Filter element for air cleaner

A filter element for an air cleaner including a filter medium which has a plurality of basic filter units and is integrally formed of a porous sintered material produced by sintering powdered synthetic resin.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a filter element to be incorporated into 
an air cleaner which filtrates or purifies air to be sucked into an 
internal combustion engine of an automobile. 
2. Description of the Prior Art 
A conventional typical filter element for an air cleaner of an automobile 
is constituted generally of a filter medium made of a sheet-like material, 
such as a filter paper or a non-woven fabric filtrating material, and a 
frame member made of a synthetic resin for retaining the filter medium. 
The filter medium is corrugated to maximize the filtration area thereof. 
Further, different types of filter elements have been provided. For 
example, Japanese Utility Model Publication No. 5-25682 teaches a modified 
filter element which is known as a roll filter element. The filter element 
is formed by rolling up a sheet-like filter medium which is constituted of 
a flattened filter paper and a folded filter paper bonded to one surface 
of the filter paper. 
However, the filter medium made of the filter paper or the non-woven fabric 
material tends to easily deform when air is sucked through the filter 
element. Thus, if the filter medium is closely folded to increase 
filtration area thereof, the filter medium may partially contact itself 
when the air is sucked through the filter element. This may cause clogging 
of the filter medium and decreasing of filtration capacity of the filter 
medium. As a result, each conventional filter element thus constructed can 
not be miniaturized without decreasing filtration area of the filter 
medium. 
Additionally, the filter medium has to be folded and subsequently assembled 
to the frame member. This may lead to increased manufacturing cost of the 
filter element. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a filter element which may be 
miniaturized without decreasing available filtration area of a filter 
medium. 
It is another object of the invention to provide a filter element which can 
be manufactured at relatively low cost. 
In order to attain the objects, the present invention provides a filter 
element for an air cleaner which includes a filter medium having a 
plurality of basic filter units and being integrally formed of a porous 
sintered material produced by sintering powdered synthetic resin. 
The filter medium has extremely high flexural strength since it is made of 
the sintered material. Thus, the basic filter unit is prevented from 
contacting the adjacent basic filter unit when air is sucked through the 
filter element. This may effectively prevent reduction of filtration 
performance of the filter medium. 
The filter medium is integrally formed by molding the sintered material. 
This may eliminate the need for a folding process and a bonding process, 
thereby contributing to reduction of the manufacturing cost of the filter 
element. 
The filter medium exhibits excellent flexural strength and 
self-sustainability. Therefore, the filter element may be miniaturized 
without decreasing available filtration area of the filter medium. 
The filter medium may have a honeycombed structure. Further, each of the 
basic filter units may be formed in three dimensions to increase the 
effective filtration area, and may be a bag-like or pocket shaped member 
constituted of a plurality of filtration walls and may have a polygonal 
opening edge and a closed edge opposed to the polygonal opening edge. 
Preferably, the polygonal shaped opening edge defines a regular polygon 
such as a square, rectangle, hexagon, or the like. 
Each of the basic filter units may have a plurality of vertical edges each 
of which interconnects a point on the opening edge and a point on the 
closed edge. The vertical edges are defined by the filtration walls. Some 
of the vertical edges of the basic filter units may be joined with each 
other, and the closed edges of the basic filter units may be connected 
with each other. 
All or some of the filtration walls may be plane walls or skew walls. 
The filter element may include a cylindrical side wall surrounding the 
filter medium. The cylindrical side wall may be integral with the filter 
medium. 
The filter medium may have a honeycombed structure. Further, each of the 
basic filter units may be a bottomed cylindrical member constituted of a 
plurality of filtration walls and may have a polygonal opening edge and a 
polygonal closure wall opposed to the polygonal opening edge. 
The filter medium may have a corrugated structure. Further, each of the 
basic filter units may be a gutter-like or channel member constituted of a 
wedge-shaped filtration wall and a pair of side walls. 
The filter element may include a frame surrounding the filter medium. The 
frame may be integral with the filter medium, and may be formed of 
powdered synthetic resin different from the powdered synthetic resin for 
the filter medium. 
The present invention will become more fully apparent from the claims and 
the description as it proceeds in connection with the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the present invention will now be described in 
detail with reference to the drawings. 
Referring to FIGS. 1 to 6, shown therein is a first embodiment of the 
invention. 
As shown in FIG. 1, a filter element F is mainly constituted of a filter 
medium 1, and a cylindrical side wall 3 surrounding the filter medium 1. 
The filter medium 1 and the side wall 3 are integrally formed of a porous 
and rigid sintered material produced by sintering synthetic resin powder. 
