Preliminary 2010 mph vs MPG

That's what I learned back in physics class. Force= (1/2)mass(velocity)^2 minus (1/2)(drag coefficient)(velocity)^2.

It appears, according to wikipedia, that there is more involved in this equation than what I seem to remember from college: [ame="http://en.wikipedia.org/wiki/Drag_force"]Drag (physics) - Wikipedia, the free encyclopedia[/ame]

:car:lane:

 

Just think of the time you will save while using the same amount of gas!!!

Hey Bob, great graphs, thanks!
On these preliminary results I'd drive at 70mph rather than 65mph because the increase in consumption seems minimal for the increase in speed. I wonder if Toyota engineers have set things up to be most efficient at 110km/h or 70mph because it's a pretty common speed limit on the open highway and highway driving is seen as a weakness of the GenII Prius.

I'd avoid driving at 65mph and drive at 60 for economy or 70 if time is a concern. Of course if time is in abundance and economy is the greatest priority it's 50mph all the way, but I value my time.

I understand this is early days and more data is needed for accurate reporting.

 

so, i didnt track the thread about the type of gas assuming unleaded regular oct 87 E10 was ok... sooo is it ok?

 

good....figured as much... would have had a hell of time finding "88" octane anyway

 

We have a 2010 Prius III with Navi we purchased 05/17/09.

Just got back from Reno Nevada from our honeymoon and obtained 52.7 MPG for well over 1,400 miles.

Used regular grade gas all the time. I believe that Oregon, where we live, is a 10 % Ethanol requirement. (I may be wrong)

When I filled up in Nevada I did not see any mention of Ethanol on the pump.

On the flat I drove both ways north and south at 70 MPH with cruise control and A/C on. Eco-mode.

I did not write down the figures but I believe one way was about 56 MPG on the dash guage and the other way was 54 MPG. Both legs were about 5 miles long and no noticeable wind. Speed limit there in Nevada was 70 MPH. Air temp was about 80 degrees.

So far my dash guage is about 2 MPG off. So my MPG corrected would be about 52-53 MPG.

Note both my wife and me in the vehicle with a very heavy loaded ice cooler.

Alfon

 

Power equals force times speed, since the aero force is proportional to speed squared, power is proportional to speed cubed. And similarily with rolling resistance, a force that is approximately constant vesus speed, but the power requires linearly increases with speed.

Its important to undestand this, because engine efficiency is so power dependant. Fuel consumption per unit time is dependant on engine power.

Check out this web site :

Power Equations Formulas Physics Calculator - Velocity Force

 

Unfortunately, that is incorrect because you are neglecting to consider that time/distance drops an integer from the exponent. We are talking about a mileage/distance measurement, not acceleration power. You are mixing bases by talking about power in a condition where the time over which the distance is applied is inversely proportional to the function. Power is an incorrect way to measure this.

The Prius Palm Pilot Mileage Simulator Prius Palm Mileage Simulator takes a closer/more rigorous look at the aero losses. While the aero losses increase as a squared function the net increase becomes nearly linear from 40-80 mph. The fixed losses work out to about 125-105 Wh/mile throughout the range, with aero changing from 45 Wh/mile to 180 Wh/mile over the same range.

Other than the single sub-41 mph point the bundled fixed losses decline every mile per hour. I assume that this is because the losses that are purely time dependent (running electrical, etc.) are being incurred for a shorter time for each distance. So their mpg impact is negative first order with respect to velocity.

 

Get to work Al! The old x-gauges don't work. I just got done with a run of over 700 miles and the genII x gauges are dead.
It makes a good run though. I want to see what it will do after it is broken in for 3 to 5K. This trip was from Effingham, IL to Charlottesville, VA and the car only had 5 miles on it when we left.

 

Power = J/s = N*(m/s). You are right that Power equals force times velocity. However, Newtons is kg*m/(s^2). The meters are not squared. So, this is Not velocity cubed. This is (kg/s)(m/s)^2
(I apologize that I did not click on your web link - I will, when I get more time)

Anyways, can someone explain to me mathematically why the 1.8L engine gets better highway MPG than city MPG while the gen2 1.5L gets the opposite? (yes, I have ridden a "ten speed" bicycle and I know that it takes a lot of force and power when going fast in the highest gear, and I understand that a 1.8L has more torque and lower rpm than the 1.5L, but isn't the net "power" output going to be the same? And so, if gasoline is energy, and power is energy per unit time, shouldn't the gasoline consumption at a given constant speed (60mph, for example) be the same?)

