Patent Application
20220396922
The present invention relates to a magnetic marker to be laid in or on a road and a method of using the magnetic marker.
Conventionally, a magnetic marker to be laid in or on a road so as to be detectable by a vehicle has been known (for example, refer to Patent Literature 1). The magnetic marker is detectable by using a magnetic sensor mounted on the vehicle. For example, by using the magnetic markers laid along lane, it is possible to achieve automatic driving, as well as various driving assists such as automatic steering control and lane departure warning.
The acting range of magnetism occurring from the magnetic marker is not so wide. Thus, it is extremely difficult for a vehicle positioned before a laying position of the magnetic marker to detect the magnetic marker. In view of the detection performance of the magnetic sensor that is vehicle-mountable, the magnetic marker is not detectable until the vehicle arrives at the laying position of the magnetic marker.
To reliably detect the magnetic marker when the vehicle passes over the magnetic marker, high detection performance is required on a vehicle side. In general, if reliable detection with low loss is tried to be achieved, there is a possibility of an increase in erroneous detection of magnetic markers due to disturbance magnetism and so forth.
The present invention was made in view of the above-described conventional problem, and is to provide an easily-detectable magnetic marker.
One mode of the present invention resides in a magnetic marker to be laid on a traveling road where a vehicle travels, including:
a magnet as a magnetism generation source and a reflecting part which retroreflects at least part of incident electromagnetic waves.
One mode of the present invention resides in a method of detecting and using, by a traveling vehicle, a magnetic marker including a magnet as a magnetism generation source and a reflecting part which retroreflects at least part of incident electromagnetic waves and laid in or on a traveling road of the vehicle, wherein the vehicle includes a distance-measurement device which acquires an azimuth and a distance of a subject based on a direction of emitting the electromagnetic waves and a time required for reflection of the electromagnetic waves, a magnetic device which detects the magnetic marker and identifies a lateral shift amount of the vehicle with respect to the magnetic marker, and a processing circuit which calculates a target steering angle for the vehicle to travel along a target path and controls the vehicle so that the vehicle travels along the target path,
the method includes:
a process of detecting the magnetic marker by emitting the electromagnetic waves ahead of the vehicle, and measuring an azimuth and a distance of the magnetic marker;
a process of estimating a predicted arrival time point when the vehicle arrives at the magnetic marker detected by using the electromagnetic waves or a predicted lateral shift amount, which is a deviation (lateral shift amount) of the vehicle in a vehicle-width direction predicted for the magnetic marker; and
a process of identifying an actual detection time point, which is a time point when the magnetic marker is actually detected, or an actual deviation (lateral shift amount) of the vehicle with respect to the magnetic marker, and
the method performs an accuracy improvement process in which, of a result of comparison between the actual detection time point and the predicted arrival time point and a result of comparison between the actual deviation (lateral shift amount) and the predicted lateral shift amount, at least either one of the results is used to achieve an improvement in at least any of: measurement accuracy by the distance-measurement device, accuracy of detection of the magnetic marker by the magnetic device, accuracy of the target steering angle calculated by the processing circuit, and following accuracy of the vehicle with respect to the target path.
The magnetic marker according to the present invention includes the reflecting part which retroreflects at least part of incident electromagnetic waves. This magnetic marker is detectable not only magnetically but also by using electromagnetic waves. For example, electromagnetic waves such as light and electric waves have high rectilinearity and can arrive at a point relatively far away. By using electromagnetic waves, the magnetic marker can be detected before the vehicle arrives at the laying position of the magnetic marker.
AS for the magnetic marker according to the present invention that is detectable not only magnetically but also by using electromagnetic waves, of the result of comparison between the actual detection time point and the predicted arrival time point and the result of comparison between the actual deviation (lateral shift amount) and the predicted lateral shift amount, at least either one of the results can be used. This comparison result can be used for the accuracy improvement process to achieve an improvement in at least any of: measurement accuracy by the distance-measurement device, accuracy of detection of the magnetic marker by the magnetic device, accuracy of the target steering angle calculated by the processing circuit, and following accuracy of the vehicle with respect to the target path.
