Abstract: The present invention relates to an actuation device for the actuating of an adjustment surface of an aircraft such as an elevator, a rudder or the like, of landing gear or another aircraft or surface vehicle actuator, comprising an electrohydraulic actuator having a servo control cylinder, a pump for pressure fluid action on the servo control cylinder as well as an electric motor for the actuation of the pump, with the electric motor having a liquid cooling. In accordance with the invention, the actuation device is characterized in that a leak flow of the pump is guided over a leak passage through the electric motor to cool the electric motor.

Abstract: A hydraulic motor is driven by a fixed displacement, three stage gear-type pump. The three equal displacement sections provide 3 equally-stepped flows so that the hydraulic motor can have three speeds. Valving and controls are provided for remote on-the-fly shifting of the speeds, automatic pump unloading in neutral, and adjustable maximum pressure. A closed loop system permits use of a relatively small reservoir. The contamination tolerance of the system is greater than that of variable displacement piston-type pumps typically used. Direct recirculation of hydraulic fluid is provided for unused speeds to permit hydraulic fluid to recirculate in the pump without doing work. A unique control circuit is provided to control the first speed valve in conjunction with a logic cartridge which controls hydraulic motor direction to permit fluid flow to the hydraulic motor to be stopped when coming to neutral without slamming the hydraulic motor and rotating drill pipe to a stop.

Abstract: A method for reducing a torque load associated with an implement includes determining a speed associated with a power source, wherein the power source is configured to provide power to a hydraulic pump, determining a position associated with an implement system, and limiting a flow associated with the hydraulic pump based on the speed associated with the power source and the position associated with the implement system.

Abstract: A hydraulic circuit for a working machine includes hydraulic actuators which respectively drive a plurality of kinds of working devices and which are driven by a drive circuit having circuit states that correspond to the working devices, a directional control valve unit which, when one of the working devices is attached to the attachment, switches in response to a signal from a controller to select one of the circuit states, a detection sensor that detects the actual circuit state, and a display operated by the controller. The controller activates the display when the detected actual circuit state and the selected circuit state do not match.

Abstract: A hydraulic transaxle comprises: an axle; a hydraulic pump driven by a prime mover; a hydraulic motor fluidly connected to the hydraulic pump so as to drive the axle; a bypass fluid circuit bypassing between suction and delivery ports of the hydraulic motor; a bypass valve provided in the bypass fluid circuit; a bypass operation device for selectively opening or closing the bypass valve; and a reset mechanism for closing the opened bypass valve.

Abstract: A return to neutral mechanism for a dual hydrostatic transmission includes a plurality of return to neutral control arms, each return to neutral control arm biased toward a neutral position. Each return to neutral control arm moves in response to forward or reverse movement of an operator control, such as a stick or foot pedal. Additionally, switches are mounted to the return to neutral control arms. The switches enable starting of the engine if every return to neutral control arm is in a neutral position, and disable starting of the engine if at least one return to neutral control arm is out of the neutral position.

Abstract: A hydrostatic transmission on a tractor is operated by a microcontroller providing current commands to the hydrostatic transmission pump, and manual controls that provide signals to the microcontroller so the current commands cause the hydrostatic transmission to operate in either a first mode or a second mode. In the first or automatic mode the swash plate position may be continuously variable based on the position of a foot pedal. In the second or gear mode the swash plate may be moved to any of a plurality of discrete positions based on the position of a manually operable switch.

Abstract: A throttle potentiometer adapter provides a direct connection between a pivot nut on a hand throttle linkage and the internal sleeve of a potentiometer. The potentiometer provides a voltage output to an electronic controller, the voltage output corresponding to the position of the hand throttle. The adapter is of one-piece construction and includes a socket engaging the pivot nut and a shaft extending into the internal sleeve.

Abstract: An improved diagnostic system for a hydrostatic apparatus such as a hydrostatic transmission or transaxle is disclosed. A fastener having a port formed therein is used to connect a hydraulic component such as a center section to a housing. A diagnostic system may be located external to the housing and connected to the hydraulic circuit at least partially through the fastener port. A relief valve may also be located in the fastener and connected to the fastener port, or in a different fastener having a separate fastener port, to permit the fluid in the hydraulic circuit to be discharged to a sump.

