JP2008007026A - Air pressure reduction detection device, air pressure reduction detection program and air pressure reduction detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that the reduction of air pressure cannot be accurately detected in a state other than a state that a vehicle is linearly advanced on a flat road surface when a vehicle is in a turn or travels on a shape. <P>SOLUTION: Traveling track information indicating a traveling track of the vehicle is obtained, wheel rotation speed information corresponding to a rotation speed of each of plurality of wheels is obtained, and the reduction of the air pressure of the wheel is detected when actual operations of the respective wheels indicated by the wheel rotation speed information do not coincide with operations of the respective wheels when they travel on the traveling track indicated by the traveling track information. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an air pressure decrease detection device, a program, and a method for detecting a decrease in wheel air pressure.

2. Description of the Related Art Conventionally, a technique is known in which information indicating the rotational speed of a wheel is acquired by a vehicle speed sensor and a decrease in air pressure of each wheel is detected by comparing the rotational speed of each wheel (for example, Patent Document 1). In Patent Document 1, it is determined whether or not the vehicle is traveling straight, and a weight that increases the contribution rate in a straight traveling state is calculated. The weight is reflected when the tire diameter ratio is calculated based on the difference between the left and right rotational speeds of the wheels. By this process, the contribution rate of the rotational speed of the wheel at the time of turning is lowered, and the detection accuracy of the decrease in air pressure is improved.
JP 2005-1613 A

In the prior art, a decrease in air pressure cannot be accurately detected except when the vehicle is traveling straight on a flat road surface, such as when the vehicle is turning or running on a slope. That is, in the configuration in which the contribution rate in the straight traveling state is increased when detecting the decrease in the air pressure, the configuration is such that the decrease in the air pressure is substantially detected by using the information during the straight traveling, so the curve frequently occurs. When traveling on an appearing road surface, a decrease in air pressure cannot be detected. In addition, factors such as fluctuations in the rotational speed of the wheel other than turning are not taken into account when traveling on a slope. Therefore, in the prior art, it is impossible to accurately detect a decrease in air pressure except when the vehicle is traveling straight on a flat road surface.
The present invention has been made in view of the above problems, and an object thereof is to provide a technique for accurately detecting a decrease in air pressure even when the vehicle is not traveling straight on a flat road surface.

  In order to achieve the above object, in the present invention, traveling locus information indicating the traveling locus of the vehicle is acquired, and the actual operation of each wheel is consistent with the operation of each wheel when traveling along the traveling locus. Detects a drop in wheel air pressure when not. That is, when the traveling locus of the wheel is determined, the route of each wheel to be followed when traveling along the traveling locus is determined, and the operation to be performed by each wheel is determined.

  When the air pressure of the wheel is not lowered, the operation to be performed at each wheel should match the actual operation at each wheel. A decrease can be detected. Therefore, even if the travel locus of the vehicle includes a travel locus other than straight traveling on a flat road surface, such as turning or running on a slope, it is possible to accurately detect a decrease in air pressure.

  The travel locus information acquisition means only needs to be able to acquire the travel locus information, and all information that can cause a deviation in the operation of each wheel can be used as the travel locus information. For example, any or a combination of straight traveling, turning, and slope traveling can be used as traveling locus information, and information that should be traveling locus information among them depends on the scene and accuracy to detect a decrease in air pressure. It can be selected appropriately.

  Furthermore, various information can be adopted as information that is the basis of the travel locus information, such as road shape information stored in a storage medium in advance, current position information specified by radio waves from GPS satellites, and the vehicle. Any or a combination of the detection values acquired from the mounted sensors can be employed. That is, according to the road shape information used in the navigation device or the like, it is possible to easily acquire the curve angle of the road, the slope of the slope, and the like. For example, it is possible to acquire various types of information regarding the shape of the road, such as acquiring the shape of a curve based on the arrangement of nodes included in the map information, and acquiring the slope angle of a slope based on a change in altitude of the road.

  According to the current position information specified by the radio wave from the GPS satellite, it is possible to accumulate the current position information and acquire the travel locus of the vehicle based on the current position information. Moreover, according to the sensor mounted in the vehicle, information corresponding to the traveling state of the vehicle can be acquired based on the detected value. For example, by referring to detection values of a vehicle speed sensor, an acceleration sensor, a direction sensor, a steering sensor, an in-vehicle camera, etc., the accuracy of the traveling locus obtained from the road shape information and the current position information is improved and complemented. Therefore, it is possible to acquire accurate travel locus information.

  Furthermore, the wheel rotation speed information acquisition means only needs to be able to acquire wheel rotation speed information for calculating the actual operation of each wheel. For example, a vehicle speed sensor (corresponding to wheel rotation) attached to each wheel. It is possible to employ a sensor that outputs a pulse that has been transmitted. In addition, as the actual operation of each wheel, various operations can be adopted, and various parameters corresponding to the operation such as the rotational speed of the wheel, the relative speed between the wheel and the ground surface, and the traveling distance of each wheel are included in this. Equivalent to.

  In the air pressure drop detecting means, it is only necessary to be able to substantially determine the consistency between the actual operation of each wheel and the operation of each wheel when traveling on the travel locus, and to directly determine the consistency between the two. Alternatively, it may be determined indirectly. Further, when it is determined that the actual operation of each wheel does not match the operation of each wheel when traveling on the travel locus, it is only necessary to detect a decrease in air pressure, but of course the operation of each wheel is compared. Alternatively, the wheel whose air pressure is lowered may be specified by determining the consistency for each wheel.

  As an example of the direct determination of the consistency, there is a determination in which the actual operation of each wheel is directly compared with the operation of each wheel when traveling on the travel locus. For example, if an estimated value of motion for each wheel is acquired based on the travel locus information, and an actual measured value of motion for each wheel is acquired based on the wheel rotation speed information, the difference between the two exceeds a predetermined reference. It is possible to detect a decrease in air pressure by determining whether or not there is.

