Torque on Demand

[Hummer Aficionado_VT]

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

[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!! :rolleyes:

[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.

[Dino]

Food for thought ...

I wish I could mate up the hydraulic controled TOD transfer case to a 5 speed manual trans, with an engine driven hydraulic pump so it could all work. Imagine having the TOD capabilities in a manual with better mileage and safer off roading due to the mechanical link betwen engine and wheels.

I'm still seriously considering the manual conversion even though I love the TOD.

[tysamigo]

WOW, thank you very much for the description. I'm not very "mechanical" with cars....yet. I'm learning. This all makes sense, however you would think that someone would have duplicated the technology by now. It's been some time and I haven't seen any other vehicles with it. It all sounds good and I'm VERY glad I have it. It just makes my rig that much more different than the normal vehicle :)

Is the TOD durable? Are they likely to have problems and are they expensive to fix? Just a few q's for the newbie...

Thanks

[circmand]

I know the idea to match TOD to a manual transmission may seem like a good idea but todays modern automatic transmissions perform better than the driver and get better MPG than the manual transmissions.

[Chopper]

There are 4x Troopers and Rodeos made with the 6cyl/5sp.manual combo...I just don't know if it's the Borg Warner setup, or more of a GM deal. I've worked on both, but never really paid any attention to the transmissions.

[Chopper]

I can think of a lot of descriptors for this slush-box, but modern and efficient would not be among them. This thing has been around since the K car :rolleyes: It was not GMs' finest moment.

[blacksambo]

I can think of a lot of descriptors for this slush-box, but modern and efficient would not be among them. This thing has been around since the K car :rolleyes: It was not GMs' finest moment.



Is there a better system currently on the market that does everything the VX can do but is "modern and efficient" or was TOD the last word in automatic transfer of power? Just curious as to what is out there.

[Dino]

With cars, Porsche did some very cool stuff with the Carerra 4. Big bucks on the maintenance though... :rolleyes:

I don't know of another SUV that has a TOD system.

[Chopper]

I've never had issues with the TOD. It's pretty slick in that you are all but RWD till you need more, then it's there, pretty quickly, and fairly smoothly. I like it at least as much as the Audi/VW system...maybe more...but it's light years behind Acuras' new system. I am talking only about road manners here, because I know absolutely nothing about offroading. My comments were directed at the transmission itself. I generally don't like automatics, and do not care for this one at all. Lexus and MB make some amazing gear boxes, but I'm with Dino, I'd rather do it myself. A manual conversion is tempting. Has been for six years now.

[blacksambo]

I've never had issues with the TOD. It's pretty slick in that you are all but RWD till you need more, then it's there, pretty quickly, and fairly smoothly. I like it at least as much as the Audi/VW system...maybe more...but it's light years behind Acuras' new system. I am talking only about road manners here, because I know absolutely nothing about offroading. My comments were directed at the transmission itself. I generally don't like automatics, and do not care for this one at all. Lexus and MB make some amazing gear boxes, but I'm with Dino, I'd rather do it myself. A manual conversion is tempting. Has been for six years now.

Thanks for the transmision clarification. I'm not so certain about that Acura SH-AWD system. First, it sticks you 90% into front wheel drive until something tricky pops up? Second, that yaw control stuff sounds a little overblown. Meaning they state versus conventional 4WD its better because it automatically splits power between left and right tires. Doesn't limited slip differential do this? So, the only time the Acura's system is of benefit is versus locked-differential mode 4WD's. Is that really all that advanced versus VX's TOD which is biased 90% rear wheel drive with full-time LSD? I'm not so sure TOD has been really eclipsed yet, especially since it's been fairly bullet proof dependibilitywise for 11 years running. Not trying to pat Isuzu on the back here, just trying to guage the true lay of the land today.

