Abstract:
A transmission clutch module includes an inner race, an outer race, and a plurality of race engaging pawls adapted to selectively secure the races together in either a locked position or an unlocked position. The clutch module includes  5  an actuator cam configured to be moved between two angularly spaced positions to control the pawls. The inner race is comprised of two axially spaced inner race plates axially secured together by rivets for retaining, and accommodating angular limited movements of the pawls. The pawls are circumferentially disposed about the inner race plates, and are radially outwardly biased by springs  10  to engage the outer race, unless blocked by the actuator cam. The pawls are weighted at one end, so that at a threshold speed of the inner race, they can overcome spring resistance to disengage from both the actuator cam and the outer race.

Description:
FIELD OF DISCLOSURE 
     The present disclosure relates generally to overrunning clutches for automotive transmissions, and more particularly to multiple mode clutches employed in such transmissions. 
     BACKGROUND OF DISCLOSURE 
     An automotive vehicle typically includes an internal combustion engine containing a rotary crankshaft configured to transfer motive power from the engine through a driveshaft to turn the wheels. A transmission is interposed between engine and driveshaft components to selectively control torque and speed ratios between the crankshaft and driveshaft. In a manually operated transmission, a corresponding manually operated clutch may be interposed between the engine and transmission to selectively engage and disengage the crankshaft from the driveshaft to facilitate manual shifting among available transmission gear ratios. 
     On the other hand, if the transmission is automatic, the transmission will normally include an internal plurality of automatically actuated clutches adapted to dynamically shift among variously available gear ratios without requiring driver intervention. Pluralities of clutches, also called clutch modules, are incorporated within such transmissions to facilitate the automatic gear ratio changes. 
     In an automatic transmission for an automobile, anywhere from three to ten forward gear ratios may be available, not including a reverse gear. The various gears may be structurally comprised of inner gears, intermediate gears such as planet or pinion gears supported by carriers, and outer ring gears. Specific transmission clutches may be associated with specific sets of the selectable gears within the transmission to facilitate the desired ratio changes. 
     Because automatic transmissions include pluralities of gear sets to accommodate multiple gear ratios, friction drag is a constant issue; the drag arises from mechanical interactions of the various parts employed. Much effort has been directed to finding ways to reduce friction drag within automatic transmission components and systems. 
     For example, one of the clutch modules of an automatic transmission associated with first (low) and reverse gear ratios may be normally situated at the front of the transmission and closely adjacent the engine crankshaft. The clutch may have an inner race and an outer race disposed circumferentially about the inner race. One of the races, for example the inner race, may be drivingly rotatable in only one direction. The inner race may be selectively locked to the outer race via an engagement mechanism such as, but not limited to, a roller, a sprag, or a pawl, as examples. In the one direction, the inner race may be effective to directly transfer rotational motion from the engine to the driveline. 
     Within the latter system, the outer race may be fixed to an internal case or housing of an associated planetary member of the automatic transmission. Under such circumstances, in a first configuration the inner race may need to be adapted to drive in one rotational direction, but freewheel in the opposite direction, in a condition referred to as overrunning. Those skilled in the art will appreciate that overrunning may be particularly desirable under certain operating states, as for example when a vehicle is traveling downhill. Under such circumstance, a driveline may occasionally have a tendency to rotate faster than its associated engine crankshaft. Providing for the inner race to overrun the outer race may avoid damage to the engine and/or transmission components. 
     In a second configuration, such as when a vehicle may be in reverse gear, the engagement mechanisms may be adapted for actively engaging in both rotational directions of the inner race, thus not allowing for the overrunning condition in the non-driving direction. 
     Above certain thresholds of rotational speed, the need for interaction of the engagement mechanisms, particularly those associated with the first (low) and/or reverse gear ratios, may become unnecessary. Thus, rather than contributing to drag, for example at highway speeds, there is substantial motivation to reduce and/or avoid interaction of the engagement mechanisms with any of the clutch parts, particularly those associated with the low/reverse clutch module. 
     SUMMARY OF DISCLOSURE 
     In accordance with one aspect of the disclosure, a multi-mode clutch module is disclosed. The clutch module comprises an inner race; a fixed outer race disposed concentrically about the inner race, and a plurality of engagement mechanisms circumferentially disposed between the inner and outer races. Each engagement mechanism is adapted to provide a locked position, wherein the mechanism locks the inner race to the outer race in a driving rotational direction, and an unlocked position that allows the inner race to freewheel in an opposite, non-driving, rotational direction. 
