Op-Ed: More All Electric Miles Equal Less Range Extender Need For 2nd Gen Chevrolet Volt

The 2nd Gen Chevrolet Volt Volt Gen 2 Would Benefit From A Smaller, Lighter Pure Series Range Extender.

With More Electric Range Comes The Need For Less Range Extender

I think we would all agree that, as AER increases, the need for a range extender decreases. This is depicted graphically in figure 1.

If we have an EV with 200-300 miles range, no range extender is required: witness Tesla Model S. If we have an EV with 100 miles range, a small range extender will suffice: witness BMW i3.

How does the Volt fit into this picture? We need to put some numbers to the words. (Engineers love numbers..yes?)

What Does Voltstats Say?

GM pitched the Volt by saying: “We will just make the battery big enough to cover the daily driving distance of the average driver of 40 miles.”

But how many miles does the average fleet driver really drive in a day?

50 Mile Mark Is More The Sweet Spot

Referring to figure 2, we see a high concentration of drivers at the 50 mile mark using the range extender. Also, referring to figure 3 we see an average fleet MPG of 135 miles/gallon.

Figure 3 (click to enlarge)

In figure 4 the AER/ER split is calculated that gets 50 miles total range and 135 MPG. The breakdown of the average fleet driver is: 36 miles on electricity and 14 miles on gas for a total of 50 miles. The 36 mile AER is probably less than 40 because some of the fleet miles are in cold weather.

Not Use Of Sophisticated Technology To Highlight # Miles

Using this average driving cycle, we can now derive partial derivatives (influence coefficients) for the effect of AER and ICE cycle efficiency on fleet fuel consumption.

Just 5 More Miles Of AER Makes A Big Difference

Figure 5 shows that adding only 5 miles of AER has a HUGE effect on fleet fuel consumption equaling a whopping36% savings in fuel.

How does this compare with a more efficient range extender? Often discussed is a turbo 3 cylinder for Volt Gen 2. It is expected that the turbo 3 would have approximately 10% better cycle efficiency than the current Volt ICE.

The comparison of the influence coefficients is presented in figure6.

Demonstration Of Better Use Of Resources To Provide More AER Than Engine Efficiency

Five more miles of AER decreases fuel consumption by 36% while going to a Turbo 3 cylinder decreases fuel consumption by only 10%. The influence of AER is nearly 4 times as great as the influence of the Turbo 3.

Keep in mind that one of the goals for gen 2 Volt is to reduce costs. GM’s turbo 3 undoubtedly will be a pricy piece of equipment compared to the current 1.4, 4 cylinder. Is this costlier range extender justified? I say no. One would be better off by increasing AER instead.

But you say: “How much does another 5 miles AER cost? Batteries are exensive. Wouldn’t it be cheaper to go with the turbo 3 than with expensive batteries?” Again I say no. The cost of another 5 miles AER is zero. All we do is switch to Spark EV chemistry which is more robust and has a higher cycle life. We increase DOD to achieve the added 5 miles of range. Spark EV DOD is 80% versus 65% for the Volt. That is a 23% increase and it is worth an equivalent percentage increase in AER of 9 miles. Spark EV battery article found here (http://gm-volt.com/2013/08/02/spark-ev-versus-volt-battery/).

A more expensive range extender is not justified.

Conclusion

Volt Gen 2 With Smaller Range Extender/Single Transmission Is The Way To Go

Volt Gen 2 would benefit from a smaller, lighter pure series range extender. Not only do we save money on the range extender, we save money on the transmission. We can eliminate the costly 2 mode transmission we have now.

We could have a Gen 2 Volt that is:

• Lower cost
• Lower weight
• Higher performance
• More Interior room

It is hard to argue against that combo.

Real World All-Electric Range in the Chevrolet Volt During Winter Traffic Jams

Chevy Volt Driver Information Display









The EPA has determined through testing that the Chevy Volt would go a typical 35 miles on a full battery charged. Using the full 10.4 kwh of stored battery energy available, GM has determined the majority of drivers will experience from 25 to 50 miles of range.

There are several examples in which journalists and fellow advisory board drivers have gotten more than 50 miles of range in their Volts.

Today I report on my first experiences just barely crossing or not even reaching the 25 mile threshold when the engine came on.

This first time I left home on my typical daily commute with a full charge. It was a cold day of 32 degrees outside. I had the cabin temperature set to comfort mode of 72 degrees with a medium fan speed and one bar (out of three) on the heated seat control.

My drive is almost all highway with 65 MPH speed limit. I traveled mostly at that speed plus or minus a few miles per hour, and was using the Normal as opposed to Sport mode setting. Mostly I kept the car in D, or coast brake setting.

At about 11 miles into my journey I hit standstill traffic resulting from an accident on the highway. Helicopters were circling and I spent about 40 minutes in a very minimal crawl as two lanes were funneled into one in which extensive rubber necking took place.

During the stop and go portion I left the car in L mode to use motor braking, and covered about 4 or 5 miles.

After, traffic moved smoothly, and I arrived to my office parking garage just feet from my parking spot and waiting outlet when the generator went on at 25.3 miles.

On warmer days I would have arrived with about 8 miles to spare, indicating the significant drain from being in standstill traffic for 40 minutes with the cabin temp cooking.

Thus my first experience only getting 25 miles per range had less to do with extreme cold temperatures or aggressive driving style, but more to do with unexpected traffic.

On two subsequent driving days, I experienced just below 25 miles of range, with the lowest being 24.4 miles. These days were colder, in the low 20s, and included a bit more use of the Sport mode, though not continuous. In neither case did I drive meaningfully above 70 mph. The day with the lowest range included a 20 minute traffic jam.

Most recently I drove to work after the Northeast snowstorm and several of my low speed roads were a bit thickened with snow. This extra tractive effort seemed to drain a lot from the battery. The temperature was again about 30 degrees and this time I kept the cabin at 74 degrees of comfort mode. I did not use Sport mode at all and kept my speed around 65 MPH. The engine went on after 22.7 miles.

Using aggressive cabin heating combined with high speed highway driving in sub freezing weather may lead to electric ranges of less than 25 miles.

Source: GM-Volt.com