According to the different separation connecting mechanism, the fifth wheel can be divided into splint type and hook pin type. Fixed type the fifth wheel is the most widely used one at present. Its support is fixed on the frame of traction vehicle, and the fifth wheel is allowed to have a certain degree of freedom on the support.
After the tractor is connected with the semi-trailer, first pull the safety baffle to one side, and then pull and pull the handle to make the locking block move forward to the I-shaped gap away from the splint. The spring is compressed, and the front end of the splint is pulled together by the fixed spring, and it is against the locking block. Then drive the tractor forward, that is to complete the semi-trailer uncoupling. Before uncoupling, the supporting device of semi-trailer should also be lowered.
For the important device of the link between tractor and semi-trailer, the types of the fifth wheel also vary according to the different use conditions of vehicles. It is divided into two categories: 2inch(50.8mm) and 3.5 inch (90mm).
The 2inch king pin is usually enough for the normal road transport trailer, while the 3.5 inch one is mostly used on the construction machinery transport trailer and special trailer. In addition to the difference of the corresponding trailer king pin, the height of the tractor installed on the chassis of the same tractor is also different. When the fifth wheel of 2 inch is empty, the height of the fifth wheel above the ground is less than 3.5inch. Of course, the height of the trailer after coupling is lower and the vehicle stability is better.