| The Condenser-Radiator-Fan Module(CRFM)mounting system including CRFM and mounts is one of the most important subsystems in a vehicle.Under the idle,the design of the CRFM mounting system directly influences on the performance of the NVH(Noise,Vibration,and Harshness)of a whole vehicle.In this paper,the rigid modes of the CRFM mounting system are calculated by the finite element method before CRFM prototype.With the results of the modal analysis for CRFM mounting system,the stiffness and the structure of mounts are improved.The calculation method of isolation ratio for the improved mounts is proposed by basing on the identification method for the excitation forces of CRFM.The results of isolation ratio for mounts are calculated and measured by the experiment.Through comparing the calculated with the measured isolation ratio for mounts,the calculation method for isolation ratio of mounts is validated.The main contents in this paper are as follow:(1)A modal analysis model for calculating rigid modes in X,Y and Z directions of CRFM mounting system is proposed.The finite element method of calculating the three modes of modal analysis model is developed.Through comparing the calculated with the measured modes resulting from the modal testing of CRFM mounting system,it is indicated that the Y direction modes between the calculated and the measured results have obvious differences.The reason is that the modal analysis model neglects the pipeline in CRFM mounting system.Considering the stiffness of pipeline,an improved modal analysis model for calculating the three modes of CRFM mounting system is presented.The improved modal analysis model is validated by comparing the calculated with the measured three modes of different CRFM mounting systems which change the different stiffness mounts with the same CDFM.(2)With designing nature frequency of CRFM mounting system at the reasonable range,the dynamic stiffness of mounts in X,Y and Z directions are determined by trial and error.As to the rubber mounts,the dynamic stiffness is equal to the dynamic-to-static ratio times static stiffness.By using the static stiffness in Z direction of rubber mounts as design objective,the structure of rubber mounts is optimized with the topology optimization methods.The effectiveness of the designed method for mounts is validated by comparing with the measured acceleration on seat rail in a vehicle installed the original and improved mounts.(3)By assuming a CRFM as a rigid body,an identified method for excitation forces of CRFM is proposed.With the measured accelerations of mounting points at CRFM and body sides in one vehicle(Vehicle B),the excitation forces of CRFM are identified at the idle condition.Another vehicle(Vehicle C)has the same CRFM and powertrain mounting system as that of Vehicle B,but with different body and mount configuration.The identified forces of CRFM are validated by comparing the calculated with the measured accelerations of mounting points at the CRFM side on Vehicle C.(4)A calculation method for isolation ratios of mounts in CRFM mounting system is proposed.Firstly,the accelerations on mounting points at the CRFM side and the body side of Vehicle C are obtained by basing on the identified excitation forces of CRFM of Vehicle B and the measured IPI(Input Point Inertance)at mounting points at the body side of Vehicle C.Then,the results of mounts isolation ratios are estimated by the calculated accelerations of mounting points on Vehicle C.Finally,the calculated isolation ratios of mounts are validated by the experiment and the proposed method for estimating isolation ratios of mounts is verified. |
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