Power Steering Relay Contact Weld Detection via D-Axis Current Injection
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Solution Overview
Problem
Current power steering systems require complex diagnostic programs to detect contact welds in phase open relays, necessitating multiple circuit tests for each relay, which complicates the diagnostic process.
Innovation Solution
A power steering system with a control apparatus that includes a command signal calculation section, a two-phase to three-phase conversion section, a PWM control section, an inverter, a current detection circuit, and an abnormality monitor section, which uses d-axis currents to determine relay abnormalities in a single diagnosis, eliminating the need for a dedicated circuit for contact welding detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dedicated circuit for contact welding detection is used, then detection accuracy is improved, but device complexity increases
Solution Approach 1:
The existing inverter and current detection circuit are made to serve dual purposes: normal motor control and contact weld detection. By injecting d-axis currents through the existing PWM control section and using the current detection circuit already present in the system, the patent eliminates the need for separate dedicated detection circuits while maintaining detection accuracy.
Solution Approach 2:
The system uses its own existing components (inverter, PWM control section, current detection circuit) to perform the contact weld detection function. The control apparatus leverages its inherent capability to generate and monitor phase currents to detect relay contact welds without requiring external or additional specialized equipment.
2Measurement precision
If multiple circuit tests are performed for each relay, then detection accuracy is improved, but diagnostic time increases
Solution Approach 1:
Multiple diagnostic tests that would traditionally be performed separately are merged into a single diagnostic operation. By simultaneously injecting d-axis currents and monitoring phase currents through the existing detection circuit, the system can detect contact welds in all phase open relays in one go, rather than requiring separate tests for each relay.
Solution Approach 2:
The system performs preliminary detection by monitoring phase currents during normal operation or during a single diagnostic cycle. The abnormality detection section continuously monitors current values to determine relay abnormalities, allowing for early detection without requiring multiple sequential tests.
3Ease of operation
If the diagnostic program is simplified, then ease of operation is improved, but detection capability is reduced
Solution Approach 1:
The patent replaces complex mechanical/circuit-based diagnostic procedures with an electronic control-based approach. Instead of using physical test circuits or manual testing procedures, the system uses software-controlled current injection and electronic monitoring through the existing inverter and detection circuit, simplifying the diagnostic program while maintaining or improving detection capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables simple and accurate detection of contact welds in phase open relays, reducing diagnostic complexity and improving detection accuracy, while preventing abnormal operations such as self-steering by identifying and addressing relay issues before vehicle travel.
Implementation Method 1
a PWM control section (53) disposed in the control apparatus to output a PWM duty signal for each phase of U phase, V phase, and W phase in accordance with the three phase command signals; an inverter (54) disposed in the control apparatus and constituted by a switching circuit drivingly controlled by the PWM duty signal for each phase of the motor
Implementation Method 2
a current detection circuit (55) configured to detect three phase currents flowing into the inverter
Implementation Method 3
a motor (M) that provides a steering assistance force for the steering mechanism
Data Source
AI summary
In a power steering system, at least one of phase open relays in which a contact weld (an abnormality) occurs is detected. That is to say, the power steering system comprises an abnormality monitor section (57) configured to output vector control command signals to supply only a d-axis current in a positive side direction toward the motor, with all of phase open relays (58v, 58w) in an interruption state, and to determine an abnormality in at least one of the phase open relays in a case where a current value is detected by a current detection circuit which detects a current flowing into an inverter. In a case of three phase open relays installed between respective three phases of motor windings, a potential difference is detected at a neutral position of a star connection to determine the abnormality of at least two of the phase open relays.