The focus of vehicle efficiency has long been exclusively centered on the tractor in truck-trailer combinations. However, further increases in efficiency can only be achieved if trailers leverage the latest technologies in combination with truck technologies. Developments for this will become available to commercial vehicle manufacturers and fleet operators with series production commencing in the coming years. ZF presented them during a truck-trailer technology demonstration. The article describes where potential can be tapped.

Tractor and trailer today represent a very unequal team. While the tractor vehicle has reached a very high level of technical development, the trailer has received less attention. The potentials in the trailer have only been raised in recent years, for example through the Intelligent Trailer program from ZF, Figure 1. Further significant improvements of truck-trailer efficiency are almost impossible if only the tractor is considered. Today, trailer technologies have the potential to significantly improve the efficiency of road haulage. This applies both to vehicles with internal combustion engines and trucks with electrified drives. The efficiency of the drive is not the only factor contributing to the overall efficiency of a truck application. Significant potential also lies in optimizing the transport performance as well as driving maneuvers at the depot - especially against the backdrop of experienced driver shortages. This article considers the opportunity to increase efficiency in four areas.

Figure 1
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Tractor trucks have become intelligent and automated technology showpieces (blue), while trailers got less attention (red) (© ZF Friedrichshafen)

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Electrified Trailer

Hybridizing the commercial vehicle by using electric drives in the trailer offers significant potential for fuel savings and decarbonization. An innovation semitrailer was presented last year. Equipped with an electric drive axle, Figure 2, the trailer recuperates electrical energy when braking and driving downhill. This energy is stored in a battery. At the same time, brake wear is reduced, and recuperation potential can be increased even further by integration into the semi-trailer truck's brake management. The cooling and auxiliary units in the trailer can be operated with this recuperated electrical energy. As a result, the trailer no longer requires a separate diesel generator. It is even more beneficial if the recuperated energy is used to support the drive in the tractor. This way, a considerable amount of fuel can be saved. Test drives and simulations [1] demonstrate that approximately 60 % of the braking energy can be recovered, meaning that fuel consumption and CO2 reductions of 16 % are possible in the Vecto Regional Delivery Cycle. The electrified trailer even becomes a plug-in hybrid if an optional charging connection is added. Combined with variable battery sizes, this can again significantly increase the energy saving potential. It is important to emphasize that the electronic control unit prevents the trailer from being pushed against the tractor at any time and the safety of the semitrailer is guaranteed at all times. In other words, the electric drive simulates a lighter trailer. As a result, the truck-trailer combination can achieve comparable driving performance even with a smaller combustion engine. For trucks with battery-electric or fuel cell drives, the electrified trailer is also a logical supplement to increase the range or to operate with smaller trac- tion batteries.

Figure 2
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Illustration of the trailer with electric drive on the central axle (© ZF Friedrichshafen)

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The electric trailer drive is a compact and integrated system consisting of an electric axle, battery, inverter and an electronic control unit that is optimally adapted to be integrated into the recuperation and brake control of the trailer EBS. With the e-axle component, a new modular eDrive kit approach is pursued. This electric axle will have a continuous output of at least 180 kW and will be a compact and lightweight one-box solution. It will integrate the axle bridge, hairpin electric motor, gear, silicon carbide power electronics and control unit within a single box.

The electric trailer drive also boosts the driving stability and safety of the overall combination, especially in case of increased slip on the drive axle of the truck tractor.

The electric PTO system eWorX [2] can also be integrated into the electrified trailer as an interface to the cooling system and to supply other electric auxiliaries and onboard vehicles, such as forklift trucks. This also reduces the operating time of the diesel engine at idling speed as well as lowers fuel consumption.

Aerodynamic Improvements

Aerodynamic rear and side panels also contribute to both reduced consumption and CO2 emissions by minimizing air resistance. Testing under real life conditions demonstrates that fuel consumption is lowered by up to 1.5 l/100 km at 85 km/h. These add-on parts called OptiFlow were developed using CFD calculations as well as wind tunnel and road use measurements [3]. Although wheel-covering trailer skirts can effectively reduce air resistance, they are not widely accepted in fleets. The key reasons for this are the additional weight of the skirts, the feared risk of damage by forklift trucks, for example, and the increased difficulty in accessing the wheels. As a result, shorter and lighter side panels (TrailerSkirt with Flow Conductor) were developed, Figure 3, which, weighting only about one third of the OptiFlow package, reduce fuel consumption by up to 0.5 l/100 km according to CFD calculations and, at the same time, represent the underride guard required by law. The flow conductor on the leading edge is shaped like a wing profile at the front edge and enables a relatively strong reduction in aerodynamic drag for only about one-third of the cost of the OptiFlow package. This can reduce the amortization period to approximately one year for typical long-distance traffic operations. In addition, this solution is compatible with almost all trailer types.

