Suspension

Page 1: Introduction to Suspension Systems

  • Suspension System Overview

    • Function: Isolates vehicle body from road shocks (bounce, pitch, roll, sway)

    • Components: Springs and dampers collectively called the suspension system.

Objectives of Suspension System

  1. Prevent transmission of road shocks to vehicle components.

  2. Safeguard occupants from road shocks.

  3. Maintain vehicle stability during motion.

Basic Considerations

1. Vertical Loading

  • Forces acting on wheels due to road irregularities (bumps/pits).

  • Absorption through elastic deformations (compression, shear, bending, twisting of springs).

  • Damping reduces vibrations exponentially after hitting a bump.

  • Front springs should oscillate at a lower frequency than rear springs to minimize pitching.

2. Rolling

  • Center of gravity above the ground causes a tendency to roll during turns.

  • Centrifugal force acts outward, while road resistance acts inward, creating a couple.

  • Rolling motion can be stabilized with a stabilizer (discussed in later sections).

3. Brake Dip

  • Occurs while braking and depends on the center of gravity, wheelbase, and suspension characteristics.

  • Acceleration causes lifting of the front of the vehicle.

4. Side Thrust

  • Caused by centrifugal force, cross-winds, and road camber.

  • Often managed by leaf spring rigidity or Panhard rods.

5. Unsprung Weight

  • Definition: Weight of components between suspension and road (e.g., axles, wheels).

  • Larger unsprung weight increases energy stored in vibrations, leading to greater shocks transmitted.

6. Miscellaneous

  • Soft suspension provides comfort but may lead to loss of road contact affecting control.

  • A well-designed suspension balances softness and stiffness.

Function of Suspension Springs

  • Purpose: Absorb energy from road bumps and vibrations.

  • Mechanism: Springs deform when encountering bumps, storing energy, and then returning to shape, causing vibrations that gradually die down due to internal friction.

Types of Suspension Springs

  1. Steel Springs

    • Leaf springs

    • Coil springs

    • Tapered leaf springs

    • Torsion bars

  2. Rubber Springs

    • Compression and composite variations.

  3. Plastic Springs

  4. Air Springs

  5. Hydraulic Springs

Leaf Springs

  • Commonly used for vehicle suspension (light and heavy commercial vehicles).

  • Semi-elliptic leaf springs popular for rear suspension in cars.

Construction of Leaf Springs

  • Consist of multiple leaves (blades) that vary in length.

  • Master leaf has eyes (connections); spring supported by U-bolts and shackles.