I have been a member of this site for sometime now. I have seen some great ideas on how to improve the gas mileage of the prius, and most of them I have installed on my prius. But, lately I have noticed that we have started to just go around in circles with the same old stuff. I have run out of ideas but, I know that with all the people out there we can come up with some new ideas that will help everyone get even even better mileage then what we are now. Anyone?
I saw a thing on television where some engineers proved that pumping air into the area directly behind the car reduced drag by eliminating the low pressure zone. Or something like that. It got me thinking, how can a person pull in air and route it to the rear of the car? The way they were doing it on the show looked really clunky. Good luck with that and let us know how it works.
It looks like using just MG1 torque, MG2 torque, and the gear ratios, we can figure out the torque to the wheels and vehicle thrust. This works because the ICE torque is matched by MG1 torque so the ICE torque is not needed. Dividing the final wheel torque by the wheel radius provides a direct readout of the thrust matching the vehicle drag. My gear ratio sources are: http://prius.ecrostech.com/original/Understanding/PowerSplitDevice.htm http://www.autoshop101.com/forms/Hybrid02.pdf 1) -2.6 * MG1 : MG1 torque ratio to ring 2) (-2.6 * MG1) + MG2 : sum of torques 3) 3.905 * ((-2.6 * MG1) + MG2) : torque to axle ratio 4) (3.905 * ((-2.6 * MG1) + MG2)) / .2921 : N from tire radius The obvious advantage of this approach, if I haven't made a mistake, is a nearly direct readout of vehicle thrust and by implication drag and inertial load. With this formula, I've measured 193 N at a cruise control maintained, 25 mph (11.17 m/sec) at a temperature of 75F/24C over a distance of 10 miles/16 km on a 1.1 mile closed loop (1,315 samples.) But my measured thrust is lower than the NHW11 drag formula: 193 ~= 242 N : NHW11 drag formula 190 + (0.42*(V*V)) I'm running Sumitomo T4s at 51 psi and the rear wheels are metal tab aligned to 0.03 toe and equal 1.1 camber. Also, I'm using lower friction Type WS in the transaxle and the vehicle was throughly warmed up. I plan to take out my rear wheel tabs and repeat the test prior to getting the alignment checked and swapping in the EZ Shims 75800. This will let me quantify the toe and camber effects. So what happened to the ICE torque? It only exists because MG1 provides the counter torque. Because of this, we only need MG1 to account for it. Bob Wilson ps. As part of auditing this formula, I plotted the wheel thrust over the laps and included MG1 torque as a refernce: Note how when the ICE kicks in under cruise control, it substantially increases the thrust to return to the cruise control set speed. This happens when local rises in the track trigger the ICE to start, resume speed and then run until a downgrade allows the ICE to shutdown.
Actually I was addressing the "bring me a rock, no bring me a different rock" implied by the title, "Time to renew the brainstorming." I had just run the experiment this weekend and here comes a call for a "new rock." In this case, how we can instrument our Prius to measure the drag by measuring the thrust. It turns out that the vehicle thrust exactly matches the vehicle drag. If the thrust is a little higher, the vehicle accelerates to a faster speed until the drag equals the thrust. If the vehicle thrust is a little less, it decelerates to a slow speed until the drag and thrust are in balance. This is an approach to optimizing vehicle performance based upon two goals: minimize drag maximize engine efficiency The rest is simply variations of the above two goals and nothing else. Bob Wilson
Geez, Bob! When I said I was looking for the thrust of the post . . . Really, I'd love to be able to get my noggin' fully around your post, so I think I'll read through it a few more times, but I was just trying to have a bit of fun. More though: Why wouldn't you expect to find this balance? It takes so much to power through the air, that I would think it should come out like you have found. (How's that for scientific thinking?)
The practical application is as you tweak and tune a Prius for lower and lower drag, the improvements become smaller and smaller. So if I want to test rear wheel well covers aka. Insight, I need to detect very small changes in drag quickly to determine if it is a real savings or just "eye candy." I would also like to test variable, cooling air inlets, air dams and side skirts and a different tire size. I'm also testing toe and camber changes. Incrementally these are small changes so I need a fast and accurate way to evaluate the effects without being distracted by the engine performance. Engine performance is measure by shaft energy / fuel energy. I want to understand what is happening without being distracted or misled by drag effects. Once I have these understood and optimized, the last threshold is systems management. This means maximizing distance traveled per gallon based upon what we can know about our route. In a perfect world, GISS terrain data, GPS and vehicle location are used to optimize the route and driving profile. With a little historical data, this could lead to very efficient driving. Properly design, computers will handle everything and the driver only has to steer and avoid accidents. Bob Wilson