Abstract: A hydraulic actuating device for a convertible top assembly of a motor vehicle. The actuating device comprises a hydraulic pump with an associated electric pump motor and one or more hydraulic actuators, each for driving an associated movable part of the convertible top assembly. The actuating device also comprises a control circuit for effecting a defined sequence of movements of the one or more actuators and feedback means, which are connected to the control unit, for feeding information relating to the sequence of movements of an actuator back to the control unit. The feedback means comprise means for measuring the electric power consumed by the pump motor, which means transmit a feedback signal to the control unit.

Abstract: A neutral start interlock for a hydrostatic drive system that uses potentiometers to electronically monitor at least the position of the hydrostatic displacement control such that the engine will not start unless such control is in the neutral position.

Abstract: An improved diagnostic system for a hydrostatic apparatus such as a hydrostatic transmission or transaxle is disclosed. A fastener having a port formed therein is used to connect a hydraulic component such as a center section to a housing. A diagnostic system may be located external to the housing and connected to the hydraulic circuit at least partially through the fastener port. A relief valve may also be located in the fastener and connected to the fastener port, or in a different fastener having a separate fastener port, to permit the fluid in the hydraulic circuit to be discharged to a sump.

Abstract: An agricultural-implement hydraulic circuit includes a pump supplying pressurized fluid to a first service line and a second service line via a feed line and a device for varying the flow rate of the pump. A distributor valve is disposed between the first service line and the second service line, with the first service line and the second service line being connected and disconnected according to a position of the distributor valve. A hydraulic motor is coupled to the first service line through the valve and discharges fluid to a return line. A hydraulic actuator is coupled to the second service line. An indicator-valve assembly is coupled to the feed line, with the indicator-valve assembly including an indicator sensitive to pressure in the feed line such that the indicator indicates a predetermined pressure in the feed line to an operator.

Abstract: A hydraulic circuit comprises a first and a second merging line capable of supplying pressure oil from a third pump for a third circuit to directional control valves in a first and a second circuit, respectively, and a merging valve for selectively communicating or cutting off the first and the second merging line with or from the third pump. The merging valve has a first shift position at which the third pump is connected to the second merging line, and a second shift position at which the third pump is connected to the first and the second merging line. The merging valve is shifted continuously between the shift positions. The hydraulic circuit can efficiently distribute pressure oil supplied from the third pump to the first and/or second circuit as well, and can prevent lowering of the operability of each of actuators connected to the first or second circuit.

Abstract: The invention creates a vehicle pneumatics overpressure regulating circuit 1 of a supply device of a pneumatic consumer 5 in a vehicle with an operating pressure. The overpressure circuit 1 has a compressed air source 3, which furnishes compressed air for the consumer 5; a pressure switch 8, by means of which the compressed air source 3 is turned on and/or off to supply the consumer 5 with compressed air; and a supply line 4, by way of which compressed air can be carried from the compressed air source 3 to the consumer 5. The pressure switch 8 can be subjected to a measured pressure via a pneumatic measurement line 7, which is separate from the supply line, and this measured pressure characterizes a state of the operating pressure of the consumer. As a result, extremely precise regulation of the requisite operating pressure is successfully achieved.

Abstract: A hydraulic oil flow controller for a construction machine comprises an operating valve 6 for supplying hydraulic oil discharged from hydraulic pimps 1 and 2 to an attachment, an attachment operating unit 11 for transmitting a pilot signal corresponding to the manipulated variable of the operating valve 6 and a solenoid control valve 12 for changing the flow characteristics of the pilot signal in accordance with a command from a controller 19. An increase and/or decrease signal is sent to the solenoid control valve 12 through the controller 19 from a monitor device 18 so that the flow of the hydraulic oil supplied to the actuator of the attachment is increased and/or decreased. Accordingly, a coefficient of fluctuation of the flow relative to a coefficient of fluctuation of the manipulated variable can be decreased in the work of the attachment of a hydraulic shovel and the operation efficiency upon operation of the attachment can be improved.

Abstract: A hydraulic circuit comprises a first and a second merging line capable of supplying pressure oil from a third pump for a third circuit to directional control valves in a first and a second circuit, respectively, and a merging valve for selectively communicating or cutting off the first and the second merging line with or from the third pump. The merging valve has a first shift position at which the third pump is connected to the second merging line, and a second shift position at which the third pump is connected to the first and the second merging line. The merging valve is shifted continuously between the shift positions. The hydraulic circuit can efficiently distribute pressure oil supplied from the third pump to the first and/or second circuit as well, and can prevent lowering of the operability of each of actuators connected to the first or second circuit.

