JP2011080947A - Device, method and program for measuring tire air pressure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of measuring accurately the air pressure of a tire. <P>SOLUTION: An error factor generating an error in measurement of information showing a rotational frequency of a wheel provided on a vehicle is specified, a measurement section for measuring information showing the rotational frequency of the wheel corresponding to the error factor is specified, the information showing the rotational frequency of the wheel is measured in the measurement section, and the information showing the rotational frequency is compared with information showing a reference rotational frequency of the wheel when the vehicle travels in the measurement section in the state where the air pressure of the tire of the wheel is a reference air pressure, to thereby measure the air pressure of the tire. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a tire air pressure measuring apparatus, method, and program for measuring the air pressure of a wheel tire provided in a vehicle.

  Conventionally, the travel distance is measured by a navigation device, the travel distance of each wheel is measured by a wheel speed sensor, and the distance of each wheel is determined from the travel distance measured by the navigation device and the travel distance of each wheel measured by the wheel speed sensor. A technique for detecting tire air pressure is known (see, for example, Patent Document 1). That is, in the technique disclosed in Patent Document 1, the effective radius of each wheel is specified based on the difference between the travel distance measured by the navigation device and the travel distance of each wheel measured by the wheel speed sensor, A decrease in tire air pressure is detected based on the effective radius.

JP 11-295190 A

In the prior art, since the effective radius of each wheel is determined based on the difference between the travel distance measured by the navigation device and the travel distance of each wheel measured by the wheel speed sensor, it is measured by the navigation device. The travel distance is a standard for specifying the effective radius of each wheel. However, when the travel distance is measured by the navigation device, it is necessary to specify the vehicle position information at the measurement start point and the measurement end point, and the travel distance measured by the navigation device is a specific error of the vehicle position information. It can be a value that includes an error under the influence. Therefore, the travel distance measured by the navigation device is not always an accurate reference for determining the effective radius of each wheel. Furthermore, the stability of the measurement results may also vary due to the influence of the shape of the road surface and the behavior of the vehicle when measuring the travel distance of each wheel by the wheel speed sensor. However, the conventional technique does not take into account such errors as described above and fluctuations in the stability of measurement by the wheel speed sensor, so the effective radius of the wheel cannot be determined accurately.
The present invention has been made in view of the above problems, and an object thereof is to provide a technique for accurately measuring tire air pressure.

  In order to achieve the above object, in the present invention, information indicating the rotation speed of the wheel is measured by specifying a measurement section according to an error factor causing an error in measurement of information indicating the rotation speed of the wheel. Then, the tire pressure is determined by comparing the information indicating the measured rotational speed of the wheel with the reference rotational speed of the wheel when the vehicle travels the measurement section in a state where the tire pressure of the wheel is the reference atmospheric pressure. taking measurement. That is, if the error factor is different, the measurement section to be traveled to obtain a sufficient amount of measurement values to be statistically reliable is different, so in the present invention, the wheel rotation is performed in the measurement section corresponding to the error factor. It was set as the structure which measures the information which shows a number, and compares with the reference | standard rotation speed. As a result, it is possible to measure the tire pressure of the wheel based on the measurement result of the rotation speed of the wheel in the measurement section corresponding to the error factor.

  Here, the information indicating the rotational speed of the wheel is information that is substantially equivalent to the rotational speed of the wheel, and is information that can measure the tire air pressure by comparing the information with information indicating the reference rotational speed. I just need it.

  The error factor specifying means only needs to be able to specify an error factor that causes an error in measurement of information indicating the number of rotations of the wheel. In other words, if it is assumed that the rotational speed of the wheel is measured in different scenes by the same measurement sensor, the rotational speed obtained as a measurement result varies if the external situation of the vehicle is different in each scene. The magnitude of the error can also vary depending on. Therefore, if the factor that fluctuates the measurement result of the number of rotations of the wheel is an error factor, the error interval is specified and the measurement interval corresponding to the error factor is specified, so that the measurement interval corresponding to the degree of error is specified. It becomes possible to do. In addition, since the rotation speed of a wheel is measured in a measurement area, an error factor needs to be specified before specifying a measurement area. Therefore, the error factor is a factor that can estimate the possibility of occurrence before the vehicle starts running for measurement, and it can be estimated whether an error occurs even if the road section is not specified. It is a factor. For example, the environment around the vehicle is an example of the error factor.

  The measurement interval specifying means only needs to be able to specify the measurement interval according to the error factor. That is, by specifying the measurement interval corresponding to the error factor, a sufficient amount of measurement values differ statistically for each error factor, so the statistical interval can be determined by specifying the measurement interval according to the error factor. In order to obtain a sufficient amount of measurement values to be reliable, an appropriate measurement interval may be selected.

  The rotational speed information measuring means only needs to be able to measure information indicating the rotational speed of the wheel in the measurement section. That is, what is necessary is just to measure the information which shows the rotation speed of a wheel by acquiring the said signal from the sensor which outputs the signal which shows the rotation speed of a wheel directly or indirectly.

  The air pressure measuring means only needs to be able to measure the air pressure of the tire by comparing information indicating the measured number of rotations of the wheel with information indicating the reference number of rotations of the wheel. That is, the rotation speed of the wheel when traveling in the measurement section in a state where the tire air pressure is the reference atmospheric pressure can be specified in advance, and thus the rotation speed is defined as the reference rotation speed. If the reference rotational speed is compared with the measured wheel rotational speed, the tire air pressure at the time when the wheel rotational speed is measured can be specified by a relative relationship with the reference atmospheric pressure. According to this configuration, it is possible to measure the air pressure based on the information indicating the rotation speed of the wheel measured in an appropriate measurement section for each error factor, and it is possible to accurately measure the air pressure. .

