1 Tractor-trailer design
Mohd Khairul Rabani Bin Hashim
A trailer is generally an unpowered vehicle towed by a powered vehicle (tractor). It is commonly used for the transport of goods and materials.
Sometimes recreational vehicles, travel trailers, or mobile homes with limited living facilities, where people can camp or stay have been referred to as trailers.
3 Types of Trailer
4 Flat Bed Trailers
Flatbeds are extremely popular and are widely used because they exude a great sense of versatility.
Generally, a flatbed is used to load freights on its tip, sides, and rear.
With these capabilities, flatbeds have truly become the primary and leading assets of the trucking farm.
5 Dry Van Trailers
Dry Van trailers are generally enclosed and are commonly used to carry and protect the freights from the harmful elements of the weather or the roads.
Freights can be loaded on the rear and are commonly loaded using a loading dock.
It is similar to a curtain van and it can be loaded from its side too.
6 Refrigerated Trailers
Refrigerated trailer is a temperature-controlled type of trailer.
It is generally used for transporting chilled or frozen products.
The temperature inside this trailer can be controlled whatever the outside weather .
7 Lowboy Trailer
A Lowboy Trailer is an unpowered trailer which is commonly used to haul freight.
These kinds of trailers are generally designed to carry and transport taller goods and items
Basically, a lowboy that has two axles can haul around 20,000kg.
8 Basic Trailer Layout
9 Trailer Layout
Rear member/ Trailer Chassis
Wheel & axle
10 The Tongue
The tongue does a couple of important jobs apart from being the part that keeps trailer attached and at a distance from tow vehicle.
The tongue keeps trailer in balance when towing and assists in keep weight on the tow hitch which is required for controlled towing.
The tongue should be long enough to allow a reasonable turning radius and clearance to the vehicle when backing.
If the tongue is short, it may be an indication of weakness or shortcuts in the design. Short tongues affect both driveability and stability — basically back up, turning radius and jack-knife susceptibility.
11 There are 3 main styles of tongue :-
The straight tongue
The Compound tongue
The “A” frame tongue
12 The straight tongue This design harks back to the old horse and cart.
It is a bit old fashioned but still has its uses particularly on dinghy and agricultural trailers.
Whilst this design has less chance of getting jackknifed when reversing, if the tongue does get damaged it creates a highly stressed section which can rapidly cause internal cracking or failure.
13 The Compound Tongue
The composite tongue is a variation of the single tongue design with lateral supports to both strengthen the tongue and provide support to the chassis
Composite tongues give the benefits of good clearance to the tow vehicle when reversing around sharply and give more support to the sides of the trailer.
14 The “A” frame Tongue
This style tongue is one of the most common due to the strength the full angle frame gives to the trailer.
The longer a tongue can be (to a point where the tongue weight becomes excessive) the more smoothly and stable the trailer will travel. It will also be more responsive and forgiving when reversing.
A disadvantage is the greater chance of the tongue being damaged when jackknifed while reversing.
15 Axle location An axle is a central shaft for a rotating wheel or gear.
The axle should be behind the load center for stability.
Often trailers have the axle at or just barely behind the center of the bed.
This is short sighted with respect to versatility, but it is also an indication of weakness.
For most applications, the axle should be noticeably behind the center of the bed, and for maximum versatility, allow the axle position to be adjusted
16 There are 2 main styles of axle :-
Dead axle (lazy axle)
17 Dead Axle
A dead axle, also called lazy axle, is not part of the drivetrain but is instead free-rotating.
The rear axle of a front-wheel drive car is usually a dead axle.
any trucks and trailers use dead axles for strictly load-bearing purposes.
Dead axles are also found on semi trailers, farm equipment, and certain heavy construction machinery serving the same function.
18 Lift Axle
Some dump trucksand trailers may be configured with a lift axle (also known as airlift axle or drop axle), which may be mechanically raised or lowered.
The axle is lowered to increase the weight capacity, or to distribute the weight of the cargo over more wheels, for example to cross a weight restricted bridge. When not needed, the axle is lifted off the ground to save wear on the tires and axle, and to increase traction in the remaining wheels.
Lifting an axle also alleviates lateral scrubbing of the additional axle in very tight turns, allowing the vehicle to turn more readily.
In some situations removal of pressure from the additional axle is necessary for the vehicle to complete a turn at all.
A trailer was design as shown in figure below. Tongue weight of the trailer is 1025kg and wheel weight is 7200kg. Distance D (tongue end to axle) is 2.64m. Verify whether the axle position for the trailer is correct or wrong. Prove your verification by using calculation.
21 Trailer Chassis
Trailer chassis is a frame upon which the main parts of an trailer are built.
The design of a trailer chassis will be different than one for pleasure vehicles because of the heavier loads and constant work use.
Usually the loading and unloading occurs over this member, so it should be disproportionately larger (stronger) than the other cross members.
22 Trailer Stability Load distribution Trailer length Dynamic loads
Centre of gravity
23 Load distribution
The trailer load should always be reasonably distributed from side to side.
Load the trailer front to back with at least 10% of the trailer weight on the hitch.
With typical trailers, more weight on the hitch is better for stability.
15% is usually a good number.
To illustrate, 5th wheel trailers have much more weight on the hitch, and they tend to be pretty stable. The extreme example is over-the-road trucks. They carry up to 50% of the load at the front.
24 An extreme example of poor load distribution
25 Trailer length
Longer trailers typically tow better or more accurately, a greater separation between the rear most wheels of the tow vehicle and the fore most wheels of the trailer.
A long tongue can facilitate such separation.
Evaluate trailer length in the context of width.
Look at the width of the trailer with respect to the tow vehicle and with respect to length .
26 Dynamic loads
Dynamic loads exert varying amounts of force upon the structure that is upholding them.
For instance, heavy pipe isn’t tied down, it’ll roll from side to side or front to back. This constantly changing load makes the trailer move.
27 Center of gravity
A point from which the weight of a body or system may be considered to act. In uniform gravity it is the same as the center of mass.
In general, a lower center of gravity helps improve stability of the trailer.
28 Trailer Strength
29 Load Capacity
The maximum load for which the trailer is designed to carry will determine much about the strength of the trailer.
It will also determine how strong the trailer should be.
Judge trailer strength with respect to its intended capacity.
30 Calculation of load capacity
A company makes a portable bulk bin as shown in the figure below. The grid consists of nine members, AB, BC, JK, IJ, CDHI, DE, GH, EF, and FG. The members that attach the wheels to the framework, ABC and IJK, lie in the same horizontal plane as the rest of the grid. Design loads, P for the plane grid is 2kN. All the labels in the figure in unit meter (m) The company was decided to construct the portable bulk bin with rectangular solid mild steel 1090 (30mm x 40mm). 1) Calculate the reaction force for point I and C. 2) Calculate the maximum design load, P for portable bulk bin. Given ultimate tensile strength for mild steel 1090 is 841MPa.
Discuss how the three factors (construction, materials & components) contribute to trailer strength. Provide relevant evident for your discussion.
Information will be available soon.
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