P&G or steady state driving?

[donee]

Hi Va...,

Ken has said there is a guy in Japan that does his pulses at 2300 rpm, but is only going like 25 mph max, and gets 124 mpg consistently over his "practice" route.

The problem I would have here is that its not 95 F and sunny, so driving along at a constant speed of 25 mph, my engine would never get hot enough for the hybrid system to get to stage 4 for the entire length of my trip.

I had a bit of that problem today. It was not sunny, so the road was not hot (this was before the rain) and the car would not auto stop the engine, until I was 1/2 way home. Based on this I have a new hypothesis - the radiated heat from the roadway is effecting some temperature sensor - most likely the Catalytic Converter sensors - and keeping the car from going into full hybrid mode for a long time. Even so, I was able to start the day at 68.7 mpg, and end at 68.7 mpg. No 70's for this tank.

[bwilson4web]

Hey Wayne,

Originally Posted by FireEngineer

. . .
Don't forget that all of Bob Wilsons steady state in the Gen III are done with only the in car displays and no additional instruments.

My wife offered to let me use her ZVW30 for my daily commute so I'll have a chance to check the vehicle calibration. It will take about 30 days and then we'll know.

My methodology will be to fill the car twice a week, Friday evenings and Sunday evenings. This will let me separate city driving from weekend and see if the calibration is a function of factors other than the vehicle.

Originally Posted by FireEngineer

. . . His Classic runs had the Mini-Scanner to instrument the tests. Take his Gen III results with a grain of salt. My own runs show P&G will be better than steady in most cases in a Gen III. Exception being where you live, nice and flat.

I'm always interested in reading direct comparisons of P&G to the equivalent steady-speed. If you have some data, trot it out with the methodology used and maybe well all get a clue. That is why I share my results and enjoyed reading and commenting on the SAE paper, 2009-01-1332. More the point, if you have measured by other means the steady state mph vs MPH, trot it out.

Originally Posted by FireEngineer

. . . Take his Gen III results with a grain of salt.

The best criticism of facts and data is a better set of facts and data ... that is what science and engineering is about. Do the experiment and report the results and leave the unhelpful comments like "a grain of salt" somewhere else.

Bob Wilson

[bwilson4web]

Originally Posted by VABeachPrius

. . .
Has anyone ever come to the conclusion that one method yields higher mpg's WITH a higher average mpg. I was thinking about this while driving to work the other day at 21 mph (for the most part steady state neighborhood roads) and ended up with 106 mpg on the scan gage after 21.7 miles. Albeit slow, steady state is much less stressful than watching the scangage RPM, traffic on the road, instantaneous mpg during a pulse, watching the tenths section of the trip meter, traffic on the road, gliding, etc. Maybe I'm lazy, but I seem to just drive a slow steady state speed and anticipate traffic and still have mid 60's to mid 70's averages. . . .

It costs $15 but you might enjoy reading SAE 2009-01-1322, "Vehicle Inertia Impact on Fuel Consumption of Conventional and Hybrid Electric Vehicles Using Acceleration and Coast Driving Strategy," Lee, Nelson and Loshse-Busch. In one protocol, they claimed a 24-90% performance improvement. However, their testing was based upon using a dynamometer with calculated aerodynamic drag. But they also included this:

"There are some known safety issues using the PnG driving strategy on the road; traffic considerations, unstable braking performance, and unstable power steering system if the engine is off, so this driving technique should only be used on a closed course under controlled conditions." pp. 2

Their test article was an NHW20 and I only have an NHW11. Still, it is a good read and there is one interesting table in their paper:

Table 4. Summary of Results of 2004 Toyota Prius

Protocol	PnG MPG	Cruising MPG
30-40 mph, 10 seconds of acceleration (NHW20)	151.5	81.0 @35
30-40 mph, 20 seconds of acceleration (NHW20)	99.9	80.9 @35
. . . krousdb with an NHW20 . . .
30-40 mph, 'n' seconds of acceleration (NHW20)	106	93-94 @35
. . . my data with an NHW11 . . .
25-43 mph, 15 seconds of acceleration** (NHW11)	87.8	79.0 @33

pp 6.

