Prius Prime Plus in my hands

As I was planning to retire, I visited the local Toyota dealer thinking my decade of Prius and recent plug-in experience might be useful. Only it turns out their sales goals are Camry. I crossed 'car salesman' off my bucket list.

Bob Wilson

 

Ok, now we've got some new data.

STUNT:

"Drive Monitor 2" appears to have a latent bug that it only goes to 4.6 miles/kWh. In contrast, there is the true log:

The Aug. 8 drive was after midnight in a light drizzle. So headlights, intermittent wipers, and fan on to handle the high humidity conditions. Wet streets increase rolling drag along with the water that impacts the car and drips off.

Here is what happens in charge mode at a constant 35 mph:

On a standard day, we would expect:

Now we were already dealing with drizzle, night driving so there is some lose due to weather and time of day. But we have a rough order of magnitude:

	mode	miles	MPG	gallons	SOC %
1	Std. day	11.9	97	0.123	0%
2	Chg mode	11.9	36.9	0.322	44%

• 0.322 - 0.123 = 0.199 gal for 44%
• 0.00452 gal / 1 % SOC
• 0.362 gal ~= 80% SOC, maximum SOC achieved in CHARGE mode
• ~20 minutes to get 44% -> ~37 minutes

Bob Wilson

 

Thanks, I added "37 minutes" for 80% charge.

Bob Wilson

 

I am embarrassed. When I post in the BMW forums, I typically use SAE and Standard Units, but I've grown lazy. So let's add this:

• 5.1 kWh ~= 80% SOC
• 1.37 l ~= 80% SOC
• 0.362 gal ~= 80% SOC

So now we can do some simple maths in Huntsville, AL:

• $0.10/kWh * 5.1kWh ~= $0.51 for 80% charge
• $2.00/gal * 0.362 gal ~= $0.72 for 80% charge

I will try to be better with standard units in the future.

Bob Wilson

 

I try to be accurate but given Toyota claims 40% efficiency for their engine, I'm not too worried about 40% vs 42%. As for the difference, I don't have much control over the SOC level of the HV region SOC and at 35 mph (58 km/h), there can be significant differences. But the SOC % level only measures the reported EV range above the HV, SOC levels. I would expect the ambiguous HV levels to be the most likely source of any error.

I have thought about variations to the protocol including a longer drive done at a higher speed, say 65 mph (104 km/h):

• Exhaust the battery SOC
• Do 10-20 minutes warm-up at 65 mph (104 km/h)
• Run mileage test, ~40 miles (64 km) at 65 mph (104 km/h) - baseline MPG
• Re-run mileage test, ~40 miles (64 km) at 65 mph (104 km/h) in CHARGE mode - difference

At a higher speed, the car has less opportunity to turn off the engine and the HV battery level should be less subject to change. It is also long enough to achieve 80% SOC in CHARGE mode.

Bob Wilson

ps. We need to discuss the assumptions used to calculate the gasoline energy. In the USA, we have two gasoline mixes: summer and winter. We also have variations in ethanol that are never accurately described at the retail point of sale. It is an imprecise metric and we probably need to evaluate a range, a minimum and maximum.

pps. After doing my mph vs MPG chart, I added shims to the rear wheels to adjust the excessive, negative camber. Also, my benchmarks were at Toyota tire pressures but I normally run maximum sidewall. These could also contribute to the higher than expected efficiency. I prefer to share 'as built' data rather than my tuned configuration. I honestly forgot about them.

There are some who go out of their way to claim exceptional performance which I avoid. So my mph vs MPG chart reflects what anyone who has not 'tuned' their Prius Prime should achieve. But by accident or carelessness, this original chart inflated the performance AFTER tuning when I was trying to measure CHARGE characteristics.

The updated test protocol should solve that problem because the same test item will be used before and after. Not the 'as built', untuned Prime I drove home from Rhode Island.

WARNING! - I do not claim my tuning has any quantifiable result. Rather it is an uncontrolled variable in this experiment. I am not done with my tuning and am about 600 miles away from my second transaxle oil change. I also have front wheel camber adjustments pending. I tune my cars for my own enjoyment. I'll share what I do but that is all.

 

I checked Wiki and in the USA, we different grades:

• 33.56 kWh/gal - summer grade
• 32.97 kWh/gal - winter grade
• 32.78 kWh/gal - E10

When I ran the same model with the different grades, I got a range of efficiencies, 42.0%-43.0%. What this suggests is the different grades could have accounted for ~1% difference in the apparent efficiency. The new test procedure uses the same tank of gas so we don't have to compare results separated by eight months.

Bob Wilson

 

More higher speed, 90F (32C) tests:

	charge	mph	MPG	distance	gasoline
1	14%	65	46.0	16.1	0.350
2	0%	65	58.5	14.2	0.243

• estimated HV gas - (16.1 / 14.2) * 0.243 ~= 0.276
• 0.350 - 0.276 = 0.074 gal for 14%
• ~0.00529 gal / %
• ~0.423 gal for 80%

Bob Wilson

 

A few quick updates:


Temporary tag pending final:


Problem with extension cords, primarily the socket:

I have already tried a weather-proof plug and socket that did not work. So I'm going with a NEMA 5-20 in a exterior junction box.

Bob Wilson

 

The Fall weather arrived a couple of days ago with night time lows of 40F. Sure enough the ~30 mile range returned to just over 25 miles, the EPA spec. With the cool weather, the tire pressure alarm came on. As I filled the tires this morning to 47.5 psi, the initial pressure ranged from 30-34 psi. I run about 10 psi over the door jam pressure so when they inevitably leak, I'll get an alarm at door jam pressure.

Bob Wilson