Abstract: An oil hydraulic circuit for a hydraulic shovel with which a composite operation can be performed readily and smoothly without special skill in operation of the hydraulic shovel. The oil hydraulic circuit comprises a first actuator which can operate with pressure oil from a predetermined one or both of a pair of hydraulic directional control valve sets, a second actuator which operates only with pressure oil from the other hydraulic directional control valve set, a proportional changing over device interposed intermediately in a pipe line communicating the other hydraulic directional control valve set with a first actuator for adjusting the maximum meter-in opening value to the first actuator in response to a magnitude of a signal received at a signal receiving portion of the proportional changing over device, and a controller for arbitrarily adjusting the signal to be supplied to the signal receiving portion of the proportional changing over device.

Abstract: Described is a control circuit for a hydraulic power lift driven by a displacement pump which has a check valve releasable at least for lowering movements of the power lift, a actuation means switching the check valve off and on to control the flow from a pump line into an operating line leading to the power lift and vice-versa, and a load-sensing line carrying the load pressure and connected to the operating line, by which the variable-displacement pump is capable of being activated. The actuating means has an actuating unit switching the check valve off and on and a servo valve, activated simultaneously and controlling the flow to and from the power lift, with at least three switch positions. In the starting position of the actuating means, the latter connects the load-sensing line and the operating line, by way of the servo valve, with the tank and, after passage through a central position, the operating line with the pump line.

Abstract: A hydraulic vehicle brake system of the type having a high system return pressure is provided. In order to minimize the size and strength of brake return springs required, the invention provides a device to be interposed between the brake and the brake control valve. Preferred embodiments of the device include an inlet port communicating with a brake valve and an outlet port communicating fluid pressure to a vehicle brake. A control assembly is provided intermediate the inlet and outlet ports and includes mechanisms for amplifying the hydraulic pressure effect in the direction from the outlet port to the return pressure system so that the brake return pressure exerted by the brake return springs can be substantially less than the hydraulic system return pressure.

Abstract: A multiplexed hydraulic control system which avoids the use of a rotary multiplexer and thereby allows for random selection of the multiplexed outlet ports and variable dwell times for the respective ports. A single hydraulic input is multiplexed among a plurality of hydraulic outputs. A control system provides two types of signals: (1) modulation signals selected from a plurality of multiplexed input signals for producing a modulating hydraulic flow, and (2) selector signals for operating on the multiplexer means to route the modulated signal to the appropriately selected channel.

Abstract: This power plant utilizes a multi-cylinder hydraulic engine that has a plurality of pistons and cylinders arranged for reciprocal movement. Each piston is powered by a hydraulic fluid or air pressure. The fluid exhausted from one cylinder is sent to another cylinder to act as the inlet fluid to move that cylinder. The engine requires piston and cylinder arrangements in sets or multiples of four (such as 4, 8, 12, 16 and so forth) to provide a balanced system. The engine can be designed in many different arrangements such as four cylinder in line, four cylinder radial, eight cylinder radial, eight cylinder V-shaped, eight cylinder opposed and so forth. These cylinder arrangements can be linked together if desired to provide multiple engine power plants. The piston used in the present invention is a spool-type piston having distinct sections which create distinct upper and lower fluid areas in the cylinder.

Abstract: A hydraulic control valve is controlled and changed over by a hydraulic pressure output from a remote control valve. A change-over valve is provided between an output port of the remote control valve and a pilot port of the hydraulic control valve. The change-over valve connects the output port of the remote control valve to the pilot port of the hydraulic control valve when the remote control valve is operated, and it connects the pilot port of the hydraulic control valve to a tank when the remote control valve is set to the neutral position. The change-over valve comprises a hydraulic change-over valve capable of establishing the above states of connection by the hydraulic pressure output from the remote control valve, or an electromagnetic change-over valve capable of establishing the above states of connection by electrically detecting the operation of the remote control valve.

Abstract: A multiplexed hydraulic control system having a plurality of hydraulic channels for individually controlling the positions of a plurality of actuators in the respective channels in accordance with a corresponding plurality of electrical control signals. The system includes a relatively small multiplexing valve or valve array which has a common input and a plurality of individually selected outputs. The multiplexing valve has a control input which is responsive to a source of binary selector signals, such selector signals being used to directly address any particular channel connected to the multiplexer. The system also includes means for modulating a hydraulic signal in accordance with selected ones of the plurality of electrical control signals, and applying the modulated hydraulic signal to the multiplexer common input.

