22.5
TRAVEL CIRCUIT
This section describes the following.
(1) Travel forward pilot simultaneous operation circuit
(2) 2 speed travel solenoid command circuit and
auto 1-speed return function
(3) Travel main circuit
(4) Travel motor function
22.5.1
TRAVEL FORWARD PILOT
SIMULTANEOUS OPERATION
CIRCUIT
(1) Purpose:
Light operating force and shockless operation
(2) Mechatronics:
1.
If the travel lever with damping mechanism is
operated for travel right, left and forward
motions, the secondary pilot proportional pressure
comes out of the 3, 1 ports of P/V (10). The
higher of the pressures is selected, comes out of
the 6, 5 ports and acts upon the low pressure
sensors (SE9) (SE-10).
2.
The pilot secondary pressure flows to PAr and
PAL ports of the control valve (2), moves the
travel spool, and switches the main circuit.
3.
The low pressure sensor output voltage is input
into mechatro controller. The mechatro controller
performs signal processing and outputs current
corresponding to the increase of flow rate to P1
pump proportional valve (PSV-P1) and P2 pump
proportional valve (PSV-P2), and at the same time
the command current is output to P1 unloading
valve (PSV-D) and P2 unloading valve (PSV-B).
4.
The secondary pressures output by P1 pump
proportional valve (PSV-P1) and P2 pump
proportional valve (PSV-P2) exert on pump
regulator, actuating the pump on the delivery
flow rate increase side.
5.
The secondary pressure delivered in P1 unloading
valve (PSV-D) and P2 unloading valve (PSV-B)
is fed to Pcb and PCa ports provided in control
valve (2).
The secondary pressure from proportional valve
which has exerted on PCb and PCa ports
switches the unloading spool in CLOSE side.
22.5.2
2-SPEED TRAVEL SOLENOID
COMMAND CIRCUIT AND AUTO 1st
SPEED RETURN FUNCTION
(1) Purpose:
Change travel motor speed with switch.
(2) Principle:
If the switch is turned, an electric signal is
issued. It excites the 2-speed travel solenoid
which in turn converts the primary pilot pressure
and the self pressure to a tilting angle of the
variable displacement motor.
(3) Operation:
If the rabbit marked switch on the gauge cluster
is pressed, the solenoid (SV-3) of the
proportional valve block (13) is excited and
changes the proportional valve. Then the
solenoid command pressure is issued from port
A3, enters the Ps port of the travel motor (4),
opens the oil passage to the 2nd speed select
piston, and causes the motor to run in the 2nd
speed tilting mode by its self pressure. However,
when the main circuit pressure rises above 28
MPa (4060 psi), the motor's self pressure pushes
the 2nd speed select piston back to the 1st
speed.
22.5.3
TRAVEL MAIN CIRCUIT
(1) Operation:
The delivery oil from Pump A1 and A2 ports by
changing the travel spool with the operation of
travel pilot flows in each P1 port on the left side
of travel motor (4) and P2 port on the right side
of travel motor (4) through C,D ports of swivel
joint (8) from AL, AR ports of C/V, and rotates
the travel motor.
22.5.4
TRAVEL MOTOR FUNCTION
(1) Function:
1.
Prevents the motor from over running on a slope.
2.
Check valve that prevents cavitation of the
hydraulic motor.
3.
Shockless relief valve and anti cavitation valve
when inertia force stops.
4.
High/Low 2 step speed change mechanism and
auto 1st speed return at high load.
5.
Travel parking brake.
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22. HYDRAULIC SYSTEM
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22-10
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