Transportation of overweight and over-dimensional consignments weighing more than several hundred tons is a big challenge for heavy-duty freight haulers. Sharp curves, steep inclines, frequented motorways, bridges, subways, and narrow streets have to be maneuvered, and adjustments have to be made to suit the rough terrain conditions.
With the application of advanced and reliable products in transport vehicles, exceptional logistics performances can be attained, thus reducing the risks in long-distance transportation.
The hydraulically supported pendulum axle was designed by the Transporter Industry International’s (TII Group) Scheuerle in 1956. It revolutionized heavy-duty transportation around the globe and forms the basis for heavy-duty road traffic solutions worldwide in today’s world. It also provides an even distribution of the payload on several axles.
In order to keep the payload within the approved maximum load-bearing capacity limits of axles, a lightweight design is important while retaining the strength of the rigid main beams. This article describes the lightweight design of hydraulic axle and working of hydraulic trailer technology.
1. Hydraulic Axles
The hydraulically supported pendulum axle is the basis for all on-road and off-road solutions from TII Group. It consists of a bogie with upper and lower arms and a suspension cylinder which is connected to a hydraulic system.
Figure-2 illustrates the functional principle of hydraulically supported pendulum axle. Under the conditions shown, the hydraulic fluid is pushed out of the cylinder of one bogie and flows into the cylinder of the other bogie. Thus, both axles maintain ground contact and the load per axle remains constant.
For hydraulic suspension system without pendulum axles, some wheels may lose contact and cause overloading of the remaining wheels. Overloading of wheels, in turn, results in eventual damage to the road surface.
Such overloading could prove fatal in the case of bridges. Figure-3 illustrates the behavior under rough terrain conditions. Under almost all circumstances, all the wheels will remain in contact with the ground.
2. Hydraulic Support Groups
To improve stability, the trailer bogies can be hydraulically combined in support groups, Figure-4 illustrates this process. Depending on the load configuration, either a four-point or three-point configuration can be selected.
Like a chair on legs, the four-point or three-point load can be leveled in the best possible way to precisely perform lifting and lowering. A four-point support group provides optimum protection against tilting, however, torsion along the trailer may occur. Thus, in some cases, a three-point circuit is a better choice. Though it has less stability but it prevents the torsion problem.
In general, a four-point configuration will be selected for loads with a high center of gravity or with banking (side slope) of the road. Whereas three-point is the choice for payloads with a low center of gravity or for loads that need to be protected from torsion of the trailer.
To ensure safe transport of heavy loads even under severe conditions like steep inclines, rough terrain or narrow bends, a sophisticated steering system is required. In case of hydraulic trailers from TII Group, the maximum steering angle is up to 60°.
The angle of steering can be changed and adjusted easily from the top depending on the requirement from prime mover and transportation task. The various wheels run on circles with different radius to ensure maximum flexibility, as illustrated in Figure-5.
4. Engine-Supported Trailers
The basic version of a hydraulic trailer is a passive vehicle towed by a prime-mover. The hydraulic systems such as steering and suspension can be regulated when needed by an external hydraulic power unit, some of the prime movers are equipped with such a unit.
However, for certain applications, where the prime mover doesn’t have a hydraulic power unit or only has a weak power unit, a separate engine needs to be attached to the trailer. For best results and depending on the transportation task, a few basic options are available.
4.1 Working of Hydraulic Trailers
A small engine unit with typically around 10–22 kW, called power pack unit (PPU), can be mounted on the trailer. It generates sufficient hydraulic pressure to lift, lower and steer the trailer in the absence of hydraulic power unit of the prime mover. However, self-propelled operation is not possible with this configuration.
Self-propelled operation requires a more powerful engine. In this case, a power pack unit in the range of 150-200 kW is connected to enable hydrostatic drives mounted in the wheels. Figure-6 illustrates this process. These consist of a series of hydraulic pistons operated by pressure generated in the PPU.
In the normal highway mode, the PPU is switched OFF, the drives are in idle position and no additional driving power is generated. Therefore, there is no influence on the trailer operation and maximum speed of 80 km/h can be reached. Figure-7 illustrates this process.
With the PPU ON, the power pack unit can be used as traction support for steep inclines. Instead of adding more prime movers, PPU enables the hydrostatic drives in the wheels and generates sufficient power to support the main prime mover engine to maneuver. Figure-8 illustrates this process.
While transporting over fragile bridges, PPU is used instead of a prime mover in order to reduce the length and gross weight of the vehicle. The PPU can be switched ON, which propels the trailer forward at a maximum speed of 12 km/h. This mode is also very useful when smooth movement conditions are required (no sudden acceleration from prime mover). Figure-9 illustrates a typical configuration.
5. Other Applications
Wind power is becoming an increasingly important source of energy, leading to an increase in the construction of wind farms. To meet this demand, TII offers special trailers for rotor blades, wind tower segments, and other bulky components for on shore and off shore projects.
Sophisticated wind blade adapters for operation in areas with steep inclines, sharp curves, and narrow bends further help transporters to simplify their operation. Also, the adapter swings the blade upright so that the overall length is drastically reduced e.g. from more than 50 m to around 10 m. After passing the critical area, the blade can be turned back into a horizontal position.
TII group is famous for manufacturing heavy load transportation vehicle all over the world.
Hydraulically operated trailers are used to transport the overweight and over dimensional consignments with more than several hundred tons.