Mercedes-Benz Zetros press trial drive
Wörth
Mar 30, 2010
Mercedes-Benz Zetros: the all-wheel-drive cab-behind-engine vehicle for difficult terrain
  • Special vehicle based on established large-scale production technology
  • Exemplary off-road ride comfort
  • Highest level of off-road suitability
  • True to the motto: tons of work, no roads
All-wheel drive, two-axle vehicles with a gross vehicle weight of 16.5 or 18.0 tonnes, as well as three-axle vehicles with a maximum of 25.0 or 27.0 tonnes: this is what is on offer from the Mercedes-Benz Zetros range of all-terrain cab-behind-engine trucks - a range based to the greatest extent on established large-scale production technology, but which has been carefully modified for heavy-duty off-road applications. The payload (excluding body) in the case of the two-axle models is almost ten tonnes, while for the three-axle models (also excluding body) it is 16 tonnes.
The entire vehicle and components have been tested and verified for the most difficult off-road applications in accordance with the demanding quality standards of Mercedes-Benz, using simulations, test bench trials and also extreme summer and winter road tests. The driver's cab of the cab-behind-engine Mercedes-Benz Zetros has been newly developed, while the powertrain and chassis are based primarily on the Actros and Axor model series. Thanks to this modular construction principle, customers are able to enjoy benefits in terms of cost-savings, service and quality.
The Mercedes-Benz Zetros was developed at the Wörth plant and is also produced there. Production takes place on the same assembly line on which three model series of the Unimog and also the Econic low-floor vehicle are also produced.
Cab-behind-engine design is number one choice for off-road applications
The cab-behind-engine design was chosen deliberately, since it is the number one choice for off-road vehicles for a number of reasons. It allows for compact, low profiles, as well as simple servicing, and provides significantly better vehicle control and ride comfort under extreme conditions compared with the cab-over-engine truck design. Overall this translates into less stress on the driver, but at the same time increased performance in the form of significantly higher possible speeds, longer periods of operation and therefore shorter round trip times.
It is no coincidence, therefore, that the Zetros series has generated a great deal of interest in the energy and exploration sectors, and also among the firefighting and emergency services: the exceptionally good off-road ride comfort of the cab-behind-engine truck gives the driver permanent control over the off-road speeds, something which would only be possible for brief periods at best in a cab-over-engine vehicle. And when it comes to safety and ergonomics for the driver, as well as the tasks he has to perform and the period of operation, the advantage enjoyed by the Mercedes-Benz Zetros really comes into play. Compared with cab-over-engine vehicles, it is the most suitable and safest design for extreme applications.
Powertrain uses tried-and-tested components
The powertrain makes use of proven components from large-scale Mercedes-Benz truck production. Under the bonnet of all variants of the Mercedes-Benz Zetros sits the large-scale 7.2-litre in-line six-cylinder OM 926 LA engine, capable of producing 240 kW (326 hp) and a maximum torque of 1300 Nm between 1200 and 1600/rpm. Mercedes-Benz supplies this engine as a Euro-5 variant; Euro-3 variants are also available on request.
The transmission comes in two different variants: available as standard is the manual hydraulic-pneumatic nine-speed G 131-9 transmission (eight forward gears + crawler gear) with a direct ratio top gear; as an option the Mercedes-Benz Zetros is also available with the six-speed Allison 3000 SP/PR automatic transmission (fully automatic).
The transfer case for the permanent all-wheel drive is the VG 1700, a unit which has been tried and tested over many decades and features an off-road gear ratio of 1.690, a good 20 percent shorter than in the all-wheel drive vehicles of the Actros and Axor model series (they have an off-road gear ratio of 1.403). This makes extremely low speeds possible, a particularly important feature when driving downhill on the steepest of gradients, and it also increases overall tractive power by around 70 percent compared with the on-road gears. Torque distribution between front and rear axle(s) is 1:3.21 using the differential gear system, and 1:1 with the differential lock engaged.
