US20100284812A1

US20100284812A1 - Centrifugal Fluid Pump

Info

Publication number: US20100284812A1
Application number: US12/545,898
Authority: US
Inventors: Akram R. Zahdeh
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2009-05-08
Filing date: 2009-08-24
Publication date: 2010-11-11
Also published as: DE102010019425A1

Abstract

A centrifugal fluid pump has an impeller having a hub with vanes that may be airfoil shaped and may be twisted along their lengths. A shroud having an inlet is connected to the vanes to define with the impeller flow chambers between the vanes, at least a portion of each flow chamber having a substantially constant flow area to increase pump efficiency. An entrance feature may also be provided to improve entrance flow into the impeller, further enhancing pump efficiency.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 61/176,559, filed May 8, 2009, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The invention relates to a centrifugal fluid pump.

BACKGROUND OF THE INVENTION

Shaft driven centrifugal vane pumps are often used for cooling of automotive engines. Water or other fluid is directed axially into the pump and exits radially into one or more volutes. The shaft is typically mechanically driven, directly or indirectly by the engine crankshaft, and therefore rotates at some speed proportional to engine speed. Pump design affects pump efficiency. An increase in pump efficiency means less power is consumed in driving the pump, and can result in improved fuel economy. Less than ideal fluid flow results in flow separation in the flow field, which reduces pump capacity and may cause unwanted pump noise due to cavitation. Cavitation occurs when local boiling of the fluid occurs due to low pressure conditions in the separation zones of the flow. As a result, vapor bubbles are created in the flow. The bubbles collapse or implode as the flow passes from a relatively low pressure region of a pump, such as a fluid inlet, to a relatively higher pressure region, such as a discharge or outlet region.

SUMMARY OF THE INVENTION

A centrifugal fluid pump has an impeller having a hub with vanes that may be airfoil shaped and may be twisted along their lengths. A shroud having an inlet is connected to the vanes. The vanes, impeller, and shroud cooperate to define flow chambers between the vanes. At least a portion of each flow chamber has a substantially constant flow area to increase pump efficiency. The impeller vanes extend axially from the hub toward the shroud and may curve radially outward along the hub from the axial inlet. The hub, shroud and vanes define the flow chambers between adjacent vanes.
Each of the vanes may be airfoil-shaped, and gradually decreasing in thickness from the hub to a tip surface adjacent the shroud and from an inner end at the axial inlet to an outer end. The tapered, airfoil shape of the vanes minimizes flow turbulence to provide generally laminar flow through the portion of the flow chamber of substantially constant flow area, thereby increasing pump efficiency. Adjacent vanes may be nearer one another at the radially inner ends than at the radially outer ends. This allows fluid to be efficiently expelled tangentially by the rotating vanes near the outlet ends. Surfaces of the shroud and the hub defining the flow chambers are configured to maintain constant flow area in at least a portion of the flow chambers. Thus, although the width of each flow chamber may expand in a radially outward direction, the shroud tapers toward the hub in the radially outward direction so that the flow area in the portion of the chamber remains constant.
The pump may include an inlet feature that aids in reducing flow separation at the inlet ends of the vanes. The inlet feature may be a generally cylindrical extension coaxial with the shroud, a generally conical extension from the hub toward the shroud, or both.
Due to its flow-efficient design, the pump requires less power than a traditional centrifugal pump, and provides enough capacity especially if used for small to medium-sized automotive engines. If mechanically-driven (e.g., directly or indirectly by the rotating engine crankshaft), the pump requires about half of the power of a traditional centrifugal pump at a wide range of engine operation, and only one-quarter of the power at engine wide open throttle and high revolutions per minute (rpm). If electrically-driven, the pump could be powered by an electric motor using an existing electrical power supply on a vehicle (for example, a motor powered by a 12-volt battery, drawing no more than 20 amps of current). Powering the pump electrically allows the potential for varying the rpm separately from the engine, as well as starting and stopping the pump as operating conditions warrant. Energy savings advantages are realized at all phases of engine operation, including a warm-up period, during hot idle, and cruising while towing.
The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional illustration of a first embodiment of a centrifugal pump driven on a shaft and connected with a pump housing forming a volute;

FIG. 2 is a schematic side view illustration of the pump of FIG. 1;

FIG. 3 is a schematic cross-sectional illustration of the pump of FIGS. 1 and 2 taken at the lines 3-3 of FIG. 2;

FIG. 4 is a schematic perspective view of the pump of FIGS. 1-3;

FIG. 5 is a schematic perspective illustration of a hub, an entrance feature, and vanes of the pump of FIGS. 1-4 with a shroud and cylindrical extension removed;

FIG. 6 is a schematic perspective illustration of the hub, entrance feature, and vanes of FIG. 5;

FIG. 7 is a schematic bottom view of the vanes and entrance feature of FIGS. 5 and 6 with the hub removed; and

