Description:FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See section 10, Rule 13] CENTRIFUGAL BLOWER, AIR-BLOWING APPARATUS, AIR-CONDITIONING APPARATUS, AND REFRIGERATION CYCLE APPARATUS; MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED. Divisional Application Reference under Rule 13(2) of the Patents Rules: This Application is divided out of the Parent App. No. 202027017704 dated 24/04/2020 under Section 16(1) of the Patents Act and claims an invention disclosed in the complete specification of said application. DESCRIPTION Field [0001] The present invention relates to a centrifugal air blower having a scroll casing, and an air-blowing apparatus, an air-conditioning apparatus, and a refrigeration cycle apparatus that include the centrifugal air blower. Background [0002] A scroll casing of a centrifugal air blower has a bell mouth that guides an airflow sucked into a suction opening. If the axial distance between the upstream end and the downstream end of the bell mouth is short in the centrifugal air blower, the direction of the airflow changes suddenly, and turbulence occurs in the flow, resulting in a decrease in air blowing efficiency. Patent Literature 1 discloses a centrifugal air blower in which at least the portion of the bell mouth of the scroll casing having a higher air inflow velocity protrudes outward from the scroll casing. [0003] In the invention disclosed in Patent Literature 1, the axial distance between the upstream end and the downstream end of the bell mouth is partially long, and accordingly, the airflow is gradually changed at the suction opening. Thus, turbulence hardly occurs in the flow, and the decrease in air blowing efficiency can be effectively reduced. Citation List Patent Literature [0004] Patent Literature 1: Japanese Patent Application Laid-open No. 5-17400 Summary Technical Problem [0005] In the invention disclosed in Patent Literature 1, however, the bell mouth is not widened in the radial direction, and therefore, there is room for improvement of the air blowing efficiency. [0006] The present invention has been made in view of the above, and aims to obtain a centrifugal air blower with enhanced air blowing efficiency. Solution to Problem [0007] To solve the above problem and achieve the object, a centrifugal air blower according to the present invention comprises: a fan including a disk-shaped main plate and a plurality of blades disposed on a peripheral portion of the main plate; and a scroll casing. The scroll casing includes: a sidewall covering the fan from an axial direction of a rotation axis on which the fan rotates, the side wall having a suction opening for sucking air; a discharge opening for discharging an airflow generated by the fan; a tongue portion for guiding the airflow to the discharge opening; a peripheral wall surrounding the fan from a radial direction of the rotation axis; and a bell mouth formed along the suction opening of the sidewall. The bell mouth includes an upstream end and a downstream end, the upstream end being an end portion on an upstream side in a direction of flow of the air passing through the suction opening, the downstream end being an end portion on a downstream side in the direction of flow of the air. A distance in the radial direction of the rotation shaft between the upstream end and the downstream end at a location larger than the tongue portion in angle of a direction of rotation of the fan is longer than a distance in the radial direction between the upstream end and the downstream end at a location adjacent to the tongue portion. Advantageous Effects of Invention [0008] A centrifugal air blower according to the present invention has an effect of enhancing the air blowing efficiency. Brief Description of Drawings [0009] FIG. 1 is a perspective view of an air blower according to a first embodiment of the present invention. FIG. 2 is a top view of the air blower according to the first embodiment. FIG. 3 is a cross-sectional view of the air blower according to the first embodiment. FIG. 4 is a top view illustrating a first modification of the air blower according to the first embodiment. FIG. 5 is a cross-sectional view illustrating the first modification of the air blower according to the first embodiment. FIG. 6 is a perspective view illustrating a second modification of the air blower according to the first embodiment. FIG. 7 is a top view illustrating the second modification of the air blower according to the first