Vortex flow blower having blades each formed by curved surface and method of manufacturing the same

A vortex flow blower used as an air source to be incorporated into general industrial machines. The vortex flow blower is characterized in that the shape of the blade in its impeller is three dimensionally formed such that at least the inner portion of the blade can be adapted to the three dimensional internal flow. According to the present invention, the aerodynamic performance can be significantly improved and the size of a vortex flow blower can be reduced. Furthermore, an impeller having three dimensionally shaped blades is manufactured by independently manufacturing the shroud and the blades and coupling them, so that the impeller of a complicated shape can be readily manufactured. Furthermore, since the blade can be made of a thin and light material, the secondary moment of inertia of the impeller can be reduced.

FIELD OF THE INVENTION 
The present invention relates to a vortex flow blower used as an air source 
to be incorporated into a general industrial machine such as an apparatus 
for transporting pulverized materials, an absorber for paper or an 
aeration apparatus, and, more particularly, to the shape of impeller 
blades capable of significantly improving the aerodynamic performance of a 
vortex flow blower, the shape of a casing suitable for the shape of the 
blades and a manufacturing method therefor. 
BACKGROUND OF THE INVENTION 
Previously the vortex flow blower has usually been provided with blades 
formed radially in the impeller. Since the vortex flow blower exhibits an 
advantage in that high wind pressure can be obtained with reduced size, a 
variety of disclosures and studies have been made for the purpose of 
improving the above-identified advantage. 
For example, a study is disclosed in Transaction of Japan Machinery 
Society, Vol. 45 (published in August 1979), P. 1108-1116. According to 
the study, the characteristic (i.e., the characteristic about the 
relationship between discharge flow rate and discharge pressure) of the 
vortex flow blower is changed by changing the ratio R.sub.1 /R.sub.2, 
where R.sub.1 represents the radius of a circle connecting the inner end 
of a blade and the axial center and R.sub.2 represents a radius connecting 
the outer end of the blade and the axial center. According to this it is 
disclosed that both the flow rather coefficient and the pressure 
coefficient are higher when the value of R.sub.1 /R.sub.2 is 0.68 than 
when it is 0.82, and they become higher when the value is 0.75. In the 
vortex flow blowers which have been put into practical use, the smallest 
value of R.sub.1 /R.sub.2 is about 0.68. 
Although R.sub.2 must be a small value for the purpose of reducing the size 
of the vortex flow blower, the following problems arise; namely, the value 
of R.sub.1 /R.sub.2 must be decreased when the desired flow rate is 
satisfied with a reduced size of the vortex flow blower since the flow 
rate significantly depends upon the value of R.sub.2.sup.2 (1-R.sub.1 
/R.sub.2). However, if the value of R.sub.1 /R.sub.2 is reduced to 0.75 or 
less, the pressure coefficient becomes smaller as described above. 
Furthermore, since the outer radius R.sub.2 has been reduced, peripheral 
speed u.sub.2 at the outer radius R.sub.2 is also lowered, thereby causing 
the discharge pressure to be excessively lowered since the pressure 
characteristic is determined by the product of the pressure coefficient 
and the square of u.sub.2. Therefore, R.sub.2 must be a small value, and 
R.sub.1 /R.sub.2 must be a small value and the pressure coefficient must 
be significantly increased in order to reduce the size of the vortex flow 
blower. 
When improved characteristics are desired without any change in the size of 
the vortex flow blower, the following problem arises; namely, if the value 
of R.sub.1 /R.sub.2 is increased to about 0.75 for the purpose of 
improving the pressure performance in the case where the value of R.sub.1 
/R.sub.2 is constant, the flow rate is inevitably reduced and, on the 
contrary, if the value of R.sub.1 /R.sub.2 is reduced for the purpose of 
increasing the flow rate, the pressure coefficient is lowered. Therefore, 
when an improved characteristic is desired without changing the size of 
the vortex flow blower, R.sub.1 /R.sub.2 must be reduced and the pressure 
coefficient must be increased. 
Vortex flow blowers designed to improve their aerodynamic performance are 
disclosed, for example, in Japanese Patent Unexamined Publication No. 
50-5914 and Japanese Patent Unexamined Publication No. 61-155696, each of 
which is provided with an impeller formed in such a manner that only the 
axial inlet angle and the exit angle of its blade are inclined at a 
certain angle which is respectively smaller or larger than 90 degrees. 
Furthermore, vortex flow blowers, although their objects are unclear, are 
disclosed in Japanese Utility Model Examined Publication No. 55-48158 and 
Japanese Utility Model Unexamined Publication No. 56-85091, each of which 
is provided with an impeller formed in such a manner that both or one of 
the inlet angle and the exit angle in the circumferential direction of its 
blade are or is inclined at a certain angle which is different from 90 
degrees. 
Further, a method of manufacturing an impeller is disclosed in Japanese 
Patent Unexamined Publication No. 51-57011, and according to this method 
the impeller is composed of two pieces divided in its axial direction in 
order to make a core unnecessary when forming the impeller from a casting, 
and the thus divided two pieces are coupled to each other afterwards. 
Since the vortex flow blower exhibits an advantage in that it can serve as 
a clean air source with a reduced size, it has recently been recently 
widely used. Therefore, there arises a desire for the vortex flow blower 
which is capable of generating higher wind pressure and whose size is 
reduced with the discharge pressure maintained as it is. However, in the 
conventional technologies including the above-described technologies, only 
one of the exit angle in the circumferential direction, the inlet angle 
and the axial angle of the blade is taken into consideration and the shape 
of the blade is not formed so as to be adapted to the three dimensional 
internal flow which takes place inherently in the vortex flow blower, so 
that turbulence of internal flow such as swirls and stagnation cannot be 
prevented. Therefore, the following problems arise that it is difficult to 
further reduce the size of the vortex flow blower and a predetermined 
pressure maintained, and it is difficult to obtain higher discharge 
pressure with the flow rate maintained without enlarging the size of the 
vortex flow blower. 
Furthermore, since the conventional vortex flow blower have been 
insufficient in terms of noise reduction, they cannot be used as medical 
equipment or the like which are used in quiet environments. 
In addition, according to the method of manufacturing an impeller disclosed 
in Japanese Patent Unexamined Publication No. 51-57011, it is difficult to 
manufacture an impeller blade having a three dimensional shape. 
Furthermore, when the impeller is manufactured by a low pressure casting 
process, since there are problems of run or fluidity it is difficult to 
reduce thickness to the blade. Therefore, it is difficult to reduce the 
secondary moment of inertia of the impeller, thereby causing starting 
torque when starting the impeller and, as a result, the size of the motor 
cannot be reduced. 
Furthermore, the metal mold used when the impeller is manufactured by an 
integral molding process such as die-casting or chill-casting process is 
expensive, so that it is difficult to inexpensively manufacture an 
impeller having different aerodynamic performance. 
