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 hydraulic motor control circuit for use in a device for driving construction equipment, such as shovel loader, which comprises a hydraulic driving motor, a pump for feeding compressed oil to the hydraulic motor and a tank for receiving the compressed oil discharged from the hydraulic motor. The circuit comprises a pilot operation type main valve for controlling the oil flow between the pump and the motor and between the motor and the tank, and a remote control valve for feeding a pilot oil pressure to a pilot chamber of the main valve to turn the main valve to a first position for driving the hydraulic motor. As a feature of this invention, the control circuit further comprises an apparatus for detecting the slanting angle of a downward slope and feeding an oil pressure corresponding to the slanting angle to a second pilot chamber of the main valve.

Abstract: The invention concerns a method and apparatus for improving the performance of a motor-controlled hydraulic elevator, in which oil is pumped using an hydraulic pump controlled by an electric motor from a container via a main supply duct into a lifting cylinder to move the elevator upwards, and returned in a controlled manner through the pump into the container to move the elevator downwards. In order to improve the loading conditions of the motor during down-travel, the oil pressure in the main duct is reduced to a substantially predetermined constant level by means of a check valve or lowering valve which, to provide compensation for the pressure in the pump, has a feedback connection to the main duct via a pressure compensation valve which controls the volume of flow through the check valve or lowering valve.

Abstract: In a hydrostatic transmission comprising a pump and a hydraulic motor arranged in a main line having low pressure and high pressure sections, wherein an oil drain line of the hydraulic motor is connected to the low pressure section of the main line, the housing of the hydraulic motor is freed from excessively high pressures in the main line by arranging a valve having an adjustable passage cross-section which decreases with increasing pressure in the main line before--in the direction of flow--the line connection of the oil drain line.

Abstract: Cushioned swing circuits sometimes have a restricted passage between the motor conduits to allow the implement controlled by the swing circuit to coast to a stop. However, opening and closing of the restricted passage was manually controlled, thereby requiring an additional manipulative step by the operator. The present cushioned swing circuit includes a cushion valve moveable to an open position to establish communication through vent line means when a pressure differential greater than a predetermined level is generated in one of the motor conduits connecting a directional control valve to a hydraulic motor. The cushion valve is retained in the open position for a predetermined limited time after the pressure differential drops below the predetermined level so that the inertia generated pressure in the circuit is dissipated through the vent line means.

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 braking system for a dumping vehicle having a hydraulic drive system and a hydraulic dump container is disclosed. A two-section control valve is connected by conduit to a hydraulic fluid reservoir and a hydraulic motor. The control valve includes a first valve assembly for controlling the dump container and a second valve assembly for controlling operation and direction of the hydraulic motor. An anti-cavitation valve and relief valve are provided to prevent locking of the vehicle wheels during braking. Walk-behind, riding-step and riding-seat variations of the invention vehicle are disclosed.

Abstract: A control valve (10) is disclosed for use in controlling a winch motor (12) on a winch. The control valve (10) is employed with a conventional operating valve (32). When the operating valve is in the neutral position, the control valve (10) acts as a hydraulic brake and an unloading valve for a brake cylinder (20). When the operating valve (32) is moved to raise a load with the winch, the control valve provides a flow path to and from the winch motor (12) to rotate the motor to raise the load and provides sufficient hydraulic pressure in the brake cylinder chamber (18) to release the brake even if the winch has no load. When the operating valve is operated to lower the load, the control valve (10) acts as an over center valve to prevent the load and winch from running away from the winch motor (12). The control valve (10) accomplishes each of these functions with only a single valve spool (132) slidable in a valve housing (100).

Abstract: The invention contemplates hydraulic-lift mechanism which employs a power integrator in the connection between a charged hydraulic accumulator and the actuator for a vertically positionable load; the power integrator, additionally, has a prime-mover connection, and the pressurized charge of the accumulator is advisedly set to fully accommodate a preselected level of average load upon the actuator. The hydraulic circuit importantly includes check valves, with a pilot-operated check valve interposed between the power integrator and the accumulator and another pilot-operated check valve interposed between the power integrator and the load actuator. The pilot-operated check valves cooperate with other check valves to assure automatic transfer of hydraulic fluid under pressure from the accumulator to the load actuator, and vice versa, as may be determined by selected control of or via the power integrator.

