Section E - Hydraulics
Operation Description
Transmission Operation - 4WD Series 2 Machines
E-33 E-33
9803-9340-8
Forward
K Fig 27. ( T E-34)
When the operator selects forward drive, solenoid 3a is
energised causing direction control valve 3 to direct pilot
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
motors and causing the machine to move forwards.
Oil pressure and flow is fed to the rear motors M1 and M2
first which causes them to rotate. This simultaneously
sends oil pressure and flow to the front motors M3 and M4
and the machine drives forwards. The rear motors M1 and
M2 have an oil flow dividing system known as “Twin-Lock”
where once the pressurised oil has pushed the motor
pistons out against the cam, which causes the motors to
rotate, the exhaust oil from half the pistons is sent to the
front motors M3 and M4 and the other half is sent back to
the pump return. This interconnection ensures that the
front wheels are driven at the same speed as the rear
wheels and that there is a positive oil pressure feed to the
front motors which allows for better traction control,
particularly if the rear wheels lose traction and spin. Return
oil from the motors flows back into the transmission pump
through port B. Some hot oil is purged out of the drive loop
on its return (the low pressure side) to the pump where it is
combined with any ‘leaked’ oil from the motors and fed
back to the tank via cooler C.
The purge valve 14a bleeds off hot oil from the low
pressure side of the drive loop. This reduces oil
temperatures in the loop since purged hot oil is replaced by
colder oil from the hydraulic tank. In this application
purging only happens in forward drive, in reverse drive the
valve remains closed.
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 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.
Key
C Cooler
P1 Transmission Pump
M1 Motor
M2 Motor
M3 Motor
M4 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
6a Inching Pedal Connection
7 Charge Pressure Relief Valve
8 Charge Pump
10 Variable Displacement Pump
11a Series Line & Hose Protection Valve
11b Series Line & Hose Protection Valve
12 Brake Valve
13 Hydraclamp Valve
14 Porting Block
14a
Purge Valve
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