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At Miscon 2013, around Memorial Day, Missoula MT, At SoonerCon, in OKC, around June 15, also Spokon in Spokane, in July/August, Beyond that, we aren't sure.
December 2014
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The car goes in for a check…

I get to sit in the waiting room.
Fun…not so much.
It’s been nearly a year since we bought it. 2000 miles we’ve put on it. And we’re getting about 45 mpg on the highway and more than 50-something in town. We were filling the Forester’s 15 gallon tank once a week or so. This 10 gallon tank gets filled far less often. It gets roughly twice the mileage of the Forester. There’s slightly more overhead room and more cargo space than the Forester. It stops on a dime. It rolls forever on a downhill and gathers speed amazingly. It has killer ac and heating that come on very fast. People sometimes think that a hybrid is going to be a slug at a stoplight. I don’t jack-rabbit because it wastes gas, but the car moves out pretty well without that. It’s fun to drive, kind of a never-ending video game…but you need to watch the road, not the readout. We still love driving it.

The downside of the Prius is that it’s a bit bumpy on rough roads, being so light, and it stops on a dime. You don’t want to hit a speed bump hard. You don’t brake hard on this car: for one thing, the brakes are part of the recharge system, and shouldn’t be abused. For another, nobody but a hybrid can stop that short, including the guys behind you. And it gathers so much speed on a downhill with no power that you have to brake repeatedly to prevent breaking speed limits. Following cars don’t always understand this.

I was amused in the early days of hybrids when a Prius was chased down by a California sheriff at speeds over a hundred. Sales of Priuses increased amazingly nationwide after that.

19 comments to The car goes in for a check…

  • tulrose

    Kindles and their ilk are made for waiting rooms of all types.

  • paul

    I’ve heard some things that I guess I fitted together with wrong assumptions. Please correct me. :)

    One is that a gasoline engine is most, and not badly, efficient when it’s running at a constant speed. Exactly what speed depending on the engine. That’s why we’ve always heard about the “jack rabit” starts, and, well, accelerating in general.

    Secondly, I heard a hybrid (maybe only one of them in particular?) accelerates on the electrics. The gas engine only recharges the batteries with its alternator, and drives the car when it’s at a relative constant velocity, i.e. the accelerator pedal isn’t moving.

    Thirdly, I’ve assumed all braking is “regenerative” and never heard that the braking has a deleterious effect. Why? What’s happening? I don’t think the electric motor cares.

    So what have I assumed and fitted together in a nice consistent, if perhaps theoretical, understanding that’s wrong?

    (I do remember having a generator on my bike when I was a kid, powered by turning against the tire. And I do remember how much extra effort it was to power a little flashlight-sized bulb! :( )

  • CJ

    The gasoline consumption is tracked constantly on a hybrid, and reports on the dash. During a reasonable pullout from a stopsign on the flat, your MPG is about 13 at start, to 25 when you get rolling, to about 40-45 as you hit cruising and 99 on the downhills. On a jackrabbit start, about 9 up to 11, to settle at about 25 as you power along, then eases up to 45 to 99.

    The motor is not running at all at stoplights, and the electric motor is running alone only on ‘rolling’ starts, like backing out of a parking place or into one from a dead stop.

    In general, both motors work together as the car goes down the road, but the gasoline motor is constantly either switching off entirely [at lights] or [I suspect] going into something like neutral on the downhills. The regenerative braking ‘charges’ the batteries, which power the ac, heater, lights, wipers, etc, as well as the ‘rolling’ motor.

    Jamming on the brakes is mostly deleterious because a hybrid stops so instantly that the car behind you will rear-end you. But also deleterious because it doesn’t charge the batteries: only a slow, steady, light braking does that: you have a little gauge that shows you when you’re doing it right.

    The two do run simultaneously, and the gasoline motor is given an ‘assist’ by the electric, but in what way probably requires an engineering diagram and a better idea of that interface than I’ve found.

    • Treat it something like a sports car: a light foot on the gas and easy on the brake. (I’ve had to hit the brakes hard, occasionally. It does stop hard.)
      There are speed bands where you mostly are recharging, and others where you’re mostly using charge. Sometimes the difference is about 2 miles per hour.

