• Oct 2nd 2008 at 10:59AM
  • 25
Click above for high-res gallery of the Audi A4 TDI Concept e

Audi's parent company Volkswagen already produces some of the cleanest-burning, most fuel-miserly diesel engines in the world. The Jetta TDI was recently released in the U.S. and has been making waves for its hybrid-like efficiency. So it's natural that Audi would want to show off its green credentials with a new diesel sedan of its own, and it has done so with the A4 TDI concept e, introduced at the Paris Motor Show. Based on the brand-new A4 platform, the new concept gets a 2.0L four-cylinder common-rail direct-inject turbodiesel derived from the unit powering the Jetta TDI. That mill sees tweaks to its valvetrain and cooling systems, lowering its power output a bit to 120-horsepower and 214 lb-ft of torque, but increasing its fuel efficiency a great deal.

Added to the powertrain is a start/stop system that keeps the engine from idling when not needed and regenerative braking, which charges a secondary battery that keeps all your goodies running while the engine's off. The engine has also had its efficiency-robbing power steering pump removed and the rear brakes are now electrically actuated as well. All of this, plus many other small details, adds up to a remarkable 59 miles per U.S. gallon in EU combined testing! Its 10.5 second run to 60 won't win any drag races, but considering the cost of fuel and pending eco-legislation in the world's largest markets, we'd imagine that the technologies on this car will go from concept to production in short order.

[Source: Audi]


Efficiency for the future
The Audi A4 TDI concept e

Efficiency is the way into the future – Audi is introducing the current state-of-the-art for its fuel-saving technologies at the Paris Auto Show. The A4 TDI concept e technology concept has the agile handling characteristics typical of the A4, but requires just 3.99 liters of fuel per 100 kilometers (58.95 US mpg). This exemplary result was possible through the concentrated use of innovative efficiency modules.

Audi is committing major resources in order to continue improving fuel efficiency and reducing emissions. The brand is introducing a trend-setting technology concept at the Paris Auto Show: the A4 TDI concept e offers the typically agile experience of driving an Audi, yet it uses just 3.99 liters of fuel per 100 km (58.95 US mpg), which corresponds to a CO2 output of only 105 grams per km (168.98 g/mile). With this near-production study, Audi demonstrates the great potential of the technologies in its modular efficiency system.

The powertrain of the Audi A4 TDI concept e uses a direct-injection TDI engine with an output of 88 kW (120 hp) and 290 Nm (213.89 lb-ft) of torque. It propels the sedan from 0 to 100 km/h (62.14 mph) in 10.7 seconds, and tops out at 206 km/h (128 mph). An entire array of details – from soft springs on the intake valves to a new thermal management system – improves fuel efficiency. Intelligent technologies are used in the engine's functional environment as well, such as on the fuel pump and on the automatic air conditioning's compressor.

The recuperation system is another fundamental component for improving fuel efficiency. It recovers power when braking and coasting to a stop, and temporarily stores it in a battery. A start-stop system switches the engine off when the vehicle comes to a standstill. Magnesium was used to reduce the weight of the six-speed transmission, which received an insulating cover for faster warm-up and modified gear ratios.

Audi uses an electromagnetic servo assembly for steering; electrically actuated brakes are fitted at the rear. The 225/45 R17 tires have been optimized for road resistance. Sophisticated fine-tuning measures have improved the aerodynamics of the body. Two types of support are at the driver's fingertips: he can either call up an economy training program, or have the navigation system calculate the most fuel-efficient route to his destination.

At a glance


* Two-liter TDI with displacement of 1,968 cc, 88 kW (120 hp) output and 290 Nm (213.89 lb-ft) of torque
* Average consumption only 3.99 liters/100 km (58.95 US mpg), corresponds to 105 grams of CO2/km (168.98 g/mile)
* 0 – 100 km/h (62.14 mph) in 10.7 seconds, top speed: 206 km/h
* Intelligently controlled subassemblies and additional new engineering
* Recuperation system for recovering energy when braking


* Six-speed manual transmission with magnesium housing, adapted gear ratio and insulation all the way around
* Automatic start/stop for switching off the engine when it has come to a standstill