Abstract: A hydrostatic steering system of the type including a fluid controller (21) for controlling the flow of fluid from a source (11) to a steering actuator (19) in response to movement of a steering wheel (W). The controller (21) is of the type having a fluid meter (65) including a moveable star member (95), the movement of which corresponds to the flow of fluid to the actuator (19). The controller includes a sensor assembly (125) which senses the movement of the star member (95) and generates an electrical signal (127) representative of the fluid flow through the fluid meter (65).

Abstract: The present invention relates to a hydro-transformer including a hydraulic machine, a switching valve and a control means. A work port of the switching valve, which may optionally be connected hydraulically with a pressure port of the switching valve or a drain port of the switching valve, is connected with a first port of the hydraulic machine. The second port of the hydraulic machine is in hydraulic connection with a drive member. The switching valve is driven by the control means in response to a signal characterizing the volume flow into the hydraulic machine. Where the driver member is a cylinder, its extension may be carried out at a constant velocity and independently of a load, and energy may be recovered upon retraction. Due to the provision of a further switching valve between the second part of the hydrostatic motor and the drive member, a higher pressure may be generated at the drive member in the presence of a low pressure at the pressure port of the switching valve.

Abstract: A method and apparatus for diagnosing components in high-pressure pumps to indicate when a component of the pump head is malfunctioning and to identify the malfunctioning component. In one embodiment, a high-pressure pump head incorporating a diagnostic system in accordance with the invention has a pressurization chamber and a pressurizing member at least partially received in the pressurization chamber. The pressurizing member moves within the pressurization chamber along an intake action to draw fluid into the pressurization chamber and along a pressurizing action to compress fluid in the pressurization chamber. An inlet fluid control assembly is coupled to the pressurization chamber to allow fluid to enter the pressurization chamber during the intake action, and a pressurized fluid control assembly is coupled between the pressurization chamber and an outlet chamber to selectively allow pressurized fluid into the outlet chamber during the pressurizing action.

Abstract: Description of a system of a thermodynamic steam pump for water propulsion, its heating, disinfection and sterilization, or propulsion of other liquids, characterized by use of water steam pressure as the propelling media of a liquid mass directly, without intermediate equipment to convert the energy, which is composed of a pressure tank, an electric input valve, steam under pressure provided by an external source and means for introduction by gravity of the liquid mass to be impulsed, with electromechanical elements to control level and flow, including a heat exchanger where recycled steam is forced through a tube panel which over heats the liquid thus eliminating the existing microbes and bacteria or just taking advantage of said heat exchanger to pre-heat and fluidify heavy crude oils or other viscous liquids with no expense of additional energy. This same thermo-hydro-dynamic system installed in a surface vessel (ship) can act as propulsor of the same by the action and reaction principle. (Jet propulsion.

Abstract: An alarm device, an improved squeeze-pad hydraulic system for a squeeze truck, and a method for converting an existing squeeze-pad hydraulic system of a squeeze truck into a squeeze-pad hydraulic system that alerts the operator of the squeeze truck when dangerously high hydraulic pressures are approached within the squeeze-pad hydraulic system are described. The alarm device comprises: an alerting device, operationally responsive to an electrical signal, having an input terminal for receiving the electric signal, and an alarm threshold switch comprising: a pressure transducing element in fluid communication with the hydraulic lines in a manner such that hydraulic fluid within the hydraulic fluid lines will exert a pressure on the pressure transducing element, and an electrical switching device, in electrical connection with the input terminal, for directing the electrical signal to the input terminal.

Abstract: An engine/pump control device for loaders is disclosed. The control device controllably distributes the output power (rotating force) of an engine to the travelling and working units of a loader in accordance with operational conditions of the loader, thus remarkably improving work efficiency of the loader. When the loader performs an operation requiring a high tractive force prior to the driving force of the working members, the control device opens the unloading valve thereby partially returning the output fluid of a hydraulic pump to a return tank while transmitting the surplus output power of the engine to the traveling unit. Meanwhile, when the loader performs an operation requiring a high driving force of the working members prior to the tractive force, the control device closes the unloading valve, thereby totally supplying the output fluid of the hydraulic pump to the actuators in order to generate a high moving speed of the working members.

