[bwilson4web]

Hi,

I've been reading this paper closely and I think I found why their results, 25% improvement, versus mine, 11% are so different. If I read the paper correctly, they did their vehicle tests using a dynamometer and their model does not include aerodynamic drag effects. I've sent an e-mail invitation to discuss their paper in a public forum. Also, I suspect they did not include what Ken@Japan has called the 'heartbeat' or the ~300-400 W of power needed when the Prius is just sitting there. This power runs the electronics and electric assisted brakes and steering.

To show you what I mean about the 'heartbeat' load:


The 'blue' line is the expected MPG for my NHW11 based upon a drag formula published by Toyota. But when I add the fixed, vehicle overhead, I get the lower, 'gray' curve that shows there is a peak range speed in the 18 mph range. Any slower and the fixed overhead begins to predominate. Any faster and the aerodynamic drag effects reduce mileage.

I think this paper, "Vehicle Inertia Impact on Fuel Consumption of Conventional and Hybrid Electric Vehicles Using Acceleration and Coast Driving Strategy" Jeongwoo Lee, Douglas J. Nelson and Hennning Lohse-Busch used just 'road' constants (pp 2 and 3) and not aerodynamic effects. This makes sense when comparing the 2007 Ford Focus and 2004 Prius on a dynamometer (pp. 4). So when I look at "Table 4. Summary of Results of 2004 Toyota Prius" (pp. 6), I'm wondering why these data points are off by a factor of 2 from my field results.

Bob Wilson

[keanni]

I can't read the paper?

[FastMover]

If they used a dynamometer there are a few more potiential differences. One big one is that the rolling resistance on a Dyno is different because of the "double deformation" introduced by the rollers vs the single deformity for each wheel that occurs on pavement. Also, dyno testing usually only invoves two wheels. The double deformation has the effect of offseting some part of the unaccounted for rolling resistance of the non-driven wheels, but the difference is significant enough to be a factor.

[bwilson4web]

FastMover said:

If they used a dynamometer there are a few more potiential differences. One big one is that the rolling resistance on a Dyno is different because of the "double deformation" introduced by the rollers vs the single deformity for each wheel that occurs on pavement. Also, dyno testing usually only invoves two wheels. The double deformation has the effect of offseting some part of the unaccounted for rolling resistance of the non-driven wheels, but the difference is significant enough to be a factor.

They used a four-wheel, dynamometer. If you'll click on the page number links in my original posting, you'll see the specific pages my post references. Sad to say but at $15/copy, it is a little pricey unless you have an interest in the subject.

I would feel much better about this paper if they had gotten 'track time' and replicated the results 'in real life.' I know it is expensive but so too is normal dynamometer time.

One area that I would like to see is a Monte Carlo simulation of "n" vehicles with different characteristics practicing pulse and glide on a circular track. Ideally this would allow a mix of vehicles and perhaps address questions of:

• traffic density versus Pulse and Glide or steady state - is the transition smooth or are there non-linear effects that defeat pulse and glide above some given threshold?
• what happens when hetrogeneous vehicles attempt pulse and glide as the traffic density increases - is this a case where the least optimized, 'pulse and glide' drives everyone else to adopt their style?
• can we characterize the driver workload as a function of different "pulse and glide" regimens versus steady speed?

These are questions that address 'the commons', the roads we share with other drivers.

Bob Wilson

[doasc]

bwilson4web said:

. Sad to say but at $15/copy, it is a little pricey unless you have an interest in the subject.

That's been my issue. I was sure that there would be a way to get free access, either publicly or through work. However, it looks like member discounts are the best it gets. Hopefully the content from these papers makes it to the public domain (legally) soon.