Tire pressure reduction detection device, pressure reduction detection method, and pressure reduction detection program

Abstract

This invention provides a tire pressure reduction detection device that does not require an initialization operation. [Solution] The pressure reduction detection device comprises an acquisition unit, an index calculation unit, a storage unit, and a pressure reduction determination unit. The acquisition unit acquires rotational speed information of each tire included in the vehicle while the vehicle is running. The index calculation unit calculates a relative pressure reduction index that compares the rotational speeds of each tire based on the acquired rotational speed information. The storage unit stores the relative pressure reduction index calculated at a first point in time while the vehicle is performing a first run as a reference value. The pressure reduction determination unit determines whether or not pressure reduction has occurred in one of the tires based on the relative pressure reduction index calculated at a second point in time after the first point in time during the first run and the reference value.

Description

[Technical Field]

[0001] This invention relates to a detection device, a pressure reduction detection method, and a pressure reduction detection program for detecting pressure reduction in a single tire included in a wheel. [Background technology]

[0002] Traditionally, systems that automatically detect tire pressure loss (Tire Pressure Monitoring Systems; TPMS) have been studied. Information that a tire is losing pressure can be used, for example, to warn the driver. Methods for detecting tire pressure loss include methods that directly measure tire pressure by attaching pressure sensors to the tire, as well as methods that indirectly evaluate tire pressure loss using other indicators. An example of an indirect method is the Dynamic Loaded Radius (DLR) method. The DLR method utilizes the phenomenon that a tire with reduced pressure collapses during driving, reducing its dynamic load radius and causing it to rotate at a higher speed, and estimates tire pressure loss from the tire's rotation speed.

[0003] Patent Document 1 discloses depressurization indices DEL1 to DEL3 for estimating depressurization according to the DLR method. In Patent Document 1, DEL1 to DEL3 are defined as follows. However, V1 to V4 are the rotational speeds of the left front wheel, right front wheel, left rear wheel, and right rear wheel tires, respectively. DEL1=[(V1+V4) / (V2+V3)-1]×100(%) DEL2=[(V1+V2) / (V3+V4)-1]×100(%) DEL3=[(V1+V3) / (V2+V4)-1]×100(%)

[0004] In the pressure reduction determination method that combines the pressure reduction indices DEL1 to DEL3 as described above, reference values ​​for pressure reduction indices DEL1 to DEL3 are pre-stored in the vehicle. Here, as disclosed in Patent Document 1, in order to perform accurate pressure reduction determination, it is necessary to update the reference values ​​stored in the vehicle after adjusting the tire pressure. Typically, the updating of the reference values ​​is performed by an initialization operation on the vehicle by the driver. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-149340 [Overview of the project] [Problems that the invention aims to solve]

[0006] Various measures have been taken to prevent drivers from forgetting the initialization procedure described above or from performing the initialization procedure without adjusting the air pressure. However, from a different perspective, there was a need for a technology that would not reduce the accuracy of pressure reduction detection during initialization and would be useful for detecting pressure reduction.

[0007] The present invention aims to provide a tire pressure reduction detection device, pressure reduction detection method, and pressure reduction detection program that do not require an initialization operation. [Means for solving the problem]

[0008] The tire pressure reduction detection device for one-wheel pressure reduction according to the first aspect of the present invention includes an acquisition unit, an index calculation unit, a storage unit, and a pressure reduction determination unit. The acquisition unit acquires the rotational speed information of each tire included in the vehicle during the running of the vehicle. The index calculation unit calculates a relative pressure reduction index for comparing the rotational speeds of the respective tires based on the acquired rotational speed information. The storage unit stores, as a reference value, the relative pressure reduction index calculated at a first time point while the vehicle is performing a first run. The pressure reduction determination unit determines whether or not pressure reduction has occurred in one of the tires based on the relative pressure reduction index calculated at a second time point after the first time point and the reference value during the first run.

[0009] The pressure reduction detection device according to the second aspect is the pressure reduction detection device according to the first aspect, and includes a regression analysis unit that derives a regression equation having the relative pressure reduction index as an objective variable and the elapsed time as an explanatory variable based on a plurality of data sets of the elapsed time from the start of the first run and the relative pressure reduction index at the elapsed time. The pressure reduction determination unit further determines whether or not pressure reduction has occurred in one of the tires based on the regression coefficient included in the regression equation.

[0010] The pressure reduction detection device according to the third aspect is the pressure reduction detection device according to the first aspect or the second aspect, and further includes a reset unit that deletes the reference value from the storage unit after the first run when the pressure reduction determination unit does not determine that pressure reduction has occurred in the one tire during the first run.

[0011] The pressure reduction detection device according to the fourth aspect is the pressure reduction detection device according to any one of the first aspect to the third aspect, and further includes a tendency derivation unit that derives a time-series change tendency of the representative value Q(k) based on a plurality of data sets of the time t(k) corresponding to the k-th (k = 1, 2,..., n) run of the vehicle in time series order and the representative value Q(k) of the relative pressure reduction index calculated during the k-th run. The pressure reduction determination unit further determines whether or not pressure reduction has occurred in one of the tires based on the change tendency.

[0012] The tire pressure reduction detection device for single-wheel pressure reduction according to the fifth aspect includes an acquisition unit, a regression analysis unit, and a pressure reduction determination unit. The acquisition unit acquires the rotational speed information of each tire included in the vehicle while the vehicle is running. The index calculation unit calculates a relative pressure reduction index for comparing the rotational speeds of the tires based on the acquired rotational speed information. The regression analysis unit derives a regression equation with the relative pressure reduction index as the objective variable and the elapsed time as the explanatory variable based on a plurality of data sets of the elapsed time from the start of the first driving and the relative pressure reduction index during the elapsed time while the vehicle is performing the first driving. The pressure reduction determination unit determines whether pressure reduction has occurred in one of the tires based on the regression coefficient included in the regression equation.

