Estimating Wheel Torque From Engine Torque

In summary, it is possible to obtain engine torque and RPM from a truck CAN bus. However, to estimate the tractive force at the wheels, additional information such as gear ratio and wheel radius may be needed. If the CAN bus also knows vehicle speed, then the wheel size is the only necessary information. Drivetrain losses should also be taken into account for a more accurate estimation, requiring data on drivetrain efficiency. If vehicle speed cannot be obtained from the CAN bus, it can be estimated from GPS. A powertrain efficiency of 85-90% can be assumed for a decent estimation.
  • #1
ein_stein
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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?
 
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  • #2
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.
 
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  • #3
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
Very helpful, thanks. If I can't obtain vehicle speed from CAN, I assume that I could get a decent estimate from GPS?
 
  • #5
Yes, that should be fine. As for powertrain efficiency, you could probably just assume 85-90% and get a decent estimate.
 

Related to Estimating Wheel Torque From Engine Torque

What is the purpose of estimating wheel torque from engine torque?

The purpose of estimating wheel torque from engine torque is to determine the amount of force being applied to the wheels of a vehicle by the engine. This is important for understanding the overall performance and efficiency of the vehicle.

What factors affect the relationship between engine torque and wheel torque?

The main factors that affect the relationship between engine torque and wheel torque are the gear ratio, transmission efficiency, and tire size. The gear ratio refers to the number of times the engine's output shaft rotates for every rotation of the wheels. Transmission efficiency refers to the amount of power lost in the transmission process. And tire size affects the distance traveled by the vehicle for each rotation of the wheels.

How can wheel torque be calculated from engine torque?

Wheel torque can be calculated by multiplying the engine torque by the gear ratio and the transmission efficiency, and then dividing by the tire radius. The formula is: Wheel Torque = (Engine Torque x Gear Ratio x Transmission Efficiency) / Tire Radius

Why is it important to estimate wheel torque accurately?

Estimating wheel torque accurately is important for several reasons. It can help in determining the power and performance capabilities of a vehicle, as well as identifying any potential issues with the engine or transmission. It can also be helpful in optimizing fuel efficiency and ensuring the safety of the vehicle.

What are some methods for measuring wheel torque in a vehicle?

There are several methods for measuring wheel torque in a vehicle. One common method is to use a dynamometer, which measures the amount of torque being applied to the wheels while the vehicle is in motion. Another method is to use a torque wrench, which can be used to measure the torque on individual wheels. Additionally, some newer vehicles have sensors that can measure wheel torque in real-time.

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