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Electric car engines: BMW, Audi and Co. move so differently

Electric car engines: BMW, Audi and Co. move so differently

Electric cars are anything but uniform. The best example is the new Audi Q6. The 4.77 meter long electric SUV has a so-called “permanent magnet synchronous machine (PSM)” installed on the rear axle, while an “asynchronous machine” (ASM) provides propulsion on the front axle. The asynchronous motor is an electric module in which the rotating field of the rotor follows that of the so-called stator. The rotation creates an interaction between the two rotating fields and creates a torque that can be used for driving. In contrast, the rotor of a permanent magnet synchronous machine excites the magnets and thus provides the electrical drive energy.

It’s the mixture that counts

“At PPE alone, 15 automatic bending machines are used in two other systems for the three-dimensional hairpin winding and the subsequent laser welding of the ends. 140 meters of copper wire are processed per stator. 235 laser welding processes are necessary,” explains Csaba Imre Benke, head of Audi Product segment electric drives in the Győr plant, “since there are generally fewer screw connections in electric drives compared to combustion engines, but more pressing volumes, more robots can be used.”

Many of the electric vehicles are all-wheel drive models or at least available with an all-wheel drive option. In terms of driving dynamics, it makes much more sense for the electric motor to do the main propulsion work. This is especially the case with more powerful models such as the new Audi Q6. The electric motor on the rear axle does the main work for the drive and provides a large part of the system output of the normal Audi Q6 with its 285 kW / 387 hp.

Nevertheless, with a diameter of 21 centimeters, it is just 20 centimeters long. The front asynchronous motor with slightly lower power is only ten centimeters long. The great strength of the PSM motor, which is installed parallel to the axle, is its efficiency – its efficiency is well over 90 percent in the vast majority of driving situations. Another advantage: If no power is required here – depending on the driving program or the driver’s pressure on the accelerator pedal – the electric motor on the front axle rotates without any significant drag losses and the corresponding friction.

Overall, the efficiency measures surrounding the new machines for models such as the Audi Q6 or the technically closely related Porsche Macan generate around 40 kilometers more range on the newly developed PPE platform compared to the previous generation of electric motors. At the same time, they require 30 percent less installation space than, for example, the Audi Q8 Etron, while the weight has been reduced by a fifth.

The two comparatively small electric modules accelerate the Audi Q6 from a standstill to 100 km/h in under six seconds. Things are even sportier in the Audi S Q6 Etron, whose axial and synchronous motors together produce 360 ​​kW / 490 hp and can reach 230 km/h on request make it faster. The SUV accelerates even better with the appropriate boost.

380 kW / 517 HP can be accessed here for a short time. When the launch control is activated, an asynchronous machine is used on the front axle, which is equipped with its own power electronics and an axially parallel, two-stage input gearbox. There are no magnets in this electric motor and therefore no rare earths, as the necessary magnetic field is generated solely by induction. Many electric cars such as the Audi Q6 or Porsche Macan have a permanent magnet synchronous machine on the rear axle, which is also coupled to a two-stage input gearbox in an axially parallel design.

The 800-volt on-board electrical system ensures short charging times thanks to high charging power. The higher electrical voltage also means that thinner cables can be used when wiring the 100 kWh battery pack and electric motor, which saves installation space, weight and raw materials.

Mercedes-Benz is taking a different approach to electric cars

The structure of the currently most powerful electric model from Mercedes looks somewhat different. The Mercedes 5.13 meter long EQS 680 SUV is equipped with two permanently excited synchronous machines on the front and rear axles, which together produce 484 kW / 658 hp and 950 Nm. And the Mercedes AMG E53 4matic, a powerful plug-in hybrid, not only has a 3.0-liter six-cylinder in-line engine, but also a permanently excited e-synchronous machine with 120 kilowatts, which results in a system output of up to 430 kW / 585 HP / 750 Nm ensures.

The two drives ensure 0 to 100 km/h in 3.8 seconds, a top speed of 280 km/h and a maximum electric speed of 140 km/h. The electric motor in the Mercedes AMG E53 is so small that it can be installed in the housing of the nine-speed automatic transmission. The high power density of the hybrid power unit is achieved by the permanently excited internal rotor synchronous technology. The electric module’s maximum torque of 480 Nm is available from the first revolution.

The electric top model from BMW, the i7 M70 xDrive, has integrated drive units on the front and rear axles, in which the electric motor, power electronics and transmission are compactly combined in a common housing. The two motors work on the principle of a current-excited synchronous machine.

BMW does not use rare earths

Thanks to this design method, the raw materials from the rare earth metal sector required for magnetic components can be completely dispensed with in the production of the rotor. The drive unit on the rear axle of the BMW i7 is operated in six phases and has a double inverter. This makes it possible to achieve a particularly significantly increased peak performance, which is available up to high speeds. With a power density of 2.41 kW/kg, the value of the engine that drives the rear axle of the BMW i7 xDrive60 is exceeded by 25.5 percent.

Volkswagen is also particularly proud of the ID7’s drive. Its particularly efficient drive consists of a three-phase permanent magnet synchronous machine with 210 kW / 286 HP / 545 Nm, a two-stage capture gear and the necessary pulse inverter for power and control electronics.

The synchronous machine has a rotor with stronger and particularly thermally resilient permanent magnets, a stator with a large number of turns with a maximum wire cross section, a water cooling jacket for the outside of the stator and a combined oil and water cooling for greater thermal stability. Like the other ID models, the all-wheel drive version of the VW ID7 GTX Tourer has an asynchronous machine on the front axle that weighs around 60 kilograms. The PSM electric motor on the rear axle weighs just under 100 kilograms. The system performance: 250 kW / 340 HP.

Source: Stern

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