Lower Control Arm

The Lower Control arm (LCA) is one of the links between the chassis, the damper and the upright. It is built using steel tubes welded to a main block. The UCA also includes three Super-Swivel Ball Joint rod ends, weldable tube ends and a jam nut.

Finite Element Analysis

Test Conditions

At the front of the UCA, we applied the reaction loads as the car experiences bump, brake and turn. These load calculations can be seen here:

Calculations

We added a bearing load of ~800 lbf. This is the load exerted on the LCA from the shocks when it experiences compression. This was calculated using the suspension simulation software LOTUS SHARK

We also applied fixtures at the two rear ends. This is the section of the control arm that mounts to the chassis.

Result

As with all our design, we aim for a FOS of at least 1.4. This FEA study shows a that the minimum FOS of the design is ~1.8 and the nominal FOS is ~10. These are great results. The design passes!!!

Version History

For this design, we decided to use bushings to link the LCA with the chassis.

A big downside of these parallel tubes is that the load path has to turn at the junction of the angled tubes and the parallel tubes, putting a moment on that joint and placing both tubes in bending. The FEA results also indicated a stress concentration at this point.

We decided that to move to a two-tube design with rod ends that mount to the chassis.

For this design, the bushings have been replaced with rod ends, we have also eliminated the parallel arms.

An issue with this design is the shock mount. The shock mount's bolt-on plate is experiencing an awkward load as both bolts are on the neutral axis, resulting in a short moment arm. To reduce the torque and bending stress on the plate, the bolts could be spaced farther apart, or the plate could be mounted differently to avoid loading the bolts.

Also, we had to change the suspension geometry to ensure a smoother ride, we had to re-design the LCA to account for these dimension changes as well.

For the final version, we used four bolts on the shock mount and also increased the length to account for the geometry change.

Manufacturing

To be manufactured in Summer 2023