I'm wondering does the S4 & A4 have the same AWD system? Does the S4 use any mechanical diffs for the front and rear or are they open with brake assist like the A4's?
TDI1
Re: Any diff between S4 & A4 AWD system? (Audiquattroluv)
I think for the price of the new S4 they should have put a strong mechanical rear diff, like the M3 has. The regular 3 series have the brake assist thing, but the M3 has a mechanical diff for performace driving. Why wouldn't they put one in the S4?
I think for the price of the new S4 they should have put a strong mechanical rear diff, like the M3 has. The regular 3 series have the brake assist thing, but the M3 has a mechanical diff for performace driving. Why wouldn't they put one in the S4?
Re: Any diff between S4 & A4 AWD system? (TDI1)
wait a sec, A4's are brake assist? i thought it was all mechanical differentials? maybe i'm confused, but i didn't think the brakes were involved in quattro.
also, there's no need to upgrade the S4 quattro over the A4 quattro.....it's just that in the A4, the strength of it is overkill
![Image]()
wait a sec, A4's are brake assist? i thought it was all mechanical differentials? maybe i'm confused, but i didn't think the brakes were involved in quattro.
also, there's no need to upgrade the S4 quattro over the A4 quattro.....it's just that in the A4, the strength of it is overkill
Re: Any diff between S4 & A4 AWD system? (GTiTOM)
On the 2001+ S4 cars there is ESP (Electronic Stability Program) which will pulse the brakes on a wheel that appears to slip to maintain traction at that corner. This is done solely by the ABS system.
On an A4 the only brake assist is your right foot.
![Image]()
Modified by turbo90awd at 4:27 PM 10-1-2003
On the 2001+ S4 cars there is ESP (Electronic Stability Program) which will pulse the brakes on a wheel that appears to slip to maintain traction at that corner. This is done solely by the ABS system.
On an A4 the only brake assist is your right foot.
Modified by turbo90awd at 4:27 PM 10-1-2003
Re: Any diff between S4 & A4 AWD system? (turbo90awd)
right...the traction control. but on A4s, or the S4s with no ESP, it's all mechanical, right? that was always my understanding.
| Quote, originally posted by turbo90awd » |
| On the 2001+ S4 cars there is ESP (Electronic Stability Program) which will pulse the brakes on a wheel that appears to slip to maintain traction at that corner. This is done solely by the ABS system. |
right...the traction control. but on A4s, or the S4s with no ESP, it's all mechanical, right? that was always my understanding.
Re: Any diff between S4 & A4 AWD system? (turbo90awd)
exactly like i understood it. so in other words, the original poster's information is incorrect about how the A4 works. and unlike the beemer, the a4 and s4 have the AWD same system (not including ESP).
| Quote, originally posted by turbo90awd » |
| correct. The differentials only provide power to the wheels or shift it to another wheel that isn't slipping via the torsen design. They never take power away from a wheel. |
exactly like i understood it. so in other words, the original poster's information is incorrect about how the A4 works. and unlike the beemer, the a4 and s4 have the AWD same system (not including ESP).
Re: Any diff between S4 & A4 AWD system? (turbo90awd)
WRONG!!!!!!!!!!!
The A4 uses a Torsen center diff and open diffs in the front and rear. As we all know with an open diff all the power is sent to the wheel that is spinning. With the "brake assist" as I call it, the car will brake just the wheel that is spinning and fool the open diff into sending power to the other wheel which isn't slipping. If you have a mechanical differential this isn't necessary, since the mechanics of the Limited slip differential, by nature will do this. A Torsen diff is capable of multiplying the torque level by as much as typically 5 times, from one side to the other. If both rear wheels were on ice and the A4's brake system failed, it is doubtful that the car would be able to move foward. In this case the ECU would just brake both rear wheels and the Torsen center diff would then be able to multiply that torque and send it to the front wheels and move the car. This is similar to the EDL that VW's have. "electronic differential lock" basically it brakes the spinning wheel to lock the diff. If this system is so great why does BMW not use it for their M3's? Subaru STi's also have a mechanical rear diff, and suretrac front diff. Why does the S4 have the same AWD system as the regular A4's which isn't meant for performance driving????
WRONG!!!!!!!!!!!
The A4 uses a Torsen center diff and open diffs in the front and rear. As we all know with an open diff all the power is sent to the wheel that is spinning. With the "brake assist" as I call it, the car will brake just the wheel that is spinning and fool the open diff into sending power to the other wheel which isn't slipping. If you have a mechanical differential this isn't necessary, since the mechanics of the Limited slip differential, by nature will do this. A Torsen diff is capable of multiplying the torque level by as much as typically 5 times, from one side to the other. If both rear wheels were on ice and the A4's brake system failed, it is doubtful that the car would be able to move foward. In this case the ECU would just brake both rear wheels and the Torsen center diff would then be able to multiply that torque and send it to the front wheels and move the car. This is similar to the EDL that VW's have. "electronic differential lock" basically it brakes the spinning wheel to lock the diff. If this system is so great why does BMW not use it for their M3's? Subaru STi's also have a mechanical rear diff, and suretrac front diff. Why does the S4 have the same AWD system as the regular A4's which isn't meant for performance driving????
