STARTING CLUTCH FOR A CONTINUOUSLY VARIABLE TRANSMISSION

Abstract: A hydraulically-actuated starting clutch (10) utilized in a continuously variable transmission which includes a rotating shaft (11) having a housing (15,25) rotating therewith, a pressure chamber (17) in the housing receiving a piston (18), a pressure plate (45) and an end plate (38) in the housing to rotate therewith, two clutch plates (74) between the pressure and end plates (45,38) and operatively connected to a sleeve shaft (71) encompassing the rotating shaft (11), a separator (81) formed of a pair of generally parallel plates (82,83) is interposed between the clutch plates, one separator plate (82) having an annular fulcrum ridge (85), which may be slotted, contacting the other plate (83) to equalize loading on the clutch plates. The clutch may also include a diaphragm spring (52) between the piston (18) and the pressure plate (45), and also a retractor spring (48).

Description: Description The present invention relates to a hydraulically- actuated starting clutch for a continuously variable transmission in an automotive vehicle. Continuously variable transmissions have been known for a number of years as a driving means located between a vehicle engine and the road engaging wheels to provide a smooth acceleration without the usual shifting of gears by clutches and brake bands in an automatic transmission. A continuously variable transmission conventionally includes a pair of variable sheave pulleys, an endless belt extending between and in driving engagement with the pulleys and control means to alter the effective pulley diameters and thus change the belt ratio during operation of the vehicle. In automotive applications, a hydraulically-actuated clutch is required on the driven pulley shaft as a starting device and to drive a shaft leading to forward/reverse gearing to drive the final differential for the road-engaging wheels. The starting clutch is positioned on the driven pulley shaft so that the pulleys can be constantly rotating in one direction and rotation is not interrupted when shifting from forward to reverse for vehicle operation. Thus, initiating movement of the vehicle is accomplished by a speed responsive friction starting device wherein the clutch is controlled by the control means for the pulleys. In some transmission applications, it is desirable to use a two-friction plate clutch having an intermediate separator plate between the friction clutch plates and cooperating with the end plate and the movable pressure plate in the clutch housing. However, in clutch operation, the transmitted load tends to be concentrated toward the outer diameter of the friction plates which results in heavy load concentration at localised areas on the linings resulting in glazing and overheating thereof. Such a clutch is disclosed in US-A-3 862 678. The present invention overcomes the above-noted problem. The prior art portion of claim 1 is based on our earlier EP-A-0 191 987 which only uses a single clutch plate. The present invention, as defined in claim 1, relates to an improved hydraulically-actuated starting clutch wherein it is possible to use a pair of clutch friction plates operatively engaged with a shaft driving the forward/reverse gearing for the transmission containing this clutch. This clutch assembly includes an intermediate two-part separator plate between the two clutch plates, the two-part separator plate comprising a pair of substantially parallel plates, with one plate provided with a fulcrum ridge on the surface facing and contacting the other plate of the pair and at an optimum radial location, wherein the second plate engages the fulcrum ridge of the first plate to transmit and evenly distribute the applied load over the friction surfaces. Further objects are to provide a construction of maximum simplicity, efficiency, economy and ease of assembly and operation, and such further objects, advantages and capabilities as will later more fully appear and are inherently possessed thereby. Figure 1 is a front elevational view of the starting clutch with portions broken away to show the internal clutch structure. Figure 2 is a cross sectional view of the clutch taken on the irregular line 2-2 of Figure 1. Figure 3 is a cross-sectional view similar to Figure 2, but showing a different environment for the clutch assembly. Referring more particularly to the drawing wherein are shown illustrative embodiments of the present invention, Figures 1 and 2 disclose a hydraulically-actuated starting wet clutch 10 for use on the shaft 11 for the driven pulley (not shown) of a continuously variable transmission, such as illustrated in U.S. Patent No. 4,241,618. The shaft 11 has a reduced diameter splined portion 12 terminating in a threaded end portion 13 for an internally threaded nut 14. An annular hub 15 having internal splines is received on the portion 12 to rotate therewith, with the inner hub end abutting a shoulder 16 defining the portion 12. The hub extends radially outwardly to form an annular pressure chamber 17 receiving an annular piston 18 therein. The face of the hub contains a plurality of radial passages 19 connecting to passages 21 communicating with pressure chamber 17; the inner ends of passages 19 communicating with radial passages 22 from a central passage 23 in the shaft 11. A clutch housing or cover 25 has a central opening 26 in the generally radial wall 27 to receive the threaded shaft end 13 and is secured to the shaft and hub by the nut 14. Also, the cover has a plurality of annularly spaced openings 28 receiving projections 29 on the hub which are headed over to further secure the hub and cover together. Also, a resilient ring 31 is provided in an annular groove in the hub face to sealingly engage the cover. Beyond the projections 29, the cover wall extends radially outwardly and rearwardly in an inclined portion 32 terminating in a corner 33 for an axially-extending, generally cylindrical wall or flange 34 provided with internally flattened ribs 35 (see Figure 1) and openings 36 for the circulation of cooling oil in the clutch. Further, tabs 37 may be formed in the openings 36 cooperating with an end plate 38. The end plate 38 has an outer periphery with circumferentially spaced axial channels 39 cooperating with the ribs 35 in the cover for rotation therewith. A snap ring 41 is located in a groove adjacent the end of the cover flange 34 to retain the end plate in the cover, and the tabs 37 are bent inwardly to axially secure the end plate in the clutch assembly. An annular rib 42 is formed on the back side of the end plate, which material