I Love Power Mode!!!

You see a gain in mpg because you aren't using fuel during that stretch. The mileage meter only accounts for fuel, not battery charge, so in reality you are robbing Peter to pay Paul, and you lose something in the process. The fuel you save during the EV stretch is more than made up for by the fuel burned to replace the electricity in the battery.

A common misconception among new Prius owners is that battery charge is free. It's just the opposite: battery power is the most expensive way to move the car. If a Prius could be operated at a steady speed with only the engine, it would be far more efficient than it is using the hybrid system. Why? It's because of conversion losses. All energy used in a Prius comes from burning gasoline, including the charge in the battery. To get that charge in the battery, the Prius burns gas in the engine, spins a generator to make electricity, and converts the electricity into chemicals in the battery. When it uses the battery, the chemicals are converted back into electricity and the electricity is used to spin a motor. That's a lot of converting back and forth and it doesn't come for free.

So why use a hybrid drive system? It's because the real world is messy and complex. If a Prius were driven with only the gas engine, it would be a real dog. The battery and motors let the Prius work with a small, efficient engine. As a bonus, they also allow regenerative braking.

EV is fun, so use it if you want, but don't expect to save gas. The main place where EV mode saves fuel is using it to keep the engine from unnecessarily starting. For example, in stop and go traffic where you, as the driver, can see that you are going to stop after a few yards. The Prius control system can't see ahead, so it may start the engine only to shut it off immediately.

Another rare but realistic place where EV can help is before long downhills. If you know that an upcoming downhill will more than charge the battery, you can use EV mode to lower the SOC before you crest the hill.

Last, but certainly not the least, EV mode is good for running down pedestrians in parking lots.

Tom

 

Yes, I am fully aware that an Audi - much less a driver of a Honda Civic - could dust the Prius off the line if he put any effort into his right foot. I'm just making the remark that PWR mode quickens mid-range throttle responses, so much so that unsuspecting drivers will be caught out by it... By no means am I suggesting that you should take the Prius and drag race John Force with it.

 

Sure, I understand... but I made my point just so potential prospective onwers don't come here and leave with the false impression that a Prius on power mode beats the acceleration of an Audi A4... people make wrong decisions on false impressions all the time!

 

Help me out here. How is that possible. Toyota would have you believe that Eco mode is the way to go for max MPG's. That Power mode is for passing or when full power is required based on traffic or road conditions.

Maybe, just maybe, power mode engages the electric motor for max power and thus saves you on the gasoline motor.

Perhaps with the vehicle in cruise control at a steady speed, flat road, engage eco , than normal, and than power mode, and see if the mpg's go up or down in each one.

Also, when the EPA did its testing for mpg did they use, normal mode, eco mode or power mode, does anyone know?

alfon

 

Good point. For optimal MPG, I always thought, based on how the HSD works, that:

ECO mode is great for crusing in a flat hwy.

NORMAL mode for city driving or hilly hwys.

POWER mode should be used only when extra pwr is required (upon merging in a hwy or on steep inclines).

That's also the way my salesman was selling it and Toyota marketing like you to believe...

So, what's wrong???

 

Well, the Toyota manual and video also tell you to accelerate very gently until you get up to speed, then let your foot off the gas. I and others have found it to be more efficient to accelerate briskly (not flooring it, though) before letting off. If I try to accelerate gently while on a hill, trying to avoid exceeding the ECO range on the HSD, I'd probably be getting some very evil looks from the drivers behind me.

 

Even in my 2006 Prius, I always found the acceleration to be quite peppy. I'd very often be ahead of other vehicles after a stop.

In my 2010, Normal mode feels pretty much like the 2006 but ECO mode feels like the 2006 on a bad day, such as when it's cold and rainy.

 

EPA testing is done in Normal mode, but it doesn't much matter since the EPA tests are not subject to perception. Most of what happens with Eco, Normal, and Power is that the feel of the accelerator is altered, not how the car works. In Eco mode it takes a lot of pedal pressure to make the car go. Power is just the opposite. Full power is always available in all modes. In other words, you can go just as fast and accelerate just as fast in Eco mode as in Power mode. Any other way would be a safety issue.

Eco mode has one other wrinkle. In Eco mode the Prius skimps on air conditioning and other creature comforts to gain a little more mileage.

Tom

 

So, considering that, in a long hwy trip without A/C use and cruising steady, any of the 3 modes would deliver the same MPG, is that correct?

I aways thought that the acceleration sensitivity is the major change between ECO and NORMAL modes only, but the POWER mode actually changes the way the car works by changing not only the accelerator sensitivity but also the amount of overall power generated by the ICE alone. Is that wrong?

 

Correct.

We were told by the chief engineer of the Prius that full power is available in all modes. I haven't seen any testing that indicates otherwise.

Edit: As a further clarification, the Chief Engineer stated that the various modes principally affect the first half of the accelerator response. Once you stomp on it, it should feel the same.

Tom

 

Very nice. So, help me fully understand this. Say, you are not using A/C and driving in the city... which one is more efficient from a stop?

1) Accelerate quickly and cruise in the desired speed (power mode in this case would be more desirable for optimal MPG)?

OR

2) Accelerate gently until reaching the desired cruising speed (in this case, ECO would be the choice)?

I guess it all comes down to the 2 choices above...

 

This discussion assumes a clear road. Obviously it doesn't make sense to accelerate just to slow down immediately. Given that, on with the discussion:

From the standpoint of physics, it takes the same amount of energy to accelerate quickly or slowly. All that matters is the final speed. This means that for good mileage, we want to accelerate in the most efficient manner.