Re: Any diff between S4 & A4 AWD system? (TDI1)
I always thought the Quattro system used torsen diff's in the center and rear.
I really don't see a reason why BMW would need a torsen diff in a RWD car when limited slip would work great, plus I'm sure that the added expense of a rear torsen diff would greatly outweigh the benefits.
I always thought the Quattro system used torsen diff's in the center and rear.
I really don't see a reason why BMW would need a torsen diff in a RWD car when limited slip would work great, plus I'm sure that the added expense of a rear torsen diff would greatly outweigh the benefits.
Re: Any diff between S4 & A4 AWD system? (MEDEL514)
Uhh...I'm 99% sure the Quattro system only uses a Torsen center diff and like I said before open diffs front and rear.
Who said anything about BMW using a Torsen rear diff? They use a M rear LSD. That's exactly the point I was trying to make that BMW, STi and even EVO use mechanical limited slip rears, not open with traction brake controll like the S4. I'm trying to understand why Audi would put so much into the S4 and then use a crappy open rear diff with traction controll. It doesn't make sense to me, and I'd like someone to explain that.
Modified by TDI1 at 12:15 AM 10-2-2003
| Quote, originally posted by MEDEL514 » |
| I always thought the Quattro system used torsen diff's in the center and rear. I really don't see a reason why BMW would need a torsen diff in a RWD car when limited slip would work great, plus I'm sure that the added expense of a rear torsen diff would greatly outweigh the benefits. |
Uhh...I'm 99% sure the Quattro system only uses a Torsen center diff and like I said before open diffs front and rear.
Who said anything about BMW using a Torsen rear diff? They use a M rear LSD. That's exactly the point I was trying to make that BMW, STi and even EVO use mechanical limited slip rears, not open with traction brake controll like the S4. I'm trying to understand why Audi would put so much into the S4 and then use a crappy open rear diff with traction controll. It doesn't make sense to me, and I'd like someone to explain that.
Modified by TDI1 at 12:15 AM 10-2-2003
Re: Any diff between S4 & A4 AWD system? (TDI1)
Quattro is simply the best AWD system on the planet. BMW, or anybody else cannot compete with Quattro. It was banned from rally racing, what more do you want?? Also, the torsen diff can handle up to 700hp reliably. That is why ALL of their non-transverse engined cars use it. The RS6 is using the same Torsen that the A4 uses. Why use anything but the best?
Quattro is simply the best AWD system on the planet. BMW, or anybody else cannot compete with Quattro. It was banned from rally racing, what more do you want?? Also, the torsen diff can handle up to 700hp reliably. That is why ALL of their non-transverse engined cars use it. The RS6 is using the same Torsen that the A4 uses. Why use anything but the best?
Re: Any diff between S4 & A4 AWD system? (Audiquattroluv)
It is the "best" system, sure...
But the version of Quattro that was banned from the racing world was pretty vastly different from the one that we've got in our cars. Unless, that is, you have a differential locking switch somewhere on your A4 that I haven't got on mine.
I don't have the information in front of me, but I believe that our original poster may in fact be correct. The center diff is a Torsen unit. Again, I don't remember specifically right now, but I do know that the version (quattro V, I believe) that's on our A4s uses EDL, or electronic differential locking, which uses the brakes to send torque from one wheel on an axel to the other one. This would mean that the front and rear diffs are open.
If both wheels on one axel slip, then the Torsen center diff sends the torque either frontward or rearward, as needed. If only one wheel on an axel is slipping, the EDL kicks in and sends torque to the other wheel via braking the slipping one.
-Tim
| Quote, originally posted by Audiquattroluv » |
| Quattro is simply the best AWD system on the planet. BMW, or anybody else cannot compete with Quattro. It was banned from rally racing, what more do you want?? Also, the torsen diff can handle up to 700hp reliably. That is why ALL of their non-transverse engined cars use it. The RS6 is using the same Torsen that the A4 uses. Why use anything but the best? |
It is the "best" system, sure...
But the version of Quattro that was banned from the racing world was pretty vastly different from the one that we've got in our cars. Unless, that is, you have a differential locking switch somewhere on your A4 that I haven't got on mine.
I don't have the information in front of me, but I believe that our original poster may in fact be correct. The center diff is a Torsen unit. Again, I don't remember specifically right now, but I do know that the version (quattro V, I believe) that's on our A4s uses EDL, or electronic differential locking, which uses the brakes to send torque from one wheel on an axel to the other one. This would mean that the front and rear diffs are open.
If both wheels on one axel slip, then the Torsen center diff sends the torque either frontward or rearward, as needed. If only one wheel on an axel is slipping, the EDL kicks in and sends torque to the other wheel via braking the slipping one.
-Tim
Re: Any diff between S4 & A4 AWD system? (SilverSLC)
And the reason why they use it?
Cheaper?
Who knows?
Fact is, it works just fine, thanks. And to say that it's "not meant for performance driving..."
![Image]()
I dunno about that. Tell someone with an RS4 or RS6 that the quattro system in their car is "not meant for performance driving" as they blow past you.
![Image]()
-Tim
And the reason why they use it?
Cheaper?
Who knows?
Fact is, it works just fine, thanks. And to say that it's "not meant for performance driving..."
