Development And Improvement Of Idling Vibration Performance For Passenger Vehicle

The NVH performance is an important indicator of vehicle performance. Under the same NVH performance, people always feel worse than other conditions when the vehicle is operating in idling condition, so it’s very important to control the vibration and noise levels in idling condition when developing the NVH performance of complete vehicle.According to the market positioning of a newly developed vehicle, The interior vibration of the prototype vehicle in idling condition is controlled during the development and debugging phase. To meet the target NVH performance, this paper works in the following aspects:1) According to the engine idling speed, calculate the second order excitation frequency. To avoid this frequency, we set the target values of natural frequency of the BIW(body in white), TB(trimed-body) and steering system larger than 45 Hz, 32 Hz and 35 Hz, respectively. According to the test analysis of the standard model, the vibration of the steering wheel and seat track can not higher than 0.3m/s2 and 0.06m/s2 respectively when the air conditioner is turned on, and can not higher than 0.35m/s2 and 0.08m/s2 respectively when the air conditioner is turned off.2) Setting up the BIW’s finite element model. Calculate and test the BIW’s natural frequency. When the results meet the standards, calculate and test the trimed-body’s natural frequency, get the simulation values of the trimed-body’s first order bending and torsional frequency are 32.33 Hz and 37.24 Hz, respectively, and the test values are 32.6Hz and 36.8Hz, respectively. Both the simulation and test values achieve the desired target(≥32Hz). Calculate the steering system’s natural frequency in the case of constraint mode and vehicle state, and the structure of the steering system is improved accordingly. After the improvement, The calculated values of the steering system’s first-order lateral and vertical natural frequencies in vehicle state are 38.25 Hz and 42.2Hz, respectively. While the test values are 40 Hz and 34.3Hz, respectively. All the values meet the target(≥35Hz).3) According to the request of the mounting system’s natural frequency and decoupling rate, the stiffness of suspension are optimized. Test is carried out using the optimized mounting system under the idling condition, the results show that the vibration of the steering wheel and seat track can meet the target when the air conditioner is turned off. However, when the air conditioner is turned on, the vibration of the steering wheel is 0.4m/s2, which larger than the target value 0.35m/s2, the vibration of the seat track is 0.09m/s2, which also larger than the target value 0.08 m/s2. By changing ±15% of the original suspension stiffness, different combinations of harder and softer suspension stiffness are tested. Finally the vibration acceleration of the steering wheel and seat track are all meet the targets, in addition to the vibration of the seat track is 0.07m/s2 which slightly beyond the target of 0.06m/s2 when the air condition is off.