Unusual hybrid modes

[AndrueC]

I was driving tonight and noticed a couple of odd hybrids modes. One was 'Battery powering the car, engine turning but not generating power'. Basically EV but with the engine turning. It did this at 60mph for about half a minute and then the engine stopped turning and it continued on full EV for a minute. This was on a flat section of road so what's with the engine turning? Engine was well up to temperature by then.

Intrigued by that we made the HSD display full screen and noticed on a couple of occasions that it was showing power coming from the engine and Battery whilst also charging the Battery. That doesn't seem to make any sense to me. Given there are conversion losses I don't understand why it would ever operate in that mode. I can understand the battery helping the engine and the engine charging the battery whilst also providing power to to wheels but both charging the battery and powering the electric motor seems wrong.

[PeteB]

1 hour ago, AndrueC said:

I was driving tonight and noticed a couple of odd hybrids modes. One was 'battery powering the car, engine turning but not generating power'. Basically EV but with the engine turning. It did this at 60mph for about half a minute and then the engine stopped turning and it continued on full EV for a minute. This was on a flat section of road so what's with the engine turning? Engine was well up to temperature by then.

Intrigued by that we made the HSD display full screen and noticed on a couple of occasions that it was showing power coming from the engine and battery whilst also charging the battery. That doesn't seem to make any sense to me. Given there are conversion losses I don't understand why it would ever operate in that mode. I can understand the battery helping the engine and the engine charging the battery whilst also providing power to to wheels but both charging the battery and powering the electric motor seems wrong.

All perfectly normal.

1. The engine can run when not otherwise needed for a number of reasons, but often it's when the HV Battery has received or given a lot of juice rapidly (like after a long braking period from 60-70 mph or down a long hill).  It's something to do with managing the temperatures in the HV Battery or Inverter, or both.  That said, it's worth checking the Battery vent under the rear seat isn't blocked by anything (when the car's a bit older they can sometimes get choked by dust build up, but make sure a coat or blanket etc isn't blocking it).
    
2. There are actually two motor/generators (MG1 & MG2).  I can never remember which is which, but one is effectively bolted to the output shaft of the petrol engine.  It's what starts the engine so quietly and quickly when it is needed, and acts as a governor.  When cruising or accelerating, it can send power to the second, larger MG (to help drive the car), or the battery, or both.

Back in 2005 and 2007 I did a couple of 2-2½ thousand mile tours of Scotland in a 2002 Gen 1 Prius, and encountered some very long, steep hills (mountains, even).  Some were up to 6 miles long and 20% gradient, and despite being the lowest powered version of the Prius (apart from the one only sold in Japan from 1997-1999), the Cruise Control easily held 60 mph all the way up with the power provided by the engine directly plus the large MG using electricity from the engine's MG, and not drawing anything from the HV battery.  It was most impressive and surprisingly relaxed, without the high revs one might expect.  Descending some of these hills resulted in the only time I saw the HV battery fully maxed out on the car (some considerable time after all bars of the gauge were lit), and I got a taste of pure EV behaviour for a while after reaching level ground again.

The Hybrid software tries very hard never to let the battery get too full or too low, and will use as much juice as possible when it gets near to maximum allowable capacity - the gauge the car displays isn't the true picture, it's window of the allowable charge levels for the user.  If it ever showed empty, there would in reality still be about 40% charge remaining, when it maxes out with all bars lit it will be at about 80% SoC (State of Charge).  This, along with temperature management, partly explain why the Hybrid batteries are so reliable.