A road simulator reproduction method was developed to reproduce the off-road conditions of utility vehicles in a laboratory setting.
Off-road running behavior can be reproduced by considering the effects of inertial forces from jump landings owing to uneven terrain and slow-speed navigation.
However, extremely low-frequency components and behaviors, including inertial forces from jumps, vehicle acceleration and deceleration, are difficult to reproduce with a normal road simulator in the limited test space of a laboratory. Therefore, it is common practice to intentionally remove input components below 1 Hz. Alternatively, inertial forces can be reproduced by adding a restraining device to the sprung mass of the vehicle along the wheel-axle inputs. Therefore, the former method excludes extremely low- frequency components, whereas the effects between actuators, which increase the test complexity and time required, should be canceled in latter method. Furthermore, the restraining device on the sprung mass can be temporarily loaded differently from actual testing conditions, rendering the evaluation inaccurate.
To address this problem, we focused on the vertical behavior of the sprung mass and actively incorporated it into moment input control in the extremely low-frequency range. Therefore, we successfully reproduced the behavior and input owing to the inertial forces. Additionally, using different frequency response functions for each running condition, it is possible to continuously reproduce sections with significantly different behaviors in a controlled setting.
Consequently, RMS error values of less than 8% for the wheel force and 11% for the suspension stroke were achieved in road simulation. Moreover, the accumulated fatigue damage in the structural components closely matches the actual driving conditions with a high degree of accuracy. This enabled stable testing regardless of changes in weather and course conditions, thereby improving the accuracy of the evaluations.