As described above, the magnetic marker according to the present invention is detectable not only magnetically but also by using electromagnetic waves, and the degree of difficulty in detection is decreased. Also, in accordance with the magnetic marker according to the present invention, the result of comparison between the magnetic detection result and the detection result using electromagnetic waves can be acquired. This comparison result can be used to improve at least any of: measurement accuracy by the distance-measurement device, accuracy of detection of the magnetic marker by the magnetic device, accuracy of the target steering angle calculated by the processing circuit, and following accuracy of the vehicle with respect to the target path.
Modes of the present invention are specifically described by using the following embodiments.
The present embodiment is an example regarding a magnetic marker laid in or on a road (one example of a traveling road where a vehicle travels) to achieve vehicle's driving assist. Details of this are described by using
Magnetic marker 1 (
Magnetic marker 1 exhibits a flat circular shape having a diameter of 100 mm and a thickness of 2 mm. This magnetic marker 1, for example, can be adhesively bonded to a road surface. As an adhesive, for example, molten asphalt may be used.
Magnet sheet 10 is one example of a magnet as a magnetism generation source. Magnet sheet 10 of the present embodiment is a circular-shaped isotropic ferrite rubber magnet having a diameter of 100 mm and a thickness of 1.5 mm. The maximum energy product (BHmax) of this magnet sheet 10 is approximately 6.4 kJ/square m.
Reflective sheet 15 is a circular-shaped resin-made sheet having a diameter of 100 mm and a thickness of 0.5 mm. In this reflective sheet 15 forming one example of a small-piece-shaped sheet body, spherical glass beads having a diameter of several tens of μm to 100 μm and a high refractive index are dispersed and arranged inside. Reflective sheet 15 containing spherical glass beads has an optical characteristic of reflecting (retroreflecting) at least part of incident light toward an incident direction. In particular, in reflective sheet 15 of the present embodiment, the optical characteristic is adjusted so as to retroreflect laser light with high efficiency.
Magnetic marker 1 can be made by, for example, by laminating a large-sheet-shaped reflective member on a surface of a large-sheet-shaped isotropic ferrite rubber magnet to acquire an intermediate sheet (omitted in the drawing) and then punching a circular shape by punching. The outer periphery of magnetic marker 1 may be a section as it is at the time of punching. This is because, in general, a ferrite rubber magnet with iron oxide as a main material has a low possibility of being degraded by oxidation or the like and necessity of providing a protective layer or a coat layer on the section is small.
Note that in place of reflective sheet 15 of the present embodiment, a reflective layer as a coat layer with retroreflective coating having mixed therein spherical glass beans having a high refractive index may be formed on a surface of magnet sheet 10. For example, it may be such that, after a coat layer is provided on a surface of a large-sheet-shaped isotropic ferrite rubber magnet, a circular shape is punched by punching to make a magnetic marker. The magnetic marker may be fabricated by forming a coat layer with retroreflective coating on the surface of circular-shaped magnet sheet 10. Furthermore, in place of the coating, a resin material with spherical glass beads having a high refractive index dispersed therein may be adopted, and a coat layer with this resin material may be formed on a surface of magnet sheet 10. The resin material may be, for example, a transparent resin material such as epoxy resin. After the resin material covering the surface of magnet sheet 10 is cured, a process of melting the surface of the resin material may be performed, thereby exposing the spherical glass beads to an outer surface. In place of the spherical glass beads forming particles, metal powder (pulverulent body) such as alumina may be adopted. In place of the resin material, a polymer material such as asphalt may be adopted.
Magnetic markers 1 configured as described above are arranged, for example, as in
Vehicle 5 has, for example, a lane keeping function. This vehicle 5 includes, as in
Next, sensor array 51 as one example of a magnetic device, lidar unit 62 as one example of a distance-measurement device, and control unit 61 as one example of a processing circuit are generally described.
