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Discussion Starter #1
Bear with me here for a slight detour that I think might help set up my question. If you are of A Certain Age (or very well read) you might remember Mickey Thompson's Challenger I streamliner that was powered by four V-8 engines. IIRC, one of the engineering, er, challenges was to be able to sync the throttles precisely so that you didn't have one or more engines putting a drag on the others or, conversely, have one or more of them "overdriving" the others.

That's what I find myself thinking about with the Insight (though, clearly, not on that scale)....we have a Prius, too, and with that car I can kind of grasp how the planetary gearset would tie the ICE to the motor generators and still allow them to run somewhat independently. But with the Insight's motor assist being literally tied to the ICE, I can't help but wonder what keeps its force "in sync" with the power generated by the ICE, so as not to be overdriving it or, at the other extreme, failing to assist enough and, thus, creating a drag on the ICE.

Can anyone explain this in a reasonably non-tech fashion for an old liberal arts major?
 

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as far as i see it(i could be comepletely wrong :lol: )

the idea of the electric motor is to overdrive the ICE so the ICE doesnt work as hard and when in IMA assist, the electric motor does the brunt of the work

please, someone correct me if im wrong
 

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The setup of the Insight is a compromise. The compromise allows acceptable power and a smooth transition from gasoline to electric drive. Decreasing the percentage of either gas or electric torque would slow the Insight down. Decreasing the gasoline power would decrease mileage and wear the batteries out sooner. Decreasing the electric assist would increase the mileage but would make for a rather non linear throttle response. Though it is a compromise, the present setup makes the Insight fun and practical to drive while at the same time producing its legendary fuel efficiency.

There have been at least three methods to non linearize the Insight's IMA system discussed here. With extra input from the driver, hypermillers have increased their fuel efficiency by perhaps 10 or 15 percent. If you adjust your own valves, own an OBDII tool, and have more wrench sets than cable channels, this is likely your cup of tea. ;)
 

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xqqqme said:
Mickey Thompson's Challenger I streamliner that was powered by four V-8 engines. IIRC, one of the engineering, er, challenges was to be able to sync the throttles precisely so that you didn't have one or more engines putting a drag on the others or, conversely, have one or more of them "overdriving" the others.
I suspect that the balancing was simply to be sure that he was getting max output from all four engines at full throttle. At less than full throttle it would not really matter whether all four were pulling less or one was pulling a LOT less than the other three. As long as none of them was running lean at any point.
xqqqme said:
But with the Insight's motor assist being literally tied to the ICE, I can't help but wonder what keeps its force "in sync" with the power generated by the ICE, so as not to be overdriving it or, at the other extreme, failing to assist enough and, thus, creating a drag on the ICE.?
Actually your Insight does this all the time. The three cylinder engine is inherently unbalanced. Normally a balance shaft would be used to smooth it out, but that would increase frictional losses. Instead the IMA applies pulses of assist and regen on each revolution as needed to smooth out the engine.

In the larger sense it doesn't matter either:
In assist mode when the IMA is helping the ICE, it just adds torque to the torque of the ICE. In regen mode, the IMA subtracts torque from the equation to recharge the battery, for example the bars of regen you see when the battery gets low.
The fuel injection system and computers take care of ensuring that the ICE gets the correct amount of fuel and air for the situation. And try to control the IMA to apply the correct amount of torque or drag.

The idea of Honda's system is to use the electric motor to provide added torque when needed so that they can downsize (and downpower) the ICE. A smaller weaker ICE will be more fuel-efficient but would not deliver the adequate acceleration (torque) when needed. Which is where the IMA comes in.

As I understand it, Prius goes a step further and uses the electric motor for motive power at low speeds in some cases, shutting off the ICE to save fuel. This is not possible in the Insight because the ICE is bolted to the crankshaft and so will still be spinning even if no fuel is being delivered, and this would cause drag due to engine compression. In the HCHII, Honda modified their system to lift the valves when the ICE is off to reduce this drag effect, but as I understand it the HCHII still does not run on electric power alone. But I may have gotten this wrong.
 

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Perhaps a way to think about it is that the ICE and the electric motor both provide some force, and the forces are additive. For example, if you and your friend are both pulling on the rope in a tug-of-war contest, you're not "overpowering" him even if he pulls less hard than you. The total force is simply the sum of the two.
 

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Discussion Starter #6
I appreciate all of the replies. I probably shouldn't have used the term "balancing" without being more clear...I wasn't talking about the inherent balance (or lack of same) in a 3-cyl inline...I was talking about balancing, shall we say the "contributions" made by the IMA and the ICE.

But perhaps I'm working from a flawed premise. I just had this mental picture of what used to happen when you'd get your bicycle coasting downhill too fast for your legs (disregard the fact that you should have used your brakes) and when you put your feet down to the ground you found yourself running as fast as you could to match the speed of the bike.

But it occurs to me that the engine management software could be what's equalizing everything. If there were to be a situation where the IMA (the downhill bike above) was kicking in with more force than the ICE (your legs above) was providing, then fuel/valve/ignition timing would be altered to bring the ICE "up to speed."
 

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xqqqme said:
I appreciate all of the replies. I probably shouldn't have used the term "balancing" without being more clear...I wasn't talking about the inherent balance (or lack of same) in a 3-cyl inline...I was talking about balancing, shall we say the "contributions" made by the IMA and the ICE.
I understood that. I was trying to explain that it is not necessary for the power contributions from the ICE and IMA to be balanced and in fact they are not, even when the engine is idling in neutral. There are points in each revolution when the ICE is pushing on the IMA and there are points where the reverse is true.

xqqqme said:
But perhaps I'm working from a flawed premise. I just had this mental picture of what used to happen when you'd get your bicycle coasting downhill too fast for your legs (disregard the fact that you should have used your brakes) and when you put your feet down to the ground you found yourself running as fast as you could to match the speed of the bike.
That is not the situation in the Insight. The IMA is bolted on one end of the crankshaft (and the clutch/trans on the other) so that they turn together. There is no need to "balance" their power contributions because they always turn as one unit.

Think of your bike analogy with the following modifications: your feet are firmly attached to the pedals, and there is no freewheel, so you cannot stop pedaling, the pedals always turn with the rear wheel, and no brakes (this is like track racing bicycles by the way). As you go downhill, you can (a) push on the pedals to go faster, (b) exert no force on the pedals and let gravity make you go faster, or (c) resist the pedals to try to slow down. There is no need to match your exertions with the downhill acceleration of the bike.
 

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An interesting question and some great answers. Let me just throw in my 2C.
The IMA motor/generator when not producing assist or regen is virtually no additional load. Our hand crank Prius MG1 regen demo is a good example of this.
http://www.99mpg.com/workshops/understa ... site.jpg,0

One can give the 3:1 ratio hand crank a spin with nothing connected, and it will coast around several times. Put a load on the output, and it gets progressively harder to turn, until with a short, it takes both hands and a lot of torque to even move it.
The IMA MG is a synchronous 3 phase BLDC motor, so is always syncronized to the 3 phase drive currents.
The IMA motor which has three hall effect position feedback sensors, so the controller always knows where it is in it's rotation. In the assist mode, The MCM reads the hall signals, determines RPM, and fires the IMA motor coils at a bit higher frequency than the present rotation speed, which causes the rotor to try and catch up to the three phase drive signals by producing torque. The ICE RPM will try to increase as this torque is added, and the combined power drives the car.
Regen simply changes the 3phase AC to DC, and then uses the DC to charge the batteries, which like the handcrank demo, causes energy to be pulled from the system, and slows the car.
 
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