may be removed for balancing of the clutch assembly. An axially reciprocable pressure plate 45 also is provided with axial channels similar to channels 39 in its outer periphery cooperating with the ribs 35 to rotate with the cover, and an inner lip 47 is provided to interact with a retractor plate or spring 48. The pressure plate has an annular fulcrum ridge 49 on its surface 51 engaged by an intermediate portion of a Belleville or diaphragm spring 52 having its outer edge 53 received in the corner 33 of the cover and retained therein by a snap ring 54 located in an interrupted annular groove formed in the cover ribs 35. The inner portion of the spring is divided into fingers 55 resting on the outer wall 56 of the hub forming the pressure chamber 17 when the piston is retracted. The piston 18 is formed with an inner hub 61 encompassing the hub 15 and having a snap ring 62 in a groove therein retaining the inner edge 63 of the retractor spring 48. An annular rib or lip 64 is formed on the outer periphery of the piston to engage the inner ends 57 of the spring fingers 55. An annular resilient piston sealing ring 65 is located in the pressure chamber 17 behind the piston 18 with inner and outer sealing lips 66 and 67, respectively, engaging the chamber walls. A sleeve shaft 71 encompasses the shaft 11 and is rotatably mounted thereon through needle bearings 72. The end of the sleeve shaft located within the cover is splined at 73 to accommodate a pair of clutch plates 74,74' having central splined openings 75,75; each plate having opposed friction facings 76,76 which are grooved at 77 (Figure 1) in a conventional waffle pattern. Between the clutch plates is positioned a two-part separator 81 formed of a pair of separator plates 82 and 83; each plate having axial channels 84 (Figure 1) receiving the ribs 35 of the cover flange. The plate 82 has an annular fulcrum ridge 85 on the surface facing the other plate 83 and at an optimum radial location so as to transmit and evenly distribute the applied load on the friction faces. This separator plate 82 with the fulcrum ridge 85 acts as an intermediate load reaction point of the first friction plate 74 and as an apply load point of the second friction plate 74' with an overall reaction point being at the outer diameter of the outer end plate 38. This arrangement of selective reaction and transmission of the applied load provides a uniform load distribution over the entire surface of the friction plates and prevents high unit loading at localized areas. Figure 2 discloses the starting clutch at idle rpm with the piston 18 retracted and the friction plates disengaged from the pressure plate 45, intermediate separator 81 and end plate 38. As the vehicle engine accelerates, the hydraulic pressure in the central passage 23 in shaft 11 increases, as well as the shaft rpm, with the increased pressure being transmitted through radial passages 22 and 19 and openings 21 to the pressure chamber 17 behind the piston seal 65. The piston 18 is urged to the right as seen in Figure 2, with the lip 64 acting on the inner edges 57 of the Belleville spring fingers 55 to cause the spring 52 to pivot about the corner 33 and snap ring 54 and engage the fulcrum ridge 49 on the pressure plate 45 to urge the plate towards end plate 38. Thus, the pressure plate 45 engages the first friction plate 74, which then engages the two-plate separator 81 to engage the second friction plate 74' and then the end plate 38. Cooling oil is directed toward the interior of the clutch cover 25 within the inner periphery 43 of the end plate and through openings 78 in the clutch plates 74,74' for distribution along both surfaces of the two friction plates through the waffle pattern grooves 77 in the clutch facings 76 by centrifugal force of the rotating members; the oil exiting through openings 36. Although shown as a continuous solid ridge, the fulcrum ridge 85 may be radially slotted about the circumference to provide additional cooling of both the separator plates 82 and 83 and the innermost clutch facings 76. The clutch is released upon decrease in the hydraulic pressure, and the retractor spring 48 acts to retract the pressure plate 45 and disengage the clutch plates 74,74'. Figure 3 discloses an alternate embodiment of clutch 91 utilized as one of a pair of clutches in a continuously variable transmission; the clutch acting when engaged to rotate a forward drive gear and a second clutch is actuated for a reverse drive gear. Like parts of the clutch will have the same reference numerals with the addition of a script a. A driven pulley 92, a portion of which is shown, has a fixed sheave 93 with a chamber 94 formed therein around the shaft 11a for the clutch assembly 91. A central passage communicates with an annular pressure chamber 17a in chamber 94 through inclined passages 95; the chamber 17a housing an annular piston 18a and an annular resilient seal 65a. The outer axially extending wall 96 of the sheave 93 has internal splines 97 cooperating with the splined peripheries of the pressure plate 45a, intermediate separator 81a and end plate 38a; a snap ring 41a in a groove retaining the end plate in position. Interleaved between the pressure plate, separator and end plate are a pair of clutch plates 74a having central splined openings 75a receiving the exterior splines 98 on a sleeve extension 99 of forward gear pinion 101. The plates 74a include friction facings with suitable grooving, such as shown in Figure 1. The separator 81a includes a pair of separator plates 82a and 83a, with one plate 82a having an annular fulcrum ridge 85a on the surface facing the other plate 83a; which ridge may be optionally slotted. A Belleville or diaphragm spring 52a is located in the chamber 94 with its outer periphery 53a pivotally mounted in the wall 96 in a manner similar to the embodiment of Figure 2, its inner periphery 57a engaging an annular lip or rib 64a on the piston 18a and an intermediate portion contacting an annular fulcrum ridge 49a on the pressure plate 45a. This clutch operates in substantially the same way as the clutch 10 of Figure 2 except that hydraulic pressure is applied to the piston 18a only when forward rotation of the vehicle wheels is desired, and a decrease in pressure allows diaphragm spring to return to its normal state and retract the piston 18a. In addition, due to space restrictions, the centrifugal hydraulic balance of the clutch is achieved by a sealed chamber 103 consisting of the plate 100 which also provides a pivot point for Belleville spring 52a, a seal and plate assembly 102, a sealing ring 104 and the wall 96.

