Automobile suspension system spring working principle and modification method

The existence of the suspension system has two meanings: Isolate the unevenness of the road to make driving more comfortable; keep the tires in contact with the road when traveling on uneven roads. The improved suspension has only one purpose for the “speeding party” is to improve handling.

The coil spring is the most commonly used spring of the suspension system because it is easy to manufacture, high performance and efficiency, and low price. The definition of a spring in physics is to store energy. When we apply a fixed force to the spring, it will deform. When we remove the force, the spring will have a tendency to return to its original state, but the spring will shake when it rebounds.

 

The amplitude tends to exceed its original length, and it will not slow down the free shock caused by the spring rebound until there is frictional resistance, which is usually the task of the shock absorber. The general spring is the so-called (linear spring), that is, when the spring is stressed, its compression deformation follows the physics (Hooke’s law): F=KX, where F is the applied force, K is the elastic force coefficient, and X Is the amount of deformation. For example, when a linear spring is subjected to a force of 40Kg, it will cause a compression of 1cm, and then every increase of 40Kg of applied force by 1cm will definitely increase the amount of compression.

 

In fact, there are other pressures on the suspended springs. Even when the springs are fully extended, the springs are still under pressure to fix the springs on the car. In the traditional spring and shock-absorbing cylinder suspension design, the spring acts to support the body and absorb the impact of uneven roads and other forces on the tires. The so-called other forces here include acceleration, deceleration, braking, turning, etc. The force caused by the spring. What’s more important is to keep the tires in constant contact with the road during the vibration elimination process to maintain the tracking of the car. Improving the contact between the tire and the road is our primary consideration for improving handling. The main function of the spring is to maintain the comfort of the car and keep the tires in full contact with the ground. Using the wrong spring will have a negative impact on the driving quality and handling.

 

Imagine if the spring is completely rigid, the suspension system will not work. When the car jumps up on uneven roads, the tires will completely leave the ground. If this happens when accelerating, braking or turning, the car will lose track. If the spring is very soft, it is easy to appear (sit on the bottom), that is, use up the travel of the suspension. If sitting on the bottom occurs when cornering, it can be considered that the spring coefficient becomes infinite (there is no compressed space), and the body will have an immediate weight transfer, resulting in loss of tracking.

 

If this car has a long suspension stroke, it may be possible to avoid the situation (sit bottom), but the relative body will also become very high, and a very high body means a very high center of gravity of the body. The high or low has a decisive influence on the handling performance, so too soft shock absorbers will cause handling obstacles. If the road is absolutely flat, then we don’t need springs and suspension systems. If the road is rough, a softer spring is needed to ensure that the tire is in contact with the road, and the travel of the spring must be increased. The choice of spring hardness is determined by the ruggedness of the road. The more rugged the spring, the softer the spring, but how soft it is is a key issue. Usually this requires the accumulation of experience and is also an important issue for various car manufacturers and teams.

 

Generally speaking, a soft spring can provide better comfort and maintain better tracking performance when traveling on a rougher road. However, when traveling on general roads, the suspension system will swing up and down, which will affect the handling. In a car equipped with good aerodynamic components, the soft spring will cause the height of the car to change when the speed increases, resulting in different handling characteristics at low and high speeds.

 

Modification of the spring

The modification of the spring is mainly to improve the controllability, that is, to use a harder spring or a shorter spring. The spring controls many factors related to the control, and the change of the spring will cause very complicated changes in the control characteristics. In terms of the increase in hardness, it can improve the suspension’s rolling restraint ability and reduce the rolling of the body when cornering. The reduction in vehicle height can also reduce the center of gravity of the vehicle body, reduce the weight transfer of the vehicle body when cornering, and improve stability. The reduction in vehicle height can also take into account the aesthetic effect.

 

Progressive spring

Springs have two main functions: one is to act as a suspension system or a buffer between the chassis and the ground, that is, to maintain comfort, and the other is to keep the tires on the ground when the car passes on uneven roads. To achieve these two conflicting goals, different elastic coefficients are required. Keeping the tires on the ground has a decisive influence on the handling. We need hard spring settings to keep the tires on the ground. We need a softer spring setting when encountering more bumpy roads. To achieve these two goals at the same time, the only feasible method is to use a (non-linear spring) with a composite elastic coefficient, which is generally called a progressive spring.

 

Progressive springs can increase the coefficient of elasticity with the compression of the spring, which is quite difficult in design and manufacturing. When traveling on bumpy roads, the coefficient of elasticity will increase to maintain the stability of the body. The initial softer elasticity coefficient is used to improve the tire’s grounding performance when traveling on bumpy roads. Gradually stiffer springs can avoid suspension or spring sitting on the bottom.

 

This allows the use of lower-height springs to lower the center of gravity of the vehicle body, and maintain the lowest and shortest suspension stroke when traveling on bumpy roads, and avoid sitting on the bottom. To achieve a progressive spring, it is necessary to make a non-linear spring whose elasticity coefficient changes with compression. Therefore, the current progressive springs are mostly springs with unequal pitch springs or springs with varying diameters. When the unequal pitch spring is compressed, it will produce local line contact, so that the effective number of turns will change, which will cause the change of the elastic force coefficient K. The change in the diameter of the upper and lower coils of the spring is the most direct way to change the coefficient of elasticity.

Lower body

The most important way to improve handling is to lower the center of gravity of the body, which can reduce the weight transfer and rolling of the body when cornering. The easiest way to lower the body is to start with the spring. Using a short spring is the easiest and fastest method.