Functions of Suspension Systems

As previously mentioned, it is mostly assumed that the only function of a suspension system is the absorption of road roughness; however, the suspension of a vehicle needs to satisfy a number of requirements with partially conflicting aims as a result of different operating conditions. The suspension connects the vehicle’s body to the ground, so all forces and moments between the two go through the suspension system. Thus, the suspension system directly influences a vehicle’s dynamic behavior. Automotive engineers usually study the functions of a suspension system through three important principle.

• Ride Comfort: Ride comfort is defined based on how a passenger feels within a moving vehicle. The most common duty of the suspension system is road isolation—isolating a vehicle body from road disturbances. Generally, ride quality can be quantified by the passenger compartment’s level of vibration. There are a lot of inner and outer vibration sources in a vehicle. Inner vibration sources include the vehicle’s engine and transmission, whereas road surface irregularities and aerodynamic forces are the outer vibration sources. The spectrum of vibration may be divided up according to ranges in frequency and classified as comfortable (0–25 Hz) or noisy and harsh (25–20,000 Hz).

• Road Holding: The forces on the contact point between a wheel and the road act on the vehicle body through the suspension system. The amount and direction of the forces determine the vehicle’s behavior and performances, therefore one of the important tasks of the suspension system is road holding. The lateral and longitudinal forces generated by a tire depend directly on the normal tire force, which supports cornering, traction, and braking abilities. These terms are improved if the variation in the normal tire load is minimized. The other function of the suspension is supporting the vehicle’s static weight. This task is performed well if the rattle space requirements in the vehicle are kept minimal.

• Handling: A good suspension system should ensure that the vehicle will be stable in every maneuver. However, perfect handling is more than stability. The vehicle should respond to the driver’s inputs proportionally while smoothly following his/her steering/braking/accelerating commands. The vehicle behavior must be predictable, and behavioral information should accordingly be communicated to the driver. Suspension systems can affect vehicle handling in many ways: they can minimize the vehicle’s roll and pitch motion, control the wheels’ angles, and decrease the lateral load transfer during cornering.