Featured Is Toyota Prius hybrid simply passe now that plug-in cars are here?

This led to some interesting insights:

"Efficiency" is a curious term because it can be defined in many different ways. For example, Chris Hogan pointed out that '(volume * MPG)' provides a good first order merit for any vehicle, volume*miles per gallon.

So using the 2014 metrics from the EPA:

So let's use the common range for the 2014 BMW i3-REx, Honda Accord Plug-in, and Prius Plug-in. Set the range limit to 150 miles, the longest, common range for all three cars, the BMW i3-REx, we get:

• 76.4 MPG = ((72*117)+(78*39))/150 - BMW i3-REx EPA max range 150 miles
  
• 53.3 MPG = ((11*95)+(139*50))/150 - Prius Plug-in at 150 miles
  
• 52.0 MPG = ((13*115)+(137*46))/150 - Honda Plug-in at 150 miles

If we increase the distance, eventually the Prius Plug-in will overtake the BMW i3-REx and maintain that lead for both fuel efficiency and speed. The BMW i3-REx has to refuel and/or charge. A little further and the Honda Plug-in overtakes the BMW i3-REx. But the Honda Plug-in has one peak efficiency point.

Increase the range to the largest, 570 miles of the Honda Plug-in, and it reaches this goal at the fastest time because the other two had refueling delays. Then the Honda driver races to the bathroom.

Bob Wilson

 

your thought is comprehensive,
I still suggest the the pure electric range and hybrid range should be separated, as this way is easy to measure how the vehicles efficiency are.
My idea to compare i3 and accordhy is to explain that BMW is not as good as Honda in the fields of hybrid powertrain.
or maybe BMW don't want to put more cost in the hybrid part, instead they select carbon fiber materials as their highest priority. but still the efficiency of hybrid mode can't reach accordhy level.

 

The BMW i3 is an EV first and foremost, with the option to tack on the gas generator for limited range and performance...an alternative I do find intriguing, but the BMW option is too limited, I would prefer a 200 mile gas tank and a top speed of 75 MPH to make long distance driving more bearable. Doesn't surprise me that BMW doesn't have the expertise in Hybrids though, considering they don't have much of any...easier to go straight to EV.

 

consider the i3 weight and wheel size, their EV technology seems not good enough too...

 

Actually the BMW i3-REx problem is aerodynamics:

Using the coast down coefficients from the 2014 EPA "Test Car List Data", the BMW i3-REx vehicle drag is consistent with the Prius c, Prius v, and Gen-1 Prius (my first.) The 'drop' at 70 mph is when the drag equals the engine power. Any faster and the BMW i3-REx has to draw on traction battery power, rapidly draining the SOC. I am used to cruising at 65 mph using semitrailer trucks as pacing vehicles.

With some aerodynamic tweaks, the fastest cruise speed should move to ~75 mph, possibly higher. It is likely the 65 mph cruise might achieve 42-44 MPG, enough to significantly extend the range because it works in both EV and REx modes. BTW, there is some evidence the EPA list "39 MPG" may be sandbagged as the tested vehicle weight, 4300 lbs versus curb weight 2900 lbs, suggests a massive German test driver. <grins>

One caution, I'm not 'selling' the BMW i3-REx as much as explaining why it was my answer instead of waiting for the 2017 Level 2 ECO with TSS-P. With four comfortable seats and a lot of usable interior space, it meets our family needs. It is not the car for everyone. But I also like that 168 hp, rear-wheel drive. <GRINS>

Bob Wilson

 

The i3 EV consumption is quite good for a 170hp car, about 15kwh/100km. (source spritmonitor)

 

EV is much easier than hybrid.

The i3 is also BMW's pilot model for their lower cost carbon fiber production. So the optional range extender was likely low on the list of design priorities. As a sub 100 mile BEV, the i3 likely wasn't expected to be seeing long stretches of highway use by the designers. As a city car in Europe, aerodynamics is less important at those lower speeds too.

The i3 BEV is the most efficient one available in the US. The REx model's electric efficiency is a little lower from the extra weight, but it is still high. The EV range, which is increasing a tad for the 2017 model, is higher than the Volt's, which makes it more likely owner's could spend a large portion of their miles on grid electricity. The larger the EV ratio, the less important the back ICE efficiency is for most owners.

 

Excluding detail, yet again. Makes you wonder...

Who would ever call the jump from 81 miles to 114 miles just a tad ?

 

*sigh*
It appears you are on to me.
My use of "tad" in a throw away blurb of a two paragraph post, is all part of a plot to spread FUD about the i3, and is no way do to me simply being too lazy at the time to look up the exact figure, and my memory saying it was under 100 miles. Positive statements about the i3 I have made elsewhere on these forums are all part of this plot to better this FUD. As was my repeated cursing of CARB for forcing BMW to only offer a hobbled version of the REx model.

I shall post here no more, for you truly have vanquished me with your paranoia and insinuation.

 

We need to consider its weight and wheel size. i3 is about 1100 kilogram, and using 175&155 centimeters width wheel, in this condition, it has only 2 MPGe margin in electricity mode comparing with accord plug-in which weigh 1700 kilo and use 225 width tires.
accord plug-in also use 166hp motor

 

Those 2 MPGe diff are EPA. Unfortunately there are no Accord PHEVs registered on Spritmonitor to compare with the i3 values.

