Abstract: A circuit arrangement for controlling the output torque of a hydrostatic machine connected to a hydraulic system having an impressed operating pressure. The circuit arrangement has a control element for changing the output torque of the machine based upon operating parameters corresponding to pressure, speed, temperature and the like. Control means are supplied with a desired torque value for generating a control signal for actuating the control element. Pick-up means are connected to the control means and to the control element for picking up a pivotal angle .alpha. or an eccentricity E, respectively, representing an actual displacement volume of the hydrostatic machine. The pivotal angle .alpha. and the eccentricity E are measured in either an analog or a digital manner. When measured in an analog manner, the desired value of the pivotal angle is .alpha.=M/P and the desired value of the eccentricity is E=M/P, where M is the torque and P is the pressure.

Abstract: The invention relates to a drive for a press, in particular for a sheet metal forming press, the press including a press ram which can be moved up and down and a hydraulic movable counter support. The counter support can be moved in a forward stroke in the direction towards the press ram via at least one hydraulic cylinder by a first hydrostatic machine, and in a return stroke by the press ram. In known presses, during the return stroke of the counter support, the pressure medium is displaced from the hydraulic cylinder while a predetermined pressure is maintained by means of a pressure relief valve (pressure limiting valve) or a throttle valve (flow control valve). The balance sheet of energy of such a drive of such a press is to be improved. This is achieved by providing that the first hydrostatic machine is a pressure controlled machine, preferably an axial piston machine. Preferably, the axial piston machine can be swiveled in both directions, i.e. pivoted towards both sides.

Abstract: The torque of a hydraulic machine is dependent of the fluid pressure delivered to the machine and is further dependent of the adjustment of its volume of through-put. In response to a load coupled to the machine, a speed results which is controlled by a speed control system acting on the adjusting system of the hydraulic machine. According to the invention, an electro hydraulic speed control comprises a pair of control circuits which are connected to, but operate independent of each other. Thus the electrical control circuit produces a control signal y.sub.e1 from the difference of the actual value and the desired value of the speed for adjusting a hydraulic restricting means which produces a hydraulic pressure signal p.sub.st in the hydraulic control circuit which pressure signal is compared with a hydraulic reference signal p.sub.o to produce a differential pressure signal p.sub.o -p.sub.st which is applied to the adjusting cylinder of the hydraulic machine.

Abstract: A hydraulic drive system to actuate the piston of a cylinder unit comprises a first hydrostatic machine having variable displacement, a second hydrostatic machine mechanically coupled to said first machine and operating as a signal generator either in a pump mode or a motor mode, and a third hydrostatic machine of fixed displacement mechanically coupled to said first machine, which third machine is hydraulically connected to said cylinder unit. In response to zero speed or rotation of the drive system the piston of the cylinder unit may be stopped in any position, or, respectively, raised or lowered. The variable displacement machine may operate as a pump and as a generator in which latter case energy is recovered in lowering a load.

Abstract: An adjustable hydrostatic machine is connected to a pressure line with impressed system pressure. The pressure difference applied at the machine is set at a control valve so that the stroke volume of the machine in idling operation is set to an adjustment belonging to a predetermined load torque. In idling operation the machine is thus operated at large stroke volume with small pressure difference. If it is then necessary to furnish the load torque a switching valve is opened so that at the machine the full pressure difference is immediately applied, the machine can furnish the desired torque and the time loss necessary for setting the machine is eliminated.