One completely new area of research in the field of vehicle control and operation is by-wire technology, where mechanical and hydraulic systems are replaced by electrical components (by wire). The Audi pre-development department is working intensively with this new technology; the A2 concept, the show car from the IAA 2011, already had it on board. The latest project is a technology model on the basis of the R8 e-tron on which the steering, braking and gear selection takes place electrically.
The technology model has no steering column – a sensor on the steering wheel detects the turning motions and an electric motor applies them to the steering gear. The precise and finely differentiated steering feel to which the driver is accustomed is retained or even improved. A small electric motor at the steering wheel simulates it based on the forces acting on the steering gear. The driver can choose from a variety of ratios and steering setups at the push of a button. Furthermore, because the steer-by-wire technology is networked with other systems, it can integrate numerous corrective and assistance functions.
By-wire steering can be packaged in various forms. In vehicles with a transverse engine, for instance, space can be utilised in new ways by locating the steering system ahead of the engine. It enables the steering wheel to be pulled temporarily tight against the cockpit, which makes it easier to get in and out of the vehicle and enhances safety in a frontal collision. Eliminating the steering column creates space in the cockpit for new interior and operating concepts; it also makes the development and production of left- and right-hand drive cars easier and more efficient.
Brake-by-wire technology opens up various opportunities, beginning with a hydraulic system in which pressure build-up is decoupled from the pedal, and extending as far as electromechanical wheel brakes. At the front axle, the technical model makes use of what is known as spindle-brake technology, in which electrically actuated ball and thread transmissions press the brake pads very rapidly against the discs.
Electromechanical brakes simplify the packaging of the front of the car because they eliminate the need for heavy, voluminous hydraulic components. In the cabin, the rigid brake pedal can be replaced with a small lever or a sensor surface, at which the forces are simulated. Both solutions are advantageous in the event of a crash.
The primary advantages to the customer offered by the new technology are the extremely precise regulation, which is helpful in conjunction with the chassis and assistance systems, and numerous possibilities for customization. Moreover, there is no residual torque – that slight scraping of the linings against the discs, as can occur with hydraulic brakes. In electric vehicles such as the R8 e-tron, an electromechanical system enables the perfect transition between electric recuperation and mechanical braking.
The legal situation relating to the brake-by-wire topic presents no problems: Cars with electromechanical wheel brakes can be licensed in Europe if they possess two independent electric power supplies.
Audi has extensive experience with shift-by-wire. The A2 1.2 TDI from 2001 was equipped with an automatic transmission in which commands were sent to the hydraulic unit electronically. This is similar to today’s R tronic in the Audi R8 and the eight-speed tiptronic in the flagship A8. By-wire transmissions are an excellent basis for future assistance technologies such as automated parking and piloted driving.
The equipment and data specified in this document refer to the model range offered in Germany. Subject to change without notice; errors and omissions excepted.