The new Mercedes-Benz GLK-Class - PART VII


Stuttgart, Germany, Jul 15, 2008

Drive and suspension: Tremendously impressive both on and off

The GLK-Class boasts a high level of flexibility thanks to its AGILITY CONTROL suspension, and reconciles the conflicting suspension design aims that particularly affect the SUV class: chassis engineers seek to create a vehicle that is both sportily agile and comfortably smooth, yet one which can also cope with off-road terrain. If the focus is on sporty, active handling, the suspension and, above all, the shock absorbers need to display a certain firmness, which precludes the desired levels of suspension comfort associated with the brand and limits off-road prowess. If, on the other hand, the vehicle is purpose-built for ride comfort and off-road expertise by fitting softer dampers, its driving dynamics will of course suffer.

"Amplitude-responsive damping" provides the solution: here, the shock absorber's smoothing forces are of a flexible nature, rather than having a rigid setting. During normal driving along moderately contoured roads or off-road excursions at low speeds, the system is tuned for soft response to the benefit of the occupants' sense of wellbeing and the vehicle's off-road abilities. In order to keep the occupants feeling at their ease when driving at a brisker pace or performing abrupt evasive manoeuvres, the dampers switch to a firmer setting
in such situations, permitting a high level of handling stability.

The steering systems in the GLK

At the same time, the driver is assisted by the speed-sensitive power steering that comes as standard in the V6 models and provides the optimum level of steering assistance for the situation in hand. The system therefore makes light work of parking or off-road manoeuvres by maximising power assistance. As the speed increases, however, assistance is reduced in favour of greater directional stability. The precise electrohydraulic steering is used in the GLK 220 CDI 4MATIC. Steering comfort has been further enhanced in both steering variants, thanks to meticulous attention to detail. For instance, the engineers have decoupled the vibrations associated with the airbag module in the steering wheel. Reducing the unsprung masses in the steering system in this way has given steering comfort an additional boost.

17-inch wheels and tyre pressure loss warning system as standard

All GLK models come as standard with mixed-sized tyres which, together with the AGILITY CONTROL suspension and asymmetric power distribution between the front and rear axle, form the basis for a consummate transfer of power between the wheels and the road. And the more effective this power transfer, the less frequently the electronic control systems need to intervene.

Two chassis set-up options are available. If the "off-road styling package" is specified, the GLK comes with longer spring travel and a comparatively softer basic set-up to optimise off-road handling characteristics. Should the customer opt for the "exterior sports package", on the other hand, the specification includes a sports suspension lowered by 20 millimetres with shorter springs, firmer dampers and stronger transverse stabiliser bars. This sharpens the vehicle's driving dynamics for sporty driving without significantly impairing the balanced ride comfort.
The road-oriented "exterior sports package" features size 7.5 J x 19 light-alloy wheels with 235/50 R 19 tyres at the front and size 8.5 J x 19 wheels with 255/45 R 19 tyres at the rear. If the vehicle is specified with the "off-road styling package", 7.5 J x 17 light-alloy wheels shod with 235/60 R 17 tyres are fitted at the front, while 8.0 J x 17 wheels with 255/55 R 17 tyres can be found at the rear. As an option, All Terrain tyres specially tailored to the GLK are available as accessories. All models are equipped with a TIREFIT system for repairing tyre damage. Alternatively, a compact spare wheel which can be used on both the front and the rear axle can be specified as an option.

All GLK models are fitted with a tyre pressure loss warning system to ensure potential tyre damage does not have serious consequences. The system detects any sudden drop in tyre pressure and alerts the driver to the situation by flashing up a warning message in the instrument cluster. The optional tyre pressure monitoring system improves safety yet further. Incorrect tyre pressure or a gradual drop in pressure is indicated by the "Check tyres" warning message; the "Caution Tyre defect" warning appears in the event of a rapid loss of pressure. The tyre pressure monitoring system automatically detects when new tyres or wheels are fitted.

ADAPTIVE BRAKE: sophisticated brake control system with additional new functions

The all-new ADAPTIVE BRAKE control system incorporates the basic anti-lock braking system (ABS), acceleration skid control (ASR) and yaw control functions. ABS and ASR monitor and control the driving dynamics along the vehicle's longitudinal axis, while yaw control looks after the lateral dynamics. If ADAPTIVE BRAKE diagnoses critical driving situations, precision application of the brakes and control of drive torque is used to maintain or restore traction and directional stability as far as is physically possible.
New additional braking functions make ADAPTIVE BRAKE safer and more convenient. Hill-start assist prevents the vehicle from rolling contrary to the intended direction of travel. The enhanced functionality also includes brake 'priming'. Should the driver suddenly release the accelerator, the system prepares for possible panic braking by pressing the brake pads lightly against the brake discs. If the brakes are indeed applied with full force, the stopping distance is therefore shortened noticeably by building up pressure the instant the brake pedal is pressed. The ability of ADAPTIVE BRAKE to precisely generate even minimal brake pressure means the film of water that accumulates on the brake discs when driving in the wet can be removed by briefly applying the brakes lightly, further reducing the brakes' response time in the wet and, in turn, the stopping distance. This function is triggered automatically once a certain number of windscreen wiper cycles has been reached and the driver has not applied the brakes in the meantime.
The GLK also comes with standard-fit adaptive brake lights. This system warns the traffic behind when the driver applies the brakes in a critical situation by causing the brake lights to flash if the vehicle suddenly decelerates, and, in the case of emergency braking from speeds in excess of 70 km/h, automatically switching on the hazard warning lights once the vehicle comes to a standstill.

