**6. Hardware-in-the-Loop Experimental Validation**

Taking the need for more facilities, time requirements and test yard support into account as well as the risk of losing stability while carrying out the double-lane-change test in actual vehicle experiments, a hardware-in-the-loop simulation experiment is selected to replace real vehicle testing and validate the control effect of the DDAS control strategy proposed in this paper. The testing platform of the driving simulator as shown in Figure 13 is composed of a host computer, G29 driving simulator with steering wheel angle/torque sensor and dSPACE 1103 hardware running the vehicle model.

**Figure 13.** Testing simulator platform based on dSPACE hardware.

The driver-in-the-loop experiment selects a double-lane-change test case, with a target constant-speed 40 km/h and a uniform road adhesion coefficient 0.85. The experimental results are shown in Figure 14.

**Figure 14.** Simulator experiment results: (**a**) Steering wheel angle; (**b**) Steering wheel torque; (**c**) Wheel torque of ADRC controller; (**d**) Yaw rate.

It can be seen from Figure 14a that the steering wheel angle input of the drivers in three experimental cases with different controller of DDAS system or without any power steering control are similar. Figure 14b shows that DDAS has achieved very good power steering assistance effect using both the PID controller and the ADRC controller. The peak value of the steering wheel torque is reduced from 7 Nm in the case of having no any power steering to 4 Nm in the case of having the DDAS system, a reduction rate of about 43%, and the assistance effect is obvious. Moreover, when the ADRC controller is used, the steering wheel torque fluctuation is much smaller and smoother. The disturbance estimation compensator of the ADRC controller provides a compensation function for the possible disturbance from inside or outside of the steering system, thereby effectively improving the control effect of the differential drive assist steering system. The comparison result indicates that the ADRC controller is more robust when facing possible steering wheel torque or angular sensor noise, thus achieving a better road feeling for the driver than the PID controller. As shown in Figure 14d, when DDAS is applied, it is interesting that the yaw rate of the vehicle is increased, but the steering wheel angle input of the driver in this process also increases.
