Module 7: Suspension Systems Lecture Notes

Module 7: Construction of Different Suspension Systems Overview

  • Objective: By the end of this module, students should be able to:
    • Describe different front suspension systems and the functioning of individual components (Unit 7.1).
    • Describe different rear suspension systems and the functioning of individual components (Unit 7.2).
    • Explain the importance of suspension systems in relation to safety and comfort (Unit 7.3).
    • Explain the working of different shock absorber systems (Unit 7.4).
    • Identify special tools to use when testing or working on car suspension systems (Unit 7.5).

Key Technical Vocabulary and Definitions

  • Front axle: A solid rotating shaft connecting the front wheels of a vehicle.
  • Leaf spring: A spring that is constructed from curved metal strips that are clamped together into a single unit.
  • Shock absorber: A device that absorbs mechanical bending.
  • Rigid: Stiff and resistant to bending.
  • Coil spring: A wire bent into a spring with a cylindrical outline.
  • Ball joint: A joint that consists of a ball connected to a socket, allowing rotational movement in all directions.
  • Strut: A brace or support.
  • Shock absorber and spring combo: A combination of a spring and shock absorber.
  • Body movement: The up-and-down movement of a vehicle.
  • Sway: The side-to-side movement of a vehicle.
  • Lean and roll: The tilting of a vehicle body when cornering.
  • Handling: A vehicle's ability to accelerate, brake and corner safely.
  • Dissipates: Distributes in different directions (e.g. energy).
  • Oversteer: A situation where the rear tyres lose traction in a turn.
  • Understeer: A situation where the front tyres lose traction in a turn.
  • Ride: A vehicle's ability to deliver a smooth ride when driving over rough surfaces.

Unit 7.1: Front Suspension Systems and Components

There are two main categories of front suspension: Dependent and Independent.

Dependent Front Suspension
  • Construction: In these systems, the two front wheels are connected by a solid bar referred to as the front axle.
  • Components: The front axle is held in place by leaf springs and shock absorbers.
  • Mechanism: Because of the rigid connection, the movement of the front tyres is dependent on one another.
  • Usage: This system is considered outdated and is currently only utilized on trucks.
  • Visual Components (Figure 7.1): Solid axle, Leaf spring, Axle beam, and King pin.
Independent Front Suspension

In an independent system, the two front tyres are capable of moving independently of each other. There are two primary types:

  1. MacPherson Strut:

    • Description: A light and compact suspension system often used on front-wheel drive vehicles.
    • Composition: It consists of a single unit that combines a shock absorber and a coil spring.
    • Connectivity: The unit connects to the lower arm via a ball joint.
    • Cargo/Load: In this specific system, the strut itself carries the load of the vehicle, rather than the shock absorber and spring combo.
    • Regional Popularity: This is the most common front suspension system found in vehicles manufactured in Europe.
    • Historical Note: Developed in 19471947 by Earle S. MacPherson while he was an employee at General Motors.
    • Anatomy (Figure 7.2): Includes the Shock absorber, Spring, Strut, Steering rod, Hub, Axle shaft, Rubber boot, Brake disc, and Flange.

  2. Double-Wishbone Suspension (A-arm Suspension):

    • Construction: Each front wheel is located by two wishbone-shaped arms.
    • Mounting: Each wishbone is mounted to the vehicle frame at two points and to the wheel at one point.
    • Assembly: The wishbone assembly connects to the vehicle through a shock absorber and coil spring combo.
    • Purpose: Commonly found in large cars because it reduces vehicle sway.
    • Anatomy (Figure 7.3): Includes the Upper wishbone, Half-shaft, Tie rod, and Lower wishbone.

Important Suspension Components

Springs

Automobiles utilize three primary types of steel springs:

  • Coil springs
  • Leaf springs
  • Torsion bars

Functions of Springs:

  1. To compensate for irregular driving surfaces.
  2. To maintain the suspension system at a specific height.
  3. To prevent the vehicle from sagging under the weight of additional loads.
Shock Absorbers

Shock absorbers serve two primary functions:

  1. To stabilise the vehicle by limiting lean and roll.
  2. To limit body movement and sway.
Auxiliary Components
  • Anti-roll bar (Anti-sway bar): A metal bar connecting the suspension on each side of the vehicle. It reduces sway by transferring movement from one side of the suspension to the other.
  • Control arm: A lever that serves to attach the steering knuckle to the vehicle frame.
  • Steering knuckle: The component that provides support for the wheel hub, wheel bearings, and the wheel assembly.
  • Ball joints: Joints that allow movement in multiple directions. They allow the control arm to move vertically while enabling the steering knuckle to swivel horizontally.
  • Bushings: Rubber sleeves that allow joints to move without causing wear between the two joined parts. They also serve to reduce vibrations transmitted from one part to another.

Unit 7.2: Rear Suspension Systems

There are two main types of rear suspension, mirroring front suspension principles:

Dependent Rear Suspension
  • Works identically to dependent front suspension.
  • The rear wheels are connected by a solid axle.
  • The axle is maintained in place using shock absorbers paired with either leaf springs or coil springs.
Independent Rear Suspension
  • The options for independent rear suspension are identical to those for the front.
  • Versions of the MacPherson strut or double-wishbone systems can be found on the rear axle and function in the same manner.

Unit 7.3: Importance of Suspension for Safety and Comfort

Safety and Handling

The suspension increases the vehicle's "handling" (ability to accelerate, brake, and corner safely) via the following methods:

  • Energy Dissipation: It absorbs and dissipates energy from road irregularities, preventing excessive 'bouncing' and improving driver control.
  • Tire Grip: By reducing body movement and sway, the suspension ensures tyres maintain better grip on the road.
  • Stability: It reduces lean and roll during cornering, which improves handling.
  • Directional Control: It reduces oversteer and understeer, ensuring all wheels react more effectively during turns.
Comfort and Ride

The suspension increases the "ride" (smoothness over rough surfaces) via the following methods:

  • Bounce Reduction: Ensures the vehicle does not bounce excessively, making the experience more comfortable for passengers.
  • Steady Ride: Reduces body movement, sway, lean, and roll to provide a steady, comfortable environment for occupants.

Assessment Activities

Activity 7.1: Front Suspension (Pairs Workshop)
  1. Assign a vehicle with lecturer supervision.
  2. Identify the installed front suspension system type.
  3. Identify individual components of the system.
  4. Determine if leaf or coil springs are utilized.
  5. Document findings in a logbook for lecturer sign-off.
Activity 7.2: Rear Suspension (Pairs Workshop)
  1. Assign a vehicle with facilitator supervision.
  2. Identify the installed rear suspension system type.
  3. Identify individual components of the system.
Activity 7.3: Safety and Comfort (Group Brainstorming)
  1. Discuss how road suspension systems affect comfort and safety.
  2. Share personal experiences regarding uncomfortable rides or vehicles with bad handling.
  3. Present group ideas to the class (No formal assessment).