A comparison of highway driving methods for the Toyota NHW20 Prius

[nerfer]

Originally Posted by bestmapman

From this expeiment it would seem that, for highway driving, aerodynamic improvements would yield more results than driving tehniques.

It seems from my prospecive, a lot of people have made significant mechanical mods. Has anyone made any aerodynamic mods, such as tail cone or wheel skirts.

The Kammback style uses the principle that a teardrop shape is the most aerodynamic, but the back part that narrows to a point is not needed and just adds friction, hence the shape for the Prius. So I'm not sure that a tail cone would do much, but I would think there's more room for improvement underneath, where the axle, transmission, oil pan, catalytic converter etc. are. I'm not sure how much air flow is needed for the engine, particularly if you have the front grill blocked, so that might be an issue if the bottom is covered with panels. (I remember my '87 Sentra losing power on a long winter's drive until I finally realized that freezing rain was blocking the grill and no air was getting to the engine, so every hour I'd have to stop and knock ice off the grill).

Another area is the rear-view mirrors - i doubt it would be economically justified, but for improved aerodynamics and appearance you could replace those with a small camera and use an inside LCD by the little cut-out windows instead. Wheel skirts might be more practical.

I imagine there's an aerodynamics thread somewhere?

[douglas001001]

Originally Posted by bwilson4web

ps. In the spirit of the holidays, I'll hold off on commenting about other driving protocols that have yet to be rigorously tested.

Why, in a controlled test comparing a computer that can't see the road ahead against one of the best prius drivers on the planet, do they produce similar results?

The computer is making decisions based upon the state of the car when it makes them (speed, battery charge, etc). How is the computer making those decisions?

Why does the computer go through warp stealth one day, then the next day go through super highway mode at the same spot at the same speed?

How can I use that knowledge to make better decisions when I'm driving?

A driver needs to know how to approach a highway segment under various starting conditions. How should one approach a drive when starting with a lower SoC versus higher?

Unless you can tell me why, then you shouldn't (appear to) discredit the thoughts of others who are spending time trying to figure out those answers.

I think the answers are there, if the data is collected and used in the proper manner. I don't have a way to do it.

[darelldd]

Originally Posted by nerfer

The Kammback style uses the principle that a teardrop shape is the most aerodynamic, but the back part that narrows to a point is not needed and just adds friction, hence the shape for the Prius.

Hmm. The Aptera folks sure don't agree! And I also don't agree that the Prius is tear-drop shaped with the back cut off. The Prius doesn't start with a bulb nose and taper to the back. And there's the fact that the Cd of the Prius just isn't that great when all things are considered. From where I'm sitting there are plenty of Aero improvements that the Prius could enjoy. Heck, shroud the wipers better to begin with! Smooth wheels and skirts. Make the rear end concave to decrease the vacuum. And certainly the belly pan as you mention. Lots easier to make an aero EV, so let's start with that mod.

[CatahoulaB]

Ok I read everything and unfortunately I'm still dumb.

Can someone give me a really dumb person explanation on the difference between Warp stealth and super Highway mode. I'm pretty sure I use both intuitively. I'm just not sure I understand the distinction.

Is the difference simply that one involves regeneration and one doesn't?

Thanks.

[patsparks]

Originally Posted by darelldd

Hmm. The Aptera folks sure don't agree! And I also don't agree that the Prius is tear-drop shaped with the back cut off. The Prius doesn't start with a bulb nose and taper to the back. And there's the fact that the Cd of the Prius just isn't that great when all things are considered. From where I'm sitting there are plenty of Aero improvements that the Prius could enjoy. Heck, shroud the wipers better to begin with! Smooth wheels and skirts. Make the rear end concave to decrease the vacuum. And certainly the belly pan as you mention. Lots easier to make an aero EV, so let's start with that mod.

Yep, have to agree, the Prius Cd is shocking, it's only the lowest for a 4 door or 5 door hatch in production. Get ya flipping act together Toyota. A world full of engineers and designers cant package a 5 seater 4 door as well but you are below par.

[JimboK]

Originally Posted by CatahoulaB

Ok I read everything and unfortunately I'm still dumb.

Can someone give me a really dumb person explanation on the difference between Warp stealth and super Highway mode. I'm pretty sure I use both intuitively. I'm just not sure I understand the distinction.

Is the difference simply that one involves regeneration and one doesn't?

Thanks.

OK, I'll see if I can get it to a "See Spot run" level.