Abstract: An apparatus for locking of an inertial mass drive hydraulic circuit system having a hydraulic pump, an actuator driven by the hydraulic pump for driving a relatively large inertial mass, and a directional control valve mounted in line connecting the hydraulic pump with the actuator. An on-off device is interposed between the actuator and the hydraulic pump for opening or closing the line, and a sensor is provided for sensing the discharge condition of the hydraulic pump. The sensor generates a signal for actuating the on-off device.

Abstract: A hydraulic power system having a variable displacement hydraulic pump, a hydraulic motor driven by the hydraulic pump for actuating a load, with the pump and motor being connected to constitute a closed hydraulic circuit. A hydraulic servo controls the displacement volume of the pump, and a motor stop arrangement prevents, in its operative position, the motor from rotating. The system includes a control valve responsive to a main line pressure in the closed hydraulic circuit for controlling a hydraulic fluid supply to the hydraulic servo to prevent the main line pressure from substantially exceeding a predetermined level, and a control is responsive to the operation of the hydraulic servo for releasing the motor stop arrangement from the operative position when the hydraulic servo is operating.

Abstract: A fluid flow control valve assembly provides metering of the hydraulic fluid from a cylinder port at a constant desired rate for lowering a load at a corresponding constant rate which has been raised by the cylinder. The valve assembly comprises a normally closed valve having an input orifice communicating with the cylinder port and an output orifice and is selectively actuable for permitting the flow of fluid from the cylinder. A normally closed pressure compensating valve has an input orifice communicating with the normally closed valve output orifice, an output orifice, and a control input adapted for direct communication with the cylinder port for continuously sensing the fluid pressure within the cylinder. The pressure compensating valve maintains a constant fluid flow pressure differential and a constant fluid flow rate from the cylinder.

Abstract: A mixed loop hydrostatic transmission circuit for use principally with orbit, gear, vane and other non-piston type motors, which generate contaminants making them less suitable for applications using conventional closed loop hydrostatic transmission circuits. The mixed loop hydrostatic transmission drive retains the precise load control and high efficiency of a closed loop system, while introducing the benefits of contamination control of open loop hydrostatic transmission circuits. While maintaining the speed of the motor proportional to the output flow of the pump, both in positive and regenerative modes of operation, the flow of fluid is diverted from the motor to an injector type inlet booster connected to the reservoir, which supplies the full flow of fluid, required by the pump.

Abstract: An improved drive system includes a pair of hydrostatic transmissions which are driven by a common engine or prime mover and are drivingly connected with different tracks of a vehicle. The input to output speed ratios of the hydrostatic transmissions are simultaneously varied by operating a single speed control valve to port control fluid pressure to pressure responsive secondary or control motors in pump and motor actuators of the hydrostatic transmissions. A pair of charge pumps are provided to charge the hydrostatic transmissions and provide control fluid. If the fluid pressure output of either of the charge pumps falls below a predetermined level, a control arrangement reduces the control fluid pressure transmitted to the pump and motor actuators by the speed control valve to deswash or destroke both of the transmissions. The control arrangement also short circuits the hydrostatic loops interconnecting the pump and motor units. In addition, the brakes of the vehicle are engaged to stop the vehicle.

Abstract: A mixed loop hydrostatic transmission circuit for use principally with orbit, gear, vane and other non-piston type motors, which generate contaminants making them less suitable for applications using conventional closed loop hydrostatic transmission circuits. The mixed loop hydrostatic transmission drive retains the precise load control and high efficiency of a closed loop system, while introducing the benefits of contamination control of open loop hydrostatic transmission circuits. While maintaining the speed of the motor proportional to the output flow of the pump, both in positive and regenerative modes of operation, the full flow of fluid is diverted from the motor to the reservoir, while the full flow of fluid, required by the pump, is supplied directly from the system reservoir.

Abstract: A pressurized fluid supply apparatus comprises a closed circuit including a variable delivery pump, an open circuit including a pump, a fluid reservoir and a fluid cooler, and an engine for driving said pumps having an output shaft coupled to the drive shaft of said pumps, a flow-limiter being provided in the delivery conduit of said pump of said open circuit and including a restriction whose configuration is independent of the pressure of fluid in said delivery conduit upstream of said flow-limiter.