22.9
ARM CIRCUIT
This section describes the following operations.
(1) Arm in, light-load operating pilot circuit
(2) Arm in, light-load variable normal recirculation
main circuit / internal conflux main circuit
22.9.1
ARM IN, LIGHT-LOAD
OPERATING PILOT CIRCUIT
(1) Purpose:
Speed-up and Anticavitation when the arm is at
light loaded.
(2) Principle:
The oil returning from the arm cylinder rod (R) is
recirculated variably to the head (H) at arm 2
spool in C/V.
(3) Operation:
1.
When the arm in operation is performed, the
secondary pilot proportional pressure gets out of
port 7 of the left pilot valve (9) and acts upon the
low pressure sensor (SE-7).
At the same time, the pressure is branched off
in two flows, acts upon the Paa1 port and the
PLc2 port, changes over the arm spool and the
arm lock valve CRar. releases.
2.
The output voltage by the low pressure sensor is
input into mechatro controller, and is pilot
signal-processed, and is output to P1, P2 pump
proportional valve (PSV-P1), (PSV-P2) and arm 2
inverse proportional valve (PSV-A).
3.
The secondary pressure from pilot proportional
valve, which is reduced by arm 2 inverse
proportional valve (PSV-A) switches arm 2 spool.
22.9.2
ARM-IN, LIGHT-LOAD VARIABLE
NORMAL RECIRCULATION,
INTERNAL CONFLUX MAIN CIRCUIT
(1) Operation:
1.
The P2 pump delivery oil flows in travel left
section through P2 port of C/V (2) and is
branched off in by-pass circuit and parallel
circuit, but because arm 1 spool is switched, the
delivery oil which goes through parallel circuit
opens load check valve LCa and is flowed into
arm 1 spool.
2.
On the other hand, P1 pump delivery oil flows in
P1 port of C/V (2), and the flows in travel straight
section and travel right tandem path. Then
because arm 2 spool was switched, the delivery
oil opens load check valve LCAT2, goes through
arm 2 spool, and confluences with P2 pump
delivery oil in the valve section, and then is
flowed into arm cylinder head (H) side through Aa
port of C/V (2).
3.
The return oil from arm cylinder (R) side flows in
Ba port of C/V (2) and passes through the Ba
port because the arm lock valve CRar is open,
and is flowed into arm 2 spool through arm 1
spool.
4.
Because arm 2 spool is switched to normal
recirculation position, causing restriction of
passage to tank, the return oil from arm cylinder
(R) side flows into arm cylinder (H) side.
-Because, at light load, the pressure in cylinder
rod (R) side is higher than that in the head (H)
side, it opens the check valve housed-in arm 2
spool and is recirculated in the head (H) side,
resulting in the speed up of arm-in operation at
light load.
5.
Cavitations prevention control in arm-in operation
Command current is output to arm 2 solenoid
proportional valve by signal processing of E/G
speed and arm-in pilot pressure, accordingly the
arm 2 spool is switched to neutral (cavitations
prevention) position, resulting in cavitations
prevention.
Position of arm 2 spool
Reference:
In light-load arm-in operation (normal recirculation,
conflux), when the attachment to which the circuit in
P1 pump side is applied is operated, the meter-in
path of arm 2 spool is closed, resulting in single flow
operation.
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22. HYDRAULIC SYSTEM
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22-20
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