Fuzzy logic antilock braking system for trailers equipped with electric brakes

A conventional flatbed tandem axle trailer with a gross vehicle weight of less than 10,000 lb that was equipped with commercially available electric brakes was adapted to use an intelligent antilock braking system. Readily available components were used for the wheel proximity sensors and microcontroller. The antilock braking system was controlled by an 8 bit microcontroller. A fuzzy logic program written entirely in assembly language was used for the control of the antilock braking system. Inputs to the system were the wheel speeds of two braked and one unbraked wheel. From these measurements, a ratio called the slip ratio was calculated and was one of two inputs to the fuzzy engine. The second input was the applied brake and was expressed as a percentage. The output of the microcontroller was a pulse width modulated signal which varied the amount of power to the electric brakes. In addition, a fuzzy region definition based upon sinusoidal functions was also developed and explored. The control surface exhibits smooth transitions when sinusoidal characteristic functions are used for the inputs of a fuzzy system. The antilock braking system was successfully designed and implemented. The fuzzy logic control algorithm maintained the slip ratio within safe limits.