BMW electric drivetrain evolution and the new Mini-E

BMW i, MINI | April 29th, 2015 by 5
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The new Mini-E will have the potential to be even more “electric” than the i3. The new Mini-E will be introduced circa 2019, a two-door hatch

The technology in the expected new Mini-E will draw heavily from BMW’s i3 innovations, just as Mini and BMW ICE cars now share engines and a platform. At the same time, the evolution of successive generations of BMW EVs will increasingly exploit the performance advantages and flexibility that electric drives offer, while quietly eliminating those design features that imitated some of the accepted limitations of ICE cars. The greatest potential for near-term electric drivetrain development will come from the synergy of single-pedal speed control, adoption of dual motors, and improved regenerative braking. Hopefully the new Mini-E will incorporate all of these features.

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Not too long ago car manufacturers touted how much their EVs were like their gas-powered counterparts, hoping to convince skeptical first-time buyers how familiar the EV driving experience would be—”it’ll drive just like the car you have now.” Some programmed in automatic-transmission “creep”; some piped in ICE exhaust sounds through the stereo. A couple of manufacturers even programmed simulated gear shifts in their single-speed electric drives. Many automotive pundits decried “range anxiety,” and suggested that EVs should ideally have the same range as ICE vehicles, without apparently considering that electrical vehicles can start out every morning with a full charge. Regenerative braking, not well understood by most drivers (including many automotive journalists), was typically activated through the same pedal that controlled the friction brakes.

Then BMW introduced the i3 spaceship! It was revolutionary. It didn’t look like anything that had ever been driven down a road, it was made of carbon fiber, both acceleration and braking were controlled with the same pedal, and it was fast and nimble. But that was just the opening salvo.

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The new Mini-E will have the potential to be even more “electric” than the i3. And the second-generation i3 will continue that evolution.

The key piece of this evolutionary development is the i3’s single-pedal speed control (the driver interface), coupled with the motor controller (a powerful computer). As the automotive world is discovering, with a software-controlled electric drivetrain, only the designer’s imagination sets the limits on vehicle control (well, that and driver acceptance).

BMW i3 drivers report they seldom have need to use the friction brake pedal. They control the car with the steering wheel and the speed pedal. With the addition of a second motor (driving the front wheels), the single-pedal speed control could become much more powerful.

The traditional advantages of all-wheel drive are obvious—improved traction and handling, especially in slick conditions. In ICE vehicles, AWD carries the costs of added complexity and weight (and money), and the intrusion on internal space from the longitudinal drive shaft tunnel. With an EV, these drawbacks are largely non-existent; instead of a small motor at one end of the car, you have two smaller motors, one for each axle. Supporting structure would be lighter for each, and mechanical stresses (and wear) would be lower. The combined power and torque would likely be made greater than that of the single motor they replaced—for more flexibility and better performance.

With EVs, there is another very important advantage to having dual motors—greatly improved regenerative braking (“regen”). During braking, some of a car’s weight shifts from the rear to the front wheels (due to the car’s center of gravity being higher than the tires’ contact patch on the pavement—basic physics). As a result, the front brakes do most of the work, more so with stronger braking (that’s why repeated aggressive braking covers the front wheels with brake pad dust).

With EV regenerative braking, only those wheels connected to the drive motor are able to slow the car. In the case of the i3, that’s the rear wheels. That’s fine for mild and moderate braking, but for strong braking, weight shift makes the rear wheel braking much less effective, and prone to skidding—the four-wheel friction brakes would have to be used.

Some early i3 owners reported what seemed to be a “sudden acceleration” of the car when they were using regenerative braking in low-traction situations (say, downhill turns on slick roads). What was actually happening was the i3’s traction control was shutting off the regen to avoid a potentially dangerous skid. The unexpected loss of braking made it seem the car had suddenly surged ahead—a scary event if you’re heading into a sharp turn toward a stop sign.

Regen in a dual-motor EV would not be subject to those problems. Software would control the percentage of braking handled front and rear, depending on conditions. The four-wheel regen could be as effective and consistent as friction brakes, and without the need to shift your foot between pedals.

