Numerous assistance systems support the driver. Mercedes-Benz was, for example, the first bus manufacturer worldwide to equip its vehicles with the anti-lock braking system (ABS) and the Electronic Stability Program (ESP®). On the Citaro G hybrid, the Articulation Turntable Controller (ATC) guarantees optimal steering behaviour by the rapid, requirements-based hydraulic damping of the articulation. Meanwhile, Acceleration Skid Control (ASR) prevents the drive wheels from spinning. With the Electropneumatic Braking System (EBS) the stopping distance is significantly shortened, as the brakes are actuated more quickly and precisely. Ensuring pre-emptive braking and manoeuvring are the Preventive Brake Assist and Sideguard Assist systems.
Safe. Safer. Mercedes-Benz.
Clever assistance systems.
Safely integrated hybrid technology.
The virtually maintenance-free hybrid storage module is located outside the crash area—at the back of the roof. By using the innovative 48 V low-voltage technology, the Citaro hybrid poses no increased safety risk and, moreover, the low-voltage technology requires no change in service and maintenance— saving additional costs.
Anti-lock braking system (ABS).
How ABS works: there are sensors fitted on the wheels which detect the rotational speed of each wheel and pass this information on to a central control unit. If the critical point of blocking the wheels is reached, the wheel is stopped at precisely that threshold by pressure variation. The brake pressure can be increased and decreased numerous times in the space of a second.
When braking, all the forces acting on the wheels and the rolling behaviour are continually monitored. The braking forces acting on the wheels are distributed in such a way that no wheel can lock, and the steerability of the vehicle is preserved as far as possible.
In December 1970, Mercedes-Benz presented the world's first electronically controlled ABS – a revolution in driving and road safety. Thanks to targeted electronic braking intervention, the wheels don't lock for long times. The risk of losing steering stability is minimised and, in the case of a full application of the brakes, the vehicle can be steered in the desired direction. ABS technology forms the basis for further developed electronic safety systems such as the Electronic Stability Program (ESP®) or the brake assistance system (BAS).
Electronic Stability Program (ESP®).
The Electronic Stability Program (ESP®) is an active system for increasing driving safety and stability. It makes a noticeable contribution to reducing the risk of skidding during cornering or evasive manoeuvres. This is achieved by specifically controlling the braking forces on each individual wheel in critical, dynamic driving situations, for example if the bus approaches physical limits when cornering. At the same time, the engine output is reduced. A possible "breaking-out" of the bus is thus prevented by the finely metered braking within the limits of the physical possibilities.
Among other things, ESP® monitors the lateral acceleration of the bus. If, on long bends – such as motorway exits – or with rapid lane changes, the bus reaches a critical driving situation, the vehicle speed is automatically reduced so the bus returns to a situation of driving stability. ESP® is comparable with the system installed in cars but provides additional functions adapted for use in buses.
Acceleration Skid Control (ASR).
ASR prevents the drive wheels from spinning. It does this in two ways. On the one hand, ASR minimises wheel spinning through a measured braking intervention. On the other hand, the torque of the engine is regulated via the "electronic accelerator pedal". Even at full throttle, the engine only provides as much power in critical situations as the drive wheels can transmit – a major advantage for controlled pulling away and driving stability.
When starting off, the torques applied and the wheel speeds of the drive wheels are monitored. In this process, torque distribution is controlled in such a way that spinning is prevented. This ensures that optimum power flow is always guaranteed.
ASR helps the driver to minimise the risk of the drive wheels spinning and consequently of the rear of the vehicle (rear-wheel drive) breaking out laterally when accelerating. Especially for high-torque engines, ASR thus provides increased comfort and enhanced safety when pulling away – particularly on roads with varying grip.
Articulation Turntable Controller (ATC) in the Citaro hybrid G.
If the vehicle should ever be at risk of becoming unstable – for instance on a slippery road surface – the articulation damping swiftly adjusts to the requirements of the situation. This way the articulated bus is very rapidly stabilised – within the bounds of physical possibilities – in order to prevent the rear vehicle body from oscillating or even swerving out of control, thus avoiding the dreaded jackknifing effect. The new Articulated Turntable Controller (ATC) is the only regulation system of its kind to act in a manner akin to the Electronic Stability Program (ESP®).
Preventive Brake Assist.
Preventive Brake Assist sees Mercedes-Benz being the first manufacturer worldwide to supply an active braking assistance system for urban regular-service buses. The assistance system warns in advance of a collision with moving pedestrians as well as stationary or moving objects. In the case of an acute risk of collision, an automatic partial brake application can be initiated. The warning cascade and the braking intervention are precisely adapted to use in city traffic. If there is an imminent risk of collision with pedestrians or objects which are either moving or stationary, Preventive Brake Assist warns the driver both audibly and visually with a red triangle featuring a pictogram of a vehicle which lights up in the central display. At the same time, a partial application of the brakes is initiated. This is maintained until either the driver intervenes or the bus comes to a standstill. The basis of Preventive Brake Assist is a new generation of radar technology: the radar system continuously monitors an area of road ahead of the bus up to 250 metres in length and also works reliably at night and in poor weather conditions.
The Sideguard Assist cornering assistant significantly increases the safety of unprotected road users, particularly in cities, as it helps the driver to recognise critical situations in good time when cornering. The system operates in multiple stages: in the first stage, it informs the driver, in the second stage it emits an additional warning. If a moving object is in the monitoring zone to the side of the vehicle, a triangular-shaped yellow LED light goes on in the A pillar. It intuitively draws attention towards the situation next to the vehicle. A warning symbol additionally appears on the central display. If the driver initiates or continues an action that could lead to a collision, an additional visual warning takes place: the LED light flashes red with high brightness and then remains on permanently. There is also a vibration warning issued in the driver's seat. Furthermore, Sideguard Assist warns of stationary obstacles in the cornering curve of the bus and can additionally take on the task of a lane change assistant; in doing so, it works in accordance with the same warning cascade.
The cornering light function.
The cornering light function provides significantly improved safety for night-time driving when turning corners at poorly lit junctions, at roundabouts or when manoeuvring and reversing.
The cornering light function is activated automatically at speeds of up to approx. 40 km/h if the main-beam headlamps are on, the turn signals are actuated or the steering wheel is turned. One of the two front fog lamps is switched on to illuminate the area to the side and front of the vehicle which is not lit by the main-beam headlamps. The intelligent electronic system switches the cornering lights on or off progressively in the same way as a dimmer switch. This gives the eyes a chance to adjust to the changing light situation.
Monitoring of the passenger compartment.
The video monitoring cameras installed can keep track of the events taking place on the bus. A video monitoring system can not only improve the sense of safety for the bus driver and passengers, it can also record troublemakers who commit acts of vandalism or violence.
The data is transmitted to the monitor in the bus driver's workstation. The bus driver can then better view and evaluate events occurring in the passenger compartment and, if needs be, react in the event of danger.
The vehicle is labelled with icons to inform passengers that the vehicle is video-monitored. Video monitoring enhances the subjective sense of safety for driver and passengers and thus the appeal of using public transportation. The video monitoring system is an optional extra.
More information on the video monitoring function and data storage is available from our bus sales consultant.