Active Braking Control And Application Of Brake-By-Wire System For Intelligent Vehicle

Intelligentization is an important means to deal with automobile safety problems,and it is an inevitable trend in the evolution of automobile industry.The braking system is the motion control layer of the intelligent vehicle.The execution effect of the braking system will affect the real-time and accuracy of the smart car when complete the instructions of the decision-making planning layer and the control layer.It is the key to the safe and stable running of the vehicle.In order to respond to the target command in time and reliably,the braking system needs to realize the rapid change and accurate adjustment of braking force.However,the traditional vacuum assisted braking system is limited by its structure and working mechanism,and it is hard to realize fast active braking,hold brake pressure for a long time,and meet the brake redundancy requirements of the smart cars when the brake system fails.It is difficult to obtain more accurate actual wheel cylinder pressure feedback for effective closed-loop control of the actuator to achieve accurate regulation of wheel cylinder pressure;Moreover,with the increase of braking demand of smart cars,it is easy to get into troubles such as function redundancy,processor resource waste and control target conflict.To address the issues mentioned above,this thesis depends on the university-enterprise cooperation project,takes the electric vehicle equipped with the combined e Booster and ESC Brake-By-Wire system as the research object,and carries out research on the active braking technology of the Brake-By-Wire system.The model of active braking control strategy is established and verified by off-line simulation and real vehicle test.The results show that the proposed active braking system can respond to intelligent vehicle instructions accurately and in real time under various working conditions.And the experiment results of BAS pass the EU ECE regulations R13 H by third party certification.The researches in this article includes the following parts:The First part,in the light of the dynamic property of Brake-By-Wire system,the estimation algorithms of circuit pressure and wheel cylinder pressure based on PV characteristics are established.Establish mathematical models of key components such as brushed DC motors,oil return pumps,accumulators,check valves and solenoid valves,calculate the brake fluid flow via the circuit through the check valve,isolation valve and return pump,and estimate the circuit pressure based on the circuit's PV characteristics determined by the opening of the inlet valve in the hydraulic circuit.Taking the estimated value of the brake circuit pressure as input,the brake fluid flow via the wheel cylinder through the check valve,the inlet valve and the outlet valve are calculated by the Bernoulli equation,and the wheel cylinder pressure is estimated based on the PV characteristic of the wheel cylinder.The second part,based on the dynamic feature of the actuator and estimated pressure value,a wheel cylinder pressure control algorithm coordinated by e Booster and ESC is developed.Establish mathematical models of key components such as PMSM,inverter,planetary reducer and ball screw,create double closed-loop control algorithm to achieve the target speed of PMSM by speed outer loop and current inner loop,design target speed calculation method based on pressure loop and position loop.The control algorithm of e Booster as the actuator to control the circuit pressure is realized.According to the properties of solenoid valve and the pump,and combined with the estimation results of circuit pressure,the control algorithm of ESC as actuator to control circuit pressure is realized.On the base of the wheel cylinder pressure estimation result,the effective closed-loop control of the actuator is carried out to achieve the accurate adjustment of the wheel cylinder pressure.The third part,the vehicle dynamic feature model is constructed,and the estimation methods of key state parameters such as vehicle mass,road slope and adhesion slope for engineering practice is proposed.The foundation is lay for the formulation of the control strategy of the active braking system.The real-time estimation of road slope is realized by using longitudinal acceleration signal and Kalman filtering technology.According to the driving force,longitudinal acceleration,vehicle speed and estimated pressure,the suitable driving conditions were selected,and the online mass estimation was realized based on recursive least square method.The utilization adhesion coefficient was estimated based on the extended state observer,and the peak adhesion coefficient was estimated based on the typical road curve.The fourth part,develop active braking system control strategy,construct the target braking force fusion control algorithm,and execute the dynamic driving and braking command of intelligent vehicle in real time and accurately.According to the vehicle quality and road slope identification results,design the feedforward controller,the fuzzy PI feedback controller is built in combination with the actual deceleration of the vehicle.The vehicle braking force is controlled by the feedforward and feedback controller to follow the target deceleration command.A method of indirect control of vehicle speed by controlling vehicle deceleration is proposed.On the base of the target vehicle speed and real vehicle speed,the demand deceleration is calculated according to the fuzzy algorithm.In the light of the deceleration feedback,a fuzzy PI feedback controller is constructed to get command of the braking force of the vehicle to follow the target speed.Design the parking control coordination module to control the braking force of the vehicle to ensure the stable parking of the vehicle.The target braking force of each wheel is computed by the coordinated control module according to the state of the vehicle,which is used to control the wheel cylinder pressure of the braking system,and respond to the control instructions of the intelligent vehicle decision-making planning layer to achieve service braking and parking braking.Taking into account the possible failure of the braking system,the hardware failure detection and handling process is designed to promote the reliability and safety of the active braking system.The fifth part,the Car Sim,Matlab/Siulink and AMESim co-simulation platform was built to perform offline simulation verification of pressure estimation and control effects,and active braking control policy.At the same time,on the base of the e Booster and ESC hardware with independent intellectual property rights,the proposed active braking system control algorithm was tested in real vehicles.The typical operating conditions of BAS,HBC,AEB,HDC and AVH are verified.The co-simulation and real vehicle test results show that the active braking system can well control the driving brake and parking brake of the vehicle,and meet the dynamic driving deceleration control requirements of smart cars.