-Tim
Re: Any diff between S4 & A4 AWD system? (TDI1)
i hate to keep arguing this, but i really don't think you are right. if you are, i don't understand this at all. the Torsen (the brand name of this particular "open differential") behaves as an open diff only under partial load. under full load, the GEARS IN THE AXLE lock the axle and give power to both wheels....it doesn't slow one down, it speeds the other up. here's the link from. check this out from http://auto.howstuffworks.com/differential8.htm
"The Torsen differential* is a purely mechanical device; it has no electronics, clutches or viscous fluids.
The Torsen (from Torque Sensing) works as an open differential when the amount of torque going to each wheel is equal. As soon as one wheel starts to lose traction, the difference in torque causes the gears in the Torsen differential to bind together. The design of the gears in the differential determines the torque bias ratio. For instance, if a particular Torsen differential is designed with a 5:1 bias ratio, it is capable of applying up to five times more torque to the wheel that has good traction.
These devices are often used in high-performance all-wheel-drive vehicles. Like the viscous coupling, they are often used to transfer power between the front and rear wheels. In this application, the Torsen is superior to the viscous coupling because it transfers torque to the stable wheels before the actual slipping occurs.
However, if one set of wheels loses traction completely, the Torsen differential will be unable to supply any torque to the other set of wheels. The bias ratio determines how much torque can be transferred, and five times zero is zero.
*TORSEN is a registered trademark of Zexel Torsen, Inc. "
Notice that on how stuff works, there is also a section on open differentials, and why they don't work....and then the sections on things that fix that problem. torsen is listed last, under the same section as LOCKING differentials. it works not by braking the wheel, but by transferring torque. so when you mention being on ice and not moving, it's because no torque is getting towards the wheels, so no torque can be transferred.....not because it the can't send it to the front or something. the ecu can't transfer power that isn't there, so braking the rear wouldn't send it to the front anyway.
finally, no matter the details of how it actually works, "why stuff works" sums it up with this quote: "These devices are often used in high-performance all-wheel-drive vehicles". like was said before, i don't think you are going to be able to convince someone in an S3, S4, RS4, S6, RS6, that there car isn't "high performance" because it uses the same AWD system as the A4
![Image]()
edit: you know what, i change my mind. torsen differentials definitely DO NOT use the brakes to distribute power. time for everyone to go to these links and read up:
http://www.torsen.com/index.htm
http://www.torsen.com/general/general_faq.htm
http://www.torsen.com/files/Tr...e.pdf
that last article is a technical engineering article on how it works. if you don't feel like reading the whole thing, just do a Ctrl-F search and type in the word "brakes". If torsen used brakes to work, I guarantee one of the mechanical engineers from the Institution of Mechanical Engineers who wrote this article would have at least mentioned the word in there, right?
the people at torsen were also nice enough to sum up how it works in non-technical jargon: "The Torsen differential is simply a torque multiplier that works through the use of friction generated by thrust forces from the internal gearing. It multiplies what torque is available from the wheel that is starting to spin-up or lose traction and sends that available torque, multiplied by the TBR, to the slower turning wheel with the better traction".
here's an interesting list of cars that feature torsen differentials:
http://www.torsen.com/oem.htm
notice how the 4WD and RWD cars have either a torsen rear or front and rear differentials, but that the AWD cars, have a center differential? maybe that's where you are confused: some of those 4WD cars may use some sort of brake assist to get power from the front to the rear, b/c they have no torsen center diff. but the audis (and 4mo passat) have a center diff, so the torsen can send the power front to back (and vice versa) without the brakes (again, by MULTIPLYING THE TORQUE, not using the brakes).
as for the EDL, that is used on startup, if the wheels are slipping. since there is no torque to mulitply if one wheel has ZERO traction. from http://www.mccarthyaudi.co.za
The electronic differential lock (EDL) permits smooth, comfortable STARTS on road surfaces that do not have a uniform coefficient of friction. If a wheel starts to spin, EDL brakes it as necessary so that power is transmitted to the wheel with the better traction. EDL reduces tire wear and works up to about. 40 km/h. EDL is part of the electronic stabilization program (ESP) and the traction control (ASR).
finally, here's a nice little moving picture applet thingy of how quattro works. i don't see any brakes being used here: http://www.mccarthyaudi.co.za/....html
seems like there was some confusion between the two systems, but i hope that clears everything up. not all audis with quattro have EDL or ESP, which again, only works up until about 15 mph (conversion? i think). i really hope most people aren't doing "performance driving" on bad road surfaces at 15 mph
![Image]()
oh, and two more good articles:
http://autozine.kyul.net/techn...2.htm
http://www.audiworld.com/news/...shtml
Modified by GTiTOM at 6:29 AM 10-2-2003
| Quote, originally posted by TDI1 » |
| WRONG!!!!!!!!!!! The A4 uses a Torsen center diff and open diffs in the front and rear. As we all know with an open diff all the power is sent to the wheel that is spinning. With the "brake assist" as I call it, the car will brake just the wheel that is spinning and fool the open diff into sending power to the other wheel which isn't slipping. If you have a mechanical differential this isn't necessary, since the mechanics of the Limited slip differential, by nature will do this. A Torsen diff is capable of multiplying the torque level by as much as typically 5 times, from one side to the other. If both rear wheels were on ice and the A4's brake system failed, it is doubtful that the car would be able to move foward. In this case the ECU would just brake both rear wheels and the Torsen center diff would then be able to multiply that torque and send it to the front wheels and move the car. This is similar to the EDL that VW's have. "electronic differential lock" basically it brakes the spinning wheel to lock the diff. If this system is so great why does BMW not use it for their M3's? Subaru STi's also have a mechanical rear diff, and suretrac front diff. Why does the S4 have the same AWD system as the regular A4's which isn't meant for performance driving???? |
i hate to keep arguing this, but i really don't think you are right. if you are, i don't understand this at all. the Torsen (the brand name of this particular "open differential") behaves as an open diff only under partial load. under full load, the GEARS IN THE AXLE lock the axle and give power to both wheels....it doesn't slow one down, it speeds the other up. here's the link from. check this out from http://auto.howstuffworks.com/differential8.htm
"The Torsen differential* is a purely mechanical device; it has no electronics, clutches or viscous fluids.
