Stupid driving stunt (1000 miles on 1 tank - 2010 Prius)
 

Hi,

Recently, I wasted 45.5 hours between July 3 and July 21 to burn 10.9 gallons:
http://hiwaay.net/~bzwilson/prius/1000mi_721a.jpg
Wasted because I knew the car could easily achieve 1,000 miles on a single tank. But thanks to our Japanese Prius friends, I figured out how to do it while commuting to work and the ordinary chores around town.

The full write-up is over a PriusChat but the technical details:

• Route planning - so I could avoid traffic or allow it to pass me without causing a big stink.
• Cruise control + shifting into "N" - an energy management scheme, my feet stay on the floorboard while racking up the miles.
• Minimum 1 hour on each trip - the Prius just gets warmed up in 20 minutes. Extending every trip to one hour achieves very high mileage . . . at the waste of driver time.
• +99.9 MPG loop - part of route planning, I identified public road loops where I could 'do laps' at over 99.9 MPG.

My one screw-up was I filled the tank with the nozzle upside down which gave me only a partial fill. I only burned 10.9 gallons and know a proper fill would have given another 1.2 gallons, ~130 miles.

The trick our Japanese friends taught was to break a marathon into smaller bites. So instead of my typical one hour driving each day, I averaged three hours per day including the weekends. I simply incorporated the additional driving needed to reach 1,000 miles on one tank of gas. Marathon driving is not about getting somewhere, it is about putting the maximum number of miles on one tank even if it means 'doing laps.'

BTW, I know this is accurate as I use both GPS and mile markers to verify the odometer and trip meter distances are accurate to less than 1%. So too is the indicated 91.8 MPG. It turns out the original tires are ~5% too small and that screws up the indicated mph, MPG, and miles. My replacement, Sumitomo T4s are right on the numbers as are the mph, MPG, and miles.

I'm hoping more Prius owners will replicate this approach so doing 1,000 miles in a Prius is common and for us unexceptional. Personally, it is one long boring slog relieved only by having iPad music and podcasts. I've tried to cover all of the technical details in the PriusChat thread but if there are any questions, feel free to ask.

Bob Wilson

ps. I don't think there is much operator skill as much as the excellent engineering that went into the Prius. I mostly just kept it on the road and paid for the gas . . . enough for 11 cuppa coffee from Starbucks.

I've thought about doing the same thing with my daily commute route, just knocking a bit off one end. I know I don't have a hybrid(yet), but still might get some cool numbers.

The Prius plays a trick that non-hybrids would have little chance of following. When the ICE runs, it operates at a higher power level than the vehicle needs and banks the excess power in the traction battery:

• dilutes ICE mechanical overhead to insignificance - at 25-26 mph, the car only needs ~8-10 hp and the engine mechanical overhead is about 2 hp. So an ordinary car would need to generate an extra 2 hp to handle the mechanical overhead.
• the Prius engine generates 3x power, closer to 24-30 hp yet the same mechanical drag because the ICE rpm barely increased. So only 26-32 hp is generated but the 16-20 hp is banked in the traction battery.
• turn off the engine to use stored traction energy - so when the car has enough banked energy, the engine goes off and the car uses the stored battery energy to sustain motion. No more mechanical overhead from the ICE.
• the round-trip charge-discharge overhead << engine mechanical overhead

An ordinary gas engine vehicle can be turned off but if more power is generated than needed, the vehicle accelerates into higher drag regions. In effect, the aerodynamic and stirring losses increase because of the higher speed with an ordinary vehicle. The hybrid does not increase the speed since it uses cruise control and banks the extra energy in the traction battery.

During the stunt, I had a lot of time to stare at the Scangauge II fuel consumption:

• ~0.02 - engine off, fuel burn, use of 0.02 gal/hr avoid divide by zero risk. The engine shuts off automatically under hybrid control laws.
• ~0.20 gal/hr - engine idle, no load, minimum fuel burn, which does not happen in ordinary operation. The hybrid laws turn the engine off and uses the traction battery or potential energy to maintain kinetic energy (i.e., speed.)
  • Shifting into "N" with the engine off lets the potential energy maintain or even let the least increase in speed while preserving traction battery charge from the earlier engine run. When the speed decreases to the cruise control speed, shifting into "D" and "resume" lets the traction battery preserve kinetic energy until the engine is needed.
• ~0.60 gal/hr - hybrid mode, lowest engine power level. Depending upon the vehicle drag load, any excess power is banked in the traction battery.
• ~1.20 gal/hr - hybrid mode, highest engine power level. Typically seen climbing a grade at 26-27 mph. Yet excess power is banked in the traction battery so the engine overhead has faded into insignificance.

