Beanboy Posted February 19, 2006 Share Posted February 19, 2006 Yes, but those front tires aren't getting 50% of the input torque, just getting whatever they need to spin at the same rate as the rears. "Assuming no clutch slippage, it is correct to say that the two driveshafts will spin with the same velocity and is the reason torque split can theoretically approach 100/0 or 0/100 when locked. The locked clutch causes the rotation of the two driveshafts to be equal front/rear. If there is no traction load on one axle and a heavy traction load on the other, then the amount of torque required to accelerate the unloaded driveshaft at the same rate as the loaded driveshaft will be much less than 50% of the total input torque to the diff. The split is transformed into whatever is required to accelerate these two disparate loads at the same rate. If they are equal loads, then it will indeed be 50/50." -B -B http://www.standardshift.com Link to comment Share on other sites More sharing options...
Ken S Posted February 20, 2006 Share Posted February 20, 2006 There's been discussion after discussion over at NASIOC on how the 5MT AWD works. Try a search and you'll find thread after thread of similar discussion but with hard to find clear answers. Here were two interesting posts I came across: http://forums.nasioc.com/forums/showpost.php?p=11763749&postcount=26 http://forums.nasioc.com/forums/showpost.php?p=4606385&postcount=53 Basically: - 50/50 is only under ideal non-slip conditions. Once there is slip, torque transfer occurs. How much is not as easy to explain as shown in the first link. - The VC becomes increasingly less efficent at high speed differences between front and rear axles. In an example of getting high centered, the VC may not provide enough transfer to get the vehicle unstuck. Ken Link to comment Share on other sites More sharing options...
rjoeser Posted February 20, 2006 Share Posted February 20, 2006 Did you ever hear of slowing down in the rain? Haul a$$ on dry pavement, you will live better for it Link to comment Share on other sites More sharing options...
Shangsta Posted February 20, 2006 Share Posted February 20, 2006 The quattro system is one of the greatest awd systems to date. You just have to look at their racing history. There is a reason the audi was banned from touring car racing in the 90's Link to comment Share on other sites More sharing options...
IwannaSportSedan Posted February 20, 2006 Share Posted February 20, 2006 The quattro system was one of the greatest awd systems to date. You just have to look at their racing history. There is a reason the audi was banned from touring car racing in the 90's fixored. Plus, the street versions are not always as optimized as race versions of quattro AWD. cost cutting has an effect. Audi as of late has been enamored with using the brakes to distribute torque, instead of actual limited slip differentials at the axles, even if the center differential is still the same torsen piece. It may be cheaper, and indistinguishable 9/10ths of the the time... but I am not sure it is up to it's former glory or reverence. Look at Subaru's WRC wins for the last decade... they are no slouch either, and perhaps as advanced or moreso than Quattro lately. Not necessarily the Legacy 5MT's symmetrical system, but VTD with DCCD is certainly nothing to sneeze at. Link to comment Share on other sites More sharing options...
trabbic Posted February 20, 2006 Share Posted February 20, 2006 EDIT... Don't worry, a car won't become steer by wire any time soon. There are laws in most nations that require a mechanical link between the driver and the front wheels. That doesn't mean engineers are developing these systems. EDIT... If you are worried about an electronic diff, well what about all the other electronics in the car? There are only two mechanical systems, not counting manual transmissions, left in a car, the steering and the brakes. Not even the throttle is mechanical. Only reason those two are still mechanical is there are laws that require them to be so. Sorry but this is not true, Saturn is currently using and has been for some years, a steer by wire system, and Toyota is using steer by wire and brake by wire systems, in the Prius. they are not the only manufactures doing this either and it will only become more common as soon as they can get the feed-back in the system that most drivers want. Even the transmission selector in the prius has NO direct connection to the transmission besides the wires, it is weird to use also, as the lever does not stay where it goes, it works more like a button selector. My vB Garage How to Install Steering Wheel Radio Controls Cubby Gauge Mounting Solutions Link to comment Share on other sites More sharing options...
