Function and maintenance of the automotive suspension system

A suspension system is the entire support system consisting of springs and shock absorbers between the body and the tires. The suspension system should function to support the body, improve the feeling of the ride. Different suspension settings will make the driver have a different driving experience.

The appearance of a simple suspension system to integrate various forces determines the stability of the care, comfort, and safety is one of the modern cars is very critical components.

Working principle

The suspension system exists for two reasons: to isolate the unevenness of the road to make driving more comfortable; travel through the uneven road to keep the tires in contact with the road. And improve the suspension for the “flyers,” only one purpose is to improve the handling.

Suspension springs are most commonly used as coil springs because they are easy to make, efficient in performance, and inexpensive. The definition of spring in physics is to store energy. When we apply a fixed force to the spring, it will produce deformation. When we remove the applied force, then the spring will have a tendency to return to its original state, but the spring in the spring back oscillation amplitude will often exceed its original length until the emergence of friction resistance will slow down the spring back after the free oscillation caused by this slow spring free oscillation work is usually the task of the shock absorber. A typical spring is a so-called (linear spring), which means that the amount of compression and deformation of a spring under force follows the physics (Hooke’s law): F=KX, where F is the applied force, K is the elasticity coefficient, and X is the deformation. For example, a linear spring carrying a weight of 40Kg will cause a compression of 1cm, after which each additional 40Kg of weight will definitely increase the compression of the spring by 1cm.

In fact, there are other pressures on the suspension spring, and even when the spring is fully extended, the spring is still under pressure in order to keep the spring itself in place on the car. In a conventional spring, shock-absorbing cartridge suspension design, the spring plays the role of supporting the body and absorbing the impact caused by uneven road surfaces and other forces on the tires, and the so-called other forces here include those caused by acceleration, deceleration, braking, cornering, etc. What is more important is to keep the tire in constant contact with the road during the process of vibration elimination to maintain the car’s traction. Improving the contact between the tires and the road is our primary consideration to improve the handling.

The main function of springs is to maintain the car’s comfort and keep the tires in full contact with the ground, and using the wrong springs will have a negative impact on both driving quality and handling. Imagine if the springs are completely stiff, the suspension system will not work. When the car jumps up on an uneven surface, the tires will be completely off the ground, and if this happens during acceleration, braking, or cornering, the car will lose traction. If the springs are very soft, it is very easy to bottom out, which means the suspension will run out of travel. If the bottoming out occurs during cornering, the spring coefficient becomes infinite (there is no room for compression), and there is an immediate weight transfer, resulting in a loss of traction. If the car has a long shock trip, then it may be possible to avoid bottoming out, but the relative body will also become very high, and a very high body means a very high center of gravity, which has a decisive impact on handling performance, so too soft shocks will lead to handling obstacles.

If the road is absolutely flat, then we don’t need springs and suspension. If the road is rougher, then softer springs are needed to ensure that the tires are in contact with the road, and the spring travel must be increased. The roughness of the road determines spring stiffness, the rougher the road, the softer the spring, but how soft is a critical issue, usually requiring experience, and is an important issue for all car manufacturers and teams. Generally speaking, softer springs provide better comfort and maintain better traction over rougher roads. However, it will cause the suspension system to sway up and down more when traveling over normal roads, affecting the handling. In cars with good aerodynamic components, soft springs can cause a change in height at higher speeds, resulting in different handling characteristics at low and high speeds.

The role of springs

Springs have two main functions: to act as a cushion between the suspension or chassis and the ground, that is, to maintain comfort, and to keep the tires on the ground when the car travels over uneven surfaces. To achieve these two conflicting goals requires a different elasticity factor. Keeping the tires on the ground has a decisive effect on handling. We need a stiffer spring setting to keep the tires on the ground—the more bumpy the road we encounter, the softer the spring setting.

