Abstract:
A shift assembly for a two-speed transfer case utilizes a single actuator to drive both the gear or speed range selection mechanism and a modulating friction clutch pack which selectively transfers drive torque from a primary transfer case output to a secondary transfer case output. The shift assembly includes an actuator which rotates a shift rail and cam having an intermediate helical track and a dwell region at each end. A lost motion assembly operating in conjunction with the helical cam selectively engages and disengages the friction clutch pack when the cam follower is in one of the two dwell regions. Thus, the shift assembly provides sequential operation from full clutch engagement in a first speed range through clutch disengagement in the first speed range, de-selection of the first speed range and selection of neutral, de-selection of neutral and selection of the second speed range and thence increasing engagement, up to full engagement, of the friction clutch pack in the second speed range.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates generally to shift assemblies for transfer cases and more specifically to a single actuator shift assembly for a transfer case which sequences selection and operation of both a two-speed gear reduction assembly and modulating clutch.  
           [0002]    In the majority of four-wheel drive vehicles, particularly pickup trucks and sport utility vehicles (SUV&#39;s), a transfer case is utilized to provide drive torque to a secondary vehicle driveline in response to operator inputs and automatic, adaptive drive systems. Such transfer cases may include (1) a center differential which allows speed differences between the primary and secondary drivelines, (2) a clutch which may either inhibit differentiation of a center differential, if the transfer case is so equipped, as noted above, or provide drive torque from the primary driveline to the secondary driveline if the transfer case lacks a center differential and (3) a speed reduction assembly, typically a planetary gear mechanism, to provide a low or reduced speed operating mode when it is engaged in addition to a high speed or direct drive operating mode.  
           [0003]    Both the modulating clutch and the speed reduction assembly require an operator or actuator of some type to select and engage them in accordance with the operator&#39;s desire or the command of an automatic, adaptive drive system as noted above.  
           [0004]    Various speed reduction assembly actuators are disclosed in U.S. Pat. No. 5,878,624 and 6,173,624 co-owned by the assignee. U.S. Pat. No. 5,407,024 discloses both a range selection actuator and a ball ramp friction pack clutch operator.  
           [0005]    Other transfer cases such as those disclosed in U.S. Pat. Nos. 5,330,030 and 5,363,938 have utilized a single actuator to effect both speed range selection and clutch engagement. In the latter two patents, an electric actuator provides both speed range selection and activation of a friction clutch pack. However, operating force for the clutch pack is generated through a cam and second class lever arrangement which requires that the electric actuator generate significant operated energy. Generation of such energy suggests that both the size of the actuator and its power consumption will be significant. This, in turn, suggests that improvements in single actuator transfer cases are both desirable and possible.  
         SUMMARY OF THE INVENTION  
         [0006]    A shift assembly for a two-speed transfer case utilizes a single actuator to drive both the gear or speed range selection mechanism and a modulating friction clutch pack which selectively transfers drive torque from a primary transfer case output to a secondary transfer case output. The shift assembly includes an actuator which rotates a shift rail and cam having an intermediate helical track and a dwell region at each end. A lost motion assembly operating in conjunction with the helical cam selectively engages and disengages the friction clutch pack when the cam follower is in one of the two dwell regions. Thus, the shift assembly provides sequential operation from full clutch engagement in a first speed range through clutch disengagement in the first speed range, de-selection of the first speed range and selection of neutral, de-selection of neutral and selection of the second speed range and thence increasing engagement, up to full engagement, of the friction clutch pack in the second speed range. If desired, the transfer case may include an interaxle differential.  
           [0007]    Thus, it is an object of the present invention to provide a transfer case having a two-speed gear reduction assembly and a modulating clutch which are both controlled by a single actuator assembly.  
           [0008]    It is a further object of the present invention to provide a two-speed transfer case having a modulating clutch with a single actuator shift mechanism which sequences clutch engagement, clutch disengagement and selection of a desired speed range and neutral.  
           [0009]    It is a still further object of the present invention to provide a transfer case having a two-speed gear reduction assembly, interaxle differential and modulating clutch having a single actuator for sequentially controlling selection of a speed range and engagement of the modulating clutch.  
