30/8/12

Overview: Mercedes-Benz GL-class

The GL-class is Mercedes’ Range Rover competitor, and whatever it might lack in James Bond associations, no-one need worry about a lack of engineering values or a shortage of technology. Among Daimler’s boasts for the new model are a ‘very rigid’ bodyshell — no figure is given, though — as well as an improved chassis and aeroacoustic finishing for the new version.

The latest spray-on insulation materials have been introduced. These can be applied to inaccessible and oddly-shaped areas of the bodyshell which would defy conventional insulation materials.

Three models are offered. The GL 350 Blue-Tec uses Mercedes’ 2987cc V6 diesel with selective catalytic reduction by way of urea injection — or Blue-Tec in Mercedes language; the GL 500 uses a 4662cc petrol V8 with direct fuelling and twin turbochargers; and the GL 63 AMG uses the AMG 5461cc petrol V8, also with twin turbochargers.

Included in the standard package is the fully load-bearing air suspension system known as Airmatic, which incorporates adaptive dampers and a load recognition feature. Mercedes claims greatly improved handling, roadholding and driving dynamics for the new model. Both the standard Crosswind Assist and load recognition feature are able to compensate for very varying driving conditions. The optional active tilting anti-roll bars that make up the Active Curve System compensate for roll and allow the car to be driven off-road with the anti-roll bars decoupled.

The GL-class’s standard package includes the permanent four-wheel drive system known as 4Matic, a driving-off assistant, the Downhill Speed Regulation DSR and a program for off-road driving. There are six driving programs in all — perhaps we are reaching saturation point with driving modes now, as the driver still needs to have the adaptability to deal with different road conditions. Still, there is no doubt that a car like this can cope with a wider range of ‘road’ conditions than a saloon car, so perhaps it is fair that it should be entitled to a wider range of driving modes.

From the ‘hardware’ point of view, the on-and-offroad package comprises an underrun protector for the engine, fibre-reinforced underfloor panelling, two-stage power transmission with reduction gears, a longitudinal differential lock and extended Airmatic functions allowing a maximum ground clearance of 306mm and fording depth of 600mm.

Bi-xenon headlamps with Intelligent Light System and new off-road light, adaptive Main Beam Assist or adaptive Night View Assist Plus aid visibility. The optional 360° camera actually has four cameras at front and rear as well as in the housing of the exterior mirrors. From the picture information received, the system calculates a bird’s eye view of the vehicle and its surrounding area and then relays it together with other views to the large comand display.

In addition to the handling control systems — ESP, ASR, ABS and the danger-alert Pre-safe safety concept — for the first time the standard version of the GL is also fitted with the Collision Prevention Assist and the drowsiness detector Attention Assist. Functions such as load recognition or Steer Control reduce the strain on the driver in critical borderline driving situations — for instance, by delivering steering torque to the steering column if the vehicle is oversteering. One innovation in the new GL is the standard Crosswind Assist which supports the driver with deliberate braking action when there are strong crosswinds, increasing the feeling of safety. Also available to optimise the safety of the vehicle are optional systems such as distance control Distronic Plus, braking assistant Bas Plus or the Pre-Safe brake with its autonomous braking function in certain dangerous situations that have not been recognised by the driver. Easy parking is guaranteed with the Active Park assistant. The system is able to detect suitable parking spaces and steers the GL automatically into the space.

On the rolling road, the GL 350 returns overall fuel consumption of 7.4l/100km or 38.1mpg, which is about 20 per cent. less than its predecessor. The unit also undercuts the future EU6 emissions standards. The fuel consumption of the 435PS petrol engine in the GL 500 has been reduced by 18 per cent. The AMG version is new to the range.

The 7G-Tronic Plus seven-speed automatic transmission is standard, as is a stop-start function and ‘intelligent’ generator management, which charges the battery on the overrun where this is possible.

In comparison with its predecessor, taking the diesel model as an example, the weight of the new GL-class has been reduced by 90kg due to the extensive use of lightweight construction methods. These include the use of aluminium alloys for the bonnet and wings. The front and rear suspension links are also made of light alloys, which clearly lowers unsprung mass as well as overall mass. Other weight reductions are the new acoustic windscreen, the magnesium cross beam of the dashboard, the new electric power steering, the electric parking brake and the plastic engine support.

Inside you will find a 2-3-2 seating arrangement. In comparison with its predecessor, the passengers have been given more elbow, shoulder and headroom in all three rows of seats. As a standard feature, the third row of seats can be folded down and up electrically. Another innovation is the Easy-Entry system for accessing the third row of seats from both sides, with optional electric controls.

Accident protection is provided by the passive protection systems for passengers in conjunction with the ‘electronic crumple zone’ provided by the assistance systems and the body construction. Adaptable two-stage airbags for the driver and front passenger, knee bags for the driver, sidebags for the driver and front passenger (combined thorax/pelvis bags) and window bags for all three rows of seats are part of the standard package. The integration of the optional thorax bags in the backrest of the tilt-adjustable folding seat in the middle row of seats allows the airbag to be in the best position regardless of the position of the backrest. Three-point seat belts are provided for all seven passengers. Also part of the standard package are the pyrotechnical inertia reel tensioners and constant belt force-limiters as well as electrically reversible belt reel-in tensioners at the front, inertia reel tensioners and single stage force-limiters on the outer seats of the middle bench seat as well as on the rear single seats. The GL-Class also comes with a standard active bonnet, which rises at the rear in the event of a collision with a pedestrian, cushioning the pedestrian’s head.

Quality of ride and vehicle dynamics

Mercedes emphasises: chassis quality — vehicle dynamics — ride quality — refinement ‘on par with the S-class’

Fully load-bearing air suspension — Airmatic — with adaptive dampers and load recognition are standard features. The Airmatic system with its adaptive dampers provides a comfortable basic springing with a low inherent frequency, and the full length of spring travel is available when the vehicle is fully loaded. Airmatic provides self-levelling and a level control. When driving off the beaten track, the air suspension increases ride-height. The lifting or lowering of the body can be activated at any time when the engine is running and can either be done automatically or as the driver requires using the control buttons on the centre console. The system is speed-dependent and lowers the body at high speeds to minimise aerodynamic resistance and increase stability. The main features of the air suspension are:

  • Air-springs at the front with integrated ADS dampers;
  • Air spring with offset ADS dampers at the rear;
  • Supercharger with central pressure tank and electric pressure sensor;
  • Air spring valves;
  • Sensors for regulating height and damper functions.

