McPherson Strut Suspension - Loads In Members

[garagetuner]

Hello All,
I have a few queries regarding McPherson strut type suspension systems and loads in members, in particular, the lower control arm. I would like some clarification as to the loads being experienced by the lower control arm, in particular bending loads.
(I can see tension and compression, but have also been told there will be bending present)
If anyone can provide an insight into the loads being experienced and their magnitudes, it would be greatly appreciated.

Thank you.

 

[NormPeterson]

Longitudinal forces at the ball joint due to accelerating and braking?

Bending from lateral forces due to the neutral fiber(s) of the LCA not remaining in the plane defined by the ball joint and control arm chassis-side pivot points?


Norm

 

[GregLocock]

and vertical bending from the sta bar link.

All will be revealed by a free body diagram for each loadcase.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[NormPeterson]

And if it's a modified strut, you still have the spring loads . . .

 

[rrrocket]

Looking at the picture, there are some nasty little offsets in the pick-ups at the outboard end of the LCA, and probably the axis of the spring won’t coincide with the axis of the strut, usually due to clearance issue with the tyre. Also, the spring will exert an offset load on the spring platform.
As a first pass, draw a free body diagram (as suggested) for each link as a complete system, assuming zero friction at all of the joints, with the loads due to braking, cornering, bump etc applied at the contact patch. Apply 1g braking, 1g cornering etc. Using the principle of superposition, you can calculate the effects of load combinations for real g levels for each attachment and each member. Careful with your sign convention!
Then, add reasonable estimates of friction for each joint, applied as torques at each end of each member as appropriate, and see those forces change!