Accomplish both of these things simultaneously, it is possible to use springs with a compound spring coefficient (non-linear springs), also known as progressive springs. Progressive springs increase the spring force coefficient as the spring is compressed, which is difficult to design and manufacture. When traveling over bumpy roads, the coefficient of elasticity increases to maintain body stability. The initial softer spring is used to improve tire adhesion on bumpy roads. A progressively stiffer spring prevents the suspension or spring from bottoming out. This allows a lower-height spring to lower the center of gravity and maintain the lowest and shortest suspension travel over bumps without bottoming out.

To achieve a progressive spring, make a non-linear spring with a coefficient of elasticity that changes with the compression. Most of the progressive springs use unequal-pitch springs or springs with varying diameters. When spring with unequal pitch is compressed, it produces a partial interlinear contact, which causes the effective number of turns to change and the coefficient of elasticity K to change. The most direct way to change the coefficient of elasticity is through the change in the diameter of the upper and lower coils of the spring.

Spring Modification

The main purpose of spring modifications is to improve handling, i.e., to use stiffer springs or shorter springs. Springs control many factors related to handling, and changes in springs can result in very complex changes in handling characteristics. For example, an increase in stiffness can improve the suspension’s ability to dampen the roll and reduce body roll during cornering. A reduction in height also lowers the center of gravity, reducing weight transfer during cornering and improving stability. And the height reduction can also take into account the aesthetic effect.

Troubleshooting

First, the failure phenomenon: car driving, every up and down vibration, the suspension device issued a “clucking” sound, indicating that the suspension device is not working properly.

Second, the cause of failure
   (1) shock absorber damage.
   (2) shock absorber sleeve is broken.
   (3) loose fastening bolts.

Third, the fault inspection and troubleshooting methods
The normal shock absorber will be hot when it works. If it is not hot or found that the shock absorber is leaking oil, it means that the shock absorber has been damaged. When checking, you should also check the condition of the shock absorber sleeve, and if it is found to be broken, it should be replaced together with the shock absorber in time.

Maintenance

The so-called suspension system is, between the wheels and the car body, to bear the body and absorb the work of vibration to provide the best ride comfort. After replacing the brake pads, check whether the brake pedal returns to normal, and pay attention to prevent the footpad from slipping under the brake pedal during daily driving so that the brakes cannot be applied. Under normal circumstances, the shock absorber will get hot when it works. If it does not get hot, it means the shock absorber is leaking oil. In daily use, pay attention to check whether the vehicle runs off when braking, how effective the brake is, and how effective the parking brake (hand brake) is. The braking system should be maintained. When performing vehicle maintenance, the brake system should first be inspected for brake fluid, such as whether the brake pipe is ruptured and any brake fluid leakage. The brake pedal is also a component that needs attention.

When the car is running, the suspension system will make a “thumping” sound every time it shakes up and down, and the sound will intensify when it reaches uneven roads, which means that the suspension system is malfunctioning, probably because the shock absorber is damaged or the shock absorber sleeve is broken. Brake system brake fluid should not be mixed. Most cars on the market are equipped with two sets of the braking system: foot-controlled driving brake (brake) and hand-controlled parking brake (hand brake). If the rubber sleeve is severely damaged, it should be repaired and replaced with a shock absorber.

Suspension system shock absorber should be hot when working Suspension system not only affects the car ride comfort (smoothness), but also has an impact on other performance such as passability, stability, and adhesion performance. It turns out that the suspension system contains shock absorbers, springs, anti-roll bars, connecting rods, and other mechanical components. In turn, especially a sharp turn, the body tilts too much, indicating that the shock absorber, stabilizer bar, or guide mechanism components have been damaged. When replacing the brake fluid, drain the original brake fluid, not mix it, and not mix air inside the brake fluid. Generally speaking, the degree of wear and tear of the brake pads has a great relationship with the use of habits, the brake pads of automatic cars to use than the manual gear fee, generally, more than 20,000 kilometers later, every time you do maintenance to check the sprinkler brake pads. This can better protect the suspension system.