Patent ID: 7069722

Claim:
A hydraulic system for a vehicle, comprising at least one hydraulic, load-carrying assembly which includes at least one movable structural element and at least one hydraulic device for actuating the structural element, said hydraulic system comprising a primary circuit which includes a servo device, a stationary hydraulic pump driven by a motor, a directional valve, and said at least one hydraulic device, said directional valve being arranged between the hydraulic pump and the hydraulic device for allowing hydraulic oil to flow to the hydraulic device at a servo signal from the servo device in order to operate said assembly, wherein the hydraulic system comprises a supplementary circuit which is connected to the primary circuit and includes a variable hydraulic pump which is driven by the motor and which is arranged for supplying an adjustable addition of hydraulic oil to the hydraulic device, and a proportional valve which is arranged between the variable hydraulic pump and the hydraulic device in order to regulate the flow of hydraulic oil to the hydraulic device as a function of a received flow signal, said variable hydraulic pump including a load-detecting regulator which is arranged for detecting the load on the hydraulic device when the variable hydraulic pump is in operation, wherein the proportional valve is connected to the servo device through a pilot controlled relief valve in order to receive said flow signal from the servo device via the relief valve, said flow signal being a function of said servo signal, and wherein the relief valve is connected to the primary circuit in order to receive a hydraulic pilot signal and to reduce the flow signal as a function of the pilot signal, said pilot signal being a function of the load on the assembly.