 

The 2010 1.8 is geared higher which gives better numbers at highway speeds than the 1.5 gen II. This is the reason for the larger engine.

Driving in the ECO mode at a steady state and pressing the power mode button is like nitros injection unless you back off on the throttle a lot. I haven't seen the torque curve in ECO versus Power, but there is a huge difference. It is like the ECO gives you the power of a 1.0 liter.

I tried the hills in Eastern KY, WV, and Western VA on I-64 in ECO and power modes. It was evident there is a need for power mode and the fcd was reading in the 25 mpg range in either mode. In Eco the engine was very labored though.

 

I'll try another angle to Bobs but I cast no doubt on Bob's explanation, he being far cleverer than I.

Not a mathematical explanation but I'll have a go.
The 1.5 litre engine has less torque than the 1.8 litre.
To multiply torque the HSD allows the engine to spin faster by allowing MG1 to turn and generate electricity.
This electricity is fed to the high torque MG2 where it assists to turn the wheels and power the car.

Each time energy changes state there are efficiency losses. When changing from chemical to heat in the combustion chamber there are heat losses to the cooling system, in changing from heat to kinetic there are friction losses.
Then in MG1 there are further heat losses when converting from kinetic to electric, this and the next 2 are important to our situation.
There are small transmission losses in the electrical cables and particularly the controls which is why the inverter is cooled.
Then in MG2 there are more heat losses when electrical energy is converted back to kinetic energy.

Because the 1.8 litre engine produces more torque there is less need for power to go via the electrical path with all its losses from the ICE to the wheels therefore there are less losses in the electric transmission with the larger torquier engine.

If you think this explanation is a load, please feel free to say so.

 

Bob,

Can you please explain why your description is not overshadowed by partial power losses in the form of negative manifold pressures ? How much has a combination of gearing, valve timing, and gas recirculation obviated these losses ?

 

... Adding my ignorant voice to the question of whether power is related to the square or the cube of speed:

mpg = distance/energy = distance/work
power*time = work,
So mpg = distance/power*time = speed/power OR
mpg*power = speed

Since we know that a linear increase in speed is related to a quadratric decrease in mpg, power must increase as an exponent by (mpg's_quadratic +1). That's as far as my limited math and physics takes me: power is related to speed by something greater than squaring.

 

BOB WILSON, THANK YOU!!!! Excellent explantion!!!
(what is the "fixed" vs "non-fixed" on the first graph, though?)

PatSparks, your explanation makes perfect sense for city driving, but if I'm correct, the electric motors do not power the car at highway speeds. This discussion is mainly for highway speeds. But, for city, your explanation of the second law of thermodynamics brings things into perspective for the Prius.

Sagebrush, "mpg*power = speed" I've never seen it put that way before (LAUGHING). I am laughing with you. You are certainly correct. I have just never seen it written that way before. Thanks.
I understand your logic of (linear)(power) = (something)^4 and therefore power must be ^3 , but I do not have knowledge of mpg decreasing as a quadratic (I'm not saying it does or does not. I do not have any knowledge on the subject. Feel free to enlighten me).

 

According to Toyota the cooled EGR can be up to 40% of intake and greatly reduces pumping losses bringing the intake side toward atmospheric pressure.

Wayne

 

My MFD gauge reads about 1 MPG (2%) generous. My wife's '06 is closer to 4% off. My '04 speedo is also about 2 MPH high (meaning I'm going 65 when it says 67). I presume that means that for every 60 miles I drive, the odo shows 62. Seems like that could add up after a while. The wife's '06 seems to be dead on at 60. Wonder why. BTW, it is true both with my TTs and her Integritys AND with the RSis on both cars. Tests based on Interstate measured mile, both at 60 MPH and resetting Trip B at the start and checking it at the end.