Alternator Rectifier Fault Detection Using Power Generation Efficiency

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Solution Overview

Problem

Existing methods fail to detect open failures in MOSFETs used in alternator rectifiers due to the diodes protecting them from back electromotive force, preventing detection of malfunctions.

Innovation Solution

A malfunction-diagnosing apparatus that includes a controller to diagnose alternator malfunctions based on power generation efficiency, using a parallel diode configuration to ensure power generation continues despite MOSFET failures, allowing detection through efficiency calculations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a diode is coupled in parallel to a MOSFET in the alternator rectifier, then the alternator continues to generate electric power even when the MOSFET fails open, but the open failure of the MOSFET cannot be detected by voltage-based detection methods

Engineering Contradiction:

Improvepower generation continuityVSAvoidMOSFET failure detection

Core Design Contradiction:

ReliabilityVSDifficulty of detecting and measuring

Solution Approach 1:

The system calculates power generation efficiency by comparing actual power generation (from voltage and current measurements) with expected power generation (based on engine output and alternator characteristics). This feedback mechanism detects MOSFET failures through efficiency degradation rather than direct voltage measurement, resolving the detection problem while maintaining system reliability through the parallel diode configuration

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent introduces power generation efficiency as an intermediary parameter to indirectly detect MOSFET failures. Instead of directly measuring MOSFET status (which is obscured by the parallel diode), the system measures overall alternator performance efficiency, which degrades when MOSFETs fail, enabling detection without direct MOSFET monitoring

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If voltage-based detection methods are used to detect MOSFET short-circuits, then short-circuit failures can be detected, but open failures cannot be detected due to the protective diode

Engineering Contradiction:

ImproveMOSFET failure detection accuracyVSAvoiddetection method coverage

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent changes the detection parameter from direct voltage measurement to power generation efficiency calculation. By monitoring how efficiently the alternator converts mechanical energy to electrical energy, the system can detect both short-circuit and open-failure modes of MOSFET, making the detection method versatile for different failure types

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20260063720A1Malfunction-diagnosing apparatus

Publication Date: 2026.03.05 SUBARU CORP

AI summary

A malfunction-diagnosing apparatus includes an alternator and a controller. The controller is configured to diagnose a malfunction of the alternator. The alternator includes a power generator configured to generate an alternating-current voltage by using motive power output from an engine, and a rectifier configured to rectify the alternating-current voltage into a direct-current voltage. The rectifier includes a field-effect transistor, and a diode coupled in parallel to the field-effect transistor. The controller is configured to diagnose the malfunction, based on power generation efficiency of the alternator.