Quattro vs. Symmetrical

[nhesketh]

^+1

[SLegacy99]

I disagree. I am well aware of the turning of the front wheels and rotated tires.

[RobY]

They do not. Mechanically they are 5MT's split by a 50/50 diffrential.

 

Ask racecar drivers which are pure RWD which tires tend to heat up the most.....

 

Enter answer here....

 

Thats because your front wheels do 70 percent of the braking and all of the turning adding 50 percent torque to the mix dosent help things.

[Scooter]

Thats because your front wheels do 70 percent of the braking and all of the turning adding 50 percent torque to the mix dosent help things.

 

Braking yes, but turning... I'm not so sure. Heat comes from load+friction, and I'm thinking the wheels that turn with the steering wheel might are probably doing less 'scrubbing' around a turn than the rears. And under acceleration the rears are certainly heating up faster than the front.

[2006Specb122]

The front tires also have LOTS MORE WEIGHT on them.

 

SO far no one has answered my question about the distrubution of torque front to rear. What is the maximum?

 

Thanks

[RobY]

Its 50:50 Static for a 5mt. If the wheels begin slipping the viscous coupling will distribute more torque to the wheels not slipping. Maximum? Depends on the RPM diffrence between the front and the rear.

[TSiWRX]

I couldnt tell ya the max but the 5 speeds really do run like a FWD car...

 

Until you get over-enthusiastic, and the rear comes around to bite you.

 

Like Keefe has said repeatedly, these vehicles are half front-wheel-drive, half rear. Depending on the particular situation and what is asked of the vehicle, it can and will exhibit traits that are typical of either of the two genre.

[2006Specb122]

Ok once again what I'm wondering is if the car is capable of sending 100% of the power to the front or the rear?

 

I know the Nissan Skyline / GTR is capable of and I wanted to compare its performance qulities to the legacy. Now the neat thing about the nissan is that it will act as a rear wheel drive car until the AWD is needed and only then will it distribute power to the front but it is capable of 100% to the rear and 50% of power to the front if needed.

 

Nissan Skyline GT-R's ATTESA E-TS PRO

 

http://www.autozine.org/technical_school/traction/tech_pic_traction_skyline2.jpg Since R33, Skyline GT-R also uses multi-plate clutch instead of conventional center differential, in addition, as rear differential lock too. Normally it is rear-wheel drive, the front wheels only intervene whenever necessary.

 

What makes the Skyline system catches my heart is its real world behaviour. Without driving it or reading road test reports, you might not discover its maturity.

As I have mentioned earlier, throttle-controllable oversteering is usually more desirable to real drivers than pure neutral steering. However, what a pity most permanent four-wheel drive cars are inherently unable to deliver power oversteering. Porsche 959 was one of the exception because it had 60% weight bias towards the rear, but for a front-engined car like the Skyline GT-R, the best solution is to leave it as rear-wheel drive in normal conditions.

The clever electronic control system is fed by all the information that Porsche 959 had, such as G-force, boost pressure, throttle position etc, in addition, the speed of individual wheels measured by ABS wheel speed sensors. By these information, the computer knows whether the car is running out of cornering limit or not. If not yet, the multi-plate clutches won't intervene, thus the car can power slide through the corner smoothly. In case out of limit, the multi-plate clutch will engage and send torque to front wheels, increasing traction. This makes Skyline a rare example of 4WD having oversteering ability.

http://www.autozine.org/technical_school/traction/tech_pic_traction_skyline.jpg

• 
  Advantage:Combines RWD's power oversteering with 4WD's maximum cornering limitDisadvantage:Like other active differential, a bit heavy and expensiveWho use it ?Nissan Skyline GT-R

 

vs. the Subaru..

• 3) Viscous Coupling Differential Lock
   
  

• http://www.autozine.org/technical_school/traction/tech_pic_traction_diff_lock.jpgWhile Torsen 4WD is too expensive, Viscous-Coupling LSD is part-time only, most 4WD cars, including the rally ace Celica GT4, Subaru Impreza, Mitsubishi Lancer and Ford Escort RS Cosworth adopted another kind of center differential - basically it has a regular center differential which distribute torque to front and rear under normal condition, an additional Viscous Coupling Differential Lock provides anti-slip function when needed. Characteristic of this system
   
  The Viscous-Coupling Differential Lock is virtually the same as what we have learned earlier, therefore it also has slight delay and non-linear characteristic. However, in reality this might not be as serious as we thought, otherwise it would have been impossible that all the top rally cars use it. Moreover, Viscous-Coupling Differential Lock system is lighter and cheaper than Torsen system, while having superior effectiveness over the part-time Viscous-Coupling LSD system.
  Advantage:Good balance between price and effectivenessDisadvantage:No special flawWho use it ?
  