embodiment. FIG. 8 is a cross-sectional view illustrating the second modification of the air blower according to the first embodiment. FIG. 9 is a top view illustrating a third modification of the air blower according to the first embodiment. FIG. 10 is a top view illustrating a fourth modification of the air blower according to the first embodiment. FIG. 11 is a cross-sectional view illustrating the fourth modification of the air blower according to the first embodiment. FIG. 12 is a top view illustrating a fifth modification of the air blower according to the first embodiment. FIG. 13 is a top view illustrating a sixth modification of the air blower according to the first embodiment. FIG. 14 is a top view illustrating a seventh modification of the air blower according to the first embodiment. FIG. 15 is a cross-sectional view of an air blower according to a second embodiment of the present invention. FIG. 16 is a cross-sectional view of an air blower according to a third embodiment of the present invention. FIG. 17 is a cross-sectional view of an air blower according to a fourth embodiment of the present invention. FIG. 18 is a top view of an air blower according to a fifth embodiment of the present invention. FIG. 19 is a cross-sectional view of an air blower according to the fifth embodiment. FIG. 20 is a cross-sectional view of an air blower according to a sixth embodiment of the present invention. FIG. 21 is a cross-sectional view of an air blower according to a seventh embodiment of the present invention. FIG. 22 is a cross-sectional view of an air blower according to an eighth embodiment of the present invention. FIG. 23 is a cross-sectional view of an air blower according to a ninth embodiment of the present invention. FIG. 24 is a diagram illustrating the configuration of an air-blowing apparatus according to a tenth embodiment of the present invention. FIG. 25 is a perspective view of an air-conditioning apparatus according to an eleventh embodiment of the present invention. FIG. 26 is a diagram illustrating the internal configuration of the air-conditioning apparatus according to the eleventh embodiment. FIG. 27 is a cross-sectional view of the air-conditioning apparatus according to the eleventh embodiment. FIG. 28 is a diagram illustrating the configuration of a refrigeration cycle apparatus according to a twelfth embodiment of the present invention. Description of Embodiments [0010] The following is a detailed description of a centrifugal air blower, an air-blowing apparatus, an air-conditioning apparatus, and a refrigeration cycle apparatus according to embodiments of the present invention, with reference to the drawings. Note that the present invention is not limited by the embodiments. [0011] First Embodiment FIG. 1 is a perspective view of an air blower according to a first embodiment of the present invention. FIG. 2 is a top view of the air blower according to the first embodiment. FIG. 3 is a cross-sectional view of the air blower according to the first embodiment. FIG. 3 illustrates a cross-section taken along line III-III defined in FIG. 2. An air blower 1, which is a multi-blade centrifugal air blower, includes a fan 2 that generates an airflow, and a scroll casing 4 provided with a bell mouth 3 that rectifies an airflow taken into the fan 2. [0012] The fan 2 includes a disk-shaped main plate 2a, a ring-shaped side plate 2c facing the main plate 2a, and a plurality of blades 2d disposed at the peripheral portion of the main plate 2a. The blades 2d surround a rotation axis AX between the main plate 2a and the side plate 2c. The main plate 2a has its central portion providing a boss portion 2b. An output shaft 6a of a fan motor 6 is connected to the center of the boss portion 2b, and the fan 2 is rotated by the driving force of the fan motor 6. Note that the fan 2 may have a structure without the side plate 2c. [0013] The scroll casing 4 surrounds the fan 2, and rectifies the air blown from the fan 2. The scroll casing 4 includes a sidewall 4c, a peripheral wall 4a, a discharge opening 41, and a tongue portion 4b. The sidewall 4c covers the fan 2 from the axial direction of the rotation axis AX. The peripheral wall 4a covers the fan 2 from the radial direction of the rotation axis AX. The discharge opening 41 discharges an airflow generated by the fan 2. The tongue portion 4b guides the airflow generated by the fan 2 to the discharge opening 41. Note that the radial direction of the rotation axis