Abstract:
A rotating clutch operably disposed between two rotating components includes a hydraulic operator having a piston and, on one side of the piston, an apply chamber or cavity and, on the opposite side of the piston, a balance chamber or cavity. The apply chamber is selectively provided with pressurized hydraulic fluid to engage and release the clutch to couple and de-couple the two rotating components. The balance chamber is provided with a flow of pressurized hydraulic fluid from the transmission lubrication system that flows through the transmission main shaft and flow restricting passages to the balance chamber. An exhaust port downstream of the balance chamber releases excess hydraulic fluid flow. Thus, whether, the clutch is rotating or not, hydraulic pressure is maintained in the balance chamber and proper clutch operation is assured.

Description:
FIELD 
     The present disclosure relates to clutches utilized in automatic transmissions and more particularly to hydraulically operated rotating clutches utilized in automatic motor vehicle transmissions. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     Rotating clutches, that is, devices having both rotating clutch elements and clutch operators, are often utilized within automatic motor vehicle transmissions and similar devices to transmit torque between two rotating components. Upon a suitable command, these clutches engage and disengage by stroking a hydraulically driven piston. When rotating, the oil behind the hydraulic piston in an apply cavity builds pressure due to centrifugal effects. The force thus generated must be countered by an equivalent opposing force in order to prevent unintended piston stroke and clutch engagement. This opposing force is commonly provided by a second volume of oil contained in a balance cavity on the opposite side of the piston. As the rotating clutch spins, centrifugally generated oil pressure and thus force within the apply cavity and the balance cavity cancel each other out. 
     In prior art transmission configurations, oil utilized within the balance cavity is non-pressurized lubrication oil collected and fed into the balance cavity through centrifugal effects only during rotation. In situations where the rotating clutch is brought to rest, the balance cavity will drain. The apply cavity, however, will remain fluid filled even when the clutch is released. This is done for shift quality considerations. If the clutch with a drained balance cavity is rapidly accelerated, a condition may develop in which the clutch piston is no longer force balanced. These situations are particularly common in hybrid transmissions in which rotating clutches are utilized with electric motors capable of extremely rapid rates of acceleration. 
     SUMMARY 
     The present invention provides a rotating clutch having an improved balance cavity (chamber) fill system. The rotating clutch includes a friction clutch pack that selectively connects two rotating transmission components and transmits torque therebetween. The clutch includes a hydraulic operator having a piston and, on one side or face of the piston, an apply chamber or cavity and, on the opposite side or face of the piston, a balance chamber or cavity. The apply chamber is selectively provided with pressurized hydraulic fluid to engage and release the clutch pack to couple and de-couple the two rotating transmission components. The balance chamber is provided with a flow of pressurized hydraulic fluid from the transmission lubrication system that flows through the transmission main shaft and flow restricting ports and passageways to the balance chamber. An exhaust port downstream of the balance chamber releases hydraulic fluid flow to the atmosphere (within the transmission) to prevent pressure buildup within the balance chamber that might inhibit proper clutch engagement. Thus, a proper fill of the balance chamber is maintained whether the clutch and operator are rotating or not, thereby assuring satisfactory, controlled and balanced operation of the rotating clutch, especially during periods of rapid acceleration. 
     Thus it is an aspect of the present invention to provide a hydraulic arrangement that improves the operation of rotating clutches in automatic transmissions. 
     It is a further aspect of the present invention to provide a rotating clutch having an operator with an apply chamber and a balance chamber with a hydraulic fluid supply that improves operation during periods of rapid acceleration after a stop. 
     It is a still further aspect of the present invention to provide a rotating clutch having an operator including an apply chamber and a balance chamber with a supply of lubrication oil that maintains fluid presence within the balance chamber when the clutch and operator are not rotating. 
     It is a still further aspect of the present invention to provide a rotating clutch having an operator including an apply chamber and a balance chamber which is supplied with hydraulic fluid from a lubrication passageway in the main shaft. 
     Further aspects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a sectional view of a portion of an automatic transmission incorporating the present invention; and 
         FIG. 2  is an enlarged, fragmentary sectional view of a portion of an automatic transmission incorporating the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     With reference to  FIGS. 1 and 2 , a portion of an automatic transmission for a motor vehicle is illustrated and generally designated by the reference number  10 . The automatic transmission  10  includes a typically cast metal housing  12  which locates, supports and protects the various components of the automatic transmission  10 . Among these components is a main shaft  14  which is supported for rotation by a plurality of anti-friction bearings  16 , one of which is illustrated in  FIG. 1 . The main shaft  14  defines a central, axial fluid passageway  18  which carries pressurized hydraulic fluid (transmission oil) from a hydraulic pump  20 , to a plurality of radial ports or passageways  22 ,  24  and  26 . The pressurized hydraulic fluid is utilized to maintain fluid presence in the balance chamber and lubricate the various rotating components, bearings and interfaces within the automatic transmission  10  as will be more fully described subsequently. 