Sensor array 51 is configured to include a plurality of magnetic sensors Cn (n is an integer of 1 to 15) and detection processing circuit 510 which processes magnetic measurement values of magnetic sensors Cn. Sensor array 51 is a rod-shaped unit where magnetic sensors C1 to C15 are arrayed on a straight line so as to be regularly spaced. Sensor array 51 is attached to vehicle 5 so that the longitudinal direction of the rod shape is along a vehicle-width direction.
As magnetic sensors Cn, for example, MI (Magneto Impedance) sensors can be used. MI sensors are magnetic sensors with high sensitivity by using the known MI effect (Magneto Impedance Effect) in which impedance of a magneto-sensitive body such as an amorphous wire sensitively changes in response to an external magnetic field. Magnetic sensors Cn have sensitivity in the longitudinal direction of the amorphous wire.
Magnetic sensor Cn of the present embodiment includes two amorphous wires along two orthogonal directions. Magnetic sensor Cn is configured so that the two amorphous wires are along a forwarding direction and the vehicle-width direction when sensor array 51 is attached to vehicle 5 as described above. Magnetic sensor Cn of sensor array 51 assembled to vehicle 5 can detect magnetic components acting in the forwarding direction and magnetic components acting in the vehicle-width direction of vehicle 5.
For example, when any magnetic sensor Cn moves in the forwarding direction to pass directly above magnetic marker 1, the magnetic measurement value in the forwarding direction has its sign reversed before and after passing magnetic marker 1 and changes so as to cross zero at a position directly above magnetic marker 1, as in a graph of changes over time exemplarily depicted in
Also, for example, as for a magnetic sensor with the same specification as that of magnetic sensors Cn, a movement along a virtual line in the vehicle-width direction passing directly above magnetic marker 1 is assumed. The magnetic measurement value in the vehicle-width direction from this magnetic sensor has its sign reversed on both sides across magnetic marker 1 and changes so as to cross zero at a position directly above magnetic marker 1. In the case of sensor array 51 having fifteen magnetic sensors Cn arrayed in the vehicle-width direction, the sign of the magnetic measurement value in the vehicle-width direction to be detected by magnetic sensor Cn varies depending on which side the magnetic sensor is present with respect to magnetic marker 1, as in a magnetic distribution exemplarily depicted in
That is, the position of zero-cross X2 in the magnetic distribution of
For example, when vehicle 5 travels leftward in the vehicle-width direction, magnetic marker 1 is shifted rightward with respect to sensor array 51 and, for example, as in
Here, details of process of magnetically detecting magnetic marker 1 are described with reference to
Detection processing circuit 510 (
Regarding changes over time of the magnetic measurement values in the forwarding direction, if detecting zero-cross corresponding to X1 in changes over time of
If detecting magnetic marker 1 in response to detection of zero-cross corresponding to X1 in the magnetic distribution of
Regarding the magnetic distribution of
Lidar unit 62 (
Lidar unit 62 includes a light source which performs pulse emission of laser light, a light-receiving part which receives reflected light from a subject, a time measuring part which measures elapsed time (reflection time) from light emission to light reception, and a distance calculating part which calculates a distance. Furthermore, lidar unit 62 includes an optical mechanism part which performs beam-scanning with laser light in a longitudinal direction and a lateral direction.
