Title of Invention: Shroud and rotary vane wheel of propeller fan and propeller fan Abstract: A shroud includes a body portion 5B, a mount 7 positioned at a center of the body portion 5B and supporting rotary vane wheel driver 6, and multiple support beams 10 radially extending from the mount 7 and joining the mount 7 and the body portion 5B, where each of the support beams 10 becomes thicker from an upstream side of a flow direction of air toward a downstream side thereof, and an edge portion 10ti of each of the support beams 10 on the downstream side of the flow direction of the air discharged by the rotary vane wheel 8 is oriented in a direction parallel to a rotation axis of the rotary vane wheel 8, and the edge portion on the upstream side is oriented in a direction opposite to a rotation direction of the rotary vane wheel 8. Detailed Description: Part general_description_paragraphs: Part CROSS-REFERENCE TO RELATED APPLICATIONS: This application is based upon and claims the benefit of priority from Japanese Patent Application Nos. 2005-225856, 2005-225858 and 2005-225859 filed Aug. 3, 2005, the entire contents of which are incorporated herein by reference. Part BACKGROUND OF THE INVENTION: 1. Field of the Invention The present invention relates to a shroud and a rotary vane wheel of a propeller fan and the propeller fan. 2. Description of the Related Art A vehicle is provided with a propeller fan for cooling heat exchangers such as a radiator and a condenser of an air conditioner. Japanese Patent Application Laid-Open No. 2002-47937 discloses a stay for supporting a boss of the fan to a shroud. To achieve high fan efficiency and low noise when running at low speed, this stay is of an aspect ratio>1, has a longitudinal direction of its section oriented toward a direction of an airflow generated by driving the fan and also has a cavity provided on a side of a negative pressure of the stay generated by the airflow when the vehicle is running at high speed. An engine room of the vehicle hardly has space because it has not only an engine as a power source of the vehicle but also its accessories mounted therein. For this reason, the propeller fan for cooling the radiator and condenser is limited as to its dimension in the airflow direction. Consequently, the space between the fan and the stay becomes small, and noise when operating the propeller fan becomes high. The stay is required to have strength for supporting the fan and driving means (an electric motor for instance) of the fan. This strength cannot be secured, however, if the stay is rendered thin in an attempt to reduce the noise when operating the propeller fan. Such a problem is not considered in Japanese Patent Application Laid-Open No. 2002-47937. Therefore, there is room for improvement in a conventional technology disclosed in Japanese Patent Application Laid-Open No. 2002-47937 as to reducing the noise while limiting the dimension in the airflow direction and further securing support strength of the stay (first problem). As for the propeller fan for cooling the radiator and condenser for the vehicle, it is placed in a narrow engine room and required to be further lightweight, and so there is a strong request for compactification regarding a depth dimension in a flow direction of cooling wind. If the depth dimension is thus reduced, however, a cross-section of a cooling wind channel of the shroud of the propeller fan changes drastically because the radiator on an upstream side is rectangular while an air sucking path of the propeller fan is round. For this reason, there is a problem that an uneven drift is formed in a circumferential direction of the propeller fan (rotary vane wheel) to generate unpleasant BPF (Blade Passing Frequency) noise. The radiator and condenser as cooling subjects are small-size and require high heat exchange performance so that ventilation resistance thereof is high. For this reason, the propeller fan is driven under a condition of a high static pressure difference reverse to an adverse wind direction. In this case, there is a problem that the flow on a propeller plane of the rotary vane wheel breaks away so as to increase input and the noise under the same air volume condition. As for these problems, there is a known technology described in Japanese Patent Application Laid-Open No. 7-167095 regarding a conventional propeller fan. The conventional propeller fan (electric fan) is the electric fan rotatively driven by the electric motor, which comprises a boss portion for rotating by receiving a driving force of the electric motor and 9 to 13 blades (blade portion) placed around the boss portion circumferentially apart from the boss portion. The blade is characterized by being a forward swept vane of which angle of advance overlooking a vane edge from a vane root is 35 to 45 degrees. However, the propeller fan described in Japanese Patent Application Laid-Open No. 7-167095 is not sufficient as to noise reduction performance (second problem). As the rotary vane wheel provided to the conventional propeller fan has multiple blades in general, the multiple blades rotate on rotating the rotary vane wheel by the driving means such as the electric motor so as to let the air flow by means of these blades. Thus, these blades for blowing air by letting the air flow are fixed on a hub of the rotary vane wheel. The hub is provided to connect the blades to an axis of the driving means and transfer rotation of the axis of the driving means to the blades. For that reason, the hub does not contribute to air blowing so much. Therefore, there is a conventional rotary vane wheel wherein occupancy of the blades in the rotary vane wheel is enlarged