FIG. 8 is a schematic top view illustration of an alternative embodiment of vanes for use with the pump of FIGS. 1-4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, wherein like reference numbers refer to like components throughout the views, FIG. 1 shows a centrifugal fluid pump 10, which in this embodiment is a water pump for an automotive engine, but is not limited to such. The pump 10 includes an impeller 12 mounted at a central cavity 13 to a rotatable shaft 14. The shaft 14 is rotatably driven about an axis of rotation 16. The shaft 14 may be mechanically driven, such as by a geared or belted connection to an engine crankshaft or camshaft, as is known. Alternatively, the shaft 14 may be driven by an electric motor powered by an electric power source such as a standard 12-volt battery.
Referring to FIG. 3, the impeller 12 includes a hub 18 that is coaxial with the shaft 14 when mounted as shown in FIG. 1. The hub 18 has a surface 19 from which impeller vanes 20 extend. Referring to FIGS. 1 and 2, a shroud 22 is connected to outlet ends 24 of the vanes 20. The hub 18 with vanes 20 may be die-cast, injection-molded or otherwise formed as an integral component. If the hub 18 with vanes 20 is plastic, the shroud 22 may be connected to the vanes 20 by ultrasonic friction welding. Alternatively, the entire pump 10 could be manufactured as a one-piece component. The shroud 22 is a generally frusto-conical shape that curves from an inner edge 26 to an outer edge 28, as best shown in FIG. 2. The shroud 22 forms an inlet 25 at the inner edge 26. The shroud 22 has a curved outer surface 27, and a similarly curved inner surface 30 (see FIG. 1) that generally faces toward the surface 19 of the hub 18. Additionally, the curved inner surface 30 generally tracks tip surfaces 32 of the vanes 20, best shown in FIG. 5, so that the shroud 22, hub 18, and vanes 20 define enclosed flow chambers 34 between adjacent vanes 20. The flow chambers 34 begin generally at the inlet 25 and end at the outer ends 24 (see FIG. 3) of the vanes 20. The flow chambers 34 empty into one or more volutes 38 defined by a housing 40 connected for rotation with the impeller 12. A shaft seal 42 sealingly engages the housing 40 to the shaft 14.
An optional flow-enhancing entrance feature or features may include one or both of a generally cylindrical annular extension 44, and a generally conical extension 46, as shown in FIG. 1. The cylindrical extension 44 is connected to the shroud 22 at the inlet 26 and is aligned with axis 16. The generally conical extension 46 extends from surface 19 of hub 18 coaxial with axis 16 and extends through the middle of the cylindrical extension 44. The entrance features 44, 46 direct the flow of incoming fluid through the entrance 50 of extension 44 toward the impeller 12 into the flow chambers 34 with minimal turbulence.
Referring now to FIGS. 5 and 6, the advantages of the shape and positioning of the vanes 20 are discussed. The vanes 20 taper from a relatively wide bottom surface 52 (see FIG. 7) at the base 18 to a relatively narrow tip surface 32 that is positioned adjacent the inner surface 30 of shroud 22. Additionally, as shown in FIG. 7, the vanes 20 generally taper in the radial direction from a relatively wide portion near inner end 60 to a relatively narrow portion near outer end 24. The overall shape of the vanes 20 is best shown in FIG. 7 and is described as an airfoil shape.
As best shown in FIG. 5, each flow chamber 34 is bounded by a relatively short side surface S1 of one of the adjacent vanes 20 and a relatively long side surface S2 of the other adjacent vane 20. A portion of the flow chamber 34 between line L1 and line L2 is a compression portion of the chamber. The area of the flow chamber 34 is configured to remain substantially constant throughout this area. Thus, although the width of the flow chamber 34 increases in a radially outward direction as the vanes 20 flare apart from one another, the shroud 22 slopes downward over the adjacent vanes 20, partially forming the flow chamber 34, and in conjunction with the surface 19 of hub 18 and the vanes 20, is configured to maintain the constant cross-sectional flow area A between line L1 and line L2, shown schematically in FIG. 6. Separation of fluid from the sides S1, S2 and associated pressure loss between L1 and L2 is thus avoided. The airfoil design minimizes separation of flow and frictional losses. Centrifugal forces increase as the fluid moves radially outward. Once past L2, fluid is thrown tangentially off of the side surface S2 past the curved adjacent vane 20 into the volute 38.
In addition to the tapered, airfoil shape of the vanes 20, each vane 20 is also twisted along its length L3, indicated in FIG. 7 (i.e., between its inner end 60 and outer end 24). The lengthwise twisting of the vanes 20 is evident in FIG. 5, as the tip surfaces 32 of the vanes 20 are not centered over the base surfaces 52. (The base surfaces 52 are shown best in FIG. 7 and indicated in phantom in FIG. 5.) This causes the side surfaces S1, S2 of each vane 20 to twist inward and outward relative to the adjacent flow chamber 34 that the vane 20 partially defines. The direction of twisting of the vanes 20 is configured to decrease separation of flow of fluid along the surfaces S1, S2, increasing pumping efficiency.
Referring to FIG. 8, an alternative embodiment of vanes 20A is shown having tip surfaces 32A that are slightly more centered over the base surfaces 52, resulting in less severe twisting along the length L4 of each vane 20A. The simpler shape of such an embodiment may be manufactured by die casting or injection molding more easily than other embodiments.
Computer simulation of the pump 10 of FIG. 1 with vanes 20 indicates that the pump 10 would require only 300-400 watts to pump 45 gallons per minute with a pressure drop of 120 kPa, operating at up to 84% efficiency, with an associated fuel economy savings over less efficient pumps, which typically achieve 40-42% efficiency but use up to 5 horsepower at high rpms. The pump 10 would be sufficient to provide enough capacity for small to medium size engines (e.g., a 1.4 liter engine) using an electric motor operating at 12 volts and drawing no more than 20 amps of current to power the pump 10. Thus, the pump 10 is well suited for use with a typical vehicle electric system. With the less complex shape of vanes 20A of FIG. 8, computer simulation indicates that an efficiency of 75-76% could be attained. The entrance features, cylindrical extension 44 and conical extension 46, add an additional 2% efficiency to the pump 10. If mechanically-driven, simulation indicates the pump 10 would require half the power required for a conventional impeller pump over most engine operating conditions, and one-quarter of the power of a conventional impeller pump at wide open throttle and high rpm. If electrically-driven, the pump 10 can be run at a variable rpm with the potential for starting and stopping independent of the engine.
While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.

