2010 Prius 92g/km and low emissions 89g/km version!

i am pretty sure it wont be something as water pump... solar panels are my bet, or special version with different tires, etc...

 

On straight vertical ascents and during accelerations, yes. For more mundane driving not even close. And on the highway barely a correlation.

 

I don't see why that would be true. In a frictionless world, it would take no power to maintain a vehicle along a flat. In the real world, all of the energy expended by a vehicle maintaining speed is consumed overcoming friction. Other than driveline efficiency, which should be similar for both vehicles, the primary source of friction is rolling resistance. Lets say as before that air resistance is 35%. An additional ~10% will be devoted to overcoming driveline losses, leaving the majority, 55% to overcome rolling resistance. Since rolling resistance is directly proportional to weight (mass), a vehicle that weighs 11% more will have 11% more rolling resistance. The '08 Corolla CdA is 7.7% higher, and since air resistance is linearly proportional to CdA, the Corolla will have 7.7% higher air resistance.

The increase in power required at 48mph should then be roughly:
((delta RR)*.55 + (delta AR)*.35)/(drive line efficiency)
(0.11*0.55+0.077*0.35)/0.9 = 9.7%

9.7% more power output, with the same amount of fuel consumed would be 9.7% more efficient.

Does that not seem right?

Rob

 

Rob, I think rolling resistance is directly proportional to speed and weight. The wonderful Wayne Brown has written on his website that 40% of Prius power goes towards overcoming air at 55 mph, and 60% at 70 mph. At higher speeds the transmission eats up around 10% of power reqs, and 5% at lower speeds.

So, at 70 mph, using P as total power use:
Air is .6P, Trans is .1P, RR(weight) is .15P, and RR(speed) is .15P

A 10% heavier vehicle, but all else equal shows
Air .60, Trans is .1P, RR(weight) is .165, and RR(speed) is .15P

Adds up to 101.5/100, or a 1.5% increase in fuel for a 10% increase in weight, other things held equal.
-----
I take no responsibility for any gross errors in arithmetic or mechanics (tm)

 

Drees, I used an assumed 60% of power due to air resistance at 70 mph, and not the 40% in your example. If I used 40% air, it comes out to 2.5% increased fuel for 10% weight increase.

And btw, again according to Wayne 60% air resistance is at 75 mph, and not the 70 mph I erred in using.

TMI (for sane people, anyway):
http://www.vejdirektoratet.dk/publikationer/VInot23/html/chapter05.htm

 

Drees, now that I think about it, I agree it does not make sense to assign equal weights to vehicle weight and speed in overall fuel consumption. But the link I included as an addendum in my earlier post reminded me that we have been neglecting engine friction. How about this breakdown:

P(engine) = .2
P(air) = .4
P(trans) = .05
P(RR) = .35

Now, increasing weight 10% leads to a 3.85% overall power consumption increase at the lower speed, and less at the higher speed.

 

First, I used 48mph because that is the average speed of the EPA highway mileage test. Our whole argument is based on both cars having the same fuel consumption for EPA highway. Since we don't know what their fuel consumptions are at 70 or 75 mph, we can't make any claims about their relative efficiency.

Next, I believe you are incorrect to try and apportion part of the RR to speed. RR does vary linearly with speed, but we are assuming a constant speed for both vehicles. When we do a ratio of the two in order to arrive at a percent increase, the V terms = 1. Think of it this way; if y is a constant, W is weight, and v is speed:

RR = yWv
RR1/RR2 = yW1v1/yW2v2, since v1 = v2,
RR1/RR2 = W1/W2

so the percent increase in rolling resistance is 100% equal to the percent increase in weight.

Rob

 

I think our numbers are basically the same. I'm using 35/55 instead of 40/60 to get a little closer to the 48mph average of the EPA test and taking 10% off the top to try and get from efficiency at the wheels back to efficiency at the engine. Otherwise the approach is the same.

I don't think you can make the same comparison based on the city data, for several reasons. The highway is fairly straightforward as its mostly a steady state operating condition. When you start going through a lot of acceleration and deceleration cycles there are many more variables, such as gearing, and the shape of the efficiency curves. On top of that, we are attempting to draw inferences about the Atkinson versions of these engines. They're behavior lower on the power/efficiency curve will be completely different, while in the highway cruising range they may bear a better resemblance to their otto cycle brothers. Lastly, we are talking about the application of those Atkinson cycle versions in a g/e hybrid, where the acceleration and deceleration profiles will be dominated by the electric system to compensate for the weaker torque of the Atkinson cycle. So even if you thought you could draw some inference about the efficiency through acceleration profiles of these vehicles, it will be largely irrelevant to the final application in hybrids.

To get back to the original assertion, there was a previous post saying the '10 Prius with the 1.8L engine will only be as efficient or less efficient on the highway as the current 1.5L version. As proof the poster offered the 1.5L Yaris and 1.8L Corolla as examples. I was simply trying to point out that based on the example given, the 1.8L does have to be more efficient than the 1.5L on the highway. While there are a lot of possible variables, that does say to me that its entirely plausible that the new Prius will have better highway fuel economy than its predecessor despite its larger engine. Toyota's claimed 10-15% percent improvement seems feasible to me, particularly in light on this CO2 data.

Rob

 

I would expect engine friction to be included as part of the ICE's efficiency. It should be about the same for both engines, but if it is higher for one of them, that ICE will be less efficient relative to the amount of power it puts out at its flywheel.

Rob

 

My argument is that only one major component of power use at constant velocity is mass dependent -- the rolling resistance, while engine rotation, transmission, and air resistance are not related to mass, but are proportional to speed. So as the speed of the vehicle increases, the relative weighting of RR in overall power consumption decreases. This is the approximate case in highway driving, unlike city driving where acceleration is the major power component, and is related to mass.

 

Where have Ive seen that catfish front faceview before? Was it the French citeron??

 

You are correct, all those things do come into play and are important if you are trying to get a qualitative number for a single vehicle. When you are comparing the delta between two fairly similar vehicles, its a fair assumption that most of those loses are going to be very similar and wash out. Then you are really just left with a component that is proportional to weight, and a component that is proportional to CdA. I did take the next step and include a driveline loss component, as that does de-emphasize the weight based component as you suggest.

Again, we're making a lot of generalizations and assumptions, but we're just looking for a ballpark number to assess feasibility.

Rob

 

Best Car magazine claims that the new Prius will be able to cover 40 km with one liter of fuel! I have translated the Japanese text: japanesegreencars.blogspot.com

 

Interesting, thanks! Don't think I had seen that pic of the '10 before. The numbers I had seen for the current Prius on the Japanese test cycle were in the 33-35.5 km/l range. That would put the fuel consumption improvement at 11.25-17.5%. That would put the EPA combined rating in the range of 52 - 56 mpg. Not too shabby.

Rob

 

The F1 style nose is more noticeable in red than white.