Electric Power Steering Relay Noise Reduction via Gradual Interruption
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Solution Overview
Problem
Conventional electric power steering devices lack noise reduction measures, and the mechanical relay-OFF operation method has limitations in high-output applications due to arc discharge and restricted interrupting-current capacity, which affects safety and practicality.
Innovation Solution
An electric power steering device with relay gradual interruption means, including a switch connected in parallel to the drive coil and a diode, performs normal relay-OFF operations to reduce noise and enables high-speed interruption during abnormalities, ensuring safety by controlling the relay-contact energizing current and utilizing a diode to manage back surges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the mechanical relay is gradually interrupted to reduce operating noise, then noise is reduced, but arc discharge occurs between contacts which lowers contact welding resistance and limits effective interrupting-current capacity
Solution Approach 1:
A diode is introduced as an intermediary component connected in parallel with the relay coil to provide a dedicated path for back-EMF current. This mediator allows the relay contacts to open gradually (reducing noise) while directing the induced current through the diode rather than through the contacts, preventing arc discharge and contact welding.
Solution Approach 2:
The patent replaces the purely mechanical relay interruption method with an electro-magnetic control system. By using electronic control to manage the relay coil current and incorporating the diode for back-EMF management, the system achieves gradual interruption without the harmful mechanical arc discharge that occurs in conventional mechanical relay systems.
2Object-affected harmful factors
If the mechanical relay is gradually interrupted in a state in which the mechanical relay is energized even when an abnormality occurs, then noise reduction is achieved, but arc discharge occurs which limits effective interrupting-current capacity and affects safety
Solution Approach 1:
The system dynamically adjusts the relay interruption behavior based on operational conditions. During normal operation, the relay is gradually interrupted to reduce noise. During abnormal conditions, the system maintains the relay energized longer or interrupts it differently, optimizing the balance between noise reduction and effective interrupting-current capacity for high-output applications.
3Reliability
If the relay-OFF operation is performed at high speed during abnormality, then safety is maintained, but noise reduction is compromised
Solution Approach 1:
The system employs different operational modes for different conditions: during normal operation, gradual relay-OFF action is used for noise reduction; during abnormality detection, the system switches to high-speed relay-OFF action for safety. The diode component enables this periodic switching of operational characteristics by consistently managing back-EMF in both modes.
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
The solution reduces operating noise and maintains safety by performing gradual relay-OFF operations during normal conditions and high-speed interruptions during abnormalities, preventing arc discharge and ensuring reliable power supply interruption.
Implementation Method 1
cause an amount of current corresponding to a back surge generated at ends of the drive coil to flow back to the diode when an exciting voltage of the drive coil of the at least one relay is turned OFF
Data Source
AI summary
An electric power steering device includes: a fail-safe power relay (9a) and a motor relay (10a) for interrupting power supply to an electric-motor driving unit for driving an electric motor for applying an assist torque for steering performed by a driver; and a relay driving circuit (8a) including a switch (13a) connected in parallel to drive coils of the relays (9a and 10a) and a diode (16a). A target value of a relay-contact energizing current is lowered and the relays (9a and 10a) are gradually interrupted while an amount of current corresponding to a back surge generated when the relays are turned OFF is caused to flow back to the diode (16a) of the relay driving circuit (8a) in a normal relay-OFF operation, whereas the relays (9a and 10a) are quickly interrupted without operating the relay driving circuit (8a) in case of detection of an abnormality.