Which acceleration from 0 mph has the highest MPG?

Wrt to the scangaugeII and FE for a fully warmed up Prius - a warmed up Prius FE tends to be higher if you trim the pressure on the accelerator to keep the LOD to between 60-80 percent during accelerations ... when going up hill for a dead stop this may not provide enough power and the Prius speed may be less than 25 mph as it goes uphill ... when going uphill FE it is better if the Prius has an initial velocity at the bottom of the hill instead of starting from the bottom of a hill from a dead stop (zero mph). IIRC a Prius is fully warmed up when FwT goes over 177 Fahrenheit.

Scenario : a fully warmed up Prius is stop/idling at a traffic light, no cars in front or behind you. The asphalt roads are dry, smooth, and the path is straight for then next mile or so. There is no wind, rain, sleet, ice, or snow. The driving temperature is 70 degrees Fahrenheit. The traffic light changes from red to green and you are free to go. The asphalt road is flat and you want to accelerate to 30 mph. The battery level SOC = 4 or more bars (>55%) Your goal is to accelerate to 30 mph while achieving the the highest MPG possible:

Setup: to optimize fuel efficiency set the front tire pressures to the max tire pressure setting as defined by the sidewall and the rear tire pressures to about 2 to 4 psi less than the front tire pressure. Doing this lowers your tire's rolling resistance and initial rolling resistance for a dead stop.

Technique/Procedure: Set the throttle mode to Normal (not Pwr, not EV, not Eco). You have the HSI display on. Press accelerator so the HSI display is not in the Recharge mode but just slightly past the left side but not more than 1/5 the way (so the Prius is only using its electric motors to eliminate the initial rolling resistance) until the Prius get pass 5 mph. At about 5 mph, press the accelerator so the HSI goes pass the 1/2 mark - this is to start up the ICE. When the ICE starts up, then loosen up the accelerator pressure slightly so the HSI is under the"E" of the "ECO" capsule ( this put the ICE at about 70 percent LOD most of the time). Maintain pressure on the accelerator until 30 mph is reached then switch to cruise control to maintain 30 mph -

Technique/Procedural Theory-Foundation: Cruise control is more fuel efficient than manually controlling the accelerator when the road is flat. When the roads are hilly performing the hypermiling technique Driving With Load (DWL) with a manually controlled accelerator can be more fuel efficient than cruise control. The reason I switch over to the ICE about 5 mph is that I want to avoid using and draining the traction battery. Draining the traction battery lower than 50% - will cause the Prius ICE to automatically recharge the traction battery which lowers the Prius' MPG. You want to avoid using the electric motors unless the traction battery power is from 5 to 8 bars (55%-80% SoC) . For higher MPG, try dropping the top speed from 30 mph to 27 mph. The top speed for making a 90 degree turn is about 22 mph. Driving the Prius into a curve at high speed may cause the onboard computer to apply the brakes automatically in order to keep the Prius stability - this will result in lower fuel efficiency but it will keep all four tires on the road and keep the Prius rolling over . The most efficient EV mode speed (highest Miles per kilowatt expended) for a non plug-in Prius running only the electric motors on a flat road is between 15-20 mph.

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On the other hand, the aerodynamic drag increases with the square of your velocity; and if you accelerate more slowly, you spend more time at a lower velocity. So to some extent, even if you're accelerating more slowly than you should to get the best efficiency out of the engine, you'll probably make up the difference with reduced aerodynamic drag.

Personally, I aim for ~1800 RPM on the ScanGauge, or maybe slightly into the PWR bar on the HSI. No particular data on this, but it works well enough for me.

 

It is a shame there is no easy kwHr metric to combine with the MPG. Still, use the tools you've got and share the results. The next stage is independent, replication with perhaps more technical details or an easier profile.

Good job,
Bob Wilson

 

Of course relying heavily on battery power is going to result in the best fuel economy for the short duration of measure. I can run all electric to 50 km/h and get infinite MPG.

It would be very difficult to figure in how much gasoline is later burned to generate the electricity that was used for the short acceleration.

Based on what I know of efficiency, it would be best to avoid electric motor use as much as possible, and to keep the engine as close to 80% load as possible.

In my experience with other vehicles, acceleration technique has little to do with overall fuel economy, as avoiding brake usage is the #1 rule, avoiding idling is #2.

