Fuel economy

If I understand this correctly, you are burning some gasoline (HV) to charge the battery enough so that instead of charging at home you can make it to the free charging station the next morning.

It seems to me that you need to calculate the cost of the extra gasoline you burned compared to the cost of the electricity you saved at home.

 

I don't understand why you think this is a benefit. Whether you are in EV or HV going down hill you are still regenerating the same amount of power. I always tap EV as soon as I crest a hill (assuming I have EV range left). This turns off the ICE which probably activated during the hill climb.

Its a small detail but some people also like to monitor their HV/EV percentagages. If you are always in HV even when using EV in HV your percentage will be lower. I like to see a high EV percentage.

 

Oh yes and by pressing EV at the crest of a hill, turning off the ice, you will get infinity miles per gallon. I'm no math wizard but I'm pretty sure that's better than 100mpg.

 

Im sorry but I still think it would be pointless to drive like this. Driving using EV going up a hill is inefficient and wasteful.You need to look at your average mpg not just the instantaneous. Your instant mpg MAY be higher but you cannot use your strategy on more than a couple hills (depending on the size of course) before your EV range is gone. Once its gone your stuck getting 60 mpg's.

I have found, along with many other drivers, that during long trips using HV and then switching to EV as you crest a hill and during plateau's is the way to go. You never want to use up the EV during a trip because then you cannot shut the ICE down manually once you do. I always save EV until the tail end of my trip. The trick is to time it correctly so that you use up all of the EV as you enter the driveway. I consistently get 85+ mpg on hour + long trips.

Then you recharge and head home.

 

It wouldnt be 100mpg if you were in EV. It would be infinity. But if you have EV to spare, sure go for it. EV=good.

 

A little background

Your battery pack has a limit capacity to take a charge - the higher the SoC , the more energy it takes to recharge. Why? Batteries donot recharge linearly it takes twice as long to recharge the last 1/3 of the battery's power capacity as the first 2/3 of the battery power capacity. The graph of the battery power level/Recharging time is an exponential curve that swings up before leveling off into a flat line.

Your regenerative brakes are more efficent at making electricity when it is between 100% to 50% regenerative braking and less efficient at making electricity when it is between 50% to 1% regenerative braking. Why? There is a energy overhead loss in the conversion of mechanical energy to electrical energy of about 20% most of the time but this overhead energy conversion loss is less when the electrical power levels being converted is high. The mechanical capture to electrical energy efficiency of regenerative braking is from about 30% to 50%. Techniques to conserving a vehicle's momentum and gravitational potential energy is more energy efficient than any regenerative braking mechanism.

The energy density of a battery is 1/10 that of gasoline. The power in 1 pound of gasoline equal about 10 pounds of battery power. The PiP can hold more gasoline power than electrical power - however, the electrical power can be regenerated on the fly while the gasoline power cannot be regenerated on the fly. The electrical power usage can be greater than the PiP max capacity if electrical power is alternatively being used and recharged on the fly.

As a basic FE rule for uphill road segments- use the ICE and momentum

On gasoline without hypermiling with a fully warmed up Plug in Prius the energy efficiency of the HV(ICE+M1+M2) is about 50 mpg while the EV electric drive(M1+M2) is about 4 miles/kwh of battery charge. It takes about 1.25 kwh of residential charge to recharge the battery so cost wise the electric drive efficiency is 4 miles/1.25 kwh of residential charge.

Because of aerodynamic drag - a Prius is more energy efficient under 55 mph regardless of whether its momentum/speed is generated by gasoline or electricity.

At low speeds (<45 mph) It more fuel efficent to not use regenerative braking and conserve momentum.

At high speeds (>65 mph) when driving down steep extended downhill road segments (e.g. coming down a mountain pass) it might make sense to convert mechanical energy to electrical energy to avoid mechanical energy loss from aerodynamic drag (after 65 mph, over 50% of the energy use by a car is due to energy neede to overcome aerodynamic drag).

that being said....

When there is a long stretch of empty downhill road in front of you consider the following...

if your Plug-in Prius(PiP) HV SoC is less than 3/4 full
and you have a very long downhill road segment to use
and no other vehicles are around (because your speed changes are weird)

then you might consider...

1) From the top of the hill speed up to about 35-40 mph
(higher velocity provide better recharging rates than lower velocities)
2) From the middle of the downhill segment glide/coast the PiP
(avoid using either ICE or the electric motors) and allow gravity
to increase the speed of the PiP to + 10 to +20 mph more - say upto 45 to 60 mph.
3) apply the regenerative brakes so that it is about 3/4 to 7/8 of the way
but not all the way (so you avoid using the hydraulic brakes)
causing the PiP speed to drop from say 60mph back to 40 mph.
4) Release the brakes when the PiP speed drops back to 35-40 mph
OR if the HV battery SoC is full OR
if the downhill segment has ended
5) If the downhill segment is still available and
if the battery still needs recharging Then goback to step 2)