• Lancia Delta Integrale (with Torsen in rear axle)
  
• Ford Escort RS Cosworth (with Viscous-Coupling LSD in rear axle)
  
• Mitsubishi Lancer GSR, 3000 GT VR4. (with Viscous-Coupling LSD in rear axle)
  
• Subaru Impreza and Legacy manual versions (with Viscous-Coupling LSD in rear axle)
  
• Toyota Celica GT4 (with Torsen in rear axle)
  
• Bugatti EB110 (set to 70% rear bias)

• vs. audi quattro

• • 1) Torsen differential - Audi Quattro system*
     
    

• Being the master of 4-wheel drive, Audi always insists to use the most effective system despite regardless of price. Its Quattro 4WD system* uses a pure mechanical LSD, Torsen differential. Torsen, means "torque-sensing", was invented by an American company calls Gleason Corporation. Its slip-limiting ability is implemented by cleverly using worm gears / worm wheel pair. This pair has a special characteristic: driving torque can be transfered from worm wheel to worm gear, but not reverse. Otherwise, they will be locked up. It is such characteristic that limit slip.
  http://www.autozine.org/technical_school/traction/tech_pic_traction_torsen.jpgA: Differential housing
  B: Out axle
  C: Worm wheel
  D: Worm gears
  E: Synchromeshes
  F: Hypoid wheel (from engine)
  G: Out axle
  

http://www.autozine.org/technical_school/traction/tech_pic_traction_torsen2.jpg

• The above picture explains how Torsen differential works. In normal cornering, i.e., no tyre slip in any wheel, Torsen differential provides the same function as a normal differential. The addition of worm wheel / worm gear pair does not affect speed difference between output shafts. For instance, if the car turns left, the driveshaft to right wheel runs faster than the differential housing, while the driveshaft to left wheel runs slower than the differential housing. The speed difference between left and right worm wheels can be exactly matched in the synchromesh gears. Note that the worm gears / worm wheels pair do not lock up because torque is transfered from worm wheels to worm gears. When one of the wheels, say the right wheel, loses traction due to poor road surface or whatever reason, the worm gear / worm wheel pair get into effect. At the instant just before they become effective, one must know that by the basic differential theory no torque will be sent to the left wheel, which is with traction. Instead, all the torque will be sent to the spinning right wheel. Then, the fast-rotating right worm wheel will drive its worm gear, through the synchromesh and drive the left worm gear. Now, do you still remember the basic characteristic of worm gear / wheel pair ? Well, when worm gear drives worm wheel, they will be locked up. As a result, the left worm gear and right worm gear are actually locked together, thus wheels on both side will rotate at the same speed and get the car out of the lose of traction.
  Characteristic of Torsen-equipped 4WD
   
  Except the first generation Quattro system that appeared in the early Quattro coupe, most of the subsequent Quattro systems used Torsen differential in center and rear axles. This is rather expensive. However, Torsen-equipped 4WD has many advantages. First of all, its pure mechanical parts react almost instantly to tyre slip. Secondly, it provides linear lock-up characteristic. Thirdly, it is a strictly permanent 4WD system. In normal condition, torque split between front and rear wheels is 50:50 (other ratios are possible, depends on the pitch of worm gears). Apart from Audi, few other car makers adopted Torsen LSD, mainly because of cost reason. Toyota's rally ace, Celica GT4 was one of the few exception. It used Torsen in the rear axle. This might be part of the reason why it was so expensive over competitors.
   
  Advantage:Quick response, permanent 4WDDisadvantage:Pricey, torque split not variableWho use it ?All non-Golf-based Audi quattro models, Toyota Celica GT4, Hummer etc.
  
  Note: * the "Quattro" mentioned here is the traditional Torsen system marketing in the name Quattro. That includes all Quattro models until the arrival of Audi TT (which uses the Haldex system). Since then the name Quattro becomes a marketing trade mark rather than indicating the actual mechanism. At the time of writing, all Audi Quattro models, excluding the Golf-based A3, S3 and TT, still employs the traditional Torsen system.
  
  
  
   
  

[Beanboy]

50/50 always with the MT Subarus except for the STI.

 

Torsen is good for on-road performance driving. What that torsen description failed to mention is that there is a torque bias ratio, usually 3:1 on Audis, which is the maximum amount of torque that can be sent to the non-spinning wheel. So if you have rear wheels on ice and can only take 10 lbs-ft of torque before they spin, the fronts will only receive 30 lbs-ft, which might not be enough to move the vehicle.

[2006Specb122]

50/50 always with the MT Subarus except for the STI.

 

Torsen is good for on-road performance driving. What that torsen description failed to mention is that there is a torque bias ratio, usually 3:1 on Audis, which is the maximum amount of torque that can be sent to the non-spinning wheel. So if you have rear wheels on ice and can only take 10 lbs-ft of torque before they spin, the fronts will only receive 30 lbs-ft, which might not be enough to move the vehicle.

