Mild electric hybrid using a Permanent magnet PMG 132 motor?

[mort]

Originally Posted by Daox

Any worries about brush wear when the electric motor isn't in use?

Me again.
Hi Daox,
Brush wear is proportional to brush current, and other things. For HP size motors brush wear with no current is about 5% as fast as at continuous rated power. If the motor is pushed (unpowered) all the time it is a problem, but if you power the motor half the time brush wear won't be much faster than usual.
-mort

[Ken Fry]

Originally Posted by Ryland

Sorry, my mistake with the title, would this be a mild hybrid then?
Yes, I realize that I would use less gas if the engine was not running at all, but without pulling the stock drive train or adding a 5th wheel or doing some funky set up with bolt on wheel motors, it seems like there is no good way to do an ad on hybrid drive train, also Honda Civic's are common enough that if this does work then there are a ton of people who could copy it.

This may be more complicated than you want to go, but you could find the rear end from a CRV, and do a through-the road hybrid. (Granted, mounting this stuff in the back of Civic might make you want to just buy a or swap a CRV.) This would have the advantage that you could drive with the engine off at low speeds.

If your goal is mainly to displace driving energy from gas to electric, using the car as a plug-in hybrid, then efficiency is less of an issue. The bigger the battery pack the more displacement.

If you are thinking more along the lines of home-brewed IMA, then to gain overall efficiency, you need to make the engine smaller, so it is operating at best bsfc more of the time.

Interesting, I'll have to think a bit.

[Ryland]

I've gotten 65mpg while driving 70mph just because I had a tail wind, wouldn't this be like having a constant tail wind?
Changing the whole rear suspension and adding another drive train is not something I'm interested in doing, bolting a motor to existing threaded holes and using an existing V-belt pulley is a modification I'm willing to do to my otherwise stock car that is in great shape.
I'm thinking that the big hold up on this is going to be a battery pack, because I don't want to fill my trunk with golf cart batteries I'll most likely hold off on this project until I buy the lithium battery pack for my electric motorcycle, I'll have to double check but I think that might fit where the A/C condenser would live, or at least a portion of the battery pack could, the spare tire well would be another option.
Mort, do you have any charts on how much power V-belts can handle? I would imagine it's dependent on pulley size, larger being better up to the point where the belt over speeds.

[mort]

Originally Posted by Ryland

Mort, do you have any charts on how much power V-belts can handle? I would imagine it's dependent on pulley size, larger being better up to the point where the belt over speeds.

Hi Ryland,
For a quick reference I see the Grainger catalog...
L and A B C size belts start on page 127 with power ratings. page 128 to buy belts and sheaves start on 143.
Look at the BX size belts, they should fit an automotive A/C pulley.
-mort

[Ken Fry]

Originally Posted by Ryland

I've gotten 65mpg while driving 70mph just because I had a tail wind, wouldn't this be like having a constant tail wind?

It depends on your philosophy, the efficiencies of the pieces in the chain, and how you are charging the batteries. The tailwind energy comes from an outside, completely free source. The motor energy comes from your fuel, if you are proposing an IMA-style hybrid.

Here are two possibilities:

1. If all the energy to boost the car comes from the grid, then you are getting the extra umph to get the tailwind effect at very low cost. Definite gain in essentially every respect, including environmental (although in North Dakota, it could be close to a toss up re carbon footprint -- because they are so heavily into coal).

2. At the other extreme would be a system in which the car still idles at stop lights, and in which regen is not used for braking, and in which the batteries are charged by loading the engine more heavily during cruise (at which time the engine operates at better bsfc than it would at cruise, because it is now producing, say, 23 hp of which 8 are used for charging and 15 are used for propelling the car. This one would not plug in, and work like Honda's IMA system.

You'd have to look at the bsfc chart for your engine, but I'd guess that the engine might be 24% efficient at 23 hp, and 22% efficient at 15hp. Assume the generator is 85% efficient, and the controller is 95% (both of these vary with load, etc, but these could be realistic averages), and that you use lithium x batteries that are 95% efficient each way in receiving and delivering charge. Then, for each unit of energy delivered from the engine to the generator there is an amount delivered back to the engine pulley by the motor at a later time. So we start with say 8 hp-hours delivered from engine to generator during one hour of cruising/charging. The energy returned at some later point is 8 x .85(gen) x .95(cont) x .95(bat in) x .95 (bat out) x .95(cont) x .85(mot) = 4.7 hp-hours out. To do better than break even, then, the electric propulsion aid would have to be delivered when the engine would otherwise be operating at 4.7/8 x .24 = 14% efficient. So if you could turn the engine off (disconnect it from the system mechanically too) and used the electric motor for propulsion at low speeds, you gain efficiency. But if you are using say 10 hp from the engine (at .18 effic) and 10 hp boost from the electric motor (at .14effective efficiency) then you'd be better off to put all the load on the engine, and get 20 hp at .24 efficiency.

