A real-time monitoring method for tire vertical load using strain calculation and tire with real-time load monitoring

Abstract

The present invention provides a method for real-time monitoring of vertical load of a tire by calculating strain and a tire for real-time load monitoring, comprising: step 11) installing a uniaxial acceleration sensor provided with a strain gauge on the side wall of the tire; when the sensor is installed, the direction of the uniaxial acceleration is circumferential acceleration; when the tire starts to roll, the uniaxial acceleration sensor performs sampling; step 12) when a sensor of the tire enters a tire contact footprint area by calculating the tire rotation speed, the uniaxial acceleration of the sensor has a negative value in the first half of the sampling cycle, and when the absolute value obtained in the sampling cycle is greater than a set threshold, the sensor starts sampling to obtain the strain resistance value of a specified area on the side of the tire; step 13) each time the strain resistance value obtained by sampling is compared with the previous value, and the maximum strain resistance value obtained in the sampling interval is used as the transmission data and sent to a vehicle terminal; step 14) the vehicle terminal obtains the data sent by the sensor, and obtains the vehicle load by estimating through a load correspondence table.

Description

Technical Field

[0001] The present invention relates to the field of tire monitoring, and more specifically, to a real-time monitoring method for tire vertical load using strain calculation and a tire with real-time load monitoring. Background Art

[0002] The tire pressure monitoring system can monitor the air pressure and temperature of the tire. A more complete tire condition monitoring system, also known as an intelligent tire system, can achieve more functions by collecting more useful signals. It embeds micro sensors inside the tire to directly monitor various parameters of the tire (tire pressure, tire temperature, vertical load, wear condition, six-component force and tire-road adhesion coefficient) and other information, and provides it to the vehicle's power control system. Real-time acquisition of tire force information is an important research content of intelligent tires and has important significance for automotive mechanical control. The real-time measurement of tire force has always attracted the attention of scholars at home and abroad. However, due to the nonlinearity of the tire system, it is difficult to directly obtain tire force information. Most of the studies derive or estimate tire force indirectly.

[0003] In the prior art, patent CN201410071985.7 discloses a mapping relationship between the vertical load of a tire and tire parameters through bench test calibration, and then obtains the vehicle driving parameters required for the mapping relationship through GPS vehicle speed test equipment, tire pressure monitoring system and ABS wheel speed sensor, thereby obtaining the tire load during vehicle driving.

[0004] However, the existing technology is to place the sensor at the bottom of the tire crown, and use the centrifugal acceleration value at the bottom of the tire crown to estimate the tire contact footprint length, thereby calibrating the tire vertical load. However, the acceleration at the bottom of the tire crown fluctuates too much with the speed of the vehicle (for example, the centrifugal acceleration of a 13R22.5 all-steel tire at a speed of 10 km / h is 15.4 m / s. 2 / s, the centrifugal acceleration is 1250m when the vehicle speed is 90km / h 2 / s, the general acceleration range is about ±200g). In order to improve the measurement accuracy, the load measurement is usually started at a fixed speed (such as 60Km / h). However, the above technical solution has the following technical defects, such as: 1. It is impossible to measure the tire load at low speed or when the vehicle is moving slowly (such as: it is impossible to load the cargo and move the vehicle slowly to monitor the vehicle load); 2. Acceleration sampling must be performed at a high frequency during the tire rolling cycle, which increases battery power consumption. 3. The sensor at the bottom of the tire crown is easily damaged by nails piercing it. Summary of the invention

[0005] The present invention overcomes the shortcomings of the prior art and provides a real-time monitoring method for the vertical load of a tire using strain calculation and a tire with real-time load monitoring.

[0006] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0007] A real-time monitoring method for calculating tire vertical load by using strain comprises the following steps:

[0008] Step 11) installing a uniaxial acceleration sensor provided with a strain gauge on the sidewall of the tire; when the sensor is installed, the uniaxial acceleration direction is circumferential acceleration; when the tire starts rolling, the uniaxial acceleration sensor performs sampling;

[0009] Step 12) When the sensor of the tire enters the tire contact footprint area by calculating the tire speed, the uniaxial acceleration of the sensor has a negative value in the first half of the sampling period, and when the absolute value obtained in the sampling period is greater than a set threshold, the sensor starts sampling to obtain the strain resistance value of the specified area on the side of the tire;

[0010] Step 13) Each time the strain resistance value obtained by sampling is compared with the previous value, the maximum strain resistance value obtained in the sampling interval is used as the transmission data and sent to the vehicle terminal;

[0011] Step 14) The vehicle-mounted terminal obtains the data sent by the sensor and estimates the vehicle load through the load correspondence table.

