COMPONENT OPERATION / Swing Device SWING PARKING BRAKE The swing parking brake is a wet type multiplate disc brake and a negative mechanism that releases the brake when brake release pressure acts in brake pis- ton chamber (8). The brake release pressure is supplied from the pilot pump only when either swing or front attachment is operated. In other cases (including engine stopping), the brake release pressure returns to the hydraulic oil tank, so that the brake is applied automatically by spring (4). When Brake is Applied 1.
When the swing or front attachment control lever is returned to neutral, the swing parking brake release spool in signal control valve is returned to neutral and pilot pressure to port SH disappears. 2. Check valve (7) is closed and the brake release pressure through orifice (6) is released to the swing motor housing. 3. As a result, the force of spring (4) acts on plate (2), which is engaged with the external circum- ference of rotor (1), and on friction plate (3), which is engaged with the inside of housing (9) through brake piston (5). Thus, the external cir- cumference of rotor (1) is secured with friction force.
When the engine stops, the brake is applied automatically as pressure is not applied to port SH. When Brake is Released 1. When the swing or front attachment control lever is operated, the swing parking brake release spool in signal control valve is shifted. Then, pilot pressure from the pilot pump is applied to port SH. 2. Pilot pressure to port SH pushes to open check valve (7), and acts in brake piston chamber (8). 3. As a result, as brake piston (5) is pushed upward, plate (2) and friction plate (3) are freed, so that the brake is released. T3-2-4