FEM Based Durability Simulation of Inverted Type Leaf Spring & Rubber Bolster of a Bogie Type Suspension System 2017-01-1488
The job of a suspension system is to maximize the friction between the tires and the road surface, to provide steering stability with good handling and to act as a cushioning device ensuring the comfort of the driver & passengers. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear.
Almost all heavy duty vehicles use inverted type suspension system which is also called as bogie type suspension system. The design of this type of suspension is a complex and difficult science which has evolved over many years. It was recognized very early in the development of suspensions that the interface between vehicle body and wheel needed some sort of cushioning system to reduce the vibration felt as the vehicle moved along. This was already part of road coach design and took the form of leaf (laminated) steel springs mounted on the axles, upon which the vehicle body rested.
Leaf springs are the most popular designs having multiple leaves in contact with each other and show hysteresis behavior when loaded and unloaded. Generally, the strength of these suspension systems is evaluated by endurance trials on field or Rig testing which are time consuming and costly. On the other hand, virtual testing methods for strength and stiffness evaluation provide useful information early in the design cycle and save significant time and cost. It also provides suppleness to estimate multiple design alternatives & parameters at an initial stage of development cycle.
A study has been done in our organization to predict the behavior of Bogie Type Suspension Leaf Spring entirely through the Finite Element Analysis route & correlating those results with physical test. Leaf Springs with Sliders, Bolsters, U-Clamps, & Trunnion Brackets are modeled in FEA which is similar to rig test bed setup. Physical test is performed by applying gradual load on both the axles & holding the Trunnion mount. Gauges are used to extract the data & use it for virtual co-relation. Correlations have been achieved in both Stiffness and Stress at these strain gauge locations between the Rig test & CAE results.
The Leaves are in contact with each other & the rubber bolster connects the axle with the leaf springs via slider mechanism making this particular analysis a bizarre non-linear problem. Correlating this problem in FEA with rig test is a tough task as static and dynamic friction will also play major role.
Good correlation (around 90%) has been achieved between Rig test data and FEA results at measured locations. Correlation has helped in reducing product design time and cost of running the rig until crack. This process has also reduced the cost by using soft validation. Hence, this FEA based methodology has facilitated our organization in designing an excellent suspension system which will prove beneficial to our customers.