More Range, Less CO2

From the many technical developments for freight transport, an almost ingenious invention stands out: the vehicle concept of the semitrailer – or just trailer for short. The beginnings of the semitrailer for motor vehicles go back to the early 20th century. The principle of the semitrailer is still the same. A tractor with a short truck chassis has no load bed above its rear axle, but only a fifth-wheel coupling. This coupling accommodates the semitrailer's fifth wheel and locks when coupled, creating a connection between tractor truck and trailer that is both flexible and secure. Due to their numerous advantages – including during loading and unloading as well as during maneuvering and switching cargo – semitrailers have largely replaced classic trailers with drawbars over the decades, especially in long-distance traffic.

Now, the proven semitrailer concept is undergoing a revolutionary further development that will soon be visible on the roads: a semitrailer with its own electric drive that supports the tractor truck. ZF engineers had the idea for this innovation, still called "eTrailer" back then, more than six years ago . Already in the year the concept vehicle was presented, ZF had received the "CLEPA Innovation Awards 2020" in the "Environment" category from the European Association of Automotive Suppliers. Since then, the technology company has been fostering the development of the electric drive system for trailers, now known as TrailTrax. The heart of the system is the AxTrax 2 electric drive axle from ZF's portfolio which uses the same components in different drive concepts. Trailer manufacturers and fleet operators benefit from ZF's experience and industrial volume production. With the electrification of the semitrailer, the technology company helps cut the vehicle's overallemissions : A semitrailer electrified with TrailTrax significantly saves fuel, reduces CO2 emissions and increases the range. This is because legislators are putting increasing pressure on vehicle manufacturers and fleet operators to achieve binding CO2 savings targets. As TrailTrax offers a good solution to meet these requirements, it supports sustainability in the logistics sector.

At the end of November 2023, the EU Parliament adopted stricter CO2 requirements for those trucks and buses that will enter the EU market from 2030. "The reduction targets also include semitrailers, which then have to save ten percent of CO2 compared to the standard semitrailer," says Dr Bernd Meurer, adding: "Recuperating braking energy in the electrified trailer offers the greatest potential for reducing fuel consumption and thus CO2 emissions." Meurer is responsible for the TrailTrax system at ZF.

From the outside, a semitrailer electrified with TrailTrax only differs little from a conventional semitrailer. In the standard semitrailer with three axles, the middle axle of a semitrailer electrified with ZF's AxTrax 2 is designed as the drive axle. The installation space of a conventional axle is sufficient for this. In front of the axles, safely housed in the pallet storage space under the trailer, you will find the battery system box with the battery modules, whose capacity as well as cooling and electronics can be chosen by each customer individually. The components of the eDrive are located in the middle section of the compact AxTrax 2 electric axle: a three-speed transmission, an electric motor and an inverter. In addition, there are the inverter , the axle's control unit and other electronic components . All components are proven technology with which ZF pursues a global and modular platform approach.

It is ZF's long-standing experience and the great systems expertise of ECUs, electric motors and electronic braking systems (EBS) that have led to an innovative sensor technology solution for the TrailTrax system. After all, it must be ensured that the electric drive in the semitrailer always supports the tractor truck with exactly the right driving power and automatically recuperates as soon as the truck drives downhill or brakes. The semitrailer must never push the truck, which can lead to an unstable driving situation. Technically a challenge, says Meurer, because: "The semitrailer does not have to be controlled from the tractor vehicle, a semitrailer electrified with TrailTrax is an independent system. This means that it can be coupled to any tractor truck independently of the manufacturer, regardless of whether it is diesel-powered or electric."

How that works? To turn the electrified semitrailer into an independent unit, the ZF developers use the data from the trailer EBS and the E-axle control unit. ZF engineers developed a special logic from existing measured variables such as speed, acceleration or deceleration. It specifies when the semitrailer goes into drive mode, when it has to recuperate or when the system may also have to be switched off – for example, if a driving-critical situation such as an ABS event occurs. With the chosen technical approach it is no longer necessary to integrate additional sensors into the vehicle. "The driver doesn't really notice what kind of semitrailer is coupled. When driving a diesel truck, however, the driver will notice due to the reduced fuel consumption", says Meurer.