  Note that the tire air pressure may be measured based on a relative relationship with the reference air pressure, and may be configured to measure the absolute value of the air pressure based on the relative relationship with the reference air pressure. Alternatively, a configuration for measuring a ratio to the reference atmospheric pressure may be used. As the latter, for example, it is possible to employ a configuration that measures the ratio between the tire air pressure and the reference air pressure, and determines whether the tire air pressure is reduced by a predetermined value or more from the reference state based on the ratio. .

  Furthermore, as a configuration for specifying a measurement section according to an error factor, a configuration may be employed in which a section length corresponding to the error factor is specified and a section longer than the section length is specified as a measurement section. According to this configuration, the length of the measurement section can be specified according to the degree of error corresponding to the error factor. Here, the section length is the length of a road section that can obtain a sufficient amount of measurement values for statistical reliability even if an error corresponding to each error factor occurs. Therefore, the section length corresponds to the minimum value for each error factor of the section length necessary for measuring information indicating the rotational speed of the wheel. Note that the correspondence between the section length and the error factor may be set in advance.

  Furthermore, when the section length having a length corresponding to the degree of error is specified, the section length may be specified such that the section length increases as the error due to the error factor increases. That is, the length of the section is set to be longer as the error is larger, and the length of the measurement section is set to be longer as the error is larger. According to this configuration, it is possible to accurately measure the air pressure even if the error increases.

  Furthermore, when the measurement section specified based on the section length corresponding to the error factor includes a section having a shape that varies the measurement result of the rotational speed of the wheel, the measurement section may be corrected. . For example, when the measurement section specified according to the error factor includes a curve section whose curvature is equal to or less than a predetermined value, the wheel exists on the curvature center side of the curve section when viewed from the vehicle, and exists on the opposite side of the curvature center. There is a difference in the rotational speed between the wheels. In addition, when the measurement section specified according to the error factor includes a gradient section where the amount of change in altitude per unit distance is greater than or equal to a predetermined value, the number of revolutions is determined by the wheel existing in front of the vehicle and the wheel existing behind. Differences occur. In addition, the number of rotations of the wheel is likely to be different between the driving wheel and the driven wheel. Therefore, when the measurement section specified according to the error factor includes a curve section or a gradient section, the measurement section is extended so as to be longer than the above-described section length.

  According to this configuration, in addition to the above-described error factors, when the shape of the measurement section is in a situation where the measurement result of the rotational speed of the wheel can be fluctuated, it is sufficient to be statistically reliable. An appropriate measurement interval can be selected to obtain a quantity measurement. Of course, if the measurement section specified based on the section length corresponding to the error factor includes a curve section or a gradient section, select another section that does not include the curve section or the gradient section and define a new measurement section. However, according to the configuration in which the measurement section is extended as described above, the tire air pressure can be measured even in a situation where the measurement section includes a curve section or a gradient section.

  Furthermore, the information indicating the reference rotational speed may be a reference when analyzing the information indicating the rotational speed of the wheel actually measured in the measurement section. For example, the actual rotational speed of the tire is the reference atmospheric pressure in the vehicle. It is good also as information which shows a reference | standard rotation speed by driving | running | working a measurement area and measuring the information which shows the rotation speed of a wheel in the said measurement area. That is, the information indicating the reference rotation speed as a reference is also configured by actually measured information. According to this configuration, since it is not necessary to specify the reference information by the theoretical value, information indicating the reference rotational speed is defined in a state reflecting the measurement tendency specific to each vehicle and the measurement tendency for each measurement section. be able to.

  Further, according to the present invention, the relative relationship between the feature and the vehicle is specified based on the image taken by the imaging unit included in the vehicle, and the measurement start / measurement end timing of the rotation number of the wheel is specified based on the relative relationship. You may apply to a structure. In other words, in this configuration, the degree of error that occurs in the image analysis varies depending on the situation outside the vehicle (for example, time zone, brightness, weather, etc.), and therefore an external situation that affects the degree of the error. Is an error factor. Therefore, the first feature that becomes the reference when the information indicating the external situation of the vehicle is acquired and specified as an error factor and the start position of the measurement section is specified according to the specified error factor and the end position of the measurement section The second feature serving as a reference for specifying the is specified.

  And the measurement of the rotation speed of the wheel in a measurement area is performed between the measurement start timing specified based on the image image | photographed with the imaging part, and a measurement end timing. That is, when the relative relationship between the first feature specified based on the image of the first feature captured by the imaging unit and the vehicle is a predetermined relative relationship, measurement of information indicating the rotational speed of the wheel is started. . In addition, when the relative relationship between the second feature specified based on the image of the second feature photographed by the imaging unit and the vehicle is a predetermined relative relationship, the measurement of the information indicating the rotational speed of the wheel is terminated. . According to this configuration, it is possible to select an appropriate measurement section according to the degree of the specific error in the relative relationship between the feature and the vehicle caused by the situation outside the vehicle.

  In addition, the behavior of the vehicle in the measurement section can fluctuate the measurement result of the rotation speed of the wheel, but if the behavior of the vehicle has a behavior that excessively affects the stability of the measurement result, the air pressure is not measured. It is good also as a structure. For example, when the information indicating the number of rotations of the wheels is measured, the air pressure is not measured when the running stability of the vehicle in the measurement section is lower than a predetermined reference. That is, whether or not the running stability of the wheel is so low that the reliability of the measurement result of the information indicating the rotation speed of the wheel is lowered is measured based on a predetermined criterion set in advance. In addition, it is possible to prevent the measurement of the air pressure in a state of low reliability by adopting a configuration in which the air pressure is not measured when it is determined that the running stability is lower than a predetermined reference. The running stability of the vehicle is an index for evaluating the stability of the behavior of the running vehicle, and may be an index corresponding to the degree to which the measurement result of the rotational speed of the wheel is changed. The applied acceleration, the vehicle speed, the magnitude of the angular velocity, and the degree of change may be used, or the number of times of stoppage or lane change may be performed, and various indexes can be adopted.