Warp stealth is induced the same way as a low speed glide: release the accelerator completely and then feather it back down a tiny bit. The difference between a low speed glide and WS is that in the former, all arrows disappear from the MFD (implying no current flow at all, which is actually not the case, but we'll save that for another day -- we're keeping it simple here). With the latter, the MFD shows energy flow out of the battery. WS creates a freewheeling effect similar to a conventional car running in neutral, though there is no fuel flow to the ICE. It is used for downhill segments > 40 MPH where momentum is enough to maintain or gain speed. Though not part of the WS technique itself, many that use WS often alternate it with flat or uphill segments that attempt to maintain ICE RPM in an efficient range (what I've described in my paper). The rationale for the whole package: Either the ICE runs in its most efficient range or it doesn't run at all.

SHM involves keeping the pedal mostly steady and in a position where the ICE runs nearly continuously at a very low RPM. Hobbit (and others) have suggested that the low end of ICE efficiency is in the range of 1400-1700 RPM, depending on vehicle speed. The ICE supposedly "loafs" below that. But SHM RPM is lower, generally <1300. Even though it supposedly is running inefficiently at those speeds, there is still enough power to maintain speed or allow an ever-so-gradual speed decay, depending on terrain. In my own experience, SHM probably is not for interstate driving. When the vehicle approaches interstate speeds, the power needed to overcome the increased wind resistance is not provided at those low RPMs. Nor is it suited for hilly terrain; the low RPMs won't supply the power needed to climb even modest hills. SHM seems most appropriate for non-interstate rural roads on mostly level terrain with light to moderate traffic.

Neither aims to increase regeneration. In fact, a basic principle of maximizing mileage out of the Prius is to avoid regeneration whenever possible. Instead, use kinetic energy to your advantage. (That is what WS does.) Energy actually is wasted through regeneration (though, of course, not as much as braking in a conventional car wastes).

[CatahoulaB]

Thanks Jim on behalf of all the dummies.

More questions. It seems I've been using SHM on the Interstate, definitely dangerous I guess I'll stop. Though it's addictive when nobody's behind you.

If I'm using WS down the hill, wont the ice charge the battery after it depletes? Why wouldn't I accept less speed down the hill and regenerate and then have plenty of battery after the hill? Say, in a situation where after the hill on a country road I slow down to battery only speeds.

I have a steep down then up right before I get home. I regenerate (no slight down pressure on the accelerator) on the down hill. Then when I get to the top of the hill on the other side, I use battery only the rest of the way to the house. Is this ok/better in this scenario?
Thanks.

[JimboK]

Originally Posted by CatahoulaB

Thanks Jim on behalf of all the dummies.

More questions. It seems I've been using SHM on the Interstate, definitely dangerous I guess I'll stop. Though it's addictive when nobody's behind you.

If I'm using WS down the hill, wont the ice charge the battery after it depletes? Why wouldn't I accept less speed down the hill and regenerate and then have plenty of battery after the hill? Say, in a situation where after the hill on a country road I slow down to battery only speeds.

I have a steep down then up right before I get home. I regenerate (no slight down pressure on the accelerator) on the down hill. Then when I get to the top of the hill on the other side, I use battery only the rest of the way to the house. Is this ok/better in this scenario?
Thanks.

On behalf of this dummy, you're most welcome.

Yes, if you use WS on a long enough downhill, eventually it will deplete the battery enough where the ICE insists on lighting to recharge it. But the only time I've seen that is either coming down a mountain or when I've begun WS with a low battery to begin with. When you reach the bottom and begin climbing the next one, the ICE will do its magic and gradually begin topping it off again.

Again, avoidance of regeneration is best. Regeneration involves conversion of energy forms, with a little energy lost at each step: kinetic energy converted to electrical energy converted to stored chemical energy in the battery, then a reversal of the process to use that energy again. Best is to use kinetic energy to your full advantage by reducing as much mechanical drag -- and regeneration -- as possible. Feathering the pedal slightly accomplishes this. If that becomes unsafe or illegal (from excessive speed), then next best is regenerative coasting with the go-pedal fully released, followed by regenerative braking -- light to moderate brake pressure at 7+ MPH. Below that speed or with hard braking, the friction brakes apply and most kinetic energy is lost to heat.

It may seem counterintuitive, but those with the best "hypermiling" results in the Prius generally achieve them by staying out of the battery as much as possible -- again to avoid the conversion losses.

As for the hill that approaches your house, I would glide (<40 MPH) or WS (>40) down the hill if safe and legal, developing as much momentum as possible to help carry me up the other side.