Virtual test method for motorcycle frame based on multi-axes road simulation using excitation spectrum

Abstract: Motorcycle frame is the key load-bearing part of vehicle, its fatigue reliability, stiffness, strength, quality and other factors play a decisive role in vehicle's control stability and occupant comfort. New frame products must pass the reliability test before put into market. However, current frame fatigue reliability tests mainly use road test and testing ground test, which are time-energy consuming and the results are easily affected by environmental factors; Indoor bench tests at present mainly use single axial single incentive or single axial multi incentive mode. The motorcycle frame installation and constraints on the vehicle are very complex, the actual driving loads are complicated and changeable, thus multi-axial loads on motorcycle frame due to road excitation during actual driving could not be simulated or simulation precision is low, prone to over or under test. While the computer simulation technology development provides a new solution to dynamic performance analysis and fatigue reliability evaluation of vehicles and their parts, which including complete 3D entity model building online, creating a virtual laboratory, a virtual running environment and realizing virtual test and evaluation. For accurate and efficient analysis and evaluation of motorcycle frame fatigue reliability, a multi-axes road simulation test method for motorcycle frame based on time-frequency domain error weighting and force-displacement hybrid control was put forward. A motorcycle frame multi-axes road simulation test bench was built with American MTS road simulation test device, which was arranged with two actuator input channels in horizontal axial and vertical axial. As the motorcycle frame multi-axes road simulation test system is a multiple input multiple output system, the remote parameter matrix control strategy was applied to iterate and reproduce actual driving load spectrum. As the frame front fork and shock absorber were substituted by rigid frame fixture, in the horizontal direction, the frame dynamic response was more effective to the force loading, so the horizontal actuator used force control mode and loaded force spectrum. In the vertical direction, the system used inertial loading and frame dynamic response was more effective to displacement loading, so the vertical actuator was selected displacement control mode and loaded displacement spectrum. The motorcycle frame actual road load spectra were collected and multi-axes road simulation test bench was developed. With the simulation test bench, the multi-axes road simulation test was conducted based on force-displacement hybrid control under time and frequency domain with error weighting coefficient of 0.5. The simulation iteration precision of frame actual road load spectrum achieved 93%. Therefore the multi-axes road simulation excitation spectrum were extracted. The HYPERWORKS and ADAMS were applied in building the virtual rigid-flexible coupled multi-axes road simulation test platform with reference of the actual motorcycle frame multi-axes road simulation test system. Simulation analysis was conducted with the multi-axes road simulation excitation spectrum as input and the outcomes were verified by actual multi-axes road simulation test, thus the virtual test method for motorcycle frame based on multi-axes road simulation excitation spectrum were established. The results show that, the curve trend and amplitude of simulation results coincide well with test results in time and frequency domain, only slight amplitude deviation exists near frequency value 13 and 24 Hz, while the frequency curve RMS error is within 10%. Thus the virtual test method based on multi-axes road simulation excitation spectrum could be well applied to motorcycle frame fatigue reliability assessment.