Work machine

A work machine comprising:

• a machine body;
• a winch unit detachably attached to the machine body, the winch unit including:
• a winch drum configured to wind and unwind a rope;
• a winch motor configured to rotate the winch drum;
• a clutch portion being switchable between a clutch-on state and a clutch-off state, the clutch portion configured to allow power of the winch motor to be transmitted to the winch drum while applying braking to the winch drum in the clutch-on state, the clutch portion configured to disconnect the winch drum from the winch motor so as to allow the winch drum to freely rotate with respect to the winch motor in the clutch-off state;
• and
• a cylinder portion connected to the clutch portion, and having a positive oil chamber that generates a force in a direction that the clutch portion is brought into the clutch-on state by receiving a hydraulic force and a negative oil chamber that generates a force in a direction that the clutch portion is brought into the clutch-off state by receiving a hydraulic force;
• a hydraulic source attached to the machine body and being capable of discharging working oil;
• a braking operation unit configured to receive an operation for applying braking to the winch drum, an operation amount that the braking operation unit receives being variable;
• a first main oil passage that makes a specified oil chamber that is one of the positive oil chamber and the negative oil chamber communicate with the hydraulic source, thus allowing a working oil to flow into the specified oil chamber;
• a brake valve disposed in the first main oil passage between the specified oil chamber and the hydraulic source, the brake valve being capable of adjusting a brake force applied to the winch drum in the clutch-on state by generating a differential pressure between the positive oil chamber and the negative oil chamber by adjusting a hydraulic force supplied to the specified oil chamber through the first main oil passage corresponding to an operation amount that the braking operation unit receives;
• a connecting portion configured to selectively disconnect and connect a portion of the first main oil passage between the hydraulic source and the specified oil chamber of the cylinder portion along with mounting and dismounting of the winch unit to and from the machine body;
• a sub oil passage provided independently from the first main oil passage, the sub oil passage making the specified oil chamber and a low-pressure container having a pressure that is lower than a pressure of the specified oil chamber communicate with each other;
• and
• a throttle portion disposed in the sub oil passage and configured to generate a differential pressure in the sub oil passage between an upstream side and a downstream side of the throttle portion, the throttle portion including an opening that has an opening diameter that generates a brake pressure in the specified oil chamber and allows the working oil to flow from the specified oil chamber toward the low-pressure container.