Mercedes G63 AMG Six-Wheeler Combines Off-Road Tech and AMG Power
The world of the Mercedes G63 AMG 6×6 off-road begins where anything vehicle without caterpillar tracks would have to quit
by Jim Davis | 23 September 2013
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UPDATE: Mercedes announced pricing for the 2014 Mercedes G 63 AMG 6×6, and it seems that those extra wheels come with an extra large price tag. The G 63 AMG 6×6 can be yours at a starting price of 451,010 EUR (VAT included) in Germany.
A look at the key data of the G 63 AMG 6×6 makes it clear that this model’s off-road world begins at a point where anything less than a vehicle with caterpillar tracks would have to capitulate. Six driven wheels, an off-road low-range ratio in the transfer case, portal axles and five differential locks which can be engaged on the move are features which one seeks in vain in conventional off-road vehicles. Together, they ensure that the G 63 AMG 6×6 has driving dynamics which are more than a match for the toughest terrain. As a result, the show vehicle is able to storm up the highest sand dunes with ease while sand tracks hold no fears thanks to its unshakable directional stability. Rocky terrain is negotiated with all the agility of a mountain goat; fording a river becomes almost child’s play thanks to the impressive fording capability. And anyone exploring the on-road performance is certain to be impressed by the catapult-like acceleration of this 3.85-tonne pickup.
Despite its unique drive technology, the show vehicle does not actually represent a new development in terms of technology. After 34 years of G-Class production, there is such a large array of “G” parts to draw on that the G 63 AMG 6×6 uses almost exclusively series-production components under the skin. A case in point is the drive train: the AMG V8 engine, the AMG SPEEDSHIFT PLUS 7G-TRONIC automatic transmission and the front drive system have been taken over from the G 63 AMG while the transfer case with low-range ratio has been matched with a rear twin drive train from a 6×6 version which has already proven its reliability in service with users such as the Australian army.
Technical highlight: the portal axles
Newly developed for a wide variety of applications, the portal axles which have been added to the Mercedes-Benz off-road portfolio are the real technical highlight of the show vehicle. Unlike conventional rigid axles, where the wheels are centred on the axis of the shaft, the wheels of the portal axle are significantly lower thanks to the portal gears on the axle heads. As a result, the ground clearance of the G 63 AMG 6×6 is increased to 460 millimetres (series-production G-Class: 210 millimetres) and the fording depth – or maybe it would be more accurate to say diving depth – is increased to 1000 millimetres (series-production: 600 millimetres).
This design has further important benefits which do away with the need for elaborate adaptation measures. As the position of the axles relative to the chassis remains unchanged, so too do the suspension anchorage points, the steering connection and the position of the propshafts. Furthermore, the portal gear reduction ratio compensates for the huge rolling circumference of the 37-inch tyres so that the gear ratios, speedometer drive and ABS sensors also remain unchanged. An additional benefit of the reduction ratio applied by the portal gears is that the drive torque is only applied to the wheels themselves with the result that the mechanical loads on the drive train – especially the drive shafts – are reduced.
Through-drive: the center differential
A technically sophisticated solution provides the 6×6 drive system with the necessary through-drive through the differential of the first rear axle to the rear one. The arrangement which has been developed is extremely compact and requires little more space than a conventional differential housing. An extra shaft with an integrated lock situated on the side above the differential takes the drive torque to the rear axle. A chain provides the necessary power take-off for the differential of the first rear axle.
Precisely coordinated logic governs operation of five differential locks
With a total of five mechanical 100-percent differential locks available, drivers would certainly lose track of the settings now and again if they could be engaged separately. This is why the engineers have developed a special locking logic which ensures the best possible traction is available in every situation. The whole system is controlled electrically with the usual three differential lock switches in the centre console which are to be found in all G models. Preselected and engaged locks are indicated by yellow and red lights respectively.
- Stage 1: the two inter-axle differential locks in the transfer case and in thethrough-drive through the centre differential are active
- Stage 2: the interwheel differential locks in the tworear axle differentials are additionally activated
- Stage 3: with the front axle differential locked, allfive differential locks are now active
All lock stages can be selected regardless of whether the low-range ratio in the transfer case is selected.
It is clear that, with a wheelbase of some 4.20 metres, the G 63 AMG 6×6 is not predestined for virtuoso cornering. Nevertheless, in order to ensure impressive agility with corresponding dynamism about the vertical axis of the vehicle, the engineers have varied the torque distribution. The drive torque is therefore split 30 to 40 to 30 percent between the front axle and the two rear axles.
V8 biturbo from power specialists Mercedes AMG
Much of the credit for the superior performance of the G 63 AMG 6×6 is due to the AMG V8 engine and the AMG SPEEDSHIFT PLUS 7G-TRONIC automatic transmission. The AMG 5.5-litre V8 biturbo engine develops a peak output of 400 kW (544 hp) and 760 newton metres of torque. Known in-house by the designation M 157, the engine impresses with its technological highlights. The greater thermodynamic efficiency which results from the combination of twin turbochargers, direct petrol injection and spray-guided combustion allows better fuel economy and leads to lower exhaust emissions. Fast and precise piezo-electric injectors spray the fuel into the combustion chambers, ensuring a particularly fine distribution throughout the air in the combustion chamber. An electric low-pressure pump delivers the fuel from the tank to a high-pressure pump in the engine compartment at a pressure of six bar. The fuel pressure in the high-pressure rail is controlled between 100 and 200 bar on a fully variable and demand-related basis, ensuring an agile response in any driving situation. Further highlights of the innovative and unique eight-cylinder powerplant from AMG in Affalterbach include an all-aluminium crankcase, four valves per cylinder with camshaft adjustment, air/water intercooling and alternator management.
Any doubts about the show vehicle’s ability to speak directly to the emotions are quickly dispelled by a look at the AMG sports exhaust system: twin tailpipes ahead of the rear wheels on both sides put out the hallmark AMG eight-cylinder sound.
Faster shifting with the AMG SPEEDSHIFT PLUS 7G-TRONIC
Featuring three drive modes and an automatic double-declutching function for downshifting, the AMG SPEEDSHIFT PLUS 7G-TRONIC automatic transmission delivers the drive to the transfer case with low-range ratio by means of a propshaft. “Controlled Efficiency” (C) mode calls up engine and drive control strategies designed to deliver a driving style which is as economical as possible. In the Sport (S) and Manual (M) driving modes, the engine-transmission combination displays considerably greater agility. Here, a brief and exactly defined retardation of ignition and injection during upshifting at full load provides for shorter shift times. Furthermore, in “M” mode, the G 63 AMG 6×6 maintains the gear selected by the driver to the extent that this is permitted by the engine rev limits – a particularly useful feature when negotiating challenging climbs.
The efficiency of the AMG SPEEDSHIFT PLUS 7G-TRONIC automatic transmission system is further enhanced with a new fuel economy converter with centrifugal pendulum, friction-reducing bearings and transmission oil thermal management.
It makes sense to provide an ample fuel supply for vehicles which are designed to be used in remote areas. This is why the standard production tank with a capacity of 96 litres has been complemented by a 63-litre auxiliary tank. The total tank capacity therefore amounts to 159 litres.