US20090129918A1

US20090129918A1 - Blower unit

Info

Publication number: US20090129918A1
Application number: US12/290,893
Authority: US
Inventors: Kazuhiro Takeuchi; Norihisa Sasano
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2007-11-16
Filing date: 2008-11-04
Publication date: 2009-05-21
Also published as: JP2009121424A

Abstract

A blower unit has a first axial fan and a second axial fan for generating a flow of cooling air passing through a heat exchanger disposed under an intake duct through which an intake air to be introduced to an engine flows. The first axial fan and the second axial fan are aligned in a substantially horizontal direction downstream of the heat exchanger with respect to the flow of air. A first rotation axis of the first axial fan and a second rotation axis of the second axial fan are perpendicular to the heat exchanger and located lower than a center of the heat exchanger. The first axial fan, which is disposed on a right side of the second axial fan, rotates in a clockwise direction and the second axial fan rotates in a counterclockwise direction when viewed from a downstream position with respect to the flow of air.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2007-298571 filed on Nov. 16, 2007, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a blower unit for generating air passing through a heat exchanger.

BACKGROUND OF THE INVENTION

For example, Japanese Unexamined Patent Application Publication No. 2006-160142 describes an intake device for an internal combustion engine (hereinafter, engine). The described intake device includes an intake path for introducing intake air, drawn from an air intake port, toward the engine for combustion and a covering tube covering the intake path. The covering tube forms a thermal insulation space capable of allowing air to flow. The thermal insulation space thermally insulates the intake path from an engine compartment, thereby restricting the intake air passing through the intake path from being heated by heat of the engine.
In an engine compartment, for example, a radiator for cooling an engine coolant and a blower unit for generating cooling air for cooling the radiator are arranged under an intake path. The blower unit includes a suction-type fan and is disposed downstream of the radiator with respect to a flow of cooling air. The fan blows out the cooling air, which has been heated through the radiator, toward a downstream position while diffusing the cooling air in a centrifugal direction. In such a case, intake air passing through the intake path will be affected by heat of the cooling air blown out from the fan.

SUMMARY OF THE INVENTION

To solve the above matter, it is considered to arrange the fan in an inclined position so as to blow the heated air in a diagonally downward direction, that is, in a direction separating from the intake path. In such a case, however, a dimension of the fan with respect to a vehicle front and rear direction is increased due to the inclined arrangement. As such, mountability of the blower unit in a vehicle reduces.
The present invention is made in view of the foregoing matters, and it is an object of the present invention to provide a blower unit having a structure capable of restricting intake air passing through an intake duct from being heated by cooling air heated by a heat exchanger without reducing mountability to a vehicle.
According to an aspect of the present invention, a blower unit includes a first axial fan and a second axial fan for generating a flow of cooling air passing through a heat exchanger disposed under an intake duct through which intake air to be introduced to an internal combustion engine flows. The first axial fan includes a first rotation axis substantially perpendicular to the heat exchanger. The second axial fan includes a second rotation axis substantially perpendicular to the heat exchanger. The first axial fan and the second axial fan are aligned in a substantially horizontal direction downstream of the heat exchanger with respect to the flow of cooling air. The first axial fan and the second axial fan are disposed such that the first rotation axis and the second rotation axis are lower than a center of the heat exchanger. The first axial fan is disposed on a right side of the second axial fan and is configured to rotate in a clockwise direction and the second axial fan is configured to rotate in a counterclockwise direction, when viewed from a downstream position with respect to the flow of air.
Since the first rotation axis and the second rotation axis are located lower than the center of the heat exchanger, the cooling air, which has been heated while passing through the heat exchanger, is blown in a diagonally downward direction. Since the first axial fan is rotated in the clockwise direction and the second axial fan is rotated in the counterclockwise direction when viewed from a downstream position with respect to the flow of air, rotating flows of the cooling air discharged from the first and second axial fans more gather to an area under a middle point between the first rotation axis and the second rotation axis than an area above the middle point between the first rotation axis and the second rotation axis. Such a configuration restricts the intake air passing through the intake duct from being affected by heat of the cooling air heated by the heat exchanger. In addition, since the first and second rotation axes of the first and second axial fans are substantially perpendicular to the heat exchanger, rotational plane of the first and second axial fans are substantially parallel to the heat exchanger. Therefore, a dimension of the first and second axial fans with respect to a vehicle front and rear direction is not increased. As such, a structure restricting the intake air from being affected by the cooling air heated by the heat exchanger is achieved without deteriorating the mountability to a vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:

