WO2008046005A2

WO2008046005A2 - Pre-compression relief porting for positive displacement pumps

Info

Publication number: WO2008046005A2
Application number: PCT/US2007/081111
Authority: WO
Inventors: Richard T. Friedman; Thomas Roeber; Randy S. Lessard
Original assignee: Parker-Hannifin Corporation
Priority date: 2006-10-11
Filing date: 2007-10-11
Publication date: 2008-04-17
Also published as: WO2008046005A3

Abstract

A positive displacement pump (1) having a pump element having at least one variable volume displacement chamber (2), and a relief passage (7) for relieving pressure from the displacement chamber when the displacement chamber is decreasing in volume and is not in communication with an intake (3) or discharge (4) port. A valve member (34), such as a reed valve, is provided to regulate flow through the relief passage (7).

Description

PRE-COMPRESSION RELIEF PORTING FOR POSITIVE DISPLACEMENT PUMPS

Related Applications This application claims the benefit of U.S. Provisional Application No.

60/829,011 filed October 11 , 2006, which is hereby incorporated herein by reference.

Field of the Invention The present invention relates to positive displacement pumps, and more particularly, to positive displacement pumps having low noise and pump ripples.

Background of the Invention Positive displacement pumps, such as gear pumps, typically have a rotating pump element supported in a pump housing for pumping a fluid from an inlet to an outlet. The pump element and the housing (or another rotating element) form a displacement chamber as the pump element rotates. During a pump cycle, the displacement chamber typically expands in volume during an inlet portion of the cycle and decreases in volume during an outlet portion of the cycle. The displacement chamber thereby operates to draw fluid into the chamber during the inlet portion of the cycle and force fluid out of the displacement chamber during the outlet portion of the cycle.

Many positive displacement pumps utilize a port plate for controlling flow of fluid to and from the rotating pump element. The port plate typically has an inlet port and an outlet port with which the displacement chamber or chambers alternatively communicate during rotation of the rotating pump element. The inlet and outlet are spaced apart such that a given displacement chamber communicates with the inlet port during expansion of the chamber and the outlet port during compression of the chamber. The expansion of the displacement chamber during the inlet cycle results in a drop in pressure such that fluid from the incoming source, being at a higher pressure, flows into the displacement chamber via the inlet port. Positive displacement pumps, however, often operate under conditions that do not allow the displacement chamber to fill completely with fluid during the inlet cycle. For example, the chamber can expand faster than the fluid can enter resulting in a chamber that is partially filled with low pressure fluid. The remainder of the chamber contains low pressure vapor. The vapor is typically made up of the more volatile chemicals in the fluid mixture. During the outlet portion of the cycle, the displacement chamber is exposed to the high pressure discharge port. Exposure to the discharge port is generally coincident to a reduction in volume of the chamber to thereby force the fluid out. During the first instant of communication with the discharge port, fluid in the discharge line can flow backwards (e.g., into the displacement chamber) to fill the vapor portion of the displacement chamber. Such backflow can occur very quickly and can result in what is commonly referred to as pump ripple.

Pump ripple is a rapid fluctuation of pump pressure. The change in pressure can cause the pump housing to act as a sound board and result in pump noise which is very undesirable for many applications. In addition, the rapid collapse of the vapor portion can cause a shock wave. If the vapor portion is close to a pump wall or other pump structure, the Shock wave can cause such structure to disintegrate. The term for the rapid collapse is cavitation, and the resulting disintegration is sometimes referred to as cavitation erosion.

One manner in which the above-described effects have been minimized is by causing the discharge port to communicate with the displacement chamber volume during a later portion of the cycle. This results in the chamber volume becoming smaller with no outlet for the fluid and, consequently, any vapor portion within the chamber becomes smaller and/or is eliminated. The objective is to design the porting so that the vapor portion is just disappearing (e.g., condensing) at the time that communication with the discharge port is achieved.

