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Old 11-03-2008, 10:13 PM   #1
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Lightbulb idea for Prius

So I was annoyed that I couldn't P&G in my mom's Prius this weekend and came up with a pretty ingenius but simple idea for how the Prius could have easy P&G at any speed and not the careful pressing of the gas pedal currently required to P&G. It turns out it's easier to P&G in my VX than it is in a Prius.

So my idea is this: equip the Prius with two modes of driving. The normal mode it is always in, where when you take your foot off the gas the car slows down and regenerates the brakes and a mode where it does not brake automatically. The way to implement the new mode is to put a button on the little shifter nob. When you press down on the button it engages neutral "naturally" so you don't have to push the pedal down slightly as is the current setup on the Prius' Synergy Drive. The ingenius part is that the button would press in and then pop out again whenever you press the brake or gas so as to be sure you won't inadvertently brake without regenerating the batteries.

So let's say you want to P&G at 55 to 45mph. You can accelerate to 55, press the N button on the shifter nob and let the car coast to 45 (without it braking the car like it usually does.) When you get to 45 just press on the gas again (the "natural" neutral will disengage and the button will pop out again.) When you're back up to 55mph and ready to glide again just press the N button again. Shouldn't Toyota do this? Can you think of any reason why not? As soon as you hit the break or gas it would re-engage the automatic braking mode the car is normally in. It wouldn't be unsafe.
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Old 11-04-2008, 06:12 AM   #2
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Why would you want to P&G a Prius? P&G is so that you use the engine in its most efficient load/rpm range. The Prius already does the job itself; that's the whole point of the car.
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Old 11-04-2008, 07:20 AM   #3
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Quote:
Originally Posted by theholycow View Post
Why would you want to P&G a Prius? P&G is so that you use the engine in its most efficient load/rpm range. The Prius already does the job itself; that's the whole point of the car.
Are you saying you can't get better gas mileage P&Ging a Prius? It's better to coast than to brake and then accelerate again. Anyway, seems you are missing the point of my post. Coasting is the most efficient way to save gas in a vehicle that has low Cd and LRR.
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Old 11-04-2008, 07:56 AM   #4
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I don't know, but based on my understanding of the theories behind P&G and how/why the Prius works, I'd guess that you can't get better mileage out of it by P&G.

It's better to avoid braking and accelerating again, but you don't need P&G for that, you just need to plan better and choose speeds better. However, in a Prius, the penalty for braking and accelerating again isn't so bad, because it regenerates some (a lot?) of that energy.

There are folks who hypermile Priuses, but I haven't seen any here, and they probably need a whole forum specifically about hypermiling Priuses. I'd suggest googling for such a forum and finding out what they do. I think I remember seeing such a forum once.
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Old 11-04-2008, 08:10 AM   #5
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if it were me, I would PM diamondlarry. he has a prius getting close to 90 mpg and (as far as I know) he hasn't done any kind of plug in conversion to it. that seems to push those vehicles to pretty high MPG.

I would talk to him about what he has done and how he is achieving such high numbers.
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Old 11-04-2008, 08:32 AM   #6
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diamondlarry: http://www.gassavers.org/member.php?u=14
All his posts: http://www.gassavers.org/search.php?do=finduser&u=14
All his threads: http://www.gassavers.org/search.php?...r=diamondlarry

It turns out he does EOC P&G his Prius:
http://www.gassavers.org/showthread.php?t=5319
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Originally Posted by diamondlarry View Post
To get the mileage I did, I did huge amounts of P&G and no highway. I have an EBH on a timer that I use every morning. I haven't figured out a way to plug in at work so I do have a relatively cold start every afternoon. Fortunately, the Prius' coolant thermos helps out a little.
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P&G= Pulse and glide. Pulse to a higher speed target and glide to a lower speed target and repeat. In the Prius, the glide portion is usually engine-off. EBH= Engine block heater.
I guess he knows how to get it into neutral.
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Old 11-04-2008, 08:47 AM   #7
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Having driving a couple of different years 2005 and 2007 or 8 Prius(s) the first problem is when you put it in neutral there seems to be an issue getting it back in drive when moving - there is some trick to it but I can't seem to find that post. Second - you don't have to add a button or anything - all you need to do is to find that sweet spot on the gas pedal that allows the car to coast which is just past the regen deceleration position. Then the next thing is to find that second sweet spot range where the electric motor starts to work and it varies the power to the electric motor but doesn't start the gas engine yet. These spots are already in the car throttle - they are just really tricky to find and could use a detend or different spring tension to help hold them there. I have had the newer model that I drove going 60mph on electric drive with the gas engine off on a slight down hill so I know it can be done. The earlier models would keep the engine running over 40mph no matter what you did.
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Old 11-04-2008, 09:32 AM   #8
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It's all there in the gas pedal. Touchy to find, but it's there.

My best run is 119 mpg over 16 miles. I relied very heavily on P&G to achieve that. Just hitting it into N doesn't do it - the engine still runs. You have to use the pedal position to induce a glide, then you can use N to rest your foot if you like. When you get the pedal-induced glide, the engine shuts down.

I'd suggest reading the Prius stuff at CMPG posted by DiamondLarry, Xcel and Dan. They cover it much more thoroughly.
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Old 11-04-2008, 09:37 AM   #9
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So, now that I know I was very wrong....why does P&G work? For the same reasons as it works on a normal car?
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Old 11-04-2008, 10:19 AM   #10
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Same reasons - BSFC. Low rpm and high load is the most efficient operating mode. Gain momentum efficiently, then coast to maximize your use of that momentum.

The Prius is better than other cars at running at the best BSFC naturally. It's better, but not perfect. The Prius is a more refined starting point than most, so there's less opportunity to improve on it. Look at Wayne's review run in a Prius (137% of EPA) compared to his lifetime in the Accord (167% of EPA).

Cruising at 50 mph in a midsized car, with the 1.5L engine running 13xx rpm, is pretty efficient. It loads it down a little more, pushing it into the better BSFC point, and then diverts the excess output into the battery pack for later. At lower speeds, less output is needed to keep the car rolling, so the feed to the battery is a larger percent of the total output.

If you can eliminate that feed to the battery and use all the output for momentum, you reduce the conversion losses to and from the battery. By doing P&G yourself, you're taking control and doing better than the "pretty good" internal management.
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