  That is, if the travel locus is found, the operation of each wheel when the air pressure is not reduced can be estimated from the travel locus. On the other hand, since the wheel rotational speed information corresponds to the actual operation of each wheel, the actual operation of each wheel can be measured. If the air pressure of each wheel is not lowered, the estimated value obtained as described above and the actually measured value are coincident or substantially coincide with each other, so whether or not the difference between the two exceeds a predetermined standard. It can be acquired whether the air pressure of each wheel is falling by determining. According to the above configuration, it is possible to detect a decrease in air pressure with high accuracy even if the traveling locus includes any traveling locus other than straight traveling, such as turning or running on a slope.

  Furthermore, as an example of the indirect determination of the consistency, there is a configuration in which the determination is performed based on a parameter calculated based on the wheel rotation speed information and the travel locus information. For example, an actual measurement value of each wheel is acquired, and if the correction for canceling the difference in the operation of each wheel by traveling along the travel locus is performed on this actual measurement value, the operation for each wheel after correction is compared. This makes it possible to detect a decrease in air pressure.

  That is, when the travel locus is found, the difference in motion that should occur on each wheel by traveling along the travel locus becomes clear. Therefore, if correction is performed to cancel this difference in the operation of each wheel, if the air pressure of each wheel is not reduced, the operation of each wheel after correction should be equal. Therefore, if the operation for each wheel after correction is compared, it is possible to detect a decrease in air pressure at each wheel.

  Here, it is only necessary to be able to perform a comparison so that a decrease in the air pressure of each wheel can be detected. The wheel operation may be compared by obtaining the difference in rotational speed for two wheels, or the difference between a predetermined reference, for example, the average value of the rotational speed of the wheel and the rotational speed of each wheel is obtained. Thus, the operation of the wheels may be compared, and various configurations can be employed. In any case, the above comparison makes it possible to detect a decrease in air pressure with high accuracy even if the travel locus includes any travel locus other than straight traveling, such as turning or running on a slope. Become.

  Further, the method for determining the consistency between the operation of the wheel and the actual operation of the wheel when the vehicle travels along the travel locus as in the present invention is also applied as a program or method for performing this determination. Is possible. In addition, the air pressure drop detection device, the program, and the method as described above may be realized as a single air pressure drop detection device, or may be realized by using parts shared with each part provided in the vehicle. Various embodiments are included. 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 air pressure drop detecting device. 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.

Here, embodiments of the present invention will be described in the following order.
(1) Configuration of the first embodiment:
(1a) Air pressure drop detection processing:
(1b) Modification:
(2) Configuration of the second embodiment:
(2a) Air pressure drop detection processing:
(2b) Modification:

(1) Configuration of the first embodiment:
FIG. 1 is a block diagram showing a configuration of a navigation device 10 including an air pressure drop detection device according to the first embodiment of the present invention. The navigation device 10 includes a control unit 20 including a CPU, RAM, ROM, and the like and a storage medium 30, and the control unit 20 can execute a program stored in the storage medium 30 or the ROM. In the present embodiment, the navigation program 21 can be implemented as one of the programs, and the navigation program 21 includes a function of detecting a decrease in air pressure for detecting a decrease in air pressure at each wheel.

  The navigation program 21 has a function of outputting guidance information for guiding the vehicle. To realize this function, the vehicle includes a GPS receiver 40, a camera 41, a vehicle speed sensor 42, an acceleration sensor 43, and an orientation sensor. 44, a steering sensor 45, a speaker 46, and a display unit 47 are provided, and exchange of signals between these units and the control unit 20 is realized by an interface (not shown).

  The GPS receiver 40 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. In the present embodiment, the current position is a three-dimensional position including the altitude where the vehicle is located. The camera 41 is attached to the vehicle so as to include a predetermined area outside the vehicle in the field of view, and outputs image data indicating a captured image. The control unit 20 acquires this signal via an interface (not shown) and uses it for various types of guidance.

The vehicle speed sensor 42 outputs a signal corresponding to the rotational speed of the wheels provided in the vehicle. The control unit 20 acquires this signal via an interface (not shown), and acquires a speed (relative speed between the road surface and the wheel), a moving distance (relative moving distance of the wheel with respect to the road surface), and the like for each wheel. The vehicle in this embodiment is a four-wheeled vehicle, the front right wheel speed is V _FR , the front left wheel speed is V _FL , the rear right wheel speed is V _RR , and the rear left wheel speed. _Is V _RL . The acceleration sensor 43 outputs a signal corresponding to the acceleration acting on the vehicle, the direction sensor 44 outputs a signal corresponding to the traveling direction of the vehicle, and the steering sensor 45 outputs a signal corresponding to the rotation angle of the steering of the vehicle. .

  The control unit 20 acquires these signals via an interface (not shown), and acquires information indicating the acceleration acting on the vehicle, the traveling direction of the vehicle, and the rotation angle of the steering. Of course, the acceleration sensor 43, the azimuth sensor 44, and the steering sensor 45 described above may constitute a single sensor as shown in FIG. 1, or may be calculated based on a signal output from the vehicle speed sensor 42 or the like. May be.

  By executing the navigation program 21, the control unit 20 guides the vehicle by outputting information indicating the current position of the vehicle, the route to the destination, and the like based on the various information acquired as described above. That is, the control unit 20 outputs a control signal for performing various types of guidance by voice to the speaker 46, and outputs voice as guidance information from the speaker 46. Further, the control unit 20 outputs a control signal for performing various types of guidance based on the image to the display unit 47 and displays the image on the display unit 47.

