192 clutches and power-stop control – Clutches – Automatic
Reexamination Certificate
1999-01-26
2001-02-06
Marmor, Charles A. (Department: 3681)
192 clutches and power-stop control
Clutches
Automatic
C192S054100, C192S054500, C192S058400, C192S058410
Reexamination Certificate
active
06182808
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE DISCLOSURE
The present invention relates to a driveline system for a four wheel drive vehicle, and more particularly, to a differential device for use in such a driveline system. The use of the term “differential” does not imply the presence of conventional differential gearing, but instead, the term is used primarily because the device of the present invention replaces the typical prior art center differential. However, it should be understood that the device illustrated, described and claimed herein has uses other than as a center differential in a four wheel drive vehicle driveline.
In many of the vehicles being produced today, the basic vehicle platform is a front wheel drive. However, in many such vehicles, especially in vans and sport utility vehicles, it is considered desirable to be able to provide four wheel drive, at least under certain operating conditions.
Typically, the various arrangements for achieving part-time four wheel drive have been complex and expensive, and in some cases, have required some sort of control scheme to achieve the four wheel drive (or rear wheel drive) in response to certain predetermined operating conditions.
In certain vehicle applications, it is acceptable to provide only front wheel drive under most operating conditions, and rear wheel drive is required only when the front drive wheels are slipping (e.g., under poor traction conditions). However, the prior art has not provided a suitable device wherein only front wheel drive is provided, with no substantial torque being transmitted to the rear wheels, until the front wheels begin to slip. For example, U.S. Pat. No. 4,562,897 discloses a viscous clutch in the driveline, between the front transaxle and the rear wheels, but requires a selector arrangement in order to choose among transmitting torque through the viscous coupling, or disconnecting the viscous coupling, or bypassing the viscous coupling.
It is known from U.S. Pat. No. 5,070,975 and from corresponding European Application EP 0 314 420 to use, as a center differential in a four wheel driveline, a viscous actuated ball ramp type friction clutch to transmit torque to the rear axles when there is a speed difference between the front and rear wheels. It is believed that the torque transmitting capability of the device of the cited patent and application would be somewhat limited by the fact that one of the ball ramp plates comprises the input to the viscous coupling.
In certain vehicle applications for four wheel drive drivelines, the differential device must be capable of a “through-shaft” configuration, which the known, prior art devices have not been. It should be understood that, as used herein, the term “through-shaft” is not limited to an arrangement in which there are two concentric shafts extending completely through the differential device, but instead, includes an arragement in which there is an output shaft, or some equivalent member, disposed within, and surrounded by, the differential device, over at least most of the axial length of the differential device.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an improved differential device which is capable of use in a “through-shaft” configuration.
It is a more specific object of the present invention to provide an improved differential device which accomplishes the above-stated object, and which includes additional features which facilitate such a through-shaft configuration.
The above and other objects of the invention are accomplished by the provision of an improved differential device of the type including an input adapted to receive input torque, an output adapted to provide driving torque to an output device, and a clutch pack including at least a first friction disc fixed to rotate with the input, and at least a second friction disc fixed to rotate with said output. The device includes means operable to move said friction discs between a disengaged position and an engaged position, said means comprising a cam ramp actuator including first and second ramp plates, and a plurality of cam members, each operably disposed between said 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 means operable to move said friction discs further comprises a viscous coupling including an input coupling member fixed to rotate with said input, and an output coupling member.
The improved differential device is characterized by the output comprising an elongated, generally hollow shaft member extending axially through substantially the entire axial extent of the differential device. The device includes means for interconnecting one of the input coupling member and the output coupling member of the viscous coupling with the first ramp plate for common rotation.
In accordance with another aspect of the invention, the improved differential device is characterized by the output comprising a shaft member extending axially through the clutch pack and at least partially through the cam ramp actuator. A first retention means is in engagement with one of the input and the shaft member and operable to limit axial movement of the first ramp plate in a forward direction, relative to one of the input and the shaft member. As a result, substantially all axial separation forces within the clutch pack and the cam ramp actuator are taken up within either the input or the shaft member.
In accordance with yet another aspect of the invention, the improved differential device is characterized by one of the input and the output defining a plurality N of elongated cut-out portions on the periphery thereof. One of the first friction disc and the second friction disc defines a plurality N of cut-out portions cooperating with the elongated cut-out portions defined by the one of the input and the output to define a plurality N of openings. There is a plurality N of elongated members, each member being disposed in one of the openings, and operable to transmit torque between the one of the first friction disc and the second friction disc and the one of the input and the output. The openings have an axial length L
1
, and each of the elongated members has an axial length L
2
, less than L
1
, the difference therebetween being selected such that wear within the clutch pack will permit L
1
to decrease to L
2
, but will prevent the cam ramp actuator from moving to an over-center condition.
REFERENCES:
patent: 5036963 (1991-08-01), Murata
patent: 5890573 (1999-04-01), Kwoka
Eybergen William N.
Nank Michael W.
Spring James K.
Walton Erlen B.
Eaton Corporation
Kasper L. J.
Marmor Charles A.
Waddell Tisha D.
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