Let's first look at battery propulsion: with the Prius, all energy comes from burning gasoline in the internal combustion engine (ICE). The ICE burns the fuel to make mechanical energy. The mechanical energy is used to spin a generator to make electricity. The electricity is converted to chemical energy stored in the HV battery. When used, the chemical energy is converted back to electricity which is used by the motor to make mechanical energy. The mechanical energy drives the wheels.

That's a lot of conversions, and each extracts a price. It's easy to see that for good mileage we don't want to use the battery.

Given that we don't want to use the battery, the entire task of efficient acceleration falls onto the ICE. Let's look at what makes for efficient use of an ICE:

Automotive ICEs are designed to run at a variety of speeds and power levels, but some are more efficient than others. At low speeds the ICE suffers from pumping losses as air sucks past the closed throttle plate (this is one of the reasons that diesels are more efficient). At maximum output the ICE resorts to richer fuel mixtures and other tricks to extract the last little bit of power. We want something in between, where the efficiency of the ICE is maximized.

With the Prius, as with most cars, maximum efficiency comes with brisk acceleration. You don't want a jackrabbit start, as this will push the ICE into an inefficient wide-open setting, and will call on the battery for extra power. Likewise you don't want to drive like a granny, as low power settings are very inefficient. Give it some gas, but avoid pulling power from the battery.

There are many posts on PC discussing exact RPMs and such for maximum efficiency. If you get nutty about it, you can instrument your Prius and drive it by the numbers. Otherwise go for a brisk start, but avoid the battery.

Tom

 

OK, it makes sense, thanks.

But how do I monitor for avoiding the battery during acceleration? Is the energy monitor the key? The energy monitor should reach the red zone for a few moments, or maybe for the whole time until reaching the desired speed, or what?

 

I can't help you with the 2010. On the Gen II models, you can look at the consumption screen. I assume the 2010 has something similar, but we need details from a 2010 owner. Anyone?

Tom

 

Thanks anyway.

This bloody monitor (bellow) shows exactly (with arrows) when the battery is sending energy to the electric engine, but it is a yes or no indication, it does not say the intensity of energy delivered.... so I guess, that's one way to do it...

 

Why don't you 2010 owners buy a Scangauge since you want to know what's the best sweet spot for the ICE? RPM and IGN gauges would be helpful toward your process to achieve best MPG for your specific driving routes. I wish the Scangauge or the Toyota Dash would give a satisfying tone when it at the ICE sweet spot for cruising.

 

For best acceleration (or rather most efficient) that's already been done. Other threads have documented that on the display where charge is on the left and power is on the right, being in the 75 to 100% range of of the display where the beginning of the PWR section indicates 100% is the most efficient rpm range for the ICE. So from an ICE efficiency view, you want to be just before the point where it goes red and shows you are in PWR zone.

 

I guess I'm still a Priusilliterata. I have no idea what that means. How do I "avoid the battery"?

 

Hi All;

Tom (qbee42) is dead on with his suggestions and right on the money with the losses in FE when overusing EV.

The key here is to think of the charge in battery pack as a very expensive asset. One that you do not want to use frequently or incorrectly and instead you should keep as much of it at hand for the moments where it can produce the best results.

Here are some of my personal guidelines for using EV or electric assist:

• I use EV or electric assist as a glide extender at lower speeds. The key is to use the least amount of electric (use the HSI display for this. Smaller pulses are better). As usual, avoid EV and when you use it do so strategically for maximum results.
• I use EV for Stop-n-Go traffic. In this situation I prepare and anticipate traffic jams by ensuring that my SoC is as high as possible before getting nailed with Stop-n-go. Having the ICE start midway through it is a technical hit on FE.
• I use EV only when accelerating from a stop at speeds up to 15-17 MPH. Any speed above this and I seek to have the ICE running instead at RPMS not exceeding 1300 RPM if at all possible. The key is that lower RPMS and lower rates of acceleration with the ICE on are always better.
• At lower speed steady state driving I seek to kick the ICE into an IGN of 13-16 ASAP, instead of having it run full EV then recharge afterward in a vicious never ending cycle. Charging a battery pack frequently via ICE is NOT an exercise in efficiency.
• The Energy monitor and the iFCD are sometimes VERY misleading and may misrepresent what is truly happening. Take the information presented by those as a rough indicator only. For instance, sometimes both gauges tell you the ICE is off when in fact it is not and is consuming fuel.
• Reading the HSI correctly requires additional insight into what the system is really up to. However, if you keep the power (electric and ICE) and regen (braking) amplitudes to a minimum then your results will improve dramatically.
• I never, ever, ever toggle the PWR mode on. Having a scangauge plugged in will quickly tell you why.
• To me Normal mode is just like ECO. If you do everything right in Normal mode then the results will be the same as ECO. To many drivers however, the ECO mode makes a hypermiler out of them with incredible ease.

What does all of this net me?

Well, my FE averages rarely go below 70MPG. In fact my wife even manages to hit the low 70's (calculated at the pump) without effort.


Cheers;

MSantos

 

I guess I've just learned how to use ECO mode to get the most out of the car. I tried Power Mode for my 23 mile morning commute, and while it was certainly zippy, my average dropped almost 2 miles. Using ECO mode on the trip home, I got the mpg's back up to almost where I'd started this morning - 57.6.