Physical quantity detection device

Abstract

Provided is a physical quantity detection device capable of measuring tire air pressure without using sensor components other than a strain sensor, and detecting load and wear from a strain signal corrected from the tire air pressure information. The physical quantity detection device according to the present invention detects the tire air pressure on the basis of the reference level of the signal waveform of the strain sensor, and detects the load and wear of the tire from the strain signal corrected on the basis of the tire air pressure. The physical quantity detection device according to the present invention retains reference values stored in a storage unit as a table, and detects each physical quantity by comparing with the reference values.

Description

[Technical Field]

[0001] The present invention relates to a physical quantity detection device that detects a physical quantity acting on a tire. [Background technology]

[0002] In recent years, in order to realize autonomous driving, there has been active development of tire sensor technology that detects factors such as road surface slipperiness and tire load based on information obtained from tires to provide safer driving conditions. Providing safer driving conditions will prevent tire problems such as bursts due to overloading and vehicle overturns due to load imbalance. In order to build such a safety control system, it is necessary to accurately detect physical quantities such as the load acting on the tires and air pressure.

[0003] Tire strain sensors can detect tire deformation and strain to detect the load acting on the tire and tire wear. This is expected to prevent vehicle trouble and improve driving safety by detecting driving and road surface conditions.

[0004] A strain sensor detects changes in various physical quantities (e.g., vehicle speed, temperature, air pressure, load, etc.) as strain. Therefore, the detection signal (strain signal) that represents the results of strain detected by the strain sensor may contain components caused by these physical quantities. When detecting a specific physical quantity based on the correspondence between the specific physical quantity and the strain signal, the accuracy of detecting the specific physical quantity decreases due to the components caused by these other physical quantities.

[0005] The following Patent Document 1 describes technology related to strain sensors. The document aims to "provide a method and system capable of estimating the load applied to a vehicle tire," and describes the following technology (see Abstract): "A system and method for estimating the load applied to a vehicle tire includes an air pressure measurement sensor attached to the tire for measuring the air pressure level in the tire cavity, and one or more piezo film deformation measurement sensors attached to the tire sidewall. The deformation measurement sensor generates a deformation signal at the tire footprint having a signal power level indicative of the deformation level of the sidewall near the footprint contact surface. A signal power vs. load map is generated and stored that associates a predetermined range of load levels with signal power levels, corrected by tire air pressure, so that the load level can be identified from the signal power level after correction by tire air pressure." [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-054978 Summary of the Invention [Problem to be solved by the invention]

[0007] In the technology described in Patent Document 1, the signal power level of the load sensor is corrected using the tire air pressure measured by the air pressure measurement sensor, taking into account that changes in tire air pressure change the signal amplitude of the load sensor. However, the detection signal of the load sensor may also contain components attributable to physical quantities other than air pressure. Furthermore, configuring an air pressure sensor separately increases the number of system components, which may increase product costs and complicate the system. Therefore, it is believed that the technology described in this document has room for improvement in terms of load sensor detection accuracy and product costs.

[0008] In view of the above circumstances, an object of the present invention is to provide a physical quantity detection device that can measure tire pressure without using any sensor components other than a strain sensor, and can detect load and wear from a strain signal corrected from the tire pressure information. [Means for solving the problem]

[0009] A representative aspect of the invention disclosed in the present application can be briefly outlined as follows: That is, a physical quantity detection device of the present invention detects a plurality of physical quantities from a strain sensor installed in a tire, and is characterized in that the physical quantity detection device detects the tire air pressure based on the magnitude of a reference level of a signal waveform output by the strain sensor when the tire is not in contact with the road surface. [Effects of the Invention]

[0010] The physical quantity detection device according to the present invention can detect tire pressure from the magnitude of the reference level of the strain sensor signal waveform, and can detect load and wear from the positive and negative peaks of the signal waveform. In other words, one sensor can detect three physical quantities, reducing the number of sensors required, thereby reducing product costs and achieving high detection accuracy.

