Let's talk about the kW "sweet spot" for a Gen 3, 1.8 liter engine

As far as I know, if the ICE is running, then it wouldn't be warp stealth.

 

Run an A-B-A series of tests where you switch between different driving styles and share your results. Try to hold as many variables constant as possible and only change the style of driving. Make sure you record the vehicle average speed and/or elapsed time for your standard test.

The Prius is an excellent vehicle for running such experiments. So run them and report your results.

Bob Wilson

 

I see. The way you said it originally, it sounded like the ICE was generating power. Yeah, going down the slope is the perfect time to do warp stealth. I kinda figured that out by trial and error. If the slope is really steep, I even put the car in N if the traffic condition permitted. I haven't gotten into the technical stuffs yet, I nomrally just use the HSI and I could achieve pretty high mpg. If there's no car behind me, I try to keep the bar to the left side of the HSI without going too slow.

 

Do you have any metrics for the effect of this particular technique on your trip mileage?

• Distance?
• Altitude change?
• Average speed?
• Elapsed times?
• Alternate driving technique to "Warp Stealth"?

I appreciate the pointer but I'm really curious how much this technique has improved your mileage without changing your elapsed trip times. For example:

• 50 MPG - using cruise control at 70 mph with elapsed time 20 minutes
• 70 MPG - using "Warp Stealth" at 70 mph with elapsed time 20 minutes

If you are seeing a dramatic improvement in your daily driving from this one technique, quantify it. Let us know how much of an improvement over the alternate . . . say using cruise control.

The proof of a technique is not what others do but rather the effect it has had on your driving.

Bob Wilson

 

What using "N" does is avoid transferring potential energy into battery traction energy. In "D" it will usual convert the potential energy into kinetic energy to keep the car rolling or even rolling faster. In "B", it spends some of the energy has mechanical energy to keep the car from accelerating with higher kinetic energy.

Bob Wilson

 

You may be typing differently than what you're thinking. In N, I'm trying to avoid transferring kinetic energy into stored energy or potential energy. I want to use the K energy to move the car instead of charging the battery. Like you said many times previously, use the ICE to charge instead. When going down a steep slope, I don't need "D" to keep the car rolling. In fact, when going down hill, I would put it back to "D" to slow down whenever I go 5 mph over the speed limit.

 

To make sure we're using the same terms:

• kinetic energy = m*(Vb-Va)**2 :: mass times the velocity change squared
• potential energy g*m*h :: mass times gravity accelerationg times altitude change

Shifting into "N" only prevent foot-off accelerator conversion of vehicle energy into battery stored energy. The kinetic and potential energy changes are only a function of the road geometry. If the road ascends, potential energy is increasing while the car slows, a loss of kinetic energy, and the drag loss. A descending road, potential energy will become kinetic energy if it is greater than the drag loss. A flat load, the kinetic energy is transfered into drag energy, a loss.

Close, the kinetic energy is being lost to vehicle drag energy. We agree there is no need to convert any kinetic energy into traction battery charge. Using "N" is the simplest and easiest way to accomplish this task.

The "slow down" on the down-grade is storing part of the potential energy that is trying to become kinetic energy into traction battery energy . . . minus the drag energy. The car does not increase speed, kinetic energy, and then stuff energy into the traction battery. It simply converts part of the potential energy into traction battery charge. But 'polishing the musket balls' is not why I'm posting in the thread.

I appreciate folks giving credit to good Prius friend Hobbit. What I am trying to find out if the advocates have metrics, their own experimental data, that quantifies how effective any given technique is in their own, application of the technique.

My experience has been the more involved the driving technique, the harder it is to see it consistently applied. So I look at the Top 20 lists and supporting spreadsheets and try to see some evidence of something other than slower average speeds leading to significantly improved mileage.

Bob Wilson

 

Bob Wilson - I got what you're saying. Your potential energy is when the car is on top of the hill, right? I was thinking of the energy in the battery. When I'm driving, I don't think that deep. I just want to keep the car moving without regen if traffic condition permits. The other general rule I go by is, use gas when power demand is great, when power demand is low then use battery or go to N.

