Arocs with turbo retarder clutch

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Arocs with turbo retarder clutch
Initial at-the-wheel impression of Mercedes-Benz Arocs 4145 8x4 with turbo
Press Information
retarder clutch
May 2014
Arocs with turbo retarder clutch:
starting off and manoeuvring in a new dimension
 Hydraulic start-off clutch makes Arocs suitable for extremely demanding
low-speed haulage tasks
 Exemplary efficiency thanks to all-mechanical drive apart from starting
off and manoeuvring
 Effortless starting off on 27 percent upgrade
 750 kW braking power: primary retarder in combination with engine
brake
The already diverse model range of the Mercedes-Benz Arocs is being extended
to include yet further options. The fully automatic standard-fitted PowerShift
transmission is now being joined by the optionally available turbo retarder clutch.
Of course, the manual version will continue to be installed if the customer so
wishes.
The compact unit combines a hydraulic start-off clutch with a light single-plate
dry clutch and additionally provides the function of a primary-acting,
hydrodynamic permanent brake. In contrast to a torque converter in a so-called
torque converter clutch (WSK), the start-off clutch uses the full engine torque
and allows time-unlimited manoeuvring in hydraulic mode. Also, the turbo
retarder clutch puts a good 80 kg less on the scales than a comparable torque
converter clutch, making for a commensurately higher payload.
Daimler Communications, 70546 Stuttgart, Germany
Mercedes-Benz – A Daimler Brand
Turbo retarder clutch for the two big six-cylinder engines plus 16-speed
PowerShift
The Mercedes-Benz Arocs unites the turbo retarder clutch with the high-torque
six-cylinder in-line engines of the heavy-duty OM 471 and OM 473 series. The
turbo retarder clutch fits in between the up to 3000 Nm powerful engines and the
especially finely spaced 16-speed version of the fully automatic PowerShift
transmission. Most of the Arocs vehicles equipped with the new turbo retarder
clutch and 16-speed PowerShift transmission for extra-tough applications come
from the heavy-duty Grounder family of the specialist off-road truck. The Arocs
Grounder is built with a reinforced frame and uprated suspension for extreme
applications under tough conditions.
So it came as no surprise that Mercedes-Benz opted for an off-road site for the
first press trial drive. The former military training zone in Münsingen is the place
where brand-new SLT heavy-haulage trucks weighing a total of over 170 t do
their circuits on the Panzer-Ring-Strasse, next to which heavily laden Arocs
tippers stand ready for the trial drives.
Off-road trial drive with 41-tonne four-axle Arocs
The model identification number on the truck door indicates the weight of the
vehicle: 4145 is how the sequence of digits reads. This means that 41 t of Arocs
and gravel are matched against 450 hp, the new turbo retarder clutch and the
fully automatic PowerShift version of the 16-speed G 280-16 transmission,
which has likewise yet to undergo a press trial drive.
The preparations for the initial outing are soon completed. The Arocs instructor
draws my attention to a small indicator lamp that will point to the activity of the
turbo retarder clutch. And to a switch that can be used to activate the
manoeuvring mode.
As, in terms of its operation, the vehicle does not otherwise differ from the
previous Arocs with its 12-speed PowerShift transmission, we get straight down
to the business of trying out the turbo retarder clutch. So I set the selector switch
to forwards, release the parking brakes, and wait. The Arocs doesn't move an
inch. After all, the turbo clutch is not a torque converter. Quite deliberately so.
That's also why the truck doesn't have a tendency to creep.
Daimler Communications, 70546 Stuttgart, Germany
Mercedes-Benz – A Daimler Brand
Page 2
Manoeuvring function simulates torque converter feeling
Slight pressure on the accelerator causes the turbo clutch to fill with oil, which
instantly transfers power from the engine to the transmission. The green indicator
lamp illuminates, and the Arocs pulls away. However, this all-hydraulic startingoff mode doesn't last long. Even in the sixth of 16 gears, after covering just a few
metres on the flat we reach the engagement speed at which the friction clutch
takes over loss-free power transfer.
So having brought the vehicle to a stop, I run a repeat of the entire performance.
But this time with the manoeuvring function activated. With audible and palpable
power, the torque from the engine pushes forward against the parking brake,
which is still on. When I release the brake, the over 41 t Arocs immediately
creeps forward and now needs reining back with the service brake. This is for the
benefit of all those drivers who are used to driving a truck with a torque
converter clutch and who wish to retain the accustomed creeping action of the
vehicle against the brake.
Steep start-off without any tricks with accelerator and brake
In the further course of the trial drive, it very soon becomes apparent that the
turbo clutch is a master of the hill start even under the most adverse conditions.
And so my Arocs instructor encourages me to bring the vehicle to a halt on a
27 percent upgrade in this thoroughly challenging terrain – something a driver in
the real world of construction site tippers would be reluctant to do.
Yet if the same driver is in future at the wheel of an Arocs with turbo retarder
clutch, things might change: the 8x4 tipper pulls away with unprecedented
nonchalance. Second gear had previously been selected as the appropriate startoff gear by PowerShift, which had, of course, received prior warning from the
"off-road" gearshift program. The parking brake isn't used at all, because the
brief stop on the steep hill is managed much better by the starting-off aid of the
service brake, which acts on all wheels. As I switch from brake pedal to
accelerator, the small green indicator lamp signals almost instantaneously that the
turbo clutch is beginning to fill.
Daimler Communications, 70546 Stuttgart, Germany
Mercedes-Benz – A Daimler Brand
Page 3
Reversing very slowly in forward gear
This is followed by a totally roll-back-free start-off with 41 t on the precipitously
steep 27 percent upgrade. And when, with full confidence in this still unfamiliar
technology, I ease my foot off the accelerator a little, I find myself effortlessly
able to let the heavy Arocs roll backwards down the hill under my sensitive
control.
Some practitioners liken this action to "abseiling" – while giving emphatic
assurance that this operation can be continued for almost any length of time
without concern for the hardware, i.e. mechanical system, hydraulics and
temperature. Every professional driver can still recall the days when such a
driving manoeuvre would have resulted immediately in the total destruction of
the clutch.
Pinpoint manoeuvring both forwards and backwards
This exercise very soon teaches the test driver that an Arocs with turob retarder
clutch will always be capable of reliably starting off and accurately manoeuvring
even in the most challenging of terrains – something that is repeatedly put to the
test on a host of grades during the remainder of the trial. As far as the heavy-duty
powertrain is concerned, it makes absolutely no difference whether it's called
upon to demonstrate its strengths going forwards or backwards.
So we masterfully negotiate the winding sections of the circuit time and again in
both directions, with a generous sprinkling of all-hydraulic stop-and-go
manoeuvres against the drive direction of the transmission. At the end of the
course, a glance at the digital coolant thermometer reveals a temperature not
much above 100 degrees.
In a nutshell, the retarder function with its precision effectiveness is a highly
attractive feature for the simple reason that the permanent brake in combination
with the uprated engine brake comes into play ahead of the transmission. In offroad applications, this is the correct approach for wear-free deceleration.
Kathrin Fritz, +49 (0)711 17-5 87 74, [email protected]
Claws E. Tohsche, +49 (0)711 17-5 20 68, [email protected]
Uta Leitner, +49 (0)711 17-5 30 58, [email protected]
Daimler Communications, 70546 Stuttgart, Germany
Mercedes-Benz – A Daimler Brand
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