JP2008107283A - On-vehicle radar system and radome for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an on-vehicle radar system capable of suppressing a decrease in radar performance, even if a water film adheres to the surface of a cover on the front of a radar body. <P>SOLUTION: The radar system comprises a transmission means (not shown) for transmitting radio waves directed toward a target; a reception means (not shown) for receiving radio waves reflected by the target; a measurement means (not shown) for measuring the distance to the target and the relative speed, by detecting the target from radio waves transmitted by the transmission means and radio waves received by the receiving means; a casing 101 for storing the transmitting means, receiving means, and detection/measurement means; and a cover 102 that is arranged on the front in the transmission direction of radio waves inside the casing 101 and protects an object to be stored in the casing 101. In the radar system, the cover 102 has a groove 104, in a recessed structure where water is guided to the entire outer surface in the transmission direction of radio waves by the capillary phenomenon. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to, for example, a radar device suitable for in-vehicle use or a radome mounted thereon, and in particular, the in-vehicle radar device or in-vehicle radar capable of preventing deterioration of laser performance due to a water film formed by rain or condensation. It is related to the radome for the device.

Based on the level of reflection from the water film and dirt attached to the radome (radar for radar antenna protection), the presence or absence of these (ie, attached water film and dirt) is determined. As a radar device to detect, there is an FM radar device disclosed in Japanese Patent Laid-Open No. 10-282229 (Patent Document 1).
In Patent Document 1, a low-frequency component of a beat signal is extracted by a low-pass filter, the extracted low-frequency component is AD-converted by an A / D converter, fast Fourier transform is performed by a fast Fourier transformer, radar An FM radar device is described that compares the stored frequency spectrum data of low frequency components with no dirt on the radome and the frequency spectrum data of the input low frequency components to detect that dirt has adhered. ing.

In general, when there is a deposit on the front of the radar, the reflected wave from the deposit is detected and used as a system failure, or the reflected wave from the deposit is detected and the reflected wave from the object to be detected originally is detected. And a method of improving the S / N to prevent a decrease in detection performance.
Japanese Patent Laid-Open No. 10-282229

  If the deposit is water and exists as a water film in front of the radar, both the transmitted and received radio waves are significantly attenuated due to reflection at the interface of the water film and absorption of radio waves by the water itself. It has a great influence on itself.

Moreover, since the on-vehicle radar device is used as a preventive safety device, the failure of the system using the radar due to the performance deterioration due to the attenuation of the radio wave reduces the opportunity for the driver to use. .
In particular, it is a user need and a social need to eliminate the state where the system cannot be used in rainy weather that is likely to cause a serious accident.

  The present invention was made to solve such a problem, and even if a water film adheres to the cover surface of the radar main body front surface or the vehicle-side radome surface, it is not necessary to have a special water film detection function, An object is to provide an in-vehicle radar device or a radome for an in-vehicle radar device capable of suppressing a decrease in radar performance.

  The on-vehicle radar device according to the present invention includes a transmission unit that transmits a radio wave toward an object, a reception unit that receives a reflected radio wave reflected by the object, a transmission radio wave that is transmitted by the transmission unit, and the reception unit. Detecting / measuring means for detecting the object from the received radio wave received by the receiver and measuring the distance and relative speed to the object, and a housing for housing the transmitting means, the receiving means, and the detecting / measuring means And a cover that is disposed in front of the casing in the direction of radio wave transmission and protects the contents stored in the casing, wherein the cover has water on the entire outer surface in the direction of radio wave transmission due to capillary action. A groove having a concave structure to be guided is provided.

The radome for in-vehicle radar device according to the present invention includes a transmission unit that transmits a radio wave toward an object, a reception unit that receives a reflected radio wave reflected by the object, and a transmission radio wave that is transmitted by the transmission unit. Detecting and measuring means for detecting the object from the received radio waves received by the receiving means and measuring the distance and relative speed to the object, the transmitting means, the receiving means, and the detecting and measuring means. A radome for an on-vehicle radar device that is mounted in front of an on-vehicle radar device that includes a housing to be stored and a cover that is disposed in front of the housing in the direction of radio wave transmission and that protects items stored in the housing. ,
The radome for the on-vehicle radar device is provided with a groove having a concave structure according to any one of claims 1 to 5 on a front surface or a back surface thereof.

