## 5 Simulations Results and Analysis
### Results of Switch Control Strategy
#### 5.2.2 Fishhook Maneuver  
The fishhook maneuver is applied to demonstrate the proposed switch control strategy of the hydro-pneumatic suspension, and the vehicle steering angle under the fishhook maneuver is shown in Figure 22b. The random road shown in Figure 21a and the bump road displayed in Figure 23a are used as the road input of simulation, respectively.  
Figure 21: The rescue vehicle dynamic response based on the switch strategy under the bump road condition and the J-turn maneuver: (**a**) the vehicle body vertical acceleration in time domain; (**b**) the roll angle acceleration in time domain; (**c**) the vehicle body vertical acceleration in time domain in frequency domain; (**d**) the roll angle acceleration in frequency domain; (**e**) the switch value; (**f**) the LTR.  
The dynamic responses of the HDSMC-controlled vehicle (blue lines), RCSMC-controlled vehicle (black lines), and the vehicle with the Switched SMC (red lines) are shown in Figure 23.  
Figure 23: Cont.  
Figure 22: The input signals of vehicle: (**a**) the random road; (**b**) the steering angle under the fishhook maneuver.  
Once the fishhook steering maneuver is exerted at the 5 th second in Figure 22b, the value of LTR goes up rapidly and reaches 0.8 at the 5.8 th s, and then the controller is switched to drag the LTR to the set value. Until the 9 th s, the value of LTR is reduced to less than the set value. Then the controller is switched to pursue the ride comfort of the vehicle. The switch actions are obvious, which can be observed and proved in Figure 23e. The steering angle changes rapidly in the opposite direction in the time rage of [9.4] s, but the value of LTR does not rise to the set value, and the control mode does not switch. It is easy to see that the roll angle and the LTR of the vehicle with the Switched SMC become bad and move toward the value of the RCSMC-controlled vehicle, because the Switched SMC has been pursuing the ride comfort when the vehicle is not in danger from the 9 th s. The mutation points II and III in Figure 23a are caused by the switch action, and the mutation points I, IV, and V are induced by the steering actions. From the frequency domain response of curves shown in Figure 23c,d, the same conclusion can be reached that the Switched SMC can simultaneously improve the ride comfort and handling stability under this condition compared with the conventional SMC controlled suspension.  
The rescue vehicle dynamic responses based on the switch strategy under the bump road and the fishhook maneuver (Figure 24) are shown in Figure 25. Similarly, the analysis results are the same as those in Figure 23, and the switch actions of the Switched SMC come true according to LTR value.  
Figure 23: The rescue vehicle dynamic response based on the switch strategy under the bump road and the fishhook maneuver: (**a**) the vehicle body vertical acceleration in time domain; (**b**) the roll angle acceleration in time domain; (**c**) the vehicle body vertical acceleration in time domain in frequency domain; (**d**) the roll angle acceleration in frequency domain; (**e**) the switch value; (**f**) the LTR.  
Based on the analysis of simulation results mentioned above, it is concluded that (1) the PACSA performs better than GA in terms of the parameters optimization of the SMC; (2) the switch strategy proposed in this paper is all effective under different vehicle speeds, road inputs, and the steering modes.  
Figure 25: The rescue vehicle dynamic response based on the switch strategy under the bump road and the fishhook maneuver: (**a**) the vehicle body vertical acceleration in time domain; (**b**) the roll angle acceleration in time domain; (**c**) the vehicle body vertical acceleration in time domain in frequency domain; (**d**) the roll angle acceleration in frequency domain; (**e**) the switch value; (**f**) the LTR.