  Further, the method of measuring the tire air pressure based on the information indicating the rotation speed of the wheel measured in the measurement section, which is set in the measurement section corresponding to the error factor as in the present invention, is also applied as a program or a method. Is possible. In addition, the above-described device, program, and method may be realized as a single device or may be realized by using components shared with each part of the vehicle, and include various aspects. It is a waste. For example, it is possible to provide a navigation device, a method, and a program that include the above devices. Further, some changes may be made as appropriate, such as a part of software and a part of hardware. Furthermore, the invention is also established as a recording medium for a program for controlling the apparatus. Of course, the software recording medium may be a magnetic recording medium, a magneto-optical recording medium, or any recording medium to be developed in the future.

It is a block diagram of the navigation apparatus containing an air pressure measuring device. It is a flowchart which shows an air pressure measurement fixed process. It is a flowchart which shows a measurement area specific process. It is a flowchart which shows a rotation speed information acquisition process. It is a figure which shows a vehicle and a feature typically.

Here, embodiments of the present invention will be described in the following order.
(1) Configuration of navigation device:
(2) Air pressure measurement process:
(2-1) Measurement section specifying process:
(2-2) Revolution information acquisition processing:
(3) Other embodiments:

(1) Configuration of navigation device:
FIG. 1 is a block diagram showing a configuration of a navigation device 10 including an air pressure measuring device according to the present invention. The navigation apparatus 10 includes a control unit 20 including a CPU, a RAM, a ROM, and the like, and a recording medium 30, and the control unit 20 can execute a program stored in the recording medium 30 and the ROM. In this embodiment, the air pressure measurement program 21 can be executed as this program. The air pressure measurement program 21 is executed in a state where the control unit 20 is executing the navigation process, and has a function of measuring the tire air pressure at the wheel of the vehicle on which the navigation device 10 is mounted.

  The vehicle in this embodiment includes an external information acquisition unit 40, a GPS reception unit 41, a wheel sensor 42, a gyro sensor 43, a camera 44, and a user I / F unit 45, and each unit and the control unit 20 cooperate. By doing so, the function by the air pressure measurement program 21 is realized.

  The external information acquisition unit 40 is a device that acquires external information indicating a situation outside the vehicle, which is a factor causing an error that fluctuates the measurement result of the rotational speed of the wheel based on the output signal of the wheel sensor 42. In the present embodiment, as will be described later, the relative relationship between the vehicle and the feature is specified using image analysis by the camera 44, and the acquisition start timing and the acquisition end timing of the output signal of the wheel sensor 42 are specified. Yes. Therefore, attention is paid to an error in specifying the relative relationship between the feature and the position of the vehicle by the image analysis, and the degree of brightness outside the vehicle that can vary the degree of the error is used as an error factor. Therefore, the external information acquisition unit 40 in the present embodiment is a brightness sensor that measures the brightness outside the vehicle, and outputs information corresponding to the brightness outside the vehicle via an interface (not shown). The control unit 20 acquires this signal and acquires the brightness outside the vehicle.

  The GPS receiver 41 receives radio waves from GPS satellites and outputs information for calculating the current position of the vehicle via an interface (not shown). The control unit 20 acquires this signal and acquires the current position of the vehicle. The wheel sensor 42 outputs a signal corresponding to the number of rotations of the wheels included in the vehicle. That is, the wheel sensor 42 is configured to output a pulse signal every time the wheel rotates by a predetermined angle, and the control unit 20 acquires this signal via an interface (not shown), and based on the number of pulse signals. To obtain the rotation speed of the wheel. In addition, the control part 20 can also acquire a vehicle speed based on the rotation speed of the wheel per unit time. The gyro sensor 43 outputs a signal corresponding to the angular velocity acting on the vehicle. The control unit 20 acquires this signal via an interface (not shown) and acquires the traveling direction of the vehicle. The wheel sensor 42 and the gyro sensor 43 are used for correcting the current position of the vehicle specified from the output signal of the GPS receiver 41. Further, the current position of the vehicle is appropriately corrected based on the travel locus of the vehicle.

  The camera 44 is attached to the vehicle so as to include a road behind the vehicle in the field of view, and outputs image data indicating a captured image. The control unit 20 acquires this image data through an interface (not shown), converts the image data, detects a feature on the road, and specifies a relative relationship (distance and direction) between the feature and the vehicle.

  The user I / F unit 45 is an interface unit for inputting a driver's instruction and providing various information to the driver, and includes a touch panel display, a switch, a speaker, and the like (not shown). The control unit 20 outputs various guides by outputting a control signal to the user I / F unit 45.

  The air pressure measurement program 21 includes an error factor specifying unit 21a, a measurement section specifying unit 21b, a rotation speed information measuring unit 21c, and an air pressure measuring unit 21d in order to realize a function of measuring the air pressure of the tire of the wheel. In addition, map information 30a and section length information 30b are recorded on the recording medium 30 in advance.

  The map information 30a includes node data indicating nodes set on the road on which the vehicle travels, shape interpolation point data for specifying the shape of the road between the nodes, link data indicating the connection between the nodes, the road and its surroundings Includes data indicating features (such as stop lines, white lines, and pedestrian crossings) on the road. In the present embodiment, the current position of the vehicle can be specified based on the output signals of the GPS receiver 41, the wheel sensor 42, and the gyro sensor 43 described above, and the image data output from the camera 44 can be used. Based on this, it is possible to specify the relative relationship between the feature and the vehicle. Here, since the position of the feature can be specified by the map information 30a, when the relative relationship between the feature and the vehicle is specified based on the image data output from the camera 44, the current position of the vehicle is substantially determined. Will be identified.

