AU2005316683A1

AU2005316683A1 - Reciprocating pump system

Info

Publication number: AU2005316683A1
Application number: AU2005316683A
Authority: AU
Inventors: Richard W. Caddell
Original assignee: Sullair LLC
Current assignee: Hitachi Global Air Power US LLC
Priority date: 2004-12-13
Filing date: 2005-12-12
Publication date: 2006-06-22
Also published as: US20060127252A1; CA2591345A1; EP1834093A1; JP2008523312A; CN101084373A; BRPI0518988A2; WO2006065718A1; MX2007006985A

Description

WO 2006/065718 PCT/US2005/044844 RECIPROCATING PUMP SYSTEM BACKGROUND OF THE INVENTION [0001] The present invention relates to a pump, and more particularly to a linear electric motor driven reciprocating pump. [00021 Reciprocating pumps/compressors are highly desirable for use in numerous applications, particularly in environments where liquid flow rate is relatively low and the required liquid pressure rise is relatively high. For applications requiring less pressure rise and greater flow rate, single stage centrifugal pumps may be favored because of their simplicity, low cost and low maintenance requirements. However, reciprocating pumps have a higher thermodynamic efficiency than centrifugal pumps by as much as 10% to 30%. [0003] One conventional reciprocating pump utilizes a solenoid to drive a piston within a cylinder. When the solenoid is energized the solenoid plunger pushes air out of the discharge. When the solenoid is de-energized a solenoid spring drives the solenoid plunger in an opposite direction drawing air into an inlet. Disadvantageously, a solenoid driven reciprocating pump provides the least force at the extremes of the solenoid plunger travel. The pull on the solenoid plunger increases by the inverse square of the distance between the center of the plunger and the center of the magnet such that the force across the length of travel is uneven. [0004] A typical air compressor load increases almost linearly as the piston moves to compress the air. In a typical pump application the load is generally constant along the length of travel. In either application, the force delivered by the solenoid plunger does not match the required load, which renders the solenoid pump relatively inefficient. Furthermore, solenoids have relatively limited linear travel which further increases the inherent inefficiencies thereof. [0005] Accordingly, it is desirable to provide a reciprocating pump which generally matches the required load to provide efficient operation. 1 WO 2006/065718 PCT/US2005/044844 SUMMARY OF THE INVENTION 100061 A reciprocating pump assembly according to the present invention includes a linear electric motor having a cylinder, a rotor, and a stator. A multiple of check valves are located near each end of the cylinder. Pairs of check valves are mounted within a T-shaped fitting which permit each fitting to operate alternatively as an inlet and a discharge depending on the direction of the rotor stroke. [0007] Operation of the pump assembly utilizes the rotor as a piston within the cylinder. As the rotor is driven toward one endplate, one check valve within each fitting is open and one is closed to permit the opposed fittings to alternatively operate as the inlet and the discharge. When the rotor is driven toward the opposite endplate, the check valves reverse and the fittings reverse operation. The reciprocating pump assembly provides compression during each stroke of the rotor. [00081 Another embodiment of the pump assembly utilizes the rotor to drive separate pistons through pushrods. The check valves may be reed valves located directly within the piston cylinders to provide other packaging possibilities. [0009] The present invention therefore provides a reciprocating air compressor which generally matches the required load to provide efficient operation. BRIEF DESCRIPTION OF THE DRAWINGS [00101 The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: [0011] Figure 1 is a general sectional view of a reciprocating pump assembly according to the present invention; [0012] Figure 2A is a sectional view of a reciprocating pump assembly in a first position; [0013] Figure 2B is a sectional view of a reciprocating pump assembly in a second position; [0014] Figure 2C is a sectional view of a reciprocating pump assembly in a third position; 2 WO 2006/065718 PCT/US2005/044844 [00151 Figure 2D is a sectional view of a reciprocating pump assembly in a fourth position; and [00161 Figure 3 is a sectional view of another reciprocating pump assembly according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0017] Figure 1 illustrates a schematic sectional view of a reciprocating pump assembly 10. The pump assembly 10 generally includes a linear electric motor 11 having a cylinder 12, a rotor 14, and a stator 16. A first check valve 18, a second check valve 20, a third check valve 22 and fourth check valve 24 are located in pairs near each end of the cylinder 12. It should be understood that although the pump assembly 10 is described as a compressor for a gas, other uses such as compressor and pump uses for gases and/or fluids will likewise benefit from the present invention. [0018] The cylinder 12 defines a longitudinal axis A. Preferably, the cylinder 12 is a tubular member which surrounds the rotor 14. The cylinder 12 includes opposed endplates 26, 28 which may be selectively opened to receive the rotor 14. It should be understood that the cylinder need not be linear. [0019] The rotor 14 is preferably an inductor rotor which includes an iron core 30 with alternating bands of copper 32 and iron 34 mounted about said iron core 30. It should be understood that other induction rotors with an inner core of ferrous material