AX is a direction perpendicular to the rotation axis AX. The inside of a scroll portion 4e defined by the peripheral wall 4a and the sidewall 4c is a space in which air blown from the fan 2 flows along the peripheral wall 4a. [0014] The discharge opening 41 has an end portion 41a located on the side of the tongue portion 4b, and an end portion 41b located on the side away from the tongue portion 4b. The peripheral wall 4a extends from the end portion 41a to the end portion 41b in the direction of rotation of the fan 2. Accordingly, the scroll portion 4e is contiguous with the discharge opening 41 without the peripheral wall 4a being provided therebetween. A distance between the rotation axis AX of the fan 2 and the peripheral wall 4a becomes longer as an angle ? relative to the tongue portion 4b in the direction of rotation of the fan 2 increases between the tongue portion 4b and a location at which the peripheral wall 4a is contiguous with the discharge opening 41. The distance between the rotation axis AX of the fan 2 and the peripheral wall 4a is shortest at the end portion 41a. [0015] A suction opening 5 is formed in the sidewall 4c of the scroll casing 4. The sidewall 4c defines the bell mouth 3. An airflow to be sucked into the scroll casing 4 through the suction opening 5 is guided by the bell mouth 3. The bell mouth 3 is formed at a position at which the fan 2 faces the suction opening 5. The bell mouth 3 has an upstream end 3a and a downstream end 3b. The upstream end 3a is an end on an upstream side of an airflow to be sucked into the scroll casing 4 through the suction opening 5, and the downstream end 3b is an end on a downstream side of the airflow. The bell mouth 3 is shaped to provide an airflow path narrowing from the upstream end 3a toward the downstream end 3b. In the air blower 1 according to the first embodiment, the bell mouth 3 has a curved surface having a curved cross-sectional shape in the plane including the rotation axis AX. However, the bell mouth 3 may have a curved surface having a linear cross-sectional shape in the plane including the rotation axis AX. In other words, the bell mouth 3 may be like the side face of a circular truncated cone. [0016] The peripheral portion of the bell mouth 3 has a curved portion 31 having a curved surface convex in a direction away from the main plate 2a, and smoothly connects the bell mouth 3 and the peripheral wall 4a of the scroll casing 4. Here, the phrase “smoothly” means that the tilting of the curved surface continuously changes between the bell mouth 3 and the peripheral wall 4a, such that any edge is not formed at the boundary between the bell mouth 3 and the peripheral wall 4a. [0017] A step 42 is formed at the boundary between the discharge opening 41 and the scroll portion 4e, such that the airflow is reduced in the cross-sectional area as the air flow travels from the scroll portion 4e toward the discharge opening 41. Since the cross-sectional area of the airflow that travels from the scroll portion 4e toward the discharge opening 41 is reduced, the flow rate of the airflow blown out of the scroll casing 4 through the discharge opening 41 becomes higher. [0018] A radial distance between the upstream end 3a and the downstream end 3b of the bell mouth 3 is longer at a location where an angle relative to the end portion 41a in the direction of rotation of the fan 2 is larger between the end portion 41a and the end portion 41b. [0019] L? represents the radial distance between the upstream end 3a and the downstream end 3b of the bell mouth 3 at a location where an angle relative to the end portion 41a in the direction of rotation of the fan 2 is ? degrees. L0 can be defined as the distance between the upstream end 3a and the downstream end 3b on the line segment interconnecting the end portion 41a and the rotation axis AX as viewed from above. Further, L270 can be defined as the distance between the upstream end 3a and the downstream end 3b on the line segment interconnecting the end portion 41b and the rotation axis AX as viewed from above. In the air blower 1 according to the first embodiment, L90 is longer than L0, and L180 is longer than L90. The radial distance L between the upstream end 3a and the downstream end 3b of the bell mouth 3 becomes longest at L270 where the scroll casing 4 is connected to the discharge opening 41, after which the radial distance L becomes shortest at L360 corresponding to the end portion 41a. For example, the