Electro-hydraulic actuator and brake device

An electro-hydraulic actuator comprising:

• a motor that outputs rotational power;
• a pump operated by the rotational power of the motor;
• a hydraulic actuator operated by hydraulic fluid pressurized by the pump;
• a reservoir for storing the hydraulic fluid;
• and
• a hydraulic circuit for hydraulically controlling operation of the hydraulic actuator,
• wherein the hydraulic actuator reciprocates between a first operating state and a second operating state in response to a hydraulic pressure of the supplied hydraulic fluid, and is constantly biased in a direction returning to the first operating state;
• wherein the hydraulic circuit includes:
• a pressurizing flow path for supplying the hydraulic fluid pressurized by the pump to the hydraulic actuator;
• a pressure reducing flow path that connects the hydraulic actuator and the reservoir via an unloading valve in an openably closable manner;
• a pilot flow path for supplying hydraulic oil pressurized to a pilot pressure to the unloading valve in order to close the pressure reducing flow path;
• a pilot pressure generating mechanism that generates the pilot pressure;
• and
• a check valve disposed within the pressurizing flow path for allowing the hydraulic fluid to pass only in a forward direction from the pump to the hydraulic actuator,
• wherein the pilot pressure generating mechanism generates the pilot pressure during operation of the pump,
• the pilot flow path branches off midway from the pump to the check valve in the pressurizing flow path and reaches the unloading valve, and
• during operation of the pump, the pilot pressure is generated, causing the pump to transition to the second operating state, and when the pump stops, the pilot pressure disappears, the pressure reducing flow path is opened, and the pump returns to the first operating state,
• wherein the pilot pressure generating mechanism is composed of an unloading relief valve having a parent valve and a child valve, and a throttle mechanism,
• the parent valve has a built-in throttle valve, a parent valve primary port connected to the pilot flow path, a parent valve secondary port connected to a flow path communicating with the reservoir, a parent valve pilot port communicating with the parent valve primary port via the throttle valve, and has, with a predetermined direction being the up-down direction, a parent valve spool that is urged upward by hydraulic pressure at the parent valve primary port, and a parent valve spring that urges the parent valve spool downward,
• the child valve has a child valve primary port connected to the parent valve pilot port, a child valve secondary port connected to a flow path communicating with the reservoir via the throttle mechanism, and a child valve pilot port connected to a flow path from the check valve to the hydraulic actuator, and has, with a predetermined direction being a vertical direction, a valve body that is urged upward by hydraulic pressure at the child valve primary port, a child valve spool that is urged upward by hydraulic pressure at the child valve pilot port, and a child valve spring that urges the valve body downward,
• the child valve distributes hydraulic pressure P1 at the child valve primary port into hydraulic pressure P2, which presses the valve body upward, and hydraulic pressure P3, which presses the child valve spool downward, with P2>P3, and when the hydraulic pressure P1 reaches a predetermined cutout pressure, the valve body is pressed in one direction, opening the child valve primary port and the child valve secondary port to enter an unloaded state,
• the parent valve spool is pressed upward by a pressure difference between the hydraulic pressure P1 on the parent valve pilot port side, which has been reduced in association with the unloaded state of the child valve, and hydraulic pressure P5 on the parent valve primary port side, thereby opening the parent valve primary port and the parent valve secondary port and putting the parent valve in an unloaded state,
• when the child valve is in an unloaded state, the unloaded state is maintained by hydraulic pressure P4 at the child valve pilot port,
• when both the parent valve and the child valve are in the unloaded state, the hydraulic pressure P5 is maintained at the pilot pressure by the hydraulic pressure P1 generated by the passing resistance of the throttle mechanism and the hydraulic pressure generated by the parent valve spring urging the parent valve spool downward, and the hydraulic actuator is maintained in the second operating state by the hydraulic pressure P4.