While such a design is effective in conditions when a vapor portion is present in the chamber, under conditions when the displacement chamber is completely filled with fluid (e.g., during low speed operation), the pump can become hydraulically locked. To avoid hydraulic lock, the discharge port is typically connected to the chamber volume via a small passage (e.g., a bleed groove) to bleed off the excess fluid as the chamber volume decreases. This configuration, however, is less efficient at collapsing and/or eliminating a vapor portion if present in the displacement chamber because the bleed chamber can prevent sufficient pressure from building in the displacement chamber. Further, such design reduces pump efficiency, particularly when no vapor portion is present in the chamber, and such designs work optimally only when a pump is operated at a certain speed.

Summary of the Invention

The present invention provides a positive displacement pump having low pump ripple without the aforementioned inefficiencies of previous pump designs. The invention can achieve greater pump efficiency and prevent cavitation at a range of pump speeds. Accordingly, a positive displacement pump comprises a pump element having at least one variable volume displacement chamber that cyclically increases and decreases in volume to displace fluid from an inlet of the pump to an outlet of the pump, the displacement chamber communicating with the inlet when the displacement chamber is increasing in volume and communicating with the outlet when the displacement chamber is decreasing in volume. A relief passage for venting fluid from the displacement chamber communicates with the displacement chamber while the displacement chamber is decreasing in volume but prior to the displacement chamber communicating with the outlet. A pressure relief valve controls the flow of fluid through the relief passage. More particularly, a port plate is provided including an intake port and a discharge port configured to direct flow to and from the inlet and outlet of the pump and the pump element. The intake port is spaced circumferentially from the discharge port and the relief passageway is spaced circumferentially from the intake port and the discharge port. A surface of the port plate between the intake port and discharge port can form a part of a surface of the displacement chamber, and the relief passage can open to the surface of the port plate forming part of the displacement chamber. The relief valve can include a check valve biased to a closed position blocking flow from the displacement chamber. The relief valve can include a reed valve having a flexible reed movable toward and away from an opening to respectively block and permit flow through the opening. The relief valve can include an electromechanical valve, such as a proportional valve for modulating flow from the displacement chamber as a function of pump displacement. The pump element can include a gerotor gear set, and the relief passage can vent fluid from the displacement chamber to the outlet or inlet.

In accordance with another aspect of the invention, a port plate for a positive displacement pump for directing flow to and from an inlet and outlet of the pump and a pump element comprises a body having an intake port and a discharge port spaced circumferentially from the intake port, the intake port for communicating with a displacement chamber of the pump element when the displacement chamber is increasing in volume and the discharge port for communicating with the displacement chamber when the displacement chamber is decreasing in volume. A relief passage is circumferentially spaced from the intake port and the discharge port, the relief passage for communicating with the displacement chamber while the displacement chamber is decreasing in volume but prior to the displacement chamber communicating with the outlet. A pressure relief valve for controls the flow of fluid through the relief passage.

A surface of the port plate between the intake port and discharge port forms part of a surface of the displacement chamber when installed in a pump, and the relief passage opens to the surface of the port plate that forms part of the displacement chamber. The relief valve can include a check valve. The relief valve can include a reed valve having a flexible reed movable toward and away from an opening to respectively block and permit flow through the opening. The relief valve can include an electromechanical valve, such as a proportional valve for modulating flow through the relief passageway.

In accordance with another aspect of the invention, a method of controlling pump cavitation in a positive displacement pump having a pump element having at least one variable volume displacement chamber that cyclically increases and decreases in volume to displace fluid from an inlet of the pump to an outlet of the pump, the displacement chamber communicating with the inlet when the displacement chamber is increasing in volume and communicating with the outlet when the displacement chamber is decreasing in volume, the method comprises decreasing the volume of the displacement chamber a prescribed amount prior to the displacement chamber communicating with an outlet of the pump and, during the decreasing step, venting fluid from the displacement chamber when the pressure in the displacement chamber exceeds a prescribed level. The venting includes regulating the flow of fluid from the displacement chamber with a valve member, such as a reed valve. Further features of the invention will become apparent from the following detailed description when considered in conjunction with the drawings.

Brief Description of Drawings

Fig. 1 is a schematic diagram of an exemplary positive displacement pump in accordance with the invention.

Fig. 2 is a perspective view of an exemplary port plate having a reed valve for controlling flow through a relief passage in accordance with the invention.