4MATIC: high-performance all-wheel drive with sophisticated control systems

The 4MATIC powertrain at the heart of the GLK-Class is one of the most capable all-wheel drive systems on the market, incorporating control systems that set new standards. The basic concept, with the engine installed longitudinally and the transmission and transfer case designed as a single block, produces a compact and lightweight arrangement that minimises frictional losses, as well as heralding a number of advantages over its counterparts where the drive unit is installed transversely. The upshot of this is that fuel consumption is on a par with that of a comparable model with conventional two-wheel drive, while the minimal vibration and noise levels rival those of today's luxury-class models.
The basic 45:55 split of drive torque between the front and rear wheels combines with the ESP®, ASR and 4ETS dynamic handling control systems to produce supremely assured and perfectly predictable performance. When tuning the control systems, the engineers at the Mercedes-Benz Technology Center (MTC) made a defined level of understeer a priority. All GLK models display these characteristics under all manner of road conditions, come rain or shine, snow, ice or unsurfaced tracks.
The newly developed multiple-disc clutch in the centre differential comes to the system's aid when friction between the tyres and ground is particularly low, for example when driving over snow or ice. A basic interaxle lock of 50 Newton metres gives a major boost to traction – setting the benchmark for vehicles with no additional differential locks without any loss of handling stability.

"Off-road engineering package" provides superlative off-roading

The "off-road" button on the centre console makes GLK models equipped with the off-road engineering package even more assertive in rough terrain. Pressing the button activates a special driving program which varies the shift points of the 7G‑TRONIC transmission, "softens" the accelerator pedal characteristics and activates the ESP® off-road functions including off-road ABS and a custom off-road 4ETS. In this mode, there are fewer interventions involving the engine manage-ment system; the system is also designed to tolerate a higher degree of wheel slip. This control strategy improves traction off-road, particularly on low-friction surfaces such as sand, gravel or stone chippings. The off-road ABS on the GLK was premiered in the current M‑Class and detects a wide range of different terrains by permanently referencing the wheel-slip models. This produces the best possible deceleration strategies for off-road adventuring over rocks, sand, stone chippings, gravel or slush.

On models with the off-road engineering package, the automatic transmission features a Manual drive mode (M) in addition to the Comfort (C) and Sport (S) modes, which enables the individual gears to be selected with shift paddles on the multifunction steering wheel. This operating mode promises maximum fun at the wheel when venturing off-road.
A further switch activates the Downhill Speed Regulation (DSR) system, which automatically maintains a pre-programmed speed between 4 and 18 km/h on steep downhill inclines. The GLK driver can vary the speed at any time during the descent using the cruise control lever. Mercedes-Benz is the only car maker to offer this important equipment detail for off-road motoring. Conventional systems offered by competitors can only maintain the speed programmed at the outset, meaning the speed cannot be altered while the system is in action. A heavy-duty, weight-optimised underguard and underbody protection round off the all-terrain specification of the GLK with off-road engineering package.
If the COMAND APS system is specified, the navigation system has a useful extra feature designed specifically for off-road vehicles. If the vehicle enters an area not covered by digitised maps, the driver can activate a tracking system to automatically save the vehicle's route. This means that GLK drivers can always find a way back to their starting point, based on the principle of Ariadne's thread.

The off-road-related body dimensions are equally impressive. The ground clearance of 201 millimetres and the short body overhangs (front 816 mm, rear 957 mm) make for favourable angles of approach and departure – 23 degrees and 25 degrees, respectively; the breakover angle is 19 degrees. The GLK can negotiate inclines up to 70 per cent, while the maximum tilt angle is 35 degrees. Meanwhile the relatively compact wheelbase length of 2755 millimetres and the vehicle weight of 1830 kilograms, which is comparatively low for an SUV, allow the GLK to make good headway in even the most topographically challenging terrain.
As well as a tyre pressure loss warning system, the Electronic Stability Program (ESP®) incorporates a vehicle/trailer stabilisation function as standard, which can defuse precarious handling situations resulting from towing a trailer at an early stage by applying the individual wheel brakes as and when required. The permitted towing capacity is 2,000 kilograms.

Complete range of diesel and petrol engines

The state-of-the-art engine line-up ensures an exceptionally high level of drive smoothness and impressive performance right across the GLK range, not to mention low fuel consumption and emissions figures when compared to its rivals. Customers have a choice of four model variants: diesel aficionados can opt for the GLK 220 CDI BlueEFFICIENCY or GLK 320 CDI, while those with a preference for petrol can select the GLK 280 or GLK 350, both of which feature a V6 powerplant.

