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SLOW WITH THE FLOW
Page 64
Page 65
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MAN's revolutionary new retarder runs on water.
Colin Barnett is the first to test it on British roads.
Exclusive
Never underestimate the power of water. From Boscastle to Banda Aceh, people have felt its malevolent force, but harnessed correctly it can be a valuable ally. Water can be used to generate power, cut metal and even make beer. But as far as we know it's never been used to stop a truck, unless it gets into the electrics.
Now, however, with some help from Voith, MAN has perfected a system that can control the speed of a 44-tonne artic using no more than the water in the radiator. At the heart of the system is the Voith Aquatarder which, when fitted to an MAN engine and combined with an exhaust brake, becomes the PriTarder.
We first heard of the PriTarder nearly three years ago — MAN admits that perfecting the installation has taken a bit longer than planned. Mind you, this is much more than a bolt-on afterthought so MAN really had to allow for its installation at the design stage.
It's currently available on the 12.8-litre D28 engine rated at 480 and 530hp and should appear on the D20 within a year or so. MAN has an exclusive agreement with Voith, so don't expect to see the Aquatarder on rival brands before 2007.
The PriTarder costs £3,440, compared with MAN's charge of £4,220 for a ZF Intarder.The other significant figure is the weight penalty and here again the PriTarder wins the day, at 32kg compared with the Intarder's 74kg.
How it works
The mechanical bits live in a housing on the nearside front of the cylinder block. It contains what is effectively a traditional fluid coupling; the fluid in this case is cooling water.The moving rotor half of the coupling is directly connected to the crankshaft with the stator half fixed to the housing.
When retardation is required water is diverted through the coupling and the flow from the rotor against the stator is restricted. As a result the rotor, and hence the rotating mass of the engine, is slowed down.
It's hard to believe that this arrangement could produce enough retardation to slow a bicycle; in fact its maximum braking torque measured at the propshaft is 1.450Nm.
With all this energy being dissipated by the coolant you might also be excused for assuming that it would rapidly boil up. Not so. says MAN — evidently the TGA's cooling system was designed with the PriTarder in mind and can cope, helped by the cooling fan which begins to spin as soon as retardation commences.
Needless to say, all of these functions are controlled by the truck's on-board computer systems.
Driving impressions
So much for the theory; thanks to its tolerant operator, CM was able to try out the first example of a PriTarder to be sold in the UK. From MAN's Swindon HQ it was an obvious move to head north up theA419/417 and see how the PriTarder coped with the challenge of Birdlip Hill.
On the undulating run up to Gloucester we had a chance to get familiar with the controls. The TGA 530 boasted the fully automated TipMatic transmission s° we could largely forget about the gears.
PriTarder's principal control is a stalk on the right side of the steering coltunn, further away and slightly smaller than the cruise control stalk. Pulling the stalk towards you gives six levels of retardation, or press the button on the end for maximum effect in one go.
Integration with the cruise control is highly effective,coming into play at any set speed plus 7km/h. Operating the brakes or retarder above cruise speed doesn't disengage it: neither does changing gear.The retarder blends with the foot brake smoothly.
The real test started at the top of Birdlip Hill. It took a few minutes to get the right balance of gear and retardation but thereafter the effect
recommend' it
was impressive. Unlike a conventional retarder mounted on the gearbox output shaft, the PriTarder responds to a lower gear, and higher revs, in the same way as an engine compression brake.
Having switched the TipMatic to manual and changed down the box, we soon established that eighth gear and maximum retard was enough to hold the 44-tonner at a steady 58km/h on the steepest part of the descent. As the hill flattened out slightly it began to slow rapidly.
We could have reduced the retardation level to maintain the speed,but changing up to 10th gear increased the speed to 65km/h and held it — all without having to touch the foot brake.
Worries about overheating were quickly
1g ter an at east as
dispelled. After three descents, and two climbs back to the top the temperature gauge needle rose no more than 2mm, and fell back instantly when the PriTarder was disengaged.
This was with an ambient temperature around 12°C, but the TGA's owner reports that so far it has coped just as easily in Spain.
In more normal use on the open road. PriTarder works effectively as a service brake substitute. On the level when approaching a roundabout you can really feel the cab nod as it digs in, and it will easily bring the truck to a standstill given enough space.
We're not often easily impressed, but there really don't appear to be any downsides to the PriTarder. Making the inevitable comparison with the ZF Intarder, it's cheaper, lighter and at least as effective. For an operator with any serious hills on their route, we have to recommend it. •