Piecewise Linear Mount

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• Can we have a perfect steering mechanism?
• G. Nakhaie Jazar,
• Presented at
• Meeting at the
• Department of
• Mechanical Engineering Applied Mechanics
• North Dakota State University

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North Dakota
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Outline

• 1- Geometric Conditions
• 2- Quadrilateral Problem
• 3- Short Steering Arm Problem
• 4- Historical Notes
• 5- Recommendations

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System, Nomenclatures

• t Track
• l Wheel Base
• Steer Angle

Mathematical model of front steering wheels
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Inner Wheels,
Inner Wheels Geometrical Constraint
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Outer Wheels,
Outer wheels Geometrical Constraint
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Inner-Outer Relationship
Inner Steer Angle
Outer Steer Angle
Inner-Outer Steer Angle
Ackerman Steering, or Ackerman Geometry
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Ackerman Steering
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Ackerman Steering, t / l
0.4
0.6
0.8
1.0
1.2
1.4
1.6
2.0
2.6
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Steering Mechanism
A Quadrilateral 4-Bar Linkage
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Steering Mechanism
A Quadrilateral 4-Bar Linkage
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Steering Mechanism
A Sample Design, Using Quadrilateral Geometry
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Steering Mechanism
A Quadrilateral 4-Bar Linkage
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Steering Mechanism
A Quadrilateral 4-Bar Linkage
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Pollone Equation
Pollone Equation, or Quadrilateral Equation
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Ackerman-Pollone Error
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Effects of Error

• 1- Increasing wear of front tires.

• 2- decreasing the value of centering torque.

With a correct Ackerman geometry, the centering
torque increases with steer angle.
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Rudolf Ackerman mechanism
Rudolf Ackerman patented steering mechanism, 1817
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Rack and Pinion
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Rack and Pinion
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Rack and Pinion
Alfa Romeo 6, Articulated rack-pinion steering
shaft
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Steering Mechanism
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Steering Mechanism
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Steer Joint Displacement
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Steer Joint Displacement
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Lateral Steering Arms
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Short Lateral Steering Arm
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Rudolf Ackerman mechanism
Rudolf Ackerman patented steering mechanism, 1817
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History
La Mancelle, 1878
LObeissante, 1873
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History
Oldsmobile
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History
Central relay steering system, the first
parallelogram
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New Generations
Ferrari 250 GT and Fiat 465 steering system
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New Generations
Rolls-Royce, steering system
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Recommendations

• Is there any recommended geometry for steering
  mechanism?

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Recommendations
A rule of thumb.
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Ackerman-Pollone Error
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Recommendations

• Low lateral acceleration (Street Cars)
• 1- Use Ackerman geometry to ensure that all the
  wheels roll freely.
• High lateral acceleration (Race Cars)
• 2- Use Parallel or Reverse Ackerman geometry to
  balance load and lateral force.

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Recommendations
Recommended steering system for race cars.
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Recommendations
Application of reverse Ackermann .
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Thank You