TECHNICAL FIELD

The invention relates to a crossflow fan.

BACKGROUND

Fans are designed in accordance with different design principles to meet different application needs. One type of fan is a Cross Flow Fan (CFF). CFFs are widely used for ventilating machines owing to their unique properties such as low noise, compact size and adjustable axial length for different flow rates. A CFF can typically be long in relation to the diameter, so the flow

approximately remains two-dimensional away from the ends. The CFF can use an impeller with forward curved blades, placed in a housing consisting of a rear wall and vortex wall. The main air flow in the CFF moves transversely across the impeller. CN202326400 describes a cross flow fan where the different blades groups have different radius values.

There is a constant desire to improve fans. Hence, there exists a need for an improved cross flow fan.

SUMMARY

It is an object of the present invention to provide an improved cross flow fan.

This object is obtained by a crisper as set out in the appended claims.

In accordance with the invention a cross flow fan with variable blade angles is provided.

This means that the angle of each blade can vary in relation to the body of the impeller between a maximum and minimum value in the span of one revolution of the impeller rotor. In accordance with one embodiment a cross flow fan comprising a housing having an air inlet and an air outlet is provided. The cross flow fan has an impeller comprising fan blades and the fan blades are pivotable. Hereby the impeller can have variable blade angles at different rotation angles whereby there is provided greater freedom in designing the cross flow fan.

In accordance with one embodiment, a radial edge of the blades follow a cam curve. Hereby it is possible to set the different angles at different rotational positions in an easy manner. For example, the outer radial edge of the blades follow the cam curve.

In accordance with one embodiment, the cam curve is formed in side sections of the housing. Hereby, the cam curve can be easily manufactured. The cam curve can for example be a groove.

In accordance with one embodiment, the cam curve is a circle with a center radially displaced from the axis of the impeller. Hereby, a cam curve that makes the blade angle vary can easily be obtained.

In accordance with one embodiment the fan blades are pivotable around a member that is connected to a side member of the impeller. Hereby, an easy pivoting mechanism can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example, and with reference to the accompanying drawings, in which:

Figure 1 shows a cross flow fan, Figures 2a and 2b show a section of a cross flow fan, and

Figure 3 shows a cross flow fan from the side. DETAILED DESCRIPTION

The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. For examples like or similar components of different embodiments can be exchanged between different embodiments. Some components can be omitted from different

embodiments. Like numbers refer to like elements throughout the

description.

In conventional Cross Flow Fans, the blade angle is fixed and the designers are forced to compromise between a fan that performs well for higher flow rates but with lower static and dynamic pressures or vice versa. By providing a Cross Flow Fan (CFF) with variable blade angles, such a design limitation can be removed or at least eased.

In Fig. 1, a CFF 10 in accordance with one embodiment is shown. The CFF comprises a housing. The housing can be formed by a first housing part 12 and a second housing part 14. The housing 12, 14 forms an air inlet 13 and an air outlet 15. The housing will typically form a volute at the air outlet side of the housing. The CFF 10 further comprises an impeller 16. The impeller 16 is rotatably mounted in the housing of the CFF 10. The impeller 16 comprises a number of blades that drives an air-flow in the CFF 10 when the impeller is rotated.

In Figs 2a and 2b, the second part 14 of the housing is shown together with a fan blade 18 of the impeller 16 mounted therein. The other blades are not shown in order to simplify the view. The fan blade 18 is pivotably arranged on the impeller to allow the blade to alter its angular position with respect to the center of the impeller such that the angle at which the fan blade is driven towards the air can alter around one revolution of the impeller. Hereby it is achieved that the fan blade 18 can have different angles at different rotational positions within the housing. In the embodiment of Fig. 2 the fan blade 18 is pivotable around a member 19 that is connected to a side member 20 (see Fig. 2b) of the impeller. To achieve the different blade angles at different rotational angles, the fan blade 18 can be made to follow a cam curve 22 that is not a circle centered around the center axis of the impeller. The cam curve 22 can be a circle having a center axis parallel to but displaced in relation to the center axis of the impeller. The cam curve can for example be formed in side sections of the housing (12, 14). In Figs. 2a and 2b, the fan blade 18 follow an outer cam curve 22 and the fan blade is pivotable around a member 19 connected to an inner section of the fan blade 18. However, the fan blade 18 could also be mounted in another manner with, for example, the member 19 mounted at an outer section of the fan blade 18 and the inner section of the fan blade 18 following a cam curve 22. Thus, the fan blades of the impeller pivot on one edge and follow a groove in an off-center cam on the other edge. The cam displacement and direction can be chosen to provide the optimal values of blade angles for a particular application. The cam curve 22 can be circular oval or have other suitable characteristics.

The impeller 16 can be mounted in the housing, here the second housing part 14, in a bearing arrangement 24.

By removing the limitation of having a fixed fan blade angle, the fan design described herein allows for a higher efficiency by using the optimal angle in each polar position of the fan blade. Also, the extreme values of this angle and where they occur can be modified to give different characteristic curves to the fan. The fan blades pivot on one edge and follow a groove in an off-center cam on the other edge. The cam displacement and direction can be chosen to provide the optimal values of fan blade angles for a particular application. In Fig. 3 a side view of a Cross Flow Fan is shown. As can be seen in Fig. 3, the fan blades 18 have different angles at different positions. This can be achieved by displacing the cam curve 22 in a radial direction in relation to the center axis of the impeller 16.

The invention has been described above with reference to a few

embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended claims.

The fan as described herein can be used for many different applications. For example, the fan can be used in residential or industrial ventilation, ideally for indoor units of split type of air conditioners. It can further be used in any product that requires moving air. It can also be used in more demanding conditions such a tunnel ventilation or for light aircraft propulsion and similar applications.