Smart Brake Pad Shear Sensor Layout to Minimize Force Cross-Talk
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Solution Overview
Problem
Existing piezoelectric shear sensors face challenges in minimizing cross-talk between normal and tangential force measurements, and in situ polarization of devices is complicated due to the need for high voltages and specific electrode configurations.
Innovation Solution
A vehicle smart brake pad incorporating a shear force sensing device with a sheet of screen-printed piezoelectric material, featuring interdigitated electrodes on parallel main faces, allows for bulk electric polarization with a vector field oriented tangentially to the shear stress direction, reducing the normal component of the electric field and enabling in situ polarization with lower voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional piezoelectric shear sensors are used, then shear force measurement is enabled, but cross-talk between normal and tangential force measurements occurs
Solution Approach 1:
The sensor is segmented into distinct functional zones: a polarization zone with interdigitated electrodes for creating the electric field, and a separate sensing zone for detecting shear forces. This spatial segmentation allows the electric field to be confined primarily to the polarization region, reducing its interference with shear force measurements in the sensing region.
Solution Approach 2:
The polarization function is extracted and separated from the sensing function. The interdigitated electrodes are positioned specifically to generate electric field lines that extend laterally into the piezoelectric material without directly interfering with the shear stress measurement path, thereby taking out the harmful normal stress component from the measurement zone.
2Reliability
If high voltage polarization is applied to piezoelectric materials, then proper electric polarization is achieved, but the process becomes complex and requires specific electrode configurations
Solution Approach 1:
The polarization process is made dynamic and flexible by using interdigitated electrodes that can generate the necessary electric field configuration without requiring complex pre-established electrode patterns. The lateral extension of electric field lines naturally achieves the desired polarization effect during the polarization phase.
Solution Approach 2:
The interdigitated electrode structure serves multiple functions: it generates the strong electric field needed for polarization, creates the appropriate field distribution pattern, and can be integrated into the final sensor structure without requiring additional specialized components. This multi-functionality reduces overall device complexity.
3Productivity
If screen-printing technology is used for electrode deposition, then manufacturing cost is reduced and productivity increased, but electrode precision and film thickness control may be compromised
Solution Approach 1:
The design accepts the parameter range inherent to screen-printing technology, optimizing the electrode geometry and polarization voltage parameters to work within the thickness tolerances of screen-printed films rather than requiring ultra-precise thin film deposition. This approach leverages the robustness of screen-printing while achieving functional 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
This configuration enhances signal collection while minimizing distortions, allowing for accurate measurement of shear forces and reducing production steps, enabling flexible polarization during or after installation, and improving the robustness and cost-effectiveness of the sensorized brake pad.
Implementation Method 1
Piezoelectricity is the electric charge that accumulates inside a particular type of solid materials in response to external applied mechanical stress
Implementation Method 2
a strong electric field of several kV/mm is applied to create an asymmetry in the previously unorganized ceramic compound. The electric field causes a reorientation of the spontaneous polarization
Data Source
Figure 1~2
Figure 3~4
Figure 5~7
AI summary
A vehicle brake pad (100) comprising: a support plate (21); a friction pad (20); at least a shear force sensing device; and an electrical circuit configured to collect signals from the shear force sensing device (1); wherein the shear force sensing device (1) comprises: a sheet (2) of piezoelectric material having a first and a second main faces (3, 4) parallel to each other identifying a shear stress direction (S); at least a first digitated reading electrode (5) located on the first main face (3); at least a second digitated reading electrode (6) located on the second main face (4), the first and second reading electrodes (5, 6) having digits (5a, 6a) aligned along a reading direction (R) orthogonal to the stress shear direction (S); at least a first digitated polarizing electrode (7) located on the first main face (3) and interdigitated with the first digitated reading electrode (5); and at least a second digitated polarizing electrode (8) located on the second main face (4) and interdigitated with the second digitated reading electrode (6); and wherein the piezoelectric material has a bulk electric polarization with vector field (E) transversally oriented to the reading direction (R), each pair of aligned digits (5a, 6a) of the first and second reading electrodes (5, 6) enclosing a respective zone (2a) of the piezoelectric material having the vector field (E) most tangentially oriented to the shear stress direction (S).