Testing Technology And Equipment Study Of Passenger Vehicle Suspension Kinematics And Compliance Characteristics

Automotive inertial parameters, the tyre characteristics, the suspension kinematics andcompliance characteristics (suspension KnC characteristics in short), the dampercharacteristics and automotive aerodynamics are major factors to the vehicle dynamics. It isvery practical to improve the performance of vehicle dynamics by adjusting the suspensionKnC characteristics when it is very difficult to change other characteristics. And thesuspension kinematics and compliance characteristics test rig is used of high frequency inthe chassis tuning process.This thesis mainly includes: Developing a suspension kinematics and compliancecharacteristics test rig for the passenger vehicle to measure the Ackermann error and the6-DOF displacements of the wheel relative to the vehicle body; Building a mathematicalmodel to calculate the angles and positions of the kingpin axis based on the steering test data;Finding out a method to test the tyre scrub torque on a moving vehicle; Building a low-speedvehicle dynamics model to study the automotive low-speed portability which could calculatethe hand-wheel torque with the tyre forces and the kingpin geometry parameters.The study of the suspension KnC characteristics would include the theory research part,testing work and the application part. Calculation of the positions and angles of the kingpinaxis based on steering test data and determining the suspension anti-dive or anti-rollcharacteristics would make up the theory research part. Developing a suspension KnC testrig for the passenger vehicle would make up the test work. Studying effects of thesuspension KnC characteristics to the vehicle slow speed steering portability would make upthe application work when the castor offset and the steering Ackermann error changes withthe road wheel steering angle. The content of this paper includes five parts primarily:Firstly, the method to calculate the suspension anti-dive characteristics or thesuspension anti-roll characteristics is studied.Secondly, a mathematical model determining the hub rotating about a fixed axis is builtto research the relationship between the kingpin geometry parameters and the wheel6-DOFdisplacements. An ADAMS suspension model is built to research the influence of theuniversal-joint deflection angle on the traction-force radius. The results prove that the kingpin castor offset would change with the road wheel steering angle due to the kingpininclination angle. The storing torque due to the wheel load is influenced by the kingpininclination angle while having no relationship with the kingpin castor angle. Themathematical model could compute the angles and positions of the kingpin axis based on thesteering test data of a suspension KnC characteristics test rig.Thirdly, a mathematical model computing the hub rotating about the imaginary kingpinaxis is built to calculate the angles and positions of an imaginary kingpin axis based on thesteering test data of a suspension KnC characteristics test rig. The model shows arelationship between the kingpin positioning parameters and the derivative of the wheel’sdisplacements when the wheel steering angle equals to zero. The kingpin inclination angleequals to the derivative of the wheel rotation angle with respective to the wheel steeringangle. The kingpin castor angle equals to the derivative of the tyre inclination angle. Thecastor offset at wheel centre equals to the derivative of the wheel center lateral displacementwith respective to the wheel steering angle. The steering-axis offset at wheel centre equals tothe derivative of the wheel center longitudinal displacement. The initial value of the castoroffset at ground equals to the derivative of the lateral displacement of the nominal tyrecontact point with respective to the wheel steering angle. The kingpin offset equals to thederivative of the longitudinal displacement of the nominal tyre contact point. The change ofthe castor offset at ground equals to the product of the wheel rotation angle and the wheelload radius. The simulate results of an ADAMS suspension model and the test data of aforeign test bench are used to verify the accuracy of the model. The solver results of themathematical model are accurate, and meet the requirements.Fourthly, a suspension KnC characteristics test rig is developed to measure6-DOFdisplacements of the wheel and the tyre forces. The suspension kinematics and compliancecharacteristics test rig for the passenger vehicle is composed of two wheel deflectionmeasure systems, two platforms loading wheels in four directions, an automatic steeringmechanism and the software. The wheel deflection measure system could accuratelymeasure6-DOF displacements of the wheel with the sensor data, the system dimensions andthe geometry parameters relative to the wheel which is identified by the measure system.Through simulating bounce and roll of the vehicle body, making up force between the tyreand the road, the test rig measures the alignment parameters. Measurement results areconsistent with that of the foreign test bench. The facility could measure the suspensioncharacteristics with no care of the suspension structure and provide great benefits for the vehicle design. The facility has been put into use in some domestic automotive companies.Finally, a method is developed to test the scrub torque when the vehicle corning slowly.And a low-speed vehicle dynamics model is built to calculate the tyre lateral force inducedby the Ackermann error and to compute the hand-wheel torque with the tyre forces and thekingpin geometry parameters. Test results show that the tyre aligning moment of the rearaxle equals to the tyre scrub torque when a front-wheel drive car cornering slowly.Simulation results show that the tyre scrub torque, the tyre steering torque, the storing torquedue to the wheel load, and the lateral acceleration would increase the hand-wheel torquewhile the tyre lateral force would decrease it. The aligning moment due to the tyre slip angleshows no effect to the hand-wheel torque. The tyre traction forces of a front-wheel drive carwould increase the hand-wheel torque as the longitudinal force of outer wheel changesdirection to balance the moment of the inner traction force about the cornering centre.Major Innovations of the Dissertation:Firstly, a new wheel deflection measure system is developed to measure6-DOFdisplacements of the wheel with the sensor data, the system dimensions and the geometryparameters relative to the wheel that is identified by the measure system.Secondly, a mathematical model determining the hub to rotate about an imaginarykingpin axis is built to calculate the angles and positions of the kingpin axis. The model is fitto the McPherson suspension, the double wishbone suspension and the multi-linksuspension.Finally, a method is developed to test the scrub torque when corning slowly. Thelow-speed vehicle dynamics model is built to research the automotive low-speed portability.Simulation results show that the scrub torques and the storing torques are the maininfluencing factors of the hand-wheel torque.