  Further, the storage medium 30 stores map information 30a and operation correspondence information 30b for carrying out guidance by the navigation program 21. The map information 30a includes node data indicating nodes set on the road, link data indicating connection between nodes, data indicating the altitude of the road, data indicating a target, and the like. Reference numeral 30a corresponds to road shape information for specifying the shape of the road.

  The motion correspondence information 30b is data in which the output value of the vehicle speed sensor 42 is associated with the speed of the wheel at the output value, and is stored in the storage medium 30 for each wheel combination. That is, since the output value of the vehicle speed sensor 42 is a signal corresponding to the rotational speed of the wheel (for example, a pulse corresponding to the rotational speed), even if the output value of the signal is the same, the actual vehicle speed depends on the diameter of the wheel. May be different. Therefore, in the present embodiment, the operation correspondence information 30b that associates the output value of the vehicle speed sensor 42 with the wheel speed at the output value is stored in the storage medium 30 for each wheel combination, and is attached to the vehicle. The vehicle speed is obtained with reference to the motion correspondence information 30b corresponding to the combination of wheels.

  In the present embodiment, the operation correspondence information 30b is stored and held in the storage medium 30 by the exchange processing unit 21d, which is a part of the functions constituting the navigation program 21. That is, the replacement processing unit 21d displays an interface for inputting the fact when the wheel attached to the vehicle is replaced on the display unit 47, and a combination of information and wheel indicating that the replacement is completed by an input device (not shown). And information for specifying the ID.

  When this input is made, the exchange processing unit 21d stores the operation correspondence information 30b in which the wheel combinations are associated with each other in the storage medium 30. The motion correspondence information 30b may be determined based on the wheel diameter, or may be updated as appropriate according to correction such as map matching performed by the navigation program 21. However, the motion correspondence information 30b is associated with a combination of wheels, and the original data is retained even after the wheels are replaced. Then, when returning to the wheel combination that has been used before (for example, replacement of the wheel for each season, etc.), setting is made to refer to the operation correspondence information 30b corresponding to the wheel combination by the processing of the replacement processing unit 21d. Is done.

  The operation correspondence information 30b described above is used when acquiring the vehicle speed based on the output value of the vehicle speed sensor 42, and the output value is referred to when detecting a decrease in air pressure, as will be described later. Therefore, by adopting a configuration that uses the motion correspondence information 30b, it is possible to accurately detect a decrease in air pressure even when the wheels are replaced.

  In the present embodiment, the navigation program 21 includes a travel locus information acquisition unit 21a, a wheel rotation speed information acquisition unit 21b, and an air pressure decrease detection unit 21c in order to perform the air pressure decrease detection function. The travel locus information acquisition unit 21a is a module that acquires travel locus information based on the GPS reception unit 40, the camera 41, the vehicle speed sensor 42, the acceleration sensor 43, the azimuth sensor 44, the steering sensor 45, the map information 30a, and the motion correspondence information 30b. It is.

  That is, the current position of the vehicle is specified at predetermined time intervals based on signals from the GPS receiver 40 and the camera 41, the vehicle speed sensor 42, the acceleration sensor 43, the direction sensor 44, and the steering sensor 45, and the map information 30a is obtained. The history of the current position matching the road is acquired by referring to the map matching. Since the current position history is combined to form a travel locus, in the present embodiment, the current position history is travel locus information. The travel locus information acquisition unit 21a refers to the operation correspondence information 30b when acquiring the speed of each wheel from the output value of the vehicle speed sensor 42. The wheel rotation speed information acquisition unit 21b is a module that acquires the speed of each wheel with reference to the output value of the vehicle speed sensor 42 and the operation correspondence information 30b.

  The air pressure drop detection unit 21c acquires an estimated value of a distance that each wheel should move when the vehicle travels on the travel locus and an actual measured value of the moving distance of each wheel, and based on the estimated value and the actual measured value. This module detects a decrease in the air pressure of each wheel. In order to perform this detection, the air pressure drop detection unit 21c includes an estimated value acquisition unit 21c1, an actual measurement value acquisition unit 21c2, and a comparison unit 21c3. The estimated value acquisition unit 21c1 is acquired by the travel locus information acquisition unit 21a. With reference to the travel locus information, the distance that each wheel should move when traveling along the travel locus is calculated at predetermined time intervals. This distance is an estimated value of the movement distance because it is a distance to be moved when traveling along the travel locus.

  On the other hand, the actual measurement value acquisition unit 21c2 acquires the movement distance of each wheel at a predetermined time interval based on the speed of each wheel acquired by the wheel rotation speed information acquisition unit 21b. Since this movement distance is acquired based on a signal (output value of the vehicle speed sensor 42) corresponding to the actual rotation of each wheel, it becomes an actual measurement value of the movement distance of each wheel.

  The comparison unit 21c3 compares the above estimated value and actual measurement value for each wheel, and when there is a wheel whose difference is larger than a predetermined threshold value Th, the air pressure of the wheel is reduced. Is detected. When a decrease in air pressure is detected, the air pressure decrease detection unit 21c outputs information indicating that the wheel and the air pressure are decreasing to the display unit 47. As a result, the driver of the vehicle can recognize the wheel whose air pressure is decreasing. In the present embodiment, an estimated value is acquired based on any travel trajectory of the vehicle, not limited to a flat road surface, and compared with an actually measured value. Therefore, it is possible to accurately detect a decrease in air pressure even when the vehicle is not traveling straight on a flat road surface.

(1a) Air pressure drop detection processing:
Next, a process for detecting a decrease in air pressure performed by the navigation device 10 in the above configuration will be described. FIG. 2 is a flowchart illustrating a process for detecting a decrease in air pressure in the present embodiment, and FIG. 3 is an explanatory diagram illustrating an example of calculating an estimated value based on travel locus information. In the present embodiment, the navigation program 21 performs the processing shown in FIG. 2 when performing the above-described guidance, and the travel locus information acquisition unit 21a includes a GPS receiver 40, a camera 41, a vehicle speed sensor 42, and an acceleration sensor. 43, travel locus information is acquired based on the direction sensor 44, the steering sensor 45, the map information 30a, and the motion correspondence information 30b (step S100).

