(Kirpal Singh) Steering

Introduction to Front Axle and Steering

  • Primary Function of Steering System: Achieves angular motion of front wheels to negotiate turns.

    • Achieved through linkage and steering gear converting rotary motion of the steering wheel into angular motion of front wheels.

  • Secondary Functions:

    1. Provides directional stability when driving straight.

    2. Ensures perfect rolling motion of road wheels at all times.

    3. Facilitates recovery to straight position after turns.

    4. Minimizes tire wear.

  • Steering Mechanisms:

    • Traditionally, all vehicles used front wheel steering with the rear wheels following.

    • All-wheel steering is now being utilized in some new vehicle designs.

Requirements of a Good Steering System

  1. Accuracy and ease of handling.

  2. Minimal steering effort, ensuring it is not tiresome for the driver.

  3. Provides directional stability, meaning vehicles should return naturally to the straight position after turning.

Front Axle

  • Axle Types:

    • Dead Axle: Typically a drop forged steel beam; more common in heavier vehicles today.

    • Live Axle: Common in four-wheel and most modern cars.

  • Material:

    • Common steels include 0.4% carbon steel or 1.3% nickel steel, capable of bearing bending and torque loads due to vehicle weight and braking.

  • Shape:

    • Usually I-section in the center for strength with either circular or elliptical ends.

    • Downward sweep at central portion helps maintain low chassis height.

Front Axle Structure

  • Main axle beam connects to stub axles via king pins.

  • Stub Axle Shapes:

    • Can have various configurations including Elliott types.

    • Material typically 3% nickel steel and alloy steels (chromium and molybdenum).

Wheel Assembly and Bearings

  • Front wheel stub axle assembly includes ball bearings adjusted by a nut to manage lubrication leakage from bearings.

  • Independent suspension on modern vehicles replaces rigid axle but retains stub axles connected through ball joints.

Wheel Alignment

  • Defined as positioning of steered wheels to achieve:

    1. Directional stability.

    2. Perfect rolling on steering.

    3. Smooth recovery post turn.

  • Factors: Proper alignment requires wheels that are parallel when moving straight, avoiding conditions of toe-in or toe-out.

    • Toe-In: When wheels are closer at the front.

    • Toe-Out: Closer at the rear.

    • Both configurations induce excessive tire wear and complicate steering.

Key Effects of Alignment Variations

  • Toe-In and Toe-Out Causes:

    • Inefficient wheel angles cause lateral slipping during forward motion.

    • Result in uneven tire wear and increased fuel consumption.

  • Set Back: Distance between front tires; set backs under 6mm are often acceptable.

  • Thrust Angle: Angle between thrust line and centerline of vehicle; if not zero, the vehicle may 'dog track'.

Steering Geometry Factors

  • Includes:

    1. Wheel Balance: Essential for dynamic stability.

    2. Tyre Inflation: Affects steering precision.

    3. Brake Adjustment: Proper adjustment is critical; dragging brakes can pull to one side.

Specific Steering Geometry Terms

  • Camber: Tilt of car wheels from vertical, affecting tire wear and steering stability. Positive camber improves steering returnability but may increase effort required.

  • King Pin Inclination (KPI): The axis from which steering is controlled; influences stability. Normal inclination ranges from 7 to 8 degrees.

  • Combined Angle: The angle between the wheel centerline and king pin centerline; influences steering behavior under driving conditions.

  • Caster: Angle between king pin line and vertical; affects directional stability.

  • Toe-In or Toe-Out: The measure of how closely the wheels sit towards each other during stationary positioning.

Mechanical Properties of Steering Angles

  • Steering adjustments from positive to negative camber impact tire life and steering precision during curves.

  • The correct camber settings are usually limited to 2 degrees for optimal performance.

Steering Mechanisms**

  • Types:

    1. Ackermann Mechanism: Commonly used for its simplicity and effectiveness; turns stub axles based on wheel angles during cornering.

    2. Worm and Wheel: Simplistic design converting rotational motion into linear; adjustable for wear compensation.

    3. Rack and Pinion: Frequently used in modern vehicles for its responsiveness and small space requirement.

Advanced Steering Features

  • Power Steering:

    • Hydraulic assistance reduces required steering force. Ideal for larger vehicles, enhancing maneuverability, and driver comfort, while also absorbing road shocks.

  • Electronic Steering Systems: Use sensors and control units to optimize steering dynamics and assist in driver efforts, enhancing performance without the downsides of fluid leakage or dependency on engine running.

Conclusion

  • Four-Wheel Steering: Involves steering of both front and rear wheels enhancing cornering stability and maneuverability, but complexity prevents widespread adoption.

  • Steering Adjustments and Diagnostics: Key for maintaining optimal vehicle operation; each factor must be considered to ensure safety and performance.