Structural Strength Verification of Rubber Ended Leaf Spring Suspension in Commercial Vehicle via FEM 2017-01-1495

At the time of invention of road coaches, the vehicle consisted only of an axle with wheels and a body attached. Smooth roads were built for a better ride comfort however they were not consistent. The road coaches were too bumpy and uncomfortable for the passenger along with the driver who was not able to control the vehicle. That's why the engineers had to shift their attention to the suspension system for a better ride comfort and handling.

The technology has advanced with time so as the suspension system. Rubber ended type leaf spring is one of the suspension system types available in the industry. The main function of a suspension in order of importance is as below:

1. 1
   Acts as a cushioning device ensuring the comfort of the driver and passengers;
2. 2
   Maximizes the contact between the tires and the road surface to provide steering stability with good handling;
3. 3
   Protects the vehicle itself and any cargo or luggage from damage and wear.

Design of Rubber ended Type Leaf springs is a combination of semi-elliptical leaf springs and Rubber mounts at the ends of leaves. The Rubber mounts at the end of these leaves play a major role while loading and unloading is done. A study has been conducted in VECV to calculate and understand the behavior of Rubber ended Type Leaf Spring suspension completely via the Finite Element Analysis route and verifying those results with physical test. The leaf springs with rubber mounts, U-clamps, and center bolts are modeled in FEA which is similar to rig test bed setup. Physical test is performed by applying gradual load on the axle and holding the rubber mounts. Gauges are used to extract the data and use it for virtual co-relation. Correlations have been achieved in both stiffness and stress at those strain gauge locations between the rig test and CAE results.

The Leaves are fully in contact with each other and at the time of loading the leaf ends gets pushed into the rubber mounts making this particular analysis a tricky non-linear problem. Correlating this problem in FEA with rig test is a quite intricate task as dynamic friction and rubber elastomer will play major role.

Good correlation (around 94%) has been achieved between rig test data and FEA results at measured locations. Correlation has assisted in reducing product design time and cost of running the rig until crack.

This method has also reduced the cost by using soft validation. Hence, this FEA based methodology has aided VECV in designing an exceptional suspension system which will prove valuable to our customers.