Design And Performance Study Of Permanent Magnet Slip Clutch In The E-ECHPS

Currently hydraulic power steering system(HPS) has been generally used in heavy vehicles, the assist characteristic of which is fixed, being unable to both guarantee low-speed maneuverability and high-speed stability. Furthermore, the steering pump of HPS keeps working in high rotatonal speed during vehicle running process, causing a large amount of overflow waste. Electric power steering system(EPS) is becoming more and more popular among passenger cars and light commercial vehicles, but it does not apply to heavy vehicles due to the motor power restriction. Electric hydraulic power steering system(EHPS) now is a feasible scheme for improving steering performance of heavy vehicles. On the basis of electromagnetic slip clutch by the research group, this paper proposes a new electric hydraulic power steering system(E-ECHPS) which aims to achieve low energy consumption as well as variable assist characteristic by adopting permanent magnet slip clutch(PMSC) to adjust output power of steering pump. As the core device of system, the permanent magnet slip clutch is studied and designed, which lay foundation for the R&D of E-ECHPS. The main work is as follows:Firstly, the structure and working principle of both E-ECHPS and PMSC is analyzed, then the parabola type assist chacteristic curve of E-ECHPS is designed according to experiment driver preferred steering torque and simulated equivalent steering resistance moment. Torque matching of E-ECHPS steering pump is carried out based on the analysis of pump flow rate characteristic, which give a base for the design and performance verification of PMSC.Secondly, design flow of PMSC is built which borrows the field and circuit combination method of permanent magnet machine. Design requirements and technical parameters of PMSC are confirmed according to relevant parameters of prototype vehicle and E-ECHPS performance. It is modeled and analyzed in Ansoft Maxwell. Mechanical and electromagnetic parameters of PMSC are fixed by means of repeated simulations and modifications. Torque-slip relation of PMSC is analyzed and the effiency is improved by optimizing critical slip. PMSC prototype and slip clutch test system is constructed and experiment results suggest that the prototype performance basically meet the design requirements.Thirdly, external control speed-governing circuit is designed on the basis of DC chopping principle and IGBT is used as switching device. During high load and low load speed-governing simulation, the circuit functions well, in addition, it responds quickly. External control circuit is developed to carry out speed-governing experiment. The relation between PMSC prototype speed and duty cycle of IGBT tallies with speed-governing simulation results.Lastly, this paper makes caculations of energy consumption of PMSC in straight running and steering conditons at typical vehicle speed. The comparison results verifies good energy saving potential of PMSC, which lay a solid foundation for further research of energy recovery of E-ECHPS.