Patent Description:
A traffic sign (a road sign) that displays information related to a speed limit for a vehicle traveling on a road is installed on the road. Document <CIT> describes a speed limit display device for a vehicle, which displays a speed limit indicated on this traffic sign. This device recognizes a traffic sign in an image based on data of an image of the landscape in front of the vehicle that is captured by a camera mounted on the vehicle, and displays this recognized traffic sign on a display provided in a position visible by a driver of the vehicle. Documents <CIT> and <CIT> also disclose generic speed limit display devices.

There are cases in which an expressway is provided parallel to a general road. In this case, a camera of a speed limit display device for a vehicle traveling on the expressway may capture a traffic sign for a vehicle traveling on the general road (i.e., a traffic sign for the general road). In this case, the speed limit display device may end up displaying the speed limit indicated on the traffic sign for the general road on a display, which is undesirable. Similarly, a speed limit display device for a vehicle traveling on the general road may end up displaying the speed limit indicated on a traffic sign for the expressway that is provided parallel to the general road, which is also undesirable.

It is the object of the invention to provide a speed limit display device for a vehicle, in which the likelihood of a speed that is not a speed limit that should be applied being displayed is reduced. According to the present invention, the above object is solved by a speed limit display device having the features of claim <NUM>. Advantageous embodiments are performed according to the dependent claims.

According to the invention, a speed limit display device for a vehicle, comprises:.

The processing portion is configured to obtain an actual sign installation distance that is the distance between the traffic sign and the vehicle when the vehicle is closest to the traffic sign obtained from the distance at the diameter matching point, and the relationship, measured in advance, between the actual sign installation distance and the distance between the center of the traffic sign on the specific screen and the center line that extends vertically through the center of the specific screen, the relationship being stored in a storage element of the speed limit distance device.

The processing portion is configured to determine whether a predetermined condition is satisfied when the traffic sign is detected based on the image data, the predetermined condition including a condition that the actual sign installation distance between the vehicle and the traffic sign be less than a predetermined distance.

The processing portion is configured to display the detected speed limit on the indicator when the predetermined condition is satisfied; and
the processing portion is configured to not display the detected speed limit (Vst_new) on the indicator when the predetermined condition is not satisfied.

As a result, when a traffic sign is installed near a road on which a vehicle is traveling and this traffic sign is a traffic sign that indicates a speed limit that should be applied to the vehicle, the speed limit indicated on the traffic sign is able to be displayed on the speed limit display device. Also, when a traffic sign is installed away from a road on which a vehicle is traveling and there is a possibility that this sign is not a traffic sign that indicates a speed limit that should be applied to the vehicle, the speed limit indicated on the traffic sign is able to be prevented from being displayed on the speed limit display device. As a result, the likelihood that a speed limit that is not a speed limit that should be applied will be displayed by the speed limit display device is able to be reduced.

The predetermined condition may include a condition that the detected speed limit be equal to or higher than a speed threshold value. Also, the speed threshold value may be set to a value equal to or greater than a speed that is lower, by a predetermined value, than a speed limit being displayed by the indicator at a time when the speed limit is detected.

As a result, it is possible to determine whether to display the detected speed limit on the speed limit display device, based on the speed limit that is being displayed on the indicator.

The processing portion may be configured to set the predetermined distance larger when the detected speed limit is higher than a predetermined speed, than when the detected speed limit is equal to or lower than the predetermined speed.

The distance between the vehicle and a traffic sign installed on the road on which the vehicle is traveling tends to be greater when the width of the road is wider. In addition, the speed limit indicated on the traffic sign installed on the road also tends to be higher when the width of the road is wider. Therefore, when the speed limit indicated on the traffic sign is high, the width of the road is wide, so the distance between the vehicle and the traffic sign tends to be large.

Therefore, it is possible to accurately determine whether the detected speed limit is a speed limit that should be displayed on the speed limit display device, by setting the predetermined distance larger when the detected speed limit is higher than a predetermined speed than when the detected speed limit is equal to or lower than the predetermined speed.

Hereinafter, a speed limit display device according to example embodiments of the invention will be described with reference to the accompanying drawings.

<FIG> is a block diagram schematically showing a speed limit display device (hereinafter, simply referred to as "execution device") <NUM> according to an example embodiment of the invention. The execution device <NUM> is mounted in a vehicle (an automobile, a vehicle). The execution device <NUM> includes a camera (an image obtaining device) <NUM>, a processing portion <NUM>, and a display (an indicator) <NUM>.

