Method and device for diagnosing a reservoir capacitor of a vehicle passenger protection system, and vehicle safety system incorporating such device

摘要

A method of measuring a capacitor value comprises the steps of loading the capacitor up to a given voltage value; obtaining a first measure of a time for discharging the capacitor by a fixed voltage drop, the discharge of the capacitor being caused by a first current; reloading the capacitor up to the given voltage value; obtaining a second measure of a time for discharging the capacitor by the fixed voltage drop, the discharge of the capacitor being caused by the first current and by a second current of known value added to said first current; and determining the capacitor value from the difference between the first measure and the second measure, based on the given voltage drop or the given time, respectively, and based further on the known value of the given second current.

主权项

1. A method of diagnosing a reservoir capacitor of a vehicle safety system, the method comprising:
loading the reservoir capacitor up to a given voltage value; obtaining a first measure of a discharge rate of the reservoir capacitor when discharging the reservoir capacitor by a first undetermined current; reloading the reservoir capacitor up to the given voltage value; obtaining a second measure of the discharge rate of the reservoir capacitor when discharging said reservoir capacitor by the first undetermined current and by a second fixed current of known value added to said first undetermined current; determining a capacitance value of the reservoir capacitor from the difference between the first measure and the second measure, based on the known value of the second fixed current; comparing the capacitance value of the reservoir capacitor to a threshold; and if the capacitance value is below said threshold, triggering an alarm signal indicating so.