BMW Working on a REx Upgrade to Increase Performance

The 650cc twin cylinder engine used in the i3 is borrowed from BMW's Motorrad division and modified for the REx

From the first word that the North American version of the i3 REx would have restrictions not found on its European counterpart, i3 enthusiasts and customers in the US and Canada have wondered how well it would work under strenuous driving conditions.

In fact, it is by far the topic I now get the most correspondence over. I have probably received over 100 emails through this blog from followers that want to know how well the range extender works and how capable it is. People want to know things like what speed the car can maintain in charge sustaining mode and for how many miles can the car maintain highway speeds on a certain percentage upgrade, and so on. I even have had people ask me if I could conduct specific tests with my car to confirm it can do what they need it to. The reason being is the 34hp REx engine can only deliver about 25kWs (although some reports say BMW upped it to 28kWs) of power. That is plenty of power for nearly all normal driving needs, but not enough for continued high speed or long upgrade driving. The problem then arises if you continue to consume more energy than the REx can deliver.

My i3 when the REx turns on. Notice the tiny little bar of electric reserve to the left of the triangle. That indicates the 6.5% SOC position where the REx initiates and tries to maintain. There isn't a lot of buffer there for strenuous driving conditions.

The root of the problem reverts back to BMW's desire to have the i3 REx certified a BEVx vehicle by the California Air Resource Board. This allows BMW to get the most ZEV credits per vehicle, and also allows the i3 REx to qualify for other perks, like sales tax exemption in New Jersey and Washington State. It also allows the owner to get the full $2,500 California CVRP rebate, unlike all other PHEVs which only get $1,500. However this came with a cost, one that everybody with an i3 REx from every state has to endure. BMW had to restrict the REx use to comply with CARB's BEVx classification. The European i3 REx can be manually turned on any time the state of charge is lower than 75%. This is called a Hold Mode and allows the driver to hold a higher state of charge and keep a higher battery buffer which they may need for continued strenuous driving conditions later in the journey. The North American version has no Hold Mode, and the range extender only comes on when the battery is reduced to a critically low 6.5%. For normal driving that is fine, but when really pressed for continued periods, the car cannot maintain full power.

The European i3 REx has a Hold Mode which allows the driver to manually turn on the range extender if they need to. This feature is disabled for North America and is that is the root of the problem.

This creates a problem when the driver needs to drive for an extended period which demands an energy draw of more than 25kWs. The meager 6.5% battery reserve can quickly deplete in these conditions. When this happens, the car goes into a reduced power mode and can only maintain a speed of about 40mph. To make matters even worse, the driver gets no warning and the car just slows down. This is not what you want happening to you when you are on a highway and cars are whizzing by you at 70mph. This is a real issue, and compounded by the problem that most BMW client advisers didn't know how to communicate this to the customers and sold them the cars without informing them how to properly operate the vehicle in REx mode. I've had people contact me that were completely unaware of how the range extender worked and said they were told by their client adviser that "the car can do anything in range extender mode as it can in all electric mode, it just doesn't have quite as much power." That isn't true, and many early i3 REx customers were disappointed when they found out they couldn't drive up that mountain to their summer home, for example. In fact, one the Born Electric guest bloggers here mentioned an instance where he went into reduced power mode with a car full of friends.  

Don Parsons of Denver, Colorado recently took his i3 REx to the summit of Mt Evans which is the highest elevation with paved road in the US. He did experience the REx reduced power mode, but it didn't stop him from completing the14,000 ft ascent to the summit. This, of course is about as taxing on the range extender as it gets!

All that said, I now have over 10,000 miles on my i3 REx and not once have I ever gone into reduced power mode, and I've actually tried to make it happen! The "problem" I'm having is the highways are relatively flat here in New Jersey and the REx can basically handle anything I give it. The times I have tried to make it happen the flow of traffic wasn't fast enough for me to maintain a speed of over 75mph for a long enough period. 75 mph on relatively flat ground seems to be the upper limit the REx can handle for continued driving. There is plenty of energy to go up and down the hills I routinely drive over, and also to have short bursts of power well past 80 mph for passing if needed in REx mode, so for me the car works perfectly and I really don't need a modification. However my friends in California and other areas of the country that have long, steep inclines to negotiate disagree, and want to see some kind of modification to allow the range extender to turn on at a higher state of charge so the vehicle has a larger electric buffer. In fact, there will soon be a two-part post here by an i3 Rex owner in California that has been obsessing a bit over this very topic. (well, I call it obsessing, he calls it studying - I'll let you be the judge when you read his post next week!)

The Chevy Volt has a much more robust range extender engine and can operate under just about any condition without an issue. However it has about half the electric range as the i3 REx, meaning you will need to use it much more, so it has to be more capable. With a 70-80 mile all electric range, most i3 owners will not need to use the REx frequently.

So now that we understand the problem, what is the solution. Should BMW simply give up the value of the BEVx designation and allow the driver to initiate Hold Mode as the European i3 REx owners can? That isn't happening as far as I can tell. What I do believe is going to happen? Well for starters there will be software updates that include better indicators that the car may be headed to reduced power mode if you don't take action to alleviate it. Perhaps by slowing down 5-10 mph you can completely avoid having a problem at all. I also expect there will be a better state of charge display so the driver has more accurate display of how much power they have left. I would also love if BMW could add a display that would show the actual power draw you are using, so the driver can see if they are drawing more energy than the REx is producing. That would be an awesome tool for the driver to use in these situations and I do hope the BMW engineers consider adding it.. However I'm saving the best for last. It is my belief that BMW is working on an update that will indeed allow the range extender to turn on much earlier than the 6.5% threshold if the car determines you will need the extra power. This will work with the navigation system which accounts for topography. Once a destination is entered, the car will determine how early the REx will need to be turned on so it avoids reduced power while climbing an upgrade at the end of the journey. 

