Study on two-stage mounting systems having distributed intermediate mass
The design logic and calculation method for determining mount stiffness and damping for a Powertrain Mounting System (PMS) based on reductions of vehicle vibration and noise contributed by mounts is proposed in this paper. Firstly, the design target for a PMS with regard to vibration and noise limitations of vehicle level contributed form mounts is described. Then a vehicle model with 13 Degree of Freedoms (DOFs) is proposed, which includes 6DOFs for the powertrain, 3 DOFs for the car body and 4DOFs for the four unsprung mass, and the dynamic equation for the model is derived. Some widely used models, such as the 6 DOFs model of the powertrain for the design calculation of a PMS, the 7 DOFs model (Body’s 3 DOFs; unsprung mass’s 4 DOFs) and the 9 DOFs model (powertrain’s 6 DOFs; Body’s 3 DOFs) for ride analysis of a vehicle, are the specific cases of the presented model of 13 DOF. Thirdly, the calculation method for obtaining the vibration of seat track and evaluation point and the noise at driver right ear is presented based on the mount forces and the vibration and noise transfer functions. An optimization process is proposed to get the mount stiffness and damping based on minimization of vehicle vibration and noise, and the optimized stiffness is validated by comparing the calculated vibration and noise and limitations. In the end of this paper, the natural frequencies and mode energies for the powertrain, the body and the unsprung mass are calculated using different models and the results are compared and analyzed.
Nowadays, two-stage ballast mounting system having integral intermediate mass is widely applied and researched to attenuate vibration of marine machinery equipment, while two stage mounting system having distributed intermediate mass which has the feature of lightweight and installation dimension is rarely used and studied. The theoretical models of two types of mounting systems are set up and force transmissibility rate of the two mounting systems are deduced through four-pole parameters method. A scale experimental prototype is established to test the isolation efficiency of the two-stage mounting system having distributed intermediate mass. FEMs of the two systems are established to make a comparison ascertaining the difference between the two about vibration isolation efficiency at the different frequency. The result shows that two stage mounting system having distributed intermediate mass achieve better vibration isolation efficiency and take less space than two-stage mounting system having integral intermediate mass if with equivalent intermediate mass. Two-stage mounting system having distributed intermediate mass can meet the requirements of practical projects and provides a new way for engineer to refer to when meet with machinery equipment vibration problems.
Keywords: two-stage mounting system, distributed intermediate mass, integral intermediate mass.
In many segments of industry the trend in the past few years has been towards more complex equipment and machines, which are lighter and more compact than their predecessors and which operate at greater speeds and power ratings. To the vibration engineer this trend has meant more problems associated with vibration isolation problems: i.e., more excitation available and more components likely to be affected adversely by them so that it has become increasingly important to provide vibration isolation systems that will retain their effectiveness [1, 2]. Machinery ground mounting system is one of the most significant vibration and noise attenuation technology of mechanical equipment [3-5].
It has been extensively believed that the intermediate mass of two-stage double pole mounting system would be better to improve isolation efficiency than one-stage mounting system [6, 7]. At present, two-stage mounting system having frame structure intermediate mass like raft mounting system is widely used in the field of naval vessels which have been gaining widespread attention. In practical application, the intermediate mass usually takes amount of 20-30 % of the isolated mass , but in special cases where dimensions and weight are strictly limited, this way may not be suitable. Thus, the other Machinery mounting system that is two-stage mounting system having distributed intermediate mass which takes less space would play a more important role in the field of vibration noise controlling.
The simplified theoretical and finite element model of the two kinds of two-stage mounting systems are analysed in the paper. The equation of two kinds of mounting systems’ isolation effectiveness expressed by transmissibility were deduced through four-pole parameter method. A comparison between the Single Pole Mounting System to ascertain the difference about vibration isolation efficiency at different specific frequency through FEM model analysis was made. A scale experimental platform was established to test the isolation efficiency of the two-stage mounting system having distributed intermediate mass.