  When the travel locus information is acquired by the travel locus information acquisition unit 21a, the estimated value acquisition unit 21c1 acquires the movement distance (the estimated value described above) for each wheel at predetermined time intervals based on the travel locus information ( Step S110). Here, it is only necessary to be able to acquire an estimated value that reflects the difference in motion that can occur on each wheel by traveling on the travel locus. For example, the estimated value is acquired by reflecting the effects of turning of the vehicle or traveling on a slope. To do.

FIG. 3 shows an example of calculation of an estimated value reflecting the effect of turning, and a solid line arrow A _RL indicates a travel locus. That is, in this example, the current position is acquired with reference to the position of the left rear wheel, and the current position P _n as shown in FIG. 3 is obtained by acquiring the current position at predetermined time intervals. It is done. When such a row of current positions P _n is not arranged in a straight line, it is possible to calculate the turning center O if it is assumed that at least three points are extracted and the three points are arranged on an arc. FIG. 3 shows the turning center O calculated based on the current positions P _{1 to} P ₃ .

Here, if it is assumed that the vehicle is turning around the turning center O at a predetermined time interval before and after the current position P ₁ , and the movement distance is L _RL , the position of each wheel is determined based on the arrangement of each wheel. The moving distance can be calculated. That is, if it is considered that each wheel is turning about the turning center O in this time interval, the traveling locus of each wheel is specified as shown by broken arrows A _FL , A _FR , A _RR in FIG. Can do. In FIG. 3, the traveling locus of the front left wheel is an arrow A _FL , the traveling locus of the front right wheel is an arrow A _FR , and the traveling locus of the rear right wheel is an arrow A _RR .

Therefore, the movement distance of each wheel can be calculated by the following formulas (1) to (3) based on information indicating vehicle specifications acquired in advance (in this example, the wheel base L and the tread W). is there.
Moving distance of front left wheel L _FL = L _RL × R _FL / R _RL (1)
Front right wheel travel distance L _FR = L _RL × R _FR / R _RL・ ・ ・ ・ (2)
Rear right wheel travel distance L _RR = L _RL × R _RR / R _RL・ ・ ・ ・ (3)
Here, the distance from the turning center O to the front left wheel is R _FL , the distance from the turning center O to the front right wheel is R _FR , and the distance from the turning center O to the rear right wheel is R _RR. It is.

Each distance can be calculated by the following equations (4) to (7).
R _RL = L × tan (π / 2−θ) (4)
R _RR = R _RL −W (5)
R _FL = (R _RL ² + L ² ) ^1/2 ... (6)
R _FR = (R _RR ² + L ² ) ^1/2・ ・ ・ ・ (7)
Here, θ is an angle when the front left and rear left wheels are viewed from the turning center O. Of course, in the above formula, it is only necessary to be able to calculate the moving distance of each wheel, and it is not essential that the reference is the rear left wheel, and the distance from the turning center O to the wheel using other formulas is not necessary. Etc. may be calculated.

  In any case, in step S110, the moving distance of each wheel is calculated at predetermined time intervals, and this is held as an estimated value. When the estimated value acquisition unit 21c1 acquires the estimated value, the wheel rotation speed information acquisition unit 21b acquires the output value of the vehicle speed sensor 42, and acquires the operation correspondence information 30b corresponding to the current wheel combination (step S115). ), And passes to the actual measurement value acquisition unit 21c2. The actual measurement value acquisition unit 21c2 acquires the movement distance (the above-described actual measurement value) for each wheel at predetermined time intervals based on these pieces of information. That is, referring to the motion correspondence information 30b, a signal corresponding to the rotation of each wheel is converted into the speed of each wheel, and the moving distance of each wheel is calculated by multiplying the same time interval as in step S110.

  When the estimated value and the actual measurement value of each wheel are calculated as described above, the comparison unit 21c3 calculates the difference between them and compares it with a predetermined threshold value Th (step S125). Here, the threshold value Th may be set so that it can be determined whether or not the actual operation of each wheel is consistent with the operation of each wheel when traveling along the travel locus. Therefore, it may be set for the difference between the estimated value for each time interval and the actual measurement value, or may be set for the difference between the estimated value for each time interval and the accumulated value of the actual measurement value. good. In the latter case, for example, a threshold value or the like that determines whether or not a difference of 5 m or more is detected between the estimated value and the actually measured value in the time interval of traveling a travel distance of 1 km can be employed.

  In step S125, when it is not determined that the difference between the estimated value and the actual measurement value of each wheel exceeds the threshold value Th, no notification is made that the air pressure has not decreased. If it is determined in step S125 that there is a wheel whose difference between the estimated value and the actual measurement value exceeds the threshold value Th, the air pressure drop detection unit 21c outputs a signal to the speaker 46 and the display unit 47, and the wheel. Is notified that the air pressure has decreased (step S130). In this notification, various notifications can be adopted, and in addition to the configuration that identifies the wheel in which the air pressure is reduced by letters, voice, etc., the navigation program 21 guides the tire replacement service provider, etc. Various guidance can be implemented. As described above, if the estimated value of each wheel is calculated based on the travel locus information and the actual measured value of each wheel is calculated based on the output value of the vehicle speed sensor 42, not only when the vehicle is traveling straight, Even when the vehicle is turning, a decrease in air pressure can be notified.

