1. What is multi-axles a trailer?

Multi-axles trailer are of two general types: The Low bed trailer and the modular trailer. In this post, we will mainly introduce multi-axles low bed trailer.

Typically, a multi-axle trailer has a group of axles that are disposed remotely from the point of steering of the vehicle. They include on the minimum two axles where one is immediately in front of another.

Trailer axles that are used for carrying the ground wheels are normally carried on springs that engage appropriate bearing members on the vehicle chassis and including a rocker to make it possible for the weight supported by the axles to be accurately distributed in reference to the frame of the trailer. 

It is required to use radius arms in such assemblies between the brackets and axles engaged through the springs. The radius arms are use to keep the axles in desired operating positions with reference to the frames of the trailer.

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2. Key Specifications of Multi Axle Trailers

The multi-axle trailer has a chassis that is pivotally attached to a turn heavily horizontally in relation to a sub-chassis.

It is provided with a drawing link to the forward section to make it possible for the trailer to be mounted pivotally to the towing vehicle.

There is also the sub-chassis carrying the front pair of wheels and is able to turn in relation to the adjacent sub-chassis. A second pair of wheels with is own pivot point licked with each of the front wheels is also provided.

Other specifications include the need for a steering arm, a mounting that is movable with the use of the steering arm, a system of linkages that are connected in between each of the pivot points of the wheels and the said mounting.

The linkages should be operated to facilitate the turning of the first wheels due to the resulting turning motion of the front section of the trailer to allow the trailer to follow the towing unit.

Steering system linkages

Steering system linkages 1

Steering system linkages 2

Steering system linkages 2

The first and the second set of wheels should be mounted on the first and second axles in that order.

An axle alignment system is required for a multi-axle trailer. This includes a mounting bracket, a mounting pin, an equipment spacer and an adjustable spacer. The equipment spacer and the adjustable spacers could be more.

When the mounting bracket us used together with the equipment spacer and the mounting pin, the axle alignment system will exclusively take a non-adjustable standard conformation.

However, when the mounting bracket is used together with the adjustable spacer and the mounting pin, the axle alignment system gets activated and takes one of the several possible adjusted conformations letting one to align an axle of the trailer.

There are 2 types steering structures:

  • Mechanical steering axles 

When gooseneck steering, the system will control the rods and support arm to steer the tires. This is the type to go for on economic grounds and again to enjoy a long service life.

self steering axle

It comes with low maintenance costs and most importantly, it is highly available.

  • Hydraulic steering axles (PENDULAR AXLES)

This type offers a larger steering angle of up to 65°. Most importantly, it has a higher capacity compared to other options out there.

cylinder transmission

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3. Steering system

Multi-axles trailers steering system is similar to that of a modular trailer.

The steering system for a multi-axle trailer comprises several hydro-mechanical jack systems of steering that are interconnected through a mechanical linkage that has an cylinder in it for taking up slack in the interconnection irrespective of the direction of steering of the vehicle.

Slack may be present following the mechanical connection in between the linkages or may be as a result of the dead band of the system’s hydraulic valves.

The steering system is able to simultaneously and precisely effect the steering motion of the trailer wheels linked with over two axles.

This is possible in a multi-axle vehicle to the point of producing the desired steering effects while keeping everything in balance.

In addition, the system works to allow the vertical oscillation of a single wheel of the motor vehicle by not causing the undue wear of tyres due to the steering geometry of the wheels.

This has been the issue especially in trailer axle configurations where 3 or 4 of them need coordination to produce a simultaneous steering.

In the hydraulic control unit provided in the multi-axle trailer, various fluid sources are offered for various steering mechanisms so that hydraulic failures in either of the vehicle hydraulic system will not lead to simultaneous malfunctioning of the means of steering for the other wheels.

  • The Mechanism of Steering

The steering mechanism consists of the steering central panel, steering orifice plate, steering cylinders, and steering rods. The steering orifice plate is welded together with the bogie frame.

