Unravelling Engine Braking - pre-'09 and post-'08
#21
04-11-2015, 01:52 AM
Re: Unravelling Engine Braking - pre-'09 and post-'08
OK, this is a pretty old thread, but it's the right one for my questions and observations.
As an answer to one of the questions above, I frequently used "L" in my 08 to control my downhill speed, and below 40MPH the ICE stayed off, even if I briefly used light brake pedal, until charge hit max.
Now I'm driving my 09 daily, and "L" ALWAYS causes the engine to rev up a bit. Also, I thought that 09 started the ICE shutting down whenever you took your foot off the gas. My 09 won't shut down the ICE any time I'm above 40MPH. (and I ain't happy about it!)
As an answer to one of the questions above, I frequently used "L" in my 08 to control my downhill speed, and below 40MPH the ICE stayed off, even if I briefly used light brake pedal, until charge hit max.
Now I'm driving my 09 daily, and "L" ALWAYS causes the engine to rev up a bit. Also, I thought that 09 started the ICE shutting down whenever you took your foot off the gas. My 09 won't shut down the ICE any time I'm above 40MPH. (and I ain't happy about it!)
#22
04-11-2015, 11:08 PM
Re: Unravelling Engine Braking - pre-'09 and post-'08
Your observations are correct. I think Gary pointed out to me that the '08 and earlier use "L" differently from the later FEH's.
Using "L" in the '08 and earlier causes regeneration, and therefore speed reduction, without using the brake pedal. If you're below the ev speed limit, the engine will stay off. If you're above the ev speed limit, I don't know if the rev's increase because so far no one has posted about that.
Using "L" in the '09 and later also causes regeneration and speed reduction without using the brake pedal. However, using "L" will force the ICE to run, and it will run at a higher rpm than it would otherwise. Since the '09 and later don't use any gas if your foot is off the gas pedal, using "L" will not directly hurt mileage. However, since the engine parts are being spun around, this wastes energy that otherwise could be captured by regeneration. The way to capture it for regeneration while not using "L", is to leave it in "D" and use the brakes. Normally, this will retard speed by regeneration and it won't use the mechanical brakes.
The advantage might appear to be with the '08, but as far as I can see the '09 can do whatever the '08 can do, plus it has the engine braking "L" mode for long steep descents where you exceed the capacity of the hybrid battery anyway. Trailer towing causes similar situations. After the battery is full on a long hill, you're on the mechanical brakes only, and "wasting" energy by engine braking with an '09 in "L" means less wear on the brakes.
The '09 should be able to remain in ev mode to a higher speed than the '08.
Using "L" in the '08 and earlier causes regeneration, and therefore speed reduction, without using the brake pedal. If you're below the ev speed limit, the engine will stay off. If you're above the ev speed limit, I don't know if the rev's increase because so far no one has posted about that.
Using "L" in the '09 and later also causes regeneration and speed reduction without using the brake pedal. However, using "L" will force the ICE to run, and it will run at a higher rpm than it would otherwise. Since the '09 and later don't use any gas if your foot is off the gas pedal, using "L" will not directly hurt mileage. However, since the engine parts are being spun around, this wastes energy that otherwise could be captured by regeneration. The way to capture it for regeneration while not using "L", is to leave it in "D" and use the brakes. Normally, this will retard speed by regeneration and it won't use the mechanical brakes.
The advantage might appear to be with the '08, but as far as I can see the '09 can do whatever the '08 can do, plus it has the engine braking "L" mode for long steep descents where you exceed the capacity of the hybrid battery anyway. Trailer towing causes similar situations. After the battery is full on a long hill, you're on the mechanical brakes only, and "wasting" energy by engine braking with an '09 in "L" means less wear on the brakes.
The '09 should be able to remain in ev mode to a higher speed than the '08.
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