In general, the filter element F additionally includes a frame (not shown) 
mounted on the side wall 3. The filter element F is incorporated into an 
air cleaner (not shown) of an automobile through the frame so as to 
filtrate or purify air to be introduced into an internal combustion 
engine. 
The filter medium 1 has a square-based honeycombed structure with an upper 
or inlet side surface 12 and a lower or outlet side surface 13 parallel to 
the inlet side surface 12. The filter medium 1 is constituted of a 
plurality of basic filter units 2 each having a specific geometric 
configuration. 
As best shown in FIG. 6, each basic filter unit 2 is a bag-like or pocket 
shaped member constituted of four filtration walls 7, and has a square 
inlet port 4 opening to the inlet side surface 12 and a closed linear end 
8 terminating in the outlet side surface 13. The basic filter unit 2 
includes an opened square edge 5 having four vertexes 5a, 5b, 5c and 5d, a 
closed linear edge 6 having two end points 11a and 11b and a midpoint 11c, 
a pair of vertical edges 9a one of which interconnects the vertex 5a and 
the end point 11a and the other of which interconnects the vertex 5c and 
the end point 11b, and a pair of inclined vertical edges 9b one of which 
interconnects the vertex 5b and the midpoint 11c and the other of which 
interconnects the vertex 5d and the midpoint 11c. The square edge 5 is 
coplanar with the inlet side surface 12 and defines the square inlet port 
4. The linear edge 6 is contained in the outlet side surface 13 and 
defines the linear closed end 8. The vertical edges 9a and the inclined 
vertical edges 9b cooperate with the square edge 5 and the linear edge 6 
to confine the four filtration walls 7. 
It is to be noted that the linear edge 6 extends along a projected line of 
a diagonal line interconnecting the vertexes 5a and 5c, that is, the end 
points 11a and 11b and the midpoint 11c correspond to projected points of 
the vertexes 5a and 5c and a center 5e of the square edge 5, respectively. 
In other words, the vertical edges 9a extend along perpendicular lines 
drawn from the vertex 5a and 5c to the outlet side surface 13, 
respectively, and the midpoint 11c is contained in a perpendicular line 
drawn from the center 5e to the outlet side surface 13. Therefore, each 
filtration wall 7 is a three-dimensional skew wall having a linear 
cross-sectional configuration. Additionally, the width of the filtration 
wall 7 is reduced toward the linear edge 6. 
In the filter medium 1 thus constructed, the inlet side surface 12 is 
divided by the square edges 5 into a square gridded pattern (FIG. 2). On 
the other hand, the outlet side surface 13 is also divided by the linear 
edges 6 into an enlarged square gridded pattern (FIG. 4). As will be 
appreciated, the gridded pattern of the outlet side surface 13 is inclined 
at 45 degrees relative to the gridded pattern of the inlet side surface 12 
since each linear edge 6 corresponds to the diagonal line of the square 
edge 5. Additionally, the linear edges 6 cooperate to define a plurality 
of square outlet ports 17 (FIGS. 3 and 4). Thus, as shown in FIG. 3, the 
filter medium 1 includes a plurality of inlet channels 15 into which air 
to be filtrated is introduced through the inlet ports 4, and a plurality 
of outlet channels 16 from which air as filtrated is discharged to the 
outlet ports 17. Moreover, it is important to note that the filtration 
walls 7 of each basic filter unit 2 do not contact the filtration walls 7 
of the adjacent basic filter unit 2 except for the square edge 5 and the 
vertical edges 9a. 
As shown in FIG. 5, the filter medium 1 and the side wall 3 are integrally 
formed by utilizing an upper die 60 and a lower die 61 which has a molding 
space 62 therebetween. That is, the powdered synthetic resin, for example, 
polypropylene resin powder having particle diameter of from 100 to 800 
micro meter, is filled in the molding space 62, and is then sintered at 
temperatures 10.degree. to 50.degree. C. higher than the melting point of 
the resin, thereby forming the filter medium 1 and the side wall 3. 
The sintered synthetic resin is a porous and air permeable material and has 
high rigidity due to bonding of the particles of the powder. Therefore, 
the filter medium 1 thus formed exhibit filtration function for purifying 
the air, and has flexural strength and self-sustainability which may 
resist filtration load applied thereto. The filter medium 1 has extremely 
high flexural strength than a conventional filter medium made of a filter 
paper. Thus, the filtration walls 7 of the basic filter unit 2 are 
prevented from contacting those of the adjacent basic filter unit 2. This 
may effectively prevent reduction of filtration performance of the filter 
medium 1. 
According to the present embodiment, the side wall 3 also exhibits a 
filtration function. This may lead to increased filtration capacity of the 
filter element F. 
The filter medium 1 may be cleaned by water-washing since the sintered 
synthetic resin exhibits excellent water-resistivity. This may lead to 
easy maintenance of the filter element F. 