to increase a sent air volume so as to improve air blowing performance. In Japanese Patent Application Laid-Open No. 2004-218513 for instance, a joint of the blades and the hub is extended inward in a radial direction centering on a rotation axis of the hub to increase length of the blades in the radial direction. It is thereby possible to improve the occupancy of the blades in the case of axially viewing the rotary vane wheel so as to increase the sent air volume and improve the air blowing performance. In the case of the above-mentioned rotary vane wheel, however, there is little difference in that the hub does not contribute to improvement in the air blowing performance so much because the hub is basically in a cylindrical shape. As with the above-mentioned rotary vane wheel, the blades are extended inward in the radial direction centering on a rotation axis of the hub so that a radial step is generated on an end of the upstream side of the hub in the circumferential direction of the rotation axis. Therefore, there is a possibility that the airflow may be disturbed in this part. In the case where the airflow is thus disturbed, the efficiency lowers and so there is a possibility that the air blowing performance may lower and the noise may be easily generated (third problem). Part SUMMARY OF THE INVENTION: Objects of the present invention are at least to solve the above-mentioned problems. According to one aspect of the present invention, a shroud of a propeller fan includes a body portion for accommodating a rotary vane wheel of the propeller fan; a mount positioned at a center of the body portion for supporting rotary vane wheel driving means for driving the rotary vane wheel; and multiple support beams radially extending from the mount for joining the mount and the body portion, wherein each of the support beams becomes thicker from an upstream side of a flow direction of air discharged by the rotary vane wheel toward a downstream side thereof, an edge portion of each of the support beams on the downstream side of the flow direction of the air discharged by the rotary vane wheel is oriented in a direction parallel to a rotation axis of the rotary vane wheel, and the edge portion of each of the support beams on the upstream side of the flow direction of the air discharged by the rotary vane wheel is oriented in a direction opposite to a rotation direction of the rotary vane wheel. According to another aspect of the present invention, a propeller fan includes the shroud of the propeller fan; rotary vane wheel driving means attached on a mount; and a rotary vane wheel driven by the rotary vane wheel driving means. According to still another aspect of the present invention, a propeller fan includes a rotary vane wheel having multiple blade portions arranged on a hub portion which is a rotor; a motor for rotating the rotary vane wheel; and a shroud having a motor holding portion for holding the motor, wherein, a ratio H/DF between an axial width H and a diameter DF at an end of the rotary vane wheel is in a range of H/DF≦0.12, a ratio Dm/DF between a diameter Dm of the hub portion and the diameter DF at the end of the blade portion is in the range of Dm/DF≦0.50, a ratio P/C between a circumferential pitch P and a chord length C of the blade portion is in the range of 1.0<P/C<1.2, and an outer circumferential side of the blade portion is swept forward in a rotation direction of the rotary vane wheel. According to still another aspect of the present invention, a rotary vane wheel includes multiple blade portions; and a hub having the multiple blade portions provided on its outer circumferential surface, wherein, in the case where, of both edges of the outer circumferential surface in an axial direction of a rotation axis of the hub, one edge is an upstream side end portion and the other edge is a downstream side end portion, the outer circumferential surface has an inclined portion inclined against the rotation axis in a direction to be further away from the rotation axis as directed from the upstream side end portion to the downstream side end portion and a parallel portion formed along the rotation axis, the parallel portion is formed between a connecting portion connecting the blade portion to the outer circumferential surface and the downstream side end portion, and positioned more inward in a radial direction of the rotation axis than an extended inclined portion which is a virtual extended portion of the inclined portion continued from the inclined portion between the connecting portion and the downstream side end portion. According to still another aspect of the present invention, a propeller fan includes the rotary vane wheel; driving means for supporting the rotary vane wheel rotatably centering on the rotation axis; and a shroud for placing the rotary vane wheel therein and fixing the driving means. Part DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS: Hereunder, the present invention will be described in detail by referring to the attached drawings. The present invention will not be limited by embodiments described below. Components of the following embodiments include the ones easily assumable by those in the art or the ones which are substantially the same. Part First Embodiment: While a propeller fan according to a first embodiment is not limited as to its application, it is suitable in particular to the propeller fan which is limited as to a dimension in a rotation axis direction of a rotary vane wheel provided to the propeller fan. Such a propeller fan can be exemplified by the one used for cooling of a heat exchanger mounted on a vehicle, such as a passenger car or a truck. FIG. 1 is a plan