Reluctance Sensor for Tire Tread Thickness Measurement
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Solution Overview
Problem
Existing tire tread thickness measurement systems, particularly those using eddy current sensors, are unsuitable for tires with non-conductive crown reinforcements, leading to inaccurate measurements and reduced sensitivity.
Innovation Solution
A system employing a single excitation and measurement coil operating in reluctant mode, surrounded by materials with high electrical resistivity and magnetic permeability, such as ferrite, which increases inductance with decreasing distance, allowing for precise measurement of tire tread thickness regardless of reinforcement conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If eddy current sensors are used to measure tire tread thickness, then measurement automation is achieved, but the system becomes unsuitable for tires with non-conductive crown reinforcements
Solution Approach 1:
The patent changes the operating principle of the sensor from eddy current mode to reluctant mode, fundamentally altering the physical parameter being measured. Instead of detecting electrical conductivity variations, the sensor now detects magnetic permeability variations, which allows it to function regardless of the electrical properties of the tire reinforcement materials.
Solution Approach 2:
The patent substitutes the eddy current detection mechanism with a magnetic reluctance detection mechanism. By replacing the electrical conductivity-based sensing with magnetic permeability-based sensing, the system overcomes the limitation of non-conductive materials while maintaining automated measurement capability.
2Speed
If eddy current sensors operate at high frequency, then measurement speed is improved, but sensitivity to non-conductive materials decreases
Solution Approach 1:
The patent changes the operating frequency range from high frequency (typical for eddy currents) to low frequency (below 150 kHz for reluctant mode). This parameter change allows the magnetic field to penetrate the rubber layer effectively and interact with the magnetic reinforcement, providing both adequate measurement speed and high sensitivity to thickness variations.
3Length of stationary object
If the coil is placed directly against the tire surface, then measurement range is maximized, but noise interference from external magnetic fields increases
Solution Approach 1:
The patent introduces a magnetic circuit core as an intermediary between the coil and the tire surface. This core serves multiple functions: it concentrates and directs the magnetic field lines toward the measurement point, provides magnetic shielding against external interference, and enhances the coupling between the coil and the magnetic reinforcement in the tire.
Solution Approach 2:
The patent extracts and isolates the measurement function from direct environmental exposure by using the magnetic circuit core to confine and control the magnetic field. This separation allows the coil to operate at optimal distance while the core handles the interaction with the tire, reducing susceptibility to external noise.
4Measurement precision
If multiple coils are used for measurement, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent makes the single coil multi-functional by combining excitation and measurement capabilities in one component. The coil serves both to generate the magnetic field and to detect the changes in magnetic flux caused by variations in tread thickness, eliminating the need for separate excitation and sensing coils.
Solution Approach 2:
The patent merges the excitation function and measurement function into a single coil assembly. By combining these functions and integrating them with the magnetic circuit core, the system achieves accurate measurements while maintaining simple structure and ease of implementation.
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 system provides sensitive and accurate measurements of tire tread thickness, unaffected by reinforcement anisotropy and orientation, with improved range and reduced noise interference, enabling effective monitoring of tire wear without the need for frequent maintenance.
Implementation Method 1
a sensor capable of measuring the distance d between the bonded face and the free face of the layer of rubbery material. The sensor comprises a single excitation and measurement coil, and the frequency and the excitation power of the coil are such that the inductance at the terminals of the coil increases when the distance d decreases
Implementation Method 2
the reinforcement of certain tires is such that the crown of the tire is not sufficiently conductive to allow the establishment of eddy currents. Consequently, these measurement systems are unsuitable for measuring the thickness of the tread of these tires
Data Source
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Figure 3~4(b)
Figure 5~8(b)
AI summary
The invention concerns a system for measuring the thickness of a layer of rubber material for a tyre, the layer having a face connected to an adjacent metal reinforcement and a free face which is in contact with the air. The system comprises a sensor which can measure the distance d between the connected face and the free face of the rubber material layer, the sensor comprising a single exciting and measuring winding, and the exciting power and frequency of the winding being such that the inductance at the winding terminals increases as the distance d decreases.