Electric Power Steering Controller Failure Current Reduction
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Solution Overview
Problem
Conventional electronic power steering devices face issues with maintaining safe and continuous steering assistance when a failure occurs, as they often result in increased manufacturing costs, vibration, and lack of driver awareness of the failure due to the need for multiple relays and inhomogeneous electromagnetic forces.
Innovation Solution
An electronic power steering device with a controller that reduces the current instruction value when a failure is detected, allowing the normal system to supply reduced current to the windings, alerting the driver through a reminder element, and maintaining stable operation by controlling the electric power converters and relays to prevent overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the current to be supplied from the inverter to the three-phase windings is doubled after failure, then the magnetic flux generated in the stator is almost the same as normal operation and the driving force of the motor is substantially equal to that before failure, but it is necessary to increase heat resistance of semiconductor elements and electronic elements, which increases manufacturing cost
Solution Approach 1:
The patent applies partial action by supplying current to only two normal phase windings after failure instead of all three phases. The controller detects failure and limits current supply to the remaining functional phases, avoiding the need to double current through all windings and thereby reducing heat resistance requirements for semiconductor elements.
2Reliability
If multiple relays are arranged between each phase element of the inverter and corresponding phase of the windings to cut current, then the broken phase winding or element can be isolated, but the number of parts in the power steering device increases and manufacturing cost increases
Solution Approach 1:
The patent applies universality by using a single relay that can cut current to any failed phase winding. The relay is controlled by the controller to isolate different phases as needed, replacing the need for multiple dedicated relays for each phase while maintaining the same failure isolation capability.
3Reliability
If the motor is driven by two-phase windings after failure, then the electro-magnetic attractive force is inhomogeneous, but the driver may feel anxiety due to vibration transmitted through the steering wheel
Solution Approach 1:
The patent applies periodic action by controlling the motor to operate in a stop-and-go manner after failure. The controller periodically activates and deactivates the motor to prevent continuous vibration, allowing the motor to rest and reducing the transmission of harmful vibrations to the steering wheel while maintaining the ability to provide assistance when needed.
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 ensures safe and continuous steering assistance by reducing the steering force, alerting the driver to failures, and minimizing manufacturing costs and vibration, while maintaining stable electromagnetic forces and reducing the required heat resistance specifications of semiconductor and electronic elements.
Implementation Method 1
a plurality of electric power converters for converting the first current from the electric power source to second current corresponding to the current instruction value
Implementation Method 2
a plurality of pairs of windings, each of which correspond to a respective electric power converter, and generates the driving force of the motor when the second current is supplied from the electric power converter to the winding
Data Source
AI summary
An electric power steering device includes: an electric power source for supplying first current; a controller for setting a current instruction value; multiple electric power converters for converting the first current to second current corresponding to the current instruction value; multiple pairs of windings for generating a driving force of a motor; and a failure detection element for detecting failure of the electric power converters and the windings. The controller reduces the current instruction value to be equal to or smaller than a predetermined instruction value of a normal operation when the failure detection element detects the failure. The controller controls the electric power converter in a normal state to supply the second current to a corresponding winding.