Friday, April 29, 2011

Trip record from URI, 72.4 mpg

This post is less for public consumption, more for me to keep track of trip records on one of my favorite routes and give myself some helpful notes for the future. Great route, so many driving challenges, fun and interesting ride.

-Outside temps mid to high 60s.
-Engine coolant started around 80 something° F, lower than previous record.
-Grill blocked for first several miles, took out at stop sign for rest of trip.
-Stage 4 later than previous record.
-69.4 mpg at end of Saug. Previous was 72.0.
-Biggest change: tried to maintain 15 kW at all accelerations even at low speeds, no babying the engine. This seems to have given me better mileage over latter half.
-Was able to be going a couple mph at tough uphill light before start, but then was stopped at the next one still uphill. Also stopped behind a school bus (kept rolling probably 10 mph) and used engine much more to pass the bus to avoid future stops. One or two more traffic light stops.
-End result 72.4 mpg on dialed down Scangauge, 71.1 mpg previous record.

EDIT: Next day, I got 72.3 mpg on same route. Remember, this is the dialed down, relatively accurate Scangauge, not the overestimating display. Thing was, I got stopped at basically every single stop light. Outside temps were actually 10°F cooler than yesterday. The change from yesterday was that I always accelerated at 15 kW, even at the start of the trip (yesterday I started trying it halfway through). Easily would have been over 75 mpg if I didn't stop and start 6 times, including the big uphill light. Ended with much higher state of charge, too. Absolutely incredible, this maximum torque thing...

Thursday, April 28, 2011

Hypermiling attempt #2, 92.4 mpg over 14.9 miles

Attempt numbah two:

92.4 "real" mpg
from Scangauge



With the warmer weather and recent talk of hypermiling on PriusChat, I couldn't help but go out (even on an otherwise busy day!) for a little under an hour of fuel economy practice. With my limited time, the only place nearby was up the big hill in my town, on some back roads with low speed limits and relatively sparse traffic. The biggest problem was the route: I could only drive for about 5 minutes before coming to the end of the road, and would have to do a 180 to go the other way. There was also a stop sign in the middle. This means I had to stop every 2.5 minutes.

I didn't glean too much from this run, other than some useful ideas regarding pulsing and gliding on slight hills. I actually tend to get better mileage in the middle of one of my commutes - I can usually get over 100 mpg for fifteen minutes straight if I don't get stopped at too many lights. This run was interesting for me since I was trying to use lower speeds for a change, not more than 35 mph, sometimes lower, and also seeing what's possible while stopping so much.

While the best results on flat ground historically tend to be between about 18-20 mph on the low end and around 34-35 mph on the high end, I found slowing to 18 mph on a hill and then accelerating to be a bad idea. You're still trying to accelerate with a gas engine going at relatively high RPM but low torque with the slow speeds. This results in a longer burn time to reach the desired speed.

The simple solution is - well, there isn't one, but at least in the particular terrain I was on, I did try to go a little faster, keep momentum, and make sure I came into the hills with some speed, which I would sort "artificially" maintain with a very short pulse to not destroy momentum while cresting at the top. Using a small amount of EV while heading into the hill (not more than 10 amps, so it's less than warp stealth use) will help keep it moving a tad more than jumping straight to gas, but without a huge drain on the battery.

I don't have specific segment mpgs, but the 5 minute segments approaching the hills with more speed, air resistance be damned, easily yielded better mileage visually than the other bars.

Finishing up the stop and go section of the trip, I had about 88 mpg on the Scangauge. I tried an interesting, circuitous, and mostly downhill route home to get it up to 92 :-)

Meanwhile, still searching for an appropriate road for pulsing and gliding near my home - without stop signs or lights!

Thursday, April 21, 2011

Fill-up, Friday, April 22, 2011

483.1 miles
7.910 gallons
$3.899/gallon

61.07 mpg
3.85 L/100km


Wentworth's complete fueling history

Whew, first tank over $30, gas is indeed getting pricey!

This tank started out terribly, with a couple trips out of the ordinary. One roundtrip was about 14 miles at under 50 mpg (with hypermiling!), and there was an evening where I took the highway in a heavy rainstorm with constant heavy winds and 40 mph gusts. I got the lowest mileage of any "lengthy" trip ever on Wentworth that night, a nightmarish 46 mpg (nightmarish is used lightly - the worst mileage imaginable in my car is over double the mileage of the average American passenger vehicle).

I still managed over 60 mpg for the tank, which is more a testament to the slightly warmer temperatures than anything else. It means that besides the trips I listed above, I averaged around 63 mpg. I'm pretty sure I could get near 70 mpg for a normal tank in warm weather and great conditions, but I have a feeling I'm going to be much more limited than most in the attempt by the terrain of my commutes.

Maybe I should start parking at the top of the big hill near my house and walking a couple miles home? :-) Seriously, for most of the week that would make a huge difference. I've previously calculated using about 20% of all the gas in a 27 mile trip in the first 2 miles, a trip that I do at least three times a week. On that commute the other week, with the big hill at the beginning, my 5-minute mpg bars were as follows:

25 mpg, 100 mpg+, 95 mpg, 100+ mpg

Maybe just for one tank I could take drastic measures for the fun of it!

Monday, April 18, 2011

Wentworth's first oil change

As the original intention of this blog was to document my ownership in addition to my fuel economy notes, here's a rundown on Wentworth's first oil change.