RobY Posted February 21, 2006 Share Posted February 21, 2006 The quattro system is one of the greatest awd systems to date. You just have to look at their racing history. There is a reason the audi was banned from touring car racing in the 90's Cause audi likes to cheat. They became prominent in rally racing cause they were the only ones with 4wd when the competition was all 2wd. Until the Lancia came out with its viscous locking AWD system and kicked its butt. Same thing in touring car racing. AWD with 2wd competiton. The only reason why quattro recieved so much fame in rallying is because it was an AWD car competing against 2WD competitors. The AWD systems in current Subarus bares little resemblance to that of Audi. Audi was based on torsens differentals. Subaru uses viscous lockers. Abbriviated VCLD (viscous coupling locking differentials) it is still the prefered diffrential for use in group N rally racing. This is not to be confused with a viscous coupling which is completely diffrent. As a VCLD uses a mechanical differental in conjunction with a viscous slip limiter. Whereas a viscous coupler has no mechanical differental. The advantage of a VCLD is that it maintains a constant 50:50 split which is always there and requires no action of the viscous coupling to maintain the split. The coupling comes into play in situations where one wheel becomes unladen or one set of wheels is significantly more tractive than the other. Rarely do we find GrN or ametur rally teams using torsens for the simple fact that a torsens system can be disabled and a car rendered completely immobile simply by unloading 1 of the 4 wheels. It is a worm gear based system and its "limited slip" action relies on a mathmatical bias ratio. You unload one wheel the unladen wheel produces zero tractive torque and any multiple of zero is zero. Meaning zero torque is able to be delivered to the other 3 wheels. Audi was able to avoid this shortcoming in its latest gen IV quattro offering by using the brake system to arrest wheelspin. Now if you unload a wheel the brakes kick in and then you have your brake torque for that individual wheel times the bias ratio and that is what gets delivered to the other 3 tractive wheels. The disadvantage of this is that if you use it for extended periods of time you are going to cook your brakes. And due to stability problems of individual braking, the system shuts itself off once you pass 45 mph. Leaving you with a center torsens and 2 open axle diffs. Even Audi's Latest Haldex Offerings have some major shortcomings. Described Here... http://www.legacygt.com/forums/show...59&postcount=79 Audi AWD has since been FAR surpassed by the latest generation E-diff AWD systems such as Mistu ACD, Nissan ATESSA, Honda SH, Subaru VCD. All based on similar technology used in championship WRC cars. Link to comment Share on other sites More sharing options...
2006Specb122 Posted February 21, 2006 Share Posted February 21, 2006 I'm starting to think I shouldn't have revived this thread. There is way more to it than I originally thought. My mind is already filled with too much information after 8 hours of new training today. I'm officially signing off of this thread. Thanks for the info! Link to comment Share on other sites More sharing options...
fzanetti Posted February 21, 2006 Share Posted February 21, 2006 Interesting discussion... http://www.ridemonkey.com/forums/showthread.php?t=117492 Flavio Zanetti Boston, MA Link to comment Share on other sites More sharing options...
ilh Posted April 16, 2006 Share Posted April 16, 2006 After reading about all the negatives of a Torsen differential, one has to wonder why the 07 SpecB will have one in the rear vs. the viscous unit in the 06. Link to comment Share on other sites More sharing options...
RobY Posted April 16, 2006 Share Posted April 16, 2006 A torsens better for a road going car (ie) ample traction at both wheels. When it starts snowing or you go offroad a VC has advantages. Its all about what you use the car for. But I welcome the change as it means more factory upgrades. Link to comment Share on other sites More sharing options...
