JPS63262518A - Navigation apparatus for vehicle - Google Patents

Abstract

PURPOSE:To increase the precision in recognition of a present position, by conducting offset correction of a geomagnetic sensor by utilizing the azimuth of running detected at two different points by a position measuring means utilizing a satellite. CONSTITUTION:A navigation apparatus has a GPS receiver 2 receiving an electric wave from a satellite, a vehicle-speed sensor 4a, a geomagnetic sensor 4b, a present position recognizing means 3 and a control unit 10. The recognition of a present position by the present position recognizing device 3 is conducted on the basis of a history of running measured by the vehicle-speed sensor 4a and the geomagnetic sensor 4b. On the occasion, offset correction for magnetization of the geomagnetic sensor 4b is conducted on the basis of the azimuth of running of a vehicle which is detected by the GPS receiver 2.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a navigation system for an automobile, and particularly to a navigation device configured to detect the running direction of a vehicle using geomagnetism.

(Prior art) As an automobile navigation device, for example,
As disclosed in Japanese Patent No. 8-70117, a vehicle is known that displays the current location of the vehicle and a map of its surroundings on the screen of a display device to provide driving guidance.

As means for recognizing the current position of a vehicle in such a navigation device, one using a geomagnetic sensor has already been put into practical use. That is, this current position recognition means is capable of recognizing the current position of the vehicle by detecting the distance traveled by the vehicle from the reference position and the direction using the odometer and the geomagnetic sensor. Therefore, it can be constructed at relatively low cost.

(Problem to be Solved by the Invention) However, in the current position recognition means using the geomagnetic sensor as described above, the current position of the vehicle is determined relative to the reference position by integrating the driving history from the reference position. Since the vehicle is recognized as a position, as the vehicle moves away from the reference position, measurement errors in travel distance and direction accumulate, and the accuracy of recognizing the current position decreases.

The above measurement error (includes the measurement error of the vehicle's travel distance by the odometer and the measurement error of the vehicle's running direction by the geomagnetic sensor), but the main cause of the decrease in the recognition accuracy of the vehicle's current position is the The error lies in the measurement error of direction.

The measurement error of this running direction is the error due to the declination angle (
That is, there are two types of errors: errors caused by the geomagnetic sensor indicating a north (magnetic north) that is different from true north on the map, and magnetization errors caused by the geomagnetic sensor being magnetized by disturbances.

Generally, when using a geomagnetic sensor as an orientation sensor,
As shown in Fig. 6, the output is a solid circle centered on the reference value (for example, (5, 5>)) when the vehicle rotates once.However, if the vehicle body is magnetized, The broken line circle is translated (offset) in the direction indicated by the arrow in the tra magnetic field, and therefore the reference value (5, 5
) There is a problem in that an output difference occurs between north, south, east, and west directions, and an error occurs in detecting the driving direction.

Therefore, in order to maintain high recognition accuracy of the current position of the vehicle, it is necessary to correct the declination or magnetization, that is, correct the orientation detected by the geomagnetic sensor at an appropriate time. However, it is extremely troublesome and difficult for a driver or the like to perform such correction.

(Means for Solving the Problems) In view of the above, the present invention corrects the error of the geomagnetic sensor, especially the offset of the Lissajous circle due to magnetization, so that the current position can be recognized. The aim is to provide a means by which the level of performance can be improved.

For this purpose, the present invention is provided with a satellite-based positioning means that receives radio waves from a satellite and detects at least the running direction of the vehicle, and this satellite-based positioning means detects the running direction of the vehicle at two different points. However, the detected traveling direction is used to correct the offset caused by the magnetization of the geomagnetic sensor.

(Function) When the navigation device with the above configuration is used, the current position is recognized as a relative position to the reference position by measuring the travel history from the reference position using the direction detected by the geomagnetic sensor. Since the offset correction by magnetization of the geomagnetic sensor is appropriately performed using the running direction of the vehicle detected by the positioning means, measurement errors due to magnetization can be reduced, and the recognition accuracy of the current position is improved.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an overall configuration diagram showing an example of a vehicle navigation device according to the present invention. This navigation device
A GPS receiver 2 that receives radio waves from satellites, a vehicle speed sensor 4a that detects vehicle speed, a geomagnetic sensor 4b that detects geomagnetism, and recognizes the current position from the driving history based on signals from the vehicle speed sensor 4a and the geomagnetic sensor 4b. A control device 10 receives signals from the current position recognition means 3 and performs various signal controls.