[0011] Further features related to the present invention will become apparent from the description of the present specification and the accompanying drawings. In addition, problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a configuration diagram showing a vehicle equipped with a physical quantity detection device according to a first embodiment. [Figure 2] 1 is a cross-sectional view of a main part of a tire of a vehicle equipped with a physical quantity detection device according to a first embodiment. [Figure 3] 1 is a configuration diagram showing a physical quantity detection device according to a first embodiment. [Figure 4]3 is an explanatory diagram showing a sensor signal waveform of a strain sensor according to a rotation state of a tire according to the first embodiment. FIG. [Figure 5] FIG. 3 is a waveform diagram showing a sensor signal waveform of a strain sensor according to the rotation state of a tire according to the first embodiment. [Figure 6] FIG. 3 is an explanatory diagram showing a sensor signal waveform of a strain sensor in one period according to the first embodiment. [Figure 7] 4 is a flowchart for deriving a table of parameters mixed in a sensor signal waveform of the strain sensor according to the first embodiment. [Figure 8] 4 is an explanatory diagram showing a speed correlation table indicating the correlation between speed and the correction amount of the reference level of the sensor signal waveform of the strain sensor according to the first embodiment; FIG. [Figure 9] 4 is an explanatory diagram showing a temperature correlation table indicating the correlation between the temperature and the correction amount of the reference level of the sensor signal waveform of the strain sensor according to the first embodiment; FIG. [Figure 10] 4 is an explanatory diagram showing an air pressure correlation table indicating the correlation between air pressure and the correction amount of the reference level of the sensor signal waveform of the strain sensor according to the first embodiment; FIG. [Figure 11] FIG. 2 is an explanatory diagram showing a table including various tables according to the first embodiment. [Figure 12] 4 is a flowchart for estimating air pressure from a sensor signal waveform of a strain sensor according to the first embodiment. [Figure 13] 10 shows the results of verifying whether the strain sensor according to the first embodiment can estimate air pressure. [Figure 14] FIG. 3 is an explanatory diagram showing a first table of parameters mixed in a sensor signal waveform of the strain sensor according to the first embodiment. [Figure 15] FIG. 10 is a configuration diagram showing a physical quantity detection device according to a second embodiment. [Figure 16] 10 is a flowchart for deriving a table of parameters mixed in a sensor signal waveform of a strain sensor according to the second embodiment. [Figure 17] FIG. 10 is an explanatory diagram showing a table including various tables according to the second embodiment. [Figure 18] 10 is a flowchart for estimating a load from a sensor signal waveform of a strain sensor according to the second embodiment. [Figure 19] 10 shows the results of verifying whether the strain sensor according to the second embodiment can estimate a load. [Figure 20] 10 shows the results of verifying whether the strain sensor according to the third embodiment can estimate air pressure. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all drawings used to explain the embodiments, the same components are generally designated by the same reference numerals, and repeated explanations thereof will be omitted. The present invention should not be interpreted as being limited to the description of the embodiments shown below. Those skilled in the art will readily understand that the specific configuration can be changed within the scope of the idea or intent of the present invention.

[0014] The designations "first," "second," "third," etc. in this specification are used to identify components and do not necessarily limit the number or order. Furthermore, numbers used to identify components are used in different contexts, and numbers used in one context do not necessarily indicate the same configuration in another context. Furthermore, this does not prevent a component identified by a certain number from also serving the function of a component identified by another number.

[0015] In order to facilitate understanding of the invention, the position, size, shape, range, etc. of each component shown in the drawings etc. may not represent the actual position, size, shape, range, etc. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings etc.

[0016] As used herein, elements referred to in the singular are intended to include the plural unless the context clearly indicates otherwise.

[0017] [First embodiment] <Overall vehicle configuration> FIG. 1 is a configuration diagram showing a vehicle 100 equipped with a physical quantity detection device 10 according to a first embodiment. As shown in FIG. 1, the vehicle 100 includes four tires 101, one ECU 102, and one reporting unit 103. The vehicle 100 also includes four temperature sensors 2 and four strain sensors 3. Note that the vehicle 100 is not limited to a four-wheeled vehicle that travels on a road surface 20 (FIG. 4), but may also be a two-wheeled vehicle, a three-wheeled vehicle, or a vehicle with five or more wheels.

[0018] The vehicle 100 travels on a road surface 20 by rotating four tires 101. A person rides in the vehicle 100.

[0019] The tire 101 is in contact with the road surface 20 and receives the load of the vehicle 100. The tire 101 rotates. The tire 101 is a rubber member.

[0020] The ECU 102 is a control unit that controls the vehicle 100. The ECU 102 has an arithmetic processing unit, a storage unit, and an input / output port electrically connected to various sensors, an arithmetic processing unit such as a CPU, a storage unit such as a memory, and the reporting unit 103.

[0021] The reporting unit 103 is a monitor of the car navigation system. The display screen of the reporting unit 103 is switched between a car navigation screen and a report screen of tire pressure, etc., by interrupt processing from the ECU 102. The display of the display screen of the reporting unit 103 is controlled based on the control of the ECU 102.

[0022] The temperature sensor 2 acquires the temperature of each tire 101 and outputs it to the ECU 102 .

[0023] The strain sensor 3, which is a sensor element, acquires a sensor signal waveform 15 (see FIG. 4, etc.) in each tire 101 and outputs it to the ECU 102. Note that the strain sensor 3 can also detect the temperature of each tire 101 instead of the temperature sensor 2.

[0024] FIG. 2 is a cross-sectional view of a main part of a tire 101 of a vehicle 100 equipped with the physical quantity detection device 10 according to the first embodiment. As shown in FIG. 2, the tire 101 mainly includes a sidewall portion 111 and a tread portion 112. Grooves (also referred to as tire grooves) 113 are formed on the surface (tread surface) of the tread portion 112. The strain sensor 3 is installed on the inner surface of the tread surface of each tire 101, particularly on the inner surface of the tire directly below the grooves 113 on the tread surface. Installed in this manner, the detection sensitivity of the sensor is improved. The strain sensor 3 detects displacement in the rotational direction or cross-sectional direction (direction of rotation axis) of the tire 101, that is, in the cross-sectional direction, a decrease in the curvature of the inner tread surface as the air pressure increases (conversely, an increase in the curvature of the inner tread surface as the air pressure decreases), and horizontal (rotational) elongation of the tread surface. In other words, the strain sensor 3 acquires the sensor signal waveform 15 from the magnitude of the radius of curvature of the inner surface of the tire tread (FIG. 2) and the magnitude of the horizontal (rotational) extension of the tire tread.

