Virtual Steer Axis Vector

Request Number: 80000320

The kingpin axis or steer axis on an SLA or Macpherson strut suspension is defined by two points (the upper ball joint and the lower ball joint in the SLA suspension, the upper strut mount location and the lower ball joint in the case of the Macpherson strut suspension). When the steer axis is not defined by two distinct points, it must be calculated virtually, using the motion of the spindle to calculate the instant axis of rotation of the knuckle. The virtual requests (numbers 50000310-50000350) use this method to calculate the steer axis location, and the parameters that rely on it. These requests should be used on suspensions that do not have a clearly defined steer axis, such as a 4 link or 5 link front independent suspension.

For the computation of the steer axis, the steering needs to be free (no motion) and the suspension travel needs to be locked. The locking is done numerically on the compliance matrix, rather than by adding a motion to the suspension. This information needed for the lock is included in Wizard build models. If you built your own suspension model, see Locking Steering and Spring Travel for details about adding locks to your model.