Active safety: Attentive assistants

Sep 7, 2010
  • Active Blind Spot Assist and Active Lane Keeping Assist
  • ATTENTION ASSIST: warns of drowsiness
  • Speed Limit Assist: shows the currently permitted speed on the display
  • Adaptive Highbeam Assist: the optimum light settings, automatically
  • DISTRONIC PLUS: keeping a safe distance with the help of radar
  • PRE-SAFE® Brake: "electronic crumple zone"
Along with the proven technologies ABS, ESP® and Brake Assist, in the new-generation CL a dozen or so newly developed or improved driver assistance systems help to avoid accidents or reduce their severity. They make the luxury coupé an "intelligent" partner which is able to "see", "feel" and act "on its own initiative". With this concept, the Mercedes-Benz model protects not only its occupants, but can do much to make the road safer for other users too.
The trailblazing driver assistance systems, unique in the luxury coupé segment, are based on cutting-edge radar, camera and sensor technology. They are geared to frequent causes of accidents such as failure to maintain a safe distance, drowsiness and darkness. As world firsts the Active Blind Spot Assist and Active Lane Keeping Assist will find use, simultaneously with their introduction in the S-Class.
Active Blind Spot Assist: course correction through brake actuation
An example of an ultramodern radar-based assistance system is the Active Blind Spot Assist which Mercedes-Benz offers for the CL as part of its Driving Assistance package. The system warns the driver if it detects a risk of collision when changing lanes. Short-range radar sensors housed on both sides of the rear bumper monitor the areas directly alongside and behind the car.
This process enables them to see if there is another vehicle in the next lane –
in the so-called blind spot. In such situations, the system informs the driver by illuminating a red warning signal in the glass of the exterior mirror. If the driver fails to see this warning and indicates to change lanes, a warning signal sounds as well.
A novel feature of the system in its latest development stage: if the driver ignores the warnings and comes dangerously close to a vehicle in the neighbouring lane, the Active Blind Spot Assist reacts with a corrective braking intervention via the Electronic Stability Program® on the wheels of the opposite side of the vehicle. The result is a yaw movement of the CL, caused by the unequal distribution of the braking forces, which counteracts the collision course. At the same time a display in the instrument cluster informs the driver. If despite this change of course an accident cannot be avoided, the Active Blind Spot Assist system can reduce the consequences of a collision through the course correction. If the system detects vehicles or obstacles at close quarters on the other side of the vehicle too, it adjusts the braking action accordingly. For this purpose the Active Blind Spot Assist also makes use of the front sensor data of the DISTRONIC PLUS proximity control. Both systems consequently are available as part of the Driving Assistance package.
Brake actuation to correct the course occurs between 30 and 200 km/h. The effect is limited to longitudinal and latitudinal deceleration of 2 m/s2. The system is intuitively deactivated as soon as the driver corrects his steering because of the brake intervention or accelerates the vehicle. When ESP is in OFF mode, Active Blind Spot Assist also is switched off. The visible warning in the exterior mirror is active up to a speed of 250 km/h.
New: Active Lane Keeping Assist with ESP® support
In the new-generation CL the Active Lane Keeping Assist is now also linked to the ESP® for the first time. This system kicks into action if the Mercedes coupé inadvertently drifts over a solid line to the right or left of a lane. In this case, Active Lane Keeping Assist uses the ESP® to brake the opposite wheels and thereby prevent the vehicle from crossing the line. A display on the instrument cluster warns the driver at the same time. If broken lane markings are crossed, the system controls an electric motor in the steering wheel which generates brief vibrations – a discreet but highly effective cue to countersteer immediately. Before the braking system intervenes, the steering wheel always vibrates to provide a warning. The course-correcting brake application is active between 60 and 200 km/h.
The heart of the Active Lane Keeping Assist, which also is offered as part of the Driving Assistance package, is a camera on the inside of the windscreen. It is able to recognise lane markings by analysing the difference in contrast between the road surface and the boundary lines. The image processor informs an electronic control unit which determines and detects the position of the vehicle if it drifts out of this lane to the left or right. For maximum reliability, the new generation of Lane Keeping Assist also evaluates radar signals in addition to image processing. Only when both lane algorithms concur is braking force applied to correct the course.