and an outer layer of conductive material may also be used with the present invention. [0020] A seal 36 such as an 0-ring is preferably located near each end of the rotor 14 to center and seal the rotor within the cylinder 12. The seal 36 essentially provides a sliding bearing seal for the rotor 14. That is, due to the seals the rotor 14 operates as a piston within the cylinder 12. [0021] Each endplate 26, 28 mounts a pair of check valves 18, 20 and 22, 24 within a T-shaped fitting 38, 40. The check valves are each preferably mounted within the T-shaped fitting 38, 40 such that the check valves 18, 20 and 22, 24 permit each fitting 38, 40 to operate alternatively such that when one check valve is open 18, 22 the opposed check valves 20, 24 are closed. The fittings 38, 40 alternate between operation as either an inlet or a discharge from the cylinder 12. The fittings 38, 40 provide communication through a multiple of conduits C1-C4 to transfer a fluid medium from a source to a destination. 3 WO 2006/065718 PCT/US2005/044844 [0022] The stator 16 is mounted about the cylinder 12 to drive the rotor 14 in response to a controller 44. The stator 16 includes a multiple of cooling fins 46 interspersed between a multiple of magnets 48. The multiple of cooling fins 46 and the multiple of magnets 48 are axially retained with a tie-rod 49. The magnets 48 are preferably electromagnetic stator windings such as wire wound into coils, however, other magnets may also be utilized by the present invention. Preferably, only three windings (one for each phase) need be used with the present invention. [00231 The controller 44 may be a variable speed controller, a switched reluctance speed controller or other controller which controls a poly-phase power source 50. The controller 44 reverses movement of the rotor 14 along the longitudinal axis A by interchanging two of the three phases as generally known. Known chip sets and transistor modules are available to provide an induction variable speed drive controller 44 and need not be fully described herein. [00241 Referring to Figure 2A, operation of the pump assembly 10 begins with the rotor 14 being driven toward one endplate 26 as indicated by arrow X1. In this embodiment, the rotor 14 operates as a piston within the cylinder 12. As the rotor 14 is driven toward endplate 26, the check valve 18 located within the T-shaped fitting 38 is open and the check valve 20 within the T-shaped fitting 38 is closed such that fitting 38 operates as a discharge and fitting 40 operates as an inlet. Fluid within the cylinder 12 forward of the rotor 14 discharges through check valve 18. Simultaneously therewith, the rotor 14 moves away from endplate 28 (Figure 3B) such that the check valve 24 located within the T-shaped fitting 40 is open and the check valve 22 within the T-shaped fitting 40 is closed such that fluid is drawn in behind the rotor 14 (relative to Arrow Xl). It should be understood that relative positional terms such as "forward," "aft," "upper," "lower," "above," "below," "behind" and the like are with reference to the figures only and should not be considered otherwise limiting. [00251 Referring to Figure 3C, the rotor 14 has reached the end of stroke and is adjacent to the endplate 26. Fluid forward of the rotor 14 has been expelled through check valve 18 and fluid is drawn in behind the rotor 14 through check valve 24. At the end of stroke, the controller 44 reverses direction of the rotor 14 (Figure 3D) and the cycle begins again with the check valves operating in reverse. [0026] Referring to Figure 2D, the rotor 14 is driven toward the endplate 28 as indicated by arrow X2. As the rotor 14 is driven toward endplate 28, the check valve 18 located within the T-shaped fitting 38 is closed and the check valve 20 within the T-shaped fitting 38 is open such that the fitting 38 operates as an inlet and fitting 40 operates as a discharge. 4 WO 2006/065718 PCT/US2005/044844 Simultaneously therewith, the rotor 14 moves away from endplate 26 such that the check valve 24 located within the T-shaped fitting 40 is closed and the check valve 22 within the T-shaped fitting 40 is open such that air is drawn in behind the rotor 14 (relative to arrow X2). The T shaped fitting 40 now operates as discharge. [0027] The pump assembly 10 thereby operates to compress fluid as the rotor 14 moves in both directions improving the efficiency thereof. The pump assembly 10 thereby cycles between fittings 38, 40 to provide intake/discharge on each stroke of the rotor 14. The controller 44 preferably controls the cycle time of the rotor 14 to provide a desired output. [0028] Referring to Figure 3, another pump assembly 52 includes a linear electric motor 54 which drives a first and a second piston 56, 58 within a respective piston cylinder 60, 62. The pistons 56, 58 are respectively linked to a rotor 64 of the linear electric motor 54 through pushrods 66, 68. In this embodiment the rotor 64 and pistons 56, 58 are separate which provides different packaging possibilities. Pairs of check valves 70, 72 and 74, 76 are located within the respective piston cylinders 60, 62. The check valves 70-76 are preferably reed valves, however other one-way valves may also be used with this embodiment. A stator 78 is mounted about the rotor 64 to drive the rotor 64 and connected pistons 56, 58 in response to a controller 80. As the rotor cycles along axis A, the check valves 70-76 operate generally as described above to provide pumping and compression during each cycle of the rotor 64. [0029] Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention. [0030] The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention. 5

