tabs 20 on radial outflow impeller blades 22. An inner shroud 24 has circumferentially spaced apertures that receive tabs 26. The blades thus are retained between the impeller shell 12 and the inner shroud 26. Turbine blades 28 are arranged in juxtaposed radial inflow disposition with respect to the blades 22. The blades are retained by a turbine shell 30 which has apertures that receive tabs 32 formed on the turbine blades 28. A circular inner turbine shroud generally similar to the impeller shell 24 is shown at 34. It has slots that receive tabs 36 on the inner margin of the blades 28. Thus the blades 28 are held together to define radial inflow passages that are a part of a toroidal fluid flow circuit. The radially inward portion of the turbine shell 30 is secured by rivets 38 to turbine hub 40, which has internal splines 42 to permit a driving connection with a turbine shaft. Impeller shell 12 has a hub 44 that is adapted to be journalled on a stationary sleeve shaft that forms a part of a transmission housing. Bladed stator assembly 46 includes stator blades 48 disposed between the flow exit section of the turbine in the flow entrance section of the impeller. An inner stator shroud 50 surrounds the radially outward ends of the stator blades 48. A stator hub which carries the blades 48 is shown at 52. An outer overrunning brake race 54 is secured within an opening in the hub 52. An inner overrunning brake race 56 has internal splines to permit a connection with the aforesaid stationary sleeve shaft. Overrunning clutch roller elements 58 establish a one way braking action between the races, the outer race being cammed to cooperate with the individual roller elements in known fashion. Cover 14 has a radially extending portion 60 at its outer margin. The inner surface 62 of the portion 60 serves as a friction surface. It is adapted to be engaged by friction material carried by the radially outward portion 64 of a clutch plate 66. The clutch plate is adapted to be connected to turbine hub 40 by means of a damper assembly. The damper assembly comprises a driven plate 68 which is splined at 70 to the turbine hub 40. A cover plate 72 of the damper assembly cooperates with the clutch plate 66 to define an enclosure for tangentially disposed damper springs 74. These are arranged in spring pockets formed in the outer portion of the driven plate 68. Torque is transmitted from the clutch plate 66 to the driven plate 68 through the tangentially disposed springs. Spacers 76 join the plate 72 with the clutch plate 66. They extend through slotted openings formed in the driven plate 68 to permit limited axial displacement of the clutch plate 66 with respect to the driven plate 68. The chamber 78 defined by the cover 60 and clutch plate 66 is a control pressure chamber which communicates with a control pressure source in the manner described in U.S. Patent US-A-4,633,738. By controlling the pressure in chamber 78, the pressure differential across the clutch plate 66 can be controlled. The pressure in the torus flow cavity on the right hand side of the clutch plate 66 will cause the friction surfaces on the cover 60 and on the clutch plate 66 to become frictionally engaged. By appropriately modulating the pressure in chamber 78, a controlled slipping will occur between the friction surfaces whereby torque fluctuations developed in the driveline due to engine pertubations and other torque transmitting irregularities can be absorbed. The thermal energy that is developed by reason of this slipping action can be controlled by means of my invention. This will be described in the following portions of the specification. In Figure 3A the radially outward part of the torque converter cover is shown at 80. This corresponds to the cover 14 of Figure 1. The cover includes a radially extending portion 82 having a flat annular inner surface 84. A clutch plate 86 has a peripheral portion 88 on which is formed a friction surface 90. A friction disc 92 comprises an annular disc with an inner margin 94 and an outer margin 96. The inner margin is welded by means of a continuous weld, as shown at 98, to the surface 84. Bonded to the disc 92 is friction material 100. The composition of the friction material is commonly referred to as "paper face" material. It is bonded to the steel disc 92 by a bonding technique described by Frosbie, Milek and Smith in SAE Design Practices, Vol 5, (1962). When the clutch plate 86 engages the friction material 100, the engaging surfaces tend to seal the control pressure chamber 102 from the torus circuit. Because the weld 98 is a continuous weld, it acts as a seal which prevents transfer of fluid under pressure from the torus circuit to the lower pressure control pressure chamber 102. As seen in Figure 4, the friction material 100 has formed therein four concentric annular grooves 104, 106, 108 and 110. These grooves can be machined by turning or they may be formed by pressing a die on the face of the disc during the formation of the disc as the friction material is pressure bonded to the steel disc 94. The friction material 100 is formed also with radial grooves located 45 degrees apart as indicated in Figure 4. The radial grooves at the 12:00, 3:00, 6:00 and 9:00 o'clock positions communicate with the radially outward region of the clutch and interconnect each of the four concentric grooves. The alternately spaced radial grooves situated between each of the aforesaid radial grooves do not communicate with the radially outward region, but they do communicate with the radially inward region. They also interconnect each of the four annular grooves. The radial grooves that communicate with the radial outward region are indicated by reference character 112, and the radial grooves that communicate with the radial inward region are indicated by reference character 114. Fluid in the torus cavity of the converter is under a pressure that is higher than the pressure in the chamber 102. Thus the fluid tends to flow radially inward through the grooves 112 where it is transferred to the circumferential grooves. The fluid then travels circumferentially to the adjacent grooves 114. From there the fluid is transferred to the radial inward region to the pressure chamber 102. Fluid thus circulates continuously across the friction surfaces during operation of the clutch in an engaged condition as it is slipping, and the fluid is tranferred circumferentially through the grooves thereby creating a maximum cooling effect. Heat is dissipated to the fluid and carried to chamber 102 and the control system where it is transferred to a cooler and then recirculated to the inlet side of the control pump for the transmission. The control pump