The camera <NUM> is fixed to a stay or the like of an inner rearview mirror (a so-called room mirror) of a vehicle body front portion. An optical axis of the camera <NUM> is aligned with a vehicle body front-rear direction (vehicle advancing direction) when the camera <NUM> is fixed to the vehicle body. Therefore, the camera <NUM> is able to obtain an image (image data) <NUM> of the landscape in the vehicle advancing direction (in front of the vehicle) by capturing the landscape, as shown in <FIG>. Upon receiving a capture command from the processing portion <NUM>, the camera <NUM> captures an image of the landscape in front of the vehicle. The camera <NUM> is a CCD camera, for example.

Traffic signs <NUM> and <NUM> and the like indicating a maximum speed limit (hereinafter, simply referred to as "speed limit") for a vehicle shown in <FIG> are installed near the road (on the side of the road or above the road or the like). The traffic sign <NUM> shown in <FIG> is a traffic sign (a standard traffic sign) without a supplemental sign that indicates a condition under which the speed limit (a standard speed limit) indicated on the traffic sign <NUM> applies. On the other hand, the traffic sign <NUM> shown in <FIG> is a traffic sign with a supplemental sign 52a (a traffic sign with a supplemental sign, a supplemented sign) that indicates a condition under which the speed limit (a supplemental speed limit) indicated on the traffic sign <NUM> applies. The conditions under which the speed limits apply here include, for example, conditions regarding the weather, class of vehicle, and time of day or night and the like.

The processing portion <NUM> is an electronic control unit (ECU) that includes a well-known microcomputer that includes RAM (a storage element), ROM, and a CPU and the like. The processing portion <NUM> is configured to detect (recognize) the traffic sign <NUM> or <NUM> by processing the image <NUM> (image data, captured image, or image signal) obtained by the camera <NUM>, as will be described in detail later.

Furthermore, when the standard traffic sign <NUM> is detected in the captured image <NUM>, the processing portion <NUM> detects (recognizes) a speed limit indicated on the detected standard traffic sign <NUM> as a standard speed limit Vst_new, and determines whether to display this detected standard speed limit Vst_new on the display <NUM>, as will be described in detail later. Moreover, when the traffic sign <NUM> with a supplemental sign is detected in the captured image <NUM> as well, the processing portion <NUM> detects (recognizes) a speed limit indicated on the detected traffic sign <NUM> with a supplemental sign as a supplemental speed limit Vsub_new, and determines whether to display this detected supplemental speed limit Vsub_new on the display <NUM>, as will be described in detail later.

The display <NUM> is provided in a position visible from a driver's seat of the vehicle (such as in a meter cluster panel, for example). As shown in <FIG>, the display <NUM> includes a first display portion 13a that displays a main speed limit (the standard speed limit), and a second display portion 13b that displays a supplemental speed limit (the supplemental speed limit). The display portions 13a and 13b display the standard speed limit and the supplemental speed limit, respectively, according to a display command of the processing portion <NUM>.

A vehicle speed sensor <NUM> is configured to detect a speed of the vehicle (a vehicle speed), and output a signal indicative of this vehicle speed SPD. The signal output from the vehicle speed sensor <NUM> is input to the processing portion <NUM>. The processing portion <NUM> obtains the vehicle speed SPD based on the input signal.

An alarm <NUM> issues a warning by a sound in response to a command from the processing portion <NUM>.

Next, the operation of the execution device <NUM> structured as described above will be described. In actuality, this operation is realized by the CPU provided in the processing portion <NUM> of the execution device <NUM> (hereinafter, simply referred to as "CPU") executing processes described next according to programs (instructions) stored in the ROM.

In this example, when an ignition switch is turned on, data Vst of the standard speed limit and data Vsub of the supplemental speed limit are erased from the RAM. That is, data indicating that the data Vst of the standard speed limit and the data Vsub of the supplemental speed limit are invalid is stored in a predetermined region of the RAM as the data Vst of the standard speed limit and the data Vsub of the supplemental speed limit.

The CPU is configured to repeatedly execute the processes in the routine shown by the flowchart in <FIG> each time a predetermined period of time (e.g., <NUM> second) passes, when the ignition switch is on. Therefore, at a predetermined timing, the CPU starts processing from step <NUM> in <FIG>, and then performs steps <NUM> and <NUM> that will be described later, in order.

Step <NUM>: The CPU outputs a capture command to the camera <NUM>, directs the camera <NUM> to capture an image, and obtains the captured image (image data) <NUM> captured by the camera <NUM>.

