Interesting Mileage Observation Today

I've heard this on the forums as well, but it doesn't make sense to me. Going 2 miles on battery power give you infinite mpg. You can't glide for 2 miles, so you would have to use the engine to keep the battery charged, meaning maybe ~50-60mpg. I think infinite, plus a little lower mileage to recharge later, beats the alternative every time. I think the less time the ICE is on the better.

I'm sure everyone will disagree, but I'm averaging 60mpg.

 

You would be better served in most case by pulsing and gliding instead of trying to use battery only or ICE only in such situations. Draining the battery to the point the ICE needs to recharge it causes losses as does trying to just use the ICE mainly. Better to a modified pulse and glide depending on how many stop signs there are on that two mile stretch.

 

I mainly use my Prius C to commute to work which is 80 miles one way and I get on average 50 MPG at around 65-72 MPH.

 

If you don't have the opportunity to brake or coast often enough, then it's exactly as you describe. The energy used to recharge the battery may use up some of the savings from driving on battery alone. But I think it's pretty rare that it will wipe out all the savings. There are lots of variables, and even the same route can be different depending on traffic and how many red lights and left turners you encounter.

Sometimes you have to make these opportunities to coast that you might not have noticed before. There are plenty of them on rural and city roads. Not as much on highways. After a while, you get used to slowing down earlier than you used to BP (before Prius). I stopped tailgating years ago, but have found since getting my C that if I keep a 1 car length for every 10 MPH distance at all times, I do plenty of coasting, and never worry at all about being in EV mode too often.

 

This is a complicated issue, but your theory is definitely wrong. The reason you're wrong is because of the cost of converting energy. The Prius battery charges in one of two ways... power regeneration during braking and using the ICE to generate power. Regenerating power during braking is a good thing and helps to reclaim some energy that would otherwise be lost, however, it's not really a significant factor in keeping the Prius batteries charged. For the most part the batters are charged almost entirely by using the ICE to generate power, and as you know, the ICE uses gas to generate that power.

However, as I stated above, nothing is 100% efficient. There is energy lost to heat and friction when the generator is running and producing power. There is more energy lost when that power is used to charge the batteries and additional energy is lost when the batteries are used to power the electric motor to move you forward. Due to these losses it would be more efficient to use the ICE to directly power the wheels and move the car forward than to use the ICE to generate power to charge the battery, then use the battery to drive an electric motor to move you forward.

Sure, you get infinite MPG while the ICE is off and you're using the battery to move the car, however, when the ICE does fire up to recharge the battery to replace the power you used it will use more gas than if you had just used the ICE in the first place.

Of course, this leads to the question of why even bother to have a hybrid vehicle at all if running on electric power is so inefficient. And, like the answer above, this answer is also rather complicated.

The issue is that the ICE operates most efficiently at certain RPM ranges and under certain load conditions. And the Atkinson cycle engine that the Prius uses can be even more efficient than a standard engine, however, it also has an even more narrow band where it is most efficient. The beauty of the hybrid vehicle is that it can utilize the electric portion in conjunction with the Atkinson cycle engine to help keep that engine operating in it's most efficient range.

If you start accelerating hard and that otherwise would cause the engine to work too hard for maximum efficiency then the hybrid can use the electric motor to handle some of that load so the engine can stay in it's most efficient range. If you start going down a hill or traveling slowly down a surface street and the ICE doesn't have enough load to operate efficiently then the hybrid can turn on the generator and increase the load on the ICE to charge the battery, or simply turn off the ICE entirely and operate on electricity only.

Toyota has worked very hard to make sure that the gas and electric systems work in sync and operate the vehicle as efficiently as possible under all circumstances and just letting it do it's thing without trying to force it into electric only mode will usually result in the best overall fuel economy numbers over the whole trip. I'll admit that it can be fun to see MPG and watch as your average MPG numbers quickly raise as you're running in electric only mode, however, you'll take an MPG hit once the ICE fires back up again and it needs to recharge that battery and your MPG average for the whole trip will be lower than it otherwise would have been.

 

BrettS, that was actually a really enlightening explanation, thanks!

 

I learned a lot from your post...thanks BrettS!

I think this reinforces my gut instinct to mostly just drive the car instead of over thinking it much. For the most part, the car is smarter than me in choosing what engine to run. My job is to not stomp too hard on any pedals ;-)

 

The problem is, to recharge the battery with the engine in just 2 miles, mpg during recharge won't a little lower, it will be a lot lower, like under 25-30 mpg. Then review the arithmetic of averaging. Infinite mpg for 2 miles, followed by 25-30 mpg for 2 more miles, averages out to just 50-60 mpg overall for the 4 total miles.

A lot of people get tripped up when 'averaging' different mpgs, because the correct arithmetic is not the straightforward intuitive method commonly used for most other averaging. Instead, one must first compute the total fuel used, then divide that into the total distance traveled.

This is where the European fuel economy measure, liter/100km, is superior our bass-ackwards MPG scale. We'd be better served using Gallons/100 miles instead of Miles/gallon, because it produces simpler math and a linear scale, leading many to a better intuitive understand about what is really happening.

This part is true. But gliding without energy conversion generally beats multiple energy conversions.