FIG. 1 is a schematic side view of a blower unit mounted in a vehicle according to a first embodiment of the present invention;

FIG. 2 is a rear view of the blower unit, when viewed from a downstream position with respect to a flow of air, according to the first embodiment;

FIG. 3 is a schematic side view of a blower unit according to a modification of the first embodiment; and

FIG. 4 is a rear view of a blower unit, when viewed from a downstream position with respect to a flow of air, according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

A first embodiment of the present invention will now be described with reference to FIGS. 1 to 3. FIG. 1 shows a blower unit 1 of the present embodiment when mounted in a vehicle. An up and down direction of FIG. 1 substantially corresponds to a vertical direction. A left and right direction of FIG. 1 corresponds to a front and rear direction of the vehicle. Although the blower unit 1 has a first axial fan 20 and a second axial fan 30, the second axial fan 30 is mainly illustrated in FIG. 1 as an example. FIG. 2 shows a rear view of the blower unit 1 when the blower unit 1 is viewed from a rear side of the vehicle, that is, a downstream position with respect to a flow of air generated by the first and second axial fans 20, 30.
As shown in FIGS. 1 and 2, a water-cooled engine 10 as a driving power source is mounted in an engine compartment of the vehicle. An intake duct 11 is disposed to extend from the engine 10 in a vehicle frontward direction. The intake duct 11 has a substantially tubular shape and forms an air inlet 12 opening in the vehicle frontward direction at its front end. The intake duct 11 defines an intake path therein for introducing intake air to the engine 10 for combustion. The intake air is inhaled from the air inlet 12 in accordance with ram pressure. Although not illustrated, the intake air is introduced to the engine 10 through an air cleaner and an air intake manifold.
A radiator 13 is disposed in front of the engine 10 and under the intake duct 11. The radiator 13 is in communication with an engine coolant circuit through which an engine coolant circulates. The radiator 13 performs heat exchange between the engine coolant flowing inside of the radiator 13 and air flowing outside of the radiator 13, thereby to cool the engine coolant.
The radiator 13 is, for example, a horizontal flow-type. The radiator 13 includes a core 13 a performing the heat exchange and a pair of tanks (not shown) connected to right and left ends of the core 13 a. The core 13 a includes flat tubes and fins. The tubes and the fins are alternately stacked in the up and down direction and thermally connected to each other. The tubes are oriented horizontally and in communication with the pair of tanks. The tubes define coolant passages therein through which the engine coolant flows.
The core 13 a has a substantially flat and rectangular shape, and is substantially parallel to the up and down direction and a vehicle right and left direction. That is, the core 13 a is substantially perpendicular to a flow of air, which is generated when the vehicle travels. For example, a horizontal dimension of the core 13 a with respect to the vehicle right and left direction is greater than a vertical dimension of the core 13 a with respect to the up and down direction. In FIG. 1, reference numeral H denotes the vertical dimension, such as a height, of the core 13 a.
Although not illustrated, a condenser is arranged in front of the radiator 13. The condenser 13 is one of devices of a refrigerant cycle of a vehicle air conditioner. The condenser performs heat exchange between refrigerant flowing inside of the condenser and air flowing outside of the condenser, thereby condensing the refrigerant. The condenser is arranged on a rear side of a grill portion of the vehicle formed at a front end of the vehicle. Thus, air introduced from the grill portion is introduced to the condenser and the radiator 13.
The blower unit 1 is arranged on a rear side of the radiator 13. The blower unit 1 is configured as in an air suction-type and causes cooling air for cooling the condenser and the radiator 13 to pass through the condenser and the radiator 13. The blower unit 1 includes the first axial fan 20 and the second axial fan 30. For example, the first and second axial fans 20, 30 have the substantially same diameter. The first and second axial fans 20, 30 are aligned in the vehicle right and left direction and arranged in parallel with each other with respect to a flow of cooling air.
