Karakterisering en evaluering van 'n hidrouliese enjinmonteerstuk

Abstract

The engine mount system is an important aspect to achieve vibration isolation, and has a very important effect on the ride standards and noise in a vehicle's compartment. In this study a hydraulic engine mount was designed and built and two mathematical models were developed. The first mathematical model was used to determane the dynamic properties of the hydraulic engine mount as well as the rubber engine mountings for various frequencies and amplitudes. The dynamic properties were determined in a test assembly that was designed and build for this application. These dynamic properties were used to evaluate the vibration isolation. The second mathematical model was a two degree of freedom model that was developed and implemented in a computer programme in a Matlab environment. This programme was used to predict the natural frequencies for the vertical bounce and rotational mode by using the dynamic properties of the engine mountings. This second model was also used to predict the engine response and dynamic forces transmitted to the vehicle structure with the help of a computer program. The engine unbalance forces and fluctuating moments were determined with the use of certain parameters. The engine mass and the moment of inertia, as well as the coordinates and dynamic properties of the three engine mountings, were also determined and used as input in the computer programme. The predicted engine response was compared with corresponding measured values for the same conditions. The engine mountings must also be able to support the static weight of the engine, with allowable displacement at each mount. The static and dynamic displacement was determined for various operating conditions. Two engine mounting systems were evaluated in the test vehicle. The standard engine mounting system consists of three rubber engine mountings. The modified mounting system has two rubber mounts that were replaced with hydraulic engine mounts. Response measurements were taken on each of the engine mounting systems in the vertical direction respectively. The dynamic forces transmitted to the vehicle structure were determined and compared for the two mounting systems, by using this measured values as well as the mounting dynamic properties for different operational conditions. Sound measurements inside the vehicle cabin were also measured separately for the two mounting systems and compared with each other. This study shows that the hydraulic engine mount has a big improvement on the isolation system, and that the biggest benefit was at road inputs as operational conditions.