Abstract: Each attachment for a hydraulically actuated device includes a digitally coded connector which informs a control device about its identity. The control device includes a library which relates the digitally coded identity with fluid parameters of pressure and flow rate required for operation of the hydraulically operated device. The control device outputs signals which control the accelerator of an engine, and also controls pump operations to establish the fluid parameters appropriate for the hydraulically actuated device. When a second device is actuated simultaneously with the original device, the control device automatically compensates with adjusted fluid parameters to permit optimum operation of both devices at the same time.

Abstract: A process for adjusting the characteristics of infinitely variable transmissions of a vehicle with two drive mechanisms including detecting the output speeds of the transmissions and comparing them by means of an operating variable to determine the gear ratio. Adjusting the gear ratio as a function of a deviation for matching the characteristics. The characteristics are completely carried out for the operating variable and are detected and stored in a close point sequence by measuring the output speeds. When the vehicle is travelling, the deviations of the characteristics are compensated by an electronic unit which influences the predetermined operating variables so that when the transmissions are operated with the same predetermined operating variable, the output speeds are identical despite different characteristics.

Abstract: In a hydraulic device at least one control valve with at least three control positions is connected with a variable capacity pump, whereby the controlling device of the variable capacity pump is connected with the supply line downstream the control valve via a feedback line with the purpose of adjusting the pump output so as to maintain a constant operational pressure gradient. The back flow pipe is conducted over the control valve, which is connected with the consumers by connecting valves associated to mentioned consumers, whereby a transducer is associated to the back flow pipe, which together with the transducer of the supply line constitutes a regulating variable for a control unit. This way a precise and energy saving regulation or control of the consumers in both flow directions by a control valve at a reasonable price is achieved.

Abstract: In a hydraulic system with a pump (1) and a load (4, 104), a pressure relief valve (16) is connected to the pump pressure side (3) and open when a difference between pump pressure and maximum load pressure exceeds a predetermined pressure. Pump pressure is controlled by a pump controller (22), such that the pressure difference set by the pressure relief valve is greater than a pressure difference set by the pump controller. A controller (20) presets the pump delivery rate, depending on changes in input signals (s1, s2) and regulates the pump delivery rate in dependence on a pressure difference signal (U). The pressure relief valve includes a position sensor, which generates the pressure difference signal.

Abstract: A hydraulic system has a pump (1) with at least one load (4, 5) and accompanying bi-directional valves (8, 8a). A first comparator (A) establishes which motor line (6, 7) is carrying the higher load pressure. A second comparator (B) establishes whether the input-side motor line (6, 7) allocated a directional signal identifying the direction of the valve displacement is carrying the higher pressure or whether a load (4, 5) is being operated with negative loading. Depending on the result of the comparison, the load pressure signal (y1, y2) can be processed differently.

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: A hydrostatic transmission with a pair of pump/motor connected in a closed loop state by a pair of hydrostatic circuit. The hydrostatic transmission comprises a differential pressure detecting means which detects the differential pressure between the circuits and a displacement correcting means which, in case an operation to establish a neutral status has been carried out, controls the displacement volume of the pump/motor on the side where the pumping action is carried out toward a direction in which the magnitude of this differential pressure is held within a set range.In case the set range is set to a value with which a vehicle cannot run, the phenomenon of creep running will not occur.

Abstract: A vehicle headboard defining a hydraulic oil storage tank for use on a vehicle is disclosed. The vehicle headboard can include a top header, a bottom header, a plurality of spaced apart transfer tubes connected between the top and bottom headers, and mounting brackets attachable to the vehicle. The top header has at least one fluid inlet, a plurality of outlets to the transfer tubes, and receives a portion of hydraulic oil in an interior volume. The bottom header has a plurality of inlets from the transfer tubes, at least one fluid outlet, and also receives a portion of hydraulic oil in an interior volume. The invention is mountable in place of a conventional headboard, and obviates the need for any further hydraulic tank, while placing the storage volume higher than the pump and also improving cooling. The headboard can accommodate various functional storage tank accessories.

