Patent Description:
In recent years, head-up displays (in the following, also referred to as an "HUD") have become more and more popular. In a head-up display, an image is reflected on a front windshield of a vehicle so that predetermined information is displayed in a driver's view. However, for driver viewing of a view outside the vehicle or of the information displayed by the HUD, there may be a case where a double image is a problem.

A double image that becomes a problem for a driver of a vehicle includes a transparent double image and a reflected double image. When the front windshield includes a HUD display region used for the HUD and a region outside the HUD display region (transparent region) that is not used for the HUD, although a transparent double image may be a problem in the HUD display region, generally a reflected double image is the main problem, and in the region outside the HUD display region a transparent double image is a problem.

It has been known that such reflected double image or transparent double image can be reduced by using, for a front windshield, a laminated glass having a cross-section having a shape of a wedge viewed from the horizontal direction. For example, a laminated glass obtained by holding with two glass plates an intermediate film having a cross section having a shape of a wedge, a wedge angle of the intermediate film being changed depending on a location in the front windshield, has been proposed (See, for example, <CIT>).

Moreover, a laminated glass, in which one of two glass plates used for a front windshield is made thinner so as to reduce a weight, in order to improve fuel efficiency, and the two glass plates hold an intermediate film having a cross section having a shape of a wedge, has been proposed (See, for example <CIT>).

<CIT> discloses a glass having an inner surface and an outer surface, including a first area used by a head-up display, and a second area adjacent to the first area, and not used by the head-up display.

<CIT> describes interlayers having enhanced optical properties.

<CIT> discloses a curved vehicle windshield made from laminated glass.

<CIT> describes a thermoplastic film for a laminated-glass pane having a non-linear continuous wedge insert in the vertical direction in some sections.

<CIT> relates to a laminated glass having a reduced thickness for a head-up display.

<CIT> discloses a windshield for a head-up display system.

However, with the laminated glass that has been proposed conventionally and a combination of the techniques thereof alone, it is difficult to obtain a high-quality transparent image and a high-quality reflected image.

The present invention was made in view of such a problem, and it is an object of the present invention to obtain a transparent image and a reflected image quality which are higher than with a conventional image, on a laminated glass having a wedge angle which is not constant.

The subject matter of the present invention is defined in the appended set of claims.

According to an aspect of the present invention, in a laminated glass having a wedge angle that is not constant, a transparent image and a reflected image quality which are higher than with a conventional image can be obtained.

Other objects and further features of embodiments will become apparent from the following detailed description when read in conjunction with the accompanying drawings, in which:.

In the following, with reference to drawings, embodiments of the present invention will be described. In each drawing, the same reference numeral is assigned to the same components, and redundant explanation will be omitted. In the following, a front windshield of a vehicle will be described as an example, but the present invention is not limited to this, and the laminated glass according to the embodiment can also be applied to other than the front windshield of the vehicle.

First, concepts of a reflected double image and a transparent double image will be described. <FIG> are diagrams for explaining concepts of a double image. <FIG> illustrates a reflected double image, and <FIG> illustrates a transparent double image. In <FIG>, a front-back direction of a vehicle in which the front windshield <NUM> is installed is the X-direction, a left-right direction of the vehicle is the Y-direction, and a direction perpendicular to an XY-plane is the Z-direction (The same applies to subsequent drawings).

As illustrated in <FIG>, a part of light beam 11a emitted from a light source <NUM> of HUD is reflected on an interior surface <NUM> of the front windshield <NUM> of the vehicle, and guided to an eye <NUM> of a driver as a light beam 11b (primary beam), and is visually recognized by the driver as an image 11c (virtual image) in front of the front windshield <NUM>.

Moreover, a part of light beam 12a emitted from the light source <NUM> of HUD enters an interior from the interior surface <NUM> of the front windshield <NUM> of the vehicle, and is refracted. A part thereof is reflected on an exterior surface <NUM>. Then, furthermore, the part thereof emerges from the interior surface <NUM> to the outside of the front windshield <NUM> of the vehicle by refraction, and guided to the eye <NUM> of the driver as a light beam 12b (secondary beam), and is visually recognized by the driver as an image 12c (virtual image).

