Torque on Demand

[Hummer Aficionado_VT]

Can someone explain to me a little more how TOD works? Is it AWD?

[ojmagg]

Torque-on-Demand is a hybrid between part-time four-wheel drive and all-wheel drive. Isuzu, in conjunction with Borg-Warner Automotive, created the patented Torque-on-Demand system. This system performs like a conventional part-time four-wheel drive system when the transfer case is in the 2 High (two-wheel drive/High-range) position or the 4 Low setting (four-wheel drive/Low-range). When the transfer case is set to the "TOD" position (which stands for Torque-on-Demand), it acts like an all-wheel drive system.

The following components are contained in the Torque-on-Demand system: An electromagnetic multi-plate clutch (which is located in the transfer case), a computerized control unit, front and rear speed sensors, and a throttle position sensor that monitors engine output.

In the TOD setting, the amount of torque transferred to the front wheels is determined by the amount of force pressing on the clutch - when the clutch is completely disengaged, only the rear wheels are driven; when the clutch is completely engaged, a 50/50 torque split is achieved (50 percent of the torque goes to the front wheels and 50 percent of the torque goes to the rear wheels). The torque split (the amount of torque transferred to each axle) varies continuously as the vehicle is driven.

Briefly, here's how it functions when driving: When the transfer case is in the "TOD" position, the Torque-on-Demand control unit receives signals sent from the speed sensors and the throttle position sensor. Based on that input, it varies the amount of force that's applied to the clutch. When the rear wheels begin to slip, the control unit detects the slipping and determines the optimum level of torque based on the feedback control logic, and then increases the torque to the front wheels.

The control unit also uses the signal from the throttle position sensor to predict future conditions - including acceleration and deceleration - then determines the torque distribution.

Isuzu vehicles equipped with TOD have a TOD indicator lamp on the instrument panel that provides the driver with active feedback regarding the performance of the system and the torque split status. There are four lights on the TOD indicator, representing:

One bar illuminated: approximately 100 percent rear-wheel drive; 0 percent front-wheel drive.
Two bars illuminated: approximately 85 percent rear-wheel drive; 15 percent front-wheel drive.
Three bars illuminated: approximately 70 percent rear-wheel drive; 30 percent front-wheel drive.
Four bars illuminated: approximately 50 percent rear-wheel drive; 50 percent front-wheel drive.
Torque-on-Demand can make changes as quickly as 20 milliseconds (or, in the time it takes for a fly to flap its wings once).

Torque-on-Demand is superior to passive all-wheel drive systems (like those using a viscous clutch) because it responds to specific driving conditions. For example, some competitive systems don't know the difference between turning a corner, or slipping the tires in mud. That type of system often overreacts, providing more torque than is needed, and it is not as quick responding to the changing conditions.

The primary benefit of the Torque-on-Demand system is that the driver can select the TOD setting and leave it there for all driving conditions. The vehicle then makes all the decisions and provides positive feedback (via the TOD display on the instrument panel) so the driver is aware of how the system is functioning. Then, if the driver ever needs additional traction, he or she can select the 4 Low setting.

Thanks to the variable torque split, Isuzu vehicles with TOD have superior handling in adverse conditions because it constantly adjusts to the available traction. In addition, the Torque-on-Demand system anticipates what will happen next and adjusts the torque split accordingly. For example, if a driver is going down a hill and takes his or her foot off the accelerator, the TOD system automatically increases torque to the front wheels to improve handling and stability. Best of all, this happens without the driver sensing any changes. This makes the Isuzu vehicle more sure-footed and better balanced.

It took 12 years to develop this Torque-on-Demand system. It was first introduced in off-road racing trucks, where it had to handle engines producing between 800 - 1,000 ft.-lbs. of torque.

[etlsport]

nice description.. a few things are different/ misleading about the VX though

on the VX you can't select TOD or not, with the VX you are either in 4Hi (TOD, normal driving) or 4Lo..

the part about the bars is misleading too.. there is a digram of the vehicle with each of the rear wheels represented by a large light, which is always lit, each of the front wheels is represented by three lights, when none of them are lit 100% of power is in the rear.. almost never happens save for 0-5mph on dry roads.. after about 5mph one of the lights representing the front wheel will light up.. indicating 15% front and 85% rear.. as the wheels slip power is sent to the front and more lights will light up and go out as the TOD system adjusts

[Dino]

I love TOD!!

I live down a 1.5 mile road that starts out patched, broken & nasty asphalt, then turns to bumpy dirt. There are a couple hairpin corners where the TOD really keeps the VX pullin on the line the front wheels are pointing. One such corner is radicaly uphill and sharp left. It's fun to manualy shift to 2nd then feed the throttle on as it just rails it's way around the turn!! The lower the gear you're in, the more sensitive the TOD engagement is to the throttle movement.

I've driven other vehicles on the same turn and had the rear wheels spin. It's a ranch road and I see pickup trucks spinning there all the time.
No spinning with the VX and TOD thank you!!

[Hummer Aficionado_VT]

WOW! Thanks for the amazing description guys. That is very helpful!

[blacksambo]

Now! How does TOD compare to other up to date systems like the new Land Rover Terrain sensing system, and does anybody else offer this type of TOD technology in conjunction with a locked differntial low mode? Thx.