When the engine runs, the control laws bank energy in the traction battery and potential energy as the car climbs gentile grades. But as soon as there is enough traction battery and/or potential energy, the ICE is off, the engine mechanical drag goes away yet the car preserves its kinetic energy at a low drag speed range.

Still, you are welcome to the effort. I found it a long and boring waste of time. I already knew I could achieve any indicated MPG over any arbitrary distance. Going a 1,000 miles was just validation.

GOOD LUCK!
Bob Wilson

I am curious about your warm up. Even though you can achieve higher mpg, what is your fuel consumption? Isn't it better to optimize your route for lowest fuel consumption rather than mileage?

Understood, Bob. I'd be doing it for the same reason, more or less. Basically, to see what the car and I were capable in nearly ideal conditions. Kind of like being in a rally all alone:D. It would also give a target to shoot for on my bi-weekly fill up.

Could you clarify the question? The simple answer:

• stunt - 1000.8 miles, 10.9 gallons, 91.8 MPG, two weeks
• typical - 600 miles, 11 gallons, 52-56 MPG, three weeks

This is why I call it a 'stunt':

• Incredibe waste of my time - tripled the number of hours spent in my commute and other chores around town.
• Refined but did not increase my understanding of Prius performance.
  • I already knew at 25 mph on cruise control, the Prius could achieve 99.9 MPG after being warmed up. I simply extended each drive enough to get the car warmed up and into the 99.9 MPG performance range. The extra miles of efficient driving brought each trip MPG up.
• Instead of filling the tank roughly ever three weeks with +600 miles, it took two weeks and covered 1,000 miles.
  • Taking 'days off' by using our second Prius and leaving my wife's parked every third or fourth day, would have stretched it out to three weeks or longer. Even with 'days off,' the stunt still would wasted the same amount of my life in the cabin just stretched out over a longer calender period.

I don't think such stunts really accomplish much. Think of it as a 'bowling trophy' or 'Hole in One' certificate with no more intrinsic value.

Bob Wilson

I could beat that with almost no effort. Just jack up the front end, put it in drive, and walk away. After all, it seems your purpose was just to see how high a number you could get on the FE indicator. Sure, the car isn't actually going anywhere, but if you were driving with no purpose, what's the difference? A car like the Prius was built for the purpose of efficiency, be it for economic or ecological. What you did was neither. More power to you, if for nothing else than for your patience. It is an interesting intellectual exercise. Now do some mods and see if you can test the results doing so (although for the sake of your sanity I might recommend using a smaller amount of fuel than a full tank).

Edit: that was a lot harsher than I meant it to be. I just meant to encourage you to take it a step further.

Even easier, get a display from a wrecker and spoof the car or just Photoshop. Why waste the gas and car?
No argument from me. I called it a 'Stupid driving stunt' too.
Actually I did when I picked up the car at the dealer. On the way home, I charted the following:
http://hiwaay.net/~bzwilson/prius/pri_2010_800.jpg
I knew before starting the marathon that I would achieve a 1,000 mile tank and it is no accident that I parked it Sunday afternoon, July 21 with this on the display:
http://hiwaay.net/~bzwilson/prius/1000mi_721a.jpg
I actually calculated on the 'loop' when to drive to my work and park the car. My goal was 1,000 miles.

When I've read about the days and man-hours wasted in marathon drives, I would shake my head and mutter to myself that it only takes 10 miles to map car performance. But earlier this year, I realized I could incorporate the marathon hours into my normal work commute . . . do it in small bites.

Instead of doing a multi-day, dedicated, drive (plenty of examples exist,) I added extra time to my regular 15-20 minutes per trips . . . extended to an hour. I spent the extra 40-45 minutes listening to podcasts or music. Still mostly a waste of time but tolerable.
I agree with your criticism which is why I called it a 'stunt'. I've thought about a 'step further' but it isn't clear there is any opportunity.

My normal Prius is a 2003 model. Adding a couple of microcontrollers networked together:

• Accelerator and cruise control spoof - takes the cruise control input, brake-light, and vehicle speed to operate the accelerator interface for 'hill billy' speed control. The existing cruise control cuts out at 23 mph but the 'hillbilly' cruise control could go down to as low as I want with any degree of speed 'slop' I want to handle local conditions.
• Shifter spoof - working with the 'hill billy' cruise control, handles shifting including use of "N" automatically when driving.

In effect the microcontrollers would spoof the driver accelerator and shifter to make the car behave more efficiently . . . all the time. But could I sell it?

A lawyer would take one look at it and after laughing hysterically say not just no but "H*LL NO!" But is this approach any worse than Google's self-driving cars?

Well Toyota has been sued for 'runaway acceleration' and I have no interest in wasting time in court. Like this marathon driving stunt, I know it can be done but that does not mean it is worth my time.

Bob Wilson