2010 Prius EV mode Hack

Mine kicks out of EV at 13mph almost every time. Why?

 

Mine kicks out of EV mode at all different speeds depending on the variables used in the software that determines when to terminate EV mode.

I can get up to 25mph in EV mode at times.

It would be great if someone that knew these variables would post them.

 

What is it with the "EV mode" obsession?

There is a lot of confusion when it comes to the electric-only driving.

STEALTH is still available at speeds up to 45 MPH.

The engine isn't moving (0 RPM if you have an aftermarket gauge available) and you can clearly see the resulting 100 MPG on the new meter by the speedo.
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People wanting to age their batteries prematurely? Or not understanding that you can be going 40 MPH on battery only, and thinking the EV button has to be pressed or it didn't happen?

Not to mention that an over-obsession with operating under battery power only will mess up your mileage. (For that matter, over-obsession with instantaneous MPG and the HDI displays will do the same thing. As I've taken a big-picture view of things, my mileage has gone up. The last tank is, so far, 10% better than the previous tank.)

 

Try using EV + Power Mode together.

I find that when I use EV + ECO mode, the accelleration is so slow I end up having to hit the gas so hard, that the ICE starts up.

With EV + Power mode, I can accellerate 'briskly' with electric only, and if I let up on the gas when hitting 24 MPH, it will sometimes go up to 26-28 MPH, still in EV mode.

Once the engine kicks in, I switch to Eco mode.

I'm totally new to the Prius, so thake that into consideration. I purchased my 2010 (IV, w/ NAV, white, dk leather) about 5 weeks ago. Commuting to work 10 miles each way, stop/go traffic, I'm getting about 53 MPG.

As for avoiding EV mode (as per a HyperMiler article that I read), it doesn't really work for me. I live about 1 mile from the freeway onramp, and I can sometimes get there in EV mode (engine warmup takes about 2 blocks). The freeway run charges up the battery, until I hit stop/go traffic, and then it's back to EV mode for a while.

I'm very happy with the Prius so far, and I'm leaving tomorrow for a 2500 mile trip from SoCal to Idaho & Montana. I'll share my results when I return.

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Huh?

You're driving along at 40 MPH. The engine automatically stops. Only the electric motor is providing propulsion. That's EV without the need to push a button.
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You've only got a finite amount of electricity available.

Using the big electric motor in combination with the engine can be more efficient overall than just the motor alone.

Remember, the small electric motor generates electricity while the engine runs. That can be a good thing... which won't happen if you prevent engine from starting.
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First, keep in mind that the Prius only real source of energy is the gasoline engine (unless you have a modified plug-in Prius). The battery is there just for temporary storage.

Excessive use of "EV mode", or trying to use it under the wrong circumstances will definitely have a slight negative impact on your MPG. The reason is that if you intentionally cause the engine not to run, then that will force the car to use temporary energy stored in the battery. Think of the battery as a middleman, or even as a bank. The middle man always gets his cut. You give a bank money, they'll give you 3% return. You borrow money from the bank - they'll take 7%, or more. Energy is lost in the process of converting torque from the engine to chemical energy in the battery. The process is not 100% efficient. I don't know the actual efficiency - perhaps it's 80% or less. Energy is also lost in withdrawing energy from the battery to turn the electric motor. So, it's your choice -- run the engine with minimal loss (just friction losses) between the engine and the wheels, or charge the battery (with it's loss of efficiency), then deplete the battery to spin the motor (with it's loss of efficiency).

The battery is not useless, however. It is good for recapturing energy that would normally be wasted during braking. It is also more efficient to intentionally use EV mode for very short, low speed jaunts -- such as moving your car in the driveway, or driving from one store to another just 1/4 mile away. The reason this is better than running the engine is that the worst MPG that the Prius will experience is during the first minute after starting the car, when the engine goes into a warmup cycle.

Another good use of it is just before reaching the top of a hill where there is a long incline on the way down that would normally result in reaching the max 80% charge cutoff in the battery. The circuitry (gen 2 Prius) won't let you charge beyond 80%. If the battery reaches 80% before you reach the bottom of the hill, the Prius will intentionally turn on the engine and adjust the MG1 and MG2 field voltages to waste some of the battery's energy. To avoid this (and if the traffic and speed allows), slow down and go into EV mode to "create space" in the battery before reaching the top of the hill.

 

Every time you convert from kinetic to potential or vice versa you have conversion loss. If you run the battery down the car will have to charge it with the engine at a later date. So all you are doing in EV mode is postponing when the engine runs and creating a pretty significant loss at the same time. You end up with two conversions ...Kinetic (engine running) is converted to potential (electricity stored in a battery) and then back out in EV mode. You are much better off just moving the car with the gas engine than doing the conversions.

If you think about it you aren't really using the electric when on the highway and most people get close to 50 MPG. So all the electric is really doing is two things... re-capturing the energy of motion that is normally wasted as heat generated by the brakes ... and providing backup power for acceleration.

A typical hybrid sequence is like this: 1. Accelerate up to speed using a combination of electric and gas somewhat depleting the battery but with much more power than a super efficient gas engine could by itself. 2. Move along at cruising speed on gas only, adding a little electric on the upside of hills and recapturing it on the downside. 3. Slow to a stop where a big chunk of the energy of motion is recaptured and stored back in the battery... hopefully refilling the battery to where it was before we started. Of course due to the aforementioned loss it never quite fills back to the same level as before so the engine must make it up by directly charging the battery.

So to re-iterate if you drain the battery by using EV mode excessively you will force the engine into a direct charge cycle later on and hurting your overall mileage. The only time that EV mode makes sense is when you are doing something like pulling your car out of the garage to wash it or something and you don’t want it to go through its warm up cycle since you won’t be driving it.

There are a lot of people here that can explain this better and shorter than I just did but I did my best.

Edit: I see carz89 had almost the exact same explanation and beat me by 20 mins... hehe

G

 

The change in speed was due to the smaller MG and battery pack per the Chief Engineer at NAIAS.

 

FYI,
We see 35km/h(22mph) EV cancel speed during cold coolant temperature and 60km/h(37mph) after warming up on Japanese 2010 Prius.

Anyway, another thermistor hack will help you avoiding the 9mph limit on the US Prius before warming up.

Ken@Japan