The VSC gets disabled with a locked CDL....there is no way to disable TRAC.
ATrac question
- Thread starter Aznwolf118
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Shotts- thanks for the vid. That's definitely on the more extreme side of what I plan to be doing as right now my LX is a DD.
And agaisin, ya, good points. But doesn't it seem like there's a hack potentially available with the ATRAC since the baby cruiser boys have figure it out?
And agaisin, ya, good points. But doesn't it seem like there's a hack potentially available with the ATRAC since the baby cruiser boys have figure it out?
Hack to diable? Nope.
Ya, but effectively you still could, right? Here's an example: CDL locked. rear has zero traction. front has traction on the left side. ATRAC inhibits spin on right side, giving *most* power (less whatever is lost to ATRAC slippage) to the left front. Because the CDL has both F/R shafts locked there won't be waste energy on the slipping rear wheels. So all usable torque is effectively given to the wheel with traction. If the CDL were open and both rears had zero traction then all of that energy would be lost to the rear.
The only downside I see is that if the rear were in soft stuff, the slippage allowed by the right front wheel would translate into the rear axel digging.
I guess this also depends upon what the truck thinks the 'target speed' is and how that's calculated.
Stepping out of the theory into the reality, it does work very well - for the vast majority of overland requirements. The only criticism I have is what others have expressed: when you get into some ugly stuff it's not always completely predictable what's going to slip. The art of making the intervention transparent also limits feedback to the driver of what strategy ATRAC is employing. There's been more than once when I'd rather just have them locked and have predictable wheelspin. Maybe I just need more seat time getting used to how it will respond.
The change was made in 2007, not 08
Some where around early 2007 (production date) they started allowing the a-trac and rear locker to work together. I had a 06/07 built 2007 and A-Trac and the rear locker function together.
Quick question on the 100 series with A-TRAC, is it always on when you are in 4LO? THe FJ has the ability to turn it on and off but there doesn't appear to be a button to do that in the LC/LX (2000+)
yep it is always on...only thing I can select is 4HI-4LO and CenterDiff Lock... I dont think the FJC then got the combined use until later build year...I had 2008 and was told it was first year...friend has 2007 and does not have it. He was pre-wired for rear locker so only had to buy the button rather than pay the dealership but his 2007 would require the hack to work together. So maybe later builds in year came with it,,,
Nope! 50% torque goes to a rear wheel and 50% to the front. Go watch my video again. And with the CDL unlocked there's no way to get TRAC to compare and/or transfer power between axles. It doesn't monitor it.
John, your video is a great example of how ATRAC is more like a LSD and how lockers can make a difference.
I don't agree with your statement above. It's not that 50% of the torque is being diverted to the rear. In my example, the CDL is locked and the rear is locked. So 100% of the power is going to the system. The issue, therefore, is eliminating the path of least resistance, right? So with center and rear locked, the only other path (in my example) would be the spinning right front. If ATRAC was clamping down on the right front then the only other path would be to turn the left front. Again, the rear may spin but only because it's effectively locked to the left front in this example.
From another perspective, you wouldn't say that with a locked rear that 50% of the torque was going to the left and 50% to the right would you? It's 100% to the system since they are behaving as a single locked unit. It wouldn't matter if the left or right was spinning as it couldn't be spinning independently of the other.
So is it providing zero torque to 3 and 100% torque to the remaining 1? No. Is it forcing the 1 wheel with traction to turn? Yes.
It doesn't matter what's locked and what's not. 100% of the torque always is going to the "system" / driveline. No matter how you wanna say it, A-TRAC cannot sent ALL or 100% of the engine output to ONE wheel. Not happening with this system. If you have THREE wheels with zero traction and one with, you will not move in inch!
ShottsUZJ100 said:
I respectfully disagree. The system can easily do this with the cdl engaged, and I suspect that it might be able to accomplish the same with the center diff open. The limiting factor is how much power it can transfer; whether it be enough to get/keep you moving depends on the situation.
And to clarify, the above is not the same as sending all the force to a single tire. To be sure, in the above scenario force is being applied to each tire, even the ones without traction...
The reason why i'd like to be able to turn it off is that sometimes i want to be able to fully control the vehicle myself as much as possible.
Also, i have found in mud and sand that A-TRAC hinders more than it helps on my FJ Cruiser. While i know that there might be differences between the A-TRAC on the FJC and the LC100, i'd still imagine this would be similar between them.
referencing my example, what's the one wheel with traction doing then?
