Hydraulic-pressure control system for four-wheel drive vehicle w

Details Hydraulic-pressure control system for four-wheel drive vehicle w Hydraulic-pressure control system for four-wheel drive vehicle w

1996-02-12

1999-03-02

Boehler, Anne Marie

Motor vehicles

Having four wheels driven

With differential means for driving two wheel sets at...

180249, 91444, 192 85R, B60K 17344

Patent

active

058758658

ABSTRACT:
A hydraulic-pressure control system for a four-wheel drive vehicle with a hydraulic-pressure operated transfer clutch, which is responsive to a controlled clutch pressure applied thereto to distribute a driving torque passing from a transmission between main drive wheels and auxiliary drive wheels, comprises a pilot-operated directional control valve connected to the transfer clutch for cutting off a supply of hydraulic fluid of the controlled clutch pressure to the transfer clutch and for directing hydraulic fluid of the controlled clutch pressure to the transfer clutch. The system includes a clutch pressure control valve provided upstream of the directional control valve, which pressure control valve is responsive to an external pilot pressure for producing the controlled clutch pressure, and a duty-ratio controlled solenoid valve for decreasingly adjusting the external pilot pressure to be output to the pressure-reduction valve in accordance with an increase in a duty ratio. A controller is provided for forcibly outputting a duty-cycle controlled exciting current of a predetermined high duty ratio such as 100% to the duty-ratio controlled solenoid valve to reduce the controlled clutch pressure to a low pressure level (preferably a minimum clutch pressure) when the directional control valve is maintained at the cut-off position in case of 4L range wherein the transmission is loaded heavier.

REFERENCES:
patent: 4858646 (1989-08-01), Kato
patent: 5103930 (1992-04-01), Gierrer
patent: 5171294 (1992-12-01), Takano
patent: 5687824 (1997-11-01), Hara et al.

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