It happened to be my first solo oil change(!). A friend who's building his own car and likes to do some racing showed me how to change the oil on one of his cars. That same weekend he also showed me how his car can go 0-60 in about 4 seconds, and what it's like to travel over 100 mph (which was awesome!), though of those three things the oil change seemed the only thing in common with the Prius that I could try myself.

I should mention that this thread on Priuschat was also a great resource.

Clearance is quite low on the Prius, and being difficult to get to the car's floor jack point(s), I forewent my neighbor's borrowed hydraulic jack and instead bought a pair of Rhino Ramps 8000 for about $47 total with tax, which I'll be able to use for many years. It was easy to get up on the ramps, and didn't scrape as far as I could tell.





This last pic also shows Wentworth's wonderful makeshift grill blocking. Better contains heat in the engine and allow it to warm up faster in cooler weather - for better mileage, of course!


I needed a 14mm socket for the wrench. (don't bother reading the computer screen in the background, it's just this post in the works!)



Now under the car we can see the oil drain plug (and a bunch of rust, that's for another day, though).





This thing was on tight. I believe it had only been previously changed at the dealer by the first owner, and being the skinny, opposite of brawny sort of guy I am, after struggling with it for awhile, I had this terrible feeling that after buying the filters and "crushable" washers in bulk that I'd have to go to the dealer anyway to get it changed.

My dad suggested gently hitting the end of the wratchet wrench with a hammer, or warming up the engine for two minutes, but luckily I found a slightly longer wrench before I had to try any of this. All it needed was a little more leverage, and it came off no problem.

I then saw why Hobbit suggests unloading the suspension on the driver's side for an oil change. It took forever to drip out, what seemed like much longer than when my friend showed me on his car, and would've drained much more quickly if it were tilted a little bit. Not an option with the ramps, though, so no big deal, just took longer.

Then came the filter. I had bought an oil filter wrench which conveniently attaches to a ratchet.

Oil filter and filter wrench (and Mac!).


On the ratchet.


Fits right onto the filter.


On the car, the filter's really wedged up there. Not really knowing what the hoses around it do, I just tried not to touch anything else!



At first it wasn't working too well, and there were a couple minutes of medium level panic when I thought I wouldn't get the filter off after draining the engine of all its lube (ruh-roh!), but in the end it worked out. There's no possible way that would've come off by hand - the oil filter wrench was essential.

I also learned a valuable lesson (which I'm sure all of you know - humor the newbie with some laughter): push UP on the oil filter while unscrewing it to keep the gasket sealed so that it doesn't drip all over you as you continue to unscrew it. Oil covered hands after the filter...

Drain plug back on with a new washer, new oil filter with a little oil smeared around the gasket snugly hand tightened to avoid the ├╝ber-tightness of the dealer, and in went three quarts of 5w-30 up top. Since it's almost summer and since my engine has been used to it for almost four years, I'm going to stick with that weight even though we've heard recently 0w-20 is alright even on older model Prii. No need to make my car the test case.

I then ran the engine for a minute, then let the oil settle so I could check the level and add a bit more.

Cleanup as I waited for the oil to drain into the pan:



The oil ended up so light on the dipstick that I couldn't tell where it went up to, so I may skip this in the future. I put in another half quart. Today after I drove somewhere, I checked it and found it slightly below the top dot, so it appears 3.5 quarts is absolutely perfect for the 2004-2009 second Gen Prius (mine is 2007), I'll just aim for that in the future.

All done!


Such a cool little beast under there. Can't wait to try the transaxle fluid at some point...



Altogether a good deal. Took me way longer than everyone else in the world, being my first time, but learned a lot, and it didn't cost much. Filter from a pack of 10 was $4.80 total, and $1.40 for the drain plug washer. Oil was oil. Easily under $20 for the change, and was a lot of fun!

Wednesday, April 13, 2011

Fill-up, Tuesday, April 12, 2011

478.1 miles
7.567 gallons
$3.639/gallon

63.18 mpg
3.72 L/100km


Wentworth's complete fueling history

Understanding the numbers

You may be wondering why I "only" get low 60 mpgs or high 50 mpgs on my tanks when all my mileage pictures seem to be easily up in the 60s or 70s (well, at least I was wondering!). While I have lots of nice shorter trips, my other, longer commutes involve a series of hills and hard accelerations, as well as lengthy periods over the Prius glide threshold of 42 mph. One route I take twice a week is apparently net uphill, and while I can usually maintain 60 true mpg (as opposed to optimistic Prius display mpg) on the first leg of the trip, it can be tricky. The way back I can often get mpg of 62-66 mpg fairly easily, despite those same hills in reverse, and 21 stop lights to contend with once I get off the higher speed portion of the trip.

I also have a series of short trips for work that are unavoidable. I've estimated before that over the course of two weeks, they knock off a small 2 mpg or so from the tank. Not a big deal, but just enough to drag you down to 60 or below.

Three times a week when I leave the house, I head south - directly toward a huge hill that means I never get better than 25 mpg during the first five minutes, which kills the mileage for the trip from the get go. On these trips of 27 miles I use nearly 20% of my gas for the trip in the first 2 miles!