view showing an example of the propeller fan according to the first embodiment mounted on the heat exchanger for a vehicle. A description will be given by using FIG. 1 as to an example of mounting a propeller fan 1 according to the first embodiment. The propeller fan 1 is used for cooling of the heat exchanger such as a radiator 2 or a condenser 3. In general, a vehicle such as a passenger car or a truck has the radiator 2 for cooling engine coolant or the condenser 3 of an air conditioner mounted at a front of the vehicle (hereafter, vehicle front) L in its traveling direction, and leads a driving wind thereto so as to cool the coolant and condense a refrigerant. In the example shown in FIG. 1, the condenser 3 and the radiator 2 are united by fasteners 4. The propeller fan 1 according to the first embodiment is mounted on the radiator 2, and its position is at a rear of the vehicle (hereafter, vehicle rear) T side in its traveling direction. Thus, this example has the condenser 3, radiator 2 and propeller fan 1 configured as one and mounted in an engine room of the vehicle on the vehicle front L side. FIG. 2 is a front view showing a state of the propeller fan according to the first embodiment viewed from the vehicle front side. FIG. 3 is an A to A arrow view of FIG. 2. FIG. 4 is a front view showing the rotary vane wheel provided to the propeller fan according to the first embodiment. The rotary vane wheel is omitted in FIG. 2. As shown in FIG. 3, the propeller fan according to the first embodiment comprises a rotary vane wheel 8 shown in FIG. 4, a shroud 5 shown in FIG. 2 and an electric motor (rotary vane wheel driving means) 6 shown in FIGS. 2 and 3. The rotary vane wheel 8 shown in FIG. 4 is configured by a hub 8H and multiple blade portions 8W mounted on an outer circumferential portion thereof. The rotary vane wheel 8 comprises 7 blade portions 8W. However, the number of the blade portions 8W is not limited thereto. As shown in FIG. 3, the hub 8H of the rotary vane wheel 8 is mounted on a rotation axis 6S of the electric motor 6. The electric motor 6 rotates the rotary vane wheel 8 centering on a rotation axis Zf, and lefts air W flow from the vehicle front L side to the vehicle rear T. In that process, the air W exchanges heat with the coolant and refrigerant flowing inside the radiator 2 and the condenser 3. Here, a rotation direction of the rotary vane wheel 8 is a direction Fr in FIGS. 2 and 4. And the rotation axis Zf is the rotation axis of the electric motor 6 and the rotary vane wheel 8. The shroud 5 comprises a mount pedestal 7 for mounting the electric motor 6 as the rotary vane wheel driving means. As shown in FIG. 2, the mount 7 is supported on a body portion 5B of the shroud 5 by multiple support beams 10 radially extending from the rotation axis Zf. A ventilation flue 9 is formed between the mount 7 and the body portion 5B. As shown in FIG. 2, the ventilation flue 9 is divided off by the support beams 10. Here, the number of the support beams 10 is 11 in the first embodiment. However, the number of the support beams 10 is not limited thereto. The engine room of the vehicle hardly has space because it has not only an engine as a power source of the vehicle but also its accessories mounted therein. In particular, it is necessary in recent years to secure a crushable zone for the traveling direction of the vehicle for the sake of improving collision safety so that devices mounted in the engine room are limited as to a dimension in the traveling direction of the vehicle. For this reason, the propeller fan 1 for cooling the condenser 3 and radiator 2 is also limited as to the dimension in a flow direction of the air W, that is, the direction parallel with the rotation axis Zf of the rotary vane wheel 8 of the propeller fan 1. Because of this limitation of the dimension, space between the support beams 10 and the blade portions 8W of the rotary vane wheel 8 is also limited so that a sufficient dimension cannot be secured. Here, during operation of the propeller fan 1, the rotary vane wheel 8 rotates at high speed and so the support beams 10 on a stationary side and the blade portions 8W of the rotary vane wheel 8 perform relative movement at high speed. In the case where the space between the support beams 10 and the blade portions 8W of the rotary vane wheel 8 cannot be secured sufficiently, it furthers pressure interference generated by the relative movement between the support beams 10 and the blade portions 8W and generates harsh noise called discrete frequency noise. Thus, the propeller fan 1 according to the first embodiment has the following configuration of the support beams 10 provided to the shroud 5 in order to cope with this problem. FIG. 5 is a plan view showing the support beam provided to the shroud of the propeller fan according to the first embodiment. FIG. 5 shows a state of one of the support beams provided to the shroud viewed from the vehicle front side. FIGS. 6 and 7 are sectional views of the support beam provided to the shroud of the propeller fan according to the first embodiment. FIG. 8A is a B to B sectional view of FIG. 5, FIG. 8B is a C to C sectional view of FIG. 5, and FIG. 8C is a D to D sectional view of FIG. 5. Here, a section of the support beam means a longitudinal direction of the support beam, that is, the section orthogonal to the radial direction of the rotary vane wheel. The support beams 10 provided to the shroud 5 of the propeller fan 1 according to the first embodiment are configured so that thickness h of the support beams 10 becomes larger from an upstream side (IN side of FIG. 6) of the flow direction of the air discharged by the rotary vane wheel 8 