Wheel speed sensor

A wheel speed sensor or vehicle speed sensor (VSS) is a type of tachometer. It is a sender device used for reading the speed of a vehicle's wheel rotation. It usually consists of a toothed ring and pickup. A wheel speed sensor or vehicle speed sensor (VSS) is a type of tachometer. It is a sender device used for reading the speed of a vehicle's wheel rotation. It usually consists of a toothed ring and pickup. The wheel speed sensor was initially used to replace the mechanical linkage from the road wheels to the speedometer, eliminating cable breakage and simplifying the gauge construction (elimination all moving parts except for the needle/spring assembly). With the advent of automated driving aid, such as electronic ABS, the sensor also provided wheel speed data to the controllers to assist the operator in maintaining control of the vehicle. The vehicle Speed sensor is also used for the proper shifting up of gears for the vehicle maintenance. The most common wheel speed sensor system consists of a ferromagnetic toothed reluctor ring (tone wheel) and a sensor (which can be passive or active). The tone wheel is typically made of steel and may be an open-air design, or sealed (as in the case of unitized bearing assemblies). The number of teeth is chosen as a trade-off between low-speed sensing/accuracy and high-speed sensing/cost. Greater numbers of teeth will require more machining operations and (in the case of passive sensors) produce a higher frequency output signal which may not be as easily interpreted at the receiving end, but give a better resolution and higher signal update rate.In more advanced systems, the teeth can be asymmetrically shaped to allow the sensor to distinguish between forward and reverse rotation of the wheel.