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Ok, I started looking at the specifications of the new honda insight. I'm not afraid to say that I am thouroughly disgusted at the performance of this ugly little car. 65 mpg is good, but nothing to really boast about. A 1985 vw rabbit diesel gets 50 mpg and looks better to boot. not cleaner, i digress,
but was done in 1985. Just to start with, a few specs (i chose the honda insight as it seems the most popular).
Engine: inline 3 cylinder, 995cc displacement, 67hp@5700 rpm/66lb.-ft at 4800rpm.
electric motor/generator: permanate magnet motor, power output- 10kw at 3000 rpm.
batteries: Ni-MH 144v (120 cells @1.2v)
From what I understand, the engine is linked to the electric motor/generator through a clutch, the petrol engine drives the wheels and generator up to/at "x" speed, when this speed is reached, the clutch disengages and the batteries take over and drive the electric motor and the petrol engine idles. It's just a rough explanation, but you see the process. Seems like a very indirect way to move the car, not to mention the 500lbs or so of batteries, that will have to be replaced a couple of times in the life span of the engine.
Now im not pretending to know everything about electric motors and the mechanics that drive them, (i prefer big honkin V8's and my high revving rotory) i'm just going by what is written in various sources. The engine produces 67hp largely because at some point it powers both the wheels and the generator. What if the engine wasn't linked directly to the wheels and just powered the generator, which sent electricity to a controller/amplifier, which sent electricity to four motors, one at each wheel. Then you have fully independent drive, the ultimate traction control. Notice not the need for batteries. With this way, you wouldn't need 67hp to produce the 10kw, 20hp would be sufficiant, around briggs and stratton levels. Why there's several 10kw generators on ebay that run 20hp briggs engines and produce 240 volts. Just a comparison, I recently ran my 21hp briggs powered riding lawn mower at full throttle (3500 rpm) and full load for 2.5 hours on 1 gallon of fuel. A rough conversion to fuel mileage would be about 112.5 MPG (avg. speed of 45 mph for 2.5 hrs).
Am i missing something here?
Plantary gear set
http://auto.howstuf...com/hybrid-car5.htm
howstuffworks [evilpenguin, Jun 29 2007]
[link]
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Yes. You're missing that, without batteries, you'll only get drive while the gas engine is running, which somewhat defeats the point of hybrids. What you have here, if I understand correctly, is the same system as is used in diesel-electric locomotives, namely an internal combustion engine which, instead of providing motive power directly, runs a generator which powers electric motors.
The purpose of a gas-electric hybrid is to use each power source in the circumstances where it is the more efficient; thus the gas engine provides immediate acceleration and the electric motor provides constant-speed cruising. Additionally, inertia is recovered during deceleration by a regenerative braking system. |
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Hang on... no. The Insight runs primarily on a direct-drive IC engine in the same way as any other car. When cruising, the electric motor does nothing. For extra acceleration, the motor kicks in for an extra 25lbft of torque. That 67hp is what is primarily moving the car, rather than just generating 10kW electrical power. |
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The grade A number one point point of a hybrid vehicle is better fuel milage. It's damn sure not efficiancy. It can't be efficiant to convert mechanical energy into electricity then back to mechanical energy, But it can be economical. |
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Ok, why in gods name would you want to add an electric motor, controllers, amplifiers, capacitors, and 1/4-1/2 a ton worth of batteries for 25 foot pounds of freakin torque. Geeze you could leave all that crap out, and the weight savings alone would make up for more than that. I'm gonna go out on a limb and say honda's not that dumb. |
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The four motors probibly wouldn't work so well, as they would be terribly complex and have to have a transmission for each one. So a single or twin motor with a solenoid or manual shifted constant mesh siquential transmission with about 10-15 gears would suffice. |
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So far I havent heard a good reason "why not" and already have -2. |
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Although diesel locomotives have for decades used electrical 'transmissions', one major difference between locomotives and cars is that in the latter, weight is a BAD thing, while in the former, it's a GOOD thing. |
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IMHO, the real key to improving automotive efficiency will be developing a crank linkage which can vary displacement and compression ratio effectively, preferably doing so separately for the compression and exhaust strokes. Don't know how to make that work mechanically, though. |
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//:So far I havent heard a good reason "why not" and already have -2:// |
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Correction, you have -4, and for good reasons no one apperently wants to explain to you. |
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The GM Impact, renamed the EV1 for the "production" model, had only one motor and a pretty typical differential. the GM hi-wire (sp) had wheel motors, but nothing like that is close to production. Wheel motors sound nice conceptually, but for many applications the design tradeoffs don't come out positive. They add a lot of unsprung weight. Four motors are usually less efficient and heavier than 1 motor 4 times as powerful. Also, you can get more power for a given motor size by running at a higher RPM than most tires turn, so some gear reduction is usually a good idea. Gear reduction can be done inside the wheel, but makes it more complicated |
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[david_scothern] is correct, though I can't confirm the torque and kW ratings of the motor off the top of my head, they sound about right. You should note that when you see the power and torque rating for a motor it may look small, but it does a lot to get the car moving because it is available over a very wide range of RPMs, compared to RPM ranges that engines are close to their peak torque and RPM. The additional power from the battery pack and motor more than makes up for its own weight. |