The Torsen (from Torque Sensing) works as an open differential when the amount of torque going to each wheel is equal. As soon as one wheel starts to lose traction, the difference in torque causes the gears in the Torsen differential to bind together. The design of the gears in the differential determines the torque bias ratio. For instance, if a particular Torsen differential is designed with a 5:1 bias ratio, it is capable of applying up to five times more torque to the wheel that has good traction.
These devices are often used in high-performance all-wheel-drive vehicles. Like the viscous coupling, they are often used to transfer power between the front and rear wheels. In this application, the Torsen is superior to the viscous coupling because it transfers torque to the stable wheels before the actual slipping occurs.
However, if one set of wheels loses traction completely, the Torsen differential will be unable to supply any torque to the other set of wheels. The bias ratio determines how much torque can be transferred, and five times zero is zero.
*TORSEN is a registered trademark of Zexel Torsen, Inc. "
Notice that on how stuff works, there is also a section on open differentials, and why they don't work....and then the sections on things that fix that problem. torsen is listed last, under the same section as LOCKING differentials. it works not by braking the wheel, but by transferring torque. so when you mention being on ice and not moving, it's because no torque is getting towards the wheels, so no torque can be transferred.....not because it the can't send it to the front or something. the ecu can't transfer power that isn't there, so braking the rear wouldn't send it to the front anyway.
finally, no matter the details of how it actually works, "why stuff works" sums it up with this quote: "These devices are often used in high-performance all-wheel-drive vehicles". like was said before, i don't think you are going to be able to convince someone in an S3, S4, RS4, S6, RS6, that there car isn't "high performance" because it uses the same AWD system as the A4
edit: you know what, i change my mind. torsen differentials definitely DO NOT use the brakes to distribute power. time for everyone to go to these links and read up:
http://www.torsen.com/index.htm
http://www.torsen.com/general/general_faq.htm
http://www.torsen.com/files/Tr...e.pdf
that last article is a technical engineering article on how it works. if you don't feel like reading the whole thing, just do a Ctrl-F search and type in the word "brakes". If torsen used brakes to work, I guarantee one of the mechanical engineers from the Institution of Mechanical Engineers who wrote this article would have at least mentioned the word in there, right?
the people at torsen were also nice enough to sum up how it works in non-technical jargon: "The Torsen differential is simply a torque multiplier that works through the use of friction generated by thrust forces from the internal gearing. It multiplies what torque is available from the wheel that is starting to spin-up or lose traction and sends that available torque, multiplied by the TBR, to the slower turning wheel with the better traction".
here's an interesting list of cars that feature torsen differentials:
http://www.torsen.com/oem.htm
notice how the 4WD and RWD cars have either a torsen rear or front and rear differentials, but that the AWD cars, have a center differential? maybe that's where you are confused: some of those 4WD cars may use some sort of brake assist to get power from the front to the rear, b/c they have no torsen center diff. but the audis (and 4mo passat) have a center diff, so the torsen can send the power front to back (and vice versa) without the brakes (again, by MULTIPLYING THE TORQUE, not using the brakes).
as for the EDL, that is used on startup, if the wheels are slipping. since there is no torque to mulitply if one wheel has ZERO traction. from http://www.mccarthyaudi.co.za
The electronic differential lock (EDL) permits smooth, comfortable STARTS on road surfaces that do not have a uniform coefficient of friction. If a wheel starts to spin, EDL brakes it as necessary so that power is transmitted to the wheel with the better traction. EDL reduces tire wear and works up to about. 40 km/h. EDL is part of the electronic stabilization program (ESP) and the traction control (ASR).
finally, here's a nice little moving picture applet thingy of how quattro works. i don't see any brakes being used here: http://www.mccarthyaudi.co.za/....html
seems like there was some confusion between the two systems, but i hope that clears everything up. not all audis with quattro have EDL or ESP, which again, only works up until about 15 mph (conversion? i think). i really hope most people aren't doing "performance driving" on bad road surfaces at 15 mph
oh, and two more good articles:
http://autozine.kyul.net/techn...2.htm
http://www.audiworld.com/news/...shtml
Modified by GTiTOM at 6:29 AM 10-2-2003
Re: Any diff between S4 & A4 AWD system? (SilverSLC)
Yes, you know what you are talking about, thank you! Will all you people saying we are wrong please go back and read all of my posts and this post again very carefully and reconsider your answer.
