| 主权项 |
1. A cooling device, comprising:
a cooling fan; a shroud provided at an outer circumferential side of the cooling fan; an inner circumferential wall provided on the shroud and spaced apart from an outer circumference of the cooling fan in a radial direction of the cooling fan by a predetermined distance to surround the cooling fan, the inner circumferential wall being outside of and facing the cooling fan in the radial direction of the cooling fan; and an outer circumferential wall provided to surround the inner circumferential wall, the outer circumferential wall being outside of and facing the inner circumferential wall in the radial direction of the cooling fan, an air-flow-direction downstream side end of the outer circumferential wall being positioned downstream, in an air flow direction, of an air-flow-direction downstream side end of the inner circumferential wall, at least a portion of the outer circumferential wall including a cylindrical surface, wherein the cooling fan is rotatable in a space on a radially inner side of the inner circumferential wall, wherein an air-flow-direction upstream side end of the cooling fan is positioned upstream, in the air flow direction, of an air-flow-direction upstream side end of the inner circumferential wall and an air-flow-direction upstream side end of the outer circumferential wall, wherein the air-flow-direction downstream side end of the outer circumferential wall is positioned upstream, in the air flow direction, of an air-flow-direction downstream side end of an outer circumferential edge of the cooling fan, and wherein an exterior covering ratio is in a range of 55 to 95%, the exterior covering ratio being a ratio of (i) an air-flow-direction length of a portion of the cooling fan covered by the shroud and the outer circumferential wall to (ii) a maximum air-flow direction length of the cooling fan in the air flow direction of the cooling fan. |
