Patent Publication Number: US-2013248317-A1

Title: All wheel drive disconnect clutch

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/615,655 filed Mar. 26, 2012, which application is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates a drive disconnect clutch for providing torque to a secondary drive shaft in an all-wheel drive vehicle, specifically, a drive disconnect clutch providing synchronization with frictional engagement of clutch plates and a locked connection with expanding wedge plates. 
     BACKGROUND 
     For providing torque to a secondary drive shaft of an all-wheel drive vehicle, U.S. Pat. No. 7,150,694 is an example of using a clutch in a power transfer unit (PTU), which adds to the mass and size of the PTU. U.S. Pat. No. 7,150,694 and U.S. Pat. No. 7,309,301 are examples of using a transfer (typically wet) clutch in a differential to control torque to a secondary drive shaft. Pressurized fluid must be continuously supplied to keep the clutches in a closed mode, adding to the power usage associated with usage of the clutches. U.S. Pat. No. 6,520,885 is an example of using a roller or dog clutch to control torque to a secondary drive shaft. However, a vehicle must be at a stand still to use of such clutches. 
     SUMMARY 
     According to aspects illustrated herein, there is provided a drive disconnect clutch assembly, including: an input component arranged to receive torque from a motor; an output gear; and a clutch. The clutch includes: a piston plate; at least one clutch plate; at least one wedge plate; and respective friction material disposed between the at least one clutch plate and the at least one wedge plate. The piston plate is arranged to: displace a first distance in a first axial direction to clamp the at least one clutch plate and the at least one wedge plate to lock rotation of the input component to rotation of the output gear; and displace further in the first axial direction to displace the at least one wedge plate to lock respective rotations of the input component and the output gear via contact of the at least one wedge plate with the input component and the output gear. 
     According to aspects illustrated herein, there is provided a drive disconnect clutch, including: an input component arranged for driving connection to a motor; an output gear; and a clutch. The clutch includes: a piston plate; at least one clutch plate; at least one wedge plate; and respective friction material disposed between the at least one clutch plate and the at least one wedge plate. In a synchronizing mode, the at least one wedge plate is rotationally connected to the input component and the at least one wedge plate is rotatable with respect to the output gear. In the synchronizing mode, the piston plate is arranged to displace a first distance in a first axial direction to clamp the at least one clutch plate and the at least one wedge plate to lock rotation of the input component to rotation of the output gear. In a locked mode, the piston plate is arranged to displace further in the first axial direction such that: the at least one wedge plate is rotated with respect to the input component; and the at least one wedge plate is compressively engaged with the input component and the output gear to lock rotation of the input component to rotation of the output gear. 
     According to aspects illustrated herein, there is provided a drive disconnect clutch, including: an input component arranged to receive torque from a motor and including an outer circumference formed by a first plurality of flat sides; an output gear; and a clutch including: a piston plate; at least one clutch plate; at least one wedge plate including an inner circumference formed by a second plurality of flat sides in contact with the first plurality of flat sides; a key plate including a plurality of radially displaceable keys; and respective friction material disposed between the at least one clutch plate and the at least one wedge plate. While the plurality of radially displaceable keys rotationally locks the at least one wedge plate and the input component, the piston plate is arranged to displace a first distance in a first axial direction to clamp the at least one clutch plate and the wedge plate to lock rotation of the input component to rotation of the output gear. The piston plate is arranged to displace further in the first axial direction such that: the plurality of radially displaceable keys retract to enable rotation of the at least one wedge plate with respect to the input component; the first plurality of flat sides slide along the second plurality of flat sides; an inner circumference of the wedge plate is in compressive engagement with the input component; and an outer circumference of the wedge plate is in compressive engagement with the output gear. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments are disclosed, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, in which: 
         FIG. 1A  is a perspective view of a cylindrical coordinate system demonstrating spatial terminology used in the present application; 
         FIG. 1B  is a perspective view of an object in the cylindrical coordinate system of  FIG. 1A  demonstrating spatial terminology used in the present application; and, 
         FIG. 2  is a schematic representation of a vehicle with a drive disconnect clutch assembly in a differential assembly; 
         FIG. 3  is a cross-sectional view of a drive disconnect clutch assembly in a differential assembly; 
         FIG. 4  is a detail of the drive disconnect clutch assembly in  FIG. 3  in a disengaged mode; 
         FIG. 5  is a detail of the drive disconnect clutch assembly in  FIG. 3  in a synchronizing mode; 
         FIG. 6  is a sectional view generally along line  6 - 6  in  FIG. 5 ; 
         FIG. 7  is a detail of the drive disconnect clutch assembly in  FIG. 3  in a locked mode; and, 
         FIG. 8  is a sectional view generally along line  8 - 8  in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the disclosure. It is to be understood that the disclosure as claimed is not limited to the disclosed aspects. 
