Just bought my first prius! A few questions.

Wow, lots of questions for a newbie. Glad you're interested in optimal fuel economy. Let's see if we can keep things fairly simple.

By "brisk" acceleration, I would avoid accelerating so quickly that the battery has to help. You are correct to stay out of the battery when you can avoid it. There are efficiency losses from converting one form of energy to another, so to run the car on only the ICE in normal driving is more efficient than large, sustained, and repeated draws from the battery that require the ICE to recharge it. Better to let the energy go directly to propulsion. The battery and electric motor are there when you really need the immediate torque and added power for, say, accelerating quickly onto a highway to merge into a small break in traffic.

Not sure where your iMPG vs. MPH formula came from, but I proposed a rule of thumb, that others have validated to a degree, of keeping iMPG above half the vehicle speed. That keeps ICE RPM out of inefficiently high ranges and minimizes use of the battery for acceleration. At the other end of the spectrum, a simple rule is to keep iMPG at or below MPH. I don't think that one is as critical as the first one. Low RPM may or may not hurt fuel economy, depending on whose experiences and opinions you believe.

On the highway, with level terrain or only slightly rolling hills, I use cruise control at the slowest speed I can safely go. I did a controlled test for this, and found that CC is as good as warp stealth. For highways with steeper hills, I use warp stealth on the downhills and aim to keep RPM in efficient ranges (which, without a tach, can be done with the aforementioned rule of thumb) on uphills to the extent that traffic and safety allow. I do this based largely on Hobbit's work, though I'd still like to do a controlled test in hilly terrain too.

As for gliding, a "no arrows" glide is best. That allows the best use of available kinetic energy. Regeneration, though a more energy-efficient means of braking or decelerating than in a conventional car, still results in losses as kinetic energy is converted to electrical energy and then to stored chemical energy in the battery -- with the process reversed to actually use the energy.

Hope that helps. Let us know if you have more questions or need clarifications.

 

From a dead stop is a little different. Because of the immediate low-end torque provided by the electric motor, it's nearly impossible to start without a brief power burst from the motor and, with it, a brief but large current draw from the battery. Give it enough pedal and the ICE will light within a second or two.

Frankly, I don't know if the iMPG/MPH rule applies during those first few seconds. Both change so quickly and the duration is so short -- and the waters are muddied by that electric power burst -- that I haven't spent much time looking at it; I proposed the rule more for sustained driving. These days I pay attention more to RPM and current flow into and out of the battery. Once the ICE lights I aim for about 1600-1800 RPM for acceleration unless traffic conditions mandate something higher and faster. That keeps iMPG well above half the vehicle speed at least at speeds above 15-20 MPH. Give me a couple of days and I'll see if I can give you a better idea of the iMPG/MPH/RPM relationship from a stop.

As for what acceleration rate is best, opinions vary. It seems clear to me that RPM >2400 is inefficient. There was a time when I would aim for 2000-2200 RPM. During the MPG Challenge at least year's Hybridfest, I used that target for my pulse segments during P&G. I got beat by others using lower targets -- 1600, for example, by at least one competitor. There were certainly other factors at work in the competition, but since then I've been using lower engine speeds. Anecdotally, results seem at least comparable if not better. But I'd like to verify that too with another test.

The battery gets charged either by the ICE or from regeneration. The car is happiest with a state of charge (SOC) of about 60% (6 blue bars), and manages itself very well to keep SOC between 40% (no bars) and 80% (8 green bars). As it starts dropping below that level, the ICE will start diverting power to charge it. Below 50%, the ICE tends to light for recharging even if not needed for propulsion. Again, inefficient if you can avoid it.

 

Re: ok Jim

That's what I do.

The energy monitor is helpful as soon as the ICE lights to show direction of current flow. What I'm less certain of is how helpful iMPG is during acceleration from a stop.

Ideally, you'd like to avoid regeneration completely, again because of the conversion losses. Most efficient is gliding, next is regenerative coasting, then regenerative braking, and least efficient is using the friction brakes, which engage only with hard braking or below 7 MPH. It takes timing and practice. The better you learn your normal routes with their traffic light timing and typical traffic patterns, and the better you anticipate upcoming changes, the better you'll time your decelerations. I'm happiest when I never have to stop or even hit the brakes.

Regardless, your results are quite respectable for a rookie in a NJ winter. I know it's been pretty mild along the Atlantic coast recently, but you're still well above the new EPA estimates. Just wait 'til warmer weather. Keep up the good work!

 

For a newbie he is doing great, just wait in another month and a half when your temps go up to about 60 degree's, you may be flirting with 60 MPG tanks. Or even 65 MPG tanks if you can keep the short trips out of the equation.

Quick question for Jimbo, What tires and pressure are you running.

 

PLEASE!! No 52-62 warp stealth or something

At least not while being followed. It's not only REALLY annoying to follow someone who can't or won't "maintain a steady strain", but for non-hybrids, it's really inefficient. Just keep the cruise control at the average speed of the furthest car you can see ahead of you and everyone will be happier! Remember, "The well being of the many outweighs that of the few".

 

Frankly, I don't watch the bars. For trip averages I use added instrumentation, previously ScanGauge and now CAN-View.

I have Michelin Hydroedges. I'm running ... uh ... <whispering> ... 60. Not necessarily recommended for the masses.