JPH0629735B2 - Vehicle direction detection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a vehicle azimuth detection method, and more particularly to a detection method for detecting a vehicle azimuth using a geomagnetic sensor in a vehicle-mounted navigation device.

BACKGROUND ART In recent years, a vehicle-mounted navigation device that guides a vehicle to a predetermined destination by storing map information in a memory and reading the map information from the memory on a display device together with the current location of the vehicle has been researched and developed. Has been done.

An azimuth sensor that detects the azimuth of the vehicle is indispensable to such a navigation device, and as the azimuth sensor, for example, a geomagnetic sensor that detects the azimuth of the vehicle based on the geomagnetism (earth magnetic field) is used. However, this geomagnetic sensor is easily affected by the disturbance magnetic field, and when the vehicle crosses the railroad crossing, the railway bridge, or a large vehicle (for example, a truck or a bus) passes by the vehicle, the output data is output. A large error will be included.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide a vehicle heading detection method that enables more accurate detection of a vehicle heading.

A vehicle heading detection method according to the present invention includes a geomagnetic sensor that outputs heading data of a vehicle based on geomagnetism, and detects a heading of a vehicle based on output data of the geomagnetic sensor. When the vehicle is traveling at a predetermined speed or higher, the vehicle's current location is recognized every time it travels a predetermined distance based on the map data. When the processing is being performed, the azimuth obtained from the map data is used in the processing, and the azimuth obtained from the output data of the geomagnetic sensor is not used.

Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a vehicle-mounted navigation device to which the vehicle direction detection method according to the present invention is applied. In the figure, 1 is a geomagnetic sensor for outputting the azimuth data of the vehicle based on the geomagnetism (earth magnetic field), 2 is an angular velocity sensor for detecting the angular velocity of the vehicle, and 3 is for detecting the moving distance of the vehicle. A mileage sensor, 4 is a GP for detecting the current position of the vehicle from latitude and longitude information, etc.
This is an S (Global Positioning System) device, and the output of each of these sensors (devices) is supplied to the system controller 5.

The system controller 5 receives the outputs of the respective sensors (devices) 1 to 4 as an input, performs interface A / D (analog / digital) conversion, and the like, and performs various image data processing, and sequentially sends from the interface 6. A CPU (central processing circuit) 7 for calculating the amount of movement of the vehicle based on the output data of each sensor (device) 1 to 4;
A ROM (Read Only Memory) 8 in which various processing programs of the CPU 7 and other necessary information are written in advance, and a RAM (Random Access Memory) in which information necessary for executing the program is read and written. A memory 9 and a so-called CD-ROM, an IC card or the like, a recording medium 10 in which digitized (numerical) map information is recorded, and a graphic memory 11 including a V-RAM (Video RAM) or the like, The graphic controller 13 is configured to draw graphic data such as a map sent from the CPU 7 in the graphic memory 11 and control the graphic data to be displayed as an image on the display 12 such as a CRT. The input device 14 is composed of a keyboard or the like, and issues various commands to the system controller 5 by key input by the user.

Next, the basic procedure executed by the CPU 7 will be described with reference to the flowchart of FIG.

The CPU 7 first performs initialization for executing the program (step S1), and thereafter determines whether or not the current position of the vehicle is set (step S2). If the current location has not been set, the current location setting routine is executed (step S3), for example, the current location is set by key input on the input device 14. Next, the traveling distance is set to zero (step S4), and then it is determined whether or not there is a key input from the input device 14 (step S5).

When there is no key input, the map around the current position is displayed on the display 12, and the current position and the direction of the vehicle are displayed on this map by, for example, a vehicle mark. When the vehicle moves, the map scrolls with the movement. If the vehicle position is likely to exceed the range of the map data currently stored in the graphic memory 11, the necessary map data is read from the recording medium 10 and displayed on the display 12 (step S6).

If there is a key input, the current position is reset (step S7) and the sensor is corrected (step S) according to the input data.
8), destination set (step S9) and map enlargement
The reduction (step S10) routines are executed.

Further, the CPU 7 always calculates the heading of the vehicle based on the output data of the geomagnetic sensor 1 and the angular velocity sensor 2 at a constant time interval as shown in FIG. 3 by the interrupt processing by the timer (steps S11 and S12).

