On-demand transfer case with controllable bi-directional overrunning clutch assembly

#The present invention relates generally to bi-directional overrunning clutch assemblies and, more particularly, to an actively-controlled, multi-mode, bi-directional overrunning clutch assembly used in a four-wheel drive transfer case.

#Four-wheel drive vehicles are in great demand due to the enhanced on and off road traction control they provide. In many four-wheel drive vehicles, a transfer case is installed in the drivetrain and is normally operable to deliver drive torque to the primary driveline for establishing a two-wheel drive mode. The transfer case is further equipped with a clutch assembly that can be selectively or automatically actuated to transfer drive torque to the secondary driveline for establishing a four-wheel drive mode. These “mode” clutch assemblies can range from a simple dog clutch that is operable for mechanically shifting between the two-wheel drive mode and a “locked” (i.e., part-time) four-wheel wheel drive mode to a more sophisticated automatically-actuated multi-plate clutch for providing an “on-demand” four-wheel drive mode.

#On-demand four-wheel drive systems are able to provide enhanced traction and stability control and improved operator convenience since the drive torque is transferred to the secondary driveline automatically in response to lost traction of the primary driveline. An example of passively-controlled on-demand transfer case is shown in U.S. Pat. No. 5,704,863 where the amount of drive torque transferred through a pump-actuated clutch pack is regulated as a function of the interaxle speed differential. In contrast, actively-controlled on-demand transfer cases include a clutch actuator that is adaptively controlled by an electronic control unit in response to instantaneous vehicular operating characteristics detected by a plurality of vehicle sensors. U.S. Pat. Nos. 4,874,056, 5,363,938 and 5,407,024 disclose various examples of adaptive on-demand four-wheel drive systems.

#FIG. 1 is a schematic view of a four-wheel drive motor vehicle equipped with a transfer case constructed according to the present invention;

#FIG. 2 is a sectional view of the transfer case equipped with a controllable, multi-mode, bi-directional overrunning clutch assembly and shift control system of the present invention;

#FIG. 3 is a sectional view of the bi-directional overrunning clutch assembly shown in FIG. 2;

#Referring now to FIG. 1, a drive system 10 for a four-wheel drive motor vehicle is shown to include a power source, such as engine 12, which drives a conventional transmission 14 of either the manually or automatically shifted type. The output shaft of transmission 14 drives an input member of a transfer case 16 which, in turn, delivers drive torque to a primary output shaft 18 that is operably connected to a primary driveline 20. Primary driveline 20 includes an axle assembly 22 having a differential 24 driving a first pair of wheel assemblies 26 via axleshafts 28, and a drive shaft 30 connected between primary output shaft 18 and differential 24. Transfer case 16 further includes a secondary output shaft 32 that is operably connected to a secondary driveline 34. Secondary driveline 34 includes an axle assembly 36 having a differential 38 driving a second pair of wheel assemblies 40 via axleshafts 42, and a driveshaft 44 connected between secondary output shaft 32 and differential 38.

#Drive system 10 also includes an electronic controller 48 which receives mode signals from a mode selector 46. Controller 48 receives the mode signals and generates control signals that are used to actuate a controllable shift system associated with transfer case 16. According to the arrangement shown, primary driveline 20 is the rear driveline of a rear wheel drive vehicle while secondary driveline 34 is its front driveline. However, it will be understood that the teachings of the present invention could easily be adapted for use in a front wheel drive vehicle in which the front driveline would be designated as the primary driveline.

#Referring primarily to FIG. 2, transfer case 16 is shown to generally include an input shaft 50, rear output shaft 18, a planetary reduction gearset 52, a range clutch 54, front output shaft 32, a transfer assembly 56, a bi-directional mode clutch assembly 58, and a power-operated shift system 60, all of which are mounted to a housing assembly 62. Input shaft 50 is adapted for direct connection to the output shaft of transmission 14. Planetary gearset 52 includes a sun gear 64 fixed for rotation with input shaft 50, a ring gear 66 non-rotatably fixed to housing assembly 62, and a plurality of planet gears 68 rotatably supported on a planet carrier 70. Range clutch 54 includes a range collar 72 that is fixed via a splined connection 74 for rotation with and axial bi-directional movement on rear output shaft 18. Range collar 72 is moveable between a high-range (H) position, a neutral (N) position, and a low-range (L) position via axial translation of a range fork 76. In the H position, clutch teeth 78 on range collar 72 engage internal clutch teeth 80 on input shaft 50 so as to establish a direct ratio drive connection between input shaft 50 and rear output shaft 18. In the L position, clutch teeth 78 on range collar 72 engage internal clutch teeth 82 on planet carrier 70 so as to establish a reduction ratio drive connection such that rear output shaft 18 is driven at a reduced speed ratio relative to input shaft 18. In the N position, range collar 72 is disengaged from coupled engagement with both input shaft 50 and planet carrier 70 such that no drive torque is transmitted from input shaft 50 to rear output shaft 18.