(1b) Modification:
In the above-described embodiment, the distance traveled by the wheel is estimated based on the fact that the vehicle is turning. Of course, the information that can be adopted as the travel locus information is not limited to turning, but a decrease in air pressure is detected. Therefore, the operation of the wheel is not limited to the moving distance of the wheel. FIG. 4 is an explanatory diagram for explaining a configuration example in which it is detected that the vehicle is traveling on a slope from the travel locus information and the speed of the wheel is estimated. FIG. 4A acts on the vehicle when traveling on a flat road surface. FIG. 4B shows the force acting on the vehicle when traveling on a slope, and FIG. 4C shows an enlarged view of the wheel.

  Here, for the sake of simplicity, an example is assumed in which there is no height difference in the vehicle left-right direction on the slope, and there is a height difference only in the vehicle front-rear direction. In this case, the diameter of the front and rear wheels changes due to the difference in load acting on the front and rear wheels, and a difference occurs in the estimated values of the front and rear wheels. Note that the estimated values of the left and right wheels are the same value. Therefore, in the example shown in FIG. 4, the speed of each wheel when traveling on the slope is estimated based on the load distribution when traveling on a flat road surface and the load distribution when traveling on the slope, The change in wheel diameter is calculated assuming that the wheel response is equivalent to a spring.

That is, the radius of the wheel (the length from the center of the wheel to the road surface) R is expressed by the following equation (8) according to the radius R _W of the rim and the distance R _T from the outer periphery of the rim to the road surface as shown in the enlarged view 4C. Can be expressed.
R = R _W + R _T (8)
Furthermore, the radius R of the wheel can be expressed by the following formula (9) by a spring constant k that takes into account both the force F received by the wheel from the road surface and the left and right wheels.
R = R _W + R _T0 −F / k (9)
R _T0 is the distance (free length) from the outer periphery of the rim to the road surface when the force F received by the wheel from the road surface is 0, and the spring constant k is determined in advance.

The speed of each wheel can be calculated by the following formulas (10) and (11) based on the radius of each wheel.
V _DF = V _SF × R _DF / R _SF・ ・ ・ ・ (10)
V _DR = V _SR × R _DR / R _SR・ ・ ・ ・ (11)
V _DF is the speed of the front wheel when traveling on a slope, V _SF is the speed of the front wheel when traveling on a flat surface, R _DF is the radius of the front wheel when traveling on a slope, R _SF is the radius of the front wheel when traveling on a flat surface, and V _DR Is the speed of the rear wheel when traveling on a slope, V _SR is the speed of the rear wheel when traveling on a flat surface (= V _SF ), R _DR is the radius of the rear wheel when traveling on a slope, and R _SR is the rear wheel when traveling on a flat surface Is the radius.

Therefore, the load and the spring constant in each state are specified and appropriately substituted into equation (9), and further substituted into equations (10) and (11), so that the following equations (12) and (13) Wheel speed can be estimated.
_{V DF = V SF × (R} WF + R TF0 -W DF / k F) / (R WF + R TF0 -W SF / k F) ···· (12)
V _DR = V _SR × (R _WR + R _TR0 −W _DR / k _R ) / (R _WR + R _TR0 −W _SR / k _R ) (13)
R _WF is the radius of the rim of the front wheel, R _TF0 is the free length of the front wheel, W _DF is the load of the front wheel when running on a slope, k _F is the spring constant of the front wheel, and W _SF is the load of the front wheel when running on a flat surface _Yes , R _WR is the radius of the rim of the rear wheel, R _TR0 is the free length of the rear wheel, W _DR is the load of the rear wheel when running on an inclined surface, k _R is the spring constant of the rear wheel, and W _SR is when running on a flat surface It is the load of the rear wheel. R _WF , R _TF0 , k _F , R _WR , R _TR0 , and k _R are values specified in advance. Of course, if the wheel characteristics are common to the front and rear wheels, a common value may be used. .

According to the above formulas (12) and (13), the speed of each wheel can be specified by specifying the load acting on the wheel when traveling on a flat surface and when traveling on a slope. The load when traveling on a flat surface can be calculated in advance. For example, the load during traveling on a flat surface is calculated based on the position of the center of gravity G, the weight W of the vehicle, and the wheel base L. be able to. More specifically, as shown in FIG. 4A, reaction forces W _SF , W _SR are defined as reaction forces W _SF and W _SR , respectively, and the position of the center of gravity G, the weight W of the vehicle, and the wheel base L are defined. By doing so, the load at the time of running on a flat surface can be calculated.

That is, considering the moments around the shaft extending in the left-right direction of the vehicle from the ground contact point X of the front wheel and the ground contact point Y of the rear wheel, respectively, the following equations (14) and (15) are obtained. ) The load can be calculated as in (17).
Around point X: L _F × W−L × W _SR = 0 (14)
Around Y point: L × W _SF −L _R × W = 0 (15)
W _SR = L _F × W / L (16)
W _SF = L _R × W / L (17)
Here, L _F is the distance between the position Z (the intersection of the perpendicular line descending from the center of gravity G onto the road surface and the road surface) and the grounding point X, and L _R is the distance between the position Z and the grounding point Y. The position, vehicle weight W, and wheelbase L are specified in advance.

On the other hand, whether or not the vehicle is traveling on a slope can be specified by the travel locus information, and when it is determined that the vehicle is traveling on a slope, the load on the front and rear wheels may be calculated. That is, since the travel locus information is a history of the current position, it can be determined that the vehicle is traveling on a slope by determining an altitude change of the current position based on the travel locus information. For example, as shown in FIG. 4B, when a specific altitude change exists in the current positions P _{D1 to} P _D5 constituting the travel locus A _RL , it can be determined that the vehicle is traveling on a slope, and the slope Can be specified.

