Details on EPA test of Volt & Leaf : Response to FOIA Request

Thanks for posting. I will digest the information tomorrow.

 

Good information. With the test the way they are I think we need to use a fudge factor. That said they really need to revise the tests so that a smaller safety factor is used. On hybrids the big eye opener for me was short trips, and how much that deteriorated my real world mileage. On EVs guidelines that should be published to show the effects of heat and air conditioning in the test. For everything we should have test runs that more closely move where Americans ride. 35miles and 73 miles are good ev ranges for many drivers, and the important thing is that consumers get good information.

 

Some interesting info I dug out.

Interior Volume (including Prius for comparison)

Prius: 93.7 Passenger + 21.6 Luggage = 115.3 cu.ft.
Leaf: 90 Passenger + 23 Luggage = 113 cu.ft.
Volt: 90 Passenger + 18 Luggage = 108 cu.ft.

Since Midsize is 110 to 119 cu.ft, both Leaf and Prius were catagorized as Midsize and Volt as Compact. I thought GM said Volt's luggage volume is 10.6 cu.ft.

Battery Capacity

Leaf: 360v x 66 Ah = 23.76 kWh
Volt: 348v x 45 Ah = 15.66 kWh

 

If the Volt goes 35 miles electric and the Leaf goes 100, How can that be? You'd think that either the volt would be less than 11kWh or the leaf would be over 30kWh ... even after factoring the weight disadvantage of the Volt's ICE.

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EPA range for Volt is 35 miles and Leaf is 73 miles. Leaf is also more efficient (34kWh per 100 miles) than Volt (36kWh per 100 miles). Leaf utilizes the battery with wider SOC window also.

 

How is the "fudge factor" calculated?
The documents in the link suggest that it can be "up to" 30%.
If I remember what I saw on EPA pages giving raw and adjusted test numbers, the percentage really does differ from car to car, and the percentage difference between raw and adjusted numbers seemed high for the Prius (I guess about 30%).
Why are they different for different cars?
Thanks to whoever can answer!

 

If you download the a datafile from Download Fuel Economy Data, the unadj columns are the numbers prior to being fudged.

The article I linked to from http://priuschat.com/forums/other-c...uth-about-epa-city-highway-mpg-estimates.html talks about about the old 10% fudging down for city and 22% for highway but then in 08, more test cycles were added.

 

The Car and Driver article is pretty good, but it doesn't say how the fudge factor is calculated and why it might be a bit different for each vehicle, as it appears to be from a quick glance at the EPA datafile. (OR am I wrong about that??)

 

I can't speak to the "a bit different for each vehicle", but prior to model year 2008, it was a straightforward 10% downward for city and 22% for highway. It's mentioned at Fuel Economy - On-road Vehicles and Engines | Cars and Light Trucks | US - EPA and EPA's Fuel Economy Programs | Fuel Economy | US EPA.

I think for MY08 and beyond, it's more complicated since per EPA's Fuel Economy Programs | Fuel Economy | US EPA

For example, I don't believe the 08 and 09 Priuses were retested w/the 5 tests and were just adjusted by formula.

If you download the 07 datafile and do the 10% and 22% adjustments to the Prius, you should arrive at the right sticker (for the time) 60 mpg city and 51 mpg highway numbers. I did and it should hold true for all the cars there.

 

I like the Leads efficiency over the Volt but do not like the wider SOC window and even worse the lack of an active battery temperature management system.

The Volt not only can heat its battery but it has a better cooling system as well. I still trust the Leaf but I think there will be more warranty issues with the battery. Thankfully the warranty is eight years on both and I do think that is enough.

 

Leaf does have active cooling like Prius. It is air cooled.

Volt does have liquid cooling because it uses the battery pack twice as hard as the Leaf! Volt has more powerful electric motor to move more mass (gas powertrain gets free piggyback ride) and smaller battery. Therefore, it is forced to use narrower SOC.

 

Little has come out yet, but the Focus BEV is supposed to have an active heating system for its battery like the Volt. Keeping the battery at the preferred temperature while charging allows the battery to more efficiently accept the charge and reach full capacity.

Nissan choose to go without an active heating system to cut costs, and I suspect to get to market sooner.