Exploring the eTrailer
Dr. Christian Brenneke, chief technology officer at Wabco, discusses the workings of the company’s hybrid trailer that can generate, store and re-use electrical energy on the road
What is the concept behind the eTrailer?
Wabco’s eTrailer integrates a powerful (300kW) electric drive in the semi-trailer, and embeds the control of the e-Drive system in the synergistic cooperation of both truck and trailer braking systems.
The eTrailer generates electrical energy during vehicle deceleration via recuperation of brake energy, stores the energy in batteries and then uses the energy for the next acceleration event, the next elevation, to compensate for rolling resistance, or to run electrical on-board units such as reefer cooling systems.
While the space in the towing vehicle is limited, the trailer can be more easily fitted with a system like the e-Drive. All it takes is the installation of a few standardised modular components, whereas the towing vehicle would need complex modifications with expensive components.
Although there are more trailers than tractors to be equipped with an e-Drive system, the longer lifespan of a trailer would undoubtedly compensate for this.
How does the eTrailer work?
The eTrailer recuperates kinetic and potential energy during braking. This energy is temporarily stored in a battery in the trailer. When the situation requires it, the trailer’s electronic controller transforms this stored energy back into mechanical energy.
In order to maximise energy recuperation, the electric drive is prioritised in the brake management system of the electronic braking system (EBS) over the friction and endurance brakes. The brake management prioritises which brakes to apply to support the driver’s request by maximising energy recuperation.
Through existing communication lines, the trailer EBS (TEBS) and tractor EBS are connected. TEBS supervises the e-Drive system in the trailer and arbitrates demanded power versus capability variations with e-Drive components.
About 72 per cent of the deceleration energy can be accessed for recuperation which would otherwise, as today with standard trailers, be transformed to heat by conventional brakes. In this use cycle, when reusing the energy for traction, 6.5l diesel savings can be realised (VECTO Regional Delivery cycle).
If the energy is used to power a reefer, for example, then the benefits change: instead of saving fuel on the truck, the reefer becomes fully electric and therefore a separate diesel generator is not required. This significantly lowers the noise level to keep cooling the trailer, and allows night transport in noise-restricted areas.
What control systems are required for the eTrailer?
Like electric vehicles, eTrailers require complex control systems. These systems are interconnected in multiple ways to achieve the optimal performance for energy gain, component durability, drive quality, vehicle dynamics and safety.
This includes powering electronics controls, thermal management, as well as a holistic approach for the overall brake system and functions – EBS, ESC and ADAS – that trigger external brake events.
At the heart of the eTrailer concept is the deep integration of the electric drive’s energy recovery capabilities into the overall vehicle deceleration and stability control by the EBS system of both the towing vehicle and the trailer.
A point-to-point communication via the standardised ISO 11992-2 data interface integrates the deceleration capabilities of the entire vehicle.
The electronic braking system in the truck sends a balanced torque demand to the trailer’s electronic controlled brake system (TEBS), which is the trailer’s interface to the e-Drive, comfort and safety functions.
The TEBS controls the positive and negative torque of the e-Drive based on the demand received by the truck. For deceleration this function allows applying braking in the preferred order: recuperative braking (e-machine), driveline retarder (truck), engine retarder (truck) and balanced friction braking of both vehicles.
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Have you conducted initial tests outside of the lab and what has been tested?
Wabco recently tested the prototype of the eTrailer on its test track in Jeversen, Germany. Driven to achieve as objective and exact values as possible, Wabco has compared vehicle combinations with and without eTrailer under identical weather conditions.
Additionally, we have taken into account gradients, uphill and downhill, road surfaces, as well as long-haul and short haul trips and varied speed ranges. In addition to testing and improving basic and advanced (driving) functions, practical checks were undertaken during prototype validation and the simulation program was validated and optimised.
While fuel economy is a key focus, the testing program also examined the vehicle’s behaviour in stability-critical situations. To prevent the drive axle of the eTrailer from spinning or locking during critical driving maneuvers, the control of the e-Drive must be integrated with the ABS, RSS, ATC and EBS stability functions.
Embedding the eTrailer function in the existing EBS and Trailer EBS functions ensures that the vehicle remains stable and the trailer does not slide or push.
As part of the road tests, the potential savings of the eTrailer in the VECTO Regional Delivery Cycle was determined at 6.5 l / 100 km. This is equivalent to a reduction in CO2 emissions of 172 g/km (16 per cent).
With the eTrailer alone, the interim goal of a 15 per cent reduction in distribution traffic defined in the EU CO2 regulation for 2025 could thus be achieved.
What implications does the eTrailer have for current vehicle systems?
An important advantage of the eTrailer is its ability to form a hybrid electric vehicle unit together with a conventional truck without additional sensors, ECUs or communication lines other than an ISO 11992-2 standard interface and adapted EBS on truck and trailer.
Where regulations allow trailers with active motor control and EBS with SAE truck-trailer communication standards are established, this approach will be usable worldwide.
When do you expect the eTrailer to be available?
Since unveiling the eTrailer prototype at IAA 2018, significant progress has been made in testing and advancing its capabilities and future potential. Breakthrough technologies such as electrification require significant testing and development before they are launched on the market, and the results so far are greatly encouraging. I am convinced we will see the eTrailer on our roads in the next few years.