[0025] <Physical quantity detection device 10> 3 is a configuration diagram showing a physical quantity detection device 10 according to the first embodiment. The physical quantity detection device 10 relates to a safe driving support device for a vehicle 100, and in particular, is intended to prevent accidents caused by insufficient brake control by providing a safe driving state. The physical quantity detection device 10 is a device that detects the air pressure and other factors that affect the durability and grip of tires 101 mounted on the vehicle 100.

[0026] 3, the physical quantity detection device 10 includes a strain sensor 3, an air pressure estimation unit 4, and a reporting unit 103. The physical quantity detection device 10 detects the air pressure of a tire 101 based on the output signal waveform.

[0027] <Strain sensor 3> The strain sensor 3 is a sensor element. The strain sensor 3 is a semiconductor, and converts a change in resistance into a strain amount and outputs the converted amount. One strain sensor 3 is disposed in each tire 101. The strain sensor 3 outputs a sensor signal waveform 15 having a reference level 151, a positive level that changes to the positive side of the reference level 151, and a negative level that changes to the negative side of the reference level 151 (see FIG. 4, etc.).

[0028] <Air pressure estimation section 4> The air pressure estimating unit 4 performs the function of the air pressure estimating unit 4 by executing a program in the ECU 102. The air pressure estimating unit 4 receives the sensor signal waveform 15 output by the strain sensor 3.

[0029] The air pressure estimation unit 4 acquires the temperature of the tire 101 from the temperature sensor 2. The air pressure estimation unit 4 acquires the speed by subtracting the tire circumference from the output period of the sensor signal waveform 15. The air pressure estimation unit 4 may also acquire the speed from a speed sensor or the like. The air pressure estimation unit 4 corrects the sensor signal waveform 15 output by the strain sensor 3 according to the acquired parameter conditions such as temperature and speed, and estimates the air pressure and the like from the difference between this corrected signal and a reference waveform (reference value) stored in the memory unit 411. The air pressure estimation unit 4 transmits the estimated air pressure and the like to the reporting unit 103.

[0030] The tire pressure estimation unit 4 includes a storage unit 411 , a signal waveform correction unit 412 , and a determination unit 413 .

[0031] The storage unit 411 has a first table 5 containing reference waveforms (peak values ​​of positive level, peak values ​​of negative level, reference levels) acquired under reference conditions (air pressure, temperature, speed) of the sensor signal waveform 15 output by the strain sensor 3, and the amount of change for each parameter condition. The acquired data is, for example, data on an asphalt road surface.

[0032] The signal waveform correction unit 412 corrects the air pressure, speed, and temperature, which are parameters of the mixed signal mixed in the sensor signal waveform 15, from the values ​​of the first table 5 stored in the memory unit 411 to a signal waveform under specified conditions so as to cancel the difference from the reference conditions, and transmits the corrected signal waveform to the judgment unit 413.

[0033] The determination unit 413 compares the corrected positive level peak value 152, negative level peak value 153, and reference level 151 sent by the signal waveform correction unit 412 with the correlation characteristics for each parameter condition stored in the first table 5 stored in the storage unit 411, and determines the air pressure amount from the characteristic difference from the reference level 151. The determination unit 413 sends the estimated air pressure amount to the reporting unit 103.

[0034] <Sensor signal waveform 15> 4 is an explanatory diagram showing a sensor signal waveform 15 of the strain sensor 3 according to the rotation state of the tire 101 according to the first embodiment. As shown in FIG. 4, the strain sensor 3 disposed inside the tire 101 outputs a sensor signal waveform 15 that changes depending on the state of the rotating tire 101.

[0035] The strain sensor 3 outputs a sensor signal waveform 15 having a reference level 151, a positive level that changes to the positive side of the reference level 151, and a negative level that changes to the negative side of the reference level 151.

[0036] The strain sensor 3 maintains the reference level 151 of the sensor signal waveform 15 when the tire 101 is not in contact with the road surface 20. The strain sensor 3 outputs a positive level peak value 152 of the sensor signal waveform 15 when the tire 101 (the portion of the tire where the strain sensor 3 is installed) is in contact with the road surface 20. The strain sensor 3 outputs a negative level peak value 153 of the sensor signal waveform 15 at the moment when the tire 101 (the portion of the tire where the strain sensor 3 is installed) touches or separates from the road surface 20. Here, the moment when the tire 101 touches or separates from the road surface 20 is the sensor displacement point. The period between two sensor displacement points is a contact period when the tire 101 (the portion of the tire where the strain sensor 3 is installed) is in contact with the road surface 20.

[0037] The sensor signal waveform 15 thus detected varies depending on various physical quantities (load, air pressure, speed, temperature).

