Steer angles are different for same Rack Travel in Suspension analysis and Full vehicle analysis.

Question

Dear all,

Rightnow I am going through one problem and that needs to investigate as soon as possible.

I have optimized the hardpoints to get the desired steer angles for 85mm rack travel at suspension level.

---- Suspension Level Analysis

Now, While I am running steering analysis at suspension level, I am getting following results.

Inner_Wheel_Angle = 42.5deg (Optimized Value)

Outer_Wheel_Angle = 35.6deg

---- Full Vehicle Analysis

Now, when I have used the same suspension in my full vehicle and running Turn Diameter event, I am getting following results with same rack travel.

Inner_Wheel_Angle = 43.5deg

Outer_Wheel_Angle = 35.0deg

Then I have adjusted the rack travel to get Inner_Wheel_Angle = 42.5 deg but then Outer_Wheel_Angle is reduced to 34.2 deg.

----

So now my confusion is why full vehicle event showing me different steer angles for same rack travel ?

Also, why outer angle is different for same inner angle in full vehicle event compare to suspension level analysis ?

Just to note, I am running the full vehicle event at very slow speed and using PAC tire model but I guess same geometry should give the same result.

It will be very helpful to have your comments on this confusion.

Thank you very much in advance.

Regards,

Darshan

Jesper Slattengren · Accepted Answer

And I am a suspension expert.... And I would not expect the same steer angles in a full vehicle dynamic event as in a static steering test rig.

Vertical travel is one thing, but there is also roll in the full vehicle test. The outer wheel will be jounced and the inner wheel in rebound. That can have a big effect.

Another potential influence is elasto-kinematics. The suspension test rig does not apply any horizontal forces on the tire. In the full vehicle test, tire forces are applied to the suspension. Setting steering system and suspensions to kinematic mode will reduce this effect, but it is an actual thing that we always have to live with.