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Friday, February 1, 2013
By Adrian-Liviu Dorofte at Friday, February 01, 2013
As early as 1897, in other words just one year after the invention of the truck by Gottlieb Daimler, the Daimler Motor Company launched a vehicle that would carry a payload of five tonnes. The arrival of what became known as winched tippers in 1904 subsequently paved the way for the transport of heavy bulk goods: with the help of a crank and a toothed rack, it was now possible to tilt one side of the load platform upwards. With the correct crank ratio, two people could easily deal with a five-tonne load with just two winches per truck.
Things were still being done this way well into the 1920s, when the hydraulic lift ram began to take over from manual labour as a means of tilting the platform. At this point the three-way tipper was born: for with the hydraulic ram as the driving force, bulk goods could now be tipped off in three directions instead of just two, as had been the case until then.
The dedicated tipper however, as seen working on construction sites to this day, did still not exist. The structure used back then as a chassis by both the building industry and disposal companies was technically pretty much the same as that used for road-going vehicles with, at the very most, a shorter rear overhang or certain modifications to the suspension and frame to differentiate it.
Nevertheless: even that very first Daimler truck anticipated the planetary axles that are still used on construction vehicles today. The belt transmission transferred the engine power to a shaft mounted at right-angles to the longitudinal axis of the vehicle. At each end of this shaft was a pinion that gripped the sprockets on the inside of a gearwheel, which in its turn was securely connected to the wheel being driven.
In the years running up to the war, tipper payload was gradually increased by Mercedes-Benz to ten tonnes, as for example carried by the three-axle LK 10000 of 1937. Also known as the "Reichsautobahn-Strassendienstwagen" (or "state highway services vehicle") it featured a double-drive rear axle (axle configuration 6x4).
From 1949 onwards it was above all medium-sized conventional cab-behind-engine vehicles such as the LK 3250 and LK 3500 that came into their own as tippers working on post-war reconstruction. Heavy-duty two-axle tippers then rejoined the range in the mid-1950s, but it was not until the 1960s that Daimler-Benz once again built a three-axle model for the construction sector.
By the time those first heavy-duty three-axle models, with their 6x4 axle configuration, came onto the market in 1964, they found themselves up against established competition from a variety of sources. Such vehicles bore the name Büssing, Henschel, Krupp, Magirus or MAN: all of these brands were already offering a 6x4 or 6x6 by the time the short-nosed Mercedes known as the LK or LAK 2220 appeared on the scene. That these vehicles would ultimately become such firm favourites with drivers, above all in the Middle East and Africa, that they would go on to be used for a good 30 years, was something that very few people back then would venture to have predicted.
Robust concept: quality wins through
However, the LK 2220 of 1963 was designed from the outset to deal with the extraordinary challenges that it would go on to face all over the world. Not only did it feature a 154 kW (210 hp) engine that, in its day, was the most powerful ever fitted in a three-axle construction vehicle, but also a generously proportioned six-speed constant-mesh transmission and an exceptionally robust frame. The drive axles were configured to carry an axle load of 13 tonnes each, even though the maximum per axle housing on the road in Germany was eight tonnes and no more than ten tonnes even in off-road use. "Trucks you can trust" was thus a motto that was lived up to even then, above all in the construction sector.
A whole range of further refinements ensured that this new three-axle model was ideally suited for work in extreme terrain. The backbone of the vehicle was provided by an exceptionally robust fish-belly frame with riveted cross members, and which was somewhat wider towards the front than in the rear. Two lower and one upper maintenance-free control arms on each side bore the brunt of the driving and braking forces from the rear axles, which meant that the leaf springs had only to cope with the transverse and load forces.
Strategic realignment in the 1960s
The relatively late arrival of this short-nosed heavy-duty tipper on the market was not only due to the very thorough testing to which the new construction vehicles were subjected. This period between the late 1950s and the early 1960s saw the brand under the three-pointed star experiencing something of a reorientation phase as far as its truck strategy was concerned. The cab-over concept was still being eyed with some scepticism and the company was making only cautious advances into the very heavy segment. The broad direction, however, was clear: the objective that Mercedes-Benz had set itself for its truck business from the mid-1960s onward was to become a high-volume generalist.
And so it was that, one after another, segments that had until now been neglected were gradually appropriated for the brand. Gaggenau – at that time the plant responsible for the heavy-duty models – was in the mid-1960s producing both cab-over-engine models (the LP series with cuboid cab introduced in 1963) and the short-nosed models that had first appeared on the scene in 1959. In parallel to this, the Mannheim plant was building medium-duty cab-over-engine and short-nosed models, while the new plant at Wörth had taken up manufacturing the light-duty LP 608 cab-over-engine model as a completely new product.
