Research On Center Point Steering Independent Suspension With Self-Aligning

With the rapid development of automobile industry, the vehicle performancerequirements in handling stability and ride comfort are also increasing. The suspensionsystem plays a vital role on the stability, comfort and security et al. The conventional leafspringtype non-independent suspension，mainly used in some hardcore off-road vehicles andcommercial vehicles, has many shortcomings such as heavy weight, high stiffness, poorcomfort et al. While the independent suspension system, mainly used in passenger cars,possess many advantages:1)Relative light weight in unsprungmass, which can reduce thebody shock and improve the traction of the wheels;2)softer spring can be used to improvethe ride comfort;3)the positionof the engine and the vehicle center of gravity can be loweredto improve the vehicle handling performance. From the view of suspension performance,the independent suspension is better than non-independent suspension. However, theindependent suspensionis rarely appliedon the larger commercial vehiclesdue to itsdrawbacks such as complex structure, high cost, inconvenience to repair and poor bearingcapacity.Considering the aforementioned problems, a self-aligningindependent suspension ofsteering on center is proposed in this dissertation:1)the carrying capacity of commercialvehiclescan be met, while the suspension layout is flexible;2)the turning ball bin has smallfriction;3)the self-aligning performance is realized by utilizingthe spring lateral stiffnesswhen turning. This paper is carried out by following aspects:1)the independent suspension system of steering on center and its matched steeringsystem are preliminary designed.Firstly, the structure and characteristics of multi-rodindependent suspension of steering on centerare analyzed, furthermore, the principle ofself-aligning performanceis analyzed.Secondly, the front suspension of a non-independentsuspension vehicle is upgradedto the independent suspension of steering on center, then thedesign and calculation of the main parameters of the suspension system,such asthe stiffness of the suspension, the offset frequency, static deflection, spring parameters, the suspensiondamping, are carried out. Thirdly the design methods of the steering mechanism areanalyzedqualitatively and the steering system matched with independent suspension ofsteering on center is designed. Finally, the length and layout of steering arm and the middlerod, the length and angle of the steering tie rod and the steering knuckle are optimizedtakingthe steering angle ratio, the relationship of left and right wheelsAckermanangle as theoptimizedtarget. on the work of the preliminary designed for the independent suspensionsystem of steering on center and its matching steering system make it easier to study theaccurate suspension and steering model.2)Theoptimal design for the suspension and steering systems are conducted,based onthe suspension K&C characteristics and steering characteristics.The independent suspensionsystem of steering on center dynamics model is built via the multi-body dynamics softwareMSC.Adams, based on the structure principle and the main parameters of the proposedsuspension.In conventional manner, the spring is simulated by building the spring unit andthe properties file, it only reflect the influence of the axial stiffness of the spring onsuspension kinematics. However, the self-aligning performance of the independentsuspension system of steering on center is realized by utilizing lateral stiffness of the spring,besides the vertical movement, the spring has lateralmovement, and compound movementwith vertical and lateral movement, which can’t be simulated by the conventional springunit.In this dissertation, the spring model is materialized innovatively, a flexible springmodel is establised, and then applied to the independent suspension.The movement of thespring inEach direction, and the force generated in all directions can be accurately fed intothe knuckle and the vehicle body.Lateral loads generated by the lateral movement of thespring, will produce kingpin aligning torque. Furthermore, the hard point optimizations ofthe proposed suspension are studied based on the K&C characteristics. Then the steeringsystem is builtto match the suspension system, and the hard point optimizations of theproposed suspension are studied based on the steering characteristics. In order to ensurethat the design of the proposed suspension system to meetthe reasonable suspension K&C characteristics and steering characteristics, the multi-objective optimization of frontsuspension is carried out based on the above two features.According to the optimized hardpoint locations of the suspension and steering systems, the structure of suspension andsteering system,the suspension guide bar, steering knuckles, spring bracket and the shockabsorber bearing are designed.A three-dimensional motion model of suspension system isadoptto conduct the motion check to ensure the feasibility of structural design. Taking themain load