By the way, the geomagnetic sensor 1 is generally composed of a pair of magnetic detection elements arranged on the same plane with a phase angle of 90 °, and one of the pair of elements is, for example, U.
The geomagnetic component in the direction (north direction) is detected, and the other is detected in the direction V (east direction).
When the geomagnetic sensor 1 having such a configuration is rotated once on a horizontal plane, the origin O of the UV orthogonal coordinate system as shown in FIG. 4 is obtained from the output data from both the U and V detection elements.
A locus of a circle I centered on is drawn. Thus, for example, the azimuth angle θ clockwise from point north of _{P (U} 1, _{V 1)} (U-axis), is calculated by the following equation (1).

θ = tan ⁻¹ (U / V) (1) Therefore, such a geomagnetic sensor 1 is attached to the vehicle at a predetermined angle with respect to the front-rear direction or the left-right direction of the vehicle,
The azimuth of the vehicle can be detected by performing the calculation of the equation (1) based on the output data from both the U and V detecting elements.

Here, it is ideal that only the magnetic flux due to the earth's magnetic field exists around the geomagnetic sensor 1, but in the vehicle,
There is generally an extra magnetic flux due to the magnetization of the body steel plate. Therefore, in order to eliminate the influence of the magnetization of the vehicle body and accurately detect the direction,
For example, the method disclosed in JP-A-57-28208 is proposed. In this method, when the U and V magnetic detection elements are fixed to the vehicle and there is no relative displacement between the two, the center of the circle drawn by plotting the output obtained by turning the magnetic detection element once. In consideration of the fact that the distance from the coordinate origin is due to the effect of body magnetization, the output data obtained from both detection elements are corrected so that the center of the drawn circle moves to the origin, and the body The effect of magnetism is removed. More specifically, the circle drawn by the outputs of both detection elements is at a position where the center Q of the circle is moved from the origin, as indicated by II in FIG. Therefore, the maximum values Umax and Vmax and the minimum values Umin and Vmin of the outputs U and V of both detection elements are obtained, and the coordinates of the center Q are calculated from these by the following equation (2).

Using the calculated values U ₀ and V ₀ , the output values U and V of each magnetic detection element are corrected by the following equation (3), and the azimuth is calculated from the corrected U ′ and V ′. .

Further, in order to increase the reliability of the output data of the geomagnetic sensor 1, an allowable range (hereinafter, referred to as a window) that allows the variation of the output data of the geomagnetic sensor 1 is set based on a certain rule. That is, as shown by hatching in FIG. 5, a window is set in the angle direction with reference to the previously obtained direction data (U _n-1 , V _n-1 ) and the previously obtained direction data and the presently obtained direction data are set. If the direction data obtained this time is significantly different from the direction data obtained last time, that is, if it is outside the window, that data is regarded as an error and the specified data, for example, the previous data or the past number of times The reliability of the output data of the geomagnetic sensor 1 is improved by substituting the average value of (any number of times) data. Further, since the data output from the geomagnetic sensor 1 mathematically applies to the equation of the circle, the data not on this equation can be determined to be an error. However, since the data varies due to A / D conversion errors and the like, the window is set with a certain width in the radial direction. In FIG. 5, α indicates an angle allowable value and β indicates a radius allowable value.

Since the difference in azimuth differs depending on the time interval for obtaining the azimuth data, it is also possible to obtain it by the relationship between the angular velocity and the vehicle speed. For example, if the maximum angular velocity is 30 [degrees / s] when the vehicle speed is 40 [km / h], an error occurs if the angular velocity based on the output data of the geomagnetic sensor 1 exceeds this range, and the previous data or past Replace with the average of several data. Also, when setting the window by angle,
It is also possible to set the angle according to the change in vehicle speed, and not only to set the angle to the vehicle speed with a linear function,
By providing a certain hysteresis, it is not necessary to frequently change the corresponding angle according to the change in vehicle speed.

Next, the procedure of the vehicle azimuth detecting method according to the present invention executed by the CPU 7 will be described with reference to the flowcharts of FIGS. 6 (A) to 6 (C).

The CPU 7 first determines whether or not so-called one-rotation correction is completed (step S20). If not completed, the one-rotation correction routine is executed (step S2).
1). In this one-rotation correction routine, the vehicle equipped with the geomagnetic sensor 1 is rotated once, and the values of U ₀ , V ₀ (center values) and the radius r are obtained. The obtained value is stored in the RAM 9.

