1. Field of the Invention
The present invention relates to a vehicle surrounding viewing system for picking up images of surrounding scenes, which are located at dead angles for the driver in the right/left and the front/rear of the vehicle, in the situation that the visibility is bad, and then displaying them to the driver.
2. Description of the Related Art
When a vehicle reaches crossroads, safety confirmation is needed on the right and left sides of a road. At the crossroads in which the visibility is poor, the driver must slightly bring the vehicle into the crossroads to check the safety on both sides. That is, the driver must pay attention to entering into the crossroads, and check the safety by viewing directly both sides of the road respectively. Accordingly, such behaviors are mental burdens on the driver.
In order to solve the problems, Patent Application Publication (KOKAI) Hei 10-229512 discloses a vehicle surrounding viewing system that can pick up images on both sides of the vehicle simultaneously to display the images on a display portion in a cabin of the vehicle.
In the vehicle surrounding viewing system, the images in both side directions are picked up simultaneously by a camera by providing a prism and a focusing lens on the front side of the camera, which is provided to the front bumper, etc. of the vehicle and then guiding the rays of light from both sides around the vehicle to the camera via the prism and the focusing lens, and then such images are displayed on the display portion in the cabin.
FIG. 13 shows a configuration of the vehicle surrounding viewing system in the conventional art. The vehicle surrounding viewing system 1 comprises a image pick-up device 11 that has a light shielding case 3 which is provided on the outside of the vehicle and has a pair of right and left transmit windows 2R, 2L on the right and left sides respectively; a image inverting process portion 12; and a display portion 15. In the light shielding case 3, a prism 4 having the isosceles triangle section shape is installed/arranged to have an attitude that its vertical angle 5 is directed to the front portion of the case 3 (upper portion of the case 3 in FIG. 13) and its left and right prism side surfaces 8L, 8R facing to two equal sides of the isosceles triangle respectively are directed to the right and left transmit windows 2R, 2L sides respectively, and also an image pick-up element 10 for converting rays of light 18L, 18R, which are input from the prism side surfaces 8L, 8R and then the optical paths of which are changed by the prism 4 and which are then guided onto the image pick-up plane via the predetermined focusing lens 9, into the image signals is installed/arranged on the rear side of the prism 4. An image inverting process portion 12 executes the image inverting process of the image signal supplied from the image pick-up element 10. A display portion 15 is provided in the cabin to display the image signal obtained from the image inverting process portion 12.
Such a vehicle surrounding viewing system 1 is fitted to a front bumper 17 such that, as shown in FIG. 2, the front portion of the image pick-up device 11 (front portion of the case 3) is directed to the front portion of the vehicle 16 and the right and left transmit windows 2R, 2L are directed to the right and left sides respectively, for example. In this situation, a ray of light 18L, that enters into a transmit window 2L from the left side scene, passes through a prism side surface 8L, then internally reflects at the prism side surface 8R, then emits from a prism rear surface 8B, and subsequently is focused by the focusing lens 9 to be guided onto a left half plane 10L of the image pick-up plane of the image pick-up element 10. Similarly, a ray of light 18R that enters into a transmit window 2R from the right side scene passes through the prism side surface 8R, then internally reflects at the prism side surface 8L, and then emits from the prism rear surface 8B, and subsequently is focused by the focusing lens 9 to be guided onto the right half plane 10R of the image pick-up plane of the image pick-up element 10. Then, both of the rays of light 18L, 18R are converted into the image signals by the image pick-up element 10.
The left and right side scenes are picked up in this manner. Then, the picked-up image signals are subjected to the image inverting process by the image inverting process portion 12 and then supplied to the display portion 15. Then, the left side scene that is introduced via the transmit window 2L is displayed on the left half screen 15L of the display portion 15 as the left half image, and also the right side scene that is introduced via the transmit window 2R is displayed on the right half screen 15R of the display portion 15 as the right half image.
However, according to such vehicle surrounding viewing system 1, for example, in the situation that the vehicle that has a headlight 21 thereon is approaching from the front on the opposite lane in the night, in some cases a ray of light 21a emitted from the headlight 21 enters into the transmit window 2L from the front side, for example, then passes through the prism side surface 8L, then reflects toward the focusing lens 9 at this time, then emits from the prism rear surface 8B without the internal reflection by the side surface of the prism 4, and subsequently is guided directly onto the right half plane 10R of the image pick-up plane of the image pick-up element 10 via the focusing lens 9. The ray of light 21a of the headlight 21 guided to the right half plane 10R enters into the transmit window 2R from the right side scene, then passes through the prism side surface 8R, then reflects internally at the prism side surface 8L, and then emits from the prism rear surface 8B, and subsequently is synthesized with the ray of light 18R that is guided onto the right half plane 10R of the image pick-up plane of the image pick-up element 10 and then subjected to the image processing.