[0013] The tire pressure reduction detection device for single-wheel pressure reduction according to the sixth aspect includes an acquisition unit, an index calculation unit, a trend derivation unit, and a pressure reduction determination unit. The acquisition unit acquires the rotational speed information of each tire included in the vehicle while the vehicle is running. The index calculation unit calculates a relative pressure reduction index for comparing the rotational speeds of the tires based on the acquired rotational speed information. The trend derivation unit derives the time-series change trend of the representative value Q(k) based on a plurality of data sets of the time t(k) corresponding to the k-th (k = 1, 2,..., n) driving of the vehicle in chronological order and the representative value Q(k) of the relative pressure reduction index calculated during the k-th driving. The pressure reduction determination unit determines whether pressure reduction has occurred in one of the tires based on the change trend.

[0014] The tire pressure reduction detection method for single-wheel pressure reduction according to the seventh aspect is a pressure reduction detection method executed by one or more computers connected to a storage unit, and includes the following. (1) Acquiring the rotational speed information of each tire included in the vehicle while the vehicle is running (2) Calculating a relative pressure reduction index for comparing the rotational speeds of the tires based on the acquired rotational speed information (3) Saving in the storage unit the relative pressure reduction index calculated at a first time point while the vehicle is performing the first driving as a reference value (4) During the first run, determine whether or not pressure has been reduced in one of the tires based on the relative pressure reduction index calculated at a second time point after the first time point and the reference value.

[0015] The method for detecting a single-wheel depressurization according to the eighth aspect is a method for detecting a single-wheel depressurization performed by one or more computers, and comprises the following: (1) Obtain rotational speed information of each tire included in the vehicle while the vehicle is in motion. (2) Based on the rotational speed information obtained, calculate a relative pressure reduction index to compare the rotational speeds of each tire. (3) While the vehicle is performing the first run, a regression equation is derived based on multiple datasets of the elapsed time since the start of the first run and the relative decompression index during the elapsed time, with the relative decompression index as the dependent variable and the elapsed time as the independent variable. (4) Based on the regression coefficients included in the regression equation, determine whether or not pressure is being reduced in one of the tires.

[0016] The method for detecting a single-wheel depressurization according to the ninth aspect is a method for detecting a single-wheel depressurization performed by one or more computers, and comprises the following: (1) Obtain rotational speed information of each tire included in the vehicle while the vehicle is in motion. (2) Based on the rotational speed information obtained, calculate a relative pressure reduction index to compare the rotational speeds of each tire. (3) Based on multiple datasets of time t(k) corresponding to the kth (k=1,2,…,n) run of the vehicle in time series and representative value Q(k) of the relative pressure reduction index calculated during the k run, the time series change trend of the representative value Q(k) is derived. (4) Based on the trend of change, determine whether or not pressure is being reduced in one of the tires.

[0017] The pressure reduction detection program for single-wheel pressure reduction related to the 10th perspective causes one or more computers connected to the memory unit to perform the following: (1) Obtain rotational speed information of each tire included in the vehicle while the vehicle is in motion. (2) Based on the rotational speed information obtained, calculate a relative pressure reduction index to compare the rotational speeds of each tire. (3) The relative pressure reduction index calculated at the first point in time while the vehicle is performing the first run is stored in the storage unit as a reference value. (4) During the first run, determine whether or not pressure has been reduced in one of the tires based on the relative pressure reduction index calculated at a second time point after the first time point and the reference value.

[0018] The pressure reduction detection program for single-wheel pressure reduction related to the 11th perspective causes one or more computers to perform the following: (1) Obtain rotational speed information of each tire included in the vehicle while the vehicle is in motion. (2) Based on the rotational speed information obtained, calculate a relative pressure reduction index to compare the rotational speeds of each tire. (3) While the vehicle is performing the first run, a regression equation is derived based on multiple datasets of the elapsed time since the start of the first run and the relative decompression index during the elapsed time, with the relative decompression index as the dependent variable and the elapsed time as the independent variable. (4) Based on the regression coefficients included in the regression equation, determine whether or not pressure is being reduced in one of the tires.

[0019] The pressure reduction detection program for single-wheel pressure reduction related to the 12th perspective causes one or more computers to perform the following: (1) Obtain rotational speed information of each tire included in the vehicle while the vehicle is in motion. (2) Based on the rotational speed information obtained, calculate a relative pressure reduction index to compare the rotational speeds of each tire. (3) Based on multiple datasets of time t(k) corresponding to the kth (k=1,2,…,n) run of the vehicle in time series and representative value Q(k) of the relative pressure reduction index calculated during the k run, the time series change trend of the representative value Q(k) is derived. (4) Based on the trend of change, determine whether or not pressure is being reduced in one of the tires. [Effects of the Invention]

[0020] According to the present invention, a tire pressure reduction detection device, pressure reduction detection method, and pressure reduction detection program are provided that do not require an initialization operation. [Brief explanation of the drawing]

[0021] [Figure 1] A schematic diagram showing how a pressure reduction detection device according to one embodiment of the present invention is mounted on a vehicle. [Figure 2] A block diagram showing the electrical configuration of the pressure reduction detection device. [Figure 3A] A flowchart showing the flow of the first depressurization detection process. [Figure 3B] A diagram illustrating the principle of the first pressure reduction detection process. [Figure 4A] A flowchart showing the flow of the second depressurization detection process. [Figure 4B] A diagram illustrating the principle of the second pressure reduction detection process. [Figure 5A] A flowchart illustrating the flow of the third depressurization detection process. [Figure 5B] A diagram illustrating the principle of the third pressure reduction detection process. [Modes for carrying out the invention]

[0022] Hereinafter, with reference to the drawings, a pressure reduction detection device, a pressure reduction detection method, and a pressure reduction detection program according to embodiments of the present invention will be described.

