Centrifugal blower

1. A centrifugal blower comprising:

a rotation shaft;

an impeller having a circular cylindrical shape and rotating about an axis line of the rotation shaft to draw an air therein in an axial direction of the rotation shaft and discharge the air outward in a radial direction of the rotation shaft, the impeller including a plurality of blades arranged radially about the axis line of the rotation shaft, and a side panel having an annular shape and connecting end parts of the plurality of blades in the axial direction of the rotation shaft; and

a casing accommodating the impeller and including an air intake portion positioned adjacent to the side panel, the air intake portion having a bell mouth shape through which the drawn air is guided to an inside of the impeller, wherein

the air intake portion includes a downstream end portion that is an end portion of the air intake portion located downstream of an airflow, and an inner wall surface located on an inner side of the air intake portion in the radial direction of the rotation shaft;

the side panel includes an upstream end portion that is an end portion of the side panel located upstream of the airflow, and an inner panel surface that is an inner surface of the side panel located on an inner side of the side panel in the radial direction of the rotation shaft;

the downstream end portion and the upstream end portion face each other across a space in the axial direction of the rotation shaft at least in an angular range in the rotation direction;

a difference between a smallest inner radius of the inner wall surface of the air intake portion and a smallest inner radius of the inner panel surface is smaller than or equal to a thickness of the side panel at least in the angular range;

the smallest inner radius of the inner wall surface of the air intake portion is equal to or smaller than the smallest inner radius of the inner panel surface;

the casing is a scroll casing that includes a side wall portion defining an airflow passage having a volute shape on an outside of the impeller;

the angular range is located within a sector spreading in the rotation direction from a radius of the side wall portion on a scroll start point of the casing to a radius of the side wall portion on an intermediate point of the casing, the intermediate point being located at a middle position between the scroll start point and a scroll end point of the casing in the rotation direction; and

the difference between the smallest inner radius of the inner wall surface of the air intake portion and the smallest inner radius of the inner panel surface is larger on a radius of the side wall portion on the scroll end point than in the sector from the radius on the scroll start point to the radius on the intermediate point in the rotation direction.

2. The centrifugal blower according to claim 1 , wherein the difference between the smallest inner radius of the inner wall surface of the air intake portion and the smallest inner radius of the inner panel surface is larger than the thickness of the side panel, on the radius on the scroll end point.

3. The centrifugal blower according to claim 1 , further including a deflection passage between the air intake portion and the side panel, the deflection passage deflecting a direction of a backflow flowing through a gap between the downstream end portion and the upstream end portion toward an air intake side of the impeller such that the backflow is deflected to be closer to a main flow flowing from the air intake portion toward the air intake side of the impeller.

4. The centrifugal blower according to claim 3 , wherein

the deflection passage includes the gap between the downstream end portion and the upstream end portion; and

the downstream end portion includes a downstream end surface facing the upstream end portion, the downstream end surface being angled to the inner wall surface such that a radius of the downstream end surface about the rotation shaft decreases in a downstream direction of the main flow.

5. The centrifugal blower according to claim 4 , wherein the upstream end portion includes an upstream end surface facing the downstream end portion, the upstream end surface being angled to the inner panel surface such that a radius of the upstream end surface about the rotation shaft increases in an upstream direction of the main flow.

6. A centrifugal blower comprising:

a rotation shaft;

an impeller having a circular cylindrical shape and rotating about an axis line of the rotation shaft to draw an air therein in an axial direction of the rotation shaft and discharge the air outward in a radial direction of the rotation shaft, the impeller including a plurality of blades arranged radially about the axis line of the rotation shaft, and a side panel having an annular shape and connecting end parts of the plurality of blades in the axial direction of the rotation shaft;

a casing accommodating the impeller and including an air intake portion positioned adjacent to the side panel, the air intake portion having a bell mouth shape through which the drawn air is guided to an inside of the impeller;

the air intake portion includes a downstream end portion that is an end portion of the air intake portion located downstream of an airflow, and an inner wall surface located on an inner side of the air intake portion in the radial direction of the rotation shaft;

the side panel includes an upstream end portion that is an end portion of the side panel located upstream of the airflow, and an inner panel surface that is an inner surface of the side panel located on an inner side of the side panel in the radial direction of the rotation shaft; and

a deflection passage between the air intake portion and the side panel, the deflection passage deflecting a direction of a backflow flowing through a gap between the downstream end portion and the upstream end portion toward an air intake side of the impeller such that the backflow is deflected to be closer to a main flow flowing from the air intake portion toward the air intake side of the impeller, wherein

the downstream end portion and the upstream end portion face each other across a space in the axial direction of the rotation shaft at least in an angular range in the rotation direction;

a difference between a smallest inner radius of the inner wall surface of the air intake portion and a smallest inner radius of the inner panel surface is smaller than or equal to a thickness of the side panel at least in the angular range;

the downstream end portion includes a downstream end surface;

the upstream end portion includes an upstream end surface;

the downstream end surface and the upstream end surface face each other across the deflection passage; and

the downstream end surface extends outward from the inner wall surface of the air intake portion in the radial direction of the rotation shaft and is inclined away from the upstream end surface in the axial direction.