How much power does it take to spin a 1.0l geo engine?

[Stubby79]

As the title says:
How much power(in watts) does it take to spin a 1.0l geo engine?

Not that I think anyone will have an exact figure.

I'm pondering ways to hybrid. I want to run the electric motor through the trans but want to retain the ICE. I notice that the Geo ICE, using engine compression to slow it down, barely does anything, so I found myself wondering how much electrical power would be wasted if the electric motor ran sraight through the crankshaft, making the engine spin at the same time.

Yes, it would be wasting power on friction and on compression, but there are benefits...such as you'd have vaccuum for braking and when you turn the ICE back on, it would be seamless because it would already be spinning at the same speed as the motor. This means you could go back and forth between battery power and gas power a dozen times in a minute and never notice. You'd have no reaon to idle, because the electric motor could start you off. It'd drive just like a normal car because all the power goes through the clutch.

There are a numbe rof benefits. The drawback is in how much power is going to be wasted spinning the engine. It would be completely pointless in a normal car with lots of displacement and high compression, but I can turn the geo engine over by hand. So, again...how much power does one think would be wasted doing it this way?

My only guesstimate is going off of the starter motor's rating of 1.2kw. That is a lot to waste, but might be worth it. Bear in mind I'm looking for a figure based on an already spinning engine, not the added surge needed to get it spinning in the first place.

[razor02097]

Remember the starter motor has a massive gear reduction due to the flywheel.

The effort it will take to spin the engine will vary greatly... Factors like the engine temp and if you are talking about spinning it from a dead stop or keeping it rotating would be 2 things right off the bat.

If you want to know how much it will take to rotate the crank you could get a gauge style torque wrench and do some experimentation.

[jakobnev]

Maybe a coast down - clutch in vs clutch out and the ignition off, would give you meaningful data.

[Stubby79]

Originally Posted by jakobnev

Maybe a coast down - clutch in vs clutch out and the ignition off, would give you meaningful data.

Playing around with this is what gave me the thought in the first place. I've found it pretty pointless to use the engine to slow the car down unless you start a mile ahead. You gear down and barely anything happens, whereas in my other vehicles, you gear down and the engine is slowing you down more than the brakes until you get down to about bicycling speed. (call it 20mph)

At higher speeds, the air drag slows you down more than the geo engine does. Hmm...maybe using that information coupled with the "Aerodynamic & rolling resistance, power & MPG calculator", I can get an idea of how much power it's using to spin the engine...

[Stubby79]

Originally Posted by razor02097

If you want to know how much it will take to rotate the crank you could get a gauge style torque wrench and do some experimentation.

Hmm...I didn't think that'd be useful at first, but I could take the torque measurement as a baseline of how much power it would take to keep overcoming the compression and assume I'd lose that much torque at any rpm as waste. Technically there'd be two compression strokes every 3 revolutions, and you'd probably gain back some of that energy when you pass TDC and the compressed air now pushes the piston down in favour of the direction it's rotating...bla bla bla...but I could write off that and the extra 1/3rd as estimated friction losses...

So if it took 10 ft-lbs and it took my motor 100 amps to make 10 ft/lbs, I could assume I'd be throwing away a constant 100 amps. Hmm. Maybe, maybe not. I doubt it'd take ~10hp to maintain whatever rpm I'd get at 72v. It might take that much to start it though.

I think I should just make a rough bracket to hold my motor to the engine, slap a belt around it and the crank pulley and read how many amps it's sucking down to keep the engine rotating. I'd know exactly how much I'd be wasting that way.

[jamesqf]

Of course the simple/sensible thing is to do what Honda did: keep the engine running, and use the electric motor to assist. (And do autostop/start etc.)

[razor02097]

Originally Posted by Stubby79

Hmm...I didn't think that'd be useful at first, but I could take the torque measurement as a baseline of how much power it would take to keep overcoming the compression and assume I'd lose that much torque at any rpm as waste. Technically there'd be two compression strokes every 3 revolutions, and you'd probably gain back some of that energy when you pass TDC and the compressed air now pushes the piston down in favour of the direction it's rotating...bla bla bla...but I could write off that and the extra 1/3rd as estimated friction losses...

So if it took 10 ft-lbs and it took my motor 100 amps to make 10 ft/lbs, I could assume I'd be throwing away a constant 100 amps. Hmm. Maybe, maybe not. I doubt it'd take ~10hp to maintain whatever rpm I'd get at 72v. It might take that much to start it though.

