how does 997 TT AWD system work?

How is torque split when there is no wheel speed difference / no loss of traction?

Once ECU detects loss of traction, how is torque split achieved?

How does the transfer case/center diff work? By oil pressure?

 

The 997TT uses an electronically controlled center differential lock which actively controls torque distribution. The PTM control unit calculates wheel speeds independently of lateral and longitudinal acceleration in relationship to steering angle and works with the optional rear differential lock. The multi clutch center differential opens and closes in 100 milliseconds to shunt power between front and rear axles as required to maintain optimum traction. It also opens instantly to free the axles under ABS activation.

In comparison to the older viscous coupling system on the 996TT, the 997TT multi plate clutch is capable of transfering 80 to 100% of the torque instantaneously from rear to front. This allows delivery of as much as 100% drive power to be transferred to either axle during slip...(although on a dry road under constant throttle, it send 60 percent of the power to the rear axle.) The 996tt viscous coupling (like the 993) is limited in the amount of torque it can transfer to the front...I've read as little as 50 foot pounds of torque is transferred to the front.

The differential normally sent 31% to the front axle and 69% to the rear. The rear differential also incorporated a similar clutch acting as a limited slip differential. The clutch was controlled by the computer and ABS sensors for each individual wheel. It was criticized as being over-corrective of the tail-happy 911, creating understeer.

Then Porsche changed it's design radically, and moved to a viscous coupling LSD. To make the viscous coupling system engaged in the front, Porsche made the rear wheel/tire diameter smaller, causing a small speed difference between the drive shafts in the front and rear. The viscous liquid normally transferred 5-15% torque to the front axle (which was much less than the 964.) If conditions were necessary, the viscous coupling LSD could send 100% torque to the other axle.

I think the 996 and 993 AWD viscous coupling designs are very similar, and a limited amount of torque can be transferred to the front.

With the 997, Porsche came full circle back to what is essentially a multi plate design.

 

Terrific answer bbywu, reps given!

 

Great explanation. The 993 under normal conditions was 95%-5% and could go up to 70%-30% if rear slip was detected. It was quite pronounced around turns when the rear would start slipping a bit you could feel the power/tq move to the front and the car would change from a push characteristics to a pull characteristics.

 

bbywu,
Is there a link showing the center diff and its wiring connections?

Does it have an electric motor, is it pulsed?

 

great question , jus wana know also , how the traction Distributed on the car , is the rear more than front or not its equal ?

thanks,yousef

 

bump...

 

would you guys say avoid cars without the rear diff lock option?

can anyone comment on driving experiences with and without this option? would be interesting to hear feedback.

I cant imagine it makes that much difference except on hard launches which is a NO NO in first gear with a porsche (manual)

 

By center differential I think you are talking about the PTM unit?

The PTM unit is a solenoid controlled multi clutch system. It is controlled by the PTM control unit which has various sensors throughout the drivetrain. I guess to answer your question - technically, it is electronically controlled, but it is not a motor...it's just an actuated solenoid with a primary and main clutch.

The set point for torque distribution is calculated by PTM and a pulse modulated signal is generated and sent to control the clutch via a solenoid. Once triggered, the solenoid activates the pickup plate and pulls it back toward the primary clutch, generating torque in the clutch. In the active state, the pick up plate functions as a friction plate for the primary clutch. When torque is generated against the primary clutch, a ball ramp turns actuating the main clutch and allows for frictional connection (i.e. modulated slip) between the drive shaft and output shaft.

This multi clutch (primary clutch is controlled, main clutch transfers torque) design allows the primary clutch to be operated with a very small current, and only a small amount of force is necessary to operate the larger main clutch (which is less sensitive but transfers significantly greater torque.)

 

I take it you don't get all this technical wizardry in a carrera 4

 

great read, thanks for the education

 

I still do not get it.

So when I am in my 997 Turbo on a dry road, how much power is transfered to the front if:
1) I do a normal standing start (say from red light)?
2) I do a very vigorous standing start?

I've read somewhere that in 997 Turbo 95% of power is normally transfered to the rear, making it mostly RWD, but if I understand the data presented here the car has 40 (front) - 60% (rear) power split most of the time?

 

From the turbo product information -

 

Grazie mille

 

Bumping this old thread...
How to check 997TT awd function properly?
Reason I ask is that my 997TT feels way more rear wheel drive than my 996TT and come sideways much easier. Reason can be that my 996TT had fresh PS tires, vs my 997TT that have old Contact5P tires.
The 997TT also feels much stronger at lower rpms...
I have never driven any other 997TT to compare either...
No fault code stored.


Thanks