Step <NUM>: The CPU processes the captured image <NUM> obtained in step <NUM> by a well-known method (see <CIT>, for example), and determines whether the traffic sign <NUM> and/or <NUM> indicating the speed limit is included in the captured image <NUM> based on the data of the processed captured image <NUM>. Furthermore, if it is determined that the standard traffic sign <NUM> is included in the captured image <NUM> (i.e., if the CPU recognizes (detects) the standard traffic sign <NUM> in the captured image <NUM>), the CPU detects the speed limit indicated on the standard traffic sign <NUM> as a standard speed limit Vst_new. In addition, if it is determined that the traffic sign <NUM> with a supplemental sign is included in the captured image <NUM> (i.e., if the CPU recognizes (detects) the traffic sign <NUM> with a supplemental sign in the captured image <NUM>), the CPU detects the speed limit indicated on the traffic sign <NUM> with a supplemental sign as a supplemental speed limit Vsub_new.

Next, the CPU proceeds on to step <NUM> where it determines whether the standard traffic sign <NUM> is included in the captured image <NUM>, based on the determination result in step <NUM>. If the standard traffic sign <NUM> is included in the captured image <NUM>, the CPU makes a determination of "Yes" in step <NUM> and proceeds on to step <NUM>.

In step <NUM>, the CPU obtains a distance between the vehicle and the standard traffic sign <NUM> in the captured image <NUM> (hereinafter, referred to as the "standard sign installation distance ΔDst").

The distance between the vehicle and the traffic sign (hereinafter, referred to as the "sign installation distance ΔD") may be obtained in the manner described below, for example. The sign installation distance ΔD is the "standard sign installation distance ΔDst" described above, or a "supplemental sign installation distance ΔDsub" that will be described later.

As illustrated in <FIG>, when it is assumed that the captured image <NUM> is displayed on a specific screen (display), the distance between the vehicle and the traffic sign in the vehicle advancing direction may be regarded as having reached a certain specified distance when a diameter of the traffic sign on the display screen matches a certain constant diameter (hereinafter, also referred to as the "diameter matching point"). This is based on the fact that the diameter of the traffic sign is substantially constant.

Therefore, at the diameter matching point, the relationship between the actual sign installation distance ΔD and a distance Δd between a center C50 of a traffic sign <NUM> on the specific screen and a center line C60 that extends vertically through the center of the specific screen, is measured in advance, and this relationship is stored in the ROM.

Then, when the diameter matching point arrives while the vehicle is actually traveling, the CPU obtains the distance Δd at this diameter matching point, and obtains the actual sign installation distance ΔD from this distance Δd and the relationship described above stored in the ROM. The actual sign installation distance ΔD obtained at this time is the distance between the traffic sign and the vehicle when the vehicle is closest to the traffic sign.

The CPU may also regard the distance between the vehicle and the traffic sign in the vehicle advancing direction as having reached the certain specified distance by a well-known image processing method of the image <NUM> using a well-known distance measurement sensor. Furthermore, the image <NUM> may be converted into data that gives an overhead view by a well-known image processing method, and obtain the sign installation distance ΔD from this data.

Next, the CPU proceeds on to step <NUM> where the CPU determines whether the standard sign installation distance ΔDst obtained in step <NUM> is shorter than a predetermined distance ΔDth. This predetermined distance ΔDth is set to a value that is definitely smaller than the distance between the vehicle and a traffic sign for a road that is different from the road on which the vehicle is traveling.

If the standard sign installation distance ΔDst is shorter than the predetermined distance ΔDth, the CPU makes a determination of "Yes" in step <NUM> and performs steps <NUM> and <NUM> described below, in order.

Step <NUM>: The CPU outputs a command (a display command) to display the standard speed limit Vst_new newly detected in step <NUM> on the first display portion 13a, and outputs a command (a hide command) to stop displaying the supplemental speed limit on the second display portion 13b. As a result, the newly detected standard speed limit Vst_new is displayed on the first display portion 13a, and the supplemental speed limit stops being displayed on the second display portion 13b.

Step <NUM>: The CPU stores the standard speed limit Vst_new newly detected in step <NUM> in the RAM as the data Vst of the standard speed limit being displayed on the first display portion 13a, and erases the data Vsub of the supplemental speed limit being displayed on the second display portion 13b from the RAM. Then, the CPU proceeds on to step <NUM>.

On the other hand, if the standard traffic sign <NUM> is not included in the captured image <NUM> obtained in step <NUM>, the CPU makes a determination of "No" in step <NUM> and proceeds directly on to step <NUM>. In this case, the display of the standard speed limit on the first display portion 13a is not changed, and the current display on the first display portion 13a is continued.

Moreover, even if the standard traffic sign <NUM> is included in the obtained captured image <NUM>, when the standard sign installation distance ΔDst is equal to or greater than the predetermined distance ΔDth, the CPU makes a determination of "No" in step <NUM> and proceeds directly on to step <NUM>. In this case as well, the display of the standard speed limit on the first display portion 13a is not changed, and the current display on the first display portion 13a is continued.