The first axial fan 20 has a first rotation axis 20 c that is substantially parallel to the horizontal direction and perpendicular to the radiator 13. Likewise, the second axial fan 30 has a second rotation axis 30 c that is substantially parallel to the horizontal direction and perpendicular to the radiator 13.
The first axial fan 20 includes a first boss part 22 and multiple first blades 23 (e.g., four blades) extending from the first boss part 22 in a radially outward direction. The first boss part 22 has a substantially cylindrical shape and is coupled to an output shaft of an electric motor (not shown). Each of the first blades 23 has the symmetrical shape with respect to a longitudinal axis of the first blade, the longitudinal axis extending in a radial direction and passing through the first rotation axis 20c.
Likewise, the second axial fan 30 includes a second boss part 32 and multiple second blades 33 (e.g., four blades) extending from the second boss part 32 in a radially outward direction. The second boss part 32 has a substantially cylindrical shape and is coupled to an output shaft of an electric motor (not shown). Each of the second blades 33 has the symmetrical shape with respect to a longitudinal axis of the second blade, the longitudinal axis extending in a radial direction and passing through the second rotation axis 30 c.
The first and second axial fans 20, 30 are disposed such that rotational planes on which the first and second axial fans 20, 30 rotate are substantially parallel to the up and down direction and the vehicle right and left direction. In other words, the first and second axial fans 20, 30 are disposed such that the rotational planes thereof are substantially parallel to the radiator 13.
The first and second axial fans 20, 30 are rotated such that flows of air in the generally vehicle rearward direction are created. Further, the first axial fan 20 and the second axial fan 30 are rotated in opposite directions to each other. Specifically, the first axial fan 20, which is on a right side of the second axial fan 30 when viewed from the rear side of the vehicle, is rotated in a clockwise direction as shown by an arrow R1 in FIG. 2 in the plane parallel to the radiator 13. The second axial fan 30, which is located on a left side of the first axial fan 20 when viewed from the rear side of the vehicle, is rotated in a counterclockwise direction as shown by an arrow R2 in FIG. 2 in the plane parallel to the radiator 13.
The first rotation axis 20 c and the second rotation axis 30 c are arranged at the substantially same height. Also, the first rotation axis 20 c and the second rotation axis 30 c are located lower than a center 13 c of the core 13 a such that a gap Δh between the first and second rotation axes 20 c, 30 c and the center 13 c in the up and down direction is relatively large. For example, the first and second axial fans 20, 30 are arranged such that the gap Δh and the vertical dimension H of the core 13 a satisfy the relationship of Δh≧H/10.
Further, upper ends of the first and second axial fans 20, 30 are lower than an upper end 13 b of the core 13 a, and lower ends of the first and second axial fans 20, 30 are on the substantially same height as a lower end of the core 13 a. Also, the first and second axial fans 20, 30 are arranged such that a middle point 25 between the first rotation axis 20 c and the second rotation axis 30 c is positioned under the intake duct 11 in the up and down direction, such as exactly under the intake duct 11.
The blower unit 1 further includes a shroud 40 for introducing the cooling air passing through the core 13 a to the first and second axial fans 20, 30. The shroud 40 forms a first fan opening 41 and a second fan opening 42 at locations corresponding to the first axial fan 20 and the second axial fan 30, respectively. The first and second fan openings 41, 42 have the circular shape.
