Electric boosting Gas Engine in Crusie

The electric boost that you describe does not help your mileage. Sure, the displayed mileage goes up when more power is drawn from the battery, but then the mileage goes down even more when the battery is recharged. Energy is lost in the charge/discharge cycle.

Thinking that electric drive improves mileage is a common misconception. You would get the best possible mileage if the battery were never used: just the ice - no brakes, no electric motor. Of course a Prius built like that would be undrivable in the real world, so we need those motors and the battery to handle all of the special cases.

Tom

 

Sure it helps momentarily. That's a function of how the MFD calculates mileage. The mileage on the MFD divides miles driven by gallons of gas burned. It does not consider battery charge in the calculation. When you use electric boost, you are borrowing from the battery, which makes the mileage look better at that instant. It's like using a credit card to support your life style: you live better at the moment, but eventually you have to pay it back, with interest.

How and when the battery is used is a balancing act between several controllers. It's not simply a matter of swapping out a few sensors. The biggest contributor is battery state of charge (SOC). When your battery has a high SOC, the controller is more likely to use electric power in order to bring the battery SOC back down to its target value. A low SOC will force the controller to use less battery power and run the engine more often.

None of these are user configurable settings. Differences in your two Prius batteries are the likely cause of your perceived boost difference. There is not much you can do about it.

Tom

 

I have found that you can get a little mini stealth mode with some mpg benefit if you run on the highway with cruise at 55 or 60 but give a tiny bit of gas pedal on the down hill sections so that you see a tiny bit of energy going from the battery pack to the wheels instead of energy going from the wheels to the battery pack (charge mode) as often happens on the downhills. It will move the speed up quite a bit sometimes which will carry you up the next hill quite a way before the ice kicks in with the cruise control. I know it seems that you are going to have to pay later and charge that pack but I find that I get enough of that in other locations when I am forced to brake - like exits and such. I wonder if I am really saving mpg but it sure seems like it has made a difference in my average tank mpg numbers.

 

I believe what you are seeing is the following:

At constant highway cruising, there is a small amount of electricity being generated and stored in the battery. You can see this on the screen, as there is almost always arrows from the ICE to the wheels, and e-motor to the battery in this operating condition. The Prius' controllers try to maintain the battery right at 60% SOC, or all blue bars. The slow steady charge will cause the SOC to slowly drift upward. When it hits a certain point, the controller decides to use a little electric boost to bring the battery back down to where it wants to be. How quickly this all happens depends on how quickly the battery charges up. That will be a function of all the electrical loads in the car, headlights, AC etc. The less loads, the more quickly charge will accumulate in the battery, and the more often it will have to be burned off.

Rob

 

The utility of battery use can only be understood in the context of ICE efficiency. Actual battery use is also affected by algorithms meant to protect the battery and keep it around 50% capacity, and if I remember correctly, no higher than 80% SOC and no lower than 20% SOC.

It's true that energy taken from the battery will eventually be replaced by burning petrol, but it isn't a zero sum game because the payback typically happens at a time when the ICE is in a more efficient powerband. In a regular car ICE efficiency tends to average out around 20%, but ranges from 15 - 35% or thereabouts. A Prius has the same range, but averages around 30% by using the battery to avoid conditions that would otherwise force low engine efficiency operation.

The Prius can be 'helped' to better mpg in city driving, but on the highway there just isn't that much more that can be done. So drive around 60 mph, and enjoy the ride and 55 mpg.

 

I don't think I can agree with that. Maybe it depends where you live. If you are on a proper downslope, the car will run at speed (55 MPH, 65 MPH) on electric only with CC engaged (i.e. I'm not forcing anything). Why would it be BETTER to run it on ICE instead? The battery will be recharged when the slope decreases and the ICE is generating electricity.

I am currently maintaining 57 MPG plus on the current tank gliding downhill and using 'light foot' electric where possible. When it is colder, and the car won't go into electric, I'll be lucky to hold low 40s MPG on the same route (little to no Interstate) since it is "all ICE, all the time".

 

I know that many folks already realize this... but I would be remiss if I did not emphasize that this info ONLY pertains to a gasoline hybrid. Electric drive ABSOLUTELY is more efficient than a gas engine. It is more efficient and improves gas mileage in a plug-in hybrid. The more battery power you can use the better! Unless - UNLESS - you have to then charge that battery with the inefficient gasoline engine.

 

You don't have to agree with it, but it is true. The most efficient transmission is no transmission at all. With a Prius, all of the energy comes from the ICE. The most efficient way to get that energy to the road is through a straight drive with no gears or electric motors. This is why track bicycles have only one fixed gear (and no brakes!).

Obviously, you can't drive a car with only one fixed gear. You can't get it up to speed, and even if you could, it would only be the correct gear for one speed and no hills.

The same thing is true for the hybrid part of the Prius. The battery and electric motors are all energy wasters. Ideally you don't want to use them. From a practical standpoint, you have to use them for real world driving. The point I am trying to make is that regenerative braking and EV driving are all net wasters of energy. You don't want to use them unless the alternative is worse. Many new Prius owners make the mistake of trying to maximize the use of regenerative braking and EV, which is exactly to opposite of what you want to do for good mileage.

Darelldd's comment is correct. Darell, since your comment applies only to drivers of fully electric vehicles, wouldn't it be better for you to just call both of them on the phone, rather than post to this forum.

