US20170023022A1

US20170023022A1 - Fluid pump

Info

Publication number: US20170023022A1
Application number: US14/803,394
Authority: US
Inventors: Daniel Herrera; Partab Jeswani; John G. Fischer; Mohammed Aslam
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies IP Ltd
Priority date: 2015-07-20
Filing date: 2015-07-20
Publication date: 2017-01-26
Also published as: CN106368866A

Abstract

A fluid pump includes an inlet; an outlet; a motor; and an impeller rotated by the motor about an axis, the impeller being positioned axially between an inlet plate and an outlet plate. The inlet plate includes a channel that receives fluid from the inlet, the channel being defined by an inner wall and an outer wall. The channel has a first region extending over an angle of at least 150° and a second region extending from the first region over an angle of 61.8° to 71.8°. The inner wall has a first radius centered about the axis which is constant over the first region and the second region. The outer wall has a second radius centered about the axis which is constant over the first region and also has a third radius not centered about the axis which is constant over the second region.

Description

TECHNICAL FIELD OF INVENTION

The present invention relates to a fluid pump; more particularly to a fuel pump; even more particularly to a fuel pump with an electric motor which rotates an impeller that is located axially between an inlet plate and an outlet plate; and still even more particularly to an inlet plate flow channel of the inlet plate which minimizes noise due to structural vibrations induced by fluid hammer at the end of the inlet plate flow channel.

BACKGROUND OF INVENTION

Fluid pumps, and more particularly fuel pumps for pumping fuel, for example, from a fuel tank of a motor vehicle to an internal combustion engine of the motor vehicle, are known. U.S. Pat. No. 6,824,361 to Yu et al. shows a typical electric fuel pump which includes and impeller with a plurality of blades that is located axially between stationary inlet and outlet plates. The inlet plate includes an inlet which allows fuel to enter the fuel pump such that the inlet is in fluid communication with an inlet channel formed in a face of the inlet plate that faces toward the impeller. The inlet channel is arcuate in shape such that the inlet opens into a first end of the inlet channel and such that fuel flows from the first end to a second end of the inlet channel when the impeller is rotated by an electric motor of the fuel pump. Fuel that reaches the second end of the inlet channel is pushed through spaces between the blades of the impeller and into an outlet channel formed in a face of the outlet plate that faces toward the impeller. One end of the outlet channel includes an outlet passage which extends axially through the outlet plate. Consequently, the fuel that has been pressurized by the impeller passes through the outlet passage and past the electric motor to an outlet of the fuel pump. Motion of the blades of the impeller causes fluid pressure fluctuations which in turn causes vibration of the inlet plate which propagates through the rest of the structure of the fuel pump. Furthermore, when the fuel reaches the end of the inlet channel, a fluid hammer effect may be produced, thereby resulting in a high frequency noise that may be objectionable. While not shown in U.S. Pat. No. 6,824,361 to Yu et al., it is known to decrease the depth of the inlet channel at the end of the inlet channel such that the inlet channel may decrease in depth at a first constant rate over a first distance and then taper at a second constant rate over a second distance such that the first rate is greater than the second rate.
What is needed is a fuel pump which minimizes or eliminates one or more of the shortcomings as set forth above.

SUMMARY OF THE INVENTION

Briefly described, a fluid pump includes an inlet which introduces fluid into the fluid pump; an outlet which discharges fluid from the fluid pump; a motor within the fluid pump; and a pumping member rotated by the motor about an axis such that rotation of the pumping member by the motor pumps fluid from the inlet to the outlet, the pumping member being positioned axially between an inlet plate which is stationary and an outlet plate which is stationary. The inlet plate includes an inlet plate flow channel in an inlet plate face of the inlet plate that faces toward the pumping member such that the inlet plate flow channel receives fluid from the inlet, the inlet plate flow channel being defined by an inner wall and an outer wall. The inlet plate flow channel has a first region and a second region, the first region extending over an angle of at least 150° and the second region extending from the first region over an angle of 61.8° to 71.8°. The inner wall has a first radius which is constant over the first region and the second region, the first radius being centered about the axis. The outer wall has a second radius which is constant over the first region and which is centered about the axis. The outer wall also has a third radius which is constant over the second region and which is not centered about the axis. The arrangement of the second region minimizes the fluid hammer effect at the end of the inlet channel and also minimizes vibration of the inlet plate during operation, and consequently, noise generated by the vibration of the inlet plate is also minimized.

