الفهرس 
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Abstract
An essential component of a manually operated vehicle transmission is the synchronizer. Synchronizer has the task of minimizing the speed difference between the shifted gearwheel and the shaft by means of frictional torque before engaging the gear. Proper operation requires a sufficiently high coefficient of friction. It is common practice to investigate the friction and wear behavior under various loading conditions on test rig or in vehicle tests. An optimized design of the system with regard to appropriate function and durability on the one hand as well as low cost, low mass and compact over all dimensions on the other hand requires eX1ensive testing.
A major German car manufactures apply in motor vehicle transmission synchronizations with a friction pairing molybdenum (cone) / steel (sliding sleeve, hollow cone). In order to save production costs, a finishing of the sprayed coating by a grinding process was omitted, but after a number of shifting, an unacceptable DROP in the coefficient of friction was noted.
The characteristic of the coefficient of friction is affected by the structure of the tribosystem. The goal of this investigation is to determine the dependence of the coefficient of friction behavior on the surface finish for two different tribosystems.
Two different surfaces finish for coated molybdenum synchronizer cones with experimental geometry were tested. During the long-term tests \\ith three different sliding speeds. The measurements of surface topography after different numbers of shifts were carried out. The friction characteristics were monitored continuously.
The results obtained in this study showed that: -
The increase of the increase of the initial sliding velocity tends to decrease coefficient of friction due to the occurrence of hydrodynamic effect for not ground cones. However, the coefficient of friction increases with the increase of the initial sliding velocity as a result of the occurrence of the hydrodynamic effect for ground cones.
Quantitatively, increases of initial velocity to 12 rn/s cause a remarkable increase of the coefficient of friction to a maximum value of 0.3 where a complete damage of the cone surface takes place. As for the surface topography, there are significant changes ground surfaces become rougher since the not ground cones became smoother.
The effect of oil drainage system on the coefficient of friction is significant. For 8xl mm the distribution of the oil slots with 1 mm width around the cone contact surface caused
significant decrease of the coefficient of friction compared to oil drainage system Ix8mm.
The surface fmish in additions to the initial sliding velocity affected the (minimum coefficient of friction! maximum coefficient of friction) ratio. This ratio was higher for not ground surfaces while lower for ground surfaces. A Comparison of surface topography and friction characteristics (flmin/flmax ratio) after running-in shows:
There are better long term friction characteristics that mean less steep friction increase during one shift, with the rougher ”not ground” surfaces.
The best correlation exists with Abbott curves as a whole or the central roughness depths sRk and sPk.