Abstract: A 3/2 proportional control valve is provided with an actuating piston which is subjected to the control pressure set in a pilot valve. The area relationships of the actuating piston are so chosen that at the actuating piston a high pressure gradient obtains and the adjustment dynamics of the regulating piston are increased.

Abstract: The invention relates to an electrically activated two-way throttle valve. The opening stroke of the valve piston is determined by an electrical desired value. To control the valve a circuit is provided to obtain a predetermined flow relation in response to the valve member position. According to the invention the pressure difference prevailing at the valve is measured. The pressure differential signal is exponentiated with an exponent. The product of this exponential function and of an input signal defines the desired value for the valve member position. By selecting different values for the exponent, the volume of flow in response to the valve member position is adjusted to an optimum and still further a variety of valve functions may be obtained to operate the valve as flow controlled or pressure controlled for example.

Abstract: A rotary piston engine having a commutator valve in a cooperating connection with the output shaft so as to supply and remove pressure medium to and from tooth chambers. Said engine further comprises passages which end adjacent to the commutator valve in ellipse shaped control openings. The commutator valve is integrally formed with the output shaft and all control channels are in the outer circumference of the commutator valve in the form of grooves which are parallel to the axis. Lands are provided between said grooves. The width of the lands defining said grooves is selected such that the width of the lands changes alternately, one land having a width approximately corresponding to the smaller width of the control ellipse, while the alternate land has a width which is increased by an oversize over the width of the smaller width of said control ellipse.

Abstract: The invention relates to a safety arrangement for a controlled drive which is connected to a conduit with impressed pressure. When the safety arrangement responds the machine is separated via shutoff valves from the inlet and outlet and a via a switchover valve the pivot angle of the machine is set to the maximum value so that the largest possible braking torque can be automatically set.

Abstract: A cylinder unit is supplied with pressurized fluid from a hydraulic machine which is variable in speed and/or displacement. The machine may be operated as a pump and as a motor to increase the pressure or, respectively, to decrease the pressure so that the piston of the cylinder unit may be actuated in both directions and, furthermore, the brake energy is recovered by the machine when the piston is driven through an external load. This results in an increased efficiency of the control apparatus for the cylinder unit avoiding any problems arising from heat.

Abstract: A hydraulic vane-type pump is provided having a venting valve which is located immediately at the pressure space of the pump, i.e., avoiding any additional passage means between the pressure space of the pump and the venting valve.

Abstract: For path control of a plurality of drives, i.e. for driving a plurality of drives in different axes in geometrical path dependence, to obtain high accuracy it is necessary for the lag error of the drives to remain constant. According to the invention for this purpose a circuit arrangement is proposed in a cascade structure in which from the speed of each individual path drive and the control deviation determined from the actual value and desired value of the position a difference signal is formed which is integrated and added to the output signal of a P controller.

Abstract: For the production and exact control and regulation of very high pressures, in particular for actuating a press, two pressure intensifiers are provided which each have a differential piston. The second pressure intensifier is connected via a shutoff valve to the first pressure intensifier and to the load or consumer. Both pressure intensifiers have a small volume compared with the volume required by the consumer. By activating the second pressure intensifier fluid can be exchanged between the consumer and the first pressure intensifier to replenish the first pressure intensifer in a pressure buildup phase and to empty the first pressure intensifier in a pressure relief phase.

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 hydrostatic gear wheel mechanism has two intermeshing gear wheels in the work space of a housing. To continuously rinse the gear wheel and housing surfaces which slide on each other, grooves on the gear wheel convey lubricant from the work space to between the gear wheel front faces and the axial end walls of the work space.

Abstract: A hydraulic driving device includes a working cylinder for moving a machine component, and an electro-hydraulic servo system. The servo system includes a servo-valve, a position-error control, a circuit for emulating speed and acceleration of the working cylinder, and a regulator for weighting the ascertained position error according to the emulated speed and acceleration, and generating a setting signal for the servo valve.

Abstract: To reduce the noise on response of a pressure-limiting valve, downstream of the valve seat an annular space, an annular gap and a further annular space are provided. This flow-off system gives a reduction of the noise level. Moreover, in pressureless circulation the flow resistance of the valve is low because the annular gap is freed by the piston.

