Can using CHG Mode be more efficient?

For this experiment, the SoC level should be started at 0%. I am not comparing wall-charged EV mode. The question is, does converting gasoline energy to electric energy and using it on EV mode make it more efficient than just driving the car on the HV mode. Charging the battery from the wall complicates the comparison.

 

No. To keep the comparison simple, I will only drive on either in CHG mode or in EV mode (from CHG mode SoC only). There will be no switching back and forth. This way, the HV mode will be always driven with 0% SoC in either case. Besides, I have done driving my 2017 PP with 0% SoC or 100% SoC, but all drives on HV mode. Under my driving condition, I did not see noticeable differences in mpg. Maybe in very congested stop-and-go traffic under hypermiling conditions, you are seeing HV efficiency differences with or without SoC, but under my normal driving condition of ~35mph no stop-and-go traffic for ~40miles trips, there seems to be SoC has no effect on mpg.

 

I completely disagree. As I said, I have never seen any mpg gain on HV mode drive with SoC compared to without SoC under my driving conditions. So, that 5 mpg gain you are suggesting is absolutely irrelevant under my usual driving conditions. And, even if there is some benefit of mpg gain with SoC, that is just fine. As long as SoC gained is from CHG mode, then it is using the gasoline engine to gain that SoC which is now contributing to the overall mpg gain. So that is an overall increase in efficiency with the use of CHG mode compared to without using CHG mode. It is not a comparison of HV mode vs CHG mode. As we all know CHG mode mpg is always lower than similarly driven HV mode. I am trying to compare the overall efficiency with CHG mode and subsequent EV mode from the SoC gained vs. simply driving with HV mode. As long as the use of CHG mode for the same driving condition gets better mpg than without the use of CHG mode, then my original question is answered unequivocally as "Yes, under certain driving conditions using CHG mode can be more efficient than without using CHG mode."

 

It is not my goal to achieve the best possible fuel economy in HV driving. That is where you are making the wrong assumption. It is not about hypermiling PP by constantly driving under 30mph with very slow acceleration and deceleration and maximizing the regen in between to achieve the highest mpg possible. You have done that with your PP, and many others have done it with previous generations of Prius to achieve seemingly impossible high mpg. I have seen the record of Gen2 drivers getting over 100mpg, so I know it is possible.

But that's not the point I am trying to test. I am certainly not trying to beat your mpg record by using CHG mode on my trips. Being possible is not always practical for day-to-day driving situations. What I am interested to test is under my normal driving conditions without any particular hypermiling techniques deployed, can using CHG mode be more efficient than not using CHG mode for the overall efficiency. I initially thought the answer was flat out "NO", but I am having some reservation to that notion now that I have seen some evidence that CHG mode use can sometimes be beneficial to the overall fuel economy. And for testing that, the SoC level is irrelevant. Of course, I can test it with some SoC left in the battery, but the use of the wall charge on any portion of driving is going to complicate the comparison. Plus trying to finish the travel with exactly at the SoC I started is going to be way too difficult than just using up all the SoC produced by CHG mode. If your intuition tells us that driving PP without SoC making it a pure Gen4 Prius hybrid car is going to be less efficient than having a larger traction battery to stock up the energy by using CHG mode and later on EV mode, then that is exactly what I want to test.

 

Again, it doesn't matter what SoC it is on. I am not comparing EV range or EV efficiency. The only thing I am looking at is the overall mpg for the same trip under similar driving conditions (since I can't control every variable, so it will not be identical).

 

Just like any variations of numbers in trials, it has to be averaged out. One experiment is not enough to show the conclusive result one way or another. If the beginning and ending SoC affect the result, then so be it, that's the natural variable just like everything else, like temperature, weather, wind, etc. Again, SoC can be set at 10% to start and finish, but that will make the driving so difficult and not likely the example of my ordinally day-to-day driving condition. The easiest way to do the testing is just to drive without having any wall charge. That way there is no contribution of electricity fed to the traction battery other than the engine under the CHG mode.

 

Well, I went to town today and saw the gas price jumped to $3.25/gal. I am postponing CHG vs HV efficiency testing. At least for a while, unless I have to do some unplanned longer drive when there is no time to charge my car. Most of my current regular drivings are within the EV range of ~37 miles. Especially I now have free L2 charge stations at work, my commuting can be driven 100% EV without paying anything. There is no point in buying gas to generate electricity using CHG mode to do the testing. For the first time owing PP over 4 years, the EV mode is the most cost-effective way of transportation.

 

However, this is going to hurt me going into winter. I have to run on HV mode at least in the morning for heat. Oh, and I also have to buy oil to heat our house...

 

Today was unseasonably warm, but we already had a light frost last week. It is a matter of time, I have to turn up the thermostat above 60F. I just had #2 oil delivered to fill the tank for the first half of the heating season. I paid $2.95/gal. That's more than double what I paid last year. The highest price in 7 years. The last time I paid above $3/gal for heating oil was the first half of 2014.