In this way, the two images 11c and 12c visually recognized by the driver are reflected double images. Moreover, an angle between the light beam 11b (primary beam) and the light beam 12b (secondary beam) is an angle α of the reflected double image. The angle α of the reflected double image is preferably close to zero. In the present application, a reflected double image in the case where the secondary beam is viewed upwardly from the driver is defined as a positive value.

Moreover, as illustrated in <FIG>, a part of a light beam 41a emitted from a light source <NUM> enters an interior from the exterior surface <NUM> of the front windshield <NUM> of the vehicle and is refracted. Then, a part thereof emerge to the outside of the front windshield <NUM> from the interior surface <NUM> and is refracted, and guided to the eye <NUM> of the driver as a light beam 41b, and visually recognized by the driver as an image 41c.

Moreover, a part of a light beam 42a emitted from the light source <NUM> enters an interior from the exterior surface <NUM> of the front windshield <NUM> of the vehicle and is refracted. A part thereof is reflected on the interior surface <NUM>. Then, furthermore, the part thereof is reflected on the exterior surface <NUM>, and furthermore a part thereof emerges to the outside of the front windshield <NUM> from the interior surface <NUM> by refraction, and guided to the eye <NUM> of the driver as a light beam 42b, and visually recognized by the driver as an image 42c.

In this way, the two images 41c and 42c visually recognized by the driver are transparent double images. Moreover, an angle between the light beam 41b (primary beam) and the light beam 42b (secondary beam) is an angle η of the transparent double image. The angle η of the transparent double image is preferably close to zero.

<FIG> are diagrams depicting a front windshield of a vehicle, and schematically a state in which the front windshield is visually recognized from inside the vehicle to the outside of the vehicle. In <FIG>, as a matter of convenience, a HUD display region is indicated by a dotted pattern.

As illustrated in <FIG>, the front windshield <NUM> includes, for example, a HUD display region A<NUM> used in HUD (first HUD display region) and a HUD display region A<NUM> (second HUD display region), and a region outside the HUD display region B that is not used in HUD (transparent region). The HUD display region A<NUM> and the HUD display region A<NUM> are regions in the front windshield irradiated with light from a mirror configuring HUD, which is rotated, and viewed from a V1 point with respect to JIS R3212.

In the examples illustrated in <FIG>, when the front windshield <NUM> is attached to the vehicle, the HUD display region A<NUM> and the HUD display region A<NUM> are arranged along the front windshield <NUM> at a prescribed interval L in the vertical direction, so as not to contact each other. The region outside the HUD display region B is arranged near the HUD display region A<NUM> or the HUD display region A<NUM>.

The HUD display regions A<NUM>, A<NUM> may be arranged over the entire Y-direction, as illustrated in <FIG>, or both the HUD display regions A<NUM>, A<NUM> may be arranged in a part of the Y-direction, as illustrated in <FIG>. Alternatively, only one of the HUD display regions may be arranged in a part of the Y-direction. Moreover, when the HUD display region is arranged in a part of the Y-direction, length of the respective regions in the Y-direction need not be the same.

Moreover, when the HUD display region is arranged in a part of the Y-direction, positions of centers of the respective regions may be shifted in the Y-direction. Moreover, the front windshield <NUM> may include three or more HUD display regions which are arranged along the front windshield <NUM> at a prescribed interval L in the vertical direction so as not to contact each other.

Moreover, the region outside the HUD display region B may be provided with a region having a cross section having a shape of a wedge, in which a thickness of an upper edge side is greater than a thickness of a lower edge side when the laminated glass is attached to the vehicle, or having a thickness that is constant (may not be provided with the region having a cross section having a shape of a wedge).

The HUD display region is a region on the front windshield <NUM> that can reflect an image (virtual image) of HUD. When a concave mirror configuring the HUD is rotated and an image on the front windshield <NUM> is moved, a position at which the image on the front windshield <NUM> vanishes is present. The position is a boundary between the HUD display region and the region outside the HUD display region.

The HUD display region A<NUM> and the HUD display region A<NUM> are regions in which virtual images having different imaging distances are displayed. The imaging distance is a distance between a viewpoint of a driver and the virtual image. For example, the HUD display region A<NUM> is a region in which a virtual image is displayed near the vehicle (e.g. the imaging distance is less than <NUM>), and the HUD display region A<NUM> is a region in which a virtual image is displayed far from the vehicle (e.g. the imaging distance is <NUM> or more).