The adaptive damping system, ADS, is a fully automatic, electronically controlled system which adjusts the dampers on each wheel as required. If the response of the body movement is low, the GL-Class drives at level 1. When the speed of the body movement exceeds a certain level, the system uses the so-called ‘skyhook algorithm’ and switches as needed back and forth between the second and third damper rates using its fast magnet valves in order to compensate the tilting and pitching motion of the body. In more dynamic driving situations, level 4 is activated, and in Sport mode only level 4 is used. The regulation of each individual wheel takes place almost immediately. Depending on the command received, the valves can adjust between characteristic curves in less than 0.05s.

The driving situation is determined by a steering angle sensor, four yaw-rate sensors and the driving speed from the ESP signal and brake pedal switch. With the aid of these signals, the control unit calculates the current damping rate required and activates the appropriate characteristic curve. Using a switch, the driver can preselect Sport or Comfort modes manually.

An electromechanical direct-steer system works with a variable steering ratio which becomes perceptibly more direct as the steering angle is increased. In addition, electric steering gives speed-dependent assistance.

New load sensors have been developed to improve driving dynamics. The system is able to recognise various vehicle loads carried by the GL and with the data received it is able to alter the regulating thresholds of the ESP. Up to now, the ESP always assumed that the vehicle was loaded to the maximum, including a roof load. The new load sensor system now intervenes only when required by the actual load carried.

A sensor system within the air suspension recognises the load. The difference in pressure between the front and rear axles serves as a reliable measurement for moving the height of the centre of gravity, as the wheel pressures determined by the Airmatic pressure sensors are proportional to the wheel loads. The adjustment of the regulating threshold is effected according to the wheel pressures; the ESP interventions are carried out more sensitively and according to the actual load carried.

The ESP adaptation takes place after driving a short distance. When the vehicle starts driving, the load sensor system presumes that the vehicle is fully occupied with a full load. This means that safest driving situation possible is always guaranteed.

Active curve system

The optional active tilting anti-roll bar, known as the Active curve system, is combined with the air-suspension system with the adaptive damping system (ADS) and with the on-and-off road package. The system uses its active anti-roll bars on the front and rear to regulate the systems automatically depending on the lateral acceleration, speed, and the position of the ADS Comfort/Sport switch. The active curve system compensates for the roll angle of the body when driving around bends, providing an improved vehicle response. At the same time, the system improves handling and safety when driving at high speeds. An improved ride both driving around bends as well as on straight roads, and increased scope when driving off-road, are among the advantages of the active curve system. Individually, the control strategies are:

Improved vehicle dynamics when driving around bends as the starting torque and torque angle of the anti-roll bars are controlled. Also, the starting torque of the anti-roll bars remains constant even when subject to a load on one side — for instance, when driving over a pothole or around a curve. The independent regulation of the front and rear axles distributes the roll moment variably so that under- and oversteer are corrected. When driving on country roads the handling is regulated so that it is particularly responsive, and on motorways so that it is especially stable.

In extreme off-road situations at low speeds, both of the anti-roll bars are decoupled to allow an improved degree of axle articulation.

A belt-driven hydraulic pump and an oil reservoir in the engine compartment, together with one valve block each and active anti-roll bars on both front and rear axles, are among the important components of the active anti-roll bars. In comparison with a passive anti-roll bar, the active anti-roll bars are divided in the middle and connected to each other by hydraulic actuators. Pressure sensors and a lateral acceleration sensor use CAN signals to pass on the required information to the electronic control unit for regulating the hydraulic pressure.

The active curve system pumps oil from the reservoir into the hydraulic circuit. A pressure regulator integrated in the valve blocks of the front and rear axles, along with the directional valves, set the desired pressure and turn the active anti-roll bars in the correct direction depending on the driving situation. A hydraulic rotary actuator integrated in each active anti-roll bar has six oil-filled chambers in its interior; of these, three are used to apply pressure for each driving direction — that is, left- and right-hand curves. In addition, the front valve block is responsible for distributing the oil flow between the two axles independent of load.

Offroad driving mode

The GL, like the Range Rover, is designed to be capable of more than its owners would ask of it. In addition to its permanent four-wheel drive (known as 4-Matic) and electronic traction control (4ETS), the specification includes an off-road button which activates a special off-road driving mode. In this mode, the slip threshold of the wheels and the switching points of the 7G-Tronic Plus transmission are raised to improve traction; a flatter response curve for the accelerator allows it to be regulated more sensitively; and off-road ABS is calibrated for gravelly and sandy surfaces.

In addition, the Start Assist and the Hold function support the driver when starting off on a hill. The Downhill Speed Regulation (DSR) automatically keeps the car at the speed set using the Tempomat lever.

The on- and off-road package for the new GL-class has six driving modes. Mercedes claims a perceptible improvement in comparison with the Offroad-Pro Technik package which has been offered previously. Previously there was one driving program for on-road driving and one for going across country. The new package has one automatic program, two special off-road programs and three on-road modes. The driving modes for four-wheel drive aim to reconcile the conflicting aims of on- and off-road motoring which have made life difficult up to now for the development of the 4-Matic system, the electronic traction system (4ETS) as well as ESP and ASR. For example: On rough tracks it is important that the control systems regulate very gently because of the low friction values; but that makes it almost impossible to have sporty responses. On the other hand, a sporty basic tuning reduces the vehicle’s performance off-road. In the past, engineers have found good compromises which functioned fairly well in every situation. However, the new on- and off-road package, with its six specific driving modes, allows vehicle dynamics and handling safety to be tailored more for specific driving situations.

