I'm curious as to what engine RPMs you folks are seeing with your ScanGauge. Pretty much anything of note you feel like posting, such as warm idle, cold idle (Stage 1), cruising at various speeds, freeway 5%, 6% grades at various speeds, passing RPMs (say 30 to 50, or 60 to 80mph)

I'm sure others would be interested in knowing too. Thank you in advance!

 

I drive to reduce RPM on my 32 mile commute. I use 50 MPH as a target cruise in the winter with Primacy snow tires on, and 55 MPH in summer with the Energy tires. Tires are at 38 PSI in Winter and 40 PSI in summer.

Right now, in winter configuration at 50 MPH, I see an ICE RPM of from 1450 up to 1650 on level pavement in good condition when everything is stable and the ratio has backed off as much as I can make it do, ICE RPM will be somewhat higher if traffic conditions demand it or on a hill. I drive to keep the MPG indication under or about 40 MPG as much as possible. I figure that RPM gives me a shade under (-)1400 on MG1. The car is very quiet and smooth when I am in this condition. This does not include snow days or days when traffic prevents reaching 50 MPH. On those days, mileage suffers accordingly.

Last summer at 55, I was getting an ICE RPM range from slightly over 1580 up to about 1700 depending on weather and conditions. Target mileage in this configuration is 45 MPG, with the same limitations as above. That runs MG-1 at about the same speed, so I think the ECU must like the MG-1 RPM range or some other condition that puts it around 14 or 15 hundred. Again, this is when the car goes "quiet" like has often been discussed on this forum.

These seem to be minimum sustaining values. I usually cannot get below them unless its a small downhill or I accept a decelerating coast.

 

FastMover — For a road speed of 50 mph, and for the ICE rpm's that you cite at this road speed, I compute quite different values for MG1's rpm using my formulas (from the thread "Heretical Mode" post #40):

• ICE = 1450 rpm => MG1 = -684 rpm (Heretical mode)
• ICE = 1550 rpm => MG1 = -324 rpm (Heretical mode)
• ICE = 1650 rpm => MG1 = +36 rpm (Normal mode)

We really must try to resolve this discrepancy, which has cropped up before. If I am wrong, I'd like to correct my formulas; and if you're wrong I'm sure that you'd like to do likewise. I've clearly explained the derivation of my formulas in the thread cited above. They are deduced from Toyota's published gear ratios for the TCH. In the interests of accuracy and transparency, please tell us your formulas and their derivation!

Stan

 

I found this is not easy when your at speed. I tried to get a reading at 40 miles per hour for better accuracy. I picked the same 1/4 mile stretch of road and took a average both ways.

Idle a 163 degrees was 832 rpm. I could not get a 190/193 degree reading as the engine would shut off. I held the brake twice and it would start then shut right off.

Cruise at 40 miles per hour = 1300 rpm

Cold start, engine rev to 1535 rpm at 50 degrees outside temperature.

 

Most seems about right. It might be an outside temperature thing, but the idle seems a little low compared to what I see. I am at 895 rpm when temps are stable, in cold Washington at about 158 degrees.

 

The question about the idle could be that i'm at 4500 feet elevation. I know the computer should compensate but maybe not exactly.

 

OK Stan, just for you.

Attached is my little spreadsheet toy. At 50 miles per hour, 1450 RPM, it gives -1202, and at 1650, it gives -482.43. It is based on published gear ratios and data in all cases, and cross-checked against the P311 Service Manual data (the "Sanity Checks") . The highlighted areas are inputs, and you can play with it to discover some things. For example, at 121 miles per hour, MG2 is turning faster than 10K, and closer to 15K. To keep MG1 under 10K you need to have at least 1550 ICE turn, irrespective of any torque loads. (It will always be much higher at that speed, as we all know.) Interestingly, if you take the ICE to the redline at 6250, mg1 will also be in tolerance, but turning positive.

Either way, we should know sometime this month, I have the frequency sensors working now on MG2 and MG1 power leads, and should be able to read them directly on the triple tach. I have also attached the RPM/Frequency curves for the triple tach as some asked if I could get the resolution.

RFB

 

FastMover — Thanks for posting your formulas. Having examined them and compared them with mine, I now believe that the error is not yours but mine! It seems to be simply the result of my using the wrong (i.e., "unloaded") radius for the TCH's tires, instead of the correct (i.e., "loaded," what you call "static") radius, in my formulas. This relatively small error is enough to throw out my numbers significantly. I'll report back once I've checked a bit more, but I think I now have this discrepancy sorted out.

Incidentally, the behavior of the tire as it rolls is strange indeed! If r0 is its unloaded radius, and r1 its loaded radius (r1 < r0), then the car moves forward a distance of 2*pi*r1 for each revolution of the wheel, whereas the circumference of the tread is the somewhat larger number 2*pi*r0. One would naively think that the car must move forward by a distance equal to the circumference of the tread, but this isn't so! The tire must thus continuously deform as it rotates to accommodate this difference. This deformation must be a primary cause of tire rolling resistance. Am I correct?

Stan

 

Yes. There is some data on it HERE: http://thecartech.com/subjects/auto_eng/report1w.htm .

I used the Tire Static Radius as a baseline. To be absolutely precise, the Tire Rolling Radius should be used, but it is a function of speed, loading and also tractive effort, which is hard to define as it takes into account the power used, pavement or rolling surface and several other variables. Several benchmarks in the industry use 46% of the undistorted tire diameter as the static radius at published inflation. Since we typically overinflate, the actual number may be higher, which in turn would decrease the axle RPM per rolling mile.

RFB

 

FastMover — Thanks for the reference. Now I'm more puzzled than ever!

The Michelin Web site does not appear to give a tire "rolling radius" specification for the Energy MXV4 S8 P215/60 R16 94V tire. It gives a static "overall diameter" of 26.2 inches, which corresponds to the 13.1 inch = 0.3327 m radius that I (incorrectly) used — I rounded this to 0.333 m. It also gives "tire revolutions per mile" of 793 at 45 miles per hour, which translates into a 12.716 inch = 0.3230 m "rolling radius with tractive effort." This is only ~3% smaller than the figure I used. Your figure of 12.052 inches = 0.3061 m for "static radius" corresponds to an even smaller number, which is a more significant ~8% lower than the figure I used. By the way, where did you get your number? Did you actually measure the static radius on one of your own tires? (A quick measurement by me gives a number close to yours.)

So, which number should we agree to use? It would seem that the "rolling radius with tractive effort" is probably the most meaningful. That being the case, the Michelin figure of 12.716 inches = 0.3230 m seems like a better choice than either of our choices. It would be good if we could agree to both use the same number, so that we our predictions are in agreement. This is all about a relatively minor discrepancy, of course, but we might as well get our numbers as accurate and consistent as possible. What do you think?

Stan