Drive mechanism and tilt-trim device

A drive mechanism comprising:

• a tank configured to store a hydraulic fluid;
• a cylinder unit in which a piston rod advances and retreats due to the hydraulic fluid fed from the tank;
• and
• a pump unit configured to feed the hydraulic fluid from the tank to the cylinder unit, wherein
• the cylinder unit includes:
• a cylinder having a cylindrical shape;
• a piston that partitions an inside of the cylinder into two chambers including a first chamber and a second chamber;
• and
• the piston rod having one end fixed to the piston and another end protruding outside the cylinder,
• a protruding amount of the piston rod from the cylinder decreases by feeding the hydraulic fluid to the first chamber, and the protruding amount of the piston rod from the cylinder increases by feeding the hydraulic fluid to the second chamber, and
• the pump unit includes:
• a first pump configured to discharge the hydraulic fluid from a first discharge portion by rotating in a first direction, and configured to discharge the hydraulic fluid from a second discharge portion by rotating in a second direction opposite to the first direction;
• a second pump different from the first pump, operating in conjunction with an operation of the first pump, configured to discharge the hydraulic fluid from a third discharge portion by rotating in the first direction, and configured to discharge the hydraulic fluid from a fourth discharge portion by rotating in the second direction;
• an intake path through which the hydraulic fluid is sucked to feed into the first pump or the second pump;
• a first flow path connecting the first chamber to the first discharge portion, and through which the hydraulic fluid flows;
• a second flow path connecting the second chamber to the second discharge portion, and through which the hydraulic fluid flows;
• a third flow path connecting the first chamber to the third discharge portion, and through which the hydraulic fluid flows;
• a fourth flow path connecting the second chamber to the fourth discharge portion, and through which the hydraulic fluid flows;
• a second branch path branching from the second flow path to reach at least one of the tank or the intake path;
• and
• a second on-off valve provided in the second branch path, and configured to open the second branch path in a case where a pressure in the first chamber is higher than a predetermined pressure when the first pump rotates in the second direction or in a case where a pressure in the second flow path is higher than a predetermined pressure when the first pump rotates in the first direction.