pdw Posted April 17, 2006 Share Posted April 17, 2006 Cause audi likes to cheat. They became prominent in rally racing cause they were the only ones with 4wd when the competition was all 2wd. Until the Lancia came out with its viscous locking AWD system and kicked its butt. Same thing in touring car racing. AWD with 2wd competiton. The only reason why quattro recieved so much fame in rallying is because it was an AWD car competing against 2WD competitors. The AWD systems in current Subarus bares little resemblance to that of Audi. Audi was based on torsens differentals. Subaru uses viscous lockers. Abbriviated VCLD (viscous coupling locking differentials) it is still the prefered diffrential for use in group N rally racing. This is not to be confused with a viscous coupling which is completely diffrent. As a VCLD uses a mechanical differental in conjunction with a viscous slip limiter. Whereas a viscous coupler has no mechanical differental. The advantage of a VCLD is that it maintains a constant 50:50 split which is always there and requires no action of the viscous coupling to maintain the split. The coupling comes into play in situations where one wheel becomes unladen or one set of wheels is significantly more tractive than the other. Rarely do we find GrN or ametur rally teams using torsens for the simple fact that a torsens system can be disabled and a car rendered completely immobile simply by unloading 1 of the 4 wheels. It is a worm gear based system and its "limited slip" action relies on a mathmatical bias ratio. You unload one wheel the unladen wheel produces zero tractive torque and any multiple of zero is zero. Meaning zero torque is able to be delivered to the other 3 wheels. Audi was able to avoid this shortcoming in its latest gen IV quattro offering by using the brake system to arrest wheelspin. Now if you unload a wheel the brakes kick in and then you have your brake torque for that individual wheel times the bias ratio and that is what gets delivered to the other 3 tractive wheels. The disadvantage of this is that if you use it for extended periods of time you are going to cook your brakes. And due to stability problems of individual braking, the system shuts itself off once you pass 45 mph. Leaving you with a center torsens and 2 open axle diffs. Even Audi's Latest Haldex Offerings have some major shortcomings. Described Here... http://www.legacygt.com/forums/show...59&postcount=79 Audi AWD has since been FAR surpassed by the latest generation E-diff AWD systems such as Mistu ACD, Nissan ATESSA, Honda SH, Subaru VCD. All based on similar technology used in championship WRC cars. Have you ever actually driven an Audi with the torsen based quattro? I got my A4 high centered such that one wheel was up in the air, two wheels were lightly touching snow and the last was low and got traction. The one tire pulled me off the snow bank. As you say, they use EDL. So what's the problem there? We're not talking rally cars. We're talking about street cars. As for Haldex, it's quite similar to the system used in Subaru's with automatics. Finally, I've also owned another torsen equipped car. That was a Miata with a torsen rear diff. It was great. Link to comment Share on other sites More sharing options...
LotusSeven Posted April 17, 2006 Share Posted April 17, 2006 Oh, this is interesting too about who were the first ones to introcdue front-drive. In 1965 Oldsmobile introduced the front-wheel drive Toronado, the first FWD car to be built and sold in the U.S. since the 1930s. Sorry not trying to hijack the all wheel drive thread, just pointing out facts in response to those saying Japanese and Euro cars having front drive first. The first successful FWD car was the US made 1930 Cord L-29 Phaeton. Back on the thread: My last car was a 1999-1/2 A4 2.8 Quattro with F1 GSD-3 tires (size 205/50/16). My current 05 LGT has F1 GSD-3 215/45-17 tires. The Audi was more front weight biased than the LGT and ultimately understeered sooner. However, at 9/10's the Audi was easier to drive (than the LGT) and the traction transitions were transparent as opposed as being noticible on the Subaru. It's hard to beat a torsen center diff. without going to a very sophisticated, race prepared, all-electronic system for all three diffs. Heavy Metal Killed Beethoven Support Classical Music Link to comment Share on other sites More sharing options...
