I've had my '06 Prius for about six months now and love it. I appear to be constantly learning about the vehicle and my latest observation triggered this post.

I live in a mountain state and as a result have frequent opportunities to use the "B" gear. It works quite well but recently I have noticed that when I am on a particularly long or steep downhill slope and the battery reports as being fully charged (full green/yellow bars all the way to the top) the engine begins to rev at a much higher frequency than when the battery isn't quite at a full reading.

Any thoughts as to why this revving would occur? Is it related to the inability of the EV to provide any drag once the battery has a full charge?

Thoughts?

UTpiper

 

Hi,

I ran some tests last summer on "B" looking at 'grade vs speed_change' since my interest was more in safety than anything else. This is pure speculation on my part but it would be perfectly OK for the engine to run higher to supply power to MG2 as 'reverse', to limit the speed. There is an absolute power rating so it can't over-drive MG2.

I didn't have a Graham scanner last summer so I'll try to replicate some of that testing once the weather warms up a bit. For now, treat this as a 'hypothsis', not empirically verified fact.

Bob Wilson

 

BTWs of "B" mode . . . have you noticed that it is possible to "glide" above 40 mph without intervention of both ICE and or Electric motor? Would it be agood idea to use this mode on highway?

 

Actually, the critical speed is 42 mph and near as I can tell, we can 'glide' at high speed in one of two modes: (1) no fuel with MG1 supplying a little torque to keep the ICE spinning, or (2) very little fuel with the ICE just slightly turning over. These are the closest to a 'glide'.



Bob Wilson

 

Went in to the dealer yesterday for my 15,000 mile service and asked the question. He confirmed the EV shuts off (in essence) when the battery pack reaches a full charge and no longer provides any drag. Hence, the ICE takes over the engine braking process and thus the RPMs increase causing the higher pitched revving. Makes sense. I asked if I can run into an RPM issue with the smaller ICE when this occurs (I go down some pretty steep inclines back to the city) and he didn't think there would be any issues but without an RPM gauge (or reading via computer hookup) he couldn't guarantee I wouldn't hit some maximum RPM level.

FWIW

UTpiper