  • paul

    Thanks for the pointer. Wasn’t too far off, but I wasn’t clear on the parallel/series differences. That’s probably where my confusion came from. In a series setup the engine only generates electricity, for the batteries or the motors. Your Prius is a hybrid series-parallel setup.

    Braking isn’t all regenerative. “When you stop your car, the electric motor in the hybrid acts like a generator and takes some of the energy out of the car while slowing it down. If you give the electric motor more time to slow the vehicle, it can recover more of the energy. If you stop quickly, the brakes on the car will do most of the work of slowing the car down, and that energy will be wasted.

    The engine is running mostly where it does best, at relatively constant velocity. Acceleration comes from the motors, even at speed. “Its engine only runs at an efficient speed and load.The engine only starts once the vehicle has passed a certain speed. And once the engine starts, it operates in a narrow speed band.

    When you accelerate, initially the electric motor and batteries provide all of the power. … As the car accelerates, the generator spins at whatever speed it needs to in order for the engine to remain off. Once you reach about 40 mph (64 kph), the gasoline engine will turn on. The generator suddenly changes speed, causing the planet carrier to turn and start the engine. Once the engine is running, it settles into a constant speed while the generator varies its speed to match the output speed with the electric motor. [Emphasis mine.] If you are really accelerating hard, the motor will draw extra power from the batteries. Once you are up to freeway speed, the car will move under a combination of gas and electric power, with all of the electricity coming from the generator.

    I hope I understand it now. ;)

    • Walt

      “Jamming on the brakes is mostly deleterious because a hybrid stops so instantly that the car behind you will rear-end you.”

      Any modern car in good condition can stop from 60 mph in ~120 feet (100 kph, ~40 m). You will notice this is longer that the six car lengths (~90 feet) some recommend as a following distance. It’s not enough to use the 2 seconds rule (~175 feet) when you add in reaction time (220 feet total stopping distance), much less wet weather (270 feet). In any case, it’s much more room than most people allow. And, if you drive over 60 remember that braking distance increases by the square–it’s not linear! (Stopping distances from wolframalpha.com. They use 1.1 seconds as reaction time; it sounds long, but remember the time it takes to switch from a shocked OMG–and other TLAs–to actually doing something constructive like braking.)

      Leaving aside the deleterious effects of a collision, if you slow down smoothly enough in a hybrid, you recapture as much energy as possible from regenerative braking. If you brake too fast, you’ll actually apply the brakes and wear the pads and generate heat instead of electricity.

      As far as when the engine runs, in the side bar on page 10 of the article, it states that running the car with A/C on the freeway takes something like 20 horsepower. The motor can provide 67 (linked page above). So, you don’t need to run the engine continuously, like a Honda Insight does with its serial system. And you don’t want to fill the battery, so you have room to capture power from slowing down or going downhill. (As it happens, staying in the middle of battery capacity is also best for many kinds of batteries.)

      So, my understanding is that the Prius is essentially “drive by wire”. You press on a pedal (accelerator or brake), and the drive by wire system figures out how to satisfy your request with the motor, engine, and brakes. I expect, though I haven’t driven a Prius, the engine comes on only when the engine needs to come on: hard acceleration, or battery getting low. It might be 30, 40, 50 or never depending on how hard or gently you accelerate and the slope you’re traveling on–well, it will eventually come on to recharge the battery.

      • My driver-ed classes at work went for the four-second rule. It gives you enough room – I found that from the occasional experience (the station wagon that suddenly went 90 degrees to traffic and hit the rear corner of the box truck in front of me – I was back far enough to stop without getting hit by the guy behind me, who was far closer).

  • CJ

    It’s really quite a piece of tech and machinery. YOu can drive it like a kid in a go-kart, or you can get with the process of driving it well—not inconveniencing other drivers, while getting the most mileage out of it. It’s a fun drive.

  • using the motors as a means of braking isn’t a new concept. General Motors Electromotive Division (EMD) built the F-series locomotives in the late 1940s – 1950s with what they called “dynamic braking”. This used the electric motors, which drive the locomotives wheels, as generators. I don’t recall what they did with the electricity generated, I’ll have to go back and research that. The E-series, which was the passenger series locomotive, didn’t have the dynamic brakes, just the F-series for freight. I wonder if that was a reflection on which commodity was more important to the railroads……passenger rail has never been profitable for any railroad since they were established. Freight is the big moneymaker, which is why we have so few passenger trains available in this country, as well as devotion to the automobile, and no real incentive to use rail over a car.

