Centrifugal multiblade blower

A centrifugal multiblade blower comprising:

• a multiblade fan (2) having a plurality of blades (2a);
• a fan motor (3) having a motor shaft (3a) on which the multiblade fan (2) is mounted;
• a scroll casing (4) that accommodates therein the multiblade fan (2) and has a discharge port (4c) and cooperates with an outer periphery of the multiblade fan (2) to define a spiral scroll chamber (4a);
• the casing comprising:
• (i) a suction-side case plate (4d) having a suction port (4b);
• and
• (ii) a motor-side case plate (4e) which is located opposite to the suction-side case plate (4d) in such a manner as to sandwich the multiblade fan (2) between the suction-side case plate (4d) and the motor-side case plate (4e), and on which a motor body (3b) of the fan motor (3) is mounted;
• a first counter-flow prevention means (10) for preventing part of air flowing through the scroll chamber (4a) from flowing through a first aperture (G1) defined between the multiblade fan (2) and the suction-side case plate (4d) back to the suction port (4b);
• a second counter-flow prevention means (20) for preventing part of air flowing through the scroll chamber (4a) from flowing through a second aperture (G2) defined between the multiblade fan (2) and the motor-side case plate (4e) back to an upstream side of the scroll chamber (4a);
• a length (L1) of the scroll chamber (4a) measured in an axial direction of the motor shaft (3a) being dimensioned to be longer than a length (L2) of the multiblade fan (2) measured in the axial direction of the motor shaft (3a), and the scroll chamber (4a) being gradually enlarged toward the discharge port (4c) of the casing (4);
• the second counter-flow prevention means (20) comprising:
• (i) a second fan rib (21) provided on the multiblade fan (2) so that the second fan rib is protruded from the multiblade fan (2) to the second aperture (G2), and coaxially arranged with respect to the axis of the multiblade fan (2) and extending completely in the circumferential direction of the multiblade fan (2) around an entire circumference of an outer peripheral portion of a base of the multiblade fan (2) facing a rear end of the motor shaft (3a);
• and
• (ii) a second case rib (22) provided on the motor-side caseplate (4e) so that the second case rib (22) is protruded from the motor-side case plate (4e) to the second aperture (G2), and coaxially arranged with and radially spaced apart from the second fan rib (21), and extending completely in the circumferential direction of the multiblade fan (2) so that the second fan rib (21) and the second case rib (22) are located close to and radially spaced from each other by a predetermined distance;
• a motor protective case (3c) that protects the motor body (3b);
• a motor cooling passage system using a pressure differential between a pressure in a high-pressure area of the scroll chamber having a comparatively high pressure and a pressure in a low-pressure area of the scroll chamber having a lower pressure than the pressure in the high-pressure area, the motor cooling passage system comprising:
• (i) a communication portion (6) that intercommunicates an interior space of the motor body (3b) and the high-pressure area of the scroll chamber;
• (ii) a cut-out portion (23) formed in the second case rib (22) and exposed to the low-pressure area of the scroll chamber to intercommunicate the low-pressure area of the scroll chamber and a space (S) which is defined between the motor-side case plate (4e) and the multiblade fan (2) and into which a portion of the motor body (3b) is exposed;
• and
• (iii) at least one communication hole (3d), which is formed at a portion of the motor protective case (3c) exposed into the space (S) and through which the interior space of the motor body (3b) and the space (S) are intercommunicated.