The 2009 Audi A4 TDI is already setting records as being extremely fuel-efficient, but with the A4 TDI concept e, Audi takes the idea fuel-sipping diesel sedan to the next level.
At the heart of the A4 concept e is the same 2.0-liter turbo-diesel I-4 that powers the new Volkswagen Jetta TDI - but Audi's made a few slight tweaks in the name of efficiency. Engineers added softer springs on the intake valves, a new coolant-management system, and revamped its engine-control software. The diesel's coupled to a six-speed manual transmission, which now sports magnesium hardware to reduce weight.
Like Volvo's DRIVe diesels, the concept e also is fitted with a start/stop system, allowing drivers to wait in traffic without constantly idling the engine. A secondary battery, which is recharged through regenerative braking, powers all accessories when the A4 comes to a halt.
Other changes on the concept e include low rolling-resistance tires, electric power steering and electrically-actuated rear brakes, and a number of aerodynamic tweaks (including a new grille and smoothed body pans).
The modifications may be subtle, but they allow the A4 TDI to achieve an amazing 58.95 mpg (European combined cycle testing) and emit only 105 grams of carbon dioxide per kilometer.
Though Audi isn't talking production details, we'd imagine in light of competitive vehicles (e.g. Volvo's DRIVe range) and increasingly strict CO2 regulations, it's a matter of when - not if- they appear in production.