  As described above, in the present embodiment, the position of the vehicle can be specified by two types of methods, but in the current technology, the current position of the vehicle based on the output signals of the GPS receiver 41, the wheel sensor 42, and the gyro sensor 43. The specific accuracy of the relative relationship between the feature and the vehicle based on the image data output from the camera 44 is higher than the specific accuracy. Therefore, in the present embodiment, the relative relationship between the feature and the vehicle is specified based on the image data output from the camera 44, and the wheel sensor 42 determines the wheel relationship when the feature and the vehicle have a specific relative relationship. It is set as the structure which starts the measurement of rotation speed. And even if the position of the vehicle is specified by such a relatively high accuracy method, it is unavoidable that a specific error occurs, and the error varies depending on the situation outside the vehicle. In the present embodiment, the measurement interval is specified for each error factor.

  The section length information 30b is information that is referred to in order to specify the measurement section for each error factor, and is information that indicates the correspondence between the error factor and the section length. In the present embodiment, the section length information 30b is information indicating the correspondence between the brightness outside the vehicle and the section length. In the present embodiment, the longer section length is set as the error due to the error factor is larger (that is, the longer section length is set as the brightness outside the vehicle is darker). Further, the section length set for each error factor indicates the minimum value of the length of the section necessary for measuring information indicating the number of rotations of the wheel for each error factor.

  The reference rotation speed information 30c is information indicating the rotation speed of the wheel when the vehicle travels through the measurement section in a state where the tire pressure of the wheel is the reference pressure, and the pressure of the wheel tire is the reference pressure. Then, after traveling in the measurement section by the vehicle, it is recorded in the recording medium 30 in association with the measurement section and an error factor at the time of traveling through the measurement section.

  The error factor specifying unit 21a is a module that causes the control unit 20 to implement a function of specifying an error factor that causes an error in measurement of information indicating the number of rotations of the wheel. That is, the control unit 20 specifies the brightness outside the vehicle as an error factor based on the output information of the external information acquisition unit 40 by the process of the error factor specifying unit 21a.

  The measurement section specifying unit 21b is a module that causes the control unit 20 to realize a function of specifying a measurement section that performs measurement of information indicating the number of rotations of a wheel according to an error factor. That is, the control unit 20 refers to the section length information 30b by the process of the measurement section specifying unit 21b, and specifies the section length corresponding to the external brightness of the vehicle specified as the error factor. And the area more than the said section length is specified as a measurement area from the road which exists ahead of a vehicle. In the present embodiment, the control unit 20 specifies the first feature serving as a reference when specifying the start position of the measurement section and the second feature serving as a reference when specifying the end position of the measurement section. To define the measurement interval. That is, the control unit 20 refers to the map information 30a, specifies the positions of a plurality of features on the road existing ahead of the vehicle, and selects two features whose distance between the features is equal to or longer than the section length. The feature closer to the vehicle is designated as the first feature, and the feature far away from the vehicle is designated as the second feature.

  The rotation speed information measurement unit 21c is a module that causes the control unit 20 to realize a function of measuring information indicating the rotation speed of the wheel in the measurement section. That is, the control unit 20 starts acquiring image data output by the camera 44 before reaching the first feature indicated by the map information 30a by the processing of the rotation speed information measuring unit 21c, and the feature indicated by the image data It is determined from the quantity whether the first feature is included in the image. Then, when the image of the first feature reaches a predetermined position of one image, it is determined that the first feature and the vehicle are in a predetermined relative relationship, and the output of the wheel sensor 42 is determined. The measurement of the rotational speed based on the signal is started.

  Further, the control unit 20 continues to acquire the image data output from the camera 44 by the processing of the rotation speed information measurement unit 21c, and whether or not the second feature is included in the image from the feature amount indicated by the image data. Determine. Then, when the image of the second feature reaches a predetermined position of one image, it is determined that the second feature and the vehicle are in a predetermined predetermined relative relationship, and the output of the wheel sensor 42 is determined. The rotation speed measurement based on the signal is terminated.

  FIG. 5 is a diagram schematically showing the vehicle C and the feature traveling on the road. In FIG. 5, the pedestrian crossing P is a feature that defines the start position of the measurement section, and the stop line S is the end position of the measurement section. That is, in this example, the control unit 20 sets the crosswalk P as the first feature and the stop line S as the second feature. In this example, for example, when the distance between the vehicle C and the feature is L, when both are defined to have a predetermined relative relationship, the control unit 20 determines the vehicle based on the image of the first feature. When it is determined that C has reached the distance L from the pedestrian crossing P, measurement of the rotational speed based on the output signal of the wheel sensor 42 is started. Moreover, the control part 20 complete | finishes the measurement of the rotation speed based on the output signal of the wheel sensor 42, when it determines with the vehicle C having reached | attained the distance L from the stop line S based on the image of a 2nd feature. In the present embodiment, the rotational speed of the wheel measured in the measurement section in this way is acquired as the rotational speed of the wheel reflecting the current tire air pressure.

  The air pressure measurement unit 21d is a module that causes the control unit 20 to realize a function of measuring tire air pressure. That is, the control unit 20 refers to the recording medium 30 by the processing of the air pressure measurement unit 21d, acquires information indicating the reference rotation number of the wheel indicated by the reference rotation number information 30c, and reflects the current tire pressure. The tire air pressure is measured by comparing the rotation speed of the wheel and the reference rotation speed of the wheel indicated by the reference rotation speed information 30c. In the present embodiment, when the difference between the wheel rotational speed reflecting the current tire air pressure and the reference rotational speed is equal to or greater than a predetermined threshold, the tire air pressure is below the reference. It is the structure which determines with it being (decompression state). When it is determined that the tire air pressure is in a reduced pressure state, the control unit 20 outputs a control signal to the user I / F unit 45 to output information indicating that the tire air pressure is in a reduced pressure state. .