The GLK 220 CDI 4MATIC BlueEFFICIENCY comes with a brand new generation of diesel engine under its bonnet that redefines standards for power output, torque, emissions characteristics and fuel economy. The compression-ignition engine also delivers impressive environmental performance and, like all diesel engines for Mercedes passenger cars, features exhaust gas recirculation, an oxidising catalytic converter and a maintenance-free diesel particulate filter as standard. The smooth-running four-cylinder unit limits itself to 6.9 litres of diesel for every hundred kilometres, whilst emitting 183 grams of CO2 per kilometre. The Mercedes-Benz engineers have also succeeded in further reducing levels of untreated engine emissions. Even without an active denoxification process, the new four-cylinder diesel already meets the future EU5 emissions standard. The state-of-the-art powerplant propels the GLK 220 CDI 4MATIC from 0 to 100 km/h in 8.8 seconds and on to a top speed of 205 km/h.
Cutting-edge technology was deployed in order to attain these class-beating figures.

The principal features of the new Mercedes diesel engine:
  • Two-stage turbocharging ensures high power output and optimum torque delivery.
  • Fourth-generation common-rail technology with a rail pressure that has been increased by 400 bar to 2,000 bar, plus a new piezoelectric injector concept featuring direct injector needle control creates the ideal basis for more flexible injection timing, leading to smoother engine running.
  • The maximum ignition pressure is 200 bar, which also contributes to the
    high output.
  • Both the oil-spray nozzles and the water pump are activated in accordance with requirements to save energy.
  • The camshaft drive is positioned at the rear in order to enhance running refinement and achieved high standards of pedestrian protection.
  • The engine block is made from cast iron, the cylinder head from aluminium.
  • Two water jackets guarantee maximum cooling even at the points of greatest thermal radiation; it is this that enables an ignition pressure of 200 bar and such a high power-to-displacement ratio.
  • The aluminium pistons slide up and down in cast-iron barrels for minimum frictional resistance.
  • The connecting rods are made from forged steel, and their weight has been optimised by the Mercedes engineers.
  • In the interests of vibrational comfort, the forged crankshaft with its eight counterweights turns supported by five bearings. The radii of the crankpins are rolled and are notable for their high strength.
  • To compensate for the free vibration moments which are inherent to four-cylinder inline engines, there are two Lanchester balancer shafts at the bottom of the engine block running in low-friction roller bearings rather than conventional plain bearings.
The new 125-kW/170-hp drive unit has a powerful feel to it, its response is agile, it delights with its tremendous pulling power and impresses with exemplary levels of smoothness for a four-cylinder engine. Besides its exceptional output, the new power unit offers breathtaking torque delivery from low revs along with the best torque characteristic curve in its displacement class: peak torque of 400 Newton metres is on tap over a wide rev band from 1400 up to 2800 rpm. This means that the engine can be run extremely economically at low rev speeds in everyday driving situations.

Supreme six-cylinder comfort comes to the compact-SUV segment

The diesel line-up is augmented by the proven V6 powerplant in the GLK 320 CDI, which develops 165 kW/224 hp and delivers a peak torque of 540 Newton metres. This propels the GLK to even more admirable performance, with a top speed of 220 km/h and a time of just 7.5 seconds for the sprint from 0 to 100 km/h. The V6 engine also features exhaust gas recirculation, an oxidising catalytic converter and a maintenance-free diesel particulate filter, burns 7.9 litres of fuel per hundred kilometres and complies with the EU4 emissions standard.
The two smooth-running V6 petrol models – the GLK 280 4MATIC and GLK 350 4MATIC – develop 170 kW/231 hp and 200 KW/272 hp respectively. Both make their mark with nifty performance combined with moderate fuel consumption. The 3.5-litre V6 in the GLK 350 4MATIC is particularly noteworthy, achieving figures similar to those of a sports car: it has a top speed of 230 km/h and races from 0 to 100 km/h in 7.1 seconds. Both engines fulfil the Euro 4 limits and consume 10.4 litres and 10.6 litres per hundred kilometres respectively.

7G-TRONIC seven-speed automatic transmission as standard

All of the engine variants are matched with the 7G-TRONIC 7-speed automatic transmission as standard, which includes a Comfort (C) and a Sport (S) shift mode. The "C" drive mode prioritises drive smoothness and economy combined with high power reserves. Switch to the "S" mode selects a significantly sportier set-up, with a modified driving strategy and accelerator characteristic curve. In conjunction with the optional off-road engineering package, the automatic transmission also comes with a manual drive mode (M), complete with shift paddles on the multifunction steering wheel.

The 7G-TRONIC come with a special function that decouples it when stationary. This technical feature reduces the transmission absorption torque when the vehicle is stationary with a gear engaged. This eases the burden on the engine, which has the effect of reducing fuel consumption, as well as improving vehicle acoustics, passenger comfort when stationary and the idling characteristics. The slip-controlled clutch is engaged the instant the driver releases the service brake pedal, enabling the vehicle to pull away without any delay or loss of comfort. This operating state is achieved by controlling a mechanical clutch so as to produce a defined level of slip. The clutch itself was designed for operating with constant slip.

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