Sweet Spot for Electric Only Driving

I do that too, but fear I'm building a traction battery debt that will cost fuel to replenish.

 

Research "pulse and glide"

 

Exactly, and the debt is greater than the gain.

Tom

 

The point is you will find the reasoning behind the method is exactly as said in post #2. When you use electric, you are forming a gas debt most of the time. You can put it off for a while, but eventually you have to recharge.

 

Yes but recharging it via the engine is less efficient then if it didn't need to be recharged at all. Yes electric is fun, but it is the opposite of efficiency without a plug-in conversion.

I use electric mode all the time around parking lots, moving the car out of the garage and back in again, or to carry 10 heavy garbage bags all the curb at once. No gas engine kicks on, no worry of a cold start problem later, and I take the mpg hit. But I do not gain efficiency with any of this.

 

Having seen and heard of driving in that area, I would say screw efficiency and just dont be killed or side swiped by a motorbike.

 

You want to use this in extreme moderation.
Recharging the battery using the gas engine means converting gas to kinetic motion, converting that to electric energy, storing that chemically in the battery, then when you need to use it, convert it chemically back to electrical power, converting that back to kinetic energy (wheel movement), with losses at each step.

It's much more efficient to pulse (go up to speed with the ICE gas engine), then glide with no electric or gas power for awhile, then use the gas engine again and repeat. This eliminates use of the battery and those conversion steps.

The primary benefits of the main battery is to allow the engine to turn off while gliding, coasting or stopped (or gentle acceleration for short periods of time if in stage 3, but this might be different for the Gen III Prius), without loss of power to accessories. It also provides extra power during acceleration, so a smaller engine can be used, and one that is more efficient but has less torque (atkinson cycle). Its benefit does not include driving the car only on electric power on a regular basis. This is a common misperception.

 

That's not a gas debt when it starts charging up with not moving. That is you finally having to pay the piper for bad driving style. The engine charges the battery no matter how low or high its SOC is (within limits). But it takes more to charge it when the SOC is low. So creeping along in traffic with electric only increases your debt. If you got to 2 bars, and then all the traffic disappeared and you got to drive steady and recharge, it would still be just as bad. Right now you are going to 2 bars, and then the engine kicks on and recharges to 3. Same payment, different installments.

Next time in traffic, dont pulse and glide. But slam the accelerator fast so that the ICE spins up and you start to creep. Then back off the pedal and glide to a stop.

 

SparkieBlues, I agree with you here and I think that this method can work.

As a bit of background, right now my commute is about 22 miles and only 3 of those are on the highway. The rest is surface streets with speed limits that vary from 25MPH to 55MPH, but most if it is in the 35-45 range.

Now, as a bit of a disclaimer, I'm not big on pulse and glide... the traffic in the morning doesn't really support it and I find it takes a bit too much attention. I fully realize that I could probably do better if I was using P&G, but I'm not. Maybe someday I'll revisit that.

That said, during my commute I try to stay in electric only mode whenever I can when the speed limit is under 40. Typically I'll use the ICE to gently accellerate up to speed (leaving the HSI in the 'ECO' range), then drop back and cruise in electric only mode. Above 40 I'll gently accellerate up to speed as above, then I'll maintain my speed using the ICE.

I look ahead to anticipate lights and stopped traffic and try to coast/glide into red lights (or slow down enough so that they're green by the time I get there) as much as possible to use my brakes as little as possible.

The speed limits are arranged such that the low speed limits and high speed limits are mixed and I often drain my battery to 2 or 3 bars while I'm in a low speed limit zone in electric mode, but only rarely do I drain it so much that it needs to start the ICE before I get out of the speed zone. Then, when I'm in a zone with a faster speed limit and it has to run the ICE it also recharges the battery, so I'm set with nearly a full charge by the time I get to the next low speed limit.

Again, I fully realize that I'm getting lower fuel effeciency while the ICE is running and charging as I'm driving.

Doing this I regularly average 64-68MPG on both directions of my commute and I've managed to get into the low 70's on occasion when conditions are perfect.

Because of threads like this where people talk about how lossy the conversions are I've tried on several occassions to limit my all electric mode. I'll still accellerate slowly as I always do, and I still anticipate lights and try to use my brakes as little as possible, but once I'm up to speed I don't back off the pedal for a second to get it to shut off the ICE. Instead I just maintain my speed and let the ICE continue to run. Whenever I've tried that I can get into the high 50's, but I can't manage to break 60MPG.

I do not know... maybe I just need to spring for a PHV conversion kit so I can run in electric only mode whenever I want

 

I'm new to driving Prius but found that there is great benifit in using EV at 30-40 as long as you don't go below 3 bar and can charge battery by braking and down hill events. I drove about a mile this morning doing this taking kids to day care. I have a nice down hill both ways so charging battery naturally I recon.

This said, also found out the first day got Prius, when I pushed the EV mode and drove about 1/4 mile to my daughters house that I depleted the battery and wow did I see the mpg computer drop when engine kicked in. I had to pay the price for using battery power.

I guess each driving situation would be different, bottom line two much battery use, U pay fur it!

 

Yes, Brett, absolutely. (edit: the absolutely is about "the traffic in the morning doesn't really support it")

I also realize that mathematically EV on the Prius is not as efficient. The problem is that the blanket statement that "thus EV is always less efficient" can't be correct given our individual driving routes. I have plenty of snapshots of my mileage from one of my commutes which is only about 12-13 miles, but for which I average 24 mph, not by choice, but because those are the speeds of the routes I have to take. You can guess that when taking a half hour or more to drive 12 miles that you are in quite congested traffic, and on the one-lane road this commute is on, pulsing and gliding for maximum efficiency is near impossible (though I do it regularly anyway :-D).

Using the ICE, on the other hand, to do stop-and-go 24 mph for a half hour - well, there's no way I'd break 50 if I used only that method on this particular route.

Using a judicious combination of pulse and glide and EV to extend glides and even drive for sometime when I know I have a regen opportunity or long hill coming up where the ICE will run anyway, my record has been 67.7 mpg displayed. This is not a flat route, by the way.

On days when I've had a good SOC but the ICE runs no matter what, my average drops enormously. There's one given point where I remember arriving at 40 mpg (ICE running) and other days at 60 mpg (glide and little EV).

I do have to say, given your flat conditions down there, you could probably do even better than your already wonderful numbers with more gliding instead of EV in the slower speeds. I know pulsing at 30 mpg seems less efficient that EV, but I like to think like: 30 mpg pulse over .2 miles, then glide over .4 miles = 90 mpg, etc. In any case, cool to see another newbie like me so obsessed with their mpgs