The driving modes are selected using a rotary switch on the central console. The Airmatic, ADS, the drivetrain and the electric power steering are adjusted to suit the specific requirements. The six driving modes are:

  • Automatic: covers everyday driving;
  • Offroad 1: for easy cross-country driving, tracks, fields, sand;
  • Offroad 2: for more demanding off-road terrain with climbing sections;
  • Winter: for driving in wintry road conditions with freezing-over wet roads, snow, ice or with snow chains;
  • Sport: ambitious driving on very winding roads;
  • Trailer: optimises starting-off, manoeuvring and braking with a trailer.

The program selected is shown in the multi-function display in the instrument cluster as well as on the central command screen. The latter presents a stylised image to represent the driving mode: for example, if the driver selects the ‘Winter’ mode, the display shows the GL in snow. The depiction shown is also interactive: the steering angle and spring travel correspond to the real values. Also, the display gives additional information about the steering, climbing and tilting angles, the Airmatic level, the pre-selected speed for driving downhill (Downhill Speed Regulation, DSR) and the selected drivetrain settings with reduction gear and lock.

Reduction gear, DSR and the Airmatic level control system can all be selected individually regardless of the drive program chosen. Just as with the basic settings for the on- and off-road package, the driver cannot make a mistake here: settings which are not considered logical, and which have a negative influence on the handling of the vehicle, its safety or traction, are excluded. If there is any doubt, the Automatic mode is activated.

From the hardware point of view, the on- and off-road package comprises a steel underrun protection for the engine, fibre-reinforced underfloor panelling, a two-stage power transmission with reduction gears, a centre longitudinal differential lock and extended Airmatic functions allowing a maximum ground clearance of 306mm and fording depth of 600mm.

Refinement

Mercedes claims that, so far as refinement is concerned, the new GL is on a par with luxury saloons like the S-class. The improvements for the new model include:

  • Lower perception of noise in the interior due to the use of sprayable acoustic materials in the body-in-white, fibre-reinforced plastic partitions between equipment;
  • Rigid front end design with V-strut, upper and lower levels of the side supports connected, light hybrid construction for front module;
  • Plastic engine supports;
  • Rigid cockpit cross-member made of high-strength magnesium alloy;
  • Highly insulating acoustic front windscreen, with optional acoustic side windows at the front;
  • Electric power steering;
  • Reduction of the unsprung mass by using weight-optimised aluminium control arms and alloy wheels;
  • Aluminium Transmission Bridge with integrated vibration damper;
  • Air suspension Airmatic ADS, as an option with Active Curve System (dynamic tilt stabilising);
  • Body-in-white with new D-ring structure to increase torsional strength;
  • Improved aeroacoustics.

A perceptible improvement in ride comfort with a simultaneous reduction in the mass of the vehicle by 90kg has been achieved by using new approaches. The plastic engine support, the rigid cockpit cross beam made of high-strength magnesium alloy or the electric steering are examples of what Mercedes calls the ‘weight-optimised increase in comfort’. The highly insulating front windscreen and the optional insulating side windows using multi-layer glass technology give much better sound insulation, but weigh less than conventional multilayer glass. The weight savings on the axles and alloy wheels are also noteworthy: mass per axle is reduced by 18kg by using high-strength aluminium alloys. In this way the unsprung mass is reduced. The lower the mass of the wheels and axles, the lower the amount of energy dissipated when driving over potholes or uneven surfaces.

Up to now, the automatic tailgate was operated by a hydraulic drive situated at the rear in the upper frame of the roof. In the new model, the hydraulic system has been replaced by an electric spindle. This saves 2kg, with a significant effect on the handling, as weight-saving measures on the roof of a vehicle, way above the centre of gravity, are much more useful than comparable mass reductions lower down.

Visibility and safety

Highlights include:

  • Active bonnet: improves protection of more pedestrians and cyclists;
  • Assistance systems act as ‘electronic crumple zone’;
  • Premiere: radar-assisted Collision Prevention Assist;
  • Stability: Crosswind Assist and steering assistant as standard;
  • Mercedes-Benz emergency call;
  • Visibility and vision: 360° camera, NightView Assist Plus and Intelligent Light System with new off-road lights;
  • Active Parking Assist.

In conjunction with the assistance systems’ ‘electronic crumple zones’ and the bodywork design, the occupant protection systems represent the last line of defence in an accident. These include:

  • Two-stage airbags for driver and front passenger;
  • Driver knee-bag;
  • Side-bags for driver and front passenger (combined thorax airbag/pelvis-bag);
  • Side-bags available for the central row of seats upon request;
  • Window-bags across three rows of seats from A- through to D-pillar;
  • 3-point seat belts for all seven seats;
  • ISOFIX child seat anchorages on the left and right in the central and the rear row of seats;
  • Belt-height adjustment for driver and front passenger;
  • Belt-status indicator for rear-compartment passengers in instrument cluster;
  • ACSR automatic child seat recognition system (optional) with front-passenger airbag deactivation when using Mercedes-Benz child seats.

The front-end structure comprises two straight front longitudinal members, a second upper longitudinal-member plane and a subframe that supports the drive unit, connects the structure’s two halves and deforms when subjected to high frontal impact loads. The lateral connections in the front-end activate the side opposite of the impact point in offset frontal impacts. The long front-end, short V-engines and the articulated shaft with its deformation element also contribute to the front-end assembly’s deformation potential. In the event of major deformations, the wheels are supported against the strong bulkhead. The bulkhead itself is reinforced by an exterior cross member resting against the A-pillars above the pedal floor.

The passenger compartment’s strength is tailored to the deformation resistance of the front-end assembly. The rigidity and strength result in part from the floor system with its separate transmission tunnel and longitudinal members integrated into the sidewall that, together with cross-members set onto the floor, forms a stable supporting structure. The high-strength sidewall assembly comprises the body pillars, the lateral roof frame and the lateral longitudinal [sic] members. The sidewall assembly’s outer shell is formed by the outer panelling. The inner shells are partially made up of several components with large-surface nodes between the pillars, roof frame and lateral longitudinal members.

The dual-shell A-pillar is stabilised along the transverse line by the front roof frame and various cross members. The latter are located in the area beneath the windscreen, above the pedal floor and below the dashboard.