If the inclination angle φ of the slope can be specified, the weight W of the vehicle is divided into a component W _V perpendicular to the road surface and a component W _α perpendicular to the road surface, and the component W _α and the braking force F _B are suspended in a short time interval. The load when traveling on a slope can be calculated by considering that these forces are offset and that these forces cancel each other. That is, considering the moments around the shaft extending in the left-right direction of the vehicle from the ground contact point X of the front wheel and the ground contact point Y of the rear wheel, the following equations (18) and (19) are obtained, respectively, and the relationship of W _V = W × cosφ and By changing the equation using equations (16) and (17), the load can be calculated as in equations (20) and (21).
Around point X: L _F × W _V −L × W _DR = 0 (18)
Around Y point: L × W _DF −L _R × W _V = 0 (19)
W _DR = L _F × W _V / L = W _SR × cosφ (20)
W _DF = L _R × W _V / L = W _SF × cosφ (21)

Therefore, by substituting the above equations (20), (21), (16), and (17) into the above equations (12) and (13), it is possible to estimate the speed of the front and rear wheels when traveling on a slope. become. Note that the speed V _SF of the front wheel when traveling on a flat surface and the speed V _SR of the rear wheel when traveling on a flat surface are equal, and a speed at a predetermined time interval may be acquired based on the traveling locus A _RL .

The estimation at the time of running on the slope as described above can be realized by the same configuration as in FIG. 1, and if the processing similar to the flow shown in FIG. 2 is performed in this configuration, a decrease in air pressure can be detected. it can. However, in this modification, it is determined in step S110 in FIG. 2 whether or not the vehicle is traveling on the slope based on the travel locus information, and when traveling on the slope, equations (20), (21), and (16) Based on (17), the estimated values V _DF and V _DR of the speed of each wheel are obtained.

  In step S120, an actual measurement value of each wheel speed is acquired based on the wheel rotation speed information. In step S125, whether or not the difference between the estimated value and the actual measurement value exceeds a predetermined threshold value Th. It is possible to detect whether or not the air pressure has decreased. Therefore, according to the above configuration, it is possible to notify a decrease in air pressure not only when the vehicle is traveling on a flat surface but also when traveling on a slope.

  In the present modification, the estimated values for the left and right wheels are the same value. Therefore, in the comparison in step S125, the measured values for the front right and left wheels are compared with the estimated values for the front wheels, and the rear right side, A configuration that compares each of the measured values of the left wheel and the estimated value of the rear wheel may be adopted, or an average value of the measured values of the left and right may be compared with the estimated value, and various configurations are adopted. Is possible.

In the above example, the component W _alpha and braking force F _B at short time intervals is balanced, that is, the vehicle is calculated load as it has a uniform motion, course, components W _alpha And the braking force F _B are not equal, and the moment may be calculated assuming that the vehicle is accelerating. In the above example, a slope with no change in height in the left-right direction was assumed. However, if a change in height in the left-right direction of the slope can be detected by a sensor in the vehicle, the effect is reflected. The wheel speed may be estimated.

  Further, if the response of the wheel to the load can be described by a model other than the spring, the wheel speed may be estimated based on the model. Furthermore, you may use this modification and the above-mentioned 1st Embodiment together. Further, as in the above-described example, in addition to the configuration for calculating the wheel operation (load, moving distance, etc.) according to the travel locus, table data in which the angle of the slope and the wheel operation are associated with each other is stored in advance. Alternatively, the estimated value may be acquired with reference to this table data.

Further, a configuration may be adopted in which the speed of the wheel is estimated by reflecting the influence of the turning of the vehicle and compared with the actual measurement value. For example, according to the following formulas (22) to (24), based on the reference wheel speed V _RL (here, the speed of the rear left wheel and can be estimated based on the travel locus information). The speed of other wheels can be estimated.
V _RR = V _RL × R _RR / R _RL (22)
V _FL = V _RL × R _FL / R _RL (23)
V _FR = V _RL × R _FR / R _RL・ ・ ・ ・ (24)
Here, V _RR is the speed of the right rear wheel, V _FL is the speed of the left front wheel, and V _FR is the estimated value of the front right wheel speed. R _FL , R _FR , R _RR , and R _RL are distances from the turning center O to each wheel, calculated in the same manner as in FIG.

As described above, when the estimated value of the speed of each wheel is obtained, the actual value of the speed of each wheel is obtained based on the wheel rotation speed information, and the estimated value and the actual value are compared for each wheel. It is possible to detect a decrease in air pressure for each wheel. The reference wheel speed V _RL can be acquired based on the travel locus information, but an actual measurement value may be adopted as the reference wheel speed V _RL .

(2) Configuration of the second embodiment:
In the first embodiment described above, the estimated value based on the travel locus information and the actually measured value based on the wheel rotation speed information are compared to determine the consistency of the wheel operation. In addition to such direct determination, various other methods can be employed. For example, the above-described actual measurement value may be corrected based on the travel locus information to cancel the influence of the travel locus, and the decrease in air pressure may be detected based on the corrected wheel speed.

  FIG. 5 is a block diagram showing a configuration of the navigation device 10 including the air pressure drop detecting device according to the second embodiment of the present invention. In this figure, the same reference numerals are given to the same components as those in the first embodiment, and description thereof is omitted. As shown in FIG. 5, the second embodiment and the first embodiment mainly differ in the configuration of the air pressure drop detection unit 210c.

  The air pressure drop detection unit 210c acquires an actual measurement value of the speed of each wheel, corrects the actual measurement value based on an inner wheel difference when the vehicle travels on the travel locus, and compares the corrected wheel speed. This is a module that detects a decrease in the air pressure of each wheel. In order to perform this detection, the air pressure drop detection unit 210c includes an actual measurement value acquisition unit 210c1, a correction unit 210c2, and a comparison unit 210c3, and the actual measurement value acquisition unit 210c1 is acquired by each wheel rotation speed information acquisition unit 21b. The wheel speed is acquired as an actual measurement value.