And of course, once or twice a tank you get crappy weather, and all the pulsing and gliding in the world won't save you from the wind and rain. At the beginning of this tank I had a miserable 55.8 mpg displayed (so probably 53-54 mpg in real life) over my longer distance commute in a delightful little bout of wind and rain Mother Nature had sent our way.

Trip o' the week

I loved this trip. Yes, I've gotten and can get better mileage on other trips, like the short trips where I just glide and EV most of the time, but this one is the most satisfying, since it's not at all pure pulse and glide land - half the trip is too fast for gliding anyway. There are hard accelerations from 0 to 50 mph, hills to climb from a standstill, some 2400+ RPM spots (pedal to the metal! well, not really, but maximum desirable warp, let's say) and after all that, the dreaded 21 stop lights.

The previous trip record for this particular route by the Prius display was 73.3 mpg. I knew I was likely going to break it right from the start. My coolant was still warm from the drive over, so I got into stage 3 very quickly and was able to glide/EV within a couple minutes of starting up. I waved a tailgating wench around me at a stop sign (no accusations of the Prius holding up traffic - I was already going 10 mph over the speed limit leading up to it), and warp neutraled it down a slight hill. At the next stop sign I did my new favorite routine, which is forcing the gas engine on to get to stage 4. After the engine turned off, on I went.

At the end of a road where I usually end up with mpg in the 60s, I was greeted with this:



Nice! The mileage wasn't going to stay there for long, since just after taking the picture, I had to accelerate from 0-50 mph quickly, and uphill. Soon followed another 0-50 acceleration (I had more time on this one and went EV until 20 mph). As soon as I'm up to speed, there's this great slight uphill that I can maintain 50 mph on getting 50 mpg. All the other cars on the incline around me were surely getting about 20 mpg or worse at that point - which is why every car should have an mpg display, but I digress :-)

Warp stealth, hill, warp stealth, hill, warp stealth, bridge, warp stealth, some burn and gliding as speed limit goes down to 40 mph. I slow to a stop to pay a toll - record mpg as of this point in the trip, nice!



Then 4 to 38 mph acceleration up a bridge, the killer - 2500 RPM to keep speed, then I was able to ease up to 2000 RPM somehow for the upper half, losing speed slightly.

After the downside of the bridge, I'm back to the 21 stoplight part of my drive. I remembered from the record in February that I got very lucky with all green lights, and realized that they would be the deciding factor. Things were going OK until one spot where I needed the ICE for safety where I would normally glide, and then got stuck at a complete stop at the worst light of the entire commute. It's halfway up a relatively steep slope, and I'm the first one in line, meaning a brisk acceleration will be needed uphill. I climb the hill at the green light, and try not to shudder seeing the numbers - 4 mpg, 5 mpg, 6 mpg (did you even know a Prius could get that low?? :-D). It shaved a ton of the average, and I was now slightly below where I had been the last time at this point.

I managed to scoot through the second to worst light (before an uphill) while it was yellow, salvaging the trip, and while I had to slow at other ones, only got completely stopped at one more.

Toward the end of the trip I went to town using EV where I would normally need the ICE, and it worked. Barely beat the record. 73.8 mpg display, Scanguage a more realistic 71.1.



The awesome part is seeing the improvement you've made hypermiling. I got stopped at two more stoplights than the last time, including the huge uphill one, and still managed to beat the record. Very happy!

Monday, April 11, 2011

Wentworth in the shop - again

Lest you think the title implies trouble, let me disabuse you of this notion from the start :-)

Last month, Wentworth went in to get a little preventative work done, and also fix a potential problem, which was a rattle/clunk at low speeds over bumps.

The clunk was given the attempted fix of a 2008 engine mount Toyota service bulletin, but alas, after driving it home, it was clear the sound was still there. I thus wanted to bring it back to check it out, and at 40,000 miles, it was time for a tire rotation anyway.

Over the last month I've actually grown less concerned with the sound. It has been mentioned in PriusChat (one such thread here) by numerous people, which, at first glance, should be cause for concern, but with another look, tells me more that the sound is apparently a "Prius thing", and while not my favorite thing about the car, it appears that it has no adverse effects over the course of many years, despite its widespread presence.

Patrick Wong (incredibly helpful Prius guru for whom I have great respect) also told me that his three Prii over the years have done the same thing, and he hasn't been able to figure it out, and so just lives with it. If Patrick feels that it's fine and not a long-term issue, then I'm inclined to think along those lines, too.

I will update this is there is ever a problem, but for now, it seems innocuous, and the thing still gets me 70 mpg on occasion.

On another maintenance note, Prius owners, to keep rust off your infrequently used rotors, just shift into neutral while going down a hill sometime and brake nice and hard with no one behind you.

Tire rotation was $19.95, air set to 42 psi front and 40 rear, no other charges. I went to Premier Toyota of Newport again, much better experience than last time. More communicative, the tech went out and rode with me to hear the sound, and they followed up a couple days after to make sure everything was going well. Definitely feeling better about them after this.

Wednesday, April 6, 2011

Dawdlers get the best mileage

Looks like I'm getting the hang of pulse and glide. Luck is involved here, too - green lights, no one behind me. Was aiming for around 76 or 77 on the Prius display - you can see that toward the end whatever experimentation I did with a slightly different route was a total mpg failure :-)

I've dialed down Scangauge's peppy fuel economy optimism by about 5%, so these days it's showing the approximate true mileage. I'll happily take it for weather in the 30s!

