Hybrid System Walkaround - 2010 Honda Insight EX Long-Term Road Test
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2010 Honda Insight Long Term Road Test

2010 Honda Insight EX: Hybrid System Walkaround

November 06, 2009

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Ever wondered what it takes to build a hybrid? Well, that depends on what sort of hybrid you're talking about.

The hybrids that Toyota and Ford put out are complex (and effective) series-parallel hybrids, meaning they can run on gas, electricity, a direct parallel blending of the two or a series piggyback mode where the gas engine generates electricity for the battery while an electric motor uses that electricity to drive the car. It takes two powerful electric motors that are integrated into a mind-bending (but mechanically quite simple) planetary CVT system to pull this off. Powerful control software continually switches between these modes so you don't have to think about it.

But our 2010 Honda Insight is based on a simpler parallel-only setup, in which the engine and transmission are prised apart so a thin, flywheel-sized electric motor (just over 2-inches thick) can be slipped between them. This electric motor goes by the name of Integrated Motor Assist or IMA, for short.

It's basically laid out like this:
Engine --> IMA --> Transmission

Let's have a look, starting at the back of the car.

The above shot from my suspension walkaround series shows why the simple twist beam suspension configuration was used here: it leaves plenty of room between the wheels for a deep central well that houses the spare tire and battery pack.

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There's even room for several storage nooks. The optional spring-loaded roll-up cargo cover can actually fit in the slot at the bottom of the photo.

Now let's pull that styrofoam out of there for a minute.

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I see a spare. But there's something else under there.

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Eureka! It's the battery pack. But I have to say, it's not a very big one. Especially when you consider that the voltage-conversion and charge-monitoring electronics are housed here, too.

The batteries themselves are made up of Nickel-Metal Hydride (NiMH) cells, the type used in nearly all current production hybrids and electric cars.

Together they consitute a 100.8-volt pack that has a 5.75 amp-hour capacity. That greek to you? Let's multiply volts with amp-hours (and divide by 1,000) to look at this in Kilowatt-hours (kWh), the electrical equivalent to the number of gallons in a gas tank.

The Insight's electrical tank is therefore a scant 0.58 kWh, and that, among other things, makes it a mild hybrid. The Prius, a more hybrid-y "full" hybrid, has a battery capacity of around 1.3 kWh.

Move up to a plug-in hybrid, like the much ballyhooed Chevy Volt, and battery capacities start to range up to 9 kWh to accomodate a bit of extended electric-only range courtesy your wall socket. Continue on to something like our 2009 Mini E, a full electric car that depends on juice for everything it does, and you'll find a battery with a usable capacity of 28 kWh. All-electric battery capacities will doubtless grow upwards from here.

How does the Insight make do with 0.58 kWh? Well, the electric motor-generator (which we shall see in a moment) is not very big, so it neither consumes nor regenerates very much electricity. Standard hybrid batteries get ALL of their juice from regenerative braking, and the amount they can take in is thoroughly dependent on the size of the electric motor-generator.

The Insight's battery essentailly stores enough to recover energy from in-town stops for immediate use when you drive away from a stop and for restarting the engine each time it shuts down while "idling" at traffic lights. There isn't much in the way of all-electric range. We're talking seconds, not minutes at a time in most situations.

Like all hybrid batteries, these are considered to be part of the car's emissions system because if they fail the car will run on gasoline more of the time and emit more pollutants.

An that means you'll probably never have to worry about battery replacement cost or landfill impact of spent hybrid batteries, becuase they must last through California's stringent emissions warranty lifetime of 10 years or 150,000 miles.

How is this possible? By never letting the battery drain to 0% and never charging it to 100%. The key to maintaining long battery life is careful management of its State of Charge or SOC. Hybrids and electric cars take this aspect far more seriously than the charging system of a Makita screw gun or other rechargeable home electronics.

A typical NiMH hybrid battery will, in very rough hypothetical terms, only use the thin slice of SOC from, say, 30% to 70% SOC. People are excited about Lithium batteries because, by comparison, a wider range of SOC can be used, such as from 25% to 75% or from 20% to 80% SOC. And that means more electricity can be stored in a same-sized Lithium-Ion battery.