toward a downstream side (OUT side of FIG. 6) of the flow direction of the air discharged by the rotary vane wheel 8. And an edge (hereafter, a downstream side edge) 10to of the support beams 10 on the downstream side of the flow direction of the air discharged by the rotary vane wheel 8 is inclined to be oriented toward a direction parallel with the rotation axis Zf of the rotary vane wheel 8, and an edge (hereafter, an upstream side edge) 10ti of the support beams 10 on the upstream side of the flow direction of the air discharged by the rotary vane wheel 8 is inclined to be oriented toward a direction opposite to the rotation direction Fr of the rotary vane wheel 8. Here, the thickness of the support beam 10 means the dimension in a direction orthogonal to a center line S of the support beam 10 in a cross-section of the support beam 10. In such a configuration, when the air discharged by the rotary vane wheel 8 passes through the support beams 10, the flow of the air discharged from the rotary vane wheel 8 (arrows Wi of FIG. 6) is changed to the direction of the rotation axis Zf of the rotary vane wheel 8 (arrows Wo of FIG. 6) by the support beams 10. To be more specific, the support beams 10 rectify the flow of the air discharged by the rotary vane wheel 8 to reduce circling components thereof. As an upstream side 10i of the support beams 10 is inclined toward the direction opposite to the rotation direction Fr of the rotary vane wheel 8, the air discharged by the rotary vane wheel 8 flows smoothly along the upstream side 10i of the support beams 10 and the direction of the flow is gradually changed. It is possible, by these actions, to reduce pressure interference between the rotary vane wheel 8 and the support beams 10 so as to prevent generation of the noise of discrete frequency components as a noise source. The thickness h of the support beams 10 becomes gradually larger from the upstream side edge portion 10ti toward the downstream side edge portion 10to, and the downstream side edge portion 10to faces the direction parallel with the rotation axis Zf of the rotary vane wheel 8. To be more specific, as shown in FIG. 6, the thickness of the support beams 10 becomes gradually larger from the upstream side edge portion 10ti toward the downstream side edge portion 10to in order of hi, hm and ho. As the support beams 10 have such a cross-section, it is possible to increase geometric moment of inertia and secure a cross section on the downstream side 10o of the support beams 10 so as to secure sufficient strength of the rotary vane wheel 8 in the rotation axis Zf direction. It is thereby possible to secure sufficient strength to bear a road surface vibrational acceleration when mounted on the vehicle in addition to a static load and a vibrational load of the electric motor 6 and the rotary vane wheel 8. Here, the upstream side 10i of the support beams 10 refers to the range further on the blade portion 8W side of the rotary vane wheel 8 than an approximate center M of a length H of the support beams 10 in the rotation axis Zf direction of the rotary vane wheel 8. The downstream side 10o of the support beams 10 refers to the range further on the downstream side (OUT side of FIG. 6) of the flow direction of the air discharged by the rotary vane wheel 8 than the approximate center M of the length H of the support beams 10 in the rotation axis Zf direction of the rotary vane wheel 8. The cross-section of the support beam 10 can be configured as shown in FIG. 7 for instance. Reference character S refers to the center line in the cross section orthogonal to the longitudinal direction of the support beams 10. The center line S is rendered as an arc of ¼ or less centering on a virtual center point P, and the center of a first circle C1, configuring the downstream side edge portion 10to is placed on the center line S. And, as well as the first circle C1, a second circle C2, a third circle C3 and so on having their centers on the center line S are placed by rendering their radiuses smaller gradually toward the upstream side edge portion 10ti according to a distance from the downstream side edge portion 10to to the upstream side edge portion 10ti. The center of an n-th circle Cn configuring the upstream side edge portion 10ti is placed on the most upstream position on the center line S, that is, the position opposed to the rotary vane wheel 8. Here, if the radius of the first circle C1, is r1, the radius of the second circle C2 is r2, . . . and the radius of the n-th circle Cn is rn, it is r1>r2>rn. Thus, after placing the first circle C1, configuring the downstream side edge portion 10to to the n-th circle Cn configuring the upstream side edge portion 10ti in sequence, they are connected by an envelope including parts on circumferences of the first circle C1, second circle C2, third circle C3 to n-th circle Cn, irrespectively. The cross-section of the support beam 10 according to the first embodiment is composed of a contour configured by two envelopes SC1, and SC2, the arc of the first circle C1 on the downstream side in the airflow direction and the arc of the n-th circle Cn, on the upstream side in the airflow direction. A technique for deciding the cross-section of the support beam 10 according to the first embodiment is not limited to this. The support beams 10 provided to the shroud 5 according to the first embodiment has the inclination of the upstream side edge portion 10ti varied toward the outside of the longitudinal direction of the support beams 10 (arrow Do direction of FIG. 5), that is, as directed from the mount 7 side to the body portion SB of the shroud 5. As shown in FIG. 7, reference character l1 denotes