U.S. patent application number 09/774205 was filed with the patent office on 2002-10-03 for axial-flow fan having inner and outer blades.
Invention is credited to Medamaranahally, Lakshimikantha.
Application Number | 20020141871 09/774205 |
Document ID | / |
Family ID | 25100535 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020141871 |
Kind Code |
A1 |
Medamaranahally,
Lakshimikantha |
October 3, 2002 |
Axial-flow fan having inner and outer blades
Abstract
There is provided an axial-flow fan which is capable of
producing axial-flow wind near the outer circumference of a fan
clutch to extend the functional life of the fan clutch, and which
is capable of decreasing the inertia moment of an engine cooling
plastic fan and hence vibration loads to be transmitted to the
bearing of the fan clutch, thereby extending the structural life of
the fan clutch and increasing the burst speed of the engine cooling
plastic fan. The axial-flow fan includes an inner plastic hub,
plural inner plastic blades each of which extends radially from the
inner plastic hub and is twisted near its extending end and
connected to a portion immediately below the base of the
corresponding one of the outside blades, an outer plastic hub
connected to the plural inner plastic blades, and plural outer
plastic blades which extend radially from the outer plastic
hub.
Inventors: |
Medamaranahally,
Lakshimikantha; (Novi, MI) |
Correspondence
Address: |
CASELLA & HESPOS
274 MADISON AVENUE
NEW YORK
NY
10016
|
Family ID: |
25100535 |
Appl. No.: |
09/774205 |
Filed: |
January 30, 2001 |
Current U.S.
Class: |
416/193R ;
416/203 |
Current CPC
Class: |
F04D 29/326 20130101;
F04D 29/023 20130101; F05D 2300/43 20130101; F05D 2260/96
20130101 |
Class at
Publication: |
416/193.00R ;
416/203 |
International
Class: |
F04D 029/38 |
Claims
1. An axial-flow fan fitted to an output shaft of an internal
combustion engine and provided with inner and outer blades,
comprising: an inner plastic hub; plural inner plastic blades each
of which extends radially from the inner plastic hub and has a base
side parallel to a plane of rotation and is twisted near its
extending end and connected to a portion immediately below a base
of the corresponding one of the outside blades; an outer plastic
hub connected to the plural inner plastic blades; and plural outer
plastic blades which extend radially from the outer plastic
hub.
2. An axial-flow fan provided with inner and outer blades according
to claim 1, wherein a steel insert is embedded in the inner plastic
hub.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an improved structure of an
engine-driven type of axial-flow plastic cooling fan to be used for
cooling an internal combustion engine for an automobile or a
similar engine and, more particularly, to an synthetic-resin-made
engine cooling fan which has a reinforced structure made of a hub
and fan blades formed as an integral component and is driven mainly
via a fan clutch, and which is improved in the performance of
cooling the fan clutch.
[0003] 2. Description of the Prior Arts
[0004] This kind of engine cooling fan has heretofore been divided
into two major structure types of axial-flow plastic fans. Either
of these types of plastic fans has a circular steel insert for
fitting a fan to a fan clutch fitted to the shaft of a water pump.
FIGS. 5 and 6 respectively illustrate the states where the two
prior art major structure types of axial-flow fans are fitted to
fan clutches. In the axial-flow plastic fan shown in FIG. 5, a
circular steel insert 20 having a locking hole 21 in its outer
circumferential portion is bent by 90.degree. near the outer
circumferential portion, and that bent portion is embedded in a
plastic hub 22 which has a structure integral with a fan blade 23.
In the axial-flow plastic fan shown in FIG. 6, a circular steel
insert 30 which does not have a bent portion but has a locking hole
31 in its outer circumferential portion is embedded in a plastic
hub 32 which has a structure integral with a fan blade 33 in a
similar manner to the plastic hub 22. The respective axial-flow
plastic fans shown in FIGS. 5 and 6 are fitted to fan clutches 24
and 34.
[0005] The respective axial-flow plastic fans shown in FIGS. 5 and
6 have structures in which the steel inserts 20 and 30 extend into
the plastic hubs 22 and 32. Plastics are respectively
injection-molded together with the steel inserts 20 and 30 so that
the steel inserts 20 and 30 are respectively embedded into the
plastic hubs 22 and 32, and the plastics are charged into the
locking holes 21 and 31, thereby providing full adhesion or
connection between the steel insert 20 and the plastic hub 22 as
well as between the steel insert 30 and the plastic hub 32. Each of
these two types of fans serves as an engine cooling fan for an
internal combustion engine which has a cylindrical hub and plural
fan blades radially disposed on the outer circumferential wall of
the cylindrical hub with the cylindrical hub and the plural blades
being integrally formed by injection molding with plastics. Both of
the prior art structures only have one hub and outside plastic
blades.