The plate has specific quantities of assembling holes that are used to install steering rods. The positions where steering rods are installed on the steering orifice plate can be changed to suit different combination modes of the modular unit.

The unit can meet the minimum steering radius and the maximum turning angle of 55 degrees.

The modular unit uses three major steering modes that include the all-wheel steering along (over five axle lines), diagonal steering along, and the front-wheel steering mode.

The steering rods can be adjusted quickly and easily to suit the desired steering angle.

steering rods

steering rods

The modular has a hydro-mechanical all-wheel system with a two-circuit system, which ensures that the steering system maintains its functionality even when one or more steering circuit fails.

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4. Steering Operations

The multi-axles trailer has many axles even up to 10 axles. So, the trailer’s axles need to be steered by either self-steering or automatic steering. Steering without wheels causes serious wearing.

In order to minimize the tear and wear on the tyres and the trailer chassis stress, it is advisable to let the trailer wheels to accurately follow the towing vehicle wheels regardless of whether it is on a tractor or a lorry. 

For this to be achieved, it is normally important that successive wheel pairs take up slightly varying angles and positions under the trailer chassis.

Conventional steering systems for trailers make use of the bogie system for steering through means where both the wheels of a pair get turned concurrently through the changing axle angle where the axle links up the wheels together or maybe by allowing the rear axle wheels to act as a pivot point.

  • Automatic Steering Operations

The automatic steering device capabilities should include the swivel bogies that support the platform ends.

In this setup, the bogie wheels are steered automatically through the use if a system of linkages that are connected onto a mounting attached to a towing bar.

The towing bar on the other hand should be pivoted as the platform at the front part negotiates a corner. This way, the steering of one pair of the wheels on each bogie is achieved.

This system is not applicable directly to multi-axle trailers because it will be required to travel at slow speeds. At high speeds the vehicle will become unstable hence its suitability may be left to certain systems like the factory trains.

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  • Self-Steering Operations

This is a method of controlling and managing the sideways motion of a trailer that forms part of a combination vehicle used in the transportation of heavy cargo.

Ideally, the combination will include a motor vehicle positioned to the front and the first trailer connected in a way that allows it to be towed from the rear section of the motor vehicle. 

There could also other trailers connected to it to be towed as well leading to several vehicle units linked up behind each other. The self-steering is normally done on the trailer body with an adaptation to take up goods.

A dolly mounted under the front of the trailer body with road wheels attached in several axles sets to a dolly frame would also be needed.

Each of the axle set that extends across the said dolly frame, the axle sets that are mounted behind each other from the rear section of the dolly frame to the trailer body through a pivoting linkage.

The system will also need a draw bar connection at a tow coupling joint and the dolly frame to the motor vehicle unit immediately in front of it.

The tow coupling section moves towards one side and again, away from the opposite side through the use of the draw bar connection to the coupling section in order to steer the dolly frame in the direction of the desired side in relation to the trailer body.

Again, the steering will at least allow some of the wheels on each of the axle sets in relation to the dolly frame in away that the vehicle unit will turn towards the said side during high road travel speeds.

During this moment, some of the wheels relative to dolly frame will cause the dolly to move towards the said side.

At low road travel speeds, the vehicle unit turns in the direction of the said side, the steering wheels on this occasion relative to the frame of the dolly will cause the dolly to move in the direction of the opposite side. 

5. Trailer Structure

Based on their shape and construction, the multi-axle trailer can take different forms: flatbed model, low loader model and the extendable model.  Here are key things to note about the different trailer structures.

  • Flatbed model
multi axles trailer

Flatbed Model

It offers a low loading height hence ensuring that maximum-height goods are sufficiently loaded. It includes the use of brand components. It is a good option for a long service life and is also recommended for use due to its high availability.

  • Low Loader Model
Widen device on low loader trailer

Low Loader Model

This model has a small height difference between the bridge and bogie. It is ideal for loads with an overhang and is suitable for high payloads. The low loader model has a high axle suspension, a large steering angle and sensational maneuverability.

