Page 497 - Mechatronics with Experiments

JWST499-Cetinkunt
October 9, 2014 8:41 254mm×178mm
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JWST499-c07
ELECTROHYDRAULIC MOTION CONTROL SYSTEMS 483
Hydraulic power supply To tank
To implement valve
and steering valve
Pump
Ride control pressure switch
LS relief 300 PSI
NC
3 x .031 60 PSI Ride control
(optional)
Load sensing signal
Compensator
Tank
Boom
cylinders
Pressure reducing valve module
Pilot enable
PRV/Source Main flow control valve 1
Regulated
valve pressure
(625 PSI)
From Compensator
pump Differential
lock Bucket
cylinders
To brakes Boom
down
To tank To axel/pin disconnect
Main flow control valve 2
Compensator
Auxiliary
cylinders
Main flow control valve 3
From steering
load sensing
signal Relief valve
From pump
Loader control valve

Pilot valves
and joystick
Auxiliary valves
To tank and joystick
FIGURE 7.61: Hydraulic system circuit diagram for the bucket motion of the John Deere wheel
loader model 644H: only the hydraulic circuit for bucket motion is shown. Hydraulic circuits for
the steering, brake, and cooling fan are not shown. The pump is of the variable displacement
axial piston type. The main flow control valves are connected to the hydraulic supply in parallel
configuration. They are closed-center type and post-compensated for pressure drop.

The rest of the hydraulic circuit for the machine (steering, brakes, cooling fan drive) is not
shown. The key features of this hydraulic circuit are

1. the pump is of variable displacement type and controlled by a load sensing hydraulic
mechanism,
2. the valve–cylinder pairs for each function are of closed center type and are connected
to the hydraulic supply lines (P and T) in parallel configuration,
3. each proportional directional main flow control valve has a post-compensator valve
in order to maintain constant pressure drop across each main valve.

The hydraulic circuits (steering, implement hydraulics, and brake hydraulics) are
supplied by a single variable displacement axial piston pump. The pump is controlled by
a load sensing hydraulic circuit. Since the same pump supports multiple hydraulic circuits