[0012] Furthermore, the Z-axis acceleration of the sensor is a circumferential acceleration.

[0013] Furthermore, the load correspondence table is obtained through the following steps:

[0014] Step 31) installing the tire with the uniaxial acceleration sensor equipped with the strain gauge on the load calibration equipment and filling it with standard air pressure;

[0015] Step 32) loading the tire to the maximum load, starting the sensor internal calibration program through the excitation device, and slowly rolling the tire to allow the sensor to find the maximum tire strain, that is, the maximum sensor strain resistance value;

[0016] Step 33) The tire is stationary, and the load calibration device continuously reduces the load from the maximum load to 0, and then loads from 0 to the maximum load, and the sensor records the strain resistance value change data of the whole process;

[0017] Step 34) The relationship between the strain resistance value change data of the sensor and the load will be automatically uploaded and stored through the load calibration device, so as to obtain a load calibration correspondence table.

[0018] Furthermore, the load correspondence table may be a relationship between strain resistance value and load.

[0019] Furthermore, the uniaxial acceleration sensor is a Z-axis acceleration sensor.

[0020] Furthermore, in step 12), when the tire sensor enters the tire footprint area, the sensor uses a low-speed sampling rate f1 to collect the Z-axis acceleration of the tire rolling direction in real time, and compares it with the set threshold in real time. When the Z-axis acceleration of the sensor has a negative value in the first half of the sampling period, and the absolute value obtained in the first half of the sampling period is greater than the absolute value of the set threshold, the sensor is triggered to perform a high-frequency sampling rate f on the strain resistance value. n , and the strain resistance value is calculated after filtering.

[0021] Furthermore, when the resistance values ​​obtained by three consecutive calculations are gradually decreasing, the sensor stops the high-frequency sampling rate f for the strain resistance value. n .

[0022] Furthermore, the load calibration equipment is automatically uploaded to the cloud, and the cloud combines the sensor resistance value change data with the load relationship to calculate and convert a load correspondence table under different air pressures, temperatures and speeds.

[0023] A tire with real-time load monitoring uses a strain tire vertical load real-time monitoring method to obtain the real-time load.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. The present invention is different from the prior art. The present invention does not calculate and monitor the real-time load by detecting radial centrifugal acceleration. When the vehicle tire is rolling at a low speed (such as when the vehicle is moving after loading the cargo and the cargo weight needs to be known), the acceleration value at the bottom of the tire crown is too small. Since the resolution of the large-scale acceleration is not enough when the acceleration value is small, the load measurement accuracy is affected. Therefore, this patent can well avoid the technical defect of "calculating the real-time tire load by radial centrifugal acceleration" when the vehicle is at a low speed.

[0026] 2. Adopt acceleration sensor chip, based on the absolute value of Z-axis acceleration and the absolute value of the set threshold, in the non-imprint area, the calculation is performed through the tire speed. At this time, the sensor only performs low-frequency sampling on the Z-axis, and can be in a dormant or low-frequency sampling state for collecting the resistance value change of the strain gauge. When entering the ground imprint area, the Z-axis acceleration of the sensor is sampled at a lower frequency. When the sampled Z-axis acceleration value has a negative value in the first half cycle, and the absolute value of the Z-axis acceleration in the first half cycle is greater than the absolute value of the set threshold, the sensor is triggered to perform high-frequency sampling of the strain resistance value. In other words, the sampling of the strain resistance value does not need to be turned on throughout the process. It judges the high-frequency sampling work when needed through the Z-axis acceleration value, which reduces power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the installation direction of an acceleration sensor equipped with a strain gauge;

[0028] Figure 2 It is the strain direction of the strain gauge under the state of tension direction under load;

[0029] Figure 3 Schematic diagram of the changes of the strain gauge before and after loading of the 13R22.5 tire;

[0030] Figure 4 It is a schematic diagram of the change of Z-axis acceleration in the theoretical state during one cycle of the tire;

[0031] Figure 5 This is a schematic diagram of the change in resistance value of the strain gauge during tire rolling;

[0032] Figure 6 The circuit structure diagram of real-time monitoring of tire vertical load for strain calculation.

[0033] Description of the drawings: strain gauge 1 DETAILED DESCRIPTION

[0034] The following specific embodiments further illustrate the present invention.