[0023] <1. Configuration of the pressure detection device> FIG. 1 is a schematic diagram showing a state where the pressure reduction detection device 2 according to the present embodiment is mounted on a vehicle 1. The vehicle 1 may include an internal combustion engine as a prime mover, may include an electric motor, or may include both an internal combustion engine and an electric motor. The vehicle 1 is a four-wheel vehicle and includes a left front wheel FL, a right front wheel FR, a left rear wheel RL, and a right rear wheel RR. The vehicle 1 has tires T FL ,T FR ,T RL ,T RR mounted on these wheels. The pressure reduction detection device 2 has a function of detecting a single-wheel pressure reduction, which is a pressure reduction of any one of the tires T FL ,T FR ,T RL ,T RR . When a single-wheel pressure reduction is detected, the pressure reduction detection device 2 gives an alarm to that effect via an alarm indicator 3 mounted on the vehicle 1. Details of the flow of such pressure reduction detection processing will be described later.

[0024] The single-wheel pressure reduction is detected based on the rotational speeds of the left front wheel FL, the right front wheel FR, the left rear wheel RL, and the right rear wheel RR. Wheel speed sensors 6 are respectively attached to the left front wheel FL, the right front wheel FR, the left rear wheel RL, and the right rear wheel RR, and each wheel speed sensor 6 detects a rotational speed signal representing the rotational speed of the wheel to which it is attached (in other words, the rotational speed information of the tire T FL ,T FR ,T RL ,T RR ). The wheel speed sensors 6 are connected to the pressure reduction detection device 2 via a communication line 5 or wirelessly. The rotational speed signals detected by the wheel speed sensors 6 are sequentially transmitted to the pressure reduction detection device 2.

[0025] Any wheel speed sensor 6 can be used as long as it can detect the wheel speeds of the FL, FR, RL, and RR wheels while the vehicle is in motion. For example, a sensor that measures wheel speed from the output signal of an electromagnetic pickup can be used, or a sensor that generates electricity using rotation, such as a dynamo, and measures wheel speed from the voltage generated at that time can be used. The mounting position of the wheel speed sensor 6 is not particularly limited and can be appropriately selected depending on the type of sensor, as long as it is possible to detect the wheel speed.

[0026] The warning indicator 3 can be implemented in any form, such as a liquid crystal display element or a liquid crystal monitor, as long as it can inform the user that tire pressure is decreasing. The mounting position of the warning indicator 3 can also be selected as appropriate, but it is preferable to install it in a location easily visible to the driver, such as on the instrument panel. When the control unit (pressure detection device 2) is connected to a car navigation system, the car navigation monitor can also be used as the warning indicator 3. When a monitor is used as the warning indicator 3, the warning can be displayed as an icon or text information on the monitor.

[0027] Figure 2 is a block diagram showing the electrical configuration of the pressure reduction detection device 2. The pressure reduction detection device 2, as hardware, is a control unit (on-board computer) mounted on the vehicle 1. As shown in Figure 2, it includes an I / O interface 11, a CPU (Central Processing Unit) 12, a ROM (Read Only Memory) 13, a RAM (Random Access Memory) 14, and a non-volatile, rewritable storage device (storage unit) 15. The I / O interface 11 is a communication device that enables communication with external devices such as the wheel speed sensor 6 and the warning indicator 3. The ROM 13 stores a program 9 for controlling the operation of various parts of the vehicle 1. The program 9 is written to the ROM 13 from a storage medium 8 such as a CD-ROM. The CPU 12 reads and executes the program 9 from the ROM 13, thereby virtually operating as a reset unit 20, an acquisition unit 21, an index calculation unit 22, a regression analysis unit 23, a trend derivation unit 24, a pressure reduction determination unit 25, and a warning generation unit 26. Details of the operation of each unit 20-26 will be described later. The storage device 15 consists of a hard disk, flash memory, or EPROM, etc. Note that the storage location for the program 9 may be the storage device 15 instead of the ROM 13. The RAM 14 and storage device 15 are used as appropriate for calculations performed by the CPU 12.

[0028] As described later, the pressure reduction detection device 2 uses a method according to the dynamic load radius (DLR) method to detect the tire T FL ,T FR ,T RL ,T RR The system is configured to perform three different pressure reduction detection processes to detect any one of the following pressure reductions. These first to third pressure reduction detection processes share the common feature of being able to detect single-wheel pressure reduction without requiring an initialization operation by the driver, and they also use the same relative pressure reduction index. However, the first to third pressure reduction detection processes each target single-wheel pressure reduction caused by different events and can be executed in parallel and independently for the same vehicle 1 during the same run.

[0029] Hereafter, a single unit of travel for Vehicle 1 may be referred to as "the kth (k=1,2,...,n)th travel." A single unit of travel can be, for example, the travel time during which the internal combustion engine or electric motor is turned ON / OFF once. Here, k represents the relative chronological order in which the travels occurred. In other words, "the first travel" represents the travel that occurred first within "the kth travel," and "the nth travel" represents the travel that occurred last within "the kth travel." "The k+1th travel" represents the travel that occurred after "the kth travel" was completed and followed the kth travel.

