Traction control wheel spin rpm?

Sorry if it’s been asked. Does anyone know at what wheel speed/spin rpm that traction control starts to apply the brakes? 1 full wheel rotation? 3? Just curious if anyone knows.

 

It compares the rate of acceleration of the slipping wheel to the other wheels. Not just the distance traveled. ABS works the same way when the wheels are decelerating

 

I would speculate that there is no set distance or rate. It kicks as soon as it detects discrepancy between wheel sensors and/or between wheels, steering position and yaw sensor.

 

It seems to be revolutions a bit faster than idle in 1st gear.

I believe it is tighter on the ORs / Pros when MTS is set to the higher settings (A-TRAC is On for the MTs).

 

Well thanks for the answers. Obviously it’s more complicated then I wanted to hear, but it makes sense. I guess I was thinking of it like a LSD and that’s like comparing a bottle rocket to a space ship.

 

No doubt, but the ability to get traction without the mechanical parts of an LSD is pretty neat. I've had wheels in the air and still moving, which is pretty neat.

 

Absolutely. I remember back in days before traction control. You could find the limits of open differentials in your driveway. Oh how the world has changed.

 

Your are 100% right about that. In fact, right next to my driveway growing up was were my too-proud cousin got his CJ5 stuck. Being a kid, I thought 4WD was near invicible until I saw that it was only really 2WD and both of them were the ones we didn't want turning.

 

Idk for tacoma's specifically but what we were taught in school and gm training was between a 15-50 rpm difference in wheel speeds will trigger a traction control event. I do also notice these trucks will be triggered by steering input not just detected wheel slip

 

It's a bit more nuanced than that. Fundamentally the systems are not based on angular displacement but angular velocity (speed). And they aren't based on how much speed, but how different the speed is to a reference. What that reference speed is and what the threshold for intervention is will depend on the control strategy and varies between trucks and what mode you're in (normal, auto-LSD, A-TRAC, etc.). Also, some modes don't just apply the brakes, they may also cut engine output.

If you really wanted to know the slip % required for intervention for a particular set of circumstances you could reverse engineer it using Techstream and logging the necessary channels.

I think we recently discussed this concept in the thread about ABS in reverse. Decel/accel can be a trigger for the ABS and/or traction control systems, but fundamentally it's not the main trigger or target. It's differential wheel speed/s that are the actual output being controlled and the target or threshold is based on the mode and multiple sensed parameters.

It does not intervene at *any* discrepancy. Again, the tune and mode matters. There is some acceptable threshold for variance before any action is taken. The threshold is a part of the design of the system and varies with the selected mode. If it intervened at any variance then you wouldn't be able to change tires sizes or even wear a tire down before VSC started intervening all the time. Typically the target is some percentage speed difference to a reference speed. The reference may be a calculated or directly sensed/measured.

 

The "reference" is the speed of the other 3 wheels.

If one wheel is decelerating faster than the others, it sees lockup coming and applies ABS activity (either block brake pressure to that wheel or dump it altogether)

If it sees a wheel accelerating faster than the others is sees a slip happening and applies Trac control (sending brake pressure to that specific wheel)

 

Nope, not always. In 2wd the front 2 wheels will be the reference. For autoLSD and ATRAC the opposing wheel on the same axle is the reference. In 4 wheel drive you must derive a reference from somewhere else because it can't be the other wheels. For VSC the reference yaw rate is calculated from speed, steering angle, wheelbase, etc.

This alone doesn't work in practice unless it is applied on top of a basic control algorithm that is closed loop on speed differential. But it can be used as a trigger on top of a speed based control strategy. For instance, if it was only accel based then after a lockup event the controller could re-match decelerations but there'd be no guarantee the wheel isn't still slipping because the wheel decels can match while the wheel speeds don't. If it starts matching decel at each wheel while each wheel is at a different velocity it would be maintaining matching decels with mismatching speeds. This is why the system needs to use a speed reference in the controller. Otherwise the system cannot converge to desired steady state.

 

Where does that speed reference come from if not the other wheels

 

Another part I forgot but the yaw sensor in the truck is also an input in that the traction control system is programmed typical yaw rates for a "controlled maneuver " (ie turns, accel, decel) and a deviation from the preprogrammed yaw rate will also trigger a traction/control event

 

I listed where speed references often come from in the very first part of the post.

 

Which post? You've responded several times, to several different people.

When I see the term "reference" I'm thinking either a sensor signal coming from one or more actively turning wheels or some kind of "known value" the controller can substitute if it loses a signal from a sensor.

I think we're actually agreeing on 80% of this, just words and stuff get lost in translation

 

Start of post 12

 

Seemed to me OPs original question was just about traction control operation during general driving. He didn't say anything about operation during 4wd or A-trac. I responded with a general answer about the controller comparing rates of acceleration among the wheels.

Points of difference get lost in translation on the internet

 

My response to you was strictly to address the use of wheel speeds as opposed to accelerations.