Adams Assignments – Problem 4 – Steering geometry 2

The double wishbone assembly used for this problem is as follows:-

The initial hard points are as follows:-

Using this model, parallel wheel travel simulation was performed as shown below:-

For achieving the given targets, hard points were optimized as shown below:-

The values of required parametes are as follows:-

1) Caster Angle-

a) Initial caster angle = 5.4 deg

b) After tuning the hard points, the final caster angle = 4 deg as required.

Effects:- Reducing the caster angle value will reduce the steering effort but, it will also slightly reduce the straight line stability and high speed stability.

2) Caster Moment Arm -

a) Initial Caster Moment Arm = 8.5 mm

b) After tuning the hard points, the final caster moment arm = ~20 mm.

Effects:- Increasing the caster moment arm value will increase the self-centering torque in the steering system.

3) KPI Angle -

a) Initial Kingpin Inclination Angle = 10.08 deg

b) After tuning the hard points, the final KPI angle = ~13 deg as required.

Effects:- Increasing the kingpin inclination angle will increase the self-centering torque.

4) Steer Axis Offset (Resultant) -

a) Initial Steer Axis Offset (Resultant) = 85.77 mm

b) After tuning the hard points, the final steer axis offset (resultant) = ~86 deg.

Effects:- Steer Axis resultant offset usually has an effect on torque steer. As there is no major change in the before and after value of offset, the effect on torque steer will be negligible.

5) Steer Axis Longitudinal Offset -

a) Initial Steer Axis Longitudinal Offset = -18.74 mm

b) After tuning the hardpoints, the final steer axis longitudinal offset = 0 mm as required.

Effects:- As the longitudinal offset reduces to zero, it will make the moment acting at the wheel center due to this offset as zero and hence, improve the stability of the vehicle.

6) Scrub Radius -

a) Initial Scrub Radius = 33 mm

b) After tuning the hard points, the final scrub radius = ~20 mm as required.

Effect:- Reducing the scrub radius value will reduce the tire wear, increase braking stability and will make the steering less responsive.

The answer to whether we can control all the above the parameters independently is no because all the parameters are interdependent on each other.

The above mentioned targets are achieved by changing the control arm's outer ball joint hard point. If we consider the side view, the X-hard point modification will change the caster angle, the caster moment arm and the steer axis longitudinal offset values. If we change the hard point for tuning any of the three values, the other two are affected.

Similarly, if we consider the front view, the Y-hard point modification of outer ball joint will change the kingpin inclination angle, scrub radius and the steer axis lateral offset. For a particular value of KPI inclination angle and scrub radius, there will be a particluar value of steer axis lateral offset. If we change the offset, the KPI angle may be same, but the scrub radius will change. Thus, in short if we change the hard point for tuning any of the three values, the other two are affected.

Thus, all the values are dependent on each other and we cannot tune each value independently.

The model file for this challenge is attached...