[0030] <2-1. First pressure reduction detection process> The first pressure reduction detection process, which is performed during the k-th run, will be described below with reference to Figure 3A. The first pressure reduction detection process starts when the k-th run begins and ends when the k-th run ends.

[0031] In step S10, the reset unit 20 deletes data stored in the storage device 15 during the (k-1)th run (i.e., during the previous run). The data to be deleted includes the reference value R(k-1) stored during the (k-1)th run. The reference value R will be described later. Step S10 resets the reference value storage area in the storage device 15.

[0032] In step S11, the acquisition unit 21 acquires time-series rotational speed signals from each wheel speed sensor 6 attached to wheels FL, FR, RL, and RR. The acquisition unit 21 then outputs the acquired rotational speed signals to the respective tire T FL ,T FR ,T RL ,T RR The rotation speeds are converted to V1-V4 and stored in RAM14 or storage device15.

[0033] In step S12, the acquisition unit 21 determines whether the data saved in step S11 is valid. Valid data is data acquired when the vehicle 1's driving conditions are steady. Since the dynamic load radius of the tire changes not only with respect to the tire pressure but also with respect to the vehicle 1's driving conditions, it is preferable that data acquired during extreme acceleration / deceleration or cornering, for example, is rejected and not used in subsequent processing. If the data is determined to be valid (YES) in step S12, then step S13 is executed. If the data is determined to be invalid (NO) in step S12, the data saved in step S11 is rejected, and steps S11 to S12 are executed again.

[0034] In step S13, the acquisition unit 21 determines whether a predetermined number of valid data has been stored in the RAM 14 or storage device 15. The predetermined number is the number of data points for rotation speeds V1 to V4 required to properly perform the processing described later, and is predetermined. If it is determined in step S13 that a predetermined number of valid data has been stored (YES), then step S14 is executed. If it is determined in step S13 that the number of valid data is less than the predetermined number (NO), then steps S11 to S13 are executed again.

[0035] In step S14, the index calculation unit 22 calculates the relative pressure reduction index DEL1 based on the rotational speeds V1 to V4. The relative pressure reduction index in this embodiment is an index that compares the rotational speeds of each tire, as defined by the following formula (1). DEL1={(V1+V4) / (V2+V3)-1}×100(%) (1)

[0036] The index calculation unit 22 substitutes the rotation speed data V1 to V4 acquired at the same time into equation (1) and calculates multiple DEL1 values ​​and their average value. The DEL1 values ​​or their average value calculated in this way are examples of relative pressure reduction indices calculated at the first point in time during the kth run. The first point in time is, for example, about 1 to 3 minutes after the start of the kth run, and may be a period of time lasting from a few seconds to several tens of seconds. The index calculation unit 22 stores the calculated DEL1 values ​​or their average value as a reference value R(k) in the storage device 15.

[0037] In step S15, the acquisition unit 21 further acquires time-series rotational speed signals from each wheel speed sensor 6. Similar to step S11, the acquisition unit 21 then outputs the acquired rotational speed signals to the respective tire T FL ,T FR ,T RL ,T RR The rotation speeds are converted to V1-V4 and stored in RAM14 or storage device15.

[0038] In step S16, the acquisition unit 21 determines whether the data saved in step S15 is valid. This determination is the same as in step S12, so the explanation is omitted. If the determination in step S16 is YES, then step S17 is executed. If the determination in step S16 is NO, the data saved in step S15 is rejected, and steps S15 to S16 are executed again.

[0039] In step S17, the index calculation unit 22 calculates the relative decompression index DEL1 based on the rotation speeds V1 to V4 that were determined to be valid in step S16. The relative decompression index DEL1 calculated in step S17 is an example of the relative decompression index calculated at the second time point.

[0040] In step S18, the pressure reduction determination unit 25 determines whether or not a single-wheel pressure reduction has occurred based on the reference value R(k) and the relative pressure reduction index DEL1 calculated in step S17. Specifically, the pressure reduction determination unit 25 compares |DEL1-R(k)| with a predetermined threshold Th1, and determines that a single-wheel pressure reduction has not occurred (NO) if |DEL1-R(k)| is less than or equal to the predetermined threshold Th1, and determines that a single-wheel pressure reduction has occurred (YES) if |DEL1-R(k)| exceeds the predetermined threshold Th1.

[0041] A predetermined threshold Th1 is, for example, tire T FL ,T FR ,T RL ,T RR One of these is determined based on the change in DEL1 when the internal pressure is reduced by 16% to 20% from the normal pressure. Thus, if DEL1 changes relatively large relative to the reference value R(k) during one unit of driving, the tire T FL ,T FR ,T RL ,T RR It is thought that a puncture occurred in one of the tires. In this case, as shown in Figure 3B, DEL1 begins to deviate from the reference value R(k) from a certain point in time, and the absolute value of the difference from the reference value R(k) is thought to increase irreversibly over time. For this reason, by repeatedly executing steps S15 to S18 at a predetermined cycle from step S14 onward, it is possible to detect a single tire pressure drop based on the reference value R(k) and DEL1 at the second point in time.

[0042] Referring again to Figure 3A, if it is determined in step S18 that no single-wheel pressure reduction has occurred (NO), steps S15 to S18 are executed again. In other words, unless single-wheel pressure reduction is detected in step S18, steps S15 to S18 are repeated at a predetermined cycle. If it is determined that single-wheel pressure reduction has occurred (YES), step S19 is executed.

