Abstract: A suspension system dampens motion between two components of a vehicle, such as the wheels and the chassis. An assembly of a cylinder and a piston is connected to both components. The piston defines first and second chambers in the cylinder and has a shaft with an end surface exposed to pressure within a third chamber of the cylinder. A first accumulator is connected to the first chamber by a first accumulator valve and a second accumulator valve connects a second accumulator to the second chamber. A damping valve alternately connects the third chamber to either the second chamber or a fluid tank wherein that connection defines the stiffness of the suspension system and is made in response to force acting on the suspension system. A load leveling circuit also is described.

Abstract: A hydraulic circuit controls flow of fluid between first and second ports of a hydraulic actuator, such as a cylinder/piston arrangement and each of a supply conduit and a tank return conduit. The hydraulic circuit operates in standard powered operating modes as well as powered and unpowered regeneration modes. In a powered operating mode, a conventional pressure compensated spool valve determines the velocity of the hydraulic actuator. A workport blocking valve connects one workport of the spool valve to the first port and the other workport is connected to the second port. A regeneration shunt valve is directly connected between the first and second ports of the hydraulic actuator. In a regeneration operating mode or a mix of powered and regeneration modes, a combination of the spool valve, the workport blocking valve, and the regeneration shunt valve determines the velocity of the hydraulic actuator.

Abstract: A hydraulic system has first and second functions in which separate control valves govern the flow of fluid between actuators and both a supply conduit and a return conduit. The second function is connected to a load sense passage. When pressure in the load sense passage exceeds a given level an anti-stall valve opens a restricted path between the supply and return conduits. Fluid flow through that restricted path reduces a likelihood that a prime mover driving the pump of the hydraulic system will stall. When only the first function is active the anti-stall valve is closed and does not affect the supply of fluid to that function.

Abstract: A system operates a hydraulic actuator, such as a cylinder, in one of several modes that include powered extension and retraction, self-powering regeneration modes in which fluid exhausting from one cylinder chamber is routed into the other cylinder chamber, and cross function regeneration modes wherein the fluid exhausted from one actuator is routed in the supply conduit to power a different actuator. A controller determines which modes are viable based on existing system conditions and selects from among the viable available modes. That determination is a function of the desired velocity for the actuator, the hydraulic load on the actuator, and pressures in the supply and return hydraulic conduits. The system also can recover potential or kinetic energy through pressure intensification which recovered energy can be used to power another simultaneously active hydraulic function or to drive the prime mover via an over-center variable pump/motor.

Abstract: When different implements are attached to an agricultural tractor, various hydraulic actuators on the implement are operated by connection to the hydraulic system on the tractor. A single hydraulic fluid connector on the tractor has first and second ports with a separate valve assembly provided to control fluid of fluid to and from each port. This enables one doubling-acting hydraulic actuator to be connected to both connector ports so that the fluid flow to and from the actuator is controlled. For a different implement, one single-acting hydraulic actuator can be connected to one connector port and another single-acting hydraulic actuator can be connected to the other port of the same connector. Individual operation of the valve assembly for each port in this case allows independent control of the two single-acting hydraulic actuators.

Abstract: A spool type control valve is operated by an electrically driven pilot valve. A pilot piston is attached to the control spool. As an electrical actuator moves the pilot spool, a greater pressure is applied to one side of the pilot piston than the other side, which causes movement of the control spool. When the control spool reaches the desired position, its positional relationship to the pilot valve defines a pressure differential across the pilot piston which exerts a net force on the control spool that counterbalances a spring force acting on the control spool. This defines an equilibrium position at which the control spool remains until subsequent motion of the pilot spool occurs which alters the pressure differential across the pilot piston.

Abstract: A check valve system controls the flow of fluid between a spool valve and a hydraulic actuator and includes a pilot operated check valve that is controlled by a lock-out valve. The check valve has a poppet that engages and disengages a first valve seat in response to a pressure in a control chamber. The lock-out valve has an inlet connected to the control chamber, an outlet connected to an opening in the bore of the spool valve, and an second valve seat between the inlet and the outlet. A valve member that selectively engages and disengages the second valve seat and spool of the spool valve applies force to the valve member which responds by moving into engagement with the second valve seat. Thus in one position, the spool valve maintains the lock-out valve closed which traps pressure in the control chamber which tend to keep the check valve closed.