For example, in the HUD display region A<NUM>, a speed of the vehicle is always displayed, and in the HUD display region A<NUM>, a warning is displayed only when necessary. However, content of display illustrated here is an example, and the present invention is not limited to this. Moreover, the HUD display region A<NUM> may be a region in which a virtual image is displayed far from the vehicle (e.g. the imaging distance is <NUM> or more), and the HUD display region A<NUM> may be a region in which a virtual image is displayed near the vehicle (e.g. the imaging distance is less than <NUM>).

In the following description, the front windshield <NUM> is assumed to include the HUD display regions A<NUM> and A<NUM>, as an example.

<FIG> is a partial cross-sectional diagram depicting the front windshield <NUM> illustrated in <FIG>, cut along a XZ-direction and viewed from a Y-direction, and illustrates a neighborhood of the HUD display region A<NUM>, a transition region B<NUM>, and the HUD display region A<NUM>. The transition region B<NUM> is a part of the region outside the HUD display region B.

As illustrated in <FIG>, the front windshield is a laminated glass provided with a glass plate <NUM> that is a first glass plate, a glass plate <NUM> that is a second glass plate, and an intermediate film <NUM>.

In the laminated glass, the glass plates <NUM> and <NUM> have lines generated by drawing upon manufacturing, respectively. The intermediate film <NUM> is located between the glass plate <NUM> and the glass plate <NUM>, and bonds with the glass plate <NUM> and the glass plate <NUM> so that the lines in the glass plate <NUM> run, for example, orthogonally to the lines in the glass plate <NUM>.

An interior surface <NUM> of the front windshield <NUM> that is one surface of the glass plate <NUM> which is inside the vehicle, and an exterior surface <NUM> of the front windshield <NUM> that is one surface of the glass plate <NUM> which is outside the vehicle may be flat surfaces or curved surfaces.

The HUD display region A<NUM> is formed so as to have a cross section having a shape of a wedge, in which a thickness varies from a lower edge side of the front windshield to an upper edge side when the front windshield <NUM> is attached to the vehicle, and a wedge angle is δA1. The HUD display region A<NUM> is formed so as to have a cross section having a shape of a wedge, in which a thickness varies from a lower edge side of the front windshield to an upper edge side when the front windshield <NUM> is attached to the vehicle, and a wedge angle is δA2.

The transition region B<NUM> is a region located between the HUD display region A1 and the HUD display region A<NUM>, formed so as to have a cross section having a shape of a wedge, in which a thickness varies from a lower edge side of the front windshield to an upper edge side when the front windshield <NUM> is attached to the vehicle, and a wedge angle is δB1. The thickness of the transition region B<NUM> may vary non-linearly and continuously.

The region of the front windshield <NUM> where a cross section has a shape of a wedge is designed so that a wedge angle measured in the radial direction along the front windshield <NUM> is not constant. That is, the region of the front windshield <NUM> where a cross section has a shape of a wedge includes a region provided with a variable wedge angle.

In the front windshield <NUM>, the wedge angles in the respective regions vary within a range of <NUM> mrad or more but <NUM> mrad or less. Within a transparent region of the front windshield <NUM>, a difference between the maximum value and the minimum value of the wedge angle measured in the vertical direction along the front windshield <NUM> is <NUM> mrad or more. This is because when the difference between the maximum value and the minimum value of the wedge angle is less than <NUM> mrad, an effect of the variable wedge angle cannot be applied, and there is no significance of using the variable wedge angle.

The difference of the wedge angle measured in the radial direction along the front windshield <NUM> is preferably <NUM> mrad or less. This is because when the wedge angle changes rapidly, upon pressure bonding of the intermediate film and the glass degassing failure may occur, or a quality of laminated glass other than reflected double images or transparent double images may degrade. Therefore, the difference of the wedge angle measured in the radial direction along the front windshield <NUM> is preferably <NUM> mrad or more but <NUM> mrad or less, more preferably <NUM> mrad or more but <NUM> mrad or less, and further preferably <NUM> mrad or more but <NUM> mrad or less.

A slope m of the wedge angle in the front windshield <NUM> is preferably <NUM> mrad/mm or more but <NUM> mrad/mm or less. This is because when the slope m of the wedge angle is less than <NUM> mrad/mm, changing the wedge angle becomes meaningless, and when the slope m is greater than <NUM> mrad/mm, even if the glass plates <NUM> and <NUM> follow a change in the shape of the intermediate film <NUM>, the change is too rapid and a transparent distortion readily occurs in the region.

