Case 580SR Service Manual page 181

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SECTION 21 - TRANSMISSION 115
THE TRANSMISSION CONTROLS
The transmission is controlled by an electronic gear
selector (EGS). This unit has a microprocessor
which receives certain inputs (gear selector position,
speed sensor...) which are processed and will give
output signals to the control valve.
The valve assembly has: 6 solenoid, 6 shift spools,
a pressure reducer, an electronic controlled modula-
tion valve, an accumulator, a pressure booster and
a speed sensor.
Operation of the valve is as follows:
Regulated pressure 20 bar is directed to the shift
spools, pressure booster and pressure reducer.
In the pressure reducer, regulated pressure is re-
duced to 5.5 bar. This reduced pressure is used as
supply for the solenoid and electronic controlled
modulation valve.
When activated, the electronic controlled modulation
valve will give an output pressure curve from 0 to 5
bar.
This pressure curve is multiplied in the pressure
F27728
boost valve. In this way, for the directional clutches
The transmission controls
a curve of 0-20 bar is available.
Between the electronic modulation valve and the
booster is an accumulator to damper any hydraulic
vibration.
When forward is selected the electronic modulation
valve and the forward solenoid are activated.
The pilot pressure of the forward solenoid will move
the shift spool so that a forward clutch can be fed
with modulated pressure.
If the high/low solenoid is not activated the forward
high clutch is engaged, if it is activated the forward
low clutch is engaged.
When reverse is selected the electronic modulation
valve and the reverse solenoid are activated, the pi-
lot pressure of the reverse solenoid will move the
shift spool so that the reverse clutch can be fed with
modulated pressure.
The shift spools from forward and reverse are locat-
ed against each other with a return spring in be-
tween; this is to make sure that only one direction
can be selected.
Range is selected as follows:
if the range solenoid (2nd/1st) is not activated, regu-
lated pressure is fed through the modulation shift
spool and through the 2nd/1st shift spool to the 2nd
clutch.
If the range solenoid (2nd/1st) is activated, the pilot
pressure will move the shift spool so that 1st clutch
is fed.