Furthermore, a storage device 5 consisting of a compact disk, ROM, etc. that stores map information, etc., and an operating device 7 for performing various key operations are connected to the control device 10 via a decoder 6 and an encoder 8, respectively. , a display device 16 such as a CRT, and a video RAM 15 are connected via a display control device 14 .

The storage device 5 stores maps and the like showing information such as roads, buildings, etc. necessary for vehicle travel guidance. The operating device 7 is a key switch or the like that can be operated by a driver or the like, and can change the content displayed on the display 16 in response to this operation. The control circuit 10 includes an arithmetic circuit 12 and ROMs 11a, R
It consists of a microcomputer equipped with an A M 11b, and an arithmetic circuit 12 is connected to a current position recognition device 3 and the like via an interface 13 as shown in the figure. Then, in this control circuit 10, the current position of the vehicle is calculated based on the signal from the current position recognition device 3, a map around this current position is pulled out from the storage device 5, and this current position is displayed on the display 16. It is displayed or stored in the video RAM 15. Note that the current position recognition device 3 recognizes the current position based on the driving history measured by the vehicle speed sensor 4a and the geomagnetic sensor 4b as described above. Offset correction for the magnetization of the geomagnetic sensor 4b is performed based on the traveling direction.

As shown in FIG. 2, the geomagnetic sensor 4b has a detection coil 41, which includes a ring-shaped magnetic core 41a made of laminated permanent thin plates, and a ring-shaped magnetic core 41a that extends over the entire circumference of the magnetic core 41a. An excitation coil 41b wound around the cross-sectional centerline as the coil centerline, a U-axis coil 41-u wound around the outside of the magnetic core 41a along one diameter of a circle drawn by the magnetic core 41a, and a magnetic core 41a. It consists of a V-axis coil 41v wound outside the magnetic core 41a along another diameter perpendicular to the above-diameter of the circle drawn by.

Further, this geomagnetic sensor 4b is provided with an excitation oscillator 42, and the 8-1-(characteristic of the detection coil 41 is saturated by the signal of the frequency f given from the excitation oscillator 42. When the H characteristic is saturated, an AC signal is generated by electromagnetic induction in the U-axis coil 41u and the V-axis coil 41v in response to the external magnetic field Ha (horizontal component of earth's magnetism).

The geomagnetic sensor 4b further includes frequency doubler filter circuits 43u, 43v that filter these outputs, and AC amplifiers 44u, 44v that amplify the filtered output voltages.
, a frequency multiplier 45 that doubles the frequency output from the excitation oscillator 42 , a phase shifter 46 , and a phase signal with a frequency of 2f is manually inputted via the phase shifter 46 to the AC amplifier 44 .
Each phase detector 47u, 4 outputs a DC signal corresponding to the direction by phase-detecting the output of 44v.
7v and a DC amplifier 48u that amplifies these DC signals.
, has 48v. This DC amplifier 48u, 48v
The outputs U and V are output to the current position recognition device 3 at the next stage.

When the above-mentioned detection coil 41 is rotated around the central axis of the detection coil 41 which is orthogonal to both the U and V axes, as shown in Fig. 3(A).
As shown in FIG.
Corresponding to the intersection angle α of u, the output voltage U from the U-axis output coil 41u is 1-10 sin α, and the output voltage V from the V-axis output coil 41v is H8CO5α. Therefore, theoretically, the average value of each output voltage U, is not zero but is offset, and the gains in the U-axis direction and the v-axis direction differ depending on the sensor sensitivity, so the Lissajous curve drawn by both output voltages U and V is shown in Figure 3<B). This will draw an ellipse offset from the origin.

Therefore, the current position recognition device 3 includes a geomagnetic sensor 4.
From the output signals U and V of b, calculate the direction of the vehicle moving due north in the +y force direction from the origin to 1 on a circle centered on this point.
A direction determining means (not shown) is provided which can measure the direction of a vector toward the point (x, V).