 

Near as I can tell, each acceleration run is for a different distance, so he altering both gasoline used and miles traveled.

 

Yes, deceleration technique is much more critical than "acceleration technique." A Prius automatically takes care of your rule #2 reasonably well, except when cold. Another very important "rule" is avoiding unnecessary speed.

 

I agree with all the issues raised above with this technique - it's interesting, but I'm not sure it's the right data to make a decision about how to drive most efficiently.

The electric one is probably the hardest to account for; maybe one could record the delta between SoC when stopped and SoC at 50 kph, and then determine the amount of gas used to force charge that same amount (or measure how much gas it takes when the car starts charging itself around 40% SoC to 45% SoC, and use that as a metric for gallons per percent SoC)...

I also agree that because you're measuring across different distances that you won't get a meaningful answer - it will have the tendency to favor very slow acceleration, as you've discovered. One possible way to account for that to some extent would be to start with the slowest method acceleration first - when you reach 50 kph, note not only the mpg but also how far you traveled since you started moving. When trying the faster methods, once you reach 50 kph, start gliding until you reach that same distance - only then should you note the mpg measurement. You won't be going 50 kph any more, but the "miles" part of mpg will be the same for all the measurements, and the "gallons" part will be exactly the number of gallons required to get you to 50 kph. Another way would be to just measure total fuel consumption during the acceleration.

Most likely, the only way to get really accurate data on this would be to use a dynamometer and instrument the fuel line (or exhaust) to have an accurate measurement of what's being burned. Oh, and the battery current too.

Alternately, drive with each of the different methods for a full tank of gas. Unfortunately, the differences between many of them are probably in the noise when it comes to tank-to-tank variation from outside factors like weather, routes taken, traffic, etc.

 

Umm, you do know that MG2 is geared directly to the drive wheels so MG2 RPM is determined only by vehicle speed, right?

 

Sorry for the weak BSFC chart. Someone posted a link to the Toyota EU set of charts and it has a much better BSFC chart in one of the pages. Regardless, here is a handy one:

• the '10kW, 20kW, 30kW' lines should correspond to the power lines on the 'ECO' display

Notice there is a broad range of engine rpm that along with the engine torque map into the 'sweet spot' of peak ICE rpm. From memory (I hope someone posts the link again to the charts,) ~2,200 rpm was in the middle. The engine controller will adjust everything else to put the torque in the middle of the high efficiency range.

Now when I was doing my initial miniVCI studies, I looked for the highest, recirculated-cooled-exhaust percentage. I found this at ~3,200 rpm. Cooled exhaust is needed at higher power settings, like climbing a hill or rapid acceleration. So this remains my 'rule of thumb' as the highest power setting to still deliver best, practical engine efficiency. Notice my measurement versus the inflection point in the BSFC chart at 3,650 rpm.

First off, KUDOS and my appreciation for anyone who 'looks through the telescope' (i.e., does the experiment.) All engineering comes from those who 'go to the lab' and I want to encourage everyone to promote yourself to empiricists. Although instruments are nice, never forget Newton only had pulse for timing and he gave us the rules of physics for objects moving at planetary speeds away from black holes . . . ordinary speeds we live in.

So please continue to measure and observe. That is how we learn what works and doesn't. Most of all, nobody has all of the answers . . . including me which separates me from other 'experts.' Use the experiment first, middle, last, and always.

Bob Wilson

 

In the linked and mentioned video by Wayne Gerdes, he mentions at one point that anywhere between 1/2 and 3/4's of the way along the eco zone is good acceleration range. I don't stick slavishly to that, but once through the initial kick, I try to keep it in that zone when accelerating. All bets are off on an uphill grade though.

 

Accelerating from a stop to speeds faster than 30 mph is quite different.

In that case, you want to take. advantage of the engine. That's where the BRISK recommendation come from.

You intentionally go into the "Power" range then. The key is to make it brief.

Watching an aftermarket gauge, you'll hit that sweetspot RPM of 3200. For only a few seconds, that's an efficient overall use of the hybrid system.

 

Used to own this beast! Used to not really care about what's in this thread (although I did keep track of the pitiful mpg religiously)..... Now I do... Keep up the good work all and thanks all for the good info on how to maximize potential.

 

Does someone have the link to that Toyota EU presentation that had the BSFC charts and breakout of efficiency gains? I tried searching but came up empty handed.

 

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