Max Rebo Posted April 17, 2006 Share Posted April 17, 2006 All this talk about the negatives of a Haldex system has me wondering. How many people have actually driven a car with Haldex AWD? My point of reference is my former VW R32. We can talk theories and principles of operation until we're blue in the face. On paper, Haldex might not look to be that good for an "enthusiast." Go drive an R32 at a track, though. Real world results trump paper theories. With a stock, or even an aggressively-tuned controller, Haldex systems such as the one in the R32 are extremely easy to drive at the track, at 10/10ths. As such, I know several people who match or beat times of competing cars with more power. The system is very good at what it does. Nothing weird happens at the limits, either. When you push it hard around a hairpin turn, the car just grips and goes wherever you want it. All I'm really saying is that it's better than one might think. Depending on the application, though, you can get different results. RobY: I had a difficult time understanding this: The sharper the turn the more you need AWD the less active the haldex system must be to allow the wheels to spin freely. If it fully engages the front wheels which are spinning faster than the rear wheels mid turn will try to mesh together causing some pretty frightening stuff to happen. Oversteer and understeer at the same time alternating, who knows it depends on which set of tires loose grip first as a result of wheels spinning at diffrent rates and a coupling trying to mesh them together when the driver adds power. This is unavoidable in a coupling. While I'm not one to drive very aggressively or to track my car, I know people who do and have. They *tried* to get their R32 to swap ends, lose control, or just plain get the car unsettled in a sharp turn or through a series of maneuvers. They just couldn't do it. These are/were experienced track fanatics, too. Haldex isn't as unpredictable as you make it seem. Link to comment Share on other sites More sharing options...
iyalla Posted April 17, 2006 Share Posted April 17, 2006 I hear you Rebo. Its makes no sense what some are saying AT ALL. Maybe its because the Haldex (or Haldex like) system is put on SOME "lesser" models so people figure oh hey it must be inferior, then they try an prove it with their limited knowledge. The older systems were controlled by crude computers that had a set of maps to choose from and were set per axle. The newer systems are continous and variable and use more sensors and info from those sensors are not applied to a specific map. The computer just uses the info in real time. You're not going to get the sudden change of torque to the rear wheels in mid turn or whatever. That stopped years ago. Old info has a way of just circulating forever on the web:rolleyes: Link to comment Share on other sites More sharing options...
Max Rebo Posted April 17, 2006 Share Posted April 17, 2006 Exactly... Current and next-gen Haldex systems are fantastic. I can't say that they're truly better than Subaru's, Mitsubishi's, or Audi's Torsen system, but it's certainly different and effective. Torque distribution to the rear is continuously variable -- from nothing to 50% in current FWD-based systems. FWIW (and many people don't know this), Audi uses Haldex in the TT. However, most consumers just see "Quattro" and assume it's all the same. Haldex and Torsen are shared by Audi & VW. As mentionened earlier, Volvo and other car makers use Haldex as well. I bet some Audi TT 3.2 owners would be surprised to learn that VW's R32 is pretty much the exact same car... engine, drivetrain, and all... except they paid nearly $15k more, and both use Haldex. Link to comment Share on other sites More sharing options...
busski Posted April 19, 2006 Share Posted April 19, 2006 I was just reading an article in the biggest German car magazine which compared 12 different kind of AWD systems including Merc, BMW, Audi, Subaru. I don't know if it's useless with the language difficulty, but I thought it might be worthwhile. If anyone is intereested I can do a quick translate. I'm attaching the file. Holler if you want me to take a pass at an English version. -c- Left to right on thumbnails: Subaru Outback 2.5 Automatick + factors: Good Tracking Very Well Controllable Neutral Steering - Factors Only middle-of-the-road traction Sedate Handling The benefits of the outback lay in its high driving safety. It rarely comes to critical situations, even without ESP, which is not offered in this version. This driving stability is comes with the price of significant compromises in its willingness to drive on curvy roads. Also here it prefers to drive straight ahead. 2nd Image: VW Golf 4Motion + factors: Good traction Agile Handling Good straight-tracking Neutral in curves - Factors Tends towards oversteer Hard ESP initiation The allroad gold belong to those cars that are particularly fun in the snow. It is very ready to take on curvy roads, but stay well controllable. Occasional break-out of the rear when giving gas are easily regulated. Audi s4 Quattro + factors: Very good traction Very good handling Easily controllable Easily anticipated driving characteristics - Factors Hard ESP initiation Tends towards oversteer In the S4 you sense the rally gene. underscored by the powerfull V8 sound, it masters nearly every grade on the snow. By giving gas in the curves, you can temporarily allow the rear to break out. Other than that, the driving character is very safe and easily controllable. Link to comment Share on other sites More sharing options...