SUMMARY OF THE INVENTION 
The present invention has been accomplished in view of the foregoing, and a 
first object of the present invention is to provide a vortex flow blower 
exhibiting improved aerodynamic performance in comparison with the 
conventional vortex flow blower. 
A second object of the present invention is to provide a vortex flow blower 
having reduced noise. 
A third object of the present invention is to provide a vortex flow blower 
whose aerodynamic performance is significantly improved and whose 
discharge pressure can be controlled to a set value. 
A fourth object of the present invention is to provide a vortex blower 
having a reduced size. 
A fifth object of the present invention is to provide a method of 
efficiently and easily manufacturing an impeller even if it has a 
complicated shape. 
A sixth object of the present invention is to provide a method of 
manufacturing an impeller having reduced secondary moment of inertia. 
A seventh object of the present invention is to provide a method of 
inexpensively manufacturing impellers having different aerodynamic 
characteristics by manufacturing only the blades of different shapes. 
In order to achieve the above-described objects, the first aspect of the 
present invention lies in that the shape of the blade is formed in a 
proper three dimensional shape such that at least the inner portion of the 
blade is adapted to the three dimensional internal flow. 
That is, when it is assumed that the radius of a circle connecting the 
inner end of the blade and the axial center is R.sub.1, the inlet angle of 
the front edge of the blade in the inner end is .gamma..sub.1, the inlet 
angle at the front edge of the blade in an intermediate portion between 
the inner end and a central portion is .gamma..sub.i, the radius at a 
center between the inner end and the outer end is R.sub.c, the shape of 
the blade is formed by a smoothly curved surface so as to make at least 
.gamma..sub.1, .gamma..sub.i and .gamma..sub.c smaller than 90 degrees and 
to meet the relationship of .gamma..sub.1 &gt;.gamma..sub.c or .gamma..sub.1 
&gt;.gamma..sub.c. Further, it may be formed so as to make .gamma..sub.1 less 
than 90 degrees and to meet the relationship of .gamma..sub.1 
&gt;.gamma..sub.c. 
Furthermore, the position of the blade at its front edge on a circle whose 
radium is R.sub.c is arranged to delay with respect to the direction of 
rotation of the impeller than that at its inner end. 
The second aspect lies in that the shape of the blade of the impeller is 
three dimensionally formed such that the inner and the outer portions of 
the blade are adapted to the three dimensional internal flow, thereby 
projecting the front edge of the outer portion of the blade with respect 
to the direction of rotation of the impeller. 
The third aspect lies in that the front edge of the outer portion of the 
blade is retracted with respect to the direction of rotation of the 
impeller and .gamma..sub.0 is greater than 90 degrees. 
The fourth aspect lies in that as mentioned before the shape of the blade 
of the impeller is three dimensionally formed and R.sub.1 /R.sub.2 is set 
to 0.75 or less and, preferably, in a range of between 0.75 or less and 
0.3 or more. 
The fifth aspect lies in that the shape of the casing of the vortex flow 
blower is formed in such a manner that the shape of a partition wall 
thereof is formed so as to cause fluid to be introduced and discharged 
along the shape of the blade. 
The sixth aspect lies in that the blade is formed in such a manner that a 
lower most or bottom portion of the blade at a shroud side is retracted 
with respect to the rotational direction compared with a front edge of the 
blade at its inner end and a center portion of the blade becomes situated 
substantially right above a portion of the blade adjacent the shroud wall 
surface. 
Further, the seventh aspect lies in that the blade is formed in three 
dimensional shape so as to form a three dimensional passage defined by the 
neighboring blades and the shroud wall surface to provide therein an 
inflow portion, a flow direction converting portion and an outflow 
portion. And, it is adapted such that, in the inflow portion, an inclined 
flow is caused, in a direction opposite to the rotational direction of the 
impeller and towards the shroud side; that, in the flow direction 
converting portion, the inflowing inclined flow is caused to flow along an 
outer circumferential side of the shroud wall surface; and that, in the 
outflow portion, the flow is caused to flow in the same direction as the 
rotational direction of the impeller and in a direction going away from 
the shroud wall surface. 
The eighth aspect lies in that a thickness of the blade is increased in a 
backface side of the blade adjacent the shroud wall surface. 
In order to achieve the fifth object of the present invention, the method 
of manufacturing an impeller according to the present invention comprises 
the steps of independently manufacturing the shroud and the blades so as 
to form the impeller. Further, as occasion demands, a filler may be filled 
into the corners between the base portion of the shroud and the blades. 
Furthermore, in the method of manufacturing an impeller according to the 
present invention, grooves into which the blades are to be inserted are 
formed in the annular groove formed in the shroud by the number 
corresponding to the number of the blades so that the impeller is formed 
by inserting the blades into these grooves. 
Furthermore, in the method of manufacturing an impeller according to the 
present invention, cores each of which has such a structure that, when the 
impeller has been formed by casting, neighboring blades partitioning the 
annular groove of the shroud, are positioned on the circumference at a 
predetermined interval, fluid (e.g. molten alloy) is poured between the 
neighboring cores and between the core and the outer mold, and the fluid 
is solidified so that the impeller is manufactured. 
Furthermore, in the method of manufacturing an impeller according to the 
present invention, impeller component units each of which has neighboring 
blades and a part of the annular groove of the shroud formed therebetween 
are manufactured, and a plurality of these units are assembled to each 
other on the circumference so that the impeller is manufactured. 
In order to achieve the above-describe sixth object, in the method of 
manufacturing an impeller according to the present invention, the blades 
are made of thin and light material. 
In order to achieve the above-described seventh object, the method of 
manufacturing an impeller according to the present invention is 
characterized in that the impeller is manufacture by manufacturing only 
the blades so as to have different shapes and coupling the manufactured 
blades and the shroud.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings wherein like reference numerals are used 
throughout the various views to designate like parts and more particularly 
to FIG. 1, according to this figure, a vortex blower in accordance with 
the present invention includes an impeller 1 represents a casing 4 forming 
an annular passage 8, and represents a motor 4 for rotating the impeller 
1. The impeller 1 and the casing 2 are formed to face each other and the 
impeller 1 is fastened in such a manner that the impeller 1 can rotate 
with respect to the casing 2. The motor 4 is placed on the base member 7a 
in such a manner that the motor 4 is secured to both the base member 7a 
and the casing 2. An end of the annular passage 8 is communicated to an 
inlet passage 6a and the other end of the same is communicated to an 
outlet passage (not shown in FIG. 1). The inlet passage 6a and the outlet 
passage are formed in a muffler 7 which also serves as a base member. The 
annular passage 8 is formed around the rotational center of the impeller 
1, that is, around the rotational shaft 3 of the motor 4. The cross 
sectional shape of the annular passage 8 forms a semicircular arc when it 
is cut by a plane passing through the axial center of the rotational shaft 
3. A partition wall is formed between an inlet port and an outlet port 
each of which is communicated with the annular passage 8, the partition 
wall being formed with a small gap maintained for the purpose of 
permitting a plurality of blades 5 formed in the impeller 1 to pass 
through. Thus, the communication between the inlet port and the outlet 
port is prevented by the partition wall. The impeller 1 is constituted by 
a wheel 9 and a shroud 11 which are secured to the rotational shaft 3 of 
the motor 4 and are capable of rotating with integrated to each other. The 
shroud 11 has a passage 10 formed therein, with the passage 10 having a 
plurality of blades 5 formed in a direction traversing the passage 10. 