Abstract: Overheating of hydraulic fluid in a hydraulic motor system subject to aiding loads can be avoided without paying a weight or volume penalty by providing a return port (64) adapted to be connected to the system return (22) in fluid communication with a cavity (46) within an hydraulic motor housing (32) that houses the swash plate (34). A pressure relief valve (62) is connected to the supply port (38) of the hydraulic motor (30) as well as to the return port (64) and is operative to open when the pressure at the supply port (38) increases as a result of an aiding load so as to allow recirculation of hydraulic fluid through the motor (30). By placing the swash plate cavity (46) in the recirculation line, increased heat sink capacity is added to the system without increasing weight or volume.

Abstract: A fail-safe electric actuator, for use with a control mechanism such as a valve, is disclosed. The actuator device eliminates the possibility of the control mechanism being locked in operative position by the interruption of electric power, by automatically and mechanically returning the control mechanism to its inopertive position as soon as current is cut off. This is accomplished by the release of a torsion spring, wound previously by the rotation of a fluid-driven vaned torque actuator in turning both the control-mechanism and the electric fail-safe actuator into operative position.

Abstract: A pumping unit particularly for pumping oil from an oil bore has an inner stationary cylinder unit and an outer cylinder unit reciprocatable relative to the inner unit by hydraulic fluid; the units are enclosed in a casing and the outer unit functions as a piston in the casing; as the outer unit moves downwardly in the down-stroke, under the action of gravity and hydraulic fluid, air in the casing beneath it is displaced into a reservoir to form a supply of pressurized air; in the upstroke the supply of pressurized air is exploited to drive the outer cylinder upwardly, aided by the hydraulic fluid.

Abstract: A method and a device for monitoring hydro turbine plants. The device comprises one or several hydro turbines, at least one of them having adjustable vanes. For optimum utilization of the available amount of water, the vane angles in the turbine are automatically adjustable in dependence on the level in the water dam, which level is measured at predetermined intervals. When the plant comprises several turbines, the level indicator is also used for start and stop.

Abstract: A hydraulic lifting and lowering system for battery-powered lift trucks includes an electronic control system which reduces or limits operator selected lifting commands in accordance with the current being drawn by an electric motor connected to drive a variable-displacement pump, and in accordance with the state-of-charge of the vehicle battery, to control a proportional valve which meters fluid flow to a lift cylinder.

Abstract: A hydrostatic transmission including a pump and motor unit wherein the pump unit is displaceable effectuated by an operative member integral to the pump unit. A neutral start switch communicating with a carrying machine is mounted in the pump unit to contact the operative member in a manner causing the neutral start switch to become operative only when the operative member is assuming a neutral position.

Abstract: A failure detection system for a hydraulic pump (1) having a displacement volume varying device (1a) and connected to at least one hydraulic actuator (4) to constitute a hydraulic circuit for driving the hydraulic actuator. The system includes means (7a, 7b) for sensing the discharge pressure of the pump, means (6) for detecting the value of shifting of the displacement volume varying device, means (5, 24) for closing the hydraulic circuit to block the flow of a hydraulic fluid through the circuit, starting means (9) for giving a command to start checking on the pump to see if it is normally functioning, and a control unit (2, 23, 28, 29) for performing checking on the pump to see if it is normally functioning. The control unit includes means (S-5, S-5') responsive to the command given by the starting means for giving a command to activate the closing means, data collecting means (S-11) for causing the displacement volume varying device to shift based on information (P.sub.a, P.sub.

Abstract: An hydraulic supply circuit for a vehicle power steering system of the type having a steering actuator and control valve therefor with hydraulic input, sump and overflow (by-pass) connections and in which any fluid not actually consumed by the actuator is diverted to the overflow connection. A positive displacement pump is provided having an output line connected to the input connection of the steering system. An accumulator having a charging line and a discharging line is used to supply fluid pressure in lieu of the pump. To control flow of fluid to and from the accumulator a charge-discharge valve is provided having charge and discharge modes. In the charge mode the accumulator is charged by the overflow and in the discharge mode pressure fluid is supplied from the accumulator to the input connection for maintaining the steering system in operation while blocking the overflow.

Abstract: A hydraulic fluid power system includes an accumulator which stores a reserve of pressure fluid at pump standby pressure. The charging and discharging of the accumulator is controlled by an emergency steering valve which is operable in response to a predetermined minimum fluid pressure outputted by the steering pump to discharge the stored fluid for emergency steering. The emergency steering valve also has components which serve as a pressure switch which is actuated to complete a circuit through an indicator light whenever the emergency steering valve moves to effect the discharge of the accumulator. The steering valve components are arranged so that premature actuation of the indicator light during pressure drops of short duration are avoided.

