Quote:
Originally Posted by raubvogel
I wonder what made them change. From your diagram it looks closer to the Toyota system but still able to allow you to run directly off the engine. In other words, it leads itself to more combined power at the wheels than the Toyota system.
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My guess, the new system is far lighter and more simple than both their old system and Toyota's. Honda's new system allows the car to drive on electricity alone, and to toggle the gas engine on and off while keeping the car in motion. The old IMA system required the gasoline engine to always be spinning while the car was moving forward, which caused a need for Honda to build some complex valve and cylinder deactivation systems for the engines in their hybrids. And unlike Toyota's system, there is no large and heavy planetary gear system. It's just an electric motor directly driving the wheels, and a clutch that can connect the gas engine in parallel with a single speed reduction. Compared with a 6 speed manual, which has approximately 17 actual gears and pinions in it, this one has 2 (or possibly 4 if the electric motor has a reduction).
Toyota's planetary gears are a more flexible system that allows more combinations of output and input from engine and electric motors. The gearbox is not *that* large (it's still smaller and more simple than traditional transmissions), but it's relatively much larger and heavier than Honda's new one. It also requires the electric motors to be spinning and pulling power from the engine at certain road speeds and loads. Sometimes one motor needs to be pulling power from the engine to spin the other motor faster, to lower or raise engine RPM. Converting from mechanical to electrical to mechanical is an efficiency loss.
Driving the wheels directly from the gasoline engine is more efficient, so long as you can keep load and RPM within its island of peak efficiency. That's how the original Insight was able to see 100mpg+ at certain highway speeds, but had such a huge gap between city and highway RPM. Toyota's system by contrast brings up the average system efficiency tremendously (city mpg sees a huge increase) at the expense of peak efficiency.
All 3 systems have pretty major compromises. GM and Ford have both used systems similar to Honda's original IMA, and Toyota's planetary gears. I *think* Honda's new system is still unique in a production car.