Research On Front Wheel Steering Characteristics And Control Strategy Of Flexible Chassis

Steering is the most basic motion in a vehicle.The most basic requirement for steering is that all wheels roll purely without slipping,and conventional vehicles rely on rigid mechanical structures such as steering trapezoids and differentials when steering.For the four-wheel independent drive and independent steering flexible chassis,to realize the differential steering control function,the design of the differential control strategy for steering and the development of software and hardware systems are required.Based on ackerman principle,this paper studied the front wheel steering characteristics and control strategy of four-wheel independent drive and independent steering flexible chassis.Through the test bench test and hardened pavement test,the following research conclusions are obtained:(1)The differential steering geometry model and dynamic model of the front wheel steering of the flexible chassis based on the ackerman principle were established.The relationship between the angles of the steering wheels and the relationship between the speeds of the four drive wheels were derived.(2)The electronic differential control strategy for the front wheel steering of flexible chassis was studied.The steering controller needs to coordinate the four-wheel speed of the flexible chassis in both straight and steering states.The threshold of 5%?10%is set on the circuit of each driving electric wheel.When the speed of each driving electric wheel exceeds or below this threshold,the controller needs to modulate the rotational speed of the drive wheel,so that the actual rotational speed of each drive electric wheel satisfies as much as possible the theoretical rotational speed derived from the flexible chassis front wheel steering model,ensuring that the flexible chassis can complete the steering process with the center of rotation O as the center.(3)Designed and produced software systems and hardware systems that are compatible with the differential control strategy.Hardware aspect:according to the differential steering control strategy of the whole vehicle,the circuit diagram of the steering control of the flexible chassis was given.The STM32F103ZET6 single-chip microcomputer with good cost performance was selected as the main control chip,and other equipments were also selected,and the steering control system was built.Software aspect:the software control part of the receiving program of the signal of steering wheel simulator,throttle simulator and each sensor,the transmission program of the control signal,the drive control program for driving the electric wheel,and the speed control program were designed.(4)The front wheel steering characteristic test based on the horizontal disc test rig was completed.Single factor test and ternary quadratic orthogonal rotation combination test were performed to study the effects of steering wheel simulator angle,steering wheel simulator rotational speed and wheel rotational speed on motion control characteristics of the flexible chassis which was in the process of front steering.The test results showed that with the steering wheel simulator angle signal,the two driving steering wheels reached the target angle almost at the same time,the maximum lag time difference was 0.103s;There is a linear relationship between the response angle of the steering wheels with the steering wheel simulator angle,and between the response time of the steering wheels with the steering wheel simulator angle and the steering wheel simulator speed;The angle response error of the inner steering wheel is in the range of 0.23°to 0.54°,the angle response error of the outer steering wheel is in the range of 0.29°to 0.41°,ackerman rate is in the range of 97.89%to 106.32%.The above results verify the feasibility of the front wheel differential control strategy for flexible chassis.(5)The front wheel steering characteristic test based on the cement hardened pavement was completed.The test results showed that with the rotation of the steering wheel simulator angle signal,the change of the angle response of the two drive steering wheels is similar to that on the test bench,but the fluctuation angle of the rotation angle is larger than that of the test bench,the response time is significantly shorter,and the maximum lag time difference is 0.321s;There is also a linear relationship between the response angle of the steering wheels with the steering wheel simulator angle,and between the response time of the steering wheels with the steering wheel simulator angle and the steering wheel simulator speed;The angle response error of the inner steering wheel is in the range of 0.65°to 0.9°,the angle response error of the outer steering wheel is in the range of 0.770°to 0.98°,ackerman rate is in the range of 97.16%to 111.58%.The correctness and accuracy of the steering control strategy were further verified.