Abstract:
A clutch assembly for disposition in a motor vehicle drive line includes an internal reaction force circuit. The clutch assembly includes a multiple disc friction clutch disposed adjacent an operator assembly which selectively applies force to the friction clutch to selectively transfer torque therethrough. The clutch components are disposed between a flange and a stop on an elongate member which functions as a reaction force member to self-contain the reaction force from the clutch operator. The clutch finds particular application in motor vehicle drive line components such as a rear (secondary) axle wherein it is disposed in pairs to independently control torque supplied to each axle and in applications where it is advantageous to contain or ground the reaction force generated by and associated with the clutch operator compactly within the clutch structure rather than its housing.

Description:
CROSS REFERENCE TO CO-PENDING APPLICATION 
     This application is a divisional application of Ser. No. 09/272,460, filed Mar. 19, 1999 now U.S. Pat. No. 6,098,770 granted Aug. 8, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates generally to multiple friction plate clutches for motor vehicle drive line components and more specifically to friction plate clutches having an internal reaction force circuit for use in pairs with a front or rear axle. 
     Vehicle drive line and control systems having both electric and hydraulic modulating clutches have found broad application in adaptive vehicle drive systems. Such systems generally monitor the speeds of the front and rear drive shaft or compute such speeds by averaging individual readings of the two front and two rear wheels and, upon determining a speed difference between the drive shaft speeds or average speeds of the wheels, energize the modulating clutch according to a predetermined program to drive the speed difference and thus wheel slip toward zero. Such systems may also monitor and adjust modulating clutch activity in response to throttle position, steering angle and other variables. 
     Typically, such modulating clutches are physically disposed in a transfer case, adjacent and driven by the output of the vehicle transmission, and operably disposed between the primary and secondary drive lines. Such systems are disposed in co-owned U.S. Pat. No. 5,407,024 granted Apr. 18, 1995 and U.S. Pat. No. 5,485,894 granted Jan. 23, 1996. 
     An alternate approach to vehicle skid control comprehends association of an individually operable clutch with each axle of a secondary, that is, part-time drive line. Selective, modulating activation of one or both of the clutches directs drive torque to one or both secondary drive wheels to adjust or correct vehicle yaw. An early system utilizing hydraulic clutches is disclosed in U.S. Pat. No. 4,681,180. Here, a control unit having steering angle, vehicle speed and engine torque inputs and adjust torque distribution between only the two rear wheels. 
     U.S. Pat. Nos. 5,195,901 and 5,119,900 both teach a vehicle having two independently operable rear axle clutches in a drive line which provides primary drive torque to the front wheels and selectively and independently provides torque to the rear wheels. 
     In U.S. Pat. No. 5,353,889, a rear axle includes a pair of hydraulically operated independent clutches controlled by associated hydraulic pressure clutches and pumps. 
     In U.S. Pat. No. 5,383,378, a twin clutch axle disposed at the front of a vehicle provide drive torque to the front (secondary) drive wheel in response to steering angle. U.S. Pat. No. 5,540,119 teaches a differential drive assembly for transferring rotational power without the use of conventional differential gearing. The device utilizes pairs of clutches and cam mechanisms which actuate said clutches in response a predetermined relative rotation. 
     While many problems have been addressed and new operational schemes achieved by the devices found in the prior art, it is apparent that certain problems have not been addressed. For example, it should be appreciated that, according to Newton&#39;s third law of motion, the direct or action force generated by a clutch operator to compress an adjacent clutch pack creates an equal and opposite reaction force which is transmitted through whatever structural components of the clutch assembly constitute the reaction force path or circuit. 
     Typically, such reaction force path will be through or contained in an outer housing in devices where the clutch pack is disposed adjacent the clutch operator and both are contained within the housing. Such a configuration can apply significant reaction force, not only to the housing, but also to whatever fasteners are utilized to secure the housing components together. Such a configuration can be disadvantageous, causing either fastener or housing failure or necessitating heavy and therefore costly housing and fastener configurations. Accurately controlled modulation of the clutches may also be compromised due to flexure or distortion of the housing or other components in the reaction force path. Accordingly, the operation of devices containing such clutches may be compromised. The present invention addresses such matters. 