To deal with rear impacts, long deformation paths result from the box-shaped rear longitudinal members.

The GL-class also sets out to provide the greatest possible protection for more vulnerable traffic participants such as pedestrians and cyclists. Besides the yielding areas of the front-end, the folding exterior mirrors and the smooth contours, the risk of suffering injury from impact with the vehicle has been reduced through modifying the bonnet and increasing the distance to the components in the engine compartment. In addition, the active bonnet is a standard feature. It has the potential to reduce the severity of any injuries suffered by an impacting pedestrian or cyclist and further increases the deformation space. Acceleration sensors have been integrated into the front bumper to trigger the active bonnet.

In developing the GL-class, the test specifications and criteria for accident testing applied in-house went beyond those required by law. The GL was therefore able to fulfil even the most stringent requirements of the most important international test institutions:

  • Frontal collisions: New full-width front impact in accordance with US-NCAP (U.S. New Car Assessment Programme);
  • Side impact: New mast impact in accordance with Euro-NCAP (European New Car Assessment Programme);
  • New side impact in accordance with US-NCAP;
  • Roof strength: New roof strength test in accordance with IIHS (U.S. Insurance Institute for Highway Safety);
  • Pedestrian protection: Impact testing according to Euro-NCAP.

The capacity of the driving assistance systems to predict or pre-empt accidents allows them to act as an ‘electronic crumple zone’. In addition to the driving dynamics control systems ESP and 4ETS, the GL comes as standard with an electronic brake control system known as Adaptive Brake that improves traction, driving safety and operating comfort. The Adaptive Brake electronic brake control system comprises the basic anti-lock braking (ABS) function and anti-slip regulation (ASR) as well as active yaw control (GMR). The ABS and ASR primarily monitor and affect longitudinal dynamics, while GMR controls lateral driving dynamics. Where critical driving conditions are detected, and where the physics will allow, selective wheel braking and engine torque adjustments are applied in order to maintain or recover traction and driving stability. In addition, Adaptive Brake communicates with all other assistance systems, and further comprises the following functions as standard:

  • BAS: Brake Assist
  • Pre-safe
  • Trailer stabilisation
  • DSR: Downhill Speed Regulation
  • Cruise control
  • Tyre pressure loss warning
  • Hold, hill start assist, brake priming and brake drying

With the GL-class, Collision Prevention Assist premieres in the SUV segment. Also featured as standard kit are the fatigue detection system Attention Assist and a steering assistant. Optional systems such as the distance and cruise control system Distronic Plus, Bas Plus Brake Assist or Pre-safe Brake featuring autonomous braking are also available to increase safety in the event of hazards not recognised by the driver. The available options also include Active Lane Keeping Assist, Active Blind Spot Assist and Speed Limit Assist.

Radar-assisted Collision Prevention Assist

According to Mercedes, almost fifty per cent. of all rear-end collisions can be prevented, or their severity reduced, with the aid of radar-based safety systems such as collision warnings and adaptive brake assistants. It for this type of situation that Distronic Plus and Bas Plus were designed. Collision Prevention Assist is the next step. This new brake assistance system is not designed just for urban driving, but rather it aims to provide protection against typical rear-end collisions in all traffic situations. The Company expects the collision warning system to have a significant effect on accident figures. The results of tests using simulators show that Collision Prevention Assist reduced the accident rate in three typical accident scenarios from forty-four per cent. to eleven per cent.

Collision Prevention Assist issues visual and audible warnings when detecting obstacles to drivers who may be distracted and prepares the brake assistant to apply the brakes. This brake application is then triggered as soon as the driver exerts pressure on the brake pedal. The system also meets the fundamental ‘Forward Collision Warning’ requirements of the U.S. National Highway Traffic Safety Administration (NHTSA) and is capable of:

  • Identifying the distance to the vehicle in front as too short in a speed range from 30km/h to 250km/h;
  • Detecting a reduction in distance. Where there is a risk of collision, the driver receives a visual and audible warning.
  • Detecting stationary obstacles along the path of motion and issuing corresponding warnings.
  • Identifying specific driving situations, such as driving in queued traffic, and adapting the trigger threshold for warnings and the adaptive brake assistant accordingly.
  • In the event of a collision risk, calculating the precise brake force ideally required to avoid impact and make the best-possible use of the remaining distance. This inherently increases a following driver’s chances of himself avoiding a rear-end impact.
  • Readjusting the brake pressure when the situation changes — if the vehicle in front accelerates, brake pressure is returned to the degree requested by the driver; if the distance to vehicles driving or stopping ahead drops, brake pressure is increased even further.
  • Activating, where necessary, preventive safety systems such as Pre-Safe or belt tensioners.

In what Mercedes calls ‘the extreme range of driving physics’, drivers are aided by a number of systems, including the steering assistant which, for instance, helps the driver by applying steering torque to the steering wheel when the vehicle oversteers. An innovation and a highlight in the new GL is the standard Crosswind Assist, which uses targeted brake application to aid the driver when driving in high transverse wind force conditions.

The situation is well-known: the occupants suddenly feel a crosswind from the side, for instance when overtaking a truck or driving onto a bridge. Depending on the direction and intensity of the crosswind, the control systems apply corresponding brake pressure to the wheels to compensate, or at least substantially mitigate, the wind’s effects on the vehicle. The intervention manoeuvre is handled by Adaptive Brake. The required information is supplied by the sensors of the Electronic Stability Program, the Airmatic ADS air suspension and the electromechanical steering.

If the system identifies a need to intervene, the driver is assisted through brake application on the front and rear wheel on the upwind side. This intervention results in a steering effect that reduces the impact of the crosswind. Crosswind Assist is active when driving straight ahead or through light bends at a speed of 80km/h or more. The driver always remains in control: in the case of substantial and/or rapid steering corrections, Crosswind Assist is automatically suspended. The system filters minor crosswinds and only becomes active at a certain threshold. Continuous, constant crosswinds are also ignored. Research has shown that the latter driving situation affects comfort and perceived safety far less and is intuitively compensated for by drivers.