Only a very short run-in period was to prove necessary before both the novices in the product range – the very light-duty as well as the very heavy-duty –had worked their way up to become the market leaders in their respective disciplines.
Broad portfolio with increasing specialisation
The product portfolio of Mercedes-Benz was thus not only growing horizontally, but also vertically, as it were: that is to say in the form of increasing specialisation, as was now being seen more and more with the construction vehicles. Special tipper variants had been available for virtually all post-war truck models. But in terms of the actual construction specification, this generally quite simply included – as had been the case since the early days of the truck - a shortened rear overhang, modified frame and adaptations to the suspension.
The move to the three-axle truck with a double drive axle represented a first cautious step in the direction of a purpose-built specialist tipper as we might understand it today. There was however, for example, as yet no direct output shaft between the two rear axles. Instead, on the LK 2220, each of the two rear axles was connected by a separate shaft to the transfer case, which could if required also drive the front axle via a third shaft, so turning the LK 2220 into the all-wheel-drive LAK 2220.
The drive axles of these early three-axle models at this point did still not operate as planetary axles but instead worked according to a sort of precursor principle known as spur gear hub drive. This was already established technology – used, for example, in the classic post-war model L 6600 – and similarly used a two-stage process for the transmission of power: partly in the form of a conventional axle gear mounted centrally in the axle housing, and partly in the form of further spur gearing between the axle head and the wheel, via a large gearwheel linked to the hub. This same engineering approach and the same direct injection engines as for the short-nosed models were also used in the first cab-over-engine construction vehicles, with cuboid cab and 6x4 axle configuration, which took over from the short-nosed models in 1963.
Debut for a new family of components
Planetary axles, still widely represented among construction vehicles today, arrived on the market from 1971 onwards. They made their debut not in the short-nosed models, but in the cab-over-engine vehicles. Pre-empting the subsequent New Generation vehicles – and reflecting the requirement for eight horsepower per tonne – Mercedes-Benz introduced the new V10 in 1971. This vehicle had an output of 320 hp and featured the new planetary axles as well as a tilting, cuboid cab. Synchromesh transmissions were standard with these new variants, as well as a direct output shaft for the tandem planetary axle of the LP 2232 with its typical 6x4 axle configuration.
There were still two things missing in the product range at this time: on the one hand a cab-over-engine vehicle with all-wheel drive, and on the other a short cab for the cab-over-engine units. The heavy-duty LP, for example, was only available with a medium-long or long cab. Although the LP was due to be replaced soon afterwards, an unusual interim solution was found that meant that it could be adapted for all-wheel-drive use: the cab-over-engine vehicle built by Hanomag-Henschel, which had recently been taken over by the company, was quickly fitted with Mercedes-Benz's own V engines, transfer case and planetary axles.
And so the axle configurations 4x4 and 6x6 were now also represented among the cab-over models, until the New Generation of 1973 heralded the arrival of a completely new and logically structured range of models in the hitherto rather bewildering field of the heavy-duty trucks. It was perhaps somewhat unusual that the construction trucks should be the first vehicles in a new model series to be introduced, but there was a plausible reason for this approach: the manageable numbers of construction vehicles meant that production in the Wörth plant, which had gradually been taking over building the heavy-duty range since 1965, could begin in a calm and controlled way.
Modular system for the New Generation
In manufacturing technology terms, the New Generation was part of one of the most radical upheavals in the Daimler-Benz commercial vehicle programme at that time. Having said that, the introduction of the so-called modular system marked a major and significant step forward for the company. For by this time Daimler-Benz had become one of the big names among heavy-duty trucks and had managed to achieve steady growth in its market shares – in the international markets as well. For the business year 1974, for example, the plan was to build 35,000 units in the heavy-duty sector. By comparison: the figure for 1965 had been just under 8000 units. an increase, in other words, of almost 440 percent.
Despite the high level of demand, a period of economic difficulty was not far away. The oil crisis was just around the corner, commodity prices were on the rise and, to add insult to injury, floating exchange rates were making business very difficult. The answer to it all was to be the sophisticated modular system that lay behind the New Generation, which would meet the double challenge of the time head on: despite much-needed international diversification, market prices could be kept at a fair level. Development chief Arthur Mischke summarised the approach in a single sentence back in 1974: "The modular system was applied so systematically that we were able to build the maximum number of models to suit all transport requirements using a minimum of assemblies and components."