     Disposed within the housing  12  of the automatic transmission  10  is an electric motor  30  having a stator  32  with electrical windings  34  and a rotor  36  which is supported on a pair of anti-friction bearing such as ball bearing assemblies  38 . The ball bearing assemblies  38  are, in turn, supported by a stationary bulkhead  40  which is secured to or integrally formed with the transmission housing  12 . The rotor  36  is coupled through an interengaging spline set  42  to a flange  44  that extends radially from a tubular drive member or quill  50 . The tubular drive member or quill  50  extends axially and concentrically along and about the main shaft  14  and terminates at another interengaging spline set  52  which couples the tubular drive member or quill  50  to a drive hub  54  having female splines  56  which function as the drive member of a first friction clutch assembly  60 . 
     As is particularly well illustrated in  FIG. 2 , the first friction clutch assembly  60  includes a first plurality of larger diameter clutch plates or discs  62  having males splines  64  complementary to and engaged by the female splines  56  on the drive hub  54 . The first plurality of clutch plates or discs  62  are interleaved with a second plurality of smaller diameter clutch plates or discs  66  having female splines  68  which are complementary to and engage male splines  72  on an inner hub  74  of a planet gear carrier  76  which is a component of a compound planetary gear assembly  80 . 
     It should be understood that although the planetary gear assembly herein described and illustrated is a compound assembly having a plurality of gear trains comprising two planet gears in a planet gear carrier, the present invention may alternatively be utilized with a simple planetary gear assembly, that is, a planetary gear assembly having a plurality of planet gears disposed between and each meshing with both a sun gear and a ring gear. As a further alternative, the planet gear carrier  76  may be replaced by any torque carrying member such as a shaft, quill or similar component. The inner hub  74  of the planetary gear carrier  76  includes a first plurality of oblique lubrication passageways  78  which generally align with and receive lubricating and cooling fluid from the radial port  24 . in the main shaft  14  and provide and direct it to the plates or discs  62  and  66  of the first friction clutch assembly  60 . 
     In addition to the planetary gear carrier  76 , the compound planetary gear assembly  80  includes a plurality of pairs of stub shafts  82 , one of which is illustrated in  FIG. 1 , which support on needle or roller bearings  84  a like plurality of pairs of planet gears  88 , one of which is illustrated in  FIG. 1 . The planetary gear assembly  80  also includes a sun gear  92  which is coupled to the main shaft  14  by an interengaging spline set  94  and is in constant mesh with one of each of the pairs of planet gears  88  and a ring gear  96  that is in constant mesh with the other of each of the pairs of planet gears  88 . A plurality of oblique passageways  98 , one of which is illustrated in  FIG. 1 , provide and direct a flow of pressurized hydraulic (lubricating and cooling) fluid from the radial ports  26  in the main shaft  14  to the stub shafts  82  and the bearings  84  of the planetary gear assembly  80 . 
     The first friction clutch assembly  60  also includes a balanced hydraulic operator  100  having an apply cylinder, chamber or cavity  102  which is formed or defined by the drive hub  54 . Axially slidably disposed within the apply cylinder or cavity  102  is a piston  104  which engages and compresses and releases the first and second pluralities of clutch plates or discs  62  and  66 . Controlled, pressurized hydraulic fluid is provided to the apply chamber  102  of the balanced hydraulic operator  100  through an oblique passageway  106  which is isolated by suitable rotating seal rings  108 . A plurality of radial stops or bumpers  110  on the back wall of the apply chamber or cavity  102  prevent the piston  104  from fully seating or bottoming against it. 
     On the side or face of the piston  104  opposite the apply chamber or cavity  102  is a balance chamber or cavity  112 . A circular plate or dam  114  which is retained in position by a snap ring or stop  116  includes suitable fluid tight seals and closes off the balance chamber or cavity  112  and allows axial translation of the piston  104 . Disposed within the balance chamber or cavity  112  is a Belleville spring or wave washer  118  that provides a biasing or restoring force to translate the piston  104  to the left in  FIGS. 1 and 2  and urges disengagement of the friction clutch assembly  60 . 
