SONIC DETECTOR FOR VERIFICATION OF AUTOMOTIVE BRAKE DISCS.

Abstract

The present invention describes a sonic detector for detecting structural defects in automotive brake discs, employing acoustics in the audible sound range between 20 Hz and 20 kHz. The device comprises subsystems that work together: a disc clamping system, a disc tapping system, a universal base for disc inspection, a mechanical sound filtering and stabilization system, and a data acquisition and interpretation system. The equipment allows the disc to be rotated, and by tapping its surface, both the sound and the resulting vibration are captured. This data is compiled by a microcontroller and sent to a computer for mathematical processing of the sound, in order to obtain a graphical characterization of the disc, which serves as a reference for decision-making.

Description

SONIC DETECTOR FOR CHECKING AUTOMOTIVE BRAKE DISCS Field of the invention The present invention pertains to the technical field of devices for checking automotive brake discs; more particularly, it pertains to the technical field of sonic sensors. State of the art In Mexico, the automotive industry is one of the most important, second only to the food industry. The automotive sector accounts for 3% of the national GDP and 16% of the manufacturing GDP, representing 22% of manufacturing employment nationwide. According to INEGI and AMIA, the automotive industry's GDP grew 12.3% from 2010 to 2017, generating more than 800,000 direct jobs. Mexico is considered one of the largest exporters of vehicles and auto parts in the world, providing continuous growth in various areas of research and development in our country. This creates an opportunity for the creation of new tools and techniques, thus encouraging the creativity and capacity of Mexican researchers to address not only the country's problems but also to confront and solve problems globally. Car sales and production in Mexico are increasing annually. According to figures from INEGI, in 2021, production reached 1,090,304 units between January and April, and more than 83,000 units in April alone. The vehicle fleet in Mexico is large, with more than 50 million cars circulating in the country by 2019, and of these, 34,649,011 were automobiles. However, the real concern is the condition of the vehicles. A study conducted by the University of Pretoria in South Africa shows that developing countries are more susceptible to car accidents because older cars are used more than newer ones, making them more prone to mechanical failure. Data from Accident Response Units (ARUs) indicates that tires and brakes were the main contributors to mechanical failures that caused accidents in the Pretoria region (Gauteng province). However, the reported percentage of approximately 3% is i comparable to similar statistics from developed countries. These data are worrying, and hence the need to establish methods and systems that allow for the timely detection of mechanical failures and prevent car accidents. When we go for a braking system check, elements such as the master cylinder are inspected, brake fluid in good condition and with sufficient quantity, thickness and quality of the brake pads, rear and front, and if necessary, their respective replacement or adjustment. Finally, the drum or disc is inspected, depending on the car model. A visual examination is commonly performed, considering the roughness of the disc, thickness, or any damage due to fracture, and depending on the results, the decision is made to replace the disc or perform a rectification. However, this diagnosis is not reliable, since currently auto specialists do not have the necessary equipment to allow a correct analysis. Ultrasound is a technique that has gained relevance in the industry due to its low cost, speed, and efficiency in detecting faults such as those in bearings, pressure or vacuum leaks, and electrical installations. This technique has supported the development of new acoustic technologies for fault detection in the automotive industry, such as the implementation of neural networks for fault detection in car engines. Likewise, acoustics has been used to characterize common or specific faults in essential components, such as spark plugs, in order to obtain a comparison with fuel consumption. Brief description of the figures Figure 1 is various isometric views of the sonic detector. Figure 2 is an isometric view of the sonic detector, where (1) is the base for supporting the mechanical filter and tapping system, (2) are the gauges for height adjustment, (3) is the brake disc fixing and rotation system, (4) is the cam mechanism for moving the filtering system, (5) is the tapping system, (6) is the electronic control unit, (7) is the mechanical disc rotation system, (8) is the analysis surface graduated in 12 sectors, (9) is the mechanical filtering and stabilizing system, and (10) are the universal base support elements. (3a) is the upper coupling base, (3b) is the adjusting nut for both bases, (3c) is the brake disc, (3d) is the lower coupling base, (3e) is the adjusting screw, (3f) is the rotating base, (5a) is the actuator clamping and adjusting element, (5b) is the punch displacement magnetic base, (5c) is the wedge-shaped air microphone base, (5d) is the air microphone, (5e) is the actuator body, (5f) is the actuator seal, (5g) is the cam system for punch movement, (5h) is the servomotor, (5¡) is the positioning unit for contact microphone, (5j) is the contact microphone, and (5k) is the punch. Best method for carrying out the invention Example 1. Disc clamping system Brake discs have a common characteristic: a hollow in the center, their diameter varies minimally, so this characteristic is used to design a universal cone-shaped base (base 1) resulting in different diameters, where the disc naturally fits the geometry of the cone. Once the disc rests on this first base, a second base is inserted above the disc bell, this is of a diameter such that it does not exceed the diameter of the bell, this second base is screwed to the first, since base 1 has a screw in the center and base 8 has a nut in its center. Base 8 is circular and comes graduated by 12 sectors, this allows the user to divide the