A drive train with hybrid technology lowers fuel consumption and CO2 emissions. At the same time this introduces high-voltage electricity and sophisticated battery systems into passenger car engineering, however. Thanks to their long experience with fuel cell technology, Mercedes development engineers are extremely well prepared for the new challenges this presents. A comprehensive, seven-stage safety concept is the result.
The challenge lay in not only complying with all the worldwide and in-house crash test requirements, but also in ensuring the greatest possible safety for the electrical components. This safety system already applies in production, includes workshop personnel during servicing and maintenance, and also takes the emergency services into account when passengers need to be recovered following an accident. The seven-stage concept in detail:
1. In the first stage all the wiring is colour-coded to eliminate confusion, and all components are marked with safety instructions. This makes the regular technical inspections easier to carry out.
2. The second stage comprises comprehensive contact protection for the entire system by means of generous insulation and newly developed, dedicated connectors.
3. As part of the third stage, the lithium-ion battery has been given a whole package of carefully coordinated safety measures. This innovative battery is accommodated in a high-strength steel housing, and also secured in place. Bedding the battery cells in a special gel effectively dampens any jolts and knocks. There is also a blow-off vent with a rupture disc and a separate cooling circuit. An internal electronic controller continuously monitors the safety requirements and immediately signals any malfunctions.
4. The fourth stage of the safety concept includes separation of the battery terminals, individual safety-wiring for all high-voltage components and continuous monitoring by multiple interlock switches. This means that all high-voltage components are connected by an electric loop. In the event of a malfunction the high-voltage system is automatically switched off.
5. Active discharging of the high-voltage system as soon as the ignition is switched to "Off", or in the event of a malfunction, is part of the fifth stage.
6. During an accident, the high-voltage system is completely switched off within fractions of a second.
7. As the seventh and last stage, the system is continuously monitored for short circuits.