Reduction of Powerplant Vibration Level in the Acceleration Noise Region Based on Analysis of Crankshaft System Behavior 922087

Increased attention has been directed toward noise and vibration characteristics of vehicles in recent years and the performance requirements in this area continue to become more rigorous every year. The acceleration noise in a frequency range of 250 ∼ 800Hz caused by powerplant vibration is important, and there is a need to reduce this noise level. In addition to reducing noise and vibration, however, there is also a growing need to achieve further weight reductions. Consequently, it is essential to reduce the weight of a powerplant without increasing its vibration levels. This make it necessary to predict powerplant vibration characteristics accurately at the planning and design stage so that suitable specifications can be determined.

Specifications for reducing powerplant vibration have traditionally been found by experimentation. However, in powerplant excitation tests it has not been possible to take into consideration the effect of the crankshaft system on powerplant vibration. It has been necessary to determine the final powerplant specifications on the basis of excitation tests conducted on the powerplant under actual operating conditions.

Since this process takes considerable time and manpower, there has been a need to develop analytical techniques that would reduce the amount of labor and man-hours required.

In this work, an analytical method for predicting powerplant vibration phenomenon under actual operating conditions has been developed in order to meet the foregoing requirements for powerplant performance. This method is characterized by two major fueatures.

1. (1)
   By inputting into a finite element model the inertial forces and conbustion forces that act on a powerplant under actual operating conditions, it is possible to predict the vibration level of the powerplant with good accuracy.
2. (2)
   Studies can be carried out simultaneously of the crankshaft system specifications and of the crank bearing stittness and also of the coupling stiffness between the engine and the transaxle.

This analytical model was applied to a study of a powerplant consisting of an in-line 4-cylinder engine and a manual transaxle in a front-wheel-drive configuration. Analysis were made of the behavior of the crankshaft system including the stiffness of the crankshaft bearings and predictions were made of the powerplant vibration level. The results showed that the use of an aluminum oilpan and a flexible flywheel made it possible to discontinue the bearing beam without increading the vibration level. The basic construction was clarified for an in-line 4-cylinder front-wheel-drive engine that achieves low noise and vibration characteristics and also allows weight reductions.