disc for a quick visual examination, also allows the disc to be adjusted to the home position. Example 2. Tapping system It is responsible for hitting the disc to characterize it, the disc has to be hit only once instantly, so that the mass of the actuator does not interfere with its natural vibration. Because the entire surface of the disc is analyzed, the hit must be exactly the same in each case, that is, hit with the same force and provide the same energy to the disc. For this purpose, the tapping system is composed of a punch (5k) type punch in the shape of a cylinder, which runs freely inside the actuator, a servomotor that has the purpose of moving the punch along the actuator, internally there is a clamping link that allows the punch to be held by means of a magnet, this link is what moves the servomotor, so the punch is free at all times. When the tapping process begins, the servomotor lowers the magnetized link, adhering to the punch. The servomotor then raises the punch to a predetermined distance. Internally, the actuator has a cylindrical cavity where the punch moves. In the position where the punch should be released, there are stops that prevent the punch from rising further. However, the magnetic link is smaller, so it can pass through them. This is how the magnetic force holding the punch is broken, and due to gravity, it tends to fall in free fall. To prevent the punch from remaining attached to the disc after hitting it, the punch is cushioned in its final stage by a spring. Due to the force with which the punch falls, it manages to contract the spring and hit the disc.Due to Newton's third law, the force with which the punch was struck is responsible for moving it upwards again, once there the spring prevents it from producing a second blow (figure 3). The actuator base itself attaches to the air microphone, allowing it to capture the sound emitted by the disc up close. Example 3. Contact microphone Unlike the air microphone, this one must make contact with the disc, so strictly speaking an extra mass with different characteristics is added to the disc, to prevent the microphone from affecting the result of the disc, it has a fastening system which allows the microphone to adhere to the disc by means of a magnet, so the microphone vibrates at the same frequency as the disc, because the mass of the disc is constant throughout the test, this is taken as a constant of the experiment, so it can be neglected in the results.On the other hand, the contact microphone must be very close to the tapping point and always at the same distance, for this to be possible the actuator base has a microphone relocation system, comprised of two cam-shaped channels, that is, one end narrower than the other, the contact microphone base has two screws on its upper surface, in turn these screws enter the channels in such a way that when the disc begins to rotate the narrowest part of the channels serves as a guide, orienting the microphone in a specific position, once this is achieved the disc rotates 5º in the opposite direction, thus the disc moves again with the microphone; however, this is free from the guide base and the actuator because now the screws are in the widest part of the channel leaving them completely free. Example 4. Mechanical filtration and stabilizer system When the record is struck, the sound travels normally to the line of action, causing the entire surface of the record to vibrate. However, the goal is to capture only the sound from the area being analyzed. To achieve this, a sound filtering system was developed using a circular plate with a larger surface area than the record itself, lined with acoustic foam. This plate has a single cutout with the same area being analyzed, so the plate absorbs the sound from the rest of the record. Furthermore, the disc begins to vibrate from the first impact, so there's no certainty that the next analysis has stopped, which can lead to erroneous results. To prevent this, once the first analysis is complete, the system moves the mechanical filter downward, pressing it against the disc until it stabilizes. Once it stabilizes, it moves back up and releases the disc, allowing the next analysis to begin. Example 5. Universal base for disk inspection Because brake discs vary in size depending on the car model, a system was developed that can be easily adapted. This work surface incorporates all the subsystems described above. The disc clamping system is incorporated into a rotating mechanical system, which, using bevel gears and a controlled motor, can rotate the disc precisely every 30°, allowing us to analyze all 12 sectors of the disc or a specific sector. The mechanical filtering and stabilization system is assembled to a base that can be easily adjusted to the disc via channels to which it is bolted, allowing it to be raised or lowered. The tapping system is bolted to this same base, allowing its height and the distance from the disc radius where it will strike to be calibrated. Inside the base there is a section specifically for the electronics necessary for the system to operate, such as the power supply system, the preamplification system, and the data acquisition and control system. Example? Data acquisition and control system The device features a microcontroller to rotate the brake disc in a controlled manner and also controls the movement of the mechanical filtering system. This microcontroller is also responsible for digitizing the sound captured by the microphones. Once this task is completed, the data is sent via USB to a computer for the appropriate mathematical processing. Example 8. Operating Mode For each test, two microphones are used, one contact and one air, each obtaining 11,000 samples per sector with a sampling time of 10 microseconds, that is, the sound of the discs is captured for a time of 110 ms. The contact microphone is fixed to the disc by means of a magnetic base and is completely isolated from the machine, to avoid any type of affectation inherent to it, so strictly speaking an additional mass of the contact microphone is added to the mass of the disc, which possibly causes a slight change in its real spectrum, however this affectation is present throughout the