Using EV when Starting From a Stop?

Nope! won't hurt a thing but!
I think for best MPG, it's best to go only to about 15 MPH then let the ICE take over.
I might be wrong, but I think that is what I have heard.

 

I do it often, but you need at least 4 bars showing on the battery meter to get away with it, and not very often cause it'll drain the battery pretty quick. 3 bars on the battery and the computer will ignore you. It's also dependent on the ICE temp.

I'd be interested in hearing some discussion on why 15 MPH would be better for MPG.

 

Since the battery is charged by the gasoline engine, doing this would give you worse fuel economy under normal conditions. There is no best way to drive as it depends on road conditions and your destination. In general though, it is recommended not to force EV mode and accelerate as quickly as you can without entering the PWR zone. Once cruising speed is reached, apply enough throttle to maintain that speed.

 

The battery is also charged by regenerative braking, it's not ALL gotten from the engine. If you have a lot of down-slope driving, its not going to cost you any gas. There's no absolute answer for every situation. But I agree that on the straight and flat road, it's not going to save you anything. I have a lot of long downhill stretches where I arrive at a light at the bottom of the hill with a full battery. There's no harm is using some of that "free" energy.

 

But the energy to get you moving to do that regen had to come from gas, same with getting to the top of the hill. The regen is more of a bandaid, a compromise to coasting to a complete stop, which would be most efficient, and keeping other drivers from killing you. The more times you convert the energy, the less efficient the process becomes. There is no free lunch, just ways to make the best of what you have. I personally accelerate like mmmodem said, briskly without trying to stay in EV or going too crazy. EV is reserved for parking lots and sub-15MPH cruising.

 

I do this when I have the battery half or better and the car has been running for a while. Once I get off the highway, the whole mile to my house is 25mph. I go into EV mode and take the rest of the way at about 24-25mph.

I figure that the engine has to get warmed up again in the morning anyway and I'll be right back on the highway in about 1/2 mile so I'll have the battery recharged again in no time.

It'll be interested to see how this pans out over the course of a full tank (that Prius in my sig is my wife's car and I've never driven the entire tank.)

 

YUP! ....

 

I never use EV to launch the vehicle. It's to much of a power loss on the EV side.
I use the ICE to start and get up to speed and use the EV to maintain that speed
or pulse and glide as needed. I let the ICE to the heavy lifting, so to speak

 

i believe actual testing has been done by hypermilers showing 0-15 in ev and ice after that is the most efficient way to go. i'm not sure if that's in ev mode tho, as it allows faster accelleration and wouldn't be as efficient as keeping the ice off in hv mode. this is very slow and cannot be done with traffic behind you.

 

While I do not use the EV button at all, the above statement is not correct. Reclaimed energy, while maybe not free, is very, very cheap. Using the battery and the regen system is a large part of what makes to Prius so efficient.

 

Not so. I can start out from home and drive for 5-6 miles without once using the ICE, its all downhill. Likewise, if I'm at a light and the road is downhill from there, I can recover all the energy spent in EV mode (while going down the hill). Not ALL energy comes from gasoline, and if my battery has a good SOC I'll use it. That's the whole point - if you can use battery energy instead of gas, and recover that energy without using gas to do it, its free energy. If you drive in hilly country, there's lots of ways to take advantage and get free energy.

 

I'm not saying it doesn't help, but its by no means perfect. Some people seem to think that accelerating and then regenerating is good, when its really much better to coast. I've read that regen reclaims about 30% of the energy, which is better than nothing, but not exactly the pinnacle of efficiency. In my opinion, less regen is better in the sense that you're minimizing braking (including the regen from just lifting off the gas).

 

The only energy source put into a non-plugin is gasoline. The hill, or even a pulse, isn't much different from the battery. You charge it by burning extra gas to get to the top/getting up to speed. The going down/gliding part might not take any gas, but the whole cycle required gas. Regardless of how or where you drive, gas is still the only energy source put into the system.

There is nothing wrong with using EV, but to maximize mileage it has to be used at the right time.