Robust planetary axles for high ground clearance
Also proven over many decades are the highly-prized AL 7/HL 7 planetary axles, which are still indispensable components used in the construction vehicles of the Actros and Axor series. Mercedes-Benz supplies the Zetros with three manual differential locks as standard, which the driver can easily engage with the aid of a practical rotary switch. This switch also indicates the appropriate sequence in which the locks should be engaged when faced with increasingly difficult terrain: first interaxle, then rear interwheel and finally front interwheel. This helps to avoid the risk of incorrect operation.
The standard ratio of the rear axle(s) in combination with the manual trans­mission is i = 5.33 (corresponding to a Vmax of 94 km/h at rated engine speed and with standard 14.00 R20 tyres). Alternatively a rear axle with a somewhat longer ratio of i = 4.83 (corresponding to a Vmax of 103 km/h at rated engine speed) is also available.
Optional automatic transmission, ABS as standard
In conjunction with the fully automatic Allison transmission, Mercedes-Benz supplies a rear axle ratio of i = 7.73 (corresponding to a Vmax of 105 km/h at rated engine speed and with standard 14.00 R20 tyres) as standard. The Allison 3000 SP/PR automatic transmission is also available as an option in combination with the longer axle ratio of 6.82 (corresponding to a Vmax of 112 km/h at rated engine speed).
The Mercedes-Benz Zetros comes fitted with single 14.00 R20-size tyres as standard, which thanks to their larger diameter add to the vehicle's ground clearance by around a further 75 millimetres compared with the largest regular truck tyres (13 R22.5). The 14.00 R20 tyres also help to achieve a maximum load-carrying capacity of 9.0 tonnes per single-tyre axle, whereas with single 315 R22.5 tyres the maximum would be precisely 8.0 tonnes. As an option, the Mercedes-Benz Zetros can be delivered ex-works with a tyre pressure control system which enables the tyre pressure to be adjusted, depending on the demands of the terrain, direct from the cab whilst driving.
When it comes to brakes, the Mercedes-Benz Zetros has opted for classic drum brakes all round, which are easy to maintain and more than a match for even the harshest of off-road applications, whatever the weather conditions. An ABS anti-lock brake system is fitted as standard – however this particular ABS system can be disengaged if necessary while driving off-road (useful for example when driving downhill on gravel or stones so that a braking wedge can build up in front of the tyres).
Optimised chassis for off-road use
Axle suspension at both front and rear is taken care of with wide gap parabolic springs in conjunction with stabilisers and shock absorbers. The entire design of the suspension system has been specifically tuned for long deflection and a high degree of ride comfort to meet the requirements of the harshest off-road applications. Variations to match different axle loads are also possible. Comprehensive adjustments to the individual components and assemblies of the Mercedes-Benz Zetros ensure that the vehicle is able to cope with fording depths of up to 0.8 metre as standard and up to 1.2 metres as an option.
The chassis frame of the Mercedes-Benz Zetros is a ladder-type frame which is resistant to bending (important for on-road use) but torsionally soft (important for off-road use), therefore giving it very good torsional flexibility. It also features open C-profile longitudinal members as well as bolted-on C-profile crossmembers. Originating from the Actros model series, it has been specifically strengthened and modified for more demanding applications: the overall design of the chassis frame is such that even when fully laden, the vehicle is not only able to be towed, but also raised via both the frame head and the rear.
Designed with good body-mounting ability
The connection points for mounting bodies in the case of the Mercedes-Benz Zetros are identical to those used in the Actros and Axor series. In principle, adapting the widest variety of implement and attachment systems does not therefore involve any additional expense. At the same time, the even, straight and extremely durable chassis frame is suitable for all kinds of tailor-made and individual body/equipment solutions. Furthermore, the reinforced and bolted-on frame head of the Mercedes-Benz Zetros has been designed especially for the attachment of front-mounted implements.
The fact that the Mercedes-Benz Zetros is also even able to draw extensively on the large-scale production pool of Mercedes-Benz components is particularly advantageous for operators the world over when it comes to servicing or procuring spare parts. More than 5000 outlets in 160 countries ensure worldwide availability, pricing in line with the market, and quick, professional servicing, even in the remotest corners of the globe.
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