Motor vehicles – With means for detecting wheel slip during vehicle...
Reexamination Certificate
1999-02-09
2001-02-13
Johnson, Brian L. (Department: 3618)
Motor vehicles
With means for detecting wheel slip during vehicle...
C180S233000, C192S1030FA, C192S083000, C475S088000, C475S093000, C701S088000, C701S089000
Reexamination Certificate
active
06186258
ABSTRACT:
TECHNICAL FIELD
This invention relates to all wheel drive powertrains and more particularly to such drives having a control element to disconnect the all wheel drive from one pair of driving wheels.
BACKGROUND OF THE INVENTION
Many modern vehicles employ four wheel drive systems. These systems have been marketed in two forms. Systems generally termed four wheel drive (4WD) have a transfer case which is controlled by the operator to select two wheel or four wheel drive. If the operator selects the four wheel drive condition, the vehicle drives all four wheel continuously. Some of these systems have employed overrunning clutches at two of the wheel to alleviate some of the disadvantages of 4WD which result from tire pressure differential and cornering to name a few.
All wheel drive (AWD) systems also provide the benefits of a four wheel drive vehicle and do not require the operator to intentionally select this condition. These systems often employ a viscous clutch in the center differential to transfer torque to the drive wheels that are not sensed as slipping. In tight cornering situations and during towing, these AWD systems present a disadvantage. The vehicle must be placed on a flat-bed type towing vehicle to prevent overheating of the powertrain during towing. In cornering situations, noise and vibration can result from the AWD system being engaged. While this is not detrimental to the powertrain during short durations, it can be disconcerting to the operator.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved all wheel drive powertrain.
In one aspect of the present invention, a powertrain has a pair of fluid operated clutch mechanisms which are engaged to connect drive axles to a drive shaft. In another aspect of the present invention, a fluid pump is employed to selectively engage each of the clutches. In yet another aspect of the present innovation, a control valve is disposed in fluid communication between each pump and a reservoir from which the pumps draw fluid.
In still another aspect of the present invention, the control valve is normally closed preventing pressurization of the clutches and thereby disconnecting the all wheel drive. In yet still another aspect of the present invention, the control valve is a solenoid controlled valve which receives operating signals from a vehicle traction control system. In a further aspect to the present invention, the operating signal is also dependent on an anti-lock brake system of the vehicle.
In one embodiment of the present invention, a front wheel drive system is continuously drivingly connected with the front wheels of a vehicle.
A transfer gear arrangement is driven by the differential output of the front wheel drive system. A rear drive shaft is driven by the transfer gear arrangement which in turn drives a clutch housing and a first member of each of a pair of positive displacement pumps. A pair of rear drive axles are rotatably supported in the clutch housing and drivingly attached to respective drive wheels.
A pair of fluid operated selectively engageable multi-disc type clutches are supported in the clutch housing. A first set of the discs are splined or otherwise drivingly connected with the clutch housing. A second set of the discs are interspersed with the first set and are drivingly connected with respective ones of the drive axles. A second member of respective ones of the pumps is connected to respective ones of the drive axles. The pumps are operable to supply pressurized fluid from a reservoir to apply pistons of the clutches respectively.
The pumps must have a differential rotation between the first and second members and have the inlets thereof connected with the reservoir. A solenoid controlled valve is disposed between the reservoir and the inlet of the pumps to establish fluid communication therebetween. The vehicle is equipped with an anti-lock brake control system (ABS) and a traction control system (TCS). The solenoid valve responds to operating signals from ABS/TCS to open the valve and permit fluid communication between the pump inlet and the reservoir.
As is well-known with TCS equipped vehicles, the ABS/TCS issue command signals when the drive wheels and the vehicle speed are not in agreement. When a command signal is issued, the solenoid valve is energized. Thus the pumps only pump fluid when the ABS/TCS recognize the front drive wheels and the vehicle speed are not in unison. This permits the rear wheels to be free from drive connections during certain vehicle maneuvers, such as cornering, and during vehicle towing when the front wheel are removed from ground contact.
REFERENCES:
patent: 5162024 (1992-11-01), Yoshiba
patent: 5562192 (1996-10-01), Dick
patent: 5632185 (1997-05-01), Gassmann
patent: 5827145 (1998-10-01), Okcuoglu
patent: 5938556 (1999-08-01), Lowell
patent: 6056658 (2000-05-01), Illmeier
patent: 570841 (1993-11-01), None
Deutschel Brian William
Straitiff Donald Graham
General Motors Corporation
Johnson Brian L.
Leahy Charles E.
Lerner Avraham H.
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