Unlike conventional systems of this type, the intelligent Mercedes assistance system also assesses the behaviour of the driver and is therefore able to determine according to the situation whether the vehicle is leaving the registered lane intentionally or unintentionally. For example, the system recognises when the driver is accelerating before overtaking or joining the motorway, is deliberately cutting a corner, is moving back into the original lane after overtaking, or is actively correcting his steering. In this case the driver feels no warning in the form of steering wheel vibrations.
Furthermore, Lane Keeping Assist is deactivated immediately if ABS, ESP®, Brake Assist or another active safety system intervenes.
Speed Limit Assist: speed limit signs displayed in the instrument cluster
Intelligent electronic image processing is also the basis for the Speed Limit Assist, used for the first time in the CL and available as part of the Navigation package (standard for the CL 600). This assistance system, presented in the Mercedes-Benz E-Class and the S-Class saloon in 2009, reminds the driver of the current speed limit. The detected speed limit is shown on a display in the instrument cluster and in the map display of the navigation system, and remains visible until no speed limit applies or a different speed limit is registered – an important contribution to safety, as unsuitable speeds are the cause of most, and the most serious, accidents worldwide.
A windscreen-mounted camera continuously monitors the area in front of the coupé. A computer scans the camera image for round surfaces only and then highlights these. As a next step, a system of algorithms filters out all objects that are round but do not resemble traffic signs. Finally, a comparison with stored patterns eliminates all but those objects which the system is programmed to detect: round traffic signs indicating the speed limit. The symbols are sent to the instrument cluster and the map display of the navigation system, meaning that the driver is always aware of the current speed limit and can adjust the car's speed accordingly.
Some of the speed limit signs in Europe – for example those seen when entering or leaving towns – are rectangular, however. In such cases, the assistance system also scans the data stored on the digital map of the navigation system in the COMAND APS control and display system to check the plausibility of the camera image. For example, the last speed limit detected disappears from the display in the instrument cluster as soon as the car enters a built-up area. If there are no traffic signs with speed limits, again the Speed Limit Assist falls back on the data stored in the navigation system.
In its most recent version the Speed Limit Assist additionally recognises important signs and information which qualify a speed limit, for example making it applicable only to trucks. In this case the traffic sign does not appear on the instrument cluster. Moreover, the system recognises signs which cancel a speed limit. For smaller daytime roadworks, for example, if there is no sign cancelling a temporary speed limit after the specified distance, the speed limit stored in the navigation system automatically is shown in the instrument cluster. This interlinkage of navigation system and Speed Limit Assist is a major advantage over a retrofit solution.
Thanks to the huge advances made in computer-based image-processing technology, Speed Limit Assist is able to work in real time, analysing the images within a fraction of a second so as to provide the driver with the required information very rapidly. It also makes no difference whether the speed-limit sign is at the side of the road or on a gantry above the road.
Adaptive Highbeam Assist: always the best possible road illumination
Another camera-based system that enhances active safety in the new-generation CL is Adaptive Highbeam Assist. It recognises oncoming vehicles or vehicles ahead with their lights on, and dips the headlamps. It also adjusts the beam range of the headlamps to give the driver the best possible visibility – without dazzling oncoming road users. The driver is able to see the course of the road, pedestrians and potential hazards more easily, and respond at an earlier stage. In addition, he can better concentrate on the road since he no longer has to operate the lever on the steering wheel.
Once the system registers oncoming vehicles or vehicles ahead with their lights on, it continuously adjusts the beam range to the distance so that the cone of light ends before it meets these vehicles. Adaptive Highbeam Assist also takes the steering angle into account, dipping the headlamps on tight bends. On clear stretches of road the system smoothly switches over to main beam.
Lightning-fast: data transfer in 40-millisecond cycles
Adaptive Highbeam Assist is based on a multi-purpose camera located on the inside of the windscreen and used also by the Speed Limit Assist and Lane Keeping Assist. Thanks to a special image-processing algorithm, the system is able to detect other vehicles and the distance to them. The range of the standard-fit, variable-control bi-xenon headlamps then is set based on these findings and adapted continuously depending on the distance to the vehicle in front or the oncoming traffic. The system operates at lightning speed, sending new data to the headlamps every 40 milliseconds and controlling the beam of light so that it always ends in front of the other vehicles.
