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Audi Introduces New 7-Speed S tronic Transmission
19 March 2008
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| The new seven-speed S tronic. |
Audi is introducing a new seven-speed S tronic transmission. The new twin-clutch transmission, designed to work with longitudinally installed engines and the quattro all-wheel drive system, offers a 550 Nm torque capacity. Audi will introduce the new S tronic into multiple model lines in series production this year.
The new transmission, developed entirely by Audi, is intended for the mid-range model lines and has been designed to be both sporty while also being efficient.
Audi drivers can use the new seven-speed S tronic in various modes. The fully automatic mode, in which the computer selects the gear, keeps the D (Drive) and S (Sport) programs available. The gears can also be manually switched with the shift selector lever or with the optional rocker switch on the steering wheel.
The seven-speed S tronic is composed of two transmission structures. It integrates two multidisk clutches that control different gears. The large K1 clutch located on the outside conducts the torque via a solid shaft to the gear wheels for the odd gears 1, 3, 5 and 7. They are located in the rear of the cast-aluminum transmission housing, toward the center of the vehicle.
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| Operation of the seven-speed S tronic accelerating in first gear (top) and second gear (bottom). Click to enlarge. |
A hollow shaft rotates around the solid shaft. It is connected to the smaller K2 clutch, which is integrated into the inside of its larger sibling, and which controls the gear wheels for the even gears 2, 4 and 6, as well as reverse gear. All gear wheels are located in a single row on both drive shafts, in the order 4, 6, 2, R, 1, 3, 7 and 5.
Both transmission structures are continuously active, but only one is powered at a time by the engine.
The power flows from the drive shaft to the self-locking center differential of the quattro drivetrain, which distributes it into two directions. In the basic distribution, 60% of the torque flows over the cardan shaft to the differential for the rear axle, and 40% flows over a side shaft to the bevel gear of the front-axle differential. Because this shaft is installed at a 7.2 degree angle, it uses a slanted, beveloid gear. To reduce weight, it is also hollow.
The asymmetric-dynamic power distribution provides sporty and agile driving characteristics with slight emphasis on the rear end. When needed, the center differential can deliver up to 85% of the power to the rear axle or a maximum of 65% of the power to the front axle.
Highly precise management of both multidisk clutches was one of the most important development goals. This was achieved in part with a compact pressure cylinder, electronically controlled rotation speed compensation and the use of an optimized coil spring package. This package of technology provides maximum precision and comfort at startup and shifting.
The transmission is managed by the mechatronic module. This module involves a compact group of control units and hydraulic control valves that is integrated on the left of the transmission when facing the direction of travel. Its control concept allows the speed of the gear shifting process to vary and extremely precise control of the power necessary for the process.
The required control pressure is provided by an efficiently operating oil pump that is located next to the mechatronic module and is driven by a gear section. The oil pump is supported by a vacuum booster for cooling the twin clutch during starting. This allows the amount of oil pumped to be roughly doubled as needed without increasing power.
A distinctive feature of the seven-speed S tronic is its two separate oil systems. While the twin clutch, mechatronic module and oil pump are supplied by their own oil circuit with seven liters of automatic transmission fluid (ATF) oil, the wheelsets and the central and front-axle differential are lubricated with about 4.5 liters of hypoid gear oil. This separation allowed the development engineers to position all of the components ideally, without being forced to compromise by using a single lubricant.
The maximum possible transmission-ratio spread of 8.0:1 allows a sporty, short transmission ratio for the first gear as well as an rpm-sinking, long ratio for the last gear.
March 19, 2008 in Transmissions | Permalink | Comments (11) | TrackBack (0)
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Comments
550Nm = ~410lb-ft. Considering there is only one point of contact between the active spur gears, that's pretty darn high.
Note the location of the front transaxle, on the *engine* side of the two-mass flywheel. Putting it there allowed Audi to move the engine back a few inches to reduce the traditional visual overhang and understeer.
