相对转速对湿式多片离合器磨合过程摩擦磨损特性的影响

The running-in process of the freshly manufactured friction components was of great significance to extend the service life of friction components and ensure the stable clutch operation. The effect of rotational speed on the friction and wear properties of the friction components was investigated in a wet multi-disc clutch. Based on actual speed range of the transmission, the running-in experiments of friction components were performed via the SAE#2 clutch tester. The friction discs and separator plates were made of copper-based powder metallurgy and 30CrMnSiA, respectively. The running-in evolutionary process was explored in terms of two aspects: the global friction performance and the instantaneous friction characteristics. Moreover, the friction surfaces before and after experiments were obtained to investigate the micro-morphology characteristics and wear mechanism by a metallurgical microscope. The main conclusions were as follows. The maximum values of the average friction torque and the average friction coefficient showed up at the beginning of the running-in process. Simultaneously, the maximum value of the average friction coefficient decreased with the increase of the rotational speed. At the early running-in process, the average friction coefficient gradually decreased and the corresponding decrease rate was reduced by increasing of the rotational speed; however, the average friction torque barely changed. Under the low rotational speed conditions, the average friction coefficient presented a downward trend and the fluctuation range was extremely large; on the contrary, under the high rotational speed conditions, the average friction coefficient showed an upward trend and the fluctuation range gradually became narrow. Additionally, the running-in process could be divided into two stages: the interface matching stage and the plastic deformation stage. Under low rotational speed conditions, the asperities were severely sheared due to the large contact pressure in the interface matching stage. As the rotational speed goes up, the increasing oil film reduced the actual contact pressure of asperities, which resulted in the decrease of asperities spalling; the asperities undergone progressive shearing along with elastic-plastic deformation throughout the entire running-in process. It should be highlighted that increasing the rotational speed would not prolong the interface matching stage, but could obtain a smooth friction surface. Accordingly, the fluctuation range of instantaneous friction was reduced during the clutch engagement process. Nevertheless, when the rotational speed was high enough, a dramatic temperature rise on the friction interface occurred, which changed the friction status and brought about the thermoplastic deformation. Therefore, the instantaneous friction fluctuation became more and more severe with the increase of clutch engagement cycles. This work not only extended our knowledge for the evolution of the running-in process of a wet multi-disc clutch, but also provided theoretical guidance to select an optimal running-in rotational speed.