Most 3 cylinders engines have large crankshaft counterweights, an intentionally unbalanced and heavier flywheel, and/or a balance shaft, because 3-pots are far less balanced than 4's. The Insight has neither of these. Normally the IMA motor performs idle smoothing, where it "regens" at the peak of each cylinder's torque and "assists" in each trough, like this:
From wikipedia:
Quote:
Inline 3 with 120° crankshaft is the most common three cylinder engine. They have evenly spaced firing and perfect phase balance on reciprocating mass, with 4., 6., 14. and 16. imbalances. Just like in a crossplane V8, these first order rocking couples can be countered with heavy counterweights, and the secondary balance is comparable to, or better than an ordinary inline 4 because there are no piston pairs that move together.
This secondary balance advantage is beneficial for making the engine compact, for there is not as much need for longer conrods, which is one of the reasons for the popularity of modern and smooth turbo-charged inline 3 cylinder engines on compact cars. However, the crankshaft with heavy counterweights tend to make it difficult for the engine to be made sporty (i.e. quick revving up and down) because of the strong flywheel effect.
Unlike in a crossplane V8, the bank of three cylinders have evenly spaced exhaust pulse 240° (120° if two stroke) crank rotational angle apart, so a simple three-into-one exhaust manifold can be used for uniform scavenging of exhaust (needed for uniform intake filling of cylinders, which is important for uniform amount of torque generated and uniform timing of torque generation), further contributing to the size advantage.
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Honda wanted to keep the engine light and quick, so they didn't add anything to it to balance it. Without the IMA system smoothing it out, idling (~900rpm) results in the glove box chattering and a sensation similar to one of those vibrating back massagers.
The first few times I drove the car without the IMA, I stalled it in intersections. Presumably this is because the flywheel is very light as normally there's a pulse of assist when dropping it into 1st gear. I was able to learn around that by slipping the clutch at ~2000rpm for a second or two every time I started off, but it makes the car need more attention to just drive.
To keep the CEL off, a member over on Insight Central figured out you could send the ECU as few as two analog signals (IMA state and battery SoC) and it would think everything is peachy. Tell the car the battery is above ~15% however and the engine shuts off every time you drop below 22mph - a problem in city driving as normally there's also a ~4 second delay before the backup starter motor kicks in when you turn the key - it's expecting the IMA motor to be there.
Setting the battery SoC below 15% prevents autostop, but also results in the ECU thinking the car needs to be charging a flat battery while driving, which results in a slightly higher idle (~1100rpm) and a slightly different timing map which makes it more torquey. This is generally good. However, it also disables lean burn.
My solution? Feed the ECU that the battery is at ~50% charge when going faster than 22mph, and <15% when it's going at or below 22mph.