Fig. 3 is a perspective view of a gerotor gear set and the port plate of Fig. 2 showing the components of the reed valve in accordance with the invention. Fig. 4 is another perspective view of the gerotor gear set and port plate of Fig. 3.

Fig. 5 is another perspective view of the gerotor gear set and port plate of Fig. 3. Fig. 6 is a perspective view of another exemplary port plate having a check valve for controlling flow through a relief passage in accordance with the invention.

Detailed Description Referring now to the drawings in detail, and initially to Fig. 1 , an exemplary positive displacement pump 1 in accordance with the invention is illustrated. The positive displacement pump 1 can be any type of positive displacement pump, such as a piston pump, gear pump, gerotor pump, vane pump, etc. The pump 1 has a displacement chamber 2 for displacing fluid from an intake port 3 to a discharge port 4. The intake port 3 and discharge port 4 are connected to pump supply and discharge lines 5 and 6, respectively. Although not readily apparent in Fig. 1 , it will be appreciated that the displacement chamber 2 cyclically increases and decreases in volume while alternatively communicating with the intake port 3 and discharge port 4 to pump fluid. A relief passage 7 for venting fluid from the displacement chamber 2 extends between the displacement chamber 2 and the discharge port 4, and a pressure relief valve 8 controls the flow of fluid through the relief passage 7.

As will be better understood in view of the following, the relief passage 7 communicates with the displacement chamber 2 when the displacement chamber is decreasing in volume to vent fluid from the displacement chamber 2 when pressure in the displacement chamber exceeds a prescribed level. Thus, the relief passage 7 can be provided in any suitable member of the pump. For example, in a vane pump, the relief passage 7 can be provided in an appropriate location of the cam contour that forms a surface of the displacement chamber 2. In a gear or piston pump, the relief passage 7 can be provided in a port plate, as will now be described. Turning now to Figs. 2-5, a port plate 10 for a positive displacement pump is illustrated. The port plate 10 is generally similar to a conventional port plate with the exception of the porting arrangement and the relief valve, as will be described. It will be appreciated that the port plate 10, although shown in the context of a gerotor pump, can be used in a wide variety of positive displacement pumps such as gear pumps, piston pumps.

The port plate 10 has a generally cylindrical body 12 having an opening 13 for the passage of a shaft, such as an input shaft, for rotating a pump element. The port plate 10 has extending therethrough an intake port 14 and a discharge port 16. The intake and discharge ports 14 and 16 are generally kidney-shape and circumferentially spaced apart. Separating the intake and discharge ports are two lands 20 and 22. As will be appreciated, land 20 cooperates with a rotating pump element, such as gerotor gear set 24 (see Figs. 4 and 5), to form a displacement chamber 26 for displacing fluid from the intake port 14 to the discharge port 16. The relationship of the intake and discharge ports 14 and 16 and the size of land 20 is such that the displacement chamber 26, after expanding and drawing fluid from the intake port 14, begins to decrease in volume prior to communicating with the discharge port 16. Accordingly, the fluid within the displacement chamber 26 is compressed prior to being discharged to the discharge port 16. As will be appreciated, compression of the fluid in the displacement chamber 26 prior to being discharged can effectively compress and collapse any vapor portion within the displacement chamber 26 thereby avoiding or reducing the problems that can otherwise occur (e.g., pump ripple, cavitation, etc.).

Unlike prior art port plates, the port plate 10 further includes a relief passage 30 and valve 34 for relieving pressure from the displacement chamber 26 prior to the displacement chamber 26 communicating with the discharge port. In the embodiment of Figs. 2-5, the valve 34 is a reed valve operable to permit flow from the displacement chamber 26 to the discharge port 16 when pressure in the displacement chamber 26 exceeds a prescribed level. A relief passage port 38 in land 20 of the port plate 10 leads to the relief passage 30 such that the displacement chamber 26 communicates therewith when sealed from the intake and discharge ports 14 and 16. A flexible reed element 40 is retained in the relief passage 30 for respectively blocking and permitting flow through the relief passage port 38 by reed valve shoe 42 and shoe clamp 44. Shoe clamp 44 can be secured to the port plate 10 via a fastener, such as a bolt (not shown), for example.

