Abstract: A control system for controlling a flow control valve to drive a hydraulic actuator in response to operation of a control device. This system includes a position detecting sensor for detecting a shift position of the control device, a speed detecting unit for detecting a shifting speed of the control device, and a controller for generating a control signal to control the flow control valve based on the shift position and shifting speed of the control device, and outputting this control signal to the flow control valve.

Abstract: A high efficiency heat transfer system includes a power circuit (350) and heat pump circuit (352). Each circuit having a working fluid flowing therein. In the power circuit, a heater (354) vaporizes the working fluid which is periodically delivered and exhausted through a valve assembly (358) to a power unit (362). The power unit is also a compressor for the working fluid in the heat pump circuit. Fluid exhausted from the driven section of the power unit is passed to a four-way valve (406) which selectively delivers the working fluid to an interior coil (416) or an exterior coil (408) to heat or cool an area. In extremely cold ambient temperatures, the area is heated directly from the power circuit using a by-pass exchanger (428).

Abstract: An electrohydraulic steering system has a pair of proportional valves for controlling displacement of a steering valve for normal steering functions. The proportional valves are selectively energized by a position sensor in response to rotation of a steering wheel. However, should an electrical malfunction occur, rotation of the steering wheel beyond the normal operating range causes a steering control member to mechanically move an armature of the proportional valves through a spring to provide mechanical/hydraulic steering. Making the armatures of the proportional valves responsive to a mechanical input through the springs provides a simple, cost effective mechanical/hydraulic backup for the primary electrohydraulic steering control.

Abstract: When an operator makes the reversing-lever operation by operating a control lever 4A in a direction x.sub.2 in the event a solenoid proportional valve 91A of a directional control valve 8A is failed to be left open, an operation position sensor 30A.sub.2 outputs a low-level signal and operation position sensors 30A.sub.1, 30B.sub.1, 30B.sub.2 output high-level signals. Therefore, an AND circuit 6b.sub.2 outputs a low-level signal and an AND circuit 6b.sub.1 outputs a high-level signal, whereupon a switch signal is output from an amplifier 6h to a solenoid switching valve 121 for shifting it to a right-hand position shown in FIG. 1 so that a pilot line 51 is kept communicated with a reservoir 97. No switch signal is output from the amplifier 6h to a solenoid switching valve 122 for holding it in a left-hand position shown in FIG. 1 so that the pilot line 52 is kept communicated with a pilot pump 96.

Abstract: A hydraulic system for a construction machine includes a pump for delivering fluid under pressure from a fluid reservoir to at least first and second main valves. First and second input devices are included for producing first and second control signals that are indicative of a desired operation of the hydraulic system. A controller responsive to at least the first and second control signals is provided and produces a compensating signal in response to the first and second control signals. The second main valve is operated in response to both the second control signal and the compensating signal.

Abstract: An automatic air balancer system capable of maintaining various kinds of load at a predetermined position and then moving the load at a desired speed, or applying a desired mechanical force to various kinds of object. The system includes a device for controlling the pressure at one end side of a balance cylinder to a desired level by a first pressure control valve and for controlling the pressure at the other end side of the balance cylinder to a predetermined level by a second pressure control valve, and a device for obtaining a balance pressure signal for the balance cylinder. Another signal is added to or subtracted from the balance pressure signal, and the resulting signal is input to the first pressure control valve.

Abstract: An exhaust manifold (25) of a fluid power and control system, the pressure of which is varied when the fluid motor (10) is subjected to a bidirectional positive or negative type load (W). This exhaust manifold (25) is also supplied from a source of exhaust manifold pressurizing oil (29) other than the system pump (18). This source of exhaust manifold pressurizing oil (29) may include a flow amplifying device (57) which is activated when the fluid motor (10), in the form of a cylinder, moves a load in the direction of its piston rod end (11) and when the piston rod end (11) of cylinder (10) is subjected to a negative load pressure and when the pressure in the exhaust manifold (25) drops below a certain minimum preselected level.

