Modern vehicle safety systems typically comprise a main control unit, which is the hub of the system. The main control unit comprises one or more accelerometers to measure the rate of change of velocity of the vehicle, a processor operable to perform a decision algorithm on the signals output by the accelerometers in order to establish whether a crash situation has occurred and implement a crash algorithm to activate one or more safety devices accordingly, an energy source, normally in the form of one or more capacitors, storing sufficient ignition energy to activate the safety device, and an ignition circuit, which is controlled by the output of the crash algorithm, and which connects the capacitor(s) to the safety device(s) to deploy the safety device(s) upon detection of a crash situation. The control unit may also comprise means for controlling the communications between the control unit and various external units, and have a diagnostic function.
Due to the fact that the control unit comprises accelerometers, the control unit must be physically located in a part of the vehicle where the sensed acceleration will be representative of the acceleration of the vehicle as a whole. The ideal location for this purpose is the central tunnel of the vehicle, which comprises a ridge running along the centre of the floor of the chassis of the vehicle, and in many known systems the control unit is mounted on an upper surface of the control tunnel, i.e. within the vehicle cabin.
Due to the number of components contained in the control unit, the control unit is rather large and heavy. It may, therefore, be difficult to allocate sufficient space to the control unit on the central tunnel of the vehicle, which typically also carries other components such as the gear stick.
In addition, a heavy control unit will generate substantial vibration while the vehicle is moving, and this is likely to compromise the accuracy of the signal output by accelerometers provided therein.
It is an object of the present invention to alleviate one or more of the above difficulties.