Vehicle lamp and method of manufacturing the same

To form a reflection surface, a free curved surface conformed to a configuration of a car body is set for a fundamental surface of a reflection surface. A group of paraboloids of revolution having different focal distances are set, thereby to determine a group of closed curves as the lines of intersection of the fundamental surface and the group of paraboloids of revolution. The respective paraboloids of revolution are partially allotted to a portion between each pair of the adjacent closed curves of the closed curve group, whereby a plural number of reflection steps are formed. The reflection steps are arranged about the central parts in multiple loops, and the central parts are offset from the principal optical axis of the reflection mirror.

BACKGROUND OF THE INVENTION 
The present invention relates to a lamp of a vehicle. More particularly, 
the invention relates to a novel reflection mirror of a vehicle lamp which 
removes the difficulty in the surface working when a number of reflection 
step faces arranged in multiple loops are formed on a fundamental surface 
conformed to a configuration of a car body, and a method of manufacturing 
the reflection mirror. 
As for recent styling of the automobiles, there is a design trend to round 
or streamline a car body in shape in the light of aerodynamics and design. 
In this circumstance, an attempt to reduce the vertical length of the lamp 
(design trend of height reduction) has been made. 
If the height of the lamp is reduced, the area of the reflection surface is 
also reduced, as a matter of course. Therefore, it is preferable to use a 
reflection mirror having the reflection surface of which the solid angle 
when the reflection angle is seen from the light emission center of a 
light source is as large as possible. That is, as shown in FIG. 16, when 
comparing with the paraboloid of revolution indicated by a two-dot chain 
line, one may adopt a curved surface such as a reflection surface a having 
a solid angle .omega., when one sees the reflection surface from the light 
emission center P of a light source, set to be larger than a solid angle 
of the paraboloid of revolution. 
In GB 2 262 980 assigned to the same assignee as this application, there 
has been proposed a reflection mirror in which the reflection surface 
consists of a number of reflection steps disposed in a looped fashion 
about an optical axis of the reflection mirror. In the reflection mirror, 
the fundamental surface of the reflection surface is formed as a free 
curved surface. When the reflection steps are allotted to the fundamental 
surface, the reflection surface is formed such that the tangential vector 
of a micro-reflection face at a reflection point on the reflection step is 
coincident with the outer product of a normal vector of the 
micro-reflection face at the reflection point and a normal vector of an 
osculating plane on the fundamental surface. 
A metal mold for manufacturing such a reflection mirror is formed in the 
following steps of forming a fundamental surface of the reflection surface 
as a free curved surface conformed to a configuration of a car body, 
setting a reference line on the fundamental surface, and designating a 
plural number of reflection points on the reference line, setting 
micro-reflection faces at the reflection point by using the rule of 
reflection so that when light beams, which are emitted from a light source 
and directed to the reflection points, are reflected at the reflection 
points, these reflection light beams are parallel to the optical axis, and 
generating closed curves by a spline approximation in which direction 
vectors at the plural number of reflection points arranged about the 
optical axis are used as the tangential vectors. In this case, the outer 
product of the normal vector of the micro-reflection face at the 
reflection point and a normal vector on the fundamental surface at the 
reflection point is used as the direction vector for determining the 
orientation of the reflection step formed. Further, V-shaped grooves which 
have the slant faces corresponding to the micro-reflection faces at the 
respective reflection points, are formed along the closed curves on the 
metal mold. 
FIG. 17 is a view showing an example of the reflection surface of a 
reflection mirror b which has the step faces formed by the method as 
mentioned above. As shown, a multiple of closed curves q are formed about 
the axis f--f of the light source, and reflection steps are formed in a 
looped fashion, using the closed curves g as reference lines. In other 
words, the adjacent closed curves are disposed so as not to intersect, and 
the axis f--f passes through the center of a group of closed curves. 
When the closed curves q are always formed about the axis f--f of a light 
source (the principal optical axis of the reflection mirror), and the 
reflection steps are allotted along those closed curves, according to the 
shape of the fundamental surface, a metal mold cannot be formed for some 
portions of the reflection mirror so that the portions of the reflection 
mirror cannot be used as an effective reflection surface. 
FIG. 18 is an explanatory diagram for explaining why the metal mold of the 
reflection mirror cannot be formed on a specific portion of the reflection 
mirror. A front view of a surface h as a fundamental surface of the 
reflection surface is shown in the upper portion of FIG. 18, and closed 
curves i are set on the fundamental surface h. A mark "X" indicates a 
position where the axis f--f of the light source intersects the surface h 
at the central part of the group of closed curves. 
