Viscous actuated ball ramp clutch

Reference Number: N 04-03

Inventors: Walton, Erlen B.

Owner: NISTAC

USPTO Link:6102178

Invention Summary

Accordingly, it is an object of the present invention to provide an improved center differential device for use in a driveline of a part-time four wheel drive vehicle, wherein the improved device is capable of transferring no substantial torque to the rear wheels until the front drive wheels begin to spin, and thereafter, automatically transfers a substantial amount of torque to the rear drive wheels, i.e., the device is "speed sensitive".

It is another object of the present invention to provide such an improved center differential device which accomplishes the above-stated object without the need for any separate control arrangement, speed sensors, etc., and wherein the device is relatively simple and compact.

It is a related object of the invention to provide an improved center differential device which achieves the above-stated objects, while overcoming the disadvantages of the prior art devices.

The above and other objects of the invention are accomplished by the provision of an improved center differential device of the type including an input shaft adapted to receive input torque, at a speed of rotation representative of the speed of rotation of a pair of primary drive wheels. The device also includes an output shaft adapted to provide driving torque to a pair of secondary drive wheels, and a clutch pack including at least a first friction disc fixed to rotate with the input shaft and at least a second friction disc fixed to rotate with the output shaft. The device includes means operable to move the friction discs between a disengaged position and an engaged position.

The improved center differential device is characterized by the means operable to move the friction discs comprising a cam ramp actuator including first and second ramp plates, and a plurality of cam members, each operably disposed between the first and second ramp plates, and in engagement with first and second ramp surfaces, respectively. The second ramp plate is disposed axially adjacent the friction discs, and is operable to move the friction discs toward the engaged position, the second ramp plate being fixed to rotate with the output shaft. The means operable to move the friction discs further comprises a viscous coupling including an input coupling member fixed to rotate with the input shaft, and an output coupling member. The output coupling member is fixed to rotate with the first ramp plate whereby, any speed difference between the input and output shafts will result in a corresponding slip speed between the input and output coupling members, thus generating a viscous shear torque representative of the slip speed, the viscous shear torque being applied to the first ramp plate to displace the cam ramp actuator from a neutral position to a clutch actuating position.

In accordance with a more limited aspect of the invention, the improved differential device is characterized by the viscous coupling comprising a housing member fixed to rotate with the input coupling member, and being disposed axially between the output coupling member and the first ramp plate. The output coupling member is fixed to rotate with the first ramp plate, whereby, any speed difference between the input and output shafts will result in a corresponding slip speed between the input and output coupling members, thus generating a viscous shear torque representative of the slip speed. The viscous shear torque is applied to the first ramp plate to displace the output of the cam ramp actuator from a neutral position to a clutch actuating position.