A closed-loop hydraulic circuit associated with a swing mechanism of a machine is controlled to obtain both a pressure control during acceleration and deceleration of the swing mechanism and a velocity control during coasting. In this manner, a system pressure in closed-loop hydraulic circuit is maintained below a maximum allowable pressure during acceleration and deceleration, and the swing mechanism can be rotated at a desired constant speed during coasting. This is achieved by controlling a hydraulic actuator adjusting the displacement of a variable displacement pump in different control modes, depending on a comparison between a desired displacement of the pump and an actual displacement of the same.

A system and method is provided for monitoring a hydraulic power system having at least one light emitter and a button. The method includes powering on the hydraulic power system, receiving an actuation at the button and detecting a release of the button after a first time interval, and entering a diagnostic state. The method further includes retrieving a code and displaying the code by turning on the emitter in a first pattern. In some embodiments, a system and method is provided for regulating a temperature of a hydraulic power system. In some embodiments, a system and method is provided for controlling operation of a hydraulic torque wrench.

To provide a traveling control mechanism and a traveling control method capable of controlling a traveling mechanism taking into consideration operation contents of a remote control valve. The problem is solved by a traveling control mechanism comprising a remote control valve (21, 22, 23, 24), a pressure adjusting solenoid valve (61, 62), a setting mechanism (70), and a controller (60). The traveling mechanism (8) allows a traveling speed to be switched between a high speed and a low speed in accordance with an operation amount of the remote control valve (21, 22, 23, 24). An HST circuit (30) is provided with a pump (31, 32) and a traveling motor (33), the pump (31, 32) connects to a pilot line (41, 42, 43, 44) allowing a hydraulic oil supplied from the remote control valve (21, 22, 23, 24) to flow therethrough, a pressure sensor (45) is attached to the pilot line (41, 42, 43, 44), and a rotation sensor (65) is attached to the traveling motor (33). The controller (60) controls a pressure of the hydraulic oil supplied from the remote control valve (21, 22, 23, 24) independently of a manual operation of the remote control valve (21, 22, 23, 24), on the basis of a setting signal, a pressure signal, and a rotation speed signal. The remote control valve (21, 22, 23, 24) controls a flow rate of the hydraulic oil discharged from the pump (31, 32) by changing or keeping constant the pressure inside the pilot line (41, 42, 43, 44).

Provided is a construction machine on which a hydraulic closed circuit for driving a single rod-type hydraulic cylinder and a swing hydraulic motor is mounted and that has good swing deceleration responsiveness. In this construction machine that drives each of a single rod-type hydraulic cylinder and a swing hydraulic motor in a closed circuit, a minimum passage area from a second flushing valve to a tank in a case the second flushing valve is fully open is smaller than a minimum passage area from a first flushing valve to the tank in a case the first flushing valve is fully open.

A bi-directional pump connected to a motor by a pair of supply/discharge lines; a regulator changes the bi-directional pump tilting angle; and a controller controls the regulator based on a turning signal outputted from a turning operation valve. At the turning acceleration, at which the signal increases, the controller calculates a motor flow rate passing through the motor and an instruction flow rate determined based on the turning signal. If the instruction flow rate is greater than a reference flow rate obtained by adding a predetermined value to the motor flow rate, the controller controls the regulator so the bi-directional pump tilting angle is adjusted to a tilting angle realizing the reference flow rate. If the instruction flow rate is not greater than the reference flow rate, the controller controls the regulator so the bi-directional pump tilting angle is adjusted to a tilting angle realizing the instruction flow rate.

Hydraulic fluid flushing valve for hydrostatic units usable in closed hydraulic circuit propel applications, having a flushing valve housing with a first inlet port connected to a first working line, a second inlet port connected to a second working line, and a discharge port for draining hydraulic fluid. A two-sided flushing valve flushing valve spool which can be shifted is mounted within the flushing valve housing in a cylindrical valve bore, which, in a shifted position, enables a fluid flow from one of the first or the second inlet port at which the lower hydraulic pressure is present, to the discharge port. The flushing valve spool includes on each side a pressure surface each of which is connected to one of the two inlet ports. At each side of the flushing valve spool a flushing valve spring is located in the flushing valve housing in such a manner that, when the flushing valve spool is in its centre, non-shifted position, at each side of the flushing valve spool a distance between a spring contact surface on the flushing valve spool and a spring support surface in the flushing valve housing is greater than the axial length of the corresponding flushing valve spring.

The present disclosure relates to a hydraulic drive system having a hydraulic circuit architecture operable in first and second modes. In a first mode, a main hydraulic pump (22) is used to drive a hydraulic actuator (24) via a closed hydraulic circuit, and a charge pump (42) provides charge flow to the closed hydraulic circuit. In a second mode the main pump set to zero displacement and the charge pump (42) is used to drive the hydraulic actuator (24).

The present invention relates to a closed hydraulic circuit between a hydraulic pump and a hydraulic motor that are connected to one another via working lines, a flushing pump being provided in order to feed a pressure medium into the working lines, and an output connection being provided in order to discharge excess pressure medium from the working lines. At least one hydraulic consumer, which is provided to convert at least some of the volume flow discharged from the hydraulic circuit into mechanical power, is connected downstream of the output connection.

A hydraulic circuit is disclosed. The hydraulic circuit may include a hydrostatic pump to provide, at a flow rate, a fluid to a hydraulic motor, wherein the hydrostatic pump has a displacement, and wherein the hydraulic motor drives a swinging element; a swing circuit pressure sensor to sense a circuit pressure of the hydraulic circuit; a pilot pressure actuator to control, based on a supply pressure, the displacement of the hydrostatic pump; a pilot pressure override valve to control the supply pressure; and a controller configured to adjust, based on sensed signals and with the pilot pressure override valve, the supply pressure, wherein the sensed signals include: a circuit pressure signal based on the circuit pressure sensed by the swing circuit pressure sensor; and a sensed swing speed signal based on a swing speed of the swinging element sensed by one or more machine sensors.

A system and method is provided for monitoring a hydraulic power system having at least one light emitter and a button. The method includes powering on the hydraulic power system, receiving an actuation at the button and detecting a release of the button after a first time interval, and entering a diagnostic state. The method further includes retrieving a code and displaying the code by turning on the emitter in a first pattern. In some embodiments, a system and method is provided for regulating a temperature of a hydraulic power system. In some embodiments, a system and method is provided for controlling operation of a hydraulic torque wrench.