In the on-vehicle radar device according to the present invention, the cover that is disposed on the front surface of the housing in the direction of radio wave transmission and protects the contents in the housing is a groove having a concave structure that guides water to the entire outer surface in the direction of radio wave transmission by capillary action. Therefore, even when water droplets adhere to the outer surface of the cover due to rain or the like, the water droplets are drawn into the groove by capillary action.
Therefore, an area where a water film cannot be formed on the outer surface of the cover can be generated, transmission / reception that is not affected by the water film can be performed, and deterioration of radar performance due to the water film can be suppressed.

In addition, the in-vehicle radar device redome according to the present invention is mounted in front of the in-vehicle radar device, and has a concave groove for guiding water by capillarity on the front surface or the back surface thereof. Even when water droplets adhere to the surface of the water droplets, the water droplets are drawn into the grooves by capillary action.
Therefore, an area where a water film cannot be formed on the surface of the radome can be generated, transmission / reception that is not affected by the water film can be performed, and deterioration of radar performance can be suppressed.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the drawings, the same reference numerals indicate the same or equivalent ones.
Embodiment 1 FIG.
FIG. 1 is a diagram for explaining the structure of an in-vehicle radar device (also simply abbreviated as a radar device) according to Embodiment 1 of the present invention.
In FIG. 1, reference numeral 101 denotes a millimeter-wave radar casing (that is, a casing of a radar apparatus using millimeter-wave radio waves), 102 is a cover that is a casing in the radio wave transmission direction, and 103 is a polarization plane of the transmission radio waves. .
Reference numeral 104 denotes a plurality of grooves provided in parallel to each other on the entire outer surface of the cover 102 in the radio wave transmission direction, and the grooves 104 are cut perpendicularly to the polarization plane 103 of the transmission radio wave.
1A is a perspective view conceptually showing the overall appearance configuration of the in-vehicle radar device according to the present embodiment, and FIG. 1B is a partially enlarged view of the groove 104.

FIG. 2 is a cross-sectional view taken along the line A-A in FIG.
In FIG. 2, the width of the concave portion 202 is set to a width at which capillary action occurs, and the width of the convex portion 201 is set to a width that does not collect water droplets.
The smaller the widths of the convex portion 201 and the concave portion 202, the greater the effect.
That is, the smaller the width of the convex portion 201, the fewer water droplets collect on the convex portion 201, and the smaller the width of the concave portion 202, the more pronounced the capillary phenomenon.

In this embodiment, considering that the diameter of a general raindrop is 1 mm to 3 mm, no matter where the 1 mm raindrop hits the cover 102, the raindrop does not form a water film in the convex portion 201, but in the concave portion 202. The widths of the convex portion 201 and the concave portion 202 are set to 0.5 mm so that raindrops are drawn by capillary action.
In this configuration, since the greater the force drawn by the capillary phenomenon, the more efficient it is, it is possible to select a cover material whose contact angle between water and the cover 102 is 90 deg or less, which is the limit at which the capillary phenomenon occurs. It is a premise.

FIG. 3 is a diagram for explaining how water droplets are drawn into the grooves by surface tension in the radar device according to the present embodiment.
With reference to FIG. 3, the behavior when water droplets adhere to the outer surface of the cover 102 will be described.
FIG. 3A is a schematic diagram when water droplets adhere to the outer surface of the cover 102 provided with unevenness (that is, provided with the groove 104). In the figure, reference numeral 301 denotes an attached water droplet.
Since the water droplet 301 spreads to a contact angle θ determined by the casing material (that is, the material of the cover 102), the water droplet 301 spreads around the corner of the concave portion 202 as shown in FIG. Then, a force that is drawn into the recess 202 is generated by the force of T cos θ.

As a result, the water droplet 301 is drawn in the concave portion 202 by capillary action as shown in FIG. 3C, and the water droplet can be excluded from the surface of the convex portion 201.
Since the water droplets 301 behave in this manner, when raining is assumed, water is collected in the concave portions 202 of all the grooves, but water is not collected on the surfaces of the convex portions 201.
Therefore, the transmission radio wave or the reception radio wave is reflected or attenuated in the concave portion 202 of the groove, but stable transmission / reception is possible in the convex portion 201 of the groove to which water droplets are not attached regardless of the amount of rain.

