IC & RC points - different approching

Question

IC & RC points - different approching

Daniel Ursache (Mechanical)

(OP)

11 Nov 18 17:59

Hello gentlemen,

Let's consider an independent front suspension (e.g. double wishbone / SLA). Everywhere on Internet is described the way you can easily find out the location of IC and RC points.

In all explanations and in all pictures I saw only that unique case where the mounting points of Lower Control Arm / Upper Control Arm to the chassis both are on the same plane.

Here it comes my question, how do I supposed to determin the IC and RC points for that case where my mounting LCA / UCA to the chassis are not on the same plane ?

Please check the imagines below for more detailing. Thank you very much for your time.

Best regards,
Daniel

BrianPetersen (Mechanical) · Answer 1 · 2018-11-12 19:54:13

At a certain point you have to give up with simple 2D methods and use 3D analysis software.

For that specific situation, you can draw a line in 3D space between the two attachment points for the upper arm (which will be inclined in 3D space), identify the point where that line aligns with the upper ball joint in the fore/aft direction, then draw a line between the ball joint and the point that you just identified, and use that as an approximation.

Proper analysis isn't done using 2D and drafting paper any more. It's done in 3D using force based analysis. Many multilink rear suspension designs in particular defy the use of 2D methods. Too many complicated 3D relationships that can't be simply neglected.

GregLocock (Automotive) · Answer 2 · 2018-11-13 04:17:22

I agree with Brian, but perhaps you could construct the motion at the wheel centre in the YZ plane. That will give you the FVIC for the wheel centre, which is probably what you want. Of course that rather depends what you want it for.

Cheers

Greg Locock

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chez311 (Automotive) · Answer 3 · 2018-11-13 15:11:30

Quote (BrianPetersen)
Proper analysis isn't done using 2D and drafting paper any more. It's done in 3D using force based analysis.

Forgive me for asking simple questions - the last time I had to do such calculations it was all 2D analysis. Could you provide some sources/examples how things like IC and RC translate to 3D analysis?

GregLocock (Automotive) · Answer 4 · 2018-11-13 18:02:21

Check out Force Based Roll Centre Height. GeometricRCH is established on a K&C rig (and hence in any decent 3D suspension program) by looking at the camber gain curve. FBRCH is measured by looking at dFz/dFy in a lateral compliance test. Incidentally the OP's geometry is going to give very dodgy numbers until he considers compliances, the upper arm angle will prise the body side attachment points.

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

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IC & RC points - different approching