John's video in post #19 did a pretty good job of showing this. With the diagonal wheels unweighted the truck doesn't move. When he locks the rear, the one wheel with traction - right rear in this case - pulls him out. It doesn't matter that the left rear had zero traction; no torque was 'transferred' to the left rear because the entire rear axel was operating as one component and with the center locked the right front couldn't run away by itself.
OregonLC said:
ill take a look at the video tonight (work now) but the fact that there's still a question/disagreement about what atrc an/cant do with 3 wheels slipping tells me the video isnt going to answer that question....
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This should put this to rest:
In order for a traction control system to send 100% of the power to ONE wheel the system would have to be able to send ALL of the power to only ONE axle via the center differential. The only way this is possible is if the traction control system can brake BOTH wheels on the SAME axle at the SAME time. NOT POSSIBLE ON THE 100-Series. This is the ONLY scenario where all the power would be send to ONE axle.
If this is possible on the 100 then my video would have been 100% different. The second the system would lock BOTH brakes on the same axle that truck would move. As you can see it cannot...both wheels with the least traction get the power. Plus, it's always TWO wheels getting the power...not one.
In order for a traction control system to send 100% of the power to ONE wheel the system would have to be able to send ALL of the power to only ONE axle via the center differential. The only way this is possible is if the traction control system can brake BOTH wheels on the SAME axle at the SAME time. NOT POSSIBLE ON THE 100-Series. This is the ONLY scenario where all the power would be send to ONE axle.
If this is possible on the 100 then my video would have been 100% different. The second the system would lock BOTH brakes on the same axle that truck would move. As you can see it cannot...both wheels with the least traction get the power. Plus, it's always TWO wheels getting the power...not one.
Wait up now - you said "If you have THREE wheels with zero traction and one with, you will not move in inch!"
It does not require 100% of power to one wheel to move an inch. With CDL engaged there should be 50 to front and 50 to rear. If front right wheel is only one with traction, braking on front left should provide some power to the opposite wheel with traction.
And with CDL disengaged (and no rear locker) the same scenario it would require brakes on the other 3 wheels. What's your source for ATRAC not being capable of braking both wheels on same axle - don't take it personally but there's lot of incorrect information out there on the topic so the only way to put it to rest is (for me personally) is either demonstrating it real world or pointing to the Toyota documentation that explains this clearly.
If your video does in fact demonstrate this beyond the shadow of a doubt, I apologize for not having viewed it yet (at work).
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Nevermind...too many scenarios, hard to do in words...think about it, study it on the trail, on roads, in ice...the type of diffs....
In most situations. Yes, it is possible that the one tire could yank you along depending on what you're up against. That's because even if the other three are slipping, TRAC can alternate the brakes on the axle that has one tire with traction and that might move you.
Didn't work in my video despite TWO wheels getting traction though. What would have worked? TRAC locking BOTH wheels on a given axle...wish this system could.
Here's the difference:
"4MATIC all-wheel drive: 4MATIC four-wheel traction control applies the brakes to any of the four drive wheels whenever the wheel speed sensors indicate the wheel is going faster (slipping) than the others. This brake action works hand in hand with front, center and rear “open” differentials of the Mercedes-Benz all-wheel-drive systems to control torque distribution to the four wheels. As a result, Mercedes-Benz has one of the few systems that will get the vehicle going even when three wheels are slipping. 4MATIC is standard on the GLK-, GL-, G-, R- and ML-Class sport utility vehicles, as well as on the CL550 coupe. 4MATIC is an option on the C-, E- and S-Class passenger cars."
MB trac system monitors speed sensors between ALL FOUR wheels and can apply brakes to ANY THREE wheels if needed.
Toyota's trac system only monitors speed between the TWO wheels on EACH axle.
This is why you will always see a Toyota spinning 2 wheels, one on each axle. On the Benz you can see as little as one wheel spinning at a time because it's the only one getting any power at that moment.
"4MATIC all-wheel drive: 4MATIC four-wheel traction control applies the brakes to any of the four drive wheels whenever the wheel speed sensors indicate the wheel is going faster (slipping) than the others. This brake action works hand in hand with front, center and rear “open” differentials of the Mercedes-Benz all-wheel-drive systems to control torque distribution to the four wheels. As a result, Mercedes-Benz has one of the few systems that will get the vehicle going even when three wheels are slipping. 4MATIC is standard on the GLK-, GL-, G-, R- and ML-Class sport utility vehicles, as well as on the CL550 coupe. 4MATIC is an option on the C-, E- and S-Class passenger cars."
MB trac system monitors speed sensors between ALL FOUR wheels and can apply brakes to ANY THREE wheels if needed.
Toyota's trac system only monitors speed between the TWO wheels on EACH axle.
