I just got a 2011.. I am wondering - when you let off the gas like about 65mph. Does the engine actually stop truning. Or does it continue to have RPS's and just the Gas shut off ? Also - when you put it in "B" to slow down - what is actually happening. is the engine compression slowing you? Thanks..
#1) At lower speeds the engine stops spinning, forcing MG1 to spin backward. As speed increases the rotational speed of MG1 approaches a high limit, and the engine starts to spin to keep the speed of MG1 at an acceptable level. The speed at which this happens differs between the Gen II and Gen III Prius. If I recall correctly, the limiting speed is somewhere around 43 mph in the Gen II, higher in the Gen III, but don't quote me on it. #2) B mode causes engine compression braking to start. MG2 applies regenerative braking force, but instead of sending all of the regenerated power to the battery, some or all is sent to MG1 which then spins the engine as a large air pump, dissipating the excess power. This is essentially the same as compression braking automatically invoked when the battery SoC reaches a high limit, but it starts immediately due to B mode. Tom
To #1's point - the engine will rarely idle below 1000 RPM in a Prius, thus once the engine is kicked over at 46mph in a standard non-plug-in Prius, ~1000 RPM will be what is maintained, whether it's using fuel or drive-line rotation to maintain it.
I see 960 RPM when no power is needed but rotation is and you can add electricity to the three things maintaining engine rotation. As in when the battery is charged "too much" the HSD uses the excess charge to spin the engine.
I also see the 960 RPM when no power is needed on my Gen III. When fuel is being used the minimum RPM is around 1200 to 1400 RPM.