a tangent of the upstream side edge portion 10ti at an intersecting point j between the upstream side edge portion 10ti configured by the arc and the center line S of the support beam 10 on the cross section orthogonal to the longitudinal direction of the support beams 10. And reference character l2 denotes a straight line orthogonal to the tangent l1 while reference character θ denotes an angle of gradient made by the straight line 12 and a plane including the rotation axis Zf of the rotary vane wheel 8. To be more specific, the angle of gradient θ indicates the inclination of the upstream side edge portion 10ti (inclination to the plane including the rotation axis Zf of the rotary vane wheel 8). As shown in FIGS. 8A to 8C, the angle of gradient θ becomes larger as directed toward the outside of the longitudinal direction of the support beams 10. To be more specific, it is θ3>θ2>θ1. To be more specific, as directed from the inside of the longitudinal direction (the mount 7 side) of the support beams 10 toward the outside of the longitudinal direction (the body portion 5B of the shroud 5), an opening becomes larger between the plane including the rotation axis Zf of the rotary vane wheel 8 and the upstream side edge portion 10ti. A circumferential velocity of the rotary vane wheel 8 becomes higher from the inside toward the outside of the rotary vane wheel 8, and the circling components of the air discharged by the rotary vane wheel 8 become stronger accordingly. To be more specific, the flows of the air discharged by the rotary vane wheel 8 become those denoted by reference characters Wi, Wm and Wo as directed toward the outside of the radial direction of the rotary vane wheel 8 respectively. However, the components in the rotation direction Fr of the rotary vane wheel 8 become larger as the flows of the air discharged by the rotary vane wheel 8 are directed toward the outside of the radial direction of the rotary vane wheel 8. The support beams 10 provided to the shroud 5 according to the first embodiment enlarges the opening between the plane including the rotation axis Zf of the rotary vane wheel 8 and the upstream side edge portion 10ti. It is thereby possible to reduce the pressure interference between the rotary vane wheel 8 and the support beams 10 all over the longitudinal direction of the support beams 10 so as to prevent generation of the noise of the discrete frequency components more effectively. As the downstream side edge portion 10to is directed toward the rotation axis Zf of the rotary vane wheel 8, it is also possible to increase geometric moment of inertia and secure sufficient strength. FIG. 9 is a partial sectional view showing the propeller fan according to the first embodiment. FIG. 10 is a schematic diagram of a ventilation range of the propeller fan. FIG. 11 is a schematic diagram showing a relation of a discharge flow of the rotary vane wheel, a specific sound level KPWL-BPF relating to acoustic power based on a discrete frequency BPF and a flow concentration coefficient value R against a distance between the blade portion of the rotary vane wheel and the heat exchanger. Here, a distance t shown in FIG. 9 indicates the distance between the blade portion 8W of the rotary vane wheel 8 and the heat exchanger. The value R shown in FIG. 11 will be described by using FIG. 10. FIG. 10 shows on its left side a ventilation range A ∞ of the propeller fan 1 in the case where the distance t is infinite, that is, the distance between the blade portion 8W of the rotary vane wheel 8 and the heat exchanger is infinitely apart. The value R in this case is 0 so that the air flows from the heat exchanger to the propeller fan with complete uniformity. FIG. 10 shows on its right side a ventilation range A0 of the propeller fan 1 in the case where the distance t is 0, that is, there is no distance between the blade portion 8W of the rotary vane wheel 8 and the heat exchanger. The value R in this case is approximately 2.5 so that the air flows from the heat exchanger through the portion of the blade portion 8W of the rotary vane wheel 8. Here, the value R is represented by a formula (1). R=√((1/A)×∫A(u(a))−u—av)2da) (1) Here, A denotes area of the entire region, u (a) denotes dimensionless velocity in a miniregion a. And u_av is an average of the velocity in the entire region rendered dimensionless, which is 1. As shown in FIG. 11, a discharge flow Q of the rotary vane wheel 8 increases as the distance t is rendered larger, that is, as the distance between the heat exchanger and the blade portion 8W of the rotary vane wheel 8 is rendered larger. If the value R is rendered larger than t2, the value R becomes asymptotic to an approximately fixed value. Therefore, it is desirable to render the distance t between the blade portion 8W of the rotary vane wheel 8 and the heat exchanger as large as possible, that is, at least larger than t2. If the t is rendered larger, however, the distance between the blade portion 8W of the rotary vane wheel 8 and the support beams 10 becomes closer so that noise components based on the discrete frequency BPF (Blade Passing Frequency) (that is, the specific sound level relating to the acoustic power based on the BPF of FIG. 11) become larger. Here, BPF_SQ of FIG. 11 is the noise component based on the BPF having a rectangular cross section of the support beam, and BPF_W is the noise component based on the BPF of the support beam 10 according to the first embodiment. In the case where the distance t between the blade portion 8W of the rotary vane wheel 8 and the heat exchanger is the same, the support beam 10 according to the first embodiment can render the noise component based on