Abstract: When a swinging boom driven by a hydraulic cylinder stops, inertia causes continued motion of the boom which increases pressure in a chamber of the hydraulic cylinder. Eventually that pressure reaches a level which causes the boom to reverse direction. Then pressure in an opposite cylinder chamber increases until reaching a level that causes the boom movement to reverse again. This oscillation continues until the motion is dampened by other forces acting on the boom. As a result, an operator has difficulty in properly positioning the boom. To reduce this oscillating effect, a sensor detects when the cylinder chamber pressure increases above a given magnitude and then a determination is made when the rate of change of that pressure is less than a defined threshold. Upon that occurrence, a control value is opened to relieve the pressure in that cylinder chamber.

Abstract: When a swinging boom driven by a hydraulic cylinder stops, inertia causes continued motion of the boom which increases pressure in a chamber of the hydraulic cylinder. Eventually that pressure reaches a level which causes the boom to reverse direction. Then pressure in an opposite cylinder chamber increases until reaching a level that causes the boom movement to reverse again. This oscillation continues until the motion is dampened by other forces acting on the boom. As a result, an operator has difficulty in properly positioning the boom. To reduce this oscillating effect, a sensor detects when the cylinder chamber pressure increases above a given magnitude and then a determination is made when the rate of change of that pressure is less than a defined threshold. Upon that occurrence, a control value is opened to relieve the pressure in that cylinder chamber.

Abstract: An industrial lift truck has a boom that is raised and lowered by a first hydraulic actuator and a load carrier that is pivoted with respect to the boom by a second hydraulic actuator. In the event that the supply of hydraulic fluid for powering the actuators fails, the boom may be lowered by gravity by draining fluid from the first hydraulic actuator. To prevent a load from sliding off the load carrier as the boom descends, the load carrier is pivoted to maintain a substantially constant angular relationship to the ground. This is accomplished by selectively conveying fluid drained under pressure from the first hydraulic actuator into the second hydraulic actuator. Changes in the position of the boom are sensed and, in response, the flow of fluid into the second hydraulic actuator is controlled to produce corresponding changes in the load carrier position.

Abstract: A system for simultaneously operating first and second hydraulic cylinders has an inlet node for connection to a source of pressurized fluid and an outlet node for connection to a tank. A two-position, three-way primary control valve has a first port connected to the inlet node, a second port connected to the outlet node, and a common port. A first electrohydraulic proportional valve connects the common port to a first port of the first cylinder, and a second electrohydraulic proportional valve connects the common port to a first port of the second cylinder. A third electrohydraulic proportional valve connects the inlet node to a second port of the first cylinder and a second port of the second cylinder. Selectively operating the primary control valve and one of the third and fourth electrohydraulic proportional valves determines the direction in which the first and second cylinders move.

Abstract: An industrial lift truck has a boom that is raised and lowered by a first hydraulic actuator and a load carrier that is pivoted with respect to the boom by a second hydraulic actuator. In the event that the supply of hydraulic fluid for powering the actuators fails, the boom may be lowered by gravity by draining fluid from the first hydraulic actuator. To prevent a load from sliding off the load carrier as the boom descends, the load carrier is pivoted to maintain a substantially constant angular relationship to the ground. This is accomplished by selectively conveying fluid drained under pressure from the first hydraulic actuator into the second hydraulic actuator. Changes in the position of the boom are sensed and, in response, the flow of fluid into the second hydraulic actuator is controlled to produce corresponding changes in the load carrier position.

Abstract: A regeneration method for a hydraulic system enables the fluid being forced from a first actuator to be used to power a second actuator. Often the force of the load acting on a hydraulic actuator is used to move the actuator into a given position which motion forces fluid from the actuator. Rather than simply draining that fluid to the system tank, the fluid is routed to a second actuator to be powered when the pressure of the fluid draining at the first actuator is greater than the pressure required to power the second actuator. At other times the draining fluid can be used to drive the pump which has been configured to operate as a motor thereby driving the prime mover connected to the pump. Alternatively the draining fluid can be routed to an accumulator where it is stored under pressure until needed to power an actuator of the system. A unique bidirectional pilot operated poppet valve.