[0043] In step S19, the alarm generation unit 26 generates alarm data indicating that a single tire pressure drop has occurred and displays it on the alarm display unit 3. The alarm data can be in any form that can notify the driver that a single tire pressure drop has occurred. The alarm data may also include information that identifies the tire that is thought to be experiencing pressure drop. For example, the tire experiencing pressure drop can be the tire with the rotational speed that deviates the most from the other three tires when comparing the effective rotational speeds V1 to V4 at the same time. The alarm display unit 3 may, for example, display a graphic modeled after the vehicle 1 and highlight the location on the graphic that corresponds to the wheel position of the tire experiencing pressure drop.

[0044] <2-2. Second Depressurization Detection Process> The second pressure reduction detection process, which is performed during the k-th run, will be described below with reference to Figure 4A. The second pressure reduction detection process starts when the k-th run begins and ends when the k-th run ends.

[0045] Steps S21 to S24 are the same as steps S11 to S14, which are performed in the first depressurization detection process. Therefore, a further explanation is omitted. When both steps S22 and S23 are determined to be YES, step S24 is then executed.

[0046] In step S24, the index calculation unit 22 calculates multiple DEL1 values ​​based on valid data of rotational speeds V1 to V4 acquired at the same time. This generates multiple datasets, each combining the elapsed time from the start of the k-th run with the DEL1 value at that time. The number of these datasets is not particularly limited and can be determined as appropriate. The predetermined number in step S23 can be set to a number sufficient to generate these multiple datasets. The index calculation unit 22 stores the generated datasets in RAM 14 or storage device 15.

[0047] In step S25, the regression analysis unit 23 performs regression analysis based on the multiple datasets generated in step S24. Specifically, the regression analysis unit 23 derives a regression equation in which DEL1 is the dependent variable and the elapsed time t from the start of the k-th run is the independent variable. In this embodiment, the regression equation is the equation of a straight line represented by DEL1 = M(k)·t + N(k). In other words, the regression analysis unit 23 derives the slope M(k) and intercept N(k), which are regression coefficients that identify this straight line. The derivation method is not particularly limited, and for example, least squares method, successive least squares method, Kalman filter, etc. can be used, but from the viewpoint of saving computational resources, successive methods such as successive least squares method and Kalman filter are preferred.

[0048] In step S26, the pressure reduction determination unit 25 determines whether or not a single-wheel pressure reduction has occurred based on the slope M(k) derived in step S25. Specifically, the pressure reduction determination unit 25 compares the absolute value of the slope M(k) with a predetermined threshold Th2. If the absolute value of the slope M(k) is less than or equal to the predetermined threshold Th2, it determines that a single-wheel pressure reduction has not occurred (NO). If the absolute value of the slope M(k) exceeds the predetermined threshold Th2, it determines that a single-wheel pressure reduction has occurred (YES).

[0049] This is based on the following principle: If no tire pressure reduction occurs, DEL1 is expected to converge to a certain range regardless of the elapsed time since the start of the k-th run. However, for example, during the previous run, tire T FL ,T FR ,T RL ,T RR If a sharp object such as a nail pierces any of these holes, the internal air is retained when the vehicle is stopped, but air leaks out of the puncture hole when it rotates. Therefore, theoretically, DEL1 changes irreversibly with the elapsed time from the start of the k-th movement, and as shown in Figure 4B, the absolute value of the slope M(k) also changes in the direction of increasing with the elapsed time.

[0050] In addition to the above determination, the pressure reduction determination unit 25 may also compare the absolute value of the difference between the latest DEL1 and the initial intercept N(k) |DEL1-N(k)| with a predetermined threshold Th3 to determine whether |DEL1-N(k)| is less than or equal to the predetermined threshold Th3 or exceeds the predetermined threshold Th3. For example, if it is determined that a single-wheel pressure reduction has occurred due to the slope M(k), and |DEL1-N(k)| exceeds the predetermined threshold Th3, it is considered that the possibility of a single-wheel pressure reduction has occurred is even higher. Thus, the determination using |DEL1-N(k)| can be used as an auxiliary method to improve the accuracy of the pressure reduction determination using the slope M(k). Note that the initial intercept N(k) is the theoretical DEL1 at the start of driving. Therefore, the comparison between the latest DEL1 and the initial intercept N(k) is equivalent to the determination of whether or not a single-wheel pressure reduction has occurred in step S18 of the first pressure reduction determination process.

[0051] Referring again to Figure 4A, if it is determined in step S26 that no single-wheel pressure reduction has occurred (NO), then steps S27 and S28 are executed. Steps S27 and S28 are the same as steps S21 and S22, so their explanation is omitted. If it is determined in step S28 that YES, then steps S24 to S26 are executed again. In other words, a new relative pressure reduction index DEL1 is calculated based on the newly acquired rotation speeds V1 to V4, and the slope M(k) and intercept N(k) are updated sequentially.

[0052] On the other hand, if it is determined in step S26 that a single-wheel pressure drop has occurred (YES), then step S29 is executed. Step S29 is the same as step S19, so its explanation is omitted.

[0053] <2-3. Third Depressurization Detection Process> The third pressure reduction detection process will now be explained with reference to Figure 5A. The third pressure reduction detection process detects pressure reduction caused by factors that are difficult to detect during a single unit of driving, such as a slow puncture. The process shown in Figure 5A starts, for example, when the power to the electrical system of vehicle 1 is turned ON, and stops when it is turned OFF.