[0035] For the embodiments of the present invention, the strain gauge is in a reasonable deformation range, which is beneficial to sensor measurement and resolution improvement, and can also avoid damage to the strain gauge due to excessive deformation. Therefore, the placement of tire sensors corresponding to different models should meet the following requirements: 1) the tire strain area meets the measurement accuracy, and the deformation amount is approximately linearly related to the tire load, and 2) the deformation of this area will not cause excessive deformation and damage to the strain gauge when the tire is deflated and rolled.

[0036] In order to further illustrate the technical solution of the present invention, the embodiments all take a 13R22.5 tire as a tire example.

[0037] Embodiment 1:

[0038] like Figure 6 As shown, the strain gauge sensor includes: a resistive strain gauge, a measuring bridge, an operational amplifier, an MCU, a uniaxial acceleration sensor (Z axis), a tire temperature and pressure sensor, and a battery power supply. The resistive strain gauge is connected to the measuring bridge, and the resistance value change of the strain gauge is detected by the measuring bridge. The measuring bridge is connected to the operational amplifier and then connected to the MCU. The uniaxial acceleration sensor (Z axis), the battery power supply, and the tire temperature and pressure sensor are respectively connected to the MCU and controlled by it. The MCU communicates wirelessly with the wireless vehicle-mounted receiving terminal through the Bluetooth radio frequency module.

[0039] The resistance of the resistive strain gauge changes as the material stretches, stretches or compresses. The measuring bridge converts the resistance change into a weak voltage signal, which is then amplified by an operational amplifier. After being sampled and filtered by the MCU's ADC digital-to-analog conversion, it is converted into a strain resistance value and combined with the current values ​​of the tire temperature and pressure sensors, it is sent to the on-board receiving terminal via Bluetooth.

[0040] Production stage:

[0041] First, the sensor chip is packaged and integrated into the housing, and then the housing is embedded in the rubber sleeve formed by the mold. During the packaging process, the orientation of the acceleration sensor corresponds to the installation orientation on the rubber sleeve. Figure 2 and 3 As shown, the resistive strain gauge uses a strain gauge made of conductive rubber, which is at the bottom of the sensor rubber sleeve. Its surface is firmly adhered to the side of the tire through low-temperature vulcanization technology. During the rolling process of the tire, the material in the tire area stretches and slightly expands and contracts. The two poles of the strain gauge are connected to the measuring bridge. The strain gauge produces resistance changes as the material stretches, stretches or compresses, and the resistance value change of the strain gauge is detected by the measuring bridge.

[0042] In this way, the acceleration sensor assembly for measuring the vertical load of the tire (including components such as battery, Bluetooth, air pressure, temperature and acceleration, circuit board, etc.) has been fully prepared.

[0043] Different from the prior art that sets the acceleration sensor assembly at the bottom of the tire crown, the present invention installs the rubber patch embedded with the acceleration sensor assembly in the corresponding area of ​​the inner side wall of the tire airtight layer. Since the working principle is completely different from the prior art, it does not need to detect the radial acceleration of the tire. Preferably, the corresponding area of ​​the inner side wall of the tire airtight layer can be calculated according to the tire parameters. After finding the corresponding area, the subsequent specific installation method can be, for example, installed by a robot. After cleaning, polishing, applying a vulcanizer, heating, pressing, applying sealant and information binding processes, the sensor and the tire are firmly adhered, see patent A system for automatically bonding TPMS sensors inside a tire CN201911088548.

[0044] like Figure 1 As shown in the figure, during the pasting process, it is necessary to ensure that the Z-axis acceleration arrow marked on the rubber patch embedded with the velocity sensor assembly points to the sensor installation direction, which is the circumferential acceleration. Figure 3 In the figure, the Z-axis acceleration points in the direction through the paper.

[0045] Secondly, calibrate and obtain the tire load comparison table. Figure 3 As shown, the tire embedded with the uniaxial acceleration sensor equipped with the strain gauge is installed on the load calibration device and filled with the standard air pressure (such as 930 kPa).

[0046] Step 1: First, load the tire with the maximum load, start the sensor internal calibration process through the excitation device, and slowly roll the tire to make the sensor mounting position of the tire have the maximum deformation (the condition for the sensor to measure the side deformation of the tire is that the mounting position of the sensor must be rolled to the bottom, and the sensor is generally mounted at the light point of the tire dynamic balance. The light point of the tire can be rolled directly to the bottom first, so as to quickly locate it near the maximum deformation point and improve the calibration efficiency). Preferably, in order to improve the accuracy, it is necessary to roll back and forth three times in the maximum deformation area to confirm the maximum point.

[0047] Step 2: The tire is stationary, and the load calibration equipment continuously reduces the load from the maximum load to 0, and then loads from 0 to the maximum load, and repeats the measurement. The sensor records the change data of the strain resistance value during the whole process. The strain resistance value is the smallest when the tire is not loaded, and starts to increase after loading.