The optical mechanism part has, for example, a polygon mirror (multifaceted mirror) which reflects laser light for projection ahead, and a driving part which rotates the polygon mirror at high speeds. Laser light emitted from the light source is reflected by the polygon mirror to go ahead of vehicle 5. The light mechanism part physically changes the direction of laser light by the polygon mirror, thereby beam-scanning a two-dimensional area ahead serving as distance-measurement area 620 (
As depicted in a flow diagram of distance-measurement process of
Lidar unit 62 controls a light-emitting part for repetitive pulse-light-emission of laser light. Also, lidar unit 62 rotates the polygon mirror in synchronization with pulse-light-emission of laser light to achieve beam-scanning with laser light. As with image scanning for use in image transmission in television or the like, lidar unit 62 beam-scans each row in a horizontal direction sequentially from top to bottom, thereby achieving beam-scanning of the entire two-dimensional area serving as distance-measurement area 620 as in
By performing the distance-measurement process (
Control unit 61 (
As in
Control unit 61 refers to the distance image by lidar unit 62 and acquires a distance and azimuth to each detected magnetic marker 1 (S302, refer to
Control unit 61 calculates a target steering angle for traveling along target path 1R (S304), and estimates a time point of arriving at nearest magnetic marker 1 as a predicted arrival time point (S305). For example, when a current time is tr, a distance to nearest magnetic marker 1 is D, and a speed of vehicle 5 is V, predicted arrival time point to is tr+D/V.
Control unit 61 performs vehicle control for letting vehicle 5 travel along target path 1R by taking the target steering angle calculated at step S304 as a control value (S306). Then, control unit 61 performs vehicle control with the target steering angle calculated at step S304 (S306) until time arrives at predicted arrival time point to (S307: NO). By performing vehicle control at step S306 in this manner, control unit 61 tries to achieve vehicle traveling along target path 1R (
When time arrives at predicted arrival time point to (S307: YES), control unit 61 tries to perform detection process for magnetically detecting magnetic marker 1 by using sensor array 51 (S308). Control unit 61 repeatedly performs magnetic detection process (S308) until magnetic marker 1 is detected (S309: NO).
If magnetic marker 1 has been magnetically detected (S309: YES), control unit 61 acquires a lateral shift amount of vehicle 5 identified by sensor array 51 (S310). Then, control unit 61 corrects the target steering angle so as to reduce the lateral shift amount of vehicle 5 with respect to magnetic marker 1 (S311). Then, control unit 61 takes the corrected target steering angle as a control target value, and performs vehicle control (S312).
Note that for determination at step S309, a temporal limitation may be combined. For example, if a predetermined time has elapsed after the lapse of predicted arrival time point to, it may be determined that no magnetic marker 1 has been detected, and the process may directly proceed to step S312. In this case, the target steering angle is not corrected with the lateral shift amount, but vehicle control with the target steering angle calculated at step S304 can be performed.
As described above, magnetic marker 1 including reflective sheet 15 having retroreflection characteristics can be optically detected from a position before arrival at magnetic marker 1. If vehicle 5 includes lidar unit 62, it is possible to simultaneously detect a plurality of magnetic markers 1 ahead arrayed along lane 500 and set a path passing over these magnetic markers 1 as target path 1R. By setting target path 1R, smooth lane keeping traveling along lane 500 can be achieved. Furthermore, if magnetic marker 1 is magnetically detected when vehicle 5 passes over it, a lateral shift amount of vehicle 5 with respect to magnetic marker 1 can be identified with high accuracy. If the target steering angle is corrected with the lateral shift amount of vehicle 5, it is possible to adjust the vehicle position in the vehicle-width direction within lane 500.
Here, steering control of the wheel to be steered of the vehicle by the lateral shift amount at the time of passing over magnetic marker 1 is described as a comparative example. In this control of the comparative example, there is a possibility of occurrence of unsteady driving of the vehicle due to little-by-little steering control at each time of passage over magnetic marker 1. This unsteady driving of the vehicle is similar to, for example, unsteady driving that can occur due to driving by beginners who try to adjust the position of the vehicle within the lane (position in the vehicle-width direction) by viewing the vicinity. To reduce this unsteady driving of the vehicle, control gains can be set to be small. However, if control gains are small, there is a high possibility that control delay at the time of entering a curve zone poses a problem.