The shroud 40 has a first ring portion 43 and a second ring portion 44. The first ring portion 43 has a cylindrical shape and defines the first fan opening 41 therein. The first ring portion 43 surrounds an outer periphery of the first axial fan 20. The second ring portion 44 has a cylindrical shape and defines the second fan opening 42 therein. The second ring portion 44 surrounds an outer periphery of the second axial fan 30.
An upper end 43 a of the first ring portion 43 is located lower than the upper end 13 b of the core 13 a. Likewise, an upper end 44a of the second ring portion 44 is located lower than the upper end 13 b of the core 13 a. Lower ends of the first and second ring portions 43, 44 are located on the substantially same height as the lower end of the core 13 a.
The shroud 40 further includes an air introducing portion 45 extending from upstream ends of the first and second ring portions 43, 44 with respect to the flow direction of cooling air in the vehicle frontward direction. The air introducing portion 45 defines an air passage space for introducing the cooling air passing through the core 13 a toward the first and second fan openings 41, 42. The air introducing portion 45 expands toward the core 13 a. That is, a cross-sectional area of the air passage space of the air introducing portion 45 increases toward the core 13 a. The shroud 40 has a shroud peripheral portion 40 a at an upstream end of the air introducing portion 45 with respect to the flow of cooling air. The shroud peripheral portion 40 a has a substantially rectangular shape to correspond to the core 13 a.
The air introducing portion 45 smoothly connects the shroud peripheral portion 40 a and the first and second ring portions 41, 42. The air introducing portion 45 includes an upper wall 45 a extending between an upper portion of the shroud peripheral portion 40 a and upper portions of the first and second ring portions 43, 44. At least the upper wall 45 a is smoothly inclined from the shroud peripheral portion 40 a toward the first and second ring portions 43, 44. Since the upper ends 43 a, 44 a of the first and second ring portions 43, 44 are lower than the upper end 13 b of the core 13 a, the upper wall 45 a of the air introducing portion 45 is sloped downward with respect to the flow direction of the cooling air. For example, the upper wall 45 a defines a curved surface curving or projecting inside, that is, toward the air passage space. Since the lower end of the first and second ring portions 43, 44 are on the substantially same height as the radiator 13, a lower wall of the air introducing portion 45 extends in the substantially horizontal direction, for example. In such a case, an axis of the air passage space is inclined in the diagonally downward direction.
The shroud 40 further includes a first air guide portion 46 and a second air guide portion 47. The first air guide portion 46 extends from a lower portion of the first ring portion 43, such as a lower half of the first ring portion 43, toward a downstream position with respect to the flow of cooling air. The second air guide portion 47 extends from a lower portion of the second ring portion 44, such as a lower half of the second ring portion 44, toward a downstream position with respect to the flow of cooling air. The first an second air guide portions 46, 47 are configured to guide the cooling air blown from the first and second axial fans 20, 30, that is, heated air heated by the radiator 13, in a diagonally downward direction. The first and second guide portions 46, 47 have a diffuser shape that expands toward the downstream position with respect to the flow of cooling air.
Next, an operation of the blower unit 1 will be described.
The engine coolant, which has received heat generated from the engine 10, flows in the tubes of the radiator 13. The cooling air, which is introduced in the engine compartment from the grill portion in accordance with the rotations of the first and second axial fans 20, 30 and/or the ram pressure caused when the vehicle travels, passes through spaces defined between the adjacent tubes of the radiator 13. Thus, the engine coolant is cooled by the cooling air passing through the core 13 a, and the cooling air is heated by the heat of the engine coolant.