In the vortex flow blower of this embodiment, the shape of the blade 5 is, 
as shown in FIGS. 2 to 6, formed in such a manner that at least the inner 
portion thereof has a three dimensional shape. 
The air flow in the annular passage 8 will be described before explaining 
about the shape of the blade 5, the air flow in the annular passage 8 
being shown in FIGS. 7 to 11. Air introduced through an inlet port 6c 
passes, as shown in FIGS. 7 and 8, through a passage 2a in the casing 2 
formed in the impeller 1, with the passage 2a being in the form of a 
circular cross sectional shape. The air passes through the passage 2a 
while swirling around the center of the circular cross section and the 
pressure of which is being raised due to the rotation of the blades 5 
until the air reaches the outlet port 6d through which the air is 
discharged. 
It has been found that air passes as shown in FIG. 9 to 14 as a result of 
visual tests and measurements of the speed of the internal flow. 
Assuming, as shown in FIGS. 3 to 7, that the inner end of the blade 5 is 
5b, the outer end of the same is 5a and the central portion between the 
outer end 5a and the inner end 5b is 5c, the distribution of speed of air 
passing through the annular passage 8 after it has been introduced through 
the inlet port 6c with respect to the speed of the blade 5 becomes as 
shown in FIG. 10. That is, the speed of internal flow becomes positive 
with respect to the direction of rotation of the impeller 1 in the region 
from the outer end 5a to a position near the central portion 5c, while the 
space becomes negative values in the region from the position near the 
central portion 5c to the inner end 5b. 
Therefore, in this embodiment, at least the more the air approaches the 
central portion 5c from the inner end 5b, the larger becomes the speed 
component of air passing through the annular passage 8 in the inverse 
direction to the direction of the rotation, so that the shape of the blade 
5 facing the annular passage 8 is formed to be retracted in the region 
from the inner portion to the central portion in order that air can flow 
without separation even when it passes through the portion near the 
central portion 5c at which air passes at high speed. 
That is, in this embodiment, angle .beta.1 in the circumferential direction 
is determined so as to retract the blade 5 to the central portion 5c at 
the inner portion thereof, thereby making the internal flow uniform. 
On the other hand, as is known, the speed distribution of the flow passing 
through the annular passage 8 in the transverse direction toward the 
rotational shaft 3 has, as shown in FIG. 11, speed vector running toward 
the casing 2 in a region from the outer end 5a to a position near the 
central portion 5c, and it has speed vector running toward the impeller 1 
in the region from the position near the central portion 5c to the inner 
end 5b. 
Therefore, in this embodiment, the axial inlet angle of the blade 5 is 
determined so as to be adapted to the resultant vector of the speed vector 
of the air passing through the annular passage 8 with respect to the blade 
5 as shown in FIG. 10 and the speed vector of the air passing in the 
transverse direction toward the rotational shaft 3 with respect to the 
blade as shown in FIG. 11, that is, the vector .sub..gamma. 1 in the speed 
triangle shown in FIG. 14. 
That is, the resultant speed vector changes in such a manner that the inlet 
angle of the front edge of the blade 5 is about 9.degree. at the inner end 
5b and it becomes smaller in going toward the central portion 5c, so that 
the axial inlet angle is determined to be adapted to this change. 
Referring to FIG. 2, a shaft hole 20 for fastening the rotational shaft 3 
is formed in a central portion of the impeller 1. As shown in FIG. 3, the 
impeller 1 has blades 5 and passages 10 between the blades 5 formed 
annularly in a space between radii R.sub.1 and R.sub.2 from the center of 
the shaft hole 20. In this case, the structure is arranged in such a 
manner that the cross sectional shape, which is obtained by cutting the 
passages 10 between the blades 5 with a plane passing through the center 
of the shaft hole 20, forms a semicircular arc. 
The cross sectional shape of the blade 5 is formed so as to be adapted to 
the aforesaid resultant speed vector of air in such a manner, for example, 
as shown in FIGS. 2 to 6. 
It is assumed, as shown in FIGS. 2 to 6, that the radius of a circle 
connecting the inner end 5b of the blade 5 and the center (the rotational 
center of the rotational shaft 3) of the shaft hole 20 is R.sub.1 the 
radius of a circle connecting the outer end 5a and the center of the shaft 
hole 20 is R2 and the radius of the midpoint between the inner end 5b and 
the outer end 5b is R.sub.c and, under this assumption, position 5c of 
point R.sub.c in the front edge of the blade 5 is delayed from the inner 
end 5b when viewed in the direction of rotation of the blade 5. Further, 
it is assumed that the inlet angle at the inner end 5b of the blade 5 is 
.sub..gamma. 1 and the inlet angle at the position 5c is .gamma..sub.c. 
both .gamma..sub.1 and .gamma..sub.c being less than 90.degree. and having 
the different values from each other with a relationship of .gamma..sub.1 
&gt;.gamma..sub.c held and, under this assumption, the blade 5 is formed by 
smoothly curved surface. Furthermore, the axial exit angle .gamma. is 
formed to be 90.degree. in a region from the central portion to the outer 
portion. In addition, as shown in FIG. 3, the front edge of the blade 5 is 
formed in such a manner that it is delayed with respect to the direction 
of the rotation of the impeller 1 in the region from its inner end to a 
position slightly outer than the midpoint and it extends radially with 
respect to the center of the shaft hole 20 in the region outer than the 
above-described region. That is, as shown in FIG. 3, it is arranged in 
such a manner that the angle .beta..sub.1 formed between the line tangent 
to the inner end 5b and the line connecting the midpoint 5c and the inner 
end 5b is less than 90.degree. and the angle .beta..sub.2 formed between 
the line tangent to the outer end 5a and the line connecting the midpoint 
5c and the outer end 5b is 90.degree.. The reason for this lies in that 
the direction of air flow is inverted at a portion slightly out from the 
central portion. 
The axial angle ".gamma." is defined, here, to be an angle formed by the 
smoothly curved surface in the rotational direction side of the front edge 
portion of the blade 5 with respect to the plane in the front edge of the 
blade 5. Alternatively, it may be defined with respect to the center line 
of the cross section of the blade 5. 
The angle .beta. in the circumferential direction is defined to be an angle 
which is in the opposite direction to the direction of rotation, among the 
angles formed at the intersections between concentric circles with respect 
to the axial center of the impeller 1 and the front edge of the blade 5 
between the lines tangent to the above-described circles and the 
above-described front edge. 
