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 Post subject: Making sense of mpg for A3 e-tron
PostPosted: Wed Oct 10, 2018 11:49 am 
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Joined: Sun Sep 16, 2018 9:26 am
Posts: 6
Making sense of mpg for A3 e-tron

Here are the data from Dash:
1177 miles
57.4 mpg
7.0 m/kWh
Image

And data from MMI:
1000 miles
39% ICE
61% EV
Image

Assuming I have the same 39%-61% ratio for the whole 1177miles, the gas range is 459 miles, and EV is 718 mile.

The gas used is 1177miles / 57.4mpg = 20.5gal, which will result in 22mpg = 459m / 20.5gal, for the gas engine only. This 22mpg is apparently too low, even for gas engine only.

In order to calculate more real mpg for gas engine, I need to know real miles by ICE or EV. I think 7.0m/kWh and 718 mils are both inflated, maybe Audi is adding re-generative braking? However, the electricity 718m / 7.0m/kWh = 103kWh should be accurate, which is somewhat close to the number I got from SoCal Edison.

Assuming 3m/kWh for the EV driving, the real EV range is 308miles and gas is 869miles. Therefore the real mpg for gas engine only is 869m / 20.5g = 42mpg.

The other way to look at real mpg without the 3m/kWh assumption, is to use 0.15$/kWh for charging at home, and 4.00$/g for gas price. In this case, the equivalent gas for the 103kWh is 3.8gal, which give me total of 24.4gal equivalent gas for the total 1177 miles. In this case, I got 48mpg for the ICE/EV combined.

A few words on my driving condition.
For commute only.
50mile round trip in LA traffic on 405, mostly in hybrid mode.
Charge overnight at home only.


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 Post subject: Re: Making sense of mpg for A3 e-tron
PostPosted: Wed Oct 10, 2018 1:05 pm 
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Joined: Sun Sep 16, 2018 9:26 am
Posts: 6
The real question I have is how does Audi come up with EV efficiency of 7.0 miles/kWh, for driving in hybrid mode most of time.
For pure EV driving, I get about 3.5 miles/kWh. Therefore I suspect the 7.0 miles/kWh is inflated, possibly due to re-generative braking (after gas engine acceleration). But still the difference is too big for me to understand.


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 Post subject: Re: Making sense of mpg for A3 e-tron
PostPosted: Thu Oct 18, 2018 9:14 am 
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Joined: Tue Aug 08, 2017 11:32 am
Posts: 27
I at first assumed that the car would drive with electric power or with the gas engine on. What I notice is that the car likes to turn off the gas motor whenever it can. Even with 0 miles electric range, or in battery hold mode, the graphic shows the ICE off and electric propulsion being used if only light propulsion is needed. It also coasts whenever it can. I’ve found that with 0 electric range I get about 42 mpg at speeds below 60 around town and about 38 pounding the interstate at 75+.


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 Post subject: Re: Making sense of mpg for A3 e-tron
PostPosted: Thu Oct 18, 2018 7:49 pm 
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Joined: Sun Sep 16, 2018 9:26 am
Posts: 6
Yes, I was also very surprised to see a lot of EV milage, even with presumably empty battery.
In my experiment, I have about 50% of EV mileage, on 25 miles commute from work to home, with empty battery and average speed of 25MPH. The gas MPG is about 42~45. It is slightly higher in hybrid mode than in battery hold mode, which seems reasonable.
It seems the ICE is off during low speed, during coasting, and during braking. And all these were counted as EV mileage.


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