System Evaluation Method for Two Planetary Gears Hybrid Powertrain under Gray Relational Analysis Based on Fuzzy AHP and Entropy Weight Method 2020-01-0430

Millions of configurations of power-split hybrid powertrain can be generated due to variation in number of planetary-gear sets (PG), difference in number, type and installation location of shift actuators (clutches or brakes), and difference in connection positions of power components. Considering the large number of configurations, complex structures and control modes, it is vital to construct an appropriate multi-index system evaluation method, which directly affects the requirement fulfillment, the time and cost of 2-PG system configuration design. Considering one-sidedness (dynamics and economic performance), simplicity (linear combination of indicators) and subjectivity (relying on expert experience) of previous system evaluation method of 2-PG system design, a more systematic evaluation method is proposed in this paper. The proposed evaluation system consists of five aspects, involving dynamic, economy, comfort, reliability and cost, and more than 20 indexes. To reduce the influence of the different experts' subjective opinions and the one-sidedness of objective data, a comprehensive system evaluation method based on fuzzy analytic hierarchy process (FAHP), entropy weight method (EWM) and grey relational analysis (GRA) is put forward. The consistency of subjective judgment and evaluation results is enhanced by FAHP; the objectivity and rationality are enhanced by EWM based on a large number of sample data; finally, the candidate solutions are obtained and ranked using GRA. The system evaluation method proposed in this paper is applied to a case study of 2-PG system configuration evaluation, and the evaluation results not only give the ranking of candidate solutions, but also give suggestions for improving the design. The evaluation method integrates the advantages of three evaluation methods, the calculation process is simple, and the results are intuitive. It provides a new evaluation method for power-split hybrid system design.