Electromechanical Steering Angle Plausibility Check for Gear Fault Detection
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Solution Overview
Problem
Existing electromechanical steering systems face issues with inaccurate determination of steering angles due to potential malfunctions in the steering gear, leading to incorrect steering angle calculations.
Innovation Solution
A method and system that utilize two angle sensors to detect the rotation angles of the steering shaft and motor shaft, with a control unit checking for plausible value pairs based on a transmission model, including parameters like gear ratio, to monitor transmission functionality and detect tooth skips, thereby ensuring accurate angle determination and providing warnings or corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single angle sensor is used to detect steering shaft rotation angle, then the device complexity is reduced, but the measurement precision and reliability of steering angle determination deteriorates due to undetected transmission malfunctions
Solution Approach 1:
The system uses the second angle sensor on the motor shaft to provide feedback about transmission performance. By continuously comparing the expected steering shaft angle (calculated from motor shaft angle and gear ratio) with the actual measured angle (from the first angle sensor), the system can detect transmission malfunctions such as tooth skips. This feedback mechanism enables accurate steering angle determination even with potential transmission issues.
Solution Approach 2:
The control unit acts as an intermediary that processes data from both angle sensors and the transmission model. It calculates the expected relationship between motor shaft and steering shaft angles using the stored transmission model, and uses this intermediate calculation to verify the plausibility of the first angle sensor readings, thereby ensuring measurement accuracy.
2Reliability
If additional angle sensors and plausibility checks are implemented, then the reliability of steering angle determination improves, but the device complexity increases
Solution Approach 1:
The second angle sensor serves multiple functions: it enables plausibility checking of the first angle sensor, allows determination of absolute steering angles exceeding 360°, and provides data for detecting transmission malfunctions. This multi-functionality justifies the additional sensor by extracting maximum value from it across multiple operational aspects.
Solution Approach 2:
The system uses its own existing components (the second angle sensor and the transmission model) to perform self-diagnosis and self-verification. The control unit continuously monitors the relationship between motor shaft and steering shaft angles using data already being collected for normal operation, enabling the system to detect its own malfunctions without requiring external monitoring equipment.
3Reliability
If the steering gear experiences tooth skips or malfunctions, then the transmission functionality deteriorates, but the system lacks the capability to detect these issues without additional sensors
Solution Approach 1:
The system establishes a feedback loop where the expected steering shaft angle (derived from motor shaft angle and transmission model) is continuously compared with the actual steering shaft angle measurement. When a tooth skip or transmission malfunction occurs, this comparison reveals a discrepancy between expected and actual values, enabling detection of the malfunction.
Solution Approach 2:
The system pre-stores the transmission model with the gear ratio in the control unit before operation. This preliminary preparation enables real-time plausibility checking by allowing the control unit to immediately calculate and compare expected versus actual angle relationships without requiring additional measurement infrastructure during malfunction events.
Data Source
Figure 1a~1b
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Figure 5~7
AI summary
The present invention relates to a method for operating an electromechanical steering system (1) for a motor vehicle, comprising a steering shaft (2), a control unit (3), and a feedback actuator (4) which includes an electric motor (5) with a motor shaft (6) and is configured to apply torque to the steering shaft (2) via a transmission (7) with a gear ratio. At a given time, a first angle sensor (8) detects the rotation angle of the steering shaft (2) as the first sensor value, and a second angle sensor (9) detects the rotation angle of the motor shaft (6) as the second sensor value. Based on a model stored in the control unit (3) that takes the gear ratio into account as a parameter of the transmission (7), the control unit (3) checks whether the detected first sensor value and the detected second sensor value form a plausible pair of values. In particular, this allows the faultless operation of the transmission (7) to be verified.Furthermore, the invention relates to an electromechanical steering system (1) with a control unit (3) configured to operate the steering system (1) according to such a method.