The filter medium 1 is formed by molding of the powdered synthetic resin. 
This may eliminate the need for a folding process and a bonding process 
which are required in the conventional filter element, thereby 
contributing to reduction of the manufacturing cost of the filter element 
F. 
The filter element F may be miniaturized without decreasing available 
filtration area of the filter medium 1. This is because the filter medium 
1 has the honeycombed structure and exhibits excellent flexural strength 
and self-sustainability. 
Although the basic filter units 2 are arranged in such a way that the 
linear edges 6 form the square gridded pattern on the outlet side surface 
13, arrangement of the basic filter units 2 may be preferably modified, if 
required. 
Referring to FIG. 7, shown therein is a second embodiment of the present 
invention. This embodiment is a modification of the first embodiment. 
Therefore, only the construction which is different from that in the first 
embodiment will be explained. Further, elements which are the same as or 
similar to those in the first embodiment are given like reference numbers 
and their description will not be repeated. 
Each basic filter unit 2 is a bag-like or pocket shaped member constituted 
of eight filtration walls 7, and has a square inlet port 4 opening to an 
inlet side surface 12 and a closed cross-shaped end 8 terminating in an 
outlet side surface 13. The basic filter unit 2 includes an opened square 
edge 5 having four vertexes 5a, 5b, 5c and 5d and four midpoints 5f, 5g,5h 
and 5i, a closed cross-shaped edge 6 having four end points 18a, 18b, 18c 
and 18d and an intersection 18e, four vertical edges 19a which 
interconnect the midpoints 5f, 5g, 5h and 5i and the end points 18a, 18b, 
18c and 18d, respectively, and four inclined vertical edges 19b which 
interconnect the vertex 5a, 5b, 5c and 5d and the intersection 18e, 
respectively. The square edge 5 is coplanar with the inlet side surface 12 
and defines the square inlet port 4. The cross-shaped edge 6 is contained 
in the outlet side surface 13 and defines the cross-shaped closed end 8. 
The vertical edges 19a and the inclined vertical edges 19b cooperate with 
the square edge 5 and the cross-shaped edge 6 to confine the eight 
filtration walls 7. 
It is to be noted that the cross-shaped edge 6 extends along projected 
lines of two cross lines interconnecting the midpoints 5f, 5g, 5h and 5i, 
that is, the end points 18a, 18b, 18c and 18d and the intersection 18e 
correspond to projected points of the midpoints 5f, 5g, 5h and 5i and a 
center 5e of the square edge 5, respectively. In other words, the vertical 
edges 19a extend along a perpendicular line drawn from the midpoints 5f, 
5g, 5h and 5i to the outlet side surface 13, respectively, and the 
intersection 18e is contained in a perpendicular line drawn from the 
center 5e to the outlet side surface 13. Therefore, each filtration wall 7 
is a three-dimensional skew wall having a linear cross-sectional 
configuration. 
Referring to FIG. 8, shown therein is a third embodiment of the present 
invention. This embodiment is a modification of the first embodiment. 
Therefore, only the construction which is different from that in the first 
embodiment will be explained. Further, elements which are the same as or 
similar to those in the first embodiment are given like reference numbers 
and their description will not be repeated. 
Each basic filter unit 2 is a bag-like or pocket shaped member constituted 
of eight filtration walls 7, and has a square inlet port 4 opening to an 
inlet side surface 12 and a closed cross-shaped end 8 terminating in an 
outlet side surface 13. The basic filter unit 2 includes an opened square 
edge 5 having four vertexes 5a, 5b, 5c and 5d and four midpoints 5f, 5g, 
5h and 5i, a closed cross-shaped edge 6 having four end points 22a, 22b, 
22c and 22d and an intersection 22e, four vertical edges 24a which 
interconnect the vertexes 5a, 5b, 5c and 5d and the end points 22a, 22b, 
22c and 22d, respectively, and four inclined vertical edges 24b which 
interconnect the midpoints 5f, 5g, 5h and 5i and the intersection 22e, 
respectively. The square edge 5 is coplanar with the inlet side surface 12 
and defines the square inlet port 4. The cross-shaped edge 6 is contained 
in the outlet side surface 13 and defines the cross-shaped closed end 8. 
The vertical edges 24a and the inclined vertical edges 24b cooperate with 
the square edge 5 and the cross-shaped edge 6 to confine the eight 
filtration walls 7. 