[0048] At this point, the relationship between the strain resistance value and load of this model of tire obtains the load calibration correspondence table of the tire, which is automatically uploaded to the tire intelligent system cloud storage through the load calibration equipment. The tire can also realize a tire load calibration work. Preferably, the intelligent system platform will calculate and convert the load correspondence table under different air pressures, temperatures and speeds based on the data. When the tire with real-time load monitoring is used on a certain vehicle, after the user binds the unique ID of the tire, the system sends the load correspondence table of the tire to the vehicle terminal. The load correspondence table includes the influence of factors such as tire temperature, air pressure and speed.

[0049] The angle change measurement principle of the present invention is as follows Figure 2 and Figure 3 As shown, the length of the strain gauge before loading is L0 = 8.2573mm, and after loading is L1 = 8.4119mm (when the tire acceleration sensor rotates to contact the road surface, the radial centrifugal acceleration of the tire in this area is 0; the sensor has a built-in filtering algorithm to remove the influence of ground interference acceleration). When the tire is loaded, the strain gauge set on the tire is strained, resulting in a large change in its resistance value.

[0050] Preferably, after receiving the data from the acceleration sensor, the vehicle-mounted terminal uses the data in combination with a filtering algorithm, a terminal tire load comparison table and tire distribution to estimate the vehicle load.

[0051] Operation phase:

[0052] In the embodiment of the present invention, when the tire rolls, in the non-contact footprint area of ​​the tire, the tire sidewall sensor mounting area is basically not deformed, and the resistance values ​​that are not in the tire contact footprint area due to strain changes are invalid. At this time, detecting the resistance value in this area is also invalid. At this time, the sensor can be in sleep or low-frequency sampling for strain resistance value sampling, thereby saving energy.

[0053] In the operation stage of the embodiment of the present invention, during one rolling cycle of the tire, the sensor only needs to measure the period at the tire contact patch at high frequency. Preferably, the present invention can be achieved by measuring the data of most of the period at the tire contact patch at high frequency according to the change of the strain resistance value, and the sampling frequency can be further increased according to the speed of change of the resistance value, thereby further saving power and improving the load measurement accuracy.

[0054] like Figure 4As shown, the data sampled by the Z-axis acceleration in the sensor of the present invention, i.e., the circumferential acceleration of the tire, has the greatest characteristic that the acceleration suddenly increases greatly when it just contacts the ground, and gradually decreases to 0 as the tire-mounted sensor area further contacts the ground, and then gradually increases in the second half of the cycle in the footprint area. The present invention utilizes the fluctuation of the Z-axis circumferential acceleration as the starting point condition for judging the load measurement. When specific conditions are met, the measurement accuracy is improved by increasing the sampling frequency. When the conditions are not met, the sensor is in dormancy or low sampling frequency for sampling the strain resistance value, thereby saving electric energy. Compared with the published scheme of collecting radial acceleration to calculate tire load measurement, it has the advantage that it does not need to continuously turn on the high-speed acceleration sampling frequency in real time within a measurement cycle, thereby reducing data processing calculations and saving electric energy.

[0055] The specific steps are as follows:

[0056] Step 1: Set the absolute value threshold of Z-axis acceleration |a z |, the |a z | for a z When the tire starts rolling, the time when the tire enters the contact patch area is calculated by the tire speed. At this time, the Z-axis acceleration of the sensor is sampled at a lower sampling rate (for example, the setting of f1 value can be sampled more than 4 times in the contact patch area, for example, lower than 100Hz). The MCU in the sensor collects the Z-axis acceleration in real time, filters it, removes interference, and communicates with the sensor in real time. z |Comparison. When the tire is in the non-contact footprint area, the absolute value of the Z-axis acceleration is less than |a z |At this time, the sensor is in a dormant or low-frequency sampling state for sampling the strain resistance value to save power.

[0057] When entering the tire footprint area, the sensor samples the Z-axis acceleration at a lower sampling rate f1.

[0058] Step 2: When the tire enters the contact patch area, the Z-axis acceleration value obtained by sampling has a negative value in the first half of the sampling cycle. If f1 is set to sample 4 times in the contact patch area, the Z-axis acceleration value obtained in the first or second sampling is a negative value, and in the first half of the sampling cycle, when the absolute value of the Z-axis acceleration value is greater than |a z |When the sensor is triggered to sample the strain resistance value at a high-frequency sampling frequency fh, for example, a frequency of 3000 Hz or higher, the resistance value is calculated after filtering and removing interference data.