radial distance L? between the upstream end 3a and the downstream end 3b of the bell mouth 3 becomes longer as the angle ? increases in the range of 0 degrees to 270 degrees. The radial distance L? between the upstream end 3a and the downstream end 3b of the bell mouth 3 may continuously become longer from the end portion 41a toward the end portion 41b, or may become longer stepwise. Note that the angle at which the radial distance between the upstream end 3a and the downstream end 3b of the bell mouth 3 becomes longest may be any angle between 0 degrees and 360 degrees, and is not limited to 270 degrees as illustrated as an example. In other words, the radial distance between the upstream end 3a and the downstream end 3b of the bell mouth 3 may become longest at a location where the angle relative to the end portion 41a in the direction of rotation of the fan 2 is between 0 degrees and 360 degrees, and may become gradually shorter in the direction of the rotation of the fan 2. [0020] Here, the peripheral wall 4a is continuous with the discharge opening 41 at a location where the angle relative to the end portion 41a in the direction of rotation of the fan 2 is 270 degrees. However, the peripheral wall 4a may be contiguous with the discharge opening 41 at a location where the angle relative to the end portion 41a is any angle other than 270 degrees. [0021] When the fan 2 rotates, the air outside the scroll casing 4 is sucked into the scroll casing 4 through the suction opening 5. The air sucked into the scroll casing 4 is guided by the bell mouth 3 and is sucked into the fan 2. The air sucked into the fan 2 is blown out of the fan 2 in the radial direction toward the outside. The air blown out of the fan 2 passes through the scroll portion 4e, and is then blown out of the scroll casing 4 through the discharge opening 41. [0022] Since the distance between the upstream end 3a and the downstream end 3b of the bell mouth 3 at any location other than the end portion 41a is longer than the distance between the upstream end 3a and the downstream end 3b at the end portion 41a, the airflow sucked into the scroll casing 4 through the suction opening 5 is not easily separated from the bell mouth 3. Thus, the air blower 1 according to the first embodiment can reduce the decrease in air blowing efficiency, and reduce noise. [0023] In the air blower 1 according to the first embodiment, the bell mouth 3 and the peripheral wall 4a of the scroll casing 4 are smoothly connected to each other by the curved portion 31. Thus, the air on the side of the peripheral wall 4a flows along the curved portion 31, and is guided to the bell mouth 3. Since the boundary portion between the bell mouth 3 and the peripheral wall 4a of the scroll casing 4 is defined by the curved portion 31, air blowing efficiency is enhanced. [0024] FIG. 4 is a top view illustrating a first modification of the air blower according to the first embodiment. FIG. 5 is a cross-sectional view illustrating the first modification of the air blower according to the first embodiment. FIG. 5 illustrates a cross-section taken along line V-V defined in FIG. 4. In the air blower 1 according to the first modification, the scroll casing 4 is defined by two components joined together. The two components have their engaging portions 44 each defined by a recessed portion of one of the components and a protruding portion of the other component, the recessed portion and the protruding portion engaging each other. One of the two engaging portions 44 is disposed on the sidewall 4c between the upstream end 3a of the bell mouth 3 and the peripheral wall 4a of the scroll casing 4. Note that the engaging portion 44 may be provided at the connecting portion 43 that interconnects the upstream end 3a and the sidewall 4c. [0025] In the air blower 1 according to the first modification of the first embodiment, at least one of the engaging portions 44 that join the components of the bell mouth 3 is disposed between the upstream end 3a of the bell mouth 3 and the peripheral wall 4a of the scroll casing 4 and closer to the main plate 2a in the axial direction of the rotation axis AX than the upstream end 3a. Accordingly, it is less likely that the airflow sucked into the scroll casing 4 through the suction opening 5 is hindered by the engaging portion 44. Thus, the air blower 1 according to the first modification can achieve a higher air blowing efficiency than an air blower that has all the engaging portions