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Steering System

Steering System. Ackerman Linkage geometry Road wheel geometry Caster Kingpin inclination Compliance effects. d. i. Ackerman Steer. L. L. d = tan -1 ----- = ----- . o. d. R+t/2. R+t/2. o. L. L. d = tan -1 ----- = -----. i. R-t/2. R-t/2. For large radii, R >> t/2. L.

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Steering System

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

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

  3. Ackerman – Truck Steering System Straight ahead Right turn Left turn

  4. Ackerman Steer 50% Parallel Ackerman

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

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

  7. Compliance in Steering System

  8. Geometry at the Wheel

  9. Lateral Inclination Angle

  10. Torques from Lateral Inclination

  11. Caster Angle

  12. Torques from Caster Angle

  13. Lateral Force

  14. Tractive Force

  15. d (1 + d /d ) r f f 4 Wheel Steer - Low Speed L R =

  16. 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

  17. 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

  18. 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

  19. Steering Ratio

  20. 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

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