BMW Is Testing a New Quad-Motor M xDrive Electric Powertrain
BMW announced Wednesday that it is developing and testing a new M xDrive four-wheel drive system with four electric motors -- one for each wheel -- using a modified BMW i4 M50 four-door coupe as the test bed.
The compact size of electric motors makes dual-motor setups -- one for each axle -- fairly commonplace among premium and high-performance electric vehicles. Three-motor setups are more rare, but can be found on certain Audi E-Tron, GMC Hummer EV and Tesla Model S models. Ford even built a seven-motor, gymkhana-spec Mustang Mach-E 1400 that still has me scratching my head. However, BMW's four-motor system is noteworthy not just because it ups the motor quantity ante, but also because it all fits inside a sedan.
The i4 M50 chassis is normally a dual-motor affair, so BMW has modified the body with wide wheel arches to fit twice as many electric motors inline with the specifically manufactured, high-performance front and rear axles. The prototype's front suspension and the EV's cooling hardware have both been adapted from BMW M3/M4 components and also required modification. BMW hasn't released specs for the motors themselves, but the standard i4 M50 outputs a combined, rear-biased 536 horsepower from its two motors, so presumably the prototype is packing more than that -- though probably not twice as much.
The primary benefit of the new system is control. A central control unit reads road conditions, pedal position, steering angle, G-forces and more. It can send precisely the right amount of torque "via a multi-plate clutch and differentials to the four motors" and onward to each contact patch with millisecond-precise variability.
That bit with the clutches and diffs is odd -- you'd think that dedicating a motor to each wheel would do away with the need for such hardware. We'll have to wait for BMW to tease out more info to learn exactly how they're being used.
BMW says that this "extremely precise, extremely variable" M xDrive four-wheel drive system allows for an unprecedented level of agility, with highly flexible torque vectoring keeping understeer in check and boosting control right up to the grip limit. The system also reaps benefits in low-traction conditions. The automaker states that the sensitive application of drive torque without latency permits significantly higher cornering speeds, even on rain-soaked or snow-covered roads.
And because each motor can also function as a regenerative braking generator, the prototype is able to feed electricity back to the battery right up to the limits of dynamic driving, which should at least help to preserve some range and keep the performance party rocking.
Testing has only just begun on the concept, following virtual and then bench testing, so it may be some time before we see an electric BMW M car powered by M xDrive four-wheel drive. BMW's M performance division turns 50 this year and is looking toward electrification as the future of high-performance driving, beginning with the dual-motor i4 M50 and iX M60 -- which both hit the road earlier this year -- and the i7 M70 electric luxury sedan, expected next year.
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