I'm curious if anyone has any data or good arguments as to the most efficient way to accelerate in a Prius from a stop? Who wins the efficacy race, Grandma or the Jackrabbit?
If by Jackrabbit, you mean spinning tires, then it loses in many ways. (Traction Control, wasted energy, altered valve timing, battery drain and recharge, etc.) Brisk acceleration that does not call on battery power, and does not run the cams out of Atkinson mode is much more economical.
So is brisk acceleration more efficient than slow acceleration? In a simple and perfect world, it seems they would be the same as they physics of accelerating a given mass to a given speed requires the same amount of energy. However the engine has a peak efficiency so it would seem to me the most efficient way to accelerate would be to keep the engine at its peak efficiency during the acceleration. With the Prius I would think this would be much easier than a car with a standard transmission. The peak efficiency is typically a fairly high RPM. I just wonder if there are other variables.
When watching a SG2 while accelerating in the power range with steady pressure, the draw from the battery to devices and the electric motor will fluctuate between 90 amps and -30 amps (regen). More control over each would help.
Wayne Gerdes recommends (for 2010+ models) keeping the car in electric mode until 16 mph, then accelerating briskly to 3/4 on the wide HSI bar (not including power section). For an older model year, this probably means keeping the MPG meter in the range of 1/2 to 3/4 of the MPH. So, in short, neither ultra slow acceleration, nor ultra fast acceleration is best, but rather something in between.
Yes, neither. It will all depend on the situation and the distance from a stop to the next stop; or the slope/inclination of the road. If you're entering a highway or it will be miles before the next stop, then a moderately brisk acceleration at 40-50% throttle is good because you can get up to speed quickly and be on the efficient range the soonest. Then you have the opportunity to glide or hold that speed for long distances at zero to minimal gas consumption. Having a ScangaugeII will help as you can monitor things like RPM, IGN, BTA, etc. I still rely on the MFD too as it is a good indicator of what's happening. If the distance to the next stop or crawl is like a typical block then accelerating hard will just consume the most gas compared to a slow, low rpm pulse... then just glide just in time for the stop. If it's an uphill from a stop, then brisk acceleration with battery assist to the ICE is ideal to get up to the desired speed then controlling the throttle to manage a slow deceleration right up to the peak. Of course it still depends on the distance. If a downhill section is anticipated soon, a slow acceleration using the HV battery can be used instead of firing the ICE. It also depends on how long the downhill goes for. If it's short, then use minimal energy from the HV battery. If it's a long one, then one can demand a bit more juice from the HV battery to get some momentum going and just recover the used energy with controlled regenerative braking. So the key word here is distance... in relation to the least amount of energy (or gas) required to move the car to cover that distance (and perhaps recover some of it for the next start-stop cycle). At least that's how I see it and apply it.
This is true with the Otto cycle engines in typical nonhybrids, though I believe the peak efficiency is usually at high torque but moderate RPMs. Grandma acceleration misses the high torque portion completely, jackrabbits uses too much RPM. The Atkinson cycle engine in a Prius has a comparatively flat 'peak efficiency' spread over a wide RPM range, as shown in Jimbo's post above. And with Toyota's HSD system, the engine is managed to stay at fairly high torque under most load conditions. The result is very good efficiency over a much wider variety of conditions. Thus acceleration style has much less MPG impact in a Prius than it does in common nonhybrids.
Moderate RPM's from what I have seen on my HUD screen. There are so many different driving conditions around me, hills, flats, stop and go traffic, its hard to really control my rpm's beyond driving like a normal person would in the given situation. With that said it seems that the genII Prius has a wide tolerance range as my fuel consumption stays relatively the same. Just my 2cents...
It's mostly a function of how much the HSD is loading MG2. Check out one of the pages about the HSD and you'll see where most losses are from.