As described above, the on-vehicle radar device according to the present embodiment includes a transmission unit (not shown) that transmits radio waves toward an object and a reception unit (not shown) that receives reflected radio waves reflected by the object. And a detection / measurement means (not shown) for detecting the object from the transmission radio wave transmitted by the transmission means and the reception radio wave received by the reception means, and measuring the distance to the object and the relative speed, the transmission means, and the reception In the radar device, the cover 102 is provided with a casing 101 that houses the means and the detection / measurement means, and a cover 102 that is disposed in front of the casing 101 in the direction of radio wave transmission and protects the items stored in the casing 101. A groove 104 having a concave structure through which water is guided by capillary action is provided on the entire outer surface in the radio wave transmission direction.
Therefore, water droplets adhering to the entire outer surface of the cover 102 are drawn into the concave groove 104 by a capillary phenomenon, and the deterioration of the radar performance due to the water film on the outer surface of the cover 102 can be suppressed.

Embodiment 2. FIG.
FIG. 4 is a schematic diagram for explaining a characteristic operation of the in-vehicle radar device according to the second embodiment.
In the first embodiment described above, the behavior of water droplets in the case of rainy weather has been described, but in this embodiment, the case of fine weather is considered.
FIG. 4 is a cross-sectional view of the casing portion (that is, the cover 102) on the front surface of the radar apparatus, and shows a state of radio wave transmission in a state where water droplets are not attached to the outer surface of the cover 102.
In FIG. 4, 401 represents a radio wave transmitted through the groove concave portion 202, and 402 represents a radio wave transmitted through the groove convex portion 201.
A radio wave 401 and a radio wave 402 in FIG. 4 schematically represent changes in the wavelength of the radio wave that passes through the cover 102.

The wavelength of the radio wave transmitted through the casing member (cover 102) is 1 / √εg shorter than the wavelength in air when the relative dielectric constant εg of the material of the casing member is used.
Note that “√εg” is the same as “(εg) ^1/2 ”.
Therefore, in the radio wave 401 and the radio wave 402, interference and attenuation are caused by the fact that the phases are different from each other on the surface a which is the outlet of the casing portion (cover) 102 unless the distances through the material are appropriately selected. In the worst case, it is assumed that they cancel each other.

Here, in order to prevent radio waves from being attenuated, it is essential to align the phases in the a-plane.
In order to align the phase of the radio wave on the a-plane, the frequency of the radio wave 401 traveling through the outside of the casing member (that is, the concave portion 202 of the cover 102) and the inside of the casing member (that is, the convex portion 201 of the cover 102). The depth of the groove may be selected so that the difference in the frequency of the radio wave 402 that travels through) becomes an integer.
Now, when the wavelength of the radio wave in the air is λ and the relative dielectric constant of the casing member (cover 102) is εg, the wavelength λg of the radio wave traveling in the casing member is
λg = λ / √εg (1)
It becomes.

When the groove depth is “L”, the difference between the number of λ (frequency) and the number of λg (frequency) in this section (ie, the section corresponding to the groove depth “L”) is arbitrary. Since the integer n of
L / λ−L / λg = n (2)
Should just hold.
Here, substituting (1) into (2) and rearranging,
L = nλ / (√εg−1) (3)
Is obtained.
Therefore, if the depth L is selected so as to satisfy the expression (3), neither the transmission radio wave nor the reception radio wave interferes or attenuates, and the radar performance can be prevented from deteriorating.

Furthermore, when the dielectric constant of water is εr and the wavelength traveling in water is λr, an arbitrary integer m is used,
L / λ−L / λr = m (4)
That is,
L = mλ / (√εr−1) (5)
Therefore, by selecting n and m so that Eqs. (3) and (5) can be established simultaneously, the attenuation and radar performance of the radio wave are different due to the difference in the place where the radio wave travels in fine weather and rainy weather. The decrease can be suppressed.

