Enhancing pedestrian safety is a significant aspect of vehicle design, with a need to achieve cost-effective and not overly complex solutions. Creating vehicles that can avoid pedestrian impacts, or cause reduced levels of trauma when they do occur, has become crucial in the past decade. Continental and Trelleborg have each come up with new technologies created to help meet those criteria.
Continental’s new system, which is linked to an active hood, uses an air hose connected to two pressure sensors and is flexibly built into a vehicle’s bumper. The sensors can detect an impact with a pedestrian and activate other appropriate safety systems to trigger protective measures.
Continental passive safety specialist Lorenz Pfau explained that within 10-15 ms of an impact, the active hood is triggered and raised by actuators to prevent the pedestrian (particularly his or her head) coming into contact with hard engine components and particularly the block.
Pfau stated that fiber optics or acceleration sensors were commonly used for detecting collisions with pedestrians but that the pressure hose sensor (developed in collaboration with Daimler) offered advantages over those. These include easy integration into any vehicle, because Continental’s system can be easily adapted to a chassis.
“This means that there are no restrictions on vehicle developers if they alter a vehicle’s design—for example, as part of a facelift. Also, the system’s technology is extremely robust and offers high resolution and strong signal quality, boosting the reliability of crash detection,” he added.
The hose is positioned across the width of the bumper behind an energy-absorbing foam block. Standardized pressure sensors are positioned at each end of the air-filled pressure hose; the sensors are the same type as those used for the car’s side-impact airbags.
If an impact occurs with the bumper, pressure is put on the hose through the bumper and foam block. A waveform is created and detected by the two sensors in the bumper; information is sent to an airbag control unit, and crash algorithms in the analysis software plus speed information from the vehicle’s information network provide sufficient data to identify the type of collision (i.e., pedestrian). Time taken is 100th of a second.
“The signal relay time even allows conclusions to be drawn about the location [on the bumper] of the impact,” said Pfau. Protection systems are then activated. These are particularly effective in accidents in urban traffic with a precrash speed up to 55 km/h (34 mph) and an impact speed of 20 to 30 km/h (12 to 19 mph).
Continental and Daimler state that the system has been designed to exceed the requirements stipulated by Euro NCAP for pedestrian protection. Achieving this enhanced capability places particular demand on the sensors, which need to recognize a pedestrian impact regardless of the size of the person—from a small child to a large adult—and to detect, differentiate from, and ignore the effects of striking a small animal or hitting a curb with the front air dam.
Trelleborg Automotive’s contribution in the area of pedestrian safety involves the use of what it describes as an “innovative bump stop.” An alternative to an active hood, it is placed beneath the hood and again prevents the pedestrian coming into contact with hard components, including the engine block.
The company states that the system has been engineered to facilitate easy integration beneath any car hood. The technology incorporates an adjustable EPDM (ethylene propylene diene monomer) element and a collapsible metal component fixed to a plastic support.
When an impact occurs, the metal structure flattens instantly, absorbing pedestrian deployed energy. The metal part can be replaced to enable the bump stop facility to be used again.
Eric Martinuzzi, Product Development Manager, Trelleborg Automotive, particularly emphasized the potential importance of the bump stop in reducing the risk of a serious head injury.
In the Euro NCAP crash test, which is mandatory for new vehicles, pedestrian protection has a 20% weighting in the overall assessment. Adult occupant protection accounts for 50% and child occupant protection for 20%, while “assistant” systems such as ESC (Electronic Stability Control) and seatbelt reminders are 10%.
To achieve a 5-star rating, a vehicle must also achieve 60% of the maximum points available for pedestrian protection. Reducing head injuries is regarded as particularly important.
The German authorities have issued figures concerning pedestrian accidents that show that last year there were some 29,500 involving a vehicle. As would be expected, most (28,000) were in urban/built-up areas. Of the total, 559 pedestrians died. According to the German Federal Statistical Office, some 8000 people were injured.
Across Europe in 2007, about 1600 people died in traffic accidents just in capital cities, 43% of them pedestrians.
The figures are stark reminders to designers and engineers of the need to place pedestrian protection high on their priority list.