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Easing the burden

25th November 2010
Page 46
Page 47
Page 46, 25th November 2010 — Easing the burden
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With the arrival of its new 'turbo coupling', Mercedes-Benz has been able to make a number of significant changes to its Actros SLT heavy hauler

voids/image: t wviL:ai.rti Ley If you're Looking for a stump-pulling heavy-hitter for STGO work at 250-tonnes. there's no shortage of contenders. Volvo and Seania both offer 700hp in their Special Types chassis (in the case of Scania it's a 'world-heating' 730hp), while Mercedes and MAN aren't far behind with 650hp and 680hp respectively in theirs Naturally, the real challenge has been to find a gearbox and clutch that can handle up to 3,000Nm of torque and the shock load of starting a 250-tonne load from rest, especially on a gradient.That's traditionally meant specifying a heavy-duty manual transmission, usually with a torque converter clutch, for despite all the in-roads that automated multi-speed transmissions have made into the regular artic market, they've remained pretty much absent in ultraheavy haulage tractors greater than 200 tonnes.

Volvo's I-Shift is restricted to 120 tonnes in the UK, while the maximum rating for Scania's Opticruise is 180 tonnes. MAN's V8-powered 680hp 'FGX is a notable exception, being offered with ZF's 12-speed AS-Tronic TC (torque converter clutch) automated transmission capable of working at 250-tonnes CiCW. Otherwise. Allison has a 4000 Series auto box (CM19 November 2009) specced for engines up to 600hp and 2500Nm but with fewer gears to play with.

However, with the arrival of Mercedes-Benz's SLT 4165 S Actros there's now another 'auto' heavy-hauler on the block, ready, willing and plated for 250-tonne operations. And it's all down to the adoption of the latest 'turbocoupling' developed jointly by Mercedes and Voith. Used in combination with Merc's own 16-speed PowerShift auto, it allows the German truck maker to dispense with the old ZF WSK torque converter clutch and 16-speed manual box used on the previous SLT 4160 (above left).

Lighter but still stronger

Like its WSK predecessor, the new turbo coupling is a hydrodynamic unit, transmitting power via an oil-filled coupling, thereby saving the truck's single dry-plate clutch from abuse when pulling away from rest. It's lighter (by 90kg), smaller (allowing for easier chassis packaging) and does away with the need for a full-time oil pump with all the associated parasitic power losses. It also doubles as a powerful downhill brake. with 2,400Nm of retarding power.

With the adoption of the turbo coupling, and consequently the PowerShift auto, Mercedes has made further improvements to the SL1 chassis. You can now order a 4165 S with the tallest high-roof flat-floor MegaSpace cab. which will doubtless be appreciated by a driving crew. Up until now, its predecessor needed the extra under-floor clearance provided by the smaller tong Distance' cabin's engine hump for the manual box's mechanical linkage.

CM recently drove the latest SLT 4165S 8x4 with a 10-axle row Goldhofer trailer in Germany at a gross weight of 160 tonnes and we were impressed — not least having earlier driven the 'old' SLT 4160 with a manual box and torque converter at 150 tonnes on the same track, With the turbo coupling and PowerShift controlling starting-off and all gear-shifts, heavy haulage drivers can now begin to enjoy the ride rather than worry about the next gear change.

The quality of change is fast, smooth and stress-free — especially when we restarted the rig on 6% and 7% gradients on the test track. The retardation provided by the turbo coupling was also comfortably reassuring. Ultimately, we can see it attracting a lot of interest among the small but highly skilled band of UK and Continental ultra-heavy haulers. And STGO drivers need never develop serious forearms again... •

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