Abstract: A power-take-off of a utility vehicle such as an agricultural tractor has a clutch (3) and a brake (18) to retain the output shaft against rotation when the clutch is disengaged. The invention provides a means of automatically disengaging the brake to permit rotation of the output shaft for the purpose of coupling an implement thereto. In one embodiment, the clutch and brake are engaged by fluid under pressure, and are disengaged by stopping the vehicle engine and thus allowing engine generated fluid pressure to decay.

Abstract: A hydraulic system for a power-take-off in a utility vehicle is described, having a pump (8) supplying hydraulic fluid to the clutch (1), the brake (2) and a lubricating circuit, a control valve for engaging and releasing the clutch and a device containing a pressure-limiting valve (12) which makes a high system pressure available when the clutch is engaged and a lower system pressure when the clutch is released.In order to keep loss of power in the pump as low as possible and reduce the number of components required in a hydraulic system of this type, the system pressures are controlled by the pressure applied to the engaged clutch. Consequently, the system pressures can be adjusted regardless of the design of control valve used. This means that less expensive 3/2-way valves or 3/2-control valves can be used. This also has an advantage in that different system pressures can be produced using a single pressure-limiting valve.