Abstract: A hydraulic system controls the flow of fluid to and from several functions on a machine. Each function has a valve assembly through which fluid is supplied under pressure from a source to an actuator and through which fluid returns from the actuator to a shared return line connected by a return line metering valve to the system tank. There are several regeneration modes of operation in which fluid exhausted from one port is supplied into the other port of the same actuator, which eliminates or reduces the amount of hydraulic fluid that must be supplied from the source. In some regeneration modes, input fluid for an actuator is obtained from another hydraulic function via the shared return line. In these regeneration modes an electronic controller operates the return line metering valve to restrict fluid from flowing into the tank from the shared return line, so that the fluid will be available to be supplied into an actuator port.

Abstract: A hydraulic system controls the flow of fluid to and from several functions on a machine. Each function has a valve assembly through which fluid is supplied under pressure from a source to an actuator and through which fluid returns from the actuator to a shared return line connected by a return line metering valve to the system tank. There are several regeneration modes of operation in which fluid exhausted from one port is supplied into the other port of the same actuator, which eliminates or reduces the amount of hydraulic fluid that must be supplied from the source. In some regeneration modes, input fluid for an actuator is obtained from another hydraulic function via the shared return line. In these regeneration modes an electronic controller operates the return line metering valve to restrict fluid from flowing into the tank from the shared return line, so that the fluid will be available to be supplied into an actuator port.

Abstract: An assembly of a pair of electrically operated bidirectional proportional control valves and a four-way direction control valve governs the flow of fluid to and from a hydraulic cylinder. The four-way direction control valve alternately connects a pump supply line to one of a pair of intermediate conduits and a tank return line to the other intermediate conduit. That connection determines the direction of movement of the cylinder piston. The intermediate conduits are coupled to chambers of the cylinder by a separate one of the proportional control valves which meters the fluid flow to or from the respective chamber. Thus the proportional control valves control the rate of piston movement.

Abstract: A discharge valve is provided to open an electrically controlled pilot valve in emergency situations such as during an electrical or hydraulic failure. The discharge valve has a poppet that operates in response to a pressurized control signal, which may be produced by a hand operated pump. When the poppet opens in response to the control signal, a path is established for fluid to flow from a control chamber of the pilot valve, thereby opening the latter valve.

Abstract: A pilot operated valve is provided to control a bidirectional flow of fluid between two ports. A main poppet selectively controls flow of fluid between the ports in response to pressure in a control chamber on one side of the main poppet. A pilot passage in the main poppet extends between the second port and the control chamber A first pair of check valves allow fluid to flow only into the pilot passage from the two ports. A second pair of check valves allow fluid to flow only into the control chamber from the two ports.

Abstract: A method of shifting a transmission having both a hydrostatic portion, including a variable pump (15), and a hydraulic motor (29), and a mechanical transmission (33) portion, including a shift cylinder (37). The method includes relieving the output torque of the motor (29), shifting the mechanical transmission to neutral, and controlling the. displacement of the pump (15) to synchronize motor output speed with the required input speed to the desired gear ratio of the mechanical transmission (33). Then fluid flow to the shift cylinder (37) occurs to shift to the desired gear ratio. The shifting method includes a series of steps in which the feasibility of the prospective shift is determined, and only when the prospective shift can be completed, without detriment to the operation of the vehicle, will the shift be completed. As a result, the shifting between low gear and high gear can occur without bringing the vehicle to a stop each time.

Abstract: A full fluid-linked steering system, especially for use in on-highway steering, in which the system includes a fluid controller (21) including a fluid meter (65) operable to provide follow-up movement to controller valving (87,89), in response to the flow of fluid through the meter. The controller (21) includes a centering or biasing spring assembly (75) which provides sufficient torque that, upon rotation of the steering wheel (W), fluid is communicated to the steering actuator (19) without relative displacement of the valving, thus providing driver with the desired road feel. The system includes an EHC valve assembly (23) which controls flow to or from the actuator (19) in response to appropriate input signals (113,115) to maintain steered wheel to steering wheel registry.

Abstract: A two speed gerotor motor in which the rotary disk valve (47) and the balancing ring (67) cooperate with a control valve assembly (87) to define four different fluid zones arranged within a housing (21) in a generally concentric pattern to provide a relatively compact arrangement. Among the four fluid zones one (95) is always connected to an inlet (51) while another (101) is always connected to an outlet (53). The middle two zones (97, 99) communicate with each other in the high speed, low torque mode. Operatively associated with the control valve assembly (87) is a shuttle valve (103) such that high pressure is always communicated to the middle two zones, such that high pressure is always circulated within the gerotor gear set (17) in the high speed, low torque mode. The control valve (87) includes a spool valve (107) including dampening passages (123, 125, 127) which dampen or cushion the shifting of the spool valve between the high speed and low speed conditions.