[0054] Steps S30 to S32 are the same as steps S11 to S13, and are the process in which the acquisition unit 21 acquires the rotation speeds V1 to V4 of each tire and accumulates a predetermined number of valid data. The predetermined number of data to be accumulated may be the same as or different from that of the first pressure reduction detection process and the second pressure reduction detection process.

[0055] In step S33, the index calculation unit 22 calculates the relative decompression index DEL1 from the data of effective rotational speeds V1 to V4 according to equation (1). In this embodiment, the index calculation unit 22 calculates multiple DEL1s from multiple data sets of effective rotational speeds V1 to V4. The multiple DEL1s are relative decompression index DEL1s at different points in time during the k-th run.

[0056] In step S34, the index calculation unit 22 determines a representative value Q(k) of DEL1 for the k-th run based on the multiple DEL1 calculated in step S33. The algorithm for determining the representative value Q(k) is not particularly limited, but for example, the simple average of the multiple DEL1 calculated in step S33, the weighted average weighted by elapsed time, or the median can be adopted as the representative value Q(k).

[0057] In step S35, the trend derivation unit 24 derives the trend of the representative value Q(k) with respect to the elapsed time t from the start of the first run. The elapsed time t is the cumulative time from the start of the first run, including the elapsed time between the k run and the (k+1) run. In this embodiment, the trend derivation unit 24 derives the slope O(k) of a regression line (see Figure 5B) with elapsed time t as the explanatory variable and the representative value Q(k) as the dependent variable. The method for deriving the slope O(k) is not particularly limited, and for example, the least squares method, successive least squares method, Kalman filter, etc. can be used, but in this embodiment, a successive method is adopted. That is, the slope O(k) is updated successively each time the latest representative value Q(k) is newly acquired.

[0058] In step S36, the pressure reduction determination unit 25 determines whether or not a single-wheel pressure reduction has occurred based on the slope O(k). Specifically, the pressure reduction determination unit 25 compares the absolute value of the slope O(k) with a threshold Th4. If the absolute value of the slope O(k) is less than or equal to a predetermined threshold Th4, it determines that a single-wheel pressure reduction has not occurred (NO). If the absolute value of the slope O(k) exceeds a predetermined threshold Th4, it determines that a single-wheel pressure reduction has occurred (YES).

[0059] This is based on the following principle. Figure 5B is a graph showing an example of the change in the representative value Q(k) with respect to elapsed time t. However, the elapsed time t(k) in the graph is assigned for explanatory convenience as the elapsed time corresponding to the kth run. Between elapsed times t(1) to t(4), the representative value Q(k) does not show any particular trend with respect to elapsed time t. In such cases, the absolute value of the slope O(k) converges to a relatively small value close to 0. On the other hand, between elapsed times t(4) and t(5), when one tire begins to depressurize little by little, the representative value Q(k) changes in one direction on the vertical axis between elapsed times t(5) and t(8). The representative value Q(k) may change in the opposite direction in the short term, as in the example of elapsed times t(6) and t(7), but in the long term it shows an increasing or decreasing trend. When a trend appears in the representative value Q(k), the slope O(k) changes in the direction of increasing absolute value, and unless air pressure adjustments are made, its absolute value will eventually exceed a predetermined threshold Th4. This makes it possible to detect single-wheel pressure depressurization even if the rate of single-wheel pressure depressurization is too slow to be detected by the pressure depressurization detection process in one unit of driving. The predetermined threshold Th4 can be predetermined by considering the speed at which the tire pressure depressurizes to the warning threshold under predetermined conditions such as the distance or number of drives of vehicle 1 per certain period.

[0060] In addition to the above determination, the pressure reduction determination unit 25 may also compare the absolute value of the difference between the latest representative value Q(k) (Q(8) in the example of Figure 5B) and the latest regression intercept P(k) (P(8) in the example of Figure 5B), |Q(k)-P(k)|, with a predetermined threshold Th5 to determine whether |Q(k)-P(k)| is less than or equal to the predetermined threshold Th5, or exceeds the predetermined threshold Th5. Theoretically, the regression intercept P(k) is equal to or close to the representative value Q(1) at the elapsed time t(1). Therefore, if it is determined that a single-wheel pressure reduction has occurred based on the slope O(k), and |Q(k)-P(k)| exceeds the predetermined threshold Th5, the possibility of a single-wheel pressure reduction is considered to be even higher. Thus, the determination using |Q(k)-P(k)| can be used as an auxiliary method to improve the accuracy of the pressure reduction determination based on the slope O(k).

[0061] Referring again to Figure 5A, if it is determined in step S36 that no single-wheel pressure reduction has occurred (NO), the third pressure reduction detection process for the k-th run is terminated. However, data such as the regression coefficients, including the representative value Q(k), slope O(k), and intercept P(k) determined in step S34, which are necessary for executing steps S34 to S35 during the (k+1)-th run (i.e., the next run), are stored in non-volatile memory such as the storage device 15 or an EPROM (not shown).

[0062] On the other hand, if it is determined in step S36 that a single-wheel pressure drop has occurred (YES), then step S37 is executed. Step S37 is the same as step S19, so its explanation is omitted.

[0063] <3. Features> (1) According to the pressure reduction detection device 2 and the first to third pressure reduction detection processes of the above embodiment, the driver can detect a pressure drop in the entire vehicle without performing any special initialization operations. Therefore, there is no need to worry about a decrease in the accuracy of pressure reduction detection due to neglecting or performing initialization operations at the wrong time. In addition, there is no need to take measures to ensure that the driver performs initialization operations in a timely manner, and the configuration can be simplified.