[Chopper]

Drive that new Acura RDX hard, you'll feel the difference. Having the outside wheel dig in on a hard turn, rather than slipping the inside one is a huge advantage. The RDX is no lightweight, but the awd they are using makes it seem smaller

[VehiGAZ]

My two cents:

Cent #1: Acura's system isn't all that new - I had its one-axle progenitor on my 1997 Prelude SH. It does not work like an LSD, by the way. An LSD keeps the inside drive wheel from spinning too much in a turn compared to the outside wheel, since the spinning wheel decreases the amount of torque going to the outside wheel in a conventional differential. The SH system actively transfers torque to the outside drive wheel to get it turning faster than the inside wheel so that neither of them spins, and you get extra turning help when you need it (that's where the yaw sensor comes in). To illustrate the differences numerically, consider these three cases:

a) a regular differential in a hard turn under power with poor traction under the wheels: the inside drive wheel will spin, so up to 100% of the torque will go to the spinning wheel, and 0% torque will be delivered to the ground.

b) a limited slip differential in the same conditions: the inside wheel will start spinning, but the LSD will only allow it to spin a certain amount compared to the outside wheel. With the 40% LSD on my other car, the outside wheel will get something like 50% of the torque, the inside wheel will get 40% of that (20%), and the rest (30%) is lost to spinning the inside wheel, resulting in only 70% of the torque getting transferred to the ground (these numbers are for illustration purposes only! I have no idea how to calculate the actual values, which probably involve differential equations, the friction coefficient of the road surface, etc.)

c) the front-axle SH system in the same conditions: the system will sense the slippage and yaw rates and apportion torque to the outside wheel so that neither wheel spins, and the car goes where the tires are aiming. Let's say that amounts to 80% to the outside wheel and 20% to the inside wheel, resulting in transfer of 100% of the available torque to the ground.

It's a great system - another example of Honda engineers cheating physics (the much-copied V-TEC valve train being another good example). I beat on my SH system for 145,000 miles and it never gave me any problems. In the SH-AWD system, I think they are using the same principle to apportion torque not just left-right but also front-back.

Cent #2: The Isuzu TOD system works pretty well, except that it doesn't hold the engagement of the front axle long enough when driving on snow. When starting from a dead stop on a snow-covered road, it senses slip in the rear, it engages the front, then sees that there is no speed differential between the axles, and disengages the front 0.1 seconds later. Of course, the rear axle starts spinning again, it engages the front for a tenth of a second, sense no speed difference, etc... It would be great if after fully engaging the front axle, it held it there for a couple of seconds before gradually decreasing torque to the front axle. It operates much better on dirt, though, I'll give you that.

[blacksambo]

Great commentary! But how do we countenance the 90% front drive bias of the SH-AWD system? They claim it's for fuel efficiency sake, but I think that only compensates for the energy expended spinning a rear wheel drive drive shaft, which I believe is a neglegible energy expenditure compared to having the handling advantage provided by the full-time rear wheel drive biased VX? Also, the Acura vehicles don't offer the option of going "combat" and utilizing raw 4x4 locked differential low range torque, which they claim is made superfluous by their SH-AWD system. Again, I think that's probably overpromise as a true lowrange mode behaves so much differently than any automatic device does, it's just brute rubber eating force and I noticed that Acura in their literature make not statement about consuming precious tire rubber on pavement with their system. If it really had that brute force available I think they would have cautioned against its effects. The VX literature does.

[VehiGAZ]

Thanks!

As for ToD vs. SH-AWD, I guess I would not compare the two systems so directly. ToD is an appropriate system for enhancing traction in off-road vehicles like the VX and Trooper, while the SH-AWD system is appropriate for enhancing cornering and handling in a sports sedan, while at the same time giving it a measure of all-wheel-drive traction enhancement, much like Audi's Quattro system.

I don't think any AWD system is a suitable replacement for true 4WD on a off-roading truck. They are nice enhancements to traditional non-truck drivetrains, and may help you get home in the snow, but I don't think Acura or Audi or even Subaru intend or market their AWD systems to be substitutes for true 4WD.

[blacksambo]

First, I wanted to say that this has been a most informative dialog. I've learned a lot from this groups positive exchange of knowlege on this topic. This board is a great way to share perspectives.

Second, I wanted to point out that the Acura while offering sexy transfer of power technoadvancements (if there is such a word) still relies on unit body costruction instead of a body on frame constuction like the VX. I'd have to guess that the use of unit body is why that MDX/RDX is biased towards front drive as the hull lacks the torsional rigidity found in body on frame constuction for effectively sending power to the rear except under difficult surface situations when it's required. We all know front drivers tend to understeer due to weight distribution balance issues. Nevertheless, the VX has near neutral weight distribution and the torsional strength to drive the rear wheels most of the time. When it comes to performance driving, like road racing, I don't think there are any teams using solely front drive configurations due to understeer considerations. Just some additional perspective.

