jcb Mini CX - Page 199

Section E - Hydraulics
Operation Description
Transmission Operation - 2WD Series 2 Machines
E-29 E-29
9803-9340-8
Forward
K Fig 24. ( T E-29)
When the operator selects forward drive, solenoid 3a is
energised causing direction control valve 3 to direct charge
pressure from the DA valve 6 to the swash control piston
2. As the pilot pressure increases, due to engine speed
increase when the accelerator is depressed, the swash
plate control piston 2 moves to one side causing the swash
plate to swivel. This causes the oil to be pumped from the
B port of the pump drive circuit to the A port which
increases the pressure on the A side, thus driving the
motor and causing the machine to move forwards.
Drive pressure is also fed to the motor shuttle valve Ma
causing it to move to connect the return side (low pressure
side) of the loop circuit to the motor case drain. This is
necessary for the lubrication of the motor bearings and
also for the purging of some hot oil from the loop circuit
which is diverted through the oil cooler C before being
returned to the tank. The purged oil is then replaced by
cooler oil supplied from the tank via the charge pump
though valves 5a and 5b depending on machine direction,
thus maintaining the loop circuit oil level and temperature
within tolerance levels.
Pump feed pressure to the motor is controlled by the
pressure cut-off valve 4 whilst the non return valve in 5a
stays closed preventing constant high pressure being fed
back to the charge pump 8. Should an overload situation
occur in the high pressure side of the loop circuit, the high
pressure relief valve in 5a will open briefly releasing oil
which will then flow into the pump case via the charge
pressure relief valve 7. The charge pump 8 replaces any
oil losses from purge, leakage and relieved oil to the drive
loop via the non return valve in 5b which is the low
pressure side of the loop circuit. Any surplus charge oil is
released into the pump case through the charge pressure
relief valve 7 where it returns to tank via oil cooler C.
860761-1
Fig 24.
Key
C Cooler
P1 Transmission Pump
M Motor
Ma Motor Shuttle Valve
S Suction strainer
T Tank
2 Swash Control Piston
3 Direction Control Valve
4 Pressure Cut-off Valve
5a High Pressure Relief Valve
5b High Pressure Relief Valve
6 Displacement Angle Control Valve
7 Charge Pressure Relief Valve
8 Charge Pump
10 Variable Displacement Pump
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