Record your Prime and Gas Fill-ups

Too late! I'm starting another week, 7 days, of pure EV. Then I'll burn just enough gas to knock it down from 199.9 and top off the tank. <GRINS>

Bob Wilson

 

She continues to live with me since 1977 and still as young in spirit, gentle in kindness, and periodic ornery as when I first met her. She still laughs at my jokes. But there are some prime technical questions:

1. Can I drive a prime a week without charging? - A. Yes, 301 miles, by charging during lunch at nearby chargers, 1 mile or closer, to wipe-out the morning commute miles. Then running errands, shop where there are chargers on the way home to wipe-out the trip to the shopping centers. In effect, I only have to pay for the last leg home, less than my work commute, ~9 miles. At 16A, L2 chargers add 10 miles of EV for every hour.
2. How are indicated MPG calculated? - A. I don't know, yet. Setting Trip A to a non-trivial number of miles, we know it will clamp at 199.9 MPG even after 301 miles. What is it using for the divisor because the gallons are "0"? So once I've got a non-trivial number of EV miles, ~100 miles, I'll reset the second trip meter and drive in normal HV/EV mode but continue to monitor the original EV MPG. Eventually the EV MPG will take a step down from 199.9 MPG and at that point I will pull over and take a photo of both trip meters to calculate an equivalent divisor for EV miles. I'll have to do it twice using a different number of EV miles, say ~200 miles, to detect and partially map any step functions.

These benchmarks will answer my questions so if someone reports any MPG in the range of 25:199.9, I can reverse engineer an equivalent profile, not exact, but an approximate driving profile.

We know from the Gen-1 and Gen-3 experience that someone will complain about their Prius Prime mileage. In the past it has been easy to spot the lead-footed in acceleration and highway speeds. But the 6.3-6.4 kWh battery throws a new twist in prime performance as well as the effects of intermediate charging. For example, charging on cross-country trips.

This car has the ability to drive 10 hours on a single tank of gas. The actual segments will be broken up by biology breaks, mostly bathroom. But what about meals? What strategy works best?

• Drive through fast food and eat in the car.
• Take a quick sit-down, 20 minutes, with and without charging.
• Take an hour with and without charging.
• Charging with and without a fee.

I know this seems somewhat obscure but I've had to face these questions from my first drive home of a BMW i3-REx from Charlotte NC to Huntsville AL.

Bob Wilson

 

You mean without payable charge? Also, 310 miles will not be EV only, include one 'housekeeping ICE session'.

 

Probably 0.0005 as the car reports miles in 0.1 intervals.

 

My protocol was to run Trip B in EV mode and Trip A when the car started the engine. Much to my chagrin, we had a cold morning with fogged up windows. When I hit front defrost, the engine started. OPPS! I only had 44 miles on the EV trip meter showing 199.9 MPG. Regardless, I reset Trip A and ran the rest of my drives in hybrid mode.

	trip-mode	miles	MPG	gallons
1	HV mode - A	23.5	57.7	0.41
2	EV mode - B	68.1	163.3	0.42
3
4	EV mode - A	14.4	199.0	0.07
5	HV mode - B	4.3	60.9	0.07

What this suggests is the EV mileage calculation may require a minimum of ~0.4 gallons be burned before it begins normal MPG calculations. This makes a lot of sense as divide by zero is undefined.

I need to run another set of tests with more EV miles and operate in HV mode. In contrast, the Gen-1 and Gen-3 always had a non-zero fuel consumption rate which we could see on the Scangauge and Techstream data. The engine controller was reporting fuel consumption, very small, even when the engine was off.

Although undocumented, I like this approach much better.

Bob Wilson

 

If I understand it correctly, ~0.4 gal were used during your 23 miles in HV mode, not the minimum burned before normal calculation begins (which I assume is way lower tan 0.4 gal).
I do not quite understand the purpose of your test as described:

If it is to find the 'artificial' denominator the system use in zero gallons situation - then it is not needed as it can be calculated as follows:
If the shortest distance the car reports on the display is 0.1 miles, forcing the display to overflow at this distance (showing 199.9 mpg) you need 0.0005 or smaller figure (0.1/200) if I was to write the algorithm I would use 0.0005 or gallons used whichever is greater.

If it is to find the gas volume meter resolution I would:
Reset trip meter, drive a distance in EV, switch to HV, take the reading (miles + mpg) immediately when mpg report jumps to real calculation.
If after (total) 6 miles it jumps to 188.5 mpg the resolution is ~0.032 gal (6/188.5), lower than this volume it reports zero.
If after (total) 16 miles it jumps to 179 mpg the resolution is ~0.09 gal.
Doing it for 3,4 distances can pinpoint the meter resolution quite accurately.

