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.