Estimating Wheel Torque From Engine Torque

1. Jan 13, 2016

ein_stein

It seems possible to obtain engine torque and RPM from a truck CAN bus. I'd like to estimate tractive force at the wheels given these two values.

How should I go about computing torque at the wheels? Wouldn't I need gear ratio, which doesn't seem obtainable from the CAN bus?

Do I need to manually measure wheel radius to estimate tractive force at the wheels?

2. Jan 13, 2016

billy_joule

If the CAN bus also knows vehicle speed then all you need is the wheel size. You don't need to know the gear box ratios or diff ratio, engine rpm over wheel rpm gives the total drive train mechanical advantage. From vehicle speed and wheel size you can find wheel rpm, and then total MA then tractive force.

3. Jan 13, 2016

billy_joule

Of course, that'd ignore drivetrain losses. so, to correct, good data on drivetrain efficiency is a must (This may vary with road and engine speed?).

4. Jan 13, 2016

ein_stein

Very helpful, thanks. If I can't obtain vehicle speed from CAN, I assume that I could get a decent estimate from GPS?

5. Jan 13, 2016

cjl

Yes, that should be fine. As for powertrain efficiency, you could probably just assume 85-90% and get a decent estimate.