Abstract: A control valve apparatus is described which is intended for selective transmission of pressure to at least two pressure spaces. A magnetic control device is provided for selectively applying a hydraulic system pressure to the respective pressure spaces. As another function, the apparatus may simultaneously depressurize the two pressure spaces through the application of a control pressure to the control valve apparatus. To minimize the required installation space and the manufacturing cost, the control valve apparatus is comprised of a single control valve, the control piston means of which can be exposed to the control pressure against the force of a restoring device and can be moved into intermediate control positions by means of the magnetic control device.

Abstract: A method of controlling an attachment to an agricultural tractor in which the absolute movement of the attachment is determined by a motion sensor mounted thereon and is utilized as a control standard while the relative motion of the attachment with respect to the tractor, influenced by the controller and carried out by a power lift, is determined in such a way that the absolute movement of the attachment becomes zero. This control method achieves that the attachment maintains a constant position in space in spite of the pitch movements of the tractor acting as disturbances. This guarantees an automatic tilling process, for instance a uniform depth of the furrows when plowing. By utilizing superimposed feedbacks of further control standards, such as relative position and motor load, changes in the absolute position of the attachment are possible and overloading of the motor is avoided.

Abstract: An electro-hydraulic servo-valve having a valve spool and comprising: an adjustment motor, and a control apparatus for adjusting said adjustment motor to depending on the input nominal value, wherein said adjustment motor transmits its movement directly to the valve spool of the hydraulic valve, and wherein a preferably electrically operating additional drive is provided which will be switched on in case the valve spool gets stuck so as to release the valve spool from its stuck condition.

Abstract: A hydraulic system includes a multi-position valve which controls the flow of system fluid pressure to various work stations. The multi-position valve is biased by a centering spring to a neutral position from which it can be shifted to a selected working position. A retaining mechanism is able to retain the valve in the selected working position when the system pressure is in a prescribed pressure range. The retaining mechanism is urged to its retaining position by a control fluid pressure which is derived from the system pressure. When the system pressure is below or above the prescribed pressure range the retaining mechanism is unable to resist the force of the centering spring and the valve assumes a neutral position. When the system pressure is in the prescribed range, a constant control pressure is supplied to the retaining mechanism for effectively resisting the force of the centering spring.

Abstract: Speed regulation of pump drive is set by a pressure-regulating valve providing a constant control pressure for a plurality of normal loads. If a high fluid consumption load such as the lifting cylinder of a forklift truck is to be simultaneously actuated the pump speed and net volumetric displacement must be increased. A higher speed-regulating control pressure from the pressure-regulating valve is required. The control valve for the high consumption load has a spool with an extending inclined cam contacting the biasing spring of the pressure-regulating valve. Upon actuation of this control valve the preload of the biasing spring is increased thereby adjusting the speed-regulating control pressure output of the pressure regulating valve. The pump engine or drive speed and the net volumetric displacement are increased.

Abstract: For setting and guiding a band running round two rolls the bearings of the roll on either side are each adjustable by a hydraulic or lifting cylinder. Each hydraulic cylinder comprises a position control circuit. The position desired value applied jointly to the position control circuits is varied by a tension-dependent control in such a manner that in the position adjustment a maximum admissible tension force is not exceeded. Furthermore, the position desired value has superimposed thereon a correction control by which the center setting of the band is monitored. The arrangement is preferably provided for positioning and tension-dependent adjustment of the encircling metal band of a sheet casting apparatus.

Abstract: According to the parent patent on inadequate power of the delivery pump the flow rate set at the directional control valves for the consumers is reduced in equal proportions in that electrical signals proportional to the flow rates 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 delivery flow. When the limit value is exceeded a control signal is generated with which the stroke of all the driven directional control valves can be jointly reduced. According to the application of addition the signal voltage supplied to the summation stages and corresponding to the respective flow rate can be obtained in a displacement pickup associated with each directional control valve or in a pressure pickup measuring the pilot pressure if the directional control valves are not controlled electrically but hydraulically.

Abstract: A pump supplies a plurality of consumers each via a directional control valve with pressure balance. When the pump delivery is not adequate, manifesting itself in a dropping of the pump pressure, the pressure balance of the consumer with the highest load pressure is displaced out of the end position of its regulating position into a further control position in which a control pressure line is connected via a throttle point to a discharge so that by means of the throttle point a control pressure is generated which is used for equiproportional reduction of the supply flow to the consumers. This is done either by reducing the stroke of the directional control valves or by acting on the pressure balances in the closure direction.