It is to be noted that the cross-shaped edge 6 extends along projected 
lines of two diagonal lines of the square edge 5, that is, the end points 
22a, 22b, 22c and 22d and the intersection 22e correspond to projected 
points of the vertexes 5a, 5b, 5c and 5d and a center 5e of the square 
edge 5, respectively. In other words, the vertical edges 24a extend along 
a perpendicular line drawn from the vertexes 5a, 5b, 5cand 5d to the 
outlet side surface 13, respectively, and the intersection 22e is 
contained in a perpendicular line drawn from the center 5e to the outlet 
side surface 13. Therefore, each filtration wall 7 is a three-dimensional 
skew wall having a linear cross-sectional configuration. 
Referring to FIG. 9, shown therein is a fourth embodiment of the present 
invention. This embodiment is a modification of the first embodiment. 
Therefore, only the construction which is different from that in the first 
embodiment will be explained. Further, elements which are the same as or 
similar to those in the first embodiment are given like reference numbers 
and their description will not be repeated. 
Each basic filter unit 2 is a bag-like or pocket shaped member constituted 
of a pair of filtration walls 7A and a pair of filtration walls 7B, and 
has a square inlet port 4 opening to an inlet side surface 12 and a linear 
closed end 8 terminating in an outlet side surface 13. The basic filter 
unit 2 includes a square edge 5 having four vertexes 5a, 5b, 5c and 5d, a 
linear edge 6 having two end points 27a and 27b, a pair of inclined 
vertical edges 28 which interconnect the vertexes 5a and 5d and the end 
point 27a, and a pair of inclined vertical edges 28' which interconnect 
the vertexes 5b and 5c and the end point 27b. The square edge 5 is 
coplanar with the inlet side surface 12 and defines the square inlet port 
4. The linear edge 6 is contained in the outlet side surface 13 and 
defines the cross-shaped closed end 8. The adjacent inclined vertical 
edges 28 and 28' cooperate with the square edge 5 and the linear edge 6 to 
confine the filtration walls 7A. The adjacent inclined vertical edges 28 
cooperate with the square edge 5 to confine one of the filtration walls 
7B. Further, the adjacent inclined vertical edges 28' cooperate with the 
square edge 5 to confine the other of the filtration walls 7B. 
It is to be noted that the linear edge 6 extends along a projected line of 
a line interconnecting a midpoint 5f between the vertexes 5a and 5d and a 
midpoint 5g between the vertexes 5b and 5c, that is, the end points 27a 
and 27b correspond to projected points of the midpoints 5f and 5g, 
respectively. In other words, the end points 27a and 27b are contained in 
perpendicular lines drawn from the midpoints 5f and 5g to the outlet side 
surface 13, respectively. Therefore, each filtration wall 7A is an 
inclined two-dimensional flat wall having a rectangular configuration. On 
the other hand, each filtration wall 7B is a two-dimensional flat wall 
having a triangular configuration and extending perpendicular to the 
outlet side surface 13. 
In the fourth embodiment, the outlet side surface 13 is divided by the 
linear edges 6 into a striped pattern (FIG. 9). Additionally, the linear 
edges 6 cooperate to define a plurality of elongated outlet ports (not 
shown). As will be appreciated, the both ends of each elongated outlet 
port are defined by the peripheral edge of the side wall 3. Thus, the 
filter medium 1 includes a plurality of inlet channels (not shown) into 
which air to be filtrated is introduced through the inlet ports 4, and a 
plurality of gutter-like outlet channels (not shown) from which air as 
filtrated is discharged to the outlet ports. Moreover, it is important to 
note that the filtration walls 7B of each basic filter unit 2 are common 
to the filtration walls 7B of the adjacent basic filter units 2. 
Referring to FIGS. 10 to 14, shown therein is a fifth embodiment of the 
invention. This embodiment is a modification of the first embodiment. 
Therefore, only the construction which is different from that in the first 
embodiment will be explained. Further, elements which are the same as or 
similar to those in the first embodiment are given like reference numbers 
and their description will not be repeated. 
As shown in FIG. 10, a filter element F is mainly constituted of a filter 
medium 1, and a side wall 3 surrounding the filter medium 1. The filter 
medium 1 and the side wall 3 are integrally formed of a porous and rigid 
sintered material produced by sintering of synthetic resin powder. 
The filter medium 1 has a hexagon-based honeycombed structure with an inlet 
side surface 12 and an outlet side surface 13 parallel to the inlet side 
surface 12. The filter medium 1 is constituted of a plurality of basic 
filter units 2 each having a specific geometric configuration. 
