Because VehiCROSS is an "all-around sports" vehicle emphasizing the thrill
of driving, only the full-time, automatic, four-wheel drive TORQUE-ON-DEMAND
(TOD) and 4L modes are provided. The VehiCROSS TOD system
is capable of distributing torque to the front wheels before
tire slip occurs by monitoring twelve different input sensors,
including vehicle speed and accelerator pedal angle. The information
is fed back to the TOD system and torque is distributed to the
front wheels as determined by a patented, preprogrammed software
map. This ensures a smooth, stable ride at all times and optimizes
torque distributon. The TOD system is a means of controlling
the vehicle's drive condition. According to the position of the
Transfer shift lever, the TOD system controls a torque-split
multi-plate clutch. In the 4L rnode, it activates the mechanical
lock switches to low range. When the shift lever is set to
the TOD mode, input sensors monitor conditions for potential
or actual tire slippage. This ensures that the driving force
matching the road surface is transmitted to the front tires. In general, understeering occurs
when too much driving force is applied to the front tires. Oversteering occurs when too much driving force is applied to the rear tires.
However, with the TOD system, the optimum driving force is consistently
applied according to the computations made by the system's ECU
(electronic control unit). The TOD mode is for all-around
driving comfort over a wide range of conditions, from paved roads
to snowy roads. The 4L mode is for heavy-duty off-road driving. Part-time 4WD vehicles gained
popularity with their simple construction and high drivability.
But they needed precise drive mode switching according to road
conditions to counteract "tight-corner braking phenomenon,"
which may occur on paved road surfaces. The TOD mode operates
in place of and has an advantage over the conventional 'Air'
mode in that it eliminates the "tight-corner braking phenomenon."
This allows TOD vehicles to use 4WD on any road surface. The TOD system also has advantages over conventional full-time 4WD
vehicles, in that torque is distributed as needed, there is less
wear and tear on the vehicle and fuel economy is improved. ln TOD mode under standard driving
conditions, torque distribution will be close to basic rear-wheel
drive. Then, according to the driving conditions, the distribution
of torque is electronically controlled to the front wheels. The driving force is transmitted
to the rear wheels through direct coupling, whereas the driving
force to the front wheels is applied by varying the amount of
torque transmitted. This is done by controlling the pressure
applied to the electromagnetic multi-plate clutch built into
the Transfer. The pressure on the electromagnetic multi-plate
clutch is controlled by varying the duty ratio of voltage supplied
to the electromagnetic clutch solenoid, located on the rear of
the electromagnetic multi-plate clutch. when the electromagnetic
multi-plate clutch is fully open, the front wheels are freed
completely and the vehicle is rear-wheel driven. When the electromagnetic multi-plate
clutch is fully coupled, the vehicle becomes a direct-drive 4WD
vehicle. Conditions between the two are therefore controlled
by the TOD system, which incorporates front and rear sensors
installed on the output shafts on either side of the Transfer
as well as the TPS (Throttle Position Sensor), which detects
engine output condition. Based upon signals from sensors,
the system sets torque distribution between front and rear by
varying the pressure applied to the electromagnetic multi-plate
clutch. When drive torque applied to the
rear wheels increases under normal rear-wheel drive conditions
and the rear wheels develop a tendency to slip, the torque corresponding
to the slippage is redistributed to the front wheels. Optimum
torque is determined by the feedback control mechanism which
checks whether the distributed torque is appropriate. This occurs
at intervals in the order of milliseconds. The signals from the TPS are also
used predictively, to estimate both vehicle coditions and the
driver's plan to accelerate or decelerate. TOD calculates the
initial torque distribution by also taking data from the rear
and front speed sensors into consideration. For example, while
the torque transmitted to the front wheels is "ordinary"
on a good road surface, it increases to maintain vehicle stability
if sudden acceleration is expected according to data received
from the TPS. During parking, the pressure applied
to the electromagnetic multi-plate is minimized to prevent the
"tight-comer braking phenomenon." Furthermore, when
the ABS is activated, pressure to the electromagnetic multi-plate
is optimized to help maintain braking stability. The use of an electronically-controlled,
wet multi-plate clutch gives the TOD mode optimal and continuous
control over the distribution of the drive force to the front
wheels from 0 to lO0%, enabling the vehicle to exhibit excellent
handling stability and traction perfomance on road surfaces ranging
from paved to wet and slippery. The front output drive uses a
drive chain to reduce noise from the drive system. The highlow range change is performed
by a planetary gear mechanism, making the Transfer light in weight
and compact in size. The Transfer is lubricated by
an oil pump designed to stabilize both the multi-plate clutch
characteristics as well as the lubricant temperature. In Transfer position "4L"
the driving force is reduced by the planetary gear before being
transmitted to the wheels. The force to the rear wheels is transmitted
by direct coupling and, in order to transmit the force to the
front wheels, the drive sprocket is mechanically locked by a
sleeve. The force is directly transmitted to the front wheels
via the drive chain, bypassing the electromagnetic multi-plate
clutch altogether. 
AMERICAN ISUZU
MOTORS INC.
ISUZU MOTORS AMERICA,INC.
Taken From:
Isuzu Multimedia Press Kit |