           [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 drive assembly of a four wheel drive motor vehicle incorporating the present invention;  
         [0012]    [0012]FIG. 2 is a side elevational view in full section of a transfer case having a lost motion shift actuator according to the present invention;  
         [0013]    [0013]FIG. 3 is an enlarged, fragmentary view in full section of a transfer case incorporating a lost motion shift assembly according to the present invention;  
         [0014]    [0014]FIG. 4 is a perspective view of a shift fork and cam assembly of a lost motion shift assembly according to the present invention;  
         [0015]    [0015]FIG. 5 is a graph illustrating clutch engagement and shaft rotation in a lost motion shift assembly according to the present invention;  
         [0016]    [0016]FIG. 6 is an enlarged, sectional view of a portion of a lost motion shift assembly according to the present invention taken along line  6 - 6  of FIG. 2; and  
         [0017]    [0017]FIG. 7 is an enlarged, fragmentary, full sectional view of a lost motion shift assembly according to the present invention taken along line  7 - 7  of FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    Referring now to FIG. 1, a four-wheel vehicle drive train utilizing the present invention is diagramatically 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 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 .  
         [0019]    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 each of the front axles  36  and a respective one of the tire and wheel assemblies  38  to selectively couple 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.  
         [0020]    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 control system.  
         [0021]    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.  
         [0022]    Referring now to FIGS. 2 and 3, the transfer case assembly  16  includes a multiple piece metal housing  70  having various cast and machined surfaces, flats, openings, flanges and bores for receiving various internal components of the transfer case assembly  16  as will be readily appreciated. The transfer case assembly  16  includes an input shaft  72  having a plurality of female splines or gear teeth  74  disposed upon an inner surface and engageable by complementarily configured male splines or gear teeth disposed upon an output shaft (not illustrated) of the transmission  14  (illustrated in FIG. 1). The input shaft  72  is rotatably supported by an anti-friction bearing such as a ball bearing assembly  76 . An oil seal  78  provides a suitable fluid tight seal between the input shaft  72  and the housing  70 .  
         [0023]    The transfer case assembly  16  also includes a planetary gear speed reduction assembly  80  having a stationary ring gear  82  which is retained within the transfer case housing  70  by a snap ring  84  or other suitable retaining device. A planetary gear carrier  86  is generally aligned with the ring gear  84  and includes and supports a plurality of fixed stub shafts  88  which freely rotatably support and retain a like plurality of pinion gears  92 . Each of the pinion gears  92  engage the teeth of a sun gear  94  which may be integrally formed with the input shaft  72  or may be a separate component coupled thereto by, for example, splines. Secured to the carrier  86  of the planetary gear assembly  80  is a circular disc  96  having peripheral splines or gear teeth  98 . The planetary gear speed reduction assembly  80  thus provides a reduced speed output to the carrier  86  and the circular disc  96 .  
         [0024]    Adjacent the planetary gear speed reduction assembly  80  is a synchronizer assembly  100 . The synchronizer assembly  100  receives the reduced speed output of the planetary gear assembly  80  and the disc  96  as well as a direct input from a drive collar  102  driven by the input shaft  72  through a set of inter-engaging splines  104 . The synchronizer assembly  100  is conventional and includes obliquely oriented friction or clutch faces  106  disposed between a center drive member  108 . An annular clutch collar  110  includes a plurality of female or internal splines or gear teeth  112  which are in constant engagement with a plurality of complementarily configured male splines or gear teeth  114  on the center drive member  108 . When the annular clutch collar  110  resides in the position illustrated in FIG. 3, the splines or gear teeth  112  engage complementarily configured male splines or gear teeth  116  on the drive collar  102  coupled to the input shaft  72 . As the annular clutch collar  110  is moved to an extreme left position, the female splines or gear teeth  114  engage the male splines or gear teeth  98  on the disc  96 . In this position, a low gear or reduced speed drive is achieved. The annular clutch collar  110  may be moved to a neutral position intermediate the left and right positions just described wherein the other components of the transfer case assembly  16  are not driven. The annular clutch collar  110  also includes female or internal splines or gear teeth  118  which engage components of an interaxle differential assembly  120 .  
