General: Traction Control Temporarily Off

[domhart10]

thats amazing, thanks for that nice to know what was actually behind that message rather than just assuming

[IainG]

Hi
Just found this

Some facts:
TC is mainly intended for use when moving off on slippery surfaces at speeds up to approximately 60 km/h (37 mph).
At speeds between 60 -100 km/h TC control has a limited function. The TC function is not active at speeds above 100 km/h (62 mph).
For the TC to be activated there must be a speed difference between the wheels.
The speed difference required varies depending on the car type, driving situation and vehicle speed.
In principle, the higher the speed of the car the greater the difference in speed between the wheels must be for TC to be activated.
The BCM continuously calculates how much the brakes are used and calculates the temperature of the brake discs of the front wheels.
If the calculated temperature exceeds approximately 450°C, TC is shut off to prevent the brakes overheating. A DTC is stored in the BCM, the general warning lamp lights and a text message is displayed in the DIM.
The function is reactivated and the warning lamp in the DIM goes out when the temperature falls below 300°C.
Note that high brake temperature can also be caused by hard use of the brake system, for example extended braking when driving with a trailer on long downhill stretches.
• TC is disactivated when the brake pedal is depressed.

From this

https://www.volvoclub.org.uk/tech/S40MY2005-Brakes.pdf


Iain

[LizardOfBodom]

So did I read it correctly that reported temperature is the "calculated" value not the actual, similar to i.e. current fuel consumption?
How would that work? Based on amount of time pedal is pressed and the force of press + speed of car? seem pretty inaccurate, if thats really true...

[dme123]

Originally Posted by LizardOfBodom

So did I read it correctly that reported temperature is the "calculated" value not the actual, similar to i.e. current fuel consumption?
How would that work? Based on amount of time pedal is pressed and the force of press + speed of car? seem pretty inaccurate, if thats really true...

That's exactly how it works. It's actually very easy to work out and accurate. You know the kinetic energy of the vehicle at any given speed, you then use the brakes and take it down to a new speed at which you can again calculate it's kinetic energy. You can thus work out exactly the change in kinetic energy of the vehicle, and very neary all of that kinetic energy will have been turned into heat in the brakes. You also know the exact mass and material of the brake discs, so you can work out exactly the temperature rise that much energy would cause.

You can also easily know how much heat the brake discs will give up to the atmosphere for a given speed and external air temperature, both factors known to the ECU, to calculate temperature drops in the disc.


You could even monitor engine braking and compensate for that.

I wouldn't be surprised if it's accurate to within 10%.

[LizardOfBodom]

Originally Posted by dme123

You could even monitor engine braking and compensate for that.

I wouldn't be surprised if it's accurate to within 10%.

Wow, thats an interesting piece of information. Would not suspect that at all, thanks.

But then, assuming it works as you say - how does it detect difference between normal and seized caliper for example? It should only know when and how much force the brake pedal is pressed so if pads for example are not retracted on one side, it should think its "released" no?
Also - it would mean that BCM would not know the difference between standard and racing brakes that cools down much quicker and dont heat up as much so would trigger false warnings?
Would having actual temp readout even in ABS sensors not make more sense?

[domhart10]

Originally Posted by LizardOfBodom

Also - it would mean that BCM would not know the difference between standard and racing brakes that cools down much quicker and dont heat up as much so would trigger false warnings?
Would having actual temp readout even in ABS sensors not make more sense?

Hmmm thats what I was thinking, if I upgrade my brake calipers and disc this is obviously going to throw out these calculations.

Its almost like the car could do with a traction control switch off and on

[LizardOfBodom]

Originally Posted by domhart10

Hmmm thats what I was thinking, if I upgrade my brake calipers and disc this is obviously going to throw out these calculations.

Its almost like the car could do with a traction control switch off and on

*cough* de-nanny mod *cough*...