| Combined with the current research on forest fire prevention requirements and the fire brigade in China, this paper takes a type of small multi-function fire engines modified by SUVs’chassis as the research object and makes a systematic study of the vibration characteristics of the prototype vehicles by using the combination of theoretical analysis, experimental study and computer simulation method.Considering the actual operation situation of the prototype vehicles, the study of vibration smoothness includes no-load working condition and full load working condition. According to GB/T4970, this paper selects three kinds of commonly used speed under both B and D pavement level to carry out laboratory road simulation test and the Matlab simulation, and makes the appraisal in the way of root mean square of weighed acceleration based on GB/T7031.The simulation and experimental analysis shows:the fire engine vibration response value is bigger, this is mainly due to the factors such as road conditions, load and speed, and because the Matlab simulation to establish the mathematical model is an ideal model for fire engines, which ignores the influence of the engine and fluid motion, so the results of the smoothness is better than that of the test results. The error value is around 5%. In addition, by means of suspension natural frequency and damping ratio to match realizes the simulation of the optimization of the fire model, the optimized acceleration RMS improves about 8%.Refitted fire truck is mainly used for water delivery, so in this study, the effect of load on automobile vibration is intensively researched. First, the fluid-solid coupling mode of fire tank at no-load, half load, three-quarter load and full load is analyzed by Hypermesh and Nastran, identifying the natural frequency value of vibration at the first three orders under all load conditions, as well as the responsive vibration mode. According to the analysis, the tank vibrated obviously with load increasing, and that the vibration is normal since there is no catastrophe. Afterwards, an experimental research is conducted at 20km/h on a Grade-D road under the four load conditions, determining a value for vibration response. Then, a frequency domain analysis is carried out to refine the effect of fluid-solid coupling on automobile vibration.In addition, this text analyzes the effect of engine excitation have on vehicle vibration via experimental study. By measuring the idle speed (850 RPM),1500 RPM,2500 RPM, six points of acceleration time curve under the maximum speed (3500 RPM) and acceleration power spectrum curve, the results are analyzed in time domain and frequency domain. It is concluded that the faster the engine speed is, the larger the effect on vehicle vibration is, which mainly reflects in the influence on the vertical, horizontal and the front of axle seats.Through this study, it is concluded that the prototype vibration is affected by the road surface conditions, speed, load (fluid-structure interaction), engine drive, etc. And the vehicle overall vibration response value is bigger which means the vibration is obvious. Based on the research, it is preferred to optimize suspension, water wave insulation board and the engine mounting system, and control the speed when using, meanwhile avoiding half loaded water condition. |
