Patent GB-1465831-A (GB)
Title: Vehicle occupant passive restraint system and the monitoring  thereof
IPC: B60R21/16
Filed: 1974-02-05
Abstract: 1465831 Motor vehicle crash bags EATON CORP 5 Feb 1974 [14 Feb 1973] 05293/74 Heading B7B [Also in Division G1] Crash bags are inflated from a gas reservoir on energization of electric detonators in response to operation of switches which are sensitive to vehicle deceleration. In normal circumstances, test current is continuously passed through the circuitry of the switches and detonators, and a fault indicator is energized if the magnitude of the current strays beyond limits which represent normal circuit conditions. Crash bag operation.-As illustrated, the system is normally powered from the vehicle battery B and includes a forward sensor FS located near the vehicle radiator and comprising a pair of inertia switches 20 and 22 whose movable contacts 24 are shown in their unactuated positions in which they maintain resistors 30 in circuit. The resistors 30 act to limit current through them to test current level, i.e. to a level which is insufficient to operate the detonators. In the event of vehicle deceleration greater than a predetermined level, e.g. 7 to to 14 G, contacts 24 move to short circuit the resistors 30. A further inertia operated sensor LS is mounted behind the vehicle dashboard and has a contact 40 which is displaced under decelerations greater than 1G to bridge contacts 44 and 46 and allow current flow through detonator firing circuits SW and PS. If switches 20 and 22 are also actuated, the current through SW and PS will be large enough to fire the detonators. Circuit SW is associated with a steering wheel crash bag and comprises a pair of detonator coils 50 and 52 connected in parallel so that failure of one of them does not result in malfunction. Circuit PS is associated with a front passenger crash bag and also comprises two coils 54 and 56 connected in parallel. Reserve operating voltage.-In normal operation with the vehicle battery developing normal voltage, a diode 74 maintains a capacitor 72 in a state of charge. However, should the battery voltage fail, the diode bias is not maintained and when sensors FS and LS are operated, the capacitor discharges to operate the detonators. Testing fault indicator.-In normal operation, as described below, an NPN transistor Q1 becomes conducting to energize a fault indication lamp FI when the test current strays from normality. However, when the ignition switch IS is moved to its "start" (as opposed to its "run") position, the fault indicator should be energized to demonstrate that it and its associated circuitry are functioning properly. Testing sensor and firing circuits.-In normal operation, the movable contact of sensor LS is in its illustrated position so that a circuit is completed through resistor 42, and the magnitude of the voltage developed across that resistor will be indicative of the sensor switch circuitry. Similarly, the voltage at a point 46 will be indicative of the condition of the firing circuitry. The point 46 is in a line through which current passes to the detonator coils from a point 76 between diodes 74 and 68. The current is limited to test magnitude by a resistor 80. The monitored test voltages are processed by logic circuit A2 and its associated resistance network RN2 which are illustrated in detail in Fig. 4 (not shown). Logic circuit A2 acts to compare the test voltages with reference voltages taken from resistance network RN2. If a fault develops, for example in the form of a short circuit or an open switch, then the test voltages will be affected to cause logic circuit A2, acting through a further logic circuit A1, to bias transistor Q1 into conduction to energize fault indicator FI. Testing other system components.-Other parts of the system are monitored by logic circuit A1 acting in conjunction with resistance network RN1. This results in energization of the fault indicator FI if a pressure switch 150 opens to indicate inadequate gas reservoir pressure, if the voltage across capacitor 72 would be insufficient to operate the detonators, and if position switches PS1 or PS2 open to indicate that switches 20 and 22 are not properly interconnected with the control circuit. Suppressing transients.-Transient suppressors 170, 172 prevent operation of the fault indicator FI when conditions momentarily occur (e.g. on starting the vehicle engine) which would be falsely indicative of a malfunction. The suppressors act by introducing a time delay into the operation of NAND gates in logic circuit A1. Timing duration of fault condition.-When there is a fault condition, current flows through a coulometer timing cell 182. The cell has gold and silver plated electrodes, and the amount of silver deposited on the gold electrode can be measured to indicate the duration of a fault condition.