# Research on Hierarchical Control Strategy of Automatic Emergency Braking System

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## Abstract

**:**

## 1. Introduction

## 2. Vehicle Dynamics System Modeling

#### 2.1. Software Overview

#### 2.2. Establishment of Vehicle Dynamics Model

#### 2.3. Establishment of Vehicle Inverse Dynamics Model

#### 2.3.1. Switching Control Strategy of Inverse Dynamics Model

#### 2.3.2. Throttle Opening Inverse Dynamics Control Model

#### 2.3.3. Inverse Dynamic Model of Brake Pressure

## 3. Research on AEB System Control Strategy

#### 3.1. AEB System Algorithm

#### 3.2. Algorithm of Upper Fuzzy Control System

#### 3.2.1. Upper TTC Control Logic

#### 3.2.2. Upper Fuzzy Control System

#### 3.3. Lower PID Control

#### 3.3.1. Throttle Opening PID Control

#### 3.3.2. Brake System Pressure PID Control

## 4. Simulation Results and Analysis

#### 4.1. CCRs Test

^{2}. The deceleration is stable at about −0.4 m/s

^{2}in 1.3 s to 2.7 s. As the real-time distance between the two vehicles decreases, the collision risk level increases. In 2.7 s, the TTC value calculated by the AEB system is less than the secondary braking threshold. After receiving the secondary braking request, the braking system brakes, so that the vehicle acceleration rises to −0.8 m/s

^{2}. Finally, the self-vehicle stops at a distance of 2.22 m from the target vehicle, avoiding the occurrence of collision.

#### 4.2. CCRm Test

^{2}. In 4.4 s, the speed of the self-vehicle is equal to that of the target vehicle. The TTC value calculated by the vehicle is greater than the threshold set by the system. The AEB system issues an instruction to stop braking and restore the normal driving state of the self-vehicle. Under this condition, the nearest distance between the vehicles is 2.11 m.

^{2}, but due to the ground adhesion limit it will produce shock, resulting in unstable deceleration, even more than −0.4 m/s

^{2}. After 4.4 s of simulation time, the actual deceleration oscillation was due to the fluctuation in self-vehicle deceleration detected by the sensor due to the braking of the self-vehicle. In general, the simulation results show that the designed control strategy can effectively avoid collision under the condition of being close to the uniform braking target vehicle.

#### 4.3. CCRb Test

^{2}, as the simulation progresses, the relative distance between the two vehicles gradually decreases. The distance between the two vehicles reaches the minimum value at 6.8 s, and then the relative distance between the two vehicles remains unchanged at 1.56 m.

^{2}. At 5.6 s, the TTC value reaches the secondary braking threshold. At this time, the vehicle performs full braking, and the braking deceleration is close to −0.8 m/s

^{2}until the vehicle stops moving. At this time, the distance between the self-vehicle and the target vehicle is 1.56 m, which proves that under this condition, this algorithm can ensure that the vehicle does not collide. In this condition, the braking time of the vehicle with primary braking deceleration is shorter. This is because the distance between the self-vehicle and the target vehicle is relatively close, and the front vehicle brakes at a deceleration of −4 m/s

^{2}, resulting in the calculated TTC value rapidly falling to the secondary braking TTC threshold. The AEB system quickly sends out the secondary braking deceleration signal, and the vehicle performs emergency braking.

^{2}from 50 km/h, and the shortest distance between the two vehicles is 1.23 m. When the self-vehicle is close to the target vehicle at 12 m ahead at a relative speed of 50 km/h, the target vehicle slows down at a speed of −6 m/s

^{2}from 50 km/h, and the shortest distance between the two vehicles is 1.56 m. When the self-vehicle is close to the target vehicle at 12 m ahead at a relative speed of 50 km/h, the target vehicle slows down at a speed of −2 m/s

^{2}from 50 km/h, and the shortest distance between the two vehicles is 1.05 m. When the self-vehicle is close to the target vehicle at 40 m ahead at a relative speed of 50 km/h, the target vehicle slows down at a speed of −6 m/s

^{2}from 50 km/h, and the shortest distance between the two vehicles is 1.07 m.