Upon proceeding to step <NUM>, the CPU determines whether the traffic sign <NUM> with a supplemental sign is included in the captured image <NUM>. If the traffic sign <NUM> with a supplemental sign is included in the captured image <NUM>, the CPU makes a determination of "Yes" in step <NUM> and proceeds on to step <NUM>.

Upon proceeding to step <NUM>, the CPU obtains a distance between the vehicle and the traffic sign <NUM> with a supplemental sign in the captured image <NUM> (hereinafter, referred to as "supplemental sign installation distance ΔDsub"). This supplemental sign installation distance ΔDsub is obtained by a method similar to that for obtaining the sign installation distance ΔD.

Next, the CPU proceeds on to step <NUM> where it determines whether the supplemental sign installation distance ΔDsub obtained in step <NUM> is less than the predetermined distance ΔDth. If the supplemental sign installation distance ΔDsub is less than the predetermined distance ΔDth, the CPU makes a determination of "Yes" in step <NUM>, and performs steps <NUM> and <NUM> described below, in order.

Step <NUM>: The CPU outputs a command (a display command) to display the supplemental speed limit Vsub_new newly detected in step <NUM> on the second display portion 13b. As a result, the newly detected supplemental speed limit Vsub_new is displayed on the second display portion 13b.

Step <NUM>: The CPU stores the supplemental speed limit Vsub_new newly detected in step <NUM> in the RAM as the data Vsub of the supplemental speed limit being displayed on the second display portion 13b. Then, the CPU proceeds on to step <NUM> where this cycle of the routine ends.

If the traffic sign <NUM> with a supplemental sign is not included in the captured image <NUM>, the CPU makes a determination of "No" in step <NUM> and proceeds directly on to step <NUM> where this cycle of the routine ends. In this case, the display of the supplemental speed limit speed limit on the second display portion 13b is not changed, and the current display on the second display portion 13b is continued.

Moreover, even if the traffic sign <NUM> with a supplemental sign is included in the obtained captured image <NUM>, if the supplemental sign installation distance ΔDsub is equal to or greater than the predetermined distance ΔDth, the CPU makes a determination of "No" in step <NUM> and proceeds directly on to step <NUM> where this cycle of the routine ends. In this case as well, the display of the supplemental speed limit on the second display portion 13b is not changed, and the current display on the second display portion 13b is continued.

The operation of the execution device <NUM> is as described above. According to this execution device <NUM>, when a vehicle <NUM> is traveling on a road under the circumstances shown in <FIG>, for example, the speed limit is displayed on the display <NUM> in the manner described below.

In the example shown in <FIG>, a general road and an expressway extend parallel to each other. Furthermore, a standard traffic sign 51a for a general road that indicates a standard speed limit of <NUM>/h is installed on the left side of the general road. In addition, a standard traffic sign 51b for an expressway that indicates a standard speed limit of <NUM>/h is installed between the general road and the expressway. The standard traffic sign 51b is installed in front of the standard traffic sign 51a in the vehicle advancing direction.

A case will be assumed in which, at the point when the vehicle <NUM> is traveling in front of the traffic sign 51a on the expressway, a standard speed limit of <NUM>/h is displayed on the first display portion 13a, and a supplemental speed limit of <NUM>/h is displayed on the second display portion 13b.

When the vehicle <NUM> advances and approaches the traffic sign 51a, the camera <NUM> of the vehicle <NUM> captures an image of the landscape including this traffic sign 51a. At this time, the execution device <NUM> obtains a distance (a standard sign installation distance) ΔDst_a between the traffic sign 51a and the vehicle <NUM>.

In the example shown in <FIG>, this standard sign installation distance ΔDst_a is equal to or greater than the predetermined distance ΔDth, so the execution device <NUM> does not output a command to display the standard speed limit (= <NUM>/h) indicated on the traffic sign 51a on the first display portion 13a, even if the vehicle <NUM> passes by the traffic sign 51a.

That is, the CPU makes a determination of "Yes" in step <NUM> in <FIG>, and makes a determination of "No" in step <NUM>. Therefore, the standard speed limit displayed on the first display portion 13a remains <NUM>/h.

When the vehicle <NUM> advances further and approaches the traffic sign 51b, the camera <NUM> of the vehicle <NUM> captures an image of the landscape including the traffic sign 51b. At this time, the execution device <NUM> obtains a distance (a standard sign installation distance) ΔDst_b between the traffic sign 51b and the vehicle <NUM>.

In the example shown in <FIG>, this standard sign installation distance ΔDst_b is less than the predetermined distance ΔDth, so when the vehicle <NUM> passes by the traffic sign 51b, the execution device <NUM> outputs a command to the display <NUM> to display the standard speed limit (= <NUM>/h) indicated on the traffic sign 51b on the first display portion 13a, as well as outputs a command to the display <NUM> to stop the supplemental speed limit from being displayed on second display portion 13b.