  The correction unit 210c2 refers to the travel locus information acquired by the travel locus information acquisition unit 21a, and corrects the difference between the speeds of the wheels generated by traveling along the travel locus. After this correction, the influence of traveling on the traveling locus is eliminated, so that the speed of each wheel should be equal (or almost equal) if the air pressure of each wheel is not reduced. Therefore, the comparison unit 210c3 can detect whether or not the air pressure of each wheel is reduced by comparing the speed of each wheel. Accordingly, it is possible to accurately detect a decrease in air pressure even when the vehicle is not traveling straight on the road surface.

(2a) Air pressure drop detection processing:
Next, a process for detecting a decrease in air pressure performed by the navigation device 10 in the above configuration will be described. FIG. 6 is a flowchart showing a process for detecting a decrease in air pressure in the present embodiment. In the present embodiment, the navigation program 21 performs the process shown in FIG. 6 when performing the above-described guidance, and the traveling locus information acquisition unit 21a acquires the traveling locus information as in the above-described embodiment ( Step S200), the wheel rotation speed information acquisition unit 21b acquires the wheel rotation speed information corresponding to the output value of the vehicle speed sensor 42 and the current wheel combination from the operation correspondence information 30b (Step S205).

  When the wheel rotation speed information acquisition unit 21b acquires the wheel rotation speed information, the actual measurement value acquisition unit 210c1 acquires the speed (measurement value) for each wheel at predetermined time intervals based on the information (step S210). That is, with reference to the operation correspondence information 30b, a signal corresponding to the rotation of each wheel is converted into the speed of each wheel. Next, the correction unit 210c2 acquires the traveling locus of each wheel from the traveling locus information acquired in Step S200, and corrects the speed of each wheel based on the traveling locus (Step S215). Here, by analyzing the traveling locus of each wheel in the same manner as in FIG. 3, the difference in the speed of each wheel due to the different traveling locus in each wheel can be canceled out.

That is, as shown in FIG. 3, when the traveling locus _ARL of the left rear wheel is used as a reference, the traveling locus of the front left, front right, and rear right wheels is calculated by calculating the turning center O based on the current position. A _FL , A _FR , A _RR can be specified. The distance from the turning center O to each wheel in the travel locus can be calculated by the above-described equations (4) to (7).

Therefore, if these distances are used and the speed of each wheel is corrected by the following formulas (25) to (27) with reference to the speed V _RL , wheels other than the reference wheel are shown in FIG. It is possible to perform correction that cancels the influence of traveling.
V _RR '= V _RR × R _RL / R _RR・ ・ ・ ・ (25)
V _FL '= V _FL × R _RL / R _FL (26)
V _FR '= V _FR × R _RL / R _FR・ ・ ・ ・ (27)
Here, V _RR is an actual measured value of the speed of the right rear wheel, V _FL is an actual measured value of the speed of the left front wheel, V _FR is an actual measured value of the speed of the right front wheel, and the left side of each formula Is the corrected wheel speed.

  In the wheel speeds after the above correction, the influence of traveling on the traveling locus is canceled out, so that the speed of each wheel should be equal when there is no decrease in air pressure. Therefore, the comparison unit 210c3 compares the speeds of the wheels (step S220), and determines whether or not there is a wheel that does not satisfy the predetermined standard (step S230). In step S230, when it is not determined that there is a wheel that does not satisfy the predetermined standard, no notification is made that a decrease in air pressure has not occurred. In step S230, when it is determined that there is a wheel that does not satisfy the predetermined reference, the air pressure drop detection unit 210c outputs a signal to the speaker 46 and the display unit 47 to notify that the wheel air pressure has dropped. (Step S235). Of course, various notifications can be adopted in this notification as described above.

In the predetermined reference, it is only necessary to compare the speed of the wheel so that the wheel air pressure is lowered and the wheel having the lowered air pressure can be specified, and various configurations can be adopted. . For example, the absolute value of the difference (V _RL −V _RR ′, V _RL −V _FL ′, V _RL −V _FR ′) between the speed of the reference wheel and the corrected speed of each wheel is calculated. When the air pressure is not reduced, the absolute value becomes 0 or almost 0. Therefore, if it is determined whether or not the absolute value exceeds a predetermined threshold value, the wheel having the decreased air pressure is determined. be able to.

That is, if any one of the absolute values exceeds the threshold value, the wheel corresponding to the second term of the expression for calculating the difference (for example, the right rear wheel if V _RL −V _RR ′). It can be determined that the air pressure is reduced. If all the absolute values exceed the threshold value, it can be determined that the air pressure of the reference wheel (the left rear wheel in the above example) has decreased.

  Of course, various other comparisons can be used to compare the speeds of the wheels, such as the speeds of the left and right wheels, the speeds of the front and rear wheels, and diagonally positioned wheels (for example, the front left wheel and the rear right side). The speed of the wheels may be compared. Also, a configuration is adopted in which the difference or sum of the speeds of any wheel is calculated and the ratio of the difference or sum is calculated, or the speed of each wheel is compared with the speed of the vehicle based on the vehicle speed. Various comparisons can be made. As described above, if the measured value of each wheel is corrected based on the travel locus information and the speed of the corrected wheel is compared, not only when the vehicle is traveling straight, but also when turning. It is also possible to notify a drop in air pressure.

(2b) Modification:
As described above, even in the configuration in which the measured value is corrected and compared based on the travel locus information, an operation other than the speed of the wheel can be adopted as the operation of the wheel for detecting a decrease in air pressure. For example, it is possible to detect a decrease in air pressure by correcting the moving distance of each wheel based on the travel locus information and comparing the moving distance of each wheel.