bearing component and the suspension knuckle for example, the strength analysisis carried out to ensure the safety of structural design.3)Aligning performance of on-center independent suspension is designed and analyzed.The design objective of aligning moment is set via studying the causes of aligning resistancemoment and the calculation method of main resistance. The main factors influencing thesteering aligning performance are the transverse stiffness of spring and arrangement angle ofspring.Firstly, the relationship between the aligning moment and the transverse stiffness isstudied. The relationship between the transverse stiffness of spring and the spring parametersis analyzed and the calculation method of the transverse stiffness of spring is obtained. Thetransverse displacement value of the spring in the process of steering is obtained accordingto the steering simulation of on–center independent suspension. The transverse stiffness ofspring is calculated based on aligning moment and transverse displacement value of thespring. Optimization of spring size was carried out based on the transverse stiffness, and thenspring model meeting aligning moment is achieved.The variation of the spring transversestiffness influencingon the suspension K&C characteristics is analyzed. The relationshipbetween spring inclination angle and aligning moment and the spring inclination angleinfluencing on the suspension K&C characteristics is studied.According to the suspensionhard point set in chapter3, the hard points of suspension guiding mechanism and steeringpart, and the design of spring size and inclination angle, all structural parameters ofon–centerindependent suspension is achieved. Finally, the accurate model of the suspension isobtained via simulation analysis and experimental verification.4)A vehicle model with on–center independent suspension as front suspension is built to study the vehicle ride comfort and handling stability of the proposed suspension system. Afull-car vehicle model, including the front suspension model, the rear suspension, steeringsystem model, tire model, and the body modelis buildedin ADAMS/Car. Simulation analysisand experimental verification are carried out focusing on K&C characteristics of frontsuspension, steering system model and rear suspension. UniTire tire model proposed byguo konghui academician is selected as Tire model, to obtain higher simulation accuracyunder large lateral acceleration. In order to identify parameters of UniTire tire model, the sixdegrees freedom tire testing machine developed by guo konghui academician and his team isused to test tire performance.The simulation model is verified by ride comfort test andhandling stability test. The validation results show that the simulation results fells well withexperimental results, sothe vehicle multi-body dynamics model is accurate enough todescribe the linear and nonlinear dynamic of the vehicle characteristics. Ride comfort testresults show that the total weighted acceleration root mean square value is reasonable; thedesign of on–center independent suspension can satisfy the requirement of the vehicle ridecomfort. Steering portability test results show that the steering wheel torque is small in theprocess of steering, and vehicle with on–center independent suspension as front suspensionhas light steering characteristic.Returnability test results shows that response time of the yaw rate is within the normalrange, meanwhile the yaw rate is reduced into the limit range. the steering testresults showthat the on–center independent suspension satisfy the requirement of aligning performanceand can realize automatic correction.Major Innovations of the Dissertation:(1) A new type of independent suspension with following adavantages is proposed in thispaper: the ball pin has small friction resistance and long applying time.a)smallfriction resistance in the ball pin prolong its lifespan; b)small steering resistance whilestreering led to good road feeling; c)wheel move around its center when Steering,which reducing the wear of the tire; d)due to spring load through the center ofimprinting, the roll moment of the wheel assembly is reduced;e)the layout of height ofthe two connecting rod is flexible. (2) A car is taken as an example, the design method of on–center independent suspension isput forward: from the basic parameters’ selection of suspension form, basic space layout,and initial design of suspension hard point to optimization of suspension hard pointbased on the suspension K&C characteristics and steering characteristics, thenmovement checking and strength calculation of the suspension is carried.(3) Design method on the aligning performance of on–center independent suspension is putforward, namely, based on transverse stiffness of spring and the spring inclination angel,to make its produce aligning moment around the virtual king pin; The spring as flexiblebodyassemble into the suspension dynamic model, which can accurately simulate thespring stiff influencing on the suspension kinematics and steering aligning performance.