Abstract: A valve control unit includes a main hydraulic oil circuit and a pilot oil circuit. The main circuit includes a main pump, a main valve downstream from the main pump, and a hydraulic actuator downstream from the main valve. The pilot oil circuit circulates pressurized pilot oil to control the main valve and includes a pilot oil pump, an automatic control switching valve downstream from the pilot oil pump, a manual limit switching valve downstream from the pilot oil pump, a manual control switching valve downstream from the manual limit switching valve, and a pilot oil chamber downstream from the manual control switching valve. The pilot oil chamber is located near the main valve such that the flow of pressurized pilot oil moves the main valve.

Abstract: Disclosed is a rodless cylinder having a cylinder barrel with a slit formed axially therein. A piston is movably housed in the cylinder barrel. A mounting table is disposed movably along the external surface of the cylinder barrel and connected to the piston through the slit. An external actuator is mounted on the mounting table and designed to be driven by a pressure fluid. A passage, through which a pressure fluid can pass, is defined in the cylinder barrel. An inlet is provided in the cylinder barrel so as to introduce the pressure fluid in the passage to the mounting table side. An outlet is provided on the mounting table so as to supply the pressure fluid introduced from the inlet to the external actuator.

Abstract: A controller for a hydraulic motor (11) comprises a directional valve (12) for communicating hydraulic pressure fluid from a pressure source (10) to the motor (11), a pilot pressure operated activating device (13, 14), pilot valves (17, 18) connected to the activating device (13, 14) and to the pressure source (10), and a manually operable activating lever (15) mechanically connected to the directional valve (12) via a coupling (24, 55, 56). A pressure fluid operated actuator (25, 47, 48) is associated with the coupling (24, 55, 56) to shift the coupling when pressurized from an engaged condition and a disengaged condition, and a mode shifting valve (19) is connected both to the actuator (25, 47, 48) and to the pilot valves (17, 18) and is arranged to pressurize simultaneously the pilot valves (17, 18) and the actuator (25, 47, 48) of the coupling (24, 55, 56) to avoid double activation of the directional valve (12).

Abstract: This is an electro-pneumatic control device which includes a valve station (2) designed similar to a subassembly. The valve station (2) is provided with a fluid conductor (4) which is equipped with a plurality of valves (12) and a central electronic control unit which is formed by a control block (19). The control block (19) is a direct component of the valve station (2),so that a external central control unit is eliminated.

Abstract: A hydraulic control system for controlling a flow control valve to drive a hydraulic actuator in response to operation of a control device. This system includes a position detecting sensor for detecting a displacement of the control device, an operation detecting sensor for detecting an operating state of the flow control valve, and a hydraulic control unit for receiving detection signals from the position detecting sensor and the operation detecting sensor.

Abstract: Disclosed is a process for operating a pressure-operated positioning tool or gripping and clamping tool and a tool itself, in which the position of at least one adjusting member is determined and the valve-actuated supply of pressure medium to the adjusting member is regulated depending on position. To take into account the elasticity of the contact elements in the target position and to exert influence after the target position has been reached in a process and in a tool of the generic type, the regulating of the valve-actuated supply of pressure medium is not only effected in a position-dependent manner, but also takes into account the pressure of the pressure medium.

Abstract: A hydraulic circuit comprising at least two double acting hydraulic piston-cylinder devices, for opening and closing a folding roof of a vehicle, with both ends of each piston-cylinder device each connected to a conduit supplied with pressurized fluid by a common hydraulic pump and to a return conduit leading to a source of hydraulic fluid, via 3/2 electrically activated valves. The 3/2 valves include a main ball (22) and seat (22a), with a check valve (32) of the ball seat type upstream of the main ball seat in a connection to the conduit supplied with pressurized fluid.

Abstract: An electrohydraulic regulating device, particularly for a motor vehicle rear axle steering assembly, includes an adjusting cylinder. An electrically actuated control valve controls a hydraulic fluid flow to the adjusting cylinder. At least one electrically actuated switching valve blocks or admits a hydraulic fluid flow. A control unit generates control signals for the control valve and the switching valve. A regulating circuit supplies a pulse-width-modulated regulating signal for regulating a mean current of the control valve. A pulse-width-modulated control signal controls a mean current of the switching valve. The same supply voltage is applied to the switching valve and to the control valve. A pulse-duty factor of the control signal for the switching valve is referred to a pulse-duty factor of an adjusting signal for the control valve.