     SUMMARY OF THE INVENTION 
     A clutch assembly for disposition in a motor vehicle drive line includes an internal reaction force circuit. The clutch assembly includes a multiple plate or disc friction clutch disposed adjacent an operator assembly which selectively applies compressive force to the friction clutch to selectively transfer torque therethrough. The clutch components are disposed on an elongate member. The elongate member includes a preferably integrally formed circular plate or flange which functions as a first stop against which one side of the clutch pack abuts. A circular collar which may, in fact, be an anti-friction bearing is retained on the elongate member by a pair of snap rings. The circular collar or anti-friction bearing functions as a second stop against which one side of the operator assembly abuts. The elongate member thus functions as a reaction force member and self-contains the reaction force generated by the clutch operation. The clutch operator may be a ball ramp assembly which is actuated by an electromagnetic coil. Alternatively, the operator may include an electric motor and cam assembly which generates compressive force. Direct acting hydraulic or air driven piston and cylinder operators or pilot and main clutches which are electrically, pneumatically or hydraulically operated are also useful with and within the scope of the present invention. 
     The clutch finds application in motor vehicle drive line components such as a rear (secondary) axles in which it is disposed in pairs to independently control torque supplied to each axle and in other applications where it is advantageous to contain or ground the reaction force generated by and associated with the clutch operator within the clutch structure rather than its housing. 
     It is thus an object of the present invention to provide a multiple friction plate clutch having an internal reaction force path. 
     It is a still further object of the present invention to provide a multiple friction plate clutch and operator which are juxtaposed upon an elongate member which functions as the reaction force return path. 
     It is a still further object of the present invention to provide a multiple plate friction clutch assembly having an internal reaction force path for use in motor vehicle drive lines. 
     It is a still further object of the present invention to provide a multiple plate friction clutch assembly having an internal reaction force circuit for use in pairs in a rear (secondary) axle independently controlling torque delivery to associated wheels. 
     It is a still further object of the present invention to provide a multiple friction plate clutch and operator assembly are juxtaposed and assembled upon a common member which functions as a reaction force containing member. 
     Further objects and advantages of the present invention will become apparent by reference to the following description of the preferred embodiment and appended drawings wherein like numbers refer to the same component, element or feature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic view of a vehicle drive system for a four-wheel vehicle incorporating the twin clutch axle of the present invention; 
     FIG. 2 is a full, sectional view of a twin clutch axle incorporating clutches having internal reaction force circuits according to the present invention and, 
     FIG. 3 is an enlarged, sectional view of a clutch having an internal reaction force circuit according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, an adaptive four-wheel vehicle drive train incorporating the present invention is diagrammatically illustrated and designated by the reference number  10 . The four-wheel vehicle drive train  10  includes a prime mover  12  which is coupled to and directly drives a transaxle  14 . The output of the transaxle  14  drives a beveled or spiral beveled gear set  16  which provides motive power to a primary or front drive line  20  comprising a front or primary propshaft  22 , a front or primary differential  24 , a pair of live front axles  26  and a respective pair of front or primary tire and wheel assemblies  28 . It should be appreciated that the front or primary differential  24  is conventional. 
     The beveled or spiral beveled gear set  16  also provides motive power to a secondary or rear drive line  30  comprising a secondary propshaft  32  having appropriate universal joints  341  a rear or secondary differential assembly  36 , a pair of live secondary or rear axles  38  and a respective pair of secondary or rear tire and wheel assemblies  40 . As utilized herein with regard to the secondary differential assembly  36 , the terms “differential” and “axle” are used interchangeably to identify a device for receiving drive line torque, distributing it to two transversely disposed wheels and accommodating rotational speed differences resulting from, inter alia, vehicle cornering. As such, the terms are intended to include devices such as the present invention which provide these functions but which do not include a conventional epicyclic gear train. 