BRIEF DESCRIPTION OF DRAWINGS

This invention will be further described with reference to the accompanying drawings in which:

FIG. 1 is an exploded isometric view of a fuel pump in accordance with the present invention;

FIG. 2 is an axial cross-sectional view of the fuel pump in accordance with the present invention;

FIG. 3 is an exploded isometric view of a portion of the fuel pump in accordance with the present invention;

FIG. 4 is an isometric view of a motor frame of the fuel pump in accordance with the present invention;

FIG. 5 is an isometric view of the motor frame of FIG. 4 now shown in a different orientation;

FIG. 6 is an axial view of an inlet plate of the fuel pump in accordance with the present invention;

FIG. 7 is an unfolded cross-sectional view of the inlet plate taken through section line 7-7 of FIG. 6;

FIG. 8 is an axial cross-sectional view of the inlet plate taken through section line 8-8 of FIG. 6; and

FIG. 9 is an unfolded cross-sectional view similar to FIG. 7 showing an alternative arrangement.

DETAILED DESCRIPTION OF INVENTION

Reference will be made to FIGS. 1 and 2 which are an exploded isometric view and an axial cross-sectional view respectively of a fluid pump illustrated as fuel pump 10 for pumping liquid fuel, for example gasoline or diesel fuel, from a fuel tank (not shown) to an internal combustion engine (not shown). While the fluid pump is illustrated as fuel pump 10, it should be understood that the invention is not to be limited to a fuel pump, but could also be applied to fluid pumps for pumping fluids other than fuel. Fuel pump 10 generally includes a pump section 12 at one end, a motor section 14 adjacent to pump section 12, and an outlet section 16 adjacent to motor section 14 at the end of fuel pump 10 opposite pump section 12. A housing 18 of fuel pump 10 retains pump section 12, motor section 14 and outlet section 16 together. Fuel enters fuel pump 10 at pump section 12, a portion of which is rotated by motor section 14 as will be described in more detail later, and is pumped past motor section 14 to outlet section 16 where the fuel exits fuel pump 10.
Motor section 14 includes an electric motor 20 which is disposed within housing 18. Electric motor 20 includes a shaft 22 extending therefrom into pump section 12. Shaft 22 rotates about an axis 24 when an electric current is applied to electric motor 20. Electric motor 20 will be described in greater detail later.
With continued reference to FIGS. 1 and 2, pump section 12 includes an inlet plate 26, a pumping member which is illustrated as an impeller 28, and an outlet plate 30. Inlet plate 26 is disposed at the end of pump section 12 that is distal from motor section 14 while outlet plate 30 is disposed at the end of pump section 12 that is proximal to motor section 14. Both inlet plate 26 and outlet plate 30 are fixed relative to housing 18 to prevent relative movement between inlet plate 26 and outlet plate 30 with respect to housing 18. Outlet plate 30 defines a spacer ring 32 on the side of outlet plate 30 that faces toward inlet plate 26. Impeller 28 is disposed axially between inlet plate 26 and outlet plate 30 such that impeller 28 is radially surrounded by spacer ring 32. Impeller 28 is fixed to shaft 22 such that impeller 28 rotates with shaft 22 in a one-to-one relationship. Spacer ring 32 is dimensioned to be slightly thicker than the dimension of impeller 28 in the direction of axis 24, i.e. the dimension of spacer ring 32 in the direction of axis 24 is greater than the dimension of impeller 28 in the direction of axis 24. In this way, inlet plate 26, outlet plate 30, and spacer ring 32 are fixed within housing 18, for example by crimping the end of housing 18 proximal to outlet plate 30. Axial forces created by the crimping process will be carried by spacer ring 32, thereby preventing impeller 28 from being clamped tightly between inlet plate 26 and outlet plate 30 which would prevent impeller 28 from rotating freely. Spacer ring 32 is also dimensioned to have an inside diameter that is larger than the outside diameter of impeller 28 to allow impeller 28 to rotate freely within spacer ring 32 and axially between inlet plate 26 and outlet plate 30. While spacer ring 32 is illustrated as being made as a single piece with outlet plate 30, it should be understood that spacer ring 32 may alternatively be made as a separate piece that is captured axially between outlet plate 30 and inlet plate 26.
Inlet plate 26 is generally cylindrical in shape, and includes an inlet 34 that extends through inlet plate 26 in the same direction as axis 24. Inlet 34 is a passage which introduces fuel into fuel pump 10. Inlet plate 26 also includes an inlet plate flow channel 36 formed in an inlet plate face 26a of inlet plate 26 that faces toward impeller 28. Inlet plate flow channel 36 is in fluid communication with inlet 34. Inlet plate 26 and inlet plate flow channel 36 will be described in greater detail later.
