## 4 Simulations and Analysis
### Experiment Results and Analysis  
The experiment results are shown in Figure 10, and the indicators are listed in Table 6. The abbreviations are almost the same as the simulations, with the addition of Acc, Brake, TBT, and TDT, which represent acceleration pedal travel, braking pedal travel, total braking torque, and total demanded braking torque, respectively.  
Figure 9: Schematic diagram of HIL experiment setups: (**a**) is the hardware level and (**b**) is the software level.  
Figure 10: Experiment results of the proposed emergency braking control strategy under three track-ground conditions. They are respectively the curves of accelerator pedal and brake pedal travel, vehicle and track speed, braking torque, and the slip ratio of: (**a**) a muddy road; (**b**) snow; (**c**) ice. Acc, Brake, TBT, and TDT represent acceleration pedal travel, braking pedal travel, total braking torque, and total demanded braking torque, respectively.  
Because of the introduction of a real driver and premeditated speed control of tapping pedals, the stopping time and stopping distance in the experiments were longer than those in the simulations to varying degrees. However, the slip ratios deviation of various track-ground conditions in the simulations and experiments were different from each other. As mentioned in Section 3, the emergency braking control strategy was triggered when the brake pedal exceeded a certain value or the slip ratio was higher than a threshold. In the simulations, the emergency braking control strategy was triggered by the brake pedal, so that the slip ratio curve had an ascent stage from zero included in the calculation of D, which made it unfair to compare with the same indicator in the experiments, which was calculated from the slip ratio rising up to 0.15; thus, the slip ratio deviation of the simulations needed to be revised. The amended slip ratio deviation \(D_{a}\) is listed in Table 7.  
As shown in Figure 10, the trigger time of emergency braking was 2.02 s, 2.09 s, and 2.15 s for a muddy road, snow, and ice, respectively. The emergency braking control strategy was triggered by brake pedal travel when braking on a muddy road, while triggered by the slip ratio when braking on snow or ice. We found that the largest deviation of total braking torque with total demanded braking torque occurred at the time when the emergency braking control strategy was triggered, shown in the Zoom 1 of all Panels (a), (b), and (c) of Figure 10, where a sharp increase of total demanded braking torque can be found. The largest braking torque demanded converted to the drive wheel when braking on a muddy road, snow, and ice were nearly 174 kNm, 68 kNm, and 60 kNm, respectively, which were far more than the braking system could provide. This phenomenon was caused by the large difference of the sliding mode \(s_{\mathrm{s}}\) with the desired sliding surface, and most of it was allocated to be provided by the regenerative braking of PMSM according to Section 3.2. The compensating coefficient \(\chi\) was exactly designed to narrow the gap as much as possible in this situation.  
Both the motor torque and slip ratio fluctuated a little more in these experiments compared to in the simulations due to the communication delay and the slower computing speed of the TCU than a PC, and we can also find in the Zoom 2 of Figure 10c that even in the flatter stage, sometimes the PMSM needed to provide a positive torque to trace the demand. The slip ratio deviation in experiment was just slightly larger than in the simulation for a muddy road, and snow and even better for ice due to the smaller overshoot caused by the brake pedal input being more gradual than in the simulations. In conclusion, the proposed emergency braking control strategy can still maintain a good control effect applied in a real TCU and actuated by real driver input.