However, Equations (3) and (5) are optimal value calculations. Under actual conditions of use, n and m do not need to be exact integers, and alleviate to the target allowable level of radar performance. It is possible.
For example, it is generally considered that there is no significant influence on the performance of the radar device if the deviation is less than 1/4 of the operating wavelength λ.
Therefore, since an arbitrary integer and λ are multiplied in equation (3) and equation (5), if λ can be allowed to ± 1/4, if this allowable width is replaced with an arbitrary integer width, n Both m and m can be tolerated to any integer ± 1/4.
Of course, since the allowable width is determined by the target performance, a width necessary for actual design may be set.

As described above, in the in-vehicle radar device according to the present embodiment, when the relative dielectric constant of the material constituting the cover 102 is εg and an arbitrary integer is n, the depth L of the groove of the concave structure is
L = nλ / (√εg−1))
By doing so, the attenuation of radio waves in a clear sky can theoretically be zero.

Embodiment 3 FIG.
In the casing means (that is, the cover 102) having the above-described structure, the removal of the water film using the capillary phenomenon is described in the first embodiment, and the depth of the groove to be drawn in by the capillary phenomenon is described in the second embodiment. In this embodiment, the direction of the groove will be described.
In this embodiment, when the direction of the groove is considered, the worst condition, that is, a case where water enters all the grooves by capillary action will be described as an example.
This state can be interpreted as having a dielectric slit in the transmission direction when viewed from the radio wave transmission unit (transmission means) inside the radar device.
Therefore, from the viewpoint of “effective transmission of transmitted radio waves”, it is necessary to select the direction of the groove so as to minimize attenuation elements (reflection, confusion) other than water absorption.

Here, although water is generally a dielectric, its dielectric constant is large, and when considering raindrops in an actual natural environment, it contains a lot of impurities and is interpreted as a large resistor. It is natural to keep it.
Considering that the water contains impurities, when the plane of polarization of the transmission radio wave and the groove are in parallel, the plane of polarization is represented by an electric field, so there is some potential difference between the moisture surface in the groove. It appears that some reflected waves are present.
On the contrary, when the polarization plane of the transmission radio wave is perpendicular to the groove, the potential difference cannot be generated, so that it can be expected that the reflected wave is reduced.
Therefore, it is desirable that the direction of the groove and the plane of polarization be perpendicular to each other. At the time of design, it is more efficient to transmit radio waves if the groove is configured to be perpendicular to the plane of polarization of the radar. convenient.

  As described above, in the present embodiment, by setting the direction of the groove of the concave structure perpendicular to the polarization plane of the transmission radio wave, attenuation of the radio wave due to water (water droplets) drawn into the groove is minimized. can do.

Embodiment 4 FIG.
FIG. 5 is a diagram for explaining the in-vehicle radar device according to the fourth embodiment, and is a diagram showing a force relationship acting on water droplets attached to the outer surface of the cover.
In the configuration of the groove 104 described above, in order to draw water into the concave portion 202 more efficiently, the force for pulling the water droplet at the convex portion 201 may be reduced and the force for pulling the water droplet at the concave portion 202 may be increased.
That is, when the contact angle with water droplets on the surface of the convex portion 201 is θ1 and the contact angle with water droplets on the concave portion 202 is θ2, it can be understood that Tcos θ1 <Tcos θ2 as shown in FIG. .
Therefore, since θ1> θ2, it is only necessary to increase the contact angle θ1 of the convex portion 201 and decrease the contact angle θ2 of the concave portion 202, and it is understood that the larger the difference, the higher the effect.

Increasing the contact angle θ1 with the water droplet on the surface of the convex portion 201 can be realized by imparting hydrophobicity or water repellency to the surface of the convex portion 201.
In addition, reducing the contact angle θ2 in the recess 202 can be realized if the recess 202 is made hydrophilic.
For example, if the material of the casing means (cover 102) is a resin, both water repellency and hydrophilicity can be easily realized by application of a coating agent or surface modification.

As described above, in the in-vehicle radar device according to the present embodiment, the hydrophilic treatment is performed on the inner side of the concave groove, and the water repellent treatment is performed on the upper surface of the convex portion between the concave groove. Because
In addition, water droplets can be effectively drawn into the groove.

