The valve module can be installed regardless of an oil level, for example of an oil level of an oil sump of a motor vehicle. By means of a buffer volume having an overflow it is always guaranteed that a leakage flow conveyed past a valve piston includes no air but consists solely of hydraulic medium, since the overflow guarantees a level of hydraulic medium which lies above an upper face of the valve piston in a preferred installation position. As a result, foaming of the hydraulic medium can be prevented. The valve module can also be installed above the oil sump, for example in an upper region of a gearbox of the motor vehicle. In addition, the oil from the overflow can be used for cooling/lubrication of further drive train components.

A fitting clearance of a relief valve functions as an air bleeding orifice. When a discharge pressure reaches a relief pressure so that the relief valve turns into a relief state, a spool is moved so as to limit flow-out of hydraulic oil through the fitting clearance. As a result, generation of air trapping is suppressed by air bleeding function of the relief valve in a closed state. Air in a discharge oil passage is discharged quickly in the initial period of the startup of an electric oil pump, thereby improving rise-up of discharge pressure. During normal pump operation in which the relief valve is held in a relief state, pressure loss due to flow out of the hydraulic oil from the fitting clearance is suppressed and consequently, an electric oil pump having substantially the same discharge performance as conventionally can be used.

A hydraulic control device for a hydraulic actuation machine including a main oil pump configured to supply oil to the hydraulic actuation machine, a sub oil pump configured to temporarily supply oil to the hydraulic actuation machine based on a drive request so as to compensate for an oil shortfall when supply of oil from the main oil pump to the hydraulic actuation machine is stopped or insufficient, and a drive unit configured to drive the sub oil pump, wherein when an elapsed time elapsed from a time point when the sub oil pump is driven reaches a predetermined time, the hydraulic control device generates an air discharge command for discharging air accumulated in the sub oil pump and outputs the air discharge command to the drive unit, and the drive unit drives the sub oil pump to discharge the air accumulated in the sub oil pump based on the output air discharge command.

A hydraulic control system includes a first oil passage, a first oil pump, a second oil passage, a second oil pump and a check valve. The first oil pump is disposed in the first oil passage. The second oil passage bypasses the first oil pump, includes an intake oil passage and a discharge oil passage, the intake oil passage and the first oil passage are connected to each other at a connection point, and the discharge oil passage includes an air vent hole. The second oil pump is disposed in the second oil passage, configured to take in oil from the intake passage, and configured to discharge the oil into the discharge oil passage. The check valve is provided between the connection point and the air vent hole, configured to restrict flow of the oil from the air vent hole toward the connection point via the second oil pump.

An automatic transmission is provided with a frictional engagement member that is operated by hydraulic pressure for shifting the automatic transmission, and includes an air vent opening. An automatic transmission controller includes a pressure regulator and a control section. The pressure regulator regulates the hydraulic pressure in response to a hydraulic pressure control signal. The control section performs an air vent operation of venting air from the frictional engagement member through the air vent opening. The air vent operation includes: a preliminary operation of setting the hydraulic pressure control signal to a preliminary pulse indicative of a preliminary value of pressure, wherein the preliminary value is lower than a normal value of pressure; and a normal operation of setting the hydraulic pressure control signal to a normal pulse indicative of the normal value, wherein the normal pulse follows the preliminary pulse.

A hydraulic control device includes a C1 relay valve 70 whose state is switched based on a signal pressure that is generated based on a line pressure PL, and a check valve 80 attached to a drain oil passage L7. A set pressure of the check valve 80 is adjusted to an oil pressure that is lower than the maximum oil pressure obtained by discharge capability of an electromagnetic pump 60 and higher than an SL1 pressure Psl1 remaining in a hydraulic servo of a clutch C1 when the state of the C1 relay valve 70 is switched after a mechanical oil pump 42 is stopped. Operation of the electromagnetic pump 60 is started before the state of the C1 relay valve 70 is switched after the mechanical oil pump 42 is stopped.

The valve module can be installed regardless of an oil level, for example of an oil level of an oil sump of a motor vehicle. By means of a buffer volume having an overflow it is always guaranteed that a leakage flow conveyed past a valve piston includes no air but consists solely of hydraulic medium, since the overflow guarantees a level of hydraulic medium which lies above an upper face of the valve piston in a preferred installation position. As a result, foaming of the hydraulic medium can be prevented. The valve module can also be installed above the oil sump, for example in an upper region of a gearbox of the motor vehicle. In addition, the oil from the overflow can be used for cooling/lubrication of further drive train components.

There present disclosure relates to a hydraulic apparatus for an agricultural work vehicle, the hydraulic apparatus including: a hydraulic passage, and an oil tank configured to store hydraulic oil supplied to the hydraulic passage; a hydraulic pump configured to supply the hydraulic oil to the hydraulic passage; an oil supply conduit disposed on the hydraulic passage, and configured to connect the oil tank and the hydraulic pump to each other; an oil return conduit disposed on the hydraulic passage, connected to the oil tank at one end thereof, and configured to guide the hydraulic oil to the oil tank; and an air drain conduit formed such that one end thereof is connected to the oil supply conduit and the other end thereof is connected to the oil return conduit, and configured to guide air, contained in hydraulic oil flowing through the oil supply conduit, to the oil return conduit.

There present disclosure relates to a hydraulic apparatus for an agricultural work vehicle, the hydraulic apparatus including: a hydraulic passage, and an oil tank configured to store hydraulic oil supplied to the hydraulic passage; a hydraulic pump configured to supply the hydraulic oil to the hydraulic passage; an oil supply conduit disposed on the hydraulic passage, and configured to connect the oil tank and the hydraulic pump to each other; an oil return conduit disposed on the hydraulic passage, connected to the oil tank at one end thereof, and configured to guide the hydraulic oil to the oil tank; and an air drain conduit formed such that one end thereof is connected to the oil supply conduit and the other end thereof is connected to the oil return conduit, and configured to guide air, contained in hydraulic oil flowing through the oil supply conduit, to the oil return conduit.