GMR Sensor with Ferromagnetic Encoder and Separated Magnet
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Solution Overview
Problem
GMR-based wheel rotation speed sensors are not suitable for use with ferromagnetic encoders due to the strong magnetic field of permanent magnets, which either damages the sensors or provides a weak magnetic field, limiting their effectiveness.
Innovation Solution
A speed sensor arrangement using a GMR or TMR sensor element with a ferromagnetic encoder and a separate, strategically positioned permanent magnet, housed in a plastic enclosure with a defined distance and mounting system, including a retaining element and coupling element, to effectively detect the modulated magnetic field and generate a speed signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a permanent magnet is used with a ferromagnetic encoder to generate a magnetic field, then the magnetic field strength is improved, but the GMR sensor element is damaged or its detection capability deteriorates due to the strong magnetic field
Solution Approach 1:
The system is divided into separate functional components: the permanent magnet is separated from the sensor assembly and mounted on the encoder, while the GMR sensor remains in a protected housing. This spatial segmentation allows the magnet to generate a strong field without directly exposing the sensor to damaging magnetic intensity.
Solution Approach 2:
The ferromagnetic encoder acts as an intermediary between the permanent magnet and the GMR sensor. The magnet modulates the magnetic field through the encoder's periodic structure, which then presents a weakened, modulated field to the sensor, protecting it from direct exposure to the strong permanent magnet field.
2Illumination intensity
If the permanent magnet is positioned close to the GMR sensor element to provide a strong magnetic field, then the magnetic field strength is improved, but the sensor detection accuracy deteriorates due to field saturation or interference
Solution Approach 1:
The magnetic field characteristics are made non-uniform and location-dependent through the encoder's periodic structure. The sensor detects local field variations caused by the encoder's teeth or slots passing by, rather than experiencing a uniform strong field, enabling precise detection of positional changes.
Solution Approach 2:
The system transitions from a static strong magnetic field to a dynamic modulated field. As the encoder rotates, it dynamically modulates the magnetic field strength at the sensor location, creating time-varying signals that encode positional information while maintaining sensor operating conditions within optimal ranges.
3Ease of manufacture
If magnetic particles bound into injection-molded material are used as permanent magnets, then the geometric flexibility and directed magnetic field are improved, but the magnetic field strength becomes relatively weak
Solution Approach 1:
The solution combines the advantages of both approaches: injection-molded magnetic particles provide the geometric flexibility and directional field control, while a separate high-strength permanent magnet mounted on the encoder provides the necessary magnetic field strength. The two components work together to achieve both manufacturability and performance.
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 accurate, robust, and cost-effective detection of ferromagnetic encoder movements, improving the magnetic field strength and sensor durability while maintaining a safe distance from the magnet, suitable for applications in vehicles like motorcycles.
Implementation Method 1
The magnetic field sensor element is designed in accordance with an aspect of the invention as a GMR sensor element, i.e. a giant magnetoresistive sensor element or one based on the giant magnetoresistive principle
Implementation Method 2
or as a TMR sensor element, i.e. as a tunnel magnetoresistive sensor element
Implementation Method 3
the magnetic field provided by the permanent magnet is modulated by the ferromagnetic encoder
Implementation Method 4
ferromagnetic encoder, the magnetic field of which is modulated by the ferromagnetic encoder
Data Source
AI summary
A speed sensor arrangement, implemented in particular as a wheel rotation speed sensor arrangement, including: a sensor and a ferromagnetic encoder. The sensor has at least one magnetic field sensor element and a signal processing circuit. The speed sensor arrangement having a permanent magnet and the magnetic field provided by the permanent magnet is modulated by the ferromagnetic encoder at least during a movement of the encoder and the magnetic field sensor element of the sensor detects this modulated magnetic field. The magnetic field sensor element is implemented as a GMR sensor element or as a TMR sensor element and the speed sensor arrangement is implemented such that the permanent magnet is arranged at a defined minimum distance from the magnetic field sensor element.