Brushless Motor Sensor Redundancy for EPAS
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing Electric Power Assist Steering (EPAS) systems face high failure rates of motor position sensing, leading to sudden removal of power steering assist without prior symptoms, which can be startling and annoying to drivers, especially during transitions from hydraulic to electric power systems.
Innovation Solution
The implementation of an alternative sensing system that uses back-EMF detection of brushless motor coils to provide redundant position signals when primary motor sensors fail, allowing for a gradual reduction in steering assist and providing feedback to the driver, thereby maintaining system safety and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single motor position sensor is used in EPAS systems, then device complexity is reduced, but reliability deteriorates due to high failure rates and abrupt loss of steering assist
Solution Approach 1:
The motor position sensing function is segmented into multiple independent sensors (primary sensor and backup sensor) that can operate independently. Each sensor provides redundant positioning capability, ensuring that if one sensor fails, the other can maintain steering assist functionality. This segmentation approach resolves the contradiction by distributing reliability across multiple components while keeping each individual sensor simple.
Solution Approach 2:
A backup motor position sensor is implemented in advance to cushion against the potential failure of the primary sensor. The backup sensor is pre-positioned and ready to take over immediately upon detection of primary sensor failure, preventing abrupt loss of steering assist. This beforehand cushioning approach ensures continuous reliability without requiring complex real-time sensor switching mechanisms.
2Reliability
If the system removes power steering assist upon sensor failure detection, then safety is improved, but driver experience deteriorates due to startling and annoying failures
Solution Approach 1:
The system dynamically transitions between different operational modes based on sensor status. When the primary sensor is functional, full power steering assist is provided. Upon detecting sensor failure, the system dynamically switches to backup sensor operation, maintaining steering assist with reduced or modified characteristics. This dynamic adaptation allows the system to preserve safety while minimizing disruption to driver experience, avoiding abrupt removal of assist.
Solution Approach 2:
The system continuously monitors sensor status and provides feedback to the control unit, which then adjusts steering assist accordingly. When backup sensor operation is activated, the system provides feedback to the driver through modified steering characteristics or warnings, allowing the driver to understand the changed system state. This feedback mechanism maintains safety while improving driver awareness and reducing the startling nature of failures.
3Reliability
If alternative sensing system is implemented with back-EMF detection, then reliability is improved through redundancy, but device complexity increases due to additional sensing circuitry
Solution Approach 1:
The motor control unit performs multiple functions: it controls motor operation, monitors primary sensor status, and implements backup sensing through back-EMF detection of motor coils. By making the motor control unit multi-functional, the system avoids adding separate dedicated backup sensing circuitry. The same motor coils used for driving the motor also serve as sensing elements for position detection, reducing overall device complexity while maintaining reliability through redundancy.
Solution Approach 2:
The motor coils serve dual purposes: they are both actuators for providing steering assist and sensors for position detection through back-EMF. The system uses the motor's own operational characteristics (back-EMF generation during motion) to provide redundant sensing capability. This self-service approach eliminates the need for separate sensing hardware, reducing device complexity while improving reliability through the inherent redundancy of the motor's dual function.
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
This solution reduces the obtrusiveness and startling nature of power steering failures by enabling a less abrupt transition to alternative sensing, ensuring continued steering functionality and driver awareness of issues, while maintaining system safety and reliability.
Implementation Method 1
The implementation of an alternative sensing system using back-EMF detection of brushless motor coils
Data Source
AI summary
An electric power assist steering motor sensor redundancy system is disclosed comprising a brushless motor selectively providing a first predetermined level of steering assistance for a vehicle. A first sensor and second sensor provide position information of the brushless motor to a motor controller. An alternative sensing system for the brushless motor may be selectively utilized to provide position information of the brushless motor to the controller when at least one of the first sensor or the second sensor fails.