Then, the initial direction is set (step S22).
When the engine is started, the vehicle is stationary, and the azimuth of the vehicle should be constant. Therefore, it is preferable to set the initial value at this time. After setting the initial azimuth, the output data of the geomagnetic sensor 1 is fetched, and this data is sequentially stored in the ring buffer in the RAM 9 (step S23). The amount of data stored in this ring buffer may be for a certain predetermined time. Next, it is determined whether or not this output data is in the above-mentioned window (hatched portion in FIG. 5) (step S24). If it is in the window, the azimuth of the vehicle is calculated from the fetched output data of the geomagnetic sensor 1 based on the above-described equations (1) to (3) (step S25). Then, both the count value N of the window error counter that counts the number of times the output data of the geomagnetic sensor 1 is out of the window and the count value E of the center value shift determination counter that counts the number of times of center value shift are set to zero. (Step S26) Further, a flag indicating no window error is set (step S26).
27). The above flow is the flow during the normal operation in which the output data of the geomagnetic sensor 1 enters the window without being affected by the disturbance magnetic field.

Next, the flow for determining the vehicle direction is entered. First, in step S40, the azimuth obtained from the map data currently stored in the recording medium 10 (hereinafter referred to as the map azimuth)
Is determined by whether or not a map orientation use prohibition flag, which will be described later, is “0”. It should be noted that whether or not the map orientation can be used is determined by the method described later. If the use of the map direction is not permitted, the direction that has been obtained so far is set as the own vehicle direction (step S41), and then the process returns to step S23. If the use of the map orientation is permitted, it is further determined whether or not the output data of the geomagnetic sensor 1 has been stored in the window based on whether or not the window error-free flag is set (step S42). When there is a window error, the map orientation is used as it is (step S43),
Then, the process returns to step S23. If there is no window error, it is determined whether or not the difference between the orientation obtained from the output data of the geomagnetic sensor 1 and the map orientation is equal to or more than a predetermined value (step S44). Since it seems that there is a suspicion, it is prohibited to use the map orientation as the vehicle orientation for a predetermined time (step S46),
The azimuth obtained from the output data of the geomagnetic sensor 1 is used (step S47). If it is less than the specified value,
The map orientation is used as it is (step S45), and then the process returns to step S23.

On the other hand, when it is determined in step S24 that the output data of the geomagnetic sensor 1 is not in the window,
The count value N of the window error counter is incremented by "1" (step S28), and then it is determined whether or not the count value N has reached the window error maximum value Nmax (step S29). Until the window error maximum value Nmax is reached, the output data of the geomagnetic sensor 1 captured this time is regarded as an error, and the output data of the geomagnetic sensor 1 is obtained based on the previous value or the average value of the past several times. Using the direction (step S30),
Further, a flag indicating that there is a window error is set (step S31), and then the process proceeds to step S40 to perform the above-mentioned operation.

When the count value N of the window error counter reaches the window error maximum value Nmax, the count value E of the center value deviation counter is incremented by "1" (step S32), and then the count value E is set to the center value. It is determined whether or not the value deviation determination maximum value Emax has been reached (step S33). Then, a timer for a certain fixed time is set until the center value deviation determination maximum value Emax is reached (step S34), and the output data of the geomagnetic sensor 1 is fetched until it is determined that the time is up in step S35 (step S36). The azimuth is calculated based on the data (step S37). That is, when the output data of the geomagnetic sensor 1 does not enter the window for a certain period of time, the window is temporarily released and the error processing is not performed for a certain period of time. By this processing, even when non-standard data is taken in by, for example, an abrupt handle, this can be dealt with.

Next, it is determined whether or not the current map orientation is available in the same manner as in step S40 (step S4).
8). If the use of the map direction is not permitted, the direction that has been obtained so far is set as the own vehicle direction (step S4).
9) If the use of the map orientation is permitted, the map orientation is used as it is (step S50), and then the process returns to step S35.

