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

dmvachhani
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
 
  • 0
    Do you have the same vertical position of the suspension in the suspension analysis as you have in the full vehicle analysis?
    I am not a suspension expert, but it seems that vertical travel could have an influence on steering angle ...
  • 0
    Hi Henrik,
    Thank you very much for the giving me insight.
    I can see that starting position is little lower in full vehicle setup but then after behaviour is same.
     
    I will take this further and see if this can lead to any clear conclusion.
     
    Thanks again.
  • 0
    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.
     
  • 0
    Thank you very much Jesper for clear answer !!
    Yes, it seems same as you said and it's fully convincible.
     
    But to take clear understandings, I have tried few observations as below.
     
    As I have relation between wheel travel and steer angles from suspension analysis, I tried to run both the simulation kinematically at low speed and I am expecting that wheel angle should change within certain range based on the relation with wheel travel.
     
    But what I found is that wheel angle changes are higher and not following the relation with wheel travel. So, it made me to take doubts on my models or techniques.
     
    OR Is there any way I can accurately predict the Turning Radius at early stage using suspension analysis ?
     
    Regards,
    Darshan
     
  • 0
    Have you verified same lateral Forces are generating ?
    And have checked the all the joint motions ?. If any Flex bodies are there , It might cause to more angles.
     
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