Abstract:
A four-wheel drive center disconnect electric actuator is provided. The actuator includes a one-way motor that actuation of a cam mechanism for causing engagement and disengagement of the center disconnect. The actuator achieves improved reliability and efficiency through a less expensive construction than conventional actuators.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to drive lines for four-wheel drive vehicles, and more particularly, to a drive line disconnect actuator with reduced cost and improved reliability.  
       BACKGROUND AND SUMMARY OF THE INVENTION  
       [0002]     Four-wheel drive vehicles are popular for use off road and for providing improved traction on snowy, icy, and other slippery roads. Four-wheel drive vehicles are often provided with the capability of disconnecting the secondary driving axle in order to provide a two-wheel drive mode when using four-wheel drive mode is not beneficial. However, even in the two-wheel drive mode, many of the drive components are driven by rotation of the wheels which are in engagement with the road. Accordingly, wheel end disconnects and center disconnects have been developed in order to disconnect either the wheels or the axles from the remaining driveline system so that all of the components of the driveline are not rotated by rotation of the non-driven wheels of a four-wheel drive vehicle. It has been found that disconnection of the driveline components from the non-driven wheels can significantly reduce the amount of torque demand for driving the vehicle as well as increasing the fuel efficiency of the vehicle when operated in the two-wheel drive mode. Although suitable disconnect mechanisms have been developed for use with four-wheel drive vehicles, it is still desirable to provide a more reliable and less expensive driveline disconnect system.  
         [0003]     Conventional driveline disconnects utilize actuators that include a threaded lead screw which is engaged by a nut follower for providing connection of the driveline disconnect. When these conventional systems are shifted into the four-wheel drive (connect) position, the force exerted by the axle return spring and/or actuator block shift spring to the actuator nut follower is transmitted back to the actuator gear train. These forces, along with vehicle vibration over long periods of time, can potentially backdrive/creep the nut follower so as to negatively impact the operation of the conventional actuator device. In addition, conventional actuators require the use of a bi-directional motor for moving the driveline disconnect between the connected and disconnected positions. The bi-directional motion in these conventional actuators applies excessive stress on the motor, shafts, gears, and supporting joints, especially during a rapid shift cycle. Hence, these excessive stresses deteriorate the actuator&#39;s life and performance. Additional components and electrical circuitry are required that contribute to added cost and complexity. The travel of a nut follower, in conventional actuators, is also constrained by a mechanical stop. This mechanical stop creates a potential for the actuator to be jammed. Furthermore, in the conventional actuator, the motor needs to develop a high torque level at the beginning of a shift that applies undesirable stresses on the motor and other actuator components.  
         [0004]     The disconnect actuator of the present invention provides the force and stroke required by a coupling member to engage and disengage a coupler for providing connection between a first and second rotatable member. A one-way electric motor is utilized and is operable to drive a gear mechanism and associated cam mechanism. A cam follower is engaged with the cam mechanism and is supported for linear motion relative to the cam mechanism and is engageable with the coupler device for moving the coupler to one of an engaged and disengaged position. The cam mechanism and cam follower are arranged such that rotation of the cam mechanism in  180  degree increments provides connection and subsequent disconnection of the coupler device while utilizing the one-way motor. The driveline disconnect actuator of the present invention utilizes a relay switch (for example, a single pole double-throw) with a stationary encoder and a rotating wiper that provides a relatively simple low cost switching circuit as compared to the costly electronic circuitry typically required for conventional actuators using bi-directional motor control.  
         [0005]     Furthermore, the system of the present invention is immune to the backdrive phenomenon associated with conventional actuators in that the rotation of the worm/cam from 0 to 180 degrees transfers into linear displacement of the cam follower to cause a shift from a two-wheel drive operating mode to a four-wheel drive operating mode. The rotation of the worm gear from 180 degrees to 360 degrees transfers into linear displacement of the cam follower to cause a shift from the four-wheel drive mode to a two-wheel drive mode. Therefore, either at the 0 or the 180 degree position of the cam, the exerted forces are transmitted to the worm gear, supporting pin, and the housing and do not contribute to a backdrive phenomenon as experienced with conventional actuators.  
         [0006]     The use of a one-way motor also improves the disconnect actuator&#39;s performance and reduces the cost. Because the motor and gear train rotate in one direction only, it reduces the stress on the motor, shaft, gears, and supporting joints. The bi-directional motion in conventional actuators applies excessive stress on the motor, shafts, gears, and supporting joints.  
         [0007]     The driveline disconnect actuator of the present invention also eliminates the problem of jamming, since the use of a 180 degree rotating cam mechanism does not utilize a mechanical stop, there is no potential for jamming. Finally, since the actuator linear displacement of the present invention is the sine function of a one gear angular rotation, and since the motor&#39;s peak torque is at 90 degree rotation of the worm gear, the motor starts up with ease since at start-up, minimum torque is required. At the start of any shift, the present invention allows the motor to accelerate to high speed before approaching a peak torque. However, in conventional actuators, the motor needs to develop a higher torque immediately at a beginning of a shift. Furthermore, the worm gear drive of the present invention is less noisy than a conventional planetary gear system.  