 

SO WHAT CAN THE SUBARU SEND TO FRONT OR REAR? WHAT PERCENT OF POWER AT ANY GIVEN TIME CAN BE SENT TO FRONT OR REAR?

 

IF 50/50 split is normal what if the front has no traction how much power can you put to the rear?

 

Thanks

[Beanboy]

50/50! So 250lbs-ft from the motor... 125 go to to the front, 125 to the back all of the time. Front has no traction, viscous coupling locks after a tiny bit of slip, and 125 goes to the front, and 125 to the back.

 

**yeah, I was wrong... Eventhough power is even 50/50, applied torque is going to be near 250 for the wheels with traction**

[SLegacy99]

Until you get over-enthusiastic, and the rear comes around to bite you.

 

 

And it bites hard

[IwannaSportSedan]

the key is... the Legacy and WRX 5-speed manual transmissions use "Symmetrical AWD", which is symmetrically split front to rear, and fixed ratio. It is better but similar to 4WD, as it it a constant split, but does have the added benefit of having differential action in the center, so the front and rear axles can differ in speed. Axle speed is acted upon by engine torque, but not limited by it. That is why a subaru doesn't have trouble turning corners, like my 4x4 does.

 

Subaru 5-speed electronic automatic transmissions, and 6-speed manual transmissions use VTD AWD, (Variable Torque Distribution All-Wheel-Drive) which CAN distribute torque on demand. 45% front 55% rear for the 5EAT, 35%-65% F-R for the 06 STI, 50-50 for previous STIs, IIRC. I think it can go 90%-10% in either direction on demand, though.

 

The WRX STI's 6MT for the last few years has had the added feature of manual override control of the center differential (DCCD - Driver Controlled Center Differential) to switch from automatic (VTD) to a fixed ratio in a few choices between standard split, to full-rear-wheel-drive.

 

Someone can correct this information, if I am innaccurate. Also, interesting is that the 07 Spec B is rumored, and likely confirmed to get the 6MT transmission. Likely with VTD, but slightly possible to have DCCD.

[fzanetti]

Someone can correct this information, if I am innaccurate. Also, interesting is that the 07 Spec B is rumored, and likely confirmed to get the 6MT transmission. Likely with VTD, but slightly possible to have DCCD.

 

If this is really truth, it may be a very interesting car.... Probably a 3.0 turbo engine, 6MT and DCCD? ?Hmmmm sweet!!!!!!!!!!!!!

 

 

Flavio Zanetti

Boston, MA

[IwannaSportSedan]

Now... don't jump the gun.

 

2007 Spec B is rumored to get a 6MT, with the same 2.5T engine that is in the Legacy GT now.

 

It will almost definitely have Variable Torque dist. I can't imagine that it wouldn't, or why they would change inside the transmission. I would put a slim but possible chance that it will have driver control (DCCD) as they may want to keep that trick solely for the WRX STI. (I'd think it would be a very nice little feature for a little fun... but I wouldn't die without it.)

 

3.0T has all but been completely ruled out of the US market, for emissions reasons, if it materializes anywhere else... at least thats what the people with contacts inside say.

 

MY2008 bears rumors for a Legacy STI... which is still VERY much hyperbole and conjecture.

[Garandman]

Without driving it or reading road test reports, you might not discover its maturity.

As I have mentioned earlier, throttle-controllable oversteering is usually more desirable to real drivers than pure neutral steering.

Why do you think this to be so?

 

What is a real driver?

[RobY]

Now... don't jump the gun.

 

2007 Spec B is rumored to get a 6MT, with the same 2.5T engine that is in the Legacy GT now.

 

It will almost definitely have Variable Torque dist. I can't imagine that it wouldn't, or why they would change inside the transmission. I would put a slim but possible chance that it will have driver control (DCCD) as they may want to keep that trick solely for the WRX STI. (I'd think it would be a very nice little feature for a little fun... but I wouldn't die without it.)

 

3.0T has all but been completely ruled out of the US market, for emissions reasons, if it materializes anywhere else... at least thats what the people with contacts inside say.

 

MY2008 bears rumors for a Legacy STI... which is still VERY much hyperbole and conjecture.

 

Japan and Europe already have the 6mt. Its a viscous unit with an extra gear.

[rporter]

SO WHAT CAN THE SUBARU SEND TO FRONT OR REAR? WHAT PERCENT OF POWER AT ANY GIVEN TIME CAN BE SENT TO FRONT OR REAR?

 

IF 50/50 split is normal what if the front has no traction how much power can you put to the rear?

 

Thanks

 

I have not pawed through all eight pages of this thread, but in case this wasn't listed before, the SOA site has a good explanation of each of the AWD systems they offer.

