Steering System Ackerman Linkage geometry Road wheel geometry

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Steering System • • • Ackerman Linkage geometry Road wheel geometry Caster Kingpin inclination

Steering System • • • Ackerman Linkage geometry Road wheel geometry Caster Kingpin inclination Compliance effects

Ackerman Steer do L = ----L d o = tan-1 ----- R+t/2 L =

Ackerman Steer do L = ----L d o = tan-1 ----- R+t/2 L = ----L d i = tan-1 ----R-t/2 For large radii, R >> t/2 di L d. Ack = -R L R t/2 Turn Center

Ackerman – Truck Steering System Straight ahead Right turn Left turn

Ackerman – Truck Steering System Straight ahead Right turn Left turn

Ackerman Steer ra a P l lel 50% n ma r e Ack

Ackerman Steer ra a P l lel 50% n ma r e Ack

Car Steering Systems Rack and pinion Steering arm Gearbox Rack Tire rod Gearbox Idler

Car Steering Systems Rack and pinion Steering arm Gearbox Rack Tire rod Gearbox Idler arm Relay link Steering arm Pitman arm

Truck Steering Systems Tire rod Steering arm Gearbox Pitman arm Drag link

Truck Steering Systems Tire rod Steering arm Gearbox Pitman arm Drag link

Compliance in Steering System

Compliance in Steering System

Geometry at the Wheel

Geometry at the Wheel

Lateral Inclination Angle

Lateral Inclination Angle

Torques from Lateral Inclination

Torques from Lateral Inclination

Caster Angle

Caster Angle

Torques from Caster Angle

Torques from Caster Angle

Lateral Force

Lateral Force

Tractive Force

Tractive Force

4 Wheel Steer - Low Speed R= L d (1 + dr /df )

4 Wheel Steer - Low Speed R= L d (1 + dr /df ) f

4 Wheel Steer - High Speed • Four-wheel in-phase steering • Only at high

4 Wheel Steer - High Speed • Four-wheel in-phase steering • Only at high speed (typically above 35 mph) • Rear steer angles less than front • Rear steer angles limited to a few degrees

Steering System Applications • Effect of steering geometry on performance – Understeer (linear range)

Steering System Applications • Effect of steering geometry on performance – Understeer (linear range) – Limit cornering (non-linear range) • Steering torques and feel – On-center feel – Torque gradients – Linearity – Power assist characteristics – Friction and damping • Evaluate effects of asymmetry – Manufacturing tolerance

Steering Ratio = Steering wheel angle (deg) / Road wheel angle (deg) Steering ratio

Steering Ratio = Steering wheel angle (deg) / Road wheel angle (deg) Steering ratio for cars = 15 to 20 Steering ratio for trucks = 20 to 40

Steering Ratio

Steering Ratio

Assignment • Design linkage geometry to meet requirement of the minimum turn radius and

Assignment • Design linkage geometry to meet requirement of the minimum turn radius and provide close to Ackerman geometry (X-Y plane is ok) • Design steering ratio with measurements on your car