Saturday, April 2, 2011

Prius-ing for Dummies - beginner Prius mileage tips

It just so happens at my place of work there's a lovely bunch of environmentally minded people who own Prii (sometimes you see 5 or 6 of them in the little parking lot, including one of Wentworth's twin charcoal grey brothers or sisters). Now, most of them would fall under the umbrella that 95% of drivers fall under: they have to get places, and they need their car to get them to those places.

It's hard to remember for Prius enthusiasts armed to the teeth with engine coolant temperatures and doing mental math while driving to compute the requisite engine-off glide distance needed for a given mileage figure that everyone else in the world just drives, and many, including me at this point (though I'm learning!) have no idea what's even going on inside their engine.

Recently some of these people have made passing comments expressing interest about improving their mileage. This post is thus for the "beginner" Prius driver. Even if you've owned it for several years, if you don't know how to initiate an engine-off glide, for example, you will be able to learn a couple techniques to improve mileage by 5-10% at the very least while still driving "normally" with the flow of traffic. Since this is intended for anyone to be able to use, don't worry about any technical specifics - they're just fyi, but not necessarily relevant to general operational knowledge.

Please note that while most of this post is for general Prius use, some of the info and all of the pictures involved are specifically for model years 2004-2009, aka the Generation II Prius. If you have a model year 2010 or newer, please refer to this link, which is a very good starting point, but not too detailed, and has the occasional easily forgivable minor information error.

You'll find info here on the following topics:
1. Glide
2. Warp stealth
3. Super highway mode
4. Regenerative braking
5. EV mode

I would suggest taking one technique at a time and learning to apply it quite well, and then learning another one. You want to feel comfortable enough to use it without having to stare at your multi-function display the whole time, mostly for safety reasons. So, onto our first technique.

Technique #1 - The Glide

What it is

This is a big one, the meat and potatoes of higher mileage in non-highway driving. In its very basic form, the Prius glide is a state achievable under 42 mph where the gas engine turns off completely while at speed. A very small, practically negligible current comes out of the battery pack to keep the car rolling a little easier than if you were in neutral, or more than a conventional vehicle rolling while off in neutral (don't try this at home, kids). The Prius glide is a built-in, perfectly legal function that shouldn't be confused with illegal neutral coasting in other cars. The fuel savings are enormous, as we'll see in a minute.

Preparation

A glide is only possible when the engine is properly warmed up. On a warm day, that might take you 3 minutes. In frigid weather, over 10 minutes. The other day in 27°F weather, it annoyingly took me about 3 miles. I remember once in 19°F weather it took well over 10 minutes, even with the heat produced from some highway driving.

It will also be easier if you have already driven your car that day, or just a few hours prior. The Prius has a thermos (like you may for your morning coffee) to keep the engine coolant hot/warm even outside of car use. When you turn your car off, it pumps hot coolant into the thermos so that when you turn on the car next, it can get up to optimal temperatures more quickly, providing the heat needed for the engine, electronics, and various emissions reductions systems. As an example, the other morning my coolant was very cold, around 30°F (outside temperature). I drove to work. I parked at 8:30am with coolant now at 177°F. When I left to go home four hours later at 12:30pm, the coolant, thanks to the thermos, was still easily over 100°F despite sitting out in 30s and low 40°F weather for four hours.

To provide a little extra information for the curious (though this is not essential to remember), there is one more requirement for a glide once warmed up. This next paragraph will likely be cause for mild confusion to the new reader, but I can assure you once you try it yourself it becomes simple to understand. If you're in the area I'd be happy to demonstrate.

The first time in a given drive that you warm up the car (at the start of the drive, of course), you will enter what is known as stage 3 operation. There is no indication on your display for the different stages, you just have to know what they are. During stage 3 in the Prius, you can only enter a glide when the speedometer reads 35 mph or higher, but not higher than 42 mph, as mentioned above. If you try to do a glide with the speedometer reading 34, even if you feel you're going 34.99 mph, the engine will just stay on. To get to the next, final, and most desirable stage, known as stage 4, where you can glide at any speed under 42 mph, you must:

Allow the engine to idle for 5 to 10 seconds, and then shut down completely by itself. You can guess that this usually happens at a stop sign or stoplight. The moment the engine shuts down, congrats, you'll be in stage 4, and likely for the rest of the drive! Now you can initiate a glide at any speed under 42 mph, not just at or above 35 mph as in stage 3.

"Just get to the point already!" How to use it

On your multi-function display (screen in the middle), touch "Energy" if it's not already selected. Although it's fun and more user friendly to look at the bar chart on the "Consumption" screen, you actually need info from the energy screen to get the best mileage.

Normally when driving and accelerating your energy display will look something like this:



Or maybe this, if you're just starting up an acceleration:



Once you've satisfied the above conditions to enter a glide, simply lift your foot completely off the pedal. At this point you'll see this:



The blue or green arrows (which color depends on your model year, they mean the same thing) pointing into the battery indicate a state of regenerative braking. When this happens, you can easily feel that you're slowing down! To get into a glide, you want to conserve momentum, so jump to this next part quickly.

Push down ever so slightly on the pedal. You should see all arrows disappear:



You're now in a glide. If you see the following, though, you've pushed the pedal too far:



The yellow arrows indicate EV mode (electric vehicle mode), which is sometimes useful, however is not a true glide. Let up a bit to get into the no-arrows state you saw above.

