IC "hiccuping" ...

I get the same thing. First, I assume the engine is running to recharge the battery. Sometimes it seems to me it's not sure if it should shut down and I feel 2 or 3 light jolts.

 

I THINK and this is a big THINK, that maybe the engine is positioning itself at TDC for optimal restarting. Mine (04 with 38k) does this sometimes and I don't even give it a thought. It mainly does it when the engine is cold. I don't think there is any reason for concern.

 

I had to search for a wlhile but finally found the thread that covers this topic.

http://priuschat.com/index.php?showtopic=11350&hl=

Bill's post is the best answer that I have seen on the subject:

"The smart Prius needs its HV battery and protects it, not letting it get too high a charge, and turning on the ICE when the charge gets too low. If you have a full green battery (about 80% battery saturation), usually by going down hills with regenerative braking, and then stop, a little too much charge might have been put in the battery. To drain off this excess charge, the Prius uses the electric motor to spin the ICE. The ICE isn't supplying power, it's draining power. Excess electric energy is being used to compress air and blow it out the exhaust. The ICE sounds like it's running, and it cycles on and off, but look at the screen and you'll see a full battery. When the charge is right, the ICE stops cycling."

 

Turn the AUTO A/C off and I'll bet you find that the engine shuts down immediately.

 

Bill's post explains the ICE turning on and off at a stop when the SOC is 8 bars. I believe Uncle Groove is referring to the shudder at stops.

Tends to shudder or be reluctant to shut down more when it is cold or not warm enough. I suspect it shudders because of the extra fuel vapor in the intake manifold and charcoal packet in the aircleaner housing being burned (spark, but injectors cut off). The fuel vapor in the intake is on account of how the aktinson cycle works, pushing fueled vapor back out of the cylinder during the early part of the compression stroke.

 

I based my answer on Paul's question which appears to indicate "full green SOC" when it occurs.

 

He said he was PUSHING for a full SOC, but didn't say he achieved it, and that's when he sees his symptoms. Symtoms described (shudder, reluctant [delayed] shutdown) corrolate with cold shutdown. Repeated restart would correlate with maxed SOC. A delayed shutdown does not draw down SOC, but instead would add to it. A cycled stop and start would draw it down.

 

I never understood why Toyota had the car do that. If the battery gets full, all that's left to do is use friction brakes like any other car.

Except maybe coasting, that could be a problem dumping the regen energy that simulates AT drag.

 

Paul,
I have a similar commute and find that this (Full Green SOC) is an ideal time to use the EV mode. I push the EV switch on the off ramp prior to the stoplight; this precludes the “Engine Run-on/Battery Equalization†and allows me to complete the 18-20 block trip in city traffic in EV mode. By the time I get to my office the battery is usually down to 3-4 blue bars and I have been able to use the excess charge and not wasted it.

 

The engine runs to actually drain some power from the slightly-overcharged battery.