![Image]()
| Quote, originally posted by SilverSLC » |
It is the "best" system, sure... But the version of Quattro that was banned from the racing world was pretty vastly different from the one that we've got in our cars. Unless, that is, you have a differential locking switch somewhere on your A4 that I haven't got on mine. I don't have the information in front of me, but I believe that our original poster may in fact be correct. The center diff is a Torsen unit. Again, I don't remember specifically right now, but I do know that the version (quattro V, I believe) that's on our A4s uses EDL, or electronic differential locking, which uses the brakes to send torque from one wheel on an axel to the other one. This would mean that the front and rear diffs are open. If both wheels on one axel slip, then the Torsen center diff sends the torque either frontward or rearward, as needed. If only one wheel on an axel is slipping, the EDL kicks in and sends torque to the other wheel via braking the slipping one. -Tim |
Yes, you know what you are talking about, thank you! Will all you people saying we are wrong please go back and read all of my posts and this post again very carefully and reconsider your answer.
Re: Any diff between S4 & A4 AWD system? (TDI1)
did you read what i wrote?
| Quote, originally posted by TDI1 » |
Yes, you know what you are talking about, thank you! Will all you people saying we are wrong please go back and read all of my posts and this post again very carefully and reconsider your answer.
|
did you read what i wrote?
Re: Any diff between S4 & A4 AWD system? (GTiTOM)
Did you actually READ my post???? What you just said is EXACTLY what I said in my post which you quoted!!!
![Image]()
Last time people
Quattro
1) Torsen Center Diff
2) Open front and rear Diffs with traction control
If you actually read that stuff on howstuffworks.com you would see that one of the limitations of a Torsen Diff is it's inablitly to transfer torque, when torque on one end of the diff is Zero. ( 0 * 200 = 0) This means if a wheel is off the ground or on ice it has to have a traction brake controll system to back it up, this is how the Hummer works. The difference being with the Torsen as the center diff, we are now looking at it in terms of the front axle vs. the rear axle, not the left wheel vs. the right wheel, however the concept behind it's operation remains the same.
So like I carefully pointed out in my example where one axle is on ice, the center torsen diff wouldn't be able to transfer torque to the axle with grip without braking BOTH slipping wheels!!!!!!
And like it was said before the Quattro system in the current A4 is different from the rally version.
If someone would like to actually answer my question, it is why does
Audi use a rear open diff with traction controll???? BMW, STi, EVO, Corvette, etc...all use mechanical rear LSD's in their true performance vehicles why not Audi, BTW...they used too!!!!!!! 50K+ S4 should have a better AWD system then the standard A4's. Can someone answer that?
![Image]()
Modified by TDI1 at 9:33 AM 10-2-2003
| Quote, originally posted by GTiTOM » |
i hate to keep arguing this, but i really don't think you are right. if you are, i don't understand this at all. the Torsen (the brand name of this particular "open differential") behaves as an open diff only under partial load. under full load, the GEARS IN THE AXLE lock the axle and give power to both wheels....it doesn't slow one down, it speeds the other up. here's the link from. check this out from http://auto.howstuffworks.com/differential8.htm "The Torsen differential* is a purely mechanical device; it has no electronics, clutches or viscous fluids. The Torsen (from Torque Sensing) works as an open differential when the amount of torque going to each wheel is equal. As soon as one wheel starts to lose traction, the difference in torque causes the gears in the Torsen differential to bind together. The design of the gears in the differential determines the torque bias ratio. For instance, if a particular Torsen differential is designed with a 5:1 bias ratio, it is capable of applying up to five times more torque to the wheel that has good traction. These devices are often used in high-performance all-wheel-drive vehicles. Like the viscous coupling, they are often used to transfer power between the front and rear wheels. In this application, the Torsen is superior to the viscous coupling because it transfers torque to the stable wheels before the actual slipping occurs. However, if one set of wheels loses traction completely, the Torsen differential will be unable to supply any torque to the other set of wheels. The bias ratio determines how much torque can be transferred, and five times zero is zero. *TORSEN is a registered trademark of Zexel Torsen, Inc. " Notice that on how stuff works, there is also a section on open differentials, and why they don't work....and then the sections on things that fix that problem. torsen is listed last, under the same section as LOCKING differentials. it works not by braking the wheel, but by transferring torque. so when you mention being on ice and not moving, it's because no torque is getting towards the wheels, so no torque can be transferred.....not because it the can't send it to the front or something. the ecu can't transfer power that isn't there, so braking the rear wouldn't send it to the front anyway. finally, no matter the details of how it actually works, "why stuff works" sums it up with this quote: "These devices are often used in high-performance all-wheel-drive vehicles". like was said before, i don't think you are going to be able to convince someone in an S3, S4, RS4, S6, RS6, that there car isn't "high performance" because it uses the same AWD system as the A4