Mileage

The glide practically, or at least for mathematical purposes, gets you infinite miles per gallon. Use it, use it, use it!

As a mileage example, let's say you have your foot on the gas for 0.3 miles with the instant mpg reading exactly 30 mpg. If you are then able to engine-off glide for an equivalent distance of 0.3 miles, your average for the entire distance is 60 mpg. If you glide for another 0.3 miles after (so 0.3 miles of acceleration or "pulse" on gas, then 0.6 miles of engine-off glide), you are at 90 mpg over the entire 0.9 miles. Not bad! This is, of course, almost never practical, and not safe in heavy traffic. But even without extreme use of glides, they will be notably beneficial to your mileage.

For a normal driver, without delving too much into the hypermiling technique known as pulse and glide (an example of which you just saw in the previous paragraph), you can use the glide on downhills, when coming to a stop, or even on flat roads in normal driving when you are content to just about maintain speed or there is a slower vehicle ahead of you but you want to avoid losing momentum by braking. Most Prii come with fairly low rolling resistance tires, and all have wonderful aerodynamics, meaning they'll roll a good deal just on momentum compared to other cars. Give it a try, see how far you can go when there's not any traffic behind you.

Table of contents


Technique #2 - Warp Stealth

What it is

Warp stealth is a mode that allows you to cut fuel to the injectors while travelling at higher speeds. On a generation II Prius (2004-2009), the gas engine must run at and above 42 mph to safeguard the electric motor (46 mph on model years 2010-present). What this has traditionally meant is that the best mileage is only available under speeds of 42 mph, since only then is it possible to perform a true, high mileage-inducing, engine-off glide. Luckily, warp stealth (yes, it must have been Star Trek fans that devised these names...) allows you to at least slightly circumvent that problem on the highway, allowing for a sort of high-speed glide using no gas. While the gas engine must still spin at very low RPMs, usually around 960 or so, this is accomplished with a relatively small amount of energy from the battery - about double the energy of a simple glide, or the same power as running your air conditioner.

Warp stealth is best used on a slight downhill, or if you are approaching your exit. You will slowly decelerate with warp stealth, so you'll find if you overuse it on non-downhills, you may actually waste more energy trying to accelerate back up to speed.

How to use it

Luckily, the muscle memory required for warp stealth is identical to that of a glide. When travelling at a speed higher than 42 mph, simply lift your foot quickly off the gas, invoking regen:

Then reapply oh-so slightly, and instead of no arrows like a glide, you'll see yellow arrows coming from the battery.



You're now in warp stealth, using zero fuel.

Interesting to note that at these speeds, it is a rare occurrence to get no arrows like you would see in a glide, and while I've seen cruise control magically do this somehow (though the engine was still spinning, to be sure), you'll find that 999 out of 1,000 times or so you won't be able to do it - so don't waste your time :-)

If you slow under 42 mph in warp stealth, you'll see that somewhere between 40-42 mph the engine will cut out, and you'll be back in a glide, or perhaps electric mode if the pedal is depressed enough.

Mileage

Since warp stealth uses no gas at all (though some energy) you can use the same logic to calculate mpg over a given segment. If you are travelling along getting 40 mpg on a slight rise on the highway for half a mile, and then have a similarly long descent ahead of you, you would get 80 mpg on that overall segment. These numbers are not practical in real life, since you usually are unable to find such a nice downhill, but even if you only could use warp stealth for half the distance of the climb without losing too much or any momentum, you would get 60 mpg over the segment, a more realistic and certainly possible number to achieve. While I am a relative newbie to highway driving, with most of my driving in what the EPA calls "city" (in other words, just not the highway), I can offer a recent personal example, when I drove down route 24 from near Boston. Even with those pesky hills, my novice attempt at steady acceleration followed by warp stealth when possible yielded 58.5 mpg on the display over 51 miles.

If you are a frequent bridge traveler, as many here in Rhode Island are, use the backside for warp stealth all the way! No need to use any gas - gravity will pull you along very nicely.

Table of contents


Technique #3 - Super Highway Mode

What it is

Another dramatically named technique you can use in certain situations at higher speeds. The engine and battery pack go back and forth with their energy use - arrows will be all over the place on your screen, so don't even worry about them. You can use SHM to maintain speed on a flat surface, or else accelerate very slowly on a downhill.

How to use it

The best place to test it out is on a flat piece of highway once you're already going your desired speed. Simply let up considerably on the accelerator, but not enough to enter into regen or warp stealth. At about 55 mph, it should be very easy to get the instant mpg at about 75 mpg. This is SHM. You'll be able to just about hold your speed if on flat ground at this very low state of fuel consumption. Even 60 mpg is a decent mileage to shoot for. You'll find that once you try to milk it and go higher than 75 mpg, toward 80, and eventually 99.9+ mpg, you'll be loafing, and will lose speed very easily. Maintain that momentum! It's better than slowing down too much and having to accelerate again later.

If you find that you're trying SHM on a slight downhill, and are holding speed just fine with instant mpg at 80 or higher, just switch to warp stealth, it's much more efficient than having the engine loaf in SHM.