         [0025]    The interaxle differential assembly  120  includes a generally conventional cylindrical housing  122  having male splines or gear teeth  124  disposed about its periphery. The annular shift collar  110  is thus in constant engagement with the housing  122  of the interaxle differential assembly  120  by virtue of the engagement of the splines or gear teeth  118  and  124 . The interaxle differential assembly  120  includes a plurality of beveled drive gears  126  which are formed integrally with or disposed upon stub shafts  128  which are freely rotatably received within suitable radially extending bores  132  formed in the housing  122  of the differential assembly  120 .  
         [0026]    Engaging the plurality of drive gears  126  on the left side as illustrated in FIG. 3 is a first beveled output gear  138  which is splined to and therefore rotates with a primary output shaft  140 . Symmetrically disposed with the first beveled output gear  138  on the right side of the beveled drive gears  126  is a second beveled output gear  142  which is formed upon a portion of a chain drive sprocket  144  having chain drive teeth  146 . The chain drive sprocket  144  is freely rotatably disposed upon the primary output shaft  140 .  
         [0027]    The chain drive sprocket  144  is also coupled to and rotates with the output of a modulating friction clutch pack assembly  150 . The modulating friction clutch pack assembly  150  includes an input hub or collar  152  which is splined to the primary output shaft  140  and rotates therewith. A first plurality of clutch plates  154 A are splined to and driven by the input hub or collar  152  and are interleaved with a second plurality of friction clutch plates  154 B which are splined and interconnected to a bell housing  156 . The friction clutch plates  154 A and  154 B include suitable clutch facing material (not illustrated) on their adjacent faces. The bell housing  156  is rotationally coupled to the chain drive sprocket  144  through inter-engaging splines  158  and an intermediate collar  162 . Thus, the bell housing  156  rotates with the chain drive sprocket  144  and actuation of the friction clutch pack  150  drives the speeds of the primary output shaft  140  and the chain drive sprocket  144  into synchronism and inhibits operation of the interaxle differential assembly  120 .  
         [0028]    The modulating friction clutch pack assembly  150  also includes an apply plate  164  disposed adjacent the interleaved clutch plates  154 A and  154 B. Adjacent the apply plate  164  is a ball ramp actuator assembly  170 . The ball ramp actuator assembly  170  includes a first, fixed circular member  172  which defines a plurality of aligned, arcuate, tapering recesses which receive a like plurality of load transferring balls  174 . Disposed in opposed relationship with the first circular member  172  is a second, rotatable circular member  176  having a like plurality of arcuate, tapering recesses  178  which are mirror images of those in the first circular member  172 . Between the apply plate  164  and the second circular member  176  is a thrust bearing  182  which transmits axial force between the second circular member  176  and the apply plate  164  but permits the apply plate  164  to freely rotate. Rotation of the second circular member  176  from a center position causes the load transferring balls  174  to move to shallower regions of the recesses  178 , thereby driving the second circular member  176  to the left as illustrated in FIG. 3. It will be appreciated that analogous mechanical devices such as tapered roller bearings in complementary recesses or devices such as opposed cams which provide axial motion upon relative rotation may replace the balls  176  and recesses  178 . A plurality of springs  184  such as Belleville springs or wave washers, is disposed between the clutch collar or hub  152  and the second circular member  176  and provides a biasing or restoring force which drives the second circular member  176  to the right as illustrated in FIG. 3.  
         [0029]    The right end of the primary output shaft  140  is preferably supported by an anti-friction bearing such as a ball bearing assembly  186  and an oil seal  188  provides a suitable seal between an output flange  192  secured to the primary output shaft  140  by a threaded nut  194  and the housing  70  of the transfer case assembly  16 .  
         [0030]    Turning now to FIGS. 3, 4 and  7 , the lost motion shift assembly  200  will now be described. The lost motion shift assembly  200  includes a bi-directional electric drive motor  202  which may include a direct drive or drive through a worm gear or similar speed revolving mechanism to a bi-directionally rotating shift rail  204  to the microprocessor  56 . The shift assembly  200  includes a position sensing assembly  206  which may be a pulse counting device, may include contact tracks, Hall effect sensors or other sensing devices capable of providing real time information regarding the angular position of the shift rail  204 . The end of the bi-directionally rotating shift rail  204  opposite the drive motor  202  is received within a suitable counterbore  208  formed within the housing  70  of the transfer case assembly  16 .  