A sectional view of the surface h is illustrated in the lower portion of 
FIG. 18. The surface h is illustrated as a plane slanted upward to the 
right, for ease of explanation. 
Parabolas j1 and j2 indicate the paraboloids of revolution, which form a 
group of paraboloids of revolution of which the axis f--f is coincident 
with the axis of rotation. The closed curves are formed as the lines of 
intersection of the surface h and the group of the paraboloids of 
revolution. 
Since the surface h, which provides the fundamental shape of the reflection 
surface, is arbitrarily set as a curved surface, if a group of paraboloids 
of revolution, of which the axis of revolution is coincident with the axis 
f--f of the light source, is used, a portion where surface-working cannot 
be performed is present between a portion (shaded by lines slanted down to 
the right) between the paraboloid j1 of revolution and the surface h and a 
portion (shaded by lines slanted down to the left) between the paraboloid 
j2 of revolution and the surface h (in other words, no closed curve is 
formed along the boundary between those slanted portions). If this 
location is compulsively worked, a relation between the worked portion and 
the surface h is lost. 
SUMMARY OF THE INVENTION 
To solve the problems as mentioned above, there is provided a vehicle lamp 
including a reflection mirror with a reflection surface formed of a number 
of reflection steps which are formed in a manner that a fundamental 
surface of the reflection mirror is defined as a free curved surface so as 
to be conformed to a configuration of a car body, and respective 
paraboloids of revolution are partially allotted to a portion between each 
pair of the adjacent closed curves of a group of closed curves formed as 
the lines of intersection of the fundamental surface and a group of the 
paraboloids of revolution having different focal distances, characterized 
in that the reflection steps are arranged about a plurality of central 
parts in multiple loops, and the central parts are offset from the 
principal optical axis of the reflection mirror. 
A method of forming the vehicle lamp including the reflection mirror, 
comprising the steps of: 
1) forming a fundamental surface of a reflection surface as a free curved 
surface to conform to a configuration of a car body; 
2) setting a group of paraboloids of revolution having different focal 
distances; 
3) determining a group of closed curves as the lines of intersection of the 
fundamental surface and the group of paraboloids of revolution; and 
4) allotting partially the respective paraboloids of revolution to a 
portion between each pair of the adjacent closed curves of the closed 
curve group, thereby arranging a number of reflection steps about the 
central parts in multiple loops, the central parts being offset from the 
principal optical axis of the reflection mirror. 
In the present invention, there are provided a plural number of groups each 
consisting of closed curves arranged about a central part, at which the 
fundamental surface contacts with the paraboloid of revolution. The 
central part of each group of the closed curves is offset from the point 
of intersection of the fundamental surface and the principal optical axis. 
Thus, a required connection of the step faces each allotted to a portion 
between the adjacent closed curves is ensured. Then, a portion for which 
face-working can not be performed, is not created on the reflection mirror 
.

DETAILED DESCRIPTION OF THE INVENTION 
Preferred embodiments of a reflection mirror of a vehicle lamp according to 
the present invention will be described with reference to the accompanying 
drawings. 
A method of forming a reflection surface will be described with reference 
to FIGS. 1 to 5 before description of a shape of the reflection mirror. 
First, as shown in FIG. 1, a curved surface 1 which defines a fundamental 
shape of the reflection surface is set. The curved surface 1 as a free 
curved surface that cannot be mathematically expressed by an algebraical 
expression, is shaped so as to be conformed to a configuration of a car 
body, by using a CAD. 
A group 2 of curved surfaces, which determines the performance of the 
resultant reflection surface, is prepared as shown in FIG. 2. The curved 
surface group 2 consists of a number of paraboloids of revolution 2a which 
have a common axis of rotational symmetry and different focal distances. 
The paraboloids of revolution 2a will never spatially intersect with each 
other. The focal positions of the paraboloids of revolution 2a are not 
always coincident with one another. The focal points may lie dispersively 
within a range on the axis of the rotational symmetry. 
The lines of intersection 3 of the curved surface 1 and the curved surface 
group 2 are determined as shown in FIG. 3. The lines of intersection 3 
form closed curves or part of them. The lines of intersection 3 will never 
intersect each other on the curved surface 1. When the curved surface 1 
has an axis of rotational symmetry, the central part of the closed curves 
of the lines of intersection 3 lies at a point where the axis of 
rotational symmetry intersects the curved surface. When the curved surface 
is not rotationally symmetric, it is determined by a point where one of 
the paraboloids of revolution contacts with the curved surface 1. 
