unnecessary engine restarts at max charge

[tkil]

My 2005 Prius has had this issue for at least a few months: at the end of a long highway drive, I coast the last half mile or so (downhill, then down a ramp) to a complete stop. At that point, the state-of-charge meter shows full, and the gas engine seems to cycle on and off continuously. Creeping forward even a little bit seems to stop it.

Is this the "dieselling" that I've seen mentioned elsewhere? Is anyone else seeing this?

Temperatures are generally moderate (inland north county San Diego, so from 90F down to 50F). My commute is 25mi each way, of which about 23 is highway; I'm coming off 25 minutes at 65mph (on cruise) when I drop the cruise and do the coast to a stop.

My best guess is that the computer decides the battery is a bit overcharged, and cycling the motor is the best way to work off the extra charge (since the Prius doesn't have a resistor bank, at least so far as I know...) Thanks for any info!

[olends]

Originally posted by tkil@Jan 26 2006, 05:51 PM

My best guess is that the computer decides the battery is a bit overcharged, and cycling the motor is the best way to work off the extra charge (since the Prius doesn't have a resistor bank, at least so far as I know...)  Thanks for any info!

[snapback]198215[/snapback]

this is correct

[tideland_raj]

Originally posted by tkil@Jan 26 2006, 06:51 PM
My best guess is that the computer decides the battery is a bit overcharged, and cycling the motor is the best way to work off the extra charge (since the Prius doesn't have a resistor bank, at least so far as I know...)  Thanks for any info!

[snapback]198215[/snapback]

Since this is the case, if it's a mild descent, you may want to alternate between neutral and drive, I find this useful because neutral is faster (ie, HSD is disengaged), and the only reason you want HSD engaged is to gain battery charge thru HSD.

Of course, being in neutral is bad if you *do* brake, since it will not use the regenerative brake and you'll be wasting brakepads. So I usually keep my hand on the silver knob whenever im in neutral just in case I need to throw it back into drive to hit the brake.

[john1701a]

Originally posted by tkil@Jan 26 2006, 05:51 PM
the gas engine seems to cycle on and off continuously

[snapback]198215[/snapback]

But it actually isn't.

The engine never uses any gas during that cycling. What's really happening is the computer is utilizing the startup process (spin the engine up to the ignition point) to use up that excess electricity. Then it allows the engine to slow down. Then it repeats... and repeats.

This is one of those cases where you'd what to take advantage of "B" mode, since that reduces the amount of recharging.

By the way, I've only experienced that once. And it was intentional, to find out firsthand what the heck owners dealing with long decents with a stop at the bottom were talking about.

[hdrygas]

Originally posted by tkil@Jan 26 2006, 02:51 PM
My 2005 Prius has had this issue for at least a few months: at the end of a long highway drive, I coast the last half mile or so (downhill, then down a ramp) to a complete stop.  At that point, the state-of-charge meter shows full, and the gas engine seems to cycle on and off continuously.  Creeping forward even a little bit seems to stop it.

Is this the "dieselling" that I've seen mentioned elsewhere?  Is anyone else seeing this?

Temperatures are generally moderate (inland north county San Diego, so from 90F down to 50F).  My commute is 25mi each way, of which about 23 is highway; I'm coming off 25 minutes at 65mph (on cruise) when I drop the cruise and do the coast to a stop.

My best guess is that the computer decides the battery is a bit overcharged, and cycling the motor is the best way to work off the extra charge (since the Prius doesn't have a resistor bank, at least so far as I know...)  Thanks for any info!

[snapback]198215[/snapback]

As far as I know the Prius never "diesels". Yes there is a shutter on stop but this does not represent traditional "dieseling" as some of us remember in carbureted cars. See John1701a post, on the running of MG1 to use up excess charge. The shutter of stopping of the ICE is also confused with "dieseling" but it seems clear that the mechanism of the shutter and dieseling caused by compression combustion of fuel in older carbureted cars is different.

[Ken Cooper]

Originally posted by john1701a@Jan 26 2006, 07:19 PM
But it actually isn't.

The engine never uses any gas during that cycling.  What's really happening is the computer is utilizing the startup process (spin the engine up to the ignition point) to use up that excess electricity.  Then it allows the engine to slow down.  Then it repeats... and repeats.

This is one of those cases where you'd what to take advantage of "B" mode, since that reduces the amount of recharging.

By the way, I've only experienced that once.  And it was intentional, to find out firsthand what the heck owners dealing with long decents with a stop at the bottom were talking about.

[snapback]198323[/snapback]

Now that's interesting, and it makes sense, and it matches what I've experienced. I used to experience this daily as I'd wait at the light after the long down hill drive from my former home. The battery indicator would show all green bars, the engine would seem to cycle on and off, but the display showed no indication of the engine running/delivering power (via generator) to the battery.

I mentioned this to my local Toyota Prius mechanic but all he could say was that the diagnostic tests showed everything within the hybrid system operating correctly. I'll share your comments with him.

Thanks!

[hobbit]

If you don't have a hill handy and want to duplicate this behavior
yourself, you can always force-charge the battery up to max-
indicated-SOC and then watch it do the dance. [hold down brake,
press accelerator till the ICE starts]
.
_H*

[tochatihu]

Originally posted by hobbit@Jan 26 2006, 11:02 PM
...you can always force-charge the battery up to max-indicated-SOC...

[snapback]198490[/snapback]

Or if force charging is too slow, try hyper-force-charging!

On, park gas gas, neutral gas gas, park gss gas, (HV flash), start.

Now you are in inspection mode and have a ! on the mfd. Force-charge at 30 amps or better. But don't go driving in slippery places.

Shut down cancels inspection mode. Hope I don't regret sending this.

[hobbit]

Erm ... I don't think force-charge current changes if you're in
inspection mode or not. It does, however, change depending on how
far you press the accelerator. Yes, ideally you need a battery-
current meter to tell this, but without one you can sort of tell
what's going on by listening carefully to the inverter whine.
.
When the ICE slows down by itself and goes back to idling despite
how hard you've floored the accelerator, you're done.
.
Oh, right, I should clarify that all of this happens in Drive...
.
_H*

[tkil]

Originally posted by olends@Jan 26 2006, 02:53 PM
this is correct

[snapback]198216[/snapback]

Spiffy, thanks for the (insanely!) quick answer. Between your reassurance and john1701a's explanation, I feel much better about it.