Hall wheel speed

Active wheel-speed sensors have been available for years. New features in modem cars to enhance comfort require more information about the behavior of the car. One important piece of information is the rotational direction of the wheels, and hence the direction of the car. The Bosch DFlli was the first sensor to deliver this information, and it was used in the Bosch EHB system in 2001. The sensor transmits this additional information by modulation of the pulse width of the speed signal. The sensor contains three Hall elements two for speed measurement by the difference principle, and a third arranged in such a way that an addi-... 

The wheel speed is calculated based on the input from a Hall Effect sensor. Such a sensor may produce a sine wave signal with a frequency that is proportional to the rotational speed of the wheel, as depicted in Fig. 8. 

The result of applying the oscillation fault model may vary depending on the implementation of the Hall Effect sensor signal conditioner. In our implementation, we assume that the number of zero crossings will increase as an effect of oscillations superimposed on the Hall Effect sensor signal, as shown in Fig. 9. This will cause the estimated wheel speed to be higher than the actual wheel speed (154 RPM in Fig. 9 instead of 98 RPM in Fig. 8). Since we inject faults directly into the behavior model, which takes the estimated wheel speed as input, we use the offset fault model to represent an oscillation superimposed on the Hall Effect sensor signal. 

The machines are very complicated, so they are simplified to a level which maintains the main features observed. In this case, the hall already existed, and the ventilation system needed to be improved. In the lower parr of the machines are rotating wheels and axes which lead to a net flow across the floor in one direction through all the machines. Such a flow was generated by adding moving walls in the lower part of the machine model (Fig. 11.24), and the size of the velocity was adjusted to fit the measured speed in the real hall. Periodic boundary conditions are attached to the walls to the left and right in Fig. 11.24. 

Steele D., J. Hall, R. Stubstad, A. Peekna, and R. Walker. 2009. Development of a high speed rolling wheel deflectometer. 88th Transportation Research Board Annual Meeting. Washington, DC. 

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