I was reading a thread on priuschat.com (Thanks Bob for introducing me to that forum) http://priuschat.com/forums/kb.php?mode=article&k=23

I was very anxious to try out a new techniqye that I had read there:

"I accelerate fairly briskly getting to speed. I don't floor it, but maybe depress the pedal 1/3rd way or so. Once I get over the 25-30mph mark I begin trying to 'Dead-band'--on the energy screen all power is from Engine (ICE) to wheels with no arrows to or from the battery. This is the most efficient power phase as there are no losses from converting the energy to potential energy in the battery back to kinetic energy for the wheels.:"

I tried it yesterday, and it seems to really help me. I took about 5 cold trips (a few hours gap between each trip) for about 7 miles (I go to pray a few times in day) each, and I consistently made 65.0 mpg! I am sure, if I had made 7*5=35 miles in one trip itself, I could have easily broken the 65.0 mpg mark.

Also, with the "DEAD BAND" mode, the acceleration is very good, and I saved about 2 minutes on each trip!

The auhor in the above link suggests that he accelerates 'fairly briskly' to come to speed. But this is how I did it: I started from a static position. If the HSD system determines that I can go off on the battery, then, I accelerate a little slowly. Once the ICE kicks in, I try to pus hthe accelerator pedal a little hard to try to get the dead band. I try to maintain the dead-band until I come upto the criusing speed, and then I try to P&G.

Can other veterans in the forum comment on this method?

One thing that puzzles me a little is that when I am kind of flooring the accelerator pedal (which is not exactly flooring it .. but I drive with a light foot on the accelerator pedal, so I had to try a little harder from my 'normal' driving habits) to get the 'dead-band', then the MPG readings on MFD are really low. but the ultimate MPG reading of a trip comes out to be great!! How?! .. That is a little puzzling to my engineering mind. On theother hand, when I push the accelerator with not as much force, I see that the MPG readings are much better with the lighter push. Shouldn't then the average MPG readings come out to be even better than the 'dead-band and PG' technique? The AVG MPG readings are close but the dead-band technique has clearly come out as a winner in my experiments...

Any more comments??!!

Cheers!

 

As was explained to me. The losses from converting to electrical and back to mechanical are outweighed by the inefficiencies of the ICE when it is not at its best output. So the ice under certain circumstances is less efficient than the motor.

 

So, it means that when the ICE might be strained too hard, it might actually be running very inefficiently - worse than the scenario of loss of energy involved in the ICE running at a modest pace and outputting elec. energy which is saved in the batteries to be utilized later?

So, how we do know where does the optimum point lie? How much should the engine be strained so as to get the maximum benefit from the elec-ICE combination taking into account the ICE's efficiency at various RPM levels and the energy losses involved in conversion of energy from one form to another?

 

That is the $64,000 question.

What many advanced Prius drivers do is get an Onboard Board Diagnostic interface and monitor key parameters to adjust their driving. Another enthusiast, Ken posted a link of a Japanese enthusiast who has a single board computer that reads the OBD codes and using the MFD, puts up a real engineering control screen. Another enthusiast, Hobbit has been known to drive around with an oscilliscope and various creative instrumentation packages. Then too, I have my moments including using a laptop to record data.

Folks who like to really understand Prius engineering tend to hang out in "Prius Technical Stuff", a Yahoo Group. There is an extensive data library of SAE and other technical papers and reports. In fact, it got so large, a second one was formed just to hold the papers. It is an engineering playground but gosh it has some interesting stuff going on.

Bob Wilson

 

So what we really need, Bob, is someone like you to read all that engineering stuff and explain it in simple terms so that the average user can understand it. Just tell us, "Accel quickly, drop into the dead zone for 20 seconds, then ICE all the way," and we won't ask why it works. };-)

 

After I get my current tasks done, maybe. Five days a week and most weekends, I'm in urban traffic so tweaking highway performance is not high on my list.

Bob Wilson

 

I agree with uwaku .. we need someone like Bob to comprehend all the techie stuff and explain it all in layman's langugage to all of us here ..

Back of the $64,000 question - I am just wondering what strategy is the best for PG in ORDINARY CITY DRIVING? Is accelerating quickly with dead-band zone better than the scenario where the ICE is on and is charging the battery pack as well as providing the power to the motor? Or is it better to start with a dead band (quick acceleration) followed with a slight charge to the batery pack? Once I reach the cruise speed, and start to glide, it is very easy? But the question, how do I get back to the cruise speed from the low speed? What is the best technique of 'pulsing'?

 

I'm using my cruse control for this and simply let it "resume" to cruise speed. Then I hit the 'suspend' and feather throttle - coast. But it is something I only do late when there is no other traffic around. A variable speed driver in traffic is a hazard. It is not something to practice with other traffic and I'll even use the 'flashers' to let folks know "road hazard."