Tesla seems already to have made the move to dual motors, after the success of its P85D. Its new base Model S, the 70D, has dual motors, and the upcoming Model X will only be available with dual motors. Besides greater traction and improved regenerative braking, Tesla has found that by separately controlling the power sent to each of the two motors to suit changing driving demands, they can attain greater efficiency (and longer range), and greater performance. Double the number of motors and you have more than doubled the ways you can control an electric car.


With the success Tesla is seeing with dual motors in their cars, I would be surprised if the mainstream Model 3 does not also have dual motors. And if that happens, any future BMW or Mini EV with only one drive motor would be hard pressed to call itself “premium.” Nissan LEAF, anyone?

What would more powerful (and reliable) regenerative braking mean to the driver? In a nutshell—more effective and predictable braking. The caveat is that the driver has to understand how it works.

With the i3’s single-pedal speed control, the driver is able to seamlessly control the level of regen from zero to maximum by the amount they lift up on the pedal. Of course, quickly lifting your foot completely off the pedal immediately engages maximum regen, and many drivers (and reviewers) mistakenly thought that was how the i3’s regen was engaged—all or nothing.


There is no established convention for how EV regenerative braking should work—it tends to be different from one manufacturer to the next. I recently read comments on Model S regen on the Tesla forum, and it was revealing that there was no agreement even among owners about how their regen worked.

And of course many EV owners react to sudden changes in traffic patterns by reverting to long-held ICE habits, quickly lifting their foot off the “gas pedal” and expecting to gradually slow (coast). If they are traveling at high speed on a busy highway, a sudden unexpected braking caused by strong regen would be unnerving, or even dangerous.

A BMW i engineer told me they programmed the level of the i3’s maximum regen as a function of speed. At lower speeds, maximum regen would be strong, but as the car’s speed increased, maximum regenerative braking was reduced. Why? There was no technical reason to do this. In fact, the faster the motor/generator spins, the stronger the regen can be—if it is programmed to do so. BMW reduced the level of regen at high speeds simply because drivers participating in their Active E test program asked for it.

One would expect that a driver could react to changes in traffic better if they always had instant access to strong regenerative braking. But old habits die hard, especially in stressful situations. As i3 drivers gain more time and miles, old habits undoubtedly change—but only to the extent the car allows. If the car is programmed to reinforce their old habits, the full potential of EVs will not soon be realized.

How can a manufacturer accommodate engrained ICE habits, while fostering driver acceptance of advanced EV capabilities? The answer is, of course, software. Give the driver a choice. Let the driver go into the menu and select values for a range of parameters, such as the maximum level of regenerative braking at both city and highway speeds. Let the driver’s skills evolve.

Adapt the car to the driver, rather than making the driver adapt to the car. Comfort mode, eco pro, sport, race, insane . . .

Control. If you’re BMW or Mini, building driver’s cars, give the EV driver more control over the drivetrain.

Imagine driving a 2500-pound Mini-E with dual-motor power and traction, aggressive four-wheel regenerative braking, all seamlessly controlled by a single-pedal, coming up on a twisty stretch of deserted road . . . Exquisite control.

A future true?

With my crystal ball before me (and rose-colored glasses firmly in place), I’m looking out through the next five hazy years. BMW i and Mini EV planning will mesh. New battery technology will permit more design choices, and as the number of electric models grows, the needs of different market segments can be accommodated.

A mid-life refresh for the first-generation i3 will bring an improved battery and greater range. Fewer buyers will opt for the REx version.

The new Mini-E will be introduced circa 2019, a two-door hatch (Mini’s bread and butter). With 120-mile range, this personal car will emphasize handling, performance, and lightness. It will be built with the same construction materials and tire size as the i3, the same single-pedal speed control, and a dual-motor drive train.

The second-generation i3 will be launched around 2020, also with dual motors. It will be a little longer for better highway performance. The rear coach doors will be replaced with traditional doors for easier access to the back seat (which will accommodate three). It will go 200 miles on a charge; a REx version will no longer be an option (increasing interior space).

Around the same time, the long-rumored i5 will finally be released with the same new battery chemistry as the 2nd-gen i3, but in plug-in hybrid form. It will be larger than the i3, inside and out, with more luxury features—a very comfortable and fast highway cruiser.

Okay, so my crystal ball is a fake, but that’s what the rose-colored glasses are for.