Outlet plate 30 is generally cylindrical in shape and includes an outlet plate outlet passage 40 that extends through outlet plate 30 in the same direction as axis 24. Outlet plate outlet passage 40 is in fluid communication with outlet section 16 as will be describe in more detail later. Outlet plate 30 also includes an outlet plate flow channel 42 formed in the face of outlet plate 30 that faces toward impeller 28. Outlet plate flow channel 42 is in fluid communication with outlet plate outlet passage 40. Outlet plate 30 also includes an outlet plate aperture, hereinafter referred to as lower bearing 44, extending through outlet plate 30. Shaft 22 extends through lower bearing 44 in a close fitting relationship such that shaft 22 is able to rotate freely within lower bearing 44 such that radial movement of shaft 22 within lower bearing 44 is substantially prevented. In this way, lower bearing 44 radially supports a lower end 46 of shaft 22 that is proximal to pump section 12.
Impeller 28 includes a plurality of blades 48 arranged in a polar array radially surrounding and centered about axis 24 such that blades 48 are aligned with inlet plate flow channel 36 and outlet plate flow channel 42. Blades 48 are each separated from each other by a blade chamber 49 that passes through impeller 28 in the general direction of axis 24. Impeller 28 may be made, for example only, by a plastic injection molding process in which the preceding features of impeller 28 are integrally molded as a single piece of plastic.
Outlet section 16 includes an end cap 50 having an outlet 52 for discharging fuel from fuel pump 10. Outlet 52 may be connected to, for example only, a conduit (not shown) for supplying fuel to an internal combustion engine (not shown). Outlet 52 is in fluid communication with outlet plate outlet passage 40 of outlet plate 30 for receiving fuel that has been pumped by pump section 12.
With continued reference to FIGS. 1 and 2 and with additional reference to FIGS. 3 and 4, electric motor 20 includes a rotor or armature 54 with a plurality of circumferentially spaced motor windings 56 and a commutator portion 58, a motor frame 60, a pair of permanent magnets 62, and a flux carrier 64. Each magnet 62 is in the shape of a segment of a hollow cylinder. Motor frame 60 includes a top section 66 that is proximal to outlet section 16, a plurality of circumferentially spaced legs 68 extending axially from top section 66 toward pump section 12, and a base section 70 axially spaced apart from top section 66 by legs 68. Top section 66, legs 68, and base section 70 are preferably integrally formed from a single piece of plastic, for example only, by a plastic injection molding process.
Top section 66 of motor frame 60 includes a first electrical terminal 72 and a second electrical terminal 74 extending therefrom and protruding through end cap 50. First electrical terminal 72 and second electrical terminal 74 are arranged to be connected to a power source (not shown) such that first electrical terminal 72 and second electrical terminal 74 are opposite in polarity. First electrical terminal 72 and second electrical terminal 74 may be disposed within pre-formed openings in top section 66 or first electrical terminal 72 and second electrical terminal 74 may be insert molded with top section 66 when motor frame 60 is formed by a plastic injection molding process. First electrical terminal 72 is in electrical communication with a first carbon brush 76 while second electrical terminal 74 is in electrical communication with a second carbon brush 78. First carbon brush 76 is disposed within a first brush holder 80 that is defined by top section 66 and is urged into contact with commutator portion 58 of armature 54 by a first brush spring 82 that is grounded to end cap 50. Second carbon brush 78 is disposed within a second brush holder 84 defined by top section 66 and is urged into contact with commutator portion 58 of armature 54 by a second brush spring 86 that is grounded to end cap 50. First carbon brush 76 and second carbon brush 78 deliver electrical power to motor windings 56 via commutator portion 58, thereby rotating armature 54 and shaft 22 about axis 24.
Top section 66 of motor frame 60 defines an upper bearing 88 therein which radially supports an upper end 90 of shaft 22 that is proximal to outlet section 16. Shaft 22 is able to rotate freely within upper bearing 88 such that radial movement of shaft 22 within upper bearing 88 is substantially prevented.
Legs 68 are preferably equally circumferentially spaced around top section 66 and base section 70 and define motor frame openings 92 between legs 68. Motor frame openings 92 extend axially from top section 66 to base section 70. One magnet 62 is disposed within each motor frame opening 92. Magnets 62 may be inserted within respective motor frame openings 92 after motor frame 60 has been formed. Alternatively, magnets 62 may be insert molted with motor frame 60 when motor frame 60 is formed by a plastic injection molding process. In this way, magnets 62 and legs 68 radially surround armature 54. While two legs 68 and two magnets 62 have been illustrated, it should be understood that other quantities of legs 68 and magnets 62 may be used.
