Why the BMW i3-REx

I think the mistake was not getting the Range Extended version. LA is so huge that a single 'errand' will deplete the battery. With the range extender, the 150 miles is at least long enough the driver would make at least one donut stop. <grins>

There is a high-speed, DC charger option that can put 80% of the charge on in 30 minutes. So if they are co-located with Dunkin and Krispy Kreme ...

BTW, LiON battery and carbon fiber body on aluminum frame:


FYI:

Source: Tesla News Source

Bob Wilson

 

Source: 2014 BMW i3-REX | Argonne National Laboratory

Argonne National Labs does the BMW i3-REx.

Bob Wilson

 

Argonne Labs does great work and makes a lot of engineering data available. So I took the best case test file, 61504060.txt:

• UDDS protocol
• 24 C, climate control off, hood down, windows down (on a dyno!)
• 7.48 miles
• 51.6 MPG (others range from 36. to 50.7, this is the best)

Now this is just my first analysis plotting dyno kW, battery kW, and REx kW:

• car is driving the dyno - the upper left quadrant, shows how power from the battery and REx provide the energy needed to spin the dyno for acceleration. The brief negative REx power is the car spinning up the engine.
• car is stopping on the dyno - the lower right quadrant is when the car is braking, actually regenerative braking, and absorbing power from the dyno. This is when the REx is no longer needed so its power drops from ~7 kW to zero.

Now I have more interesting metrics to analyze including a raw BSFC chart for the REx. I also need to take the other extreme, the worst case, and see what is going on. Finally there is a sub-freezing and +90F set of data. But there are a whole set of tests in EV-only mode. It will keep me busy. <GRINS>

Bob Wilson

 

With the Argonne data, I learned the traction battery overhead is about 540W and updated the mph vs mi/kWh chart:

This data begins to show how sensitive the BMW i3-REx is to rolling drag effects. I intend to use the Prius trick of maximum sidewall pressure.

Bob Wilson

 

So here is the former Prius, now owned by our housekeeper, and our replacement, BMW i3-REx:

	EPA and Mfg. metrics	2003 Prius	2014 BMW i3-REx
1	Drive	Front-Wheel	Rear-Wheel
2	HP	114 hp	168 hp
3	Curb lbs	2765 lbs	2899 lbs
4	Fuel tank gal	11.3 gal	2.0 gal
5	Traction battery	no plug	18.7 kWhr
6	Passenger volume/seats	89 ft{3}/5	84 ft{3}/4
7	Luggage	12 ft{3}	15 ft{3}
8	MPG@65 mph	52 MPG	40 MPG
9	$Gas to Drive 25 Miles	$1.45	$1.81(*1)
10	$Elect. to Drive 25 Miles	no plug	$0.94
11	5 year savings	$3000	$4000
12	Odometer bought	49250 mi.	6440 mi.
13	Paid	$17500	$29900

*1 - BMW approves of 89 octane, plus, but EPA uses premium. I use plus but Costco only sells regular and premium.

Bob Wilson

 

I'm not ready to go for a larger tank, yet:

Yes, I've looked at it but it is low on my list of priorities. The tank is pressurized and even if a larger tank is fabricated, you need empty volume in the body. I am looking at adding a receiver hitch which would provide a place to add things that don't have to fit in the body.

Right now, my focus is on efficiency with fully inflating the tires high on my list. This morning I repeated my 30 mph test and got 7.5 mi/kWh, no significant improvement over the pre-alignment and new tires. First at bat, fully inflating the tires. This was especially brought home when I did a 75 mph test, 3.4 - 3.7 mi/kWh. Making a car more efficient is the 'low hanging fruit'.

In that line, other things to explore:

1. Aerodynamic mods - the 0.29 Cd is the same as our 2003 Prius. I suspect some areo-tricks might make a significant improvement.
   
2. engine efficiency - possibly some form of cooled, EGR into the air intake and; engine oil change to something better than stock BMW practices (0-20W is already approved for the 2017.)

Bob Wilson

 

Pretty much the same as the 2003 Prius. I've sat in the back and it is no better or worse than the 03 but with only two seat-belt sets, not three.

Bob Wilson

 

Since I've had to switch between the two:

• sense of space - feels more open with lots of pockets. It helps to raise seat which is not as easy as Prius. Best done when outside of BMW.
• foot wells - about the same although the Prius may have more side-to-side. It doesn't feel as narrow as the 2016. Smaller to larger: 2016 < BMW < 2010 Prius
• rear seats - not great but not torture either. One full-size adult, OK, and two works also. So far, the dogs don't complain. Not the first choice for double-dating with another adult couple but OK for short trip.

It has the same, short wheelbase as the 03 Prius. This means you can sense the 'wave' of the highways. Also, the steering responds RIGHT NOW SIR!!

Bob Wilson

 

My driving huristic is changing:

1. Fast and free - go to charging stations for free miles and survey walking area for best value bars and bookstores.
2. Sheltered and free - again survey walking areas to find a place to enjoy the wait.

In contrast, this Prius driver never cared about where but quality of the destination. The Prius made destination the highest priority over parking for a free 'power charge.'

The one exception is if a quality place is along my route, I will still visit. But it is incidental to the Howl search for an EV fix.

Bob Wilson

Howl - Alan Ginsberg

I saw the best minds of my generation destroyed by
madness, starving hysterical naked,

dragging themselves through the negro streets at dawn
looking for an angry fix,

angelheaded hipsters burning for the ancient heavenly
connection to the starry dynamo in the machin-
ery of night,
. . .​

 

More accurately,'beyond'. <grins> I never found 'pulse and glide' to be a practical solution for ordinary traffic. It works in isolation, one car, one road, but utter nonsense when a second car shows up. Maintaining a constant kinetic energy is the simplest and most efficient method that works in all traffic. Still, there is a question of comparing "N" to i3 regeneration.

So last night, I did a quick sanity test to compare regeneration in the i3 versus coasting in "N". If there is a difference, my very brief ad hoc test did not reveal any. The test was using a short, shallow grade, and not optimum. However, I can clearly see the difference with our 2010 Prius where "N" is significantly better over regeneration.

My test is also looking at our i3 to see if there is something 'going on' that needs further investigation. Fortunately, I have 10 years of 2003 Prius data and can easily compare the i3.

Bob Wilson

 

So this afternoon I used my roll-down hill normally used in freezing weather. In 85F, the BMW i3 was doing 20 mph when I had to stop. Although not definitive because of the temperature, no evidence of a rolling drag problem.

Bob Wilson