[0059] Preferably, when the Z-axis acceleration value is judged to be negative, the purpose is to further judge that the tire is just in the contact footprint area. Therefore, no matter how the sampling rate f1 of the Z-axis acceleration value is set, only the first two times are needed for the negative value judgment.

[0060] For example, corresponding to Figure 4 or Figure 5 As shown, the Z-axis acceleration is negative, and its absolute value is greater than |a z |, which means the sensor has just touched the ground, between t-1 and t1, and the strain gauge resistance value is valid at this time. Suppose the sampling time of the strain gauge resistance value when the sensor is turned on is t0, and the calculated strain gauge resistance value is

[0061] Step 3: Compare the strain resistance values. Figure 5 As shown, when the tire sensor first enters the tire contact footprint area, the strain resistance value gradually increases. When the area has rotated over half of the tire footprint area, the strain resistance value begins to decrease. The strain resistance value should satisfy the process of gradually increasing and then decreasing.

[0062] After each data collection, it is compared with the previous sampled data until the strain resistance value begins to decrease. The resistance value stored in the maximum strain gauge is used as Bluetooth transmission data and sent to the vehicle terminal. At this time, sampling is stopped, and the threshold for stopping sampling is determined by the strain resistance value, so that the sensor does not need to sample the resistance value of the strain gauge in the entire tire contact footprint area, further shortening the working time and saving electricity. However, the technical effect of the present invention can also be achieved by judging whether the Z-axis acceleration value is positive as the basis for judging whether the sensor is off the ground.

[0063] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the concept of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A real-time monitoring method for calculating tire vertical load using strain, characterized in that: The method comprises the following steps: Step 11) installing a uniaxial acceleration sensor provided with a strain gauge on the side wall of the tire; when the sensor is installed, the uniaxial acceleration direction is circumferential acceleration; when the tire starts rolling, the uniaxial acceleration sensor performs sampling; Step 12) When the sensor of the tire enters the tire contact footprint area by calculating the tire speed, the uniaxial acceleration of the sensor has a negative value in the first half of the sampling period, and when the absolute value obtained in the sampling period is greater than a set threshold, the sensor starts sampling to obtain the strain resistance value of the specified area on the side of the tire; Step 13) Each time the strain resistance value obtained by sampling is compared with the previous value, the maximum strain resistance value obtained in the sampling interval is used as the transmission data and sent to the vehicle terminal; Step 14) The vehicle terminal obtains the data sent by the sensor and estimates the vehicle load through the load correspondence table; the Z-axis acceleration of the sensor is the circumferential acceleration; In step 12), when the tire sensor enters the tire footprint area, the sensor uses a low-speed sampling rate f1 to collect the Z-axis acceleration of the tire rolling direction in real time, and compares it with the set threshold in real time. When the Z-axis acceleration of the sensor has a negative value in the first half of the sampling period, and the absolute value obtained in the first half of the sampling period is greater than the absolute value of the set threshold, the sensor is triggered to perform a high-frequency sampling rate f1 on the strain resistance value. n , and the strain resistance value is calculated after filtering.

2. The real-time monitoring method for calculating tire vertical load by using strain according to claim 1, characterized in that: The load correspondence table is obtained by the following steps: Step 31) installing the tire with the uniaxial acceleration sensor equipped with the strain gauge on the load calibration equipment and filling it with standard air pressure; Step 32) loading the tire to the maximum load, starting the sensor internal calibration program through the excitation device, and slowly rolling the tire to allow the sensor to find the maximum tire strain, that is, the maximum sensor strain resistance value; Step 33) The tire is stationary, and the load calibration device continuously reduces the load from the maximum load to 0 load, and then loads from 0 load to the maximum load, and the sensor records the strain resistance value change data of the whole process; Step 34) The relationship between the strain resistance value change data of the sensor and the load will be automatically uploaded and stored through the load calibration device, so as to obtain a load calibration correspondence table.

3. A real-time monitoring method for calculating tire vertical load by using strain according to claim 1 or 2, characterized in that: The load correspondence table is the relationship between resistance value and load.

4. The real-time monitoring method for calculating tire vertical load by using strain according to claim 1, characterized in that: When the resistance values ​​obtained by three consecutive calculations are gradually decreasing, the sensor stops sampling the strain resistance value at a high frequency rate f. n .

5. A tire with real-time load monitoring, characterized in that: The real-time load is obtained by using the real-time monitoring method for calculating the vertical load of a tire by using strain as described in any one of claims 1 to 4.

Images