Calculating The Equivalent Stiffness Of The Wheel Center Of The Independent Suspension

Suspension is one of the important components of an automobile. The main role of thesuspension is passing all the forces and torques between the wheel and the body, such as thesupport force, braking force, driving force and cornering force, easing the impact force whichis caused by the uneven road and passed by the frame or the body, attenuating the vibrationwhich caused by the impact force, ensuring the occupant comfort and reducing the dynamicload of the vehicle. Through many years development, some kinds of suspensions aredesigned in foreign countries. We have imported the above suspensions from foreigncompanies. But if we want to improve performance of a vehicle and develop a kind of vehicleof self-owned intellectual property rights, design of independent suspension is one of key step.Because improvement of a suspension will change stability, ride comfort, handling, especiallysafety of a vehicle. So the researching of the suspension system play an important role in thedevelopment of China’s automobile industry.This article starts from the Equivalent Elastic Mechanism(EEM). The paper firstintroduces the EEM, and this mechanism can greatly simplify the stiffness matrix of thesuspension system. The EEM can not only be used to evaluate the suspension system, but alsocan be used to optimize and design of the suspension system. The prerequisite of the realizingthe EEM is known the overall stiffness matrix of the suspension system. However afterinspecting a variety of literature, I find that there is no researcher given such a theoretical tocalculate the overall stiffness of the suspension. And in the all inspected literature, we needsthe stiffness of the suspension to theoretical derivation or calculation we assume the stiffnessof the suspension is already known. The stiffness of the suspension obtains by experimentalmeasurements or the Finite Element simulation. So it is very meaningful to research thestiffness of the suspension.The suspension system is a complex structure, The stiffness of the suspension is mostlyprovided by the linkages and the bushings which connect the vehicle frame with thesuspension, the stiffness of the bushing and linkage can be easily measured, but it hard tomeasure the overall stiffness of the suspension. This paper firstly consider the connectinglinkages are rigid: firstly this paper find the relationship between the stiffness of thesuspension system and the stiffness of a single stiffness; then this paper uses the mathematical induction deduce the relationship between the stiffness of the suspension and the stiffness ofthe multiple bushings, and finding the main factors which affects the stiffness of thesuspension system. Then this paper consider the connecting linkages are flexible: firstly thispaper find the relationship between the stiffness of the suspension system and the stiffness ofa single stiffness and the stiffness of one linkage; then this paper uses the mathematicalinduction deduce the relationship between the stiffness of the suspension and the stiffness ofthe multiple bushings and the multiple linkages, and finding the main factors which affects thestiffness of the suspension system. At the end, this paper calculate the overall stiffness of thesuspension through the example in the two cases, using the EEM method to analyze thecalculated stiffness of the suspension. After comparing the overall stiffness of the suspensionis down while we consider the linkages are flexible, which means the suspension softened.Comparing the direction of the Elastic Screw Axes(ESA) we find that whether consider theflexible of the linkage the direction of the ESA will change dramatically, that’s to say thestiffness of the linkage have a great effect on the direction of the ESA. Comparing thedirection of the Translation-Only Compliances(TOCs), we find that whether consider theflexible of the linkage the direction of the TOCs will not change significantly, that’s to say hestiffness of the linkage have little effect on the direction of the TOCs.