Adams Assignments – Problem 4 – Steering geometry 2

Work Flow

1-Caster Angle

2-Caster Moment Arm

3-KPI Angle

4-Steer axis offset

5-Steer axis Long. offset

6-Scrub Radius

Firstly the suspension model is opened and runned I parallel wheel travel simulation.

According to this simulation;

1- Caster Angle=5.36 (deg)

Caster angle is the inclination of the steering axis in the side view. İt's effects the stability and steering effort. Pozitif caster inreases steering effort and also creates a counteracting moment when a disturbing side force acts.

2-Caster Moment arm= 8.22 (mm)

İt's also known as mechanical trail. İt is the perpendicular distance between the steering axis and the point of contact between the front wheel and the ground. The larger the distance is the more Self Aligning Moment will produce.

3-KPI angle = 10.1 (deg)

Kingpin angle is a measure of the angle of the suspension steer axis relative to vertical in front view. İt's effects the camber change and also creates the scrub radius.

4-Steer Axis Offset = 85.77 (mm)

İt is the distance between the center of KPI angle and the wheel center point in fornt view. With a larger steer axis offset/spindle length the amount of lift will increase with any steering this causes to have a kickback on the steering.

5-Steer Axis Long. Offset = -18.7 (mm)

İt is a measure of the longitudinal distance between the steer axis and the wheel centre in side view.

6-Scrub Radius = 34.3 (mm)

The scrub radius is the distance in front view between the king pin axis and the center of the contact patch of the wheel, where both would theoretically touch the road. Scrub radius affects the tire's tendency to change the dynamic toe angle during braking and acceleration.

Modification

Firstly we need to know which hardpoint must be change. By considering the side view we can see the Caster angle, Caster Moment arm and Steer Long. axis offset which all depens on the out ball joint of control arms. İf we change these hardpoints then the Caster Angle ,Caster Moment arm and Steer Long. axis offset values will also change.

İf we consider the front view we can see the KPI, Steer axis offset or spindle length and scrub radius. These parameters also depens on the outer ball joint off control arms. That's why we need to arrange the outer ball joint hardpoints.

Changing the hardpoint of a outer ball joint will effect all other parameters. Accroding to this, parameters can not be change individually, because all parameters depends on each other.

Target is to have ;

Caster angle : ~4.00 deg

Caster moment arm : ~21.00 mm

KPI angle : ~13.00 deg

Steer axis offset (resultant) : ~85.00 mm

Steer axis longitudinal offset : ~0.00 mm

Scrub radius : ~20.00 mm

To not have a steer long. axis offset, the inclination axis must be intersect the wheel center in side view.

İf we can set the caster angle 4 degree the caster moment arm must be near to 21 mm automatically.

For Side View Parameters (Caster Angle, Caster Moment arm and Steer Long. Axis offset)

Modified Hardpoints

1- Modified Caster Angle = 3.98 (deg)

2- Modified Caster Moment Arm = 19.98 (mm)

3- Modified Steer Long. Axis Offset = 0 (mm)

For Front View Parameters (KPI, Steer Axis offset and Scrub Radius)

4-Modified KPI Angle = 13.03 (deg)

5- Modified Steer Axis offset = 84.6 (mm)

6-Modified Scrub Radius = 20.6 (mm)