O ver a 23-year production run the Mercedes-Benz SK range of
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maximum-weight tractive units benefited from an orderly programme of chassis and driveline development. Then, in January 1997, the company made a major step forward by incorporating many of the latest technical advances into its new Actros range. Bearing in mind the conservative nature of the average truck operator this was a bold step: although M-B's sales across the board have increased, its share of the UK's tractor market is smaller today than it was in 1996. The blame for this was put on a shortage of right-hookers during the first year of production—last year the company's market share did show signs of recovery.
Evoknion
Two new four-valve engines, at a nominal 12 and 16 litres, range from 313 to 571hp. The V6s and V8s share a common under-square design with a 150mm stroke, i3omm bore and two-litre cylinder volume. They also share the Telligent vehicle protection system, using on-board computers to control individual Kt. functions which can also communicate with each other.
The Telligent electronic engine management system controls fuel delivery and injection timing; the Telligent servicing system monitors levels such as fuel, coolant, engine °oil, hydraulic steering fluid and even windscreen wash, as well as keeping a check on air filters, fuel filters, batteries and brake linings.
It sounds like an electrician's nightmare but wiring looms have been simplified from 143 cables in the previous model to just eight on the Actros.
The vee engine is not as common in the UK as the in-line six but M-B has built over a million 400-Series units since 1970 and many operators favour its light, low and compact installation. Its successor, the charge-cooled 500-Series, generates a high peak torque at the relatively low engine speed of 1,08orpm throughout the range. A flat torque curve means there is little drop-off in performance up to peak power at 1,8(x:wpm. 3
This also gives advantages in engine braking, which is further enhanced by M-B's inclusion of a decompression valve in each cylinder head. This gives between 4o and r00% more braking power than the butterflytype exhaust brake. A speed-set function allows downhill pace to be limited in advance.
To obtain the clean, efficient burn demanded by current emission levels, fuel is injected by a unit pump mounted close to each cylinder. These pumps work at a very high pressure: between r,roo-L8Gobar, depending on engine speed.
M-B has been specifying electronic gearshifting on UK models ever since it introduced the Powerliner in 1988. Telligent's electronic control has speeded up gearshifts, particularly when passing through the rangechange.
With 16 gears to choose from, most drivers appreciate the fascia display of the selected ratio and available options for moving up or down the box. The clutch pedal remains an integral part of gear changing which, in many opinions, is the more wearing operation for the driver. Ventilated disc brakes are fitted on all axles—and as if this were not a radical enough step on its own, they are controlled by an electro-pneumatic system. The conventional dualcircuit compressed air system works at fo bar—r7.6%—higher than on previous models. An electrical brake signal is transmitted by the brake pedal to brakes valves at each wheel to eliminate any delay. In case of an electrical failure, the failsafe design reverts to standard air. Inevitably, the Telligent brake control incorporates both ABS and ASR.
Air suspension is standard on the rear axle of all Actros tractive units, and can be used to lower the height of the chassis by Gomm. Optional electronically controlled shock absorbers adapt axle damping to the load and road surface conditions.
The one feature the old SK cab lacked was interior space, and the Actros's all-steel cab substantially deals with this criticism. There are four to choose from: the M day cab, L sleeper cab, high-roof L sleeper and the flatfloored MegaSpace cab. They all have rounded front contours to cheat the wind. The two top models have four-point suspension as standard (this is an option on the other cabs) but full air is reserved for long-distance cabs.
It's hard to imagine a truck cab giving the crash protection of a modern car, as overall dimensions simply don't allow for crushing zones. Undeterred, Mercedes has designed the interior of the cab as a survival space by strengthening the floor and doors to withstand a frontal impact better. Interior protection extends to an air bag and integral seat belts with tensioners on the driver's suspension seat.
All models can be supplied with central locking or comfort locking which closes any window and the sun roof. Seat and steering are almost infinitely adjustable while all the gauges, instruments and controls are well arranged in order of priority. The flat binnacle in front of the driver houses a flat tachograph with automatic disc insertion and a large rev counter. A 24V power supply for accessories comes as standard.
The heating and ventilation system can be set to take in fresh air or to recirculate it; the fresh air intake features a particle filter and air conditioning is optional.
The cabs are trimmed in a colourful material and are well insulated against noise and cold.
For long-distance and MegaSpace models a wall-mounted cabinet can be specified in place of the second bunk. As well offering additional storage space the cabinet will house a refrigerator, microwave oven and coffee machine.
• by BM Brock