For example, a sufficiently experienced driver operates the steering wheel by capturing a road shape ahead as a whole, and thus can achieve smooth driving which follows the road shape. The control of the present embodiment of setting a target steering angle based on target path 1R and correcting the target steering angle with the lateral shift amount of vehicle 5 is similar to driving by an experienced driver. Setting a line passing over magnetic marker 1 ahead as target path 1R corresponds to a whole grasp of the road shape ahead. According to the control of the present embodiment of not directly controlling the steering angle with the lateral shift amount with respect to magnetic marker 1 but correcting the target steering angle with the lateral shift amount, unsteady driving of vehicle 5 can be reduced without causing control delay.
In the present embodiment, magnetic marker 1 including reflective sheet 15 which covers the entire surface of magnet sheet 10 is exemplarily described. Reflective sheet 15 may be a sheet which covers part of the surface of magnet sheet 10 or maybe a sheet larger in size than magnet sheet 10. In the present embodiment, circular-shaped sheets are exemplarily described as magnet sheet 10 and reflective sheet 15. The shapes of magnet sheet 10 and reflective sheet 15 may not be limited to circular shapes but may be polygonal shapes such as triangles or quadrangles, and one of magnet sheet 10 and reflective sheet 15 may be in a circular shape and the other may be in a polygonal shape.
A coat layer with retroreflective coating may be provided to part of the surface of magnet sheet 10. Also, while magnet sheet 10 having a thickness of 1.5 mm is exemplarily described in the present embodiment, when a thicker magnet is adopted, a reflective layer by a reflective sheet, a coat layer with retroreflective coating, or the like may be provided to an outer peripheral side surface of the magnet.
Magnetic marker 1 of
In the present embodiment, light such as laser light is exemplarily described as electromagnetic waves, and lidar unit 62 is exemplarily described as a device which performs process of detecting magnetic marker 1. Magnetic marker 1 can be detected also by using electric waves (electromagnetic waves) such as millimeter waves. When magnetic marker 1 is detected by a millimeter-waves radar, a reflective sheet provided with ridge-shaped ribs extending in the vehicle-width direction may be adopted. Since electric waves such as millimeter waves have high rectilinearity, in the case of a reflective sheet with a flat surface, there is a possibility that millimeter waves cannot be sufficiently retroreflected. With a reflective sheet provided with ribs, the retroreflectivity of millimeter waves can be enhanced. Note that the ribs also effectively act to enhance the retroreflectivity of laser light. In place of the reflective sheet, ribs (reflective ribs) exhibiting retroreflective characteristics maybe provided on the surface side of the magnet sheet. The ribs can be utilized as non-slip portions.
In the present embodiment, by laminating reflective sheet 15 on the surface of magnet sheet 10, the reflective layer formed on the outer surface side of magnet sheet 10 is exemplarily described as a reflecting part of magnetic marker 1. On the surface of magnet sheet 10, a protective sheet and a reflective sheet may be laminated, with the reflective sheet put on outside. In this case, strictly speaking, it cannot be said that the reflective layer is formed on the outer surface of magnet sheet 10. However, the reflective layer is formed on an outer surface side of magnet sheet 10.
The present embodiment is an example in which, based on the magnetic marker of the first embodiment, the form is changed to a tape shape. Details of this are described with reference to
Magnetic marker 1 (
In continuous-sheet-shaped magnetic marker 1, magnet sheets 10 are positioned with pitches of, for example, 2 meters. According to magnetic detection process, as with the first embodiment, magnet sheets 10 are detectable.
On the other hand, in continuous-sheet-shaped magnetic marker 1 of the present embodiment, reflective tape 151 is adopted as a tape (continuous sheet) which retains magnet sheets 10. Therefore, a result of optical detection process on magnetic marker 1 is different from that of the first embodiment.
When a lidar unit optically detects magnetic marker 1 of the present embodiment, magnetic marker 1 is continuously detectable as in a hatching area of
It is not an imperative configuration that the width of reflective tape 151 is a width exceeding the diameter of magnet sheets 10 as in the present embodiment. The reflective tape may have a width narrower than the diameter of magnet sheets 10.
