Research On Control Strategy And Fault Tolerant Control Of Four-wheel Independent Steering By Wire Electric Forklift

With the improvement of national environmental protection requirements,the new energy vehicle industry has developed rapidly.At the same time,the modern automobile industry technology has made great progress.The wire controlled four-wheel independent steering technology is moving to the forefront of development research.This technology gives the electric forklift the advantages of four-wheel independent steering,independent driving,significantly reducing the turning radius,reducing the weight of steering mechanism and improving the accuracy of control.However,due to the large number of electronic devices used in the wire-controlled four-wheel steering system,compared with the traditional mechanical structure,its reliability is reduced.At the same time,in view of its own particularity,it is necessary to establish a reliable and complete fault diagnosis and fault-tolerant control mechanism to improve the safety and stability of forklift driving.This paper presents the research work from four aspects.(1)The input and output parts of the steering-by-wire system are modeled.According to the working characteristics and nonlinear characteristics of the electric forklift,a three degree of freedom dynamic model is established.To take the influence of forklift's load into account,a suitable wheel model and tire model are selected to provide a good model platform for verifying the control algorithm proposed in this paper.(2)On the basis of Ackerman's principle,the relation of one instantaneous center of steering to the Ackerman's turning angle is proposed.In Consideration of the influence of tire side force and forklift load changing frequently on vehicle stability,the sideslip characteristics of tire has been analyzed and the influence of it has been removed.An optimal Ackerman angle distribution algorithm and a load-based optimal driving torque distribution control algorithm are proposed to obtain the steering angle of four wheels and the optimal driving torque.a series of evaluation criteria have been introduced to evaluate the effectiveness of the control algorithm.(3)In order to ensure the accuracy of the parameters obtained by the control algorithm that distributes the steering rotation angle and the driving torque and increase the reliability of the system,a fault diagnosis and isolation algorithm is introduced.On the basis of forklift system model,system failures and disturbances are added to establish a forklift failure model.An adaptive sliding mode observer is selected as the fault observer,and the residual signal is used to design the adaptive rate.Then,the idea of multiple observers is used to realize the simultaneous detection and isolation of multiple faults.(4)The fault characteristics of the sensor are modeled to judge the fault type of the sensor.Different fault-tolerant output compensation algorithms are selected according to the type of fault.At the same time,an active fault-tolerant control algorithm is designed.When the sensor fails,the working state of the system will be restored to the level close to the normal working state,and the stability of the control system will be maintained.