     Furthermore, it is understood that this disclosure is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present disclosure. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. It should be understood that any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure. 
       FIG. 1A  is a perspective view of cylindrical coordinate system  80  demonstrating spatial terminology used in the present application. The present invention is at least partially described within the context of a cylindrical coordinate system. System  80  has a longitudinal axis  81 , used as the reference for the directional and spatial terms that follow. The adjectives “axial,” “radial,” and “circumferential” are with respect to an orientation parallel to axis  81 , radius  82  (which is orthogonal to axis  81 ), and circumference  83 , respectively. The adjectives “axial,” “radial” and “circumferential” also are regarding orientation parallel to respective planes. To clarify the disposition of the various planes, objects  84 ,  85 , and  86  are used. Surface  87  of object  84  forms an axial plane. That is, axis  81  forms a line along the surface. Surface  88  of object  85  forms a radial plane. That is, radius  82  forms a line along the surface. Surface  89  of object  86  forms a circumferential plane. That is, circumference  83  forms a line along the surface. As a further example, axial movement or disposition is parallel to axis  81 , radial movement or disposition is parallel to radius  82 , and circumferential movement or disposition is parallel to circumference  83 . Rotation is with respect to axis  81 . 
     The adverbs “axially,” “radially,” and “circumferentially” are with respect to an orientation parallel to axis  81 , radius  82 , or circumference  83 , respectively. The adverbs “axially,” “radially,” and “circumferentially” also are regarding orientation parallel to respective planes. 
       FIG. 1B  is a perspective view of object  90  in cylindrical coordinate system  80  of  FIG. 1A  demonstrating spatial terminology used in the present application. Cylindrical object  90  is representative of a cylindrical object in a cylindrical coordinate system and is not intended to limit the present invention in any manner. Object  90  includes axial surface  91 , radial surface  92 , and circumferential surface  93 . Surface  91  is part of an axial plane, surface  92  is part of a radial plane, and surface  93  is a circumferential surface. 
       FIG. 2  is a schematic representation of a vehicle with drive disconnect clutch assembly  100  in differential assembly  102 . 
       FIG. 3  is a cross-sectional view of drive disconnect clutch assembly  100  in differential assembly  102 . 
       FIG. 4  is a detail of drive disconnect clutch assembly  100  in  FIG. 3  in a disengaged mode. The following should be viewed in light of  FIGS. 2 through 4 . Vehicle V has a standard four-wheel-drive drive vehicle architecture, for example, M is a transverse engine powering the front wheels FW via right front axle RFA, left front axle LFA, and differential assembly  102 . Assemblies  100  and  102  are used for connecting and disconnecting a secondary drive shaft SDS, for example, a rear drive shaft, with torque from motor M. Shaft SDS provides torque to rear wheels RW via rear differential assembly DIFF and rear axles RA. Assembly  100  is integrated into differential assembly  102 . Thus, as further described below, assembly  100  provides a synchronizing function and a locking clutch to engage and disengage the output/torque of the motor with SDS. 
