How do you measure and minimize torsional vibration in the drivetrain?

1 What is torsional vibration?

Torsional vibration is the angular oscillation of a rotating shaft or a system of connected shafts. It is caused by the difference between the applied torque and the resisting torque of the load. The applied torque varies with the engine speed and load, while the resisting torque depends on the inertia, stiffness, and damping of the drivetrain components. When the applied torque exceeds the resisting torque, the shaft accelerates; when the applied torque is less than the resisting torque, the shaft decelerates. This results in a periodic change in the rotational speed of the shaft, which is called torsional vibration.

2 Why is torsional vibration harmful?

Torsional vibration can have serious consequences on the performance, durability, and reliability of the engine and drivetrain. It can generate audible noise and vibration, which can affect the comfort and safety of the driver and passengers, as well as interfere with other electronic devices and sensors in the vehicle. Furthermore, it can cause friction, heat, and stress on components such as the crankshaft, flywheel, clutch, gearbox, driveshaft, differential, and axles; leading to premature wear and fatigue of the materials. Additionally, torsional vibration can induce resonance; matching the natural frequency of a component with the frequency of the vibration. This can amplify the amplitude significantly and result in severe damage or failure of that component. For example, it can cause crankshaft failure, flywheel fracture, clutch slippage, gear tooth breakage, driveshaft twisting, or differential lock-up.

3 How to measure torsional vibration?

To measure torsional vibration, you need to use a device that can capture the rotational speed and angle of the shaft or system of shafts. Tachometers can provide a simple and accurate measurement of the average speed, but they cannot capture the instantaneous speed or angle variations due to torsional vibration. Alternatively, encoders measure the rotational angle of a shaft using a sensor that detects a series of marks or slots on the shaft surface, yet require a reference point or zero position to calculate the angle. Lastly, strain gauges measure the strain or deformation of a shaft using a sensor that changes its electrical resistance when stretched or compressed; however, they require calibration and power supply to operate.

4 How to minimize torsional vibration?

To minimize torsional vibration, you need to reduce the sources of torque variation, increase the stiffness and damping of the drivetrain components, and avoid resonance conditions. Balancing, tuning, isolating, and matching are some of the methods and tools that can be utilized. Balancing is adjusting the mass distribution of a rotating component to reduce its unbalance, which is a cause of torque variation. This can be done with a balancing machine or portable balancer. Tuning is adjusting the parameters of the engine or transmission system to optimize their performance and efficiency, which can reduce torque variation. This can be done with a tuning software or device. Isolating is inserting a device or material between two components to reduce transmission of torque variation and vibration. This could involve an isolator or damper such as a rubber coupling, viscous coupling, spring coupling, torsional damper, or dual mass flywheel. Matching is selecting or designing the components of the drivetrain to match their natural frequencies and avoid resonance. This can be done with a software or formula to calculate natural frequencies and compare them with frequency range of torsional vibration. Additionally, a vibration analyzer or device can measure and monitor frequency and amplitude of torsional vibration to detect any resonance.

5 How to learn more about torsional vibration?

Gaining an understanding of torsional vibration requires knowledge of internal combustion engines and drivetrain systems. To learn more about torsional vibration, you may read books and articles that cover the fundamentals and applications, watch videos and tutorials that demonstrate how to measure and minimize the vibration, or take courses and workshops that teach and train you how to do so. You can find these resources online or in your local library, as well as on YouTube, Udemy, Coursera, and other platforms.

6 Here’s what else to consider

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