Abstract: The device according to the invention includes at least one rotational actuator fitted with a return spring and a connecting rod connected to the rotational actuator to transmit a linear movement to a mechanical part. The rotational actuator is moved by a rotational electromagnet whose angular position is controlled by a pulsed, periodic current. The device also includes apparatus for removal of the magnetizing energy stored in the electromagnet.

Abstract: A reciprocating piston fluid powered motor which has a fluid inlet and a fluid outlet. Reciprocation of the piston is controlled by a reciprocable valve spool which communicates with the fluid inlet and fluid outlet. The valve spool cooperates with a valve slide which is shiftable on said valve spool to control spool reciprocation. Fluid flow through the fluid inlet and outlet is controlled by electrically actuated solenoid valves connected in flow communication to the fluid inlet and a park port. An electric pulse width modulating switch is connected to each solenoid valve and has a plurality of positions to enable the piston to reciprocate at continuous low and high speed as well as in an intermittent mode. The switch may also be connected to an air powered washer fluid pump to deliver cleaning fluid on command.

Abstract: A closed loop control system for a pneumatic actuator using position and pressure feedback signals. The feedback signals are supplied to a microprocessor which successively generates a desired acceleration, a desired actuator force, a desired gas pressure, and a gas mass flow rate command for a gas flow controlling valve. The use of the gas flow rate as a control variable decouples pneumatic ronlinearities from the control loop. Nonlinear viscous friction, coulomb friction and load effects are decoupled from the control loop prior to the calculation of the desired pressure. An improved trajectory is achieved by employing a plurality of trajectory phases, including a velocity control phase.

Abstract: A system for hydraulically amplifying the deflection of a deflectable, resilient member into a greater displacement of a subject member. The system includes a deflectable resilient member, a fluid filled space in the pathway of and into which the deflectable, resilient member is deflectable, a subject member adjacent the fluid filled space, and an electroexpansive module for deflecting the deflectable, resilient member into the fluid filled space, wherein when the deflectable, resilient member is deflected into the fluid filled space the hydraulic pressure of the fluid in the space increases and acts against the subject member displacing the subject member a distance greater than the deflection of the deflectable, resilient member.

Abstract: The invention relates to a pressure regulation device for a hydraulic system comprising at least one generator (30) of fluid under pressure, a brake actuator (28) and a reservoir (32) of fluid under low pressure, and including an electrovalve controlled by a computer, the electrovalve being connected via a duct (29) to the generator (30) of fluid under pressure and via a duct (31) to the brake actuator (28), and comprising in a casing (8) an electrical coil (10) and a sliding magnetic core (12) controlling a slide valve (16) sliding in a bore provided in a body (18), the slide valve (16) determining two chambers (22, 40) arranged on either side of the slide valve (16) and being formed with a valve (48) with ball (50) co-operating with a seating (52) formed on the casing (8), the slide valve (16) being formed with a groove (34) delimited by two bearing surfaces (36, 38).

Abstract: In a stability compensating mechanism of an electro-hydraulic servo system which includes a load-displacement detecting unit for detecting a displacement of a piston of actuator or a displacement of a load connected to the piston, and a control valve for supplying a hadraulic oil to the actuator to drive the load and in which a piston-displacement detection signal of the load-displacement detecting unit is fed as a feedback signal back to a forward circuit and the control valve is operated by a deviation signal between the feedback signal and a command signal, the stability compensating mechanism comprising a valve-displacement detecting unit for detecting a valve displacement of the control valve and outputting a valve-displacement detection signal representative of the valve displacement, and a load-pressure computing unit for computing a load pressure that is acted on the actuator due to the load, on the basis of the piston-displacement detection signal of the load-displacement detecting unit and the valve

Abstract: In a hydraulic system, several consumers (4) are supplied by a common pump. In so doing, the consumers (4) are controlled by control valves (6). When the required oil flows exceed the quantity which can maximally be delivered, a control becomes operative which allows to adapt the reference value signals by which the valves (6) are controlled, to the actually measured pump flow, preferably to the weighting of the actually measured pump flow with the maximally predetermined pump flow.