I think I should just make a rough bracket to hold my motor to the engine, slap a belt around it and the crank pulley and read how many amps it's sucking down to keep the engine rotating. I'd know exactly how much I'd be wasting that way.

It would only take higher amperage to accelerate it. There would be a big draw to start it from a dead stop. Once it is at speed the inertia will keep the ICE turning with less effort. All that said maybe you could use the inertia of the engine spinning down for regen?

[Stubby79]

The inertia of the engine spinning down would not gain you much, maybe a few hundred wats for a couple of seconds. However, being able to gear down to regen brake through the motor could gain you a fair bit (probably only limited to how long you have before you have to engage the "real" brakes and up to the programming of your controller). There'd be tens of thousands of watts pumped back in to your batteries that way.

However, having it connected directly to the engine would enable you to get a small bit of regen while at idle(at the cost of extra fuel), so between that and regen braking, your battereies would have a good chance of staying topped up in stop and go traffic. That's if you don't just have the engine shut off when you are idling. That adds another dimension to the question of efficiency: would it be worth sucking off power at idle at the cost of a bit of extra gas? or would you only do that if the batteries got low and stick to charging them before every trip?

I have figured a way to do it that doesn't involve driving the engine yet has the engine drive the motor any time it's running. The issue with it is, due to lack of space along the input shaft on the trans, you'd have to remove the clutch (or at least the throw out bearing and the clutch fork) and it would also force the engine to grind to a halt when you come to a stop. Any time you're moving, it wouldn't be a problem, but when you get below idle speeds in any given gear, it'd have to shut off. You could idle in neutral, but you'd have to shut it off to get it into gear without the clutch.

I was poking around the forum and notice the bit about accessing the 5th gear shaft off the side of the transmission. This might be an option, perhaps having the motor coupled with a CVT so that you actually have the torque necessary to move the car, but you would lose any ability to regen while the car idles and you'd not be running through the gears, so your electric motor will be doing speeds completely different from your engine...and finally you'd have drive line losses through the use of a V belt that you could get around if you were directly coupled to the engine.

All that means I'm still thinking of/leaning towards the idea of running it through the crankshaft. Now if the gas engine ran through the CVT and the electric through the trans, that combination would be more fuel efficient. That isn't happening unless the geo engine blows up beyond the point of repair (and I replace it with, say, a 10hp single cylinder engine running off of propane or something).

[GreenHornet]

Hey Stubby,

You are looking at a common parallel hybrid configuration here. What you want to do is what Honda does with there insight. You need enough E-motor torque to run the car on its own. As the E-motor will also be adding to the ICE when needed for higher acceleration of hill climbing.

So you figure this out by determining your speed needs. This will give you an idea of the power you will need in your E-Motor always round up HP as you will need roughly 10-15% more in order to balance gear train mechanical losses.

With a geo metro sedan if stock you would have roughly these specs!

Coef Drag = .32
Frontal area = 19.5
Curb weight = 1,694lbs
Speed = 65mph

So with these inputs you would need 11.5 HP = 8.57kw to cruise at 65mph. However this is not really accurate because you will add weight to the car while hybridizing it and again mechanical losses. I would use 12kw continuous and 30kw peak or around 40hp peak motor output for a car this size and going at a steady cruise with ICE augmentation. What you need here is solid low end torque and a solid RPM range up to like 5000 RPM

Now depending on how you do your gearing as well as tire selection this will have a major impact on your overall top performance. Go for low 1st and 2nd gear ratios like in the 4.1 range with super high final drive ratio like in the .60 range this will give you good around town E drive ability and excellent freeway cruise economy! You would have better acceleration than original Metro and better fuel economy with this plan. I think stock gear in 1st for metro is like a 3.42 with a 5th gear of like .76!

Its always better to go with a custom box if price is not an issue. With the right E-Motor you can stick with the stock tranny and go with the highest final drive ratio avail for the Metro which I believe is the 3.524. The E-motor will offset this sluggish ride of the 1.0L ICE with this gear ratio selection. This gear ratio was not avail in the US and was only on the larger 1.3L engines I believe however I do think its possible to swap the gears however I would double check it to be sure as I am not 100% on that.

Good luck Stubby,

GreenHornet