Running of juice is one of the biggest fears around purchasing electric cars, but if your car can go further on a single charge and the way you drive can help you achieve that, then we’re one step closer to having more people adopt them.
When we peel the stickers of the Audi e-tron prototype we’re going to have the first fully electric car from Audi. We’ve taken a closer look at the virtual mirrors and what the interior will look like, now we’re going to dive into the electric engine.
The Audi e-tron offers strong performance, it’s electric system produces 300kW and can go from 0-100km/h in less than 6 seconds. In the WLTP test cycle this electric SUV can cover over 400km on a single charge. Thirty percent of the range is created by the recuperation system.
Mobile Geeks headed to 4,302m in Pikes Peak in Colorado to learn how the variable recuperation in the Audi e-tron prototype worked. Driving up the mountain if the car were to carry on with these driving conditions it would have been able to drive 167 more kilometers, going down the mountain the conditions are favorable for range, so we rose to 285km in predictive range. Though it appears we which means that for every kilometer driven we gained 3km of range, in reality, it’s 1km lost to basically 1km gained, the predictive range is making these estimates on the current drive pattern since HERE maps driving data isn’t available on pikes peak.
Audi claims one of their innovative recuperation concept bests their competitors and we are seeing an electrohydrautically integrated brake control system (iBRS) appear in a fully electric car for the very first time.
The Audi e-tron prototype recuperates energy with up to 300Nm of torque (221.3 lb-ft) and 220kW of electric power – more than 70% of its operating energy input.
How does the e-tron prototype recuperate energy?
Recuperation refers to the use of kinetic energy during deceleration.
On our drive down Pikes we were shown the two ways the e-tron was able to recuperate energy:
Coasting recuperation takes place when the driver’s foot releases the right-hand pedal and the car is moving down without the use of the engine.
Braking recuperation is when the driver depresses the brake pedal below 0.3g of pressure.
The iBRS is a variation of brake by wire, but there is no longer a wire in the traditional sense, the whole thing is connected with hydraulic pressure. You can think of the iBRS as a smart machine deciding when and how the electric motors come into play and when the traditional friction brakes should slow the car. As a driver, you won’t notice a difference in handling or braking between the traditional friction brakes and recuperation braking.
The iBRS has a hydraulic piston in the compact brake module, which generates additional pressure and thus additional brake force for the recuperation torque. To break it down you can think of a squash ball inside of a tube, when you press the brakes you increase the pressure inside the tube, and on the ball, this turns into energy the car can recuperate.
Up to 0.3 of g-force, the Audi e-tron prototype recuperates energy solely via the electric motors, without using the conventional brake. This covers over 90% of all decelerations.
If the brakes try to apply more than 0.3g of force the wheel brakes are applied because it’s implied that you’ll want to stop to avoid something. What’s interesting is that when the car figures out that you want to stop short, which can be in combination with the front camera, you’ll be able to stop 20% shorter to help avoid whatever is in your path.
When the system uses the engines for electric deceleration, the system uses the Quattro recuperation function, which decides which axle contributes to the recuperation and to what extent. The drive control unit figures out the ideal distribution of the recuperation torque between the two motors. In most cases, it will be the rear motor that is activated in order to achieve the highest efficiency.
There are three different recuperation modes that the driver can access: manual coasting recuperation uses the shift paddles, automatic coasting recuperation via the predictive efficiency assist, and brake recuperation with a smooth transition between electric and hydraulic deceleration.
The driver can select the degree of coasting recuperation in three stages using the paddles on the steering wheel. At the lowest stage, the vehicle coasts with no additional drag torque when the accelerator pedal is released. At the highest stage, you’ll feel the car notably slow down. Here are a few shots from the video, you can see the different levels in action, the driving style that goes along with them and in real time where the e-tron is recuperating energy.
Since Audi is all about driving performance this gives you the ability to control the braking using the engine directly using the steering wheel paddles. You can even control the deceleration using just the accelerator pedal. When you pull your foot off the “gas”, the car will slow down naturally. Audi is calling this the one-pedal feeling as there is no need to use the brake pedal in this deceleration scenario.
If you’re looking for more detail on how the e-tron manages the recuperations under different conditions these illustrations provide extra detail.
Predictive efficiency assist
Typically most drivers will let the car manage the energy consumption and recuperation. Predictive efficiency assist works together closely with adaptive cruise control or the adaptive cruise assist. It accesses predictive route data from navigation and Car-to-X information. The efficiency assist uses the front camera as well as data from the front and rear-facing radar sensors.
Mapping data is needed to plan the driving style, the front-facing cameras and radar don’t see far enough to be able to predict elevation changes. HERE provides the supporting mapping data, however, on the Pikes Peak drive this stretch of road did not have mapping data which is why the range forecasting based its estimations on driving style.
A look at the asynchronous electric motors
The e-tron prototype comes equipped with two electric motors, the main engine is on the rear axel, the secondary motor appears on the front axel. The two electric motors have an output of 265kW and develop 561Nm of torque. They can hold this peak performance for 60seconds. The e-tron is electronically limited to 200km/h and it can accelerate several times consecutively without output losses. The maximum drive torque is present within fractions of a second and provides enormous torque. By shifting from drive range D to S and fully depressing the right-hand pedal, the driver can activate boost mode. It is available for eight seconds. Here, the drive produces 300kW of system output and 664Nm (489.7 lb-ft) of torque. The Audi e-tron prototype sprints from 0 to 100km/h in less than six seconds.
As we descended Pikes Peak there was a mandatory stop to check the temperature of the rotors since the drive requires a lot of braking. Our rotors measured
Mobile Geeks will be at the launch of the e-tron in San Fransisco in mid September, so be sure to check back to find out everything you need to know about Audi’s first fully electric car.