By forming the shape of the blade 5 in this manner, air passes through the 
inside portion of the casing 2 while swirling from the outer portion of 
the annular passage 8 formed in the casing 2 before being introduced into 
the inner portion of the impeller 1 along the surface of the blade 5 in 
the casing 2, thereby forming an internal flow passing smoothly and three 
dimensionally along the surface of the blade 5 without any significant 
speed reduction. That is, since air is introduced so as to be adapted to 
the inlet flow including the counter flow component in the circumferential 
direction, the air flow can be introduced between the blades 5 with the 
resistance reduced satisfactorily. The air which has reached the outer 
portion changes in its flowing direction due to the axial exit angle of 
90.degree., so that the direction of the internal flow is changed into the 
forward direction with respect to the circumferential direction and, as a 
result, the work is imparted to the fluid from the blade 5 by one swirl, 
thereby causing the pressure of air to be raised. In this manner, a smooth 
internal flow passing along the blade 5 can be formed three dimensionally 
in at least the inside portion without any significant speed reduction, so 
that a flow having no excessive swirls and stagnation can be created. As a 
result, the discharge pressure can be increased and a vortex flow blower 
whose noise is low can be obtained. 
FIG. 15 illustrates the ratios between the pressure coefficients in the 
present invention and those of the conventional example when the value of 
.beta..sub.1 of the impeller 1 according to the present invention is 
varied as 100, 90, 80, 60, 45 and 20 degrees and that of .gamma. of the 
same is varied as 10, 20, 45, 70, 80 and 90 degrees. The pressure 
coefficient .phi..sub.0 of the conventional example is obtained when all 
of .beta..sub.1, .beta..sub.2, .gamma..sub.i, .gamma..sub.c and 
.gamma..sub.0 are 90.degree.. The value of .gamma..sub.c when obtaining 
the pressure coefficient .phi. in an embodiment of the present invention 
was set to a value which is smaller than .gamma..sub.c by 13 degrees. The 
value of .beta..sub.2 was fixed to 90.degree. and the value of R.sub.1 
/R.sub.2 to a constant value of 0.58. 
If the values in the frame are larger than 1.0, it means that the pressure 
coefficient is higher than that of the conventional example. If it is 
somewhat larger than 1.7, the pressure coefficient corresponds to 14 or 
more. 
Therefore, the pressure coefficient can be increased to a value greater 
than 14 when .beta..sub.1 is 45 to 80 degrees, .gamma..sub.i by 13 
degrees. 
Similarly to FIG. 15, FIG. 16 illustrates the values of the pressure 
coefficient ratio when the value of .beta..sub.2 was set to 70 degrees. As 
shown in FIG. 16, the pressure coefficient ratio obtainable when 
.beta..sub.2 is 70 degrees less than that when .beta..sub.2 is 90 degrees. 
However, the pressure coefficient in this case is larger than that 
according to the conventional example when .beta..sub.1 is 45 to 80 
degrees, .gamma.i is 20 to 70 degrees, and .gamma..sub.c is smaller than 
.gamma..sub.i by 13.degree.. 
That is, a fact is shown that the axial inlet angle, and the inlet angle in 
the circumferential direction of the front edge of the blade 5 are 
critical factors of the aerodynamic performance. 
FIG. 17 illustrate the relationship between the flow rate coefficient .phi. 
and pressure coefficient .phi. in each of the embodiment of the present 
invention and the conventional vortex flow blower. It can be understood 
that both the flow rate coefficient and the pressure coefficient in the 
embodiment of the present invention are higher than those in the 
conventional vortex flow blower. 
FIG. 18 illustrates the relationship between the flow rate coefficient 
.phi. and the pressure coefficient .phi. when the inlet angle .beta..sub.1 
in the circumferential direction is set to 20 degrees and 90 degrees. As 
seen from this drawing, both the flow rate coefficient and the pressure 
coefficient are higher when the inlet angle .beta..sub.1 in the 
circumferential direction is set to 20 degrees. 
FIG. 19 illustrates the ratios of the pressure coefficients when the inlet 
angle .beta..sub.1 in the circumferential direction is varied. In this 
case, the exit angle .beta..sub.2 in the circumferential direction is 
fixed to 90 degrees and they are compared with the case in which both 
.beta..sub.1 and .beta..sub.2 are 90 degrees. As shown in FIG. 19 the 
range from 90 degrees to 20 degrees the lesser the value of .beta..sub.1 
is, the larger becomes the pressure coefficient ratio. 
FIG. 20 illustrates the ratios of the pressure coefficients where the axial 
inlet angle .gamma..sub.1 in the front edge of the blade 5 is varied with 
both .beta..sub.1 and .beta..sub.2 set to 90 degrees, as a standard in the 
case where both .gamma..sub.1 and .beta..sub.2 is set to 90 degrees. As 
shown in FIG. 20 the lesser the value of .gamma..sub.1 is, the larger the 
pressure coefficient ratio. 
As described above, at least the axial inlet angle in the inner portion in 
the front edge of the blade 5 and the inlet angle in the circumferential 
direction are determined to be adapted to the resultant vector of the 
speed vector of the air flow passing through the annular passage 8 and the 
speed vector of the air flow passing in the traversing direction toward 
the rotational shaft in the annular passage 8 and thereby form the three 
dimensionally shaped blades. Therefore, turbulence of the internal flow 
such as swirls and stagnation of air introduced into the internal portion 
can be satisfactorily prevented and, as a result, the aerodynamic 
performance can be significantly improved in comparison with the 
conventional vortex flow blower. That is, an advantage can be obtained in 
that the aerodynamic performance can be significantly improved by forming 
the inner portion of the blade into a three dimensional shape which can be 
adapted to the flow of fluid. As a result, the drawback inherent in the 
conventional vortex flow blower in that the pressure coefficient is 
inevitably reduced when the ratio R.sub.1 /R.sub.2 is reduced to 0.75 or 
less for the purpose of reducing the size of the vortex flow blower can be 
overcome. Therefore, even if the ratio R.sub.1 /R.sub.2 is set to 0.75 or 
less and 0.3 or more, the discharge pressure can be significantly 
increased in comparison with the conventional vortex flow blower and, as a 
result, an advantage can be obtained in that the outer diameter of the 
impeller can be reduced and the size of the vortex flow blower can thereby 
be reduced. 
In the embodiment of FIGS. 21-35, the shape of the blade 5 from the inner 
portion to the central portion thereof is formed as shown in FIGS. 2 and 
3. Further, as described above, the speed distribution of air with respect 
to the speed of the blade 5 in the annular passage 8 becomes, as shown in 
FIG. 10, positive with respect to the direction of the rotation of the 
impeller 1 and, in the portion from the central portion 5c to the outer 
end 5a, the speed component in the annular passage 8 becomes steeply 
increased in the forward direction with respect to the direction of the 
rotation of the blades 5. Therefore, the shape of the blade facing the 
annular passage 8 is formed to project from the central portion 5c to the 
outer end 5b in the direction of the rotation of the blade 5. 
