Hans Bastiaan Pacejka (12 September 1934 – 17 September 2017)[1] was an expert invehicle system dynamics and particularly intire dynamics, fields in which his works are now standard references.[2][3] He wasProfessor emeritus atDelft University of Technology inDelft,Netherlands.[4]
Pacejka developed a series oftire design models during his career. They were named the "Magic Formula" because there is no particular physical basis for the structure of the equations chosen, but they fit a wide variety of tire constructions and operating conditions. Each tire is characterized by 10–20coefficients for each important force that it can produce at thecontact patch, typically lateral and longitudinal force, andself-aligning torque, as the best fit betweenexperimental data and the model. These coefficients are then used to generate equations showing how much force is generated for a given vertical load on the tire,camber angle andslip angle.[5]
The Pacejka tire models are widely used in professional vehicle dynamics simulations, and racing car games, as they are reasonably accurate, easy to program, and solve quickly. A problem with Pacejka's model is that when implemented into computer code, it doesn't work for low speeds (from around the pit-entry speed), because a velocity term in the denominator makes the formula diverge.[6] An alternative to Pacejka tire models are brush tire models, which can be analytically derived, although empirical curve fitting is still required for good correlation, and they tend to be less accurate than the MF models.[7]
Solving a model based on the Magic curve with high frequency can also be a problem, determined by how the input of the Pacejka curve is computed. The slipping velocity (difference between the velocity of the car and the velocity of the tire in the contact point) will change very quickly and the model becomes astiff system (a system whoseeigenvalues differ a lot), which may require a special solver.
The general form of the Magic Formula, given by Pacejka, is:[8]
whereB,C,D andE represent fitting constants andy is a force or moment resulting from a slip parameterx. The formula may be translated away from the origin of thex–y axes. The Magic Model became the basis for many variants.[9]
Pacejka was a co-founder in 1972 and editor-in-chief ofVehicle System Dynamics–International Journal of Vehicle Mechanics and Mobility until 1989. At the time of the founding of the journal, Pacejka had been an associate professor at Delft University, specializing in vehicle dynamics. His 1966 doctoral thesis addressed the "wheel shimmy problem".[10] He published approximately 90 academic papers and was advisor to 15 PhD and 170 M.Sc. graduate students.[9]