In the above configuration, the accuracy of image analysis by the camera 44 described above decreases as the brightness outside the vehicle decreases, and the accuracy in specifying the relative relationship between the feature and the vehicle decreases. Therefore, the measurement accuracy of the rotational speed of the wheel in the configuration in which the measurement start timing and the measurement end timing of the rotational speed of the wheel are determined using the identification of the relative relationship is lowered as the brightness outside the vehicle becomes darker. For example, in the example shown in FIG. 5, when the error of the specific accuracy of the distance L from the feature is ± E _{1 in the} daytime, it becomes ± E ₂ (E ₂ > E ₁ ) at night. As a result, the measurement accuracy of the rotational speed of the wheel is lower at night than at daytime. As described above, the accuracy in specifying the relative relationship between the feature and the vehicle depends on the brightness of the outside of the vehicle, but the image analysis by the camera 44 is a process performed individually for each feature on the road. Therefore, it does not depend on the distance between features, that is, the distance of the measurement section.

  On the other hand, the output signal of the wheel sensor 42 is a pulse signal that is output every time the wheel rotates by a predetermined angle, and the number of pulse signals increases in proportion to the distance of the measurement section. When the tire air pressure is in a reduced pressure state lower than the reference pressure, the diameter of the tire is reduced. Therefore, the number of pulse signals is greater in the reduced pressure state than in the reference pressure. However, since the proportional relationship between the distance of the measurement section and the number of pulse signals is maintained, the number of pulse signals increases as the distance of the measurement section increases even if the tire air pressure is in a reduced pressure state or the reference pressure. . Therefore, the longer the distance of the measurement section, the higher the statistical accuracy when measuring the number of wheel rotations based on the pulse signal.

  As described above, when the brightness outside the vehicle becomes dark, the degree of error increases. However, if the distance of the measurement section is set to be long, the statistical accuracy is improved while maintaining the degree of error. Therefore, in the present embodiment, in the section length information 30b, as described above, the section length is set to become longer as the brightness outside the vehicle becomes darker. The measurement interval is set to be long. That is, in the present embodiment, even if the degree of error increases due to the brightness of the outside of the vehicle, the section length is set so as to ensure statistical accuracy that exceeds the degree of increase in the error. As a result, it is possible to measure the tire pressure of the wheel by measuring the rotation speed of the wheel in the measurement section of the section length corresponding to the error factor, and even if the error due to the error factor fluctuates, the air pressure is highly accurate. Can be measured.

(2) Air pressure measurement process:
Next, the air pressure measurement process according to the present embodiment will be described in detail. FIG. 2 is a flowchart showing the air pressure measurement process, and the air pressure measurement process is executed every predetermined period (for example, every 100 ms) in the course of traveling of the vehicle.

  In the air pressure measurement process, first, the control unit 20 specifies an error factor by the process of the error factor specifying unit 21a (step S100). That is, the control unit 20 acquires the output information of the external information acquisition unit 40, acquires the brightness outside the vehicle, and specifies it as an error factor. Next, the control part 20 performs a measurement area specific process by the process of the measurement area specific part 21b (step S105). That is, the control unit 20 specifies the measurement section based on the error factor acquired in step S100.

(2-1) Measurement section specifying process:
FIG. 3 is a flowchart showing the measurement section specifying process in step S105. In the measurement section specifying process, the control unit 20 first specifies the section length corresponding to the error factor (step S200). That is, the control unit 20 refers to the section length information 30b and specifies the section length corresponding to the brightness outside the vehicle that is an error factor.

  Next, the control unit 20 specifies a section that is equal to or longer than the specified section length as a measurement section (step S210). That is, the control unit 20 identifies the current position of the vehicle based on the output signals of the GPS receiving unit 41, the wheel sensor 42, and the gyro sensor 43, and refers to the map information 30a at two locations existing in front of the vehicle. A feature whose distance between features is equal to or longer than the section length is specified, and a feature closer to the vehicle is a first feature and a feature farther from the vehicle is a second feature.

  Next, the control unit 20 determines whether or not the measurement section includes a curve section or a gradient section (step S220), and when it is determined that the measurement section includes a curve section or a gradient section, the measurement section Is extended (step S230). That is, when the measurement section includes a curve section or a gradient section that is a section having a shape that can change the measurement result of the rotation speed of the wheel, the measurement section specified in step S210 is corrected. Specifically, when the vehicle travels in a curve section where the curvature is equal to or less than a predetermined value, the number of revolutions is determined by the wheel existing on the curvature center side of the curve section viewed from the vehicle and the wheel existing on the opposite side of the curvature center. Differences may occur and the measurement results of the wheel speed may vary. In addition, when the vehicle travels in a gradient section where the amount of change in altitude per unit distance is greater than or equal to a predetermined amount, there is a difference in the rotational speed between the wheel existing in the front of the vehicle and the wheel existing in the rear. Measurement results can vary. Therefore, when the measurement section specified in step S210 includes a curve section or a gradient section, the measurement section is extended to be longer than the section length specified in step S200.

