It replaces the viscous clutch in four-wheel drive. As soon as a difference in speed comes about between front and rear axle, the swash plate begins to turn. In this, it operates the pump plunger, which presses hydraulic oil into the plunger of the friction disks. After less than one revolution, adhesion has resulted. With the help of the electronically operated throttle valve, the slip can be adapted to the driving situation in question.