Base section 70 may be annular in shape and connects legs 68 to each other. Base section 70 includes a base section recess 94 extending axially thereinto from the end of base section 70 that faces away from top section 66. Base section recess 94 is coaxial with upper bearing 88 and receives outlet plate 30 closely therein such that radial movement of outlet plate 30 within base section recess 94 is substantially prevented. Since base section recess 94 is coaxial with upper bearing 88, a coaxial relationship is maintained between lower bearing 44 and upper bearing 88 by base section 70. Base section 70 also defines an annular shoulder 96 that faces toward top section 66. Annular shoulder 96 may be substantially perpendicular to axis 24.
Flux carrier 64 is made of a ferromagnetic material and may take the form of a cylindrical tube. Flux carrier 64 closely radially surrounds legs 68 of motor frame 60 and magnets 62. Flux carrier 64 may be made, for example only, from a sheet of ferromagnetic material formed to shape by a rolling process. The end of flux carrier 64 that is proximal to base section 70 of motor frame 60 axially abuts annular should 96 of base section 70 while the end of flux carrier 64 that is proximal to top section 66 of motor frame 60 axially abuts a portion of end cap 50 that radially surrounds top section 66 of motor frame 60. In this way, flux carrier 64 is captured axially between end cap 50 and annular shoulder 96 of base section 70.
Since motor frame 60 may be made as a single piece, for example only, by a plastic injection molding process, upper bearing 88 and base section recess 94 can be made by a single piece of tooling, thereby allowing a high degree of control over the relative positions of upper bearing 88 and base section recess 94. Consequently, lower bearing 44 can more easily be maintained in a coaxial relationship with upper bearing 88. Similarly, since first brush holder 80 and second brush holder 84 may be defined by top section 66, for example only, by an injection molding process, first brush holder 80, second brush holder 84, and upper bearing 88 may be formed by a single piece of tooling, thereby allowing a high degree of control over the relative positions of first brush holder 80, second brush holder 84, and upper bearing 88. Consequently, first brush holder 80 and second brush holder 84 can be easily maintained parallel to axis 24 which may be important for first carbon brush 76 and second carbon brush 78 to adequately interface with commutator portion 58 of armature 54.
Reference will now be made to FIGS. 6-8 which are respectively an axial view of inlet plate 26 looking toward inlet plate face 26a, an unfolded cross-sectional view taken through section line 7-7 of FIG. 6, and an axial cross-sectional view taken through section line 8-8 of FIG. 6. The inventors have discovered geometry of inlet plate flow channel 36 which minimizes fluid hammer effects and fluid pressure fluctuation within inlet plate flow channel 36, thereby minimizing vibration of inlet plate 26 which can be propagated through fuel pump 10 and also minimizing audible noise that results from the vibration of inlet plate 26 propagating through fuel pump 10. Inlet plate flow channel 36 will be described in greater detail in the paragraphs that follow.
As shown in FIG. 6, inlet plate flow channel 36 is generally arcuate in shape and includes an inlet region 98 at one end of inlet plate flow channel 36, an outlet region 100 at the other end of inlet plate flow channel 36, and an intermediate region 102 between inlet region 98 and outlet region 100. Inlet plate flow channel 36 is defined by an inner wall 104, an outer wall 106 which is located radially outward of inner wall 104, and a bottom wall 108 which joins inner wall 104 and outer wall 106.
Inlet region 98 extends over approximately 30° of inlet plate flow channel 36. Inlet 34 extends axially through inlet plate 26 at inlet region 98; consequently, fluid is introduced into inlet plate flow channel 36 at inlet region 98 through inlet 34. At least a portion of bottom wall 108 within inlet region 98 is oblique to inlet plate face 26a as can best be seen in FIG. 7. Consequently, bottom wall 108 within inlet region 98 eases the change in direction of fuel flow from axially through inlet 34 to laterally through inlet plate flow channel 36.
Intermediate region 102 extends over the majority of inlet plate flow channel 36 and extends over at least 150°, and preferably extends about 215° as illustrated herein. Inner wall 104 within intermediate region 102 is defined by a radius R₁₀₄where inner wall 104 intersects inlet plate face 26 a such that radius R₁₀₄is constant over intermediate region 102 and is centered about axis 24. As shown in FIG. 8, inner wall 104 may be arcuate in cross-section shape across the width of inlet plate flow channel 36 within intermediate region 102. Similarly, outer wall 106 within intermediate region 102 is defined by a radius R_106awhere outer wall 106 intersects inlet plate face 26 a such that radius R_106ais constant over intermediate region 102 and is centered about axis 24 and such that radius R_106ais greater than radius R₁₀₄. As shown in FIG. 8, outer wall 106 may be arcuate in cross-section shape across the width of inlet plate flow channel 36 within intermediate region 102. Intermediate region 102 may be defined by an intermediate region first section 102 a and an intermediate region second section 102 b such that intermediate region first section 102 a is located between inlet region 98 and intermediate region second section 102 b. Intermediate region first section 102 a and intermediate region second section 102 b are substantially the same except for their respective depths, i.e. the distance that bottom wall 108 is located axially from inlet plate face 26 a. More specifically, the axial distance from bottom wall 108 within intermediate region first section 102 a to inlet plate face 26 a is greater than the axial distance from bottom wall 108 within intermediate region second section 102 b to inlet plate face 26 a. Consequently, a step 110 is defined by bottom wall 108 at the transition from intermediate region first section 102 a and intermediate region second section 102 b.
