Suspension is the term given to the system of springs , shock absorbers and linkages that connects a vehicle to its wheels . Suspension systems serve a dual purpose — contributing to the car’s road holding handling and braking for good active safety and driving pleasure, and keeping vehicle occupants comfortable and reasonably well isolated from road noise, bumps, and vibrations, etc. These goals are generally at odds, so the tuning of suspensions involves finding the right compromise. It is important for the suspension to keep the road wheel in contact with the road surface as much as possible, because all the forces acting on the vehicle do so through the contact patches of the tires. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear. The design of front and rear suspension of a car may be different.
Figure 1: Locating Suspension Units
A suspension system comprises springs, shock absorbers and linkages. This suspension connects an automobile to its wheels. The suspension systems not only help in the proper functioning of the car’s handling and braking, but also keep vehicle occupants comfortable and make your drive smooth and pleasant. It also protects the vehicle from wear and tear. To know about the suspension system, one needs to know about the spring rate or suspension rate. Various spring types are used for different vehicles. In case of heavier suspension loads, the spring rate is higher and vice versa. Spring rate is measured as a ratio used to measure how resistant a spring is to being compressed or expanded during the spring’s deflection Besides spring rate, one needs to take in account the wheel rate. Wheel rate is the effective spring rate when measured at the wheel. It is generally equal to or considerably less than the spring rate.
There are two types of suspension systems- dependent and independent. A dependent suspension comprises a beam that holds wheels parallel to each other and perpendicular to the axle. An independent suspension helps in the rising and falling movement of the wheels. There is also a semi-dependent suspension where the motion of one wheel affects the position of the other but they are not rigidly attached to each other.
The dependent suspension includes Trailing arms, Satchell link, Panhard rod, Watt’s linkage, WOBLink and Mumford linkage. The independent suspensions includes Swing axle, Sliding pillar, MacPherson strut/Chapman strut, Upper and lower A-arm (double wishbone), multi-link suspension, semi-trailing arm suspension, swinging arm and leaf springs.
Air springs combine spring and shock absorbing action in one unit and were often used without metal springs. The first one was developed by Cowey Motor Works of Great Britain in 1909. It was a cylinder that could be filled with air from a bicycle pump through a valve in the upper part of the housing. The lower half of the cylinder contained a diaphragm made of rubber and cord which, because it was surrounded by air, acted like a pneumatic tire. Its main problem was that it often lost air.
The newest air spring, developed by Goodyear, is found on some late-model Lincolns. Like the ones that have preceded them, these ride-on-air units are more costly than conventional springs and hydraulic shock absorbers.
The air suspension system is an air-operated, microprocessor controlled suspension system. This system replaces the conventional coil spring suspension and provides automatic front and rear load leveling. The 4 air springs, made of rubber and plastic, support the vehicle load at the front and rear wheels’.
An air suspension supports the vehicle on the axles with an arrangement of air bags instead of some type of steel spring, leaf or coil, or some type of torsion spring arrangement. The air bags are sometimes referred to as air springs or bellows. Suspensions that have steel or torsion springs that are supplemented by the use of air bags are not considered air suspensions. There are combination systems that have both air and steel springs. Usually the air suspension components are used on the rear of the vehicle.
Figure 2: Advanced Air Suspension
Depending on the situation, this type of air suspension will probably have to be dealt with for leveling purposes. Normally, the air suspension is just one part of the air system on the vehicle. Most (but not all) vehicle with an air suspension also have air brakes along with other equipment that may be operated with air. Any of these other systems can cause problems with the air suspension. Other air systems including the brake systems in general, will not be discussed in this school. It is important to understand that on vehicles with air systems, especially with air brakes, manufacturers must follow specific regulations when designing their air systems. The brake system will always be the main concern for the air system. There will be safety features installed in the system that make the brake system the main priority for the air system.