On the engine front, the DAF 4.5-litre four-cylinder PX-5 and the 6.7-litre six-cylinder PX-7 have both enjoyed a full redesign, removing the need for EGR and enabling the previous variable geometry turbo to be exchanged for a far simpler wastegate version. The 3.8-litre PX-4, originally introduced as a simpler, SCR-only engine for the LF City, has been quietly dropped from the line-up, as has the less popular 148bhp version of PX-5, but otherwise horsepower and torque remain roughly the same as previous iterations.
There is up to a 3% improvement in fuel efficiency to be had with the new engines as well, when they’re combined with the new SCR aftertreatment system, but DAF has chosen not to make a song and dance about it. The LF is principally used by those in the urban multidrop game, where there isn’t, perhaps, the same level of obsession with such things as the long haul market, plus the removal of EGR has meant a slight increase in AdBlue consumption.
But it is the other half of the powertrain that really caught the eye, as it brings the option of a new, fully automatic ZF gearbox to the party: PowerLine. Tried and tested in smaller vehicles, including both BMW and Aston Martin cars, as well as the IVECO Daily, this is PowerLine’s first appearance in the truck market. An eight-speed transmission offering three torque ratings, it replaces both the six- and 12-speed ZF AS Tronic AMTs (automated manuals) in LF, sitting alongside the nine-speed and six-speed manual, the last of which currently comes as standard in these vehicles.
The big difference between a fully automatic transmission and AMT is the complete lack of any kind of hesitancy to pull away. While a skilled and experienced foot on the pedal can produce good results from AS Tronic, with PowerLine the same foot can behave with far less precision, yet the gearbox will perform far more effectively. This is largely thanks to the presence of a torque converter, in place of the AMT’s dry clutch.
PAUSE
Having the usual dry clutch between engine and gearbox means there will always be a point in the gear-changing cycle where the two are completely disengaged. Whether manually, via the driver’s left foot, or automatically, in the case of AMT, which effectively incorporates the left and right pedals into one, there will always be a pause in which the shift between gears is made. It is this mechanical action which makes AMT boxes feel like they are pausing, unless driven very precisely.
In contrast, a torque converter is filled with hydraulic fluid. An impeller, driven by the engine, throws fluid outwards thanks to centrifugal force and into a turbine which sits opposite within the torque converter housing. The blades on the turbine are angled such that the fluid is thrown back towards the impeller again, creating a fluid coupling. A third, smaller wheel between the two, the stator, has blades which force the flowing fluid to turn at an angle, slowing it down as it travels back to the impeller. This is what creates torque conversion.
Torque converters also use a ‘lock up’ clutch to transmit the energy through to an output shaft, which in turn leads to the gears themselves. But because it is constantly bathed in fluid, it does not wear like a dry clutch – another advantage of fully automatic gearboxes.
PowerLine, in common with most modern automatic gearboxes, uses planetary gears, cogs which revolve within and around each other. There is no separate layshaft carrying these gears, and therefore nothing to be disengaged. To make a change, an electronic control unit switches between different combinations of these rotating cogs, without traction within the torque converter ever being lost, hence there is no delay – there is no clutch to open and then close, except when the gearbox is placed in neutral.
FROM THE DRIVER
From the driver’s seat, something the author was able to experience in both four- and six-cylinder versions of the upgraded LF, this gives the automatic LF the classic ‘creep’, whereby the vehicle will move slowly forward as soon as pressure on the brake pedal is lightened. This makes manoeuvring in tight spaces – something urban distribution vehicles like this inevitably spend a lot of time doing – very easy, as there is no clutch control to worry about therefore, again, no delay.
The other notable thing is the sheer speed with which PowerLine makes its changes – it defies being matched by a manual, no matter how skilled the driver. For applications where the driver is in and out of the cab, making stop-start deliveries to multiple locations, things really couldn’t get any simpler than a vehicle as responsive as this. Experience proves that multi-dropping is tiring work, so reducing fatigue built up behind the wheel can only be a positive.
Like any modern commercial vehicle, downspeeding for economy is the name of the game. To this end, top gear in the eight-speed PowerLine box is a double overdrive, enabling the revs to stay good and low on longer stretches of road. While the author initially found that choice a little counter-intuitive, on the basis that direct drive is more efficient, and therefore normally what is chosen for top gear, it is once again important to remember the intended applications. In urban distribution, of course, the most regularly used and held gear is actually further down the box, so it makes sense for that to have the benefit of direct drive.
It is interesting to note that the Allison 2K and 3K Series automatic transmissions are still available as options in LF, alongside the new transmission. PowerLine offers PTO options at three levels of torque output, so there’s no obvious reason why the Allison would be needed. Equally, if Allison is still available, why is DAF using PowerLine at all?
“The Allison has a well-established, trusted relationship with some operators, especially in the municipal sector,” marketing manager Phil Moon responds. “It offers a larger number of PTO options than PowerLine, making it ideal for applications like refuse collection.” So arguably Allison still has a place, and DAF knows it’ll do itself no favours by pushing operators to make the change. “I think we’ll allow the market to evolve towards PowerLine, rather than forcing it on them,” Moon says, pragmatically.
Like it or not, though, there are still technical reasons why the ZF is a better alternative. “Although the Allison has got better and better over the years, it’s always been seen as offering less fuel efficiency,” Moon explains. “The torque converter in PowerLine locks up very quickly after pulling away, which means there is very little mechanical inefficiency in the form of slip.”
This means that PowerLine is at least as good on fuel as a manual, possibly even better in some situations – all of which, when looked at alongside its other benefits, makes one ask why we’re bothering with the halfway house that is AMT at all. “You’re not the first to ask, and I don’t know the answer,” comes the reply. “But it does beg the question, doesn’t it?”