[0006] In general, engine cooling fans are subjected to the
influence of hard vibrations of engines during high-speed rotations
thereof in particular. For this reason, the engine cooling fans are
repetitively subjected to the influences of not only vibrations of
engines but also resonance phenomena caused by nonuniform
aerodynamic loads due to the complicated and nonuniform shapes of
the lower hoods of automobiles. Moreover, such an engine cooling
fan is also subjected to vibration loads due to the deviation
between the axis of a water pump and the axis of the fan as well as
the static unbalance of the fan which causes the dynamic unbalance
thereof during high-speed rotation. Since the engine cooling fan is
driven via a fan clutch, the vibration force of the fan is
transmitted to the bearing of the fan clutch. As the mass and the
inertia moment of the fan are larger, the force to be transmitted
to the bearing of the fan clutch is larger. If large vibration
loads are repetitively applied to the bearing of the fan clutch,
fatigue and other damages occur in the bearing. There has been,
therefore, the risk that the prior art engine cooling fans give
structural damage to the fan bearings of fan clutches.
[0007] There are many cases where another problem of a viscous fan
clutch which drives a prior-art general axial-flow plastic fan
gives rise to degradation of the silicone oil of the fan clutch
which drives the engine cooling fan with high viscosity. High
shearing stress which occurs in the silicon oil owing to a slip
between the engine cooling fan and the fan clutch generates heat
which causes the temperature of the silicone oil to rise to an
extent exceeding 170.degree. C. If this viscous silicone oil is
exposed to such a high temperature, the characteristics of the
silicone oil change and the viscosity retention of the silicone oil
decreases with time. As a result, the malfunction of the fan clutch
occurs. To avoid this malfunction, it is necessary to improve the
capability to cool the clutch.
[0008] However, the structure of the prior art axial-flow fans
shown in each of FIGS. 5 and 6 has the problem that air flows near
the outer circumference of the fan clutch circulate in the axial
direction (axial flow) and cannot reach an engine side by the
planer steel inserts 20 and 30 of major diameter of a internal hub,
so that the fan clutch cannot be fully cooled. Either of such prior
art fans has a large steel insert and hence the problem that the
inertia moment of the plastic fan increases. As a result, since
loads to be transmitted to the bearing of the fan clutch in a
vibrating state increase, the life of the bearing of the fan clutch
becomes short, so that there is a possibility that the structural
life of the fan clutch becomes short.
SUMMARY OF THE INVENTION
[0009] The invention has been made to solve the above-described
problems of the prior art cooling fans, and provides an axial-flow
fan which is capable of producing forced axial-flow cooling air for
a fan clutch to extend the functional life of the fan clutch, and
which is capable of decreasing the inertia moment of an engine
cooling plastic fan and hence vibration loads to be transmitted to
the bearing of the fan clutch, thereby extending the structural
life of the fan clutch and increasing the burst speed of the engine
cooling plastic fan.
[0010] The gist of the invention resides in an axial-flow fan
fitted to an output shaft of an internal combustion engine and
provided with inner and outer blades, which includes an inner
plastic hub in which a steel insert is embedded as required, plural
inner plastic blades each of which extends radially from the inner
plastic hub and has a base side (the vicinity of a root portion)
approximately parallel to a plane perpendicular to the rotational
axis so as not to interfere with the case of a fan clutch and is
twisted near its extending end and connected to a portion
immediately below the base of the corresponding one of the outside
plastic blades, an outer plastic hub connected to the plural inner
plastic blades, and plural outer plastic hubs which extend radially
from the outer plastic hub.
[0011] In accordance with a particular structure according to the
invention, the bases of the outer blades near the plastic-made
outer hub extend inwardly and meet another hub having a small
circumference (the inner plastic hub). Since the outer fan blades
further radially inwardly from the lower outer hub and meet the
inner hub, the radially extending portions of the respective blades
constitute the inner blades. Incidentally, a circular steel insert
having holes in its outer circumferential portion may be embedded
into the inner hub after being bent by 90.degree..
