BMW HOPES to reduce the number of fires started by car crashes. Beginning this autumn BMW will equip all its cars with a new kind of battery terminal that automatically disconnects the starter cable in an accident severe enough to deploy the front airbags.
The maker's Battery Safety Terminal uses a small explosive to break the connection between the battery and starter cable. Disconnecting the terminal prevents sparks from a short circuit - a major cause of fires after a crash.
Although most electrical circuits in a vehicle are protected by fuses or circuit breakers, this has not been possible with the starter cable. The centimeter-thick cable that connects the battery to the starter motor has to carry a lot of power. This rules out a conventional fuse.
But if the starter cable is broken in a crash, its direct connection to the battery can create sparks. These can ignite leaking fuel.
The explosive is linked to the car's airbag system. It is triggered when an airbag deploys.
Gas from the explosive pushes the battery cable rearward in its housing, which is connected to the battery terminal. This breaks the electrical contact. Springs in the housing prevent the cable from recontacting the battery terminal.
The BMW cable system prevents the engine being restarted after an accident.
Separate wiring within the terminal continues to provide power for the airbag system, crash sensors, interior lights, warning indicators and the automatic door-unlocking system.