Experimental study and numerical analysis of vacuum thermal characteristics of brush DC motor

Abstract

Brush direct current (DC) motors have several qualities that make them very attractive for space flight applications. Considering the high reliability requirements of aerospace missions, the thermal characteristics and thermal failure of the brush DC motor in the space environment were studied. Using a motor thermal resistance network model, a special thermal test method was determined and combined with a thermal conductivity analysis model, the thermal parameters were obtained via item-by-item stripping, and the motor temperature field was constructed. By introducing the arc discharge factor to evaluate the electric-corrosion heat consumption, the numerical analysis results were in good agreement with the test results under the conditions of stalled rotor, normal rotation, single brush, and multiple brushes. The analysis and test results show that continuous operation for 110 s will lead to melting of the brush solder joints, and electrical corrosion heat consumption is one of the main factors that cannot be ignored. The reliability model of vacuum applications should be established in the normal working mode of at least two brushes in both the positive and negative electrodes. To improve the reliability, a sealed air-filled structure of the motor was proposed, a heat-flow co-simulation model of a continuous medium flow with a large curvature and constant without a gravity field was established, and the temperature and velocity fields under different sealed pressures were obtained. The results show that the temperature of the single brush reduced to below 140 °C from 204.5 °C in vacuum, which can meet the long-term continuous working requirement of high reliability of brush motors in space missions. In addition, it was found that with the decrease in pressure, the effect of convective heat transfer gradually weakens, the temperature gradually increases and converges to the unique heat conduction process of the gas, while the effect of convection is negligible. As the pressure continues to decrease, the sealed gas evolves from continuous medium flow to transitional and free molecular flow, and the heat conduction effect of the gas weakens again until it approaches the singleness solid conduction process.