ZF TraXon transmission: Review

The ZF TraXon automated transmission is the German brand's latest generation of AT, or automated transmission, and it raises the bar significantly from ZF's previous generation of AS-Tronic transmissions.

While engine development has been spurred on in recent years by increasingly tighter emissions standards, clutch and transmission development is largely driven by engineering innovation and competitive advantage, and so ZF's TraXon series is focused on enhancing efficiency and maximising engine/driveline integration, while maintaining durability and reliability.

DAF, like most European manufacturers these days, now only offers automated transmissions as its standard gearbox option. That's because, whether the application is local distribution or linehaul work, an AT is an essential component in today's fuel-economy race. Besides that, with tailored software changes, all ATs can adapt their operation to better suit specific applications.

If you take a quick glance at the major European heavy truck makers, you'll immediately see two different methodologies where transmissions are concerned. On one side of the fence, with their in-house drivelines, is Mercedes-Benz with its PowerShift 3, Scania with its Opticruise, and Volvo with its I-Shift. On the other side is DAF, IVECO and MAN, who all do very well with equipment from transmission specialist, ZF.

These manufacturers don't suffer in terms of technology either: ZF's latest TraXon transmission is among the most advanced on the market. The fact that DAF's latest Euro 6 models are top sellers in Europe is proof the pairing of PACCAR's MX powerplant and ZF's TraXon transmission has been delivering the goods.

While the acronyms applied to various functions afforded by the TraXon transmission may differ across OEM brands, the principles remains the same – 'CC' for cruise control, 'ACC' for adaptive cruise control, and so on.

The engine and transmission's sophisticated smarts deliver what's now called a 'cruise function', which incorporates multiple systems that integrate to improve driveability, economy, performance, and safety for the driver.

The cruise function is made up of the traditional cruise control (CC), adaptive cruise control (ACC) to autonomously regulate the distance to the vehicle in front, and predictive cruise control (PCC) that uses satellite mapping to adjust the truck's shifting strategy for the load and grade.

These systems are combined with downhill speed control (DSC) to control the speed of the truck on descents and an ECO-Roll function, which slips the transmission into neutral (when appropriate and certain parameters are met) to harness the truck's momentum and save fuel.

The speed and precision of shifting gears in ATs continues to improve, with DAF's ZF TraXon transmission providing 'super-fast-shift' performance in its top two ratios. The engine smarts and transmission also allow an extra 100-150Nm of torque to be deployed in what's called a multi-torque feature, reducing the frequency of downshifts.

The TraXon transmission's ability to deliver slick, super-fast shifts is the result of a combined effort of the PACCAR MX engine's smarts, the TraXon transmission's function-specific sensor modules, the lineal shift actuation and the addition of the ConAct pneumatic release actuator for the Sachs clutch.

The ConAct clutch actuator mounted on the input shaft shifts gears with exceptional speed, precision and smoothness. The innovative system features a release cylinder, positioned concentrically around the transmission input shaft, which replaces the traditional fork actuation with the clutch booster, fork and clutch release bearing.

The other advantages of the release system lie in the actuation of clutches for up to 3200Nm of engine torque and in reducing the interfaces outside the transmission. The pneumatic clutch actuator simplifies the clutch assembly, allowing a streamlined design. In addition, maintenance costs are reduced due to the elimination of hydraulics and lower system weight.

The TraXon transmission with ConAct system automatically determines the PACCAR MX engine and transmission speed, including the accelerator pedal position, from data provided via the CAN bus. The ECUs then make gear-shift decisions from conclusions of the CAN data regarding the optimal release position. Furthermore, ZF says the system works exceptionally well in challenging driving conditions such as launching, maneuvering and shifting on hills with heavy loads.

Dependent on the intended application and DAF model, the TraXon can be optioned in 12-speed or 16-speed overdrive formats, providing considerable reductions in engine speed while cruising in top gear, further enhancing efficiency.

The DAF/TraXon software package brings truck operators systems that are more common in modern prestige and luxury cars, like ECO-Roll or high-performance power shift programs that change the driving strategy and shift dynamics to suit the operating environment.

These systems can be activated by the driver with manual over-ride or set automatically through the software. Conversely, stop-start (or idle-stop) systems widely adopted by the car and light commercial vehicle industry can be optioned on the TraXon transmission; this shuts the engine down during extended traffic delays and then provides a quick-start solution when the traffic ahead starts to move, enabling further fuel savings.

In applications where difficult terrain is often encountered, the 'rock-free' function provides an extended clutch control that is able to free the vehicle from in-ground depressions and other obstacles by invoking a rocking movement.

For the traditional linehaul sector, the DAF/TraXon transmission's predictive cruise control feature effectively provides a link between the engine and transmission with GPS data and topographic mapping. This function eliminates unnecessary gearshifts, allowing the truck to forecast changes in the terrain ahead along with bends and twists in the road, minimising shifting and making the best possible use of the truck's momentum.

The skill that was once deployed by professional truck drivers in executing smooth gear shifts has now evolved to a different one: that of understanding how all these systems in the engine and transmission work, and how to get the best out of them.

An automated transmission is superficially very easy to operate, but the driver now needs to be making educated decisions about which system to employ to maximise fuel efficiency and which to utilise for power.

For example, an AT can implement the ECO-Roll function when approaching situations where the vehicle needs to slow down, such as roundabouts, lights, and stop signs, without traditional engine braking, minimising wear and tear on the service brakes. In an era when no other big win than fuel economy remains, these sorts of subtle changes to driving style are essential.

Engine and transmission performance and economy refinements now come from electronics concealed in a black box. The timeline on the arrival of road-legal, fully autonomous trucks is still anyone's guess, but as drivers and operators today we can already reap many of the efficiency and safety benefits of such cutting-edge technology through modern drivelines such as ZF's TraXon.