Steering assistant

The standard steering assistant becomes active whenever the assistance systems identify unstable driving conditions that can be eliminated through simple steering actions. The system determines a steering torque corresponding to the driving condition and applies this torque through the electric power steering. When oversteering, the steering assistant requests the driver to countersteer via the steering wheel until the vehicle has stabilised.

The second main feature is assistance when braking on a surface that displays different friction coefficients on the right and left of the vehicle, as is the case for example on partially iced-up carriageways in winter. This is known as ‘split-µ’, where µ is the coefficient of friction. The steering assistant notifies the driver of the direction in which the steering wheel should be turned in order to neutralise the yawing impulse. Even if the driver ignores the steering assistant’s recommendations, ample reserves remain to stabilise the vehicle in the form of the driving dynamics systems such as Adaptive Brake, ESP or 4ETS. The steering assistant is always available to provide the driver with recommendations, but never takes over.

Occupant protection after a crash

After a substantial crash, the hazard warning lights are switched on automatically in order to warn the approaching traffic. At the same time, the door locks are automatically disengaged in order to facilitate the best-possible access to the vehicle occupants for emergency services. Thanks to the partial opening of the side windows, the interior is more efficiently ventilated after restraint systems have triggered.

Where a collision is detected, the central control unit shuts off the fuel system. After determining the cylinders’ positions, the engine management opens the injectors on cylinders not in compression stroke and relieves the fuel high-pressure area by releasing the remaining fuel directly into the combustion chambers. This reduces the risk of fuel escaping. As a further measure to prevent fuel from escaping, the relevant points feature cut-proof fuel lines and this also increases safety in the event of a collision.

If COMAND Online is fitted, the automatic Mercedes-Benz emergency call is included as standard. In the event of a serious accident, emergency services are notified automatically and within minutes are given extensive information on the precise accident location and the respective vehicle model. The operating principle: if airbags or belt tensioners are triggered in a crash and COMAND Online is connected to a mobile phone, the system transmits the vehicle’s precise GPS location and its chassis number (VIN) to both the emergency services and the Bosch Communication Centre’s service control room by text message. The location data is also transmitted by DTMF (dual-tone multi-frequency). Even if the occupants are unconscious or do not know their precise location, the emergency services called by the Communication Centre can be informed precisely and rapidly.

The vehicle also quickly establishes a voice connection to the Bosch Communication Centre. The language used does not correspond to the respective country’s language but to the language set in COMAND Online by the driver. Emergency calls can also be placed manually as the ‘Mercedes-Benz emergency call’ entry is always located at the very top of the phone book list. With the launch of the GL-Class, the emergency call will be able to access the phone network in nine European countries: Germany, France, Italy, Spain, the United Kingdom, Austria, Belgium, the Netherlands and Switzerland. By late 2012, nineteen further countries will have been added. Apart from any mobile phone rates, a Mercedes-Benz customer will incur no costs for using the Mercedes-Benz emergency call service.

The GL sees all: 360° camera, NightView Assist Plus and off-road lights

Together with the compact GLK, the GL-Class will be available for the first time with the 360° camera. The 360° camera is always combined with Parktronic and is supplied with imaging information by a total of four cameras located respectively in the radiator frame, in the tailgate above the number plate and in the two exterior mirrors. The system uses the imaging information to compile various views, among them a depiction of the vehicle and its surroundings from a bird’s-eye perspective. Occupants view the picture in real time in the central COMAND display. This allows the areas behind, in front and to the side of the vehicle to be observed and can thus prevent collisions in a multitude of different manoeuvres both on- and off-road. Supplemented dynamic guiding lines assist orientation. For example, the 360° camera indicates the vehicle’s turning area in accordance with the steering-wheel angle.

The 360° camera is automatically activated when reverse gear is engaged or when selected directly in COMAND. The camera images in the display switch depending on the transmission position selected: when reverse is engaged, the display automatically shows the image relayed by the rear camera. Bird’s-eye view or the individual images can be selected by the driver by means of the COMAND controller at any time. Specifically, the 360° camera can provide assistance to the driver through the following functions:

  • Virtual bird's-eye view shows the GL from above and the three metres ahead and behind as well as 2.5 metres of the area next to the vehicle.
  • Depiction of perspectives not actually physically attainable. Example: when manoeuvring inside a multi-story car park with low ceilings, the GL and its surroundings are depicted from a bird's-eye view more than three metres above the vehicle, even if the ceiling is only a few centimetres above the vehicle.
  • Visualisation of vehicle sides and their surroundings to prevent contact damage, e.g. of the exterior mirrors or rims.
  • Visualisation of obstacles outside of the field of vision below the vehicle’s beltline.
  • Visualisation of crossing traffic when manoeuvring out of tight parking spaces or departing from driveways.
  • Visualisation of pedestrians on the pavement when manoeuvring out of tight parking spaces or departing from driveways.
  • Assistance when driving off-road in difficult and confusing terrain.
  • The GL-Class is always depicted in the COMAND display in the vehicle’s actual colour.

For the first time, the cameras in the GL now feature high-performance digital CMOS image sensors (Complementary Metal Oxide Semiconductor). Each camera processes images at a resolution of one megapixel and covers a 180-degree field of vision. The virtual bird’s-eye view is almost entirely distortion-free. Unlike the familiar systems, which utilise black bars to separate the individual images, the 360 camera displays the total image homogeneously without transitional elements. In addition, the 360° camera adapts to the various vehicle heights: for example, if the maximum-possible ground clearance of 600mm that comes with the on- and off-road package has been chosen. The driver is also kept aware of the surroundings when manoeuvring at night. At speeds of up to 10km/h with the headlamps switched on, activating the 360° camera also activates the surround lighting. The 360° camera also offers another special feature that prevents occlusion of the rear camera through soiling, for example during long journeys through muddy terrain or when driving on wet, salt-strewn motorways in winter. A flap covers the camera and provides reliable protection from soiling. The flap opens automatically when the 360° camera is activated.