  • Extendable model

The extendable model version is suitable for very long rotor blades and is commonly used in wind power generation industry to transport wind plant blade.

extendable trailer

Extendable Model

The extendable model apparatus is a combination of a fixed frame and a frame that is slid-ably linked to the fixed frame and can be moved relative to the fixed frame structure for shortening and lengthening the apparatus of the trailer.

The movable frame at the back of the trailer has wheels and an axle onto which they are secured allowing the load to be safely secured on the fixed framed.

The two frames can move to allow adjustments for the load weight on the trailer axles together with the axles secured firmly to the fixed part of the trailer with the axles also secured on the movable frame.

An embodiment of the apparatus has an end dump bed that has tapered sides and sloping bottom that facilitates the dumping operations.

The extendable trailer apparatus is a combination of first frame means that support a load to be lifted and towed having a first general length. This includes a bed system where the load is disposed.

The first bed system is secured to the bed systems for supporting the load and the bed system.

The second bed system is spaced separately from each other and disposed generally parallel to the first beam system and secured to the bed system for providing the bed system with support and the load with the first beam system.

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6. Key Multi-Axle Trailer Parts

  • The Frame

The frame is the main component for bearing weight considering the most dangerous load condition.

In its scope, the main bearing parts of the modular unit are the main girder of the frame, the wheel bogie and several others. These adopt firm box-type beam structure made of high-performance welding plate material.

The recommended material should have a yield strength of 690MPa. The whole frame which has strong strength and great ability to withstand bending moment can solve the problem of concentrated loading efficiently.

The surface of the main structure should be treated carefully through a sand blasting process. Again, the thickness of the painting used on the surface should meet the recommended national standards.

Still, the brand of the painting used should be among the top brands in the world. All the small-sized parts of the frame should be zinc-plated.

modular trailer frame

Figure 6 Modular Trailer Frame

The box-shaped center beam and the stable crossbeams give the frame a high degree of rigidity. Hence, the frame can achieve its optimal loading level.

The steering system, air tank, and hydraulic oil tank are all integrated into the bogie frame. Thus, the parts are protected against damage and corrosion.

The frame has a reinforced loading deck, which allows extreme point loads. The optimized bolt-plate coupling, on the other hand, eliminates any problems that may arise when assembling the longitudinal combinations.

  • Hydraulic System

The pump in a trailer uses the hydraulic technique, which is effective in controlling the driving speed. The steering and suspension pumps use the constant pressure controller to realize a quick response whenever they need steering power.

The driving motor on the other hand switches between driving and follows the use of a large torque radial motor. All the hydraulic cylinders in the transporter have anti-block valves, which are important when the pipe line is broken.

  • Brake system

The trailer is equipped with a compressed air brake system. The system consists of double brake chambers, single brake chambers, relay valves, brake drums, and reservoirs.

The brake system consists of two brake lines that function as the service brake and the parking brake.

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Conclusion

The multi-axle trailers are quite common. Due to the permanent unbalanced loading and weight distribution on these types of trailers or due to various circumstances, the trailer axles may get misaligned during operation.

However, the multi-axle trailer is designed in a way that takes care of all that. With the help of an axle alignment system, its activation is used to correct any misalignment of the said axles that may result.

Initially, this was the fear of its use and operation among owners. However, its performance has greatly been improved through the elimination of the misalignment occurring at the axles.

This way, the service life of the multi-axle tyres is greatly increased alongside improving the efficiency of the trailer.

Most precisely, the tread on these tyres wears evenly and they run cooler hence lowering the risk of blowouts. Additionally, the towing resistance is largely reduced hence increasing the fuel consumption economy and efficiency of the vehicle.

Based on the benefits and purposes defined in here, the axle alignment system which is important for the multi-axle trailer is always provided.

The multi-axle trailer is therefore a perfect solution for the loading and transportation of heavy weight loads in a way that is efficient in terms of reduced tyre wear and fuel consumption requirements.

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