[0038] FIG. 5 is a waveform diagram showing the sensor signal waveform 15 of the strain sensor 3 according to the rotation state of the tire 101 according to the first embodiment. As shown in FIG. 5, as the tire 101 rotates, the sensor signal waveform 15 of the strain sensor 3 alternates between a reference level 151, a negative level that changes to a negative side relative to the reference level 151, a positive level that changes to a positive side relative to the reference level 151, and a negative level that changes to a negative side relative to the reference level 151. The signal value of the sensor signal waveform 15 can be expressed by signal amplitude. In FIGS. 4 and 5, the sensor signal waveform 15 is also expressed by signal amplitude. The signal amplitude here may be any value that represents the amplitude of the sensor signal waveform 15. The sensor signal waveform 15 has a waveform in which a falling waveform is successively formed before and after a rising waveform, as shown in FIG. 6. For example, the amplitude of the second falling waveform can be treated as the amplitude of the sensor signal waveform 15. This is assumed below.

[0039] Fig. 6 is an explanatory diagram showing a sensor signal waveform 15 of the strain sensor 3 in one cycle according to the first embodiment. Fig. 6 is an enlarged view of part A in Fig. 5. As shown in Fig. 6, both the positive level peak value (hereinafter sometimes referred to as the positive peak value) 152 and the negative level peak value (hereinafter sometimes referred to as the negative peak value) 153 contain information about the road surface type.

[0040] <How to create Table 15> FIG. 7 is a flowchart for deriving the first table 5 that stores the correlation between the sensor signal waveform 15 of the strain sensor 3 according to the first embodiment and the reference level under each condition including the reference condition.

[0041] 7, in S101, a predetermined control unit (not shown) for table creation testing runs the vehicle 100 while maintaining the reference air pressure, temperature, and speed, and acquires the output of the strain sensor 3 for the reference conditions. In air pressure detection, attention is paid to the reference level of this waveform.

[0042] In S102, the control unit obtains a relationship that indicates the change in sensor signal waveform 15 of strain sensor 3 from the reference waveform when vehicle 100 is driven while changing each of the reference air pressure, temperature, and speed.

[0043] In S103, the control unit stores in the first table 5 the reference waveform and the amount of change thereof for the sensor signal waveform 15 acquired in S102.

[0044] The change in sensor signal waveform 15 when each condition changes does not necessarily have to be expressed using the difference from the reference and the difference from the reference signal value. However, since the absolute value of the signal value differs for each vehicle model and tire type, it becomes necessary to create data similar to first table 5 for each absolute value in advance, which would significantly increase the amount of data. Therefore, by describing the data using the difference from the reference value, the amount of data is reduced.

[0045] The correlations between the reference level 151 of the sensor signal waveform 15 of the strain sensor 3 and the air pressure, temperature, and speed were stored in advance as a table in the storage unit 411 by varying these values.

[0046] 8 is an explanatory diagram showing a speed correlation table of the first table 5 indicating the correlation between the speed and the correction amount of the reference level 151 of the sensor signal waveform 15 of the strain sensor 3 according to the first embodiment. The table shown in FIG. 8 shows a correlation in which the correction amount of the reference level 151 of the sensor signal waveform 15 increases as the speed increases.

[0047] 9 is an explanatory diagram showing a temperature correlation table of the first table 5 indicating the correlation between the temperature and the correction amount of the reference level 151 of the sensor signal waveform 15 of the strain sensor 3 according to the first embodiment. The table shown in FIG. 9 shows a correlation in which the correction amount of the reference level 151 of the sensor signal waveform 15 increases as the temperature increases.

[0048] 10 is an explanatory diagram showing the air pressure correlation table of the first table 5, which shows the correlation between the air pressure and the correction amount of the reference level 151 of the sensor signal waveform 15 of the strain sensor 3 according to the first embodiment. The table shown in FIG. 10 shows a correlation in which the correction amount of the reference level 151 of the sensor signal waveform 15 decreases as the air pressure increases.

[0049] Fig. 11 is an explanatory diagram showing the first table 5 including various tables according to the first embodiment. As shown in Fig. 11, the first table 5 includes the reference table of the first embodiment and the various correlation tables of Figs. 8 to 10. Therefore, the correction amount is estimated from the first table 5 stored in the storage unit 411 for the reference level 151 of the sensor signal waveform 15 output by the strain sensor 3 in the vehicle 100 while it is running in various ways.

[0050] <Air pressure detection method> FIG. 12 is a flowchart for estimating the air pressure at which the tire 101 runs from the sensor signal waveform 15 of the strain sensor 3 according to the first embodiment.

[0051] The flowchart of the tire pressure detection method shown in FIG. 12 is repeatedly executed at certain intervals while the vehicle 100 is running.

[0052] When the tire pressure detection method is performed, in S201, the tire pressure estimation unit 4 checks the driving conditions in the signal waveform correction unit 412 while the vehicle 100 is running. The driving conditions are conditions that match the driving conditions when deriving the first table 5. Once the driving conditions are checked in S201 by the signal waveform correction unit 412, the process proceeds to S202.

[0053] In S202, in order to correct the sensor signal waveform 15 output by the strain sensor 3 to a signal waveform under the same reference conditions as the reference waveform, the tire pressure estimation unit 4 extracts a correction value that matches the conditions stored in the memory unit 411 and subtracts it from the sensor signal waveform 15 to obtain a corrected signal waveform. After processing S202, the process proceeds to S203.

[0054] In S203, the air pressure estimation unit 4 compares the reference level of the reference waveform with the reference level 151 of the corrected signal waveform obtained by correcting the sensor signal waveform 15 detected by the strain sensor 3. After the process of S203, the process proceeds to S204.