  • CJ

    We’re so spread out: on the one hand it would seem logical that rail would work; but on the other, I’ve ridden pre-Amtrack trains—and Amtrack: not the greatest idea. Europe’s countries are more the size of our states, and gaps between towns are shorter, and their parking is amost all off-street and not that cheap, compared to hailing a cab, so you’re better off in Europe with the trains; but in the US, if you arrive at a city without a car, you just about have to rent one to get to where you need to be, or to have any flexibility. Baltimore is the most European city I’ve ever lived in, and indeed, it did work like that. Getting to the old colonial cities by rail makes sense for the same reason it makes sense in Europe.

    Anyway, back to the Prius: it’s working well, and we like driving it on the highway as well as the city. Which we had wondered. It’s holding up mechanically, which pleases us immensely.

    And on the computer front, it’s dead, Jim. It’s most sincerely dead. HP is going to get it by mail, and we hope HP will fix what ails it. Honestly, I wouldn’t be surprised if it would be a breakeven between fixing its problems or sending us a new one.

    • chondrite

      Where there is a good public transit system, you don’t miss a car too hard. Honolulu has an excellent (although frequently disparaged) bus system. The New York subway system, in conjunction with buses and the trains from outside Manhattan proper, is also outstanding. We visited San Francisco for SiL’s wedding, and despite a car being slightly more convenient than public transit, discovered that between parking costs and unfamiliar driving habits, we ended up returning the rental on the second day we had it. The Tube in London and Le Metro in Paris are second to none, although again, the locals mock them. We did take one vacation where we got a sleeper compartment on Amtrak and went across the US, from LA to the east coast, and found it much more restful and pleasant than flying, although pricey. Maybe it was the novelty factor?

      If the initial outlay for an all electric vehicle drops to where it is only a little higher than a gas powered car, I will seriously consider it for my next vehicle. Right now, not only is it several thousands higher at cheapest, but we pay through the nose for electricity, although with more solar panels and windmills coming on line, that may change.

      • CJ

        we certainly got along without a car in Baltimore…we had one, but paid to have it garaged about 2 blocks away, and only took it out once in the entire year.

        Re the hybrids, if it gets twice the mileage of the Subaru, it will save us about 1500-2000 a year in gas. Over 10 year, which it could go, that would be a fair bit. And if the cost of gas rises, even more so. Of course it produces all the electricity it uses.

        The wide open spaces out here in the West make an all-electric a bit less helpful. But there is that initial investment. We hope to run this one long enough to have it pay us. But to our surprise, when we priced the Subaru Forester, and this one, they came up about even. Not so much with other models, however.

      • paul

        Santa Cruz, California, had excellent public transit when I was there, some 30-35 years ago.

  • It ought to have engine-braking for long downgrades – on mine it’s the ‘B’ to the right of ‘drive’. It puts all the energy into charging the batteries. You still have to brake, but not so often.

  • pence

    Re Amtrack: when doing price comparisons to flying – you have the nights of travel going across the country. If you factor in overnight hotel costs, the comparisons are not so far apart. And you are not trying to subsist on airplane peanuts.
    For me, the ability to stretch my legs, and have my luggage arrive when I do is a great plus.
    Anyway my sinuses have gotten to the point that I am not sure that I would dare to fly as the air pressure changes are so painful.

  • nighthawkatshejidan

    We think of nights on the train as part of the vacation, and comparing the costs of the sleeper (which includes meals) and transportation to other modes of travel Amtrak comes out pretty well. But you need to enjoy the train; we do, some people don’t. Generally, it’s faster than driving, because you don’t need to stop and sleep.

    The Washington Post had a fun set of 3 articles, 3 people taking the same trip by train, car, and plane. Here’s a link to the train article, it includes links to the other 2.
    http://www.washingtonpost.com/lifestyle/travel/taking-amtrak-to-raleigh-nc-and-whistling-all-the-way/2014/05/15/0e970d5e-d615-11e3-aae8-c2d44bd79778_story.html

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