Centrifugal impeller and housing

Details Centrifugal impeller and housing Centrifugal impeller and housing

2000-08-21

2002-12-31

Verdier, Christopher (Department: 3745)

Fluid reaction surfaces (i.e., impellers)

Rotor having flow confining or deflecting web, shroud or...

Radially extending web or end plate

C416S22300B, C416SDIG002

Reexamination Certificate

active

06499954

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to centrifugal impellers and, more particularly, a unique blade design and housing. Particular utility of the present invention is found in automotive heating, ventilation, and air conditioning (HVAC) systems.
BACKGROUND OF THE INVENTION
Centrifugal impellers are often used in automotive heating, ventilation, and air conditioning (HVAC) systems to provide air flow into the passenger compartment. Typically, a cylindrical impeller located within a housing is driven by an electric motor and rotates in a predetermined direction. The impeller blades draw air in axially (i.e. along the impeller's axis of rotation) and discharge air radially away from the axis of rotation. Generally the housing surrounding the impeller is scroll shaped and directs incoming air along a flow path from an air inlet to an air outlet.
Prior art impellers have been designed to rotate in a single direction, such as clockwise. Consequently, in order to ensure that the motor driving the impeller always rotates the impeller in the same desired direction, the system designer must choose an appropriate electric motor. Typical electric motors available to the designer include both brush and brushless motors.
Impeller blades may be forward or rearward curved, depending on the angle of the blade tip relative to a tangent to the blade at the tip. This angle is called the blade exit angle. If the blade exit angle is greater than 90°, the impeller is said to have forwardly curved blades; if the blade exit angle is less than 90°, the impeller is said to have rearwardly curved blades. In general, rearwardly curved blades are more nearly flat than forwardly curved blades, which are often distinctly concave or scoop shaped.
The contour of prior art impeller blades has traditionally been designed using a combination of complex curved sections. Impeller blade designers often use French curves to draw each complex curved section and to connect the complex curved sections together. In this manner, impeller blade design has been often more art than engineering. Also, the more complex the curves and the more of them, the more expensive the resulting blade is to manufacture and balance. These complex curves and the lack of understanding of the principals of air flow often result in undesirable audible noise during impeller operation that represents a continuing source of frustration for impeller designers.
There is a need for an impeller that does not suffer from the deficiencies of the prior art. There is a need for an impeller with a simply formed blade contour which is easier to balance, easier to manufacture and has a smaller packaging size. There is also a need for an impeller that can be rotated in either the forward or backward (e.g. clockwise or counterclockwise) direction which has the same achievable mass flow rate such that it may be used in combination with a brushless motor without added control circuitry.
Impellers typically reside in impeller housings. The overwhelming majority of centrifugal impeller housings comprise a single scroll. In other words, a volute or spiral shaped air flow channel extending for upwards of 270 degrees around the perimeter of the impeller. The purpose of the volute is to decrease the speed of the air exiting the impeller blades at the perimeter of the impeller and increase its static pressure. In this manner, air contained in the volute flows out from an area of high pressure within the volute to an area of lower pressure outside the volute without any added work.
In order to decrease the speed of the air exiting the impeller blades at the perimeter of the impeller and increase its static pressure, the volute increases in cross-sectional area as it extends radially around the impeller. The increase in cross-sectional area decreases the speed of the air exiting the perimeter of the impeller. At the outlet of the volute, there may be located a flow inhibitor (e.g. damper) which controls air flow out of the impeller housing which acts to further control the static pressure built by the volute of the housing.
In the automotive industry, it is typically necessary for the volute to extend for 270 degrees around the perimeter of the impeller. A typical impeller measures 5 inches in diameter by 4 inches in height. The air flow generated by the impeller generally must act upon an evaporator with a size of 13 inches by 11 inches. The evaporator is typically located adjacent the outlet of the volute. Consequently, the volute must generally increase from approximately 4 inches in a height and minimal width at its inception to a size of 13 inches by 11 inches at its outlet. In doing so, it has been found that the rate of increasing cross-sectional area is inversely related to static pressure. In other words, the lower the rate of increasing cross-sectional area the greater the static pressure. Thus, automotive HVAC designers are generally predisposed to extending the volute around the impeller substantially for its entire perimeter in order to reduce the rate of increasing cross-sectional area as much as possible in efforts to gain static pressure.
While impeller housings with a single volute extending substantially around the perimeter of an impeller are common place, they present several problems. First, the increase in cross-sectional area of the volute as it extends around the impeller is typically obtained by progressively increasing the outer radial dimension of the volute outward away from the impeller axis as it extends around the impeller. Consequently, the packaging space (i.e. size) of the impeller housing substantially increases. As a solution to this problem, an impeller housing has also been designed in which the increase in cross-sectional area of the volute occurs by progressively increasing the axial dimension of the volute as it extends around the impeller. For another solution, an impeller housing has been designed in which the increase in cross-sectional area of the volute occurs by progressively increasing the axial dimension of the volute as it extends around the impeller in combination with progressively decreasing the inner radial dimension of the volute towards the impeller axis as it extends around the impeller.
The example above of an impeller housing design in which the increase in cross-sectional area of the volute occurs by progressively increasing the axial dimension of the volute as it extends around the impeller in combination with progressively decreasing the inner radial dimension of the volute towards the impeller axis as it extends around the impeller may be found in U.S. Pat. No. 4,919,592. While the '592 Patent may offer an impeller housing providing a constant outer radial dimension, the static pressure which may be generated within the impeller housing is believed less than which may be created from more conventional impeller housings (i.e. where the increase in cross-sectional area of the volute is obtained by progressively increasing the outer radial dimension of the volute outward away from the impeller axis as it extends around the impeller). As shown in
FIGS. 4-5
of the '592 Patent, the collection chamber
42
enlarges radially inward below the impeller
38
. Also as shown in
FIG. 3
of the '592 Patent, outlet
46
is located beneath the compressor. As a result, a portion of the impeller
38
must pass directly above the outlet
46
. Consequently, due to the overlying relationship, any air flow generated from the impeller
38
at this point does not enter the collection chamber
42
, but rather is lost through the outlet
46
. Accordingly, this loss of air flow reduces the static pressure which may be generated within the collection chamber as compared a more conventional impeller housing where no such loss is incurred.
While solutions have been proposed to solve the packaging space problem associated with impeller housings having a single volute extending substantially around the perimeter of an impeller, none of these solutions address the structural imbalance of such a design. By it

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