Audi working on electric suspension

Everybody assumes traditional engines will one day be replaced by electric power. But if a select group of Audi engineers has its way, so too will traditional suspension dampers.

The German premium car-maker’s skunkworks is deep into the development of a system of electric motors that turn bumps into electric power.

It already has prototypes running around Europe with electrical damper units that harvest kinetic energy from wheels moving up and down over bumps, then convert it into electricity to feed into the car’s energy supply.

Not only that but, critically, the electric dampers replace the traditional telescopic dampers that almost every production car uses, and can be told to stiffen up for sporty driving or to soften off for increased comfort.

Smaller and easier to package than traditional vertical (or almost vertical) damper units, the new system will even allow Audi’s designers to free up their crayons around the front-end of the car, especially, since the main reason for the current generation of low-edge, high-centre bonnets is to cushion the engines and the top mounts of traditional telescopic dampers to meet pedestrian-impact laws.

The innovation also teases at a rethink of rear suspension and luggage-area layouts, with the promise of no damper strut intrusions into the side of the cargo area.

Audi powertrain development engineer Alexander Kruse said the system used what was, in effect, a set of Ohmic resistors as a rotational dampers at each corner, connected to a fast-discharge 48-volt battery. For sportier driving, the motor-dampers will work at their hardest to deliver the firmest resistance.

The system in clearly in its infancy, but Kruse suggests Audi is looking at a target weight no more than 10kg heavier than the telescopic system that has been developed for more than a century.

“Normally the damper shaft moves up and down and that generates heat and that heat is lost to the environment and that’s just a straight loss of energy,” he explained. Damping units could heat up to 125 degrees Celsius on bad country roads, he said.

“Using a rotational damper generates energy. It’s like a drop-link that links a generator of kinetic energy to a generator of electrical energy.

“We can use that in other parts of the car -- in the powertrain, for example -- or we can use it in the suspension going the other way, making that electrical generator force work as a damping force on the wheel movement,” he said.

The real long-term benefit of this sort of system was made obvious by Mercedes-Benz’s Magic Body Control on its S-Class, in which a stereo camera in the windscreen “sees” bumps, then tells the car’s air suspension when and how hard to work to cancel them out.

This, an Audi spokesman said, would become far more accurate with electric damping units.

In European tests on road surfaces ranging from urban to rural to the Nurburgring, Kruse claimed the system was recuperating 150 Watts on average, but up to 600 Watts on a country road.

“If you can get 100 Watts from the damping, that’s two grams of CO2/km you’ve saved.

“It’s also generating the energy it needs to do the damping we ask it to do.

“It’s an electrical damper control so in theory the bandwidth is far greater than you can manage with normal dampers.”

There has been one significant hurdle for engineers working this idea through their systems in the past: amplitude.

Audi’s set-up kills two birds with one stone, using an internal gearbox to turn linear movement into rotational movement and to step up the amplitude.

“We get the amplitude in the damper we need because of the gearbox. A smaller amplitude becomes a bigger one, but we are still looking at the optimal ratio.”

That’s not the only way Audi is planning to make electricity do the damping work for it, because it will introduce an electro-mechanical anti-roll bar next year (it won’t say on which model, but the A8 replacement is a safe bet).

It will stiffen up for sportier driving by cranking up the electric motor, soften the ride by relaxing it, or decouple the motors altogether, and they each work with three-stage planetary gear sets. The front electric motor they’re testing can manage up to 1200Nm of force to cancel out body roll, while the rear version works less, with a 1000Nm ceiling.

“The voltage peaks at up to 1.5kW, but the general energy supply is not very high, and we can also horizontalise the movements for roll-moment stabilisation,” Kruse said.

While fancy electrical suspension systems are one strong reason to move from 12-volt to 48-volt onboard electrical systems, they’re not the main reason.

“A 48-volt motor gives us belt-driven integration for 12kW of regeneration and more comfortable start-stop, too,” Kruse said.

“With the current system, we get up to 3kW of recuperation when the car slows down, but 48-volt will allow us to turn off the engine when it’s coasting or free wheeling.

“Because it recuperates more energy it uses less energy from the internal combustion engine.”

That doesn’t spell the end of the 12-volt battery at Audi, though, because it’s still working on new applications for it, especially in its cheaper cars.

“In the future there will be a 12-volt lithium-ion battery with a belt-start generator. It will have many of the advantages of the 48-volt systems, with recuperation of 5kW.”