Capacitive Rotary Angle Sensing for EMI-Robust Position Indexing
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Solution Overview
Problem
Existing rotary angle sensors in electric power steering systems face challenges in accurately determining steering angles and torque without interference from external magnetic fields, particularly in electromobility applications, where inductive solutions are susceptible to electromagnetic compatibility issues.
Innovation Solution
A capacitive position detection device for rotary angle sensors using rotors with different dielectric materials and an evaluation unit to detect predetermined rotational positions, eliminating the need for absolute angle determination by generating switching signals for indexing and counting rotor blade segments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If inductive solutions are used for position sensing in rotary angle sensors, then absolute angle determination can be achieved, but susceptibility to electromagnetic interference and magnetic field interference increases
Solution Approach 1:
The patent replaces inductive (electromagnetic) sensing with capacitive sensing for position detection. The capacitive sensor uses electric field coupling between stator and rotor elements rather than magnetic field coupling, fundamentally substituting the physical principle to eliminate susceptibility to magnetic interference while maintaining position sensing capability
Solution Approach 2:
The patent changes the fundamental sensing parameter from magnetic field coupling (inductive) to electric field coupling (capacitive). By using capacitive coupling between stator and rotor elements with different dielectric materials, the system achieves position sensing without being affected by external magnetic fields
2Reliability
If capacitive position detection with different dielectric materials is used, then robustness against magnetic interference is improved, but device complexity increases due to multiple dielectric layers
Solution Approach 1:
The patent combines multiple functions into the capacitive sensor structure: position detection, indexing, and rotor blade segmentation are all achieved through the capacitive coupling mechanism. The different dielectric materials on rotor blades serve both as structural elements and as the sensing mechanism itself, merging what could be separate components into a unified system
Solution Approach 2:
The capacitive sensor with different dielectric materials serves multiple functions simultaneously: it detects rotor position, provides indexing signals for absolute positioning, and enables torque measurement. This multi-functionality reduces the need for separate magnetic sensors and indexing mechanisms, ultimately simplifying the overall system
3Loss of information
If indexing and counting of rotor blade segments is implemented, then absolute position determination is achieved, but measurement precision requirements increase
Solution Approach 1:
The patent segments the rotor circumference into discrete blade elements, each with different dielectric materials. This segmentation creates distinct capacitive coupling variations as each blade passes the stator, providing natural indexing points and enabling absolute position determination through counting and identification of specific blade patterns
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
The capacitive solution provides robustness against magnetic interference, enabling precise indexing and torque determination with reduced complexity and cost, suitable for steering systems in electric vehicles.
Implementation Method 1
A capacitive sensor has a stator and a rotor with at least one rotor blade. A first dielectric with a first permittivity is present between the at least one rotor blade and the stator. Between a second rotor blade or a free space adjacent to the at least one first rotor blade in the circumferential direction of the rotor and the stator, a second dielectric with a second permittivity is present.
Implementation Method 2
A first dielectric with a first permittivity is present between the at least one rotor blade and the stator. Between a second rotor blade or a free space adjacent to the at least one first rotor blade in the circumferential direction of the rotor and the stator, a second dielectric with a second permittivity is present.
Data Source
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AI summary
The invention relates to a position-sensing device for a rotational angle sensor, to a rotational angle sensor having a position-sensing device of this type, and to a system having a rotational angle sensor of this kind. An exemplary embodiment of the position-sensing device comprises at least one stator, at least one rotor and an evaluation unit. The at least one rotor has a main body and at least one rotor blade extending radially outward from the main body. Between at least one first of the at least one rotor blade and the at least one stator, there is a first dielectric having a first permittivity. Between at least one second of the at least one rotor blade, or at least one free space adjoining the at least one first rotor blade in the circumferential direction of the rotor, and the at least one stator, there is a second dielectric having a second permittivity. The first permittivity and the second permittivity are different from each other. The evaluation unit is designed to sense if the at least one first rotor blade reaches, has reached or exceeds a predefined rotational position.