[0055] In S204, the air pressure estimation unit 4 determines the air pressure based on the result of comparing the reference waveform with the corrected signal waveform obtained by correcting the sensor signal waveform 15 output by the strain sensor 3 detected in S203. First, the comparison with the reference level 151 is performed, for example, five times, and the difference from the average value is calculated. Next, the difference between the five averages is compared with the first table 5, and the air pressure corresponding to the difference is estimated. In this way, the air pressure estimation unit 4 corrects the magnitude of the reference level 151 of the sensor signal waveform 15 output by the strain sensor 3 when the tire 101 is not in contact with the road surface 20 (changing it according to the reference level 151) for the temperature and vehicle speed of the tire 101, and estimates (detects) the tire air pressure from the corrected value. The air pressure estimation unit 4 also holds the reference waveform (reference value) saved in the memory unit 411 as the first table 5, and estimates (detects) the tire air pressure by comparing it with this reference waveform (reference value). The estimated air pressure is transmitted to the reporting unit 103. After the process of S204, the process ends for the time being.

[0056] <Verification of tire pressure detection method> 13 shows the results of verifying whether air pressure can be estimated according to the flowchart of FIG. 12 based on an example of an actual sensor signal waveform of the strain sensor 3 according to the first embodiment. FIG. 13 shows the air pressure sensitivity of the reference level 151 in the sensor signal waveform 15 of the strain sensor 3 for the reference conditions (temperature, speed). As the air pressure increases, the reference level 151 decreases linearly (monotonically decreases), and it can be seen that it is possible to construct the first table 5 shown in the flowchart. Note that FIG. 13 shows the case where the reference level 151 decreases linearly (monotonically decreases) with respect to the air pressure, but the same applies when the reference level 151 increases linearly (monotonically increases) with respect to the air pressure.

[0057] FIG. 14 is an explanatory diagram showing a first table 5 of parameters mixed in the sensor signal waveform 15 of the strain sensor 3 according to the first embodiment. As shown in FIG. 14, the first table 5 is a proportional graph of correlation in which the same correction amount is obtained regardless of changes in air pressure with respect to the sensor signal waveform 15. This is because temperature and speed are insensitive to air pressure and show constant values. The first table 5 is stored in the memory unit 411. The first table 5 is derived by subtracting the correction amounts of various physical quantities, which are mixed together in the speed correction and temperature correction lines, from the reference level 151 line of the apparent sensor signal waveform 15 to obtain the line of the actually desired air pressure.

[0058] <Effects> As described above, the sensor signal waveform 15 output by the strain sensor 3 is corrected according to the parameter conditions such as temperature and speed, and the air pressure is estimated according to the difference between this corrected signal and the reference waveform (reference value) stored in the memory unit 411, thereby enabling the strain sensor 3 to detect the air pressure.

[0059] [Second embodiment] The following describes an embodiment that is a modification of the above embodiment. In addition to detecting tire pressure as in the first embodiment, the following describes a device that corrects distorted waveforms from tire pressure information to detect load and wear. Furthermore, because the overall vehicle configuration is the same as in the first embodiment, a description of that configuration will be omitted.

[0060] <Physical Quantity Detection Device 2010> 15 is a configuration diagram showing a physical quantity detection device 2010 according to the second embodiment. The physical quantity detection device 2010 relates to a safe driving support device for the vehicle 100, and in particular, is intended to prevent accidents caused by insufficient brake control by providing a safe driving state. The physical quantity detection device 2010 is a device that detects load, wear, and the like that affect the durability and grip of tires 101 mounted on the vehicle 100.

[0061] 15 , the physical quantity detection device 2010 includes a strain sensor 2003, an air pressure estimation unit 2004, a load estimation unit 2104, a wear estimation unit 2204, a storage unit 2411, and a reporting unit 2103. The physical quantity detection device 2010 estimates the load and wear amount acting on the tire 101 based on the air pressure detected based on the output signal waveform, as well as the signal waveform.

[0062] <Air Pressure Estimation Section 2004> The air pressure estimating unit 2004 performs the function of the air pressure estimating unit 2004 by executing a program in the ECU 102. The air pressure estimating unit 2004 receives the sensor signal waveform 15 output by the strain sensor 2003.

[0063] The air pressure estimation unit 2004 acquires the temperature of the tire 101 from the temperature sensor 2002. The air pressure estimation unit 2004 acquires the speed by subtracting the tire circumference from the output period of the sensor signal waveform 15. The air pressure estimation unit 2004 may also acquire the speed from a speed sensor or the like. The air pressure estimation unit 2004 corrects the sensor signal waveform 15 output by the strain sensor 2003 according to the acquired parameter conditions such as temperature and speed, and estimates the air pressure and the like from the difference between this corrected signal and a reference waveform (reference value) stored in the memory unit 2411. The air pressure estimation unit 2004 transmits the estimated air pressure to the reporting unit 2103, the load estimation unit 2104, and the wear estimation unit 2204.

[0064] The tire pressure estimation unit 2004 includes a signal waveform correction unit 2412 and a determination unit 2413 .