The cooling air, that is, the heated air heated through the core 13 a, is introduced to the first and second fan openings 41, 42 through the air introducing portion 45 of the shroud 40. In the present embodiment, the first and second axial fans 20, 30 are arranged such that the first and second rotation axes 20 c, 30 c are lower than the center 13 c of the core 13 a. Also, the upper wall 45 a of the air introducing portion 45 is sloped downward toward the first and second ring portions 43, 44. Therefore, the heated air is conducted by the air introducing portion 45 in a generally diagonally downward direction, as shown by an arrow B1 in FIG. 1. That is, the arrow B1 shows a general flow direction of the heated air.
Further, the heated air is discharged from the first and second fan openings 41, 42 in the diagonally downward direction with respect to the vehicle rearward direction along the general flow direction B1, such as in a direction separating from the intake duct 11. In other words, the heated air is discharged from the first and second fan openings 41, 42 such that a distance from the intake duct 11 increases in the vehicle rearward direction. The heated air discharged from the first and second fan openings 41, 42 in the diagonally downward direction smoothly flows toward the downstream position along the first and second air guide portions 46, 47.
The first axial fan 20, which is located on the right side when viewed from the rear side of the vehicle, is rotated in the clockwise direction R1. Therefore, the heated air discharged from the first fan opening 41 in accordance with the rotation of the first axial fan 20 has a rotating force in the clockwise direction R1, which is a counterclockwise direction when viewed along the general flow direction B1. In contrast, the second axial fan 30, which is located on the left side when viewed from the rear side of the vehicle, is rotated in the counterclockwise direction R2. Thus, the heated air discharged from the second fan opening 42 in accordance with the rotation of the second axial fan 30 has a rotating force in the counterclockwise direction R2, which is a clockwise direction when viewed along the general flow direction B1.
Thus, on the rear side of the shroud 40, the heated air discharged from the first and second fan openings 41, 42 flows such that rotating components thereof come close to each other in an area A1 under the middle point 25 between the first and second rotational axes 20 c, 30 c. Also, the heated air discharged from the first and second fan openings 41, 42 flows such that the rotating components thereof separate from each other in an area above the middle point 25 between the first and second rotational axes 20 c, 30 c. As such, the heated air discharged from the first and second fan openings 41, 42 gathers more to the area A1 and less to the area above the middle point 25.
As discussed above, the first and second rotational axes 20 c, 30 c of the first and second axial fans 20, 30 are lower than the center 13 c of the core 13 a, and the heated air passing through the core 13 a is discharged in the diagonally downward direction. The first axial fan 20 is rotated in the clockwise direction R1, and the second axial fan 30 is rotated in the counterclockwise direction R2, when viewed from the rear side of the vehicle. Thus, the heated air discharged from the first and second fan openings 41, 42 easily gathers to the area A1 under the middle point 25 between the first and second rotational axes 20 c, 30 c, than the area above the middle point 25. In other words, the air discharged from the first and second fan openings 41, 42 easily gathers to the area Al, which is separated from the intake duct 11. Accordingly, it is less likely that the intake air passing through the intake duct 11 will be affected by the heated air.
The first and second axial fans 20, 30 are arranged such that the middle point 25 between the first and second rotational axes 20 c, 30 c is located under the intake duct 11 with respect to the up and down direction. The heated air less gathers to the area above the middle point 25 than the area A1 under the middle point 25. Therefore, an increase in temperature of the intake air in the intake duct 11 is effectively restricted.
Further, the general flow direction B1 of the air conducted by the air introducing portion 45 is the diagonally downward direction. Therefore, the intake air passing through the intake duct 11 is restricted from being heated by the heated air heated through the core 13 a.
