A Novel Semi-active Magnetorheological Bushing Design for Variable Displacement Engines

Abstract

This study introduces the concept of smart materials, namely magnetorheological (MR) fluids, to the design of automotive engine isolation systems. Hydraulic bushings and mounts are widely used in the automobile industry to isolate the engine and chassis from each other. The simplicity and low cost associated with these types of bushing, in addition to their dual frequency response characteristics, are the main reasons for their industrial popularity. Recently with the introduction of variable displacement engines (VDE), the conventional bushings have reached their performance limits. A more versatile isolator is therefore required to handle the additional vibration and disturbances in VDE, associated with the change in the engine displacement whenever the automobile does not use its full displacement capacity for maintaining the desired speed. The realization is that the appropriate isolator should be half as stiff in the operating frequency range of the three cylinder mode of the engine. In addition, in the full cylinder mode the isolator must maintain the performance levels comparable to existing conventional products. This study introduces a cost-effective semi-active bushing for the VDE isolation problem. After a study of the VDE systems, different modes of engine performances in those systems are discussed, and the ideal isolator features for this type of engine are identified. The hydraulic bushing frequency response is then obtained experimentally. Based on the experimental results, a simple semi-active bushing proof-of-concept design is developed and tested, which utilizes a short inertia track to satisfy the soft isolator requirement in VDE mode. A mathematical model of the semi-active system is generated, and its validity is verified experimentally. The damping requirement of this semi-active isolator is produced by utilizing a MR compliance chamber. This innovative solution reduces the amount of expensive MR fluid requirements of the bushing. The experimental results on the semi-active bushing system, using a magnetic shaker, show the merit of the system for the VDE application.