TCM FB-8 Series, Service Manual

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6A.1.3 ORBITROL
The orbitrol sends pressure oil from the pump selectively to the steering cylinder. It consists
primarily of a control valve and a metering device.
The control valve used in the orbitrol is not an ordinary spool valve whose spool moves in
the axial direction, but a rotary valve which consists of a sleeve and a spool that rotate together
forming different oil passages through the combination of their oil holes. The valve housing is
provided with four ports which lead to the pump, tank, right and left chambers of the cylinder.
Between the inlet port and return port is a check valve.
The metering device consists of an internally toothed stator and an externally toothed rotor.
During normal operation, it operates as an oil motor. In an emergency, it can be used as hand
pump. The rotor is mechanically linked with the sleeve through the drive shaft so that feedback
operation is possible.
The sleeve is interlocked with the motor’s rotor through the cross pin and drive shaft while the
spool is splined to the steering shaft.
L
T
P EF
R
Fig. 6A.7 Orbitrol
ORBITROL
VP VALVE
T PORT
Ef PORT
L PORT
R PORT
P PORT
Oil pressure symbols
6A. STEERING SYSTEM (ORBITROL type)