As best shown in FIG. 14, each basic filter unit 2 is a bag-like or pocket 
shaped member constituted of six filtration walls 7, and has an opened 
regular hexagonal inlet port 4 opening to the inlet side surface 12 and a 
closed Y-shaped end 8 terminating in the outlet side surface 13. The basic 
filter unit 2 includes a regular hexagonal edge 30 having six vertexes 
30a, 30b, 30c, 30d, 30e and 30f, a closed Y-shaped edge 6 having three end 
points 31a, 31b and 31c and a center 31d, three vertical edges 32a which 
interconnects the vertexes 30a, 30c and 30e and the end points 31a, 31b 
and 31c, respectively, and three inclined vertical edges 32b which 
interconnects the vertexes 30b, 30d and 30f and the center 31d. The 
regular hexagonal edge 30 is coplanar with the inlet side surface 12 and 
defines the square inlet port 4. The Y-shaped edge 6 is contained in the 
outlet side surface 13 and defines the Y-shaped closed end 8. The vertical 
edges 32a and the inclined vertical edges 32b cooperate with the regular 
hexagonal edge 30 and the Y-shaped edge 6 to confine the six filtration 
walls 7. 
It is to be noted that the Y-shaped edge 6 extends along projected lines of 
three segment lines interconnecting the vertexes 30a, 30c and 30e and a 
center 30g of the regular hexagonal edge 30, that is, the end points 31a, 
31b and 31c and the center 31d correspond to projected points of the 
vertexes 30a, 30c and 30e and the center 30g of the regular hexagonal edge 
30, respectively. In other words, the three vertical edges 32a extends 
along perpendicular lines drawn from the vertex 30a, 30c and 30d to the 
outlet side surface 13, and the center 31d is contained in a perpendicular 
line drawn from the center 30g to the outlet side surface 13. Therefore, 
each filtration wall 7 is a three-dimensional skew wall having a linear 
cross-sectional configuration. 
In the filter medium 1 thus constructed, the inlet side surface 12 is 
divided by the regular hexagonal edges 30 into a regular hexagon-based 
honeycombed pattern (FIG. 11). On the other hand, the outlet side surface 
13 is also divided by the Y-shaped edges 6 into a regular hexagon-based 
honeycombed pattern (FIG. 13). As will be appreciated, the pattern of the 
outlet side surface 13 is inclined at 60 degrees relative to the pattern 
of the inlet side surface 12. Additionally, the Y-shaped edges 6 cooperate 
to define a plurality of regular hexagonal outlet ports 17 (FIG. 13). 
Thus, as shown in FIG. 12, the filter medium 1 includes a plurality of 
inlet channels 15 into which air to be filtrated is introduced through the 
inlet ports 4, and a plurality of outlet channels 16 from which air as 
filtrated is discharged to the outlet ports 17. Moreover, it is important 
to note that the filtration walls 7 of each basic filter unit 2 do not 
contact the filtration walls 7 of the adjacent basic filter unit 2 except 
for the regular hexagonal edge 30 and the vertical edges 32a. 
Referring to FIG. 15, shown therein is a sixth embodiment of the present 
invention. This embodiment is a modification of the fifth embodiment. 
Therefore, only the construction which is different from that in the fifth 
embodiment will be explained. Further, elements which are the same as or 
similar to those in the fifth embodiment are given like reference numbers 
and their description will not be repeated. 
Each basic filter unit 2 is a bag-like or pocket shaped member constituted 
of four filtration walls 7A, two filtration walls 7B, and has a regular 
hexagonal inlet port 4 opening to the inlet side surface 12 and a closed 
linear end 8 terminating in the outlet side surface 13. The basic filter 
unit 2 includes an opened regular hexagonal edge 30 having six vertexes 
30a, 30b, 30c, 30d, 30e and 30f, a closed linear edge 6 having two end 
points 34a and 34b and a center 34c, two inclined vertical edges 35a and 
35b which interconnects the vertexes 30a and 30b and the end points 34a, 
respectively, two inclined vertical edges 35c and 35d which interconnects 
the vertexes 30d and 30e and the end points 34b, respectively, and two 
inclined vertical edges 35e and 35f which interconnect the vertexes 30c 
and and 30f and the center 34c, respectively. The regular hexagonal edge 
30 is coplanar with the inlet side surface 12 and defines the square inlet 
port 4. The linear edge 6 is contained in the outlet side surface 13 and 
defines the linear closed end 8. The inclined vertical edges 35a and 35b, 
and 35c and 35d cooperate with the regular hexagonal edge 30 to confine 
the two filtration walls 7B. On the other hand, the inclined vertical 
edges 35b and 35e, 35c and 35e, 35d and 35f, and 35a and 35f cooperate 
with the regular hexagonal edge 30 and the linear edge 6 to confine the 
four filtration walls 7A. 
