Redundant Control Device for Electromechanical Steering Systems
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Solution Overview
Problem
Current electromechanical steering systems for vehicles are not adequately designed to provide continuous steering assistance during faults, particularly in autonomous or semi-autonomous driving modes, where reliability and redundancy are critical for safety.
Innovation Solution
A redundant control device with a primary and secondary control path, each comprising a computing unit, gate driver module, and performance module, that detects faults and switches off the faulty path, allowing the other path to maintain steering assistance, using a signal line for communication and redundant power supplies to ensure continuous operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a redundant control device with primary and secondary control paths is implemented, then the reliability of steering assistance is improved, but the device complexity increases
Solution Approach 1:
The control device is segmented into independent primary and secondary control paths, each capable of autonomous operation. This segmentation allows the system to maintain steering assistance functionality even when one path fails, thereby improving reliability while keeping each individual path relatively simple in structure.
Solution Approach 2:
Each control path is designed with identical local structure and functionality, ensuring that both paths can independently provide steering assistance. This local quality approach simplifies the overall design by using standardized modules while achieving redundancy for improved reliability.
2Reliability
If galvanic separation is implemented between control paths, then the independence of partial drives is improved, but the communication cost increases
Solution Approach 1:
A signal line is introduced as an intermediary communication channel between the primary and secondary control paths. This signal line enables cost-effective communication while maintaining galvanic separation, allowing the control paths to remain independent for reliability while avoiding the high cost of full galvanic isolation infrastructure.
3Reliability
If fail-silent design is used, then the safety of the system is improved, but the steering assistance is lost during faults
Solution Approach 1:
When a fault is detected in one control path, the system discards the faulty path and recovers by switching to the operational path. This allows the system to maintain steering assistance functionality during faults by utilizing the redundant path, rather than completely losing assistance as in traditional fail-silent designs.
Solution Approach 2:
The redundant control path serves as a pre-prepared backup that can immediately take over when a fault occurs. This beforehand cushioning ensures continuous steering assistance availability while maintaining safety, as the redundant path is ready to compensate for failures in the primary path.
Data Source
AI summary
Methods for providing steering assistance for an electromechanical steering system having a redundant control unit with a primary and a secondary control path. Respective primary and secondary control paths each have a computing unit, gate driver module, and power module. The method includes detecting an applied steering torque; calculating a primary and secondary motor target torque in the primary computing unit as a function of the applied steering torque; transmitting the primary motor target torque to a primary motor controller of the primary computing unit; determining primary motor currents to operate a primary electric motor or a primary winding group of the electric motor in the primary motor controller; transferring the secondary motor target torque from the primary computing unit to a secondary motor controller and determining secondary motor currents for operation of a secondary electric motor or a secondary winding group of the electric motor.