Abstract: A hydraulic system provides failure protection by incorporating an isolator adjacent a hydraulic actuator. The isolator has a first port connected to the hydraulic actuator and a second port with an electrically operated isolation valve connected between those ports. A pressure relief valve responds when pressure in the hydraulic actuator exceeds a given level by relieving pressure thereby enabling the isolation valve to open without application of electricity and release the pressure in the hydraulic actuator. A control valve assembly is remote from the hydraulic actuator and connected to the second port for metering flow of fluid between a source and the hydraulic actuator.

Abstract: A hydraulic system has an electrohydraulic valve that controls flow of fluid to operate a hydraulic actuator, such as a cylinder or motor. A set of characterization data is provided which describes performance of the electrohydraulic valve as a function of changes in differential pressure across that valve. The hydraulic system is operated by specifying desired movement of the hydraulic actuator and in response deriving a desired valve flow coefficient which designates a level of fluid flow through the electrohydraulic valve. A compensated control signal is produced from the desired valve flow coefficient and the characterization data, to counter act effects that changes in differential pressure have on flow of fluid. The electrohydraulic valve is activated in response to the compensated control signal.

Abstract: Cushion chambers (8) disposed in the vicinity of both ends of a hydraulic cylinder (1) to throttle inflow or outflow of an operating oil caused by a piston (5) moving close to a piston stroke end, pressure sensors (16, 17) to detect pressures in the cushion chambers (8), and a control valve (13) disposed in a passage to supply/drain the operating oil to and from oil chambers (6, 7) of the hydraulic cylinder (1) for varying a flow amount of the operating oil are provided. A controller (9) varies an opening degree of the control valve (13) within a piston stroke end range based upon outputs of the pressure sensors (16, 17), adjusts a cushion pressure and controls a moving speed of the piston (5). Thereby deceleration degrees of the piston (5) can be freely adjusted within the piston stroke end range based upon a change of the operating conditions of the hydraulic cylinder (1).

Abstract: The flow of fluid to a hydraulic actuator is controlled by a valve assembly which operates in different metering modes at various points in time for energy conservation. The metering mode to use is selected in response to the hydraulic load acting on the hydraulic actuator. Specifically, the present magnitude of hydraulic load is determined and compared to first and second thresholds. Below the first threshold only a first metering mode is activated, and only a second metering mode is activated above the second threshold. A combination of the first and second metering modes is utilized when the hydraulic load is between those thresholds, wherein the metering modes are used in proportion to a proportional relationship of the hydraulic load to the first and second thresholds. Using a metering mode combination in this manner smoothes transitions between the first and second metering modes.

Abstract: A vehicle has an axle connected to a frame by at least one hydraulic cylinder with two chambers separated by a piston. A hydraulic circuit controls flow of fluid between two cylinder chambers and between the chambers and an accumulator to dampen motion of the frame relative to the axle. The hydraulic circuit includes a control valve and a pair of check valves arranged so that the single control valve is able to lock-out the cylinder to emulate a rigid connection of the frame to the axle, as needed.

Abstract: A servomechanism includes a controller which dynamically estimates the resistance of the solenoid coil in an electrohydraulic valve as part of determining a level of electric voltage to apply to open the valve. The servomechanism receives a current setpoint designating a desired electric current level and senses the actual level of current flowing through the coil. A proportional term is derived from the current setpoint and the actual level of current. Creation of a derivative term is based on the difference between the current setpoint and the actual level of current. A feedforward term is produced by estimating the resistance of the electrohydraulic valve and limiting the feedforward term to a predefined range of acceptable values. The proportional term, derivative term, and the feedforward term are summed to define a desired voltage level, and a PWM signal for driving the electrohydraulic valve is generated based on the desired voltage level.

