Torque Sensor Weighting for Steering Reliability
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Solution Overview
Problem
The electric power steering apparatus faces challenges in accurately recognizing steering states when a torque sensor fails, leading to inadequate steering assist, as existing solutions with dual torque sensors and control means are costly and inefficient in utilizing both sensor elements.
Innovation Solution
A control unit and method that weights and calculates steering torque using outputs from both sensor elements even when one is abnormal, allowing continued steering assist by adjusting weighting based on sensor output correlations, differences, and rate of change, and limiting motor output to ensure safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two torque sensors are provided to ensure normal control when one fails, then reliability is improved, but device complexity and production cost increase
Solution Approach 1:
The patent merges the functionality of two separate torque sensors into a single torque sensor that contains two sensor elements (first sensor element and second sensor element). These two sensor elements are integrated within one sensor housing and processed by a single control unit, reducing the number of separate components while maintaining the redundancy needed for reliable operation. The control unit processes outputs from both sensor elements and can determine when one has failed, allowing continued operation using the remaining functional sensor element.
2Reliability
If two torque sensors are provided to ensure normal control when one fails, then reliability is improved, but production cost increases
Solution Approach 1:
The patent combines two sensor elements into a single torque sensor assembly, reducing the number of separate parts that need to be manufactured, assembled, and tested. This integration reduces production complexity and cost while maintaining the functional redundancy of having two sensor elements for reliability.
3Reliability
If one Hall IC is assumed to have failed and is immediately discarded, then safety is maintained, but the functions of the torque sensor are not fully utilized
Solution Approach 1:
The control unit continuously monitors the outputs of both sensor elements and compares them to determine their operational status. When a failure is detected in one sensor element, the control unit provides feedback to switch to using only the functional sensor element, allowing the system to continue operating safely without complete loss of function. This feedback mechanism enables the system to adapt to failure conditions while maintaining safety.
Solution Approach 2:
The control unit changes the operational parameters of the torque sensor system based on the detected failure condition. When one sensor element fails, the control unit adjusts by using only the output from the functional sensor element, effectively changing the system's operational mode from dual-sensor to single-sensor operation while maintaining safety and continuity of 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
Enables continuous steering assist and notifies the driver of malfunctions by reducing assist force, effectively utilizing both sensor elements and maintaining safety even with sensor failures.
Implementation Method 1
A pair of Hall integrated circuit (IC) are typically used as a torque sensor. A pair of Hall IC include a first sensor element and a second sensor element.
Data Source
Figure 1~2
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AI summary
An electric power steering apparatus includes a torque sensor (9) including a first sensor element (91) and a second sensor element (92), a control unit (10), and a motor (5). When the first sensor element (91) and the second sensor element (92) are both normal, the first sensor output that is output by the first sensor element (91) and the second sensor output that is output by the second sensor element (92) have a predetermined correlation corresponding to a steering operation performed by a driver. When the first sensor element (91) or the second sensor element (92) is abnormal, the control unit (10) executes weighting with respect to the first sensor output and the second sensor output and calculates a steering torque on the basis of the weighted first sensor output and the weighted second sensor output.