edit: you know what, i change my mind. torsen differentials definitely DO NOT use the brakes to distribute power. time for everyone to go to these links and read up: http://www.torsen.com/index.htm http://www.torsen.com/general/general_faq.htm http://www.torsen.com/files/Tr...e.pdf that last article is a technical engineering article on how it works. if you don't feel like reading the whole thing, just do a Ctrl-F search and type in the word "brakes". If torsen used brakes to work, I guarantee one of the mechanical engineers from the Institution of Mechanical Engineers who wrote this article would have at least mentioned the word in there, right? the people at torsen were also nice enough to sum up how it works in non-technical jargon: "The Torsen differential is simply a torque multiplier that works through the use of friction generated by thrust forces from the internal gearing. It multiplies what torque is available from the wheel that is starting to spin-up or lose traction and sends that available torque, multiplied by the TBR, to the slower turning wheel with the better traction". here's an interesting list of cars that feature torsen differentials: http://www.torsen.com/oem.htm notice how the 4WD and RWD cars have either a torsen rear or front and rear differentials, but that the AWD cars, have a center differential? maybe that's where you are confused: some of those 4WD cars may use some sort of brake assist to get power from the front to the rear, b/c they have no torsen center diff. but the audis (and 4mo passat) have a center diff, so the torsen can send the power front to back (and vice versa) without the brakes, and not just from side to side (again, by MULTIPLYING THE TORQUE, not using the brakes). as for the EDL, that is used on startup, if the wheels are slipping. since there is no torque to mulitply if one wheel has ZERO traction. from http://www.mccarthyaudi.co.za The electronic differential lock (EDL) permits smooth, comfortable STARTS on road surfaces that do not have a uniform coefficient of friction. If a wheel starts to spin, EDL brakes it as necessary so that power is transmitted to the wheel with the better traction. EDL reduces tire wear and works up to about. 40 km/h. EDL is part of the electronic stabilization program (ESP) and the traction control (ASR). finally, here's a nice little moving picture applet thingy of how quattro works. i don't see any brakes being used here: http://www.mccarthyaudi.co.za/....html seems like there was some confusion between the two systems, but i hope that clears everything up. not all audis with quattro have EDL or ESP, which again, only works up until about 15 mph (conversion? i think). i really hope most people aren't doing "performance driving" on bad road surfaces at 15 mph
Modified by GTiTOM at 6:17 AM 10-2-2003 |
Did you actually READ my post???? What you just said is EXACTLY what I said in my post which you quoted!!!
Last time people
Quattro
1) Torsen Center Diff
2) Open front and rear Diffs with traction control
If you actually read that stuff on howstuffworks.com you would see that one of the limitations of a Torsen Diff is it's inablitly to transfer torque, when torque on one end of the diff is Zero. ( 0 * 200 = 0) This means if a wheel is off the ground or on ice it has to have a traction brake controll system to back it up, this is how the Hummer works. The difference being with the Torsen as the center diff, we are now looking at it in terms of the front axle vs. the rear axle, not the left wheel vs. the right wheel, however the concept behind it's operation remains the same.
So like I carefully pointed out in my example where one axle is on ice, the center torsen diff wouldn't be able to transfer torque to the axle with grip without braking BOTH slipping wheels!!!!!!
And like it was said before the Quattro system in the current A4 is different from the rally version.
If someone would like to actually answer my question, it is why does
Audi use a rear open diff with traction controll???? BMW, STi, EVO, Corvette, etc...all use mechanical rear LSD's in their true performance vehicles why not Audi, BTW...they used too!!!!!!! 50K+ S4 should have a better AWD system then the standard A4's. Can someone answer that?
Modified by TDI1 at 9:33 AM 10-2-2003
Re: Any diff between S4 & A4 AWD system? (TDI1)
yes, i did read your post. maybe you shoud read mine again, and the part where i talked about edl. again, the EDL works up until 15 mph or so....not while driving at full speed like the quattro. who cares what it does when you are slipping on launch. if i'm stuck on ice, i don't give a rat's ass about the peformance. the m3 might have a better differential system for launching, but who cares....everyone knows quattro cars aren't for drag strip racing.
and anyway, your question is pointless in comparing it to other cars. "why does bmw use a different system in their high end cars and audi doesn't?" seriously, that's like going on a BMW board and saying "why doesn't BMW use turbo in their high end cars while Audi does in the RS6?". i'm sure there are plenty of reasons, which are just going to be speculation. i'm sure one reason is cost....each diff is at least a grand, so i'm sure putting 3 in the car raises the costs. and maybe another reason is it's not needed.....i'll take the rs4 and it's "non-performance driving system" over a vette, sti, or m3 any day.
and yes, i know how the hummer works....but how is the performance of that relevant to the performance of the quattro cars? you're not going to be racing in a hummer, and you definitely aren't going to be rock crawling with 2 wheels in the air in an audi
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Modified by GTiTOM at 7:04 AM 10-2-2003
| Quote, originally posted by TDI1 » |
Did you actually READ my post???? What you just said is EXACTLY what I said in my post which you quoted!!!
