Abstract: A hydraulic unit for a motor vehicle consisting of a housing comprising two housing chambers separated by a wall located inside the housing, in which a reciprocating pump is supported by the wall located inside the housing and is arranged in a first housing chamber which forms a hydraulic fluid reservoir. A drive member for the reciprocating pump is led out of the first housing chamber. A nonreturn valve provided in the wall located inside the housing establishes a fluid communication from the reciprocating pump to a pressure chamber in the second housing chamber, which is separated from a gas pressure reservoir also provided in the second housing chamber by a reservoir piston guided in the second housing chamber.

Abstract: A four-wheel drive vehicle has a permanently driven axle. A planetary gear set and viscous clutch are located in the power train leading to the second axle. The annular gear of the planetary gear set is mounted rotatably and can be stopped by a brake band. When the brake band is tensioned, the four-wheel drive, which is running via the viscous clutch, is in the state of readiness, while it is ineffective when the brake band is released.