Intelligent Light System: the right light in any driving situation
Mercedes-Benz combines the Adaptive Highbeam Assist in the CL ex factory with the Intelligent Light System, which offers five different bi-xenon light functions, each of which is suited to typical driving or weather conditions:
  • The familiar low-beam headlamps are replaced by country mode, which illuminates the road verge on the driver's side more broadly and brightly than before. This enables drivers to orientate themselves even more easily in the dark, and respond more rapidly when other road users cross the road.
  • Motorway mode, which comes on automatically when driving above 90 km/h, increases the range of vision by up to 60 percent. This lighting function is activated in two stages: the Intelligent Light System first increases the output of the bi-xenon bulbs from 35 to 38 watts, thereby increasing the light intensity and providing noticeably better illumination of the road ahead and the side verges. The second stage of motorway mode is triggered at 110 km/h, when the beam of the bi-xenon module on the driver's side is elevated slightly. Motorway mode has a range of around 120 metres, and the driver is able to see about 50 metres further at the centre of this cone of light than with conventional low-beam headlamps.
  • With the enhanced foglamps, Mercedes-Benz improves driver orientation when visibility is poor. The new lighting function is activated at speeds below 70 km/h, as soon as the rear foglamp is switched on. The variable headlamp technology incorporated in the Intelligent Light System makes it possible to pivot the bi-xenon headlamp on the driver's side outwards by eight degrees, while lowering the beam of light at the same time. This adjustment illuminates the inner half of the road more brightly and reduces the degree of glare from light reflected back by the fog.
  • Depending on the steering angle, yaw rate and vehicle speed, the active light function pivots the headlamps sideways by up to 15 degrees in fractions of a second to greatly improve road illumination. On a long sweeping bend with a radius of 190 metres, the driver is able to see 25 metres further than with conventional low-beam headlamps thanks to the active light function, which, incidentally, operates with both low and high beam.
  • The cornering light function improves safety at crossroads, at T-junctions and on tight bends. It is activated automatically when the driver operates the turn indicators or turns the steering wheel at a speed below 40 km/h. The foglamps then swivel to illuminate the area diagonally in front of the vehicle for a distance of around 30 metres, with an angle of coverage of 65 degrees.
The standard equipment includes the Headlamp Assist, which automatically switches on the lights in the rain, at dawn or dusk, in the dark or when entering a tunnel.
LED technology: better to be seen
Apart from seeing, being seen also plays an important role in road safety – not only at night. For this reason, as standard the CL is fitted with two seven-piece LED strips for daytime running lamps on either side of the front apron. They are distinguished by high light output, but low energy consumption of only ten watts. They are automatically switched on when the engine starts. If the ECO start/stop function shuts the engine off at a traffic light, the daytime running lamps remain activated. When the low-beam headlamps are switched on, the LED strips are dimmed. The turn indicators and position marker lamps also feature LED technology.
Mercedes-Benz uses LED technology as standard also in the tail lights for the indicator, rear position lamp, brake light and rear foglamp. One of its advantages is rapid response. The LED brake light warns drivers approaching from behind more quickly in the event of danger. Like many up-to-date Mercedes passenger cars the CL also is equipped with adaptive brake lights. During emergency braking they flash four times faster than the hazard warning signals and are especially effective for warning drivers coming from behind of the danger of a rear end collision. LED technology also is used for the number plate lamp.
Night View Assist Plus: highlighting pedestrians on the display
The Night View Assist Plus system likewise available for the CL uses infrared technology to enhance the driver's range of vision when the main beams cannot be used: two separate headlamps illuminate the road with invisible, non-dazzling infrared light. A separate windscreen-mounted camera designed to pick up precisely this type of light records what happens in front of the car and sends the image to a display in the instrument cluster. The clear, needle-sharp greyscale image that appears here shows the scene in front of the car, allowing the driver to see pedestrians, cyclists or obstacles on the road at an early stage.
The latest development stage of the Night View Assist features a special pedestrian-detection function: as soon as the system detects pedestrians ahead of the car, they are highlighted on the display to make it easier for the driver to see them.