         [0008]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0010]      FIG. 1  is a schematic diagram of a vehicle driveline incorporating a center disconnect electric actuator, according to the principles of the present invention;  
         [0011]      FIG. 2  is a perspective view of the disconnect actuator, according to the principles of the present invention;  
         [0012]      FIG. 3  is a perspective view from a different angle of the center disconnect actuator, according to the principles of the present invention;  
         [0013]      FIG. 4  is a bottom perspective view of the disconnect actuator, with the housing removed to better illustrate the components thereof;  
         [0014]      FIG. 5  is a schematic plan view of the printed circuit board of the present invention showing the trace pattern of the encoder/wiper utilized in the controller according to the principles of the present invention; and  
         [0015]      FIG. 6  is a schematic diagram of an electric control circuit according to the principles of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0017]     With reference to  FIG. 1 , an exemplary vehicle driveline  8  for a four-wheel drive vehicle incorporating a center disconnect electric actuator, according to the principles of the present invention, will now be described. The rotative power of the vehicle engine  10  is transmitted to the rear wheels  20  by the transmission  12  rotating the propeller shaft  14  which is coupled to the rear differential  16 . Axle shafts  18  extending from the differential  16  rotate the rear wheels  20 . The rotative power of the engine  10  is transmitted to the front wheels  30  by a transfer case  22  (coupled to the transmission  12 ) that selectively rotates the front propeller shaft  24  coupled to the front differential  26 . Axles  28 L,  28 R extending from the front differential  26  rotate the front wheels  30 L,  30 R, respectively. As is known in the art, the transfer case  22  has a shift mechanism to selectively provide rotative power to the front propeller shaft  24  or not to provide rotative power. Thus, the vehicle may be operated in two-wheel drive or four-wheel drive mode depending on the shift selection of the transfer case  22 .  
         [0018]     The front wheels  30 L,  30 R of the vehicle are steerable and the vehicle is provided with steering knuckles, generally known in the art. The front axles  28 L,  28 R extend from the front differential and are provided with universal joints  32  to accommodate the steering capability. The center disconnect device  40  is provided between one of the axle shafts  28 R and the differential  26 . The center disconnect  40  includes a shift fork  42  and coupler sleeve  44  which is operable to provide an engaged position and a disengaged position relative to the axle shaft  28 R and the differential output shaft  46 . The center disconnect  40  allows the axle shaft  28 R to be disconnected from the differential  26  so that in the two-wheel drive operating mode, the rotation of the wheels  30 L,  30 R in contact with the road and the associated rotation of the axle shaft.  28 L,  28 R can be isolated from other driveline components such as the front propeller shaft  24  and differential ring gear  48 . An actuator device  50  is mounted to the housing of the center disconnect  40  for providing actuation of the center disconnect  40  between the engaged and disengaged positions.  
         [0019]     With reference to  FIGS. 2-4 , the driveline disconnect actuator, according to the principles of the present invention, will now be described. The driveline disconnect actuator  50  includes a housing  52  which is connected to the housing of the disconnect mechanism  40  by threaded interface  53 . A motor  54  is drivingly engaged with a gear mechanism  56  which is drivingly engaged with an eccentric cam mechanism  58  which in turn engages a cam follower mechanism  60 . A cover  61  mounts to the housing  52 .  
         [0020]     The motor  54  includes an output spindle  62  having a drive gear  64  mounted thereon. Drive gear  64  is meshingly engaged with a driven gear  66  which is larger in diameter and includes more teeth than the drive gear  64 . The motor and gear mounting are provided in an angled orientation on the housing  52  in order to conserve space. Driven gear  66  is mounted to, and rotatable with, an intermediate shaft  68  that includes a worm  70  fixedly mounted thereto. Worm  70  meshingly engages a worm gear  72  which is rotatably mounted to the housing  52  about an axis  74 . An eccentric cam member  76  is fixedly mounted to the worm gear  72  and rotatable about axis  74 . Eccentric cam  76  includes an outer surface  78  which engages a cam follower  80 . The cam follower  80  is engaged with a linkage  82  which is slidably received in a forward portion  84  of housing  52 . As best shown in  FIG. 4 , the linkage  82  includes a slot portion  82   a  which slidably receives a spindle on the cam follower  80 . The linkage  82  further includes a spring boss portion  82   b  which receives an end of a spring  83  that engages a plunger  86  at a second end thereof. As seen in  FIG. 4 , the plunger  86  is slidably received in the second end  82   c  of the linkage  82 . The spring  83  allows the linkage  82  to be moved along with the cam follower  80  even when the plunger  86  is unable to move due to the coupler sleeve  44  being misaligned. Once the coupler sleeve  44  is aligned for engagement, the spring  83  applies a biasing force to engage the coupler sleeve  44 .  