NightView Assist Plus is an optionally available assistance system that uses two infrared headlamps. The emitted light is invisible to the human eye and covers the carriageway ahead of the GL-Class at a range corresponding to main beam. The camera located in the windscreen in the area of the rear-view mirror records the infrared image and, after processing by the control unit, relays it to the COMAND display. Here, the scene is depicted in high-definition grey-scales. Detected pedestrians are additionally highlighted by ‘photo corners’ to make them more easily visible. The system is available at full performance from a speed of 10km/h.

When driving in difficult terrain at low speeds, it is useful to illuminate the area ahead of the vehicle as brightly and as widely as possible. The new GL, if equipped with the on- and off-road package in conjunction with the Intelligent Light System, will feature special off-road lights. If the driver activates either the Offroad 1 or the Offroad 2 driving program while the headlamps are switched on, the off-road lights are automatically activated as well. The bi-xenon headlamp modules are swivelled outward through six degrees, the xenon burners’ output is increased by three watts and the light cone is set to symmetrical. In addition, the LED cornering lights on both sides are switched on permanently, while both the dynamic cornering light function and the headlamp beam adjustment are deactivated. These settings combine to give a wider and brighter illumination of the area ahead of the vehicle than is provided by the Intelligent Light System, which is configured for optimal illumination when driving on roads. Orientation during off-road driving is substantially improved and any obstacles can be seen earlier. The off-road lights are active at speeds up to 50km/h. When the driver exceeds this threshold, the Intelligent Light System automatically resets the lighting functions to optimum road operation.

As 40 per cent. of all serious accidents occur at night, the light ‘temperature’ of the xenon burners used by the Intelligent Light System has been raised to 5000 Kelvin to further increase safety. This results in an illumination slightly yellower than daylight (6500K), which is considered to improve comfort and relieve strain on the driver.

Active Parking Assist

The new-generation Active Parking Assist utilises ultrasonic sensors at a speed of up to 35km/h to identify potential parking spaces along the road on the side the vehicle is travelling on, or on both sides in one-way streets. Suitable parking spaces are indicated in the central display. The driver can then start Active Parking Assist by pressing a button on the multifunction steering wheel. The system calculates a suitable trajectory from the vehicle’s current position. The driver then only needs to accelerate or brake — the required steering motions are completed fully automatically by the system. Departing from parking spaces works the same way. Active Parking Assist comprises six ultrasonic sensors in the front bumper and four in the rear bumper. The ultrasonic sensors on the corners of the front bumper have a greater range than the other sensors in order to facilitate reliable detection of parking spaces when driving past them.

Get your bearings: parking and manoeuvring aids through the years

In the early days of the automobile at the beginning of the last century, car manufacturers were already thinking about ways to aid drivers in keeping an overview when manoeuvring their vehicles. First efforts using a variety of marker rods on the outer ends of the bumpers only caught on with commercial vehicles. In 1959, with the Mercedes-Benz passenger car models referred to as Heckfloße or ‘fintails’, the first real attempt was made to integrate orientation aids into the general design concept of a car. The tailfins on Mercedes-Benz medium-sized and premium-class saloons, officially termed marker bars, allowed the driver to have a good guess at where the tail was. For a long time, the more or less substantial bulges on the rear wings remained in favour.

Mercedes 220SE Heckfloße (‘fintail’), 1959.

This did not change until the early 1990s and the new model series 140 S-class. At up to 5.2m in length, this car offered its occupants superior space in the interior but also required aids to make the rear end of the body visible when manoeuvring. The solution was extendable, chrome-plated marker bars on the rear wings that were pneumatically lifted when reverse gear was engaged.

And then, in 1995, Mercedes presented the Parktronic system. The new system adopted a natural model by adapting the ultrasound orientation system familiar from bats and combining it with sophisticated electronics. The distance to obstacles was indicated by coloured LCD displays in the dashboard. If the driver ignored the displays, closer approaches were accompanied first by a clearly audible intermittent tone and then by a continuous tone warning of imminent collision.

Parking Assist, available for the S-class as of 2005, provided even greater precision by relying not on ultrasound like Parktronic but on the radar sensors of the Distronic and Brake Assist Plus systems. The advantage compared to the bat principle was that the territory monitored around the vehicle was significantly larger. Here too, the driver was notified of the proximity of solid objects by way of an audible alert. Visually, a colour display in the instrument cluster now provided substantially greater detail. In addition, engaging reverse gear also automatically activated an additional display in the rear roof lining.

In the same year, the first reversing camera premiered in the S-class, available then in conjunction with Parktronic which was still on offer. The camera eyed the surroundings from the boot lid above the number plate, relaying its image to the COMAND display once reverse gear was engaged. The system’s electronic director also calculated the optimum path into the targeted parking space and supplemented the camera's image with corresponding guide lines.

In 2008, searching for a parking space and parking ‘manually’ became a thing of the past. The then-latest generation of the A- and the B-class were offered to Mercedes-Benz customers for the first time with the option of Active Parking Assist. The electronic passenger kept an eye open for parking spaces on both sides of the vehicle up to a speed of 35km/h. Once it found a parking space, an arrow in the instrument cluster indicated the side on which the parking space was located. The driver then needed to engage reverse gear and give the go-ahead by pressing a button on the multifunction steering wheel. The assistant then took over steering while the driver needed only accelerate and brake.

A further step followed a year later. Parallel to Active Parking Assist, the E-class was offered with the classic Parktronic including the new parking guidance. This version also looked for parking spaces as described above; however, the driver here needed to handle the steering himself, albeit with the aid of indicators in the instrument cluster display describing the necessary steering manoeuvres.

The state of the art so far in manoeuvring assistants is the GL-class’s Active Parking Assist with automatic parking and departing function as well as the 360° camera that displays the surroundings to the driver from a variety of perspectives: from the complete panorama of bird’s-eye view to the various detailed views that facilitate accurate manoeuvring even in difficult terrain.

Drive-trains

Both the GL 350 Blue-Tec 4-Matic’s diesel engine and the GL 500 4-Matic Blue Efficiency’s turbocharged Blue Direct V8 petrol engine offer power and efficiency advantages over their predecessors.

