Abstract:
A motor vehicle transfer case includes an input shaft and an electromagnetic brake for retarding rotation of the input shaft. An electromagnetic coil is mounted to the front of the transfer case about the input shaft. An armature plate is secured to the input shaft adjacent the electromagnetic coil. Energization of the coil retards rotation of the input shaft and cancels neutral drag torque from the transmission thereby eliminating relative rotation between the shifting elements of the transfer case and providing smoother shifts.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates generally to motor vehicle transfer cases and more particularly to an electromagnetic brake for the input shaft of a motor vehicle transfer case.  
           [0002]    The majority of four-wheel drive motor vehicles and virtually every sport utility vehicle or pick-up truck equipped with four-wheel drive utilizes a transfer case coupled to the output of the transmission to distribute drive torque to the front and rear axles of the vehicle. These transfer cases incorporate many diverse mechanical devices which may provide, among other features, a reduced speed (low gear) drive mode, interaxle speed differentiation and manual or automatic engagement of an interaxle clutch to intermittently reduce prop shaft speed differences or positively drive front and rear prop shafts.  
           [0003]    Significant developments have been made with regard to systems which sense wheel speed differences and engage interaxle clutches to reduce such speed differences. An automatically engaging system is disclosed, for example, in co-owned U.S. Pat. No. 5,407,024.  
           [0004]    In addition to developments directed to enhancing the flexibility and operation of such transfer cases are developments directed to providing smooth, seamless and imperceptible operation of the components of the transfer case—not only interaxle clutch engagement—but also selection of operating ranges. The present invention is directed to such a feature.  
         SUMMARY OF THE INVENTION  
         [0005]    A motor vehicle transfer case includes an input shaft and an electromagnetic brake for retarding rotation of the input shaft. An electromagnetic coil is mounted to the front of the transfer case about the input shaft. A circular armature plate is secured to the input shaft adjacent the electromagnetic coil. Energization of the coil retards rotation of the input shaft and cancels neutral drag torque from the transmission thereby eliminating relative rotation between the shifting elements of the transfer case and providing smoother shifts. A speed sensor on the input shaft provides data to a microprocessor that utilizes such data to command shifts at or near synchronization.  
           [0006]    Thus it is an object of the present invention to provide a transfer case having an electromagnetic brake.  
           [0007]    It is a further object of the present invention to provide a transfer case having an electromagnetic brake for retarding motion of the input shaft.  
           [0008]    It is a still further object of the present invention to provide an electromagnetic coil disposed about the input shaft of a transfer case for retarding motion thereof.  
           [0009]    It is a still further object of the present invention to provide an electromagnetic brake on the input shaft of a transfer case that cancels neutral drag torque from the vehicle transmission.  
           [0010]    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 reference numbers refer to the same component, element or feature.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a diagrammatic view of a motor vehicle power train having a transfer case incorporating the present invention  
         [0012]    [0012]FIG. 2 is a side, elevational view in partial section of a motor vehicle transfer case incorporating the present invention;  
         [0013]    [0013]FIG. 3 is an enlarged, fragmentary view of a motor vehicle transfer case incorporating the present invention;  
         [0014]    [0014]FIG. 4 is a front, elevational view of an armature of an electromagnetic transfer case brake according to the present invention; and  
         [0015]    [0015]FIG. 5 is a fragmentary view of the housing of an electromagnetic coil according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    Referring now to FIG. 1, a four-wheel vehicle drive train which may utilize 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  such as an internal combustion engine having an output which is coupled to and directly drives a transmission  14 . The output of the transmission  14  directly drives a transfer case assembly  16  which provides motive power to a primary or rear drive driveline  20  comprising a primary or rear prop shaft  22 , a primary or rear differential  24 , a pair of live primary or rear axles  26  and a respective pair of primary or rear tire and wheel assemblies  28 .  
         [0017]    The transfer case assembly  16  also selectively provides motive power to a secondary or front driveline  30  comprising a secondary or front prop shaft  32 , a secondary or front differential  34 , a pair of live secondary or front axles  36  and a respective pair of secondary or front tire and wheel assemblies  38 . The front tire and wheel assemblies  38  may be directly coupled to a respective one of the front axles  36  or, if desired, a pair of manually or remotely activatable locking hubs  42  may be operably disposed between the front axles  36  and a respective one of the tire and wheel assemblies  38  to selectively connect same. Finally, both the primary driveline  20  and the secondary driveline  30  may include suitable and appropriately disposed universal joints  44  which function in conventional fashion to allow static and dynamic offsets and misalignments between the various shafts and components.  