[AREA 51]

I think hyundai or kia is using tod on one of their suv's

[blacksambo]

It sure sounds like good 'ol TOD if you read their website. They also call it an all new system??? However, theirs is front wheel drive biased like the Acura, that's how they probably get away with calling it "all new".

[Chopper]

Neutral weight distribution? You're trippin'. Look, I love this car as much as anyone, but... Why do you think the gas tank is hanging under the rear bumper? This car will push like a rhino on wet clay, till the TOD reacts. We have lots of "shell"(sand) roads in this county, so I get to play with it alot. As far as the Low range thing...the Acura is not intended for such activity. It'll handle the sand roads, but if you want more, it's the wrong car. I got an 03 STI I am currently tearing the rubber off of. Had it for three days now, and I'm about ready to sell it. It is much faster,sticks better, and rotates much more easily, than 0177... and three days in...I'm done with it (sorry Wormgod) The engine sounds wonderful, the squeaks and rattles, not so much. It just lacks somehow. This VX appeals on some other level, beyond performance. Face it, tecnology has marched on..215hp pushing 4000 pounds cannot be considered a performance vehicle anymore. The family sedan is averaging between 265-300hp. My wifes Altima has 265 and it's NO performance vehicle. The VX stands on its own. It's unique. Trying to pump it up only cheapens it in my opinion. It's advanced for 1993 when it was designed, but it a far piece from cutting edge at this point. Compare it in context, it's great...arguing it vs. current tecnology sounds like "They don't build them like this anymore" I hear that every time some guy drags in a '67 Cougar or some such old junk. In my head I always say, "There's a good reason" ;) Wayne

[blacksambo]

Perahaps you've answered your own question? The more sheer numbers and technology you buy may not be the vehicle answer your seeking at all. Instead, it seems like the VX delivers some sort of magical or quasi sophistcated driving experience not found in these other contrived numbers-only driven package scenarios. One might say that the VX delivers some sort of very satisfying unique blend of sensory factors not easily duplicated by other attempts, no matter what the date of manufacture. I know this sounds somewhat mythical like dragons or something but don't deny its potential existence. These things due happen and its what SCCA vintage racing is all about.

[blacksambo]

Perahaps you've answered your own question? The more sheer numbers and technology you buy may not be the vehicle answer you're seeking at all. Instead, it seems like the VX delivers some sort of magical or quasi sophistcated driving experience not found in these other contrived numbers-only driven package scenarios. One might say that the VX delivers some sort of very satisfying unique blend of sensory factors not easily duplicated by other attempts, no matter what the date of manufacture. I know this sounds somewhat mythical like dragons or something but don't deny its potential existence. These things due happen and its what SCCA vintage racing is all about.

[blacksambo]

On the subject of technology marching onward. That Subaru you speak offers a system called VTD,right? Which if you read about it sounds an awful lot like the VX's TOD. So is the difference performance-wise really more down to Horsepower than a more advanced driveline? If so, don't the VXer's with the Alpine supercharger compensate somewhat for this difficiency by adding this extra? Just curious.

[Chopper]

Naa... the Subie is much bigger. Anything more than 5lbs. of boost will grenade the Isuzu engine (without MAJOR mods) I've seen Subaru engines making 400hp. on pump fuel...different deal. The flat 4 was made to be boosted, the six was not...too much compression, among other things. You are right in your nostalgia take...the old mans' series two E-type is still a special car to drive, but a Miata will out drive it everywhere but the straights, and is a better car in every measurable way ;)

[circmand]

Come on a Miata? I think the car is a cute little sports like car and would not mind having one as a 2nd car in the garage ut to name it and performance in the same breath is a stretch. I don't want to insult you or your chosen ride but I have a 1974 JH in my garage that I am restoring and the stock specs of this car in 1974 out perform a Miata in everything but breaking power since they did not have discs back then

[Chopper]