The above-described wedge angle δ is an average variation rate of a plate thickness of the front windshield <NUM> obtained by using the least squares method from <NUM> pieces of data, which are present within a range of <NUM> in front of and behind a certain point, of plate thicknesses of the front windshield <NUM> measured at an interval of <NUM> in the vertical direction when the front windshield <NUM> is attached to the vehicle. Moreover, the slope m of the wedge angle is an average variation rate of the wedge angles by using the least squares method within the same range.

The embodiment will be described as a mode in which the front windshield <NUM> includes two HUD display regions A<NUM> and A<NUM> with different wedge angles and a transition region B<NUM> that connects the HUD display regions. However, the embodiment may also be as a mode in which the wedge angle of the front windshield <NUM> varies according to a predetermined formula, or may be as a mode other than the above.

In the front windshield <NUM>, the wedge angles of the respective regions are formed by making at least the intermediate film <NUM> to be a wedge film. In addition to this, any one of or both the glass plate <NUM> and the glass plate <NUM> may be formed in a shape of a wedge.

In the case of forming any one of or both the glass plate <NUM> and the glass plate <NUM> in a shape of a wedge, a condition upon manufacturing by using the float method will be devised. That is, by controlling circumferential velocities of a plurality of rolls arranged on both ends in a width direction of a glass ribbon that moves on a melted metal, a cross section of a glass in the width direction may be a concave shape, a convex shape, or a tapered shape, and a part that has an optional thickness change may be cut out.

The glass plates <NUM> and <NUM> each include streak-shaped fine concavity and convexity (lines) parallel with respect to the moving direction, by an extension upon manufacturing by using the float method. Upon using as a front windshield for a vehicle, when the lines are viewed in the horizontal direction with respect to a line of sight of an observer, a distortion occurs and a visibility degrades.

As the glass plates <NUM> and <NUM>, for example, a soda lime glass, an alumino-silicate glass, an organic glass, or the like may be used. A plate thickness of the glass plate <NUM> located on the outside of the front windshield <NUM> is preferably <NUM> or more but <NUM> or less. When the plate thickness of the glass plate <NUM> is less than <NUM>, a resistance to flying stones is poor. When the plate thickness is greater than <NUM>, the glass plates become heavy and are difficult to be shaped.

The plate thickness of the glass plate <NUM> located on the inside of the front windshield <NUM> is <NUM> or more but <NUM> or less. When the plate thickness of the glass plate <NUM> is less than <NUM>, the glass plate becomes difficult to be handled. When the plate thickness is greater than <NUM>, the glass plate <NUM> cannot follow a shape of the intermediate film <NUM> that is a wedge film. However, the respective plate thicknesses of the glass plates <NUM> and <NUM> are not necessarily constant, but may vary according to positions, as necessary.

The front windshield <NUM> may have a curved shape or also may not have a curved shape. In the case where the front windshield <NUM> has a curved shape, when two sheets of glass that are especially deeply curved are shaped as the glass plates <NUM> and <NUM>, a difference in shape between two sheets (mismatch) occurs, and will greatly affect the glass quality (e.g. residual stress) after pressure bonding.

By using the variable wedge angle to make the plate thickness of the glass plate <NUM> greater than or equal to <NUM> but less than or equal to <NUM>, the glass quality (e.g. residual stress) can be maintained. Making the plate thickness of the glass plate <NUM> greater than or equal to <NUM> but less than or equal to <NUM> is especially effective for maintaining the glass quality of the glass that is deeply curved (e.g. residual stress).

When the front windshield <NUM> has a curved shape, the glass plates <NUM> and <NUM> are shaped by the float method, and afterwards bent and formed before bonding by the intermediate film <NUM>. The bending and forming are performed while the glass is heated and softened. The heating temperature for the glass upon bending and forming is about <NUM> to <NUM>.

<FIG> is a cross-sectional diagram depicting the front windshield <NUM> illustrated in <FIG>, cut along the XZ-direction and viewed from the Y-direction. As illustrated in <FIG>, in the case where the front windshield <NUM> has a curved shape, a distance from a line La that connects the midpoints of the opposite sides of the concave face 20D that is the front windshield <NUM>, among the longer of the two pairs of opposite sides, to the deepest portion of the concave face 20D, in a direction orthogonal to the line La, will be referred to as a maximum depth of curvature D of the front windshield <NUM>.