[0064] (2) The first to third pressure reduction detection processes are performed based on the tire rotation speed, so there is no need to introduce new equipment to vehicle 1. Furthermore, they can be performed in parallel with, for example, a pressure reduction detection process that follows another DLR method.

[0065] (3) The first to third pressure reduction detection processes each target the detection of single-wheel pressure reduction at different rates. Therefore, by using these processes in combination, the accuracy of single-wheel pressure reduction detection can be further improved.

[0066] <4. Variation> Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention. For example, the following modifications are possible. Furthermore, the gist of the following modifications can be combined as appropriate.

[0067] (1) The pressure reduction detection device 2 according to the above embodiment is configured to perform the first to third pressure reduction detection processes. However, the pressure reduction detection device 2 may be configured to perform only one of the first to third pressure reduction detection processes, or any two of them.

[0068] (2) The relative pressure reduction index can be any index that compares the rotational speed of each tire, and is not limited to the one defined by the formula in the above embodiment. For example, DEL1 may be defined by the following formula. DEL1=[(V2+V3) / 2-(V1+V4) / 2] / [(V1+V2+V3+V4) / 4]×100(%) Alternatively, instead of DEL1, the following relative pressure reduction indices, conventionally referred to as DEL2 or DEL3, may be used. However, DEL1 is an index that compares the rotational speeds of diagonally opposite tires in a four-wheeled vehicle (that is, it becomes larger as rotational speeds V1 and V4 are larger and smaller as rotational speeds V2 and V3 are larger, or vice versa). Therefore, compared to DEL2 and DEL3, it is less affected by the turning of the vehicle 1 and changes in load. For this reason, it is advantageous compared to DEL2 and DEL3 in terms of the accuracy of pressure reduction detection. DEL2=[(V3+V4) / 2-(V1+V2) / 2] / [(V1+V2+V3+V4) / 4]×100(%) DEL3=[(V2+V4) / 2-(V1+V3) / 2] / [(V1+V2+V3+V4) / 4]×100(%) DEL2=[(V3+V4) / (V1+V2)-1]×100(%) DEL3=[(V2+V4) / (V1+V3)-1]×100(%)

[0069] (3) The above units of travel are examples and can be changed as appropriate. For example, travel that continues for a predetermined time or longer, excluding temporary stops such as at traffic lights, may be defined as "the kth travel".

[0070] (4) The order in which each step of the pressure reduction detection process according to the above embodiment is executed can be changed as appropriate. For example, the timing in which step S10 is executed may be after any of steps S11 to S19. In other words, the reset unit 20 can delete the reference value R(k-1), regression coefficient M(k-1), and N(k-1) from the storage device 15 at any timing after one run.

[0071] (5) The process performed by the trend derivation unit 24 in step S35 is not limited to the derivation of regression coefficients. The trend derivation unit 24 may, for example, determine whether the representative value Q(k) has been increasing for a predetermined number of consecutive times or whether it has been decreasing for a predetermined number of consecutive times. In other words, if the representative value Q(k) is increasing or decreasing for a predetermined number of consecutive times as the elapsed time t increases, it is considered that a decrease in pressure is occurring. Thus, the trend derivation unit 24 may derive the time-series trend of change of the representative value Q(k) without deriving regression coefficients.

[0072] (6) In the above embodiment, the regression analysis unit 23 derived a linear regression equation with slope M(k) and intercept N(k) as the regression equation with DEL1 as the dependent variable and elapsed time t as the independent variable. However, this regression equation is not limited to a linear equation, and may be, for example, an equation of order I or higher (I≧2) in relation to elapsed time t. Then, the pressure reduction determination unit 25 determines t I The coefficients and t I-1 The single-wheel pressure reduction may be determined based on the coefficients, etc.

[0073] (7) Each step of the pressure reduction detection process according to the above embodiment may be performed by multiple computers. That is, at least some of steps S10 to S19, steps S21 to S29, and steps S30 to S37 may be performed by other external computers connected to the pressure reduction detection device 2. [Explanation of Symbols]

[0074] 1 vehicle 2. Pressure detection device 15 Storage device (storage unit) 20 Reset section 21 Acquisition Department 22 Indicator calculation section 23 Regression Analysis Department 24 Trend derivation part 25 Pressure Depressure Determination Unit 26 Alarm generation unit

Claims

1. An acquisition unit that acquires rotational speed information of each tire included in the vehicle while the vehicle is in motion, An index calculation unit calculates a relative pressure reduction index for comparing the rotation speeds of each tire based on the acquired rotation speed information, A storage unit that stores the relative pressure reduction index calculated at a first point in time while the vehicle is performing a first run as a reference value, A pressure reduction determination unit determines whether or not pressure reduction has occurred in one of the tires based on the relative pressure reduction index calculated at a second time point after the first time point during the first driving period and the reference value, Equipped with, A pressure reduction detection device for single-wheel decompression.

2. A regression analysis unit derives a regression equation based on multiple datasets of the elapsed time from the start of the first run and the relative decompression index during the elapsed time, with the relative decompression index as the dependent variable and the elapsed time as the independent variable. Furthermore, The pressure reduction determination unit further determines whether or not pressure reduction has occurred in one of the tires based on the regression coefficient included in the regression equation. The pressure reduction detection device according to claim 1.

3. If, during the first run, the pressure reduction determination unit does not determine that pressure is occurring in one of the tires, the reset unit deletes the reference value from the storage unit after the first run. Furthermore, A pressure reduction detection device according to claim 1 or 2.

