US i3 Rex dangerous when climbing hills

[mindmachine]

It's not just a software issue. Remember that the gas tank itself has been physically stunted, it's smaller by 2L, I think.

Stupid. Just really dumb.

While I agree with you, it's only 1/2 gallon. The big deal is being denied the ability to engage the REx when needed vs the current set up where it is automatically activated at 6.5% SOC.

 

[Zzzoom3]

(My wimpy 110 hp Prius and 107 hp '13 Leaf make it over the same grade w/o issue.)

The i3 can make the grades too. It's just that in this case, there was little or no charge remaining. The REX generator doesn't output enough power to keep you going up a hill when you are out of usable battery

 

[jadnashuanh]

(My wimpy 110 hp Prius and 107 hp '13 Leaf make it over the same grade w/o issue.)

And, that's the point! Once you've essentially depleted the batteries on the i3, REx or not (this happens at different levels based on the version), you have at the most the 34Hp engine to keep it running...that makes your Prius look like a supercar in comparison. If your charge on the Leaf got down to the critical point at that location in your trip, it would have a similar issue, but no chance of recharging unless you actually did make it over the top and could regen on the way down. With the REx, as long as you have some fuel left, you might build up a moderate charge.

Bottom line, when you've reached the critical point on the batteries of the i3, it will slow down, and, if your load is more than the REx can provide, while you can continue, it may not be very fast until the load on it drops so you have excess to then start building up a charge again.

Adding the REx to the i3 increases weight, and decreases overall battery only range.

 

[ultraturtle]

The following graph from BMW’s W20 Engine Technical Training document suggests a strategy to maintain charge as one approaches an extended incline:

Simply maintain exactly 90 km/h (56 mph) – no slower, no faster (perhaps slowing to 70 km/h (44 mph) once SOC drops below ~ 1% (if that level can be discerned) .

Well prior to the climb, 90 km/h (56 mph) is the slowest speed at which the REx engine will output its maximum power in the 3.5% - 6.5% SOC range (~20 kW engine power, or 18.8 kW (94% kinetic to electrical efficiency - how awesome is that?) electrical output at 3500 RPM).

Any slower, and the RPM and power drops. Any faster, more energy is consumed and less excess power is available to bring the SOC up to 6.5% for the beginning of the climb.

Once the climb begins, 90 km/h (56 mph) remains the minimum speed that keeps the REx engine increasing its maximum electric output level of 18.8 kW as the charge state drops below 3.5% SOC through 21.1 kW at 2.5% SOC, to its maximum of 23.5 kW at 1.5 %.

For bonus points, you can monitor the SOC on the European REx dispay, or any cheap USA ScanGuage or Bluetooth OBD II enabled App while climbing that thoretical hill, and reduce speed to as little as 70 km/h (44 mph) once you detect SOC dropping to 0.7% , as this will still enable full REx power.

Numerous folks have been successful in attempts to make the system fail because the parameters for system success are well known. Horses for courses, folks. This is not brain surgery.

 

[Chrisn]

Umm.... "horses for courses?" Come on. To normal people, this is brain surgery. Read your post with the eyes of a "Soccer Mom." It is laughable to suggest that a normal consumer would find it reasonable to employ a magical sequence and OBD-II gizmo to drive up a modest grade without dramatic loss of speed and power.

I'm the OP and I was not scheming to try to make the car fail. I was driving it as I would a normal car and observing the results: complete fail.

That said, as a nerd, I truly appreciate the info.

Does anyone DISAGREE that a more reasonable fix is to have a "Mountain Mode" button that automatically reserves (or, if depleted, builds up) a bigger SOC buffer well ahead of a known hill? If so, why?

 

[ultraturtle]

It is laughable to suggest that a normal consumer would find it reasonable to employ a magical sequence and OBD-II gizmo to drive up a modest grade without dramatic loss of speed and power.

Precisely why I stated "bonus points" for that last, tiny, marginal benefit to be gained by nerds like us.

For the vast unwashed, all that needs to be remembered is 56 mph.

Try it on your next drive. You might be surprised.

 

[ultraturtle]

Does anyone DISAGREE that a more reasonable fix is to have a "Mountain Mode" button that automatically reserves (or, if depleted, builds up) a bigger SOC buffer well ahead of a known hill? If so, why?

You will not find anyone on this forum, nor on the face of the earth other than one or two complete boneheads on the CARB that cannot understand not only the safety, but the economy and ecology implications of the ridiculous decision to cripple the system by not allowing it to operate as designed for the rest of the world. There are even pinheads on this forum that advocate against the purchase of a REx based on its limitations in the USA.