When the maximum depth of curvature D of the front windshield <NUM> is <NUM> or more, the lines can be sufficiently extended by bending and forming, and the visibility can be sufficiently enhanced. The maximum depth of curvature D is preferably <NUM> or more, and more preferably <NUM> or more. Moreover, the radius of curvature of the concave face 20D is preferably <NUM> or less.

Respective colors of the glass plates <NUM> and <NUM> are not especially limited, as long as a transmissivity of a visible light (Tv) is greater than <NUM> %.

Moreover, in a peripheral portion of the front windshield <NUM>, a shielding layer referred to as a so-called "black ceramic" is preferably present. The shielding layer is formed by applying a black ceramic ink for printing on a glass surface and baking the same. According to the shielding layer, a black obscure layer is formed in the peripheral portion of the front windshield <NUM>. According to the black obscure layer, a resin such as a urethane for holding the front windshield <NUM> in the peripheral portion can be prevented from being degraded by ultraviolet light.

Moreover, a coat having a water-repellant function, an infrared light shielding function, an ultraviolet light shielding function, or a visible light reflectance reduction function, or a coat having a low radiation characteristic may be arranged outside the front windshield <NUM> (external surface of the glass plate <NUM>) or inside (internal surface of the glass plate <NUM>).

Returning back to the description of <FIG>, as the intermediate film <NUM> for bonding the glass plate <NUM> and the glass plate <NUM>, a thermoplastic resin is often used, including, a thermoplastic resin that has been used conventionally for this kind of purpose, such as a plasticized polyvinyl acetal resin, a plasticized polyvinyl chloride resin, a saturated polyester resin, a plasticized saturated polyester resin, a polyurethane resin, a plasticized polyurethane resin, an ethylene-vinyl acetate copolymer resin, or an ethylene-ethyl acrylate copolymer resin.

Among the above-described resins, a plasticized polyvinyl acetal resin is preferably used, because of its excellence in balance of performances, such as transparency, weather resistance, strength, bond strength, resistance to penetration, absorbability for impact energy, humidity resistance, thermal insulating property, and sound insulating property. The thermoplastic resin may be used independently, or two kinds or more resins may be used concurrently. The term "plasticized" in the plasticized polyvinyl acetal resin means that the resin is made plasticized by adding a plasticizing agent. The same applies to the other plasticized resins.

The polyvinyl acetal resin includes a polyvinyl formal resin that is obtained by reacting a polyvinyl alcohol (in the following, may be referred to as "PVA" as necessary) and a formaldehyde, a narrowly defined polyvinyl acetal resin that is obtained by reacting a PVA and an acetaldehyde, a polyvinyl butyral resin (in the following, may be referred to as "PVB" as necessary) that is obtained by reacting a PVA and a n-butyl aldehyde, and the like. Especially, a PVB is preferable, because of its excellence in balance of performances, such as transparency, weather resistance, strength, bond strength, resistance to penetration, absorbability for impact energy, humidity resistance, thermal insulating property, and sound insulating property. The polyvinyl acetal resin may be used independently, or two kinds or more resins may be used concurrently. However, a material forming the intermediate film <NUM> is not limited to a thermoplastic resin.

A thickness of the intermediate film <NUM> is preferably <NUM> or more even at the thinnest portion. When the thickness of the intermediate film <NUM> is less than <NUM>, a resistance to penetration that is required for a front windshield is not secured. Moreover, the thickness of the intermediate film <NUM> is preferably <NUM> or less even at the thickest portion. When the thickness of the intermediate film <NUM> is greater than <NUM>, a weight becomes greater, and a handleability becomes worse.

The intermediate film <NUM> may be provided with a region having a sound insulation function, an infrared light shielding function, an ultraviolet light shielding function, a shade band (function of reducing a visible light transmittance), or the like. Moreover, the intermediate film <NUM> may include three or more layers. For example, by configuring the intermediate film <NUM> with three layers, and making hardness of the central layer less than hardness of both adjacent layers, the sound insulation function can be enhanced. In this case, hardness of both the layers may be the same or may be different from each other.