 

The main thing to keep in mind is that as sweet as this car is, its still not a EV so don't try and make act like one. Also as sweet as this car is, its not a race car so don't try and make it act as one.Yes there are times to use your battery and yes there are times to just the ICE.

Just remember it is a hybrid, and the system is called hybrid synergy drive. You need both systems (don't really NEED a ICE could of got a real EV) to work together but the MOST important pice of the system is the driver. Thinking about how the car works and maximizing it strengths and minimizing it weaknesses is the difference between getting EPA and crushing EPA.

Now that said getting "only" the EPA of 50 mpg on this car still kicks butt. So drive how ever you dame well please, be it fast or slow or efficient.

 

Yesterday on my commute home, there was a traffic accident on the highway. For a stretch of about 4 miles, my speed ranged only from 3-8 mph. Bumper to bumper, stop and go. Unavoidable. Naturally the car went into EV mode for most of that time, causing the battery to go down to two bars. Even though I was forced to brake a lot, it was only light braking and wasn't enough, so the ICE came on frequently to keep the battery it at minimum charge.

When I started that 4 mile stretch of bumper to bumper, my average MPG was at 54.3. When I got by the wreck and traffic broke free, I was at 57.4 MPG. So even through a heavy period of ICE use just to keep the battery charged, I still managed a net gain in MPG. The computer does not attempt to recharge the battery to optimum levels in situations like this, only keep it at minimum. Conditions vary, of course, and had this 4 miles been all uphill, the gas use would have been considerably higher as it would be needed for more than just charging, and my net MPG probably would have dropped. But as an example of how the car balances ICE use and battery use, I think it's very telling. This is a smart machine and I suspect there is little need to worry about too much ICE use in most everyday driving.

 

Last night I finally had that moment when things started to "click" mentally about how to drive my C. It was a very Luke Skywalker moment: I turned off the eco score that I'd been obsessing over, and just paid attention to how the car felt. I think I could even hear Old Ben Kenobi's voice echoing "use the synergy drive, Luke" in my head. Anyway, whatever it was worked, and over my 100km trip, and I got 3.8L/100km (62mpg!!!)

Realistically, the car seems to really love nice uninterrupted stretches at 60-80km/h, where the ICE is purring not growling, and can either feed the battery or share the load as the conditions require.

Also interesting, the only other time I got close to this kind of real-world economy (outside of short downhill trips on EV) was when I was first driving it back from the dealership. I wasn't reading screens, just driving gently because it was my new baby! I think your gut can tell you better than any screen whether you are stressing the engine.

 

Also had an interesting observation in mileage change. Our city mileage average increased 10 mpgs to 59.5 average with 85 miles on the town trip so far and has stayed that way for the entire weekend. Don't understand why the increase as the winter fuel is out. The only difference I can explain is we are not using the air conditioning as the weather is finally changed here but it couldn't be that huge of a difference? The car now has over 3,000 miles for a good break-in and we are feeling more comfortable driving it and letting off the gas pedal to allow the ev to automatically operate. Not sure, but Wow! A complete surprise.

 

A/C sucks gas out of the car pretty pretty fast and i would not dismiss no a/c as not being the route of the mpg difference. I for one has not used my a/c in a long long, LONG time.

 

I stopped using my A/C a couple of times going to work to see if that made a difference and I saw no difference in gas mileage. My round trip commute is about 170 miles doing around 70-73 MPH and I get on average 50 MPG

 

Don't know what's up but will continue monitoring it this week.

 

OK, I had a freaky-weird drive to work today (as far as mpg go). So....here's the scenario:
As of Friday night, I had about 2500 miles on the car.
I've averaged 55mpg, but that has dropped a bit lately.
Starting last week, my normal drive to work went from low 50s to high 40s - chalked up to a combo of cooler morning temps and winter blend fuel.
I drove 5 hours (at about 55 mph) to Oregon Sat morning on WA gas - averaged 52 mpg (on I-5). I HAD to stay at 55 to get the 52 mpg.
On the trip home, I refilled the tank in Oregon, and had 62 mpg going 60 mph to the Oregon border, then finished the trip at 54 mpg going 70 mph most of the way through WA.
Right at 3000 miles now (so....yes, I spent about 9 hours driving on Saturday) - and btw, the C was fabulous on the freeway!

THIS morning I did my USUAL drive to work and averaged....77.5 mpg. 77.5. I still can't believe it.

So, what's different? I think for starters I got a tank of summer blend in Oregon versus maybe having driven on winter blend my last tank or two here in WA (I've wondered if it was really the cool mornings or a change to winter blend because for the last couple weeks I've had trouble hitting 50 mpg).

But....also, I'm wondering, did my engine just finally settle in with that long drive? Because, SERIOUSLY, 77.5?? That's not just summer blend fuel in my mind. (and I got regular unleaded both times).

Curious what you more experienced hybrid or techie guys & gals might think is going on.....

 

Hmm.. could be a combination. Did you happen to have more juice in the battery after the Oregon trip and ended with less when you got to work?

 

Crazy, I wonder if we are hitting a break-in break through? As we both are hitting the 3,000 mile mark on the odo. Or just other factors going on? Strange.