Mercedes-Benz Zetros press trial drive
Mar 30, 2010
Drive configuration
  • Compact, powerful engine
  • A choice of manual or automatic transmissions
  • Particularly hard-wearing clutch
  • Permanent all-wheel drive
The powertrain of the Mercedes-Benz Zetros is primarily composed of tried-and-tested, established components from the Axor. 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.
Connection to the gearbox is via the GF 395 Kerasinter single dry disk clutch with a diameter of 395 millimetres. The term "Kerasinter" stands for a special coating which is particularly hard-wearing.
A choice of manual or fully automatic transmissions
The transmission comes in two different variants: available as standard is the manual hydraulic-pneumatic nine-speed G 131-9 transmission (eight forward gears + constant mesh 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 gear ratio spread of the manual transmission (including crawler gear) is 14.57 (1.00 to 14.57), while for the full-automatic transmission it is 5.57.
The transfer case for the permanent all-wheel drive is the VG 1700, a tried-and-tested triple-shaft unit with an engageable interaxle differential lock and also featuring 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). In each case the drive system is implemented by means of a planetary differential gear system (on the front axle via the centre gear, and on the rear axle via the internal gear).
Extra short ratio off-road gear
The off-road gear has a ratio of 1.69 and makes it possible to achieve particularly low final speeds, which above all are vital when driving down steep hills in the lowest gears: the indicated maximum braking power generated by the engine brake and constant throttle is around 185 kW (252 hp). The final speed of the crawler gear, when using the on-road gear at an optimum engine speed of 2500/rpm, is approximately 7.3 km/h (standard specification with manual transmission). The speed of the off-road gear at the same engine speed is only reduced to around 4.3 km/h, and the vehicle mass is therefore easier to control with just the engine brake than when using the on-road gear. Compared with the on-road gears, in general the off-road gear increases tractive power by around 70 percent.
The VG 1700 transfer case distributes torque between the front and rear axle(s) in a ratio of 1:3.21 using the differential gear system, and 1:1 with the differential lock engaged. The all-wheel drive of the Mercedes-Benz Zetros is permanent and therefore not designed to be engageable.
Based on a planetary gear differential, this solution is more costly than an engageable all-wheel drive, which does not work as well with a differential, but has a number of advantages. For one thing, a permanent all-wheel drive is less susceptible to driving faults, and for another it constantly guarantees the best performance, and also makes for a particularly well-balanced total load of the axle assemblies.
Also proven over many decades are the highly-prized AL 7/HL 7 planetary axles. The ground clearance of these axles on a standard specification Zetros is 422 millimetres for the front axle, and 343 millimetres for the rear axle.
Three manual differential locks for different off-road requirements as standard
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.
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).
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