That is, the CPU makes a determination of "Yes" in both steps <NUM> and <NUM> in <FIG>, and performs step <NUM>. As a result, the standard speed limit displayed on the first display portion 13a switches from <NUM>/h to <NUM>/h, and the supplemental speed limit stops being displayed on the second display portion 13b.

In this way, with the execution device <NUM>, a speed limit indicated on a traffic sign installed in a location equal to or greater than the predetermined distance ΔDth away (in the left-right direction of the vehicle) (i.e., a traffic sign that is not a traffic sign indicating a speed limit that should be applied; the traffic sign 51a in the example shown in <FIG>) will not be displayed on the first display portion 13a.

On the other hand, a speed limit indicated on a traffic sign installed within the predetermined distance ΔDth (i.e., a traffic sign indicating a speed limit that should be applied; the standard traffic sign 51b in the example shown in <FIG>) will be displayed on the first display portion 13a.

Therefore, a wrong speed limit is able to be prevented from being displayed on the display <NUM>, and the correct speed limit is able to be reliably displayed on the display <NUM>.

Moreover, the CPU of the processing portion <NUM> is configured to repeatedly execute the routine shown by the flowchart in <FIG> each time a predetermined period of time (e.g., <NUM> second) passes, when the ignition switch is on. Therefore, at a predetermined timing, the CPU starts processing from step <NUM> in <FIG> and proceeds on to step <NUM> where the CPU obtains the vehicle speed SPD and the standard speed limit Vst being displayed on the first display portion 13a. The vehicle speed SPD is obtained based on a signal output from the vehicle speed sensor <NUM>.

Next, the CPU proceeds on to step <NUM> where it determines whether the vehicle speed SPD obtained in step <NUM> is higher than the standard speed limit Vst obtained in step <NUM>.

If the vehicle speed SPD is higher than the standard speed limit Vst at the time when the CPU executes step <NUM>, the CPU makes a determination of "Yes" in step <NUM> and proceeds on to step <NUM> where the CPU outputs a command to activate the alarm <NUM>. Then, the CPU proceeds on to step <NUM> where this cycle of the routine ends.

On the other hand, if the vehicle speed SPD is equal to or lower than the standard speed limit Vst at the point when the CPU executes step <NUM>, the CPU makes a determination of "No" in step <NUM> and proceeds on to step <NUM> where this cycle of the routine ends.

According to the routine described above, when the vehicle speed SPD is higher than the standard speed limit Vst being displayed on the first display portion 13a, an audible alarm that notifies the driver that the vehicle speed SPD is higher than the standard speed limit Vst is issued by the alarm <NUM>.

When a general road is parallel to an expressway, as shown in <FIG>, a standard traffic sign 51c for a general road (the standard traffic sign indicating a standard speed limit of <NUM>/h in the example shown in <FIG>) may be set between the expressway and the general road. At this time, a distance (standard traffic sign installation distance) ΔDst_c between the standard traffic sign 51c and the vehicle <NUM> may also be less than the predetermined distance ΔDth.

In this case, if the standard speed limit (= <NUM>/h) indicated on the standard traffic sign 51c is displayed on the first display portion 13a, an excessively low standard speed limit (= <NUM>/h) will end up being displayed on the first display portion 13a even though the vehicle <NUM> is traveling on the expressway.

Therefore, the execution device <NUM> may display a speed limit on the display <NUM> in the manner described below. That is, the execution device <NUM> may be configured to determine whether to display a newly detected standard speed limit Vst_new on the first display portion 13a, based on the relationship between the newly detected standard speed limit Vst_new indicated on the standard traffic sign 51c and the standard speed limit Vst being displayed on the first display portion 13a, even if the standard sign installation distance ΔDst is less than the predetermined distance ΔDth.

More specifically, the CPU provided in the processing portion <NUM> of the execution device <NUM> may be configured to repeatedly execute the routine shown by the flowchart in <FIG> each time a predetermined period of time passes, when the ignition switch is on.

The routine in <FIG> is the same as the routine in <FIG>, except for the addition of steps <NUM>, <NUM>, <NUM>, and <NUM>. Therefore, a description of the steps other than these steps <NUM>, <NUM>, <NUM>, and <NUM> will be omitted.

When the CPU makes a determination of "Yes" in step <NUM>, the CPU proceeds on to step <NUM>. Upon proceeding on to step <NUM>, the CPU determines whether the standard speed limit is being displayed on the first display portion 13a.

If the standard speed limit is being displayed on the first display portion 13a at the time when the CPU executes step <NUM>, the CPU makes a determination of "Yes" in step <NUM> and proceeds on to step <NUM>.

