Steer-by-Wire Backup Actuator Layout for Fault-Tolerant Steering
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Solution Overview
Problem
Existing SBW type electric power steering systems in vehicles lack sufficient fault tolerance and are costly, with existing redundancy solutions either complicating integration or not adequately addressing control electronics failures.
Innovation Solution
A power steering system utilizing a brush motor as an auxiliary actuator, controlled by a separate control unit, with a clutch mechanism to decouple and couple the auxiliary motor to the steering pinion, and a force feedback actuator to provide redundancy and fault tolerance without increasing cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a brushless auxiliary motor is used for redundancy, then reliability is improved, but cost and complexity increase
Solution Approach 1:
The patent applies this principle by using a brush motor instead of a brushless motor for the auxiliary steering actuator. Brush motors are simpler, cheaper, and less prone to electronic failures, providing cost-effective redundancy while maintaining reliability through mechanical simplicity rather than electronic complexity.
Solution Approach 2:
The patent replaces the electronic control system of a brushless motor with a mechanically simpler brush motor system. The brush motor's inherent mechanical commutation eliminates the need for complex electronic controllers, sensors, and power circuits, thereby reducing overall system complexity while providing redundant steering capability.
2Measurement precision
If the power circuit is placed near the steering actuator, then control precision is improved, but reliability decreases due to simultaneous failure risk
Solution Approach 1:
The patent applies segmentation by physically separating the auxiliary brush motor and its power circuit from the main steering actuator. This spatial distribution ensures that a failure of the main actuator or its associated electronics does not simultaneously affect the redundant system, thereby improving reliability while maintaining adequate control precision through the brush motor's direct mechanical coupling to the steering rack.
3Adaptability or versatility
If a clutch mechanism is added to couple/decouple the auxiliary motor, then adaptability is improved, but device complexity increases
Solution Approach 1:
The patent applies dynamics by using a clutch mechanism that allows the auxiliary brush motor to be dynamically coupled to or decoupled from the steering rack based on operational needs. This enables the system to switch between normal operation (auxiliary motor decoupled) and emergency backup mode (auxiliary motor coupled), providing adaptability while keeping the mechanical connection simple and fail-safe.
Data Source
AI summary
A method for controlling a power steering system of a motor vehicle, the method including steps of: detecting an operating state of a steering actuator coupled to a rack; when the steering actuator is operational, providing a torque setpoint to a main motor of the steering actuator, by a first control unit of the steering actuator; when the steering actuator is faulty, but provides an angular position measurement of the main motor, controlling, by a second control unit, a brushless auxiliary motor, coupled to the rack, based on measuring the angular position of the main motor and an angular position of a steering wheel; and when the steering actuator has completely failed, controlling the auxiliary motor according to the angular position of the steering wheel.