Auto LSD, VSC, Center Diff Lock, etc....

[AE1M]

OK, I am new to 4WD vehicles and the JapEnglish of the Owner's Manual doesnt really give me (as an engineer) a good understanding of the systems. Is there a primer somewhere or a better description of the workings of these systems.

I found this:
HowStuffWorks "How Four-Wheel Drive Works"

but I'm not sure of exactly how it aligns with the systems in my 08 Limited.

Thanks,
Bob

 

[SecretAgent]

Do you know how to tell if someone is an engineer?




you don't have to, they'll tell you. :lol:

but on a more serious note, search around the forums. all of the systems have been discussed in detail several times here.

 

[AE1M]

Do you know how to tell if someone is an engineer?




you don't have to, they'll tell you. :lol:

but on a more serious note, search around the forums. all of the systems have been discussed in detail several times here.

I said that because I wanted more info than just "use this feature if your wheels are stuck"

Your reply is of no help whatsoever, but thanks for your well thought out smartass retort.

 

[SecretAgent]

I said that because I wanted more info than just "use this feature if your wheels are stuck"

Your reply is of no help whatsoever, but thanks for your well thought out smartass retort.

ok, since you can't take things in good humor, let me go ahead and spell it out for you.

there is a little button at the top of the forum that says "search" if you put your mouse on this button and click the left button it will pop up a little box, and in this box you use your keyboard to type in the terms you are looking for. you will then be taken to another page listing the "search results" if you read through some of those "results" you will get the information you want, but are too lazy to look for on your own. as i said before, ALL of those aforementioned systems have been discussed IN DETAIL several times before. SEARCH FOR THEM.

thanks, and have a good day.

 

[offshorebear]

Center diff lock makes the speed of the front and rear drive shaft the same.

VSC is Vehicle Stability Control. This uses inputs from the steering wheel and an accelerometer to detect if you are skidding. It will use brakes and cut engine power to try to fix this.

Auto LSD uses the brakes to try to keep both wheels on an axle going the same speed.

Without the CDL and LSD, all the power will try to just find the path of least resistance. You could be sitting there spinning the one wheel with the least amount of traction. (this isn't exactly true because we have a Torsen center diff which works a little differently)

You don't want to drive on the street with the CDL locked. Both axles will try to spin the same speed, but when you turn you need one axle to go faster than the other. There will be binding and tire scuffing and eventually you could break something. Only use the CDL when there will be some slippage, such as in snow or mud or offroad.

VSC will get very confused very quicky offroad and will think you are skidding all over the place. It will rob you of power and you will get stuck, so turn it off before going offroad. (locking the CDL turns this off)

 

[AE1M]

Center diff lock makes the speed of the front and rear drive shaft the same.

VSC is Vehicle Stability Control. This uses inputs from the steering wheel and an accelerometer to detect if you are skidding. It will use brakes and cut engine power to try to fix this.

Auto LSD uses the brakes to try to keep both wheels on an axle going the same speed.

Without the CDL and LSD, all the power will try to just find the path of least resistance. You could be sitting there spinning the one wheel with the least amount of traction. (this isn't exactly true because we have a Torsen center diff which works a little differently)

You don't want to drive on the street with the CDL locked. Both axles will try to spin the same speed, but when you turn you need one axle to go faster than the other. There will be binding and tire scuffing and eventually you could break something. Only use the CDL when there will be some slippage, such as in snow or mud or offroad.

VSC will get very confused very quicky offroad and will think you are skidding all over the place. It will rob you of power and you will get stuck, so turn it off before going offroad. (locking the CDL turns this off)

Thank you.

 

[Maz]

Center diff lock makes the speed of the front and rear drive shaft the same.

VSC is Vehicle Stability Control. This uses inputs from the steering wheel and an accelerometer to detect if you are skidding. It will use brakes and cut engine power to try to fix this.

Auto LSD uses the brakes to try to keep both wheels on an axle going the same speed.

Without the CDL and LSD, all the power will try to just find the path of least resistance. You could be sitting there spinning the one wheel with the least amount of traction. (this isn't exactly true because we have a Torsen center diff which works a little differently)

You don't want to drive on the street with the CDL locked. Both axles will try to spin the same speed, but when you turn you need one axle to go faster than the other. There will be binding and tire scuffing and eventually you could break something. Only use the CDL when there will be some slippage, such as in snow or mud or offroad.

VSC will get very confused very quicky offroad and will think you are skidding all over the place. It will rob you of power and you will get stuck, so turn it off before going offroad. (locking the CDL turns this off)

That was extremely helpful offshorebear. A question please, about turning off the VSC. Reading through the manual on this subject is more than just a little confusing. It some places (page 175 in my 2009 Manual, and I have 4WD) it talks about turning off the VSC in order to activate the auto LSD at speeds below 62 MPH. In other places (191,194, and 195) it talks about stopping the vehicle completely and depressing the VSC switch for 3 full seconds. This while referring to turning off A-TRAC and VSC "if the vehicle gets stuck in fresh snow or mud."

The question is I assume we're talking about two completely different things involving the same turn off system?? If so can anyone help clarify this. I'm not an engineer, and I didn't stay at a Holiday Inn. Help!

 

[offshorebear]

I have an '04 so I don't have a button that just turns off VSC (I wish I did). I also don't have an auto LSD switch. These features depend on the year and if you have 4wd or 2wd.

In your example of getting stuck in snow with VSC enabled, the computer will detect large amounts of wheel spin and cut the throttle. It thinks you are going down the highway and fell into a ditch or something. Now, you are really stuck in snow and not moving at all, so you need to spin the wheels, clear the tire treads, and power out. That's why you disable VSC.

A-TRAC is traction control, or the same thing as "auto LSD". It's not really meant to work at highway speeds, but it works great off road. Let's say you are driving on some rocks and the right rear wheel lifts into the air (no traction). Normally all the power going to the rear axle will go to spin this wheel in the air (path of least resistance). A-TRAC will use the ABS sensors to detect this wheel spin and use the brakes to stop just that spinning wheel. This sends the power to the wheel still on the ground, allowing you to continue moving forward. Since you have 4wd A-TRAC will work across both the rear and front axles.

In some offroad conditions the A-TRAC will help, like when you start to lift wheels off the ground. Other times you really just need to spin the tires fast to clear the tread, such as in mud. At these times you may want to turn A-TRAC off.

 

[CJ3Flyr]

This while referring to turning off A-TRAC and VSC "if the vehicle gets stuck in fresh snow or mud."

I suspect that's an error in the manual. You wouldn't want A-Trac shut off in that situation. My guess is the manual should say "turning of the TRAC..." TRAC is the portion of the system that cuts the power. We (incorrectly) say the VSC is cutting the power when it's really the TRAC portion of the system cutting the power. The VSC is an 'umbrella' system/term that has sub-parts including TRAC. If it really does shut the A-TRAC off then you could put one side of the vehicle on ice and the other side on pavement and only the ice wheels would spin. Offshorebears comment about spinning to clear the tires is true and you might want the A-TRAC off for that. I would rather have it on and just step on the gas a little harder. I'd like both wheels of the stuck axle to be receiving power.

I'd be interested in knowing if it really shut the A-TRAC off. The one side on ice scenario I mentioned earlier would tell the tale.

Many times it seems as though the manual is written by Japanese engineers and then translated by Japanese with degrees in English. Occasionally something gets lost in translation IMHO.

 

[T4R402]

I'll admit, this clears up a thing or two I was wondering about with these systems as well. Thanks.