 

~0.4 gal were used during your 23 miles in HV mode, not the minimum burned before normal calculation begins (which I assume is way lower than 0.4 gal).​

Correct but curiously enough, the 199.9 MPG indicated did not change until enough gas was burned to register a value other than 199.9 MPG. But by accident, I'd only gone about 44 miles in EV mode. It turns out a smaller distance, say 20 miles in EV, would let me test if the minimum amount of fuel burned is all it takes to calculate a value less than 199.9 MPG.

I do not quite understand the purpose of your test as described:

If it is to find the 'artificial' denominator the system use in zero gallons situation - then it is not needed as it can be calculated as follows:
If the shortest distance the car reports on the display is 0.1 miles, forcing the display to overflow at this distance (showing 199.9 mpg) you need 0.0005 or smaller figure (0.1/200) if I was to write the algorithm I would use 0.0005 or gallons used whichever is greater.
​

My interest is understanding how the displays calculate the values shown. One piece of the puzzle is found.

If it is to find the gas volume meter resolution I would:
Reset trip meter, drive a distance in EV, switch to HV, take the reading (miles + mpg) immediately when mpg report jumps to real calculation.
If after (total) 6 miles it jumps to 188.5 mpg the resolution is ~0.032 gal (6/188.5), lower than this volume it reports zero.
If after (total) 16 miles it jumps to 179 mpg the resolution is ~0.09 gal.
Doing it for 3,4 distances can pinpoint the meter resolution quite accurately.​

Actually 'distance / MPG' gives a very accurate gallons of fuel burned. It is the distance that is wrong because the tires are undersized. Today I compared a constant indicated speed of 50 MPH and a GPS reported speed of 48 MPH. In effect, there is ~2% error. This is consistent with earlier Gen-1 and Gen-2 behavior.

To resolve the error, I'll drive ~100 miles and get a very accurate estimate, +/- 0.1%. Then I can use Tire Rack to search for a pair of tires that corrects the error.

Bob Wilson

 

toyota did a terrible job with mpg's in the pip, and now they've made it worse. they think they have people believing they're getting 83 mpg.

 

It's the new concept: If there is no gasoline flow - it is EV drive, no matter what mode you select. This will lead to terrible ICE only mpg, so what you do - you hide it.
What I miss with this concept is a report of kWh consumed (is there?) with it one can report: on a YY.Y miles trip I have done 83 mpg plus XX.X kWh which is the truth for the situation and acceptable.

 

• START EV first trip meter and let it run
• ENGINE ON, start second trip meter and let it run
• When first trip meter shows something other than 199.9 MPG, record both

The first trip meter will have both the EV and GAS usage. The second tells us the gas usage. Subtract the second from the first and you have the EV usage on that trip.

Bob Wilson

 

What is exactly 'EV usage'? usage of what?

 

I put the car in HV mode so it would run the engine as much as it does when in HV mode.

Bob Wilson

 

As I said, it is a new concept and personally I do not like it because:
- It leads to very horrible HV mpg, sometimes far below EPA rating. No wonder they are hiding HV miles. What you earn in EV miles when driving in HV mode you are loosing in mpg.
- PiP does not use it, no ICE miles in HV mode are used back to improve HV mpg.
- EPA does not use it in their rating.
- In fact, it is not Charge Sustained mode any more, it is charge addition mode.
- It can lead to artificially high EV range estimate when driving in a hilly area while big portion of this estimate are ICE generated miles not grid generated. Of course, you could achieve this with the PiP by gaming the system (playing with the HV/EV button), but here Toyota seems to game its own system.

The concept as I understand it is: 'raw' mpg (total miles i.e. HV+EV driven per gallons used) is all that is matters. I am not saying it is a bad concept, but certainly different.
At least I would expect them to report kWh used (consumed) in the trip report, alongside with total miles driven and 'raw' mpg.

 

I cannot edit any more so I want to add:
The points raised above (except for the last one) are valid IMO if you want to check HV efficiency of a single trip, starting with no EV miles or resting the trip meter when EV depleted and the car switches to HV mode.
As I understand from reports here, any regeneration charge accumulated in such a trip (i.e. generated by the ICE) is kept separate for later EV drive.
So, if this is true, then towards the end of the trip you have to manually switch to EV mode in order that these ICE generated miles will be added to the HV efficiency calculation and you will finish at the same SOC you started at, otherwise the calculated mpg for this trip will not represent the actual HV efficiency.
However, for multiple HV mode trips without grid charging in between, the trip meter mpg will represent actual more accurately, as at the beginning of the second trip the car will default on EV mode, adding the accumulated (ICE generated) EV miles into the calculation an so on.