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What you're missing with your Briggs and Stratton hybrid is power. With only 20hp, acceleration will be awful. Hybrids use the batteries to store energy so that when more power is needed they can get it from the batteries for a small preiod of time. If your only power source is a 20 HP engine, that's all you can use. Using a generator and motor doesn't do anything for you that a good transmission wouldn't do for you. |
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You said //The engine produces 67hp largely because at some point it powers both the wheels and the generator.// While accelerating, the engine isn't powering the generator. The generator is operating as a motor, taking stored energy from the batteries and helping get the car up to speed. Once the car is up to speed, 67 hp is much more than the cars needs for cruising, so runs the motor as a generator for a while to refill the batteries. When the batteries are full enough, the engine gets throttled back to whatever is needed to maintain cruise speed and the motor just freewheels. For most everyday driving, the hybrid could get even better gass mileage if it had a smaller engine and a bigger motor. However for the situations when lots of power is needed for a long period of time (say climbing over a mountain pass), if there was less horsepower from the engine, the motor would be needed just to maintain speed up the hill, and the batteries would be drained before reaching the top. |
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how do you separate "better fuel mileage" from "efficiency", seeing as the "efficiency" of a car is often defined by it's "fuel mileage"? |
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The overall efficiency (the system=the car) is clearly directly linked to "fuel mileage". [anobii] mentions low efficiency when talking about a subset of the car, namely the motor/generator system. However, the same system allows other efficiencies to be had - getting away with a smaller i. c. engine, and regenerative braking (even a 5% wheels-generator-electronics-battery-electronics-motor-wheels efficiency is better then 0% efficient brakes, assuming the mass etc of the whole car isn't increased significantly). |
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I think you're closer to The Answer here
than most. There are all flavors of
"hybrids", so it depends on what you
want. I want performance with good
fuel mileage and light weight. The
Toyota Volta is closest yet. OK, I don't
understand "unsprung weight" --
seems logical to me that having 4 in-
hub motors puts the weight where you
need it most... on the tires!? And what's
wrong with running an engine
generator all the time? If, overall, it's
more efficient, and heavy batteries are
eliminated, that's better [for me].
Benefits are no drivetrain, no
transmission, more flexible placement
of all components, more cabin and
storage capacity, and I'm sure others.
Anyone see the Honda Spocket? If you
want efficiency, buy a bicycle! |
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[dalan] -
"unsprung weight": the weight of wheels etc that moves up and down as it goes over the uneven road surface. Conversely, sprung weight is everything on the other side of the springs - the car body etc. The higher the sprung-to-unsprung weight ratio, the better the ride. Better not only means more comfortable for passengers, but more significantly the tyres stay in better contact with the road, providing better (safer) handling.
As for the second part of your anno - an electric drivetrain (generator+[electronics]+motor) is *less* efficient than a mechanical one ([gearbox]+driveshaft). An electric drivetrain only makes for better overall efficiency when the engine being used is significantly more efficient when running at some fixed rpm (notably gas turbines). With no batteries in the system, this only becomes viable for long-haul travel, not stop+go city traffic. |
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Diesel-Electrics, or (Gasoline-electrics) are only a good idea for very large engines, as in train locomotives. This is because very large engines have a very small useful RPM range, meaning a train would need some ridiculous number of gears to get up to full speed. |
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The diesel-electric combo is a means of solving the transmission problem, as electric motors can have a speed controller, etc and have good torque at all speeds. Cars work fine already with 5 regular gears... |
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Funny you should mention Briggs & Stratton. Back in the 70's there was an article in Mother Earth News where someone used exactly that engine in a home-built hybrid. Using a B&S 20hp unit, a starter motor from a DC-10 & a bank of batteries, this guy built an Opel GT (Mini-vette) hybrid. Check it out for yourself. Google, and ye shall find. |
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I believe your hybrid will work more efficiently if the efficiencies of the powertrain components are used most effectively; for example, electric motors have a flat torque curve, thus max torque is available from rest, thus better for initial acceleration. IC engines work best at a constant speed, thus better for cruising. In the intermediate range, the ICE should run the generator to charge the batteries. Under very severe load, both ICE and electric motor could supply power. |
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Mother Earth News came away from that first hybrid a bit misinformed, but baked up a better one, with a 9hp Lombardini diesel, a bank of batts, and the original clutch still in the car. They did theirs in a Subie chassis, thus building an eminently useful car with four actual seats (Opel GTs have two plus a parcel shelf that will carry a couple of limber buddies to tennis practice). They got 83 mpg at ~45 mph. |
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It doesn't take much power to roll down the road at all. I figure it's about fifteen horsepower keep my old Toyota pickup at 60 on level ground. A big Briggs V-twin with a generator that clutches in and out as needed, and a big assist motor fed by enough batt storage to run it for about two minutes (E. Tenn, lots of hills) would do well. Hey presto! 60 mpg. Maybe. |
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Dude you have a lawn mower that goes 45? Where can I get me one of those? |
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//From what I understand, the engine is linked to the electric motor/generator through a clutch// |
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NOT TRUE. Both the gas motor and electric motor drive gears of a planetary gear set [see link] the gas motor is directly mechanically connected to the drivetrain, as well as the electric motor. The plantery gear set also acts as a constantly variable transmission. |
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