improving mpg

The green cars are for regenerated energy; in other words, taking some of the momentum of the car and converting it to electricity and storing that electricity in the battery. Each green leaf car equals 50 Wh.

When you lift your foot off of the gas in the Prius, the control system applies a small amount of regenerative braking, just as if you had pressed lightly on the brake pedal. It does this to simulate the engine drag found in normal cars. That's why the Prius coasts better in N than in D with your foot off of the gas.

The manual tells you to not coast in N because it is illegal in most places. Most Prius drivers apply a light pressure to the gas pedal to remove the simulated engine drag. This will accomplish pretty much the same thing without having to shift to N.

Tom

 

Excellent advice so far. I would also like to add that, while it may sound counterintuitive, it's actually more efficient to avoid use of the EV or regenerative braking whenever possible. The reason I say that is that the regen is only 30 percent efficient at capturing energy. Therefore, it's more efficient to more properly plan your approach to a stop if you aren't able to avoid the stop(legally) than to rely on regen.

 

Keep in mind that shifting into Neutral... er.. shifting back into D from N while above 43mph can over rev MG2 (or was that MG1)

this is bad.. avoid it.

I would say to keep out of EV mode while cruising.. which the car will let you do very often. as you keep away from battery use, the battery will fill (from extra rpms off the ICE and braking) this will equal in a faster gear ratio change from the system. since a full battery is key to an optimal system.. but you choose how it charges.... since the power has to come from somewhere.

 

A bit more complicated than that.

Neither the act of shifting into Neutral, nor of shifting into D from N while above 43 MPH run any risk of over revving either of the Motor/Generators (MG1 or MG2).

Where you may potentially run into an issue is:

• You are headed downhill at a speed below 42 MPH and the Internal Combustion Engine (ICE) is off
• You shift into Neutral, and allow the vehicle to accelerate down the hill. (typically when the vehicle accelerates above 42 MPH, the Prius would allow the ICE drive shaft to begin spinning, but in Neutral this won't happen.)
• As you accelerate above 65 MPH coasting down this long steep hill, since the ICE drive shaft isn't spinning, MG1 will be spinning at over 10,000 RPM.

10,000 RPM is the rating on the Motor/Generator (MG1). While it may be reasonable to expect that the engineers allow for a margin of safety in that rating, it would be a generally poor decision to intentionally exceed the rating.

As soon as you switch back to Drive, the ICE will spin which will reduce the speed at which MG1 will need to spin. At 65 MPH with the ICE idling at just 1,000 RPM, MG1 will be spinning at a much more reasonable 6,500 RPM.

Note that if the ICE is already running when you switch to Neutral, it will continue to run and won't shut off until you either run out of gas, turn the vehicle off, or switch out of Neutral (Park, Drive, etc).

Additionally if you are already traveling faster than 42 MPH when you switch to Neutral, the ICE will have already started up, and will therefore continue to run so long as you leave it in Neutral.

While this prevents the over rev of MG1, it may burn more fuel to keep the ICE idling than otherwise might have been necessary if you had left the car in Drive.

 

Summarizing: ordinary drivers should use "N" only while being pulled through a car wash (it's the only way to allow the drive wheels to free-wheel).