[0065] The signal waveform correction unit 2412 corrects the air pressure, speed, and temperature, which are parameters of the mixed signal mixed in the sensor signal waveform 15, from the values ​​of the first table 2005 stored in the memory unit 2411 to a signal waveform under specified conditions so as to cancel the difference from the reference conditions, and transmits the corrected signal waveform to the judgment unit 2413.

[0066] The determination unit 2413 compares the corrected positive level peak value 152, negative level peak value 153, and reference level 151 sent by the signal waveform correction unit 2412 with the correlation characteristics for each parameter condition stored in the first table 2005 stored in the storage unit 2411, and determines the air pressure amount from the characteristic difference from the reference level 151. The determination unit 2413 sends the estimated air pressure amount to the report unit 2103.

[0067] <Storage section 2411> The storage unit 2411 has a first table 2005, a second table 2006, and a third table 2007 for reference waveforms (peak values ​​of positive level, peak values ​​of negative level, reference levels) acquired under reference conditions (air pressure, temperature, speed, load) of the sensor signal waveform 15 output by the strain sensor 2003, as well as the amount of change for each parameter condition. The acquired data is, for example, data on an asphalt road surface.

[0068] <Load Estimation Unit 2104> The configuration of the load estimation unit 2104 is not shown, but is similar to that of the air pressure estimation unit 2004 .

[0069] That is, the load estimation unit 2104 acquires the temperature and speed in the same way as the air pressure estimation unit 2004, and corrects the sensor signal waveform 15 output by the strain sensor 2003 based on the air pressure information obtained by the air pressure estimation unit 2004 in accordance with the acquired temperature, speed, and air pressure parameter conditions, and estimates the load from the difference between this corrected signal and the reference waveform (reference value) stored in the memory unit 2411. The load estimation unit 2104 transmits the estimated load to the reporting unit 2103.

[0070] The load estimation unit 2104, like the air pressure estimation unit 2004, corrects the air pressure, speed, temperature, and load, which are parameters of the mixed signal mixed in the sensor signal waveform 15, from the values ​​of the second table 2006 stored in the memory unit 2411 to the signal waveform under specified conditions so as to cancel the difference from the reference conditions, and determines the load.

[0071] The determination is made by comparing the corrected minus-level peak value 153 with the correlation characteristics for each parameter condition stored in the second table 2006 stored in the storage unit 2411, and determining the weight amount from the characteristic difference with the minus-level peak value 153. After the determination, the estimated weight amount is transmitted to the reporting unit 2103.

[0072] <Wear Estimation Unit 2204> Wear detection is performed by wear estimation unit 2204, but detailed description thereof will be omitted as it operates in the same manner as load estimation unit 2104. The difference is that load detection estimates the load using negative peak value 153, but wear detection uses positive peak value 152, compares corrected positive level peak value 152 with the correlation characteristics for each parameter condition stored in third table 2007 stored in storage unit 2411, and determines the amount of wear from the characteristic difference with positive level peak value 152.

[0073] <How to create the second table 2006> FIG. 16 is a flowchart for deriving a second table 2006 that stores correlations between the sensor signal waveform 15 of the strain sensor 2003 according to the second embodiment and the negative peak value under each condition including the reference condition.

[0074] 16, in S301, a predetermined control unit (not shown) for table creation testing runs vehicle 100 while maintaining reference air pressure, temperature, speed, and load, and acquires the output of strain sensor 2003 for the reference conditions. In load pressure detection, attention is paid to the negative peak value of this waveform.

[0075] In S302, the control unit acquires a relationship representing the change from the reference waveform of the sensor signal waveform 15 of the strain sensor 2003 when the vehicle 100 is driven while changing each of the reference air pressure, temperature, speed, and load.

[0076] In S303, the control unit stores in the second table 2006 the reference waveform and the amount of change thereof for the sensor signal waveform 15 acquired in S302.

[0077] Changes in sensor signal waveform 15 when conditions change do not necessarily have to be represented using the difference from the reference and the difference from the reference signal value. However, because the absolute value of the signal value differs for each vehicle model and tire type, it becomes necessary to create data similar to second table 2006 in advance for each absolute value, which would significantly increase the amount of data. Therefore, by describing the data using the difference from the reference value, the amount of data is reduced.

[0078] The correlations between the negative peak value 153 of the sensor signal waveform 15 of the strain sensor 2003 and the air pressure, temperature, speed, and load are stored in advance as a table in the storage unit 2411 by varying these values.

[0079] Each correlation table in the second table 2006 is the same as that in the first table 5, so a description thereof will be omitted.

[0080] 17 is an explanatory diagram showing a second table 2006 that includes various tables according to the second embodiment. As shown in FIG. 17, the second table 2006 includes tables of various correlations of negative peak values ​​according to the second embodiment. Therefore, the correction amount is estimated from the second table 2006 stored in the storage unit 2411 for the negative peak value 153 of the sensor signal waveform 15 output by the strain sensor 2003 in the vehicle 100 while it is traveling in various ways.

[0081] <Load detection method> FIG. 18 is a flowchart for estimating the load applied to the tire 101 from the sensor signal waveform 15 of the strain sensor 2003 according to the second embodiment.

[0082] The flow chart of the load detection method shown in FIG. 18 is repeatedly executed at a certain period while the vehicle 100 is traveling.