Outlet region 100 extends over a range of 61.8° to 71.8° of inlet plate flow channel 36 and is preferably about 66.8°. Inner wall 104 within outlet region 100 is defined by radius R₁₀₄where inner wall 104 intersects inlet plate face 26 a such that radius R₁₀₄is constant over outlet region 100 and is centered about axis 24. Consequently, inner wall 104 is defined by radius R₁₀₄within intermediate region 102 and outlet region 100. As shown in FIG. 8, inner wall 104 may be arcuate in cross-section shape across the width of inlet plate flow channel 36. Outer wall 106 within outlet region 100 is defined by a radius R_106bwhere outer wall 106 intersects inlet plate face 26 a such that radius R_106bis constant over outlet region 100. However, radius R_106bis centered about a center point 112 which is not coincident with axis 24, consequently, radius R_106bis not centered about axis 24. Radius R_106bis preferably less than radius R_106aand center point 112 is preferably offset laterally from axis 24 in a direction that is toward intermediate region 102 and toward outlet region 100, i.e. down and to the right as oriented in FIG. 6. In this way, outer wall 106 converges to inner wall 104 within outlet region 100. It should be noted that a termination radius 113 may join inner wall 104 and outer wall 106 at the end of outlet region 100 which is distal from intermediate region 102, i.e. the end of outlet region 100 which terminates inlet plate flow channel 36, such that termination radius 113 is less than about 15% of radius R_106bwhile still considering inner wall 104 to have a constant radius over outlet region 100 and while still considering outer wall 106 to have a constant radius over outlet region 100 and while still considering outer wall 106 to converge to inner wall 104. As shown in FIG. 8, outer wall 106 may be arcuate in cross-section shape across the width of inlet plate flow channel 36. The depth of inlet plate flow channel 36, i.e. the distance that bottom wall 108 is located axially from inlet plate face 26 a, preferably decrease over the entire length of outlet region 100. As shown in FIG. 7, bottom wall 108 tapers at a constant rate from the end of outlet region 100 that is proximal to intermediate region 102 to the end of outlet region 100 that is distal from intermediate region 102, thereby defining a bottom wall tapered section 114. Alternatively, as shown in FIG. 9, bottom wall tapered section 114 may include an initial tapered section 114 a that is proximal to intermediate region 102 a final tapered section 114 b that is distal from intermediate region 102 such that initial tapered section 114 a tapers toward inlet plate face 26 a at greater rate than final tapered section 114 b. However, initial tapered section 114 a and final tapered section 114 b together taper the entire length of outlet region 100 just like bottom wall tapered section 114 shown in FIG. 7. It should be noted that both initial tapered section 114a and final tapered section 114 b taper at constant rates.
In operation, inlet 34 is exposed to a volume of fuel (not shown) which is to be pumped to, for example only, an internal combustion engine (not shown). An electric current is supplied to motor windings 56 in order to rotate shaft 22 and impeller 28. As impeller 28 rotates, fuel is drawn through inlet 34 into inlet plate flow channel 36. Fuel within inlet plate flow channel 36 flows through inlet region 98, intermediate region 102, and outlet region 100. Blade chambers 49 allow fuel from inlet plate flow channel 36 to flow to outlet plate flow channel 42, primarily from outlet region 100. Impeller 28 subsequently discharges the fuel through outlet plate outlet passage 40 and consequently through outlet 52. The inventors have discovered that defining inner wall 104 with radius R₁₀₄over intermediate region 102 and outlet region 100 together with defining outer wall 106 with radius R_106aover intermediate region 102 and radius R_106bover outlet region 100 allows the fuel to be efficiently directed out of inlet plate flow channel 36, thereby minimizing the interaction between the fuel and the end of inlet plate flow channel 36 which would tend to cause vibration of inlet plate 26 that can propagate through fuel pump 10 and would also tend to cause a fluid hammer effect. Consequently, vibration of inlet plate 26 is minimized, thereby also minimizing noise generated by the vibration of inlet plate 26.
While this invention has been described in terms of preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.

