1. ** Define **
- A semi-trailer is a trailer with an axle positioned behind the center of gravity of the vehicle (when the vehicle is evenly loaded) and equipped with a coupling device that transmits horizontal or vertical forces to the tractor. It has no power itself and needs to be pulled by a tractor to drive, which is an indispensable and important means of transport in modern logistics transportation.
2. ** Structure composition **
- ** Frame ** : The frame of a semi-trailer is the skeleton of the entire vehicle, usually made of high-strength steel. The design of the frame should take into account factors such as load capacity, rigidity and lightweight. For example, the use of channel beam structure can ensure strength while reducing weight.
- ** Axle and suspension system **
- The number and type of axles depends on the purpose and carrying capacity of the semi-trailer. Common are single-axle, two-axle and three-axle semi-trailers. The suspension system is responsible for connecting the frame and the axle to cushion the vibration and impact of the vehicle during driving. Air suspension system is a more advanced suspension mode, it can automatically adjust the height according to the vehicle load, improve the driving comfort and the safety of goods.
- ** Compartment **
- The carriage is the part where the goods are loaded, and its forms are various. Flat compartment is suitable for transporting a variety of large, irregular shape of goods, such as building materials, machinery and equipment; The compartment has the characteristics of good closure, suitable for transporting goods with high environmental requirements, such as food, electronic products, etc. The warehouse compartment has unique advantages in the transportation of agricultural products and livestock.
- ** Brake system **
- The braking system of the semi-trailer is crucial. It usually includes service brake, parking brake and emergency brake and other parts. Modern semi-trailer adopts air brake system, through compressed air to push the brake shoe and brake drum contact, to achieve vehicle deceleration and parking. Some high-end semi-trailers are also equipped with anti-lock braking systems (ABS), which can prevent the vehicle's wheels from locking during emergency braking, improving braking safety.
- ** Coupling device **
- The coupling device is the key part of the connection between the semi-trailer and the tractor, mainly including the traction pin, the saddle, etc. The traction pin is installed at the front end of the semi-trailer and is matched with the tractor saddle to achieve force transfer and steering control.