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention will become more readily appreciated and
understood from the following detailed description of a preferred
embodiment of the invention when taken in conjunction with the
accompanying drawings, in which:
[0013] FIG. 1 is a perspective conceptual view showing one
embodiment of an axial-flow fan according to the invention;
[0014] FIG. 2 is a perspective conceptual view, partly broken away,
showing part of the axial-flow fan shown in FIG. 1;
[0015] FIG. 3 is an enlarged cross-sectional view taken along line
III-III of FIG. 1;
[0016] FIG. 4 is an enlarged cross-sectional view taken along line
IV-IV of FIG. 1;
[0017] FIG. 5 is a cross-sectional conceptual view showing part of
a prior art axial-flow fan; and
[0018] FIG. 6 is a cross-sectional conceptual view showing part of
another prior art axial-flow fan.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0019] In a preferred embodiment of the invention, reference
numeral 1 denotes an inner plastic hub, reference numeral 2 an
inner plastic blade, reference numeral 3 an outer plastic hub,
reference numeral 4 an outer plastic blade and reference numeral 5
a steel insert.
[0020] An axial-flow fan provided with inner and outer blades
according to the invention includes the inner plastic hub 1 in
which the small circular steel insert 5 having locking holes 5-1 in
its outer circumferential portion is embedded, the plural inner
plastic blades 2 each of which has a flat portion 2-1 and a twisted
portion 2-2 formed near the flat portion 2-1 and is connected to a
portion immediately below the base of the corresponding one of the
outside plastic blades 4, the flat portion 2-1 extending radially
from the inner plastic hub 1 and being approximately parallel to a
plane perpendicular to the rotational axis so as not to interfere
with a fan clutch, and the outer plastic hub 3. The steel insert 5
is injection-molded together with the plastic fan.
[0021] The main feature of the invention resides in the structure
in which the inner plastic hub 1 and the outer plastic hub 3 are
connected to each other by the inner plastic blades 2 each having
the flat portion 2-1 and the twisted portion 2-2 and the twisted
portion 2-2 of each of the inner plastic blades 2 is disposed
immediately below the base of the corresponding one of the outer
plastic blades 4.
[0022] Specifically, in the invention, wind which is indicated by
an arrow F in FIG. 4 is produced by the inner plastic blades 2
between the inner plastic hub 1 and the outer plastic hub 3, and
this wind flows through the spaces between fins which are radially
disposed on a fan clutch, thereby effecting additional cooling of
the fan clutch. The front end of the front side of each of the fan
and the fan clutch faces ram air which flows into a lower hood of a
vehicle. When the ram air flows into the fan, the outer plastic
blades 4 suck the inflow air and send the air toward an engine
block. At this time, since the fan is rotating, part of the air
passes through the spaces between the inner plastic blades 2 by the
fin action (blade action) of the twisted portions 2-2 between the
inner plastic hub 1 and the outer plastic hub 3, thereby forcedly
changing air surrounding the fan clutch into an axial flow to cool
the fan clutch. The upper limit of the maximum temperature of the
silicone oil inside the fan clutch that allows the fan clutch to
operate safely for a long time is about 170.degree. C., and
therefore, if the temperature of the silicone oil is lowered by
2-3.degree. C., the durability and the life of the fan clutch can
be improved to a great extent.
[0023] Accordingly, the axial-flow fan provided with the inner and
outer blades according to the invention can improve air flows
surrounding the fan clutch and hence extend the functional
durability of the fan clutch.
[0024] In addition, in the invention, each of the inner plastic
blades 2 between the inner plastic hub 1 and the outer plastic hub
3 is twisted at its extending end portion and reaches the portion
immediately below the base of the corresponding one of the outer
plastic blades 4, and the outer plastic hub 3 is disposed at a
position where the respective extending ends of the inner plastic
blades 2 and the bases of the outer plastic blades 4. In other
words, since the respective twisted portions 2-2 are formed near
the extending ends of the inner plastic blades 2, stresses
occurring due to centrifugal loads decrease. Repetitive loads
imposed on the fan produces fatigue in which the torsion moments
and tensile forces of the fan blades are combined. One experiment
which is generally carried out in the automobile industry in order
to examine the maximum strength of a fan is to rotate an
engine-cooling plastic fan until it is broken, and record the
maximum rpm of the fan. The fan structure according to the
invention is slightly high in "burst rpm" when compared with the
prior art fan structures. Accordingly, the fan according to the
invention has a mechanical strength approximately equal to or
greater than those of the prior art fans.