The GL 350 uses selective catalytic reduction (SCR) technology with urea injection; it meets the EU6 emissions standard planned for 2014. At a consumption of 7.4-8.0l/100km (NEDC combined), the diesel model consumes 20 per cent. less than its predecessor. At the same time, performance has been increased: while the first-generation GL 350’s outputs were 211PS and 540Nm, the new model now manages 258PS and 620Nm.

Mercedes’ Blue-Tec system injects aqueous urea, often known by the brand name AdBlue, into the exhaust gases. This releases ammonia, which then reduces up to 80 per cent. of the NOx to nitrogen and water in the SCR catalytic converter. The AdBlue tank is located under the luggage-compartment floor to protect it in the event of a crash, has a capacity of 31.2l and is refilled at the regular 25,000km maintenance intervals. The filler aperture is located behind the fuel filler flap on the side of the vehicle, behind the fuel filler neck, and is easily recognisable by the bright blue cap. GL drivers can thus easily refill the tank themselves. AdBlue is available in refill containers at motorway service areas and Mercedes-Benz dealerships. The need for a refill is indicated in good time in the instrument cluster.

With NEDC consumption figures of 11.3-11.5l/100km, the GL 500 uses a turbocharged 4.6-litre power unit with a headline output pf 435PS. The latest generation consumes an average eighteen per cent. less fuel.

The new V8 engine produces 12 per cent. more power — 435PS — from 15 per cent. less swept volume — 4663cc compared to 5461cc. At the same time, torque has been increased from 530Nm to 700Nm — a 32 per cent. increase. The maximum torque is available from 1800rpm. Mercedes achieved the higher specific output primarily by means of two turbochargers, one serving each cylinder bank.

The turbochargers are designed to provide high torque even at low engine speeds. Compared to the previous engine, the new unit develops 40 per cent. more torque at 2000rpm. The maximum figure of 700Nm is available from 1800rpm to 3500rpm.

The latest generation of petrol V8 also incorporates such innovations as the third-generation direct injection featuring guided-spray combustion and piezo-injectors as well as multi-spark ignition.

GL 63 AMG

The GL is for the first time available as an AMG variant. The GL 63 AMG features an AMG 5.5-litre V8 biturbo engine with 557PS and a maximum torque of 760Nm. Fuel consumption on the rolling road is 12.3l/100km (equivalent to 288g/km of CO2).

The AMG V8, designated M157, features guided-spray petrol direct injection, piezo injectors, two turbochargers, air/water charge-air cooling, aluminium crankcase, four-valve heads with camshaft adjustment, generator management and a stop-start system.

Power is transmitted to the four permanently driven wheels by the AMG Speedshift Plus 7G-Tronic gearbox. The seven-speed transmission has three driving programs and an automatic double-declutching function for downshifts. In ‘Controlled Efficiency’ (C) mode, Eco stop-start is active and switches off the engine whenever the vehicle comes to a standstill. ‘C’ also incorporates a soft accelerator-pedal and gearbox characteristic with early shift points; in this mode, the vehicle generally pulls away in second gear. An ‘ECO’ icon in the AMG instrument cluster tells the driver that Eco stop-start is active.

The Speedshift gearbox features a mass-damper pendulum in the torque converter, low-friction bearings and thermal management for the transmission fluid. Additional fuel-consumption reductions are achieved by low-friction axle drives, the electromechanical AMG speed-sensitive sports steering and the adaptive management of all auxiliary units and pumps.

For the 4Matic permanent four-wheel drive, Mercedes-AMG employs an autonomous transfer case: it distributes drive power between the front and rear axle at a ratio of 40:60. Also the AMG Ride Control sports suspension with Airmatic package, comprising air suspension, special spring struts, automatic ride height adjustment and the Adaptive Damper System (ADS), is combined with Active Curve System anti-roll stabilisation.

Blue Efficiency

Besides the state-of-the-art engine technology, fuel economy is further aided by a package of ‘Blue Efficiency’ measures. These include, in addition to the standard stop-start, the new 7G-Tronic Plus seven-speed automatic gearbox. Further fuel-consumption reductions are achieved by the low-friction axle drives, electric steering and low-rolling resistance tyres.

The redesigned 7G-Tronic Plus comes as standard for the GL 350 and GL 500. It is characterised by integrating stop-start and by its reduced torque converter clutch slip. The most important details include the new torsion damper that now attenuates rotational imbalances and vibration in the gearbox more effectively. Such vibration becomes potentially greater the lower the engine speed and the lower the number of cylinders. This results in a conflict of interests between comfort and economic operation. The conflict is resolved by employing a so-called twin-turbine damper which, in the diesel models, additionally features a mass-damper pendulum. The damper shifts the centre of gravity in accordance with the engine speed and allows for comfortable vehicle operation even at low revs. Additionally, the improved damping also allows for a substantial reduction in torque converter clutch slip even at low loads, again contributing to better fuel economy. The improved absorption of imbalances and vibration in the gearbox also ensures a faster response to accelerator pedal actuation. Low-friction bearings and a new thermal management for the transmission fluid further reduce fuel consumption.

The energy requirements of the new GL-Class are reduced by a belt drive with decoupler and the intelligent, adaptively controlled activation of all auxiliary units and pumps. In the same way as the fuel pump in the vehicle’s rear, the engine’s oil and water pumps are activated only as much as required. The same control logic is used in the standard Thermatic (GL 350) and Thermotronic (GL 500) climate control systems, which activate the refrigerant compressor only when necessary. In addition, an internal heat exchanger and the sensor system which includes a misting sensor on the windscreen ensure a good level of efficiency for passenger-compartment climate control.

Aerodynamics

With a drag coefficient of Cd 0.35 (for the GL 350), the new GL-Class improves upon its predecessor; the CdA of 1.05m² beats the previous model’s 1.07m². Much of the development work was carried out using simulations as part of the digital prototyping process, with the wind-tunnel reserved for fine-tuning.

The most important aerodynamic improvements are:

  • Adjustable radiator shutter allowing adaptive limitation of the cooling air intake.
  • Aerodynamic 18- and 19-inch alloy wheels that reduce flow separation and airflow losses around the wheels.
  • Sealed panel gaps between bonnet and headlamps.
  • Wheel spoilers on the front wheels to improve airflow around the tyres while simultaneously reducing lift.
  • Engine compartment and underbody panelling that optimise outflow of the cooling air from the engine compartment and prevent flow losses caused by accumulation and turbulence in the underbody area.