When in city traffic on ordinary access roads with lots of side streets AND NOT HEAVY TRAFFIC, I get in the slow lane and set the cruise control to 35-38 mph. Folks just figure I'm planning to make a right turn and my frequent squinting at the business addresses and street signs, encourages that impression.

The key is staying away from transitions through 42 mph that force the ICE on for other than load reasons.

Bob Wilson

 

Hi folks,

Let me explain something about my engineering philosophy - KISS (Keep It Simple Son . . . I'm Southern.) My approach is to find 'low hanging fruit' and avoid tricky things. If I have no choice but to do tricky things, I find a way to make a computer do it for me. So let me review what that leads to:

- mapping "bad speeds" -> there are always some speeds that tend to cause poor performance. In automatics and manual transmission vehicles, these tend to be the shift point. In the Prius, it is 42 mph, the transition between demand driven ICE operation and 'protect MG1' ICE-on all the time. So I recommend speeds from 0-38 and 51-65 mph. These speeds give great mileage using cruise control speed management.

- mapping inefficient modes -> the Prius ICE, transmission and battery need to 'warm-up' even in the summer. For the first 1-2 miles, try to use neighbor street speeds of 25 mph to get everything up to efficient operating temperatures. Then drive normally while avoiding "bad speeds."

- mapping inefficient systems -> the Prius transaxle seems to have a temperature as well as a possible oil life-time problem. Thus I've already switched to a compatible synthetic oil for my NHW11, 01-03 Prius. Oil testing results suggest this has been a good thing and I've been sharing my results. I have not conducted a transaxle oil study on the NHW20, 04-06 Prius!

Now 'pulse-and-glide' has a lot of promise but my near term goal is to automate the 'glide' part. This will be done probably by tapping into the cruise control control and automating an energy neutral glide. The goal is to make it work without the driver having to even think about it except as selecting "normal" or "efficient" cruise control operation. This will work for both the NHW11 and NHW20. The 'pulse' can be either the cruise control resuming speed or the accellerator pedal for those who prefer the manual approach.

In parallel, I'm looking at a total thermal management system for my NHW11. This will probably use the JC Whitney 750 W., coolant heater, something like their 250 W. oil pan heater, and something for the traction battery. Thermostat controlled, each will seek a given temperature level for the ICE, transaxle and traction battery so they can be used year round. My expectation is to eliminate all but catalytic converter warm-up delays and improved, year round operation.

This thermal management system may include a variable air inlet. This will allow me to avoid chilling and higher drag from cold dense air in the winter. Again, this will be a dynamic system that requires no driver intervention.

Now that I have a trailer receiver hitch, I plan to do a detailed airflow study around my NHW11 03 Prius. Earlier tests indicate some form of abnormal flow condition starts around 65 mph and gets fully involved by 70 mph. This is beyond the v**2 of ordinary objects. If I can not mitigate the effects, at least I will come up with a detector that gives a cabin indication of when this happens so I can adjust my cruise speed for maximum, efficient speed.

I'm also starting an ICE oil study but aimed at ICE longevity. I MAY look at improving ICE performance but not at the expense of longevity.

I have some other plans to improve my Prius capabilities beyond the 1 kW AC power and the light-weight trailer. My passenger seat is likly to become fully electric and reclining. I may also split-fold down half of the rear seat to allow oversized loads (aka., fishing rods) to be easily carried. I'd also like a distance-speed monitoring device that 'tickles' the cruise control to maintain a constant following distance at highway speeds (and looks like a cop radar gun to radar detectors.)

On the 'drawing board' are systems to make use of exhaust heat and energy. One is an ammonium-absorbtion cooling system and the other is a turbo-alternator. The first will minimize summer AC loading and the second will improve highway MPG. I'd also like whole house power. But these are only after the other 'low hanging fruit' have been harvested . . . KISS.

You'll notice that my engineering approach tries to minimize the human element. The reason is every manual task is distracting and leads to potential human errors. I want the human operator concentrating on what is going on around the vehicle, the traffic, and having the hardware and software do what they can accomplish. You would be amazed at how hard I work to avoid manual hard work.

Bob Wilson

 

Wow! Bob, you are truly an inspiration to hypermilers out here!

Well, some of the things that you explained that you are trying to do flew over the top of my head .. I am one of those 'simple sons' that you refered to .. Just ordinary laymen, who bought Prius recently and are learning their ways to drive it ..

Hopefully, your experiments and efforts will come to good fruition in the near future, and we will be able to use your technology to do less hard word while driving ..

Thank you so much for the hard work, both on the car experiments, as wells as answering questions on these forums!!

Regards.