The first and second air guide portions 46, 47 disposed on the downstream positions of the first and second ring portions 43, 44 have the diffuser shape, and the heated air discharged from the first and second fan openings 41, 42 can be smoothly introduced in the diagonally downward direction.
The first and second axial fans 20, 30 are arranged such that the rotational planes thereof are the substantially parallel to the radiator 13. Therefore, a dimension of the first and second axial fans 20, 30 with respect to the vehicle front and rear direction is not increased. Therefore, the mountability of the blower unit 1 to the vehicle is not deteriorated due to the structure of restricting the intake air from being heated by the heated air passing through the radiator 13.
When the blower unit 1 of the present embodiment is mounted to the vehicle, the temperature of the intake air is reduced about 5° C. and 10° C., as compared with a conventional blower unit.
The shape of the first and second air guide portions 46, 47 can be modified to another shape. For example, the first and second air guide portions can have a bell-mouth shape, as shown by reference numeral 49 of FIG. 3. The bell-mouth shape expands with respect to the flow direction of the air. Thus, the heated air discharged from the first and second fan openings 41, 42 in the diagonally downward direction can be smoothly directed along the bell-mouth shaped air guide portions 49.
A second embodiment of the present invention will be described with reference to FIG. 4. As shown in FIG. 4, a blower unit 2 of the present embodiment has a first axial fan 60 and a second axial fan 70. Structures of the blower unit 2 other than the first and second axial fans 60, 70 are similar to those of the blower unit 1 of the first embodiment. Therefore, like components are denoted by like reference numerals, and a description thereof is not repeated.
The first axial fan 60 has a first boss part 62 having a cylindrical shape and multiple first blades 63 (e.g., four blades) extending from the first boss part 62 in a radially outward direction. The first boss part 62 is coupled to an output shaft of a motor. Likewise, the second axial fan 70 has a second boss part 72 having a cylindrical shape and multiple second blades 73 (e.g., four blades) extending from the second boss part 72 in a radially outward direction. The second boss part 72 is coupled to an output shaft of a motor.
The first and second blades 63, 73 have a sweepforward shape in which a radially outer portion is located forward of a radially inner portion with respect to a direction of rotation. That is, the blade 63, 73 is inclined in the direction of rotation as a function of distance from the rotation axis 60 c, 70 c in the radial direction. For example, a leading edge of the blade 63, 73 is inclined in the direction of rotation such that a radially outer end of the leading edge is located forward of a radially inner end of the leading edge with respect to the direction of rotation.
The first axial fan 60 is rotated in the clockwise direction R1, when viewed from the rear side of the vehicle. The second axial fan 70 is rotated in the counterclockwise direction R2, when viewed from the rear side of the vehicle. The first and second axial fans 60, 70 are arranged in the similar manner as the first and second axial fans 20, 30 of the first embodiment, relative to the radiator 13.
In the present embodiment, the rotating flow generated by the first and second axial fans 60, 70 causes a pressure distribution in which negative pressure increases toward a center of rotation. With this, because the rotating flow causes a centripetal force, air diffusion in a centrifugal direction is reduced. Accordingly, in addition to the effects similar to the first embodiment, an increase in temperature of intake air passing through the intake duct 11 due to the diffusion of the heated air is further reduced.
In the above embodiments, the radiator 13 is arranged such that the tubes extend in the substantially horizontal direction. However, the radiator 13 is not limited to the horizontal flow-type, but can be any other type, such as a vertical flow-type in which the tubes extend in the vertical direction.
Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader term is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.