The i3's range extender sits next to the electric motor above the rear axle

While this isn't quite as good as having the ability to manually turn on the range extender, it's pretty close. The bottom line is people just want to be able to get to their destination without worry of a reduced power "slowdown" while driving on the highway. If the modifications that BMW are working on do indeed work, I don't think anyone will complain. In fact, I've privately asked this very question to quite a few current i3 REx owners and every one said as long as it works, and they can use the car to drive up long, sustained inclines at highway speeds, then they'll be very happy. From what I understand the update could be available as early as the first quarter of 2015 and will indeed be available as a software update to existing i3 REx owners.Of course it would have been better if this was available right from the launch, but at least BMW is working quickly (the i3 has only been available for about five months in North America) to correct the problem.

BMW i3 REx: A Hobbled Horse or a Galloping Thoroughbred?

The BMW i3 range extender engine which is made by Taiwanese manufacturer Kymco for BMW.

There is still a lot of unknown information about the i3. BMW has been extremely conservative about what information they offer. While they have stated it will have an electric range of 80 to 100 miles and cost about the same as a nicely equipped 3-Series, the two biggest questions still remain: What will the EPA range rating be and exactly what will it cost? However right behind those two questions for many people is: What will the performance be when the range extender is in use?

The range extender engine will be a 650cc Kymco engine borrowed from the BMW C650 GT scooter. It will be highly optimized to lower noise & vibration and will only put out 35hp, compared to its 65hp when used for the scooter. The gas tank will be a miniscule 2.8 gallons and BMW has stated it will extend the range of the car about another 90 miles, effectively doubling the cars range. However many journalists are wondering will that added 90 miles be an ultimate driving experience or the ultimate disappointment?

The REx will fit nicely next to the e-motor

The Chevy Volt is the closest vehicle to compare the REX i3 to, even though it's not exactly an apples to apples comparison. The Volt has a 1.4 liter gas engine that puts out 80hp to power the generator, more than double the output of the i3's gas range extender engine. However the Volt weighs 1,000lbs more than the i3 will and isn't nearly as efficient so it would naturally need a larger, more powerful range extender engine. The Volt's robust range extender allows it to drive uninhibited while the range extender is maintaining the car's charge. The million dollar question is will the same be said about the i3? That answer looks like it will be no, it won't. BMW's Product and Technology Communications spokesman, Dave Buchko said of the range extender: "The i3 range extender is meant to enable the car to go a little further than the pure BEV on those rare occasions when driver needs to go a little further. It is not intended for daily use. We've said that the REx [range extender] will double the effective range of 80-100 miles. I have not seen anything to suggest that it would not be capable of doing so.". Then BMW North American CEO Ludwig Willisch said while the range extender is running: "The car will not be as agile," Willisch said. "It will not have full power when it runs on the combination."

I'm not exactly sure what "not intended for daily use" means though. That sounds like you'll break if you use it every day and that's obviously not going to be the case. Will the cars performance be so inhibited while in REx mode you wouldn't want to drive it that way every day? I find it difficult to believe BMW would add the range extender if it was so weak it offered terrible performance while in use. Willisch must have confidence it will perform admirably in REx mode though because he predicted at least 80% of US i3 buyers will order it with the range extender. I've also heard it described by some as a "limp home mode" by some(not BMW people) and I also don't believe that is accurate either.

An i3 with the range extender was caught at a gas station refueling in this spy photo. The gas filler door will be located on the front passenger quarter panel and the charge port will be on the rear passenger side quarter panel, just above the wheel.

A big determination of how it will perform in range extender mode is how much of the battery the car holds as a buffer when the range extender turns on. Lets say the i3 normally only uses 90% of its 22kWh capacity. That means the all electric i3 will utilize about 19.8kWh's. If the REx i3 holds another 10% as a buffer to help with short bursts of needed energy than the range extender will turn on after using only 17.6kWh's of the 22kWh pack. This will allow the car to perform better when in REx mode but it will also mean the car will drive about 10 miles less on electricity. The larger the buffer the better the REx performance but the shorter all electric range. I hope BMW allows you to turn off the REx for those times when you could make your destination on pure electricity if you only need a few miles after the REx would have turned on. That way you could utilize the full ~19.8kWh that a BEV i3 has available, without reserving the buffer needed for the REx since you don't intend to need it. Of course the percentages of the battery pack utilization I'm using here are just guesses on my part, but I expect them to be pretty close to reality.

My guess is it will be pretty much in between the hobbled horse and "ultimate driving EV" when the range extender is in use. I think it will drive fine on flat terrain, and can probably even drive along at 70mph in those circumstances. However introduce an extended incline or times when you need to go 75 or more to keep up with traffic and the car could quickly find itself gasping for enough energy to maintain its motion. It definitely won't be a "It'll get you home but you'll have to crawl along at 30mph" but lets just say you'd lose if you try to autocross in REx mode. Then again, if BMW does reserve a fair amount of the battery back as a buffer, it could perform very well for the first 20 miles or so, before the stored energy gets to a minimum and the REx is working at maximum output to sustain the charge level.

The bottom line is if you really just want the security of knowing you'll never have to call a tow truck to get home, then the REx will be worth its weight in gold for you. I've been there on the side of the road a couple times in the past four years falling short of my destination so I know it will be a valuable asset for those circumstances. However if you plan to use the range extender to drive hundreds of highway miles to make a far off destination, then I'm guessing this isn't the right EV for you. Horses for courses. Hopefully, we'll get the answers to these questions and all the technical specifications of the i3 soon. It launches in Europe in the fall so the wait is nearly over.