Before the electric age, there wasn’t really a great deal of choice when it came to combustion engines in passenger cars: one motor, drive either only at the front, only at the rear, or on both axles. Cars with internal combustion engines at the front and rear were at best exotic at car shows or at fan meetings. “If electric vehicles are developed from scratch, decentralized drive concepts offer great advantages,” a 2010 study said. There are “undreamt-of possibilities” for innovative car design.
Accordingly, a lot has changed with the increasing electrification of car models. More and more technical concepts are intended to make progress on the road and off-road more efficient and safer. For example, the future all-electric version of the Mercedes G-Class will no longer have one motor, but four: one on each wheel. This ensures that each wheel can be controlled individually and as required. If the slip on slippery, wet or rocky ground is different at each corner of the vehicle, then each wheel individually regulates the optimum torque there. This also makes cornering safer and minimizing turning circles. Even turning on the spot is possible with the G-Class drive. Some time ago, Porsche Engineering also developed a torque control system for electrically powered production SUVs.
Driving safety can also be achieved in electric cars, which cost less than a third of the electric G-Class, but is not quite as complex but still effective. For example, Nissan with its e-4orce drive, which the Japanese are currently installing in their X-Trail and Ariya models. The use of two electric motors – one each on the front and one on the rear axle – makes the cardan shaft required in conventional mechanical all-wheel drive systems superfluous. This provides more space, especially at the back. The Nissan X-Trail generates an output of 150 kW / 204 hp via the front electric motor and 100 kW / 136 hp at the rear – making a system output of 157 kW / 214 hp. The internal combustion engine is completely separate from the drive train and only works as a power generator for the battery and electric motors.
With 4×4 combustion engines, the torque is usually fixed – for example, one third at the front, two thirds at the rear. At best, the ratio can be changed with an additional mechanism – such as a friction disk clutch. But it works relatively slowly. In the e-4orce, on the other hand, the torque is controlled purely electronically: The system needs just one 10,000th of a second to change the power distribution. Every millisecond, the software doses the forces in such a way that the vehicle always behaves neutrally.
Due to the individual splitting and regulation of the torque on the front and rear axles, the e-4orce models have a significantly safer driving style, especially in extreme road conditions. A few test laps on the heavily icy and snow-covered Circuito Grandvalira at 2,400 meters in Andorra show that. If you didn’t overdo it with the cornering speeds, the Ariya and X-Trail always remained easy to control: oval, slalom, race track or climb – after a slight wagging of the rear of the vehicle at first, both quickly recovered and got on track.
In addition, the brakes for each of the four wheels are controlled individually. This allows better control of the lateral dynamics. Tight corners, high speed – an uncontrolled vehicle would easily understeer. Means: The driver steers, but the vehicle slides straight ahead with undiminished speed. The electronics in the e-4orce prevent this immediately: In a left-hand bend, for example, it would brake the left rear wheel and accelerate the right one until the vehicle is back on track.
But the Nissan system also ensures safe and comfortable driving away from ice and snow. If you switch on the recuperation, the battery charges up significantly due to the strong regenerative braking effect. For the approximately 180-kilometer drive from Andorra to Toulouse, the Ariya showed a range consumption of just half – thanks to recuperation and a lot of downhill. And quite incidentally, the strong regenerative braking effect when decelerating ensures significantly less pitching movements. Sorcery? Fewer. Engineering rather.