It is to be noted that the linear edge 6 extends along projected line of a 
segment line interconnecting a midpoint 30h of the vertexes 30a and 30b 
and a midpoint 30i of the vertexes 30d and 30e, that is, the end points 
34a and 34b and the center 34c correspond to projected points of the 
midpoints 30h, 30i and the center 30g of the regular hexagonal edge 30, 
respectively. In other words, the end points 34a and 34b and the center 
34c are contained in a perpendicular lines drawn from the midpoints 30h, 
30i and the center 30 to the outlet side surface 13, respectively. 
Therefore, each filtration wall 7A is a three-dimensional skew wall having 
a linear cross-sectional configuration. On the other hand, each filtration 
wall 7B is a two-dimensional flat wall having a triangular configuration 
and extending perpendicular to the outlet side surface 13. 
In the sixth embodiment, the outlet side surface 13 is divided by the 
linear edges 6 into a striped pattern (FIG. 15). Additionally, the linear 
edges 6 cooperate to define a plurality of elongated outlet ports (not 
shown). As will be appreciated, the both ends of each elongated outlet 
port are defined by the peripheral edge of the side wall 3. Thus, the 
filter medium 1 includes a plurality of inlet channels (not shown) into 
which air to be filtrated is introduced through the inlet ports 4, and a 
plurality of gutter-like outlet channels (not shown) from which air as 
filtrated is discharged to the outlet ports. Moreover, it is important to 
note that the filtration walls 7A of each basic filter unit 2 are common 
to the filtration walls 7B of the adjacent basic filter units 2. 
Referring to FIGS. 16 and 17, shown therein is a seventh embodiment of the 
present invention. This embodiment is a modification of the fifth 
embodiment. Therefore, only the construction which is different from that 
in the fifth embodiment will be explained. Further, elements which are the 
same as or similar to those in the fifth embodiment are given like 
reference numbers and their description will not be repeated. 
Each basic filter unit 2 is a bag-like or pocket shaped member constituted 
of two filtration walls 7A, four filtration walls 7B, and has a regular 
hexagonal inlet port 4 opening to the inlet side surface 12 and a linear 
closed end 8 terminating in the outlet side surface 13. The basic filter 
unit 2 includes a regular hexagonal edge 30 having six vertexes 30a, 30b, 
30c, 30d, 30e and 30f, a linear edge 6 having two end points 37a and 37b, 
two vertical edges 38a and 38d which interconnect the vertexes 30a and 30d 
to the end points 37a and 37b, respectively, two inclined vertical edges 
38b and 38f which interconnect the vertexes 30b and 30f to the end point 
37a, and two inclined vertical edges 38c and 38e which interconnect the 
vertexes 30c and 30f to the end point 37b. The regular hexagonal edge 30 
is coplanar with the inlet side surface 12 and defines the square inlet 
port 4. The linear edge 6 is contained in the outlet side surface 13 and 
defines the linear closed end 8. The vertical edge 38a cooperates with the 
inclined vertical edges 38b and 38f and the regular hexagonal edge 30 to 
confine the two filtration walls 7B. Similarly, the vertical edge 38d 
cooperates with the inclined vertical edges 38c and 38e and the regular 
hexagonal edge 30 to confine the two filtration walls 7B. On the other 
hand, the inclined vertical edges 38b and 38c cooperate with the regular 
hexagonal edge 30 and the linear edge 6 to confine the filtration walls 
7A. Similarly, the inclined vertical edges 38e and 38f cooperate with the 
regular hexagonal edge 30 and the linear edge 6 to confine the filtration 
walls 7A. 
It is to be noted that the linear edge 6 extends along projected line of a 
diagonal line interconnecting the vertexes 30a and 30d, that is, the end 
points 37a and 37b correspond to projected points of the vertexes 30a and 
30d, respectively. In other words, the end points 37a and 37b are 
contained in a perpendicular lines drawn from the vertexes 30a and 30d to 
the outlet side surface 13, respectively. Therefore, each filtration wall 
7A is a two-dimensional flat wall having a trapezoidal configuration. On 
the other hand, each filtration wall 7B is a two-dimensional flat wall 
having a triangular configuration and extending perpendicular to the 
outlet side surface 13. 
In the seventh embodiment, the basic filter units 2 are arranged so that 
the outlet side surface 13 is divided by the linear edges 6 into a regular 
hexagonal gridded pattern. As will be appreciated, in this arrangement, 
the filter medium 1 necessarily has a plurality of empty spaces. 
Therefore, the filter medium 1 includes a plurality of closure walls 36 to 
close the empty spaces. Each closure wall 36 is coplanar with the inlet 
side surface 12 and is formed with the same material as that of the filter 
medium 1. Additionally, the linear edges 6 cooperate to define a plurality 
of regular hexagonal outlet ports 17. Thus, the filter medium 1 includes a 
plurality of inlet channels 15 into which air to be filtrated is 
introduced through the inlet ports 4, and a plurality of enlarged outlet 
channels 16 from which air as filtrated is discharged to the outlet ports. 