Bottom line is that BMW was granted BEVx credits for the REx, which enabled BMW to sell massive quantities of gas hogs in California. While most of us bemoan that fact, I could not be happier, as my wife's aluminum chassis, carbon fiber frame, sweet, sweet ride cost about half what I would have been willing to pay for the 4th most efficient, most versatile vehicle on the planet. Anyone that understands the cost and complexity of carbon fiber construction gets it. Most don't. We're being subsidized by California M3, M5, and 7 series gazzilionaires. Not gonna complain.

 

[Zzzoom3]

It is laughable to suggest that a normal consumer would find it reasonable to employ a magical sequence and OBD-II gizmo to drive up a modest grade without dramatic loss of speed and power.

Precisely why I stated "bonus points" for that last, tiny, marginal benefit to be gained by nerds like us.

For the vast unwashed, all that needs to be remembered is 56 mph.

Try it on your next drive. You might be surprised.

Yeah this is really good detective work of the BMW U info. Thanks for finding that for us. I think the OP may also be thinking that BMW ought to be doing a lot better job of educating us about REx operation and limitations :roll:

Regarding mountain mode, it shows you how good a job GM really did in thinking thru operation of the EV. There are many, many features of the Volt operation I notice being copied by others including BMW. With respect to REX, it shows you what happens when you try and add something to the design that was never originally intended! BMW is likely in between a rock and a hard place here because they have rules that need to be followed to be BEVx compliant and this limits what they can do in terms of REX modes. Just speculation on my part but likely IMO.

 

[Chrisn]

We're being subsidized by California M5 *********s.

I guess I'm subsidizing myself.....

 

[jadnashuanh]

The Volt had a much different design perspective than the i3. As a result, they put in a much bigger ICE, with sufficient power to keep the car running much longer and at higher speeds - the onboard generator can produce a bunch more than electric motor needs and as a result, under nearly all circumstances, it can maintain sustained speeds. But, it's still only got about an 80Hp generator, and if you do run the batteries down, it will revert to just the generator, similar to the i3, but at about 2.5x bigger engine (but it does weigh more - over 1,000# more than the i3 BEV). The Volt is designed to be a replacement for a conventional ICE, and is closer to that by a long shot, even allowing the motor to help drive the wheels through the transmission, rather than being solely a generator in at least one mode. If you use the i3 as originally intended, a city car with the REx addition being a range anxiety crutch, it all makes sense. 34Hp (verses the Volt's 80 or so - it is over twice the displacement) if you've gotten your SOC too low just will not support sustained high speeds or a steep grade no matter what you do. You need to understand that, and try to avoid getting into that situation. It takes some planning, but it is possible to take the i3 REx on a long trip...personally, other than a challenge, it's not worth it to me, nor is it what it was designed for. Back to my analogy about digging a ditch with a hand spade...you can do it, but it is not the best tool for the job! The i3 in either form, isn't great on a long trip unless you understand and can adjust to its limitations.

Consider that even if you could turn the REx on earlier, like elsewhere, if you're doing a long drive, you still can run into the same problems of being low on charge when you encounter a need for more power - you could be out of gas when you hit that grade, or want to merge on a high-speed roadway and your battery has been worn down - yes, you'd be further down the road than a BEV when it happens, but it will still happen. Ask yourself, does that make the BEV version dangerous, too? How about the Leaf, or any other all-electric vehicle? They aren't perpetual motion machines...they need energy to make them go, and they will slow down as that energy gets depleted to preserve the battery life. Current levels go up as the voltage drops, and there's a limit on how much you can run through the circuits before they overheat or fail. The car is programmed to prevent that degradation of the components.

 

[ultraturtle]

I guess I'm subsidizing myself.....

As well as my wife... and we both thank you.

 

[Chrisn]

Consider that even if you could turn the REx on earlier, like elsewhere, if you're doing a long drive, you still can run into the same problems of being low on charge when you encounter a need for more power - you could be out of gas when you hit that grade, or want to merge on a high-speed roadway and your battery has been worn down - yes, you'd be further down the road than a BEV when it happens, but it will still happen. Ask yourself, does that make the BEV version dangerous, too?

Do you hear yourself talking (typing)? Why are so many people apologists for BMW's insane crippling of the REX? Cars run out of gas, but after lots of warning and only after being driven beyond 100% of their range. The nonsensical REX hamstringing can kick in at 50% of total claimed range. This is NOT comparable to running out of gas in a pure ICE or running out of charge in a BEV.

Ironic that the Volt, with its much bigger ICE, has a mountain mode but the i3 does not. This is purely a case of greed (from BMW) and slavish adherence to misguided utopian dogma (CARB) winning out over simple common sense and desire to put out a well designed car.

