Motor vehicles – Having four wheels driven – With differential means for driving two wheel sets at...
Reexamination Certificate
1998-08-31
2001-04-10
Boehler, Anne Marie (Department: 3618)
Motor vehicles
Having four wheels driven
With differential means for driving two wheel sets at...
C180S248000, C701S089000
Reexamination Certificate
active
06213242
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to the field of four wheel drive systems for motor vehicles, particularly to control of a transfer case clutch that distributes torque to the front and rear axles.
2. Description of the Prior Art
In a four-wheel drive 4WD system engine torque is transmitted to a secondary pair of drive wheels in response to a control signal applied to a transfer clutch located in a transfer case. The control signal is produced when certain parameters, represented by signals produced by electronic sensors, indicate vehicle operating conditions can be improved by activating both the primary drive wheels and secondary drive wheels. U.S. Pat. No. 4,757,870 describes a transfer clutch controlled with reference to the rotational speed difference between the primary and secondary drive wheels. U.S. Pat. No. 5,010,974 describes a similar system for controlling a transfer clutch upon reference to the speed difference, vehicle speed, and engine intake manifold vacuum.
Conventionally a 4WD system includes a transfer case driveably connected to the output shaft of a multiple-speed transmission. The transfer case contains the transfer clutch, a speed-reduction gearset for increasing transmission output torque, a mechanism for engaging and disengaging the gearset and a torque path, such as a ball ramp drive, for transmitting power through the transfer case to the front driveshaft through the transfer clutch.
SUMMARY OF THE INVENTION
It is an advantage of this invention in a drivetrain that transmits forward and reverse drive to front and rear drive wheels to provide a four-wheel drive system that eliminates noise and harsh engagement in a transfer case when reversing the direction of rotation of the wheels while providing the full benefit of a locked transfer case.
It is an object of this invention to provide a four-wheel drive system that controls the torque capacity of a transfer clutch by applying a predetermined electric current duty cycle to the clutch, the duty cycle corresponding to the selected operating range of the transfer case, the engine throttle position and the lower average speed of the front and rear wheel pairs.
In realizing these objects and advantages a four wheel drive system according to the present invention for a vehicle having an engine controlled by a throttle, a first pair driving wheels, and second pair of driving wheels includes a range selector for producing a signal representing selected operation in a high speed ratio range and low speed ratio range; a transfer case for driveably connecting the power source and a first pair of wheels, and for driveably connecting the power source and a second pair of wheels through a transfer clutch whose torque capacity varies in response to a control signal applied to the clutch; means for producing a signal representing the lower speed of the average speed of the first pair of driving wheels and the average speed of the second pair of driving wheels; a sensor for producing a signal representing the position of said throttle or another measure of inferred engine torque; and control means connected to the range selector, determining means and engine torque indicating means for producing a control signal corresponding to the signals representing said selected range, engine torque and said lower average speed, and for applying said control signal to said transfer clutch.
REFERENCES:
patent: 4757870 (1988-07-01), Torii et al.
patent: 5010974 (1991-04-01), Matsuda
patent: 5032995 (1991-07-01), Matsuda et al.
patent: 5363938 (1994-11-01), Wilson et al.
patent: 5407024 (1995-04-01), Watson et al.
patent: 5662543 (1997-09-01), Forsyth
patent: 5927425 (1999-07-01), Kusano
1998 Ford 2000 Explorer Mountaineer Wokshop Manual, vol. 1.
Glab John
Rodrigues Ashok
Boehler Anne Marie
Ford Global Technologies Inc.
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