Mileage

You'll have a hard time quantifying any increases using this, and again, using it too much can cause you to slow and finding yourself needing to accelerate again, wasting energy. There are some expert Prius drivers who never use this mode, and others who use it extensively on the highway. It's more that this mode will teach you to use the minimum amount of gas to stay at your desired speed. You'll feel as though you're already doing this, getting 50 mpg over a distance, but if you let up, you'll likely find you can maintain your speed getting 60-70 mpg.

EDIT on May 1, 2011: I've somewhat revised my opinions of SHM to hold it in a very positive light, since I got wonderful mileage using it today on a 50-mile highway run, and that was far from flat ground. The trouble is, this post is for Beginning Prius tips, and you would need a Scangauge to use the same technique I did, so it may not be practical for everyone.

Table of contents


Technique #4 - Regenerative braking

What it is

Regenerative braking is a braking system that allows you to reuse some of the energy your car has stored when slowing down. Most cars use friction brakes all the time. In these systems, your brake pads come in contact with a metal disc, forcing it to slow down by all the friction created. The friction produces heat, and this energy in the form of heat is thrown away, never to be seen again. That is the kinetic, or movement-related, energy being wasted. Don't try feeling this on a regular car, since the brakes can heat up to dangerously high temperatures - like towards 1000°F. You could, though, with some caution, try feeling the wheel of a bike just after you've braked. That thing will get hot, and that's all that's left over from your wasted momentum!

In a regenerative braking scenario, the kinetic energy of the car, by way of the turning wheels, spins around the motor-cum-generator, producing electricity which is fed into your battery pack. It is not at all 100% efficient. You may only capture 30-some percent of the kinetic energy, but it's certainly better than nothing.

The Prius largely tries to use regenerative braking. The exceptions are when you brake hard/suddenly, in which case it will use the friction brakes in conjunction with regen, and also when you go below 7 mph, since hardly any energy is being produced down in that range anyway. It blends the use of regen and friction braking for when you need to brake more.

How to use it

Just hit the brake pedal! You can also just lift your foot off the gas. This much is obvious, the real question is when to use it, and the answer is almost never.



For the most part, you want to avoid using braking at all, whether regen or friction. Any typical drive on even sparsely populated roads will reveal a sea of flashing red tail lights from the cars ahead of you, as they brake at every little speed variation of the car directly in front of them. Instead of braking with everyone for the Christmas light show, instead follow a safe distance behind the car in front of you. When this braking "noise" enters into the mix, largely ignore it, since they're about to accelerate again anyway. Your job is to conserve momentum.

There will always come points in your driving when you have to brake. I'm not saying to stop braking altogether (good luck with that!), but rather learn to eliminate the useless brake-for-a-split-second/accelerate-back-to-where-I-was-a-second-ago behavior that most cars demonstrate. Even with regen braking, this is an inherently inefficient way to drive. Try to conserve momentum.

To brake to enhance power regeneration leading up to stoplights or a stop sign, slowly depress the brake pedal so that you are slowing down gradually.


Braking blend between regen and friction, from the 2004 Prius New Features Manual


You will generate more electricity this way than if you drove straight up to a light and stopped relatively quickly, as most cars do. Notice in the chart above that when little brake use is called for on the y-axis, the Prius will use all regenerative braking even over a length of time. When you see the next light (or even a light or two past that one) turning yellow, get off the gas right away, and either use a glide or regen if you think you'll have to stop or slow significantly.

Mileage

There will not be an easily quantifiable or noticeable increase in fuel economy, but it is there - have faith! Even if you never use electric mode by itself, energy from the battery pack is regularly used to assist in acceleration from dead stops, etc., and contributes to a more efficient driving scenario. The Prius takes care of all that for you, for most drivers there's no need to even give that a thought as you drive.

There are limited instances where regenerative braking will be of significant assist to your mileage. There is one bridge I have to take three times a week that is a killer on mileage. To make things worse after a huge climb, you have to come to a complete stop(!) at the end of it to pay a toll. Even with EZPass they have bars down, and you can't drive straight through until you've paid and the bar lifts up. Luckily I've found that with the right amount of regen on the backside of the bridge, I can fully charge the battery. Since the Prius likes to have a medium charged battery, it will work to get rid of that full battery by using that energy as much as possible, leading almost to a plug-in car-like efficiency. I've calculated that from the stopped tollbooth, over the next three miles, which include a start from 5 mph, a small hill, and also another bridge to climb, that I get approximately 70-80 mpg. This is an immense improvement over a regular acceleration with limited battery assist.

A picture of me trotting along on a slight uphill at 44 mph after this bridge. Notice the lack of gas use...



Please note that if you are ever going down a long hill in the mountains and find that you're braking excessively or that your battery is fully green, you should shift into B mode. Once your battery is "full" like that (really 80% charged), you will be using your friction brakes exclusively. To avoid them getting too hot (or overheating the brake fluid), go into B. That is the only practical application of B mode, to throw off heat via engine braking. Regardless of whatever your dealer told you (mine said it would miraculously charge the battery to 100% in two minutes!), it is an engine braking mode only. You can still drive in B mode, you don't have to switch back and forth from drive to B just to accelerate and brake, respectively.

Table of contents


Technique #5 - Electric vehicle mode or EV mode

What it is

EV mode is a way to use the hybrid battery pack to power the car solo at slower speeds without using any fuel. In the Prius, you have a gas engine and an electric engine. EV is pretty self-explanatory - it just uses the electric motor.