 

A recent posting about Car and Driver review reminded me that the 2014 Volt was not part of the original analysis because a 2016 car was in the list. So I reanalyzed the EPA data at fueleconomy.gov including the Volt:

• Each line includes the EV, EV+ICE, and ICE range without refueling
• Assumes starting in EV and transitioning to ICE with running average MPG

Yes, the BMW i3-REx is inefficient at distances greater than its range, 150 miles. If one recharged daily and added two gallons each day, it would be a pretty good commuting car. On the highway cruising at 65 mph, the block-to-block time is 50 mph with 40 MPG average.

Bob Wilson

 

The fuel economy data files are your friend, as they break this down more completely. I'm going to use adjusted, but unrounded, MPGe for all figures here, although it's worth noting that the datafile doesn't make gasoline usage during a test cycle that clear, but its numbers match what fueleconomy.gov says.

	Model	Mode	City	Comb	Hwy
1	2014 BMW i3 REx	CD	127.0930	116.9364	106.5310
2	2014 BMW i3 REx	CS	41.4544	39.4850	37.3180
3	2014 Honda Accord Plug-In Hybrid	CD	124.0132	114.7045	105.0654
4	2014 Honda Accord Plug-In Hybrid	CS	46.6172	46.1340	45.5569
5	2014 Toyota Prius Plug-In Hybrid	CD	90.2714	95.3887	102.4898
6	2014 Toyota Prius Plug-In Hybrid	CS	50.5282	49.7021	48.7284
7	2016 Audi A3 e-tron	CD	80.7	83	86.1
8	2016 Audi A3 e-tron	CS	33	34.5683	36.7

It's also worth noting that the i3 and Prius were tested on a 5-cycle test for their charge sustaining modes, whereas the Accord and A3 were tested on a 2-cycle test, with the 5-cycle results being derived from the 2-cycle results. (All charge depleting results are done on a 2-cycle for both 2014 and 2016, it seems.)

Another interesting thing, FWIW, in the PHEV spreadsheets is a composite MPG - I believe that's basically the MPGe of the car with one full fuel tank and one fully charged battery.

 

Ok,

Now I see how the Honda Accord got it's high MPGe:

• (117 MPGe) 27 lbs/kW = 3375 lbs / 125 kW - BMW i3-REx
• (115 MPGe) 32 lbs/kW = 4000 lbs / 124 kW - Accord Plug-in
• (98 MPGe) 36 lbs/kW = 4000 lbs / 111 kW - Volt
• (95 MPGe) 194 lbs/kW = 3500 lbs / 18 kW - Prius Plug-in

The MPGe follows the weight to electrical power ratio which makes sense. The FTP-2 and FTP-3 includes several acceleration and stops. The ability of a car to recover energy is a function the weight-to-power ratio. Now this won't be a strict linear relationship because of rates of acceleration and braking.

To meet the braking profile, the car will either be in full regeneration, 27-32 lbs/kW, or a mix of regeneration and friction braking, 36-194 lbs/kW. Sad to say, there is no Argonne test data for the Honda Accord Plug-in.

I've plotted the BMW i3-REx power during the FTP-2 and found:

This test consists of a 'cold soak' cycle; a 100 second pause, and; a 'hot' cycle' starting at seconds 700. Now the REx has an absolute maximum power but during most of the test it was under 18,650 W. Funny how the Prius Plug-in motor rating is 18 kW. <hummmm>

Speculation on my part but the Prius Prime is using a 'one-way brake' (i.e., latch-up) so MG1 can add to MG2 for more electrical power may be all it takes to get its MPGe in the same range as the BMW i3-REx and Honda Accord Plug-in.

Bob Wilson

 

It's probably because of the low gasoline prices.

 

Do you mean accord plug-in recover more energy when it brakes?whereas i3 has to waste more energy while it decelerates.

 

The right idea but reversed:

• (117 MPGe) 27 lbs/kW = 3375 lbs / 125 kW - BMW i3-REx
  
• (115 MPGe) 32 lbs/kW = 4000 lbs / 124 kW - Accord Plug-in
  
• (98 MPGe) 36 lbs/kW = 4000 lbs / 111 kW - Volt
  
• (95 MPGe) 194 lbs/kW = 3500 lbs / 18 kW - Prius Plug-in
  

The ratio of mass-to-motor_power determines how much energy can be recovered (and how fast it is off the line in EV-only mode.) The BMW i3-REx has the lowest mass per unit of motor power so it can absorb more of the kinetic energy (i.e., regen) before having to use friction braking.

Bob Wilson

 

There's a good i3 read on high regen here;
BMW i3 versus Tesla Model S 70D

What i found most intriguing was how little of the article there was that got devoted to overall battery capacity. As traction packs age, and are less & less capable of holding capacity, in essence, they become a smaller sized pack. So, more power going either in or out may generate more heat ... the #1 enemy of batteries. Conversely, a larger 60-90kWh pack would be less heat impacted via charge/discharge .... and so one would think Tesla would have the strongest regen (especially since it can utilize its dual motors & large mass). And yet, the article says the old electric mini had greater regen ... maybe due to lighter weight?
.

 

we can only say, the regenerate capability is corresponding with mass-to-motor. but whether they are really correlated?
If we use higher power motor, whether we can recapture more energy?

 

"Greater" in this case, means "will bring you to a complete stop".
The 70D generates more power through regenerative braking, and has a higher peak power.
The i3 feels as if it slows as quickly, if not a bit quicker, but is generating less power (due to weight and only one axle).

I am not sure if there is a reason the 70D doesn't come to a complete stop while the i3 does.
In city driving, I prefer the i3 style where it will come to a stop. In traffic jams, I prefer the "slow to a crawl" behavior of the 70D.
It may simply be a choice by the designers, although the guess in the article is intriguing as well and may explain it.