disposed between the upstream end of the bell mouth and the suction opening. [0026] As described above, in the air blower 1 according to the first embodiment, the radial distance between the upstream end 3a and the downstream end 3b of the bell mouth 3 increases in the direction of rotation of the fan 2 from the radial distance between the upstream end 3a and the downstream end 3b at the end portion 41a. As a result, separation of the flow in the bell mouth 3 can be reduced or prevented. Thus, the air blower 1 according to the first embodiment can achieve a higher efficiency and reduce noise by reducing or preventing the separation of the flow in the bell mouth 3. [0027] Note that the bell mouth 3 does not necessarily reach the peripheral wall 4a of the scroll casing 4 at any portion other than the end portion 41a. FIG. 6 is a perspective view illustrating a second modification of the air blower according to the first embodiment. FIG. 7 is a top view illustrating the second modification of the air blower according to the first embodiment. FIG. 8 is a cross-sectional view illustrating the second modification of the air blower according to the first embodiment. FIG. 8 illustrates a cross-section taken along line VIII-VIII in FIG. 7. The upstream end 3a of the bell mouth 3 and the sidewall 4c are connected to each other by the connecting portion 43. The air blower 1 illustrated in FIGS. 6 through 8 is the same as the air blower 1 illustrated in FIGS. 1 through 3, except that the bell mouth 3 does not reach the peripheral wall 4a of the scroll casing 4 at any portion other than the end portion 41a. Even the structure designed to provide the bell mouth 3 not reaching the peripheral wall 4a of the scroll casing 4 at any portion other than the end portion 41a can achieve the effect of reducing or preventing the separation of the flow in the bell mouth 3 provided that the radial distance between the upstream end 3a and the downstream end 3b of the bell mouth 3 increases in the direction of rotation of the fan 2 from the radial distance between the upstream end 3a and the downstream end 3b of the bell mouth 3 at the end portion 41a. [0028] FIG. 9 is a top view illustrating a third modification of the air blower according to the first embodiment. In the air blower 1 illustrated in FIG. 9, the upstream end 3a of the bell mouth 3 and the sidewall 4c are connected to each other by the connecting portion 43, as in the air blower 1 illustrated in FIGS. 6 through 8. The air blower 1 according to the third modification has a flat surface portion 45 at which the bell mouth 3 has its linear outer contour when viewed from the axial direction of the rotation axis AX of the fan 2. As illustrated in FIG. 9, the flat surface portion 45 is defined by an opposite portion to the tongue portion 4b. At the opposite portion of the scroll casing 4 to the tongue portion 4b, the angle relative to the end portion 41a in the direction of rotation of the fan 2 is larger than 120 degrees but is smaller than 240 degrees. The flat surface portion 45 illustrated in FIG. 9 has its center at which the angle relative to the end portion 41a in the direction of rotation of the fan 2 is 180 degrees. In the air blower 1 according to the third modification, the pressure fluctuation in the bell mouth 3 can be reduced or prevented by the flat surface portion 45, and thus, noise can be reduced. [0029] FIG. 10 is a top view illustrating a fourth modification of the air blower according to the first embodiment. FIG. 11 is a cross-sectional view illustrating the fourth modification of the air blower according to the first embodiment. FIG. 11 illustrates a cross-section taken along line XI-XI in FIG. 10. In the air blower 1 according to the fourth modification, one of the two engaging portions 44 is located between the upstream end 3a of the bell mouth 3 and the peripheral wall 4a of the scroll casing 4 and closer to the main plate 2a than the upstream end 3a in the axial direction of the rotation axis AX. In the air blower 1 according to the fourth modification, the engaging portion 44 is located below the upstream end 3a of the bell mouth 3. Thus, it is possible to achieve the effect of reducing or preventing separation of the flow in the bell mouth 3, without obstructing the airflow sucked into the bell mouth 3. [0030] FIG. 12 is a top view illustrating a fifth modification of the air blower according to the first embodiment. The air blower 1 illustrated in FIG. 12 