ATRAC Question - Power Distribution? (1 Viewer)

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I was watching this youtube video on differential 101... ok, can't seem to embed - using {youtube]F40ZBDAG8[/media], with { replaced with [



And it got me thinking about ATRAC. If I understand ATRAC correctly, it applies the brake to the tire that is slipping.... kinda like ABS, but the differential stays open. So ATRAC kind of simulates a locked differential, but does this braking action actually help rotational force (torque) to the tire with traction? If so, how?
 
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when ATRAC uses the brakes, the previously spinning tire now has the most traction (the break) that allows the other tire(the one on the ground) to be the tire with less traction. Thus, the open diff gives this tire more traction. This is my understanding of how the system works at least.
 

2000UZJ

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when ATRAC uses the brakes, the previously spinning tire now has the most traction (the break) that allows the other tire(the one on the ground) to be the tire with less traction. Thus, the open diff gives this tire more traction. This is my understanding of how the system works at least.
what? lol


say your driving up a off camber situation. Your passenger front tire starts to loose traction the system (abs) will start to apply the brake on that wheel only, that causes engine power to transfer to the wheel with most traction (driver side wheel that is planted on the ground). The system monitors the wheel's traction (pulsating, that is why the everything shimmies a little at first). To much throttle and the system kills ATRAC to prevent further damage (some have actually had the system kick in and blow the diff, I have almost blown my front diff via ATRAC), to little and the system cannot "push" enough power to the other wheel with traction and gets jumpy. A nice easy, steady foot will do the trick. When you get into a situation where ATRAC will kick in, creep up to it. When you start to feel the truck start to flex out or lift a wheel give it the gas and hold it until you are through the obstacle. Stopping and going will only confuse the system and create a lot of bouncing. One you have a little momentum ATRAC can do it's thing and won't nearly have to work as hard pulling you through something rather than starting and stopping where it has to get you moving off-camber again.
 
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what? lol

Your passenger front tire starts to loose traction the system (abs) will start to apply the brake on that wheel only, that causes engine power to transfer to the wheel with most traction (driver side wheel that is planted on the ground).
How?... how does braking the tire that doesn't have traction apply more power to the one that does. It would seem the wheel that doesn't have traction is getting the same amount of power, only to have the brake applied.
 

2000UZJ

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How?... how does braking the tire that doesn't have traction apply more power to the one that does. It would seem the wheel that doesn't have traction is getting the same amount of power, only to have the brake applied.
energy takes the path of least resistance. By applying brakes to the wheel with no traction, it makes the wheel that is still on the ground the path of least resistance. Making you go over stuff.


ATRAC grabs the passenger side wheel forcing drive power to contiue through the driver side wheel @ 5:40 in this video.

YouTube - Sheep Wallow

ATRAC grabbing my passenger wheel again, forcing drive power to continue through driver side.

YouTube - ATRAC violently stopping a wheel

ATRAC grabbing yet again my passenger wheel to force drive power to driver side wheel to climb the ledge.

YouTube - ATRAC pulling me up a 3' Ledge

And last one, ATRAC grabbing the drive side wheel to force power to the passenger side wheel to climb ledge.

YouTube - RiverRock Ledge Climb in a LandCruiser
 
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2000UZJ

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How?... how does braking the tire that doesn't have traction apply more power to the one that does. It would seem the wheel that doesn't have traction is getting the same amount of power, only to have the brake applied.
They both have the same power, just one has brakes on making the other spin. I don't think that tire with traction gets more power than the wheel slipping. Just power is routed to the tire with grip. If that makes sense.
 
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think of it this way...

with open diffs, the power follows the path of least resistance, ie the slipping tire. When the ATRAC forces the brake to clamp down on that tire, it no longer is the path of least resistance and therefore redirects the power to the tire with grip.
 
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what i was saying is when the atrac is applying the abs, during those pulsations, the tire on the ground has the least resistance, for split second intervals, thus giving it more, or the power getting momentum of the 100 going.
 

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Quote below is from the Toyota New Car Feature Manual. There is a lot more in this section of the manual on conditions under which ATRAC does not function and on the engine output control feature. If anyone is interested, I’ll type that in sometime.



“If a tire slips while the vehicle is being driven off-road, the function of the differential gear causes a large amount of drive force to be applied to the tire that is slipping. The ATRAC function helps restrain the slippage by controlling the engine output and brake fluid pressure that is applied to the slipping wheel and distributes the drive force that would have been lost to the slippage to the remaining wheels. It independently controls the brake hydraulic pressure to the four wheels in accordance with the extent of the slippage as detected by the skid control (ECU).

Based on the vehicle speed that has been calculated from the speeds of the wheels and the deceleration sensor, the skid control ECU computes the target control speed in accordance with the transfer case range. The ECU compares the target control speed and the speeds of the wheels to determine whether or not a slippage exists. Upon detecting a slippage, the ECU controls the solenoid valve of the brake actuator to control the brake fluid pressure that is applied to the slipping wheel. When the wheel speed becomes lower than the target control speed, the ECU stops controlling the brake fluid pressure. The target control speed and the brake fluid pressure control vary in accordance with the transfer case range:

H = gradual fluid control pressure
L = sudden fluid control pressure
L + first gear = fluid pressure control only on the front wheels (downhill slippage control)”
 

2000UZJ

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that makes sense. I have noticed ATRAC does not "bite" at hard in H than in L. If you put the 100 in Low Range, CDL Locked, first gear it really can climb quite well.
 