ATTENTION ASSIST: warns of potentially fatal micro-sleep
ATTENTION ASSIST, invented by Mercedes, is specified as standard for the new-generation CL. With this system, the Stuttgart motor manufacturer makes a further key contribution towards active safety as, according to studies, around a quarter of all serious motorway accidents are caused by drowsy drivers. The innovative drowsiness-detection system monitors the driver's behaviour on a permanent basis, recording a total of more than 70 parameters to gauge the driver's level of awareness. This continuous monitoring is crucial for detecting the floating transition from awakeness to drowsiness and for giving the driver plenty of warning.
Based on a wealth of data, ATTENTION ASSIST calculates an individual driver profile during the first few minutes of every trip. This profile is then compared with the current sensor data and the prevailing driving situation by the car's electronic control unit. In addition to the vehicle speed, lateral acceleration and longitudinal acceleration, the Mercedes system also detects use of the turn indicators and the pedals as well as certain control inputs and external influences such as side winds or road unevenness, for example.
Drowsiness detection: steering behaviour as the key indicator
Four years of development and testing work on the ATTENTION ASSIST system revealed steering behaviour to be an extremely meaningful indicator of drowsiness. In the tests involving over 670 drivers, the Mercedes scientists determined that drowsy drivers have trouble steering a precise course in their lane, making minor steering errors that are often corrected quickly and in a characteristic way. This effect occurs at an early stage when drowsiness kicks in – often before the dangerous micro-sleep phase. ATTENTION ASSIST is active at speeds of between 80 and 180 km/h.
If the system detects drowsiness, it emits an audible warning signal and flashes up an unequivocal message on the display in the instrument cluster: "ATTENTION ASSIST. Break!"
DISTRONIC PLUS: keeping a safe distance with the help of radar
With the DISTRONIC PLUS proximity control Mercedes-Benz offers another radar-based assistance system for the CL. DISTRONIC PLUS operates at speeds of between 0 and 200 km/h: the proximity control keeps the car a set distance behind the vehicle in front and can even bring the car to a complete halt, depending on the traffic situation. If the system recognises that the gap to the vehicle in front is narrowing too quickly, it gives the driver an audible warning and, as soon as this first warning signal sounds, automatically calculates the brake pressure required to prevent a collision in this situation.
This technology helps the driver to gauge the level of risk and, in combination with Brake Assist PLUS (BAS PLUS), makes the calculated brake boosting force available instantly, even if the driver does not press the brake pedal forcefully enough. Brake Assist PLUS allows controlled, targeted braking and, if necessary, increases the braking force right up to the point at which an emergency stop is performed, depending on the road speed and the distance to the vehicle in front.
When a potential accident situation is recognised, two short-range radar sensors with an 80-degree beam width and a range of around 30 metres, located behind the front bumper, and a long-range radar with a range of 200 metres instead of the previous 150, located in the radiator grille, are called upon to offer assistance. In addition, the sensor system now also has medium-range detection capability, allowing monitoring of the area up to around 60 metres ahead of the car with a 60-degree beam width. This new technology enables even more accurate monitoring of the traffic situation ahead and even better detection of dynamic events such as a car in front swerving suddenly.
PRE-SAFE® Brake: autonomous braking as "electronic crumple zone"
If the driver is distracted and fails to heed the immediate danger of a rear-end collision or ignores the visual and acoustic warnings of an assistance system, the PRE-SAFE® Brake is able to intervene and brake the CL autonomously.
This process has two stages:
  • Around 1.6 seconds before the calculated impact point – after three audible warning signals – the system initiates partial braking autonomously and decelerates the car with around 40 percent of the maximum braking power (approx 4 m/s²) and, as a precaution, activates the reversible PRE-SAFE® occupant protection systems. Designed to supplement the visual and audible warnings, autonomous partial braking gives the driver a further, perceptible signal to act. If the driver then brakes immediately, the maximum braking force is made available by BAS PLUS. If the driver swerves, the accident can be avoided at the last moment.
  • If the driver fails to react even after this autonomous partial braking, it is able to activate the maximum braking pressure in this second stage in around 0.6 seconds before what is now recognised as an unavoidable accident – an emergency braking action that can significantly mitigate the severity of the impact. Practical tests by Mercedes-Benz engineers have shown that autonomous PRE-SAFE® braking reduces impact speed by an average of 16 km/h. The PRE-SAFE® Brake therefore acts as something like an "electronic crumple zone" to give the occupants even greater protection.
