xDrive is not just xDrive: Three BMW X1 with different drives compete against each other in the snow. Do PHEV or electric all-wheel drive stand a chance against the classic combustion engine with a Haldex clutch?
A homonym means a word that stands for different things. Our homonym of the day: xDrive. In 2003, BMW used this artificial term to describe a newly developed all-wheel drive system for the X3 and X5, which, with a fast-reacting multi-plate clutch in the transfer case, was not exactly revolutionary mechanically, but was able to act and react proactively in its networking with sensors for wheel speed, steering angle, accelerator pedal position and lateral acceleration. Today, every BMW model carries an "xDrive" badge if all four wheels are driven. ,
And here is the X-factor: The way in which this happens differs significantly in some cases. Sure, Audi do the same with Quattro and Mercedes with 4Matic. Three BMW X1s can show what three different all-wheel drive concepts with xDrive certification can do in the same model on low-grip surfaces, one each as a combustion engine, plug-in hybrid or electric car.
In the white vortex
Several closed dynamic routes are available on which the three all-wheel drive vehicles have to prove themselves. From slow and fast slalom to a small circular course to a snowy mountain road and a snowy slope. The diesel gets going, at around minus 12 degrees, which caused the Ötztal to tremble on the test day, after a short time wraps the interior in cozy warmth. The two-liter diesel delivers 197 hp, the electric motor contributes 19 hp to the total output of 211 hp.
It effortlessly frees itself from deep snow when starting off. Thanks to the start-up assistance, he safely digs his way up the slope. The double-clutch transmission couples the power to the drive shafts without being too hesitant or rough. In such situations, the hang-on functional principle of the four-wheel drive is hardly noticeable, which alone shows that the hang-on principle is completely sufficient for the simple, everyday traction improvement. Targeted braking interventions on individual wheels help with power distribution. If there is enough grip, all the power goes to the front and the rear compartment has a break, which minimizes drive losses. , But that was it with the talents of the hang-on all-wheel drive, because driving dynamic excesses on slippery surfaces are not his profession. Off to the slow slalom. Even in the first tight bend, the X1 rubs over the front wheels. Step on the gas and the understeer gets worse as the drive initially sends more power to the front wheels, which requires courageous intervention just before the snowdrift. Such drives rarely transfer more than 50 percent of the power to the rear axle. Accordingly, the hang-on four-wheel drive requires some space and time.As soon as you keep the steering and gas command longer, the rear axle pushes into play, neutralizes the X1 and carries it around the cones with a very slight yaw rate. It works better shortly afterwards with deactivated ESP, since you can now work with even more effort on the accelerator pedal. The same picture in the fast slalom and on the mountain stage, where you can loosen the rear at higher speeds through targeted steering movements so that you relieve the front wheels of a bit of work and make the handling more agile. But when driving below the limit, the diesel always has traction, but understeers and is a bit sluggish. ,
Inertia could be a property that affects the next candidate, after all, at 2085 kilograms, it is an impressive 320 kilograms heavier than the diesel. But anyone who now thinks that the iX1 slides from snowdrift to snowdrift in unstoppable sluggishness due to inertia is wrong - and hugely so.
Current-excited dynamics
The battery is located between the axles and there is an almost identical drive unit at the front and rear. From a purely visual perspective, this almost mirrored chassis layout shows where the journey is headed in terms of weight distribution. Look at the diesel block on the front axle of the 23d! You can literally see his top-heaviness in the diagram. And the iX1? He just gives in. on snow. Without spikes. Without undercarriage tricks. Thanks to the better weight distribution. The front axle conveys more confidence than the diesel, and the iX1 hasn't even opened its bag of tricks yet. , Even in the small snow slalom in normal mode, it becomes clear that everything is more precise, faster and more dynamic with the iX1. Reason: In dynamic driving situations, the drive torque is increased on the rear axle - faster, more precisely and more variably than a Haldex all-wheel drive can. Together with the so-called actuator-related wheel slip limitation X (ARB-X) - a clever name for traction control - the iX1 regulates the traction on all four wheels extremely sensitively. Only the iX1 and the plug-in hybrids have ARB-X.
The system does not work as a separate control unit, but is housed directly in the engine control unit, which saves signal paths and enables faster control. Or you can simply switch off the ESP and let the iX1 drift through the snow almost Finnish. The rear axle always receives a little more torque, so that the slalom and the small circuit become a drift show. Transfer from left to right? Of course! ,
Only when the steering angle is too large do the electronics eventually cut off the forward drive, because: In electric cars, the traction control remains active to prevent dangerously high wheel speeds. After all, the drive wheels would otherwise dig up the snow at full power at speeds equivalent to 180 km/h and provoke vehicle reactions that you don't want.Disadvantages of the electric all-wheel drive? In double-digit minus temperatures, the 64.7 kWh battery empties in record time, which slows down the driving pleasure a bit. That leaves the PHEV: In terms of performance, it is ahead, on the track, well, it seems a bit hesitant.
Best of both worlds?
At first there is nothing to complain about the traction. The two drives play together cleanly and quickly find the common traction denominator. Only during dynamic driving tasks do you realize that it is a marriage that is always determined by the weaker link. , On the one hand, the hybrid with its combustion engine on the front axle also feels top-heavy, on the other hand, the actually more powerful electric motor on the rear axle must not overwhelm the combustion engine. It is always noticeable how the electric motor has to hold back until the turbocharged combustion engine generates torque from around 2,000 revolutions and the drive force on all four wheels only sets in with a delay - but then at least with a pleasantly neutral power distribution. At the same time, when ESP is deactivated, the petrol engine has to take a step back so that its high-revving endurance does not symbolically outperform the rear electric motor. The plug-in turns somewhat inhibited and understeering under load. Nevertheless, its all-wheel drive system clearly intensifies one thing: adhesion. Which brings us to the second homonym of the day. ,
Conclusion
We take two things with us from the Ötztal: Firstly, that all variants offer the expected extra traction and, with the right tires, will probably not leave skiers hanging in a snow-covered parking lot. Second: The dynamic possibilities of a twin-engine electric car on snow are beyond those of an axle hybrid or Haldex all-wheel drive vehicle. The iX1 drives in circles around diesel and hybrid, but not for very long with the resulting power consumption.