Abstract: Disclosed is a hydraulic control system mounted in a hydraulic circuit of a hydraulic excavator and adapted to increase the relief hydraulic pressure and the flow rate. In accordance with one aspect of the invention, a hydraulic control system for a hydraulic excavator having power constant control and cut-off control comprises: a variable relief valve (60) for increasing the pressure upon receipt of a pilot signal (Pc7), a solenoid valve (80) for connecting or disconnecting the pilot signal (Pc7), a variable cut-off control valve 10A which, upon receipt of a pilot signal (Pc6), cancels the cut-off control, a solenoid valve (70) for connecting or disconnecting the pilot signal (Pc6) and an electric circuit (X01) in which a switch (90) for opening or closing the solenoid valves (70, 80) is provided. In accordance with a second aspect of the invention, a timer is provided in the electric circuit (X02) used in the first aspect of the invention.

Abstract: A piston for an axial piston machine, comprising a hollow body having an axial cavity into which a filler piece of a material of lower specific gravity than the material of the piston is inserted which at least partially fills said cavity, said filler piece being secured axially in the cavity by a shoulder projecting radially inwards from the hollow body, is to be designed so that with simple construction a stable axial securing of the filler piece is ensured. This is achieved in that the filler piece has a recess arranged between its ends on its outer surface into which the section of the hollow body overlapping the recess is pressed in a form fitting and force locking manner.

Abstract: A twin master cylinder for a road vehicle brake system has master cylinders assigned respectively, to a front-axle brake circuit and to a rear-axle brake circuit. The master cylinders are arranged laterally next to one another in a common housing and are each actuable via an arm of a pivotable rocker with a variable ratio L1/L2 of the lengths L1 and L2 of arms of the rocker. A supporting element is provided which, by its support point on the pivotable rocker, marks the pivot axis of the rocker and, by support on a push-rod piece, transmits the actuating force acting on piece to the rocker. The supporting element is arranged between the rocker and the supporting surface of the push-rod so as to be displaceable transversely relative to the direction of exertion of the actuating force.

Abstract: A hydraulic circuit for a piece of construction equipment such as a hydraulic shovel. The operation of the hydraulic shovel is controlled by a number of hydraulic actuators which are provided with a high pressure oil through selector valves. A main relief valve prevents an excessive pressure from developing in the vicinity of a main pump, and port relief valves associated with the individual actuators prevent excessive pressures from reaching each actuator. Pilot lines carry a biasing oil pressure from a pilot pump to the main relief valve and to at least one of the port relief valves to boost the relief pressures in the circuit in response to a signal from an operator controlled switch. Simultaneously with effecting a boosting of relief pressure in the relief valves, the operator controlled switch renders one of the actuators inoperative using a shut-off valve so that it may not be operated while the relief pressures are boosted.

Abstract: In a hydrostatic continuously variable transmission in which a clutch valve capable of operating between a clutch-on position for setting a hydraulic closed circuit between a hydraulic pump and a hydraulic motor to a hydraulic transmitting state and a clutch-off position for setting the hydraulic closed circuit to a hydraulic transmission cutting-off state is connected to the hydraulic closed circuit, a pressure bearing chamber for urging the clutch valve to the clutch-off position, and a pressure regulating spring for urging the valve to the clutch-on position are provided in the clutch valve, and a clutch controller for regulating the set load of the pressure regulating spring is connected to the pressure regulating spring. Thus, the degree of the hydraulic transmission between the pump and the motor can be controlled as desired without influence of the viscous change of a working oil. The clutch valve is disposed at one axial end of a transmission shaft.

Abstract: A hydraulic braking system includes a piston disposed at a wall end of the bore of a master cylinder so as to move a normally open valve mechanism of the master cylinder toward a closed position by applying an output pressure from a boost device or dynamic hydraulic generator. Due to applying the output pressure of the boost device or the dynamic hydraulic pressure generator to the piston, the initial stroke of the brake pedal is reduced by decreasing the idle stroke of the master cylinder and the braking pressure is ensured from the master cylinder when the output pressure of the boost device or the dynamic hydraulic pressure generator is not applied.