That is, in this embodiment, the exit angle .beta..sub.2 in the 
circumferential direction is determined to 90.degree. or more in order to 
make the air flow on the outer side uniform by forming the blade 5 in such 
a manner that it projects from its central portion 5c toward the outer end 
5a. 
On the other hand, as mentioned before, the axial outlet angle .gamma. is 
determined to be adapted to the vector w.sub.o in the speed triangle shown 
in FIG. 12. 
Assuming that the inlet angle at the front edge of the blade 5 in the outer 
midpoint at which the radius is a value expressed by R.sub.0 =(R.sub.2 
+R.sub.c)/2 and that in the inner midpoint at which the radius is a value 
expressed by R.sub.i =(R.sub.1 +R.sub.c)/2 are respectively .gamma..sub.0 
and .gamma..sub.i, the shape of the blade 5 is formed by smoothly curved 
surface (see FIGS. 22 to 26) formed in such a manner that both 
.gamma..sub.c and .gamma..sub.i are less than 90 degrees, and the 
relationships of .gamma..sub.0 &gt;.gamma..sub.c and .gamma..sub.i 
&gt;.gamma..sub.c are met, as shown in FIGS. 24 to 26 and 27. Air introduced 
to be adapted to the inlet flow including the counter flow component in 
the circumferential direction and having reached the outer portion changes 
the direction of the internal flow into the forward direction between the 
blades 5 since the axial exit angle .gamma..sub.0 is provided. 
Furthermore, since the exit angle .beta..sub.2 in the circumferential 
direction is provided, the slow speed flow near the midpoint and the high 
speed flows in the vicinity of the outer and inner ends of the blade 5 can 
be synchronized with one another. As a result, stagnation causing internal 
loss can be prevented, the swirling component can be increased and the 
change in air speed between the blades 5 can be reduced. Since the axial 
exit angle .gamma..sub.0 and the exit angle .beta..sub.2 in the 
circumferential direction are provided as described above, the work 
obtainable by one swirl of the blade 5 can be greater and the internal 
loss taking place in the action of the blade 5 can be restricted. As a 
result, the obtainable pressure can be increased. 
The exit angle .beta..sub.2 in the circumferential direction causes, 
between the blades, the flow near the midpoint whose internal speed is 
slow and the flows in the vicinity of outer and inner ends of the blade 5 
whose internal speeds are high to be synchronized with one another. As a 
result, turbulence of the flow due to stagnation, which causes the 
internal pressure loss, can be prevented. 
As a result of the shape of the blade 5 in which the axial exit angle 
.gamma..sub.0 and the exit angle .beta..sub.2 in the circumferential 
direction are provided, the blade 5 acts to form a three dimensional 
smooth internal flow whose change in speed can be reduced in the passage 
8, so that the aerodynamic performance exhibiting a significantly high 
pressure can be obtained. 
FIGS. 29-36 shown more detailedly the impeller 1 shown in FIGS. 21-27. And, 
FIG. 28 is a front view of the impeller 1 and FIG. 29 shows a part of the 
impeller 1 in sections. The impeller 1 is sectioned radially at various 
positions IV.sub.1 and IV.sub.5 shown in FIG. 29(a) and each section 
thereof is shown respectively in FIG. 29(c)-(g) in its circumferentially 
developed state. Each of the blades 5 constituting the impeller 1 is 
formed by a three dimensional curved surface. And, the blade 5 has such a 
shape that its central or middle portion 5c is retracted, with respect to 
the rotational direction F of the impeller, in comparison with its outer 
end 5a and inner end 5b. That is, a front edge shape of the blade 5 
exhibits a bent, flattened V-shape, so a point 84 in FIG. 29(a) and a 
point 88 in FIG. 29(g) are more circumferentially retracted than a point 
86 in FIG. 29(e). Further, the blade 5 is formed, at its side opposing the 
casing (i.e., at its opening side 5t), so as to be inclined in general 
with respect to the rotational direction F. On the other hand, at its 
shroud wall surface side 5s the blade 5 is formed so as to be 
substantially perpendicular to the shroud wall surface at every section 
[FIG. 29(c)-(g)]. 
As shown in FIG. 29(b), the inflowing flow (shown with arrow mark) from the 
inlet port flows into the impeller from its inner side and flows out from 
its outer side along the shroud wall surface while becoming a swirling 
flow. Therefore, at sections IV.sub.4 --IV.sub.4 and IV.sub.5 --IV.sub.5 
constituting an inflow portion of the flow the blade has a composite shape 
wherein two inclined surfaces (i.e., a surface inclined with respect to 
the rotational direction F of the impeller 1 and a surface inclined with 
respect to a direction perpendicular to the wall surface of the shroud 11) 
are combined. 
The flow flowing into the flow direction converting position from the fluid 
inflow portion is curved at a substantially right angle in its flow 
direction. As shown in FIG. 29(e), this flow direction converting portion 
has a portion 80 adjacent the shroud bottom wall surface, which is most 
remote from the casing, and a cross sectional shape of the passage becomes 
substantially rectangular [an upper half in FIG. 29(e)] because, as 
mentioned above, at the portion 80 adjacent the shroud bottom wall surface 
the blade 5 is formed substantially perpendicular to the shroud bottom 
wall surface. Further, a center portion 82, which is a center of the blade 
5 as a whole, is formed substantially right above the portion 80 adjacent 
the shroud bottom wall surface, i.e., at a side which corresponds to the 
portion 80 adjacent the shroud bottom wall surface and is more adjacent to 
the casing. 
Further, the fluid outflow portion exists at an outer circumferential side 
shown in FIG. 29(c) and (d), and in this portion the blade 5 has at its 
front edge side such a shape that it is inclined to a side of the 
rotational direction F of the impeller 1 and is inclined also with respect 
to a direction perpendicular to the wall surface of the shroud 11. 
The above-mentioned fluid inflow portion, flow direction converting portion 
and fluid outflow portion are formed by a smooth, curved surface. 
FIG. 30 shows sections of a part of the impeller 1 radially sectioned at 
various levels. In the sections at IH.sub.3 and IH.sub.4 adjacent the 
shroud bottom wall surface the blade 5 extends perpendicular to the shroud 
wall surface. 
In the impeller 1 having the blades each formed in this manner, three 
dimensional passages are formed, and the fluid is smoothly introduced into 
the interblade passage 10 by the fluid inflow portion wherein the blades 
each have the composite shape wherein two inclined surfaces are combined, 
and then by the central flow direction converting portion the fluid is 
guided to a direction perpendicular to the rotational direction of the 
impeller 1 and, at the same time, in this flow direction converting 
portion the fluid is accelerated, and thereafter the fluid is smoothly 
discharged into the annular passage 8 in the casing by the fluid outflow 
portion with the blades each having the composite shape wherein two 
inclined surfaces are combined. 
