jcb JS300 Service Manual page 984

Section F - Transmission
Traction Motor / Reduction Gear
Operation
High Speed
When high-speed travel is selected, the electronic control
unit (MECU) sends a signal to solenoid CT5 on the 8-spool
solenoid block. The solenoid energises, allowing servo
pressure to cross the solenoid and sends a signal to port
Ps of the drive motor, which moves the two speed travel
spool E to the high-speed position. Pressure that is
available to the drive motor now crosses the two speed
spool and acts on the swash plate piston to move the
motor to minimum displacement (High speed).
The pressure in the system is also seen at the opposite
side of two speed spool E via the brake piston and acts
against the servo pressure. Due to the larger surface area
that the servo pressure acts against, the servo pressure
can hold the two speed spool in the high-speed position
2
until the system pressure rises to 258bar (3741 lb in ).
(This is based on the servo pressure being 39bar (565.5 lb
in 2 )). At this point the system pressure can overcome the
servo pressure and moves the two speed spool E back into
the low speed position. This releases the pressure acting
on the swash plate piston and allows the swash plate to
return to maximum displacement to increase the torque of
the motor.
If the system pressure then falls back below 258 bar (3741
2
lb in ) the servo pressure can overcome the system
pressure and move the 2-speed spool back into the high-
speed position.
F-7 9813/5100-1 F-7