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: A hydraulic pump for a power steering apparatus is provided. Said pump comprises a housing, an outer gerotor element and a rotating inner gerotor element arranged within said outer gerotor element. A plurality of pressure chambers is defined and a pressure valve is assigned to each pressure chamber at the output side of the pump.

Abstract: A hydraulic transmission, in particular for an automotive drive system including a combustion engine comprises at least a pair of hydrostatic pumps and at least a pair of hydrostatic motors each pump and/or motor having the same size or different size with a constant or adjustable through-put. Automatically actuated clutches are provided to connect the pumps to the engine and to connect the motors to a load. A variety of transmission ranges is obtained by activating selected ones of the individual pumps and motors by actuating corresponding clutches. Therefore, the combustion engine may be operated under conditions in which fuel comsumption is as low as possible.

Abstract: A proportional throttle valve which varies the throttle cross-sectional area in dependence upon a control signal and thus governs the flow rate. The invention relates to a throttle valve in which the position of the valve member remains constant independent of pressure fluctuations upstream and downstream of the throttle cross-section. For this purpose the pressure acts on equisized opposing faces of the valve member. An annular face of equal magnitude lying opposite the control face is subjected to the pressure in a line leading from the pressure-limiting valve for setting the control pressure to the tank so that pressure fluctuations in this tank line cause corresponding variations of the control pressure and the position of the valve member remains constant.

Abstract: The invention relates to a piston machine comprising a plurality of pistons and changeable piston displacement for varying the torque and speed. The pistons are connected via control bores and distributor passages in the distributor of the machine to a high pressure and low pressure connection. To reduce the displacement a switching valve is provided via which the inactive pistons are connected together via their distributor passages and also possibly subjected to an external very low servo pressure or tank pressure. This reduces the frictional losses, increases the efficiency and avoids flow losses of the valve.

Abstract: A hydraulic load power train control for reversible shifting with a pressure control device for the controlled build-up of a shift clutch pressure, a foot clutch valve for arbitrary control of the shift clutches, and a manually operable shift valve for shifting of the reversible power train. The foot clutch valve is connected parallel to the pressure control device. The pressure control device is formed by a changeover valve indirectly reversible by the shift valve by which the pressure controlled in the supply pressure line can be fed to two shift pressure lines which are connected to a valve device. At the same time, the valve device is so controlled by the foot clutch valve that the effective shift clutch pressure can be controlled without influencing the position of the changeover valve as a function of the actuation of the foot clutch.

Abstract: For connecting servohydraulic linear or rotation drives to a line with impressed pressure a valve means is provided which shuts off the pressure-carrying lines in leakage-free manner and connects the consumer line pressure-free to the tank. For a trial setting operation a fluid flow of reduced pressure and amount can be supplied to the consumers via an auxiliary means. The connection of the consumers is surge-free.

Abstract: A pilot-controlled proportional throttle valve is provided having pilot oil passage means provided in the spool of said throttle valve.

Abstract: A machine tool comprising an axially reciprocating tool is driven by a hydraulic jack or lifting cylinder which is controlled by a servovalve. The amplitude and velocity of the lifting cylinder is set at a control circuit to which the position and acceleration of the lifting cylinder are applied as input variables. The electrohydraulic control has a high damping and high gain. As a result the velocity change of the lifting cylinder when the tool enters the workpiece is negligibly small.

Abstract: The sweeping roller of a sweeping machine is held on the ground in sweeping operation by two hydraulic cylinders in such a manner that the degree of wear is small. For this purpose in each cylinder a static and different holding pressure must be set. The higher pressure is set at a pressure-limiting valve and the lower pressure at the series circuit parallel thereto of a nozzle with an adjustable throttle.

Abstract: In general terms the invention provides for a direct actuated pressure regulated vane-type pump having a adjustment piston which is under the influence of the pump pressure. The adjustment piston is coupled to said cam ring by means of a flexible or articulate connection means, or else the adjustment piston itself is of a flexible or articulate design.