In other words, between the neighboring blades 5 the following passages are 
formed: namely, an inflow passage along the swirling flow between the 
neighboring blades 5 at the fluid inflow portion, a guide passage at the 
flow direction converting portion, which guides the fluid introduced by 
the inflow passage to a direction perpendicular to the rotational 
direction F of the impeller 1, and an outflow passage between the 
neighboring blades 5 at the fluid outflow portion, which discharges the 
fluid guided by the guide passage to a direction along the swirling flow. 
Moreover, these passages, i.e., the inflow passage, guide passage, guide 
passage and outflow passage, are formed in a smoothly continuous state. 
A shape of single blade 5 is shown in FIGS. 31-35. FIG. 31(a) is a side 
view of the blade, FIG. 31(b) is a front view thereof and FIG. 31(c) is a 
plan view thereof. FIG. 32 shows radially various positions at which the 
blade is sectioned, and FIG. 33 shows sectional shapes thereof. This blade 
is one which is used in the impeller 1 shown in FIGS. 28-30. FIG. 34 shows 
various positions at which the blade 5 shown in FIG. 31 is sectioned in 
the direction of its height, i.e., from its front edge to its shroud 
bottom side, and FIG. 35 detailedly shows sectional shapes thereof. 
FIG. 36 shows an aspect of the impeller 1 shown in FIG. 28, from which the 
shroud has been removed. Further, FIG. 37 is a perspective view of a 
single blade 5 seen from a substantially upper-front side, and FIG. 38 is 
a perspective view of the blade 5 seen from a upper-lateral side. Adjacent 
the shroud wall surface, the blade is perpendicular to the shroud wall 
surface. 
The experimental results of the blade 5 whose outer shape is three 
dimensionally formed are shown in FIG. 39 in comparison with the 
conventional vortex flow blower in which the shape of blade is set in such 
a manner that .beta..sub.1 =90 degrees, .beta..sub.2 =90 degrees, 
.gamma..sub.0 =90 degrees and R.sub.1 /R.sub.2 =0.58. As seen from this 
drawing, when the outer shape is three dimensionally formed as described 
above, the pressure coefficient can be improved twice or more. In an 
experiment involving the vortex flow blower having the conventional two 
dimensionally formed blade in which only the exit angle .beta..sub.2 in 
the circumferential direction was taken into consideration, as shown in 
FIGS. 40 to 41, a satisfactory maximum pressure coefficient was displayed 
when .beta..sub.2 was about 90 degrees. However, if the axial exit angle 
.gamma..sub.0 is varied, the pressure coefficient becomes larger in 
comparison with the conventional vortex flow blower. Because of the 
above-described reason, with respect to the embodiment shown in FIG. 23, 
the pressure coefficient can be significantly improved by simultaneously 
changing the axial exit angle .gamma..sub.0 to 45 degrees and the exit 
angle .beta..sub.2 in the circumferential direction to 115 degrees. 
FIG. 43 is a map showing the pressure coefficient ratios when the axial 
exit angle .gamma..sub.0 and the exit angle .beta..sub.2 in the 
circumferential direction are varied. As seen from this map, the pressure 
coefficient ratio can be significantly improved in the regions of 
100.degree..ltoreq..beta..sub.2 .ltoreq.135.degree. and 
20.degree..ltoreq..gamma..sub.0 .ltoreq.70.degree.. 
FIG. 44 is a graph which illustrates the experimental results when the 
outer portion of the blade 5 is three dimensionally formed in addition to 
the inner portion of the same which has been three dimensionally formed. 
As shown in FIG. 23, the pressure coefficient can be further improved by 
three dimensionally forming the blade 5 as a whole, thereby making it 
possible to obtain a pressure coefficient of about 25. 
In this embodiment, the impeller 1 is, as shown in FIG. 23, arranged to 
have a blade 5 whose shape at the front edge is formed in such a manner 
that its central portion 5c connecting the inner portion and the outer 
portion of the blade 5 is steeply changed in its angle, but, as shown in 
FIG. 45, the shape of the blade may be modified in such a manner that the 
angle is gradually changed from the inner end 5b to the outer end 5a. 
FIG. 46 illustrates the shape of partition wall 25 for partitioning the 
inlet port and the outlet port formed in the casing 2, the partition wall 
being capable of significantly eliminating noise. The casing 2 has a 
circular arc passage 8 whose cross section facing in the direction running 
parallel to the axial line of the rotational shaft 3 is in the form of a 
semicircular arc groove. The groove is provided with a partition wall 25 
in a part thereof, with the partition wall 25 facing the impeller 1 with a 
small gap retained there between. An end of the circular arc passage 8 is 
connected to the inlet side passage 6a, and the other end of the same is 
connected to the discharge side passage 6b. The inlet side passage 6a and 
the outlet side passage 6b. The inlet side passage 6a and the outlet side 
passage 6b run parallel to each other in the muffler 7 which also serves 
as the base member. 
A guide 26, adjacent to the inlet port, is provided in a portion of the 
partition wall 25 adjacent to the inlet port. A front portion 26a of the 
guide 26, adjacent to the inlet port, is arranged to be substantially 
horizontal so as to make the blade 5 cut (intersect the front edge of the 
blade 5) from outside. It is considered that the front portion 26a acts to 
smooth introduced air, which has been introduced into the circular arc 
passage 8 through the inlet port 6c, to the inlet port (the portion in 
which the arrows face the left hand direction in FIG. 11) of the blade 5. 
When viewed from the axial direction, the inlet port 6c is hidden behind 
the guide 26 adjacent to the inlet port. This acts to prevent noise 
generated in the circular arc passage 8 from being directly transmitted to 
the passage 6a adjacent to the inlet port for the purpose of insulating 
noise. 
A guide 28, adjacent to the outlet port is provided with the partition wall 
25 adjacent to the outlet port. The front end 28a of the guide 28 adjacent 
to the outlet port is formed in such a manner that its substantially 
central portion 28b (the portion which agrees with a point of the blade 5 
at which the flow is inverted) projects in the direction opposite to the 
direction F of the rotation of the impeller 1 so as to make the blade 5 
cut (intersect the front edge of the blade 5) from inside. It is 
considered that the front end 28a acts to guide air to be discharged from 
the circular arc passage 8 to the outlet port 6d so as to be smoothly 
discharged from the outlet portion (the portion in which arrows face the 
right hand direction in FIG. 11) of the blade 5. Further, when viewed from 
the axial direction, the outlet port 6d is substantially hidden behind the 
guide 28 adjacent to the outlet port. This acts to prevent noise generated 
in the circular arc passage 8 from being directly transmitted to the 
passage 6b adjacent to the outlet port for the purpose of insulating 
noise. 
FIG. 47 is a graph which illustrates data about noise actually measured 
when a vortex flow blower composed by combining of the casing 2 shown in 
FIG. 46 and the impeller 1 shown in FIG. 36 is operated. 