Last time people Quattro 1) Torsen Center Diff 2) Open front and rear Diffs with traction control If you actually read that stuff on howstuffworks.com you would see that one of the limitations of a Torsen Diff is it's inablitly to transfer torque, when torque on one end of the diff is Zero. ( 0 * 200 = 0) This means if a wheel is off the ground or on ice it has to have a traction brake controll system to back it up, this is how the Hummer works. The difference being with the Torsen as the center diff, we are now looking at it in terms of the front axle vs. the rear axle, not the left wheel vs. the right wheel, however the concept behind it's operation remains the same. So like I carefully pointed out in my example where one axle is on ice, the center torsen diff wouldn't be able to transfer torque to the axle with grip without braking BOTH slipping wheels!!!!!! And like it was said before the Quattro system in the current A4 is different from the rally version. If someone would like to actually answer my question, it is why does Audi use a rear open diff with traction controll???? BMW, STi, EVO, Corvette, etc...all use mechanical rear LSD's in their true performance vehicles why not Audi, BTW...they used too!!!!!!! 50K+ S4 should have a better AWD system then the standard A4's. Can someone answer that?
Modified by TDI1 at 9:33 AM 10-2-2003 |
yes, i did read your post. maybe you shoud read mine again, and the part where i talked about edl. again, the EDL works up until 15 mph or so....not while driving at full speed like the quattro. who cares what it does when you are slipping on launch. if i'm stuck on ice, i don't give a rat's ass about the peformance. the m3 might have a better differential system for launching, but who cares....everyone knows quattro cars aren't for drag strip racing.
and anyway, your question is pointless in comparing it to other cars. "why does bmw use a different system in their high end cars and audi doesn't?" seriously, that's like going on a BMW board and saying "why doesn't BMW use turbo in their high end cars while Audi does in the RS6?". i'm sure there are plenty of reasons, which are just going to be speculation. i'm sure one reason is cost....each diff is at least a grand, so i'm sure putting 3 in the car raises the costs. and maybe another reason is it's not needed.....i'll take the rs4 and it's "non-performance driving system" over a vette, sti, or m3 any day.
and yes, i know how the hummer works....but how is the performance of that relevant to the performance of the quattro cars? you're not going to be racing in a hummer, and you definitely aren't going to be rock crawling with 2 wheels in the air in an audi
Modified by GTiTOM at 7:04 AM 10-2-2003
Re: Any diff between S4 & A4 AWD system? (GTiTOM)
ok, i have a theory about why no front and rear locking diffs. i could be wrong, because this is just speculation:
two more diffs = more rotational mass = less power to the wheels = slower car. especially when it's not necessary, b/c traction control is only getting used under bad conditions when most people shouldn't be driving with "performance" in mind....and only up until 15mph.
how's that sound?
and a quote from difflock.com that goes back to my theory that it's just not necessary to have a better "performance system":
"The Audi A4 quattro has been particularly successful in demolishing its two wheel drive competition in seven major touring car series last year despite severe weight handicaps"
maybe if the m3 could keep up with it on the track, then the audi engineers would start to think about making a "high performance" awd system.
Modified by GTiTOM at 7:19 AM 10-2-2003
ok, i have a theory about why no front and rear locking diffs. i could be wrong, because this is just speculation:
two more diffs = more rotational mass = less power to the wheels = slower car. especially when it's not necessary, b/c traction control is only getting used under bad conditions when most people shouldn't be driving with "performance" in mind....and only up until 15mph.
how's that sound?
and a quote from difflock.com that goes back to my theory that it's just not necessary to have a better "performance system":
"The Audi A4 quattro has been particularly successful in demolishing its two wheel drive competition in seven major touring car series last year despite severe weight handicaps"
maybe if the m3 could keep up with it on the track, then the audi engineers would start to think about making a "high performance" awd system.
Modified by GTiTOM at 7:19 AM 10-2-2003
Re: Any diff between S4 & A4 AWD system? (TDI1)
Ok, here's the deal.
Audi does use open front and rear diffs (one in the tranny, one in the rear diff housing). The torsen differential used is a Torsen T2 (from 1995-present). As you can read on http://www.howstuffworks.com and other sites, the torsen diff is a torque sensing system, which can shift torque even before a set of wheels fully slips. As soon as any amount of slip occurs, no matter how small, the torsen diff starts pushing it to the other end of the car.
In difference to a torsen diff, with a LSD you have these plates that are speed sensing not torque sensing. As one set of plates begins to spin faster (due to loss of traction) a shift of power occurs. This causes a delay in power distribution. However, it does get the job done.
Now lets look at Traction Control and Traction Stability. Traction Control and Stability depend on the ABS system to sense when a wheel's speed is higher than others and will pulse the brakes there to maintain even traction. You should note that this is in fact a speed sensing design.
So, we have LSD which is speed sensing, ABS/TCS/SCS which is speed sensing and good old torsen who is torque sensing.
If you were to setup a car with a LSD center diff, LSD rear diff and ABS/TCS/SCS, what would happen when there was slippage at an entire axle? Well, your center LSD has to come up to speed to transfer torque and your ABS/TCS/SCS system needs to come up to speed to sense a fast spinning set of wheels. By that point, you have already lost enough traction to either skid or slowdown. Then after the problem occurs and you are in trouble, the LSD and ABS/TCS/SCS come into play to help you out when you are desperate.
If you look at an S4/A4/A6/RS4/RS6 you have a torque sensing center diff and a speed sensing ABS/TCS/SCS system watching every wheel. The torsen sees the begining of a slip and starts shifting power before total loss of traction. The speed sensing system is there to cover you incase you loose a whole axle section and apply brakes as needed. At no point do have a loss of traction unless there is so little traction the ABS system cannot slow the car down to re-grip the roadway. This is in no way any different than a LSD equipped car. If a LSD equipped car had no traction across an entire axle, it would slip too.