  The extension of the measurement section is performed, for example, by selecting another feature ahead of the position of the second feature described above, and the extension amount depends on the curvature in the curve section or the grade in the slope section. Identified. That is, it is difficult to specify the position where the acceleration that changes the measurement result of the rotation speed of the wheel is applied to the vehicle in the curve section, but the smaller the curvature in the curve section (the steeper the curve), the more the wheel The possibility of changing the measurement result of the rotational speed is high. In addition, it is generally difficult to specify the position where the acceleration that changes the measurement result of the rotation speed of the wheel in the gradient section, the position of the unevenness, etc., but the measurement result of the rotation speed of the wheel becomes more steep as the gradient is steep. There is a high possibility of fluctuation. Therefore, in order to improve the statistical accuracy, the length of the measurement section is set to the curvature value or the degree of gradient when the curvature of the curve section is less than a predetermined value and when the degree of gradient in the gradient section is more than a predetermined value. Correction is made to extend by a predetermined length associated with.

  When the curvature is excessively small and the distance of the curve section having a small curvature is excessively long, the measurement may be considered to be excessively fluctuated and the processing may be stopped. Similarly, when the grade of the gradient is excessively large and the distance of the gradient section having a large gradient is excessively long, the measurement may be regarded as excessively fluctuating the measurement result of the rotational speed of the wheel, and the processing may be stopped. . Further, according to this configuration, in addition to the above-described error factors, in order to statistically trust when the shape of the measurement section is in a situation where the measurement result of the rotation speed of the wheel can be changed. An appropriate measurement interval can be selected in order to obtain a sufficient amount of measurement values. According to this configuration, the tire air pressure can be measured even in a situation where the measurement section includes a curve section or a gradient section.

  When the measurement section is specified by the above processing, the process returns to the flowchart shown in FIG. 2, and the control unit 20 determines whether or not the reference rotational speed information 30c has been recorded on the recording medium 30 by the processing of the rotational speed information measurement unit 21c. Is determined (step S110). That is, the control unit 20 has already recorded the reference rotation speed information 30c regarding the measurement section specified in step S105 for the same error factor (the brightness outside the vehicle is equivalent) as the error factor specified in step S100. It is determined whether or not recording on the medium 30 has been completed.

  If it is not determined in step S110 that the reference rotational speed information 30c has been recorded on the recording medium 30, the control unit 20 determines whether the current tire air pressure is the reference atmospheric pressure by the processing of the rotational speed information measuring unit 21c. Is determined (step S115). Note that various configurations can be adopted as the configuration for determining whether or not the current tire air pressure is the reference atmospheric pressure. For example, it is possible to employ a configuration in which the user himself / herself operates the user I / F unit 45 to set the reference air pressure after setting the tire air pressure to the reference air pressure by maintenance.

  When it is not determined in step S115 that the air pressure is the reference atmospheric pressure, the control unit 20 skips step S120 and ends the process. On the other hand, when it is determined in step S115 that the air pressure is the reference atmospheric pressure, the control unit 20 performs a rotation speed information acquisition process by the process of the rotation speed information measurement unit 21c (step S120).

(2-2) Revolution information acquisition processing:
FIG. 4 is a flowchart showing the rotation speed information acquisition process in step S120. In the rotation speed information acquisition process, the control unit 20 first determines whether or not the relative relationship between the first feature and the vehicle is a predetermined relative relationship (step S300). That is, the control unit 20 specifies the current position of the vehicle based on the output signals of the GPS receiving unit 41, the wheel sensor 42, and the gyro sensor 43, and specifies the position of the first feature with reference to the map information 30a. Then, acquisition of image data output by the camera 44 before the vehicle reaches the position of the first feature is started, and it is determined whether or not the first feature is included in the image from the feature amount indicated by the image data. To do. Then, when the image of the first feature reaches a predetermined position of one image, it is determined that the first feature and the vehicle are in a predetermined relative relationship.

  In step S300, when it is not determined that the relative relationship between the first feature and the vehicle is a predetermined relative relationship, the processing after step S305 is skipped. On the other hand, when it is determined in step S300 that the relative relationship between the first feature and the vehicle is a predetermined relative relationship, the control unit 20 starts measuring the rotational speed of the wheel (step S305). That is, the control unit 20 acquires the output signal of the wheel sensor 42 and starts measuring the number of pulse signals corresponding to the rotation speed of the wheel.

  Further, the control unit 20 determines whether or not the relative relationship between the second feature and the vehicle is a predetermined relative relationship (step S310). That is, the control unit 20 continues to measure the number of rotations of the wheel and continues to analyze the image data output from the camera 44, and the image of the second feature is a predetermined one of the images from the feature amount indicated by the image data. It is determined whether or not the second feature and the vehicle are in a predetermined relative relationship by determining whether or not the position has been reached. If it is determined in step S310 that the relative relationship between the second feature and the vehicle is a predetermined relative relationship, the control unit 20 ends the measurement of the rotational speed of the wheel (step S315).

  Further, in the present embodiment, the control unit 20 determines whether or not the vehicle is stable in the measurement section (step S320), and records the rotation speed information on the recording medium when it is determined that the vehicle is stable. (Step S325). On the other hand, if it is not determined in step S320 that the vehicle is stable, step S325 is skipped and the rotational speed information is not recorded. That is, the behavior of the vehicle in the measurement section can fluctuate the measurement result of the rotation speed of the wheel, but the rotation speed information is not recorded when the behavior of the vehicle has an excessive influence on the stability of the measurement result. In other words, the configuration is such that the measurement of the air pressure is not performed when the behavior of the vehicle is unstable by setting the rotational speed information to be referred to in later processing to be not recorded.

  Here, the running stability of the vehicle can be specified based on various indexes. For example, the change in the number of pulse signals output from the wheel sensor 42 per unit time, the change amount per unit time of the angular velocity acting on the vehicle specified based on the output signal from the gyro sensor 43, etc. It can be regarded as an index indicating stability. And when the said parameter | index shows that the behavior of a vehicle is unstable from a predetermined reference | standard, it is set as the structure which does not measure an air pressure. That is, it is determined on the basis of a predetermined criterion whether or not the traveling stability of the vehicle is so low that the reliability of the measurement result of the information indicating the rotational speed of the wheel is lowered.