The reed valve shoe 42 has a curved surface against which the flexible reed element 40 can engage when fluid is flowing from the displacement chamber 26 to the relief port. The curved surface limits the extent to which the flexible reed element 40 can deflect thereby preventing permanent deformation of the flexible reed element 40. Thus, it will be appreciated that when the displacement chamber 26 decreases in volume thereby compressing the fluid in the displacement chamber 26, reed valve 34 deflects to open the relief passage port 38 to thereby vent fluid to the discharge port 16.

For example, the displacement chamber 26 can be configured to decrease in volume a given amount, for example 20 percent, prior to communicating with the discharge port 16. In the event that 20 percent of the displacement chamber 26 is vapor, such as may occur when the pump is operating at high speed, the 20 percent reduction in volume will collapse the vapor portion prior to the displacement chamber 26 opening to the discharge port.

If, however, under different operating conditions the displacement chamber 26 contains less than 20 percent vapor but is configured to decrease in volume 20 percent, without the relief valve 34 the 20 percent reduction in volume could potentially cause a hydraulic lock condition to occur as the displacement chamber 26 becomes 100 percent liquid prior to opening to the discharge port 16. Thus, it will be appreciated that the relief valve 34 is operative to relieve excess fluid via the relief passage 30 to the discharge port 16 to prevent the pump from locking under such conditions. In order to control the pressure required to open the reed valve 34, a flexible reed element 40 having a suitable stiffness can be used. In general, a more stiff flexible reed element 40 will require a higher pressure to deflect to vent fluid from the displacement chamber. The excess fluid can be vented to the discharge port 16 as illustrated, or to the intake port 14 where the pressurized fluid can be used to supercharge the fluid flowing into another displacement chamber 26. The fluid may also be vented to any other suitable place, such as a sump or auxiliary line.

As will be appreciated, other types of valves can be used in place of the reed valve 34. For example, in Fig. 6 a ball valve 44 is illustrated in place of the reed valve 34. The ball valve 44 can be preloaded in a closed configuration thereby blocking flow from the displacement chamber 26. Preloading the valve 44 in a closed configuration may be needed upon pump startup until pressure in the discharge port 16 builds to a level sufficient to maintain the valve in a closed state. Other valve types can also be used. For example, electro mechanically controlled valves, such as solenoid valves can be used. A proportional valve can be used to modulate flow through the relief passage as a function of pump displacement, for example.

It will now be appreciated that the port plate 10 of the invention allows positive displacement pumps to operate efficiently and smoothly at a range of speeds by providing for the elimination of the vapor portion within the displacement chamber 26. In this regard, it will be understood that a for a given pump, the maximum anticipated vapor portion can be used to determine the volume reduction of the displacement chamber 26 prior to communication with the discharge port such that, under all anticipated operating conditions, any vapor portion within the displacement chamber 26 can be eliminated prior to opening to the discharge port 16.

For example, if the maximum vapor portion anticipated when the pump is operated is determined to be 30 percent, the displacement chamber 26 can be configured to reduce in volume by 30 percent prior to communicating with the discharge port. This can be achieved by having the displacement chamber 26 communicate with the discharge port 16 later during the compression portion of the pump cycle after the displacement chamber has decreased in volume by 30 percent. Thus, in this example, if a vapor portion of 30 percent exists in the displacement chamber 26, that vapor portion will be collapsed prior to the displacement chamber 26 communicating with the discharge port 16. If the vapor portion is less that 30 percent, excess fluid will be relieved via valve 34. Accordingly, the displacement chamber 26 will be 100 percent liquid when it communicates with the discharge port 16 under the anticipated operating conditions.

It will further be appreciated that by relieving fluid to the discharge port in the manner described, the efficiency of the pump is maintained over a range of operating speeds. This is because, unlike the prior art bleed grooves that bleed fluid at all times, the present invention typically bleeds fluid only when necessary to prevent a hydraulic lock condition from occurring (e.g., when the displacement chamber 26 is 100 percent liquid).

The invention is applicable to positive displacement pumps of all types including external gear pumps, internal gear pumps, piston pumps, vane pumps, etc. Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.