     Drive disconnect clutch assembly  100  includes input, or input component (final drive ring gear),  108 , arranged to receive torque from the motor, for example via final drive pinion shaft  103 , output, or output component,  104 , and clutch  110 . Output  104  transmits torque to SDS via shaft  105 . Gear  108  transmits torque to LFA and RFA via differential gear set  107 . Clutch  110  includes piston plate  112 , at least one clutch plate  114 , at least one wedge plate  116 , backing plate  117 , and respective friction material  118  disposed between the at least one clutch plate and the at least one wedge plate. In an example embodiment, the friction material is fixed to the at least one wedge plate, but in other embodiments (not shown), the friction material may be fixed to the at least one clutch plate. In the example illustrated by the figures, assembly  100  includes three plates  114  and three plates  116 ; however, it should be understood that assembly  100  is not limited to a particular number of plates  114  or plates  116  or a particular ratio of plates  114  to plates  116 . To simplify the presentation, the discussion that follows is directed to “plates  114 ,” “clutch plates,” “plates  116 ,” and “wedge plates”; however, it should be understood that the discussion is applicable to configurations including only one clutch plate or wedge plate, or only one each clutch plate and wedge plate. 
     As for a typical wet clutch arrangement, clutch plates  114  are keyed to the input such that the clutch plates are axially displaceable and rotationally connected to the input. By “rotationally connected” we mean that two or more components are directly or indirectly connected such that respective rotations of the components are locked. That is, the components rotate in unison. Slots  137  are used to key, or spline, the clutch plates to the input. 
     In the disengaged mode, the piston plate is positioned such that the piston plate does not clamp the clutch plates and the wedge plates. Further, as described below, the wedge plates are rotationally locked with the output component. Thus, the clutch plates and the input are rotatable with respect to the wedge plates and the output component and torque is not transmitted from the input to the output. 
       FIG. 5  is a detail of drive disconnect clutch assembly  100  in  FIG. 3  in a synchronized mode. The following should be viewed in light of  FIGS. 2 through 5 . As further described infra, in a synchronizing mode, the wedge plates remain rotationally connected to the output component and the piston plate is arranged to displace in axial direction D 1  to clamp the clutch plates and the wedge plates to the backing plate to lock rotation of the input component to rotation of the output. 
     The clamping of the clutch plates and wedge plates enables torque from the motor and input component to be transmitted to the output, for example, as further described infra, to synchronize energy, or rotational speeds, of the input component and the output component, as well as other components connected to the output component, such as shaft  105  and secondary drive shaft SDS. 
     As further described infra, in a locked mode, following the synchronizing mode, the piston plate is arranged to displace further in direction D 1  to displace the wedge plate keys to lock rotation of the wedge plates with rotation of the input component and the output. Specifically, the wedge plates are expanded and wedged between the input component and the output. Once the wedge plates are displaced to lock the rotation of the input component and the output, torque can be transferred from the input component to the output via the wedge plates. Thus, the clutch plates are no longer needed for torque transfer, and as further described infra, the piston can be displaced in direction D 2 , opposite D 1 , to relieve axial pressure on the clutch plates and enable the clutch plates to disengage from the wedge plates. Advantageously, the amount of force applied to the piston, for example, in the form of pressurized hydraulic fluid, during closed operation of the clutch (to maintain torque transfer from the input component to the output gear) is reduced. For example, rather than applying an amount of force needed to radially retract the wedge keys and clamp the wedge plates and clutch plates, only the lesser amount of force needed to retract the wedge keys is applied to the piston. 
     Clutch  110  includes key plate  122  rotationally connected to the output component. During the disengaged mode and the displacement of the piston in the synchronizing mode, the key plate is engaged with the wedge plates to rotationally lock the wedge plates and the output component. During the locked mode, the piston plate is arranged to displace the key plate to enable relative rotation between the wedge plates and the output component such that the wedge plates contact the input. This contact rotationally locks the wedge plates, the input component, and the output, enabling torque transmission from the input component to the output by the wedge plates without the use of the clutch plates. 
       FIG. 6  is a sectional view generally along line  6 - 6  in  FIG. 5  with assembly  100  in the synchronizing mode. The following should be viewed in light of  FIGS. 2 through 6 . In  FIG. 6 , single wedge plate  116 A is shown; however, it should be understood that the discussion is applicable to the remaining wedge plates. In an example embodiment, each wedge plate includes respective slots  124  and the key plate includes keys  126  arranged to be disposed within slots  124  during the disengaged and synchronizing modes. The keys, like the key plate, are rotationally connected to the output component; therefore, the keys rotationally connect the wedge plates and the output component while disposed in the slots. 