In this way, when the number of layers of the intermediate film <NUM> increases, thicknesses of the respective layers vary, and for example, an optical quality such as the transparent double image which is described above may be further degraded. In this case, by making the plate thickness of the glass plate <NUM> greater than or equal to <NUM> but less than or equal to <NUM>, the glass plate <NUM> becomes easy to follow the wedge film of the intermediate film <NUM>, and thereby the optical quality can be prevented from degrading. That is, making the plate thickness of the glass plate <NUM> greater than or equal to <NUM> but less than or equal to <NUM> is especially effective when the layer number in the intermediate film <NUM> increases.

Normally, a light source for HUD is located in a lower part of the vehicle interior, and projects an image toward the laminated glass. Because the projected image is reflected on the rear surface and the front surface of the glass plates <NUM> and <NUM>, in order to overlay both the reflected images so as not to generate a double image, the thickness of the glass is required to vary in parallel with respect to the projection direction. When the thickness of the glass plate <NUM> varies in a direction orthogonal to the lines, in order to be used as a glass, on which information is projected, the direction of the lines is orthogonal to the projection direction, i.e. the lines are in a horizontal direction with a line of sight of an observer inside the vehicle interior (driver), and it is required to use in a direction in which the visibility degrades.

In order to improve the visibility, the laminated glass prepared using the glass plate <NUM>, the glass plate <NUM>, and the intermediate film <NUM> is arranged so that the lines of the glass plate <NUM> are orthogonal to the lines of the glass plate <NUM>. According to the above-described arrangement, the distortion, which becomes worse with the glass plate <NUM> only, will be reduced by the presence of the glass plate <NUM>, in which the lines are orthogonal, and the intermediate film <NUM> that bonds the glass plate <NUM> and the glass plate <NUM>, and the visibility is improved.

When the glass plates <NUM> and <NUM> are not wedge glass, in the glass plates <NUM> and <NUM>, the lines are orthogonal to the line of sight of the observer inside the vehicle interior (driver), and thereby the visibility does not degrade.

In order to prepare the laminated glass, the intermediate film <NUM> is held between the glass plate <NUM> and the glass plate <NUM> to form a laminated body. Then, the laminated body is placed into a rubber sack, and the bonding is performed under a vacuum of -<NUM> to -<NUM> kPa, and at temperature of about <NUM> to <NUM>.

Furthermore, for example, by performing a pressure bonding process of heating and pressurizing under a condition of a temperature of <NUM> to <NUM>, and a pressure of <NUM> to <NUM> MPa, a laminated glass that is more excellent in durability can be obtained. However, in some cases, taking into account simplification of processes, and characteristic of a material enclosed in the laminated glass, the heating and pressurizing process may not need to be used.

Between the glass plate <NUM> and the glass plate <NUM>, other than the intermediate film <NUM>, a film or a device having a function of a heating wire, infrared light reflection, a light emission, a power generation, dimming, visible light reflection, scattering, decoration, absorption or the like may be arranged.

<FIG> is a diagram depicting an example of sizes of wedge angles in a HUD display region A<NUM>, a transition region B<NUM> and a HUD display region A<NUM>. In <FIG>, the horizontal axis indicates a distance in the radial direction from the lower edge of the front windshield <NUM>, and the vertical axis indicates a wedge angle.

As illustrated in <FIG>, the wedge angle δA1 of the HUD display region A<NUM> and the wedge angle δA2 of the HUD display region A<NUM> are set to be values different from each other. This is because the HUD display region A<NUM> and the HUD display region A<NUM> are regions in which virtual images having different imaging distances from each other are displayed, and optimum wedge angles for removing reflected double images in the respective regions are different from each other.

<FIG> illustrates an example where the HUD display region A<NUM> is a region in which a virtual image is displayed near the vehicle (e.g. the imaging distance is less than <NUM>), and the HUD display region A<NUM> is a region in which a virtual image is displayed far from the vehicle (e.g. the imaging distance is <NUM> or more). Therefore, the wedge angle δA1 (constant; not according to the present invention) is set to be greater than the wedge angle δA2 (constant; not according to the present invention).

In the case where the HUD display region A<NUM> is a region in which a virtual image is displayed far from the vehicle (e.g. the imaging distance is <NUM> or more), and the HUD display region A<NUM> is a region in which a virtual image is displayed near the vehicle (e.g. the imaging distance is less than <NUM>), contrary to <FIG>, the wedge angle δA1 (constant; not according to the present invention) is required to be less than the wedge angle δA2 (constant; not according to the present invention).