** Using cruise control resume function.

I noticed their data showed a decrease in SOC during their dynamometer-based test. Mine consisted of multiple runs in the field, a lightly traveled road, and mixing five runs along the track and each PnG run included six cycles per run or 30 PnG cycles in total.

It would be fascinating if someone with an NHW20 could replicate their protocol and report from the field the same data they reported on the dynamometer. I have my wife's ZVW30 so I can replicate the test for the 30-40 mph range although I'm also running a series of calibration runs that will take about 30 days to complete.

Bob Wilson

[krousdb]

Before the marathon, in May 2005, I drove from Pittsburgh, PA to Huntsville, AL. It took 2 days via backroads and the whole time I had cruise control set at 35mph. The trip lasted about 950 miles and returned 85.7 MPG. This was before I discovered pulse and glide.

Later that spring I was doing more experimentation in the Myrtle Beach SC area and repeatedly recorded 93-94 MPG runs on a 14 mile long test course, at 35 MPH with cruise control.

Back in Pittsburgh, around early summer 2005 I found the marathon test course. That's when I discovered P&G. I would pulse to 40 MPH and glide down to 30, pulse to 40 and repeat. The average speed was about 34 mph and recorded well over 99.9MPG. But I had no way to measure it. S I ended the test by pulling out on the interstate and held the instantaneous at about 40 MPG. Then I waited for the display to drop to 99.8, noted the time spent at 40 MPG instantaneous and calculated that the P&G yielded 104MPG.

About that time I commented on one of the Prius yahoo groups that I needed something that would measure over 99.9 MPG. That got a lot of laughs and skepticism. Then Ken messaged me about the SuperMID and sent me one just before the Marathon.

But I digress. To sum up what I am trying to say, there is some benefit to P&G over steady state. The best apples to apples comparison would be the 35MPH steady state average that I achieved at Myrtle Beach, 93.6MPG, compared to the 34 MPH average speed using P&G, where I measured 104 MPG. I guess you could call it 10%. But personally, given the choice, I would choose steady state every time. It is a lot less work and yields great results. I have also tried P&G vs steady state at highway speeds, in in that case, I could find no measureable difference.

[bwilson4web]

I updated the table ... does this seem about right?

Table 4. Summary of Results of 2004 Toyota Prius (added % improvement rjw)

Protocol	PnG MPG	Cruising MPG	%
. . . Lee, Nelson, Loshse-Busch . . .
30-40 mph, 10 seconds of acceleration (NHW20)	151.5	81.0 @35	87%
30-40 mph, 20 seconds of acceleration (NHW20)	99.9	80.9 @35	24%
. . . krousdb with an NHW20 . . .
30-40 mph, 'n' seconds of acceleration (NHW20)	104	93.6 @35	11%
. . . bwilson4web with an NHW11 . . .
25-43 mph, 15 seconds of acceleration** (NHW11)	87.8	79.0 @33	11%

pp 6, SAE 2009-01-1322, "Vehicle Inertia Impact on Fuel Consumption of Conventional and Hybrid Electric Vehicles Using Acceleration and Coast Driving Strategy," Lee, Nelson and Loshse-Busch.

** Using cruise control resume function.

Bob Wilson

[krousdb]

Originally Posted by bwilson4web

I updated the table ... does this seem about right?

Table 4. Summary of Results of 2004 Toyota Prius (added % improvement rjw)
pp 6, SAE 2009-01-1322, "Vehicle Inertia Impact on Fuel Consumption of Conventional and Hybrid Electric Vehicles Using Acceleration and Coast Driving Strategy," Lee, Nelson and Loshse-Busch.

Bob Wilson

Yes, and I would guess 15 seconds acceleration from 30-40. It's interesting that we both show 11% improvement. I have a difficult time believing the 151.5MPG. We tried a variety of accel rates during the marathon, including 10 seconds and even less than that. We found that the accel rate had little or no correllation with FE. What we did notice was that the FE went up as we extended the glides down to 25 MPH. Near the end, Wayne was dropping below 20MPH. That was on his 120 MPG segment.