Claims

1. A reciprocating pump assembly comprising: a cylinder which defines a longitudinal axis; a first check valve mounted adjacent a first cylinder end; a second check valve mounted adjacent said first cylinder end, said second check valve checking a flow from said cylinder in a direction opposite than said first check valve; a third check valve mounted adjacent a second cylinder end; a fourth check valve mounted adjacent said second cylinder end, said fourth check valve checking a flow from said cylinder in a direction opposite than said third check valve; a rotor mounted within said cylinder; and a stator mounted about said cylinder to reciprocally drive said rotor along said longitudinal axis.

2. The reciprocating pump assembly as recited in claim 1, wherein said first check valve, said second check valve, said third check valve and said fourth check valve are reed valves.

3. The reciprocating pump assembly as recited in claim 1, wherein said rotor includes an iron core with alternating bands of copper and iron mounted onto said iron core.

4. The reciprocating pump assembly as recited in claim 1, further comprising a seal mounted near each end of said rotor.

5. The reciprocating pump assembly as recited in claim 1, wherein said stator includes a multiple of cooling fins interspersed between a multiple of magnets. -6- WO 2006/065718 PCT/US2005/044844

6. The reciprocating pump assembly as recited in claim 5, further comprising a tie bar which axially retains said multiple of cooling fins and said multiple of magnets.

7. The reciprocating pump assembly as recited in claim 1, further comprising a controller to control movement of said rotor within said stator.

8. The reciprocating pump assembly as recited in claim 7, wherein said controller includes a variable speed controller.

9. The reciprocating pump assembly as recited in claim 7, wherein said controller includes a switched reluctance speed controller.

10. The reciprocating pump assembly as recited in claim 1, wherein said first check valve and said second check valve are contained within a first fitting and said third check valve and said fourth check valve are contained within a second fitting.

11. The reciprocating pump assembly as recited in claim 10, wherein said first fitting and said second fitting are T-shaped fittings.

12. The reciprocating pump assembly as recited in claim 1, wherein said first check valve and said second check valve are opposed within a first fitting and said third check valves and said fourth check valve are opposed within a second fitting.

13. A reciprocating pump assembly comprising: a cylinder which defines a longitudinal axis; a rotor mounted within said cylinder; a first piston cylinder; a first piston mounted within said first piston cylinder; -7- WO 2006/065718 PCT/US2005/044844 a first push rod mounted to said first piston and said rotor to drive said first piston along said longitudinal axis in response to movement of said rotor; a first check valve mounted to said first piston cylinder; a second check valve mounted to said first piston cylinder, said second check valve checking a flow from said first piston cylinder in a direction opposite than said first check valve; a second piston cylinder; a second piston mounted within said second piston cylinder; a second push rod mounted to said second piston and said rotor to drive said second piston along said longitudinal axis in response to movement of said rotor; a third check valve mounted to said second piston cylinder; a fourth check valve mounted to said second piston cylinder, said fourth check valve checking a flow from said second piston cylinder in a direction opposite than said third check valve; and a stator mounted about said cylinder to reciprocally drive said rotor along said longitudinal axis.

14. The reciprocating pump assembly as recited in claim 13, wherein said first check valve and said second check valve are reed valves.

15. The reciprocating pump assembly as recited in claim 13, wherein said first check valve and said second check valve are located within an end plate of said piston cylinder. -8-