* Power steering with highly efficient electro-mechanical drive
* Electrical brake system on the rear axle
* Road-resistance-optimized using 225/50 R17 tires


* Sophisticated aerodynamic fine-tuning with rear trailing edge
and partially closed single-frame grille, aero-floor and modified ride height


* Economy training program on the instrument panel display
* Navigation system with calculation of the most fuel-efficient route

The engine

The heart of the sedan is a direct-injection diesel engine – a 2.0 TDI with output of 88 kW (120 hp), just as for the A4 production models. From 1,750 to 2,500 rpm, the four-cylinder engine produces a constant torque of 290 Nm (213.89 lb-ft), which generates impressive acceleration. The piezo injectors in the common-rail system inject the extremely finely atomized fuel at a pressure of up to 1,800 bar, and the special piston geometry provides ideal thermodynamics in the combustion chambers.

The 2.0 TDI also features a comprehensive package of additional efficient technologies. The oil cooler, the oil nozzles for cooling the piston crowns, the oil pump and the water pump have been designed so that they can be switched off – when inactive they do not require any power. New piston rings resulted in lower tangential forces, the spring pressure on the intake valves was reduced slightly, and the vacuum pump for the brake booster received a new actuator. These measures as a whole reduce emissions by 5 grams of CO2/km.

Other engine-related modifications include reduced internal friction, a new thermal management system during the warm-up phase and an electronically controlled fuel pump.

Just as in the production version, Audi is using a thermostatically controlled cooling circuit with an internal heat exchanger for the automatic air conditioning system. It responds in a highly efficient manner – the system uses 20 percent less fuel than its predecessor. The A4 TDI concept e uses a new controller: the engine disconnects the air conditioning system's compressor from its drive whenever possible.

Like many Audi production models, the A4 TDI concept e uses a recuperation system that converts the energy of motion during deceleration into usable electrical energy. In the deceleration and braking phases the A4 TDI concept e operates with increased secondary voltage. At this point, it is able to convert the kinetic energy into electrical energy; it is buffered in an absorbent glass mat battery, which is a robust battery with a long life. Whenever the sedan accelerates again, the battery feeds the energy back in, thus reducing the load on the alternator.

Efficiency and agility are inextricably linked at Audi – as proved by the basic data for the A4 TDI concept e. The sedan sprints from 0 to 100 km/h (62.14 mph) in 10.7 seconds, and accelerates from 80 to 120 km/h (49.71 to 74.56 mph) in fifth gear in just 10.9 seconds. The A4 TDI concept e reaches a top speed of 206 km/h (128 mph).

Drivetrain and chassis

The 2.0 TDI transfers its power to a six-speed manual transmission which is notable for its considerably reduced internal friction. It was specially customized to the high-torque TDI engine and has somewhat taller ratios for gears three through six. Most of the housing consists of ultra-light magnesium, which reduces weight by nearly 5 kilograms. A foam-packed skin serves as insulation, ensuring that the transmission oil heats up faster after the vehicle has been started. The drive shafts from the differential to the front wheels have also been redesigned.

The transmission is coupled to a start-stop system that switches the engine off whenever the sedan comes to a standstill. The TDI is deactivated whenever the A4 TDI concept e comes to a standstill, the shift lever is in the neutral position, and the driver's foot is off the clutch pedal. It starts up again as soon as the driver steps on the clutch – a specially developed starter handles this in around two tenths of a second, which is faster and smoother than a traditional component. While the driver puts the vehicle in gear, the TDI speeds up; as he takes his foot off the pedal, it drops down to idle speed.

The start-stop system improves the exemplary fuel efficiency of the Audi A4 TDI concept e still further, meaning that 5 grams less of CO2 are produced per 100 kilometers – as measured on the dynamometer. And in actual terms this reduction may turn out even higher, as many trips to work are less than ten kilometers long and are frequently interrupted by traffic lights.

Another important feature is that an electro-mechanical part replaced the electro-hydraulic power steering. This yielded a further reduction of 4 grams of CO2/km. It does not have to circulate any hydraulic fluid, nor absorb any energy while the vehicle is traveling in a straight line – its electric motor which provides power assistance only kicks in if the driver turns the wheel.