Posted by: | Mar 19, 2008 10:21:55 AM
This transmission should do very well with a 3.0TDI in the U.S. market. I can only hope it will be used in the new A4 with a 2.0TDI (I believe the new A4 uses a longitudinal configuration just as the last one).
Ramble from here out...
People always complain that EVs are too expensive. I counter that a transmission, such as this Audi unit, would also be EXTREMELY expensive if it weren't for mass production and automation. Once the battery issue is sorted, I'd be willing to bet that EVs are actually cheaper to manufacture.
On a not green note, I wonder if this transmission will make it into the next Audi RS6. If so, wow. I've always dreamed of finishing off the Ghawar field while blasting through some switchbacks in a super saloon, most of the energy in that glorious oil being lost to mechanical inefficiencies. Sick, I know.
Posted by: GreenPlease | Mar 19, 2008 11:09:16 AM
@ GreenPlease,
Your comments are well taken, and insightful.
Intrinsically, a Li-Ion battery lends itself to easy automated manufacture. So does manufacture of electric motor drive trains with minor needs for transmissions. This is true because maximum torgue is available at zero RPM. After amortizing development costs, these battery packs should be much cheaper to manufacture than a transmission, multi-differential structure such as this complex Audi. Ironically, the generator set may turn out to cost more than the basic electric propulsion system.
Autos will get simpler and cheaper to build, even as they get more sophisticated, and therefore to sell. Electric energy to power them, is well under a dollar per gallon equivalent, even now.
Electricity is inherently more pollution free, even if the electricity is generated with the most polluting coal plants.
More importantly, we will have found an energy substitute that is expandible and scales to amounts large enough for all of humanity to enjoy a modern lifestyle without poverty.
Secondly, adopting this technology which is coming with all the force of a Tsunami, will remove the power of tyrants and shieks, who have implemented a monopolistic cartel over petroleum prices.
Thirdly, if you care about CO2 emissions, widespread adoption of electric powered autos, will reduce CO2 emissions by much more than the amounts prescribed by those seeking CO2 reductions.
The qualitative GHG hypothesis have been shown to be exagerated by the quantitive Science of the 21st century. When feared CO2 has been emasculated by modern Science, to be able to alter the climate by only a few hundreth of a degree per century, who cares?
Lastly, the methods of electric generation are multiple, with many with minor pollution side effects. Eventually, controlled Fusion will provide the clean inexhaustible source of energy that scales and solves the problem permanently. Optimistically, this will start to occure in a few decades, but even it it takes 3 or 4 decades, there is now no problem waiting for it to come. A last genration of passive, light water reactors, will serve in the interim.
Posted by: Stan Peterson | Mar 19, 2008 12:32:26 PM
?
Posted by: Bill | Mar 19, 2008 4:43:56 PM
@Stan
"Ironically, the generator set may turn out to cost more than the basic electric propulsion system."
Are you referring to a PHEV? If so, I'd agree with you. Perhaps a Stirling cycle engine with a linear alternator/generator (whatever) would help address this. Maybe a micro turbine? I remember reading that Chrysler tried to develop a gas turbine powered vehicle in the 60s. Once in mass production, the impeller would only $5/copy to make.
While I generally agree with your comments I dissent with regards to nuclear power:
1. Nuclear fusion: while I'm really not in a position to comment, I've always had a theory that the force required to contain and therefore maintain a fusion reaction could only be provided by the gravity of a star. Therefore, continuous nuclear fusion would remain out of reach for humans.
2. As I understand it, fusion bombs are energy positive (they produce far more energy when detonated than went into their construction). Perhaps a novel way to utilize fusion power would be to literally build "micro-bombs" detonate them and use them to heat a fluid. This would do away with the continuity and containment issues fusion faces. Now if we could only get to that Deuterium on the moon....
3. While we might see 50 or so LWRs come online in the next decade, such as the APE-1000s being built in China, I doubt they will make any appreciable contribution to the grid.