Note that in place of the present embodiment, after magnet sheets 10 are laid so as to be spaced along the center of lane 500, a coat line with retroreflective coating may be formed along the center of lane 500 so as to pass through magnet sheets 10. As a width of this line, a width exceeding the diameter of magnet sheet 10 or a width narrower than the diameter of magnet sheet 10 may be adopted.
The present embodiment is an example of the magnetic marker with magnet sheets 10 arranged on the back surface of reflective tape 151. A protective tape or protective sheet for protecting magnet sheets 10 maybe laminated to reflective tape 151. The protective sheet maybe a small-piece-shaped sheet which covers magnet sheet 10. Protective tape may be a continuous tape similar to the reflective tape. Magnet sheet 10 may be arranged on the reflective surface of reflective tape 151. In this case, an area which does not reflect electromagnetic waves of laser light can be identified as the laying position of magnet sheet 10.
Note that other configurations and operations and effects are similar to those of the first embodiment.
The present embodiment is an example in which, based on the magnetic marker of the first embodiment, the mode of the reflecting part is changed. Details of this are described with reference to
Magnetic marker 1 of the present embodiment is magnet sheet 10 itself, and does not include the reflective sheet exemplarily described in the first embodiment. In magnetic marker 1 of the present embodiment, spherical glass beads 108 having a diameter of several tens of μm to 100 μm and a high refractive index and forming a reflecting part are dispersed and arranged inside magnet sheet 10, and part of spherical glass beads 108 are exposed to the outer surface of magnetic marker 1.
Next, to clarify the configuration of magnetic marker 1 of the present embodiment, a method of fabricating magnetic marker 1 is described with reference to
Magnetic marker 1 is made by punching from large-sheet-shaped magnetic sheet 104. To fabricate this magnetic sheet 104, first, slurry 113 is generated, in which magnetic powder 111 (pulverulent body, powder of iron oxide as a magnetic material in the present embodiment) and spherical glass beads 108 are blended into a resin material as a base material in a molten state. Then, this slurry 113 is molded into a predetermined shape and dried, and pellet 101 is acquired. Magnetic sheet 104 is acquired by thinly drawing out pellet 101 into a sheet shape by volling roller 102. A process may be performed in which the surface of magnetic sheet 104 is melted by using a solvent such as thinner so that many spherical glass beads 108 are exposed to the outer surface.
Spherical glass beads 108 in the present embodiment are one example of particles forming a reflecting part. In place of spherical glass beads 108, a magnetic marker (magnet sheet) containing metal powder (pulverulent body) such as alumina as one example of the reflecting part may be used.
Note that other configurations and operations and effects are similar to those of the first embodiment.
The present embodiment is an example regarding a method of detecting and using the magnetic marker of the first embodiment.
Details of this are described with reference to
The present embodiment is an example in which the determination details by control unit 61 at step S307 in
In the case of the present embodiment, as in
Note that as a predetermined time, in place of the predetermined temporal period such as one second or 0.5 seconds, a time required for a vehicle to pass through a predetermined distance may be set. For example, when 0.5 meters is set as the predetermined distance, the predetermined time is a time obtained by dividing 0.5 meters by vehicle speed V.
Also, when estimating predicted arrival time point to at step S305 of
Note that the process at step S307 in
Also, factors responsible for the differential lateral shift amount between the actual lateral shift amount of the vehicle and the predicted lateral shift amount with respect to magnetic marker 1 include an error in a measured azimuth of magnetic marker 1 by lidar unit 62, an error in a target steering angle applied to steering control, and so forth.