the BPF smaller compared to the support beam of the rectangular cross section. To be more specific, the support beam 10 according to the first embodiment can render the distance t between the blade portion 8W of the rotary vane wheel 8 and the heat exchanger larger while suppressing the noise component based on the BPF. Consequently, it is possible to render the discharge flow Q of the rotary vane wheel 8 larger while suppressing the noise component based on the BPF. Next, a description will be given as to a modified example of the support beam provided to the shroud of the propeller fan according to the first embodiment. FIGS. 12A to 12C are schematic diagrams showing a modified example of the support beam provided to the shroud of the propeller fan according to the first embodiment. FIG. 13 shows a modified example of the support beam provided to the shroud of the propeller fan according to the first embodiment. It is possible to configure a center line Sa by combining two straight lines as with a support beam 10a shown in FIG. 12A. It is also possible to configure a center line Sb by combining three straight lines as with a support beam 10b shown in FIG. 12B. It is also possible to render an upstream side edge 10cti in a sharp-edge shape rather than the arc as with a support beam 10c shown in FIG. 12C. It is thereby possible to further reduce resistance of the air discharged by the rotary vane wheel 8. Here, sharp-edge refers to the case where the upstream side edge 10cti is an arc, the radius of the arc being 0.5 mm or less. Furthermore, it is also possible to form a groove 10ds on a downstream side 10do as with a support beam 10d shown in FIG. 13. It is thereby possible, for instance, to house electric wire for supplying power to the electric motor 6 in the groove 10ds so as to exploit the space effectively. It is possible, as a part of the support beam 10d is eliminated, to render the support beam 10d further lightweight. It is also possible to render the support beam as a hollow structure. It is also possible, in this case, to place the electric wire, signal line and the like in the hollow portion and render it further lightweight by providing the hollow portion. As described above, the first embodiment and modified example thereof have the upstream side of the support beam inclined toward the direction opposite to the rotation direction of the rotary vane wheel, and so the air discharged by the rotary vane wheel flows smoothly along the upstream side of the support beams and the direction of the flow is gradually changed. The downstream side edge of the support beam is oriented toward the direction parallel to the rotation axis of the rotary vane wheel. It is thereby possible to rectify the circling components of the flow of the air discharged by the rotary vane wheel to reduce them so as to reduce the pressure interference between the rotary vane wheel and the support beams and prevent generation of the noise of discrete frequency components as a noise source. The support beams become gradually thicker from the upstream side edge toward the downstream side edge, and the downstream side edge faces the direction parallel with the rotation axis of the rotary vane wheel. As the support beams have such a cross-section, it is possible to increase geometric moment of inertia of the support beams. It is possible to secure a sufficient cross section on the downstream side of the support beams. It is possible, by these actions, to secure sufficient strength in the rotation axis direction of the rotary vane wheel in particular. It is consequently possible, even in the case of limiting the dimension in the airflow direction, to reduce the noise and secure the strength of the support beams supporting the rotary vane wheel and rotary vane wheel driving means. It is thereby possible to reduce the number of the support beams and further reduce an aerodynamic drag and the noise. Part Second Embodiment: FIGS. 14 to 16 are a front view (FIG. 14), a rear view (FIG. 15) and a side sectional view (FIG. 16) showing the propeller fan according to a second embodiment of the present invention. FIG. 17 is a front side perspective view showing the rotary vane wheel of the propeller fan described in FIGS. 14 to 16. FIGS. 18 to 20 are an A to A sectional view (FIG. 18) and plan views (FIGS. 19 and 20) showing the blade portion of the rotary vane wheel described in FIG. 17. FIGS. 21 to 24 are schematic diagrams showing the action of the propeller fan described in FIGS. 14 to 16. This propeller fan 11 is placed in the downstream of the radiator for cooling the vehicle and the condenser for air conditioning and in proximity to the engine (not shown), and has a function of air-cooling the radiator and the condenser for air conditioning. The propeller fan 11 comprises a shroud 12, a rotary vane wheel 13 and a motor 14 (refer to FIGS. 14 to 16). The shroud 12 is composed of a resin material, and includes a body portion 21, a motor holding portion 22 and a rib portion 23 (refer to FIG. 16). The body portion 21 is a frame-like member having an opening for introducing air at its center. The body portion 21 has the rotary vane wheel 13 and motor 14 accommodated therein. The motor holding portion 22 is a member for holding the motor 14, and is placed at the center of the opening of the body portion 21 while supported by the rib portion 23. The rotary vane wheel 13 is an axial fan having a hub portion 31 and a blade portion 32 composed of the resin material, and is configured by having multiple blade portions 32 annularly arranged on the hub portion 31 as a rotor (refer to FIG. 14). The motor 14 is a power source for rotating the rotary vane