Abstract: A hydraulic fluid power steering system includes an accumulator which stores a reserve of pressure fluid at pump standby pressure. The charging and discharging of the accumulator is controlled by an emergency steering valve which is operable in response to a predetermined minimum fluid pressure outputted by the steering pump to discharge the stored fluid for emergency steering. The emergency steering valve also has components which serve as a pressure switch which is actuated to complete a circuit through an indicator light whenever the emergency steering valve moves to effect the discharge of the accumulator.

Abstract: A multipurpose, hydraulically actuated apparatus comprising a piston movable in response to fluid under pressure within walls defining a piston chamber. Actuating fluid is supplied to the piston chamber by a uniquely constructed hand operated fluid pump. The area of the fluid impinging surface of the piston is in multiples of one inch. Accordingly, when the apparatus is used as a hydraulic scale the weight being lifted by the piston can be read directly on a pressure gauge which is calibrated in pounds per square inch and which is connected to the piston chamber below the piston.The apparatus can readily be converted to function as a cutting device by connecting a U-shaped member to the walls of the unit and by connecting a cutting element to the outer face of the piston. The U-shaped member includes spaced apart arms and a bight portion defining a closed space adapted to encircle the nut which is to be cut.

Abstract: A hydraulic system having a reservoir fed charge pump supplying pressurized fluid through a charge passage and a filter to the inlet of a supply pump for direction controlled fluid devices includes a reservoir connected unloading valve assembly connected to the charge passage and parallel with the filter. The fluid devices return fluid through a return passage connected to the unloading valve assembly which maintains back pressure on the devices at charge passage pressure. The unloading valve assembly includes an unloading valve movable in response to a predetermined fluid pressure at the inlet of the supply pump to unload the charge and return passage by connecting them to the reservoir. As the devices require more fluid from the supply pump causing the pressure at the inlet of the supply pump to drop, the unloading valve proportionately blocks the charge and return passages from the reservoir to circulate return fluid into the charge passage.

Abstract: An electronic control device for hydraulic presses for making plywood and the like having electronic computer structure for developing a control for the desired hydraulic pressure having multiple input units on which at least the width, length and unit pressure may be set into the device for automatically effecting the calculation of the required hydraulic line pressure in order to apply the proper pressure upon the laminated plywood panels. The control device also anticipates maximum line pressure and cuts off the hydraulic pump(s) before the desired pressure is reached so that the inertia of the pump(s) and motor(s) will not increase the resultant line pressure above the predetermined desired pressure.

Abstract: Plural servo actuators are coupled to provide a redundant system for operating a common output device. Each servo actuator has plural servo valves each having one active output that causes controlled opposite operation of the output device and one passive output. A fault detector coupled to each servo actuator compares the sum of the passive output pressures with the pressures of two other fluid signals, in one case the supply and return fluid signals and in another case the two active output signals of the servo valves, to detect the condition thereof. A convenient checkout system and a fluid by-pass mechanism also are provided in the fault detector.

Abstract: A hydraulic valve actuator includes at least one piston mounted for reciprocating movement in a cylinder for bidirectionally rotating a valve shaft mounted in the housing. A resilient spring member is held in compression between one side of the piston and an end wall of the cylinder for yieldably urging the piston to rotate the shaft in one direction, in the absence of a sufficient opposing hydraulic pressure. A hydraulic pump driven by an electric motor selectively drives the piston against the force of the spring member for rotating the valve shaft in the opposite direction. An electric solenoid operated valve is connected with the cylinder at either side of the piston, to provide a selectively openable path for hydraulic fluid, by-passing the pump to relieve the pressure applied thereby.

Abstract: A vehicle hydraulic power brake and steering system has a hydraulic brake booster provided with a mechanism for operating a switch to indicate loss of hydraulic power, and for operating a control valve for admitting hydraulic pressure from another source such as an accumulator. The mechanism includes an actuating bar mounted in a recess formed in the wall of the hydraulic brake booster power cylinder and lying in the power chamber of the booster. The bar extends axially for a distance substantially equal to the power stroke of the power piston. An annular valve seat has a ramped groove which actuates a ball positioned in a radially extending passage of the booster piston and engaging the actuating bar in rolling contact. So long as hydraulic power pressure is available, the ramped groove does not move the ball radially outward.