I just finished reading the book Insurmountable Risks by Brice Smith. Brice feels that the problems that the nuclear industry faces can't really be addressed by LWRs and I tend to agree with him. Instead, he suggests that the future of the industry lies in Gen IV pebble bed reactors or an advanced version of the CANDU design. On a positive note, his analysis of Uranium resources was surprisingly comforting.
Posted by: GreenPlease | Mar 19, 2008 8:10:16 PM
I suppose it's because I've made my living from electronics that I find complex electrical control circuits to be easy and a mechanical monstrosity like this to be hard, but I just can't help thinking that if this level of complexity is what is required to produce good efficiencies and smooth power curves from an ICE, then all electrical systems are the way to go. Talk about a monster. I can just see the repair times and costs when you take this to get serviced.
Hub motor systems that allow precise torque control at each wheel and full stability and tracking seem like a lot easier way to go to me, but as I said, a lifetime (Well thirty years anyway) of working with electronic control systems may be biasing my outlook.
Posted by: Larry | Mar 20, 2008 4:32:10 AM
The reliability and performance of the Prius drive system have spoiled me. I'll never again buy a car whose transmission includes any kind of clutch, especially a Rube Goldberg monster like this one.
Posted by: richard schumacher | Mar 20, 2008 6:38:48 AM
I believe that Audi also has an 8sp gearbox on some of it's models, although at some point you reach diminishing returns as they use to say in B-school.
This concept applied to a vehichle with cylinder deactivation should result in a bigger bang per BTU, preferably NGas or E85 even with the more frequent refills.
Posted by: ken johnstone | Mar 20, 2008 8:15:23 AM
@ GreenPlease.
The idea of your comment No. 2 was published about 7 years ago in a MIT´s Technology Review magazine.
The article concludes that this can be done with the technology available today.
Posted by: Jorge | Mar 20, 2008 8:25:39 AM
@ Larry -
if you think this is complex, you should look at a conventional AT with more than 3 gears.
Electric traction motors are simpler, but they need electricity and lots of it, especially in freeway driving and rapid hill climbing. Solid-state electric transmissions (power converters) are inefficient unless they are also attached to a large energy buffer. That allows them to compensate by shifting the engine's operating point into a more favorable part of the map.
For example, the Toyota Prius uses a very simple single-mode hybrid transmission mated to a small Atkinson-cycle gasoline engine. Works a treat at low speeds, but on the freeway fuel economy is unspectacular.
Pure EVs like the Tesla Roadster are simpler still, especially this first batch with the single speed transmission :-) However, the battery packs costs an absolute fortune. Simple is elegant but sometimes, complex is much cheaper.
Posted by: Rafael Seidl | Mar 20, 2008 10:39:19 AM
@Larry,
Your understanding of electronics versus mechanical systems is exactly reversed to mine: I understand mechanical things in general, but anything electronic is a mysterious black box.
I still have to deal with industrial power electronic systems (servo drives, frequency drives) on a somewhat regular basis - although someone else does the installation and programming. A servo / frequency drive that is capable of regenerative operation (most industrial drives aren't) is neither simple nor cheap, and they get really expensive really fast when the power level goes up. And when (note: WHEN, not if) the smoke comes out ... you don't fix, you replace.
An AC motor that has a high power-to-weight ratio (suitable for automotive application) is a lot more expensive and complex with more expensive materials than the average AC squirrel cage motor in your sump pump, too.
A 75 horse AC motor of the types that I'm used to, probably weighs half a ton, maybe more.
No question pure electric vehicles don't require certain subsystems that IC vehicles have, but don't underestimate the complexity of satisfying market demands. The vehicle is going to be a lot more complicated than your average electric lawn mower. For example, you'll need an electrically driven A/C compressor, electric servo power steering (some cars already have this for other reasons), and you'll need some way of creating heat when it's -20 C outside, and you'll need some way of getting more than a feeble flicker out of the battery when the car has been sitting overnight in -20 C. I don't think the influence of cold weather operation is something that a lot of the electric vehicle proponents have considered.
Posted by: Brian P | Mar 22, 2008 3:53:02 PM