Claims

What is claimed is:

1. A positive displacement pump comprising: a pump element having at least one variable volume displacement chamber that cyclically increases and decreases in volume to displace fluid from an inlet of the pump to an outlet of the pump, the displacement chamber communicating with the inlet when the displacement chamber is increasing in volume and communicating with the outlet when the displacement chamber is decreasing in volume; a relief passage for venting fluid from the displacement chamber, the relief passage communicating with the displacement chamber while the displacement chamber is decreasing in volume but prior to the displacement chamber communicating with the outlet; and a pressure relief valve for controlling the flow of fluid through the relief passage.

2. A positive displacement pump as set forth in claim 1 , further comprising a port plate including an intake port and a discharge port configured to direct flow to and from the inlet and outlet of the pump and the pump element, the intake port being spaced circumferentially from the discharge port, and the relief passageway being spaced circumferentially from the intake port and the discharge port.

3. A positive displacement pump as set forth in claim 1 , wherein a surface of the port plate between the intake port and discharge port forms part of a surface of the displacement chamber, and wherein the relief passage opens to the surface of the port plate forming part of the displacement chamber.

4. A positive displacement pump as set forth in claim 1 , wherein the relief valve includes a check valve biased to a closed position blocking flow from the displacement chamber.

5. A positive displacement pump as set forth in claim 1 , wherein the relief valve includes a reed valve.

6. A positive displacement pump as set forth in claim 5, wherein the reed valve includes a flexible reed movable toward and away from an opening to respectively block and permit flow through the opening.

7. A positive displacement pump as set forth in claim 1 , wherein the relief valve includes an electromechanical valve.

8. A positive displacement pump as set forth in claim 7, wherein the electromechanical valve is a proportional valve for modulating flow from the displacement chamber as a function of pump displacement.

9. A positive displacement pump as set forth in claim 1 , wherein the pump element includes a gerotor gear set.

10. A positive displacement pump as set forth in claim 1 , wherein the relief passage vents fluid from the displacement chamber to the outlet.

11. A positive displacement pump as set forth in claim 1 , wherein the relief passage vents fluid to the inlet.

12. A port plate for a positive displacement pump for directing flow to and from an inlet and outlet of the pump and a pump element, comprising: a body having an intake port and a discharge port spaced circumferentially from the intake port, the intake port for communicating with a displacement chamber of the pump element when the displacement chamber is increasing in volume and the discharge port for communicating with the displacement chamber when the displacement chamber is decreasing in volume; a relief passage circumferentially spaced from the intake port and the discharge port, the relief passage for communicating with the displacement chamber while the displacement chamber is decreasing in volume but prior to the displacement chamber communicating with the outlet; and a pressure relief valve for controlling the flow of fluid through the relief passage.

13. A port plate as set forth in claim 12, wherein a surface of the port plate between the intake port and discharge port forms part of a surface of the displacement chamber when installed in a pump, and wherein the relief passage opens to the surface of the port plate that forms part of the displacement chamber.

14. A port plate as set forth in claim 12, wherein the relief valve includes a check valve.

15. A port plate as set forth in claim 12, wherein the relief valve includes a reed valve.

16. A port plate as set forth in claim 15, wherein the reed valve includes a flexible reed movable toward and away from an opening to respectively block and permit flow through the opening.

17. A port plate as set forth in claim 12, wherein the relief valve includes an electromechanical valve.

18. A port plate as set forth in claim 12, wherein the electromechanical valve is a proportional valve for modulating flow through the relief passageway.

19. A method of controlling pump cavitation in a positive displacement pump having a pump element having at least one variable volume displacement chamber that cyclically increases and decreases in volume to displace fluid from an inlet of the pump to an outlet of the pump, the displacement chamber communicating with the inlet when the displacement chamber is increasing in volume and communicating with the outlet when the displacement chamber is decreasing in volume, the method comprising: decreasing the volume of the displacement chamber a prescribed amount prior to the displacement chamber communicating with an outlet of the pump; and during the decreasing step, venting fluid from the displacement chamber when the pressure in the displacement chamber exceeds a prescribed level; wherein the venting includes regulating the flow of fluid from the displacement chamber with a valve member.

20. A method as set forth in claim 19, wherein the regulating the flow of fluid from the displacement chamber with a valve member includes using a reed valve to control flow of fluid in a relief passageway in communication with the displacement chamber.