In lidar unit 62, an axis is set which serves as a reference when a direction of emitting laser light is identified. Lidar unit 62 identifies an azimuth relation between a forwarding axis indicating a rectilinear traveling direction of the vehicle and the axis of lidar unit 62, thereby allowing measurement of the azimuth of a magnetic marker as a subject. If the azimuth relation identified between the forwarding axis of the vehicle and the axis of lidar unit 62 has an error, an error occurs in the measured azimuth of the magnetic marker, and an error occurs in the target path set by control unit 61. If the target path as a control target has an error, the above-described differential lateral shift amount increases as a result of control by control unit 61. In this manner, the differential lateral shift amount is an amount which changes in conjunction with the azimuth error of the axis of lidar unit 62. By using this differential lateral shift amount, calibration of the axis of lidar unit 62 can be performed. If the axis of lidar unit 62 is calibrated, measurement accuracy by lidar unit 62 as one example of a distance-measurement device can be improved, and the differential lateral shift amount can be reduced (accuracy improvement process).
For example, details of the accuracy improvement process when there is an error in which the axis of lidar unit 62 swings to the right of a correct direction are described. Note that in the following description, an angle on a right side with reference to a forwarding direction of the vehicle is taken as positive, an angle on a left side is taken as negative, a lateral shift to a right side is taken as positive, and a lateral shift to a left side is taken as negative. Also, an indication of left or right in parentheses in the description indicates that left or right is switched.
When the axis of lidar unit 62 swings to the right (left) of the correct direction, an azimuth measured by lidar unit 62 for the magnetic marker as a subject is leftward (rightward) with respect to the actual azimuth. Thus, the target path becomes leftward (rightward), and the actual traveling path of the vehicle by steering control becomes leftward (rightward), thereby increasing a possibility that the differential lateral shift amount obtained by subtracting the predicted lateral shift amount from the actual lateral shift amount has a negative value (positive value). In this case, a negative (positive) angle obtained by multiplying the differential lateral shift amount of the negative value (positive value) by a conversion coefficient is preferably added to the azimuth of the axis of lidar unit 62 to calibrate the axis of lidar unit 62. With this addition of the negative (positive) angle in this manner, calibration can be performed in which the axis of lidar unit 62 swinging to the right side (left side) is returned to the left side (right side). Note that the coefficient by which the differential lateral shift amount is multiplied is preferably set as appropriate.
Also, in general, an error regarding the attachment of the wheels including the wheel to be steered is inevitable in the vehicle. In vehicle maintenance, the values of wheel alignment such as camber, toe-in, toe-out, and caster are adjusted so as to fall within a range of allowable errors. Since wheel alignment has an error, the vehicle does not necessarily travel rectilinearly when a rudder angle of the wheel to be steered (steering angle) is zero degree. That is, a neutral point of the steering angle corresponding to rectilinear traveling of the vehicle does not necessarily have zero degree.
At step S304 in
For example, the neutral point of the steering angle swings to the right side (left side) of the correct neutral point, the path of the vehicle by steering control goes rightward (leftward), and the possibility that the differential lateral shift amount obtained by subtracting the predicted lateral shift amount from the actual lateral shift amount has a positive value (negative value) increases. In this case, the neutral point is preferably calibrated by subtracting the positive (negative) angle obtained by multiplying the differential lateral shift amount of the positive value (negative value) by a conversion coefficient from the neutral point of the steering angle. With subtraction of the positive (negative) angle in this manner, calibration can be performed in which the neutral point swinging to the right side (left side) is returned leftward (rightward).
Note that other configurations and operations and effects are similar to those of the first embodiment.
In the foregoing, specific examples of the present invention are described in detail as in the embodiments, these specific examples merely disclose examples of technology included in the scope of the claims. Needless to say, the scope of the claims should not be restrictively construed based on the configuration, numerical values, and so forth of the specific examples. The scope of the claims includes technologies acquired by variously modifying, changing, or combining as appropriate the above-described specific examples by using known technologies, knowledge of a person skilled in the art, and so forth.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-116765 | Jun 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/024093 | 6/19/2020 | WO |
