Is no ECO more eco than ECO...?

There's no difference in the car's acceleration ability, in ECO, PWR or "normal" (both buttons off). All these buttons do is change throttle response at intermediate gas pedal positions. In ECO the pedal needs to be depressed further to get the same reaction. But the same acceleration is possible, you just need to push the pedal down a little further. It can seem like the car's more of a pooch, but it's really just the increased pedal travel.

I used ECO for maybe the first 3 months of ownership. I finally got tired of what seemed to me to be excessive pedal travel, switched ECO off, saw no appreciable difference in fuel economy.

 

Recall that the Euro version of the PiP does not have PWR mode. It has a City mode in which it is very difficult to trigger the ICE; this is to comply with emission-free zones in some European cities.

ECO mode does have some other effects beyond the throttle response. For example, the coolant temperature target is lower, so the warmup phase is shorter.

 

I think I remember hearing that ECO mode also changes how the vehicle uses the AC. So there might be some benefit in ECO from that perspective.

But after a year plus of driving my Prius I would say that if you are "skilled" in economically driving your Prius, there is very little appreciable difference in attainable gas mileage between ECO and "normal". I've also wondered, since The Prius does so well in a "Pulse and Glide" scenario, if driving in "normal", which has a little less accelerator pedal travel, thus tending to get up to speed quicker ( Yes I know, both modes can accelerate equally...it's just mapped differently ) might sometimes actually be more efficient. Really, I'm not sure.

LOL! I got two speeding tickets this past year...I'm staying in ECO mode. I can use the extra pedal travel just in case.

Also I'm coming from a "regular" Prius POV.

Not sure if the PiP has any other differences in ECO mode.

 

I like to keep an eye on HSD bar, use that as my "rev limiter", try to keep it around 3/4, for acceleration, on level roads at least.

 

Over the course of the first half a year owing one, I've learned to get the best MPG if I don't touch any buttons. Only a gentle pedal touch.

 

> I begin to wonder whether I could do better with ECO off

I'm in a similar situation and wondering the same thing. If you are consciously driving to keep MPG high, then I think ECO mode can work against you in certain situations. For example when you need more power than ECO is willing to give, you're forced to push the pedal down and potentially waste energy in the "Power" zone. I think ECO mode also alters how the CV transmission "downshifts" (for lack of a better term) are handled and works to keep RPM/torque low to keep fuel consumption lower - at the expense of power/acceleration.

I get frustrated when starting off in EV mode having to pull out of my neighborhood from a dead stop onto a 30MPH road that everyone drives at 40MPH. If it's at all busy I need I'll need the extra engine power to avoid getting rear ended or honked/cursed at, but then the engine runs for 2-3 minutes all the while I'm being very careful and well within the EV power band. I don't get why the engine doesn't hibernate a few seconds after the power boost like it would in HV mode.

 

I believe you will find the ECO Range on the HSI is a completely separate matter than the ECO Mode. As has been stated several times the ECO Mode is primarily a mapping of how the accelerator position relates to control of the car. You can use the accelerator to stay within the ECO Range if the ECO Mode is on or not, its just a different amount of accelerator depression. Using the accelerator to stay in the ECO range will give you the same lower amount of power than being in the PWR Range regardless of the ECO Mode being on or off.

I make no attempt to stay in the ECO range because I would like the car to do (accelerate fast or slow) what the driving situation requires. That is more important than a possible (or unlikely?) change in overall mpg. I always use the ECO Mode because it gives me the most convenient control of the car.

 

That is indeed an efficient approach, excellent observation.

The recommendation for BRISK acceleration came from the days of the classic model and had held true ever since.

It takes advantage of the hybrid system, utilizing both engine & motor for an overall gain.

Accelerating slowly actually defeats the intent of the design. That Eco-Meter is there to remind you to keep power-demand brief, not to avoid it entirely.

 

The initial ICE run for 2-3 minutes is a warm-up cycle. Once initiated, it can't be interrupted other than stopping the car and powering it off for a few minutes. Look it from the bright side: ICE is not idling at that time. It either helps propel the car, either charges the batteries. Nothing gets wasted.
Once ICE is warmed-up it can engage only for a couple of seconds then hybernate back. Like in sustained HV driving.

EU models have EV City mode. When engaged it will make accidential ICE start less likely. When in EV City mode, I can accelerate in EV almost with the full pedal. The acceleration is still sub average though, but you are able to pull off a bit faster than in regular EV mode avoiding PWR zone.

 

That only applies to non-atkinson engines with fixed transmissions, although these days even that's minimized with drive-by-wire systems.

