Prius Extending Electric Mode Hacking

Hello everyone.

My goal of getting the canbus was to intercept the communication of my Prius as to when it should switch from electric mode to gas mode. My hope is to extend it from 25 mph to 40 mph and stay in electric mode until the battery is down to 50 percent or less.

Any help in accomplishing this is greatly appreciated.

The nice thing about the canbus is to reset the system back to original specs, you just have to disconnect it!

Take care,

You didn't mention which generation Prius you have, but be warned that if you force electric only without allowing MG1 to spin, you will quickly overspeed MG2. That's why there is a 25mph limit.

I have the latest generation Prius V. What would your recommendations be on how the go about increasing electric use over gas use in city driving (under 45 mph)? Perhaps I can adjust the percentages (more electric percentage unless battery is low).

Below is a good description of the Power Split Device in the Prius (ICE - internal combustion engine, MG1 - motor generator 1, MG2 - motor generator 2). I would like to adjust the conditions when MG1 and MG2 kick in.

Rotation speeds of MG1, MG2, and ICE are inter-dependent, and the speed of MG1 will always change when you vary the speed of either of the other 2. MG1 has a maximum rate of 10,000rpm in either direction (positive or negative) with a software limit of 6500 RPM if ICE is off. Using the model below, you can see for yourself why this software limit means the ICE will always spin if you're travelling above 42mph. And in case you were curious, yes MG1 can and often does change spin directions under normal driving conditions.

ICE rotation is limited to speeds between 1000rpm and 4500rpm. It can also stop completely, but anything between 0 and 1000 will force the slider up or down. That's because the internal combustion engine can't operate effectively below that speed. The hybrid computer knows, and will stop the ICE when it decides you don't need to use any gas, and start it again when you need more power, or higher speed from MG1.

Below is the link to the description I gave above and more about the Prius engine:

Correct me if I'm wrong, but the Prius V is all gasoline, meaning it's not got any other energy source than the gas. All the electricity ultimately comes from combustion. I did a plug-in conversion of my 2008 Gen2 years ago and installed a 6.5kWh Lithium-Ion pack in place of the .6kWh (usable) NiMh original. I'm not sure offhand how much usable capacity exists in the V, but it's probably around the same which means you can't really do what you want. Besides, Toyota has spent tens of thousands of engineering man hours to prefect the ratios for the best economy. I suspect if you tilt the balance toward electric it's just going to force the gas engine to run in long spurts to recharge the battery, putting more stress on the battery and actually REDUCING your mileage! If all the power has to come from gas, you are much better off avoiding to conversion losses.

Now if you plan on plugging it in, that's another story, but it's super dangerous and a lot of work for not much capacity. Mine would do about 40 miles city and 20 on the highway in all-electric with extensive mods. The internal capacity of the OEM NiMh pack combined with the larger mass and higher drag of the V, means you're probably lucky to get 2-3 miles of all electric even at only 25mph. And then, how does the battery get recharged?

Even after all the work I did on mine, it was a comparatively poor EV. I now drive a Nissan LEAF and I love it! Sadly, It's a much better solution than what I came up with and it's much more fun to drive. I still have the Prius in the family for occasional trips, but it's lucky to see a few thousand miles a year.

Thanks again for the input. I have a 2012 Prius V.
The main goal was to limit the acceleration max so that it could stay in electric mode longer. Often the car will switch to gas mode when the battery is still fully charged (or I go over 25 mph). If I could alter the configuration so that it would not switch to gas mode until 40 mph, then I could stay in electric mode until the battery goes low enough to require the gas to kick in.

Again; WHY would you want to stay in electric mode longer?

To use more battery power before kicking into gas mode. Example: I drive a few miles slightly downhill to work from home. Once I get over 25 mph it will kick into gas mode (sometimes but not always - I've noticed that randomly I can stay at 99 mph (I think electric only) when the battery is fully charged. I think it would be better to stay in battery mode until the battery is down to 25%. he battery recharges by braking and gas engine.

The only way it would be better to stay in electric mode is if the electricity was NOT coming from your gas engine, in other words from regen. So if your work is all downhill and you can regen downhill to a fully charged battery, then you could use some of that to go back up hill, and the prius does that automatically.

If you force electric mode longer without a non-ICE source of electricity, then you are going to have lower mileage because of the triple conversion losses, whereas if you just run on gas directly, you only have one conversion loss.

EV mode: ICE-->Battery-->Motor-->Wheels
ICE mode: ICE-->Wheels (mostly) and you save wear on the battery.

The only real way to benefit is to add an external charger so you can charge from the grid, this way you don't buy gas. But if you do that, you're better off with a larger battery. The Prius has about 600Wh usable in the factory battery which is only up to 3 miles (if you're lucky) on pure electric. I put a 6.5kWh in mine. I could easily do 40 miles low-speed in pure electric, and 20 miles on the highway (ICE must rotate at highway speeds, so a lot of loss!)

Thanks so much for the detailed explanation Phil! I always wanted to add an additional battery to my Prius V (flat battery in the trunk). How did you change the computer to stay in pure electric mode? Either city or highway? That is my real question. I would like to control when to go in and out of electric mode (Ideally to add a larger battery or take advantage of brake charging).

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