Forces at Upper Control Arm

For calculating loads at the UCA-upright node we can use the front wheel forces at the contact patch and make some assumptions. We assume that:

• Forces balance out
• The LCA provides no restorative moment (worst-case, actual depends on attachment)
• The UCA only resists forces in the X-Z plane
• The UCA-upright node is free to move vertically (actually constrained to an arc)
• The moment of the upright about the Y-axis is handled by the steering system.
• The UCA-upright node does not travel more than 30mm in the Y from its clevis (currently about 25mm with a coilover compression of 40mm)

This means that for analysis purposes, we can treat it as exactly horizontal. This causes no more than 0.5% of error in this analysis.

Assuming no restorative moment, the moments at the LCA-upright node must cancel out. If we take a look at the upright, we can see that the contact patch is roughly 130mm from the LCA node, and the UCA node is roughly 450mm from the LCA node.this is a distance ratio of 1:3.46. We can safely approximate this as 1:3. We then have the system.

To make the moment at the LCA node 0, we conclude that for any Fx and Fz at the contact patch acting on the wheel, the UCA must provide a reaction of ⅓ Fx and ⅓ Fz to the upright.

This will cause a moment about the Y-axis, but that should be handled by the steering system.

This gives us the forces:

We can use these forces to find the tensile/compressive forces in the arms of the UCA.

The UCA dimensions are below:

 Solving for the system of equations that arises, we get 

To get the forces on the chassis bar through the clevises, we can resolve these forces into the X and Z directions.