Borg Warner Transfer Box: Description and Operation
TRANSFER BOX
DESCRIPTION AND OPERATION
7
The selector fork is mounted on a second shaft
located within the front and rear casings but is able
to slide in the casing mountings. A cam follower on
the selector fork engages with the cam track of the
interlock spool. When the ratio control motor rotates
the interlock spool, the cam follower of the selector
fork follows the cam track of the interlock spool. This
converts rotational movement of the interlock spool
into linear movement of the selector fork.
The selector fork is engaged to the reduction hub.
Linear movement of the selector fork is transmitted
to the reduction hub, moving it between High, Low
and neutral positions. In the event of the reduction
hub gear failing to mesh with the epicyclic gear set,
wind-up of the interlock is prevented by the interlock
spool springs. The springs apply a constant torque
to the cam track casting until the reduction hub
engages with the epicyclic gear.
Ratio control motor
The ratio control motor drives the selector
mechanism and is controlled by the transfer box
electronic control unit (ECU). The ECU monitors a
number of variables including the position of the
ratio control motor, the speed of the vehicle, and the
drive ratio selected by the driver. When a ratio
change is requested, the transfer box ECU checks
that conditions are favourable for the change, for
example that the vehicle speed is sufficiently low to
permit engagement. The ECU then drives the ratio
control motor to the required position. When the
conditions for a ratio change are unfavourable, the
transfer box ECU communicates instructions to the
driver through the Message Centre and will not
attempt to change ratios until the correct conditions
are met.
INPUTS
OUTPUTS
Ratio control motor position
Ratio control motor drive
Range selector switch
ECU
Message Centre
Vehicle road speed
H-gate (automatic gearbox)
Gear lever neutral