The next generation
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ZF is about to replace its AS-Tronic automated gearbox with the Traxon, which it says will be faster, quieter and more durable
Words: David Wilcox
FIFTEEN YEARS AFTER it introduced its ground-breaking AS-Tronic automated gearbox in 1997, ZF is poised to replace it. Its successor, Traxon, will be faster, quieter, more durable and will be available with a range of output options to suit different applications. Crucially, it will cut fuel consumption by adjusting its gear-shifting strategy to suit the road ahead.
Traxon follows the same basic design as AS-Tronic, a constantmesh gearbox with either three or four gears multiplied by a range-change and splitter into 12 or 16 ratios. Shifting and clutch release is still controlled by software and operated by pneumatic actuators but, when required, is faster. In order to keep up with the escalation in engine torque outputs, ZF has raised the torque input capacity but has done so without increasing the thickness of the gears, which would have made the gearbox longer and heavier. Instead, the gear teeth proile has been reined and the material hardening process improved. Coupled with new synthetic oil, ZF says these changes also mean Traxon will be more durable than AS-Tronic. The teeth proile and a new casing design are also said to make the gearbox much quieter.
But the real innovation is the introduction of a GPS interface and new gearbox control software that modiies the shifting strategy to suit the topography. This is akin to the predictive cruise control systems recently revealed by Scania, Mercedes-Benz and Volvo, but whereas they all adjust the cruise control speed-setting to suit the terrain, ZF’s new Prevision function focuses solely on gear-shifting. Armed with threedimensional mapping and GPS, Prevision knows what gradients lie ahead and adjusts the timing of gear-shifts accordingly to save fuel. It also automatically disengages the clutch to allow trucks to coast where it is safe to do so.
Prevision was developed in conjunction with Continental, which did the groundwork several years ago on what it calls eHorizon. Although Prevision does not need cruise control, ZF engineers say it is compatible with such systems.
On the road
CM has driven a ZF development truck, an MAN TGX 18.480, itted with Traxon. Laden to 40-tonne GCW with cruise control set at 66km/h (41mph) on a rural road, the MAN engine was at the lower end of its torque plateau at just over 1,000rpm in top gear. Approaching a 4% uphill gradient, we halfexpected Prevision to choose to accelerate – the likely response of predictive cruise control systems. Instead, the truck held the set speed and then made a surprisingly early downshift to 11th, just enough to see it to the top of the hill. Without Prevision, the gearbox holds onto 12th for longer, so the truck loses momentum on the climb, which it cannot ‘see’. This means engine speed falls away, turbo boost pressure is lost and a second downshift to 10th is required, using more fuel. Approaching the top of the hill, Pre vision knows the gradi ent is about to end, pre venting any ill-timed downshifts.
On downward gradients, it calculates what speed the truck will reach if it coasts out of gear. Providing that is considered a safe speed, it disengages the clutch to eliminate driveline drag and the truck rolls down with the engine on tickover. Gears are re-engaged and enginebraking applied automatically if speed needs to be reined back.
The other major difference between Traxon and AS-Tronic is that the new box is a modular design, using a core gearbox and ive output modules to suit a variety of applications. So, for example, the standard output is a conventional clutch but it is possible to it a dual clutch module instead. ZF says this will appeal to truck manufacturers keen to use the longest drive-axle ratios to keep engine speeds as low as possible on the motorway. Such long ratios leave very little torque reserve, so even mild gradients call for a downshift, losing momentum and using fuel. A dual clutch maintains drive during the shift, so momentum is maintained and there is less chance of needing a second downshift.
Another Traxon output option is a 120kW/1,000Nm electric motor-generator, effectively producing a parallel diesel-electric hybrid driveline. ZF engineers insist there is an increasing interest in hybrids among truck manufacturers, even for heavy, long-distance trucks where the lack of stop/start work using battery power alone restricts fuel savings to about 5%. ZF argues that 5% of an artic’s fuel bill is a lot of money, so hybrids become economically feasible.
As well as powering the truck when moving off, the electrical energy generated while braking and coasting can drive auxiliaries such as air-conditioning, steering pump and air compressor, relieving the engine of their load. It also supports a stop/start engine cut-out, and when the truck is rolling out of gear, the diesel engine is cut completely, not left to idle: the motor-generator restarts it in an instant.
Production of Traxon starts next year and it will replace AS-Tronic in new trucks from early 2014, so we can expect to see it in Euro-6 heavy trucks from Daf, MAN and Iveco.
There are still no signs of a true, purpose-built, automated gearbox with six or eight ratios for lighter trucks. ZF insists it cannot make a business case to develop such a gearbox, so its AS-Tronic Lite, with actuators and controls added to a conventional six-speed synchromesh manual gearbox must sufice.
Even ZF engineers admit that its shifting is not as slick as the big ASTronic’s. Perhaps Daimler’s decision to it its in-house automated eight-speed gearbox (PowerShift) as standard in its new 18-tonne Antos (CM 12 July) will change the market’s attitude to autoshifting in lighter trucks and prompt a rethink at ZF. n
Showtime
Traxon will form the centrepiece of ZF’s stand at the Hannover show in September, but there will be plenty of other new technology alongside it. Perhaps the most interesting is an independent front suspension (IFS) system for trucks. IFS is used in some coaches and buses but apart from the odd installation (such as the Dennis Rapier fire appliance in the mid-1990s) has never reached the truck market. ZF is convinced that will change within a few years.
This is not just because of the ride and handling advantages of IFS. What is more persuasive to truck manufacturers is that ZF’s new IFS is claimed to be 40kg lighter than an equivalent conventional air-suspended beam axle and allows bigger steering angles for better manoeuvrability.