'74 is a twelve cyl. if I remember...the early ones all had that beautiful, straight six. I learned to drive a manual in my dads, at the Hatfield racetrack (long gone) in PA, when I turned thirteen. I only used a Miata as an extreme example of how much things have changed. I am not a Miata lover (I am 6'3" and 200lbs.) but I have "spec" raced them several times at Robling and Sebring road courses... I am pretty sure it is a faster way around the track. They allow you to brake sooo much later, and carry sooo much more speed thru a curve...you can even get back on the power earlier comming out. The Big Cat just can't compensate with enough in the straights. I dunno...never saw anyone race the two. (Pinks..road course edition) I never dared drive his E-type hard.... but I was in it with him goin' balls out, all opposite lock, chasing a little Alpha at Lime Rock. I think I coulda taken him in a '06 wearing Pilot Cups ;) ;) P.S. we didn't catch the Alpha

[johnnyapollo]

The only current production vehicle that still ships with a Borg-Warner TOD is the Jaguar X-type (that I know of) - they don't reference it as TOD but it's supposedly the same system. There was a brilliant commercial - showed a close up of a guy spinning around - camera pans back and you realize he's in a sedan that's spinning on an icy road - creeping up behind and eventually passing him is a Jag X-Type and then they go into the whole 4-wheel drive with sensors bit. Here's a different commercial:

http://www.youtube.com/watch?v=pfL3egQ61bU

There was also this video:
http://www.youtube.com/watch?v=2QvSymMUL4A

-- John

[Jolly Roger VX'er]

I think hyundai or kia is using tod on one of their suv's

I've come across this a few times myself when researching vehicles for a co-worker who was shopping. Case in point:

http://consumerguideauto.howstuffworks.com/2006-new-york-auto-show-kia-cga.htm

.......the new sorento will again be available with rear- or four-wheel drive and come in two trim levels: lx and upscale ex. the lx 4wd system is part-time, has a low range, and isn't designed for use on dry pavement. available on ex is kia's torque-on-demand (tod) full-time 4wd system. the tod system detects wheel slip up and automatically transfers power between the rear and front wheels. tod may be used on dry pavement. for hardcore off-road junkies, a limited slip differential for the rear axle is available.

It sounds like their version of "TOD" excludes low-range; and, I just got to laugh about the statement "for hardcore off-road junkies, a limited slip differential for the rear axle is available"...

I noticed most of you hard-core off-roaders here waiting to replace your lockers with limited-slips..lol. :p

[mcaramb]

Just a thought to save MPG... can the TOD be disengaged from the rear tires with some sort of mechanical disengagement device on the rear drive shaft? Or would the lack of torque to the rear wheels completely screw up the transmission system?

Probably, you'd have to completely change out the transmission, drive axles, rear differential, computer system, etc... :)

Just wondering, as the TOD is what makes our lovely cars so gas hungry :)

-Mike

[blacksambo]

You are right. But, the VX is body on frame, and 3,800lbs strong. Said differently, it's a match, despite its small size, for a heavy-weight collision situation, most 2wd SUV's are not. You have to always measure fuel economy benefit versus saftey, don't you?

[mcaramb]

No argument there, but a Vehicross converted to 2WD would still be 3,800 pounds, body on frame construction, still as evenly matched in a collision, just 2WD instead of 4WD. Granted, not as tight on the road as before in wet conditions, but no less than other 2WD vehicles.

Rather than steer the conversation towards safety, I was just wondering if it would be possible to convert our cars from 4WD to 2WD. And hell, if it can be done with a simple interlock, then we could get the best of both worlds. Turn on the TOD in rainy conditions, otherwise turn it off. Like a third setting on the 4WD stick... 4x4, TOD, and 2WD.

[So-CalVX]

Just a thought to save MPG... can the TOD be disengaged from the rear tires with some sort of mechanical disengagement device on the rear drive shaft? Or would the lack of torque to the rear wheels completely screw up the transmission system?

Probably, you'd have to completely change out the transmission, drive axles, rear differential, computer system, etc... :)

Just wondering, as the TOD is what makes our lovely cars so gas hungry :)

-Mike

why would u want a front wheel drive VX???:confused:

i'm fine with my 13-15 mpg 4wd VX