     One or more radial passageways  122  extend through the drive hub  54  between the balance chamber or cavity  112  and an outer elongate tubular passageway  124  and provide fluid communication therebetween. The outer elongate tubular passageway  124  is, in turn, in fluid communication, through one or more radial passageways  126  in the tubular drive member or quill  50  with an inner elongate tubular passageway  128  which, in turn, receives hydraulic fluid flow exiting the first radial passageway  22  in the main shaft  14 . Thus, hydraulic fluid flow from the central, axial fluid passageway  18  in the main shaft  14  is constantly provided through the passageways  122  to the balance chamber or cavity  112  of the balanced hydraulic operator  100 . Of course, as the piston  104  translates to the right in  FIGS. 1 and 2 , hydraulic fluid will flow out of the balance chamber or cavity  112  and through the passageways  122 . A rotating seal ring  132  retained on the outer surface of the tubular drive member or quill  50  seals against the bulkhead  40  and maintains hydraulic fluid in the outer elongate tubular passageway  124  to assist the above-described flow. 
     The transmission bulkhead  40  includes an oblique passageway  136  disposed under the main shaft  14  and extending between the outer elongate tubular passageway  124  and a concentric circular passageway  138  adjacent the terminus of the drive hub  50 . Disposed 180° opposite, that is, at a 12 o&#39;clock or vertical position when the oblique passageway  136  is disposed (preferably) at a 6 o&#39;clock or downward position, is an exhaust or vent port  140 . The exhaust or vent port  140  may be formed partially or entirely in one or partially in both of the components of the bulkhead  40 . The exhaust or vent port  140  allows any excess volume of hydraulic fluid provided to the balance chamber or cavity  112  to be vented to atmospheric pressure within the transmission  10  and returned to its sump (not illustrated). This prevents static pressure build-up in the balance chamber or cavity  112  but does not affect the centrifugal pressure build-up which counteracts the forces in the apply cavity or chamber  102 . 
     Referring now to  FIG. 1 , the planet gear carrier  76  also includes an outer hub  148  associated with a second friction clutch (brake) assembly  150 . The second friction clutch (brake) assembly  150  includes a first plurality of smaller diameter clutch plates or discs  152  having female splines  154  which are complementary to and engage male splines  156  on the outer hub  148 . The first plurality of smaller clutch plates or discs  152  are interleaved with a second plurality of larger diameter clutch plates or discs  158  having male splines  162  which are complementary to and engage stationary female splines  164  which are integrally formed with or coupled to the housing  12 . The outer hub  148  also includes a second plurality of radial lubrication passageways  166  which provide and direct lubricating and cooling oil flow to the plates or discs  152  and  158  of the second friction clutch (brake) assembly  150 . 
     The second friction clutch (brake) assembly  150  also includes a conventional (unbalanced) hydraulic operator  170 . Since the hydraulic operator  170  of the second friction clutch (brake) assembly  150  does not rotate, there is no need to provide a balanced operator. The conventional hydraulic operator  170  includes an annular piston  172  that is axially slidably received within an annular cylinder or chamber  174 . A biasing or return spring  176  which, because it does not rotate, may be one or more coil compression springs, is disposed between the piston  172  and a circular stop plate  182 . Again, if desired, a plurality of radial stops or bumpers  184  may be disposed on the back wall of the cylinder or chamber  174  to prevent the annular piston  172  from fully seating against it. 
     Last of all, it should be understood that various ball, roller and needle, shaft and thrust bearings  190  may be utilized as needed within the transmission  10  to separate components and reduce friction. 
     The balanced hydraulic operator  100  of the first friction clutch assembly  60  provides improved operation of an automatic transmission, especially when it is paired with an electric motor in a hybrid powertrain. When stationary, the balance chambers or cavities of prior art balanced clutches will partially drain. If the transmission components accelerate relatively slowly, as they typically do with an internal combustion engine power source, fluid and pressure will generally be restored to the balance chamber such that nominal clutch operation will occur. 
     In a hybrid powertrain, acceleration may be so rapid that a partially drained balance chamber will not refill quickly enough and interfere with desired and/or predicted clutch operation. The constant supply of transmission fluid through the radial ports  22  of the main shaft  14 , through the radial passageways  122  and  126  (and the flow restrictions these and other components represent) to the balance chamber or cavity  112  and the constant venting of overpressure of excess hydraulic fluid through the exhaust or vent port  140  ensure that the balance chamber or cavity  112  of the balanced hydraulic operator  100  of the present invention will be filled and achieve proper, balanced operation of the friction clutch assembly  60  under a wide range of operating and acceleration conditions. 
     The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.