[0083] When the load detection method is performed, in S401, the load estimation unit 2104 checks the driving conditions in the signal waveform correction unit 2412 while the vehicle 100 is in a driving state. The driving conditions are conditions that match the driving conditions when the second table 2006 is derived, such as temperature, speed, and air pressure calculated by the air pressure estimation unit 2004. Once the driving conditions are checked in the signal waveform correction unit 2412 in S401, the process proceeds to S402.

[0084] In S402, in order to correct the sensor signal waveform 15 output by the strain sensor 2003 to a signal waveform under the same reference conditions as the reference waveform, the load estimation unit 2104 extracts a correction value that matches the conditions stored in the storage unit 2411 and subtracts it from the sensor signal waveform 15 to obtain a corrected signal waveform. After the processing of S402, the process proceeds to S403.

[0085] In S403, the load estimation unit 2104 compares the reference level of the reference waveform with the negative peak value 153 of the corrected signal waveform obtained by correcting the sensor signal waveform 15 detected by the strain sensor 2003. After the process of S403, the process proceeds to S404.

[0086] In S404, the load estimation unit 2104 determines the load based on the result of comparing the reference waveform with the corrected signal waveform obtained by correcting the sensor signal waveform 15 output by the strain sensor 2003 detected in S403. First, the load estimation unit 2104 compares the reference waveform with the negative peak value 153, for example, five times, and determines the difference from the average value. Next, the difference between the five average values ​​is compared with the second table 2006, and the load estimation unit 2104 estimates the load corresponding to the difference. In this way, the air pressure estimation unit 2004 estimates (detects) the tire pressure based on the reference level 151 of the sensor signal waveform 15 of the strain sensor 2003, and the load estimation unit 2104 estimates (detects) the tire load from the strain signal corrected by the tire air pressure. The load estimation unit 2104 also holds the reference waveform (reference value) saved in the memory unit 2411 as the second table 2006, and estimates (detects) the tire load by comparing it with this reference waveform (reference value). The estimated load is transmitted to the reporting unit 2103. After the process of S404, the process ends for the time being.

[0087] <Load detection results> Figure 19 shows specific load detection errors. The results show a comparison of load detection errors for a passenger car tire type 225 / 65 / R17 (outer diameter 724 mm) estimated based on air pressure information obtained with a general tire pressure sensor (TPMS) and a strain sensor. The load estimation error was plotted using air pressure as a parameter (1.4-3.0 kg / cm2) under conditions of a vehicle speed of 2.4 m / s and a load of 340 kg per wheel. While the air pressure measurement error of a TPMS is generally around 5%, the load detection error is around ±8%. Meanwhile, although the load detection error estimated based on air pressure obtained with a strain sensor is slightly higher than that of a TPMS, the error is generally within ±8% overall, making it possible to detect loads with high accuracy.

[0088] <Wear detection method> The wear detection method is basically the same as the load detection method except that wear is detected using the positive peak value 152 instead of the negative peak value 153, so a detailed description thereof will be omitted.

[0089] <Effects> As described above, air pressure can be detected from the magnitude of the reference level of the strain sensor's sensor signal waveform, and load and wear can be detected from the positive and negative peak values ​​of the sensor signal waveform. In other words, one sensor can detect three physical quantities, which has the effect of reducing product costs by reducing the number of sensors required.

[0090] [Third embodiment] In the following, a device for detecting physical quantities related to truck tires will be described, in contrast to the device for detecting air pressure, load, and wear related to passenger car tires in the second embodiment. Note that since the overall vehicle configuration is the same as in the first embodiment, a description thereof will be omitted. Furthermore, since the configuration of the physical quantity detection device is the same as in the second embodiment, a description thereof will also be omitted.

[0091] <Verification of tire pressure detection method> FIG. 20 shows the results of a verification of the third embodiment, which verified whether air pressure estimation according to the flowchart of FIG. 12 is possible based on an example of an actual sensor signal waveform of the strain sensor 3 shown in the first embodiment. FIG. 20 shows the air pressure sensitivity of the reference level 151 in the sensor signal waveform 15 of the strain sensor 3 for a truck tire type 205 / 70 / R16 (outer diameter 693 mm) under reference conditions (temperature, speed). FIG. 20 also shows the air pressure sensitivity of the reference level 151 for vehicle speeds of 5 km / h and 20 km / h. It can be seen that the reference level 151 decreases linearly (monotonically decreases) with increasing air pressure, demonstrating the feasibility of constructing the first table 5 shown in the flowchart. While FIG. 20 illustrates a case in which the reference level 151 decreases linearly (monotonically decreases) with increasing air pressure, the same applies when the reference level 151 increases linearly (monotonically increases) with increasing air pressure. It can also be seen that the reference level 151 increases with increasing vehicle speed. That is, it is apparent that there is sensitivity to vehicle speed, and the reference level 151 changes depending on the vehicle speed.

[0092] <Effects> As described above, the air pressure can be detected at the reference level even for truck tires (i.e., even if the vehicle model changes).

[0093] [Summary of the first to third embodiments] As described above, the physical quantity detection device 10, 2010 of this embodiment detects multiple physical quantities from a strain sensor installed in a tire 101, and the physical quantity detection device 10, 2010 detects the air pressure of the tire 101 from the magnitude of the reference level 151 of the signal waveform output by the strain sensor when the tire 101 is not in contact with the road surface 20.

