A strange question for those hypermiling experts... I have a 2-3 mile downhill run, not a horribly steep grade but certainly noticeable. Usually I feather the gas so there is no regeneration, and I max the speed out in the low 50 mph. Today there was a lot of traffic so I had my foot completely off the gas (ie mild regeneration) and I was maxing out around 47 mph. I could still feel the ICE on at this point. Wouldn't I have better gas mileage by braking down to 45 mph and not having the ICE turn on at all? It seems counterintuitive to me, braking for better gas mileage.
Lol I'm waiting for the answer on this one too!!! but i don't think the ICE would be running if your just coasting down a hill with your foot off the gas. When i do this and start to push my foot on the gas i can feel the ICE restart once the bar goes back into the eco area.
Here is a pretty good website that will show you the power of motor & ICE [http]://eahart.com/prius/psd/
ICE is spinning, but no fuel used. So, just thinking out loud here, the question is whether you are better off having a bit more SOC, or better off with the faster speed at the bottom. If SOC high anyway, that favors keeping the extra speed for a longer glide. You should further consider N glide, if it won't yield too much speed, once your SOC is up in a good range. Momentum from the gravity has less conversion losses than regen.
If you were going downhill with your foot off the gas you probably were not burning any fuel even if the ICE was spinning. However, if you were running the ICE downhill your instaneous reading was still probably over 100mpg. Braking provides energy to charge the battery a little better than just coasting. However on a long grade you'll probably be fully charged when you're at the bottom regardless. Just let it coast.
gee...so much information, hard to really say. how much traffic? how many lanes of travel? how many lights? what is the speed limit? if the speed limit is 45 mph or less, than do it. spinning the motor even if burning no gas is energy wasted.
I would think in a 2 to 3 mile downhill coast your battery will fully charge without braking anyway. I have rodden my brakes on shorter grades in order to stay within the limits and charge my battery. If I am willing to go over the limits I would rather do that as ride my brakes to regen. If your foot is off the gas, look at the monitor and you will see the wheels doing a regen process with the battery via the generator and no flow from the engine (off or not burning fuel). That should be the best of all worlds for you. I would rather coast at 47 any day over using gas to get up to 50, even if the gas instant reading is over 100 mpg.
Hello, Excessive use of brake is nit advised for fuel run car as it is not good for the mileage of the car, though not sure about gas run car. Regards, sarah_9
The ICE spins to keep MG1 from over-revving. The only way to avoid this is to shift to N with the ICE off, at which point you take responsibility for keeping MG1 at a safe speed. Tom
if the ICE is spinning and you select neutral I think the ICE keeps spinning, if the ICE isn't spinning but the speed climbs beyond the MG1 threshhold speed there may be damage done to MG1. Just let the computers do the drive train management.
All right, looks like I finally have the answer! I emailed Ken, and it was his opinion that any speed over 46 mph would engage the ICE and thus use gasoline, albeit a small amount. Unfortunately I do not have a scangauge so today during my run I left my foot off the the accelerator completely and watched carefully as the car went from 45 to 46 mpg. In the moment I felt the ICE turn on I saw the instantaneous mpg momentarily dropped down to 90? mpg before going back over 100. As such I would say that coasting at 45 mph, even if you are using the brake to keep the speed down, is more efficient than coasting downhill at 47 mph with the foot feathering the accelerator. Realistically the difference in gas is likely to be minimal. Having said that, I imagine I will piss off other drivers if I brake all the way down this hill going 45 mph, so I'll probably just burn a small amount of gas and go a bit faster. Ken, thanks again for your advice!