         [0031]    A projection or freely rotatable cam roller or follower  212  is mounted upon a radially oriented pin  214  which is securely received within the shift rail  204 . A spur gear  216  is freely rotatably disposed upon the shift rail adjacent the cam follower  212  and defines a pair of axially extending steps or shoulders  218 A and  218 B which are approximately 200° apart. The spur gear  216  is held in position on the shift rail  204  by a snap ring  220  which is received within a suitable channel formed in the shift rail  204 . About the periphery of the spur gear  216  are gear teeth  222  which are in constant mesh with gear teeth  224  on a sector plate  226  which extends radially from the second circular member  176 . It will be appreciated that the spur gear  216 , the sector plate  226  and the meshing teeth  224  and  226  may be replaced with analogous mechanical devices such as, for example, a chain and pair of sprockets (not illustrated).  
         [0032]    Referring now to FIGS. 3 and 4, also disposed upon the shift rail  204  is a shift fork assembly  230 . The shift fork assembly  230  defines an axial bore  232  which freely rotatably receives the shift rail  204 . The shift fork assembly  230  is disposed upon the shift rail  204  between a pair of cam followers- 234 A and  234 B which engage similarly configured complex cams  236 A and  236 B, respectively. Both of the complex cams  236 A and  236 B include flat or dwell regions adjacent both ends of travel and intermediate, helical regions as diagrammatically illustrated in FIG. 5. Thus, upon rotation of the shift rail  204  no axial motion of the shift fork assembly  230  is imparted from one limit of travel while the cam followers  234 A and  234 B traverse the dwell regions of the respective cams  236 A and  236 B. During the intermediate, helical regions of the complex cams  236 A and  236 B, the shift fork assembly  230  is axially translated. Then, in the second or remaining dwell portion of the complex cams  236 A and  236 B, no further axial translation is imparted to the shift fork assembly  230  as the shift rail  204  rotates. The shift fork assembly  230  includes a yoke or fork  238  which engages a peripheral channel or groove  239  in the annular clutch collar  110 .  
         [0033]    Referring again to FIG. 2, the chain drive sprocket  144  and specifically the teeth  146  engage and drive a continuous chain  240  which engages and drives gear teeth  242  on a driven chain sprocket  244 . The driven chain sprocket  244  is secured by inter-engaging splines, an interference fit or other positive means of connection to a secondary output shaft  246 . The secondary output shaft  246  includes a flange  248  or other component which may be a portion of the universal joint  44  which is coupled to the prop shaft  32  as illustrated in FIG. 1. An anti-friction assembly such as a ball bearing assembly  250  supports one end of the secondary output shaft  246 . An oil seal  252  disposed between the housing  70  and the secondary output shaft  246  provides a suitable fluid tight seal therebetween. A gerotor pump  254  is driven by the secondary output shaft  246  and provides a flow of cooling and lubricating fluid to the various components of the transfer case  16  disposed along the primary output shaft  140 .  
         [0034]    With reference now to all of the drawing figures and particularly FIG. 5, operation of the lost motion shift assembly  200  according to the present invention and the transfer case assembly  16  will be described. As a starting point and purely for the purpose of reference, it will be assumed that the assembly  200  commences operation in the position illustrated in FIGS. 6 and 7. The position illustrated in FIGS. 6 and 7 represents the neutral position of the annular shift collar  110 , the shift rail  204  and the shift fork assembly  230 . As the shift rail  204  rotates from the neutral position in a counterclockwise direction as illustrated in FIGS. 6 and 7, the cam followers  234 A and  234 B are in the helical region of the cams  236 A and  236 B, respectively, and translate the shift fork assembly  230  and the annular shift collar  110  to the right, to the position illustrated in FIG. 2 and engage or provide high or direct drive from the input shaft  72  to the interaxle differential assembly  120 . Engagement of high or direct drive is facilitated by the synchronizer assembly  100 . As the shift rail  204  continues to rotate, no further motion of the shift fork assembly  230  occurs as the cam followers  234 A and  234 B are now operating in the dwell regions of the cams  236 A and  236 B, as illustrated in FIG. 5.  