         [0021]     Upon rotation of the motor  54 , the drive gear  64  drives driven gear  66  which causes rotation of worm  70  to drive worm gear  72  for causing eccentric cam member  76  to rotate about axis  74 . As eccentric cam  76  rotates, engagement between the cam  76  and cam follower  80  causes linear movement of the cam follower  80  and linkage  82  which, in turn, causes plunger  86  (connected to the linkage  82 ) to extend from the forward housing portion  84  as illustrated in  FIG. 3 . The plunger  86  engages the shift fork  42  of the center disconnect device  40  in order to cause engagement of the center disconnect. The shift fork  42  is normally spring biased to a disengaged position so that when the plunger  86  is retracted, the shift fork  42  and coupler device  44  are automatically moved out of the engaged position.  
         [0022]     It should be understood that the gear mechanism  56  provides a gear reduction between the motor  54  and cam mechanism  58 , and that other alternative gear mechanisms could be utilized for providing the same or different gear reduction function as required by a specific application. Furthermore, the cam mechanism and cam follower, as illustrated, generally disclose a circular cam eccentrically rotatable about an axis  74 , while other shapes of cam mechanisms could also be utilized without departing from the spirit and scope of the present invention.  
         [0023]     With reference to  FIG. 6 , driveline disconnect actuator includes a control circuit  100  for controlling the electric motor  54  in response to a vehicle command signal obtained by user activation of “4×4/4×2” selector switch  102 . The ignition switch  104  provides electric current from battery  106  to the control circuit  100 . When the ignition switch  104  is closed, electric current is supplied to an encoder/wiper module  108 . The encoder/wiper module  108  includes a “4×4 shift” contact  110  and a “4×2 shift” contact  112 . The encoder module  108  also provides current to a “4×4 light” contact  114  for activating a “4×4” indicator light  116  for indicating to the driver when the vehicle is in four wheel drive mode. The “4×4 shift,” “4×2 shift,” and “4×4 indicator” contacts  110 ,  112 ,  114  are all disposed on the encoder/wiper switch mechanism  120  disposed below the worm gear  72 , as best illustrated in  FIG. 4 . The encoder/wiper switch mechanism  120 , including contacts  110 ,  112 ,  114 , selectively engages corresponding electric traces  122  (best shown in  FIG. 5 ) disposed on the printed circuit board  124 . Traces  122   a,    122   b,    122   c  correspond respectively to contacts  110 ,  112 ,  114  of encoder/wiper switch mechanism  120 .  
         [0024]     The control circuit  100  also includes a signal relay switch  126  which communicates between “4×4 shift” contact  110 , “4×2 shift” contact  112  and a power relay coil  128 . A power relay switch  130  is associated with the power relay coil  128  and is in communication with the motor  54 . A signal relay coil  132  is associated with the signal relay switch  126 . The circuit  100  includes a 5 pin connector  134  (mounted to the housing  52 ) for making connection between the control circuit  100  and battery  106 , 4×4 light  116  and control module  102 . The control circuit  100  can also include a resettable fuse  136  in order to prevent overload of the circuit  100 .  
         [0025]     In operation, the signal relay coil  132  is energized by a 4×4 signal from the vehicle control module  102 . The energized signal relay coil  132  causes the normally open contact of signal relay switch  126  to close and supply power to the power relay coil  128  through the encoder-wiper “4×4 shift” contact  110  engaging trace  122   a.  Consequently, the normally open contact of power relay switch  130  is closed, so it can supply power to the motor  54 . The motor  54  stays energized until the encoder/wiper “4×4 shift” contact  110  with trace  122   a  is opened at 180-degree rotation of worm gear  72 . Therefore, upon completion of 180 degree rotation to the 4×4 position, the power relay coil  128  is de-energized and its normally closed power relay switch  130  provides a ground potential to the motor  54 . This applies an effective dynamic braking for the motor  54  that prevents motor coasting.  
         [0026]     At the “4×4” position, the encoder/wiper “4×4 light” contact  114  is closed by contact with trace  122   c  to provide current to the 4×4 indicator light  116 , and the 4×2 shift contact  112  with trace  122   b  is closed to set the cycle ready for the next shift from 4×4 to 4×2.  
         [0027]     For shifting from 4×4 mode to 4×2 mode, the actuator&#39;s signal relay coil  132  is de-energized by the 4×4 signal from the vehicle control module  102 . This causes the normally closed contact of signal relay switch  126  to supply power to the power relay coil  128  through the encoder/wiper 4×2 shift contact  112  with trace  122   b.  Consequently, the normally open contact of power relay switch  130  is closed, so it can supply power to the motor  54 . The motor  54  stays energized until the encoder/wiper “4×2 shift” contact  112  with trace  122   b  is opened at 180-degree rotation to the 4×2 position, the power relay coil  128  is de-energized and its normally closed contact of power relay switch  130  provides a ground potential to the motor  54 . This applies an effective dynamic braking for motor  54  that prevents undesirable motor coasting.  
         [0028]     At the 4×2 position, the encoder/wiper “4×4 indicator” contact  114  with trace  122   b  is opened to provide 4×2 status to the vehicle (i.e., the 4×4 light is no longer illuminated), and the 4×4 shift contact  110  with trace  122   a  is closed to set the cycle ready for the next shift from 4×2 mode to 4×4 mode.  
         [0029]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.