[bwilson4web]

Originally Posted by krousdb

. . . I would guess 15 seconds acceleration from 30-40. It's interesting that we both show 11% improvement.

My speed range was limited to the cruise control speed range ... key to a reproducible protocol.

Originally Posted by krousdb

. . . I have a difficult time believing the 151.5MPG.

I've monitored some of the 1,000 mile club tanks and it seems a stretch too. Now the paper mentioned their state of charge decreased during some of the PnG segments but we don't know how long these PnG test sessions were. I'm already running into problems trying to measure fuel consumption at speeds under ~35 mph because of the new battery in my wife's 2010 has the original Ahr capacity. I have a circular track posted at 25 mph so I have to run multiple laps until the system stabilizes. But I don't have a good track for the range from 25 mph to ~40-45 mph.

Originally Posted by krousdb

. . . We tried a variety of accel rates during the marathon, including 10 seconds and even less than that. We found that the accel rate had little or no correllation with FE. What we did notice was that the FE went up as we extended the glides down to 25 MPH. Near the end, Wayne was dropping below 20MPH. That was on his 120 MPG segment.

I didn't have the details but the log pretty well showed what was happening:


Thank you for the details.

Bob Wilson

[VABeachPrius]

krousdb / bwilson4web,

Thank you for your responses. While great bwilson4web, krousdb answered my question in laymans terms. It appears that his experience shows about 10% better FE using P&G over steady state.

Thinking moe, I would imagine that this may not be hard to prove on my test loop.

Is this somewhat controlled experiment:

1. Fully warm car to stage 4 operation.
2. Enter test loop.
3. Drive on EV at slow speeds to drop the battery SOC from four bars to three bars (a consistent battery SOC starting point).
4. Immediately stop.
5. Reset scangage current trip and handheld GPS (average speed)
6. Accelerate at 1600 rpm to a constant speed of xx.x and hold for 15 minutes or longer.

Holding the car at a slow steady state speed will eventually charge the battery pack to four bars. When this point is reached after step 6 above is acheived, it is time to stop to record data. To test P&G technique:

7. Drive on EV at slow speeds to drop the battery SOC from four bars to three bars (a consistent battery SOC starting point).
8. Immediately stop.
9. Reset scangage current trip and handheld GPS (average speed)
10. Accelerate at 1600 rpm to the maximum speed of P&G. 11. Start glide of P&G.
12. P&G using a range of speeds that approximates an average speed used in step 6, above. Continue for 15 minutes or longer.

P&G will eventually charge the battery pack to four bars (depending on goal mpg). When this point is reached, after the time in step 12 acheived, EV at average speed until the battery SOC drops from 4 to 3 bars. it is time to stop to record data.

[donee]

Hi Va...,

Why not drive the car until it reaches 6 bars in that test protocol. The 6 bar level is what the car wants to do. That way, you will truely see the P&G mileage, not the P/Charge&G mileage. When I am driving, I am trying to use the uphill pulses to get the charge back to 6 bars. Because with all the starts-from-stopped I do, I invaribly get down below 6, even though I back out of the throttle as quickly as possible to drop the battery bar on my starts-from-stopped. I think the Prius will shut the engine off much more readily whe SOC is 6 bars.

[bwilson4web]

Hi Chris,

Let me suggest one modification. Achieve steady state in each protocol, which may take a couple of miles and then start the measured segment. This eliminates trying to use the battery SOC indicator. But the real goal is to eliminate the transients from starting either over or undercharged. It is the steady state performance between the two driving styles that is of interest.

Also, to match the SAE paper table:

• min-max speed
• average speed
• acceleration time (given vehicle weight, lets us know to power setting used)

This will make it easy to add your entry to the table for an apples-to-apples comparison.

Thanks for performing the experiment. Controlled tests take time and effort and I for one always appreciate such efforts. It is how we learn what works and how well.

Bob Wilson