Design Methods Of The Powertrain Mounting System Based On Vibration Control Of Vehicle Level

Noise, Vibration and Harshness(NVH) are one of the main attributes in a passenger car. One of the key subsystems contributes for NVH behavior of a car is the Powertrain Mounting System(PMS).In most studies for PMS so far, design requirements are based on six natural frequencies and mode energies of the powertrain rigid mode. However, the customers of a passenger car perceive vibration and noise usually at the cabin where the vibrations at seat track or steering wheel and the noise at ear side. Compared with four- and six-cylinder engines, excitation forces and moments of a three-cylinder engine are more complex, vibration and noise at the cabin in a vehicle with a three-cylinder engine is much worse. So How to select the mount locations, stiffness and damping to meet the requirement of vibration and noise at the cabin is a challenge task for the PMS design engineers.The main work in the thesis are as follows:1. Identification and verification methods of excitation forces and moments of a powertrain are proposed. A design of experiment(DOE) is used to analyze robustness for excitation forces identification. The variations of powertrain mass and moments of inertia, mount stiffness and locations, amplitude and phase of mount accelerations are calculated to disclose the influences on the identification results.2. The design and analytical methods for a PMS with a three-cylinder engine are established. The excitation forces and moments of a three-cylinder engine are derived firstly, the derivation results are compared with the four- and six-cylinder engines. Then engine excitation forces of a three-cylinder engine and mount dynamic reaction forces with or without balance measures are calculated. Thirdly, an optimization method is proposed to estimate mount stiffness and orientations based on minimization of mount forces transmitted to the car body or sub-frame, along with meeting requirements for placing natural frequencies of the powertrain in prescribed ranges and those for maximizing modal energy distributions of the powertrain in six directions.3. 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. Firstly, the design target for a PMS with regard to vibration and noise limitations of vehicle level contributed from mounts is described. Then a vehicle model with 13 DOFs is proposed, which includes 6 DOFs for the powertrain, 3 DOFs for the car body and 4 DOFs for four unsprung mass, and the dynamic equation for the model is derived. Then the natural frequencies and mode energies for the powertrain are calculated using different models and the results are compared and analyzed. 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.