Moreover, it is important to note that the filtration walls 7B of each 
basic filter unit 2 are common to the filtration walls 7B of the adjacent 
basic filter units 2. 
Referring to FIGS. 18 to 23, shown therein is an eighth embodiment of the 
invention. This embodiment is a modification of the first embodiment. 
Therefore, only the construction which is different from that in the first 
embodiment will be explained. Further, elements which are the same as or 
similar to those in the first embodiment are given like reference numbers 
and their description will not be repeated. 
As shown in FIG. 18, a filter element F is mainly constituted of a filter 
medium 1, and a side wall 3 enclosing the filter medium 1 and having a 
square configuration. The filter medium 1 and the side wall 3 are 
integrally formed of a porous and rigid sintered material produced by 
sintering synthetic resin powder. 
The filter medium 1 has a square-based honeycombed structure with an inlet 
side surface 12 and an outlet side surface 13 parallel to the inlet side 
surface 12. The filter medium 1 is essentially constituted of a plurality 
of basic filter units 2 each having a square cylindrical configuration. 
Each basic filter unit 2 has a square cylindrical configuration and is 
constituted of four side filtration walls 42 and a bottom filtration wall 
44 coplanar with the outlet side surface 13. As best shown in FIG. 19, the 
basic filter units 2 are regularly arranged so that a plurality of square 
through bores are alternately formed between the basic filter units 2. 
It is to be noted that the filter medium 1 includes a plurality of closure 
walls 45 to close the through bores. The closure walls 45 are formed of 
the same material as that of the filter medium 1. Further, the closure 
walls 45 are integrally formed with the filter medium 1 and adapted to 
coplanar with the inlet side surface 12. Additionally, the filter medium 1 
has a plurality of square inlet ports 4 opening to the inlet side surface 
12 and a plurality of square outlet ports 17 opening to the outlet side 
surface 13. Thus, the filter medium 1 includes a plurality of inlet 
channels 15 into which air to be filtrated is introduced through the inlet 
ports 4, and a plurality of enlarged outlet channels 16 from which air as 
filtrated is discharged to the outlet ports 17. It should be understood 
that the side wall 3 is partly common to the filtration walls 42 of the 
basic filter unit 2 arranged therealong. 
The filter medium 1 in the eighth embodiment may be preferably modified. As 
shown in FIG. 22, in a modified form, each basic filter unit 2 has a 
bottomless square cylindrical configuration and is constituted of four 
side filtration walls 42. The filter medium 1 additionally includes an 
inlet side plate 46 having a plurality of inlet ports 4 and a plurality of 
closure walls 45, and an outlet side plate 47 having a plurality of bottom 
filtration walls 44 and a plurality of outlet ports 17. The inlet side 
plate 46 and the outlet side plate 47 are combined to the filter medium 1 
by bonding or welding. Thus, the filter medium 1 is formed with a 
plurality of inlet channels 15 into which air to be filtrated is 
introduced through the inlet ports 4, and a plurality of enlarged outlet 
channels 16 from which air as filtrated is discharged to the outlet ports 
17. 
The filter medium 1 in the eighth embodiment may be further modified. As 
shown in FIG. 23, in a modified form, each basic filter unit 2 has a 
bottomless square cylindrical configuration and is constituted of four 
side filtration walls 42. The filter medium 1 additionally includes a 
plurality of closure walls 45, and a plurality of bottom filtration walls 
44. The closure walls 45 and the bottom filtration walls 44 are combined 
to the filter medium 1 by bonding or welding. Thus, the filter medium 1 is 
formed with a plurality of inlet channels 15 into which air to be 
filtrated is introduced through the inlet ports 4, and a plurality of 
enlarged outlet channels 16 from which air as filtrated is discharged to 
the outlet ports 17. 
It is to be noted that the filter medium 1 of eighth embodiment may be 
further modified. For example, the basic filter units 2 may have 
triangular or rectangular cylindrical configuration. 
Referring to FIGS. 24 to 26, shown therein is a ninth embodiment of the 
invention. 
As best shown in FIG. 24, a filter element A is constituted of a filter 
medium 101, and a rectangular frame 80 to which the filter medium 101 is 
integrally incorporated. The filter medium 101 and the frame 80 are 
integrally formed of a porous and rigid sintered material produced by 
sintering synthetic resin powder. 
The filter medium 101 has an inlet side surface 112 and an outlet side 
surface 113, and is constituted of a plurality of basic filter units 102 
which are integrally connected at connecting edges 106 to form a 
corrugated structure. Each basic filter unit 102 is constituted of a 
wedge-shaped filtration wall 50 and a pair of end walls or side walls 51. 