has a curved surface portion 46 at which the bell mouth 3 has its outer contour that is a curved line protruding in a direction away from the rotation axis AX and partially having a small curvature, when viewed from the axial direction of the rotation axis AX of the fan 2. The air blower 1 according to the fifth modification, which has the curved surface portion 46 provided oppositely to the tongue portion 4b, can reduce sudden pressure fluctuations in the bell mouth 3. Thus, noise can be reduced more than in the third modification having the flat surface portion 45. [0031] FIG. 13 is a top view illustrating a sixth modification of the air blower according to the first embodiment. In the air blower 1 illustrated in FIG. 13, the scroll casing 4 has a “curling start” portion defining the flat surface portion 45. The “curling start” portion of the scroll casing 4 is a portion at which the angle relative to the end portion 41a in the direction of rotation of the fan 2 is larger than 0 degrees but is smaller than 120 degrees. The flat surface portion 45 illustrated in FIG. 13 has its center at which the angle relative to the end portion 41a in the direction of rotation of the fan 2 is 90 degrees. The air blower 1 according to the sixth modification, which provides the curling start portion of the scroll casing 4 with the flat surface portion 45, can reduce pressure fluctuation in the bell mouth 3 at the portion of the start of the curling start portion of the scroll casing 4, and thus, reduce noise. [0032] FIG. 14 is a top view illustrating a seventh modification of the air blower according to the first embodiment. In the air blower 1 illustrated in FIG. 14, the scroll casing 4 has a “curling end” portion defining the flat surface portion 45. The “curling end” portion of the scroll casing 4 is a portion at which the angle relative to the end portion 41a in the direction of rotation of the fan 2 is larger than 240 degrees but is smaller than 360 degrees. The flat surface portion 45 illustrated in FIG. 14 has its center at which the angle relative to the end portion 41a in the direction of rotation of the fan 2 is 270 degrees. The air blower 1 according to the seventh modification, which provides the curling end portion of the scroll casing 4 with the flat surface portion 45, can reduce pressure fluctuation in the bell mouth 3, and thus, reduce noise. [0033] Modifications 3 through 7 described above can be combined. For example, providing at least one of the curling start portion of the scroll casing 4, the curling end portion of the scroll casing 4, and the location opposite to the tongue portion 4b with the flat surface portion 45 or the curved surface portion 46 can reduce noise. Further, the curling start portion of the scroll casing 4 may be provided with the curved surface portion 46, as well as the engaging portion 44 being provided closer to the main plate 2a than the upstream end 3a in the axial direction of the rotation axis AX and between the upstream end 3a of the bell mouth 3 and the peripheral wall 4a of the scroll casing 4. [0034] Second Embodiment FIG. 15 is a cross-sectional view of an air blower according to a second embodiment of the present invention. In the air blower 1 according to the second embodiment, the radial distance A between the upstream end 3a and the downstream end 3b of the bell mouth 3 is longer than the axial distance B between the upstream end 3a and the downstream end 3b of the bell mouth 3, which is expressed as A>B. [0035] In the air blower 1 according to the second embodiment, the curvature of the bell mouth 3 from the upstream end 3a to the downstream end 3b is smaller than that the curvature of the bell mouth providing an arc-shaped cross-section where A = B. As a result, the air blower 1 according to the second embodiment provides the greater effect of making it separation of the suction airflow from the bell mouth 3 unlikely than an air blower with the bell mouth having the arc-shaped cross-section where A = B. [0036] Third Embodiment FIG. 16 is a cross-sectional view of an air blower according to a third embodiment of the present invention. In the air blower 1 according to the third embodiment, the distance B in the axial direction of the rotation axis AX between the upstream end 3a and the downstream end 3b of the bell mouth 3 is longer than the distance A in the radial direction between the upstream end 3a and the downstream end 3b of the bell mouth 3, which is expressed as A