Claims

We claim:

1. A fluid pump comprising:

an inlet which introduces fluid into said fluid pump;

an outlet which discharges fluid from said fluid pump;

a motor within said fluid pump; and

a pumping member rotated by said motor about an axis such that rotation of said pumping member by said motor pumps fluid from said inlet to said outlet, said pumping member being positioned axially between an inlet plate which is stationary and an outlet plate which is stationary;

said inlet plate includes an inlet plate flow channel in an inlet plate face of said inlet plate that faces toward said pumping member such that said inlet plate flow channel receives fluid from said inlet, said inlet plate flow channel being defined by an inner wall and an outer wall wherein:

said inlet plate flow channel has a first region and a second region, said first region extending over an angle of at least 150° and said second region extending from said first region over an angle of 61.8° to 71.8°;

said inner wall has a first radius which is constant over said first region and said second region, said first radius being centered about said axis; and

said outer wall has a second radius which is constant over said first region and which is centered about said axis, said outer wall also has a third radius which is constant over said second region and which is not centered about said axis.

2. A fluid pump as in claim 1 wherein said second region of said inlet plate flow channel has a first end that is proximal to said first region and a second end which is distal from said first region and terminates said inlet plate flow channel.

3. A fluid pump as in claim 2 wherein said outer wall converges to said inner wall at said second end.

4. A fluid pump as in claim 1 wherein said third radius is less than said second radius.

5. A fluid pump as in claim 1 wherein:

said inlet plate flow channel is further defined by a bottom wall which connects said inner wall to said outer wall; and

said bottom wall tapers over the entirety of said second region, thereby varying the depth of said inlet plate flow channel within said second region.

6. A fluid pump as in claim 5 wherein said bottom wall tapers at a constant rate over the entirety of said second region.

7. A fluid pump as in claim 6 wherein said bottom wall tapers at said constant rate over the entirety of said second region to said inlet plate face.

8. A fluid pump as in claim 5 wherein:

said bottom wall has an initial tapered section within said second region such that said initial tapered section is proximal to said first region;

said bottom wall has a final tapered section within said second region such that said initial tapered section is between said final tapered section and said first region;

said initial tapered section tapers at a first constant rate from said first region to said final tapered section; and

said final tapered section tapers at a second constant rate from said initial tapered section.

9. A fluid pump as in claim 8 wherein: said first constant rate is greater than said second constant rate.

10. A fluid pump as in claim 9 wherein said final tapered section tapers from said initial tapered section to said inlet plate face.

11. A fluid pump as in claim 1 wherein said third radius is centered about a center point which is laterally offset from said axis toward said first region.

12. A fluid pump as in claim 11 wherein said center point is offset from said axis toward said second region in addition to toward said first region.

13. A fluid pump as in claim 1 wherein:

said inlet plate flow channel has an inlet region at one end of said inlet plate flow channel such that said first region is between said inlet region and said second region and such that said inlet opens into said inlet region; and

said second region terminates said inlet plate flow channel.