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Page 12 of 15 Cui et al. Complex Eng Syst 2023;3:3 I http://dx.doi.org/10.20517/ces.2022.57

Figure 5. Step response Bode diagram of steering road feel.

the information from the 0-40 Hz range of the road surface can be transmitted to the driver better.

TheBodediagramofthesteeringsensibilitystepresponseisshowninFigure6. AlthoughtheNSGA-IIwithCO
method does not obtain the least steering sensibility, the optimization result obtained is still greatly improved
compared to that before optimization.

Therefore, it could be concluded that multi-objective collaborative optimization can improve the steering road
feel and reduce the steering sensitivity while improving the economy of the steering system. At the same
time, the collaborative optimization of NSGA-II with CO has better solution sets diversity and comprehensive
optimization results.

4. CONCLUSIONS
(1) On the basis of the EHPS system dynamics model and energy flow analysis, the evaluation index formula
of the steering system is derived for the first time, including steering road feel, steering sensibility, and steering
energy loss. In addition, considering the coupling relationship between subsystems, a multi-objective collabo-
rative optimization model is established to achieve parallel computing.

(2) The multi-objective collaborative optimization further improves the performance of the EHPS system com-
pared with the multi-objective optimization. Besides, the NSGA-II algorithm shows the best comprehensive
performance in optimizing the design parameters of the EHPS system in the comparison of CO combing with
multi-objective algorithms.

(3) The optimization results show that the EHPS system is optimized successfully and multiple evaluation in-