When the count value E of the center value deviation counter reaches the center value deviation determination maximum value Emax, it is determined that the center value deviation is present in step S33, and the center value deviation is corrected using other data (step S38). Both the count value N of the window error counter and the count value E of the center value deviation determination counter are set to zero (step S39), and thereafter the process returns to step S23. For example, when a vehicle passes a railroad crossing, the strong magnetic field at the railroad crossing magnetizes the vehicle body, which causes the output data of the geomagnetic sensor 1 to have a DC component, which causes a deviation in the center value as shown in FIG. As a result, the azimuth cannot be obtained correctly after that. In this way, when the vehicle body is magnetized and a center value shift occurs, the geomagnetic sensor 1
Since the output data of (1) will not enter the window forever, it is possible to determine that this state has occurred by counting the number of times the window does not enter the window for a certain period of time. Then, in such a state, even if the output data of the geomagnetic sensor 1 has a DC component, the radius r does not change but the center coordinates of the equation of the circle change (the strength of the geomagnetism changes. Since the radius r does not change unless otherwise), the center coordinates can be obtained by using other data, and thus the center value deviation can be corrected.

In this correction of the center value deviation, for example, output data of the angular velocity sensor 2 is used as other data. Although the absolute value cannot be obtained by the angular velocity sensor 2, the angle can be obtained by integrating it on the time axis. The value that is known when the center value is deviated is the geomagnetic sensor 1
Output data (U, V), the radius r obtained by the one-rotation correction, and the output data of the angular velocity sensor 2, and these values have the relationship of the following expression (4).

By modifying the equation (4), the following equation (5) is obtained.

Therefore, the current center value (U ₀ , V ₀ ) can be calculated from the equation (5).

Further, as another method of obtaining the angle θ, the angle of the road on which the vehicle is currently traveling can be calculated using map data, and the angle of this road can be set as the angle θ. That is, a road is represented by a line (segment) connecting two points, and each point is digitized and stored in the recording medium 10 as map data. From this map data, the line segment on which the vehicle is located is located. Both ends of (2
Since the value of (point) is known, the angle θ can be obtained by calculating the slope of the linear function from this value.

Next, a method of determining whether or not the map orientation can be used will be described.

When the traveling pulse is supplied from the traveling distance sensor 3 for detecting the traveling distance and the speed of the vehicle, the CPU 7 performs the interruption processing by the traveling pulse. In the interrupt processing by the travel pulse, in response to the distance error caused by the detection error of the travel distance sensor 3 or the digitizing error of the map data, etc., every time the vehicle travels a fixed distance, the above-mentioned constant position is detected from the previously detected position based on the map data. By detecting a position on the road that is separated by a distance and setting the detected position as the current position, the current position recognition processing for always accurately recognizing the current position of the vehicle is performed. A specific method of this current location recognition processing has already been proposed by the present applicant in Japanese Patent Application No. 61-156883.

In this current location recognition processing, every time the vehicle travels a certain distance, the road closest to the current location is searched for from the map data, and the current location is drawn onto the road. At this time, the CPU 7 is shown in FIG. Interrupt processing by running pulse is also performed in parallel. That is, the CPU 7 first determines whether or not the current location recognition process is being performed (step S51). When the processing for recognizing the current location is not performed, the road closest to the current location may not be found from the map data. If the current location recognition process is not performed, the flag that prohibits the use of the map orientation is set to "1", that is, the use of the map orientation is prohibited (step S52), and the process is ended. If the current location recognition process is being performed, it is determined whether the vehicle speed is lower than the predetermined vehicle speed Slmt (step S53). If the vehicle speed is lower than the predetermined vehicle speed Slmt, the process proceeds to step S52, and if the vehicle speed is equal to or higher than the predetermined vehicle speed Slmt, the process is ended.

Further, the CPU 7 judges whether the flag for prohibiting the use of the map orientation is "1", that is, whether the use of the map orientation is prohibited or not as shown in FIG. 9 by the interruption processing by the timer (step S54). When prohibited, the time is monitored until a predetermined time elapses (step S55), and when the predetermined time elapses, a flag that prohibits the use of the map orientation is set to "0" and the use of the map orientation is prohibited. Is canceled (step S56). If the use of the map orientation is permitted at the beginning, the process ends without doing anything.