The GL-class’s energy efficiency has also been improved by applying experiences gained from the energy-transparent vehicle (ETV), a process first employed during the development of the M-class. Through high-precision, in-depth examination of the energy flows within the entire vehicle (tank-to-wheel), engineers are capable of optimising all consumption-related assemblies, right down to individual components such as the wheel bearings. The notion of the ETV arose from the fact that, in the past, many consumption effects and correlations between economy measures could not be conclusively verified or validated. Thanks to the ETV, developers can now identify in detail the optimisation potential of a component or assembly by breaking down the energy-related causal loops and by analysing the correlations within the vehicle as a whole.

The process uses extremely complex high-precision measurement technology capable of recording up to 1,000 measurement values per second at around 300 energy-related measurement points. Thus, approximately 2.4 million values are obtained per minute. Their analysis provides reliable indication of the potential for improvement. The process is supplemented by energy simulation models that are validated by means of measured values. In combination, these procedures allow for the analysis and quantification of the energy efficiency of individual units and components as well as of the entire vehicle.

Dieting for improved agility

Thanks to extensive lightweight design measures, the new GL weighs around 90kg less than its predecessor (in the case of the GL 350); this is in spite of additional equipment such as the standard sliding sunroof, the significantly improved second row of seats with easy-entry on both sides and the noise-reduction measures. The front and rear-axle links as well as the bonnet and the wings, for instance, are made from aluminium alloys. The further weight reduction was achieved through the new high-insulation windscreen, the dashboard’s magnesium cross beam, the new electromechanical steering, the electric parking brake, the plastic engine bracket or the new aluminium brake booster.

Development & production: Digital worlds in real vehicles

With the new Mixed Reality development tool, which Mercedes-Benz fully implemented for the first time during the development of the new GL-class, it was possible to link data from the ‘Digital Prototype’ development program to real experimental vehicles directly for the first time. The advantage of this new method — also known by the generic term Augmented Reality — lies in the ability to speed up the entire development process significantly. However, Mercedes-Benz does not just use this accelerated process to shorten development times. The Mixed Reality engineers use it to conduct far more trials within the same time span, which significantly improves the quality of the overall development process.

Previously, digital and real processes ran consecutively: early studies were conducted during the initial development phase in the virtual environment. To ensure that these solutions could be put to the test in real-life situations, mock-ups and part builds, such as seating configurations for ergonomic studies or complete vehicle prototypes, were then produced. Engineers then made decisions either using computers in the virtual world or directly affecting the real builds. Mixed Reality linked these two worlds, the digital and the real, introducing completely new development perspectives. Modifications and new concepts from the virtual world can now be visualised, checked and assessed directly in the real-life environment.

Combining a virtual engine with a real vehicle

Mixed Reality first uses a camera to capture photos of a particular area of the prototype, such as the engine compartment. The precise spatial relationship between the real-life and digital world is established using tracking systems, which precisely determine the current position of the video camera in relation to the overall vehicle. These video images are then displayed on a monitor and a variety of different components are ‘installed’ virtually. Typical examples of application include positioning new electrical components such as wiring harnesses or control units, optimised heat shields or hydraulic functional units such as the brake force booster with corresponding lines. However, it is also possible to conduct installation tests with new engine configurations. In this case, the engineers assess whether a modified engine will fit in the existing installation space or if it can be easily mounted during the production process. Special spatial analyses are used by developers to assess the accessibility of individual components within the engine compartment to ensure that installation and maintenance work can be easily carried out on the vehicle at a future date. The first validation of virtual models is taking place in the real world with the use of Mixed Reality. This process has meanwhile been integrated into the Mercedes-Benz development program.

Production at Tuscaloosa

With the start of production of the new GL-Class in the U.S. automotive plant in Tuscaloosa, Alabama, a success story that began 15 years ago is being updated.

Production at the plant started in 1997, following the ground-breaking ceremony in 1995. The site manufactured the Mercedes-Benz M-Class and later added the GL-Class and R-Class SUVs. In 2009 the plant employees had the opportunity to celebrate a very special anniversary: the one-millionth SUV, an ML 350, left the production plant. In 2011 the plant produced more than 148,000 vehicles and employed approximately 2,800 people at year’s end.

Starting in 2014, the next generation of the current C-Class for the North American market will also be produced at the Mercedes-Benz plant in Tuscaloosa, and in 2015 a fifth Mercedes-Benz model series will be added to the production portfolio.

Mercedes-Benz GL 350 GL 500 GL 63 AMG
Cylinders 6V 8V 8V
Aspiration T 2T 2T
Swept volume 2987cc 4663cc 5461cc
Compression
ratio
15.5:1 10.5:1 10.0:1
PS/rpm 258/3600 435/5250 557/5250
Nm/rpm 620/1600 700/1800 760/2000
Maximum speed 136 155 155
0-100km/h 7.9 5.4 4.9
Urban* MPG
(l/100km)
34.8
(8.1)
19.4
(14.5)
17.8
(15.8)
Combined* MPG
(l/100km)
38.1
(7.4)
25.0
(11.3)
23.0
(12.3)
CO2* g/km 192 262 288
Emissions EU6 EU5 EU5
Transmission
— I
— II
— III
— IV
— V
— VI
— VII
— Final drive
A7
4.38
2.86
1.92
1.37
1.00
0.82
0.73
3.27
A7
4.38
2.86
1.92
1.37
1.00
0.82
0.73
3.46
A7
4.38
2.86
1.92
1.37
1.00
0.82
0.73
3.47
Driven wheels All All All
Fuel tank 100l 100l 100l
Kerb mass † 2380 2370 2505
PS/t 108 183 222
Nm/t 260 295 303
Tyres 265/60R18 275/55R19 295/40R21
Wheel location
— front
— rear

Double wishbone
Multi-link
Dimensions See graphics
† DIN kerb mass. For E.U. kerb mass, add 75kg.
* Figures vary according to tyre equipment; best figures given.
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