  When the above processing is performed in step S120 described above, the rotation speed information recorded in step S325 is reference rotation speed information, which is associated with the measurement section and the error factor as reference rotation speed information 30c. It is recorded on the recording medium 30. Accordingly, when the process returns to the process shown in FIG. 2 after performing step S325, the reference rotational speed information 30c is recorded on the recording medium 30 thereafter.

  Next, a case where it is determined in step S110 that the reference rotation speed information 30c has been recorded on the recording medium 30 will be described. In this case, the control part 20 performs the process which measures the air pressure of the present tire in a vehicle after step S130. First, the control unit 20 executes a rotation number information acquisition process by the process of the rotation number information measurement unit 21c (step S130). The rotation speed information acquisition process executed in step S130 is also the process shown in FIG. 4, and the processing content is the same as the process in step S120 described above, but when the rotation speed information acquisition process is executed in step S130. The acquired rotational speed information is rotational speed information indicating the rotational speed of the wheel at the current tire air pressure. In step S325, the rotational speed information is recorded in the RAM.

  Next, the control unit 20 determines whether or not the rotational speed information indicating the rotational speed of the wheel at the current tire air pressure has been recorded in the RAM by the rotational speed information acquisition process in step S130 (step S135). . In step S135, when it is not determined that the rotation speed information indicating the rotation speed of the wheel at the current tire air pressure has been recorded in the RAM, the process after step S140 is skipped and the process is terminated.

  On the other hand, when it is determined in step S135 that the rotational speed information indicating the rotational speed of the wheel at the current tire air pressure has already been recorded in the RAM, the control unit 20 performs the processing of the air pressure measuring unit 21d to record the recording medium. Reference speed information 30c is acquired with reference to 30 (step S140). That is, the reference rotational speed information 30c related to the error factor specified in step S100 and the measurement section specified in step S105 is acquired from the recording medium 30 and recorded in the RAM.

  Next, the control unit 20 acquires a difference between the wheel rotation speed and the reference rotation speed at the current tire pressure based on the information recorded in the RAM (step S145), and the difference is determined from a predetermined threshold value. It is determined whether it is larger (step S150). If it is determined in step S150 that the difference is greater than the predetermined threshold, the control unit 20 outputs a control signal to the user I / F unit 45 by the process of the air pressure measurement unit 21d so that the tire is in a decompressed state. A guidance to that effect is executed (step S155). On the other hand, if it is not determined in step S150 that the difference is greater than the predetermined threshold, step S155 is skipped.

  Here, the threshold value is set so that the threshold value increases in proportion to the section length. That is, the difference between the rotation speed when the tire air pressure is in a reduced pressure state and the rotation speed when the tire air pressure is at the reference air pressure is the increase in the rotation speed that is increased when the tire pressure is reduced. If there is an error in the measurement of the rotational speed of the wheel, the value is affected by the error.

  Here, the degree of the error differs depending on the error factor, and the maximum value of the error included in the above-described difference increases as the error level due to the error factor increases. However, when the degree of the error becomes large, the section length is set to be increased correspondingly, and the above-described threshold is set to increase in proportion to the section length. Therefore, by comparing the above difference with the threshold value, it is possible to determine whether or not the tire air pressure is reduced without being affected by the error even when the error due to the error is large. . Although an example in which the threshold is set according to the section length has been described here, the threshold may be set for each error factor. That is, the threshold value may be set to increase as the degree of error corresponding to the error factor increases.

  Further, in step S320, the vehicle stability in the measurement section is determined, and the rotational speed information is recorded according to the vehicle stability, so that it is possible to prevent the measurement of air pressure in a state of low reliability. be able to. The vehicle running stability index may be defined based on the number of pulse signals and the angular velocity as described above, the acceleration acting on the vehicle, the magnitude of the vehicle speed, and the degree of change. It may be the number of times of stopping or changing lanes, and various indicators can be adopted.

(3) Other embodiments:
The above embodiment is an example for carrying out the present invention. A measurement section corresponding to an error factor is set, and the tire air pressure is measured based on information indicating the rotational speed of the wheel measured in the measurement section. Insofar as various other embodiments are possible. For example, the information indicating the rotational speed of the wheel may be information that is substantially equivalent to the rotational speed of the wheel and that can measure the tire air pressure by comparing the information with information indicating the reference rotational speed. That's fine. Therefore, in addition to the pulse signal for each predetermined rotation angle such as the output signal of the wheel sensor 42, it may be configured to acquire information indicating the rotation speed of the wheel itself, or indirectly indicate the rotation speed of the wheel. For example, information indicating a travel distance for each wheel may be used.

  Further, in the present invention, since the rotational speed of the wheel is measured in the measurement section, it is necessary to specify an error factor before specifying the measurement section. Therefore, the error factor is an error factor related to an error that can be estimated whether there is a possibility of occurrence before the vehicle starts traveling for measurement. Whether or not an error occurs even if a road section is not specified. This is an error factor related to an error that can be estimated. Examples of such error factors include the environment around the vehicle, and may be the weather around the vehicle in addition to the brightness outside the vehicle as described above. In this case, the external information acquisition unit 40 includes a sensor that measures weather outside the vehicle, a communication unit that acquires weather information, and the like.

  Further, the tire pressure may be measured based on a relative relationship with the reference pressure, and in addition to the configuration for determining that the pressure is reduced, the pressure of the tire is determined based on the relative relationship with the reference pressure. The structure which measures an absolute value may be sufficient, and the structure which measures ratio with reference | standard atmospheric | air pressure may be sufficient.