Abstract: The present invention provides an apparatus for controllably actuating a work implement. The work implement includes at least a first linkage and a second linkage. The apparatus produces a control signal, senses the position and velocity of the first and second linkages and responsively produces position and velocity signals. The apparatus responsively produces a command signal as a function of the control signal and the position and velocity signals. The command signal controls actuation of the first linkage such that dynamic coupling between the first and second linkages is minimized.

Abstract: A hydraulic pressure control apparatus comprising: an introducing valve provided on a supply duct connecting to each other a hydraulic source and a control chamber for controlling a fluid-operated equipment or increasing or decreasing the hydraulic pressure of the fluid-operated equipment; and a discharge valve provided on a discharge duct discharging hydraulic fluid from the fluid-operated equipment or the control chamber. The introducing valve and/or the discharge valve are disposed in series on the supply duct or the discharge duct; at least one of a plurality of the introducing valves and/or the discharge valves consists of a flow rate-variable valve capable of changing the flow rate of the hydraulic fluid continuously according to the intensity of electric current; and the other introducing valves and/or discharge valves consist of electromagnetic change-over valves fully opened or fully closed.

Abstract: An apparatus for operating feed bars to move a workpiece between stages of a pressing machine includes cylinder devices. Each of the cylinder devices serves to move the feed bars linearly and each has a respective absolute encoder. The cylinder devices include a feed cylinder device which is responsive to hydraulic pressure to linearly advance and return the feed bars. First and second clamp cylinder devices are responsive to hydraulic pressure to move the feed bars linearly so as to clamp and unclamp the workpiece between the feed bars A hydraulic pressure supply circuit is connected commonly to each of the cylinder devices. Hydraulic pressure is applied to the cylinder devices through respective servo valves of a hydraulic valve arrangement.

Abstract: Apparatus for training an operator in use of electrohydraulics that includes an electric-motor/hydraulic-pump with an integrated fluid sump mounted on a portable support. An electrohydraulic valve on the support is preconnected to the pump, and has at least one solenoid valve responsive to valve control signals for controlling the valve to supply fluid from the pump. A hydraulic cylinder is carried on the support and preconnected to the valve for generating mechanical motion as a function of fluid supplied by the valve from the pump. An electronic controller is mounted on the support. A plurality of electrical connectors are mounted on an operator panel on the support and individually preconnected behind the operator panel to the valve controller, to the solenoid of the electrohydraulic valve and to a mechanism on the panel for generating an operator command signal.

Abstract: A hydraulic servo unit for changing the swash plate angle of a continuously variable transmission to vary its speed reduction ratio comprises a cylinder whose chamber is divided into a rod-side chamber and a head-side chamber by a piston slidably fitted therein. The rod-side chamber is supplied with working oil under predetermined hydraulic pressure through a first hydraulic pressure supply passage. A second hydraulic pressure supply passage is connected to the head-side chamber through a duty-cycle-controlled first solenoid-operated valve, and a drain hydraulic passage is connected to the second hydraulic pressure supply passage through a second duty-cycle-controlled solenoid-operated valve. The first and second solenoid-operated valves are simultaneously actuated with different duty cycles.

Abstract: The reliability of a fluid multiplexed actuation system is increased by arranging a pair of fluidic multiplexers in a parallel fluid flow path between a selector valve and several fluid actuators. Position sensors associated with the fluidic multiplexers and with the fluid actuators provide feedback signals to a microprocessor. In the event the feedback signals identify a malfunction in the fluidic multiplexer currently supplying fluid to the actuators, the microprocessor will deactivate the malfunctioning fluidic multiplexer and activate a redundant or back-up fluidic multiplexer by actuating the selector valve.