Abstract: Pressure trapped in an inactive hydraulic actuator can result in the actuator moving in a direction which is opposite to that desired upon subsequent activation. The present method detects a trapped pressure condition and takes remedial action before activating the hydraulic actuator for motion. The pressure differentials across valves that control the fluid flow to and from the hydraulic actuator are used to detect a trapped pressure condition. In response to that detection, a selected valve is initially opened in a manner that releases the trapped pressure while producing motion in the desired direction. After the trapped pressure condition has been resolved, one or more other valves are operated to produce the desired motion of the hydraulic actuator.

Abstract: A pilot operated valve has a main poppet that selectively controls flow of fluid between first and second ports in response to pressure in a control chamber on one side of the main poppet. The main poppet has an aperture extending between the control chamber and the first port. A pilot piston slides within the aperture and has the pilot passage with a pilot orifice and a first disk spring biases the pilot piston with respect to the main poppet. A pilot valve element selectively engages the pilot orifice to open and close the pilot passage and thereby controls motion of the main poppet. Forces from the first disk spring and a pressure differential between control and pilot chambers alter a position of the pilot valve seat with respect to the main poppet. The change in position compensates for effects on valve operation due to variation of the pressure at the two ports.

Abstract: A machine member driven by a hydraulic actuator may oscillate, or wag, when the hydraulic actuator decelerates or stops. The degree of oscillation is a function of the machine member's ability to track a deceleration command, which ability varies with changes in the position of the machine member and the load force acting thereon. To reduce the oscillation, a command that controls operation of the hydraulic actuator is filtered using a filter function that changes with the machine member's load. The load force exerted on the hydraulic actuator which in turn can be designated by fluid pressure that results from the hydraulic actuator. Preferably, the frequency of the filter function is varied inversely with the magnitude of the actuator load force.

Abstract: A distributed hydraulic system locates a control assembly, that has electrohydraulic valves and a electronic controller, adjacent the respective hydraulically powered actuator controlled by that assembly. The control assembly includes a manifold block with ports to that the pump, tank return and actuator fluid conduits connect. One or more pressure ports are provided on the manifold block at which to sense pressure at different locations therein. A controller housing, in addition to containing an electronic function controller, also contains a separate pressure sensor for each pressure port, and is mounted against the manifold block so that each pressure sensor connects to a pressure port. The manifold block also has a pair of exterior walls that extend on opposites sides of the controller housing to protect the electronic controller. Other features that facilitate distributing the hydraulic control adjacent the actuators are provided.

Abstract: Cushion chambers (8) disposed in the vicinity of both ends of a hydraulic cylinder (1) to throttle inflow or outflow of an operating oil caused by a piston (5) moving close to a piston stroke end, pressure sensors (16, 17) to detect pressures in the cushion chambers (8), and a control valve (13) disposed in a passage to supply/drain the operating oil to and from oil chambers (6, 7) of the hydraulic cylinder (1) for varying a flow amount of the operating oil are provided. A controller (9) varies an opening degree of the control valve (13) within a piston stroke end range based upon outputs of the pressure sensors (16, 17), adjusts a cushion pressure and controls a moving speed of the piston (5). Thereby deceleration degrees of the piston (5) can be freely adjusted within the piston stroke end range based upon a change of the operating conditions of the hydraulic cylinder (1).

Abstract: A hydraulic actuator for an active of semi-active vehicle suspension system has a cylinder with a piston therein. A piston rod is attached to the piston and extends out of the cylinder. First and second chambers are formed on opposites sides of the piston enabling the piston to be driven in a manner that counteracts vibrations in the vehicle, A third chamber is provided in the cylinder for connection to a load leveling apparatus. A novel structure reduces the overall length of the hydraulic actuator. A displacement sensor is incorporated into the hydraulic actuator to provide an electrical signal that indicated how far the piston rod extends from the cylinder.

Abstract: A hydraulic system has at least one primary hydraulic functions and a plurality of secondary hydraulic functions all of which are connected in parallel to a supply conduit and a return conduit. A first pressure relief valve prevents pressure in the supply conduit from exceeding a first limit and second pressure relief valve prevents the pressure at the secondary hydraulic functions from exceeding the lower second pressure limit. Novel pressure relief circuits are provided which enable only two pressure relief valves to provide one of two pressure limits at more than two hydraulic functions.