4. A trend derivation unit derives the time-series change trend of the representative value Q(k) based on multiple data sets of time t(k) corresponding to the kth (k=1, 2, ..., n) travel of the vehicle in chronological order and the representative value Q(k) of the relative pressure reduction index calculated during the k travel. Furthermore, The pressure reduction determination unit further determines, based on the trend of change, whether or not pressure reduction has occurred in one of the tires. A pressure reduction detection device according to claim 1 or 2.

5. An acquisition unit that acquires rotational speed information of each tire included in the vehicle while the vehicle is in motion, An index calculation unit calculates a relative pressure reduction index for comparing the rotation speeds of each tire based on the acquired rotation speed information, While the vehicle is performing the first run, a regression analysis unit derives a regression equation based on multiple datasets of the elapsed time since the start of the first run and the relative decompression index during the elapsed time, with the relative decompression index as the dependent variable and the elapsed time as the independent variable. A pressure reduction determination unit that determines whether or not pressure reduction is occurring in one of the tires based on the regression coefficients included in the regression equation. Equipped with, A pressure reduction detection device for single-wheel decompression.

6. An acquisition unit that acquires rotational speed information of each tire included in the vehicle while the vehicle is in motion, An index calculation unit calculates a relative pressure reduction index for comparing the rotation speeds of each tire based on the acquired rotation speed information, A trend derivation unit derives the time-series change trend of the representative value Q(k) based on a plurality of datasets of time t(k) corresponding to the kth (k=1, 2, ..., n) travel of the vehicle in time-series order and representative value Q(k) of the relative pressure reduction index calculated during the k travel, A pressure reduction determination unit determines whether or not pressure reduction is occurring in one of the tires based on the aforementioned trend of change. Equipped with, A pressure reduction detection device for single-wheel decompression.

7. A method for detecting a single-wheel depressurization, which is performed by one or more computers connected to a memory unit, While the vehicle is in motion, information on the rotational speed of each tire included in the vehicle is acquired, Based on the acquired rotational speed information, a relative pressure reduction index is calculated to compare the rotational speeds of each tire. The relative pressure reduction index calculated at a first point in time while the vehicle is performing a first run is stored in the storage unit as a reference value, During the first run, it is determined whether or not pressure loss has occurred in one of the tires based on the relative pressure reduction index calculated at a second time point after the first time point and the reference value, Equipped with, A method for detecting pressure loss in a single-wheel decompression system.

8. A method for detecting a single-wheel depressurization, which is performed by one or more computers, While the vehicle is in motion, information on the rotational speed of each tire included in the vehicle is acquired, Based on the acquired rotational speed information, a relative pressure reduction index is calculated to compare the rotational speeds of each tire. While the vehicle is performing the first run, a regression equation is derived based on multiple datasets of the elapsed time from the start of the first run and the relative decompression index during the elapsed time, with the relative decompression index as the dependent variable and the elapsed time as the independent variable. Based on the regression coefficients included in the regression equation, it is determined whether or not pressure is being reduced in one of the tires. Equipped with, A method for detecting pressure loss in a single-wheel decompression system.

9. A method for detecting a single-wheel depressurization, which is performed by one or more computers, While the vehicle is in motion, information on the rotational speed of each tire included in the vehicle is acquired, Based on the acquired rotational speed information, a relative pressure reduction index is calculated to compare the rotational speeds of each tire. Based on multiple datasets of time t(k) corresponding to the kth (k=1, 2, ..., n) run of the vehicle in chronological order, and representative value Q(k) of the relative pressure reduction index calculated during the k run, the time-series change trend of the representative value Q(k) is derived. Based on the aforementioned trend of change, it is determined whether or not pressure is being reduced in one of the tires. Equipped with, A method for detecting pressure loss in a single-wheel decompression system.

10. A pressure reduction detection program for single-wheel pressure reduction, which is connected to one or more computers in a memory unit, While the vehicle is in motion, information on the rotational speed of each tire included in the vehicle is acquired, Based on the acquired rotational speed information, a relative pressure reduction index is calculated to compare the rotational speeds of each tire. The relative pressure reduction index calculated at a first point in time while the vehicle is performing a first run is stored in the storage unit as a reference value, During the first run, it is determined whether or not pressure loss has occurred in one of the tires based on the relative pressure reduction index calculated at a second time point after the first time point and the reference value, To execute A pressure reduction detection program for single-wheel decompression.

11. While the vehicle is in motion, information on the rotational speed of each tire included in the vehicle is acquired, Based on the acquired rotational speed information, a relative pressure reduction index is calculated to compare the rotational speeds of each tire. While the vehicle is performing the first run, a regression equation is derived based on multiple datasets of the elapsed time from the start of the first run and the relative decompression index during the elapsed time, with the relative decompression index as the dependent variable and the elapsed time as the independent variable. Based on the regression coefficients included in the regression equation, it is determined whether or not pressure is being reduced in one of the tires. To run it on one or more computers, A pressure reduction detection program for single-wheel decompression.

12. While the vehicle is in motion, information on the rotational speed of each tire included in the vehicle is acquired, Based on the acquired rotational speed information, a relative pressure reduction index is calculated to compare the rotational speeds of each tire. Based on multiple datasets of time t(k) corresponding to the kth (k=1, 2, ..., n) run of the vehicle in chronological order, and representative value Q(k) of the relative pressure reduction index calculated during the k run, the time-series change trend of the representative value Q(k) is derived. Based on the aforementioned trend of change, it is determined whether or not pressure is being reduced in one of the tires. To run it on one or more computers, A pressure reduction detection program for single-wheel decompression.

Images