320C Excavator Hydraulic System – Swing Hydraulic System



Illustration 1 g00747565

Hydraulic schematic for SWING RIGHT

(1) Pilot line

(2) Passage

(3) Swing parking brake

(4) Swing motor

(5) Motor rotary group

(6) Relief valve

(7) Anti-reaction valve

(8) Return line

(9) Line

(10) Line

(11) Passage

(12) Load check valve

(13) Parallel feeder passage

(14) Main control valve

(15) Parallel feeder passage

(16) Passage

(17) Passage

(18) Swing control valve

(19) Stick I control valve

(20) Variable swing priority valve

(21) Passage

(22) Passage

(23) Pilot control valve (swing and stick)

(24) Pilot line

(25) Implement/swing pressure switch

(26) Line

(27) Pressure reducing valve for swing priority

(28) Left pump

(29) Right pump

(30) Pilot pump

(31) Solenoid valve (swing parking brake)

(32) Line

(33) Slow return check valve

(34) Hydraulic tank

(35) Pilot oil manifold

(36) Drain line

(37) Pilot line

(38) Pilot line

(47) Line

(48) Passage

(49) Line

(52) Center bypass passage

(53) Center bypass passage

(54) Negative flow control orifice

(55) Negative flow control line

The oil delivery for the swing hydraulic circuit is supplied by left pump (28) only. When either one of the joysticks is moved from the NEUTRAL position, swing parking brake (3) is released. The swing motor is mounted on top of the swing drive. The swing drive is installed on the upper structure. The swing drive reduces the motor speed by two stages. The swing drive rotates the upper structure.

ReferenceFor more information concerning the operation of the swing motor, refer to Systems Operation, “Swing Motor”.

ReferenceFor more information concerning the operation of the swing drive, refer to Systems Operation, “Swing Drive”.

ReferenceFor more information concerning the operation of the swing parking brake and the solenoid for the swing parking brake, refer to Systems Operation, “Pilot Valve (Swing Parking Brake)”.




Illustration 2 g00697580

Main control valve compartment

(4) Swing motor

(8) Return line

(9) Line

(10) Line

(18) Swing control valve



Illustration 3 g00697650

(31) Solenoid valve (swing parking brake)

(35) Pilot oil manifold

The oil delivery from left pump (28) flows through center bypass passage (52) in main control valve (14) to swing control valve (18) . The oil delivery from right pump (29) flows through center bypass passage (53) in main control valve (14) . Illustration 1 shows the main control valve when only the swing hydraulic circuit is activated.

When the hydraulic activation control lever is in the UNLOCKED position, the oil delivery from pilot pump (30) flows to pilot oil manifold (35) and the solenoid valve for swing parking brake (31) . The oil delivery from the pilot pump also flows to pilot control valve (23) .

When the swing joystick is moved to the SWING RIGHT position, the implement/swing pressure switch senses the increase in pilot oil pressure. 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 then energizes the solenoid for the swing parking brake (31) . The solenoid valve for the swing parking brake shifts. Pilot oil flows through pilot line (1) to swing parking brake (3) . The swing parking brake releases in order to enable a swing operation.

The oil delivery from pilot pump (30) flows from pilot control valve (23) through pilot line (26) and into swing control valve (18) . The spool in swing control valve (18) shifts upward. The pilot oil on the other end of the spool in the swing control valve flows through pilot line (37) and pilot control valve (23) to hydraulic tank (34) .

Since the spool in swing control valve (18) is fully shifted, center bypass passage (52) is blocked. None of the oil delivery from the left pump flows to negative flow control orifice (54) and no negative flow control pressure is created in center bypass passage (52) . Since no negative flow control pressure is sent through negative flow control line (55) to the left pump regulator, the left pump regulator moves the swashplate of the left pump toward the maximum angle position. The output flow rate of the left pump increases. The oil delivery from the left pump flows through parallel feeder passage (13) , load check valve (12) , passage (17) , swing control valve (18) , passage (16) and line (9) to the swing motor. The oil enters the swing motor and flows to motor rotary group (5) . The motor rotary group rotates.

The oil delivery for the swing hydraulic circuit is supplied by the left pump only. Since only a swing operation is being performed, the control valves that receive the oil delivery from right pump (29) are in the NEUTRAL position. The negative flow control pressure in center bypass passage (53) is not blocked by any of the control valves. Right pump (29) remains at the destroked position.

ReferenceFor more information concerning the negative flow control operation, refer to Systems Operation, “Negative Flow Control System”.

Return oil from motor rotary group (5) flows through line (10) to the main control valve. The return oil flows through swing control valve (18) , return passage (11) , return line (8) and slow return check valve (33) to hydraulic tank (34) . The upper structure swings to the right (clockwise direction).

The SWING LEFT operation is similar to the SWING RIGHT operation.

When the swing joystick is moved to the SWING LEFT position, pilot oil from pilot control valve (23) flows through pilot line (37) and into swing control valve (18) . The spool in the swing control valve shifts downward. The oil delivery from the left pump in parallel feeder passage (13) flows through passage (17) and line (10) . The oil delivery enters motor rotary group (5) . For a swing left operation, the supply ports and return ports are reverse of the swing right operation. This causes the upper structure to swing to the left (counterclockwise direction).

When the swing joystick is returned to the NEUTRAL position, the springs on each end of the swing control valve maintain the spool in the swing control valve in the NEUTRAL position. The oil flow to the swing motor and the oil flow from the swing motor is blocked by the swing control valve.