This direction determining means first calculates the average value Uo1vo of the output voltages U and V in each direction of the U-axis and ■-axis, that is, the offset due to magnetization, in order to remove the influence of magnetization on the vehicle body, external abnormal magnetic fields, etc. As described later, the GPS receiver 2 receives a signal from a satellite and calculates the vehicle's driving direction, and then calculates the offset by subtracting the offset of the ellipse according to formulas (1) and (2). Find the correction voltage U1■.

tJ=u−uo (1)
■ -V-vo ・・・・・・(2)
The Lissajous curve drawn by this offset correction voltage USV forms an ellipse centered on the origin, as shown in FIG. 3(C). In addition, in order to eliminate the unevenness of the offset correction voltage U1V caused by non-uniformity of the sensitivity of the sensor, the azimuth determination means uses an ellipse according to equation (3) from the maximum and minimum values of both offset correction voltages U and . It has a sensor sensitivity ellipse correction means (not shown) that calculates the ellipticity K, multiplies the y-axis direction offset correction voltage V by this ellipticity K, and further corrects the y-axis direction voltage ■ according to equation (4). .

jJP umaX -ull! nK=□−□・
...(3) VD VlaX −Vlnin V = K (v − v o ) −−
(4) The Lissajous curve drawn by the output voltage U and ■ of this sensor sensitivity ellipse correction means is circular with the origin as the center as shown in Fig. 3 (D).From the origin which is the center of this Lissajous curve One point on the Lissajous curve (Ll, V)
By the direction of the vector leading to , it is possible to determine the orientation of the vehicle in the U1V coordinate system, which is defined as the +U force direction magnetic north.

However, in the above-mentioned direction determining means, the direction of the vehicle in the U1V coordinate system where +U force direction magnetic north is taken as the true direction corresponding to that direction on the map of the x,y coordinate system where the +X direction is the true north direction. In order to process, the coordinates of the above point (U, V) are calculated using
, (6), is provided with an argument correction means for converting into (x, y) coordinates.

x = V COSθ−jl sinθ...
...(5) y = IJ cosθ+VSinθ
・・・・・・(6) The vehicle on the map of the x, y coordinate system where the direction of the +y force is set to true north by the direction of the vector connecting the origin of this x, y coordinate system and the coordinates (x, y). The true direction of the direction will be determined.

Assuming that the unit travel distance ΔL is continuously traveled in the determined direction, the amount of movement ΔX in the X-axis direction and the amount ΔY of movement in the y-axis direction of the vehicle traveling in that direction are (7 ),
It can be obtained using equation (8).

Δx−□×ΔL (7) F■ flat shoulders Therefore, the estimated current position (X) when traveling a unit mileage from the starting point whose coordinates are (Xo, Yo).

Y) is: X = Xo + Δx (11) Y = Yo + ΔY (12). Also, if we assume that X 2 + y2 = ΔL2,
The estimated current position (X, Y) of a vehicle traveling while changing its direction from the starting point (Xo, Yo) from time to time is as follows.

By the way, the offset U due to magnetization. ,■.

Detection will be explained. This detection is performed by receiving radio waves from satellites using the GPS receiver 2 and detecting the running direction of the vehicle.The operation thereof will be explained using the flowchart shown in FIG. To detect the offset, first, in step 51, it is detected whether or not radio waves are being received from the '# star. If sufficient radio waves are being received to detect the running direction θ of the vehicle, step 51 is performed. The process proceeds to step 52, where it is detected whether or not there is detection data of the previous running direction.