How to use it

EV mode can only be used in certain conditions, and the car must always be warmed up. You must be going under 42 mph, or else the gas engine will come on. To activate EV, make sure the gas engine is off while driving (you learned to do this in the glide section), and then apply the gas pedal only slightly more than a glide, to get this now familiar screen:



The car is now going along in EV mode with no gas use. Ahh, the silence...

If you have trouble getting into EV mode, but you feel the car is properly warmed up and you're under 42 mph, stop pulling your hair out, even if your engine is running while you guzzle along at 10 mph. You're in stage 3 operation, and want to get to stage 4. More info on this can be found back in the "Preparation" section of the glide tutorial.

Mileage (but with caveats and stern warnings!)

While it's fun to do, thinking that you're getting infinite mpg, EV mode must counterintuitively be extremely limited in its use, otherwise you will get worse fuel economy.

Why is that? you're likely asking about now...

The energy of the hybrid battery pack does not magically materialize. Although regen braking can provide some juice, it's not typically an abundant flow of energy. Most of the energy in your battery comes from gasoline ("What?!?"). Yes, it's true. Our beloved Prii convert gas into energy by way of the electric motor. That's why you see this most of the time with your foot on the pedal:


There are two sets of arrows from the gas engine (the engine icon at the top center, in this picture labeled "moteur"), one to the wheels (driving the car) and another to the battery (charging the battery). While this is a relatively efficient charging, some of the energy is simply lost in the conversion from gas, through combustion, to the electric generator, into the battery. If you use EV mode too much, you'll deplete the battery, not to an extent that's damaging to the vehicle, but just so that you'll be directing lots of gas into recharging, instead of driving the car.

So, what are the restrictions for EV use?

1. Push the pedal very lightly. The screen does not differentiate between intense EV use and light EV use - it only shows yellow arrows. There can be huge variations in use that you can't see, from 5 amps to 50 amps (and beyond!). Keep it low.

2. Use it in parking lots. No sudden moves, like humans in Jurassic Park.

3. Use it lightly in slow traffic and traffic jams. I've found that in 0-25 mph situations that it can be used nicely to extend glides, or even for temporary steady state driving. There's one part in my commute where I have to drive about 20 mph for about 3/4 of a mile. I switch between EV and gliding to get through it. The gas engine at those speeds is hugely wasteful, and would be kicking along at terrible mpgs. I can only justify this tradeoff by, again, being very light on the pedal.

Others have argued that more EV use is never a good idea, because of the conversion losses from gas to electricity I described above. The thing is, in practice, a strictly theoretical persective does not work.

An example of a given commute with limited EV use:



The same commute with more extensive, but careful EV use:



You get the idea.

Table of contents


Th, th, th, that's all, folks

Hope this was helpful to some. Please leave comments if you have any questions.

Friday, April 1, 2011

Prius-ing with Hobbit

fyi: non-Prius users will find this post relatively useless, except pretty pictures at the end :-) Prius drivers, read on.

Tuesday morning I headed up toward Boston to meet Hobbit. He had very kindly offered to meet and show me his highway techniques in person, since I had largely failed in the couple highway trips I had tried. I would usually get a little over 50 mpg, and felt like I was constantly jerkily speeding and slowing, speeding and slowing. It didn't feel like the right way, and the poor results confirmed it. From reading others' experiences on the PriusChat forums, I got the feeling this is a common problem.

I got up a little earlier than needed and attempted to hypermile up on unfamiliar back roads. End result: 65.5 mpg over 61 miles or so in clear, low- to mid-40°F weather. I was hoping for 70, but I killed my chances near the beginning getting stuck in a traffic jam on the ascent of a bridge while in stage 3. It was also prime school bus time, and the stops were frequent and many.

After a rather time consuming drive, I pulled into the parking lot where we'd agreed to meet and called Hobbit. He said he was parked at the parking lot perimeter - well, it wasn't too hard to spot him. Here's our Prii together. Even if you're not already familiar with Hobbit's site, you can probably guess which one is his.





We headed out onto route 93/128/1/95 (yes, it's that confusing) in Hobbit's car. Driving with him is something of an experience - I won't spoil the surprise in case a serendipitous series of events ever puts you into this situation, but suffice to say he's very into following distance.

Now for the driving technique. His sweet spot posts (first one, second one) clearly delineate the need to accelerate at an output of pretty much 15 kW. I was a bit surprised to see him jump straight to 25 kW as we merged onto the highway heading uphill. He explained it was important to just get to speed and not interrupt the flow of traffic, and plus you need more juice heading up a hill to keep moving. He eased up toward 15 kW near the crest, and, much to my surprise, didn't go into warp stealth on the downside. He used it to continue accelerating to an ideal speed (in the first part of our ride this would tend toward the low 60 mphs), and then continued a steady, slow acceleration up the next slight hill, too. At this point, even though I was watching kW since that's what he talked about a lot in his article, he was really watching the RPMs. He liked to keep it under 2000 RPM in some of these initial accelerations. The thing that struck me here was that he wasn't concerned if he was accelerating at 30-40 mpg for a good distance; it was all about accelerating at the most efficient state possible for a situation, and not at all babying the accelerator for the instant gratification of high instant mpgs on the display.

