Centrifugal fan wheels are used in a wide variety of applications. Many of these applications utilize a centrifugal wheel with a forward curved blade design, often referred to as a forward curved fan. A forward curved fan wheel has the advantage of being relatively compact in size for the amount of air that it can move. In contrast, a centrifugal fan wheel with rearward curved blades is typically larger, or must turn at a greater speed, than a comparable forward curved fan. It is for this reason that forward curved fans are used in many residential, commercial, industrial, and automotive applications.
However, a typical forward curved fan will only provide stable and efficient airflow over a relatively narrow operating range. Conditions which present too high of an airflow restriction may result in unsteady airflow delivery and excessive noise. Likewise, too little airflow restriction can have a similar effect on performance. Because of these limitations forward curved fans must be selected to avoid these undesirable affects, which in many instances will unnecessarily limit design options and lead to less desirable performance or higher costs.
A forward curved fan wheel commonly employs a centerdisk (or centerdisks), a series of blades, and two endrings. The centerdisk is driven by a shaft attached to a motor or some other suitable drive. The center of each blade is attached to the centerdisk with the blade ends secured to the endrings. Further, the blades are straight in that a straightedge will be parallel to the lateral edges of the blades. This geometry is largely responsible for the aerodynamic and acoustic performance limitations described above. The wheels are usually made of steel, although other metals and plastics are used.
Representative of the art is U.S. Pat. No. 3,854,844 which discloses an improved blower wheel is disclosed in which the end rings are formed from flat stock material which has been partially preformed by rolling and cut to the desired length. The center disks are stamped from sheet material which may be of a different gauge than that of the end rings and formed with peripheral notches and a U-shaped crimp to engage the inner section of each of the blades. The arrangement permits selection of center disk material without regard to end ring material, provides versatility in selecting blower wheel size and eliminates production inventory balance problems which occur when the center disk and end rings are stamped from the same material.
What is needed is a forward swept centrifugal fan wheel having blades having a substantially continuous arcuate form extending along an axis parallel to an axis of rotation, and each blade having a substantially continuous arcuate cross-section taken with respect to a plane which extends normally from the axis of rotation. The present invention meets this need.