Railcar damping device

1. A railcar damping device that suppresses vibration of a vehicle body of a railcar by determining a thrust to be output by an actuator as a thrust command value and controlling the actuator,

wherein the actuator comprises:

a cylinder coupled to one of a truck and the vehicle body;

a piston inserted into the cylinder to be free to slide;

a rod inserted into the cylinder and coupled to the piston and the other of the truck and the vehicle body; and

a rod side chamber and a piston side chamber defined within the cylinder by the piston,

wherein the railcar damping device comprises:

a tank that is configured to store a liquid that is supplied to and discharged from the cylinder;

a first opening/closing valve provided in a first passage connecting the rod side chamber to the piston side chamber to be capable of opening and closing the first passage;

a second opening/closing valve provided in a second passage connecting the piston side chamber to the tank to be capable of opening and closing the second passage;

a pump that is configured to be driven to rotate at a predetermined normal rotation speed in order to supply the liquid from the tank to the rod side chamber; and

a control unit configured to:

compare the thrust command value with a preset normal lower limit value, which is a lower limit value of a thrust that can be generated by the actuator when the pump is rotated at the normal rotation speed, and

reduce a rotation speed of the pump when the thrust command value is smaller than the preset normal lower limit value.

2. The railcar damping device as defined in claim 1 , wherein the control unit is further configured to reduce the rotation speed of the pump when the thrust command value remains smaller than the normal lower limit value continuously for a predetermined time.

3. The railcar damping device as defined in claim 1 , wherein a low thrust rotation speed that is lower than the normal rotation speed is set in advance and the control unit is further configured to switch the rotation speed of the pump in two stages, i.e. between the normal rotation speed and the low thrust rotation speed.

4. The railcar damping device as defined in claim 1 , wherein the control unit is further configured to return the rotation speed of the pump to the normal rotation speed when the thrust command value increases to or above the normal lower limit value after the rotation speed of the pump has been reduced.

5. The railcar damping device as defined in claim 1 , wherein the control unit is further configured to return the rotation speed of the pump to the normal rotation speed when the thrust command value increases to or above the normal lower limit value after the rotation speed of the pump has been reduced and remains at or above the normal lower limit value continuously for a predetermined time.

6. The railcar damping device as defined in claim 4 , wherein, the control unit is further configured to vary the rotation speed of the pump over time when the rotation speed of the pump is returned to the normal rotation speed or reduced.

7. The railcar damping device as defined in claim 1 , further comprising:

an exhaust passage connecting the rod side chamber to the tank; and

a variable relief valve that is provided midway in the exhaust passage and has a modifiable valve opening pressure,

wherein the control unit is further configured to control the thrust of the actuator by adjusting the valve opening pressure of the variable relief valve.

8. The railcar damping device as defined in claim 1 , further comprising:

a suction passage that is configured to allow the liquid to flow only from the tank toward the piston side chamber; and

a rectifying passage that is configured to allow the liquid to flow only from the piston side chamber toward the rod side chamber.