During deceleration, the gasoline engine is switched into fuel cut mode, and the IMA Motor/Generator is operated in generation mode. In this mode, the IMA Motor is driven by the wheels, generating electricity to be stored in the Battery Module, and slowing the Insight in the process. The amount that the IMA Motor slows the car is in proportion to the amount of regeneration being done. There are two deceleration modes:
Foot off throttle but not on brake pedal - In this mode, the charge/assist gauge will show partial charge, and the vehicle will slow down gradually.
Foot on brake pedal - In this mode, a higher amount of regeneration will be allowed, and the vehicle will slow more rapidly. During light brake pedal application, only the IMA Motor/Generator is slowing the car. With heavier brake pedal application, the conventional friction brakes also come into play.
When decelerating, regeneration will continue until engine speed falls to about 1000 rpm. At this point, the driver will typically shift into neutral. In many cases the gasoline engine will now immediately enter auto idle stop mode. If vehicle speed is such that it isn't clear whether the driver will most likely come to a stop, the engine may idle for a few moments before entering idle stop. If the battery state of charge is very low, idle stop will not be entered at all, and instead the engine will continue to run at a fast idle to recharge the Battery Module.
from: http://www.insightcentral.net/encyclope ... aking.html