Electric Power Steering Motor Control for Fault Tolerance
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Solution Overview
Problem
Conventional electric power steering apparatuses require increased driver effort to operate the steering wheel when a fault occurs, as the assist force is reduced to notify the driver, leading to an increased workload and difficulty in vehicle operation.
Innovation Solution
An electric power steering apparatus with multiple independent systems of motor coils and driving circuits, where the control unit adjusts the control values of the systems to maintain assist force by increasing the normal system's control value when a fault occurs, ensuring continued steering assistance with reduced driver workload.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If the motor instruction value is decreased when a fault occurs to notify the driver, then the driver can recognize the fault, but the steering wheel cannot be operated without applying larger steering force, resulting in increased workload
Solution Approach 1:
The motor is divided into multiple independent drive systems (first drive system with first motor coil and second drive system with second motor coil), each capable of operating independently. When a fault occurs in one system, the other system can be controlled at normal or increased levels to maintain steering assist without increasing driver workload, while the fault can still be notified through other means.
Solution Approach 2:
The control unit changes the control parameter (motor instruction value) distribution between systems based on fault status. When no fault occurs, both systems share the control value equally. When a fault occurs in one system, the control unit adjusts by increasing the control value for the normal system beyond the ordinary share, maintaining total assist torque while enabling fault notification through asymmetric control distribution.
2Reliability
If the motor instruction value is decreased when a fault occurs, then the assist force is reduced to notify the driver, but the driver's workload increases
Solution Approach 1:
The motor is divided into multiple independent drive systems (first drive system with first motor coil and second drive system with second motor coil), each capable of operating independently. When a fault occurs in one system, the other system can be controlled at normal or increased levels to maintain steering assist without increasing driver workload, while the fault can still be notified through other means.
Solution Approach 2:
When a fault occurs in one drive system, the control unit applies excessive action by increasing the control value beyond ordinary levels for the remaining normal system. This ensures that the total motor current maintains sufficient assist force to prevent increased driver workload, while the fault condition is managed through asymmetric control distribution between systems.
3Loss of information
If one system is controlled at decreased motor instruction value when a fault occurs, then the fault is notified to the driver, but the total assist torque is reduced
Solution Approach 1:
The control unit changes the control parameter (motor instruction value) distribution between systems based on fault status. When no fault occurs, both systems share the control value equally. When a fault occurs in one system, the control unit adjusts by increasing the control value for the normal system beyond the ordinary share, maintaining total assist torque while enabling fault notification through asymmetric control distribution.
Solution Approach 2:
The control unit merges the control functions of both drive systems under unified fault management. When a fault occurs, the control unit combines the decreased control value for the faulty system with an increased control value for the normal system, ensuring that the sum of motor currents from both systems maintains the required total assist torque level while still indicating fault status through asymmetric control.
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 mitigates the driver's workload and secures continued steering assist, allowing easier vehicle operation even when a system fails, without reducing the total assist torque, and provides effective fault notification.
Implementation Method 1
an electric power steering apparatus configured to produce assist torque by controlling a plurality of systems corresponding to a plurality of motor coils provided in a motor
Data Source
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AI summary
The apparatus hereinprovided includes a plurality of systems including driving circuits (20a, 20b) for driving motor coils (3a, 3b) corresponding thereto, and a control unit (10) for controlling control values of the driving circuits (20a, 20b), wherein, when a fault occurs in at least one of the plurality of systems including the motor coils (3a, 3b), the control unit (10) decreases a control value of a system(s) in which the fault occurs from an ordinary time control value or stops the drive by the system(s) in which the fault occurs, and also increases a control value of another system(s) in which the fault does not occur to more than an ordinary time control value.