[0094] The strain sensor is installed on the inner surface of the tire immediately below the grooves on the tire tread surface.

[0095] In addition, the physical quantity detection device 10, 2010 corrects (changes according to the reference level 151) the magnitude of the reference level 151 of the signal waveform of the strain sensor for the temperature of the tire 101 and the vehicle speed, and detects the air pressure of the tire 101 from the corrected value.

[0096] Furthermore, the reference level 151 of the signal waveform of the strain sensor monotonically increases or decreases with the air pressure of the tire 101 .

[0097] In addition, the physical quantity detection device 10, 2010 detects the air pressure of the tire 101 from the magnitude of the radius of curvature of the inner surface of the tire tread and the magnitude of the horizontal (rotational) stretch of the tire tread (the magnitude of the reference level 151 of the signal waveform of the strain sensor that detects this).

[0098] Furthermore, the physical quantity detection device 10, 2010 holds the reference values ​​stored in the memory unit 411, 2411 provided in the physical quantity detection device 10, 2010 as a table, and detects the air pressure of the tire 101 by comparing with this reference value.

[0099] In addition, the physical quantity detection device 2010 detects the air pressure of the tire 101 at the reference level 151 of the signal waveform of the strain sensor, and detects the load and wear of the tire 101 from the strain signal corrected by the air pressure of the tire 101.

[0100] The physical quantity detection device 2010 also holds reference values ​​stored in a storage unit 2411 provided in the physical quantity detection device 2010 as a table, and detects the load and wear of the tire 101 by comparing with this reference value.

[0101] That is, one of the ideas of this embodiment (first embodiment) is a physical quantity detection device 10 that detects multiple physical quantities from a strain sensor installed in a tire 101, which includes one strain sensor, a physical quantity calculation unit (air pressure estimation unit 4), and a memory unit, and the physical quantity calculation unit detects the air pressure of the tire 101 from the magnitude of a reference level 151 of the signal waveform output by the strain sensor when the tire 101 is not in contact with the road surface 20.

[0102] Another idea of ​​this embodiment (second embodiment) is that the physical quantity detection device 2010 detects the air pressure of the tire 101 at the reference level 151 of the signal waveform of the strain sensor, and detects the load and wear of the tire 101 from the strain signal corrected by the air pressure of the tire 101.

[0103] In this way, it is possible to estimate the air pressure from the magnitude of the reference level 151 of the strain signal output by the sensor element. In addition, it is possible to estimate the load and the amount of wear from the magnitude of the positive and negative peaks of the strain signal corrected by the air pressure.

[0104] The physical quantity detection device according to this embodiment can detect tire pressure from the magnitude of the reference level of the strain sensor signal waveform, and can also detect load and wear from the positive and negative peaks of the signal waveform. In other words, one sensor can detect three physical quantities, reducing the number of sensors and thereby reducing product costs, while achieving high detection accuracy.

[0105] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with the configuration of another embodiment. [Explanation of symbols]

[0106] 2...Temperature sensor, 3...Distortion sensor, 4...Air pressure estimation unit, 5...First table, 10...Physical quantity detection device, 15...Sensor signal waveform, 100...Vehicle, 101...Tire, 102...ECU, 103...Reporting unit, 151...Reference level, 152...Peak value of positive level, 153...Peak value of negative level, 411...Storage unit, 412...Signal waveform correction unit, 413...Determination unit

Claims

1. In a physical quantity detection device that detects a plurality of physical quantities using a strain sensor installed in a tire, The physical quantity detection device is characterized in that, when the rotation of the tire of a vehicle running on a road surface causes the installation portion of the strain sensor of the tire to not be in contact with the road surface, the physical quantity detection device corrects the magnitude of the reference level of the signal waveform output by the strain sensor for the temperature of the tire and the vehicle speed, and detects the air pressure of the tire from the corrected value.

2. 2. The physical quantity detection device according to claim 1, The physical quantity detection device is characterized in that the strain sensor is installed on the inner surface of the tire immediately below the grooves on the tire tread surface.

3. 2. The physical quantity detection device according to claim 1, A physical quantity detection device, characterized in that the reference level of the signal waveform of the strain sensor monotonically increases or monotonically decreases with respect to the air pressure of the tire.

4. 2. The physical quantity detection device according to claim 1, The physical quantity detection device detects the air pressure of the tire from the radius of curvature of the inner surface of the tire tread and the amount of horizontal extension of the tire tread.

5. 2. The physical quantity detection device according to claim 1, The physical quantity detection device has reference values ​​stored as a table in a memory unit provided in the physical quantity detection device, and detects the tire air pressure by comparing with this reference value.

6. 2. The physical quantity detection device according to claim 1, The physical quantity detection device detects the tire air pressure at a reference level of the signal waveform of the strain sensor, and detects the load and wear of the tire from the strain signal corrected by the tire air pressure.

7. 7. The physical quantity detection device according to claim 6, The physical quantity detection device has reference values ​​stored as a table in a memory unit provided in the physical quantity detection device, and detects the load and wear of the tire by comparing with this reference value.

Images