Research On Control Strategy Of The Electric Power Assisted Brake System And Pressure

The problems of limited energy,traffic congestion and driving safety have promoted the development of automobiles in the direction of electrification,intelligence,networking and sharing.So,electric intelligent vehicles have become the focus and key competitive areas for future development.And they are faced with a series of technological innovation and component change.As an important guarantee of vehicle safety,economy and comfort,braking system is facing great challenges and higher functional requirements.Pure electric vehicles first require that the brake system can get rid of the vacuum source.Then,to maximize the energy utilization,the brake system should be decoupled from the wheel cylinder in the structure,realizing the combination of hydraulic brake and electric brake in function,and the integrated control between braking and driving,etc.The intelligent vehicle equipped with adaptive cruise and automatic emergency braking function requires not only active braking function of braking system,but also rapid and accurate response to pressure requirements.In addition,as an important active safety system,the reliability requirements of unmanned vehicle for failure tolerance and functional redundancy backup of braking system are greatly improved.Traditional brake systems have many challenges and deficiencies in meeting the needs of electric intelligent vehicles.On the one hand,they are limited by their structural design and working mechanism.On the other hand,brake systems have developed to the present day,mostly progressive functional overlays and solution compromises.There is no novel scheme that meets the requirements of modern automotive brake systems in essence.The existing multi-actuator multi-controller scheme not only increases the risk of system failure,but also causes functional interference,and is easy to form functional redundancy and waste of processor resources and low system integration.Therefore,a novel braking structure for modern electric intelligent vehicles is very necessary.Relying on the National Natural Science Foundation project‘Research on Key Issues of Vehicle Chassis Integrated Control Distribution under Over-Driven Complex Constraints’(No.51605185)and the school-enterprise cooperation project‘Ebooster Principle Prototype Development’,this paper proposes an integrated electric power assisted brake system to meet the needs of modern vehicle,and studies its pressure control method.The details are as follows:(Ⅰ)Structure analysis and dynamics modeling of the electric power assisted braking system.Based on the shortcomings of the traditional brake system and the existing solution,this paper proposes an integrated electric power brake system,which has better system response and continuous working ability than the traditional brake system.In the structure design,the booster device and the hydraulic control unit are integrated into one,which simplifies the layout scheme of the vehicle chassis,improves the integration level of the mechanical and software systems,and has the characteristics of flexible control,high integration,strong fault tolerance and responsiveness.Based on the proposed scheme,this paper introduces the working mode and switching logic under full working conditions,and shows the control architecture and methods,including the vehicle application layer,execution layer for pressure controlling,and basic power assisted layer for the brake booster characteristics.In order to better realize the simulation and parameter optimization of the novel brake system,the dynamic model of the electronic brake booster is established from the unit level to the system level,and the corresponding model verification is carried out.(Ⅱ).Power assisted brake characteristic design and permanent magnet synchronous motor(PMSM)controlling.First of all,this paper explores the working principle of the vacuum brake booster,and transplants some of its design ideas into the electric power assisted braking system.Aiming at the design of the booster characteristic of the scheme,this paper first establishes the mechanical model of the reaction disc,revealing the relative relationship between the input force,the output force and the deformation difference between the primary and secondary surfaces.Secondly,combined with the reaction disk model,the PMSM target position design for the driver’s pedal feel is carried out.In the position following control of PMSM,this paper adopts the modified three closed-loop controller,including current control method(i_d=0)for surface-mount PMSM,model-free field weakening technology,friction feedforward compensation,inertia feedforward compensation,and cascaded position-speed-current PI controllers.Finally,the control methods involved were verified by RCP equipment.(Ⅲ).Research on pressure control method of electric power braking system.According to the proposed brake system and the working mode involved,the corresponding pressure control logic algorithm is designed in this section.Firstly,the working characteristics of the inlet and outlet valves are analyzed,and the corresponding linear interval and the pressure increment and decompression rate under the specific duty cycle are calibrated.Based on the different characteristics of the valve,this paper selects the pressure-regulating structure of fuzzy control in pressure decreasing stage and the feedforward look-up table+feedback PI control in pressure increasing stage,which realizes the precise pressure control.Secondly,the control logic of single-wheel control,two-wheel differential control and four-wheel control is designed according to the pressure demand of different working modes.Finally,the multi-wheel pressure control test is realized by the modified MK25E hydraulic regulating unit,dSPACE rapid prototype driver and controller.(Ⅳ)Hardware-in-the-loop platform establishing and test verification.In the process of development and verification of the electric power assisted braking system,this paper adopts the model-based design method.That is,rapid prototyping based on Matlab/Simulink and AutoBox tools is used in the algorithm development process,and hardware-in-the-loop verification based on Mid-size Simulator tool is used in the test verification process.Therefore,in order to verify the electric assisted braking system and pressure control method proposed in this paper from the vehicle perspective,this paper builds a hardware-in-the-loop simulation platform,including software system platform,real-time hardware system platform,and brake system pipeline bench.This paper sets typical test conditions,including sine with dwell(SWD)test and double line change(DLC)test to verify lateral stability,ABS test under multi-road conditions to verify longitudinal stability test;automatic emergency braking and adaptive cruise test to verify initiative Braking performance,etc.