     In accordance with another aspect, the multi-mode clutch module includes an actuator cam plate having two positions, one position locking a first, driving directional, rotational motion of the inner race, but allowing the inner race to freewheel in an opposed second direction. 
     In accordance with another aspect, the actuator cam of the clutch module incorporates a second position that assures the locking of the inner race in both directions of rotational motion with respect to the outer race. 
     In yet another aspect, the engagement mechanisms are adapted to centrifugally disengage from the races at a specific rotational speed of the inner race. 
     These and other aspects and features of the present disclosure may be better appreciated by reference to the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of an automatic transmission clutch module constructed in accordance with the present disclosure, shown with one of its two inner race plates removed to reveal certain details. 
         FIG. 2  is an exploded view of various interactive parts of the clutch module of  FIG. 1 , constructed in accordance with the present disclosure. 
         FIG. 3  is a perspective cross-sectional view of a portion of a fully assembled clutch module of  FIG. 1 . 
         FIG. 4A  is an enlarged side view of a portion of the clutch module of  FIG. 1 , again with one of two inner race plates removed to reveal a pair of engagement mechanisms interacting with a cam actuator, showing a locked position in the driving rotational direction of the inner race, and a freewheel position in the opposite non-driving rotational direction (one-way mode). 
         FIG. 4B  is a side view of the same engagement mechanisms of  FIG. 4A , but shown with the inner race subjected to locked positions in both driving and non-driving rotational directions (locked mode). 
     
    
    
     It should be understood that the drawings are not to scale, and that the disclosed embodiments are illustrated only diagrammatically and in partial views. It should also be understood that this disclosure is not limited to the particular embodiments illustrated herein. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a clutch module  10  may be adapted to be utilized as a sub-unit of an automatic transmission (not shown). Such a transmission may be employed in a front-wheel driven automobile, for example. The clutch module  10  may include an exterior case or housing  12 , as well as an interior driven hub  14  adapted for transfer of power from an engine (not shown) to a vehicular driveline (not shown). 
     Axially oriented, circumferentially spaced cogs  16  are provided on the outside periphery of the interior driven hub  14 . Referring now also to  FIG. 2 , an inner race  20 , formed as two plates  20 A and  20 B spaced along an axis “A-A”, is adapted for supporting rotary movement of the plates via the cogs  16 . For this purpose, the plates  20 A and  20 B have circumferentially spaced detents  18  on their inside peripheries adapted to engage the cogs  16 . 
     With specific reference now to  FIG. 2 , an outer race  22  is situated intermediately or between the two inner race plates  20 A and  20 B. Although the inner race plates  20 A and  20 B are specifically displayed in this disclosure as ring structures, other configurations may be suitable for use within the scope of this disclosure. The outer race  22  is rotationally fixed with respect to the interior of the exterior case or housing  12  as shown within the multi-mode clutch module  10 , and an actuator cam  24  is situated between the outer race  22  and the plate  20 B of the inner race  20 . The actuator cam  24  is adapted to be rotated over a small angle about the axis A-A between two circumferentially spaced positions, as further described hereinbelow. Within its interior periphery, the actuator cam  24  incorporates a strategically situated array of circumferentially spaced recesses, herein called slots  26 , defined by and situated between projections, herein called cam teeth  28 . The slots  26  and cam teeth  28  are adapted to interact with pawls  30 , as may now be described. 
     As disclosed, the pawls  30  are elongated hardened steel members circumferentially positioned about the axis A-A of the clutch module  10 . Alternatively, the pawls maybe forgings or other manufactured structures, otherwise generally adapted to handle required loads of engagement as necessary for any particular clutch design. The pawls are situated so as to interact with both the inner race  20  and the outer race  22 , and are arranged in sets of opposed pairs,  30 A and  30 B. The actuator cam  24  is adapted to control interactions of the pawls  30 A and  30 B between the inner race  20  and the outer race  22 , as further described below. 