wheel 13. The motor 14 is coupled to the rotary vane wheel 13 on its output side (front side) and screwed and fixed on the motor holding portion 22 of the body portion 21 on its opposite output side (backside). If the rotary vane wheel 13 is rotated by driving of the motor 14, the propeller fan 11 has the air introduced from the front (the side of the radiator for cooling and condenser for air conditioning) to the opening of the body portion 21 to be sent backward. Thus, the radiator and condenser are cooled. [Noise Reduction Structure of the Rotary Vane Wheel] Here, as regards the propeller fan 11, (1) flatness H/DF of the rotary vane wheel 13 is H/DF≦0.12 (refer to FIGS. 16 and 17). The flatness H/DF is defined by the ratio between an axial width H of the blade portion 32 and a diameter DF at an end of the blade portion 32. (2) A ratio Dm/DF between a diameter Dm of the hub portion 31 and the diameter DF at the end of the blade portion 32 is Dm/DF≦0.50. To be more specific, annular channel area of cooling wind is defined by the ratio Dm/DF. (3) A pitch chord ratio P/C of the blade portion 32 is 1.0≦P/C≦1.2. The pitch chord ratio P/C is defined by the ratio between a circumferential pitch P and a chord length C of the blade portion 32 on an arbitrary cylindrical section A to A (refer to FIG. 18) in an annular radial dimension range in which a radius ratio (vane radius ratio) of the blade portion 32 is 10(%) to 95(%). (4) The outer circumferential side of the blade portion 32 is swept forward in the rotation direction of the rotary vane wheel 13 (forward swept vane). In such a configuration, the diameter ratio Dm/DF between the hub portion 31 and the blade portion 32 and the pitch chord ratio P/C of the blade portion 32 are rendered appropriate on the rotary vane wheel 13 having a low degree of flatness H/DF while the blade portion 32 is the forward swept vane so as to prevent the rotation of the rotary vane wheel 13 from stalling. Thus, the air blowing performance (aerodynamic performance) in the sound operational area is improved so that the operation of the rotary vane wheel 13 becomes stable. This has an advantage of improving the noise performance, air blowing performance and air blowing efficiency of the propeller fan 11. For instance, if the pitch chord ratio P/C of the blade portion 32 becomes smaller, a stall point pressure (pressure whereby a differential pressure hardly increases even if an air volume φ is reduced) of the rotary vane wheel 13 increases (refer to FIG. 21). If the pitch chord ratio P/C is P/C<1.0, however, the adjacent blade portion 32 overlaps so that molding and manufacturing of the rotary vane wheel 13 made of a resin become difficult (refer to FIG. 22). Part MODIFIED EXAMPLE 1: As for the propeller fan 11, it is desirable that, when a straight line m is drawn from a point S at which a chord ratio c/C at a radial outer edge of the blade portion 32 is 50(%) to the rotation center of the rotary vane wheel 13, the chord ratio c/C of an intersecting point T of the straight line m and a radial inner edge (the hub portion 31) of the blade portion 32 is in the range of 0.10≦c/C≦0.30 (refer to FIG. 19). This renders a degree of forward sweeping of the rotary vane wheel 13 appropriate. Therefore, there is an advantage of further improving the noise performance, air blowing performance and air blowing efficiency of the propeller fan 11. The chord ratio c/C is the ratio of a distance c from an front edge (edge of an rotation advance side) of the blade portion 32 to the chord length C of the blade portion 32 in a cylindrical sectional view (refer to FIG. 19) centering on the rotation center of the rotary vane wheel 13. Part MODIFIED EXAMPLE 2: As for the propeller fan 11, it is desirable that a curve l on the blade portion 32 of which chord ratio c/C is 50(%) is an approximately arc of a radius R, and a ratio R/DF between the radius R of the curve l and the diameter DF of the rotary vane wheel 13 is in the range of 0.2≦R/DF≦0.5 (refer to FIG. 20). It is more desirable that the ratio R/DF is 0.3≦R/DF≦0.4 (R/DF≈0.36). This renders the degree of forward sweeping of the rotary vane wheel 13 appropriate. Therefore, there is an advantage of further improving the noise performance, air blowing performance and air blowing efficiency of the propeller fan 11. For instance, if the degree of forward sweeping of the rotary vane wheel 13 is too low or too high, the noise performance (KPWL) of the propeller fan 11 is degraded by the breakaway of the flow on a propeller vane plane (refer to FIG. 23). Part MODIFIED EXAMPLE 3: As for the propeller fan 11, a curve l on the blade portion 32 of which chord ratio c/C is 50(%) is drawn first. Next, a circle is drawn, which has a radius r with a ratio r/DF to the diameter DF of the rotary vane wheel chad91@example.org≦r/DF≦0.5 and is centering on the rotation center of the rotary vane wheel (refer to FIG. 20). An intersecting point of the circle and the curve l is an origin (blade portion center origin) O. A straight line passing through the origin O and the rotation center of the rotary vane wheel 13 is an axis Y. A straight line passing through the origin O and orthogonal to the axis Y is an axis X. In this case, the curve l should desirably become an arc having its center on the axis X. To be more specific, the curve l is represented as (X+R)2+Y2=R2 (R: radius of the curve l) in an X-Y coordinate system. This renders the degree of forward sweeping of the rotary vane wheel 13 appropriate. Therefore, there is an advantage of further improving the noise performance, air blowing performance and air blowing efficiency of the propeller fan 11. Part MODIFIED EXAMPLE 4: As for