Introduction to dolly semi-trailer structure and function

Dolly semi trailer structure details

The main structure of the semi-trailer towing platform includes the tow bar, the tow ring, the safety hook, the tow frame, the tow base, the traveling mechanism, the electrical circuit system, the braking system, etc..

The tow bar (including the tow ring) is the transitional structure connecting the tow tractor and the trailer.
For the A-type semi-trailer towing trailer, the tow bar can either be designed as a rigid connection, formed by welding or screwing with the trailer to form a rigid whole, or it can be designed as a hinged connection structure , so as to achieve relative swing within a certain range in the horizontal plane and improve the steering flexibility of the semi-trailer traction trailer.
For C-type semi-trailer towing trailers, the drawbars are mostly designed to be rigidly connected to improve the connection stability.

Semi-trailer towing trailer with rigidly connected drawbar

Semi-trailer towing trailer with articulated drawbar

Dolly semi trailer functions

The main function of the tow ring is to form a trailer by connecting with the hook at the rear of the trailer or bicycle. Since the traction ring is the main connecting part, it is subjected to a large longitudinal traction force during driving, so its strength must meet the requirements of relevant standards. The standards of each region have clear requirements for it. At present, standard parts and common parts have been formed in North America, Australia and Europe.

When the safety hook is connected to the rear of the trailer and the bicycle, the safety chain next to the safety hook is also connected to the coupling seat of the trailer or bicycle, so as to ensure that in case the hook between the traction ring and the front trailer (or bicycle) comes off, the towing trailer will be connected to the trailer.
The front trailer (or bicycle) continues to be connected, so as to avoid damage to other vehicles caused by unhooking during operation.
Generally, the A-type semi-trailer towing trailer is designed with 2 safety hooks (safety chains), and the C-type semi-trailer towing trailer is designed with a safety chain.

The trailer, as the main bearing structure of the semi-trailer towing trailer, is connected to the traction seat on the top, the suspension and axles on the bottom, and the front end of the trailer is connected to the tow bar.
The frame bears the vertical load transferred from the semi-trailer through the traction seat, and at the same time bears the horizontal pulling force through the tow bar.
Therefore, the bracket is the main bearing structure of the semi-trailer towing trailer, and the legal requirements for the number of axles and loads should be fully considered in the structural design.

The main function of the towing seat is to connect the semi-trailer, and the semi-trailer is connected to the preceding trailer or bicycle through the towing seat on the semi-trailer towing trailer to form a multi-trailer train. The model of the towing seat must match the model of the tow pin of the semi-trailer. At present, there are two types of traction pins commonly used in semi-trailers, 2" and 3.5". Therefore, semi-trailer towing trailers often use two types of tow bases that match these two types of traction pins. The ground clearance of the upper surface of the tow base matches the ground clearance of the semitrailer's tow plate. It is necessary to ensure that the axle load distribution of the semi-trailer trailer meets the requirements of the vehicle axle load standard when the traction seat is installed in the longitudinal position of the semi-trailer trailer.

The running mechanism of the semi-trailer trailer includes axles, suspensions, tires, steel rings, etc. Ordinary follow-up steering axles can be selected for the axles, and active steering axles can also be selected according to actual needs.
Generally speaking, at least one of the axles of the C-type semi-trailer towing trailer is an active steering axle. The suspension can be equipped with mechanical suspension or air suspension according to different road conditions and the use of trailers to transport goods.

The braking system is mainly used to brake the traveling mechanism of the semi-trailer traction trailer itself, and ABS is generally configured at present.

The electrical circuit system is more special. On the one hand, the semi-trailer trailer needs to have its own electrical circuit system to supply its own braking system and lamps.
On the other hand, due to the connection function of its trailer semi-trailer, it needs to provide power and air source for the rear semi-trailer.
Therefore, in addition to matching the conventional electrical pipelines and interfaces, the electrical circuit of the semi-trailer trailer also needs to provide electrical circuit interfaces for the rear semi-trailer.

It can be seen from the structure and functions of the above-mentioned components that the semi-trailer towing trailer itself does not have the general attributes of a vehicle, that is, it cannot realize the function of carrying goods by itself.
Its main function is to realize the connection between trailers (or bicycles) and trailers, so as to form double-trailer trains or even multi-trailer trains, so as to improve the efficiency of logistics and transportation.
At the same time, when the double-trailer train or multi-trailer train needs to be turned on the way, the steering function of the semi-trailer traction trailer can guide the subsequent semi-trailer to turn smoothly, so as to realize the steering of the entire car train.