The electrical brakes are another technology module that shows how meticulous the Audi engineers were in their approach to efficiency. Thanks to active brake control, residual brake torque is almost non-existent. It only arises if the small air gap that is necessary for a stiff feel to the pedal and immediate brake response results in a slightly unevenly shaped disk rubbing on the lining. Using electrical rear-axle brakes will achieve the same effect on the front axle: here, an enlarged air gap is also possible since the power brake system only has to carry out the lining displacement for one axle.

Body and cockpit

The A4 TDI concept e glides sleekly through the wind. A trunk lid with a restrained separating edge adds a further dimension to the already excellent aerodynamics. The partially closed grid in the single-frame grille and sporty suspension tuning with optimized ride height also contribute to the excellent drag coefficient of 0.25 (production model: 0.27).

The underbody of the technology study painted in Daytona Grey is faired much more extensively than the production model; the rear lights feature LED technology, which uses much less power than regular bulbs. Newly designed, dip-polished cast aluminum wheels, of the size 7.5 J x 17 improve the flow of air around the wheels and wheel housings. The tires are designed for smooth running, but also provide sporty grip due to their 225/50 R17 wide format.

The intricate technology package from Audi's modular efficiency system also takes the most important external factor of all into account as far as possible: the person behind the wheel. Despite the prominence of high-end technology, the driver remains primarily responsible for how fuel-efficient his vehicle is. This is a fact that Audi takes very seriously in relation to its efficiency strategy.

The driver will discover two major aids in the A4 TDI to help him drive economically. He can call up an efficiency program that shows up on the instrument panel display and which acts like an ecology trainer – pointing out open side windows or recommending rapid upshifting. And the navigation system will always offer an especially fuel-saving route as an alternative whenever the driver enters a destination.

The 'e' models from Audi

The Audi 'e' models are especially progressive, combining maximum efficiency with excellent dynamics. The Audi A3 1.9 TDI e and the A3 1.9 TDI e Sportback both achieve standardized fuel efficiency figures of 4.5 liters per 100 km (52.27 US mpg) and a CO2 value of only 119 grams per km (191.51 g/mile). Both models have an output of 77 kW (105 hp) and a top speed of 194 km/h (120.55 mph).

The new Audi A6 2.0 TDI e and its Avant equivalent are equipped with a 100 kW (136 hp) diesel. The sedan accelerates from 0 to 100 km/h (62.14 mph) in 10.3 seconds and has a top speed of 208 km/h (129.25 mph). Average fuel consumption for both models: only 5.3 l/100 km (44.38 US mpg).

The A8 2.8 FSI e, with its 154 kW (210 hp) V6 on average consumes only 8.3 liters of fuel (28.34 US mpg), making it the most efficient gasoline engine in the luxury class.

Audi plans to expand its 'e' model line in the near future and start putting further technologies from its modular efficiency assembly into production. By the year 2012, the brand with the four rings will once again have significantly reduced CO2 emissions while continuing to hone its sporty, elegant profile.

The equipment, data, and prices specified refer to the models offered in Germany. Subject to amendment; errors and omissions excepted.

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    • 1 Second Ago
      CrissTian Mlk
      • 9 Months Ago

      I love this model a4

      • 7 Years Ago
      Audis are like Skoda just more expensive .

      A friend of mine crashed his Audi resulting serious damage in the engine and the whole left side .

      He went to the Audi dealership to repair his car and they told him that they dont have the necessary spare parts !

      They recommended him to go to the Skoda dealership , guess what , all the fixed spare parts were exactly the same and price : 1/3 of what they wanted in Audi !

      A very happy customer indeed , he should have purchased a Skoda Octavia instead !

      This happened in Greece .
        • 7 Years Ago
        While I am very happy Skoda driver ('07 Fabia I wagon, 1.9/100hp PD-TDI), I wouldn't quite call them "just like Audi". Apart from the market segment and thereby model and engine choice hardly overlapping at all Audi's interior design and quality are still a class on its own.
        It's true though that they share many parts, just like all the VAG platforms do. That's no big secret and if you check the little stamp on almost any VAG plastic spare part or sticker you will notice that any combination of VW, Audi, Seat and Skoda logos may be on there.

