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Rivian has a new competitor coming in the electric SUV market as Porsche has announced that they're making a new 4-motor powertrain for an electric SUV.

They broke the news in an article on their own website:

It’s a situation that every driver dreads: a snow-covered road, a surprisingly tight corner, and barely any time to brake. With a normal vehicle, a dangerous loss of control is an all-too-real possibility. The rear could swing out, causing the car to spin and land in the ditch. Yet in this test, everything goes differently: The driver turns and the SUV steers confidently into the corner—without even slowing down. A glance at the speedometer (80 km/h is the reading) removes all doubt that this is no ordinary vehicle. The SUV being tested in this wintry environment is an electrically powered all-wheel-drive vehicle with four motors— one for each wheel.

Until now, this drive technology was seen only in Mars rovers, but now it has reached the everyday world: Porsche Engineering recently developed a torque control system for electrically powered series SUVs. It was truly pioneering work. “We had to develop a lot of it from the ground up,” says Dr. Martin Rezac, Team Leader for Function Development at Porsche Engineering. There was also an additional challenge: The driving characteristics had to be optimized exclusively through software. The Porsche engineers could not install any additional sensors and had to use the existing control devices. The task, in short, was essentially driving stability by app.

Purely electronic control of torque
An electric all-wheel-drive vehicle with multiple motors has a fundamental advantage over gasoline or diesel engines: The front and rear axles, indeed all four wheels, have their own electric motors, enabling extremely variable distribution of the drive power. “It’s almost as if you had a separate gas pedal for each axle or wheel,” explains Ulf Hintze of Porsche Engineering. In a conventional all-wheel-drive vehicle, there is just one engine at work, whose power is distributed to the axles through a central differential. As a rule, the torque ratio is fixed: one-third up front and two-thirds in the back, for instance. The ratio can, in theory, be changed, but additional mechanical gadgetry is required for that (multi-plate friction clutch), and it works rather sluggishly. In an electric vehicle, by contrast, the torque is purely electronically controlled, which works considerably faster than mechanical clutches. Every millisecond, intelligent software distributes the forces in such a way that the vehicle always behaves neutrally.

And Porsche Engineering developed just such a torque control system for all-wheel drive SUVs. The software can be used for different constellations and motor configurations—for other electric vehicle types as well, of course. In general, development begins with the base distribution, i.e. software that controls how much power is transmitted to the front and rear axle, respectively. For straight-line driving and balanced weight scenario, for example, a 50/50 distribution would make sense. If the driver accelerates, the software switches to full rear-wheel drive—or all frontwheel drive around a sharp bend. “This makes the vehicle noticeably more stable, even for the passenger,” says function developer Rezac. As the optimization is achieved entirely electronically, theoretically it would even be possible to offer the driver various different configurations: one mode for sports car sprightliness, another for smooth cruising.

The second task of the control software is to adjust the torque to the wheel speed. The algorithms follow a simple objective: All wheels are supposed to spin at the same speed. That’s easy to accomplish on a dry freeway, but it is considerably trickier when driving on a snowy mountain pass. If the front wheels encounter an icy patch, for example, they could—without electronic intervention—start spinning. But the torque control system detects the suboptimal situation immediately and directs the torque to the wheels that are turning more slowly and still have grip within fractions of a second. There is something similar in the world of combustion engines—the speed-sensing limited-slip differential, also known by the brand name Visco Lok. In this component, gear wheels and hydraulics ensure that no wheel turns faster than the others. But mechanical solutions are slow. In an electric SUV, by contrast, software assumes the role of the differential— with much swifter reactions and naturally entirely without wear.
“The vehicle feels noticeably more stable.”Dr. Martin Rezac, Porsche Engineering​
The third and most important function of the torque control system lies in its control of lateral dynamics, i.e. the ability to neutralize critical driving situations like the one mentioned at the outset: a slippery surface, a tight corner, and high speed. An uncontrolled vehicle would quickly understeer in this situation. In other words, the driver initiates the turn, but the vehicle slides in a straight line without slowing down. The control software in the e-SUV immediately puts an end to understeering. In a left-hand turn, it would brake the rear left wheel and accelerate the right one until a neutral driving situation was restored. The system takes similar measures when oversteer occurs (rear end swinging out). The driver, meanwhile, ideally notices nothing of these interventions, because the torque control system acts very subtly and quickly. “It feels like driving on rails—an SUV behaves with the agility of a sports car,” says Hintze, summarizing the effect.
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