This is why you will always see a Toyota spinning 2 wheels, one on each axle. On the Benz you can see as little as one wheel spinning at a time because it's the only one getting any power at that moment.
So I watched the video. Was the driver in 4H or 4L? Also, was RPM above or below 3000?
As I'm sure you're aware ATRAC is designed to behave more aggressively in 4LO and below 3000 RPM. Therefore if they were in 4H or were > 3000 RPMS this would only be a demonstration of how not to use ATRAC.
Also - lockers would be more effective, hands down. Could this just demonstrate that even though ATRAC was working and got some traction to the wheels, it didn't get enough drive force to get up the steep portion? In other words it just demonstrated that lockers are better for this scenario even though ATRAC was 'working' it just isn't effective enough to overcome this obstacle (although I've seen other ATRAC videos that overcame steeper obstacle with 2 wheels slipping).
I wish Toyota had better documentation on the topic. Everything I have found indicates it does brake on more than one wheel and does distribute power to more than just the opposite wheel on the same axle. They have a video (I can provide a link) that shows ATRAC applying brakes to more than one wheel but I don't know how much you can read into that.
From Toyota documentation on ATRAC: "...The A-TRAC function helps restrain the slippage by controlling the engine output and brake fluid pressure that is applied to the slipping wheel, and distributes force that would have been lost through the slippage to the remaining wheels in order to achieve an effect that is similar to the LSD (Limited Slip Differential). It independantly controls the brake hydraulic pressure to the four wheels in accordance with the extent of the slippage at the wheels, as detected by the Skid Control ECU.
The effectiveness of the control of this function is as follows:
- Offroad drivability that is equivalent to having the center and rear differentials locked has been realized.
- This function made the operation of the differential lock switches basically unnecessary to ensure the ease of driving.
- A drive mode has been added in which the center differential does not lock when the transfer is set to the L range.
- While realizing the offroad drivability that is equivalent to having the center and rear differentials locked, as compared to the differential gear in the locked state, the essential function of the differential gear itself ensures the ease of nimble steerability.
"
I know that's a lot of salesy speak but I can't find any of the limitations you describe, and the opposite - quoting from the excerpts above:
both "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... to the remaining wheels..." and "It independently controls the brake hydraulic pressure to the four wheels in accordance with the extent of the slippage at the wheels as detected by the Skid Control ECU."
If you read that literally it says it can brake at one wheel and distribute force to the remaining wheels, and it says tht it can monitor speeds and apply brakes to the four wheels.
As I'm sure you're aware ATRAC is designed to behave more aggressively in 4LO and below 3000 RPM. Therefore if they were in 4H or were > 3000 RPMS this would only be a demonstration of how not to use ATRAC.
Also - lockers would be more effective, hands down. Could this just demonstrate that even though ATRAC was working and got some traction to the wheels, it didn't get enough drive force to get up the steep portion? In other words it just demonstrated that lockers are better for this scenario even though ATRAC was 'working' it just isn't effective enough to overcome this obstacle (although I've seen other ATRAC videos that overcame steeper obstacle with 2 wheels slipping).
I wish Toyota had better documentation on the topic. Everything I have found indicates it does brake on more than one wheel and does distribute power to more than just the opposite wheel on the same axle. They have a video (I can provide a link) that shows ATRAC applying brakes to more than one wheel but I don't know how much you can read into that.
From Toyota documentation on ATRAC: "...The A-TRAC function helps restrain the slippage by controlling the engine output and brake fluid pressure that is applied to the slipping wheel, and distributes force that would have been lost through the slippage to the remaining wheels in order to achieve an effect that is similar to the LSD (Limited Slip Differential). It independantly controls the brake hydraulic pressure to the four wheels in accordance with the extent of the slippage at the wheels, as detected by the Skid Control ECU.
The effectiveness of the control of this function is as follows:
- Offroad drivability that is equivalent to having the center and rear differentials locked has been realized.
- This function made the operation of the differential lock switches basically unnecessary to ensure the ease of driving.
- A drive mode has been added in which the center differential does not lock when the transfer is set to the L range.
- While realizing the offroad drivability that is equivalent to having the center and rear differentials locked, as compared to the differential gear in the locked state, the essential function of the differential gear itself ensures the ease of nimble steerability.
"
I know that's a lot of salesy speak but I can't find any of the limitations you describe, and the opposite - quoting from the excerpts above:
both "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... to the remaining wheels..." and "It independently controls the brake hydraulic pressure to the four wheels in accordance with the extent of the slippage at the wheels as detected by the Skid Control ECU."
If you read that literally it says it can brake at one wheel and distribute force to the remaining wheels, and it says tht it can monitor speeds and apply brakes to the four wheels.