     In the synchronizing mode, the wedge plates are rotatable with respect to the input, that is, respective outer circumferences OC 1  of the wedge plates and inner circumference IC 1  of the input are separated by radial distance RD 1 . 
       FIG. 7  is a detail of drive disconnect clutch assembly  100  in  FIG. 3  in a locked mode. 
       FIG. 8  is a sectional view generally along line  8 - 8  in  FIG. 7 . The following should be viewed in light of  FIGS. 2 through 8 . In the locked mode, the piston plate is arranged to engage the wedge plate key to displace the plurality of keys radially inward such that the plurality of keys are disengaged from the plurality of slots, and the wedge plates are rotatable to compressively engage the input component and the output to lock respective rotations of the input component and the output. For example, piston element  127 , engaged with the piston and portion  122 A of the wedge plate key are mutually angled such that as  127  urges  122 A in direction D 1 ,  122 A is displaced radially inward, drawing the keys out of slots  124 . 
     In an example embodiment, the output component includes outer circumference OC 2  with flat surfaces  128  and the wedge plate includes inner circumference IC 2  with flat surfaces  130 . Pairs of mated surfaces  128  and  130 , for example  128 A and  130 A, are at an acute angle with respect to a radius R passing through the surfaces. That is the surfaces form complementary ramps with respect to circumferential directions C 1  and C 2 . In the disengaged and synchronizing modes, surfaces  128  and  130  are engaged such that plates  116  are in maximally radially inward positions (distance RD 1  is present). 
     In the locked mode, as further described infra, enabling the wedge plates to rotate with respect to the output component, for example, withdrawing the keys from the slots, causes the wedge plates to compressively engage the input component and the output (distance RD 1  is removed) to lock respective rotations of the input component and the output. 
     In the locked mode, the wedge plates are no longer fixed by keys  126  and the wedge plates rotate with respect to the output component, for example, in direction C 1 , due to contact with the clutch plates. Respective surfaces  128  then slide along respective surfaces  130 . That is, the frictional engagement of the wedge plates with the clutch plates urges the wedge plates in direction C 1 . Due to the ramp configuration described above, as surfaces  128  slide along surfaces  130 , surfaces  128  are pushed radially outward, pushing  1 C 2  of the wedge plates radially outward. In turn, as further described infra, OC 1  also expands radially outward. It should be understood that movement of the wedge plates in direction C 2 , opposite C 1 , from the synchronizing position results in the same radially outward displacement of the wedge plates described above. 
     Thus the wedge plates are in compressive engagement with the input component and the output to rotationally lock the input component and the output component and to transmit torque from the input component to the output. By “compressive engagement,” we mean that the wedge plates exert a pressure, for example in a radial direction, on the input component and/or the output, or the input component and the output exert a pressure, for example in a radial direction, on the wedge plates. In an example embodiment, the rotation of the wedge plates with respect to the output component is typically small, for example, two or three degrees. However, it should be understood that other amounts of relative rotation between the wedge plates and the output component are possible. 
     In an example embodiment, the wedge plates are discontinuous in the circumferential directions by virtue of a radially disposed space  135  separating circumferential ends  136  of the wedge plate by circumferential distance CD. In the locked mode, the piston plate, via the output component, element  127 , and plate  122 , is arranged to increase CD to expand the wedge plate radially outward. That is, space  135  enables the wedge plate to expand radially outward in response to rotation of the output and the sliding contact of surfaces  128  and  130  to contact the input. 
     Advantageously, once the wedge plates are radially expanded to compressively engage the input component and the output, that is, the wedge plates are wedged between the input component and the output, the wedge plates are able to transmit torque and the clutch plates are no longer needed to transmit torque. Therefore, the force on the piston, for example, pressurized hydraulic fluid, can be reduced as described above. Thus, the energy requirement of assembly  100  is reduced, since it is no longer necessary to provide pressurized fluid to clamp the clutch plates. As long as torque is being transmitted from the input component to the wedge plates in direction C 1 , the wedge plates remain locked to the input component and the output. 
