Gearbox Speed Sensor Design and Performance Optimization

The speed sensing applications of a gearbox demand high operational air-gaps, tight switching and timing accuracy, and excellent overall reliability. High teeth density and small-diameter helical (nonsymmetrical) teeth profiles with fine teeth pitch pose significant challenges to rotational speed sensing. For many embedded control systems, such as an automated mechanical transmission, it is critical that before the transmission control module decides whether to open or close a clutch, the speed of a shaft and the corresponding gear have to be synchronized. This requires high fidelity in the accuracy of the computed shaft´s speed. This paper presents a low-cost rotational speed sensor module with high output accuracy and resolution for gear speed sensing in a commercial vehicle gearbox. The sensor performance has been modeled using finite element analysis, and the model has been validated against experimental data from the sensor prototype. The complete sensor module is designed for ease of manufacturing and application in harsh transmission environments such as high temperature profiles ranging from -40^°C to 125^°C.