Mathematical Background of U-joint Repair

Abstract The universal joint – U-joint is type of mechanical coupling which consists of two shaft yokes connected with cross. The cross arms rides inside four needle bearings pressed into the yokes bores. With good lubrication and sealing, the life of U-joint is determined by material fatigue after more than million reversals. However, U-joint often does not achieve its predicted (calculated) fatigue life. When the lubrication is inappropriate and/or the sealing is not efficient enough, the U-joint service life is limited by the corrosion and wear. As U-joint loses its operational ability due to intensive wear it has to be replaced by a new one or to be repaired. The U-joint repair implies additional machining of worn out needle bearing parts. Therefore, dimensions are changed and entire needle bearing internal geometry is changed, as well. The internal geometry affects dynamics and load carrying capacity of the needle bearing, and appropriate geometrical and mathematical relations, primarily based on limited radial and circular internal clearance, must not be disturbed by repair process. Hence, it is necessary to establish a mathematical model of the needle bearing internal geometry and the corresponding algorithm for determining appropriate dimensions and it was carried out in this paper. This is the basis for further mathematical modelling of U-joint needle bearing dimensions, mechanical behaviour and load distribution, in order to optimize the geometry and increasing load carrying capacity.