Clarification on "dead-banding"

I have been reading numerous threads on the P&G techniques, all of which have been very helpful. But I am left with some questions. Please forgive me if I have missed something obvious.

I have had an '06 Prius for a little over a week and have been experimenting with pulse and glide. After warm-up, I can get the glide reproducibly and with relatively ease. The pulse strategy is more problematic, both practically and theoretically, and it this aspect that I want to explore in more detail.

I understand that "dead-banding" is the state of accelerating with no input or output from the battery, and that this state is difficult to achieve, especially on the flat. (With the exception of freeway overpasses, all my P&G practice on the Texas Gulf Coast where I live hs been on ffllaatttt roads...) Before today, I have been focusing on accelerating sufficiently gently to 41 mph using only the ICE, avoiding any electric assist on the assumption that sending ICE energy to the electric motor and then to the wheels would use more energy than sending ICE energy directly to the wheels. Using this approach, I have generally pulsed from about 30 mph to 41 mph in about 12 sec, and glided from 41 and about 30 mph in about 24-25 sec, achieving FE's of anywhere from 68-85 mpg depending on the day and the precise route. The problem I have had (if it is indeed a problem) is that accelerating with only the ICE (and no electric assist), I always see charging of the battery. That is, I had never encountered the "dead-band" state.

As a novice, I have nevertheless been quite pleased with mpg results, though they do not approach the spectacular FE's by a number of you more experienced P&G afficionados. I wonder whether I could do better by optimizing my acceleration strategy.

Responding to a number of suggestions from other threads, I experimented today with more brisk acceleration using both the ICE and electric assist, and may have begun to glimpse the "dead-band" condition: Arrows from the ICE to the wheels, from ICE to electric motor, and from the electric motor to the wheels, but no arrows to or from the battery. This state is indeed difficult to attain and maintain. When achieved, very little throttle movement yields blinking yellow arrows or flickering yellow arrows alternately pointing to and from the battery. Under these conditions, my acceleration from about 30 mph to 41 takes only about 5-6 sec on the flat, while I can usually glide about 25 sec as speed drops to about 30 mph. In these P&G attempts with the more brisk acceleration, I calculated that I was getting mpg in the range of 70-75 mpg, similar to the results I have been getting with the more gentle, ICE only + battery charging, acceleration approach. (I don't put too much stock in the accuracy of today's figures since they are based on a single session, I was doing a lot of experimenting with acceleration rates, and there was a 20 mph wind (head-wind down, tail-wind back.)

(General info: my SOC stays between 3-7 pips; tire pressure is 42/40 with the OEM Integrities; temperature is usually 65-85 F; my oil level is about 2 cm over the "full" line, thanks to the dealer.)

My questions are these:

1. Is "dead-banding" ONLY achievable with acceleration rates sufficient to require power from both the ICE and the electric motor? Or is there a condition I have not yet found where the ICE alone (with no electric assist) sends power to the wheels without charging the battery at the same time?

2. If the answer to (1) above is "yes," I don't understand why dead-banding would be the most efficient acceleration strategy. I would think that brisk acceleration with electric assist would consume more energy than more gradual acceleration with the ICE only, considering transduction losses going from chemical energy (gasoline) to electrical energy (motor) to kinetic energy (turning wheels).

a. Perhaps I have answered my own question: slow acceleration with the ICE only always (in my hands so far, at least) also charges the battery, resulting in even greater transduction losses than ICE to motor to wheels.

b. Concerning my inability so far to see acceleration (even gentle) with ICE only (no electric assist) without simultaneously charging the battery: I would think that when the battery is fully charged (or, more accurately, optimally charged), that the charging system would turn off the charging current and yield a "dead-band" state with only the ICE on. (Understand that I am using the MFD alone to judge current flow, so my observations are qualitative, not quantitative. Perhaps the arrows to the battery that I see with ICE on and no electric assist signals very low current flow, just enough to keep the electronics of the car operating and therefore not enough transduction loss to yield a significant drain on FE. I suppose another factor that influences the optimum acceleration rates is energy efficiency of the ICE at different acceleration rates.

Further discussion of these issues would be appreciated.

Hey, I am a geek. I admit it. Perhaps I should spring for one of the system scanners (Can View or such like) and start trying to measure some of these things for myself. Driving a Prius is a hobby, isn't it? Come to think of it, I really don't need another hobby...

 

Thanks to all (Tripp, Hobbit, EricGo and JPeachman) for the helpful comments. I understand better what the issues are and see that fine tweaking requires more sensitive instrumentation (such as the not-yet-available Can View for '06). I will continue experimenting.

Have a great day.

 

I assume that this current measurement comes from Can View? Can I infer from your comment that when you achieve the no-arrow glide, small changes in the throttle pressure cause continuous increases or decreases in the amperage drain from the battery drain and that the yellow discharge arrows appear on the MFD when the discharge rate reaches 5 amps? So, your more robust (traffic-friendly?) "glides" are not in the "arrows-off" condition, but instead in the "power from battery" (yellow arrows from battery) mode. What amperage drain from the battery is the threshhold that triggers the ICE to come on?

Thanks again for the helpful information.