analysis so it is taken as a constant inherent to the experiment and does not affect the final results. The air microphone is attached to the base of the actuator and very close to the disk impact site. There is a small phase shift between both microphones of approximately 15°, due to the geometry of the actuator and the base of the contact microphone. A graphical interface allows you to control the device from your computer, allowing you to home the machine, ensuring that the disk analysis will always be consistent. The interface allows you to manually calibrate the disk position using two adjustments: quick and fine, allowing you to choose a precise base point from which to begin the analysis. It is possible to access a specific part of the disk, that is, to analyze a specific sector of the disk through the interface. Since the machine is designed to analyze any disc model, the interface has a section to calibrate the height at which the stabilizing filter and the tapping system will be located. This way, the energy supplied to the disc will always be the same, regardless of the disc model or the number of tests performed. Example 9. Analysis The equipment features three different sound processing studios, allowing the disc to study different characteristics and obtain a complete characterization: power spectrum or power spectral density, frequency spectrum using the fast Fourier transform, and total harmonic distortion (THD) analysis. The studies are performed by dividing the disc into 12 sectors, rotating the disc 30°, and striking the surface of the disc with each rotation to uniformly characterize the entire surface. Power spectrum • The average of the 12 curves of each sector is obtained, obtaining a single curve per disk and working with this. • The 12 curves on used discs show greater differences between them in amplitude and frequency than on new discs (figure 5). • In all 12 curves, there is a tendency towards the same frequencies in new discs (figure 5). • The amplitudes of the curves at low frequencies are greater compared to the amplitudes at high frequencies and decrease linearly in new discs (Figure 6). • In used discs, there is no linearity at frequencies above 2kHz, the amplitudes are constant and if they vary, these changes are drastic (figure 7). • When comparing the curves of the used discs with the new ones, there is an evident shift and this phase shift increases as the frequencies are higher (figure 8). Frequency spectrum • An average of the curves of the 12 sectors of the disk is taken and worked with. • Just like the study of the power spectrum, the disks in good condition present their 12 curves very similar to each other (figure 9). • If the disc does not show a linear decrease in its frequency peaks as the frequency increases, it is probably in poor condition (figure 10). • The more damaged the disc is, the greater the shift towards low frequencies (figure 11). Total Harmonic Distortion Analysis • The THD is calculated for each sector, i.e., 12 per disk. Only the fundamental frequency, its amplitude, and the percentage of THD are recorded for each sector. This data is stored in three different vectors, which describe the curves of the fundamental frequency, amplitude, and percentage of THD of the disk, and these are the ones analyzed. • By comparing the 3 fundamental curves of each disc it is very easy to find the disc in poor condition (figure 12). • The more damaged the disk is, the greater the variations in amplitudes and fundamental frequencies between each sector. • There is a tendency for the fundamental amplitudes of used discs to be greater than those of new ones. Conclusions • With the necessary experience, studying the frequency spectrum could give us more detailed information about the state of the disc, such as roughness or thickness, and would help us make decisions regarding rectification or replacement. • Depending on the damage to the disc, the microphone to be used would be chosen. For example, if the disc has serious roughness problems on its surface, an air microphone is recommended; however, if working in noisy conditions, a contact microphone is recommended. • For a complete treatment, both microphones are required. • In the analysis of the frequency spectrum, higher amplitude frequencies were found for a disk in poor condition. These fault frequencies could give us specific information about the type of damage the disk has: fracture, thickness, roughness, etc. • The prototype provides highly accurate information in a short period of time, making it ideal for implementation in automotive centers. • Due to the versatility of the technology, the machine can be used at different stages of brake disc manufacturing, meaning it can be implemented in the quality control area or at an early stage of inspection of the disc already in use. • Because it is a non-destructive technique, a disc can be inspected as many times as necessary, so the disc can be inspected throughout its useful life.

Claims

1. A sonic detector for checking automotive brake discs, characterized in that it comprises: i) a base for supporting a mechanical filter and a tapping system, ii) calibrators for height adjustment, iii) a brake disc fixing and rotation system, iv) a cam mechanism for moving the filtering system, v) a tapping system, vi) an electronic control unit, vii) a mechanical disc rotation system, viii) a graduated analysis surface in 12 sectors, ix) a mechanical filtering and stabilizing system, and x) a universal base support.

2. The detector according to claim 1, characterized in that the brake disc fixing and rotation system comprises: i) an upper coupling base, ii) an adjustment nut for both bases, iii) a brake disc, iv) a lower coupling base, v) an adjustment screw, and vi) a rotating base.

3. The detector according to claim 1, characterized in that the tapping system comprises: i) an actuator clamping and adjusting element, i) a punch displacement magnetic base, iii) a wedge-shaped air microphone base, iv) an air microphone, v) an actuator body, vi) an actuator seal, vii) a cam system for punch movement, viii) a servo motor, ix) a positioning unit for contact microphone, x) a contact microphone, and xi) a punch.

Images