The IMA system has no belt losses, and the motor-generator is highly efficient (95% in a wide area of speeds and loads). The whole system is well optimized for what it is. But the difference in around-town mileage for the 2010 Hybrid Civic (40 mpg) and the 2010 Prius (50 mpg) highlights the limitation of the IMA system: for it to be effective, the engine really needs to be too small to achieve desired performance levels, so that the engine is operating at high efficiency levels (heavily loaded) most of the time. The the electric motor can make up for the low engine power to provide acceptable performance. If the engine is already large enough to provide acceptable performance, then you loose the opportunities to drive it at high loads (high efficiency levels) because to do so means you are driving too fast.

HOWEVER...

This ignores the possibilities for idle stop and regen. With them, you can gain back some of the losses of all the energy conversions. The effectiveness in doing so depends upon how you are already driving: if you spend a lot of time on the highway, regen is essentially useless. Remember that hybrids like the Prius are automatically implementing pulse and glide effects (in combination with a host of other refinements). If you are already using techniques like pulse and glide, then hybridization is less attractive.

But back to the first case, where you charge from the grid (or better, from solar panels). Then you are getting the energy at a very low price and not using gasoline to provide the energy to charge the batteries.

Re batteries: Lead acid can be helpful for prototyping, because of low initial cost: use them for a while, then recycle them. For long term usage, lithium x have reached the point where they cost less than lead acid, per mile.

Another battery issues: For regen on a car the size of the civic, it would be nice to use up to 200 amps at 72 volts (which the motor can handle periodically). (This enables the car to decelerate roughly as well as it accelerates on almost 20 hp.) This means that the battery pack should be able to charge at 200 amps. Depending on chemistry, that may mean a larger pack than would be dictated by other concerns alone.

[Ryland]

I must have left that bit out, yes, I would like this to be a plug in hybrid seeing as how I'm already set up to plug in my electric car at home and at work, because of the added complexity and added motor wear I was thinking it might be worth forgetting about the regen braking and putting a free wheel on the motor so it only spins when it's powered up, advantage would be less drag when the electric was not being used and less motor wear and a simpler design, disadvantage of course would be no regen braking and that I'm not sure who makes heavy duty free wheel ratchets.

[Ken Fry]

Originally Posted by Ryland

... disadvantage of course would be no regen braking and that I'm not sure who makes heavy duty free wheel ratchets.

Formsprag is the "Xerox" of the freewheeling clutch world (sprag clutch is the generic term.)

Automatic transmissions use them too, but you'd have more work to do to get one to fit, sealing in the lubricant, etc.

Ditching regen would open up the possibility of using a series motor, which might or might not fit more easily (a series motor being longer but skinnier.) I can imagine a 6.7 inch series motor possibly tucking in where the alternator often is on Hondas -- but I am just guessing. Series motors should be cheaper, not having the expensive magnets, and can be almost as efficient, but heavier.

Could be a pretty cool project.

It would be fun to make series hybrid with your Commutacar. Squeeze in an efficient generator (like a Perm, etc.) and a 5hp continuous engine, and you'd have it. Then you could be the first Commutacar to drive coast to coast (maybe). (Actually, I just checked... no such luck.)

[Ryland]

I might go with a series wound motor, something like a golf cart motor would work well and give more peek HP and low end torque, but they might not do well with high speeds (6,000 RPM red line of the gas engine), so yeah a free wheel, I'd also have to make an end plate for it as golf cart motors don't have them, or I could try to talk my dad out of his 36v series wound motor that is sitting in the garage as that one has an end plate and normal shaft but is not something everyone else can get their hands on, those motors are also sealed up for the most part, so dust, dirt and water wouldn't be as much of an issue.
Time to take some measurements, will a 6.7" by 9" motor fit where the A/C compressor lived?

[Ryland]

I still haven't had a chance to try building anything yet, but I was thinking about how at least the newest Prius is a beltless car, there is no belt driven alternator or water pump or even A/C, it's all electric, running off the drive battery pack with a DC/DC converter to get the 12v power for lights, why not do that same thing with a plug in like this? pull the alternator all together (10% mpg gains, right?) my other thoughts on keeping the throttle simple would be to have the electric motor match the throttle of the gas engine then have a trim knob on the dash that gives more or less boost with an EV button or thumb throttle for when you have your foot off the gas (fuel cuts off) and want to cruise along a flat road at say 25mph in 5th gear, not using any gas.

If I can get a golf cart motor to work then I might try to build this this summer, I just have a lot of other projects going on that I need to take care of first.

[Daox]

I like the idea of a thumb throttle on the shifter. It gives you full control.