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The Toyota sysnergy drive trades gear simplicity for electrical complexity. Understanding how it actually works is about as easy as describing electron orbitals. Many patents have been aplied for by Toyota on just the computer software that controls the torque and speed ratios of the two electric motor/generators versus the ICE. The Honda system is very simple as the electric motor/generator and ICE are conected to the drive shaft, rotating at the same speed and sharing the same bearings. The IMA occupies the same space as a traditional flywheel and performs the same function as well as assisting the ICE. A standby 12 volt starter for the ICE does add to the complexity of the IMA system but is only used for extreme cold weather starting.

Toyota's system is more efficient in stop and go traffic as the ICE is only on for a small portion of the time. Furthermore because the majority of the torque is provided by the electric motor a quasi Atkins cycle motor can be used to increase combustion efficiency. Honda's IMA is inherently more efficient in steady speed conditions such as highway comutes as it is inherently lighter and does not have the electrical losses associated with the Synergy drive. Honda uses lean burn and/or cylinder idling to achieve high combustion efficiencies.

Honda is on record for saying that they will not abandon the IMA technology. Two major advatages of the IMA system are:
1. It allows drop in engine choices without having to design the vehicle around the engine.
2. For hauling heavy loads and climbing long hills it provides about 40 percent more power to the wheels as it derives less of its torque from the electric motor.

It is my impression that the Toyota system efficiency is more effected by cold weather as it is more dependant on battery power. The efficiency of all batteries goes down dramatically at low temperatures so the more battery dependant the system the more accentuated the efficiency variations. In time all manufacturers will have to deal with this by finding better batteries or developing a system for keeping them warm.

Hope this helps.

:D :D
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