Abstract: A linear drive device has a linear motor which consists of a piston, an output rod and a control rod. The two rods extend through the two end plates of the motor housing. The working or output rod is designed for the transmission of power to some structure. The control rod cooperates a sensor for positioning. The sensor and also a valve arrangement is integrated in the housing end plate associated with the control rod. The valve arrangement controls flow through pressure fluid duct provided in the housing end plate at the control end for actuating the linear motor.

Abstract: The traverse apparatus of the subject invention is provided at the end of the main base 24 with a control box 38 having electromagnetic valves 57, 58, relief valves 59, 60, and manifold 61; and, one or more connectors 54 affixed at one end to sliding base 28 and at the other end to a separate sliding base 70. By these elements, the main body having cylinder 32 is separated from the rail guides 22, 23, the work of replacing a worn cylinder 32 is made easy, conveyance can be expedited, and the head mounting bases for attaching working heads can be increased readily.

Abstract: An apparatus for adjusting the pressure of working fluid provided to the load or user via a hydraulically actuatable control valve is provided. The apparatus includes a comparator that compares a given or desired control pressure for the control valve with the predominant present load pressure. The resulting pressure differential is used to re-adjust the control valve or to re-adjust a pressure compensator positioned upstream of the control valve with respect to the direction of the flow of working fluid flowing to the user.

Abstract: A fluid pressure operated piston engine assembly, such as a pump assembly, including a fluid pressure operated piston engine and a fluid valve for coupling fluid under pressure to alternative portions of the piston chamber of the piston engine. The fluid valve includes a valve spool which is translated to effect the alternative modes of coupling pressurized fluid to the piston chamber. The translation is accomplished by a shifter assembly having a shifter rod attached to the valve spool. The shifter rod includes a pair of diametrically opposed magnets attached thereto. A fork is attached to the piston engine drive shaft at one end and is mounted for limited movement along the shifter rod between the pair of magnets of the shifter rod.

Abstract: A moving speed regulator for a hydraulically driven work implement capable of automatically controlling the lifting speed of a boom, and regulating the maximum lifting speed thereof in particular during earth and sand scooping operation, and also having for its object to enable the lifting speed of the boom when the boom is lifted to a position near its highest position. This regulator comprises a pilot circuit (10) having a pilot pump (P); a hydraulic circuit for driving a work implement, which includes a work implement operating valve (g) adapted to be actuated by a pilot fluid pressure from a hydraulic pilot valve (i.sub.

Abstract: A fluid unit, for example a piston/cylinder unit, is supplied with fluid via a cyclically opened or closed on/off valve. The vacuum peaks occurring on the outlet side of the on/off valve when it is closed and the inertia forces of the flowing fluid are used to supply additional fluid to the fluid unit via a non-return valve leading from a low-pressure connection or reservoir to the fluid unit.

Abstract: A high efficiency pool heating system (10) includes a power circuit (12) and heat pump circuit (14). Each circuit having a working fluid flowing therein. In the power circuit, a heater (16) vaporizes the working fluid which is periodically delivered and exhausted through a valve section (32) to a driving section (28) of a power unit (26). The driving section drives a driven section (30) which operates as a compressor for the working fluid in the heat pump circuit. Fluid exhausted from the driven section of the power unit is passed to a first portion (48) of a heat exchanger (46) which is in fluid communication with the water of a pool. In the heat exchanger, the working fluid in the power circuit is condensed to a liquid. Thereafter, the liquid is passed through the power circuit back to the heater where it is again vaporized.

Abstract: The displacement of a variable displacement hydraulic pump (1) which is driven by a diesel engine (27) is so controlled as to be set to a first target displacement to keep a pump pressure higher than a load pressure by a predetermined target value, or a second target displacement to limit an input torque on the basis of the pump pressure. Provided is a stand-by flow rate control portion (65) which outputs a third target displacement larger than the minimum value of said first target displacement. The displacement of the pump (1) is controlled so as to be set to the third target displacement when the third target displacement is output from the stand-by flow rate control portion (65).

