About the error of the bench control of the suspension

Abstract

The principle of operation of popular suspension test benches is to apply test signals to the wheel and record the suspension response. The output parameters have a significant range, which is a prerequisite for the analysis of the benches' errors. In this work, the error of the method according to the EUSAMA standard was investigated, the nature of which is different air pressure in the tire.  The relationship between tire pressure and stiffness was established according to the W. Biedermann formula.  The suspension of SKODA FABIA car was used as an object of research. The study was conducted by simulation.  Preliminarily, to estimate adequacy of the model, the car and its suspension were tested on BOSCH SDL 260 (EUSAMA standard). The well-known two-mass model was used as a model. Modeling was done in MATLAB SIMULSNK environment. The amplitude-frequency characteristics of the dependence of the control parameter were obtained for 4 tire pressure values: 200; 210; 220; 280 kPa. As a result of the study, the following conclusions were obtained.

Reducing the tire pressure by 10 kPa (from 210 to 200 kPa - by 4.8%) leads to an increase in the "coefficient of adhesion" by 5%. The same value corresponds to the error that appeared. Increasing the pressure in the tire relative to the recommended by 10 kPa causes a decrease in the "coefficient of adhesion" by 2.2%. Accordingly, the error of the diagnostic result will increase. Finally, if the pressure in the tire is 280 kPa (33.3% increase), it will lead to a decrease in the "coefficient of adhesion" by 15.6% and the same increase in the error of the test result. All error estimates were made at a frequency close to the resonant frequency of 100 1/s.

Keywords: suspension test, eusama method, tire pressure, error.