| With the development of intelligent vehicle,the X-by-wire technology of vehicles has been extensively studied.X-by-wire comes from the control system of an aircraft.It eliminates the traditional mechanical connection between components and enables the transmission of control commands via cables or other means.The car's X-by-wire system includes Drive-by-Wire,Brake-by-Wire,Steer-by-Wire,and more.Compared with the traditional steering system,the steer-by-wire(SBW)system cancels the mechanical connection of the steering handwheel and the tie rod,and the steering wheel angle is transmitted to the steering motor via the electric signal.Due to the elimination of the steering column,the system saves space in the cabin and also avoids secondary damage to the driver by the steering system during a frontal collision,and engineers can flexibly design the steering ratio as needed without mechanical connection constraints,it is easy to make the vehicle easily steering at low speed and more stable at high speed.Despite the many advantages of steer-by-wire systems,there are still many problems.For example,in order to improve the stability of the system,redundant design of the steering motor and related algorithms should be carried out.At the same time,the conditions of the road surface cannot be transmitted to the steering wheel through the road wheels due to the cancellation of the steering column,so that the driver cannot obtain the road surface information,that is,"sense of road." Based on the project "Dynamic Coordination Control Mechanism and Energy Optimization Management of Four-wheel Drive Electric Vehicles"(U166420018),this paper studies the road-feel simulation of steer-by-wire system and completes the calculation and algorithm realization of road-sensing feedback torque.The main contents of this thesis are as follows:(1)The establishment of the influencing factors of the steering feelIn order to make the steering feel more realistic,this paper refers to the traditional steering system structure,respectively,the steering system friction,stiffness,damping and inertia.In the traditional steering structure,the steering feedback torque of the steering wheel(that is,the aligning moment)mainly comes from the aligning moment generated by the contact between the ground and the tire and the friction of the system.Therefore,a reference model with high accuracy is built to calculate the tire aligning moment.In the traditional vehicle,due to the existence of the power steering system,the driver can only feel part of the aligning moment.In order to make the steering experience closer to the traditional vehicle,the influence of the power steering system must also be considered.The contact of the ground and the tire is different when the vehicle is at very low speed and medium-high speed.Therefore,the dominant factors of the steering wheel feedback torque are different.In this paper,different speed conditions are discussed separately,which makes the method of calculating feedback moment suitable for different conditions.(2)Construction and verification of steering feel feedback algorithmIn this paper,we build the steering feel algorithm under the environment of Matlab / Simulink.The modular development mode of Simulink and the abundant function library greatly speed up the algorithm development.And Simulink-CarSim cosimulation is used to verify the vehicle reference model accuracy.After the algorithm is set up,the simulation results are compared with the real vehicle test data of traditional vehicles(steering stability test,pylon course slalom test,steering easiness test,etc.)to determine whether the feedback torque in the steer-by-wire system correlates traditional steering system.(3)The establishment of steer-by-wire feedback torque platformThe road feel feedback algorithm established in this paper will eventually be applied to the four-wheel independent-steering independent steering test car in the project group.At present,the construction of the road-feeling feedback platform has been completed.The basic structure of the platform is made of No.40 aluminum profiles and can be easily installed in the test car.The feedback torque is generated by the permanent magnet synchronous servo motor with reducer in the platform.Due to the absolute position encoder in the motor,you can measure the actual steering wheel angle.The input signals of road sense algorithm are the steering wheel angle and the current speed.So the platform just need to read the vehicle speed signal from the CAN bus to generate feedback torque.The development of the vehicle controller(ECU)has not been completed yet.Therefore,the steering feel algorithm is not downloaded to the embedded system.Instead,the PC software written by C# controls the torque of the steering feel motor to simulate the road feeling.The innovation of this paper is mainly reflected in the following aspects:(1)In the calculation,a vehicle reference model is needed to calculate vehicle state parameters,such as lateral acceleration.The vehicle model in CarSim is too complicated,while the bicycle model is too simple.Therefore,this paper builds a simple but accurate vehicle reference model.(2)The steering system's friction is modeled more accurately and the hysteresis characteristics of the road feel and steering gradient are well simulated.(3)Building the electric power steering(EPS)model,give full consideration to the impact of power steering system on the feedback torque.(4)The road feel algorithm built in Simulink is finally integrated into the host computer.The host computer sends control commands to the road-sensing motor,which can conveniently display the different control effects of different algorithms and lay a foundation for the embedded development of the vehicle controller later.The PC host software using C # has high scalability,such as through the interface function to connect to the vehicle scene model,so build the road feel platform not only can be used for steer-by-wire system,can also be used for driving simulator,racing VR game and other scenes. |
PDF Full Text Request