     The foregoing description relates to a vehicle wherein the primary drive line  20  is disposed at the front of the vehicle and, correspondingly, the secondary drive line  30  is disposed at the rear of the vehicle, such a vehicle commonly being referred to as a front wheel drive vehicle. The designations “primary” and “secondary” utilized herein refer to drive lines providing drive torque at all times and drive lines providing supplemental or intermittent torque, respectively. These designations (primary and secondary) are utilized herein rather than front and rear in as much as the invention herein disclosed and claimed may be readily utilized with vehicles wherein the primary drive line  20  is disposed at the rear of the vehicle and the secondary drive line  30  and components within the secondary differential assembly  36  are disposed at the front of the vehicle. 
     Thus, the illustration in FIG. 1, wherein the primary drive line  20  is disposed at the front of the vehicle should be understood to be illustrative rather than limiting and that the components and the general arrangement of components illustrated is equally suitable and usable with a primary rear wheel drive vehicle. In such a vehicle, the primary differential  24  would replace the secondary differential assembly  36  at the rear of the vehicle and the secondary differential assembly  36  would be moved to the front of the vehicle to replace the primary differential  24 . 
     Associated with the vehicle drive train  10  is a microprocessor  50  which receives signals from a plurality of sensors and provides two control, i.e., actuation signals to the secondary differential assembly  36 . Specifically, a first sensor such as a variable reluctance or Hall effect sensor  52  senses the rotational speed of the left primary (front) tire and wheel assembly  28  and provides an appropriate signal to the microprocessor  50 . Similarly, a second variable reluctance or Hall effect sensor  54  senses the rotational speed of the left primary (front) tire and wheel assembly  28  and provides a signal to the microprocessor  50 . A third variable reluctance or Hall effect sensor  56  senses the rotational speed of the right secondary (rear) tire and wheel assembly  40  and provides a signal to the microprocessor  50 . Finally, a fourth variable reluctance or Hall effect sensor  58  associated with the left secondary (rear) tire and wheel assembly  40  senses its speed and provides a signal to the microprocessor  50 . It should be understood that the speed sensors  52 ,  54 ,  56  and  58  may be independent, i.e., dedicated, sensors or may be those sensors mounted in the vehicle for anti-lock brake systems (ABS) or other speed sensing and control equipment. It is also to be understood that an appropriate and conventional counting or tone wheel is associated with each of the speed sensors  52 ,  54 ,  56  and  58  although they are not illustrated in FIG.  1 . 
     In order to provide optimum skid or yaw control, the microprocessor  50  also requires information regarding the output speed of the transaxle  14 . Accordingly, a variable reluctance or Hall effect sensor  62  which is associated with a tone wheel  64  on the front or primary prop shaft  22  may be utilized. In the alternative, a variable reluctance or Hall effect sensor  66  associated with the secondary differential assembly  36  and positioned adjacent a tone wheel  68  on an input shaft  70  of the secondary differential assembly  36  may also be utilized. The microprocessor  50  includes software which receives and conditions the signals from the sensors  52 ,  54 ,  56  and  58  as well as either the sensor  62  or the sensor  66 , determines corrective action to improve the stability of the vehicle, maintain control of the vehicle and/or correct and compensate for a skid or other anomalous yaw condition of the vehicle and provides two independent output signals to the secondary differential assembly  36 . 