Note that if sufficient radio waves are not received, this flowchart is ended, and the detection in step 51 is repeated thereafter. If there is no previous data, step 60
In step 61, the currently detected traveling direction θ is stored as 01, and in step 61, the current outputs ul and Vt of the geomagnetic sensor 4b are read. The graph in FIG. 5 shows this output with the U axis on the vertical axis and the V axis on the horizontal axis. As shown in FIG. 5, the output of the geomagnetic sensor 4b indicates the running direction of the vehicle, so it must match the running direction θ1 detected based on the radio waves from the satellite as described above. , Therefore, at this time, the geomagnetic sensor 4b
The center of the Lissajous circle R1 drawn by the output of is the point (Llt,
Vt) and must lie on a straight line Li with an inclination θ1. Therefore, in step 62, the point (LJl,
On the other hand, when it is determined in step 52 that there is already a previous f-ta, that is, the previous measurement of the traveling direction θ1 and the reading of the output of the geomagnetic sensor If so, the process proceeds to step 53, where it is determined whether the absolute value 1θ-θ11 of the difference between the running direction θ according to the current measurement and the running direction θ1 according to the previous measurement is larger than 315°.
It is determined whether the angle is smaller than 5°. IO-θI≦31
When the angle is 5° or ≧45°, the process proceeds to step 54 and the output values U and V of the geomagnetic sensor 4b are read. in this case,
Since the output of the geomagnetic sensor 4b indicates the traveling direction of the vehicle, in this case as well, it must match the traveling direction θ detected based on the radio waves from the satellite as described above. The center of the Lissajous circle R drawn by the output of the geomagnetic sensor 4b at this time must be on a straight line passing through the point (U, V) and having an inclination θ. Therefore, in step 55, the equation of a straight line passing through the points (U, V) and having an inclination θ %Formula %In this way, the traveling direction at two different points and the output of the geomagnetic sensor at that time are measured. , two straight lines, and Ll are found, unless there is a change in the offset due to @magnetism in the geomagnetic sensor between both chambers, the center of the Lissajous circle at both sides must be the same, and from this, , the center of the Lissajous circle (uo
, Vo) is obtained as the intersection of the above two lines 1i1L and Lo'. The center of this Lissajous circle (“Ja *
Vo) is offset, so in step 56 a straight line is drawn, and from the equation of Lo, the intersection of both straight lines (
1 o.

v. ). After this, as data for the next measurement, in step 57, a,
The values of b and θ are stored as am, bl, and θ1.

On the other hand, in step 53, 1θ-011〉3156
Or, if it is determined that the angle is <45°, the above 2.
Since the slopes of the straight lines of the book are close and the error in measuring the intersection of both straight lines is likely to be large, no measurement is performed in this case, and the process returns to step 51 to repeat the above flow.

In addition, in the above example, the offset due to magnetization is calculated as the intersection of two straight lines and Ll measured at two different points, but the magnitude of the geomagnetic field strength (radius of Lissajous circle) is For example, the straight line is calculated from the traveling direction θ and the geomagnetic sensor outputs U and V obtained in one measurement, and the points on this straight line (U, V ) The point separated by the radius "r" of the Lissajous circle can be determined as the center (Uo, VO) of the Lissajous circle, and in this way, the approximate value of the offset can be known with a single measurement. Can be done.

(Effects of the Invention) As explained above, the present invention includes a satellite-based positioning means that receives radio waves from a satellite and detects the running direction of the vehicle. The vehicle's running direction at a point is detected, and the detected running direction is used to determine the offset due to the magnetization of the geomagnetic sensor, and this offset is corrected, so the driving history from the reference position is The current position is recognized as a relative position to a reference position by measuring using the direction detected by the geomagnetic sensor, but it is possible to reduce the measurement error of the geomagnetic sensor by reducing the measurement error due to magnetization. , it is possible to improve the recognition accuracy of the current position.

[Brief Description of the Drawings] Fig. 1 is an overall configuration diagram showing an example of a navigation device according to the present invention, Fig. 2 is a block diagram showing a geomagnetic sensor, and Fig. 3 (A)
is an output signal diagram of a geomagnetic sensor that rotates horizontally with respect to the geomagnetism, Figures 3 (B) to (E) are Lissajous curve diagrams showing the correction procedure of the geomagnetic sensor by the current position recognition device, and Figure 4 is the navigation device mentioned above. Flowchart showing the offset correction operation of the geomagnetic sensor in FIG. 5 and FIG. 6 are graphs showing examples of the output of the geomagnetic sensor. 2...GPS receiver 4a...Vehicle speed sensor 4
b...Geomagnetic sensor 10...Control device 16.
...Indicator 41...Detection coil Fig. 5 Fig. 6

Claims (1)

[Claims] 1) A vehicle navigation device equipped with current position recognition means that measures the current position of the vehicle using a geomagnetic sensor, which detects at least the running direction of the vehicle by receiving radio waves from a satellite. What is claimed is: 1. A vehicle navigation device comprising a satellite-based positioning means and configured to perform offset correction of a geomagnetic sensor using traveling directions detected by the satellite-based positioning means at two different points.