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Power flows between the battery and the motor-generator (in both directions) through this orange cable.

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Behold the power that is the 1.3-liter 4-cylinder engine that makes 85 horsepower on it's own! The IMA can supply another 13 hp (10kW) when needed, bringing the maximum up to 98 ponies.

Clearly, this is no powerhouse built to light the world on fire, as the Insight achieves its fuel economy through a modern adaptation of an old Honda principle laid down in their past "HF" gasoline-only models: Light weight, a diminutive powertrain, a small vehicle cross-section with good aerodynamics and skinny low-rolling resistance tires.

The formula usually includes a manual transmission, but here an efficient CVT is used. But it's a "normal" CVT instead of the exotic electro-mechanical CVT seen in the Prius. This iteration of Insight could just as easily use a manual transmission, as the first Insight did, because the electric motor-generator is more of a booster than anything else.

Look inside the circle to see the IMA motor-generator where it sits sandwiched between the engine and transmission. How about a closer look?

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Green = Engine, Orange = CVT transmission and Yellow = IMA, the meat in the sandwich.

The IMA can add up to 13 hp to whatever the engine is outputting and it also functions as the main starter for the engine.

That engine is never fully disconnected from the IMA, because there is no clutch between the two. The IMA can nevertheless power the car by itself for the first seconds after you roll away from a stop with the engine off, but the crankshaft will still rotate and the pistons will still pump up and down.

Pumping air like this through open valves creates a lot of drag that ruins efficiency, so Honda uses their VTEC cam-switching system to provide relief. One cam has the standard profile that the engine uses whenever it is running, but the second cam profile is completely round so that the intake and exhaust valves never open as the pistons fly about with no fuel being injected.

At first this seems like it would be worse, as it takes power to compress raw air in a cylinder. But you get almost all of that back as the piston is pushed back after it reaches top-dead center due to the air-spring effect. And this motion is smoothed out by the fact that 4 pistons are doing this in different parts of the cycle, so the compression forces in one cylinder are offset by extension forces in another.

NOTE: See why suspension walkarounds are so much easier than powertrain ones???

Perhaps the most important role of the IMA is regenerative braking. When you lift off the throttle, the computer reverses the polarity inside to turn the IMA from a motor to a generator. This generated electricity flows back in the battery, and the action of generating it creates a small decelerative "braking" force as the magnets in the generator do their thing.

The force is small in this case because of the small size of the IMA and the battery: you can only generate and store so much with this mild setup. As a result, the regenerative braking force feels no more significant than plain old engine braking in top gear in your gasoline car. You still need to use the brake pedal and the conventional disc/drum brake system for most of your slowing and stopping needs. That said, gentle use of the pedal and gradual slowing over a long distance allows the regen system to take in as much as possible.

That's not the case in our all-electric Mini E, where a huge battery (50 times bigger) and a large motor-generator (the only prime mover in the car) can (and need to) swallow as much juice as they can. Electric cars have to recapture every scrap to achieve their advertised range.

And so the Mini E drives like a slot car, with substantial regenerative braking forces that occur merely by lifting your foot off the "gas" pedal. They're so strong that you can get by without using the regular brake pedal 70% of the time; so strong that the brake lights are programmed to come on via computer so the car behind doesn't rear-end you.

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Skinny 175/65R15 tires reduce rolling resistance in the Civic and CRX "HF" tradition. The final EPA fuel economy tally is 40 city/43 highway/41 combined.

The Honda Insight impressed and excited us when we first saw and drove it at the press launch, but that was when the rumor mill had the price in the $17,000 to $18,000 range and gas was over $4 per gallon.

But the Insight ended up starting at over $20k (with destination). For that you get a low-powered Honda in the traditional frugal Honda "HF" sense that gets a little performance and economy boost from a simplified mild hybrid system. With moderate fuel prices, that price seems a bit steep.

Dan Edmunds, Director of Vehicle Testing


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