     Referring now to FIG. 2, the input shaft  70  of the secondary differential assembly  36  may include a flange  72  or similar component which is secured to the input shaft  70  by a nut  74  or similar threaded fastener. The flange  72  forms a portion of a connection, such as a universal joint  34  (illustrated in FIG.  1 ), to the secondary propshaft  32 . The input shaft  70  is received within a center housing  76  and is surrounded by a suitable oil seal  78  which provides a fluid impervious seal between the housing  76  and an associated portion of the flange  72  or the input shaft  70 . The input shaft  70  is preferably rotatably supported by a pair of anti-friction bearings such as the tapered roller bearing assemblies  80 . The input shaft  70  terminates in a hypoid or beveled gear  82  having gear teeth  84  which mate with complementarily configured gear teeth  86  on a ring gear  88  secured to a flange  92  on a centrally disposed tubular drive member  94  by suitable fasteners  96 . The tubular drive member  94  is rotatably supported at each end by an antifriction bearing such as the ball bearing assemblies  102 . The tubular drive member  94  defines a hollow interior  104  into which a pair of scavengers or scoops  106  collect and deliver cooling and lubricating fluid from the interior of the center housing  76 . The tubular drive member  94  also includes sets of external or male splines or gear teeth  108  adjacent each end. 
     Turning now to FIGS. 2 and 3, the secondary differential assembly  36  includes a pair of left and right outer bell housings  114 A and  114 B which mate with the center housing  76  along left and right parting lines  116 A and  116 B and are attached to the center housing  74  by threaded fasteners  118 . The housings  114 A and  114 B are mirror-image, i.e., left and right, components which each receive and house a respective one of a pair of modulating clutch assemblies  120 A and  120 B. But for the opposed, mirror-image arrangement of the two modulating clutch assemblies  120 A and  120 B, the components of the two clutch assemblies  120 A and  120 B described below are identical and thus only the modulating clutch assembly  120 B disposed on the right of FIG.  2  and in FIG. 3 will be fully described, it being understood that the left modulating clutch assembly  120 A is in all significant respects identical to the right modulating clutch assembly  120 B. 
     Each of the modulating clutch assemblies  120 A and  120 B is driven by the male or external splines or gear teeth  108  of the tubular drive member  94  which engage complementarily configured female or internal splines or gear teeth  122  on a bell housing  124 . The bell housing includes a plurality of female or internal splines  126  on its circumferential inner surface  128 . The internal splines  126  are engaged by and rotationally drive complementarily configured male or external splines  132  disposed on a first plurality of larger diameter clutch plates or discs  134 . The first plurality of clutch plates or discs  134  includes suitable friction material and surfaces and are interleaved with a second plurality of smaller diameter clutch plates or discs  136 . 
     The second plurality of smaller clutch discs  136  also includes suitable friction material and surfaces and has female splines  138  which engage and rotationally drive complementarily configured male or external splines  140  disposed upon an annulus or collar  142 . The collar  142 , in turn, includes female or internal splines or gear teeth  146  which mate with complementarily configured male or external splines or gear teeth  148  disposed on the output shaft  150 B. The output shaft  150 B includes a preferably integrally formed radially extending flange  154  having a flat annular pressure surface  156  against which the friction material of the interleaved pluralities of clutch discs  134  and  136  abuts and aligns. Alternatively, of course, the flange  154  may be a separate component which is secured to the output shaft  150 B by any suitable means such as welding or axially restrained thereon by a suitable shoulder or other positive stop. 
     On the opposite side of the radial flange  154  is a friction reducing flat washer  158  which axially spaces it from the tubular drive member  94  and the bell housing  124 . Adjacent the flat washer  158  and disposed between a counterbore in the drive tube  94  and a reduced diameter portion  162  of the output shaft  150 B is a friction reducing bushing or journal bearing  164 . 
     The output shaft  150 B also defines an axial bore  166  which communicates with at least one radial passageway  168  through which cooling and lubricating fluid collected by the scavengers or scoops  106  (illustrated in FIG. 2) may flow to the disc pack clutch assembly  120 B. 