Claims: A hydraulically-actuated starting clutch assembly (10) for a vehicle transmision comprising an enclosure (15, 25) defining an annular pressure chamber (17) therein, an annular piston (18) reciprocally mounted in the chamber, a reciprocable pressure plate (45) actuated by the piston, an end plate (38) mounted for rotation with the enclosure, a driven shaft (71) rotatably mounted with respect to said enclosure, a clutch plate (74, 74') mounted on said driven shaft (71) for rotation therewith and having friction facings (76) located between said pressure plate and said end plate, and a driving shaft (11) upon which is secured the enclosure (15, 25) which comprises an outer wall (34), the pressure plate (45) and end plate (38) being mounted in said enclosure and the driven shaft comprising a sleeve shaft (71) encompassing and rotatably mounted on said driving shaft (11), characterised in that a pair of clutch plates (74,74') are provided with a separator (81) located between said clutch plates and mounted for rotation with said enclosure, in that said separator (81) comprises a pair of generally parallel plates (82, 83) and in that means evenly to distribute the applied load of the clutch on the friction faces comprises an annular fulcrum ridge (85) formed on one of the two plates and contacting the other plate. A hydraulically-actuated starting clutch assembly as set forth in claim 1, wherein cooling oil slots are formed in said fulcrum ring. A hydraulically-actuated starting clutch assembly as set forth in claim 1 or 2, wherein said fulcrum ridge (85) is formed on one separator plate (82) at a point radially intermediate the inner and outer edges thereof. A hydraulically-actuated starting clutch assembly as set forth in any preceding claim, including a diaphragm spring (52) having its outer periphery (53) pivotally mounted in said enclosure (25) and its inner periphery (57) in contact with said piston (18), said pressure plate (45) having a fulcrum ridge (49) at a radial location intermediate the edges thereof contacting the diaphragm spring. A hydraulically-actuated starting clutch assembly as set forth in any preceding claim, in which said enclosure comprises a hub (15) secured onto said driving shaft (11) for rotation therewith and a cover (25) secured to said hub and providing said outer wall (34). A hydraulically-actuated starting clutch assembly as set forth in claim 5, when appendant to claim 4, wherein said cover (25) has a generally radial wall (27) and an outer cylindrical wall (34) intersecting at a corner (33), the diaphragm spring (52) being pivotally mounted in said corner (33). A hydraulically-actuated starting clutch assembly as set forth in any preceding claim, wherein said enclosure defines a chamber (94), a balance plate (100), a seal and plate assembly (102) mounted on said piston, and a sealing ring to provide centrifugal hydraulic balance of the pressure chamber. A hydraulically-actuated starting clutch assembly as claimed in any preceding claim, wherein an annular retractor spring (48) is provided having an outer periphery engaging the inner periphery (47) of said pressure plate (45) and an inner periphery (63) connected to said piston (18). A hydraulically-actuated starting clutch assembly as set forth in claim 8, when appendant to claim 4, wherein said annular piston (18) includes an inner hub (61) connected to said retractor spring (48) and an outer annular lip (64) contacting the inner periphery (57) of said diaphragm spring (52). A hydraulically-actuated starting clutch assembly as set forth in claim 8 or 9, wherein a lip (47) is formed on the inner periphery of said pressure plate (45) contacting the outer periphery of said retractor spring (48). A hydraulically-actuated starting clutch assembly as set forth in any preceding claim, including tabs (37) formed in said outer wall (34) and bent inward to engage said end plate (38) and prevent axial movement thereof.

Inventors: VLAMAKIS, MARIA S.
Applicants: BORG-WARNER AUTOMOTIVE TRANSMISSION AND ENGINE COMPONENTS CORPORATION
Application year: 1988
Main classification: F16D25
IPC codes: F16D25, F16D13