Precipitation sensor

Details Precipitation sensor Precipitation sensor

2002-04-01

2003-09-30

Pyo, Kevin (Department: 2878)

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

C250S227290, C356S237300

Reexamination Certificate

active

06627910

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates by reference Japanese Patent Application No. 2001-103486 filed on Apr. 2, 2001.
BACKGROUND OF THE INVENTION
This invention relates to a precipitation sensor suitable for use in vehicles.
Referring to
FIG. 5
, a typical precipitation sensor for use in vehicles is installed on the inner surface of a front windshield W of an automobile and optically detects the presence and absence of precipitation. The precipitation sensor has a prism
1
, a beam transmitter
2
and a beam receiver
3
. The prism
1
is arranged on the inner surface of the front windshield W as shown and has a prism body
1
c
integral with plane-convex lens units
1
a
,
1
b
, which are formed on its right and left ends. The beam transmitter
2
and the beam receiver
3
, which are held by a circuit board
4
located immediately above the prism
1
, are opposed to the plane-convex lens units
1
a
,
1
b
. A control circuit
5
is mounted on the circuit board
4
.
In the precipitation sensor of
FIG. 5
, the plane-convex lens
1
a
parallelizes the light beams transmitted from the beam transmitter
2
and guides them into the prism body
1
c
. The light incident upon the prism body
1
c
enters the plane-convex lens
1
b
after it is reflected several times, as shown with the arrows in the figure, between the outer surface of the front windshield W and the center wall of the prism body
1
c
. The plane-convex lens
1
b
focuses the light traveling from the prism body
1
c
and guides the light to the beam receiver
3
.
To extend the region used for the detection of precipitation, such a precipitation sensor has an optical path for the sensor light such that the light is reflected several times between the prism
1
and the front windshield W. For this purpose, the beam transmitter
2
and beam receiver
3
have to be mounted beyond the right and left ends of the prism
1
. Thus, the dimensions of the precipitation sensor are relatively large in the lateral direction. However, the region for sensing precipitation is too small, even when the light is reflected several times between the prism
1
and the front windshield W in the optical path.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a precipitation sensor in which a prism is shaped to expand the region for precipitation detection and to allow the beam transmitter and beam receiver to be installed between the right and left ends of the prism.
A precipitation sensor according to one aspect of the present invention has a prism (
20
) to be mounted on an inner surface of a windshield (W), a beam transmitter (
40
) and a beam receiver (
50
).
The prism is constructed and arranged to be attached to an inner surface of the windshield. The prism is made with an optically transparent material into a single piece including a connection wall arranged to be bonded to the inner surface of the windshield, and an entry-side prism wall, which is located to be adjacent to the inner surface of the windshield when the sensor is installed. The entry-side prism wall includes a convex entry-side lens surface formed on an inner face, and the entry-side lens surface has an optical axis, which is inclined with respect to the inner surface of the windshield when the device is installed such that the optical axis extends away from the windshield from the entry-side prism wall. The entry-side lens surface forms an arc in a plane parallel to the plane of the windshield, and the center of the arc lies in an entry-side focal point plane that is normal to the plane of the windshield. The entry-side prism wall further includes a parabolic entry-side outer face, and a focal point of the parabolic entry-side outer face lies in the entry-side focal point plane.
The prism further includes an exit-side prism wall, which is arranged to be adjacent to the inner surface of the windshield when the sensor is installed, and the exit side prism wall and the entry-side prism wall are opposed and sandwich the connection wall. The exit side prism wall includes a convex exit-side lens surface, which is generally opposed to the entry-side lens surface, and the exit-side lens surface has an optical axis that is inclined with respect to the windshield such that the optical axis extends away from the inner surface of the windshield from the exit-side lens surface. The exit-side lens surface forms an arc in a plane parallel to the plane of the windshield, and the center of the arc lies in an exit-side focal point plane that is normal to the plane of the windshield. The exit-side prism wall includes a parabolic outer surface, and a focal point of the parabolic outer surface lies in the exit-side focal point plane.
The sensor further includes a beam transmitter, a light emitting part of which is intersected by the entry-side focal point plane. The beam transmitter is located on the optical axis of the entry-side lens surface and is spaced from the entry-side lens face in the direction of the exit-side prism wall such that light transmitted from the beam transmitter is refracted by the entry-side lens surface and such that light entering the entry-side lens surface from the beam transmitter is transmitted by the entry-side prism wall in a parallel manner. When the sensor is installed, parallel light transmitted by the entry-side prism wall enters the windshield and is reflected by the windshield to the exit-side prism wall.
The sensor further includes a beam receiver, a light receiving part of which is intersected by the exit-side focal point plane. The beam receiver is located on the optical axis of the entry-side lens face and is spaced from exit-side lens surface in the direction of the entry-side prism wall, such that light transmitted by the prism wall from the beam transmitter is refracted by the exit-side lens face and focused on the beam receiver.
As described above, the entry-side lens face is convex and arc shaped. The light transmitted from the beam transmitter to the lens face is incident upon the whole area of the lens face in a radiating form. The parallel light entering from the lens face into the prism wall travel toward the outer face in a parallel manner from the entire region of the lens face.
Subsequently, when the parallel light traveling in the entry side prism wall
20
b
toward the entry-side parabolic outer face is reflected by the parabolic outer face, the light reflected by the outer face travels as a light plane in the prism wall toward the connection wall, because the outer face has the parabolic shape.
The planar incident light beams proceed in a parallel manner toward the connection wall and to the exit-side prism wall, after being reflected by the inner face of the front windshield. When the parallel light is reflected by the exit-side parabolic outer face of the exit-side prism wall, the light reflected by the exit side outer face travels in a parallel manner toward the lens face, because the outer face has the a parabolic shape described above. Then the parallelized light proceeding to the exit-side lens face is refracted by the whole lens face and focused on the beam receiver.
According to the above structure of the optical path for the light transmitted from the beam transmitter, the precipitation detection are is relatively large, even though the beam transmitter and the beam receiver are located between the parabolic outer faces of the prism, and the dimensions of the precipitation sensor are relatively small. This is because the sensor light that passes through the connection wall and enters the front windshield along the optical path is significantly widened two-dimensionally. Also, the decay of the sensor light is low because the light is reflected only once from the inner face of the front windshield. Thus, the efficiency of light transmission is improved.
In the sensor, the optical axes preferably intersect each other at right angles, with the incident angle of the parallel light onto the outer face of the entry-side prism wall being 45 degrees a

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