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SUVs 4WD & AWD systems explained
1377 messages, Last post on Dec 05, 2009 at 1:47 PM
You are in the SUVs Forum. Your Hosts are steve_ & tidester
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The Chrysler minivans have a full-time AWD system with a viscous coupling limited slip centre differential. Power is split 90/10 in no-slip conditions, and up to 50/50 when slippage is detected. It actually works quite well, but is absolutely no help in understeer conditions. Understeer is not much fun at all in the snow since you can't steer the vehicle with your right foot. :-p The next generation V-class (if they decide to carry over the name) based on the W164 next generation M-class platform is supposed to arrive - based on what I've read (unconfirmed officially with MB, of course)- when baby Justin is about 10 years old...in other words 2009. |
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"in "Auto" mode, it is active at all times and monitoring for slippage. It's also part-time because it doesn't have a centre differential and hence cannot be used continuously on dry pavement (hence the reason why the auto mode only sends power to the opposite axle when slippage occurs)." What does the above mean Drew? can it or can it NOT be used on dry conditions where slippage could occur, i.e. dry with occasional ice spots for example? How reactive is the auto mode. Is it reactive under acceleration or only from a stop. Any help here would be appreciated. Thanks. |
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Yes, the GM's AutoTrac system can be used in "auto" mode at all times, regardless of surface (in fact, I'd recommend that one leaves it in this mode even on dry/wet surfaces, rather than the "2WD" mode). In "auto" mode, whenever rear wheel slippage is detected, power is automatically transfered to the front wheels to assist. When rear wheel slippage stops, the system reverts back to RWD mode. The 4WD High mode should not be used on anything but slippery surfaces though, since it locks the centre differential. Hope this helps! Drew Host Vans, SUVs, and Aftermarket and Accessories message boards |
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| In refernece to the GM auto with 4WD lo, hi, and auto, does it or doesn't it have a center diff. You said it doesn't but now you said in 4WD it locks it. Thanks. | |
| Is permenant vs full-time referring to being able to turn AWD on or off. My trooper has 4WD torque-on-demand (TOD) that is used in any condition. Normally, 15% front and up to 50:50 depending on slippage. 15% may not fall into the classification of AWD though. The 4WD TOD can be turned of to rear wheel drive. It also has 4WD Lo. Also, this is a vehicle with a form of AWD that falls into the less than $30k price that someone referred to above. | |
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Oops, my mistake. I was thinking of something else at the time. There is NO centre differential. The GM Autotrac equipped vehicles are basically rear wheel drive rigs. When the rear wheels slip, the AutoTrac activates an electronic control module, which uses a wet clutch pack, activated by an electric stepper motor, to send torque to the front wheels that still have traction. It is a "4WD on demand" system (or auto 4WD system), activating 4WD when needed. It has part-time 4WD and 2WD options, as well as a low range in the T-case. The Isuzu Trooper's TOD 4WD system is considered full-time 4WD. It is similar to the Acura MDX's VTM-4 full-time AWD system, except that it is RWD biased, instead of the FWD bias of the MDX's system. Heck, the Isuzu TOD system is even made by the same company as the MDX's VTM-4 system...Borg Warner. It is considered 4WD and not AWD because it has low range gearing; AWD does not. Drew Host Vans, SUVs, and Aftermarket and Accessories message boards
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| I have a Santa Fe LX 4WD! What is my type of 4WD categories fit into? Isn't Full-Time 4 Wheels Drive or Full-Time AWD, or Is just of 4WD? Please respond. Thank you. | |
| The Sante Fe has a full-time AWD system with a viscous coupling centre differential. | |
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I have a question to which would be prefered and why. AWD with the skid control/traction or AWD with the limited slip differential? Can't have it both ways. Also, on the AWD version does the TC only control the front tires or all? Obviously the 2WD version only controls the front. Thanks. |
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Read my messages here: drew_ Feb 11, 2001 7:06pm drew_ Feb 11, 2001 8:00pm VSC incorporates 4 wheel traction control, which is a component of stability control. Watch the video clip in my 2nd message (#35) linked above. Since 4 wheel TRACS simulates a locking differentials for the front and rear axles, a mechanical rear LSD would be redundant. Drew Host Vans, SUVs, and Aftermarket and Accessories message boards |
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