How long until Edmunds.com or a bigger media outlet gets footage of a $55K BMW incapable of driving over modest grades faster than 25-30 MPH? Who at BMW NA will stand up and defend the i3 REX against the common sense reaction of "WTF?"

 

[RJSATLBA]

And when someone succeeds in kicking up a public stink BMW can simply point to the fact that the i3 doesn't operate like that anywhere else and say they gave you what you asked for.

 

[cwerdna]

It is laughable to suggest that a normal consumer would find it reasonable to employ a magical sequence and OBD-II gizmo to drive up a modest grade without dramatic loss of speed and power.

Precisely why I stated "bonus points" for that last, tiny, marginal benefit to be gained by nerds like us.

For the vast unwashed, all that needs to be remembered is 56 mph.

Try it on your next drive. You might be surprised.

Sorry. Sounds like BS. The OP isn't the only story I've seen about highway speed hill climb issues solely using the REx in the US. One notable story I've seen is from another guy in So Cal.

Too bad you're on the other side of the country, otherwise I'm sure the OP and the other guy would want to challenge you.

I highly doubt given your hypothesis and even w/monitoring via tools plugged into the OBD2 port you'd be able to do significantly better up those same grades w/depleted battery. The REx engine's output is simply insufficient for those grades and speeds. You mention a max of 23.5 kW, that's only 31.5 hp.

(FWIW, my 06 Prius' curb weight is 2890 lbs, which is somewhere between 9 and 172 lbs lighter than the REx i3: http://www.bmwusa.com/Standard/Content/Vehicles/2014/i3/BMWi3RangeExtender/Features_and_Specs/BMWi3RangeExtenderSpecifications.aspx. The ICE in the Prius has a max output of 76 hp, more than double the above figure. When the Prius' tiny battery is depleted going up a steep prolonged grade, the ICE is roaring but my speeds don't fall to 40 mph, let alone 25 mph... It's been driven over highway 17 before and over the Grapevine numerous times.)

 

[RJSATLBA]

It is laughable to suggest that a normal consumer would find it reasonable to employ a magical sequence and OBD-II gizmo to drive up a modest grade without dramatic loss of speed and power.

Precisely why I stated "bonus points" for that last, tiny, marginal benefit to be gained by nerds like us.

For the vast unwashed, all that needs to be remembered is 56 mph.

Try it on your next drive. You might be surprised.

Sorry. Sounds like BS. The OP isn't the only story I've seen about highway speed hill climb issues solely using the REx in the US. One notable story I've seen is from another guy in So Cal.

Too bad you're on the other side of the country, otherwise I'm sure the OP and the other guy would want to challenge you.

I highly doubt given your hypothesis and even w/monitoring via tools plugged into the OBD2 port you'd be able to do significantly better up those same grades w/depleted battery. The REx engine's output is simply insufficient for those grades and speeds. You mention a max of 23.5 kW, that's only 31.5 hp.

(FWIW, my 06 Prius' curb weight is 2890 lbs, which is somewhere between 9 and 172 lbs lighter than the REx i3: http://www.bmwusa.com/Standard/Content/Vehicles/2014/i3/BMWi3RangeExtender/Features_and_Specs/BMWi3RangeExtenderSpecifications.aspx. The ICE in the Prius has a max output of 76 hp, more than double the above figure. When the Prius' tiny battery is depleted going up a steep prolonged grade, the ICE is roaring but my speeds don't fall to 40 mph, let alone 25 mph... It's been driven over highway 17 before and over the Grapevine numerous times.)

The i3 isn't a Prius. Personally, I've never understood why anyone would buy a car such as the Prius which has the potential to reduce one's use of fossil fuel, then drive it at 75-80mph. I had a test drive in one several years ago and it didn't appeal to me at all, unlike the i3 which had an immediate wow factor - for me.

Whilst I appreciate that the US or Californian requirements have compromised the Rex, one of the things I don't understand is why anyone relied upon marketing and sales claims in the first place. If we all believed what we are told in advertising we'd have an awful lot of kit of one sort or another that didn't live up to the claims made for it. It isn't the job of ad-men to tell us the truth.

Why would anyone who has done any homework at all buy a US spec REx and expect it to be suited to driving at 75-80mph on freeways and coping with hills after the battery has become depleted, which is obviously going to happen much more quickly at that speed.

 

[Chrisn]

Personally, I've never understood why anyone would buy a car such as the Prius which has the potential to reduce one's use of fossil fuel, then drive it at 75-80mph....Why would anyone who has done any homework at all buy a US spec REx and expect it to be suited to driving at 75-80mph on freeways and coping with hills after the battery has become depleted...

