Understanding Prime Reported MPG With EV Mode Capacity

Gasoline only does not happen , hybrid mode exists only when battery is below a certain level, after 40 miles there is still usable battery power hense hybrid mode kicks in

 

No. The EV only range will only use about 70% of the battery before HV mode kicks in. The remaining 30% wll be used and maintained to operate in true HV mode.

 

There is always (HV) Hybrid Mode available in all Prius models that are functioning correctly. That includes all Prius Primes. When EV range runs out the Prius Prime behaves almost exactly like a non-Prime Prius. It all depends on exactly how technical one wants to get about exactly what the Prime is doing when it runs out of EV range, and what the set of sensor readings are at that time for temps, speed, throttle position. and probably others as well.

Gen 5 Primes programming is slightly different than Gen 4 Primes programming from what has been posted about it. It's complicated to explain what its behavior is going to be generally, due to the ways it can change when the ECU's (computers) read the sensor data that controls both the EV and HV modes and how the switch from EV to HV and / or the switch from HV to EV work under the conditions the ECU read from the sensors.

It all depends on what one calls terrible mpg. If a driver is expecting 999.9 mpg (like when a trip is all EV, than yes, when HV mode kicks in after running out of EV range, mpgs drops like a stone (very quickly) from 999.9 mpg to 700, 600, 500, 400, 300, 200, etc and evens out below 100 mpg after driving in HV mode, especially if the engine has to complete it's warm up cycle right after running out of EV range and driving at high speeds and / or in cold temps.

 

What’s everyone’s opinion on at what speed to switch from EV to HV?

I can complete my round trip commute on EV only if I keep my highway return trip around 60 mph, anything much over and HV kicks on a couple miles before I get home usually.

My normal commute is backroads then into suburban driving into the city where I can get really good EV mileage (about 18 mile trip) due to all the regen. Normally I take the highway home and that’s around 21 miles and totally tanks the EV range quickly.

I fully understand it makes more sense just to hit HV mode once I get to the highway (I 95) and I have been trying both ways as well as taking notes on different CC set speeds with just EV.

There are a couple shorter stretches on my commute in where speeds get up to 55-60 and I tend to just leave it in EV, wondering if best to switch up often or just leave it and only switch up on the major highway drive on my way home.

At what consistent speed does it make more sense to switch over to HV? 50? 55? 60?

Might sound silly but to me it seems wasteful getting home with 75% of my charge remaining, which has happened the few times I’ve tried switching up between EV/HV often. I know EV will almost always be cheaper than gas with at home charging but I’m trying to find that balance I guess you can say.

 

I don't think anyone has done the work to answer that yet. Need the steady state efficiencies of both modes to see where the drop in EV mode makes sense to switch to HV.

If the engine is going to come on just before getting home, I'd just turn on HV when first getting onto the highway. Then let it run long enough to get the oil warmed up, and keep it on for a little more. Maybe you'll have grid charge left when arriving, but the engine coming on a mile before destination is the same as doing an extremely short trip to it. The unused charge isn't lost.

With the coming winter temps, you'll be using the engine more. Making testing difficult now.

 

I agree that it's wasteful to have a lot of charge left after a roundtrip commute. If I was commuting every day, my roundtrip commute would be nearly 80 miles. I adjust my use of EV vs HV to ensure I have little to no available EV charge left. I generally don't use speed as a guide when switching between the two modes. I start out in EV mode and once I leave the town limits and hit the highway, I switch over to HV. I pass thru a couple small towns on my commute to Portland so I switch to EV mode when I pass thru. Once I'm on the freeway for the final leg into downtown I switch to HV until I exit. Since I only commute one day per week, I use my in-office day to stop by for my weekly visit with my 90 year old mother. I charge up at her place and drive the 35 miles home early the next morning using EV only. With this weekly schedule plus my weekend running around, I usually charge up no more than four times per week.

 

What is wasteful about getting home with 75% EV range left? Sounds to me like you could go 2 days on one full charge. Nobody says you always have to run the full charge every time either, although I believe that is how most charge their Prime. Same as me most of the time.
You'll see after the first hard freeze that the warmup cycle takes longer and tanks mpg a lot more the faster you are driving, when switching from EV to HV. The same principles apply in warmer weather, they are just harder to notice when it's warmer and the car behaves so much differently.

 

On my round-trip commute, I don't use charging stations since the downtown parking garage I use does not have any. Using HV mode on the highways/freeways allows me to use EV mode where it's most efficient, in-city and stop and go driving in smaller towns. If I had free charging available in downtown Portland, I would use EV as much as possible on my commute.

What will be interesting is when I take a two week road trip next year to Utah and Arizona. Not sure I will have any free EV charging available. Some areas may not have any charging available at all. But that is why I have a plug-in Hybrid so I won't have EV range anxiety. Still, would be nice to have the solar charging roof but that is not available where I live.

 

When I have more driving to do than EV range, my choices depend on the particulars of the journey, but there are really two precepts that I follow, which have to be balanced against each other:

1. Use HV when there is a greater need for power/acceleration (climbing a mountain, driving at highway speeds). Save the battery for lower-power needs.

2. Try to minimize the difference in time from first using HV to its last use. The idea here is to minimize heat wasted warming up the engine – if you have to use the engine, ideally you want to warm it up only once. For instance, using HV only for the highway portion of the return leg of a trip that is just beyond EV range, rather than for the highway portion of each leg.

Bonus weather factor: Consider that you may get more EV range when the car is cold soaked, if you use HV early in the trip. That "waste" heat is put to good use by the Prime!

 

It is sad you cannot enjoy the "Predictive EV drive" that is available in EU on the PHEV, for the best SOC management on a given trip programmed in the Navigation system. I fail to understand why you dont have it.

First experiments in EU shows a really brilliant management, particularly if the trip have differences in elevation ad/or highway in between. You end spot on with 0% SOC available with great accuracy.

As soon i'll have my PHEV (top trim with PV roof) in January i'll post some trip data to understand the logic.

Edit: The Navi allows to put your final destination as an intermediate stop so you can also program a charge to be depleted in a trip that includes coming back to the start.