         [0018]    Disposed in sensing relationship with each of the rear tire and wheel assemblies  28  is a wheel speed sensor  48 . Preferably, the wheel speed sensors  48  may be the same sensors utilized with, for example, an antilock brake system (ABS) or other vehicle control or traction enhancing system. Alternatively, a single sensor, disposed to sense rotation of the primary or rear prop shaft  22  may be utilized. Signals from the sensors  48  are provided in lines  52  to a microprocessor  56 . Similarly, disposed in sensing relationship with the front tire and wheel assemblies  38  are respective wheel speed sensors  58  which provide signals to the microprocessor  56  in lines  62 . Once again, the sensors  58  may be a part of or shared with an antilock brake system or other traction enhancing system.  
         [0019]    Typically, an operator selectable switch  64  may be utilized and is generally disposed within reach of the vehicle operator in the passenger compartment (not illustrated). The switch  64  may be adjusted to select various operating modes such as two-wheel high gear, automatic, i.e., on-demand or adaptive operation, four-wheel high gear or four-wheel low gear depending upon the particular vehicle and configuration of the transfer case assembly  16 . One such system which provides torque delivery to the secondary driveline  30  in increments or decrements in response to a sensed wheel speed difference between the primary driveline  20  and the secondary driveline  30  is disclosed in U.S. Pat. No. 5,407,024.  
         [0020]    Referring now to FIG. 2, the transfer case assembly  16  includes a multiple piece, cast metal housing  70  having multiple and diverse openings, apertures, counter bores, ledges, slots and planar surfaces for receiving gaskets, seals and various fixed and rotating components of the transfer case assembly  16  as will be readily appreciated. Among those components is an input shaft  72  having a plurality of female splines or internal gear teeth  74  which receives a complementarily splined output shaft (not illustrated) of the transmission  14  illustrated in FIG. 1. The input shaft  72  also includes a region of male splines or external gear teeth  76 . The input shaft  72  also includes a circumferential channel or groove  78  formed in the male splines or gear teeth  76 . An oil seal  82  provides a fluid-tight seal between the input shaft  72  and the housing  70 . The input shaft  72  is rotatably supported upon an anti-friction bearing such as a ball bearing assembly  84 .  
         [0021]    The transfer case assembly  16  also includes a speed reducing planetary gear assembly  90 . The speed reducing planetary gear assembly  90  is conventional and includes a sun gear  92  which constantly engages and drives a plurality of planet gears  94  rotatably mounted within a carrier  96  and in constant engagement with a ring gear  98 . A clutch or shift collar  100  may be translated axially by a shift fork  102  to provide direct, high speed drive when engaging the input shaft  72  and a reduced speed, low range drive when engaging the carrier  96 . The shift fork  102  is axially, bi-directionally translated through the interaction of helical cams  104  and followers associated with a rotating shift rail  106  which is driven by a bi-directional electric motor drive assembly  108 .  
         [0022]    The transfer case assembly  16  also includes an electromagnetic clutch assembly  110  having an electromagnetic coil assembly  112  which cooperates with a ball ramp operator assembly  114  to compress a friction clutch pack assembly  116 . The friction clutch pack assembly  116  includes a first plurality of clutch disks splined to a primary output shaft  120  and a second plurality of interleaved clutch plates or disks splined to a bell-shaped housing  122  which is drivingly coupled to a first chain drive sprocket  124 . The chain drive sprocket  124  engages a drive chain  126  which extends about and drives a second chain sprocket  128  which is coupled by engaging splines or other positive connecting means to a secondary output shaft  130 . The secondary output shaft  130  is rotatably supported by a pair of anti-friction bearings such as ball bearing assemblies  132  and may include a flange  134  which may be a portion of one of the universal joints  44  illustrated in FIG. 1. An oil seal  136  provides a suitable fluid tight seal between the secondary output shaft  130  and the transfer case housing  70 . A ball bearing assembly  142  rotatably supports the primary output shaft  120  and an oil seal  144  provides a suitable fluid tight seal between the primary output shaft  120  and the transfer case housing  70 . An output flange  146  may be secured to the primary output shaft  120  by a fastener such as a nut  148 . Once again, the flange  146  may form a portion of one of the universal joints  44  illustrated in FIG. 1.  
         [0023]    Referring now to FIGS. 3, 4, and  5 , an electromagnetic brake assembly  150  is illustrated and includes an electromagnetic coil  152  disposed in an annular channel  154  formed in the forward portion of the transfer case housing  70 . The electromagnetic coil  152  is provided with energy through an electrical conductor  156 . The electromagnetic coil  152  is preferably disposed within a metallic coil housing  158  having a plurality of flux concentrating arcuate (banana) slots  162  arranged end to end in a circle as partially illustrated in FIG. 5.  