Therefore, a point where the principal optical axis set on the reflection 
surface intersects the curved surface is not always at the central part of 
the curved surfaces. That is, when a parabola representing the paraboloid 
of revolution contacts with a curved line c1 representing the curved 
surface 1 at a point P, an axis A, which extends in parallel with the axis 
of rotation L of the paraboloid of revolution while passing through the 
point P, will never be coincident with the axis of rotation L. Generally, 
the number of the central parts is not always one, but there are a plural 
number of central parts of the closed curve groups. In an example of FIG. 
5, it will readily be seen that two central parts of grouped closed curves 
are present if the curved surface 1 contains the axis L of revolution, and 
has surface symmetry with respect to a plane orthogonal to the paper 
surface. 
After the lines of intersection 3 are determined, reflection steps are 
determined on the basis of these lines of intersection. That is, as shown 
in FIG. 4, step faces 5 are each formed by allotting a part of the 
paraboloid of revolution to a portion between the adjacent lines of 
intersection. A front view showing the curved surface 1 is shown in the 
upper part of FIG. 6, and a cross sectional view taken along line B--B in 
the front view is shown in the lower part thereof. The lines of 
intersection on the curved surface 1 are denoted as 3a, 3b, 3c, . . . in 
this order from the central part 4 of the paraboloids of revolution to the 
outer side. These lines of intersection define the boundaries of the step 
faces, respectively. In the figure, broken lines indicate the paraboloids 
of revolution 2. A step 5a is formed within the closed line 3a of 
intersection; a step 5b is formed between the lines 3a and 3b of 
intersection; a step 5c is formed between the lines 3b and 3c of 
intersection. Thus, the step faces are regulated. That is, each step face 
is formed as a part of the paraboloids of revolution having different 
focal distances, and those are arrayed in a steplike arrangement when 
viewed in cross section. 
As seen from the fact that these steps are each a part of the paraboloids 
of revolution, when a light source is located at a common focal position 
thereof, the light beams reflected at the steps are parallel to the 
principal optical axis L of the reflection surface (viz., the axis of 
rotational symmetry of the paraboloids of revolution). Alternatively, the 
aimed direction of the reflecting light beam from the step may be varied 
for each step as shown by the light beams 6 and 7 in FIG. 7(a). In this 
case, the curvatures of the lines of intersection 3 vary with the 
curvatures of the curved surfaces. For example, the bulges of the lines of 
intersection 3 increase as in the direction of an arrow G shown in FIG. 
7(b), or those decrease as in the direction of an arrow S shown in FIG. 
7(c). 
In FIG. 6, the slanting direction of the step on the right side of the step 
5a is opposite to that of the step on the left side of the step 5a (in 
this case, the step is slanted down toward the central part of the closed 
curve). However, a case as shown in FIG. 8 may take place. In this case, 
the slanting direction of a step 5br on the right side of the step 5a is 
the same as of a step 5bl on the left side thereof. For example, as shown 
in FIG. 9, let us consider a step allotted to a portion between a closed 
curve lP1 passing through points P1 and P2 where the paraboloid of 
revolution of the parabola par1 intersects the curved surface 1, and 
another closed curve lP2 passing through points P3 and P4 where the 
paraboloid of revolution of the parabola par2 intersects the curved 
surface 1. When the step is cut along a plane containing the points P1 to 
P4, and the z-axis (vertically extending in FIG. 9), the slanting 
directions of the step, when viewed in cross section, are the same. Thus, 
as schematically illustrated in FIG. 10, there is a step, a part thereof 
is incurved, and another part is outcurved. Those incurved and outcurved 
parts are alternately connected to configure the step. The thus shaped 
step may be formed by the curved-surface working which uses a ball end 
mill. 
When a reflection surface having the reflection steps formed along multiple 
closed curves and a reflection mirror having such a reflection surface are 
manufactured using the CAD, CAM data for forming a metal mold for 
manufacturing the reflection mirror may be gathered from the reflection 
surface and the reflection mirror having the same. 
FIGS. 11 to 14 show the feature of a shape of a reflection surface 
manufactured by the reflection mirror manufacturing method as mentioned 
above. A distribution of the closed curves on a curved surface is 
illustrated. In the rectangular coordinates of these figures, the X axis 
represents a principal optical axis; the Y axis, a horizontal axis; and a 
Z axis, a vertical axis. 