Tom

 

OK, I have to do this one as well! Pertaining again only to EVs... We only have one gear. I can smoke the tires from a stand-still (with no clutch!) and can travel at 80 mph in that one gear. The Tesla can smoke the tires for many, many yards with its one gear, and go 125 mph in that same gear. Again, using no clutch! So... more correctly... you can't drive an internal combustion car with only one fixed gear. You must certainly CAN drive a "car" that way.

So, you say this form is for the Prius, huh?

Doh. That hurt!

Seriously though, there are hundreds of thousands of us in the US. I kid you not. I'm talking about all motor vehicles that are registered with the DMV with "e" as the propulsion. So that includes all hand-built, custom, low speed AND production cars. Still, a couple more than two.

 

Makes the Volt a hard sell.
Hopefully Chevy considered the inefficient part.

 

What you are seeing is commonly called "warp Stealth" around here.
Above 42 MPH, if you have yellow arrows only (electric only) going to the wheels you are achieving a very efficient, high MPG, mode of operation.
It should be sought on most any downhill incline, where maintaining speed is desired. The criuse control can do this quite well, at moderate speeds of 60 MPH and less, on declines. So can the driver, by lifting and lightly reapplying gas pedal pressure above 42 MPH. I actively seek this condition on every downhill I drive.
I think what these other folks are talking about is the HSD bleeding off excess charge from the battery, which is worthless, other than possibly reflecting being near ''SHM', something focused on by some Prius owners at another site.
Called 'Super Highway Mode', it's kinda the highest efficientcy, lowest fuel burn, mode possible with ICE operating, just before it drops off into Warp Stealth

 

While cruising at highway speeds, i tend to take that whole "tiny burst" screen as a "you're mpg is maxed out for speed"... or most efficient "gear"... gear being your SOC.

 

This may be part of the "pulse and glide" effect that is mentioned often on PC.

 

Best Fuel Economy

In reference to fuel economy using Electric Boost, here is what I have found:

I have done some extensive testing in the real world to see how different driving techniques/speeds affect mileage.

here in FL on flat level ground and driving with cruise control on locked at 45mph (daytime driving with lights off and AC off), I can repeatedly get 73-89mph assuming one to three almost stops during that run. An almost stop means its a red light up ahead and I time it just so I can release the cruise, roll just long enough to manually accelerate back up to 45 then re-engage cruise, thus not having to stop the car and start from a dead stop. I do this trip very often. For every MPH over 45 you go, you start to loose MPG's. On the highway, I get an average of 48MPG with AC on, from Fort Lauderdale to Atlanta, GA at 64MPH, the same drive with AC off boosts upwards to 51-54 and that variable depends upon wind speed. If its a windy day, I see a drastic reduction of MPG if I'm driving into it. If its at my back, of course I can see as much as 2-3 MPG increase. You will see some increases at 55MPH, but if its a long trip like the 710 mile run I have done, its virtually unbearable at 55MPG. It's just way too slow. For every electronic device you have running in the car, is more power you take from the Hybrid system so every small amount you take, you sacrifice MPG's. The only one I can measure a difference on is the AC system. The headlights I can see a difference on the Scangauge due to the increased amps the car is drawing, but have not been able to notice a difference in fuel consumption except with my AC system tests.

The more power you have stored in the hybrid battery, the more the car's computer tries to expend the energy. Ideally you would get the best mileage if your hybrid battery's SOC (State of Charge) is at the highest it can be on your display meaning all green or full to down one bar. At full, your SOC is around 76-78%, at empty, your SOC is no less than 40%.

The computer will not allow the SOC to drop below 40% nor get above 78%. This is to make your NiMh hybrid battery last the life of the car as the plates inside the battery tend to develop sulfation at lower and higher charge states. Essentially, your hybrid battery will last 10+ years with this type of charging control, however you will notice its capacity diminish over the years but it should not affect MPG too much but I would presume there will be a measureable difference if you someone like me who watches every system in detail along the way.

Driving up and down mountains in the N. GA area, I have been able to achieve 54-65 MPG by coasting down the mountains and using its enertia to get partway back up the mountain and then using the accellerator pedal as an assist only. I sometimes will use Neutral to coast down when the hybrid battery is at or close to full as this will give me maximum speed down without the hybrid drag and get me higher up the mountain next, then I put it into drive to get the rest of the way up, however you have to be alert and do this only on straight runs, some mountains have curves on them and you really don't want the car to take off to fast around those curves as it can prove to be very dangerous.

Another thing you can do, is drive in the lane to the left or right of a semi just a tiny bit behind it. You want to keep your Prius in the pull of the Semi as to reduce wind resistance. I did this for a few hundred miles and achieved 75MPG at 65MPH. The MFD reported 89MPG the entire time, however real world calculations have shown 75MPG.

All in all, over 10,400 miles I have averaged a lifetime MPG of 48.9MPG. I don't exceed 64MPH and I try to coast and regenerate energy whenever possible. I have no modifications made to this 2008 Package 5 car. Tire Pressure is maintained at 38 front, 35 rear topped off monthly.

So to sum it all up, get the most MPG by maintaining a constant 45mpg on flat level ground and don't ever stop! Your next break is at 55 and then at 64. Speeds below 42MPH work the same as speeds above 64MPH, you loose economy with speeds below 42 just not as rapidly as you do with speeds above 64. Anything over 64 the curve goes WAY DOWN! At 80 you will be lucky to average 36MPG and don't crash at 80 or you will litereally be at one with your car.

So there you have it!

 

Thanks!