Upon proceeding to step <NUM>, the CPU determines whether the standard speed limit Vst_new newly detected in step <NUM> is equal to or greater than a speed threshold value Vth. Here, the speed threshold value Vth is a value (= Vst - V1) obtained by subtracting a predetermined value V1 from the standard speed limit Vst being displayed on the first display portion 13a. This predetermined value V1 is set to an appropriate positive value.

If the standard speed limit Vst_new newly detected in step <NUM> is equal to or greater than the speed threshold value Vth at the time when the CPU executes step <NUM>, the CPU makes a determination of "Yes" in step <NUM>, then performs steps <NUM> and <NUM> described above, in order, and then proceeds on to step <NUM>. As a result, the standard speed limit Vst_new newly detected in step <NUM> is displayed on the first display portion 13a.

In contrast, if the standard speed limit Vst_new newly detected in step <NUM> is less than the speed threshold value Vth at the time when the CPU executes step <NUM>, the CPU makes a determination of "No" in step <NUM> and proceeds directly on to step <NUM>. In this case, the display of the standard speed limit on the first display portion 13a does not change, and the current display of the first display portion 13a is continued.

On the other hand, if the standard speed limit is not being displayed on the first display portion 13a at the time when the CPU executes step <NUM>, the CPU makes a determination of "No" in step <NUM>, and executes steps <NUM> and <NUM> described below, in order.

According to this execution device <NUM>, when a vehicle <NUM> is traveling on a road under the circumstances shown in <FIG>, for example, the speed limit is displayed on the display <NUM> in the manner described below.

In the example shown in <FIG>, the standard traffic sign 51c for a general road that indicates a standard speed limit of <NUM>/h is installed between the general road and the expressway, and a standard traffic sign 51d for an expressway that indicates a standard speed limit of <NUM>/h is installed on the right side of the expressway. The standard traffic sign 51d is installed in front of the standard traffic sign 51c in the vehicle advancing direction. In this example, a case is assumed in which a standard speed limit of <NUM>/h is displayed on the first display portion 13a and a supplemental speed limit of <NUM>/h is displayed on the second display portion 13b at the time when the vehicle <NUM> is traveling in front of the traffic sign 51c. In addition, the predetermined value V1 is set to <NUM>/h.

When the vehicle <NUM> advances and approaches the traffic sign 51c, the camera <NUM> of the vehicle <NUM> captures an image of the landscape including this traffic sign 51c. At this time, the execution device <NUM> obtains a distance (a standard sign installation distance) ΔDst_c between the traffic sign 51c and the vehicle <NUM>.

In the example shown in <FIG>, this standard sign installation distance ΔDst_c is less than the predetermined distance ΔDth, so the execution device <NUM> determines whether the standard speed limit (= <NUM>/h) indicated on the traffic sign 51c is equal to or greater than the speed threshold value Vth. Here, the speed threshold value Vth is a value (= <NUM>/h) obtained by subtracting the predetermined value V1 (= <NUM>/h) from a first display speed limit (= <NUM>/h).

In this case, the standard speed limit (= <NUM>/h) indicated on the traffic sign 51c is less than the speed threshold value Vth (= <NUM>/h), so the execution device <NUM> does not output a command to display the standard speed limit indicated on the traffic sign 51c on the first display portion 13a, even when the vehicle <NUM> passes by the traffic sign 51c.

That is, the CPU makes a determination of "Yes" in all of steps <NUM>, <NUM>, and <NUM>, and makes a determination of "No" in step <NUM> in <FIG>. Thus, the standard speed limit displayed on the first display portion 13a remains <NUM>/h.

When the vehicle <NUM> advances further and approaches the traffic sign 51d, the camera <NUM> of the vehicle <NUM> captures an image of the landscape including the standard traffic sign 51d. At this time, the execution device <NUM> obtains a distance (a standard sign installation distance) ΔDst_d between the traffic sign 51d and the vehicle <NUM>.

In the example shown in <FIG>, this standard sign installation distance ΔDst_d is less than the predetermined distance ΔDth, so the execution device <NUM> determines whether the standard speed limit (= <NUM>/h) indicated on the traffic sign 51d is equal to or greater than the speed threshold value Vth (= <NUM>/h).

In this case, the standard speed limit (= <NUM>/h) indicated on the traffic sign 51d is equal to or greater than the speed threshold value Vth (= <NUM>/h), so the execution device <NUM> outputs a command to the display <NUM> to display the standard speed limit indicated on the traffic sign 51d on the first display portion 13a.

That is, the CPU makes a determination of "Yes" in all of steps <NUM>, <NUM>, <NUM>, and <NUM>, and makes proceeds on to step <NUM> in <FIG>.