supplies control pressure to the control system, as the control system establishes the regulated pressure levels in the torus circuit and in the chamber 102. Because the friction material does not engage directly the cover 80 nor the radially extending portion 82, transfer of the heat generated during dynamic slipping of the clutch with respect to the casing or cover is minimized. Furthermore, because of the use of the disc 92, it is possible to maintain precise flatness of the friction surfaces on the friction material 100 and on the clutch plate portion 88. Figure 5 shows a modification of the structure shown in Figure 3A. Like the structure shown in Figure 3A, the clutch of Figure 5 comprises a steel disc as shown at 92 '. It is welded by means of a continuous weld 98' to the radial portion 82' of cover 80'. The clutch plate 116 shown in Figure 5, which corresponds to the clutch plate 86 shown in Figure 3A, includes cooling fins 118 that are machined in the back or inactive face of the clutch plate 116. These fins increase the surface area over which the fluid in the torus circuit is exposed thereby facilitating transfer of heat from the clutch plate through the circulating fluid. Grooves 118 are concentric grooves located directly adjacent the friction material 100'. In the embodiment of Figure 3B a static seal ring 120 is located in an annular recess 123 formed in the radial portion 82'' of the cover 80''. Unlike the design of Figure 5, the steel friction disc 92'' is not welded by means of a continuous weld. Thus there is a possibility that fluid may leak radially inward by reason of the differential pressure in the torus circuit with respect to the pressure in the control pressure chamber 102''. The static seal ring, however, prevents undesired leakage in a radial direction across the clutch surfaces. The static seal ring is compressed by the disc 92''. Friction material 122 is bonded to the steel disc 92''. Unlike the friction material 100 of the design shown in Figure 3A, the friction material 122 does not have annular grooves nor radial grooves. Instead annular grooves and radial grooves are formed in the friction surface of the clutch plate 86''. The pattern of the grooves in the clutch plate are generally the same as the pattern of the grooves shown in Figure 4. A steel friction disc 124 is secured to the radially outward portion 82''' of the converter cover 80''' by rivets 126 in the Figure 6 construction. It is secured by welding 128 in the embodiment of Figure 7. It is secured by means of an internal and external spline connection 130 in the embodiment of Figure 8. In the embodiment of Figure 8 external splines are formed on clutch element 132, which is welded at 134 to the converter cover. The external splines on the element 132 register with internal splines formed on the disc 124. Friction material in the embodiments of Figure 6, 7, and 8 is formed on each of the sides of the disc 124 as shown at 136 and 138. Friction material 136 is a static seal that prevents radial flow of fluid under the differential pressure of the control chamber 102 with respect to the pressure in the torus circuit of the converter. This eliminates the need for providing a continuous weld as in the embodiment of Figure 3A and the need for providing a static seal as in the embodiment of Figure 3B. The clutch plate in the embodiments of Figures 6, 7, and 8 is of the same design as the clutch plate in the embodiment of Figure 3B. Thus it has a groove pattern to accommodate the circulation of fluid across the frictional surfaces. It a so has cooling fins located on the side of the clutch plate most proximate to the torus circuit thereby increasing the surface area over which the converter fluid circulates.

Claims: A bypass or lockup clutch for a torque converter (10) comprising: an impeller shell (80, 82) defining a torus circuit cavity and enclosing a hydrokinetic turbine (28) and an impeller (22), a friction clutch plate (86; 116) in said impeller shell having an annular friction surface (90) at a radially outward location and being connected to said turbine (28), an annular friction disc (92; 124) having an inner margin (94) located in said impeller shell (80, 82) at a radially outward location, a friction material (100; 122; 138) carried on said disc adjacent said friction surface (90) of said clutch plate (86; 116), said disc being connected to the interior of said impeller shell at a location proximate to its inner margin, a control pressure chamber (102) defined by said impeller shell (80, 82) and said clutch plate (86; 116), said clutch plate when being subjected to a pressure differential establishing a bypass torque flow path through said converter (10) with a slipping frictional engagement between said friction material (100; 122; 138) and said friction surface (90) of said clutch plate; characterized by annular grooves (104, 106, 108, 110) formed at the interface of said friction material (100; 122; 138) and said friction surface (90) of said clutch plate (96; 116), said grooves being connected by first radial grooves (112) that communicate with the interior of said impeller shell (80, 82) at a location radially outward of said friction disc (92; 124) and second radial grooves (114) that communicate with said control pressure chamber (102). A bypass or lockup clutch according to claim 1 wherein said annular grooves (104, 106, 108, 110) are formed in said friction material (100). A bypass or lockup clutch according to claim 1 wherein said annular grooves (104, 106, 108, 110) are formed in said friction surface (90) of said clutch plate (86''). A bypass or lockup clutch according to any of claims 1 to 3 wherein said friction disc (92) is connected to said impeller shell (80, 82) by a continuous weld (98) to effect a seal therebetween. A bypass or lockup clutch according to any of claims 1 to 3 wherein said friction disc (124) is connected to said impeller shell (80'', 82'') by rivets (126) to effect a seal therebetween. A bypass or lockup clutch according to any of claims 1 to 5 wherein a static seal ring (120; 136) is located between said friction disc (92''; 124) and said impeller shell (80'', 82'') to effect a seal therebetween. A bypass or lockup clutch according to any of claims 1 to 6 wherein said clutch plate (116) includes cooling fins (118) that are machined in the back or inactive face of the clutch plate proximate to its friction surface (92) and exposed to the torus circuit.

Inventors: MACDONALD FRASER J, MACDONALD, FRASER J.
Applicants: FORD FRANCE, FORD MOTOR CO, FORD WERKE AG, FORD FRANCE S. A., FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1990
Main classification: F16H45
IPC codes: F16D69, F16H45