Claims

1. A blower unit for generating cooling air passing through a heat exchanger that is disposed under an intake duct through which intake air to be introduced to an internal combustion engine flows, the blower unit comprising:

a first axial fan having a first rotation axis substantially perpendicular to the heat exchanger; and

a second axial fan having a second rotation axis substantially perpendicular to the heat exchanger, wherein

the first axial fan and the second axial fan are aligned in a substantially horizontal direction downstream of the heat exchanger with respect to a flow of cooling air such that the first axial fan is on a right side of the second axial fan when viewed from a downstream position with respect to the flow of cooling air,

the first axial fan and the second axial fan are disposed such that the first rotation axis and the second rotation axis are lower than a center of the heat exchanger, and

the first axial fan is configured to rotate in a clockwise direction and the second axial fan is configured to rotate in a counterclockwise direction when viewed from the downstream position.

2. The blower unit according to claim 1, further comprising:

a shroud including a first ring portion, a second ring portion and an air introducing portion, wherein

the first ring portion has a substantially cylindrical shape defining a first fan opening therein, the first axial fan is disposed in the first fan opening,

the second ring portion has a substantially cylindrical shape defining a second fan opening therein, the second axial fan is disposed in the second fan opening,

the air introducing portion extends from the first ring portion and the second ring portion toward an upstream position with respect to the flow of cooling air and defines an air passage introducing the cooling air passing through the heat exchanger toward the first fan opening and the second fan opening, a cross-sectional area of the air passage increasing toward the upstream position, and

the first ring portion and the second ring portion are disposed such that upper ends thereof are located lower than an upper end of the heat exchanger.

3. The blower unit according to claim 2, wherein

the shroud includes an air guide portion extending from the first ring portion and the second ring portion toward the downstream position with respect to the flow of cooling air,

the air guide portion is configured to lead the cooling air passing through the first and second ring portions in a downward direction.

4. The blower unit according to claim 3, wherein the air guide portion has a diffuser shape.

5. The blower unit according to claim 3, wherein the air guide portion has a bell-mouth shape.

6. The blower unit according to claim 2, wherein

the air introducing portion is configured such that an axis of the air passage defined in the air introducing portion is inclined downward with respect to the flow of cooling air.

7. The blower unit according to claim 6, wherein

the air introducing portion has an upper wall and a lower wall,

the upper wall extending between an upper portion of the heat exchanger and upper portions of the first and second ring portions,

the lower wall extending between a lower portion of the heat exchanger and lower portions of the first and second ring portions,

the upper wall is inclined downward toward the upper portions of the first and second ring portions, and

the lower wall extends substantially horizontally.

8. The blower unit according to claim 1, wherein

the first axial fan and the second axial fan are disposed such that a middle point between the first rotation axis and the second rotation axis is located under the intake path with respect to an up and down direction.

9. The blower unit according to claim 1, wherein

each of the first axial fan and the second axial fan includes a boss part and a plurality of blades extending from the boss part in a radially outward direction, and

each of the blades has a sweepforward shape inclined in a direction of rotation.

10. An arrangement structure of a blower unit comprising:

an intake duct defining an intake air passage through which intake air to be introduced to an internal combustion engine flows;

a heat exchanger oriented in an up and down direction, the heat exchanger including a core performing heat exchange between cooling air flowing outside of the heat exchanger and an internal fluid flowing inside of the heat exchanger; and

a first axial fan disposed behind the heat exchanger and having a first rotation axis perpendicular to the heat exchanger; and

a second axial fan disposed behind the heat exchanger and having a second rotation axis perpendicular to the heat exchanger, wherein

the first axial fan is located on a right side of the second axial fan when viewed along a direction perpendicular to the heat exchanger,

the intake duct is disposed to extend above the first and second axial fans,

the first axial fan and the second axial fan are arranged such that the first rotation axis and the second rotation axis are lower than a center of the core of the heat exchanger,

the first axial fan is configured to rotate in a clockwise direction, and

the second axial fan is configured to rotated in a counterclockwise direction.

11. The arrangement structure according to claim 10, wherein

a gap Δh between the center of the core and the first and second rotation axes in the up and down direction and a vertical dimension H of the core satisfy a relationship of Δh≧10/H.

12. The arrangement structure according to claim 10, further comprising:

a shroud including a first ring portion, a second ring portion, an air introducing portion and an air guide portion, wherein

the first axial fan is disposed in the first ring portion,

the second axial fan is disposed in the second ring portion,

the air introducing portion extends from the heat exchanger to the first and second ring portions, and defines an air passage space therein for leading the cooling air from the heat exchanger toward the first and second ring portions,

the air introducing portion includes an upper wall extending from an upper portion of the heat exchanger to upper portions of the first and second ring portions and inclining downward toward the first and second ring portions,

the air guide portion extends from the first and second ring portions toward a downstream position with respect to a flow of cooling air, and

the air guide portion is inclined downward toward the downstream position.