     As noted above, the wedge plates remain engaged with input component and the output component as long as torque from the motor is present on the input component (drive mode). In a coast mode, torque from the motor is withdrawn from the input component (for example, an accelerator for the motor is released) and the wheels associated with axle SA are rotating and applying torque to shaft  105 . The torque from the axle causes the output to rotate in direction C 2 , which in turn, causes the wedge plates to rotate in direction C 2  with respect to the input component. As noted above, as long as the keys are withdrawn by the piston, rotation in direction C 2  also causes the wedge plates to radially expand and lock the input component with the output gear. That is, as the surfaces slide toward the position associated with the synchronizing mode (keys aligned with slots  124 ) the wedge plates radially contract, but as the surfaces slide past the position, the surfaces cause the wedge plates to again expand. Thus, as long as the keys remain retracted, the wedge plates continue to transmit torque in alternating drive and coast modes without the need for clamping the wedge plates. 
     In an example embodiment, clutch  110  includes resilient element  138  engaged with keys  126  and urging keys  126  radially outward, for example, urging the keys into slots  124  during the disengaged and synchronizing modes. For example, when the piston plate displaces in direction D 1  against the wedge plate key, the action of the piston plate displaces the keys radially inward against the force of the resilient element to enable rotation of the wedge plates with respect to the output component. If the piston is retracted such that the piston no longer urges the keys radially inward, element  138  urges the keys radially outward. In the locked mode, the keys are urged against surfaces  128 , but cannot enter slots  124  due to the misalignment of the keys and slots  124 . 
     To disengage the clutch (disengaged mode), the piston is withdrawn and the keys contact surfaces  128  as described above. Then, when a transition from torque in direction C 1  to torque in direction C 2  occurs (or vice versa) and the wedge plates circumferentially shift, slots  126  align with the keys and element  138  pushes the keys into slots  126 , locked the output component and the wedge plates. The re-alignment of slots  126  and the keys enables OC 1  to contract radially inward so that distance RD 1  is again formed, as described above. Therefore, the wedge plate rotates with the output component, the wedge plate rotates independently of the input, and the clutch plates are unclamped. Thus, no torque is transmitted through assembly  100 . 
     Advantageously, assembly  100  does not increase the size of a state-of-the-art bevel gear differential assembly with a disconnect clutch such as clutch  110 . 
     Clutch  110  synchronizes the energy of stationary components during initial clutch lock up, for example in the synchronizing mode. For example, when clutch  100  is disengaged, torque from the motor is not supplied to the “downstream” components such as the output, shaft  105 , and shaft SDS and these components are at rest. Thus, as described supra, to begin clutch  110  lockup, an axial force is applied by the piston plate forcing the respective friction material into contact with clutch plates  114  on opposite axial sides of the wedge plates. The axial friction force functions in clutch  110 , for example, as for a typical automatic transmission wet clutch until the entire driveline (including down stream components) has reached a synchronized speed, or a point near the synchronized speed such that noise, vibration, harshness (NVH) is satisfactory. Thus, in the synchronizing mode described supra, clamping the clutch plates and wedge plates in clutch  110  transmits torque from the motor such that the downstream components are brought from rest positions to respective rotational speeds synchronized with the input to assembly  100 . 
     In the locked mode described supra, when the driveline has reached the synchronized speed, or the point near the synchronized speed, clutch  110 , via the compressive engagement of the wedge plates with the input component and the output, transmits full driveline torque requirements to the secondary drive shaft. Thus, an abrupt transfer of torque, with an associated and undesirable jolt is avoided by first synchronizing the driveline and then engaging the wedge plates. 
     Although a particular configuration of clutch plates and wedge plates is shown, it should be understood that assembly  100  is not limited to the configuration shown. Other numbers of clutch plates or wedge plates are possible in order to satisfy surface area requirements for torque transfer. 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.