Swing Priority

The pilot oil pressure from the pilot control valve directly corresponds to the amount of movement or position of the joystick. The pilot oil pressure from the pilot control valve acts on the pressure reducing valve for swing priority and the variable swing priority valve. As the swing joystick is moved farther from the NEUTRAL position, the pilot oil pressure increases. This gradual increase in pilot oil pressure causes a gradual change to swing priority. Thus, swing priority is controlled by the position of the swing joystick and swing priority automatically activates when the joystick reaches a certain position.

When swing priority is activated, the output flow from the left pump supplies hydraulic oil to the swing hydraulic circuit. Since swing priority increases the swing acceleration, swing priority is useful for loading operations. Swing priority is also useful for leveling operations and trenching operations when higher swing force is required.




Illustration 4 g00812571

Stick I control valve (swing priority OFF)

(15) Parallel feeder passage

(20) Variable swing priority valve

(22) Passage

(24) Pilot line (swing pilot pressure)

(27) Pressure reducing valve for swing priority

(38) Pilot line (pilot system pressure)

(39) Pin hole

(40) Spool

(41) Spring

(42) Passage (stick I)

(43) Spool

(44) Drain line

(45) Check valve

(46) Orifice

(47) Line

(48) Passage

(50) Spring

(51) Passage

(56) Drain Line



Illustration 5 g00821462

SWING RIGHT operation (swing priority OFF)

(4) Swing motor

(13) Parallel feeder passage

(15) Parallel feeder passage

(18) Swing control valve

(19) Stick I control valve

(20) Variable swing priority valve

(21) Passage

(22) Passage

(23) Pilot control valve (swing and stick)

(24) Pilot line

(26) Pilot line

(27) Pressure reducing valve for swing priority

(28) Left pump

(29) Right pump

(30) Pilot pump

(38) Pilot line

(41) Spring

(47) Line

(48) Passage

(50) Spring

When the swing joystick is in the NEUTRAL position, no pilot oil pressure acts on spool (40) of pressure reducing valve for swing priority (27) . Full pilot oil pressure flows through pilot line (38) , the pressure reducing valve for swing priority (27) , line (47) and passage (22) to variable swing priority valve (20) . Spool (43) in the variable swing priority valve is shifted upward against the force of spring (41) . The oil delivery from left pump (28) in parallel feeder passage (13) flows through parallel feeder passage (15) and variable swing priority valve (20) . The oil delivery enters stick I control valve (19) .

When the swing joystick is moved slightly from the NEUTRAL position in order to perform a SWING RIGHT operation, reduced pilot oil pressure from pilot control valve (23) flows through pilot line (26) . The pilot oil then divides into two flow paths. Part of the pilot oil flows through passage (21) to swing control valve (18) . The spool in the swing control valve shifts a slight amount that corresponds to the amount of movement of the swing joystick. The remainder of the pilot oil flows through pilot line (24) and passage (48) . The pilot oil pressure acts on the shoulder of spool (40) in the pressure reducing valve for swing priority (27) . Spool (40) shifts against the force of spring (50) .

Since the reduced pilot oil pressure in passage (22) is still higher than the force of spring (41) , spool (43) in variable swing priority valve (20) remains shifted upward. The oil delivery from left pump (28) to stick I control valve (19) is not restricted. Swing priority is not activated.




Illustration 6 g00812941

Stick I control valve (swing priority ON)

(15) Parallel feeder passage

(20) Variable swing priority valve

(22) Passage

(24) Pilot line (swing pilot pressure)

(27) Pressure reducing valve for swing priority

(38) Pilot line (pilot system pressure)

(39) Pin hole

(40) Spool

(41) Spring

(42) Passage (stick I)

(43) Spool

(44) Drain line

(45) Check valve

(46) Orifice

(47) Line

(48) Passage

(50) Spring

(51) Passage

(56) Drain line



Illustration 7 g00821463

SWING RIGHT operation (swing priority ON)

(4) Swing motor

(13) Parallel feeder passage

(15) Parallel feeder passage

(18) Swing control valve

(19) Stick I control valve

(20) Variable swing priority valve

(21) Passage

(22) Passage

(23) Pilot control valve (swing and stick)

(24) Pilot line

(26) Pilot line

(27) Pressure reducing valve for swing priority

(28) Left pump

(29) Right pump

(30) Pilot pump

(38) Pilot line

(41) Spring

(45) Check valve

(46) Orifice

(47) Line

(48) Passage

(50) Spring

As the swing joystick is moved to the FULL STROKE position during a SWING RIGHT operation, the pilot oil pressure in passage (21) increases. The spool in swing control valve (18) shifts fully upward. The pilot oil pressure in pilot line (24) and passage (48) also increases. Spool (40) in the pressure reducing valve for swing priority (27) shifts fully against the force of spring (50) .

Passage (51) restricts the pilot oil flow from pilot line (38) through the pressure reducing valve for swing priority (27) . The pilot oil pressure in line (47) and passage (22) also decreases. Spool (43) in variable swing priority valve (20) is pushed downward by the force of spring (41) .

The oil delivery from left pump (28) in parallel feeder passage (15) is restricted by orifice (46) in check valve (45) . A portion of the oil delivery from the left pump flows into passage (42) . Swing priority is now activated. Most of the oil delivery from the left pump is dedicated to the swing system and flows through the swing control valve to the swing motor. As a result, swing priority and higher swing force can be achieved with the swing joystick.

A portion of the pilot oil at passage (51) flows through passage (39) to spool (40) . Pilot oil pressure that flows from passage (22) into variable swing priority valve (20) corresponds to the position of the swing joystick.