However, while in the example illustrated in <FIG>, the wedge angle δA1 and the wedge angle δA2 are constants (not according to the present invention), the wedge angle δA1 and the wedge angle δA2 are not constant according to the present invention. In such a case, an average wedge angle in the HUD display region A<NUM> and an average wedge angle in the HUD display region A<NUM> are set to be different from each other (e.g. See <FIG>). Moreover, any of the wedge angle δA1 and the wedge angle δA2 may be zero (e.g. See <FIG>; not according to the present invention).

When regions having different wedge angles from each other are arranged in contact with each other, in a region in which the wedge angle changes rapidly, a large reflection double image is generated. Therefore, in the embodiment, a transition region B<NUM> is arranged between the HUD display region A<NUM> and the HUD display region A<NUM>. The HUD display regions A<NUM> and A<NUM> are separated by a prescribed interval L, and the wedge angle is changed in the transition region B<NUM> from the HUD display region A<NUM> to the HUD display region A<NUM> with a slope m. According to the above-described configuration, the wedge angle can be prevented from varying rapidly between the HUD display region A<NUM> and the HUD display region A<NUM>, and a large reflected double image can be prevented from being generated.

The average wedge angle is obtained by dividing a difference between a thickness of a lower edge of each HUD display region and a thickness of an upper edge in the radial direction along the front windshield <NUM> by a distance in the radial direction along the front windshield <NUM>.

When the wedge angle in the HUD display region A<NUM> or A<NUM> is not constant, a slope of the wedge angle in the region may be the same as the slope in the transition region B<NUM>. In this case, a boundary between the regions A<NUM> and B<NUM>, or a boundary between the regions B<NUM> and A<NUM> is defined as a position where an image on the front windshield <NUM> vanishes when a concave mirror configuring the HUD is rotated and an image on the front windshield <NUM> is moved. The average wedge angle can also be defined by, in each region, a difference between a thickness of a lower edge and a thickness of an upper edge in the radial direction divided by a distance in the radial direction.

The prescribed interval L is <NUM> or more. The reason why the prescribed interval L is <NUM> or more is that shifting of the viewpoint of the driver readily occurs for a prescribed interval of <NUM>. That is, because when the prescribed interval L is <NUM> or more, viewpoint shifting does not occur as readily between the HUD display region A<NUM> and the HUD display region A<NUM>, images having different focal lengths can be prevented from being viewed close to each other, and it is possible to prevent a feeling of driver discomfort.

However, the prescribed interval L is preferably <NUM> or more. The reason is that when a change in a wedge angle is great, a danger of a transparent distortion or forming increases; but, when the prescribed interval L is made greater than or equal to <NUM> and the change in the wedge angle is made smaller the danger can thereby be reduced. Moreover, by making the prescribed interval greater than or equal to <NUM> or greater than or equal to <NUM>, the change in the wedge angle can be made further smaller, and the danger can be further reduced.

As illustrated in <FIG>, intermediate films of <NUM> mrad and <NUM> mrad were arranged adjacent to each other, and held between two glass plates from front and back sides, to form a curved laminated glass having a size of <NUM> (vertical) and <NUM> (horizontal). By varying a plate thickness of the glass plate acting as an interior plate, a plurality of kinds of laminated glass were prepared.

Specifically, as a comparative example, a laminated glass, in which a plate thickness of a glass plate acting as an exterior plate (in the following, simply referred to as an exterior plate) / a plate thickness of a glass plate acting as an interior plate (in the following, simply referred to as an interior plate) was <NUM> / <NUM>, was prepared.

Moreover as a practical example <NUM>, a laminated glass, in which the plate thickness of the exterior plate / the plate thickness of the interior plate was <NUM> / <NUM>, was prepared. Moreover, as a practical example <NUM>, a laminated glass, in which the plate thickness of the exterior plate / the plate thickness of the interior plate was <NUM> / <NUM>, was prepared.

After preparing the respective laminated glass, by using the multi-layered film thickness measurement system, OptiGauge by Lumetrics Inc. , plate thicknesses of each laminated glass were measured at <NUM> intervals from <NUM> to <NUM> along a measurement line, indicated by a dashed line in <FIG>, and the wedge angles were calculated by using the above-described method.