So the bottom line here is that, the combo of both a torque sensing system and a speed sensing system is the best possible combo. Not speed sensing paired with another speed sensing system.
| Quote, originally posted by TDI1 » |
| If someone would like to actually answer my question, it is why does Audi use a rear open diff with traction controll???? BMW, STi, EVO, Corvette, etc...all use mechanical rear LSD's in their true performance vehicles why not Audi, BTW...they used too!!!!!!! 50K+ S4 should have a better AWD system then the standard A4's. Can someone answer that?
|
Ok, here's the deal.
Audi does use open front and rear diffs (one in the tranny, one in the rear diff housing). The torsen differential used is a Torsen T2 (from 1995-present). As you can read on http://www.howstuffworks.com and other sites, the torsen diff is a torque sensing system, which can shift torque even before a set of wheels fully slips. As soon as any amount of slip occurs, no matter how small, the torsen diff starts pushing it to the other end of the car.
In difference to a torsen diff, with a LSD you have these plates that are speed sensing not torque sensing. As one set of plates begins to spin faster (due to loss of traction) a shift of power occurs. This causes a delay in power distribution. However, it does get the job done.
Now lets look at Traction Control and Traction Stability. Traction Control and Stability depend on the ABS system to sense when a wheel's speed is higher than others and will pulse the brakes there to maintain even traction. You should note that this is in fact a speed sensing design.
So, we have LSD which is speed sensing, ABS/TCS/SCS which is speed sensing and good old torsen who is torque sensing.
If you were to setup a car with a LSD center diff, LSD rear diff and ABS/TCS/SCS, what would happen when there was slippage at an entire axle? Well, your center LSD has to come up to speed to transfer torque and your ABS/TCS/SCS system needs to come up to speed to sense a fast spinning set of wheels. By that point, you have already lost enough traction to either skid or slowdown. Then after the problem occurs and you are in trouble, the LSD and ABS/TCS/SCS come into play to help you out when you are desperate.
If you look at an S4/A4/A6/RS4/RS6 you have a torque sensing center diff and a speed sensing ABS/TCS/SCS system watching every wheel. The torsen sees the begining of a slip and starts shifting power before total loss of traction. The speed sensing system is there to cover you incase you loose a whole axle section and apply brakes as needed. At no point do have a loss of traction unless there is so little traction the ABS system cannot slow the car down to re-grip the roadway. This is in no way any different than a LSD equipped car. If a LSD equipped car had no traction across an entire axle, it would slip too.
So the bottom line here is that, the combo of both a torque sensing system and a speed sensing system is the best possible combo. Not speed sensing paired with another speed sensing system.
Re: Any diff between S4 & A4 AWD system? (GTiTOM)
So are you saying that a speeds over 15mph EDL no longer functions?
Why do you say the M3 "might" have a better differential system for launching? Does it yes or no? Last time I checked the M3 isn't designed for the drag strip either.
My question isn't pointless since BMW wasn't the ONLY car manufacturer I compared the S4 to. Your metaphor about the turbo on BMW's is completely irrelevant to this discussion. I used BMW as an example because they use the Audi system on the rear axle of the 3 series, but the M3 gets a more substantial LSD in the rear. Your speculation as to controling costs for the reason only further surves my point being why does the mighty S4 have the same AWD system as the regular A4's.
I only used these examples in order to illustrate the basic operation of the system.
| Quote, originally posted by GTiTOM » |
yes, i did read your post. maybe you shoud read mine again, and the part where i talked about edl. again, the EDL works up until 15 mph or so....not while driving at full speed like the quattro. who cares what it does when you are slipping on launch. if i'm stuck on ice, i don't give a rat's ass about the peformance. the m3 might have a better differential system for launching, but who cares....everyone knows quattro cars aren't for drag strip racing. |
So are you saying that a speeds over 15mph EDL no longer functions?
Why do you say the M3 "might" have a better differential system for launching? Does it yes or no? Last time I checked the M3 isn't designed for the drag strip either.
| Quote, originally posted by GTiTOM » |
and anyway, your question is pointless in comparing it to other cars. "why does bmw use a different system in their high end cars and audi doesn't?" seriously, that's like going on a BMW board and saying "why doesn't BMW use turbo in their high end cars while Audi does in the RS6?". i'm sure there are plenty of reasons, which are just going to be speculation. i'm sure one reason is cost....each diff is at least a grand, so i'm sure putting 3 in the car raises the costs. |
My question isn't pointless since BMW wasn't the ONLY car manufacturer I compared the S4 to. Your metaphor about the turbo on BMW's is completely irrelevant to this discussion. I used BMW as an example because they use the Audi system on the rear axle of the 3 series, but the M3 gets a more substantial LSD in the rear. Your speculation as to controling costs for the reason only further surves my point being why does the mighty S4 have the same AWD system as the regular A4's.
| Quote, originally posted by GTiTOM » |
and yes, i know how the hummer works....but how is the performance of that relevant to the performance of the quattro cars? you're not going to be racing in a hummer, and you definitely aren't going to be rock crawling with 2 wheels in the air in an audi
|
I only used these examples in order to illustrate the basic operation of the system.
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