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.

Taken From:
Isuzu Multimedia Press Kit