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Is VTD mechanical or electronic?


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3 replies to this topic

#1 daneinbalto

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Posted 15 July 2005 - 10:01 PM

Hi, this is daneinbalto. I am a member since 1999 or 2000, but I have been inactive for a while, so I guess I got bumped off and had to reactivate...

I moved from Baltimore to Phila but decide to stick with daneinbalto as my user name.

Good to see that many of the old ones are still around.

Anyway, my question is whether the Variable Torque Distribution system is mechanical or electronic. The few pictures I have been able to locate on the Web suggest that it consists of a planetary central differential and a viscous coupling as a locking mechanism.

The planetary (aka epicyclic or epicycloid) differential is quite commonly used to achieve an uneven torque split. As such it is used on the Lancia Delta Integrale, AWD BMWs from the 325ix forward, and I believe, even on the early Huyndai Santa Fe. So it would make sense if VTD indeed had a planetary center diff.

But from the pictures, I can't tell if the planetary differential of the VTD is combined with a (mechanical) viscous coupling or an electromagnetic clutch. Does anybody know?

It would be elegant if it was wholly mechanical.

Daneinbalto

#2 nipper

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Posted 16 July 2005 - 12:06 AM

found this :
The Legacy GT automatic and all VDC models come with Variable Torque Distribution, which combines the electronically managed center clutch with a planetary gear that splits torque 45/55 front/rear, for a sportier feel.

and

With VTD, an electronically controlled, continuously variable hydraulic transfer clutch works with a planetary gear-type center differential to control power distribution between the front and rear wheels.

and

There are actually two different all-wheel-drive systems used in the WRX, depending on the transmission. Cars equipped with the optional four-speed automatic get Subaru's Variable Torque Distribution (VTD) all-wheel-drive system, its most advanced system ever offered. It employs an electronically controlled hydraulic transfer clutch and a planetary gear center differential to distribute power in a 45/55 split between the front and rear axles.

The VTD system uses multiple sensors to measure front-and-rear driveshaft speeds, throttle position and gear selection. Then it actively transfers power accordingly between the front and rear wheels for optimum traction and handling. Enter a turn under braking, and the system will bias the power toward the front for greater steering control. Lay on the throttle out of a turn, and the VTD will send the torque out back for maximum thrust; all of this done in a matter of milliseconds completely imperceptible to the driver.


hope that answers your question.

nipper

#3 daneinbalto

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Posted 16 July 2005 - 06:24 AM

That's exactly the information I was looking for.

BMW (X-drive) and Toyota/Lexus have systems that are described in a similar manner. I wonder if they are identical except for their standard torque split and the controlling software.

#4 nipper

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Posted 16 July 2005 - 07:27 AM

Could be, though with enough variation between the three so that they can all say thiers is patented.

nipper




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