         [0024]    Disposed adjacent the front of the housing  158  for the electromagnetic coil  152  is a circular armature  166  defining a through circular opening or bore  168  having side walls defining a plurality of internal or female splines or gear teeth  172 . The splines or gear teeth  172  are complementary to those external splines or gear teeth  76  on the input shaft  72 . The circular armature  166  is retained upon the input shaft  72  by a snap ring  174  or similar, suitable retainer which is received within the circumferential groove  78  on the input shaft  72 . The circular armature  166  includes a region of enhanced thickness  176  generally aligned with the electromagnetic coil housing  158 . Included in the region of enhanced thickness  176  and generally aligned with the actuate banana slots  162  in the coil housing  158  are a plurality of radially spaced apart pairs of arcuate banana slots  178  having nominal diameters slightly larger than and slightly smaller than the nominal diameter of the banana slots  162  in the electromagnetic coil housing  158 .  
         [0025]    Positively secured to the input shaft  72  is a counting or tone wheel  180  having a plurality of equally spaced apart teeth  182 . The tone wheel  180  may preferably be secured to the input shaft  72  by an interference fit or other positive means such as spot welding or splines. Disposed in sensing relationship with the tone wheel  180  is a variable reluctance, Hall Effect or optical sensor  184 . The tone wheel  180  and the sensor  184  function as a tachometer to provide data or information in a cable  186  regarding the speed of the input shaft  72 .  
         [0026]    In operation, the electromagnetic brake assembly  150  according to the present invention improves the seamlessness and smoothness of shifts within the transfer case assembly  16  by canceling out neutral drag torque from the transmission  14  and synchronizing the input shaft  72  or the planetary carrier  96  and the primary output shaft  120  across which the clutch or shift collar  100  operates. For example, when a shift is to be undertaken by components of the transfer case assembly  16 , the electromagnetic coil  152  may be energized in a modulating or proportional fashion to retard motion of the input shaft  72  to the extent necessary to bring the components to be shifted substantially or fully into synchronism not only to facilitate the shift but also to render it smooth, and to the extent possible, imperceptible. Such modulation may be achieved by pulse width modulated (PWM) electrical control or control of the electrical signal provided to the electromagnetic coil  152  or any other drive system which provides modulating or proportional control of the intensity or level of the electrical signal provided to the electromagnetic coil  152 .  
         [0027]    As noted, the speed reducing planetary gear assembly  90  provides a reduced speed operating mode (low gear) when the clutch collar  100  is moved to the right (as illustrated in FIG. 2) by the electric motor drive assembly  108  to engage the carrier  96  and provides a direct operating mode (high gear) when the clutch collar  100  is moved to the left (as illustrated in FIG. 2) to engage the sun gear  92 .  
         [0028]    The speed sensor  184  provides information to the microprocessor  56  regarding the speed of the input shaft  72  and the extent of braking or speed reduction provided by the electromagnetic brake assembly  150 . It will be appreciated that speed of the output shaft  120  may be provided by signals from the wheel speed sensors  48  which are averaged or may also be provided by a speed sensor (not illustrated) which senses the rotational speed of the output shaft  120 . The microprocessor  56  utilities such information to determine the optimal time to initiate or sequence shifts or shift commands by the electric motor drive assembly  108  within the transfer case assembly  16  thereby improving, as noted, the smoothness of shifts by the clutch collar  100 .  
         [0029]    It should be appreciated that while the invention has been described in connection with a transfer case assembly  16  having a planetary gear speed reduction assembly  90  which provides a low gear or reduced speed drive in addition to a high speed direct drive, but not an interaxle differential, it should be appreciated that the present invention is adaptable to and will function equally well with a transfer case incorporating an interaxle differential. Moreover, while the invention has been described in connection with a electromagnetic modulating clutch assembly  110  for providing proportional or modulating torque transfer from the primary driveline  20  to the secondary driveline  30 , having a ball ramp assembly  114  operator, it should be appreciated that numerous other modulating clutch designs having bidirectional operators, levers and cam linkages, electromagnetic coils operating directly upon the friction clutch pack and hydraulically or pneumatically operated clutches will function equally well and are within the scope of the invention.  
         [0030]    The foregoing disclosure is the best mode devised by the inventors for practicing this invention. It is apparent, however, that devices incorporating modifications and variations will be obvious to one skilled in the art of transfer case brakes and clutches. Inasmuch as the foregoing disclosure is intended to enable one skilled in the pertinent art to practice the instant 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 scope and spirit of the following claims.