It can be clearly seen that the guide 28 adjacent to the inlet port and the 
guide 26 adjacent to the outlet port significantly assist in the reduction 
of noise when compared with noise data shown in FIG. 47 in the case where 
the vortex flow blower from which the guide 26 adjacent to the inlet port 
and the guide 28 have been removed is operated. 
In an experiment in which dimension L from 26b to 28b (the portion which 
agrees with the point of the blade 5 at which the direction of the flow is 
inverted) in the circular arc passage 8 was selected to meet the following 
relationship: 
EQU L=1/4.lambda.(2n+1) 
where 
.lambda.=C/f 
f=Z.times.N 
Z: the number of the blades 5 
N: the rotational speed of the shroud 
C: acoustic velocity 
n=0, 1, 2, 3, . . . 
the maximum noise level shown in FIG. 47 was further lowered by 4 dB. 
In the embodiment of FIG. 48, the impeller 1 having the blades 5 is 
disposed on the side adjacent to the motor 4 and the casing 2 is disposed 
to face the impeller 1. As a result, the degree of the overhang of the 
impeller 1 can be reduced. In this manner, since the impeller 1, which is 
a body of rotation, is disposed adjacent to the bearing portion, 
vibrations of the impeller 1 can be significantly reduced, thereby causing 
the durability against the radial loads to be improved. 
In the embodiment shown in FIGS. 49 to 53, an impeller, which is a double 
blade impeller having on its both sides the shape of the blade shown in 
FIGS. 23 to 27, is employed. FIG. 49 is a perspective view which 
illustrates the vortex flow blower in which the double blade impeller is 
mounted. In this embodiment, the casing 2 is formed so as to cover the 
both sides of the double blades. The annular passage 8 is formed on both 
sides of the double blades. Partition walls are provided on both sides of 
the casing 2 so as to hinder the communication between the outlet port 6d 
and the inlet port 6c. The inlet side passage 6a and the outlet side 
passage 6b are provided adjacent to the motor 4. 
By virtue of the last-mentioned features, a vortex flow blower exhibiting a 
high pressure coefficient and capable of obtaining a large wind quantity 
can be provided. Furthermore, another effect can be obtained in that the 
outer diameter of the casing can be reduced and the size of the vortex 
flow blower can thereby be reduced. 
Next, a method of manufacturing an impeller of the vortex flow blower 
according to the present invention will be described. 
In the embodiment of FIGS. 54 to 62 the blade 5, as shown in FIGS. 63, and 
the shroud 11 are independently formed. Then, the shroud 11 having the 
annular groove 45 and a plurality of blades 5 are coupled and secured to 
each other so that the impeller 1 is manufactured. 
In this manner, by forming the blades 5 and the shroud 11 independently, 
the shroud 11 can be manufactured by using a mold formed two 
dimensionally, so that it becomes possible to be mass-produced by the 
die-casting or metal mold casting process. Further, even if the blade 5 is 
in the form of a complicated shape, it becomes possible to be die-cast or 
press-formed, so that the impeller having the three dimensionally shaped 
blades can be easily manufactured. 
Further, also in another embodiment described later, the blade 5 can be 
made of a thin and light weight material since the blades 5 are 
independently manufactured as described above. Therefore, an effect can be 
obtained in that the secondary moment of inertia of the impeller can be 
reduced. 
Further, as shown in FIG. 63, since only the blades 5 can be formed to have 
various shapes, impellers having different aerodynamic performances can be 
easily manufactured. 
In a manufacturing method shown in FIGS. 54 and 55, the shroud 11, in which 
the annular groove 45 is formed and a plurality of insertion holes 40 are 
formed, and the blade 5 provided with a plurality of caulking projections 
41 are manufactured. The shroud 11 and the blade 5 are coupled to each 
other in such a manner that the caulking projections 41 formed on the 
blade 5 are inserted into the insertion holes 40 formed in the shroud 11, 
and then they are secured by plastically working the caulking projections 
41. 
The method of plastically working may be a cold working or a hot working. 
It is preferable in terms of the appearance after subjected to the plastic 
working that the following method be employed namely, as shown in FIG. 56, 
an upper electrode 42 having a predetermined conductivity and high 
temperature strength and a lower copper electrode 43 are used and only the 
caulking projections 41 are practically worked with heat generated by an 
electric current being applied thereto. 
Further, as occasion demands, as shown in FIG. 57 when the impeller is 
manufactured by fitting the blade 5 within the annular groove 45 formed in 
the shroud 11 before being press formed, the blade 5 can be stabilized and 
further satisfactorily plastically deformed at the time of caulking, so 
that the airtightness between the blades 5 can be also improved. 
FIGS. 58 and 59 illustrate the cross sectional shape of the impeller which 
has been cut in the circumferential direction relative to the rotational 
center. As shown in FIG. 58, an insertion groove 44 having a width which 
is slightly narrower than the width of the blade 5 is formed in the 
annular groove 45 formed in the shroud 11. The blade 5 is press-fitted 
into the insertion groove 44. As a result, the airtightness between the 
blade 5 and the shroud 1 can be maintained. Further, as shown in FIG. 59, 
the fastening force can be further increased when the blade 5, having the 
caulking projections 41, is press-fitted and the caulking projections 41 
are plastically worked. 
When the airtightness is desired to be improved, the corner portions 
between the blades 5 and the shroud 11 may be filled with a filler 46 as 
shown in FIG. 60. Since the filler 46 acts to permit air to smoothly flow 
in addition to improving the airtightness, it is preferable from a view 
point of improving the aerodynamic performance. As shown in FIG. 61, the 
filler 46 can be easily formed by brazing the blade 5, to which a skin 
material 47 of the low melting point has been brazed, in a furnace. 
When the brazing shown in FIGS. 60 and 61 is performed, flux must be 
applied and then removed after it completed its roll. However, as shown in 
FIG. 62 when the impeller 1, in which the blade 5 has been secured to the 
shroud 11 by being press-fitted or by caulking its projections, is 
ultrasonic soldered in a jet type soldering tank 17 provided with a 
ultrasonic oscillator 16 while rotating the impeller 1, an oxide film 
formed on the surface to be soldered is broken by the supersonic erosion 
action, so that the application of the flux becomes unnecessary, thereby 
making it possible to efficiently manufacture the impeller 1 exhibiting 
excellent airtightness. 
Another manufacturing method can be employed in which an adhesive is 
applied to the insertion groove 44 formed in the annular groove 45. As a 
result, the shape shown in FIG. 60 can be easily formed. That is, when the 
blade 5 is press-fitted into the insertion groove 44 formed in the shroud 
11, a part of the adhesive overflows to the corner portion and solidifies, 
thereby causing an effect similar to that obtainable when the filler has 
been filled. 
According to the above-described manufacturing methods, impellers of 
complicated shapes can be easily manufactured and thus obtained impellers 
can exhibit satisfactory airtightness. 