Accordingly, if the standard speed limit indicated on the standard traffic sign <NUM> installed within the predetermined distance ΔDth is significantly lower than the standard speed limit displayed on the first display portion 13a, the standard speed limit indicated on the standard traffic sign <NUM> is not displayed on the first display portion 13a.

Therefore, a speed limit that is significantly lower than the actual speed limit is able to be prevented from being displayed on the first display portion 13a, even though the vehicle <NUM> is traveling is on an expressway.

When the vehicle <NUM> is traveling on a wide road (e.g., an expressway), the sign installation distance ΔD is relatively large. On the other hand, when the vehicle <NUM> is traveling on a narrow road (e.g., a general road), the sign installation distance ΔD is relatively small.

Therefore, if the predetermined distance is set relatively large as a result of taking into account the sign installation distance ΔD when the vehicle <NUM> is traveling on a wide road, then a traffic sign that does not indicate a speed limit for the vehicle <NUM> may end up erroneously being recognized as a traffic sign that indicates a speed limit for the vehicle <NUM>, when the vehicle <NUM> is traveling on a narrow road.

Conversely, if the predetermined distance is set relatively small as a result of taking into account the sign installation distance ΔD when the vehicle <NUM> is traveling on a narrow road, then a traffic sign that indicates a speed limit for the vehicle <NUM> may end up erroneously being recognized as a traffic sign that does not indicate a speed limit for the vehicle <NUM>, when the vehicle <NUM> is traveling on a wide road.

Therefore, the execution device <NUM> may be configured to set the predetermined distance according to the newly detected standard speed limit Vst_new. More specifically, the processing portion <NUM> of the execution device <NUM> sets the predetermined distance ΔDth larger when the newly detected standard speed limit Vst_new is large than it does when the newly detected standard speed limit Vst_new is small.

The standard speed limit typically tends to be higher the wider the road is. Therefore, when there is a high probability that the vehicle <NUM> is traveling on a wide road due to the fact that the newly detected standard speed limit Vst_new is high, the predetermined distance ΔDth is set to a large value. As a result, when the vehicle <NUM> is traveling on a wide road, the standard traffic sign <NUM> that indicates the standard speed limit for the vehicle <NUM> is able to be prevented from being erroneously determined to be a standard speed limit that does not indicate the standard speed limit for the vehicle <NUM>.

On the other hand, when there is a high probability that the vehicle <NUM> is traveling on a narrow road due to the fact that the newly detected standard speed limit Vst_new is low, the predetermined distance ΔDth is set to a small value. As a result, when the vehicle <NUM> is traveling on a narrow road, the standard traffic sign <NUM> that does not indicate the standard speed limit for the vehicle <NUM> is able to be prevented from being erroneously determined to be a standard speed limit that indicates the standard speed limit for the vehicle <NUM>.

In step <NUM> in <FIG>, the execution device <NUM> described above compares the standard sign installation distance ΔDst to the predetermined distance ΔDth. However, instead of this, the execution device <NUM> may be configured to compare a length from the center C50 of the sign in the image to a center line C60 of the image, to a predetermined length corresponding to the predetermined distance. In this case, the execution device <NUM> makes a determination of "Yes" in step <NUM> if the length from the center C50 of the sign in the image to the center line C60 of the image is shorter than the predetermined length in step <NUM> in <FIG>.

Furthermore, in step <NUM> in <FIG>, the execution device <NUM> described above compares the newly detected standard speed limit Vst_new to the speed threshold value Vth (= Vst - V1) obtained by subtracting the predetermined value V1 from the standard speed limit Vst being displayed on the first display portion 13a. However, instead of this, in step <NUM>, the execution device <NUM> may also be configured to compare the newly detected standard speed limit Vst_new to the standard speed limit Vst being displayed on the first display portion 13a. In this case, the execution device <NUM> makes a determination of "Yes" in step <NUM> if the newly detected standard speed limit Vst_new is equal to or higher than the standard speed limit Vst.

As a result, a speed that is lower than the standard speed limit being displayed on the first display portion 13a is able to be prevented from being displayed on the first display portion 13a.

In addition, in step <NUM> in <FIG>, the execution device <NUM> may be configured to compare the newly detected standard speed limit Vst_new to a value (Vst + V2) obtained by adding a predetermined value V2 (> <NUM>) to the standard speed limit Vst being displayed on the first display portion 13a. In this case, the execution device <NUM> makes a determination of "Yes" in step <NUM> if the newly detected standard speed limit Vst_new is equal to or smaller than the value (Vst + V2) obtained by adding the predetermined value V2 to the standard speed limit Vst.

As a result, a speed that is higher than a speed that is lower, by the predetermined value V2, than the standard speed limit Vst being displayed on the first display portion 13a is able to be prevented from being displayed on the first display portion 13a.

