22.8
SWING CIRCUIT
This section describes the following operations.
(1) Swing left pilot circuit
(2) Swing auto parking brake
(3) Swing main circuit
(4) Swing motor circuit
22.8.1
PILOT CIRCUIT FOR LEFT SWING
(1) Operation:
1.
When the left swing operation is performed, the
pilot proportional secondary pressure is delivered
through port (5) of left pilot V (9), and the
secondary pressure acts on PBs port of C/V (2),
and simultaneously flows out from Pss port of
C/V and acts on low pressure sensor (SE-5).
2.
The voltage output by the low pressure sensor is
input in the mechatro controller, and is
signal-processed.
3.
Then, the secondary pressure led into PBs port of
C/V (2) switches the swing spool.
22.8.2
SWING AUTO PARKING BRAKE
(1) Purpose:
Swing lock in neutral position and parking
(2) Principle:
Release mechanical brake only when required to
operate swing and arm in.
(3) Operation:
1.
The swing parking system excites the swing
parking SOL (SV-1) usually if the key switch is
turned on and works by the action of the
mechanical brake.
2.
The mechanical brake is released if the swing
parking solenoid is de-excited only when the
secondary operating pressure in the swing and
arm in actions acts upon any of the low
pressure sensors (SE-5, 7).
3.
The swing parking solenoid (SV-1) is excited five
seconds after the pressure of the swing low
pressure sensors (SE-5) is reduced to zero. In
the case of arm in operation, the swing parking
solenoid (SV-1) is excited the moment the
pressure of the arm in low pressure sensor
(SE-7) is reduced to zero. This causes the
mechanical brake to operate.
22.8.3
SWING MAIN CIRCUIT
(1) Operation:
The oil delivered from the A2 port of the P2
pump enters the P2 port of C/V (2) and is
branched off into the bypass line and the parallel
circuit. However, since the bypass line is closed
as the swing spool is shifted, the oil pushes the
load check valve LCs open through the parallel
circuit, enters the B port of the swing motor via
the Bs port of C/V (2), and rotates the swing
motor counterclockwise.
22.8.4
SWING MOTOR CIRCUIT
(1) Anti cavitation circuit at swing deceleration
(2) Preventing the swing motor from being reversed
circuit.
(3) Shockless relief valve circuit.
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22. HYDRAULIC SYSTEM
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22-18
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