 

In engineering, we like to test things . . . an A-B-A style where everything is kept as identical as possible and one variable is changed. Then three sets of tests are run:

1. A - baseline
2. B - one variable changed
3. A - repeat baseline

If the two A tests are identical, we take the difference between A and B as a credible difference that can be attributed to the difference. If A are not identical, continue flipping between now B and A until reproducible results attributable to each variable show up. Do not be surprised if the "null" result shows up . . . no difference.

So take something you do frequently, say commute to work, and the driving technique alternative, say cruise control, and do the experiment. We will own these cars for a long time, so in three weeks time, an A-B-A series can be done. But we have limited control of the weather so continue, A-B-A-B . . . until reproducible results arrive.

It is more fun to have credible data showing some variable has a measurable mileage effect and give quantitative numbers. Confirming a technique from good Prius friend Hobbit works. More importantly, this can help map the improvement:

• %_change = F(independent_variable)

Quantitative numbers for the effect, independently derived, helps us understand how effective a given independent variable is. It also helps map the limits for example, the speed range it is effective.

Bob Wilson

 

This might help:

1 hp ~= 745 W
1.34 hp ~= 1 kW

engine kW -> hp * 90% (transmission efficiency) -> wheel power -> drag limited speed

10 kW ~= 13.4 hp * 90% ~= 12.1 hp -> 61 mph
12 kW ~= 16.1 hp * 90% ~=14.5 hp -> 70 mph
15 kW ~= 20.1 hp * 90% ~= 18.1 hp -> 80 mph

From what I remember of Atlanta, these are fairly close. I remember the first time we were driving on I-20 towards Atlanta and when we reached the Georgia line, everyone sped up.

Bob Wilson

 

On Cleanmpg.com - Andrew (aka PaleMelansian) told Wayne Gerdes (xcel) that the Prius C ICE was running the most efficient when the Scangauge2 Xgauge LOD is between 70 and 90 as to avoid a wide open throttle situation -

Lets talk about the LOD setting on the scangauge - CleanMPG Forums
How do you use the various ScanGauge gauges? [Archive] - CleanMPG Forums

If you don't have a scangauge2 - the 3rd gen Prius ICE is running at or near its sweet spot approximately in the center of the HSI display when it is reading right under the "ECO" capsule.
The Scangauge2 normally reports that the ICE is burning between .50 to .90 gallons of fuel per hours at this range.

gravity and speed trumps engine efficiency.
Accelerating downhill increases engine efficiency.
Driving under 40 mph increses engine efficiency

 

Just read those articles above. What does FASing mean?

 

FAS = Forced Auto Stop(noun). This is an advanced hypermiling skill for a conventional gas motor vehicles fitted with an RPM gauge, a manual transmission, and a two start mode electronics that allows for: 1. start up electronics only , 2. start internal combustion engine (ICE) . Conventional gas Honda motor vehicles with manual transmissions are a favorite hypermiling FAS vehicle, e.g. Honda Fit with 5 speed transmission. Full Hybrids like a Toyota Prius automatically do FASing because it has built in stop-start idle technology.

Normally, in a Pulse and Glide (P&G) cycle, during the Glide phase the internal combustion engine (ICE) is idling in Drive mode so it is burning gas - not much but it still is.

The FAS cycle is a modification of a P&G. In a FAS cycle, to enter the Glide phase, while the car is still in motion and the transmission is in a drive gear (e.g. 4th speed), the driver turns off ICE and then restarts the car with the electronic on but the ICE off. During the FAS cycle Glide phase, the ICE is turned off but the car is still moving forward with only manual brakes and steering available. Anything that uses ICE to power it like power brakes and power steering is not available during this Glide phase, because of this it is easier to FAS using a lightweight vehicle. During a FAS cycle, to enter a Pulse phase, while the car is still in motion, the driver switches the transmission to Neutral, turns the ICE back on while the car is still in motion, presses the accelerator to gets the ICE to the proper RPM that matches a desired-transmission gear setting, then switching/pops the transmission to that proper target gear (e.g. 3rd speed) setting to accelerate/pulse.

clear as mud?

hope this helps

Walter