     The disc pack clutch assembly  120 B also includes a circular apply plate  172  which includes female or internal splines or gear teeth  174  which mate with the male splines  140  on the collar  142 . The apply plate  172  thus rotates with the second plurality of smaller diameter clutch plates  136  and may move axially relative thereto. The apply plate  172  is preferably fabricated of a non-magnetic metal such as stainless steel so that it does not participate in nor interfere with the magnetic circuit (flux path) of the modulating clutch assembly  120 B. The apply plate  172  includes a shoulder  176  which positions and receives a flat washer  178 . The flat washer  178  reduces friction between the apply plate  172  and a circular armature  182 . The circular armature  182  includes a plurality of discontinuous, arcuate, banana slots  184  and a plurality of male splines  186  about its periphery which are complementary to and engage the plurality of female splines  126  on the interior of the bell housing  124 . Thus, the circular armature  182  rotates with the bell housing  124  and the first plurality of clutch plates  134 . 
     The circular armature  182  is disposed adjacent a U-shaped circular rotor  192 . The rotor  192 , which is preferably fabricated of soft iron, includes a pair of spaced apart pluralities of discontinuous, arcuate, banana slots  194  which cooperate with the banana slots  184  in the circular armature  182  to create a sinuous magnetic flux path which improves operation of the disc pack clutch assembly  120 B and increases its torque throughput. 
     The rotor  192  generally surrounds a stationary housing  198  which contains an electromagnetic coil  200 . The stationary housing  198  and the electromagnetic coil  200  are secured to the outer housing  114 B by a plurality of threaded studs and fasteners  202 , two of which are illustrated in FIG.  2 . Electrical energy is selectively provided to the electromagnetic coil  200  through a conductor  204 B, also illustrated in FIG.  2 . Coupled to the rotor  192  by any suitable means such as weldments, interengaging splines or an interference fit and disposed concentrically about the output shaft  150 B is a first circular member  210 . A low friction collar  212  made of, for example, nylon is interposed the first circular member  210  and the output shaft  150 B and thus the first circular member  202  and the rotor  192  are free to rotate about both the output shaft  150 B and the housing  198  of the electromagnetic coil  200 . The low friction collar  212  reduces friction between the first circular member  210  and the output shaft  150 B when the disc pack clutch assembly  120 B is deactivated, thereby reduced drag wear and heat generation. 
     The first circular member  210  includes a plurality of curved ramps or recesses  214  arranged in a circular pattern about the axis of the output shaft  150 B. The ramps or recesses  214  represent oblique sections of a helical torus. Disposed within each of the recesses  214  is one of a like plurality of load transferring balls  216  or similar load transferring members which rolls along the ramps defined by the oblique surfaces of the recesses  214 . A second circular member  218  is disposed in opposed relationship with the first circular member  210  and includes a like plurality of complementarily sized and arranged ramped recesses  222 . The load transferring balls  216  are thus received and trapped within the pairs of opposing recesses  214  and  222 , the ends of the recesses being curved and much steeper in slope than the interior regions of the recesses  214  and  222  such that the load transferring balls  216  are retained therein. A plurality of wave washers or Belleville springs  224  are disposed between the second circular member  218  and the collar  142  and bias the second circular member  218  toward the first circular member  210 . 
     It will be appreciated that the plurality of ramped recesses  214  and  222  and the load transferring balls  216  may be replaced with other analogous mechanical elements which cause axial displacement of the circular members  210  and  218  in response to relative rotation therebetween. For example, tapered rollers disposed in complementarily configured conical helices may be utilized. 
     An important design consideration of the recesses  214  and  222 , the load transferring balls  216  and the Belleville springs  224  is that the geometry of their design and the overall clearances in the clutch assemblies  120 A and  120 B ensure that they are not self-engaging. The modulated clutch assemblies  120 A and  120 B must not self-engage but rather must be capable of modulated clamping of the clutch plates  134  and  136  and torque transfer in direct, proportional response to the electrical input to the electromagnetic coil  200 . Additional details of this mechanism may be found in U.S. Pat. No. 5,492,194 which is hereby incorporated by reference. 