FIG. 11 shows an example in which the present invention is applied to a 
high-mounted stop lamp for a vehicle. The lamp has a thin configuration 
such that a height h is very small as compared with a length. The region A 
is formed into an almost flat shape and the region B is formed into an 
extremetely and fowardly bent shape. 
As illustrated in FIG. 11, two groups of closed curves are present: the 
closed curves of one group are arranged about the central part 4a thereof, 
and those of the other group are arranged about the central part 4b 
thereof. Those central parts are offset from a point where the Z axis 
intersects the curved surface, and lie in the regions where a change of 
the curvatures of the curved surface are relatively great. 
The curved surface is symmetric with respect to the X-Z plane. One half of 
the curved surface may be formed by mirror-operating the other half 
thereof (FIGS. 12 to 14) according to the symmetry principle. 
In the front view of FIG. 12, the central part 4b of the grouped closed 
curves is located on the right side of a point (marked with X) of 
intersection of the principal optical axis and the curved surface. 
As shown in FIG. 14, the pitch of the closed curves on the right side of 
the central part 4b thereof is relatively large, while the pitch of the 
closed curves on the left side thereof is small. This arises from the fact 
that a change of the curvature of the fundamental curved surface on the 
right side of the central part 4b of the grouped closed curves is larger 
than that on the left side. 
FIG. 15 schematically illustrates a state that the central part of the 
closed curves is offset from a point where the principal optical axis 
intersects the curved surface. A front view of the curved surface 1 as a 
fundamental surface of the reflection surface is illustrated in the upper 
portion of FIG. 15. Closed curves 3 are set on the curved surface 1. In 
the figure, a mark X indicates a point where the principal optical axis L 
intersects the curved surface 1. A sectional view of the curved surface 1 
is illustrated in the lower portion of FIG. 15. The curved surface 1 is 
illustrated as a plane slanted upward to the right, for ease of 
explanation. 
Parabolas j1 and j2 typically indicate the paraboloids of revolution, which 
form a group of paraboloids of revolution having the axis L as the axis of 
rotation. The closed curves are formed as the lines of intersection of the 
group of the paraboloids of revolution and the surface 1. 
A closed curve appears as a boundary curve between a portion (shaded by 
lines slanted down to the right) between the paraboloid j1 of revolution 
and the curved surface 1 and a portion (shaded by lines slanted down to 
the left) between the paraboloid j2 of revolution and the curved surface 
1. As a result, the adjacent step faces are connected while keeping the 
configuration of the curved surface 1. 
In the reflection mirror having the reflection surface as mentioned above, 
the central parts of the groups of closed curves which define the 
orientation of the reflection steps formed are offset from the principal 
optical axis of the reflection mirror (viz., the axis extending through 
the light emission center of the light source). With such a novel and 
unique design freedom secured, the surface working can be done without 
adversely affecting the connection of the step faces when the reflection 
steps are formed each between the adjacent closed curves as the lines of 
intersection of the paraboloids of revolution and the fundamental curved 
surface of the reflection surface. In this case, the shape of the curved 
surface that provides a fundamental shape of the reflection surface, is 
faithfully transferred to the shape of the reflection step. As a result, 
there is eliminated an arbitrary shape correction when the step face is 
worked. 
As seen from the foregoing description, in the reflection mirror of a 
vehicle lamp and the method of forming the reflection mirror according to 
the present invention, a free curved surface conformed to a configuration 
of a car body is set for a fundamental surface of a reflection surface, a 
group of paraboloids of revolution having different focal distances are 
set, thereby to determine a group of closed curves as the lines of 
intersection of the fundamental surface and the group of paraboloids of 
revolution, and the respective paraboloids of revolution are partially 
allotted to a portion between each pair of the adjacent closed curves of 
the closed curve group, whereby a plural number of reflection steps are 
arranged about a plural number of central parts in multiple loops, and the 
central parts are offset from the principal optical axis of the reflection 
mirror. With this, there is eliminated the necessity of forming the 
reflection steps about the principal optical axis of the reflection mirror 
in multiple loops. Thus, a required connection of the steps can be ensured 
by setting the position of the central portion of each group of closed 
curves with respect to the principal optical axis. Then, there arise no 
portion where face-working of the reflection steps can not be performed.