Embodiment 5. FIG.
The groove configuration described so far is effective for temporary rainfall.
However, since there is an upper limit to the total volume of water drawn by capillary action, the above effect cannot be sustained if there are continuous raindrops that exceed this upper limit.
Although it can be expected that the water in the groove is drained by gravity or running wind, the capillary action is caused by the force acting on the wall surface of the groove, so the wetting force is opposite to the draining direction. Can not be discharged efficiently.

FIG. 6 is an enlarged view of the end portion (peripheral portion) 105 of the cover 102 of the in-vehicle radar device according to the first embodiment, and shows the force relationship acting on the water in the groove around the cover 102. FIG. Note Are these three lines correct?
As will be described later, the on-vehicle radar device according to the present embodiment uses the groove width of the outer surface peripheral portion (that is, the cover end portion 105) of the cover 102, which is an area that does not affect the main radar function, as the main radar function. It is characterized in that it is larger than the area that affects the area (that is, the area excluding the peripheral part of the outer surface of the cover 102).

As shown in FIG. 6, the force 601 for preventing drainage due to capillary action works on the three surfaces of the groove (that is, the both side walls and the bottom surface of the groove), and the remaining one surface is the traveling wind received by the vehicle traveling. , The force 602 to be discharged by this wind works, and further, the force 603 due to gravity works, so that the frictional force 604 resulting from this works as a force that does not drain, and the force 605 determined by the mass of the water drains Work as a force to try.
In order to drain efficiently, it is only necessary to reduce the force not to drain and increase the force to drain.
However, since the strength of gravity cannot be increased, it is important to control other parameters.

Here, the force 601 acting on the three surfaces of the groove among the forces acting so as not to drain the water is a force that is the basis of the capillary phenomenon, and therefore it is possible to prevent the capillary phenomenon from being realized by increasing the width of the groove. It is.
This means that increasing the width of the groove means increasing the mass of water existing in the groove, so the force 605 determined by the mass of water is increased, and the force 601 acting on the three surfaces of the groove is increased. Even if it does not change, this force 601 is canceled relatively.

In addition, since the area in which the running wind hits the water in the groove is increased, the force for discharging can be further increased.
Here, looking back at the structure of the entire radar device, in FIG. 1, the end portion (peripheral portion) of the cover 102 is generally outside the effective radio wave irradiation range. By widening the groove width, drainage can be efficiently performed.

FIG. 7 is a diagram for explaining a characteristic structure of the in-vehicle reader device according to the sixth embodiment, and is an enlarged view of the end portion 105 of the cover 102 in the in-vehicle reader device according to the present embodiment.
In the present embodiment, as shown in FIG. 7, the groove width (that is, the width of the concave portion 202) 702 at the end portion (peripheral portion) 105 of the cover 102, which is an area that does not affect the main radar function, is set. The groove width 701 in the area that affects the main radar function (that is, the central area excluding the peripheral portion of the outer surface of the cover 102) is larger.

As a result, drainage by running wind can be promoted, and the volume of water in the groove is reduced accordingly, so that raindrops can be drawn into the groove by capillary action even for continuous rainfall.
In addition, if the surface is processed to increase the contact angle with water droplets in the concave portion of the portion where the groove width is widened, the force acting on each surface of the concave portion will be reduced, so the force to prevent drainage will be reduced, and due to traveling wind The drainage effect is further improved.

  As described above, in the in-vehicle radar device according to the present embodiment, the groove width of the recessed structure is larger in the peripheral area of the cover 102 than in the area other than the peripheral area of the cover 102. The drawn water can be discharged effectively.

Embodiment 6 FIG.
When a radar is mounted on a vehicle, a radome is generally mounted in front of an in-vehicle radar device mounted on the vehicle for the protection of the radar or a design implication.
The structure of the groove provided on the outer surface of the cover 102 described in the first to fifth embodiments can also be applied to the front surface or the back surface of the radome mounted in front of the in-vehicle radar device.