Abstract: A fail safe hydraulic system which includes a pressurized fluid storage which is capable of delivering fluid to the actuator to return it to its inoperative position should the actuator system suffer a loss of power and a apparatus for signaling a controller when the pressurized fluid storage has been charged with fluid, wherein fluid from the reservoir cannot be delivered to the actuator until the pressurized fluid storage has been charged with fluid.

Abstract: A control system is provided for use with a hydraulic system which includes a source of pressurized fluid, a plurality of flow regulator means, and a plurality of fluidly powered components. Each flow regulator means is adapted to receive the pressurized fluid and is responsive to a respective control signal for regulating the flow of pressurized fluid to respective fluidly powered components. The control system includes a plurality of control members, each being movable to a plurality of locations for indicating a desired fluid output for a respective flow regulator means. A plurality of sensors are provided for sensing the position of respective control members and responsively producing respective position signals. A primary controller is adapted to receive the position signals, process the received signals to responsively produce the control signals, and deliver the control signals to the flow regulator means.

Abstract: The pressure medium drive is provided for opening and closing the contacts (e.sub.1, e.sub.2) of an electric circuit-breaker. It contains a pressure medium reservoir (r), a drive piston (t) which slides in a drive cylinder (c) and acts on a mechanism (j) for displacing a movable contact (e.sub.1) of the circuit-breaker, and a reversing valve (s) for the selective connection of the pressure medium reservoir (r) to the drive cylinder (c) or of the drive cylinder (c) to an outlet volume for the pressure medium.This pressure medium drive is of simple, inexpensive construction and can open the contacts of the circuit-breaker considerably faster than it can close them.This is due to an interposed valve (v) which is disposed between the pressure medium reservoir (r) and the reversing valve (s) and has a flow cross section determined by the closing time of the contacts (e.sub.1, e.sub.2), and to the much larger flow cross section of the reversing valve (s).

Abstract: A valve assembly is disclosed in two embodiments for selectively controlling pressurized fluid flow to operate a fluid operated working cylinder and piston. The valve assembly includes a valve body, groups of three bores operably paired in the body, biased plunger valves interposed in each of the bores, and a separate passage inter-connecting between each bore group on one side of the interposed valves. There is provided a pressure connection to a first one of the bores in each group on the other side of the interposed valves away from the passage and a first side cylinder connection to a second one of said bores in one of each pair of groups. The other cylinder connection is provided to a second one of the other one of each pair of groups of three bores while an exhaust connection is provided to a third one of the bores in each group.

Abstract: In a hydraulic drilling machine with a boom, arm and bucket as working parts, one or more of the working parts can be vibrated automatically to perform effective drilling with reduced resistance in various types of operations when the soil changes. Adequate vibration can be automatically generated by setting the working mode (Bo, A, Bu, Sk) and vibration mode (L, M, S) according to the soil or operation form beforehand and by setting the automatic vibration mode. Furthermore, since the control input of the working part lever can be added to the automatic vibration, simple and minute repeated operations, such as pressure-shifting, sifting or drilling conducted while the bucket is vibrated, can be performed readily and uniformly without exhausting the operator, and workability can thus be greatly improved.

Abstract: The invention relates to a system for powering the driving actuator of an aircraft undercarriage, the system including a hydraulic generator capable of delivering fluid under pressure to one or the other of two chambers of the driving actuator. According to the invention, the power supply system includes a safety device enabling any overloading of the actuator rod under the effect of pressure peaks to be avoided: said device comprises two pressure relief valves, the first valve limiting the pressure delivered to the annular chamber and being under the control of the pressure in the full-section chamber, and the second pressure relief valve being of the differential type and continuously controlling the pressure difference between the two chambers of the actuator. The invention is applicable to providing very safe power supply systems for aircraft undercarriages.

Abstract: Herein described is a method and apparatus for controlling braking and stopping of the slewing of an upper slewing body which is slewingably provided on a construction and hoists a load, represented by a rotary crane, wherein the braking torque for braking the upper slewing body and the braking torque for braking a hoisting load are separately obtained by the calculated slewing angular acceleration, and the whole braking torque is calculated on the basis of both the braking torques, thereby achieving a high accurate control of the slewing stop.