     The second circular member  218  includes a plurality of female splines or gear teeth  228  which are complementary to and engage the male splines or gear teeth  148  on the output shaft  150 B. A flat washer  230  transfers axial force from the second circular member  218  to the apply plate  172 . The axial position of the first circular member  210  is established by a thrust bearing assembly  232 . Adjacent the thrust bearing assembly  232  is an anti-friction bearing such as a ball bearing assembly  234  which rotatably supports and axially locates the output shaft  150 B within the housing  114 B. The ball bearing assembly  234  is axially located and restrained by a pair of snap rings  236  which are received within complementarily configured circumferential slots or grooves  238 . The output shaft  150 B also includes a set of external or male splines or gear teeth  240  which are adapted and intended to mate with complementarily configured female splines, gear teeth or an output flange, shaft or axle (all not illustrated). An oil seal  242  provides an appropriate fluid tight seal between the housing  114 B and the output shaft  150 B. 
     A brief description of the operation of the disc pack clutch assembly  120 B of the rear differential assembly  36  highlights the improvements and features thereof. When the electromagnetic coil  200  is not energized, the output shaft  150 B freewheels relative to the tubular input member  94  which functions as the input drive member. As current flow to the electromagnetic coil  200  commences and increases, drag is created which attempts to slow rotation of the rotor  192 , causing relative rotation between the first and second circular members  210  and  218 . As this occurs, the load transferring balls  216  ride up the recesses  214  and  222 , separate the first and second circular members  210  and  218  and drive the second circular member  218  toward the apply plate  172 . Translation of the apply plate  172  compresses the pluralities of clutch discs  134  and  136  and transfers drive torque from the tubular drive member  94  and the bell housing  124  to the collar  142  and the right output shaft  150 B. Activation of the left modulating clutch assembly  120 A results in corresponding torque transfer to the left output shaft  150 A (illustrated in FIG.  2 ). 
     It should be noted that the compressive force generated by the first and second circular members  210  and  218  passes through the washer  230 , through the apply plate  172 , the pluralities of clutch plates  134  and  136 , through the radial flange  154  and into the output shaft  150 B. Reaction force is thus carried axially along the length of the output shaft  150 B, through the snap rings  236 , the ball bearing assembly  234  and the thrust bearing  232  and thence back to the first circular member  210 . The radial flange  154  on the output shaft  150 B and the snap rings  236  thus act as fixed stops which confine the components of the disc pack clutch assembly  120 B and direct the reaction force from its operation into and along the output shaft  150 B. It will thus be appreciated that the reaction force generated by operation of the disc pack clutch assembly  120 B is effectively fully contained within the output shaft  150 B and does not pass through the outer housing  114 B, the center housing  76  or other components. Such direct containment of the clutch operator reaction force reduces forces and flexure of the housings  76 ,  114 A and  114 B and improves the modulating control and service life of the rear differential assembly  36  and its components. 
     It should also be noted that while the above-described preferred embodiment of a clutch having an internal reaction force circuit utilizes an electromagnetic operator, a piston and cylinder arrangement utilizing either hydraulic fluid or a gas under pressure such as air are all readily adaptable to actuate the clutch pack and realize the features and benefits of the internal reaction force path or circuit of the present invention. Thus, such various clutch actuator configurations are deemed to be well within the scope of the present invention. 
     Finally, it should be understood that while the output shaft  150 B has been described above as the reaction force containing member, the direction of torque flow through the multiple disc pack clutch assembly  120 B may readily be reversed or the clutch assembly  120 B may be reconfigured such that the shaft  150 B is the input shaft. In either case, the shaft  150 B functions as the reaction force containing member. 
     The foregoing disclosure is the best mode devised by the inventor for practicing this invention. It is apparent, however, that apparatus incorporating modifications and variations will be obvious to one skilled in the art of drive line clutch components. In as much as the foregoing disclosure is intended to enable one skilled in the pertinent art to practice the present invention, it should not be construed to be limited thereby but should be construed to include such aforementioned obvious variations and be limited only by the spirit and scope of the following claims.