Moreover, for the wedge angles measured within a range from <NUM> to <NUM> of the measurement line in <FIG>, as schematically illustrated in <FIG> as an example, the maximum wedge angle δmax and a position thereof, the minimum wedge angle δmin and a position thereof, and the maximum slope of the wedge angle mmax in the range between the maximum wedge angle δmax and the minimum wedge angle δmin were obtained.

Moreover, total of a difference between a designed value of the wedge angle at <NUM> intervals and the wedge angle calculated in the comparative example, and a difference between the designed value and the wedge angle calculated in the practical example (difference from the designed value) was obtained. The designed value of the wedge angle at <NUM> intervals is <NUM> mrad in the range from <NUM> to <NUM>, and <NUM> mrad in the range from <NUM> to <NUM>, and is indicated by solid line. Moreover, the wedge angles calculated in the comparative example and the practical example are schematically indicated by dashed-dotted lines in <FIG>.

The results are illustrated in <FIG> and <FIG>. As illustrated in <FIG>, and <FIG>, in any of the comparative example and the practical example, the maximum slope mmax exists between the maximum wedge angle δmax and the minimum wedge angle δmin. Moreover, the difference from the designed value is the greatest in the comparative example in which the plate thickness of the external plate and the plate thickness of the internal plate are the same, and the difference decreases as the plate thickness of the internal plate becomes thinner.

Moreover, from the results in <FIG> and <FIG>, it is found that also in a laminated glass having a variable wedge angle using a thin glass plate with the plate thickness t of the internal plate of <NUM> or less, when the relation <NUM> ≤ |m| ≤ <NUM> and |m × t| ≤ <NUM> are satisfied, the difference from the designed value of the wedge angle is reduced, and the wedge angle can be controlled precisely.

Because the wedge angle can be controlled precisely, also in the laminated glass having a variable wedge angle using a thin glass plate with the plate thickness t of the internal plate of <NUM> or less, a transparent double image can be prevented from occurring, and a high-quality transparent image and a high-quality reflected image can be obtained compared with the conventional images.

Claim 1:
A laminated glass (<NUM>) comprising:
a first glass plate (<NUM>) to be arranged on an inner side of a vehicle;
a second glass plate (<NUM>) to be arranged on an outer side of the vehicle; and
an intermediate film (<NUM>) positioned between the first glass plate (<NUM>) and the second glass plate (<NUM>) and bonded to the first glass plate (<NUM>) and to the second glass plate (<NUM>),
wherein
the laminated glass (<NUM>) includes a first region (A<NUM>), a transition region (B<NUM>), and a second region (A<NUM>), from a lower side of the laminated glass (<NUM>) when the laminated glass (<NUM>) is attached to the vehicle,
the first region (A<NUM>) includes a region having a cross section having a shape of a wedge, in which a thickness of an upper edge side is greater than a thickness of a lower edge side when the laminated glass (<NUM>) is attached to the vehicle,
the transition region (B<NUM>) is a region connecting the first region (A<NUM>) and the second region (A<NUM>), and includes a region having a cross section having a shape of a wedge, in which a thickness of an upper edge side is greater than a thickness of a lower edge side when the laminated glass is attached to the vehicle,
the second region (A<NUM>) includes a region having a cross section having a shape of a wedge, in which a thickness of an upper edge side is greater than a thickness of a lower edge side when the laminated glass is attached to the vehicle,
in the first region (A<NUM>) and the second region (A<NUM>), a region used for a head up display is present,
a plate thickness of the first glass plate (<NUM>) is <NUM> or more but <NUM> or less,
in the first region (A<NUM>), the transition region (B<NUM>), and the second region (A<NUM>), a difference between a maximum value (δmax) and a minimum value (δmin) of a wedge angle (δ) measured in a radial direction along the laminated glass is <NUM> mrad or more,
when a slope of the wedge angle (δ) in an intermediate region in which the maximum value (δmax) and the minimum value (δmin) of the wedge angle (δ) are present is m mrad/mm, and a plate thickness of the first glass plate (<NUM>) is t mm, conditions <MAT> <MAT> and <MAT>
are satisfied,
the first region (A<NUM>) and the second region (A<NUM>) are separated by a prescribed interval (L),
the prescribed interval (L) is <NUM> or more, and
the wedge angle (δ), the slope of the wedge angle (δ), and the plate thickness of the laminated glass are determined as indicated in the description.