In the embodiment of FIGS. 64-67, the blade 5 and the shroud 11 which have 
been independently manufactured are coupled to each other by using a 
screw. 
In an embodiment shown in FIG. 64, the shroud 11 may be secured to the 
wheel 9 by a screw 48 or it may be secured as shown in FIGS. 65 and 67 in 
such a manner that a part of the blade 5 is expanded so as to become an 
expansion portion 49 and a screw hole 50 is formed in the expansion 
portion 49 so as to be secured by the screw 48. It is preferable in terms 
of the performance that the expansion portion 49 be formed on the back 
side of the blade 5. Alternatively, a ring 51 connecting the outer front 
end of the blade 5 is manufactured integrally with the blade 5 and the 
wheel 9, and the shroud 11 is, as shown in FIG. 66, inserted between the 
ring 51 and the wheel 9 so as to be secured. 
The wheel 9 may be integrally formed as a whole or only a part of the wheel 
9 may be integrally formed with the blade 5. 
In this way, since the blade and the shroud are independently manufactured 
and then they are coupled to each other, the mold can, of course, be 
manufactured easily and the mold can be readily removed after the casting 
has been completed. Therefore, impellers of a complicated shape can be 
readily manufactured. 
Further, as described above, it is possible to form the annular groove 45 
in such a manner that its width becomes less than that of the blade 5 and 
to provide the blade 5 in the groove 45 by inserting it while being 
elastically deformed, by using the adhesive or by using the filler. 
A further embodiment of the present invention is shown in FIGS. 68-73. This 
embodiment differs from the above-mentioned embodiment in a point that a 
blade thickness is changed. That is, as mentioned previously, at the fluid 
inflow portion the blade is formed in such a shape that it is inclined 
with respect to both the rotational direction of the impeller 1 and a 
direction perpendicular to the wall surface of the shroud 11. And, the 
center portion 82 of the blade 5, which is situated above the portion 80 
adjacent the shroud bottom wall, is formed substantially perpendicular to 
the bottom wall of the shroud 11. 
In consequence, the flow flowing through the impeller is largely curved 
while passing from the inflow portion to the center portion, thereby 
forming a large turbulence at a backface side of the blade 5, and this 
becomes one of the causes of a pressure loss. This embodiment can suppress 
this turbulence formed at the backface 92 side of the blade and, as shown 
in FIGS. 68-71, a thickness of the blade at a side adjacent the shroud is 
increased in its backface side, thereby reducing a curve of the passage. 
FIG. 71 shows sections corresponding to FIGS. 4-6 in the first embodiment, 
and the blade thickness T.sub.2 is changed in the backface side at every 
section. 
Next, a relationship between a length l of the thus formed passage in the 
impeller and a width S of the interblade passage is shown in FIG. 72. In 
terms of a inclination .alpha. of the passage width to the passage length, 
which represents a degree of spread of the flow, in a conventional example 
there is a steeply spreading passage portion whose maximum value 
.alpha..sub.1 is greater than 10.degree., whereas in this embodiment the 
maximum value .alpha..sub.2 is smaller than .alpha..sub.1 and so the 
spread of passage is gentle. Incidentally in FIG. 72 the marks T.sub.1 and 
S.sub.1 represent a blade thickness and an interblade passage width, 
respectively, in a case wherein the blade thickness is not changed in the 
above-mentioned embodiment. 
Further, FIG. 73 shows a flow rate-pressure characteristic of a vortex flow 
blower wherein an impeller of this embodiment is used. In FIG. 73 the 
characteristic of a conventional vortex flow blower is shown by a broken 
line. Owing to the fact that the flow in the backface side of the blade 
becomes smooth, a pressure loss is reduced, a pressure characteristic is 
also improved and a maximum capacity is increased as well. 
The first advantage according to the present invention can be obtained from 
the blade formed in such a manner that at least its inner portion is three 
dimensionally formed, thereby causing air to be smoothly introduced so as 
to be adapted to the speed vector of the swirling air flow. As a result, 
the discharge pressure can be significantly raised. 
The second advantage can be obtained from the blade formed in such a manner 
that its shape is three dimensionally formed so as to be adapted to the 
speed vector of the swirling flow. Therefore, swirls and stagnation can be 
significantly prevented. As a result, a low noise vortex flow blower can 
be obtained. 
The third advantage can be obtained from the partition wall formed in such 
a manner that its front end adjacent to the inlet port of the vortex flow 
blower is cut by the blade from the outside while the front end of the 
same adjacent to the outlet port is cut by the blade from the inside. 
Therefore, the air flow from the inlet port to the circular arc passage 
and the air flow discharged from the circular arc passage through the 
outlet port can be made smooth. As a result, noise can be extremely 
reduced. 
The fourth advantage can be obtained from the blade formed in such a manner 
that the shape of the blade in the impeller is three dimensionally formed 
as mentioned before and R.sub.1 /R.sub.2 can thereby be set to 0.75 or 
less and 0.3 or more. As a result, the size of the vortex flow blower can 
be reduced. 
The fifth advantage can be obtained from the blade formed in such a manner 
that the shape of the blade at the outer portion of the impeller is 
retracted and the axial outlet angle is arranged to be 90.degree. or more. 
Therefore, work imparted by the blade to air can be restricted. As a 
result, the discharge pressure and the required operating power can be 
controlled to a low level. 
The sixth advantage can be obtained from the blade formed in such a manner 
that a middle portion in the front edge of the blade is retracted, a point 
at which the blade is connected to the shroud bottom wall surface is more 
retracted than the middle portion in the front edge and a center portion 
of the blade is provided in a direction substantially right above the 
shroud bottom wall surface. As a result, the flow flowing into the 
interblade passage can be efficiently swirled, thereby making it possible 
to increase a discharge pressure. 
The seventh advantage can be obtained from the blade formed in such a 
manner that a thickness of the blade in its backface side is made larger 
only at a side adjacent the shroud wall surface than at other portions. As 
a result, an exfoliation and turbulence of the flow, which occur in the 
backface side of the blade, can be suppressed, thereby making it possible 
to generate a smooth flow as well as to achieve a high discharge pressure 
and high discharge capacity. 
The eighth advantage can be obtained from the method of manufacturing an 
impeller, which is constituted in such a manner that the blade and the 
shroud are independently manufactured and then they are coupled to each 
other. Therefore, impeller of a complicated shape can be readily 
manufactured. 
Further, as occasion demands, the airtightness can be improved and the flow 
can be made smooth by using a filler or an adhesive. 
The ninth advantage lies in that the secondary moment of inertia of the 
impeller can be reduced and the starting torque required for the motor can 
be reduced since the blade can be independently manufactured and made of a 
thin and light material. 
The tenth advantage lies in that impellers of different shapes can be 
readily manufactured since only the blade can be independently 
manufactured and, as a result, impellers of different aerodynamic 
performance can be readily manufactured.