Figure 3
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OptiFlow TrailerSkirt side panel (left), with aerodynamically shaped front edge in the form of a wing profile (right) (© ZF Friedrichshafen)

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Optimizing Cargo Space

Last summer, ZF demonstrated a further approach to increase efficiency in its innovation vehicle, the CargoCam. This is a Time-of-Flight (ToF) camera mounted on the upper rear of the trailer, Figure 4, which provides continuous in- formation on the contents of the cargo space. These sensors make it possible to measure the distances between objects and the camera. In addition to detecting the free cargo space, the sensor software can also interpret detailed information so that, for example, individual pallets and their quantity can be identified. In addition, it is possible to monitor the condition and possible movements of the transported goods (sliding and tilting, for example), unauthorized opening of the door and the presence of people in the cargo area. The CargoCam sensor is integrated into Scalar, a digital fleet orchestration platform which provides the fleet operator ith clear recommendations for optimization in real time. These functions can improve utilization and load securing, prevent damage and load theft as well as increase the transport efficiency of entire trailer fleets.

Figure 4
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Efficient use and monitoring of the cargo space via CargoCam (left), visualization of the recorded objects (center) and associated image information (right) (© ZF Friedrichshafen)

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Driver Efficiency and Operating Costs

ZF has already presented various modern assistance functions, the latest being Automated Coupling Assist, which enables fully automated trailer coupling and decoupling, Figure 5. The system controls the truck in longitudinal and lateral directions and the height of the trailer hitch via the air suspension, significantly reducing coupling time.

Figure 5
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The Automated Coupling Assist enables automated coupling and decoupling (left); HD backup camera image of the ZF Advanced Reversing Assist eliminates the blind spot behind the trailer when maneuvering backwards, gives the driver warnings and brakes automatically if required (right) (© ZF Friedrichshafen)

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When reversing with truck-trailer combinations at loading docks, the Advanced Reversing Assist supports the driver. This function accesses an HD camera at the rear of the trailer. Special image processing algorithms enable 3-D modeling with just one mono digital camera. A sensor cleaning system helps ensure that a clear camera view is maintained. With the aid of an articulation angle sensor, a guided reversing track is calculated for the driver and displayed on the screen. If required, the system triggers safety functions. Due to the HD camera signal, Advanced Reversing Assist requires a real-time capable data link between truck and trailer. This is provided by the truck-trailer link, set up for the future connectivity standard based on the automotive Gigabit Ethernet. This standard is being prepared under the designation ISO 23870. In addition to saving time, these ADAS systems help significantly reduce maneuvering damage, repair costs and associated vehicle downtimes, especially for less experienced drivers. Importantly, the automated processes also help enhance the safety of drivers and depot staff.

The assistance functions can be scaled, depending on the technical equipment level of the truck with, for example, active steering.

Summary and Outlook

The trailer technologies described here are intended to illustrate the unused efficiency potential for trailers that can still be realized. The electric drive in the trailer contributes significantly to this. It allows to achieve significant reductions of energy consumption and CO2 in large fleets. This technology is also sustainable as it can be used as a range extender for trucks with battery- electric or fuel cell drives.

The presented aerodynamic lightweight components on the trailer also contribute to reducing energy consumption and CO2 emissions. The optimal use of the payload capacity and the cargo space must also not be overlooked. Together with cloud-based services such as Scalar fleet orchestration, CargoCam offers significant added value for fleets. Finally, assistance systems for typical driving situations at depots offer important further potential to minimize operating costs and downtimes, thereby increasing overall transport efficiency.

In order to bring electrified trailers onto public roads, work is currently underway to adapt the legal framework at European level. Its integration into the Vecto tool and the creation of further incentives (toll reduction, for example) are other areas to be considered. The basic prerequisite for realizing the efficiency potential are standardized interfaces for communication between tractor and trailer. Here, changing combinations of tractor trucks and trailers must also be considered so that the reversing sensors and sensors for turning and maneuvering situations function automatically and smoothly.

References

  1. [1]

    Müller-Deile, F.; Heseding, J.; Schünemann, G.; Dieckmann, T.: Fuel Savings of an Electrified Semi-trailer in Driving Test. In ATZworldwide 05/2020, pp. 54-58

  2. [2]

    Prystupa, P.; Bindig, S.; Ehrsam, A.; Lindner, J.: Power Take-off System for Electric Commercial Vehicles. In ATZheavyduty worldwide 03/2022, pp. 20-24

  3. [3]

    Ramirez, L.; Veldhuizen, R.; Adolf, S.: Reduction of CO2 Emissions and Cost Due to Trailer Aerodynamics. In ATZworldwide 04/2021, pp. 26-33