Braking control apparatus for slewing type working machine

A braking control apparatus which is provided to a slewing type working machine including a slewing structure, a hydraulic motor for rotating the slewing structure, and a hydraulic pump for supplying a hydraulic fluid to the hydraulic motor, to control braking of the slewing structure,

• the braking control apparatus comprising:
• a slewing motion detector which detects information about a slewing angular velocity of the slewing structure;
• a slewing operation member which is operated to specify a rotation direction and a rotational angular velocity of the hydraulic motor;
• a flow control valve which is provided between the hydraulic motor and the hydraulic pump and has a shutting position for shutting off the hydraulic motor from the hydraulic pump while being adapted to be opened from the shutting position to allow the hydraulic fluid to be supplied from the hydraulic pump to the hydraulic motor at a flow rate corresponding to the opening;
• a flow control valve actuator which increases the opening of the flow control valve according to an operation amount of the slewing operation member;
• pressure control valves each of which receives an input of a pressure command signal from outside, the pressure control valves provided at an inlet side and an outlet side of the hydraulic motor respectively to limit respective maximums of an inlet pressure and an outlet pressure to respective set values corresponding to the respective pressure command signals;
• a braking operation member which is provided separately from the slewing operation member and is operated to brake a slewing motion of the slewing structure;
• a motor-side pressure controller which inputs a pressure command signal to each pressure control valve so as to maintain the set pressure of the pressure control valve at the inlet side of the hydraulic motor to a pressure which enables the hydraulic motor to be driven and let the set pressure of the pressure control valve at the outlet side of the hydraulic motor be a set pressure to generate a braking torque corresponding to the operation amount of the braking operation member;
• and
• a valve opening limiter which reduces, in accordance with the operation of the braking operation member, the opening of the flow control valve to an opening smaller than the opening corresponding to the operation amount of the slewing operation member.