What does DTC really do?

[vachss]

I've searched around and haven't found a really consistent answer on the exact function of DTC vs. DSC on the Z4 (or other BMWs for that matter). I know basically how it works through braking and engine control and what the inputs are, but what I'd like to know is whether DTC is simply the same thing as DSC but with higher thresholds or whether the algorithms are different as well.

Without exploring too deeply it seems that in DTC I never get the engine to throttle back during hard maneuvers where that is a frequent (and annoying) occurrence if the full DSC is on.

A related question is how effective DTC can be at simulating the effect of a limited slip differential - at least in a turn where one wheel has all the traction. My guess is that by braking the slipping rear wheel a DTC system could transfer as much as half the engine torque to the outside wheel whereas a true LSD transfers all the torque where it needs to go. Does this sound about right?

[Kevlar]

DSC is the full monty... DSC incorporates dynamic traction control (the electronic limited slip), corner brake control ( over/under steer correction under braking ), stability control ( over/under steer under acceleration and excessive speed cornering ) and another acronym that I forget that ensures straightline controlled panic braking.

DTC is when you have deactivated DSC. DTC is only the electronic limited slip differential and I believe if you get too far out 'there' it will try to save you if you are not too far gone.

Then there is off ... and then you are on your own.

[trippinbillies4]

Here's the easy way to look at it as far as wheel slippage:

With DSC on, the car modulates the throttle to kill 99.9% of any wheel spin.

With DTC on, the car will allow most forward wheel spin, but if it detects side to side movement, it will cut power.

With DSC completely off (hold button for 4 seconds) it will allow any wheel spin.


The idea behind this is to give you a nice winter driving option when you need a bit of forward wheel slip to help get you through the snow, but don't want to risk sliding around on the corners.

[Zimmy1993]

According to BMW: "DTC is a function that raises the threshold for DSC intervention to allow the vehicle to start off more easily in loose snow or sand. It also reduces DSC intervention allowing even more spirited driving".

[jmillet]

Check out this website to find out what features are included on your Bimmer: http://www.bmw.com/com/en/insights/t...ide/start.html

BTW the Z4M does not have DTC as a subset of DSC.

[vachss]

BTW the Z4M does not have DTC as a subset of DSC.

If DTC acts as a simulated Limited Slip then this would make sense, since the M has no need to simulate.

[trippinbillies4]

It does not act as a simulated limited slip

[vachss]

It does not act as a simulated limited slip

That's a pity. It would seem that all the I/O is in place for this function and it would just be a matter of changing the algorithms to implement it.

[trippinbillies4]

I disagree... The inner wheel is always going to drag. There's nothing traction control can really do to prevent that...

[vachss]

I disagree... The inner wheel is always going to drag. There's nothing traction control can really do to prevent that...

You mean that braking the inner (slipping) wheel could not transfer power to the outside wheel? I certainly see that this would be less efficient than a true Limited Slip since you would be dissipating significant power in the brakes, but I would think it would have to transfer a lot more power than would be the case with an open diff.

I'm honestly curious, why couldn't this work?

[Kevlar]

braking the inside rear wheel will send power to the other side... this way, wasted power isn't going through the spinning wheel.

[trippinbillies4]

Which is great for offroading, not for performance driving...

[Kevlar]

True, but for the 80% of the market that will be driving the car, it will be enough. Plus, they never have to work about mechanical problems with the diff (namely repair/replace), the don't have the extra weight/cost, and there is no maintanence involved with it.

There are pros/cons both ways...

[jcharm]

A lot of wrong information going on here. DTC is not DSC. THey may use the same electronics, but they are not the same. If you're going to spin, DSC will save you theoretically. DTC on will allow more wheel spin for "spirited driving" On one of the other BMW country sites they do in fact state this. DTC on will allow for some more fun tail out driving. It's debatable if the DTC is offering the advantages of an "eltectronic" limited slip.

[Kevlar]

Dynamic Stability Control (DSC).

Dynamic Stability Control (DSC) adds to safety by facilitating vehicle control even in adverse driving conditions or on tough surfaces.

Dynamic Stability Control (DSC) is the nucleus of the chassis control systems in BMW vehicles. It ensures the highest possible levels of stability when driving, and it maximizes traction of all wheels when setting off or accelerating. It is able to detect the first signs of oversteering or understeering and helps keep the vehicle safely on course, even if the tyres have varying levels of grip.

Sophisticated sensors permanently check how the vehicle is driving. Information comes a range of sensors monitoring wheel rotation, steering angle, lateral forces, pressure and yaw (degree of rotation around the vertical axis). A simulation model stored in the DSC control unit to ensure stability ("one-/two-track model") and can be compared information coming from the steering wheel and accelerator: if there is too great a difference between the model and how the vehicle is currently travelling, DSC acts to increase stability or traction.

The engine and brake management systems are targeted specifically; xDrive is also included in all-wheel drive vehicles. Reducing or increasing the engine torque or braking individual wheels can improve stability and traction. Active Steering’s integrated yaw regulation system can even help significantly reduce steering effort and the extent of DSC’s contribution to stability.

Dynamic Traction Control (DTC).

Dynamic Traction Control (DTC) allows for sports-style driving dynamics even when DSC is controlling stability and when wheel traction is higher.

Dynamic Traction Control (DTC) is a sub-function of the Dynamic Stability Control (DSC) system that can be turned on and off. DTC has two major uses: to regulate traction and to enable sports-style driving while providing active stability control.

If the front wheels are stuck in snow and cannot spin properly, this leads to slip on the rear wheels (when they spin faster than the front wheels, generally a sign that performance has been exceeded) and DSC acts to change engine output: the power needed for forward movement is reduced. Switching to DTC has a positive effect on this situation, as traction is improved without a loss of power.

When DTC is on, it helps the driver alleviate the situation enough for DSC's measures to become effective. The driver retains complete control over the vehicle.

Cornering Brake Control (CBC).

For greater safety when braking on curves - Cornering Brake Control (CBC) stabilises your BMW by applying braking pressure asymmetrically despite physically difficult conditions (e.g. the car swerving towards the inside of the bend when the wheel load changes).

Cornering Brake Control (CBC) reduces the danger of vehicle instability that can arise when the brakes are applied while taking a bend at speed. Without CBC, the load shift caused by braking can reduce traction on the wheels on the side towards the inside of the bend, thereby applying excessive load to the other side. This load imbalance may result in a loss of directional control, causing the vehicle to skid out of the curve.
CBC counteracts this tendency by asymmetrically distributing brake pressure to the left- and right-side brakes or by reducing pressure (to the rear axel), even if the driver brakes outside the normal range of ABS. The result: a significant improvement in stability and safety when applying light brake pressure, even on bends.