 

It's a bit tougher to get to than on their old site, but start here:

 

http://www.subaru.com/shop/overview.jsp?model=LEGACY&trim=25_GT_LIMITED_WAGON&command=overview

 

Or go to any of the opening pages for any specific model.

 

Go down the left side of the page, and click on the "AWD Technology" link. It will take you through each system they offer, and the basics of how they work.

[Ken S]

I thought the 5MT VC "Continuous" AWD had a set point of 50/50 but infinitely variable in either direction to almost 100/0 and 0/100. In other words, the viscous coupling reacts to rotational differences and wants to keep both front and rear tires turning at the same speed, but not necessarily delivering the same torque.

 

In a theoretical example, if a 5MT vehicle had it's front tires suspended in air (or some zero traction situation) wouldn't they still turn due to the VC lock but essentially be receiving very little torque?

 

In my experience driving in snow with both 5MT and VTD Subarus, you can feel a lot more oscillation in the 5MT power distribution as the front and rear tires alternately slip.

 

Ken

[Beanboy]

Head is gonna asplode, I screwed up my example again, hehe. You are correct Ken S.

 

Same can be said, and this is where I got confused, when you see things like, "100% to the rear and 50% of power to the front if needed."

 

In fully locked state, all AWD systems (minus torsen) whether they are diffs with viscous coupling, just clutches (haldex) active clutches and diff, truck part-time mechnical system, can send nearly all torque to the wheels that aren't slipping. Instead of 50/50 spit on 5mt soobies, say it was 10/90... you still will see nearly all torque applied to wheels that aren't slipping when the VC locks...err right?

 

Now, get both sets of wheels on dry ground, and that's when you will see the differences in a applied torque to the wheels based on what the split is... 100 to the front or rear until slip, 45/55, etc...

 

I need a drink, and somebody else to explain better than I can, hehe.

[rporter]

I thought the 5MT VC "Continuous" AWD had a set point of 50/50 but infinitely variable in either direction to almost 100/0 and 0/100. In other words, the viscous coupling reacts to rotational differences and wants to keep both front and rear tires turning at the same speed, but not necessarily delivering the same torque.

 

In a theoretical example, if a 5MT vehicle had it's front tires suspended in air (or some zero traction situation) wouldn't they still turn due to the VC lock but essentially be receiving very little torque?

 

In my experience driving in snow with both 5MT and VTD Subarus, you can feel a lot more oscillation in the 5MT power distribution as the front and rear tires alternately slip.

 

Ken

 

I feel that's "basically" true, but I wouldn't call what the Continous System does as being infinitely variable. It is at 50/50, then, in case of one end losing traction, the viscous center diff will supposedly throw the power to the other axle, and I don't believe there's anything variable there. I don't feel that it reduces the amount of torque to the spinning end (usually the front, with the open diff), it just sends more rpm to the rear to try to match the front.

 

I even wonder how well it works, because at the dragstrip, I've had two runs where I got smoke off the LF tire (Fresh VHT laid down). If it supposedly works to shift the torque to the rear, it certainly doesn't do it in those situations.

[Beanboy]

"The maximum amount of torque that actually gets applied to the drive wheels, is the highest amount possible while traction is maintained."

 

"if one side offers lots of resistance, and the other none, then effectively all the "usable" or "useful" torque goes to the side where there is resistance. It's getting 100% of the available torque. The side with no traction doesn't need torque to spin helplessly, so it's not really getting 50% of the torque as you might think."

 

Above two sentences helps describe what I'm talking about, I don't have an engineering degree, hehe.

 

Since the viscous coupling needs some time to work, you are going to get wheelspin up front. LF goes first I believe because of the torque of the engine/driveshaft on the car. Can notice it on drag cars:

 

http://maxmouse007.tripod.com/Media/Classics/Buick/Grand%20National/GrandNational_wheelie.jpg

 

"It is important, of course, that you start with equal tire loading. In other words, the car, while awaiting launch, will have equal rear tire loading. Upon launch, the left front fender will jump about half a foot higher than the right front."

[rporter]

I dont have an engineering degree, either. But....we are reading the marketing hype on the SOA webpage, so we aren't really getting a technical explanation of what really occurs.

 

The viscous coupling BETTER NOT "take time" to engage!! This is something that happens in a split-second. Keep in mid that, if a front tire(s) is spinning, the center viscous diff does not drop power to the front end.....it just tries to get the rear diff turning at the same RPM. There is still some friction loss in that viscous coupling.

 

Unlike the STI, as long as we have one end with an open diff, there is a possibility of traction loss

[Scotty]

The amount of slip in the "other" AWD system is down to 1/7 of a revolution of the wheel.

[phuzaxeman]

load up gran turismo 4 on the ps2 and rally race the s4 vs. legacy and you'll see the awd on the legacy is much better :-)