Active safety: Clever co-pilots

Nov 4, 2014
State-of-the-art wheel suspension, optimised suspension geometry and latest generation ESP® form the basis for balanced handling in the smart fortwo and smart forfour. Advanced assistance systems which were previously the reserve of higher classes of vehicle further enhance safety and comfort. These include crosswind assist (standard), forward collision warning (option) and Lane Keeping Assist (option).
The smart fortwo and smart forfour have latest generation ESP® on board. The system serves to stabilise the vehicle in critical driving situations. For this, up-to-date data on the vehicle's speed, engine speed, steering angle, wheel speed of every wheel, transverse and longitudinal acceleration and the yawing moment are permanently measured and evaluated.
If deviations from the target values are detected ESP® intervenes with measures tailored to the situation concerned. First of all, the engine power is reduced and, depending on the situation, the clutch is opened to decouple the driven rear axle. Should these measures not be sufficient, there is additional intervention on individual wheels.
Assistance in strong gusts of wind: crosswind assist
crosswind assist and hill start assist are two further systems that make use of the ESP® sensors. Both assistants come as standard – a first in this segment.
Every car driver will be familiar with risky situations when surprised by strong gusts of wind while overtaking trucks or on bridges. Standard-fit crosswind assist is able to defuse such dangerous situations by carrying out specific braking intervention when the vehicle threatens to drift off track. As a result, less countersteering effort is required of the driver. Crosswind assist is active from 80 km/h when driving straight ahead and in gentle bends. The ESP® indicator lights up in the instrument cluster in response to noticeable intervention by crosswind assist.
Amongst other factors, crosswind assist uses information about yaw rate and lateral acceleration to deflect wind force. When the system senses that regulation is necessary, it uses brake intervention on the front and rear wheel of the wind-facing side. This intervention results in a steering effect by turning around the vertical axis and counters the effect of wind.
Hill start assist (a standard feature) is also part of the ESP® system. It prevents the car from rolling backwards when moving off on a hill by maintaining the brake pressure whilst the driver moves his or her foot from the brake to the accelerator.
Always keep a safe distance: forward collision warning
A brief lapse in concentration is all it takes for the driver to edge too close to the vehicle ahead – this is one of the main causes of serious traffic accidents. The forward collision warning (option) helps to defuse such dangerous situations. It can prevent rear-end collisions when the driver approaches the end of a traffic jam, for example. The system can also prompt the driver to take action in dangerous traffic situations in the city, thereby helping to avoid accidents.
Forward collision warning continuously monitors the distance to the vehicle ahead and the closing speed with mid-range radar.
The driver is warned in two stages: when a vehicle ahead is detected, a warning lamp first of all lights up in the instrument cluster if the distance is not within the safe range (stage 1). If the closeness to the vehicle ahead becomes critical, giving rise to a danger of collision, a warning tone additionally sounds (stage 2).
The driver is thus urged to take action in the form of emergency braking or a specific evasive manoeuvre to avoid a rear-end collision. The combined visual and audible warning is initiated in case of moving or stationary vehicles in the speed range from 7 km/h to top speed. Stationary vehicles are detected when the driver is travelling at a speed from 7 to 90 km/h.
To ensure reliable functioning, the control unit of the forward collision warning performs a dirt and function test every time the engine is started. This test requires an object in the area covered by the radar sensor to determine a reference value.
Always on track: Lane Keeping Assist
Vehicles veering off the road or collisions with oncoming traffic are among the most common and most severe types of accident. Lane Keeping Assist (option) helps to avoid such crashes. A video camera constantly scans road markings and detects contrast differences between the road surface and boundary lines in real time. A control unit processes the data from the camera and the driver's activities. The system is able to recognise whether the driver intends to leave the lane by checking whether an indicator has been activated, for example. If a danger is detected, an audible warning tone sounds and a visual warning is displayed in the form of a symbol in the instrument cluster.
Lane Keeping Assist is activated from a vehicle speed of 70 km/h and can be switched on or off with the switch strip to the left of the steering wheel. There is no warning when the driver actively steers, for example when performing an evasive manoeuvre, quickly changing lanes or in a tight bend.
Glide into even the smallest parking space: parking aid and reversing camera
These two optional extras facilitate parking, manoeuvring and reversing. With the rear parking aid three ultrasonic sensors in the rear bumper measure the distance to obstacles detected. The smaller the remaining distance, the shorter the intervals of the warning tone, culminating in a continuous tone.
The reversing camera equipped with a wide-angle lens switches on automatically when reverse gear is engaged. It shows the area behind the vehicle on the high-resolution display of the smart Media-System. Dynamic guidelines help to assess the driving path of the smart depending on the steering angle. The camera controller has an intelligent switch-off logic: the image is not deleted until five seconds after leaving reverse gear so that it remains available during the whole manoeuvring process. On the smart fortwo the reversing camera is in the handle of the tailgate, on the smart forfour it is concealed in the brand logo.
Tyre deflation warning, rain sensor: further assistants
Both smart models come with a tyre pressure monitoring system as a standard feature. This reduces the risk of breakdowns or accidents due to insufficient tyre pressure. During the journey special sensors on the inside of the wheels send radio signals with the pressure, temperature and rolling direction. This information is received by a controller located on the vehicle underbody. If the air pressure falls below a level relevant to safety, a warning symbol appears in the instrument cluster.
Cruise control with limiter function, which keeps the vehicle to a pre-set speed, is a further standard feature. The desired speed can be set via the multifunction steering wheel.
A rain and light sensor are elements of the optional LED & Sensor package. The rain sensor assumes control of the windscreen wipers and adapts the intermittent wiping function to the level of rainfall. The light sensor controls the headlamps automatically and switches them on when entering a tunnel, for example.