Just 650 components were required for the new V engines used in the 400 series, compared with 1600 for the previous range. Similarly, only 220 parts were needed for the new planetary axles, as opposed to the 480 used for the two previous axle series. Standardisation and thus a higher level of automation also provided the scope to increase the dimensions of such components and so improve their durability.
Standardisation creates scope for further diversification
The way was now free for the construction vehicles – where necessary – to forge their own path. One example of something that was retained was the tried and tested fish-belly frame. Customers had a choice of three final-drive ratios for top speeds of 75, 85 or 95 km/h. The vehicles of the New Generation were braked by pivoted brake shoes with a drum diameter of 410 millimetres, which were used uniformly on all the axles. For the all-wheel-drive variants Mercedes-Benz also added an enhanced ALB system (automatic load-sensitive brake pressure control), which now also acted on the front axle brakes rather than just the brakes on the rear axle(s).
While the suspension mounting for the three-axle construction vehicles was already a familiar design, the cabs acquired an all-new cab suspension system: at the front the cab was mounted on two pivot bearings with flexible rubber bushings. At the rear the cab was softly sprung on dampened spring struts, ensuring a low level of vibration. The particularly high tilt angle was a welcome addition for workshop personnel, as it afforded very easy access to the engine and ancillary units.
The driver was easily able to carry out daily checks via flaps in the front end. Peace and quiet in the cab was ensured by the cab-mounted gearshift: when the cab was tilted, the steering and gearshift linkages extended telescopically. For the first time, the shift lever thus had a fixed place in the cab, which itself was very effectively insulated against noise, heat and cold. The cabs of the New Generation now offered better ease of operation and more passive safety than ever before. Initially available in two variants - short or long – a medium-long variant was introduced in 1977.
Construction vehicle programme continues to expand
When, with effect from 1986, the precise gross vehicle weight of 32 tonnes became permissible for the four-axle model (previously: 30 tonnes), this category of vehicle would come to prove very popular with customers. It was initially built by specialist firm NAW, a company subsidiary based in Arbon, Switzerland, but production was later taken over by Wörth.
In the 1990s, by which time the New Generation had become the SK range, the construction vehicles too could be fitted as an option with the comfort cab suspension from the long-distance vehicles. At the same time the maximum engine output rose to the once unimaginable figure for this sector of 320 kW (435 hp).
By the time the construction vehicles produced under the New Generation, New Generation 80 and SK names were succeeded in 1997 by the construction variants of the new Actros, an impressive 24-year production period lay behind them.
Added refinements for Actros construction vehicles
The Actros construction vehicles would retain their dependable and robust characteristics, as well as the planetary axles, but added to these a growing number of technical refinements: the highlights of the new Mercedes-Benz construction vehicle range included parabolic instead of trapezoidal springs all round, a hydraulic/pneumatic gearshift, a new front-axle load compensating system for the four-axle models and, last but not least, off-road EPS as an option.
The automated transmission became a standard feature as early as 2003 with the introduction of the second-generation Actros in the construction vehicle sector. The high-quality feel and impeccable workmanship of the new, ergonomically designed interior pleased the drivers, as did the new air-conditioning system and the now-standard Telligent braking system – disc brakes were increasingly becoming the norm. Operators soon learned to appreciate the fact that the maintenance intervals were now twice as long.
The addition of high-payload Axor variants, with narrow cabs and in-line engines, to the Mercedes-Benz construction vehicle range from 2004 onwards was soon followed by an off-road version of the Actros 3 in 2008. Protective plates for the engine, radiator and tank meant that it was better equipped than ever before to cope with the risks inherent in rugged, off-road use. The 16‑speed Telligent automated gearshift ceded to the new PowerShift Offroad automated 12-speed box. Further refinements that were now part of the standard specification included a battery charge indicator, a compressed air connection point inside the cab and roller sun blinds on the side windows, as well as a useful folding table for the front-passenger seat.
The new Arocs: a special class of truck for the construction sector
Their successors have now arrived in the shape of the new Arocs model series, a special class characterised not just by a new name. With a new "bucket-teeth-look" radiator grille as well as a new cab interior, the Mercedes-Benz construction vehicle is clearly forging its own way forward from now on.
Whereas the New Generation saw the road-going models and the construction vehicles staying more or less in step with one another, the two categories of vehicles will diverge significantly from now on: planetary axles, for example, no longer play a significant role in today's road-going vehicles, but their robustness means that they remain the preferred option in the construction site environment.
The specialist capability that is demanded today once again sets far greater limits on the development of uniform solutions for many components than was the case in the days of the New Generation. While back then the remit was to achieve the requisite diversification through standardisation, the challenge today is to control the centrifugal forces of increasing specialisation on the basis of higher volumes and global scale.
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