As we know, the elastic components of the independent suspension of passenger cars mostly use coil springs, and the elastic components of non-independent suspension mostly use leaf springs. Due to the simple steel structure and reliable use, leaf springs are widely used, such as some off-road vehicles, pickups or vans. However, most buses and trucks use leaf springs.
Leaf springs are springs made of steel plates, which are also called leaf springs. In order to make full use of the material, the leaf spring is made into a form close to the stress beam. It has two types, one is equal thickness, the width is narrow at both ends and wide in the middle. The traditional multi-piece leaf spring is of this type. This type of leaf spring is composed of multiple steel plates with different lengths and the same width. Nowadays, most buses and trucks use this type of leaf spring.
The other is equal width, the thickness is thin at both ends and thick in the middle. The common small-leaf leaf springs are of this type. The small-leaf leaf spring refers to a variable-section leaf spring with only 1 to 4 pieces. The variable-section leaf spring refers to the thickness of the center along the length of the steel plate and gradually becomes thinner at both ends, or Leaf spring with gradual change in width and thickness. It is mostly used in light vehicles, and now some large and medium-sized passenger cars also tend to use this type of leaf spring.
Some small-leaf leaf springs use only one leaf spring. Compared with multiple leaf springs, apart from reducing noise and avoiding friction, they can also save materials, reduce weight, facilitate layout, reduce the height of the vehicle, and have good ride comfort.
The section of the steel plate of the small leaf spring changes greatly, and the section from the middle to the two ends is gradually different, so the rolling process is more complicated. In order to reduce the weight and the difficulty of the rolling process, a fiber reinforced plastic (FRP) has appeared in recent years to replace the steel plate, which can reduce the weight by more than half. This fiber-reinforced plastic is made of glass fibers and polymerized together with polyester resin.
The middle part of the leaf spring is fixed on the axle by U-shaped bolts (also called riding bolts), and the curling ears at both ends are hinged on the bracket of the frame with pins. In this way, the axle is connected to the vehicle body through the leaf spring, which plays the role of buffering, damping and transmitting force. The steel plates of multiple leaf springs are superimposed into an inverted triangle shape. The uppermost steel plate is the longest and the lowermost steel plate is the shortest. The number of steel plates is related to the weight of the car and the shock absorption effect. The more steel plates, the thicker and shorter. The greater the spring stiffness.
However, when the leaf spring flexes, the pieces will slide and rub against each other to generate noise. Friction can also cause spring deformation, causing uneven driving. Therefore, in cars with low load capacity, few leaf springs appear to eliminate the defects of multiple leaf springs.
According to calculations, the weight of a general single leaf spring is about 11-20 kg, and the weight of fiber-reinforced plastic spring is about 4 kg, and the driving is stable and the noise is very low.