TECHNICAL TRAINING ON HOW STRUTS/SHOCK ABSORBERS WORK
The job of a car suspension is to maximize the friction between the tires and the road surface, to provide steering stability with good handling and to ensure the comfort of the passengers. In this article, we’ll explore how car suspensions work, how they’ve evolved over the years and where the design of suspensions is headed in the future.
If a road were perfectly flat, with no irregularities, suspensions wouldn’t be necessary. But roads are far from flat. Even freshly paved highways have subtle imperfections that can interact with the wheels¬ of a car. It’s these imperfections that apply forces to the wheels. According to Newton’s laws of motion, all forces have both magnitude and direction. A bump in the road causes the wheel to move up and down perpendicular to the road surface. The magnitude, of course, depends on whether the wheel is striking a giant bump or a tiny speck. Either way, the car wheel experiences a vertical acceleration as it passes over an imperfection.
Without an intervening structure, all of wheel’s vertical energy is transferred to the frame, which moves in the same direction. In such a situation, the wheels can lose contact with the road completely. Then, under the downward force of gravity, the wheels can slam back into the road surface. What you need is a system that will absorb the energy of the vertically accelerated wheel, allowing the frame and body to ride undisturbed while the wheels follow bumps in the road.
The study of the forces at work on a moving car is called vehicle dynamics, and you need to understand some of these concepts in order to appreciate why a suspension is necessary in the first place. Most automobile engineers consider the dynamics of a moving car from two perspectives:
• Ride – a car’s ability to smooth out a bumpy road
• Handling – a car’s ability to safely accelerate, brake and corner
These two characteristics can be further described in three important principles – road isolation, road holding and cornering. The table below describes these principles and how engineers attempt to solve the challenges unique to each.
|Road Isolation||The vehicle’s ability to absorb or isolate road shock from the passenger compartment||Allow the vehicle body to ride undisturbed while traveling over rough roads.||Absorb energy from road bumps and dissipate it without causing undue oscillation in the vehicle.|
|Road Holding||The degree to which a car maintains contact with the road surface in various types of directional changes and in a straight line (Example: The weight of a car will shift from the rear tires to the front tires during braking. Because the nose of the car dips toward the road, this type of motion is known as “dive.” The opposite effect — “squat” — occurs during acceleration, which shifts the weight of the car from the front tires to the back.)||Keep the tires in contact with the ground, because it is the friction between the tires and the road that affects a vehicle’s ability to steer, brake and accelerate.||Minimize the transfer of vehicle weight from side to side and front to back, as this transfer of weight reduces the tire’s grip on the road.|
|Cornering||The ability of a vehicle to travel a curved path||Minimize body roll, which occurs as centrifugal force pushes outward on a car’s center of gravity while cornering, raising one side of the vehicle and lowering the opposite side.||Transfer the weight of the car during cornering from the high side of the vehicle to the low side.|
A car’s suspension, with its various components, provides all of the solutions described.
Excess vibration/movement due to worn shocks and struts may cause
unnecessary and accelerated wear on other suspension components,
including brakes and tires.
Why Shocks and Struts Wear Out…
• Under normal conditions on a smooth road, shocks stroke on average 1,750 times for every 1 mile traveled. This equals 7.5 million stabilizing actions on average every 12,000 miles (20,000 kilometers).
• Shocks and struts operate in an uncontrolled environment (weather, temperature, road conditions).
• Individual driving habits.
• Condition of other suspension components.
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