How much does the 94 Al weigh?
- Thread starter mfischer
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alohart
Well-known member
BMW estimated 114 miles for the BEV. The gasoline capacity and engine are unchanged. The 2017 i3's weigh 50 kg (110 lb) more than the 2016 models, so the 2017 REx range might be slightly less than the 2016 model.mfischer said:
I'm afraid the engineer has eaten lots of bratwurst this past year, so he's heavier.mfischer said:
What did you mean by "engineer"?
I don't know. However, the weight of the entire 60 aH battery pack and the number of battery cells have been published. Most (all?) of the 50 kg weight increase is likely due to the increased weight of the 94 aH cells. Not sure how the cell weight would help with your calculation since the weight increase of the car has been published.mfischer said:
Rated battery range means nothing. It is marketing.
The equations to figure out range is simple physics. It's algebra at this point.
You need to know the car mass (M) (is it 1419kg for BEV?)
Car speed (v)
Battery Mass (Mb) (we don't know in kg)
Effective frontal area (Aeff) (.7m^2)
Range (value in km)
Li-ion battery available (Ebatt) (118.8MJ)
Motor power rating (125kW)
Max speed (for the upper limit) (150km/h - electronically limited)
0-100km/h is probably like 7.2s like the last model. (Vmax).
There is also the coefficient of rolling resistance 0.01 (C)
Plus the motor efficiency (Me) which is about 85%.
We must calculate the total internal friction (rolling + air). We know g = 9.8m/s^2.
power to overcome rolling friction = C*M*g*v dependent on velocity v.
Air friction is a little easier. = 1/2p*Aeff*v^3
efficiency at the given moment is Me*P = CMgv + 1/2p*Aeff*v^3.
Now let's bring it all together.
R = (Ebatt*v/P) = (Ebatt*Me) / (C*M*g) + (1/2p*Aeff*v^2).
When I get to work I can do a graph based on common speeds. I can do it in kmh and mph.
The equations to figure out range is simple physics. It's algebra at this point.
You need to know the car mass (M) (is it 1419kg for BEV?)
Car speed (v)
Battery Mass (Mb) (we don't know in kg)
Effective frontal area (Aeff) (.7m^2)
Range (value in km)
Li-ion battery available (Ebatt) (118.8MJ)
Motor power rating (125kW)
Max speed (for the upper limit) (150km/h - electronically limited)
0-100km/h is probably like 7.2s like the last model. (Vmax).
There is also the coefficient of rolling resistance 0.01 (C)
Plus the motor efficiency (Me) which is about 85%.
We must calculate the total internal friction (rolling + air). We know g = 9.8m/s^2.
power to overcome rolling friction = C*M*g*v dependent on velocity v.
Air friction is a little easier. = 1/2p*Aeff*v^3
efficiency at the given moment is Me*P = CMgv + 1/2p*Aeff*v^3.
Now let's bring it all together.
R = (Ebatt*v/P) = (Ebatt*Me) / (C*M*g) + (1/2p*Aeff*v^2).
When I get to work I can do a graph based on common speeds. I can do it in kmh and mph.
jadnashuanh
Well-known member
You could extrapolate some of the info you are looking at from the differences in reported range on the BEV verses the REx. The actual weight of the i3 will vary depending on options, and that also can vary between countries or markets. Some places list weight empty, some with a nominal driver onboard. It can be tough. Even the reported cd can be off some based on options, and rolling resistance will also depend on the tire type and size and air pressure, not counting the road surface. WHat is straight forward is the amount of energy required to climb a hill based on the mass of the vehicle (assuming you can get that!). The efficiency of the regeneration process can vary considerably, and that can throw off any calculations, as some energy can be recovered, depending on road conditions and the driver.
BMW's control logic will not let you discharge the battery fully, so there is a difference between actual capacity and the useable capacity (what is show to the operator). Throw in temperature, and the battery capacity can change considerably.
BMW's control logic will not let you discharge the battery fully, so there is a difference between actual capacity and the useable capacity (what is show to the operator). Throw in temperature, and the battery capacity can change considerably.
In this model I am ignoring temperature, regeneration models (very little impact), and altitude climb. Too unpredictable so I'm looking at optimal values.
I am going to make one with max power and power limited for the safety of the batteries. I'll use same percentage ratios.
Range is a math problem.
I am going to make one with max power and power limited for the safety of the batteries. I'll use same percentage ratios.
Range is a math problem.
mfischer said:
Range is indeed a math problem. But you need a standardised test route to be able to make it real.
A route involves starting, stopping, ascents, descents, cornering, variable traffic flow, stop signs, various relevant speed limits, traffic lights and open roads. Once you have a statistically proven route you have something to plug your maths into. What we need is multiple trips over such a standard route that delivers a normal distribution of trip data with a reasonable standard deviation.
Just doing the maths on specific items of vehicle energy consumption does not equal trip energy consumption.
jadnashuanh
Well-known member
A little temperature change, preconditioning, tire pressure, etc. all can have an effect, not counting the largest factor of all, the driver. How long the trip is, verses lots of shorter trips where the car is off in between will also have a major effect. Most people do not get in the car and drive it until the battery is exhausted, which, because you only have one get up to temp situation, is often the most efficient - not as dramatic as an ICE on a cold start, but still is a factor. A real driver is not a robot that can maintain an exact speed and even the cruise control will have issues depending on the terrain and traffic. It's hard to even get a good coasting internal friction, with the regen circuits, and running it in neutral isn't recommended, or a normal driving situation.
alohart said:
For the US they are going to allow the full 2.4 gal fuel tank that 2014-2016 owners had to code to get access too. That said, the REx should receive a bump in range, not a decrease. Why would it get a decrease with a larger battery pack AND a "larger" fuel tank? Even outside of the US the REx should see a bump in range. I think the math before was 10% less for REx, so if the BEV is getting 33 extra miles, I would guess about 30 extra from REx outside of the US. More than that inside of the US, pack increase plus fuel capacity increase.
alohart
Well-known member
Thanks for reminding me about the 2017's increased usable gasoline tank size for N.A. models.imolazhp said:
However, with the recent lawsuit, BMW could program the REx engine to automatically start at a higher battery pack charge level creating a larger buffer before a power loss could occur yet still maintaining the minimum EV range to satisfy CARB's BEVx category. If so, the EV range of the 2017 N.A. REx might not increase much. Also, the REx engine's power rating was increased 12% at 500 higher RPM in the U.K. which could allow the 2017 REx to consume electricity at a higher rate before experiencing a power loss, so if that's true for the N.A.. REx, its fuel efficiency could decrease. This plus the 2017 i3's increased weight could partially offset the increased REx range due to a larger usable gasoline tank size.
We're all just guessing now. We'll just have to wait until the U.S. specs are released to know for sure.
