Abstract: A hydraulic system includes: a cylinder that moves a moving object in a vertical direction by extension and retraction of a rod; a first bidirectional pump connected to a head-side chamber of the cylinder by a first supply/discharge line; a second bidirectional pump connected to a rod-side chamber of the cylinder by a second supply/discharge line and coupled to the first bidirectional pump in a manner enabling torque to be transmitted between the first and second bidirectional pumps; a relay line connecting the first and second bidirectional pumps such that a hydraulic liquid discharged from one of the first and second bidirectional pumps is introduced into the other of the first and second bidirectional pumps; and a servomotor that drives the first or second bidirectional pump. At least one of the first and second bidirectional pumps is a variable displacement pump whose delivery capacity per rotation is freely variable.

Abstract: A hydraulic system includes: a cylinder in which an interior of a tube is divided by a piston into a first pressure chamber and a second pressure chamber; a first bidirectional pump connected to the first pressure chamber by a first supply/discharge line; a second bidirectional pump connected to the second pressure chamber by a second supply/discharge line and coupled to the first bidirectional pump in a manner enabling torque to be transmitted between the first and second bidirectional pumps; a relay line connecting the first and second bidirectional pumps such that a hydraulic liquid discharged from one of the first and second bidirectional pumps is introduced into the other of the first and second bidirectional pumps; and an electric motor that drives the first or second bidirectional pump. At least one of the first and second bidirectional pumps is a variable displacement pump whose delivery capacity per rotation is freely variable.

Abstract: A hydraulic pressure supply device includes: a hydraulic pump capable of changing a discharge capacity; an electric motor capable of changing a rotational frequency; a discharge capacity adjustment mechanism capable of adjusting the discharge capacity of the pump between a maximum and minimum discharge capacity; a pressure detector configured to detect pressure of an operating liquid discharged from the pump; a rotational frequency detector configured to detect the rotational frequency of the motor; and a controller configured to control operations of the motor and adjustment mechanism based on the rotational frequency, detected by the detector, to keep pressure of an actuator at arbitrary pressure, wherein, the controller controls the operation of the adjustment mechanism so the discharge capacity of the pump becomes a set lower limit discharge capacity. The set lower limit discharge capacity is set to be larger than the minimum discharge capacity and be adjustable by the controller.

Abstract: A hydraulic system includes: a cylinder in which an interior of a tube is divided by a piston into a first pressure chamber and a second pressure chamber; a first bidirectional pump connected to the first pressure chamber by a first supply/discharge line; a second bidirectional pump connected to the second pressure chamber by a second supply/discharge line and coupled to the first bidirectional pump in a manner enabling torque to be transmitted between the first and second bidirectional pumps; a relay line connecting the first and second bidirectional pumps such that a hydraulic liquid discharged from one of the first and second bidirectional pumps is introduced into the other of the first and second bidirectional pumps; and an electric motor that drives the first or second bidirectional pump. At least one of the first and second bidirectional pumps is a variable displacement pump whose delivery capacity per rotation is freely variable.

Abstract: A hydraulic system includes: a cylinder that moves a moving object in a vertical direction by extension and retraction of a rod; a first bidirectional pump connected to a head-side chamber of the cylinder by a first supply/discharge line; a second bidirectional pump connected to a rod-side chamber of the cylinder by a second supply/discharge line and coupled to the first bidirectional pump in a manner enabling torque to be transmitted between the first and second bidirectional pumps; a relay line connecting the first and second bidirectional pumps such that a hydraulic liquid discharged from one of the first and second bidirectional pumps is introduced into the other of the first and second bidirectional pumps; and a servomotor that drives the first or second bidirectional pump. At least one of the first and second bidirectional pumps is a variable displacement pump whose delivery capacity per rotation is freely variable.

Abstract: A hydraulic pressure supply device includes: a hydraulic pump capable of changing a discharge capacity; an electric motor capable of changing a rotational frequency; a discharge capacity adjustment mechanism capable of adjusting the discharge capacity of the pump between a maximum and minimum discharge capacity; a pressure detector configured to detect pressure of an operating liquid discharged from the pump; a rotational frequency detector configured to detect the rotational frequency of the motor; and a controller configured to control operations of the motor and adjustment mechanism based on the rotational frequency, detected by the detector, to keep pressure of an actuator at arbitrary pressure, wherein, the controller controls the operation of the adjustment mechanism so the discharge capacity of the pump becomes a set lower limit discharge capacity. The set lower limit discharge capacity is set to be larger than the minimum discharge capacity and be adjustable by the controller.

Abstract: A hydraulic system includes: a single-rod hydraulic cylinder; a variable displacement pump driven by a rotating machine; a rod-side supply line and a head-side supply line that connect the pump to the hydraulic cylinder; a first tank line that is branched off from the rod-side supply line and connects to a tank; a second tank line that is branched off from the head-side supply line and connects to the tank; and a flow rate adjuster. The flow rate adjuster is configured to: switch a delivery capacity of the pump to a first setting value when a pressure of the head-side supply line is higher than a pressure of the rod-side supply line; and switch the delivery capacity of the pump to a second setting value less than the first setting value when the pressure of the rod-side supply line is higher than the pressure of the head-side supply line.

Abstract: A hydraulic system includes: a single-rod hydraulic cylinder; a variable displacement pump driven by a rotating machine; a rod-side supply line and a head-side supply line that connect the pump to the hydraulic cylinder; a first tank line that is branched off from the rod-side supply line and connects to a tank; a second tank line that is branched off from the head-side supply line and connects to the tank; and a flow rate adjuster. The flow rate adjuster is configured to: switch a delivery capacity of the pump to a first setting value when a pressure of the head-side supply line is higher than a pressure of the rod-side supply line; and switch the delivery capacity of the pump to a second setting value less than the first setting value when the pressure of the rod-side supply line is higher than the pressure of the head-side supply line.

Abstract: The rotational frequency of a variable speed motor is set to a normal rotational frequency setting value (N1). A pressure variation range (?P) is detected based on a pressure detection value P, of a variable displacement pump, detected by a pressure detector. It is determined whether a determination that the detected pressure variation range (?P) is less than or equal to a pressure maintained state detection level (L1) has been continuously given for a period indicated by a timer setting value (T1). If the determination that the detected pressure variation range (?P) is less than or equal to the pressure maintained state detection level (L1) has been continuously given for the predetermined period, then it is detected that the current state is a pressure maintained state, and the rotational frequency of the variable speed motor is switched from the normal rotational frequency setting value N1 to a pressure maintaining rotational frequency setting value (N2(<N1)).

Abstract: The rotational frequency of a variable speed motor is set to a normal rotational frequency setting value (N1). A pressure variation range (?P) is detected based on a pressure detection value P, of a variable displacement pump, detected by a pressure detector. It is determined whether a determination that the detected pressure variation range (?P) is less than or equal to a pressure maintained state detection level (L1) has been continuously given for a period indicated by a timer setting value (T1). If the determination that the detected pressure variation range (?P) is less than or equal to the pressure maintained state detection level (L1) has been continuously given for the predetermined period, then it is detected that the current state is a pressure maintained state, and the rotational frequency of the variable speed motor is switched from the normal rotational frequency setting value N1 to a pressure maintaining rotational frequency setting value (N2(<N1)).