A pressure regulator includes an outlet pressure sensor, loading and unloading electromagnetic valves, and a regulator control circuit operatively connected to the loading and unloading electromagnetic valves and configured to pilot the loading and unloading electromagnetic valves to cancel an error signal given by a difference between an inlet signal corresponding to a desired outlet pressure and a feedback signal provided by the outlet pressure sensor. The pressure regulator includes an engaging current analysis circuit to detect and store reference characteristics of the engaging current of the solenoid of the loading electromagnetic valve in a stable inlet pressure condition, monitor the engaging current to detect any variation of its characteristics with respect to the corresponding reference characteristics, and, in the event of variation, provide a pilot modulation signal to at least one of the loading or unloading electromagnetic valves or a pressure variation signal to the regulator control circuit.

Windrow mergers employ one or more design features as described herein in connection with a suspension assembly that allows the pickup head to rise or fall relative to a frame of the merger. One feature maintains a substantially constant force or pressure between a pickup head of the merger and the terrain regardless of a height of the head. Another feature maintains a substantially constant hydraulic pressure in a hydraulic actuator that connects the pickup head to a frame assembly of the merger. Still another feature employs a hydraulic pump driven by a power takeoff (PTO) of the tractor to charge and discharge a hydraulic actuator arranged to raise and lower the pickup head of the merger between an upper limit and a lower limit.

Windrow mergers employ one or more design features as described herein in connection with a suspension assembly that allows the pickup head to rise or fall relative to a frame of the merger. One feature maintains a substantially constant force or pressure between a pickup head of the merger and the terrain regardless of a height of the head. Another feature maintains a substantially constant hydraulic pressure in a hydraulic actuator that connects the pickup head to a frame assembly of the merger. Still another feature employs a hydraulic pump driven by a power takeoff (PTO) of the tractor to charge and discharge a hydraulic actuator arranged to raise and lower the pickup head of the merger between an upper limit and a lower limit.

Provided is a hydraulic drive apparatus of a work machine capable of reducing a surge pressure. The hydraulic drive apparatus includes a control valve interposed between the hydraulic pump and a hydraulic actuator, an operation device moving the control valve in response to an actuator operation, an unload valve, an unload operation valve changing a pilot pressure of the unload valve in response to an input of an unload operation command, a target pressure calculation part, and an unload operation command part. The target pressure calculation part calculates a target pressure that increases with an increase in the holding pressure of the hydraulic actuator. The unload operation command part inputs an unload operation command to the unload operation valve to make the pump pressure of the hydraulic pump follow the target pressure.

A control valve assembly for a load handling vehicle such as forklift comprises a valve body having a bore and a spool located within the bore that is axially movable along the bore between at least two operating configurations. The valve body includes a service port connected to a hydraulic actuator, a pressure port connected to a pump, and a tank port connected to a hydraulic tank reservoir. The valve is reconfigurable between first and second operating configurations. In the first operating configuration the spool defines a fluid pathway connecting the pump port, the service port and the tank port such that in a first flow direction fluid is able to flow from the pressure port to the service port and the tank port, and in a second flow direction fluid is able to flow from the service port to the pressure port and the tank port. The spool is also controllable in the first operating configuration to variably restrict flow to the tank port. In the second operating configuration the spool defines a fluid pathway connecting the pressure port and the actuator port, and is controllable to variably restrict flow between the pressure port and the actuator port.

A hydraulic system (1, 50) for a load handling vehicle comprises lifting actuator (2, C1) that operates in a load lifting mode in which a load is induced on the actuator, and a load lowering mode in which the actuator provides hydraulic power PI to the hydraulic system. An auxiliary hydraulic actuator (4, 6, 8, C2) is also provided that has a hydraulic power demand P2. A hydraulic pump (10, 58) directs hydraulic power to the hydraulic lifting actuator and the at least one auxiliary hydraulic actuator. The hydraulic system is configured such that when the hydraulic lifting actuator is in the load lowering mode, it is required to simultaneously actuate the at least one auxiliary hydraulic actuator, and PI is greater than or equal to P2, hydraulic power may be channelled directly to the auxiliary hydraulic actuator from the hydraulic lifting actuator in order that the at least one auxiliary hydraulic actuator is actuated entirely by the hydraulic power from the hydraulic lifting actuator, and without the use of the pump.

Provided is a hydraulic drive apparatus of a work machine capable of reducing a surge pressure. The hydraulic drive apparatus includes a control valve interposed between the hydraulic pump and a hydraulic actuator, an operation device moving the control valve in response to an actuator operation, an unload valve, an unload operation valve changing a pilot pressure of the unload valve in response to an input of an unload operation command, a target pressure calculation part, and an unload operation command part. The target pressure calculation part calculates a target pressure that increases with an increase in the holding pressure of the hydraulic actuator. The unload operation command part inputs an unload operation command to the unload operation valve to make the pump pressure of the hydraulic pump follow the target pressure.

An example valve includes: a plurality of ports comprising: (i) a first port, (ii) a second port configured to be fluidly coupled to a reservoir, and (iii) a third port configured to be fluidly coupled to a source of fluid; a spool slidably accommodated in a sleeve; an annular chamber formed between the spool and the sleeve, wherein the annular chamber is fluidly coupled to the first port, and wherein a first flow area is formed between the spool and the sleeve to fluidly couple the annular chamber to the second port via the first flow area; and a solenoid coil, wherein when the solenoid coil is energized, a solenoid force the spool, thereby causing the spool to move, forming a second flow area between the spool and the sleeve to fluidly couple the third port to the annular chamber via the second flow area.

The present invention relates to An open center hydraulic system (100), the open center hydraulic system (100) comprising a tank configured to hold hydraulic fluid, a pump configured to provide pressurized hydraulic fluid from the tank, a shunt valve configured to adapt an first opening area between a first input port and a first output port of the shunt valve dependent on a first control signal, wherein the first input port is coupled to the pump and the first output port is coupled to the tank, a first actuator valve coupled to the first input port and configured to adapt a second opening area of the first actuator valve dependent on a second control signal, a hydraulic valve control unit configured to determine a first opening area value and a second opening area value based on user input data and a predetermined relation dependent on the user input data, sending the first control signal, indicative of the first opening area value and sending the second control signal indicative of the second opening area value.

An example valve includes: a plurality of ports comprising: (i) a first port, (ii) a second port configured to be fluidly coupled to a reservoir, and (iii) a third port configured to be fluidly coupled to a source of fluid; a spool slidably accommodated in a sleeve; an annular chamber formed between the spool and the sleeve, wherein the annular chamber is fluidly coupled to the first port, and wherein a first flow area is formed between the spool and the sleeve to fluidly couple the annular chamber to the second port via the first flow area; and a solenoid coil, wherein when the solenoid coil is energized, a solenoid force the spool, thereby causing the spool to move, forming a second flow area between the spool and the sleeve to fluidly couple the third port to the annular chamber via the second flow area.