Abstract: The problem of energy wastage in power drive units having fixed displacement hydraulic motors is avoided in a system having a variable displacement hydraulic motor (10) without the expense normally associated with such variable displacement systems by a construction which includes a variable displacement hydraulic motor (10) provided with a hydraulic actuator (14). A servo valve (12) is adapted to be connected to a source of hydraulic fluid under pressure and a controller (24) and is connected to the motor (10) for controlling the flow of fluid thereto in response to signals received from the controller (24). A flow limiter (16) is connected between the servo valve (12) and a return to the fluid source. A flow sensor valve (18) is connected across the flow limiter (16) and is responsive to flow therethrough to provide a hydraulic control signal to the actuator (14) to control the displacement of the motor (10).

Abstract: The position of a controlled system is regulated with a hydraulic actuator, which is directly linked to a hydraulic pump. The pump is driven in either direction by an electric motor, which is controlled by the output of rotatory direction and driving power generated from a controller based on a desired position and the feedback input of the actual position of the controlled system and the rotatory speed of the electric motor. The controller further includes a gain-variable amplifier for amplifying a deviation of the controlled value from a desired value with a gain characteristic curve of a shape appropriate to the controlled system, attaining a stable and well follow-up control of position.

Abstract: A crosshead piston bearing assembly is disclosed. The piston bearing comprises a part-cylindrical upper bearing segment, or slipper, and a pair of spaced part-cylindrical lower bearing segments, or ears, engageable with the upper segment to form a pair of spaced continuous circular bearing surfaces and having an anti-rotation projection on either the slipper or the piston bore. The slipper has an arcuate extent of less than 180.degree. to facilitate replacement of the slipper. The ears have a complementary arcuate extent. The slipper includes axially-spaced notches formed in the ends of the slipper to engage the ears to prevent the ears from moving inwardly into contact with the connecting rod.

Abstract: A hydraulic circuit suitable for use in a hydraulic operating circuit of a power shovel includes a hydraulic cylinder for driving a working component and a hydraulic change-over valve for selectively supplying the cylinder with a discharge oil pressure of a hydraulic pump driven from an engine. The hydraulic circuit prevents cavitation in an oil chamber of the cylinder and includes a pair of first signal receiving portions provided in the hydraulic change-over valve for moving the spool thereof in the forward and reverse directions away from a netural position, respectively, and a second signal receiving portion for pulling back the spool toward said neutral position.

Abstract: A method of controlling the slewing of a revolving superstructure of a hydraulic backhoe includes setting a swing mode selector valve in a driving position to supply fluid discharged from a pump through a supply-and-discharge line to a hydraulic motor to drive the hydraulic motor for a driving operation, setting one of a pair of relief valves provided between the swing mode selector valve and the hydraulic motor, associated with the supply side of the hydraulic motor for a set relief pressure higher than the set relief pressure of a main relief valve for limiting the pressure in supply-and-discharge lines to the set relief pressure of the main relief valve while the hydraulic motor is operating in a driving mode, and setting the other relief valve associated with the discharge side of the hydraulic motor for a set relief pressure lower than the set relief pressure of the main relief valve to limit the pressure in the supply-and-discharge line associated with the discharge side of the hydraulic motor to the se

Abstract: A slewing control device for a crane for supplying a discharge oil from a pump through a direction selecting valve to a slewing motor and for controlling a rotational direction of the slewing motor. The device includes a selector provided in a main circuit between the pump and the direction selecting valve for selecting either an unload condition of the pump where a hydraulic oil in the main circuit is communicated with a tank or an on-load condition of the pump where the communication from the main circuit to the tank is blocked. A controller outputs a select signal to the selector to select the unload condition in response to detecting a dangerous operating condition. The controller also outputs a pressure control signal to an electromagnetic proportional pressure control valve provided between the direction selecting valve and a discharge port of the slewing motor to control oil pressure on a discharge side of the slewing motor when slewing needs to be stopped.

Abstract: A control system for controlling a double-acting cylinder includes four pilot-operated, proportional-type poppet valves for controlling fluid flow between the cylinder, a pump and a reservoir. Four solenoid-controlled pilot valves operate the poppet valves in response to error signals generated by a control circuit. The control circuit receives a cylinder position feedback signal and an operator-generated command signal. The control circuit provides for float, shutdown, variable deadband and pressure adjustment operation.