Electric power source circuit and abnormality diagnosis system

Abstract

In a power source circuit for supplying electric power of a battery, a capacitor is charged by the battery when an ignition switch and a power supply relay are closed. The power supply relay is opened after the ignition switch is closed. The charge voltage of the capacitor falls, if the power supply relay has no fixed-closure abnormality. The charge voltage of the capacitor does not fall, if the power supply relay has the fixed-closure abnormality. A microcomputer diagnoses the power supply relay with respect to its fixed-closure abnormality based on the charge voltage of the capacitor when the ignition switch and the power supply relay are operated to open.

1 . An abnormality diagnosis system comprising:
 a power supply relay provided to open and close a current path formed between an electric power source and a power conversion circuit;   a capacitor connected between a reference potential and the current path formed between the power conversion circuit and the power supply relay;   a pre-charge path formed between the power source and the capacitor to pre-charge the capacitor by the power source, the pre-charge path bypassing the power supply relay;   a switch provided to open and close the pre-charge path; and   a diagnosis circuit for diagnosing the power supply relay with respect to fixed-closure of the power supply relay based on a drop of a charge voltage of the capacitor produced after both the switch and the power supply relay are operated to open, the fixed-closure abnormality indicating that the power supply relay maintains a closed state even if operated to open.   
   
   
       2 . The abnormality diagnosis system according to  claim 1 , wherein:
 the diagnosis circuit is connected to the power source through the switch and to the capacitor;   the diagnosis circuit includes a memory, which stores data indicating that the diagnosis circuit is operable after a predetermined time from time both the switch and the power supply relay are operated to open;   the diagnosis circuit is configured to refer to the memory in diagnosing the power supply relay when the switch is operated to close.   
   
   
       3 . The abnormality diagnosis system according to  claim 1 , further comprising:
 a motor relay provided between the power conversion circuit and a motor to open and close a current path from the power conversion circuit to the motor,   wherein the diagnosis circuit is configured to diagnose the power supply relay with respect to fixed-open abnormality based on the charge voltage of the capacitor produced when all of the switch, the power supply relay and the motor relay are operated to close, the fixed-open abnormality indicating that the power relay maintains an open state even if operated to close.   
   
   
       4 . The abnormality diagnosis system according to  claim 3 , wherein:
 the diagnosis circuit is configured to diagnose the power supply relay based on a voltage of the power source in addition to the charge voltage of the capacitor.   
   
   
       5 . The abnormality diagnosis system according to  claim 3 , further comprising:
 a switching element provided to open and close a current path formed of the power conversion circuit and the motor in parallel to the capacitor,   wherein the diagnosis circuit is configured to diagnose the power supply relay with respect to the fixed-open abnormality based on the charge voltage of the capacitor produced when the switching element is operated to open and close the current path.   
   
   
       7 . The abnormality diagnosis system according to  claim 1 , wherein:
 the diagnosis circuit is configured to diagnose the pre-charge path based on the charge voltage of the capacitor produced when the switch is in a closed state and the power supply relay is in an open state.   
   
   
       7 . The abnormality diagnosis system according to  claim 1 , wherein:
 the pre-charge path includes a pre-charge resistor connected between the switch and the capacitor for pre-charging the capacitor therethrough.   
   
   
       8 . The abnormality diagnosis system according to  claim 1 , further comprising:
 a discharge resistor connected to the capacitor in parallel for discharging the capacitor therethrough.   
   
   
       9 . An abnormality diagnosis system comprising:
 a power supply relay provided to open and close a current path formed between an electric power source and a power conversion circuit;   a capacitor connected between a reference potential and the current path formed between the power conversion circuit and the power supply relay;   a pre-charge path formed between the power source and the capacitor to pre-charge the capacitor by the power source, the pre-charge path bypassing the power supply relay;   a switch provided to open and close the pre-charge path;   a motor relay provided between the power conversion circuit and a motor to open and close a current path from the power conversion circuit to the motor; and   a diagnosis circuit configured to diagnose the power supply relay with respect to fixed-open abnormality based on a charge voltage of the capacitor produced when all of the switch, the power supply relay and the motor relay are operated to close, the fixed-open abnormality indicating that the power relay maintains an open state even if operated to close.   
   
   
       10 . The abnormality diagnosis system according to  claim 9 , wherein:
 the diagnosis circuit is configured to diagnose the power supply relay based on a voltage of the power source in addition to the charge voltage of the capacitor.   
   
   
       11 . The abnormality diagnosis system according to  claim 9 , further comprising:
 a switching element provided to open and close a current path formed of the power conversion circuit and the motor in parallel to the capacitor,   wherein the diagnosis circuit is configured to diagnose the power supply relay with respect to the fixed-open abnormality based on the charge voltage of the capacitor produced when the switching element is operated to open and close the current path.   
   
   
       12 . The abnormality diagnosis system according to  claim 9 , wherein:
 the diagnosis circuit is configured to diagnose the pre-charge path based on the charge voltage of the capacitor produced when the switch is in a closed state and the power supply relay is in the open state.   
   
   
       13 . The abnormality diagnosis system according to  claim 9 , wherein:
 the pre-charge path includes a pre-charge resistor connected between the switch and the capacitor for pre-charging the capacitor therethrough.   
   
   
       14 . The abnormality diagnosis system according to  claim 9 , further comprising:
 a discharge resistor connected to the capacitor in parallel for discharging the capacitor therethrough.   
   
   
       15 . A power source circuit for a power conversion circuit comprising:
 an electric power source;   a power supply relay provided to connect and disconnect the power source and the power conversion circuit;   a capacitor connected between a reference potential and a current path formed between the power conversion circuit and the power supply relay;   a switch provided to connect and disconnect the power source and the capacitor, the switch bypassing the power supply relay; and   a Zener diode having a cathode connected to the switch and an anode connected to the capacitor.