In such case, the image 21b of the ray of light 21a of the headlight 21, that is introduced from the front side via the transmit window 2L, is overlapped with the image 22R of the right side scene (the pitch-dark scene image herein), that is introduced via the transmit window 2R, on the right half screen 15R of the display portion 15. In other words, a part of the scene introduced from the transmit window 2L is reflected in the right half screen 15R of the display portion 15 and then displayed erroneously thereon, and similarly apart of the scene introduced from the transmit window 2R is reflected in the left half screen 15L of the display portion 15 and then displayed erroneously thereon. Thus, there is such a drawback that the visibility of the driver is aggravated.
Moreover, according to the above vehicle surrounding viewing system in the conventional art, since the prism having the regular triangle sectional shape is employed, the prism having a high refractive index must be employed in order to pick up simultaneously the images in two mutually opposite directions.
For example, in the case that the above vehicle surrounding viewing system is constructed by using the prism having the regular triangle sectional shape and formed of the glass material BK7 (refractive index n: 1.517), which is generally widely employed, and the camera having the half field angle of 22.5 degree, the image pick-up range just beside the vehicle 50 to the front side is +7.7 degree to +30 degree, as shown in FIG. 14, when the image pick-up available range of the camera is detected by the geometrical optic approach. Accordingly, the images located just beside the vehicle 250 cannot be picked up, and thus the bicycle 255, etc. that are approaching the body of the vehicle 250 laterally cannot be checked.
In this case, the expansion of the image pick-up range by using the camera having the large half field angle may be considered. In such case, the field angle of the camera can be expanded, nevertheless the area in which no total reflection is caused appears newly in the prism. Also, there is such a possibility that the images located just beside the vehicle 250 cannot be picked up.
For example, even though the camera having the large half field angle such as the half field angle of 30 degree, etc. is employed, in the case that the prism P is formed of the glass material BK7 having the low refractive index (refractive index n: 1.517), which is generally used in the conventional art, the ray of light Lp, that has the small field angle, out of the rays of light contained in the half field angle can be totally reflected in the prism P, nevertheless the ray of light Lp, that has the large field angle, cannot be totally reflected to thus transmit as it is, as shown in FIG. 15. As a result, the image located just beside the vehicle cannot be picked up yet.
In order to prevent this event, the prism having the relatively high refractive index such as the refractive index of more than 1.53, for example, must be employed. In this case, the problems in cost, etc. are caused.
It is a subject of the present invention is to provide a vehicle surrounding viewing system capable of preventing the loss of the visibility since a part of the scene introduced into an image picking-up device via a left transmit window is reflected in a right half screen of a display portion and displayed erroneously as a right image, and similarly a part of the scene introduced into the image picking-up device via the right transmit window is reflected in a left half screen of the display portion and displayed erroneously as a left image.
Moreover, another object of the present invention is to provide a vehicle surrounding imaging system for picking-up simultaneously images around a vehicle in two mutually opposite directions even if a prism having a low refractive index is employed, and its prism angle setting method.
In order to attain the above objects, according to the invention, there is provided a vehicle surrounding viewing system comprising: an image pick-up device that has a light shielding case which is provided on the outside of the vehicle and has a pair of left and right transmit windows on right and left sides respectively and in which a prism that has an isosceles triangle section shape is installed/arranged to have an attitude that its vertical angle is directed to a front portion of the light shielding case and its left and right prism side surfaces facing to two equal sides of the isosceles triangle respectively are directed to the right and left transmit window sides respectively, and also an image pick-up element for focusing rays of light, which input from one surface of left and right prism side surfaces and then reflect at other surface of the left and right prism side surfaces, and then emit from a prism rear surface of the prism, onto an image pick-up plane via a predetermined focusing lens to convert into image signals is installed/arranged at a rear position of the prism; wherein a light shielding portion is arranged on the prism to cover areas of its surface except an effective area that can pass through the rays of light that enter into the left and right transmit windows respectively, then pass through the left and right prism side surfaces respectively, then internally reflect at the left and right prism side surfaces on an opposite side, and then emit from the prism rear surface, and subsequently are focused by the focusing lens to be guided onto a left half plane and a right half plane of the image pick-up plane of the image pick-up element respectively.
At that time, the light shielding portion may be formed integrally with the case on peripheral portions of the left and right transmit windows to project from an inner side surface of the case.