The PRE-SAFE® Brake, whose first generation had its world premiere in the CL in 2006, is active in a speed range from 30 to 200 km/h when vehicles are detected driving ahead. The system responds also on approaching a standing column of vehicles, provided the car is not going faster than 70 km/h. The PRE-SAFE® Brake uses the same short-range radar sensors and the same long-range radar as DISTRONIC PLUS and BAS PLUS. Mercedes-Benz offers a combination of all three systems in the Driving Assistance package Plus.
PARKTRONIC with Parking Guidance: easier manoeuvring with ultrasound
On the basis of the information from a total of ten ultrasonic sensors, the further improved PARKTRONIC with Parking Guidance helps the CL driver to park safely: sideways inclined sensors on the front bumper record the length of a parking space as the car drives past it (at a speed of up to 36 km/h) and indicate on the cockpit display whether the space is large enough to park in. The space must be at least 1.3 metres longer than the car. After reverse gear has been engaged, instructions for safe parking appear on the display in the instrument cluster.
The standard-fit system replaces the previous Parking Assist with eight radar sensors. Once it finds a suitable parking space on the front passenger's side, a blue "P" symbol appears on the instrument cluster. Parking spaces on the driver's side are indicated upon actuation of the left turn indicator. If the driver stops the coupé at the position shown on the display and engages reverse, a bird's-eye view symbolic representation of the parking situation appears in the instrument cluster display. Coloured lines tell the driver how best to park: a red track shows the car's current steering angle, a yellow track recommends the angle necessary for parking. The driver now turns the steering wheel until the two coloured tracks coincide and can then back up slowly. As soon as target and actual steering angle agree, the auxiliary lines on the display change to the colour green. As the car reverses, an acoustic signal informs the driver when the position is reached where opposite lock should be applied.
Looking back: camera in boot lid
The proven Mercedes system PARKTRONIC, which during parking indicates the distance between the CL and an obstacle or another vehicle by means of optical and acoustic signals, also is active during this parking guidance process and supports the driver. As further parking or manoeuvring aid Mercedes-Benz offers a reversing camera (standard for the CL 600) that sweeps the area behind the coupé. It is mounted in the boot lid above the licence plate and is activated automatically when the driver engages selector position "R". The camera image is projected onto the COMAND display. Based on the vehicle dimensions, speed and steering angle, an electronic control unit calculates the optimal path the vehicle should take into the parking slot. Coloured lines are superimposed on the camera image to guide the driver.
The driver assistance systems for the Mercedes-Benz CL at a glance:
Standard: ensures that the CL remains steerable even when braking.
Standard: reduces the risk of skidding and stabilises the car.
Brake Assist (BAS)
Standard: provides full braking power almost instantaneously in the event of an emergency stop.
Standard: is able to recognise signs of drowsiness by analysing driver behaviour, and warn the driver.
Intelligent Light System
Standard: incorporates five light functions specially configured for typical driving situations and weather conditions.
Adaptive Highbeam Assist
Standard: detects vehicles in front or oncoming vehicles and, in each case, provides the optimum headlamp range.
Active Lane Keeping Assist
Optional: detects carriageway markings, warns the driver if the vehicle leaves the recognised lane unintentionally, and takes counteraction if necessary through selective braking intervention.
Speed Limit Assist
Optional: uses a camera to detect speed-limit signs and indicates the current speed limit in the display and in the navigation map view.
Active Blind Spot Assist
Optional: uses radar to monitor the areas to the sides and rear of the coupé, warns the driver if it detects another vehicle in the exterior mirror's blind spot, and if necessary takes targeted corrective braking action.
Optional: uses radar to automatically maintain a desired distance from the vehicle in front, and warns the driver if the gap narrows rapidly.
Brake Assist BAS PLUS
(in conjunction with the short-range sensors of DISTRONIC PLUS)
Optional: uses radar sensors to detect an imminent rear-end collision and calculates the necessary level of braking assistance.
(in conjunction with the short-range sensors of DISTRONIC PLUS)
Optional: initiates partial or emergency braking automatically if it recognises an acute risk of an accident and the driver fails to react.
PARKTRONIC with Parking Guidance and reversing camera
Standard: ultrasonic sensors measure the length of parking spaces as the car drives past; instructions for safe parking appear in the display.