Electronic control unit and electric power steering apparatus equipped with the same

1. An electronic control unit that driving-controls a motor by means of an inverter which comprises a bridge having upper-stage field-effect transistors (FETs) and lower-stage FETs via a micro controller unit (MCU), comprising:

an FET-short detecting section to detect a short failure of said upper-stage FETs and said lower-stage FETs based on respective connection point voltages of said upper-stage FETs and said lower-stage FETs; and

a detecting-section-failure diagnostic function to detect a failure of said FET-short detecting section,

wherein said detecting-section-failure diagnostic function diagnoses said failure of said FET-short detecting section at start up and turns-OFF said upper-stage FETs and said lower-stage FETs when said failure of said FET-short detecting section is detected, and

wherein said FET-short detecting section diagnoses said short failure of said upper-stage FETs and said lower-stage FETs when said failure of said FET-short detecting section is not detected.

2. The electronic control unit according to claim 1 , wherein said respective connection point voltages are voltage-divided by a resistor voltage-dividing circuit and voltage-divided voltages are supplied to said FET-short detecting section.

3. The electronic control unit according to claim 2 , wherein when said short failure is detected, FETs which at least said short failure is not detected are turned-OFF.

4. The electronic control unit according to claim 2 , wherein when said FET-short detecting section detects said short failure in one of said upper-stage FETs and said lower-stage FETs, said FET-short detecting section notifies a short failure detection to said MCU via a notifying terminal.

5. The electronic control unit according to claim 2 , wherein said FET-short detecting section detects said short failure based on a first threshold for said upper-stage FETs and a second threshold for said lower-stage FETs.

6. The electronic control unit according to claim 5 , wherein said inverter is driven by means of duty signals of a pulse width modulation (PWM) which are calculated in said MCU, and said detecting-section-failure diagnostic function is a diagnostic function that outputs a gate-OFF signal to forcibly switch-OFF said inverter from said MCU at start up, forcibly establishes an abnormality condition of said short failure by calculating said duty signals of said upper-stage FETs or said duty signals of said lower-stage FETs, and outputs a predetermined signal to said notifying terminal.

7. The electronic control unit according to claim 2 , wherein a dark current suppressing switch is further interposed between control system circuits, said MCU switches-ON said dark current suppressing switch at start up, said detecting-section-failure diagnostic function turns-OFF said upper-stage FETs and said lower-stage FETs when said short failure is detected, and said MCU switches-OFF said dark current suppressing switch when an operation of said MCU is stopped.

8. The electronic control unit according to claim 7 , wherein said respective connection point voltages are voltage-divided by a resistor voltage-dividing circuit and voltage-divided voltages are supplied to said FET-short detecting section.

9. The electronic control unit according to claim 1 , wherein when said short failure is detected, FETs which at least said short failure is not detected are turned-OFF.

10. The electronic control unit according to claim 9 , wherein when said FET-short detecting section detects said short failure in one of said upper-stage FETs and said lower-stage FETs, said FET-short detecting section notifies a short failure detection to said MCU via a notifying terminal.

11. The electronic control unit according to claim 1 , wherein said detecting-section-failure diagnostic function is incorporated in said MCU.

12. The electronic control unit according to claim 1 , wherein when said FET-short detecting section detects said short failure in one of said upper-stage FETs and said lower-stage FETs, said FET-short detecting section notifies a short failure detection to said MCU via a notifying terminal.

13. The electronic control unit according to claim 12 , wherein said inverter is driven by means of duty signals of a pulse width modulation (PWM) which are calculated in said MCU, and said detecting-section-failure diagnostic function is a diagnostic function that outputs a gate-OFF signal to forcibly switch-OFF said inverter from said MCU at start up, forcibly establishes an abnormality condition of said short failure by calculating said duty signals of said upper-stage FETs or said duty signals of said lower-stage FETs, and outputs a predetermined signal to said notifying terminal.

14. The electronic control unit according to claim 13 , wherein said notifying terminal is an NDIAG terminal.

15. The electronic control unit according to claim 13 , wherein said inverter is driven by means of said duty signals of PWM which are calculated in said MCU, and said detecting-section-failure diagnostic function has a diagnostic function that outputs a signal which forcibly transits an error notification of said FET-short detecting section from said MCU to an FET-short detecting state in order to confirm being capable of turning-OFF and stopping said inverter in a case that said FET-short detecting section detects said short failure, calculates with said duty signals of said upper-stage FETs or said duty signals of said lower-stage FETs, monitors upper and lower connection point voltages of said inverter, and diagnoses that a stop of said inverter is completed.

16. The electronic control unit according to claim 1 , wherein said FET-short detecting section detects said short failure based on a first threshold for said upper-stage FETs and a second threshold for said lower-stage FETs.

17. The electronic control unit according to claim 1 , wherein a dark current suppressing switch is further interposed between control system circuits, said MCU switches-ON said dark current suppressing switch at start up, said detecting-section-failure diagnostic function turns-OFF said upper-stage FETs and said lower-stage FETs when said short failure is detected, and said MCU switches-OFF said dark current suppressing switch when an operation of said MCU is stopped.

18. The electronic control unit according to claim 17 , wherein said respective connection point voltages are voltage-divided by a resistor voltage-dividing circuit and voltage-divided voltages are supplied to said FET-short detecting section.

19. The electronic control unit according to claim 18 , wherein said control system circuits include at least said MCU, said resistor voltage-dividing circuit and said FET-short detecting section.

20. The electronic control unit according to claim 17 , wherein said dark current suppressing switch is a transistor including an FET, and a parasitic diode is connected in parallel with said transistor for a reverse connection protection.

21. An electric power steering apparatus that is equipped with the electronic control unit according to claim 1 .