320C Excavator Hydraulic System – Pilot Valve (Swing Parking Brake)



Illustration 1 g00682419

(2) Swing parking brake solenoid valve

Swing parking brake solenoid valve (2) is located on the pilot oil manifold. When any one of the joysticks is moved from the NEUTRAL position, the swing parking brake solenoid valve is energized in order to release the swing parking brake. When the swing parking brake solenoid valve is energized, pilot oil flows to the swing motor in order to release the swing parking brake.

Note: Operation of the travel levers/pedals will not release the swing parking brake.




Illustration 2 g00687102

Swing parking brake (disengaged position)

(2) Swing parking brake solenoid valve

(3) Spool

(4) Spring

(5) Passage

(6) Passage

(7) Port (pilot system oil)

(8) Pilot oil manifold

(9) Spool chamber

(10) Line

(11) Body (swing motor)

(12) Friction plate

(13) Separator plate

(14) Piston chamber

(15) Port (swing motor)

(16) Cylinder barrel

(17) Brake piston

(18) Brake spring

(19) Motor head

The swing parking brake is located between motor head (19) of swing motor and body (11). The swing parking brake consists of the following components : brake spring (18), brake piston (17), separator plate (13) and friction plate (12). Friction plate (12) is splined to cylinder barrel (16). Separator plate (13) is splined to body (11). Separator plate (13) and friction plate (12) move in an axial direction.

When the joysticks are moved from the NEUTRAL position, the implement/swing pressure switch senses the increase in pilot oil pressure at the pilot control valves. The implement/swing pressure switch changes to the ON position. The implement/swing pressure switch sends an input signal to the engine and pump controller. The engine and pump controller energizes swing parking brake solenoid valve (2) .

When swing parking brake solenoid valve (2) is energized, spool (3) moves in a downward direction against the force of spring (4). Pilot oil in passage (7) flows through spool chamber (6) and line (10) to port (15) of the swing motor. The pilot oil now enters piston chamber (14). The pilot pressure causes brake piston (17) to move upward against the force of brake spring (18). The force that holds separator plate (13) and friction plate (12) together is released. When the swing parking brake is released, the swing operation of the upper structure is enabled.

Note: If the swing parking brake becomes inoperable due to failure of swing parking brake solenoid valve (2), the swing brake can be released by turning the temporary brake release screw in a clockwise direction until the temporary brake release screw stops.




Illustration 3 g00686766

Swing parking brake (engaged position)

(2) Swing parking brake solenoid valve

(3) Spool

(4) Spring

(5) Passage

(6) Passage

(7) Port (pilot system oil)

(8) Pilot oil manifold

(9) Spool chamber

(10) Line

(11) Body (swing motor)

(12) Friction plate

(13) Separator plate

(14) Piston chamber

(15) Port (swing motor)

(16) Cylinder barrel

(17) Brake piston

(18) Brake spring

(19) Motor head

When the joysticks are returned to the NEUTRAL position, left pump supply oil to the swing motor is stopped. The implement/swing pressure switch senses the decrease in pilot oil pressure at the pilot control valves. The implement/swing pressure switch changes to the OFF position. The engine and pump controller senses the change of signal at the implement/swing pressure switch. The engine and pump controller de-energizes swing parking brake solenoid valve (2) .

Spool (3) is moved upward by the force of spring (4). Spool (3) blocks pilot oil flow from port (7) to piston chamber (14). Brake spring (18) forces brake piston (17) downward. The oil in piston chamber (14) flows through port (15) and line (10) to pilot oil manifold (8). The oil then flows into spool chamber (6) and passage (9) of spool (3). The oil then flows through passage (5) to the hydraulic tank. As brake piston (17) moves downward, separator plate (13) and friction plate (12) are forced together. Since separator plates (13) are splined to body (11), the rotation of cylinder barrel (16) in the swing motor is stopped. Rotation of the upper structure is prevented.

Since the engine and pump controller does not de-energize the swing parking brake solenoid valve until approximately 6.5 seconds after the swing joystick is returned to the NEUTRAL position, the rotation of the swing motors stops before the swing parking brake is engaged. If the solenoid is de-energized before the rotation of the swing motors stops, damage and wear to the swing parking brakes would result.