I have been long thinking about starting a series of posts about news in the automotive industry that have no direkt link to Saab or NEVS but could have an effect on the way we look at future products from Trollhättan [sorry guys I don’t want to start a discussion about the brand, so till next notice I will call the cars this way]. So if you like it I will try to deliver a “Not SAAB related” post each week.
My first post is about a,quite funny in my opinion, article about the BMW i3 in the USA. The original article is from consumer report although I’ve found it somewhere else.
The guys at consumer report summarise the problem with this sentence
Relying on that gas engine when the main battery is depleted works well in most cases, including high-speed steady cruising, but not, we’ve discovered, if you demand more of it.
They’ve discovered? C’mon even some BMW manager talked about the drawbacks of such a range extender configuration at its presentation in Munich.
So let us talk about range extender and its problems.
A EREV, or REX-EV according to BMW, is a normal Battery EV with a small IC-Engine and a small tank that acts as a generator in case the Battery levels are too low. There is no mechanical connection between the generator and the wheels, so the wheels will always get the power from the e-motor. The VOLT was also an EREV, but the managers at GM decided to add a fallback solution in case the driver fully depletes the battery before letting the generator do its job, more on that later.
So on the i3 you have a generator that produces 34 kW of power that is delivered to an e-motor that can produce up to 125 kW of peak power. If you are cruising at steady speed, the car may not demand the full energy coming from the generator, so most of the electric power produced by the generator is used to keep the car moving and the rest to charge the batteries. If you press the pedal to the metal running on the generator, and the battery is still not ready to deliver the extra power needed, the car will handle as an 39-44 hp car [this is 34kW with an effectivity of 85% – 95%], no more and no less.
How will BMW approach this problem?
It [the i3] will include a battery state-of-charge indicator, an early alert prior to potentially experiencing a temporary loss of power, and a proactive boosting of the battery level based on the car’s navigation prior to encountering hilly terrain. This enhancement will also be available as a retrofit for existing i3 owners.
As you see the BMW guys have no magic. The only thing they can do is to put a lamp on your instrument panel, so you know if you will have the full power to overtake the cars in front of you and rely to your GPS to start the range extending generator sooner than expected to have enough battery charge in the mountains, so you always have to tell your car where you want to go, so it can decide what is the best range extending strategy for your drive.
Taking the drama from my words, the i3 is an urban car, and in the cities you are constantly using the brakes and the demanded speed and acceleration are lower, so I think most of the people would do well with the i3 REX, but if you decide to take a short trip outside town, remember that you have a less powerful car when the small generator starts making noise.
At the end of the day a EREV will help you reach that charging station that is couple of kilometres away from your max range, but it has its drawbacks and the car will handle quite differently running on batteries than running on the generator.
Back to the VOLT. The VOLT has a direct connection between the IC-Engine and the wheels, but although many talk about the VOLT as an PHEV (Plug-In Hybrid) it is a real EREV. Why? The car will 99.9% of the time rely on electrical power, when the battery charge is too low the generator will start and the batteries will recharge, still running only on the e-motor. Only in the case the batteries are completely depleted then the IC-engine would drive the wheels till the batteries have once again a minimum of charge that allows the e-motor to drive the wheels.
I hope you liked it, and that I can write “Not SAAB related” technical articles till I can write “SAAB related” technical posts.