  Furthermore, a plurality of sections that can secure a length equal to or longer than the section length corresponding to the error factor may be selected as candidates, and a measurement section may be selected from the candidates. For example, in the candidates, select a section with a small number of curve sections and slope sections as a measurement section, and select a measurement section including a curve section with a curvature as small as possible when a curve section exists, A configuration in which a measurement section including a gradient section where the change in altitude is as small as possible when a gradient section exists can be adopted. Of course, it is good also as a structure which does not make the area containing a curve area and a gradient area the candidate of a measurement area.

  Furthermore, in the above-described embodiment, the reference rotation speed information 30c is acquired by selecting the measurement section and measuring the rotation speed of the wheel in a state where the tire air pressure is the reference atmospheric pressure. Reference rotational speed information may be measured with For example, in a state where the tire air pressure is the reference atmospheric pressure, the rotation speed of the wheel is measured in a predetermined period, the rotation speed of the wheel per unit distance is used as the reference rotation speed information, and the distance and the reference rotation speed in an arbitrary measurement section It is good also as a structure which compares the result of multiplying the rotation speed which information shows, and the rotation speed of the wheel measured in the said measurement area. Of course, the reference rotation speed information may be calculated from the diameter of the tire at the ideal other station in a state where the tire air pressure is the reference air pressure.

  DESCRIPTION OF SYMBOLS 10 ... Navigation apparatus, 20 ... Control part, 21 ... Air pressure measurement program, 21a ... Error factor specific | specification part, 21b ... Measurement area specific part, 21c ... Rotation speed information measurement part, 21d ... Air pressure measurement part, 30 ... Recording medium, 30a ... Map information, 30b ... Section length information, 30c ... Reference rotational speed information, 40 ... External information acquisition unit, 41 ... GPS reception unit, 42 ... Wheel sensor, 43 ... Gyro sensor, 44 ... Camera, 45 ... User I / F Part

Claims (9)

An error factor specifying means for specifying an error factor causing an error in measurement of information indicating the number of rotations of a wheel included in the vehicle;
A measurement section specifying means for specifying a measurement section for measuring information indicating the rotation speed of the wheel according to the error factor;
Rotational speed information measuring means for measuring information indicating the rotational speed of the wheel in the measurement section;
The tire pressure is compared by comparing the information indicating the rotation speed with the information indicating the reference rotation speed of the wheel when the vehicle travels through the measurement section in a state where the tire pressure of the wheel is a reference pressure. Air pressure measuring means for measuring;
A tire pressure measuring device comprising: The measurement section specifying means specifies a section having a length equal to or longer than a section length corresponding to the error factor as the measurement section.
The tire pressure measuring device according to claim 1. The measurement section specifying means specifies the section length so as to increase as the error due to the error factor increases.
The tire pressure measuring device according to claim 2. The measurement section specifying means, when the measurement section specified according to the error factor includes a curve section having a curvature of a predetermined value or less or a gradient section having an altitude change amount per unit distance of a predetermined value or more. Extending the measurement interval to be longer than the interval length;
The tire pressure measuring device according to any one of claims 2 and 3. The information indicating the reference rotational speed is measured by actually running the measurement section in the vehicle with the tire air pressure being the reference atmospheric pressure, and measuring the information indicating the rotational speed of the wheel in the measurement section. Information obtained by
The tire pressure measuring device according to any one of claims 1 to 4. The error factor specifying means includes
Identifying a factor causing an error when identifying a relative relationship between a feature and the vehicle based on an image captured by an imaging unit included in the vehicle, as the error factor;
The measurement section specifying means is a first feature serving as a reference when specifying a start position of the measurement section according to the error factor and a second feature serving as a reference when specifying the end position of the measurement section. And identify
The rotational speed information measuring means includes
Measurement of information indicating the number of rotations of the wheels when the relative relationship between the first feature and the vehicle specified based on the image of the first feature photographed by the imaging unit is a predetermined relative relationship. Start
Information indicating the number of rotations of the wheel when the relative relationship between the second feature and the vehicle specified based on the image of the second feature photographed by the imaging unit is the predetermined relative relationship. End the measurement,
The tire pressure measuring device according to any one of claims 1 to 5. The air pressure measurement means does not measure the air pressure when the vehicle running stability in the measurement section when information indicating the rotation speed of the wheel is measured is lower than a predetermined reference;
The tire pressure measuring device according to any one of claims 1 to 6. An error factor specifying step for specifying an error factor that causes an error in measurement of information indicating the number of rotations of wheels included in the vehicle;
A measurement section specifying step for specifying a measurement section for measuring information indicating the rotation speed of the wheel according to the error factor;
A rotational speed information measuring step for measuring information indicating the rotational speed of the wheel in the measurement section;
The tire pressure is compared by comparing the information indicating the rotation speed with the information indicating the reference rotation speed of the wheel when the vehicle travels through the measurement section in a state where the tire pressure of the wheel is a reference pressure. Air pressure measurement process to measure,
A tire pressure measuring method comprising: An error factor specifying function for specifying an error factor causing an error in measurement of information indicating the number of rotations of a wheel included in the vehicle;
A measurement section specifying function for specifying a measurement section for measuring information indicating the number of rotations of the wheel according to the error factor;
A rotational speed information measuring function for measuring information indicating the rotational speed of the wheel in the measurement section;
The tire pressure is compared by comparing the information indicating the rotation speed with the information indicating the reference rotation speed of the wheel when the vehicle travels through the measurement section in a state where the tire pressure of the wheel is a reference pressure. Air pressure measurement function to measure,
Tire pressure measurement program that makes a computer realize.

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