Electronic control unit and electric power steering apparatus equipped with the same
An electronic control unit diagnoses a short failure of an inverter FETs and diagnoses whether the failure of the FET-short detecting section has occurred. The unit controls a motor through an inverter including a bridge having an upper-stage FETs and a lower-stage FETs via an MCU, having: an FET-short detecting section to detect a short failure of the upper-stage FETs and the lower-stage FETs based on respective connection point voltages of the upper-stage FETs and the lower-stage FETs; and a diagnostic function to detect a failure of the FET-short detecting section. The diagnostic function diagnoses the failure of the FET-short detecting section at start up and turns-OFF the upper-stage FETs and the lower-stage FETs when the failure is detected. The FET-short detecting section diagnoses the short failure of the upper-stage FETs and the lower-stage FETs when the failure of the FET-short detecting section is not detected.
1. An electronic control unit that comprises a bridge having upper-stage field-effect transistors (FETs) and lower-stage FETs and driving-controls a three-phase blushless motor, via an inverter being supplied a power supply VR, by inputting a duty signal of a pulse width modulation (PWM) calculated in a micro controller unit (MCU) into a gate driving section, comprising:
a reverse connection protective FET which is interposed between a battery and said power supply VR and turns-ON/OFF with a switching signal from said MCU;
a diagnostic resistor voltage-dividing circuit which is supplied said power supply VR and outputs voltage-divided voltages obtained by voltage-dividing connection point voltages of said upper-stage FETs and said lower-stage FETs;
an FET-short detecting section which is supplied said power supply VR, and detects at least one-side short failure of said upper-stage FETs and said lower-stage FETs based on said voltage-divided voltages and outputs an error notification; and
a detecting-section-failure diagnostic function which inputs said error notification, is included in said MCU, and detects 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 a Zener diode for absorbing an overvoltage is connected between a gate and a source for each of said upper-stage FETs and said lower-stage FETs.
3. The electronic control unit according to claim 2 , wherein when said short failure is detected, at least FETs which said short failure is not detected are turned-OFF.
4. The electronic control unit according to claim 2 , wherein when said short failure is detected, said upper-stage FETs and said lower-stage FETs are turned-OFF by inputting said error notification into said gate driving section.
5. The electronic control unit according to claim 2 , wherein said FET-short detecting section notifies said error notification to said MCU via an NDIAG terminal when said short failure is detected, said MCU sends an error signal to an alarm input circuit, and said alarm input circuit turns-OFF said upper-stage FETs and said lower-stage FETs by inputting a gate-OFF command into said gate driving section.
6. The electronic control unit according to claim 5 , wherein when a failure of said FET-short detecting section is detected, said detecting-section-failure diagnostic function outputs said gate-OFF command from said alarm input circuit or outputs said gate-OFF command by means of said duty signal.
7. The electronic control unit according to claim 5 , wherein said detecting-section-failure diagnostic function is a diagnostic function that outputs a gate-OFF signal which forcibly turns-OFF said inverter from said MCU at start up, forcibly establishes an abnormality condition of said short failure by calculating with said duty signals of said upper-stage FETs or said duty signals of said lower-stage FETs, and outputs a predetermined signal to said NDIAG terminal.
8. The electronic control unit according to claim 1 , wherein said FET-short detecting section notifies said error notification to said MCU via an NDIAG terminal when said short failure is detected, said MCU sends an error signal to an alarm input circuit, and said alarm input circuit turns-OFF said upper-stage FETs and said lower-stage FETs by inputting a gate-OFF command into said gate driving section.
9. The electronic control unit according to claim 8 , wherein when a failure of said FET-short detecting section is detected, said detecting-section-failure diagnostic function outputs said gate-OFF command from said alarm input circuit or outputs said gate-OFF command by means of said duty signal.
10. The electronic control unit according to claim 8 , wherein said detecting-section-failure diagnostic function has a diagnostic function that outputs a signal which forcibly transits said error notification 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 said connection point voltages, and diagnoses that a stop of said inverter is completed.
11. An electric power steering apparatus that is equipped with the electronic control unit according to claim 1 .