         [0035]    However, at the time the cam followers  234 A and  234 B move from the helical regions of the cams  236 A and  236 B to the dwell regions, the cam roller or follower  212  contacts or engages the step or shoulder  218 A of the gear  216  and begins to rotate the gear  216  which is coupled to the second circular member  176  through the sector plate  226  and gear teeth  224  and  222 . As the second circular member  176  rotates, it begins to axially translate as the load transferring balls  174  move to shallower regions of the recesses  178 . Axial motion of the second circular member  176  toward the friction clutch pack assembly  150  commences frictional engagement of the plates  154 A and  154 B of the friction clutch pack assembly  150  and begins to drive the speeds of the primary output shaft  140  and the secondary output shaft  246  into synchronism. Also, as noted above, such frictional coupling increasingly inhibits differentiation by the interaxle differential assembly  120 . At the limit of counterclockwise travel of the shift rail  204 , the friction clutch pack assembly  150  will be fully engaged and transmit torque and inhibit differentiation by the interaxle differential assembly  120  at its maximum level. Rotation of the shift rail  204  in the clockwise direction first of all relaxes the frictional coupling achieved through the friction clutch pack assembly  150  which is further assisted by action of the plurality of springs  184 .  
         [0036]    As the shift rail  204  continues to rotate clockwise, the cam followers  234 A and  234 B enter the helical regions of the cams  236 A and  236 B and begin to translate the shift fork assembly  230  and the annular clutch collar  110  to the left. The annular collar  110  moves to a neutral position where the electric motor  202 , the shift rail  204 , the shift fork assembly  230  and the annular clutch collar  110  may be stopped. The transfer case assembly  16  is then in its neutral position.  
         [0037]    If rotation of the shift rail  204  continues, the shift fork  230  translates the annular shift collar  110  to its leftmost position where it couples the circular disc  96 , which provides the reduced speed output of the planetary gear assembly  80 , to the interaxle differential assembly  120 . Such a shift will of course, again be facilitated by action of the synchronizer assembly  100 . As the shift rail  204  continues to rotate, cam follower  234 A and  234 B will complete traverse of the helical regions of the cams  236 A and  236 B and the cam followers  234 A and  234 B will enter the dwell regions as illustrated in FIG. 5.  
         [0038]    No further motion of the annular clutch collar  110  will occur notwithstanding continued rotation of the shift fork  204 . Such continued rotation of the shift fork  204  will cause the cam follower  212  to engage the step or ledge  218 B on the gear  216  and begin to rotate the gear  216 , the sector plate  226  and the second circular member  176  to again commence compression of the friction clutch pack assembly  150  and torque transfer therethrough. Continued rotation of the shift rail  204  will compress the friction clutch pack assembly  150 , eventually providing maximum torque transfer therethrough, synchronization of the primary output shaft  140  with the secondary output shaft  246  and inhibition of differentiation by the interaxle differential  120 . Reactivation of the friction clutch pack assembly  150  may be achieved by counterclockwise rotation of the shift rail  204 . If such rotation is continued, the annular shift collar  110  will soon return to its neutral position.  
         [0039]    While the foregoing description illustrates operation of the lost motion shift assembly  200  in a continuous manner, it should be appreciated that the electric drive motor  202  may be operated in short or long intervals or increments and that the sequence of operation illustrated in FIG. 5 and described above may occur in small or large increments in either direction in response to operator command or sensed vehicle operating conditions provided, for example, by the wheel speed sensors  48  and  58  or other signals to the microprocessor  56  from, for example, the operator selectable switch  64 . For example, selection of the low gear will typically be under the control of the driver whereas the extent of operation of the friction clutch pack assembly  150  may occur automatically through action of the microprocessor  56  based upon inputs provided thereto. It should be understood that the friction clutch pack assembly  150  is a modulating assembly, as noted above, and thus that the electric motor  202  may be selectively activated to move the shift rail  204 , the gear  216 , the sector plate  226  and the second circular member  176  to a desired position to transfer a desired level of torque through the friction clutch pack assembly  150 .  
         [0040]    The foregoing disclosure is the best mode devised by the inventor for practicing this invention. It is apparent, however, that products and methods incorporating modifications and variations will be obvious to one skilled in the art of shift assemblies and operating methods therefor. Inasmuch as the foregoing disclosure presents the best mode contemplated by the inventor for carrying out the invention and is intended to enable any person skilled in the pertinent art to practice this 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.