He then regularly started using warp stealth when he felt it was appropriate on downhill segments. He would keep burning if needed, like if there was a truck coming up quickly behind us. It's interesting to know that he often would accelerate slightly harder if heading up a hill, to keep gradually accelerating over what felt like a good deal of time - maybe 1 mph increase every 5 seconds, for example. In these cases it wouldn't be unusual to see 17 or 18 kW.

I asked about SHM - he said he doesn't believe in it, and never uses it (!). This is hugely counterintuitive, but we've all seen the 65 and 70 mpg highway photos of his over long trips, which brings up another point. If you drive for 5 or 10 minutes only on the highway each day, you may get some nice highway bars, but your overall mileage will very unlikely be up near 60, barring clement terrain. The mileage will play out over time.

Result: despite feeling like we were burning at relatively low instant mpgs for some time (anywhere from 30-50), the consumption display showed some nice bars of our highway time up near 75 mpg, and all of them were easily over 50.

It was then my turn to try it out in Wentworth. It was rather difficult to keep the feeling of 15 kW in my pedal foot, since a. I wasn't used to it, b. Scangauge has quite the lag on updating kW, and c. if I found myself going at 18 kW, I would let up just a bit, thinking it would bump down to 15, only to find myself at an inefficient 12 or 13 kW. It requires a precision more demanding than a standard glide. Despite this, Hobbit told me several times that it's important to get the feeling in your foot so you don't have to stare at the Scangauge while driving. Typically, if your instant mpg is at 75% the value of your speed in mph, you're right in the sweet spot. On the slightly harder climbs, this ratio would sometimes dip to 66% or so while Hobbit was driving.

I was constantly under the impression that my bars would return 40 mpg given how long and relatively hard the acceleration was, but miraculously all the highway bars were over 50, and there was a nice 75 mpg bar somewhere in there. It's completely counterintuitive to the non-instrumented driver.

Coming back to the parking lot, we found another Prius had sought out a parking space near Hobbit, and the opportunity was used as an excuse for a Prius photoshoot.



After a nice food court meal (Hobbit finally had to put on his shoes to go in the building :-D), I headed out on the highway to drive home, wondering how this would work in normal traffic.

At 15 kW, I found myself going surprisingly fast - it got me quite easily up to 70 mph on a couple occasions, easily faster than I've driven in four months. I would then bleed some of that speed with warp stealth, and up the mileage went. At first my mileage was in the 40s, it quickly rose sharply toward 50. I maintained 15 kW religiously, with the occasional foray into 17-18 kW territory. The mpgs kept increasing with warp stealth glides - 54, 55, 56, 57. Like any technique, it was also dependent on terrain to some extent. As route 24 got hillier, or at least was heading uphill in general for many miles, the mileage slowly came back down to 54. There were almost no opportunities to use warp stealth. While I've driven route 24 from time to time in the past, especially when I was at school in Boston, I didn't really have an intimate knowledge of the terrain coming up, so I imagine there were plenty of instances where something could have been done "better".

Nonetheless I kept on, and to get home, there were two semi-exits to take and two corresponding major accelerations to merge back onto the highway . Toward the end of the ride, where I knew the terrain well, I knew there was a couple mile long stretch where I could mostly use warp stealth, and was rewarded with the second to last bar you'll see below. The last bar I was off the highway, taking advantage of full hybrid capabilities.

Results of the trip: 58.5 mpg displayed over 51 miles (Scangauge inaccurately higher, but looks nice!), which is much better than the 50 or so I would usually get. Also keep in mind that the 2007 Prius, when adjusted for the EPA's 2008 mileage test adjustments, is only rated at 45 mpg on the highway. Hobbit's technique easily yielded at least 25% higher.



Despite the latter half being the uphill/accelerate onto other highways part, and thus lots of 50 mpg bars that you see in the picture, the first part of the trip had several 60 and 75 mpg bars once I was on the highway. Considering I was inching toward 60 mpg on my first try ever, it's pretty exciting to see how much potential is in this approach, since presumably with practice you'd improve. The one major downside is that your foot will get way more tired than pulsing and gliding, since you need a constant, precise pressure applied, either in the finicky 15 kW pedal position or the slight play you get with warp stealth. PriusChat user pEEf confirmed to me that neutral is safe at any speed with the engine running, so that may be a possibility to give your right foot some exercise from time to time in place of warp stealth (though as a side note, Hobbit was absolutely certain that his gas engine does not start at 52 mph when in neutral from a glide under 42 mph (see post #22). He said he's gone up to 70 mph or so in an engine-off neutral glide. Perhaps this is a difference in model years? Hobbit drives a 2004, pEEf a 2008).

I also want to note I never saw him head up to 3000 rpm once we were up at speed. From reading forum posts some people tried that regularly without good results - my feeling (Hobbit, correct me if I'm wrong) is that it's only to be used if you're at your mph floor and you're heading up a particularly tough hill. It's not something to do all the time (just the opposite!), and I don't think he meant to advocate it, if some read it that way.

In related news, that day, with its near-50°F temps later on and another trip I made with a warmed up engine, made for some great results. Even later at night down in the 30s, I got a record mpg number for a particular trip. Nice day for driving overall!

First time I saw 80 in the middle of an actual commute.




The end result. Admittedly the engine was warm before I left...




Trip record on another route. Notice the temperature!




One day after, guess the crazy mileage of the previous day carried over. From a cold engine start!!