Abstract: A method of controlling a vehicle hydraulic drive system of the type including a plurality of fluid pressure actuated wheel motors (13,15) connected in a parallel circuit with a source (17) of pressure. A flow restrictor valve (65) is disposed in a downstream conduit (27) of each of the wheel motors (13,15). The method involves determining the theoretical fluid flow for each motor, the actual fluid flow through each motor, and generating an error signal (107) which is then used to bias the restrictor valve (65) toward a flow restriction position. The disclosed method can be used to achieve steering at greater than kinematic, by scrubbing the inside front wheel, or can be used to prevent wheel slip of propulsion wheels, or can be used to prevent scrubbing of a wheel during hydrostatic braking, or can even be used to achieve vehicle steering.

Abstract: A steering system for an articulated vehicle (11) including steering cylinders (19, 21) wherein the steering system includes a steering control valve (31) having a housing (33) fixed to a rear bogie portion (15). The steering control valve (31) includes a spool valve (49) receiving steering input and a follow up sleeve valve (51) which receives feedback representative of a change in the articulation angle of the front bogie portion (13) by means of a linkage arrangement (123, 117, 63). Either the follow up movement of the sleeve relative to the spool, to reduce main system flow, or the follow up of the sleeve relative to the housing, to reduce the load signal, is used as a way of cushioning the steering, as the front and rear bogie portions (13, 15) approach maximum articulation.

Abstract: A fluid controller (17) is disclosed of the type including a relatively rotatable valve spool (95) and valve sleeve (97) which define a series of variable control orifices (71-76) during normal steering operations. Fluid flow to a control port (27) is controlled by a variable control orifice (74). During small steering corrections, at relatively small valve displacements, the present invention provides an additional variable control orifice (155), which opens before the control orifice (74) opens. A form of check valve (153) is in series with the additional orifice (155), and downstream thereof, to prevent reverse flow from the control port (27) through the controller. The invention is especially beneficial in controllers of the dynamic load signal type including a load signal drain orifice (76) which is open to the system reservoir (R) at the relatively small displacements.

Abstract: A torque generator steering device (10) is disclosed of the type including a gerotor displacement mechanism (19) and valving (9), by the rotation of an input shaft (1) results in a hydrostatic power assist to an output shaft (2). In parallel with the power assist path, the input shaft (1) is connected by a torsion bar (15) to a connecting shaft (3) which, in turn, is connected to the output shaft (2). The connections between the torsion bar (15) and the connecting shaft (3), and between the connecting shaft (3) and the output shaft (2) are substantially zero backlash mechanical connections, thus providing a main torque transmitting path in parallel with the power assist path. Below a predetermined level of input torque, rotation of the input shaft (1) results in an immediate and corresponding rotation of the output shaft (2), thus providing a manual steering mode.

Abstract: A controller (11) and a system for controlling the flow of fluid to a fluid pressure operated device (C) are disclosed. The controller is of the type including a rotatable spool valve (35) and a relatively rotatable sleeve valve (37). Relative rotation between the spool and sleeve define a main fluid path (MFP) and relative axial movement therebetween defines an auxiliary fluid path (AFP). An actuator (65) generates a mechanical output (71) in response to an electrical input signal (CS) to move the sleeve (37) between its neutral axial position (FIG. 6) and an axial operating position (FIG. 7). Axial movement of the sleeve is controlled by a joystick (J). The system includes various sensors (S,PS,G,P), which can sense a predetermined condition and generate an interrupt signal to interrupt or change the gain of the electrical input signal (CS).

Abstract: An open-center fluid controller (15) is disclosed for controlling the flow of fluid to a steering cylinder (25). The controller includes a fluid meter (29) and valving arrangement (27), including a valve spool (43) and a sleeve (45), which define a main fluid path. The main path includes a fixed flow control orifice (86), a variable flow control orifice (87), the fluid meter (29), and a variable flow control orifice (89). In accordance with the invention, the spool and sleeve define an amplification fluid path (101), including a variable amplification orifice (99), in parallel with the main fluid path, and disposed to amplify the flow of fluid through the meter (29). In order to facilitate manual steering, the amplification orifice (99) reaches its maximum flow area when the spool and sleeve are in a normal operating position (FIG. 6). The amplification orifice then decreases and closes as the displacement between the spool and sleeve reach a maximum displacement (FIG. 7).