Cooling fan

A cooling fan includes a fan housing and a stator and an impeller received in the fan housing. The fan housing includes a frame and a mounting portion located in the frame. The stator is received in the frame and mounted to the mounting portion. The impeller is mounted to the stator and rotatable with respect to the stator. The impeller includes a hub and a plurality of blades extending radially and outwardly from the hub. Each of the blades includes an inner end connected with the hub and an outer end distant from the hub. Each of the blades forms a tab on the outer end at the end surface.

BACKGROUND

1. Technical Field

The present disclosure relates to cooling fans, and particularly to a cooling fan with little noise.

2. Description of Related Art

With continuing developments in technology, heat-generating electronic components such as CPUs (central processing units) provide improved performance such as faster processing speeds. However, such electronic components also tend to generate increased amounts of heat, which requires immediate dissipation. Often, a heat sink incorporating a cooling fan is employed to provide such heat dissipation. The heat sink absorbs heat from the electronic component and dissipates the heat to ambient air. The cooling fan provides airflow to the heat sink for removing the hot air from around the heat sink, thereby further facilitating cooling of the electronic component. However, the cooling fan frequently generates noise during operation.

Therefore, it is desirable to overcome the described limitations.

DETAILED DESCRIPTION

FIGS. 1 and 2show a cooling fan100according to an exemplary embodiment. The cooling fan100includes a fan housing10, and a stator20and an impeller30received in the fan housing10. An air inlet17is defined at a top side of the fan housing10, and an air outlet18opposite to the air inlet17is defined at a bottom side of the fan housing10. The fan housing10includes a hollow, square frame12and a mounting portion14formed in the frame12near the air outlet18. The stator20is received in the frame12and mounted to the mounting portion14. The impeller30is received in the frame12and rotatably mounted around the stator20.

Referring also toFIG. 3, the impeller24includes a hub32and a plurality of blades34extending radially and outwardly from an outer periphery of the hub32. Each blade34extends slantwise from an upper end to a lower end of the hub32. The blade34includes a first surface341facing the air inlet17and an opposite second surface342facing the air outlet18. The blade34also includes an inner end343connected with the hub32and an outer end344distant from the hub32. The blade34forms an end surface348at the outer end344thereof. The end surface348connects the first surface341with the second surface342at the outer end344of the blade34. The end surfaces348of the outer ends344of the blades34are evenly located along a circular path which is concentric with the hub32. After the impeller30is received in the fan housing10, the end surfaces348of the outer ends344of the blades34are spaced from an inner surface of the frame12of the fan housing10, with a gap19defined therebetween.

Referring also toFIG. 4, the end surface348of the outer end344of each blade34has an airfoil shape. Each blade34includes a smooth top edge345and a sharp bottom edge346. When air is driven by the impeller30to flow towards the air outlet18from the air inlet17, the air reaches the top edge345first and the bottom edge346last. A thickness of the blade34as measured between the first surface341and the second surface342decreases from a middle portion thereof towards each of the top and bottom edges345,346thereof. The top edge345is thicker than the bottom edge346.

A tab349is perpendicularly formed on the outer end344of each blade34near the bottom edge346. The tab349is substantially coplanar with the end surface348. The tab349of each blade34protrudes from the outer end344of the blade34towards an adjacent leading blade34along a rotation direction of the impeller30during operation of the cooling fan100. The tabs349of the blades34are located along the circular path of the end surfaces348of the outer ends344of the blades34. The tabs349extend from the outer ends344along a same circumferential direction of the circular path. Each of the tabs349is substantially flat and has a curved leading edge. Thus, a protruding height of the tab349from the outer end344decreases from a middle of the tab349towards each of top and bottom sides of the tab349. Alternatively, each tab349can have other shapes, such as a shape with a semicircular leading edge.

Each tab349is located at the end surface348between the middle portion of the blade34and the bottom edge346of the blade34. A length of the tab349along the end surface348is less than a distance between the middle portion and the bottom edge346of the blade34.

During operation of the cooling fan100, the impeller30rotates with respect to the stator20and the blades34drive the air at the air inlet17to flow towards the air outlet18. Accordingly, air pressure at the air inlet17is reduced and air pressure at the air outlet18is increased. As a result, the air pressure at the air outlet18exceeds that of the air inlet17, and an air pressure differential is generated between the air above the first surface341of each blade34and the air under the second surface342of the blade34. Thus, some of the air under the second surface342of the blade34tends to flow around the outer end344of the blade34to the first surface341, and in turn escape away from the impeller30into the gap19between the impeller30and the fan housing10, colliding with the frame12of the fan housing10and generating noise. The tab349formed at the end surface348of the blade34helps prevent the flow of air from under the second surface342to the first surface341and thereupon escaping away from impeller30to collide with the frame12. Thereby, the tabs349of the blades34help reduce noise.

Maximum air pressure differential between the first surface341and the second surface342of each blade34exists near the bottom edge346of the blade34. The positioning of the tab349near the bottom edge346reduces air leakage from the second surface342around the outer end344to the first surface341of the blade34. Accordingly, noise generated by the cooling fan100during operation can be greatly reduced. Furthermore, the tab349divides the air under the second surface342into two airflows, which exit from the impeller30at different times and thus at different phases. The two airflows counteract such that noise of the cooling fan100is further reduced.