     A hydraulic actuator  32  ( FIG. 1 ) engages an actuator coupling  34  to move an actuator tab  40  ( FIG. 2 ) on the actuator cam  24  between the two angularly spaced positions noted above. Referring now also to  FIG. 3 , the inner race plates  20 A and  20 B, the outer race  22 , and the actuator cam  24  are shown assembled within the cross-sectioned partial view of the clutch module  10 . It will be appreciated that axially extending rivets  42  ( FIG. 2 ) are used to secure the two inner race plates  30 A and  30 B together. The rivets  42  extend through apertures  43  ( FIG. 3 ) in each of the plates  20 A and  20 B to hold the two plates rigidly together, and to thus assure against any relative rotation with respect to the plates. In lieu of the rivets  42 , other structural fasteners may be employed within the scope of this disclosure to secure the inner race plates  20 A,  20 B together. 
     In view of the foregoing, it will be appreciated that the actuator  32  ultimately controls the actuator tab  40  which, in turn, moves the actuator cam  24  between two distinct angular positions. Thus, the positioning of the pawls  30 A and  30 B, as axially retained between the riveted inner race plates  20 A and  20 B, is directly controlled by the actuator cam  24  against forces of springs  44 , as further described below. 
     Referring now specifically to  FIG. 3 , it will be noted that the two inner race plates  20 A and  20 B, are adapted to rotate within the case or housing  12 . Assuming the actuator cam  24  is in the first of its two specific angular positions, one set of the pawls, e.g. pawls  30 B, will lock the inner race  20  (i.e., plates  20 A and  20 B) to the outer race  22 , to drivingly rotate in one direction, for example counterclockwise. In the opposite rotational direction, e.g. clockwise, the pawls  30 A will be unlocked whenever the clutch module  10  in an automatic first or drive gear configuration so as to permit freewheeling of the inner race  20  relative to the outer race  22 . 
     Alternatively, when the actuator cam  24  is in the second of its two angular positions, both sets of pawls  30 A and  30 B, will lock the inner race to the outer race in either rotational direction to accommodate a reverse or manual first gear configuration; i.e. when in a mode during which no overrunning is desirable. In both configurations of the multi-mode clutch, it will be noted that the outer race  22  remains non-rotatable relative to the exterior case or housing  12 . For accommodating interactions with the pawls  30 A and  30 B, the inner circumference of the outer race  22  ( FIG. 2 ; see bottom portion thereof) contains circumferentially spaced notches  36 , each defined by and situated between pairs of radially inwardly projecting cogs  38 . 
     Referring now to  FIGS. 4A and 4B , first and second angular positions of the actuator tab  40  are depicted, respectively. In  FIG. 4A , the actuator tab  40  is shown in a first (angularly rightward) selectable position, representative of a first mode. In the latter configuration, the actuator cam  24  is positioned so that toe ends  50  of the pawls  30 A are blocked by cam teeth  28  from engagement with notches  36 , and hence with the cogs  38  on the interior of the outer race  22 . As such the inner race  20  is enabled to freewheel relative to the outer race  22 , and to thus provide for an overrunning condition when the inner race  20  is rotating clockwise as shown. Conversely, however, the position of the actuator cam  24  allows of the toe ends  52  of the pawls  30 B to engage the actuator slots  26  of the actuator cam  24 , and to thereby directly engage the cogs  38  of the outer race  22  to lock the inner and outer races,  20  and  22  together whenever the inner race  20  undergoes a driving, or counterclockwise rotational movement. 
     In  FIG. 4B , the actuator tab  40  is shown in a second (angularly leftward) selectable position, representative of a manual first or reverse gear mode. In the latter configuration, the actuator cam  24  is positioned so that the toe ends  50 ,  52  of both sets of the pawls  30 A and  30 B engage the actuator slots  26  of the actuator cam  24 , and interact with the outer race  22  as described above to lock the inner race  20  to the outer race  22 , irrespective of the rotational direction of the inner race  20 . 
     Continuing reference now to both  FIGS. 4A and 4B , the pawls  30 A and  30 B are asymmetrically shaped, and reversely identical. Each pair of the opposed pawls is movably retained within its own bowtie-shaped pawl aperture  60  ( FIG. 3 ) of the inner race plates  20 A and  20 B as shown. Each individual pawl  30 A,  30 B is urged radially outwardly via a single spring  44 . Each spring has a base  45 , and a pair of spring arms  46  and  48 . The spring arms  46  bear against the bottoms of the pawls  30 A, while the spring arms  48  bear against the bottoms of the pawls  30 B, each to urge respective toe ends  50 ,  52  into engagement with the cogs  38  of the outer race  22 . 
