Evaluation of Journal Bearings in Manual Transmissions

Abstract: This thesis work is an evaluation of journal bearings in manual transmissions in automobiles. Today both journal- and needle bearings can be positioned into the gearboxes and in order to reduce the power loss developed by friction when a relative angular velocity arises, the right type of bearing must be chosen. In order to succeed, this work is aimed to develop a Matlab simulation model, which should be used as a tool in the design process of manual transmissions. The program development is later supposed to be followed by real tests of journal bearings, partly to cover things that can not be covered in the model but also to confirm how well the model reflects the reality. The absence of resources resulted in no performed real test and therefore was a comparison between theoretical-  and practical results not possible. Here the plain journal bearings in full film lubrication will have an disadvantage compared to the needle bearings regarding the power lost. To reduce the drag below the values of the needle bearings a modified journal bearing in the area of boundary lubrication with a very low coefficient of friction may be an option. But problems with wear under this condition could most certainly be devastating and must be further investigated with real tests. Out of a efficiency point of view the most suitable bearing position is the gear in the most frequently used area. Here it is assumed to be the 4th gear. A suitable journal bearing design should have a small sliding surface area in order to minimize the viscous drag. To achieve low friction the boundary lubricated area could be a good idea in cases when wear is not a critical factor. To longer the useful life nitrocarburizing is recommended, which both reduces wear and lower the coefficient of friction, in cases of asperites in contact. In order to work under the full film lubricated condition, with neglected wear, the sliding area needs to be large enough to create the required oil pressure.