Roger: Firstly, normal people drive >=75MPH on 65MPH limit roads and >=80MPH on 70MPH limit roads. Normal people (not some ECO / Green fringe) are the ones who will drive mass adoption of EVs. Normal people paying $55K for a car that has been WIDELY advertised to the general public expect a car to drive like a car.

I am not normal. I am a "car guy" and a "gadget guy." This is my third EV (after the Volt and the not-really-an-EV Ford Fusion Energi). I DID research the REX, and I did NOT expect to drive 80MPH on the REX. In all the info from BMW and reviews that I read, I expected to be able to drive around 70MPH on REX and to handle grades at speeds not slower than 45MPH. I did not hear or read of anyone having a 25MPH nightmare like I had.

I am offering my personal experience NOT just as a Physics word problem, but also as feedback/prediction for BMW that the car is not safe as delivered in the US. At an absolute minimum, dealers should be required to educate buyers about the limitations and the car should warn drivers in advance of loss of power (so they can pull over if they are on a hill). Or, they could unshackle the car (Mountain Mode) and give people a car that can serve people ~99% of the time instead of the current ~90%.

 

[BrianStanier]

'Normal' people in the US might drive like that. 'Normal' people here in the UK don't. Drive on the motorways here in the North of England at a true 70 (75 indicated) and you will be overtaking much of the time and be overtaken by only a few drivers. We appear to be rather more law-abiding on this side of the pond.

 

[kevinb61]

Roger: Firstly, normal people drive >=75MPH on 65MPH limit roads and >=80MPH on 70MPH limit roads. Normal people (not some ECO / Green fringe) are the ones who will drive mass adoption of EVs. Normal people paying $55K for a car that has been WIDELY advertised to the general public expect a car to drive like a car.

Quit with the over-generalizations. In Southern California, that statement is probably correct (everybody is falling down over each other trying to get everywhere in a hurry), but in other areas (Like upper Northern California) that is just not true. I use Hwy 101 up here almost daily and I can set cruise to 70 (which we all know that's like 68 or so with BMW speedos) and only get passed occasionally.

From what I have seen (and read, and driven) it does exactly what it was designed to do. If you want a hybrid, buy a hybrid (no thank you). If you want to buy a REX so you don't have to worry about the occasional (! - not as a daily crutch), great. Personally if your calculations say you will need to use the REX so that you can use your i3 to get to work daily (and you want to drive 70+, and use A/C, drive big hills, etc.) you have bought the wrong car...you should have bought a Hybrid.

I bought my BEV knowing exactly what it excels at, and I can use it for 95% of my trips. For the other 5%....ICE baby!

 

[RJBarry]

Thanks for the info regarding 56 mph. Sounds like in my situation when I preemptively slowed to 55 mph, I was on the right track.

However...

The frustrating thing about Rex crippling, is that the presumption by the American govt is that Rex owners, if not prevented to do so, would of course waste gas. Seriously, for what possible reason would any individual that owned a BMW i3 Rex run the gas engine any more than was absolutely necessary?

This is the voice the govt thinks I have in my head --> "Won't it be great! I'll buy an electric car that I can charge using gas! Why bother plugging it in? I'll just stop every 40 minutes for gas. Heck, even better, I'll buy 3 five gallon gas cans that I can keep in the back. Why not, I'm made of money and that is way more convenient than just buying a car that actually runs on gas, right?! That is awesome, I'll never plug it in because plugging it in is bad. Go OPEC!!"

I get very annoyed when the Govt's standard operating assumption is that the American consumer is stupid.

 

[cwerdna]

Personally, I've never understood why anyone would buy a car such as the Prius which has the potential to reduce one's use of fossil fuel, then drive it at 75-80mph.

Not everyone lives and works on a highway. There's got to be some city driving at which the Prius really shines. And, even at 75-80 mph, its mileage would still be better than almost every non-plugin ICE car (sold in the US) on the road at the same speed.

Why would anyone who has done any homework at all buy a US spec REx and expect it to be suited to driving at 75-80mph on freeways and coping with hills after the battery has become depleted, which is obviously going to happen much more quickly at that speed.

Not everyone does their homework. And, even those who have done some homework can run into unexpected situations/detours that could mean the inability to charge. As the OP posted, highway 17's speed limit on that stretch is 50 mph.

Just for kicks and to provide some people context about highway 17's hill climb, using Google Earth (http://priuschat.com/threads/google-earth-can-give-you-an-elevation-profile-of-a-route-between-2-points.100653/), if you get directions from Los Gatos, CA to Santa Cruz, CA, which would take you over highway 17. Starting elevation is 361 feet. Beginning of highway travel is ~1.4 miles into the trip. Crest of the hill is ~1850 feet at about 9.2 miles into the trip. From that point on, it's all downhill. We're not talking about climbing Pike's Peak.