Steering Geometry 1
Aim:
- This challenge tests your understanding of front and side view kingpin geometry. Do these calculations manually (not using a suspension tool like Adams or MotionSolve) to enhance your understanding
It is advisable to do this exercise in an excel sheet so that you can change hardpoints and study the effects. Also, draw a rough sketch using the hardpoints to visualize the suspension
1.Calculate the following geometric parameters:
i.Caster
ii.Mechanical trail
iii.Kingpin inclination angle
iv.Scrub radius
v.Kingpin lateral offset or spindle length
2.If the pneumatic trail is 25mm and the lateral force is 2000 N, calculate the restoring moment acting at he point where the kingpin intersects the ground in the side view
- Suggest a hardpoint recommendation to change the sign of the scrub radius that you calculated
Assume the ground to be at zero elevation (vertical coordinate) and the tire radius to be 300 mm
Coordinate system
X – pointing towards back of the vehicle
Y – pointing towards the right
Z – pointing towards the top
Solution: For caster angle and the mechanical trail we need to draw the side view of the vehicle. here we only need the kingpin axis so we use LCA knuckle ball joint and UCA knuckle ball joint and also the wheel center.
To draw the side view we need to use X and Z coordinates.
The calculation of caster angle and the mechanical trail is shown below:
For Kingpin inclination, scrub radius and the lateral offset we need to draw the front view.here we only need the kingpin axis so we use LCA knuckle ball joint and UCA knuckle ball joint and also the wheel center.
To draw the front view we use Y and Z coordinates. the calculation is shown below:
Results:
Caster angle: 5.37 deg
Mechanical trail: 9.4 mm
Kingpin inclination: 10.01 deg
Scrub radius: 32.34 mm
Lateral offset: 85.30 mm
The restoring moment acting at he point where the kingpin intersects the ground in the side view is given by Lateral force * total trail.
Moment = Force * (Mechanical trail + pneumatic trail )
= 2000 * (9.4 + 25)
= 68.8 Nm
UCA_Knuckle_ball_joint is the hard point recommendation to change the scrub radius sign.