the propeller fan 11, it is desirable that the number Z of the blade portions 32 formed on the rotary vane wheel 13 is 6 to 9. It is also desirable that the number Z of the blade portions 32 is an odd number (7 or 9). Such a configuration reduces the acoustic power of BPF noise in particular out of generated noise components. Thus, there is an advantage of further improving the noise performance of the propeller fan 11. As for the relation between the number Z of the blade portions 32 and the noise performance of the propeller fan 11, the generated noise (KPWL) is rendered less and the rotary vane wheel 13 is less likely to stall as a ratio CH/DF between a chord length CH of the blade portion 32 and the diameter DF of the rotary vane wheel 13 becomes larger at the hub portion 31, which is desirable (refer to FIG. 24). It is also desirable that the generated noise (KPWL) is rendered less as the pitch chord ratio P/C becomes smaller. If the pitch chord ratio P/C is less than a predetermined value (P/C<1.0), however, the molding and manufacturing of the rotary vane wheel 13 become difficult. Therefore, the number Z of the blade portions 32 formed on the rotary vane wheel 13 is prescribed by considering these. Part MODIFIED EXAMPLE 5: As for the propeller fan 11, it is possible to adopt a configuration of having a plurality of the blade portions 32 placed on the rotary vane wheel 13 at uneven pitches P. In this case, it is desirable to have the pitch chord ratio P/C prescribed based on an average of the pitches P of the blade portions 32. Such a configuration reduces the acoustic power of BPF noise in particular out of generated noise components by having the pitch chord ratio P/C appropriately prescribed. Thus, there is an advantage of further improving the noise performance of the propeller fan 11. Part Third Embodiment: FIG. 25 is a front view of the propeller fan according to a third embodiment of the present invention. FIG. 26 is an A to A sectional view of FIG. 25. FIG. 27 is a B to B arrow view of FIG. 26. A propeller fan 101 shown in FIGS. 25 to 27 comprises a rotary vane wheel 110 having multiple blade portions 131 provided on a hub 111 and composed of the resin and a shroud 103 which is a housing for placing the rotary vane wheel 110 therein. Of these, the shroud 103 has a channel forming surface 104 and a cylinder portion 105 formed in a cylindrical shape. The rotary vane wheel 110 is provided inside the cylinder portion 105. The rotary vane wheel 110 is rotatably supported by a motor 150 as driving means, and the motor 150 is fixed on the shroud 103. To describe them in detail, the hub 111 has a front edge 112 formed like an approximately circular disk, and also has a connection hole 120 axially penetrating the circle of the front edge 112 at the center of the circle which is the shape of the front edge 112. The motor 150 rotatably supports the hub 111 by inserting a motor axis 151 as an axis rotating on driving the motor 150 into the connection hole 120 to connect it therewith. To be more specific, the rotary vane wheel 110 has a rotation axis 125 of the hub 111 as a central axis of the connection hole 120, and is rotatably supported by the motor 150 by centering on the rotation axis 125. The shroud 103 has multiple motor supporting portions 106 provided on one of both the edges in the axial direction of the cylinder portion 105. All the multiple motor supporting portions 106 are formed inward in the radial direction of the cylinder portion 105 from the cylinder portion 105. The motor 150 is fixed on the motor supporting portions 106 and thereby fixed on the shroud 103. The motor 150 has an electric cord 152 for conveying electricity from a power supply (not shown) connected thereto, and the electric cord 152 further has a connector 153 for connecting to another electric cord 152 provided on the edge of the opposite side to the edge on the motor 150 side thereof. The multiple blade portions 131 provided on the hub 111 of the rotary vane wheel 110 are formed outward from the radial direction centering on the rotation axis 125. The cylinder portion 105 of the shroud 103 is formed with a radius slightly larger than the distance between an outer edge of the blade portions 131 of the rotary vane wheel 110 and the rotation axis 125. And the rotary vane wheel 110 is provided inside the cylinder portion 105 in the orientation in which a cylindrical axis (not shown) as the shape of the cylinder portion 105 and the rotation axis 125 overlap. The channel forming surface 104 is connected to the edge of the opposite side to the edge having the motor supporting portions 106 provided thereon of both the edges in the axial direction of the cylinder portion 105. As for the shape thereof, it is formed in a rectangular shape at the position apart from the cylinder portion 105 in the axial direction of the rotation axis 125 and in forms closer to circular as directed toward the cylinder portion 105. The rotary vane wheel 110 placed in the cylinder portion 105 of the shroud 103 is in the orientation in which the front edge 112 of the hub 111 is located on the channel forming surface 104 side and the motor 150 is located on the motor supporting portion 106 side. Furthermore, a heat shield plate 107 is provided at the position further apart from the channel forming surface 104 than the motor 150 in the direction opposite to the direction in
{'bibliographic_information': "{'country': 'US', 'doc-number': '11363535', 'kind': 'B2', 'date': '20060228', 'extension': '1236', 'invention_title': 'Shroud and rotary vane wheel of propeller fan and propeller fan'}", 'source_file': './grant/2010/ipg101019.xml', 'source_data': 'USPTO-Grant'}