Auto LSD operation ?

[n5tz2000]

Hello:

Does any know definitively how the TRAC Traction Control System functions with and without the Auto LSD switch on or off ?
In other words what does the Auto LSD switch really do on 2WD 4Runners ? It's not really clear in the manual and know one that I can contact at Toyota has an answer.

Dennis


Dennis Bradley,P.E. (N5TZ) | Fax : 832-201-9803
Email : [email protected] | Mail : P.O. Box 79612
Phone : 713-408-7113 | Houston, Texas 77279

 

[Thai]

What is an "Auto LSD"?? What do you mean??

If you have a 2wd 4runner, then TRAC OFF button will result in traction control being shut off. VSC (stability control) remains on. So, even though traction control is off, you still cannot do massive donuts in your 4runner because VSC will shut you down!

Traction control has the same effectiveness as most LSD. So, i think that is what you mean. Correct me if i am wrong.

 

[dcampen]

What is an "Auto LSD"??

I think Toyota started using this term about a year ago. As best I can tell it is used interchangeably with TRAC. I guess some marketing people decided it sounded neat to be able to say that the front and rear differentials were "Auto LSD" differentials.

 

[dcampen]

Here it is in the Toyota literature:
http://www.toyota.com/4runner/models.html

"Automatic limited-slip differential (2WD models)"

 

[jeober]

2wd's have a button labelled Auto LSD. Does anyone know how this functions when enabled?

2wd [2005] has no TRAC off button. There is traction control - it can kick in regardless of the Auto LSD button.

 

[dcampen]

There is traction control - it can kick in regardless of the Auto LSD button.

What makes you say this? It seems to me that "Auto LSD" is just a new marketing term for TRAC.

 

[UoD]

On the 05 runners, the traction control is always on I believe. The instruction manual kind of explains the auto-LSD operation. Auto-LSD is useful in situations such as one where you are stuck in soft beach sand and one of your wheels in turning. It will apparently actuate the brakes or something to prevent the wheel that is slipping from turning. Or at least that is what I remember reading. You are supposed to only activate it when completely stopped ... and not use it at high speeds. It said something about overheating something when used too long (the brakes I assume?)



Ok --- I just read what I wrote and am now wondering what the heck the difference is between auto-LSD and the traction control system on the runner ....

 

[dcampen]

Auto-LSD is useful in situations such as one where you are stuck in soft beach sand and one of your wheels in turning. It will apparently actuate the brakes or something to prevent the wheel that is slipping from turning.

What you have described is traction control also called "TRAC" or "ATRAC" and now also called "Auto LSD".

 

[n5tz2000]

Near as I can tell the 'Auto LSD' switch has replaced the 'TRAC off' function but rather than turn off the TRAC system it alters the algorithm controling the system in some way, a software switch so to speak. Since the brakes, throtle, etc. are controled by the TRAC system to maintain stability and traction 'on-road' the turning the switch on may optimize the system for 'off-road' conditions.

In order to get a 'feel' for the differences I'm probably going to have to try the sytem off-road with the switch on and off.

If I get a chance to do this I'll the the group know the results.

Dennis

 

[Thai]

Damn those marketing people!!

So, if this is right, then "auto-LSD" button will turn it OFF. VSC is ALWAYS on.

 

[dcampen]

Near as I can tell the 'Auto LSD' switch has replaced the 'TRAC off' function but rather than turn off the TRAC system it alters the algorithm controling the system in some way, a software switch so to speak. Since the brakes, throtle, etc. are controled by the TRAC system to maintain stability and traction 'on-road' the turning the switch on may optimize the system for 'off-road' conditions.

My guess is that it is the same switch with a new name; the TRAC On/Off switch now called the Auto LSD On/Off switch.

Also, and now we get even farther into semantics, stability control and traction control are separate functions. The function of stability control (called VSC by Toyota) is to correct for over and understeer during cornering and may use engine throttle as well as selective braking to do this. The function of traction control (sometimes called TRAC or ATRAC by Toyota, now sometimes called Auto LSD) is to enable torque to be applied to a wheel even when the other wheel on the same (open) differential is slipping; it does this by applying the brake to the wheel that is slipping, the times when TRAC has been active on my truck I have never noticed it also controlling throttle and don't believe that it would.

 

[jeober]

The 4runner has electronic throttle control. This means the butterfly throttle plate is no longer mechanically coupled to the accelerator. Traction control is definitely tied into the throttle control but you probably won't detect it -- just like you don't everytime the transmission shifts.

I do agree that the functions of LSD, traction control and stability control are separate.

More questions:

I have 2wd. I've noticed that I get a dash board indication when traction control kicks in. And on rare occasions (slippery winter conditions) I get an audible warning -- what triggers this?

I also hear occasionally while making low speeds turns relays click like the ABS control is detecting mismatched wheel speeds. Anyone else?

 

[Thai]

More questions:

I have 2wd. I've noticed that I get a dash board indication when traction control kicks in. And on rare occasions (slippery winter conditions) I get an audible warning -- what triggers this?

I also hear occasionally while making low speeds turns relays click like the ABS control is detecting mismatched wheel speeds. Anyone else?

1. I believe that the light/beep will come on when VSC or TRAC or both are activated...it is not specific to any one function.

2. If the relay clicks occur on dry pavement while you're driving gently around a corner, then the little clicks are more likely the ABS pump charging, rather than ABS doing it's thing.

 

[dcampen]

Traction control is definitely tied into the throttle control but you probably won't detect it

Do you have any evidence to support this?

 

[n5tz2000]

I have discuused the TRAC system with a friend in the buisness, he works for Mazda but the Toyota systems are similar. He indicates that the TRAC or Stability system can control the brakes, throttle, spark advance or retard (to control engine power output) and some other parameters. Both the limited experience I have had with it and his experiences indicate that it work VERY well. He owns some other 4WD vehicles and the info he's gotten from his company and comparisons he's made with 2WD drive vehicles with the TRAC, VSC system, he claims the 2WD versions can come VERY close to 4WD performance in many circumstances.

I know that the experiences I've had with my 4Runner have convinced me that it may be the best SUV on the market and I've owned or driven Explorers, Expeditions, etc. But I guess all of you knew that anyway (hihi).

Dennis