According to the invention, there is provided a vehicle surrounding viewing system comprising: an image pick-up device that has a light shielding case which is provided on the outside of the vehicle and has a pair of left and right transmit window portions on right and left sides respectively and in which a prism that has an isosceles triangle section shape is installed/arranged to have an attitude that its vertical angle is directed to a front portion of the light shielding case and its left and right prism side surfaces facing to two equal sides of the isosceles triangle respectively are directed to the right and left transmit window portion sides respectively, and also an image pick-up element for focusing rays of light, which input from one surface of left and right prism side surfaces and then reflect at other surface of the left and right prism side surfaces, and then emit from a prism rear surface of the prism, onto an image pick-up plane via a predetermined focusing lens to convert into image signals is installed/arranged at a rear position of the prism; wherein there is provided a preventing member for preventing reflected lights, that pass through the right and left transmit window portions and the left and right prism side surfaces in sequence respectively, then totally reflect at the prism rear surface, then pass through the left and right prism side surfaces on opposite sides, and then reflect at the right and left transmit window portions, from being focused onto the image pick-up plane.
According to the invention, in the vehicle surrounding viewing system the preventing structure is preferably constructed by setting angles of the right and left transmit window portions with respect to the prism rear surface such that the reflected lights that are reflected at the right and left transmit window portions can pass through the right and left transmit window portions, then totally reflect at the prism rear surface, then pass through the left and right prism side surfaces and the right and left transmit window portions on opposite sides, and then emit to an outside respectively.
According to the invention, in the vehicle surrounding viewing system the preventing structure is preferably constructed by providing light shielding members on surface areas of the prism such that optical paths of reflected lights, that are reflected at the right and left transmit window portions, then enter again into the prism from the left and right prism side surfaces, then internally reflect at the left and right prism side surfaces on the opposite side, and then emit from the prism rear surface to enter into the image pick-up element, can be shielded.
In the vehicle surrounding viewing system, the preventing structure is preferably constructed by providing a reflection preventing film onto at least any one of inner surface sides of the right and left transmit window portions and the left and right prism side surfaces.
According to the invention, there is provided a vehicle surrounding imaging system for picking-up simultaneously images around a vehicle in two mutually opposite directions, comprises a prism which is formed as a triangular prism having an isosceles triangle sectional shape, and whose respective surfaces consist of first and second side surfaces that put a vertical angle of the isosceles triangle sectional shape between them and a bottom surface that opposes to the vertical angle, and which causes the ray of light, that enters along one direction, out of rays of light that enter in two mutually opposite directions, to enter into the inside from the first side surface, then reflect toward the base surface at the second side surface, and then emit from the base surface to the outside, and also causes the ray of light, that enters along the other direction, to enter into the inside from the second side surface, then reflect toward the base surface at the first side surface, and then emit from the base surface to the outside; and an image pick-up element for receiving the ray of light that is emitted from the base surface of the prism, and picking up images in above two directions; wherein a refractive index n of the prism, a half field angle xcex8 of the image pick-up element, and the vertical angle xcex4 of the prism are set so as to satisfy the following expressions:       α    =                  90        -                  δ          2                -                              sin                          -              1                                ⁢                      (                                                            1                  n                                ·                sin                            ⁢                              xe2x80x83                            ⁢              θ                        )                               greater than                         sin                      -            1                          ⁢                  (                      1            n                    )                                        δ        2            -                        sin                      -            1                          ⁢                  {                      n            ·                          sin              ⁢                              (                                  δ                  -                  α                                )                                              }                      ≤    0  
According to the invention, the vertical angle xcex4 of the prism may be larger than 60 degree.
According to the invention, a prism angle setting method for a vehicle surrounding imaging system, for picking-up simultaneously images around a vehicle in two mutually opposite directions, the vehicle surrounding imaging system, comprises a prism which is formed as a triangular prism having an isosceles triangle sectional shape, and whose respective surfaces consist of first and second side surfaces that put a vertical angle of the isosceles triangle sectional shape between them and a bottom surface that opposes to the vertical angle, and which causes the ray of light, that enters along one direction, out of rays of light that enter in two mutually opposite directions, to enter into the inside from the first side surface, then reflect toward the base surface at the second side surface, and then emit from the base surface to the outside, and also causes the ray of light, that enters along the other direction, to enter into the inside from the second side surface, then reflect toward the base surface at the first side surface, and then emit from the base surface to the outside; and an image pick-up element for receiving the ray of light that is emitted from the base surface of the prism, and picking up images in above two directions; wherein the vertical angle xcex4 of the prism are set with respect to a refractive index n of the prism and a half field angle xcex8 of the image pick-up element within a range to satisfy the following expressions:       α    =                  90        -                  δ          2                -                              sin                          -              1                                ⁢                      (                                                            1                  n                                ·                sin                            ⁢                              xe2x80x83                            ⁢              θ                        )                               greater than                         sin                      -            1                          ⁢                  (                      1            n                    )                                        δ        2            -                        sin                      -            1                          ⁢                  {                      n            ·                          sin              ⁢                              (                                  δ                  -                  α                                )                                              }                      ≤    0  
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