        Regarding the Octavia, it doesn't officially compete with the A4 since it's built atop the Golf/Rabbit platform. But I admit that out of the gazillions of models based on that platform the Octavia is probably the best value for money deal ever not only within VAG but also compared to the other manufacturer's offerings in that segment.
      • 7 Years Ago
      Kinda makes you wonder why some of this stuff, or even comparable ideas, weren't implemented sooner.
        • 7 Years Ago
        I dunno... awd and dual clutch trans in volume production cars were pioneered by audi, so i'd guess, as with most technology audi brings to the market first, no one else had the balls to do it.
      • 7 Years Ago
      add quattro and you have a perfect year round car for those of us with snow... slightly less mpg but cant be much
      • 7 Years Ago
      Diesel is more expensive in the states...why is that again?
        • 7 Years Ago
        Because the oil companies realized that people would start buying diesels and they'd lose out on some profits. This makes diesel roughly equivalent in cost per mile to 87 octane gasoline.
        • 7 Years Ago
        It's a combination of taxes and the use of refining techniques in US refineries that favor the fraction of gasoline from a barrel of oil over the fraction of diesel.
      • 7 Years Ago
      Impressive mileage and torque is definitely sufficient. I think I would go for a slightly lower number than the 59 MPG to get more performance. I would be plenty happy with the 3.0 TDI engine that gets 40MPG and returns 369 ft/lbs torque. That said, I could appreciate nearly 60mpg on my daily commute. WIth an 18.5 gallon tank, I could theoretically drive about two weeks before fueling. I like the idea of fueling up only two times a month! Now that diesel is again cheaper than gasoline (where I live), I'd be all over a diesel vehicle.
      • 7 Years Ago
      If this car cost $40,000+, it's almost no good unless you want to buy this type of car. I like A4 but they usually have small problems here and there. They are almost like Jetta with better image, if that's possible for them. Both are very superficial cars.

      Nearly fully optioned A3 cost $38,000.

      You could get A4 without the leather, mp3 cd changer, ect... but then... why don't you just get Civic? It's at least $15K less.
        • 7 Years Ago
        Because theres no Civic AWD, and a Civic isn't an Audi. You can get a Cayman non-S by why? Just get a Civic and save the money right? Why buy a Civic when you can get a Kia for $6K less?
      • 7 Years Ago
      59 miles per U.S. gallon! Wow I never thought a diesel could get that great milage.
      • 7 Years Ago
      Anyone still want a Prius?

      More proof that diesels kick ass over hybrids unless you drive the stop-and-go of Manhattan 24/7.
        • 7 Years Ago

        How can you compare the two when Audi starts at 32K.

        People say that Prius does not pay for itself. If Audi gets the same MPG and costs close to 20K more when fully build how can Audi pay for itself.
        • 7 Years Ago
        Or drive in London's congestion charge zone, which is totally unfair to fuel-efficient non-hybrid cars
        • 7 Years Ago
        • 7 Years Ago

        Some people don't necessarily want to drive a car that looks and handles like a shoe. This A4 is for people who might be cross shopping BMWs, Mercs or even an Acura but want better fuel economy.

        My wife used to drive a '96 Camry and if that is any impression of what it is like to drive a Prius then I think a Prius is a very unsafe vehicle. Wvery time I drove more than 10 miles in the car, I had the irresistible urge to sleep. That can't be safe. :-)
      • 7 Years Ago
      Dude, I will take it, gas mileage better than a prius, and styling.
      • 7 Years Ago
      Oh well, the era sports sedans was good while it lasted but it seems like its coming to an end. I'm all for offering efficient engines as a choice but I'd hate to see them become the law.

      And don't try to tell me that a 120 hp A4 TDI is just as much fun to drive as the 2.0 TFSI.
        • 6 Years Ago
        There have always been versions of the A4 with around 100hp, The last gen A4 had a base 102hp 1.6 and 110hp TDI. The new one has a base 120hp 1.8tfsi and 120hp TDI.
        Its the same with the 3-series and C-class.
      • 7 Years Ago
      I like it. A "green" ride that isn't dull and boring.
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