Don't think it's just a piece of iron plate

The fifth wheel is the key component connecting the tractor and semi-trailer, playing an important role in transferring the longitudinal and braking forces between the fifth wheel and the trailer.

In addition, the fifth wheel has to bear the impact of various forms of tractor movement such as starting, turning, braking, etc., and its structure directly affects the operational safety of the whole system. 

The tractor fifth wheel is a wear-resistant steel plate in the shape of a swinging horseshoe, on which the trailer pressure acts, and which has a notched semicircular hole in the center, the walls of which are made of impact-resistant forged steel parts.

I. Composition of the fifth wheel

1. fifth wheel body, the main component of the fifth wheel.

It is composed of a shell, a front frame plate, a rear frame plate, an M-shaped frame plate, an inner frame lug, an outer frame lug, a U-shaped plate, and a tail slide cover.

2. Bracket to hold the fifth wheel.

The two brackets are connected to the vehicle's beam via the fifth wheel base plate, which secures the fifth wheel and acts as a support.

3. Tie rods, which are used to govern the relative motion of the locking hook and the inclined iron.

The tie rod realizes the separation of the locking hook from the fifth wheel by driving the inclined iron to move laterally. During normal operation of the semi-trailer, the tie rods are fixed by the locking cams, thus realizing the locking of the locking hooks and fifth wheels and ensuring the connection between the tractor and the semi-trailer.

4. Inclined iron, used to govern the separation and locking of the locking hook.

The inclined iron moves laterally through the driving of the drawbar, assisting the locking hook to rotate at a certain angle to realize the locking and separation of the traction pin.

5. Locking hooks to govern the locking and disengagement of the traction pins.

When the inclined iron is moved to a suitable position, the U-shaped locking hook will be subjected to the tension generated by the spring and then rotate around the pin seat at a certain angle, realizing the locking and separation of the traction pin, and at the same time, realizing the connection and separation of the two vehicles.

II. fifth wheel working principle

1. Disengagement:

Release the insurance, manually pull the lever to the outside, due to the movement of the lever leads to lateral displacement of the inclined iron, at the same time the spring due to the deformation of the tensile force, drive the locking hook around the pin seat rotation, at the same time the locking hook opening to turn to the outside, to realize the traction pin decoupling, complete the separation of the two vehicles.

2. Connection

Repeat the above steps to make the locking hook opening to the outside, when the tractor makes the locking hook opening and the traction pin relative to the backward movement until the collision, the locking hook in the spring rebound effect of rotation to the starting position, at this time will be released by the lever inclined iron automatically return to the original position, the safety pin at the same time also return to the initial position, to realize the locking hook self-locking and realize smooth connection.

III. fifth wheel maintenance

The lifespan of the fifth wheel depends on whether or not grease is applied to the fifth wheel panels, the mating surfaces of the traction pins and the locking hooks, the locking hooks, the pin block, and the horseshoe port area when first used.

Please use qualified heavy-duty grease. Heavy-duty grease containing graphite or molybdenum disulfide is recommended. Its good extreme pressure and anti-wear properties will ensure that the fifth wheel surfaces will not wear abnormally under normal operating conditions.

During the traveling process of semi-trailer, the fifth wheel not only bears the load of the whole trailer, but also suffers from the impact load under different working conditions. As an indispensable key component of the vehicle system, the structural strength of the fifth wheel directly determines the reliability of the connection between the whole system. The fifth wheel needs to have good strength and stiffness, and will only produce a certain range of stress and deformation under various working conditions to meet its reliability requirements.