Abstract: A hydraulic system having an axial piston pump as a control pump which is regulated by a regulating device as a function of the demands with respect to volumetric flow and pressure of a load circuit supplied by it. On the suction side, the control pump is optionally provided with a partial amount of its maximum delivery volume by a feed pump, while the remaining part of the corresponding delivery quantity is drawn in directly from a storage container, bypassing the feed pump. Possibly impermissibly high vacuums on the suction side of the control pump are detected by a suction safety device which acts on the control pump via its regulating device so that the control pump delivers smaller quantities of hydraulic fluid unitl permissible operating conditions are reached.

Abstract: A control motor for a servo-valve. Adjacent to the control coil of the control motor a dampening coil is located and short-circuited, so as to provide for an improvement of the frequency characteristic of the control motor.

Abstract: A pump supplies via in each case a directional valve with associated pressure balance fluid or pressure medium to a plurality of loads. When the pump power is not sufficient a proportional quantity reduction is achieved at all loads in that the control voltages of the control members for electrical actuation of the directional valves are supplied to a summation stage and the sum voltage is compared in a comparison stage with a limit value corresponding to the maximum pump displacement, whereupon when the limit value is exceeded a control signal is generated with which the stroke of the driven directional valves is reduced.

Abstract: A plurality of mechanically coupled secondarily controlled hydrostatic machines with variable volume are connected to a line with impressed system pressure fed by a primary unit. By reducing the variable volume to 0 in individual hydrostatic machines the remaining machines are subjected to a higher torque which results in a greater pivot angle of the remaining secondary units. As a result the efficiency and controllability are improved. The changeover is effected in dependence upon an upper and lower switching point corresponding to the pivot angle of the unit remaining in engagement.

Abstract: In a radial piston machine which includes a driven rotatable rotor with radial pistons displaceable in radial recesses of the rotor by pressure medium and carrying rollers which cooperate with a cam track of the rigid cam plate, the length of the rollers can be increased due to the provision in the bores receiving the rollers respective opposing recesses in which portions of the roller are received.

Abstract: The invention relates to a three-way pressure reducing valve for reducing a primary pressure to a secondary pressure. Said three-way pressure reducing valve comprises means for monitoring the secondary pressure. First spool means of said pressure reducing valve and second spool means of said monitoring means are provided with first and second spring means, respectively. Further, first and second adjustment means, respectively, are provided said first and said second spool means being coaxially arranged.

Abstract: The invention concerns a hydraulic system for supplying a hydrostatic steering system. A central variable capacity hydraulic fluid pump supplies the steering system and a secondary consuming device via separate respective compensated pressure maintaining valves. The steering system and secondary consuming device are controlled by respective load report lines which are brought together at a changeover valve which is operative to permit the higher reported pressure to be delivered to a volume governor for the pump. Upon the secondary consuming device entering a neutral condition or a fluid loss condition, the changeover valve moves to block the load report line to the secondary consuming device; and a control circuit, including a branch line from the feed line to the steering system, maintains a higher pressure in the load report line of the steering hydraulic circuit than in the line of the secondary consuming device.

Abstract: A control block is made up of a plurality of directional valves which serve to actuate a plurality of hydraulic drives to which in some cases a different pressure is to be supplied. For this purpose two pressure-limiting valves adjustable to different pressures are provided, the valve adjustable to the lower pressure being connected to the last valve unit. This gives a simple construction and substantial freedom in the association of the drives.

Abstract: In a plastic processing machine (injection moulding machine) the amount of working medium to be supplied to the hydraulic drives and to the injection cylinder and the clamping cylinder is regulated to control the adjustment rates via a quantity control of an adjustment pump. The setting of the pressures necessary at the drives is effected in contrast via a directional valve which controls the fluid paths to one of the drives and which is adapted to be connected to the tank via a regulatable throttle point governing the pressure. This simplifies the apparatus expenditure for the pressure control of such a machine.