That is, in the above-described vehicle heading detection method, the heading of the vehicle does not change significantly when the vehicle is traveling at a predetermined speed (for example, 40 [Km / h]) or more,
Since it is judged that the line segment on the map (the road is represented by connecting line segments) can also be approximated to a straight line, in such a state, it is difficult to make an error in digitizing the map, and it is possible to obtain it from the map data. The reliability of the azimuth determined is higher than the azimuth obtained by the geomagnetic sensor 1, and when the vehicle is traveling at a predetermined speed or more and the current location of the vehicle is being recognized, map data is used in this processing. The obtained azimuth is used, and the azimuth obtained by the geomagnetic sensor 1 is not used. As a result, the vehicle direction can be detected more accurately.

In step S55 of FIG. 9, it is described that the passage of time is monitored, but it is also possible to monitor whether or not the vehicle has traveled a predetermined distance.

As described above, according to the present invention, every time the vehicle travels at a predetermined speed and travels a predetermined distance based on the map data, only the predetermined distance from the previously recognized current position. Recognize a position on a distant road as the current location Only when the vehicle's current location is being processed, the direction obtained from the map data is used as the vehicle's own direction, and the direction obtained by the geomagnetic sensor is not used. As a result, the heading can be detected based on the heading data with high reliability, so that the heading of the vehicle can be detected more accurately.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an in-vehicle navigation device to which a vehicle direction detection method according to the present invention is applied, and FIG.
FIGS. 3 and 4 are flowcharts showing the basic procedure executed by the CPU in FIG. 1, FIG. 4 is a diagram showing the locus drawn by the output data of the geomagnetic sensor, and FIG. 5 is the output data of the geomagnetic sensor. FIG. 6 is a diagram showing a state in which a window is set on a drawn trajectory, and FIGS. 6 (A) to 6 (C) are flowcharts showing the procedure of the vehicle direction detection method according to the present invention executed by the CPU in FIG. 1, FIG. FIG. 8 is a diagram showing a state where the locus drawn by the output data of the geomagnetic sensor has a center value deviation, FIG. 8 is a flowchart showing a procedure of interrupt processing by a traveling pulse, and FIG. 9 is a flowchart showing a procedure of a timer interrupt. is there. Description of symbols of main parts 1 ... Geomagnetic sensor, 2 ... Angular velocity sensor 5 ... System controller 7 ... CPU, 10 ... Recording medium 12 ... Display, 14 ... Input device

Front Page Continuation (72) Inventor Atsuhiko Fukushima 4-2610 Hanazono, Tokorozawa, Saitama Pioneer Co., Ltd. Tokorozawa Plant (56) Reference JP 60-89300 (JP, A) JP 59-191083 ( JP, A) JP-A-58-129313 (JP, A)

Claims (4)

[Claims] 1. A azimuth detecting method comprising a geomagnetic sensor for outputting azimuth data of a vehicle based on geomagnetism, wherein the azimuth detecting method detects the azimuth of the vehicle based on the output data of the geomagnetic sensor. When the vehicle is traveling, the vehicle's current location recognition processing is performed each time the vehicle travels a predetermined distance based on the map data, and recognizes the position on the road that is a predetermined distance away from the previously recognized current location as the current location. If so, the direction obtained from the map data is used in the processing, and the direction obtained from the output data of the geomagnetic sensor is not used. 2. When the process of recognizing the current location is not performed, the use of the direction obtained from the map data is prohibited for a predetermined time or a predetermined traveling distance, and during that period, the direction is obtained from the output data of the geomagnetic sensor. The azimuth detecting method for a vehicle according to claim 1, wherein the azimuth is used. 3. When the vehicle is traveling at a speed lower than the predetermined speed, the use of the azimuth obtained from the map data is prohibited for a predetermined time or a predetermined traveling distance, and during that time, the output data of the geomagnetic sensor is used. 3. The vehicle azimuth detecting method according to claim 1, wherein the obtained azimuth is used. 4. A permissible range for allowing fluctuations in the output data of the geomagnetic sensor is set, and when the output data of the geomagnetic sensor is within this permissible range, the azimuth determined from the output data of the geomagnetic sensor is set. Claims characterized in that the difference from the azimuth obtained from the map data is monitored, and when this azimuth difference is a predetermined value or more, the azimuth obtained from the output data of the geomagnetic sensor is used. 1
A method for detecting the direction of a vehicle according to the item.