1.1Purpose and significance

In recent years, with the vigorousdevelopment of the automotive electronics industry, people have put forwardhigher requirements for driving safety, handling experience and riding comfortof automobiles. According to statistics, there were morethan 210,000 road traffic safety accidents in 2011 in the country, with morethan 60,000 deaths, ranking the first in the world^[1]. Brakeperformance failure is the main factor causing traffic accidents other thanhuman factors. In the "Car Factors Ranking","security" has surpassed "price". It can be seen that increasing thestability of the car during braking can significantly reduce the probability oftraffic accidents, which is of great significance.

The development of braking technology putsforward a higher level of requirements on the performance of the brakingsystem. The electronic control technology with complete functions, simplestructure, and high efficiency and energy saving has emerged as a result^[2]. "Electroniccontrol" means electronic control and uses information instead of theoriginal mechanical and hydraulic transmission signals.In addition to thechanges in the way of connection, the electronic control technology is moreimportant than the change in the mechanism and operating methods^[3].Electroniccontrol technology can not only solve the complex and slow response oftraditional automotive pipelines, but also contribute to environmentalprotection and energy conservation. It can be foreseen that with the promotionof electronic control technology, the integrated chassis integrated controltechnology will become the focus of new technology research，and can significantlyimprove vehicle safety, handling stability and fuel economy.

This background also affects thedevelopment of smart unmanned vehicles. The intelligent unmanned vehicle is anintegrated system integrating environmental awareness, planning anddecision-making, and multi-level assisted driving. It make full use of computers, modernsensing, information fusion, wireless communications, artificial intelligence,and automatic control technologies is a typical high-tech complex. Inrecent years, intelligent driverless cars have become a hot topic in the fieldof vehicle engineering research in the world and a new driving force for thegrowth of the automotive industry. Many developed countries have incorporatedthem into key development fields.

The control system of smartcars is divided into an upper level planning system and a bottom level controlsystem. The upper level system mainly performs tasks such as collectinginformation, analyzing plans, and sending instructions, while the underlyingcontrol system directly controls the vehicles^[4]. Thispaper hopes to optimize the efficiency of the algorithm in the upper planningsystem of the braking system; in the underlying control system of the brakingsystem, a highly stable and highly reliable mechanical structure is designed toensure the braking safety and braking performance of the smart car.

1.2 analysis of foreignresearch status:

Theteam of Yoichi Hori of the University of Tokyo in Japan conducted extensiveresearch on the “UOT Electric March II” electric vehicle developed by him^[5].Yinand Hori control the drive slip ratio, estimate the maximum effective drivetorque of the wheel based on the tire dynamics, and apply the model-basedcontrol method and the drive slip rate optimization control method to achievethe drive slip control. Sakai mainly studied the precise control ofthe wheel speed, and based on this, studied steering stability control andcoupling control of regenerative braking and hydraulic braking in the anti-lockbraking process^[6]. Research shows that the rapid response ofthe motor and precise torque control can improve the instantaneous dynamiccharacteristics of the anti-lock control, thereby shortening the emergencybraking distance. Sakai studied the distribution of brakingforce in the steering process to reduce the tire working load as an evaluationindex. The proposed allocation method is not much different from the resultobtained by adopting the optimized allocation method, but it reduces the amountof calculation^[7].

HiroshiFujimoto of the University of Tokyo conducted an in-depth study on the dynamicstability control of two-wheeled distributed drive vehicles^[8]. Avehicle speed observation method and a wheel slip ratio control method based onthis are proposed for distributed driving vehicles. Farzad Tahami of Jovain Motor Company ofIran used the fuzzy logic control method to calculate the active yaw moment,and the nominal yaw rate was trained by using neural network method with theexisting data. The effectiveness of the method wasverified by single-line shifting, J-turn, and off-road braking conditions^[9].

Rosenbergerof Germany studied the damping of vibrations in a composite braking process bymotor torque^[10]. A control method based on “dynamicslippage” of the hub motor is proposed, and it is proposed that due to thestiffness-damping characteristics of the power train, the torque output fromthe motor will generate torsional vibration during the action on the tire. In therealization of ABS, the hydraulic braking force is maintained at a stablelevel, and the slip ratio of the tire is adjusted by the feedback brakingfluctuation^[11].