mlrtime Posted April 19, 2006 Share Posted April 19, 2006 translation please, or text in german to use babelfish. or a paraphrase. Link to comment Share on other sites More sharing options...
busski Posted April 19, 2006 Share Posted April 19, 2006 Left to right on thumbnails: Subaru Outback 2.5 Automatic + factors: Good Tracking Very Well Controllable Neutral Steering - Factors Only middle-of-the-road traction Sedate Handling The benefits of the outback lay in its high driving safety. It rarely comes to critical situations, even without ESP, which is not offered in this version. This driving stability comes with the price of significant compromises in its willingness to drive on curvy roads. Also here it prefers to drive straight ahead. 2nd Image: VW Golf 4Motion + factors: Good traction Agile Handling Good straight-tracking Neutral in curves - Factors Tends towards oversteer Hard ESP initiation The allroad golf belongs to those cars that are particularly fun in the snow. It is very ready to take on curvy roads, but stays well controllable. Occasional break-out of the rear when giving gas is easily regulated. Audi s4 Quattro + factors: Very good traction Very good handling Easily controllable Easily anticipated driving characteristics - Factors Hard ESP initiation Tends towards oversteer In the S4 you sense the rally gene. Underscored by the powerfull V8 sound, it masters nearly every grade on the snow. By giving gas in the curves, you can temporarily allow the rear to break out. Other than that, the driving character is very safe and easily controllable. Link to comment Share on other sites More sharing options...
Beanboy Posted April 19, 2006 Share Posted April 19, 2006 Why the hell would they compare an S4 to a Outback 2.5i automatic? And did they all have the same tires? And when the hell was the last time Audi had a factory rally team? Living on the 'old money' of ancestors the fat, 3800+ pound S4 is! Rally gene...bah! -B http://www.standardshift.com Link to comment Share on other sites More sharing options...
Rwabble Posted May 30, 2006 Share Posted May 30, 2006 Actually, the Quattro system is a mechanical all wheel drive system, not electronic. Link to comment Share on other sites More sharing options...
iyalla Posted May 30, 2006 Share Posted May 30, 2006 Rubbish. They should have tested a base Audi A4 or A3. Morons. Thats like comparing the new Mercedes S550 to the Toyota Camry LX and then declaring the S Class the winner because its soooo luxurios The 2.5i does what it does WELL. If you want a competitor to the S4 try out the spec.B for less dollars. Link to comment Share on other sites More sharing options...
IwannaSportSedan Posted May 30, 2006 Share Posted May 30, 2006 Actually, the Quattro system is a mechanical all wheel drive system, not electronic. You can't have AWD without some mechanical parts... so ALL AWD is mechanical. Mostly what they are discussing here is that Audi has largely eschewed mechanical Limited Slip Differentials for open front and rear differentials and Electronic Brade Distribution, which uses each brake to transfer power to the other end of the given axle. Electronic CONTROLS versus a nearly unassisted mechanical system with limited slip differentials. (automatic transmissions and engines being the only largely electronically controlled pieces.) Link to comment Share on other sites More sharing options...
harrydog Posted May 30, 2006 Share Posted May 30, 2006 I owned a 1994 Audi S4 and I found that Quattro system to be more seamless than either my 2002 WRX or my 2006 H6 Outback. For example, with the Audi I could take corners in the rain at elevated speeds that would break the rear end loose. I'd never feel the transition but traction would be almost instantly regained and the car would be back on track and I could power out of the corner. With the WRX I could feel the transition kick in much more abrubtly and it seemed more difficult to regain control. I really don't know what system is considered best technically, but I prefered the Audi system. Link to comment Share on other sites More sharing options...
Deer Killer Posted May 30, 2006 Share Posted May 30, 2006 Your audi had a longer wheelbase, so it could have nothing to do with the AWD. Not to mention being a different car entirely Link to comment Share on other sites More sharing options...
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