In the Prius, accelerating quickly, especially above certain power levels, is slightly less efficient. The more power you request from the engine the shorter the exhaust stroke is relative to the compression stroke, which drops efficiency a little bit. Similarly, the more power you request the more MG2 acts as a generator, which is less efficient than sending the power directly to the ground via the CVT. Of course plenty of energy still goes to the ground directly, but not as much as would be sent by keeping the car in ECO.

Is it enough to matter? Probably not, but I know that I can get ~60+mpg on gas in short city trips ~7 miles back/forth by keeping the car in ECO mode, while my wife gets ~40+ on the same trip in power mode. Some of that is her driving more aggressively and dumping more energy into the brakes/pack, and the rest is her driving more aggressively and using the engine less efficiently.

 

OK, so the HSD is less efficient in the PWR zone. But since the brisk acelleration makes the trips to PWR zone shorter, might it be, you end up using less energy anyway?

Did you notice, many of our wifes tend to love our PWR zone?

 

Haha, yeah. My wife used to have an A3. Only person I've met who could get ~20mpg in a compact wagon. That thing was terrible with maintenance too, it went through water pumps like a Prius goes through oil changes, but at least it was a lease so most of it was covered. All told she spent more on her lease than she'll spend on buying her PIP, but at least we're making better financial descisions.

In terms of efficiency, either way the car requires the same amount of energy to get to a certain speed. If it accelerates slowly, most of the power goes straight from the motor to the ground. The more power that's required the more MG1 spins up to provide current for MG2. Based on the motor efficiency curves here, in the worse case more than half the energy that goes from the engine to the wheels via MG1/MG2 is lost compared to going straight from the engine to the wheels.

http://info.ornl.gov/sites/publications/files/Pub26762.pdf
http://www.mate.tue.nl/mate/pdfs/4996.pdf
Toyota Prius - Power Split Device
World's first 2010 Prius Dyno | PriusChat

Now, it's kinda late, and I may be making some mistakes, but my guesstimate is that at 35mph/WOT, the engine->MG1->MG2->wheels only provides ~40% of what the engine->wheels provides, and is a little less efficient at speeds below that/WOT. Of course half of the power still comes from the engine at 35mph/WOT, so total efficiency is still OK if not great. Engine efficiency also suffers, but I'm not sure by how much.

In the aggregate though, the energy needed to accelerate is << than the energy needed to drive down the road, so inefficient acceleration won't hit mileage a lot. I think inefficient driving (harder braking, higher speeds) will hurt mileage more.

 

That does NOT take OVERALL efficiency into account though.

Prius is a hybrid with a power-split-device, adding into the system a generator and battery-pack along with the traction motor. So, that engine-alone efficiency assessment does not apply.

When the engine goes beyond the most efficient state of operation, there isn't as much of a loss. It seeks a higher RPM to reduce that, which as a result creates power not needed for propulsion. The unneeded power is converted to electricity for use later, something a traditional vehicle cannot take advantage of.

In other words, the penalty can actually be a wash or even a modest gain under the right circumstances.

 

I think you've got it backwards. The Prius engine generally (but not always), operates at fairly high efficiency levels.

Brake Specific Fuel Consumption (BSFC) Maps - EcoModder

When it operates at a higher rpm/lower vehicle speed, more power is pushed through MG1/MG2 than would be if the power requirements are less. The path this power takes is less efficient than engine-> wheels. The same goes for battery energy used, although there's a time lag because the engine will just charge up the battery later which will hurt efficiency later.

In the aggregate this isn't a very big difference because the energy needed to drive at some steady speed in generally >> the energy needed to accelerate, but there is still an efficiency penalty for faster acceleration beyond what the PSD can move from the engine to the wheels directly.

This is also why P&G is so effective. As the driver you're maximizing the amount of power that goes from the engine to the ground as opposed to the amount of energy that goes from the engine, through the MGs, and to the ground, or the amount of energy that goes from the engine, through MG1, to the battery, through MG2, and to the ground.

Team Achieves 110 MPG Average In Prius : TreeHugger

 

That's unrelated to providing a brief burst of acceleration power.

We're saying the same thing, but the scopes are different... duration and magnitude.

 

The first time I tried ECO mode I thought something was wrong with the car. So I never used it again on purpose except in a couple of cases:
1) Winter driving after either freezing rain or our usual lake effect snow. Keeps from spinning the wheels when the traction is iffy.
2) Again Winter driving, the fan can get quite loud when heat is asked for, and ECO mode lowers the fan speed. In a weird byproduct of lower fan speed, the cabin doesn't get up to temp as fast so the engine remains on and is assisted by EV boost for a bit longer.

 

When I purchased my PiP I put it in ECO mode and it has been there ever since. It works really well for my style of driving as related to maximizing mpg. Different strokes for different folks in a kind of a literal way.