Electric boosting Gas Engine in Crusie

[eddie27970]

I've been watching the MFD show the electric motor boosting the gas motor when cruise control set to speeds like 60, 65mph. The instant MPG goes way up. But this boost is rare, and short. What determines this extra boost?

From my obserevations, if HV battery is missing 2-bars, car set to cruise at 60mph, there is no extra boost. Once HV charged to only 1-bar missing, the extra boost starts occurring.

Would love to know what factors computer looks at (AC on or off? Etc.) And if there is a way to cause this extra boost to happen more.

Had an earlier 05 Prius that used to get the boost a lot, and would average over 50mpg's regardless of higher highway speeds. (wrecked that one) Now, antother replacement 05 does not seem to get this extra boost as much, and thus, lower mpg's.

Is there a hack to cause this extra electric boost to happen more often? Is there s sensor on gas motor I could alter or change, somehow? Thanks

[qbee42]

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

[eddie27970]

Humm? Seems you may be right. Had not thought of charging the battery back, when electric kicks in with its little boost. You cannot get something for nothing, I suppose. But it sure seems to help, momentarily.

Do you have any ideas on what causes the little boost? Any way to alter it? You know, in case I could experiment with it? What sensors are involved? Have a second Prius, and swapping sensors is easy enough. Even when I am driving wife's Prius, the electric boost seems to kick in more often, and give better overall mpg's.

Years ago, had matching Saturns. One got better mpg than other. Found over reacting knock sensor holding timing back, by swapping different sensors.

[qbee42]

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

[rpg51]

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.

[miscrms]

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

[SageBrush]

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.

[eddie27970]

OK, now you guys have done it! I can No longer just drive along, in cruise and casual thought of my surroundings. Now, my mind will be going over all you guys have told me, and I will be trying to analyze every change on the screen, plus putting my foot, lightly, on the gas peddle and observing. There goes my sanity. ha ha (yes, there are those who would say it was already gone.)

[bruceha_2000]

Originally Posted by qbee42

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

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".

[darelldd]

Originally Posted by qbee42

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

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.