     Opposite each toe end  50  and  52 , each pawl  30 A and  30 B has a heel end  54  and  56 , respectively ( FIGS. 4A and 4B ). As already described, a slot  26  in the interior circumference of the actuator cam  24  may be selectively positioned such that each toe end  50 ,  52  may engage a notch  36  ( FIG. 2 ) of the outer race  22  to permit the toe ends to engage outer race cogs  38  ( FIG. 2 ) in the interior circumference of the outer race  22  to physically lock the inner and outer races together. 
     Operationally, radially inwardly depending actuator cam teeth  28  are adapted to selectively block such toe ends  50 ,  52  of the pawls  30  from being urged radially outwardly by respective spring arms  46 ,  48  and into notches  36 . The interaction of the cam teeth  28  with such toe ends  50 ,  52  defines the mechanism that permits the earlier described freewheeling of the inner race  20  relative to the outer race  22  as, for example, in the case of the above-described configuration for manual first or reverse gear. 
     In the immediate disclosure, the heel ends  54  and  56  are designed to contain more mass than the toe ends  50 ,  52 , so that at a particular threshold rotational speed of the inner race  20 , the heel ends will tend to swing radially outwardly under centrifugal forces of rotation. This action will cause the toe ends  50 ,  52  to become disengaged from notches  36  of the outer race  22 . As such, the inner race  20  will become disengaged from the outer race  22 . Under such forces, the toe ends of pawls  30 A will bear down against the spring arms  46 , while the toe ends  52  of pawls  30 B will respectively bear against spring arms  48 . In each case, the differential in mass between heel and toe ends must be designed to 1) overcome the resistive forces imposed by the respective spring arms  46 ,  48  of the springs  44 , and 2) achieve such centrifugal force induced load against the respective spring arms  46 ,  48  at a specific rotational speed threshold. 
     Thus, in either of the first or reverse gear configurations of the clutch module  10 , and at rotational speeds of the inner race  20  in excess of a threshold of 500 RPM, for example, the pawls  30 A and  30 B of the clutch module  10  are adapted to become disengaged under centrifugal forces imposed thereon by a predetermined speed of rotation. At such threshold speed, the centrifugal forces will be sufficient to overcome the radially opposing forces of the spring arms  46 ,  48 , and the toe ends  50 ,  52  of the pawls will disengage. As such, this disclosure offers an effective way to reduce and/or avoid parasitic drag loads within the clutch module. 
     A method of making a multi-mode clutch module may include steps of providing a pair of ring plates to form an inner race, and a separate ring structure to form an outer race, with the ring plates including reversely identical pawl apertures. An actuator cam and individual pawls are also provided; the pawls may be inserted into the pawl apertures of a first of the pair of ring plates, and after positioning the outer race and the actuator cam, the second ring plate is assembled so as to sandwich the outer race and actuator cam between the two ring plates along a common axis, while assuring that the pawls are retained within each set of then aligned pawl apertures. The assembled inner race, pawls, outer race and actuator cam are inserted into a transmission clutch housing in a manner such that the outer race is non-rotatably secured to the housing, and such that in operation each of the pawls is adapted to disengage from the actuator plate and the outer race under centrifugal forces at a predetermined rotational speed of the inner race. 
     The method of making the multi-mode clutch module may also incorporate pawls that comprise elongated hardened steel members having heel ends and toe ends, with the heel ends containing more mass than the toe ends. 
     INDUSTRIAL APPLICABILITY 
     The clutch module of this disclosure may be employed in a variety of vehicular applications, including but not limited to, automobiles, trucks, off-road vehicles, and other machines of the type having engines, automatic transmissions, and drivelines. 
     The disclosed clutch module offers a unique approach to avoiding parasitic drag associated with pawls generally employed to engage inner and outer races of clutches in automatic transmissions. Each pawl may be individually and movably situated between a pair of riveted rotatable inner races, each pawl having its axially oriented lateral ends captured within and/or between pairs of opposed notches for permitting limited angular motion. 
     To the extent that the heel ends of each pawl are designed to contain more mass, the heel ends may be appropriately weighted so that the toe ends of the pawls may become disengaged from their associated outer race notches at predetermined threshold rotational speeds of the inner race. This approach provides for a relatively simple and reliable reduction of parasitic drag above speeds not requiring continued engagement or interaction of inner and outer race members in, for example, a first (low) and reverse clutch module of an automatic transmission.