Matching Analysis And Experimental Study On Powertrain Mounting System Of Heavy-Duty Truck

The noise,vibration,and harshness performance(NVH)are the main indexes to evaluate the quality of vehicle design and manufacture.With the development of vehicle technology,the improving of NVH performance is not only the goal of passenger vehicle design,but also the orientation of the technological development of heavy-duty trucks.As an important part for the engine vibration and noise controlling,the design of Powertrain Mounting System(PMS)affects the vibration transmission between powertrain and body or frame directly,and further affects the NVH performance of vehicle.As one of the vehicle motion sources,the PowerTrain System(PTS)which contributes more weight for the vehicle is one of the key sub-system.Therefore,the research on powertrain lightweighting has significance for the vehicle design.In order to meet the requirement for the technology development of the vehicle light weighting,the problem of vehicle NVH performance deterioration caused by improper lightweighting design of current vehicles should be solved effectively.The design of PMS with good vibration isolation performance has become an important topic and urgent demand to improve the performance of the vehicle NVH.To achieve the PTS lightweighting of a heavy-duty truck,the shell of transmission was replaced by aluminum from cast iron.Such a weight reduction caused the appearance of vehicle jitter and the abnormal noise in the cab.Based on the matching of the PMS,the research work is carried out based on the combination of vehicle road test and simulation analysis.The following aspects are mainly included:(1)Based on the principle of Lagrange,the PMS multi-body dynamic theoretical model of heavy-duty truck with 16 degree of freedom was established considering the contribution of cab.The influence of cab design on the frequency of PMS were studied.The study shows that the considering of cab into the dynamic system would increase the modal frequency of PMS.The evaluation indexes of PMS,such as frequency matching,vibration isolation rate,vibration transmissibility,and energy decoupling of heavy duty truck were given based on the engineering practice.(2)For the vehicle jitter of current vehicles due to powertrain lightweighting,the experimental modal test and vehicle experimental test were carried out.The results showed that neither of the natural frequency of the PMS around the X-axis and the transmissibility of rear mounting point met the requirements of the target.The redesign of rubber mounting components with smaller stiffness was needed to matching the PMS.(3)Based on the dynamic substructure modal synthesis method,a rigid-flexible coupling multi-body dynamic model is established considering the elastic frame.Modal analysis and dynamic response analysis of vehicle were carried out using the established simulation model.It can be drawn out that the modal frequency distribution of original PMS design was unreasonable.Neither of the natural frequency of the PMS around the X-axis and the transmissibility of rear mounting point in the range of low speed met the requirements of the target.There were coupling appeared at some degree of freedom.Meanwhile,the differences between the modal frequency of vehicle under elastic frame constraints and under free condition were larger.(4)The transmissibility of PMS was chosen as the optimization goal.The constraint modal frequency of the elastic frame was considered at the same time.The optimization analysis of PMS was done by the genetic algorithm to obtain the parameters of rubber mounting components which met the requirement of PMS.The modal analysis and dynamic response analysis of the PMS after optimized were conducted.It can be found out that the all of modal frequency,modal decoupling and transmissibility of the PMS meet the target requirements.Then the vehicle road test for PMS optimization verification were operated.The test results indicated that the transmissibility of the improved PMS design met the target requirements under all working conditions.(5)To study the abnormal noise in the cab with the update of the gearbox during speed up,the vehicle test was done under the fixed sweep conditions.The transfer path analysis method was applied for the problem identification of abnormal noise in the cab.The frequency mismatching of the PMS was confirmed as the main cause of the abnormal interior noise.After the optimization of the PMS,the vehicle noise test was carried out.The results showed that the abnormal noise in the cab with the update of the gearbox during speed up was disappeared after the optimization of the PMS.Meanwhile,the interior noise in the cab under other conditions was improved significantly.