 

In thermodynamic fact, you are burning gasoline to push on a piston. Since this is an irreversible process, there is no link to anything that happens afterward. Consider: Prius A and Prius B both drive to the top of a mountain pass. Both use exactly one gallon of gasoline to get there and have threes bars on the battery gauge. Prius A continues down the pass using the brakes and 'B' from time to time. The engine does not come on and they end at the bottom with a full battery. Prius B shifts into neutral with the engine off and coasts to the bottom. He ends at the bottom with two bars on the battery since it had to provide the energy to run the various systems. A now has at least 6 bars more battery energy than B, but they have both burned the same amount of gasoline. Where is the cost associated with this energy? There is some cost to the battery energy in general, as the engine will charge it when necessary. This is especially true during freeway driving where regen is hard to come by. In surface road and highway driving however, the battery is always the cheapest energy available to the car. Not using it will result in lower mileages than are possible. The Synergy firmware already knows this, of course, and does it for you. This is why the regen systems are responsible for 30% of the efficiencies found in the Prius.

 

I'm not saying regen doesn't help. In your example, though, its important to note that car A didn't create more energy, it just wasted less by capturing the excess speed from going down the hill and storing it in the battery. At the bottom of the hill, all the energy, whether wasted or reclaimed, came from that gallon of gas. The Prius isn't magic, its just efficient.

 

I suppose you can do it all you want.

But I don't really try to out think The Prius computer.

As has been pointed out, there's no free lunch here. You do it enough and you're going to quickly drain your battery and then any MPG gains you have made will be countered by the vehicle working to recharge your battery.

I've found that if my Prius is warmed up, AND the battery has a decent charge, it will start out in EV mode anyway. Then I can let my desire to accelerate and my foot on the accelerator dictate whether I stay in EV mode.

It's an over simplification, but The Prius is a hybrid, and it's Hybrid Synergy Drive. I find little advantage in routinely trying to divorce the "synergy" from the operation. Therefore I rarely use the EV button at all.

 

There is no one size fits all.You describe a specific scenario where there is a decline that will sufficiently recharge the battery to nominal after being used to start from 0. There is no argument that starting in EV is more fuel efficient as you describe.

But what about a flat surface? Or an incline? On these other two terrains using up EV that cannot be cheaply regenerated by a descent will force the ICE to replenish the battery to nominal levels. As the conversion is not 100%, you're using more gas to drive in EV mode.

You cannot have a decline without first going up an incline, therefore, at most starting in EV is more fuel efficient 50% of the time. Throw in some flat roads and not all declines sufficiently replenish the battery to nominal levels and there you have it. Starting out on EV in general is not more fuel efficient.

The hybrid system is very smart. It is almost always using battery assist in combination with the ICE. You're not wasting battery by not using EV mode. If everything is in working condition, it is not possible to drive the car without battery assist. It may come to semantics but unless you have a PiP, the cheapest source of propulsion comes from the ICE. The battery is the most expensive source of energy as it is completely generated or regenerated by the ICE at a loss.

 

The example is purposely simplified, but it is true for all regenerated energy. Flat roads, stop and go, whatever. There is little to no cost associated with the regen energy. . What you have is two cars who have used the same amount of gasoline, but one has 6 bars additional energy. You cannot assign any cost to that piece of energy because you can't assign the gasoline cost twice.

 

I think I see the disconnect.

Prius A enters a flat freeway with 6 bars of battery. Prius B enters the freeway with 2 bars because the energy was used up earlier in EV mode to get to the freeway entrance. Which car gets better fuel economy on the freeway? Prius A will get better fuel economy because it entered the freeway with more energy. The 6 bars battery in Prius A is constantly assisting the ICE to achieve better fuel economy. Prius B is at a disadvantage because its battery is empty. The ICE has to generate the needed battery level from say 2 bars to 6 bars first before it can assist the ICE.

But you'd argue that Prius B used cheap energy to start off from 0 in EV mode to get to the freeway. So if you look at the entire trip including driving from home to the freeway entrance, Prius B got better fuel economy. For the sake of argument on assigning gasoline cost twice, let's just say Prius B gets better fuel economy. (I don't concede it is true but let's just accept that for the first day).

What happens on the 2nd day? Now, the entirety of the battery capacity in both vehicle were regenerated cheaply the day before. Except 4 of those bars from Prius B were generated from the ICE on the freeway. Prius A and Prius B repeats the same freeway procedure. Can we still say Prius B gets better fuel economy? How can we, knowing those 4 bars were generated by gasoline the day before? We know the conversion to be less efficient.