## 5. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

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Vehicle Parameters | Value | Vehicle Parameters | Value |
---|---|---|---|

Complete vehicle kerb mass/kg | 1615 | Main reducer reduction ratio | 3.48 |

Air resistance coefficient | 0.32 | Tire rolling radius/m | 0.36 |

Windward area/m^{2} | 2.73 | Transmission efficiency of transmission system | 0.9 |

Rolling resistance coefficient | 0.02 | Brake disc mass/kg | 9.65 |

**Table 2.**Collision avoidance probability under dual variables of braking strength and TTC threshold.

Brake Deceleration | Probability of Collision Avoidance at Different Times | Mean Value | |||
---|---|---|---|---|---|

5% | 25% | 75% | 95% | ||

0.5 g | 0.2 s | 0.6 s | 0.5 g | 0.2 s | 0.6 s |

0.675 g | 0.15 s | 0.5 s | 0.675 g | 0.15 s | 0.5 s |

0.85 g | 0.1 s | 0.4 s | 0.85 g | 0.1 s | 0.4 s |

Early Warning Types | Average Value | Standard Deviation | µ | σ^{2} | 75% | 85% | 90% |
---|---|---|---|---|---|---|---|

Image warning | 1.13 | 0.52 | 1.03 | 0.44 | 1.38 | 1.62 | 1.80 |

Sound warning | 0.99 | 0.44 | 0.90 | 0.43 | 1.20 | 1.40 | 1.55 |

Image and sound | 0.90 | 0.34 | 0.84 | 0.37 | 1.08 | 1.23 | 1.34 |

$\mathbf{\Delta}\mathit{s}$ | $\mathbf{\Delta}\mathit{V}$ | a | $\mathbf{\Delta}\mathit{s}$ | $\mathbf{\Delta}\mathit{V}$ | a |
---|---|---|---|---|---|

Z0 | Z0 | N2 | P4 | N4 | N1 |

Z0 | N10 | N7 | P4 | N6 | N2 |

P1 | N1 | Z0 | P5 | N5 | Z0 |

P1 | N9 | N7 | P5 | N5 | N1 |

P2 | N2 | N1 | P6 | N6 | N1 |

P2 | N8 | N6 | P6 | N4 | Z0 |

P3 | N3 | N1 | P7 | N7 | N1 |

P3 | N7 | N4 | P7 | N3 | Z0 |

Initial Self- Driving Speed/(km/h) | Self-Driving Movement State | Distance between Two Vehicles/m | Initial Speed of Target Vehicle/(km/h) | Target Vehicle Movement State |
---|---|---|---|---|

50 | Uniform velocity | 40 | 0 | Static |

Initial Self- Driving Speed/(km/h) | Self-Driving Movement State | Distance between Two Vehicles/m | Initial Speed of Target Vehicle/(km/h) | Target Vehicle Movement State |
---|---|---|---|---|

50 | Uniform velocity | 40 | 30 | Uniform velocity |

Initial Self-Driving Speed/(km/h) | Self-Driving Movement State | Distance between Two Vehicles/m | Initial Speed of Target Vehicle/(km/h) | Target Vehicle Movement State |
---|---|---|---|---|

50 | Uniform velocity | 12 | 50 | Slows down at $-4{\mathrm{m}/\mathrm{s}}^{2}$ after a constant speed of 4 s |

Self-Driving Speed (km/h) | Target Vehicle Speed (km/h) | Initial Distance (m) | Target Vehicle Deceleration (m/s ^{2}) | Minimum Distance (m) |
---|---|---|---|---|

10 | 0 | 12 | 0 | 3.41 |

50 | 0 | 40 | 0 | 2.22 |

30 | 20 | 12 | 0 | 2.95 |

50 | 50 | 50 | −2 | 1.23 |

50 | 50 | 12 | −6 | 1.56 |

50 | 50 | 12 | −2 | 1.05 |

50 | 50 | 40 | −6 | 1.07 |

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## Share and Cite

**MDPI and ACS Style**

Wang, Z.; Zang, L.; Jiao, J.; Mao, Y.
Research on Hierarchical Control Strategy of Automatic Emergency Braking System. *World Electr. Veh. J.* **2023**, *14*, 97.
https://doi.org/10.3390/wevj14040097

**AMA Style**

Wang Z, Zang L, Jiao J, Mao Y.
Research on Hierarchical Control Strategy of Automatic Emergency Braking System. *World Electric Vehicle Journal*. 2023; 14(4):97.
https://doi.org/10.3390/wevj14040097

**Chicago/Turabian Style**

Wang, Zhi, Liguo Zang, Jing Jiao, and Yulin Mao.
2023. "Research on Hierarchical Control Strategy of Automatic Emergency Braking System" *World Electric Vehicle Journal* 14, no. 4: 97.
https://doi.org/10.3390/wevj14040097