Further, the correction based on the travel locus information is not limited to the above-described influence caused by the turning, but may reflect the influence caused by running on the slope. For example, if the above formulas (12) and (13) are corrected to the following formulas (28) and (29) and the measured values of the wheel speeds are substituted into V _DF and V _DR , the vehicle can travel on a slope. Corrections can be made to cancel the influence.
V _SF = V _DF × (R _WF + R _TF0 −W _SF / k _F ) / (R _WF + R _TF0 −W _DF / k _F ) (28)
V _SR = V _DR × (R _WR + R _TR0 −W _SR / k _R ) / (R _WR + R _TR0 −W _DR / k _R ) (29)

  Therefore, if the wheel speeds as described above are compared based on the corrected wheel speeds, not only when the vehicle is traveling on a flat surface but also when traveling on a slope. It is also possible to notify a drop in air pressure. Of course, as described above, various modifications can be adopted in addition to a configuration that considers that the vehicle is accelerating and a configuration that considers both turning and running on a slope.

  In all of the above-described configurations, not all of the sensors shown in FIGS. 1 and 5 are essential as sensors for acquiring the travel locus information. Depending on the cost of detecting a decrease in air pressure, the equipment of the vehicle, etc. It can be changed as appropriate. Furthermore, any accompanying technique can be applied to improve the accuracy of detecting the air pressure drop. For example, when a vehicle stability control system for preventing traction control, ABS (Antilock brake system), spin, etc. is activated, the air pressure is not taken into consideration (or the contribution to the judgment is reduced) during the operation. By determining the decrease in the air pressure, it is possible to detect the decrease in air pressure with high accuracy. Furthermore, when the operation of each sensor is unstable, such as when the signal from the GPS receiver 40 cannot be received, the air pressure is reduced without considering the wheel operation during that period (or reducing the contribution to the determination). By determining, it is possible to detect air pressure drop with high accuracy.

It is a block diagram of the air pressure fall detection device concerning a 1st embodiment. It is a flowchart which shows the detection process of the air pressure fall concerning 1st Embodiment. It is explanatory drawing explaining the example of calculation of the estimated value based on traveling locus information. It is explanatory drawing explaining the estimation of the speed of the wheel at the time of slope driving | running | working, (4A) is explanatory drawing of the force which acts on a vehicle when drive | working a flat road surface, (4B) is a vehicle in driving | running | working on a slope. Explanatory drawing of the force which acts, (4C) is an enlarged view of a wheel. It is a block diagram of the air pressure fall detection device concerning a 2nd embodiment. It is a flowchart which shows the detection process of the air pressure fall concerning 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Navigation apparatus, 20 ... Control part, 21 ... Navigation program, 21a ... Traveling track information acquisition part, 21b ... Wheel rotational speed information acquisition part, 21c ... Air pressure fall detection part, 21c1 ... Estimated value acquisition part, 21c2 ... Actual measurement value Acquisition unit, 21c3 ... comparison unit, 21d ... exchange processing unit, 30 ... storage medium, 30a ... map information, 30b ... operation correspondence information, 40 ... GPS reception unit, 41 ... camera, 42 ... vehicle speed sensor, 43 ... acceleration sensor, 44 ... Direction sensor, 45 ... Steering sensor, 46 ... Speaker, 47 ... Display

Claims (7)

Traveling locus information acquisition means for acquiring traveling locus information indicating a traveling locus of the vehicle;
Wheel rotation speed information acquisition means for acquiring wheel rotation speed information corresponding to the rotation speed of each of the plurality of wheels;
Air pressure decrease detection for detecting a decrease in wheel air pressure when the actual operation of each wheel indicated by the wheel rotation speed information is not consistent with the operation of each wheel when traveling along the travel locus indicated by the travel locus information. Means,
An air pressure drop detection device comprising: The travel locus information acquisition means may be any one or a combination of road shape information stored in a storage medium in advance, current position information specified by radio waves from a GPS satellite, and a detection value of a sensor mounted on the vehicle. Based on the travel trajectory information,
The air pressure drop detection device according to claim 1. The air pressure drop detecting means acquires an estimated value of an operation for each wheel when the vehicle travels on the travel locus, acquires an actual value of an operation for each wheel based on the wheel rotation speed information, and A drop in air pressure is detected when the difference between the measured value and the measured value exceeds a predetermined reference.
The air pressure drop detection device according to claim 1. The air pressure drop detecting means obtains an actual measurement value of each wheel based on the wheel rotation speed information, and corrects the difference between the wheel movements caused by traveling along the travel locus with respect to the actual measurement value. To detect the decrease in air pressure by comparing the operation for each wheel after correction,
The air pressure drop detection device according to claim 1. The air pressure drop detecting means holds operation correspondence information in which the wheel rotation speed information and the operation of the wheel are associated with each other for each combination of wheels attached to the vehicle in a storage medium, and the wheel after the replacement after the wheel replacement Get the actual movement of each wheel by referring to the movement correspondence information corresponding to the combination of
The air pressure drop detection device according to any one of claims 1 to 4. A travel trajectory information acquisition function for acquiring travel trajectory information indicating the travel trajectory of the vehicle;
A wheel rotation speed information acquisition function for acquiring wheel rotation speed information corresponding to the rotation speed of each of the plurality of wheels;
Air pressure decrease detection for detecting a decrease in wheel air pressure when the actual operation of each wheel indicated by the wheel rotation speed information is not consistent with the operation of each wheel when traveling along the travel locus indicated by the travel locus information. Function and
Air pressure drop detection program that makes a computer realize. A travel locus information obtaining step for obtaining travel locus information indicating a travel locus of the vehicle;
A wheel rotation speed information acquisition step of acquiring wheel rotation speed information corresponding to the rotation speed of each of the plurality of wheels;
Air pressure decrease detection for detecting a decrease in wheel air pressure when the actual operation of each wheel indicated by the wheel rotation speed information is not consistent with the operation of each wheel when traveling along the travel locus indicated by the travel locus information. Process,
A method for detecting a decrease in air pressure.

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