As shown in FIG. 26, the filter medium 101 thus constructed has a 
plurality of inlet channels 115 facing the inlet side surface 112 and a 
plurality of outlet channels 116 facing the outlet side surface 113. 
As shown in FIG. 25, the filter medium 101 and the frame 80 are integrally 
formed by utilizing an upper die 63 and a lower die 64. That is, the 
powdered synthetic resin, for example, polypropylene resin powder is 
filled in a molding space between the upper die 63 and the lower die 64, 
and then sintered at a suitable temperature, thereby forming the filter 
element A. 
As shown in FIG. 26, the filter element A thus formed is incorporated into 
an air cleaner C having an upper casing 70 and a lower casing 71, in which 
the frame 80 of the filter element A is received between a peripheral edge 
70a of the upper casing 70 and a peripheral edge 71a of the lower casing 
71. Then, the frame 80 is bonded to the peripheral edges 70a and 71a by 
welding or the like, thereby fixing the filter element A to the air 
cleaner C. It is preferable that the casings 70 and 71 are formed of 
synthetic resin having properties identical with those of the synthetic 
resin for the filter element A. 
According to this embodiment, the frame 80 exhibits filtration function. 
This may lead to increased filtration capacity of the filter element A. 
Further, the filter medium 101 is integrally formed with the frame 80. 
This may eliminate the need for a folding process of the filter medium 101 
and a connecting process of the filter medium 101 to the frame 80, thereby 
reducing the manufacturing cost of the filter element A. 
Further, the filter element A is assembled by welding the frame 80 to the 
peripheral edges 70a and 71a of the casings 70 and 71. This may eliminate 
the need for a sealing mechanism between the filter element A and the 
casings 70 and 71 of the air cleaner C. 
Further, both of the filter medium 101 and the frame 80 are made of the 
sintered synthetic resin. This may facilitate reuse of the filter element 
A. 
Additionally, the filter element A may be miniaturized without decreasing 
available filtration area of the filter medium 101. This is because the 
filter medium 101 exhibits excellent flexural strength and 
self-sustainability. 
Referring to FIG. 27, shown therein is a tenth embodiment of the present 
invention. This embodiment is a modification of the ninth embodiment. 
Therefore, only the construction which is different from that in the ninth 
embodiment will be explained. Further, elements which are the same as or 
similar to those in the ninth embodiment are given like reference numbers 
and their description will not be repeated. 
A filter element A is constituted of a filter medium 101, and a rectangular 
frame 80. The filter medium 101 is formed of synthetic resin powder. 
Whereas, the frame 80 is formed of synthetic resin powder which is 
different from the synthetic resin powder for the filter medium 101. The 
synthetic resin powder for the frame 80 has softness and elasticity 
greater than those of the synthetic resin powder for the filter medium 
101, and exhibits high affinity for the synthetic resin powder for the 
filter medium 101. 
As shown in FIG. 27, the filter medium 101 and the frame 80 are integrally 
formed by utilizing an upper die 65 and a lower die 66 for forming the 
filter medium 101 and an upper die 67 and a lower die 68 for forming the 
frame 80. That is, the powdered synthetic resin for the filter medium 101 
is filled in a molding space between the upper die 65 and the lower die 
66, and the powdered synthetic resin for the frame 80 is filled in a 
molding space between the upper die 67 and the lower die 68. Then, the 
both of the powdered synthetic resins are sintered, thereby forming the 
filter element A. As will be easily understood, the dies 65 and 66 are 
heated to a temperature suitable for sintering the powdered synthetic 
resin for the filter medium 101, and the dies 67 and 68 are heated to a 
temperature suitable for sintering the powdered synthetic resin for the 
frame 80. 
In this embodiment, the filter element A thus formed is incorporated into 
an air cleaner (not shown) having an upper casing and a lower casing, in 
which the frame 80 is closely received between a peripheral edge of the 
upper casing and a peripheral edge of the lower casing. Then, the frame 80 
is fixed between the peripheral edges of the upper and lower casings by 
clamping or the like, thereby mounting the filter element A to the air 
cleaner. 
According to this embodiment, the frame 80 of the filter element A is 
formed of the highly elastic material. This may eliminate the need for a 
sealing mechanism between the filter element A and the casings of the air 
cleaner. 
Further, the filter medium 101 is made of the sintered synthetic resin, and 
the frame 80 is made of the sintered synthetic resin similar to that for 
the filter medium 101. This may facilitate reuse of the filter element A. 
The preferred embodiments herein described are intended to be illustrative 
of the invention and not to limit the invention to the precise form herein 
described. They are chosen and described to explain the principles of the 
invention and their application and practical use to enable others skilled 
in the art to practice the invention.