Electronic Control Unit FET Short Failure Detection
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Solution Overview
Problem
Conventional electric power steering apparatuses face challenges in detecting short failures in FETs of the inverter, leading to continuous overcurrent flow and high dark current consumption, especially without the use of expensive power supply relays, and lack effective diagnosis of FET-short detecting circuit failures.
Innovation Solution
An electronic control unit with an FET-short detecting section and a diagnostic function to detect short failures in upper-stage and lower-stage FETs based on connection point voltages, and a dark current suppressing switch to manage power supply, allowing for safe operation and cost reduction by removing the need for power supply relays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If power supply relays are used to detect FET short failures and block overcurrent, then reliability improves, but device complexity and cost increase
Solution Approach 1:
The patent extracts the FET short detection function from the power supply relay system and integrates it directly into the MCU. The MCU reads connection point voltages of FETs and determines short failures through software logic, eliminating the need for separate power supply relays and their associated control circuits.
Solution Approach 2:
The patent replaces the mechanical power supply relay system with an electronic voltage detection and software-based control system. Instead of using mechanical relays to physically disconnect power, the system uses voltage sensing and MCU-controlled switching elements to achieve the same protective function.
2Device complexity
If power supply relays are removed to reduce cost and complexity, then device complexity decreases, but the ability to detect FET short failures and block overcurrent deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the MCU continuously monitors the connection point voltages of FETs, compares them against expected values, and automatically triggers protective actions (blocking power supply) when short failures are detected. This closed-loop feedback ensures reliable overcurrent protection without mechanical relays.
Solution Approach 2:
The patent introduces voltage detection circuits and software-based control logic as intermediaries between the FETs and the power supply. These intermediaries monitor FET status and mediate power flow control, replacing the direct mechanical relay connection while maintaining protection capability.
3Ease of operation
If the inverter power supply is always connected to the battery, then ease of operation improves, but dark current consumption increases
Solution Approach 1:
The patent makes the power supply connection dynamic rather than static. The connection point between the battery and inverter power supply is controlled by switching elements that the MCU can open or close based on operational requirements. This allows the system to maintain ease of operation during normal use while blocking dark current during idle or shutdown conditions.
Data Source
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AI summary
[Problem] An object of the present invention is to provide an electronic control unit, without an increase in cost, diagnoses a short failure of an inverter FETs by means of an FET-short detecting section, appropriately deals with a diagnosis result, and has a function to diagnose whether the failure of the FET-short detecting section is occurred or not, and an electric power steering apparatus equipped with the electronic control unit. [Means for solving the problem] The present invention is the electronic control unit that driving-controls a motor by means of an inverter which comprises a bridge having an upper-stage FETs and a lower-stage FETs via an MCU, comprising: 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 detecting-section-failure diagnostic function to detect a failure of the FET-short detecting section, wherein the detecting-section-failure 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 of the FET-short detecting section is detected, and wherein 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.