Is this true for Audi quattro?

"I recently became the proud owner of an A6 Avant quattro TT5. In a moment of overconfidence during a recent trip, I drove the front wheels into a snowdrift. I put the car in reverse and tried to drive out, but I thought the quattro system and electronic differential wouldn't be a problem. However, I noticed that the rear wheels briefly started to spin, but when the front wheels lost traction, no power was being transmitted to the rear wheels. I then deactivated the ESP, but the problem persisted."
Okay, I have some questions about the quattro all-wheel drive system.
-How is the power distributed between the front and rear axles? Is it normal for the rear wheels to stop spinning completely?
-How does an electronic differential work, and does it affect the front wheels?
-What does the ESP actually do, or when does it intervene?

Hi,
The current Quattros have EDS (Electronic Differential Lock) on both the front and rear axles, which means that a spinning wheel can be braked so that the other wheel on the same axle can maintain traction.
Between the front and rear axles, there is no conventional differential, but rather a Torsen differential, which does not have a brake-based locking mechanism but inherently exhibits a certain degree of "self-locking." To transfer power to the rear axle, as I understand from some posts on meckisforum.de, a significant amount of wheel spin is required on the front axle.
"True lockable differentials were only available up to the Type 44 or V8 models."

Sure, because the all-wheel drive isn't permanently engaged like it was in the older Audi 100.

The Haldex coupling only engages the all-wheel drive system once the front wheels start to spin. However, this should happen very quickly, so that the driver doesn't really notice that the vehicle doesn't have a permanent all-wheel drive system.

It occasionally happens that the clutch malfunctions, which can then cause the front-wheel drive to lose traction, especially when cornering.

The A6 (with the engine mounted longitudinally) does not have a Haldex clutch, but rather a Torsen differential.

Torsen - Torque Sensing.
"Torque-sensitive"

hello


I have edited my original post because, upon rereading it later, I realized that it was somewhat unclear.

First, let's look at the differences.

automatic locks
- viscous coupling
- torsen differential

externally controlled locks
- example Haldex

Important: TORSEN.

The Torsen differential has a torque-dependent locking effect, not a speed-dependent one, and is controlled by friction elements on the pinion gears.
Problem: If there is little or no traction with the ground, or if a wheel is off the ground, the forward motion collapses. In this specific case, the all-wheel drive turns into front-wheel drive, and there is no way to drive out of the snow, even if the electronic stability program (ESP) is active on the front wheels.

It's okay if the rear axle doesn't generate propulsion.

EDS controls the braking intervention until there is almost no difference in speed between the wheels of an axle, and torque can be transferred to the road.

peter

I like it better now.

hello
The Torsen differential has a torque-dependent locking effect, not a speed-dependent one, and is controlled by friction elements on the pinion gears.
Problem: If there is insufficient or very little traction with the ground, or if a wheel is off the ground, the forward motion collapses. In this specific case, the all-wheel drive system reverts to front-wheel drive, and there is no way to drive out of the snow, even if the electronic stability program (ESP) is active at the front.

It's okay if the rear axle doesn't generate propulsion.

EDS controls the braking intervention until there is almost no difference in speed between the wheels of an axle, and torque can be transferred to the road.

peter

I like it better now.

Are you sure about that? Doesn't that contradict the Quattro principle somewhat?
After reading that, I put our A6 TT5 on a lift and tried to hold the rear wheels in place (with three people) -> no success. Even though the front wheels were completely free to spin (and spinning quite a bit), a significant amount of force was being transmitted to the rear.
Even my 4motion is that smart.

Best regards,

Hi,

"Here's a quote from www.torsen.com:"

Quote:

Was passiert, wenn ich ein Rad in der Luft habe? As mentioned above, the Torsen differential is a torque multiplier. The Torsen requires some type of resistance or friction in the system to function properly. A wheel in the air provides zero torque or friction on the system, and as the Torsen multiplies the available torque, zero, by its TBR, the end result is still zero. In response to this, we developed the Torsen T-2R with pre-load to combat those wheel in the air situations.

It pretty much says it all, doesn't it?

That's why I'm also a fan of my viscous coupling, because in that case, it completely locks and transfers 100% of the power to the axle that still has grip.

Greetings.
dieter

What if you simply brake slightly while reversing? Wouldn't that also cause some torque to be transferred to the rear wheels?

@dieter

Visco isn't bad, but it's pretty useless in the sand.


@wolfi

Why would that happen?

peter

www.torsen.com wrote:

Was bedeutet das Drehmoment-Bias-Verhältnis? Torque bias ratio (TBR) represents the "locking effect" of the differential. More specifically, it indicates how much more torque is sent to the high traction wheel (or axle) than is sent to the spinning wheel. For example, when a differential has a TBR of 3:1, 3 times the torque the spinning wheel can maintain (75% of the total torque) will go to the higher traction wheel. If a wheel is spinning and can support 100 lb-ft, the other wheel will get 300 lb-ft.

Okay, if no torque is transmitted to the front wheels (because the wheels are slipping), then no torque is transmitted to the rear either (0 * x = 0).

What I was thinking was:
When you apply the brakes, a sudden torque is transferred forward, and consequently, also backward. In the example above, the rear wheels receive three times the torque of the front wheels, which should easily be enough to overcome the braking force of the rear brakes.

However, it's all just speculation, and it's possible that I'm thinking in the wrong direction...

Specifically, our TDI engines (and likely other engine control units) detect simultaneous operation of the accelerator and brake pedals as a misuse and reduce the fuel injection amount.

When you brake, suddenly torque is transmitted forward, and consequently, also backward.

I don't understand what you mean, sorry.


peter

Hello Peter,

Just for trying out.

Brake with the left foot and accelerate with the right.

Normally, when the brake pedal is pressed, a signal is sent to the engine control unit (ECU). This then causes the engine to decelerate or reduce the amount of fuel injected.

Sure, here's the translation:

'Hello'

Werner.

@werner

Now you're not understanding me . What you're writing, I already understand. The statement from Wolfi, which I also quoted, I don't understand. I don't know what he's trying to say. I don't think he means the same thing as we do. But he will probably get in touch.

peter

Now you're not understanding me . What you're writing, I already understand. The statement from Wolfi, which I also quoted, I don't understand. I don't know what he's trying to say. I don't think he means the same thing as we do. But he will probably get in touch.


A Torsen differential is torque-sensing. This means that it locks when a difference in torque occurs and distributes the torque according to its torque bias ratio (TBR) value.
However, if one wheel spins freely, the torque-sensing differential cannot transmit any torque to the other side. A spinning or airborne wheel has virtually zero torque. 0 * TBR = 0. The vehicle will stop.

The same thing happens in a Quattro system when, for example, one wheel spins on ice.
Visco and Haldex systems offer clear advantages in this regard, or alternatively, mechanical locking differentials.

Slightly braking can sometimes help because the differential then has to transmit a significant amount of torque again, and this also causes the previously unpowered wheel to receive torque. This works on a sheet of ice, but not in off-road conditions.

CU.

Yes, exactly, that's what I meant.