Figure 16-59 shows the release circuit of the swing motor parking brake.
The slewing motor is equipped with a parking brake, which can fix the upper slewing device in a state of lifting a heavy object on the slope, and can also prevent the upper slewing device from rotating by itself due to inertia when walking. This parking brake is a structure in which the wet disc brake holds the rotating shaft of the motor. It is a normally closed type, that is, it brakes by holding the shaft all the time when it is not actuated by spring force.
As long as the excavator is rotated or any of the working devices is operated, the return oil in the logic signal circuit of the main control valve cannot reach the oil tank, and the logic pressure rises. As soon as the logic pressure rises, the hydraulic timer is switched, and the pilot pressure oil is released through the valve to release the parking brake, so that the swing action can be performed, and the working device does not act to apply excessive force to the swing motor parking brake.
When the joystick is returned from the working position to the neutral position, the return oil in the logic signal circuit of the main control valve can be connected to the tank, and the logic pressure immediately drops. As soon as the logic pressure drops, the hydraulic timer is switched back to cut off the oil supply circuit of the pilot pump, so that the oil in the parking brake chamber is slowly returned to the tank through throttling, and the parking brake is braked again after about 5s.