Abstract: In a process for controlling an actuator which can be adjusted by means of a proportional valve, the proportional valve is controllable by means of two control magnets with control pulses acting in opposite directions. A phase angle between the control pulses is varied as a function of at least one control variable (command variable, correction variable or difference between the amplitudes or pulse durations of the control pulses), i.e. it is reduced as the control variable increases. This measure prevents undesired vibrations of the actuator and resulting noises.

Abstract: A drive system for a work vehicle is provided which includes first and second hydrostatic transmissions which are responsive to respective control signals for driving first and second ground engaging devices at a rate responsive thereto. A sensor is provided sensing the position of a manually operable control element and responsively producing a desired speed signal. A memory device is adapted to store data relates the desired speed signal to the first and second control signals in a preselected manner. A processor is provided for receiving the desired speed signal, responsively retrieving at least a portion of the data from the memory device, and producing the first and second control signals in response to the retrieved data and the desired speed signal. An adjusting device is provided for receiving at least one of the control signals, permitting controllable adjustment of the control signal so as to vary the speed of a respective ground engaging device.

Abstract: A delivery rate of a main hydraulic pump is controlled so that a load sensing differential pressure is held at a preset target value. In order to maintain the delivery rate of the pump substantially constant even in the case of external loads, inertial loads, and compressibility or leakage problems with the hydraulic fluid, there is provided a dead zone for permitting a deviation between the load sensing differential pressure and the preset target value.

Abstract: A rear wheel steering apparatus for a vehicle, comprises a hydraulic cylinder for displacing a steering rod connected to left and right rear wheels axially, a centering spring for biasing the steering rod toward a neutral position, and a centering spring cancelling mechanism for preventing a biasing force of the centering spring from acting on the steering rod. A partition wall of the hydraulic cylinder defines an oil chamber in the cylinder and is formed as a cup shape having a central concave portion which constitutes a pressure chamber of the centering spring cancelling mechanism.

Abstract: A hydraulic drive is actuated by a CNC means via an electrically actuable valve. The pressure applied to the hydraulic drive or the force excerted by the hydraulic drive is supplied in the form of a signal to a pressure control means or a force control means. The output signal of the pressure- or force control means is supplied via a switch means--shortly prior to reaching the desired position value of the drive--to the electrically operated valve as a control signal. Simultaneously, the output signal of the switch means, which can be supplied to the valve, is interrupted, wherein the switching range shortly prior to reaching the desired position value is smaller than the admissible differential value, determined by the CNC means, i.e.

Abstract: The mechanism has an actuator provided with a piston, a servo control valve which is actuated by electric input and output signals for supplying working fluid to the actuator and exhausting working fluid from the actuator, a slider which closes an oil passage from the servo control valve to the actuator and which temporarily engages with the piston of the actuator via a link mechanism, when a system for transmitting the input and output signals or the servo control valve breaks down, and a centering valve which is constructed in one body with the slider and which stops supply and exhaust of working fluid after the actuator has been returned to its neutral position by supply of working fluid to the actuator when a system for transmitting the input and output signals or the servo control valve breaks down.

Abstract: Fluid regeneration circuits are useful for filling expanding sides of a hydraulic motor with fluid being exhausted from the other side. The components of the currently available regeneration circuits are disposed in or adjacent to the directional control valve such that the fluid used for regeneration must pass through relatively long motor conduits between the control valve and the hydraulic cylinder. The regeneration circuit of the present invention includes a load check valve which forces the fluid exhausted from the head end chamber of a hydraulic motor to pass through a poppet valve controllably opened by a control signal. A low pressure relief valve causes an increase in the fluid pressure of the exhausted fluid passing through the poppet valve such that when the pressure level exceeds the pressure level of the fluid in an expanding side rod end chamber of the hydraulic motor, the exhausted fluid passes through a regeneration check valve and fills the expanding rod end chamber.