  The radome for in-vehicle radar device according to the present embodiment includes a transmission unit that transmits a radio wave toward an object, a reception unit that receives a reflected radio wave reflected by the object, a transmission radio wave that is transmitted by the transmission unit, and a reception unit. Detecting / measuring means for detecting the object from the received radio wave received by the receiver and measuring the distance to the object and the relative speed, a housing for storing the transmitting means, the receiving means and the detecting / measuring means, and the casing 101 An on-vehicle radar device radome (not shown) that is mounted in front of an on-vehicle radar device that includes a cover 102 that is disposed in front of the radio wave transmission direction and that protects the stored items in the housing 101. The radome for a radar device is characterized in that the groove having the concave structure described in any one of the first to fifth embodiments is provided on the front surface or the back surface thereof.

  Therefore, the in-vehicle radar device radome according to the present embodiment can suppress a decrease in radar performance due to a film adhering to the front surface or the back surface.

  The present invention is useful for realizing an in-vehicle radar device that does not deteriorate the radar performance even if water drops due to rain adhere to the cover disposed in front of the radio wave transmission direction.

FIG. 2 is a diagram for illustrating the structure of an in-vehicle radar device according to Embodiment 1 of the present invention. It is AA sectional drawing in FIG. In the radar apparatus of Embodiment 1, it is a figure for demonstrating a mode that a water droplet is drawn into a groove | channel by surface tension. FIG. 10 is a schematic diagram for explaining a characteristic operation of the in-vehicle radar device according to the second embodiment. It is a figure for demonstrating the vehicle-mounted radar apparatus by Embodiment 4. FIG. It is an enlarged view of the cover edge part 105 shown in FIG. It is a figure for demonstrating the characteristic structure of the vehicle-mounted reader apparatus by Embodiment 6.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Case 102 Cover 103 Polarization plane 104 Groove 105 Cover edge 202 Groove convex part 202 Groove concave part 301 Water droplet
401 Radio waves that pass through the convex portion 401 Radio waves that pass through the concave portion 701 The width of the groove that is not the end of the cover 702 The width of the groove at the end of the cover

Claims (6)

A transmission means for transmitting a radio wave toward an object;
Receiving means for receiving the reflected radio wave reflected by the object;
Detection / measurement means for detecting the object from a transmission radio wave transmitted by the transmission means and a reception radio wave received by the reception means, and measuring a distance and a relative speed to the object;
A housing that houses the transmission means, the reception means, and the detection / measurement means;
In a radar device that is disposed on the front surface of the housing in the direction of radio wave transmission and includes a cover that protects items stored in the housing,
The on-vehicle radar device according to claim 1, wherein the cover is provided with a groove having a concave structure through which water is guided by capillary action on the entire outer surface in the radio wave transmission direction. The depth L of the groove of the concave structure is defined as follows. When the relative dielectric constant of the material constituting the cover is εg and an arbitrary integer is n,
L = nλ / (√εg−1))
The on-vehicle radar device according to claim 1, wherein   The in-vehicle radar device according to claim 1 or 2, wherein a direction of the groove of the concave structure is perpendicular to a plane of polarization of a transmission radio wave.   The inside of the groove of the concave structure is subjected to hydrophilic treatment, and the upper surface of the convex portion between the grooves of the concave structure is subjected to water repellency treatment. The on-vehicle radar device according to item 1.   The in-vehicle radar device according to any one of claims 1 to 4, wherein a width of the groove of the concave structure is larger in a peripheral area of the cover than in an area other than the peripheral part of the cover. . The target from the transmission means for transmitting the radio wave toward the target, the reception means for receiving the reflected radio wave reflected by the target, the transmission radio wave transmitted by the transmission means and the reception radio wave received by the reception means Detecting / measuring means for detecting an object and measuring a distance and relative speed to the object, a casing for housing the transmitting means, the receiving means, and the detecting / measuring means, and a radio wave transmission direction of the casing A radome for an on-vehicle radar device mounted on the front side of the on-vehicle radar device provided with a cover for protecting the stored items in the housing,
The radome for an on-vehicle radar device according to any one of claims 1 to 5, wherein the groove of the concave structure according to any one of claims 1 to 5 is provided on a front surface or a back surface of the radome for the on-vehicle radar device.

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