Claims

1. A centrifugal fluid pump comprising:

an impeller having a hub with airfoil shaped vanes; and

a shroud having an inlet; wherein the shroud is connected to the vanes such that the impeller, shroud, and vanes cooperate to define flow chambers between the vanes, at least a portion of each flow chamber having a substantially constant flow area.

2. The centrifugal fluid pump of claim 1, wherein each vane is twisted lengthwise.

3. The centrifugal fluid pump of claim 1, wherein each vane has a tip surface at which the vane is connected to the shroud; and wherein each vane decreases in thickness from the hub to the tip surface.

4. The centrifugal pump of claim 1, wherein the vanes are configured such that each flow chamber is bounded by facing sides of adjacent vanes, one of the facing sides being shorter than the other of the facing sides and defining the length of the portion of the flow chamber of constant flow area, so that fluid is expelled past the shorter side by the longer side after flowing through the portion of the flow chamber of constant flow area.

5. The centrifugal fluid pump of claim 1, further comprising:

an entrance feature extending away from the shroud at the inlet and configured to provide generally laminar flow into the chambers.

6. The centrifugal fluid pump of claim 5, wherein the entrance feature includes a cylindrical extension extending from the shroud and a conical extension extending from the shroud within the cylindrical extension.

7. The centrifugal fluid pump of claim 1, wherein the shroud has an inner surface tapering toward the impeller from the inlet in a radially outward direction.

8. A centrifugal fluid pump comprising:

an impeller having a hub configured to be rotatably driven about an axis;

a shroud defining an inlet aligned with the axis and sloping radially outward toward the hub;

wherein the impeller has vanes extending axially from the hub toward the shroud and curving radially outward along the hub from the axial inlet; wherein the hub, the shroud and the vanes define flow chambers between adjacent vanes;

wherein each of the vanes is airfoil shaped, gradually decreasing in thickness from the hub to a tip surface adjacent the shroud and from an inner end at the axial inlet to an outer end; wherein adjacent ones of the vanes are nearer one another at the inner ends than at the outer ends; and wherein surfaces of the shroud, the hub, and the vanes hub defining the flow chambers are configured to maintain a substantially constant flow area in at least a portion of the flow chambers.

9. The centrifugal fluid pump of claim 8, wherein each of the vanes is twisted along its length.

10. The centrifugal fluid pump of claim 8, further comprising:

an entrance feature at the axial inlet configured to direct flow into the flow chambers.

11. The centrifugal fluid pump of claim 10, wherein the entrance feature is a cylindrical extension connected coaxially with the shroud.

12. The centrifugal fluid pump of claim 10, wherein the entrance feature is a generally conical extension mounted to the hub and extending coaxially through the axial inlet.

13. The centrifugal fluid pump of claim 8, wherein the hub and vanes are a unitary, injection molded component; and wherein the shroud is ultrasonically friction-welded to the unitary hub and vanes.

14. A centrifugal fluid pump comprising:

an impeller having a hub with vanes twisted along their lengths;

a shroud connected to the vanes and tapering outward toward the hub from an inlet; wherein the hub, vanes and shroud define flow chambers each having a portion with a substantially constant cross-sectional flow area.

15. The centrifugal fluid pump of claim 14, wherein each vane tapers from the hub to a tip, and tapers from an inner end to an outer end.

16. The centrifugal fluid pump of claim 14, further comprising:

an entrance feature extending away from the shroud at the inlet and configured to provide generally laminar flow into the chambers through the inlet.

17. The centrifugal fluid pump of claim 16, wherein the entrance feature includes a cylindrical extension extending from the shroud and a conical extension extending from the shroud within the cylindrical extension.