192 clutches and power-stop control – Clutches – Automatic
Reexamination Certificate
1999-04-16
2001-01-23
Bonck, Rodney H. (Department: 3681)
192 clutches and power-stop control
Clutches
Automatic
C074S650000
Reexamination Certificate
active
06176359
ABSTRACT:
BACKGROUND OF THE INVENTION
Four-wheel drive motor vehicles are becoming increasingly popular. Recently, certain motor vehicles have been provided with “full-time” four-wheel drive systems also known as all-wheel drive systems. In such all-wheel drive systems, the torque transfer cases are typically provided with an interaxle differential for dividing torque between the front and rear wheels of the motor vehicle. The interaxle differential enables the front wheels and the rear wheels to rotate at different speeds, during normal turning of the motor vehicle or in the event that the front wheels and the rear wheels have tires with different diameters. However, to prevent excessive relative slipping between the front wheels and the rear wheels, as might occur when one set of wheels encounters a low-traction condition, such as ice, these transfer cases typically include a selectively engageable clutch which is operative to lock the interaxle differential upon sensing a predetermined amount of relative slippage between the front output shaft and the rear output shaft of the transfer case. Locking of the interaxle differential prevents any further relative overrun or differentiation between the front output shaft and the rear output shaft of the transfer case.
Known prior all-wheel drive systems have generally required complex electronic sensors or other complex systems to monitor the overrun or differentiation between the transfer case front and rear output shafts or the front wheels and the rear wheels of a motor vehicle. Upon sensing relative overrun or differentiation, an electronic control system determines whether the relative overrun or differentiation being encountered is within a “normal” expected range or is “excessive.” If the electronic control system indicates that the overrun or differentiation being experienced is “excessive,” the electronic control system causes the clutch to lock the interaxle differential to preclude any further relative overrun or differentiation. An electronic control system of this type can be expensive to manufacture and maintain and a more cost-effective, simplified “on demand” system of limiting more than a predetermined amount of overrun or differentiation between the front wheels and the rear wheels of the motor vehicle would be desirable.
In recent years, motor vehicle all-wheel drive power-train systems have been cost-reduced by eliminating the transfer case differential, providing continuous power to a primary axle, and providing on-demand power to the secondary axle whenever primary axle slippage occurs. Typically, a torque-coupling device (viscous, hydraulic, electric) is utilized within the transfer case to drive the secondary axle. The torque-coupling device compensates for any speed difference which may occur between the primary and secondary axle. When the secondary axle is a front axle, an open differential is typically installed. Torque-sensing differentials with clutch pack pre-load are not considered acceptable for front axles due to steering issues attributable to torque bias. The front wheels tend to slide rather than turn on low coefficient-of-friction surfaces.
One prior art vehicle is offered with a speed-sensing, limited slip front axle differential to eliminate the pre-load torque bias issue. However, this design still requires an interaxle differential or in-line torque coupling to avoid driveline wind-up when operated on hard pavement.
It would therefore be desirable to provide a simplified, cost effective mechanism to allow differentiation between front and rear output-shafts in an all-wheel drive system, while providing speed-sensing limited-slip capabilities.
SUMMARY OF THE INVENTION
The present invention is, therefore, directed to a speed-sensing, limited-slip transfer case including a differential assembly which overcomes the delinquency of the prior art. The invention is also directed to a bidirectional overrunning clutch assembly which may be used in such a system or in any other power transmitting device. In a preferred embodiment, there is provided a transfer case with front & rear outputs mechanically connected, a primary axle assembly and a secondary axle assembly comprising a differential assembly including at least one bidirectional overrunning clutch assembly. In the preferred form, the clutch assembly includes two sets of struts, each set used to transmit torque in one direction. A decoupler is utilized to control which set of struts is functional. The decoupler may be a laterally sliding component capable of preventing one set of struts from engaging the outer race of the differential case. As the decoupler moves laterally, one set of struts is engaged, then neither set are engaged, then the other set becomes engaged. The decoupler may be designed to move only when the one-way clutch rotating direction is reversed. A reversing ring may be used to move the decoupler and allow the one-way clutches to function in both directions. In a preferred form, the reversing ring includes a ‘paddle wheel’ feature. As the differential case begins to rotate in the ‘forward’ or ‘reverse’ directions, the ‘paddle wheel’ contacts the axle lubricant, creating a drag force that rotates the reversing ring. This angular movement of the reversing ring is translated to linear movement of the decoupler. As the decoupler is repositioned, the one-way clutch is reoriented to function in the ‘forward’ or ‘reverse’ mode. In the preferred embodiment, two clutch assemblies are used, each clutch assembly providing power to one output shaft. When the vehicle turns, the outboard wheel & shaft speed increases, over-running the corresponding clutch assembly. All drive torque is transmitted through the inboard wheel. If the inboard wheel should lose traction and slip during a turn, the differential case speed increases until it matches the outboard wheel speed. When the speeds are equivalent, the outboard wheel begins transmitting torque; the one-way clutch prevents the differential case from over-speeding the shaft and wheel. This provides the limited-slip feature desired for increased mobility. To avoid driveline wind-up while driving on hard pavement, the primary & secondary axles are preferably geared with slightly different ratios. The secondary axle differential case rotates slightly slower than the corresponding wheels resulting in a wheel over-run condition and no torque transmission. When a primary axle wheel begins to slip, the secondary axle differential case speed increases until at least one of the one-way clutches engages and transmits torque. The amount of primary axle wheel slippage required to engage the secondary axle is dependent upon the gear ratio difference.
Accordingly, it is an object of the present invention to provide a speed-sensing, limited slip axle assembly for an all-wheel drive vehicle and bidirectional overrunning clutch assembly therefore. A differential assembly according to a preferred embodiment includes two one-way bidirectional overrunning clutch assemblies which provide for axle shaft differentiation while turning, and speed-sensing limited-slip capability, while eliminating the necessity for an interaxle differential or in-line torque coupling device in the transfer case.
Other advantages and novel features of the present invention will become apparent in the following detailed description of the invention when considered in conjunction with the accompanying drawings.
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Bonck Rodney H.
Dana Corporation
Oldham & Oldham Co. L.P.A.
LandOfFree
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