[0025] Moreover, in the invention, the inner plastic hub 1 and the
inner plastic blades 2 are formed integrally with the outer plastic
hub 3 and the outer plastic blades 4 by injection molding. The
inner plastic hub 1, the inner plastic blades 2, the outer plastic
hub 3 and the outer plastic blades 4 are all made of synthetic
resin, and the inertial moment of the fan is smaller than that of
the prior art engine cooling fan which only uses the steel-made
large-diameter insert 20 and the synthetic-resin-made outer plastic
hub 22 and outer plastic blades 23. In this manner, as the inertial
moment of the fan decreases, inertial load decreases compared to
the prior art engine cooling fan which uses the large steel insert.
In the case of the prior art engine cooling fan, a large inertial
load occurs during vibration and there is the risk of structural
destruction of the bearing. However, in the case of the axial-flow
fan according to the invention, since the inertial moment
decreases, the magnitude of vibration load to be applied to the
bearing decreases, whereby the fatigue life of the bearing of the
fan clutch is extended.
[0026] As described above, the axial-flow fan provided with the
inner and outer blades according to the invention can improve air
flows surrounding the fan clutch and hence extend the functional
durability of the fan clutch. In addition, as compared with the
prior art fan structures, the fan structure according to the
invention is slightly high in "burst rpm", whereby the fan
according to the invention can be given a mechanical strength
approximately equal to or greater than those of the prior art fans.
Moreover, since the inertial moment of the fan decreases, inertial
load decreases compared to the prior art engine cooling fan which
uses the large steel insert, and the magnitude of vibration load to
be applied to the bearing decreases, whereby it is possible to
achieve a superior advantage such as an extension of the fatigue
life of the bearing of the fan clutch.
EXAMPLES
[0027] The results of the experiments performed as to the air flow
of an axial-flow fan according to the invention and that of a prior
art axial-flow fan are shown below.
[0028] (a) Experiment as to Air Flow
[0029] Two fans each having eleven blades and the same dimensions
such as an outer diameter of 490 mm, an outer boss diameter of 238
mm and a blade width of 50 mm were selected for the experiment. One
of the two fans was a fan according to the invention, and the other
was a prior art fan of the type shown in FIG. 5 which had the same
diameter and hub diameter. The second fan is a prior art fan. The
maximum temperature occurring inside a clutch is determined by the
movement of air surrounding the clutch. As the air moves faster,
the maximum temperature becomes lower. As the experiment,
constant-temperature measurements were performed in a room at room
temperature with 500 rpm and 1,000 rpm. The results are shown in
Table 1 (the fan according to the invention) and Table 2 (the prior
art fan). Incidentally, the measurement positions are positions
which correspond to the radial positions of the twisted portions
2-2 of the blades and are immediately before an outer boss
portion.
[0030] From the data of Tables 1 and 2, it is seen that the fan,
according to the invention, produces a speed more than twice as
fast as that is observed with the prior art fan.
1TABLE 1 Speed with Fan according to the Invention DIRECTION 500
rpm 1,000 rpm AXIAL DIRECTION 2.3 m/s 4.8 m/s
[0031]
2TABLE 2 Speed with Prior Art Fan DIRECTION 500 rpm 1,000 rpm AXIAL
DIRECTION 1.1 m/s 1.8 m/s
[0032] (b) Temperature of Fan Clutch
[0033] <Condition>
[0034] Experiments were performed as to a prior art fan and a fan
having inner and outer blades according to the invention, and the
temperatures of the outer circumferential surfaces of the bearing
outer races of their respective fun clutches were measured through
their embedded thermocouples. The use conditions were: diameter of
clutch disk--132 mm; room temperature--90.degree. C.; input
speed--4,000 rpm; and fan speed--2,850 rpm.
[0035] <Result>
[0036] The measurements performed as to the prior art fan and the
fan according to the invention showed that the temperature of the
outer circumferential surface of the bearing outer race of the
prior art fan was 165.degree. C., whereas that of the fan according
to the invention decreased to 155.degree. C. by about 10.degree. C.
In the case of the fan according to the invention, it is inferred
that such temperature decrease is due to the fact that high-speed
axial-flow wind occurs inward of the hub owing to the twisted
portions of the inner blades.
* * * * *