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While we're on the topic of understanding ATRAC. Let's discuss any known manner in which it comes into play. As in, is it on 100% in all conditions? Or just when CDL is locked? Or when the trans is in 'D'?

Also, is there a way to disable the ATRAC feature? I seem to remember a pull the e-brake 3 times in 5 seconds, push the brake pedal 6 times in 6 seconds or some similar example.
 
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How?... how does braking the tire that doesn't have traction apply more power to the one that does. It would seem the wheel that doesn't have traction is getting the same amount of power, only to have the brake applied.
An open diff sends power in an instant when a brake is applied on the other because that wheel STOPS turning instantly.

To much throttle and the system kills ATRAC to prevent further damage (some have actually had the system kick in and blow the diff.

A nice easy, steady foot will do the trick. When you get into a situation where ATRAC will kick in, creep up to it. When you start to feel the truck start to flex out or lift a wheel give it the gas and hold it until you are through the obstacle. Stopping and going will only confuse the system and create a lot of bouncing. One you have a little momentum ATRAC can do it's thing and won't nearly have to work as hard pulling you through something rather than starting and stopping where it has to get you moving off-camber again.
The system does not kill ATRAC to prevent damage. It kicks out if more throttle is used to help prevent you from getting stuck...say in mud, where you need the wheelspin and power to clear the tires and maintain progress. As far as breakage and damage etc...I still disgree that it is an A-TRAC problem. It's a weak diff problem in my opinion. My 100 has been a rabbit hopping over things for 10-years and no breakage. Rover's aren't busting front diffs from their traction control. It's not A-TRAC's fault...it's the front diff.

Great advice as to technique! Well said!

While we're on the topic of understanding ATRAC. Let's discuss any known manner in which it comes into play. As in, is it on 100% in all conditions? Or just when CDL is locked? Or when the trans is in 'D'?

Also, is there a way to disable the ATRAC feature? I seem to remember a pull the e-brake 3 times in 5 seconds, push the brake pedal 6 times in 6 seconds or some similar example.
*Always ON until you give the vehicle too much throttle.

*It's on with CDL locked or unlocked. NEVER...READ NEVER...climb steep grades where you might lose traction with the CDL UNLOCKED! Like some Rover's have experienced...there is a flaw in the software on the 100's A-TRAC. If you are UNlocked...TRAC kicks in...you're still slipping...you might slide backwards...you APPLY THE BRAKES...the brakes DO NOT apply sometimes for a couple a seconds while the CPU determines who wants what to happen...can result in tragedy! I have been FREAKED on twice when I was not expecting it by rolling backwards with the brake pedal pushing and no brakes. NEVER climb steep and uneven grades with an open CDL.

*Works both directions...D and R.

*No way to disable A-TRAC and I still for the life of me don't understand why folks would...ON THE 100. The A-TRAC programing is fantastic on this rig as is the ABS.
 

2000UZJ

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*It's on with CDL locked or unlocked. NEVER...READ NEVER...climb steep grades where you might lose traction with the CDL UNLOCKED! Like some Rover's have experienced...there is a flaw in the software on the 100's A-TRAC. If you are UNlocked...TRAC kicks in...you're still slipping...you might slide backwards...you APPLY THE BRAKES...the brakes DO NOT apply sometimes for a couple a seconds while the CPU determines who wants what to happen...can result in tragedy! I have been FREAKED on twice when I was not expecting it. NEVER climb steep grades with an open CDL.
I did this... a-trac was still ticking away and I was standing on the brakes. Still rolling backwards lol. Tree in my rear view.


I still think the worse is when you are trying to climb something off camber and ATRAC says " F YOU!!!" and stops working and you come back down very quickly and unexpectantly. I have learned to control my right foot and not have that issue anymore, but I used to think like Jeremy Clarkson and think POWER!!!!!
 
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So ATRAC kind of simulates a locked differential, but does this braking action actually help rotational force (torque) to the tire with traction? If so, how?
ATRAC doesn't simulate a locked differential. If it simulated a locked differential, both wheels on an axle would spin at the same speed. Atrac simulates a sort of torsen (TORque SENsing) differential that can send 100% of the power to either side at any time. When the ATRAC system detects a wheel slipping (excess torque to one wheel), it clamps the brakes down on that wheel in order to send the power to the other wheel.

Imagine three open differentials (front, center, and rear). Let's say a CV axle freezes and locks a wheel. The car has to have somewhere else to send the rest of the power. If all the differentials were locked, all wheels would spin at the same speed and the car would screech to a halt when any wheel locked. Because the car has three open differentials, and all wheels can spin at different speeds, power gets sent to the other three wheels (which, hopefully, have traction). ATRAC capitalizes on this effect by, effectively, simulating a "frozen axle" by pulsing the ABS circuit and clamping the brake on the freely spinning wheel.

ATRAC only works if you have at least one open differential. If you locked all differentials, you'd stop moving as soon as you clamped down on the brakes (you'd also never activate ATRAC because one wheel would never spin faster than the others).

Hopefully this has made things clearer. If not, ignore all of this, as it's probably made everything even more confusing. It's much simpler than I make it sound, I promise.
 

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