When the vehicle speed SPD is higher than the standard speed limit Vst described on the first display portion 13a, the execution device <NUM> described above notifies the driver that the vehicle speed SPD is higher than the standard speed limit Vst by emitting a sound from the alarm <NUM>. However, the execution device <NUM> may also notify the driver that the vehicle speed SPD is higher than the standard speed limit Vst by indicating that the vehicle speed SPD is higher than the standard speed limit Vst on the display <NUM>. That is, the invention may also be configured to notify the driver that the vehicle speed SPD is higher than the standard speed limit Vst by warning means that includes a sound or a display on the display <NUM>.

As described above, the speed limit display device <NUM> according to this example embodiment of the invention includes the indicator (the display) <NUM>, the image obtaining device (the camera) <NUM>, and the processing portion <NUM> that displays a speed limit (the standard speed limit and/or the supplemental speed limit) on the indicator <NUM>.

The processing portion <NUM> detects the speed limit indicated on a captured traffic sign that is the traffic sign (the standard traffic sign and/or the supplemental traffic sign) <NUM> and/or <NUM> in the landscape captured by the image obtaining device <NUM>, based on the image data obtained by the image obtaining device <NUM> (step <NUM> in <FIG>), and determines whether a predetermined condition that includes a condition that a distance (the standard sign installation distance or the supplemental sign installation distance) ΔDst or ΔDsub between the captured traffic sign and the vehicle be less than the predetermined distance ΔDth, is satisfied when a captured traffic sign is detected based on the image data (i.e., when a determination of "Yes" is made in both steps <NUM> and <NUM> in <FIG>).

When it is determined that the predetermined condition is satisfied (i.e., when a determination of "Yes" is made in step <NUM> in <FIG>), the processing portion <NUM> displays the detected speed limit (the standard speed limit) Vst_new on the indicator <NUM> (step <NUM> in <FIG>).

On the other hand, when it is determined that the predetermined condition is not satisfied (i.e., when a determination of "No" is made in step <NUM> in <FIG>), the processing portion <NUM> does not display the detected speed limit Vst_new on the indicator <NUM>.

Moreover, the predetermined condition includes a condition that the detected speed limit Vst_new be equal to or greater than the speed threshold value Vth (step <NUM> in <FIG>), and the speed threshold value is set to a value equal to or greater than a speed that is lower, by the predetermined value V1, than the speed limit Vst being displayed on the indicator <NUM>.

In addition, the predetermined distance ΔDth is set larger when the detected speed limit Vst_new is higher than a predetermined speed than it is when the detected speed limit Vst_new is equal to or lower than the predetermined speed.

As a result, the likelihood that a speed that is not the speed limit that should be applied will be displayed on the indicator <NUM> is able to be reduced.

Claim 1:
A speed limit display device (<NUM>) for a vehicle, comprising:
an indicator (<NUM>) mountable in the vehicle, the indicator configured to display information related to a speed limit (Vst_new) of a road on which the vehicle is traveling;
an image obtaining device (<NUM>) configured to capture an image (<NUM>) of a landscape in a direction in which the vehicle is traveling and obtain image data of the landscape, the captured image (<NUM>) being displayed on a specific screen; and
a processing portion (<NUM>) configured to detect a traffic sign (<NUM>) in the landscape based on the image data, to detect the speed limit (Vst_new) indicated on the traffic sign (<NUM>), wherein
the processing portion (<NUM>) is configured to identify a diameter matching point when a diameter of the traffic sign (<NUM>) on the specific screen matches a certain constant diameter, and to identify that the distance between the vehicle and the traffic sign (<NUM>) in the vehicle advancing direction has reached a certain specified distance,
wherein
the processing portion (<NUM>) is configured to obtain an actual sign installation distance (ΔD) that is the distance between the traffic sign and the vehicle when the vehicle is closest to the traffic sign obtained from the distance (Δd) at the diameter matching point, and the relationship, measured in advance, between the actual sign installation distance (ΔD) and the distance (Δd) between the center (C50) of the traffic sign (<NUM>) on the specific screen and the center line (C60) that extends vertically through the center of the specific screen, the relationship being stored in a storage element of the speed limit display device (<NUM>);
the processing portion (<NUM>) is configured to determine whether a predetermined condition is satisfied when the traffic sign (<NUM>) is detected based on the image data, the predetermined condition including a condition that the actual sign installation distance (ΔD) between the vehicle and the traffic sign (<NUM>) be less than a predetermined distance (ΔDth);
the processing portion (<NUM>) is configured to display the detected speed limit (Vst_new) on the indicator (<NUM>) when the predetermined condition is satisfied; and
the processing portion (<NUM>) is configured to not display the detected speed limit (Vst_new) on the indicator (<NUM>) when the predetermined condition is not satisfied.