Hydraulic drive apparatus

A hydraulic drive apparatus comprising:

• a displacement variable first hydraulic pump that includes a first displacement variable part and delivers pressurized oil to a plurality of hydraulic actuators including one traveling hydraulic motor;
• a first tilting actuator that drives the first displacement variable part to increase/decrease a delivery amount of the pressurized oil to be delivered from the first hydraulic pump;
• a first regulator that variably controls a control pressure that is supplied to/discharged from the first tilting actuator;
• a first proportional electromagnetic valve that is connected through a first oil passage to a pressure receiving chamber of the first regulator and supplies an output pressure to the pressure receiving chamber of the first regulator;
• a displacement variable second hydraulic pump that includes a second displacement variable part and delivers pressurized oil to a plurality of hydraulic actuators including the other traveling hydraulic motor;
• a second tilting actuator that drives the second displacement variable part to increase/decrease a delivery amount of the pressurized oil to be delivered from the second hydraulic pump;
• a second regulator that variably controls a control pressure that is supplied to/discharged from the second tilting actuator;
• a second proportional electromagnetic valve that is connected through a second oil passage to a pressure receiving chamber of the second regulator and supplies an output pressure to the pressure receiving chamber of the second regulator;
• a controller configured to control the first proportional electromagnetic valve and the second proportional electromagnetic valve;
• a switching valve that supplies the output pressure of the first proportional electromagnetic valve to the pressure receiving chamber of the second regulator at the time of driving at least any one of the one traveling hydraulic motor and the other traveling hydraulic motor, and
• a drive detecting device that detects a drive of at least any one of the one traveling hydraulic motor and the other traveling hydraulic motor,
• wherein
• when none of the one traveling hydraulic motor and the other traveling hydraulic motor are driven, the switching valve cuts off the connection between the first proportional electromagnetic valve and the pressure receiving chamber in the second regulator and establishes the connection between the second proportional electromagnetic valve and the pressure receiving chamber in the second regulator,
• when at least any one of the one traveling hydraulic motor and the other traveling hydraulic motor is driven, the switching valve cuts off the connection between the second proportional electromagnetic valve and the pressure receiving chamber in the second regulator and connects the first proportional electromagnetic valve to both of the pressure receiving chamber in the first regulator and the pressure receiving chamber in the second regulator, and
• when the drive of the traveling hydraulic motor is detected by the drive detecting device, the controller gives a command signal to at least the first proportional electromagnetic valve in such a manner as to supply the output pressure from the first proportional electromagnetic valve to both of the pressure receiving chamber in the first regulator and the pressure receiving chamber in the second regulator.