WO2016068971A1

WO2016068971A1 - Multiple pressure variable displacement pump with mechanical control

Info

Publication number: WO2016068971A1
Application number: PCT/US2014/063309
Authority: WO
Inventors: Ayres Pinto DE ANDRADE FILHO; Joao Luiz De Carvalho Meira; Eduardo Gubbiotti Ribeiro
Original assignee: Melling Tool Comapny
Priority date: 2014-10-31
Filing date: 2014-10-31
Publication date: 2016-05-06
Also published as: US20170306948A1

Abstract

A variable displacement vane pump that includes a biasing assembly that applies a first biasing force to a pump control ring when the pump control ring is located a first position and a second position and applies a second biasing force when the pump control ring is located between the second position and a third position. The first position of the pump control ring corresponds to a maximum volumetric capacity of the pump, the second position corresponds to an intermediary volumetric capacity of the pump, and the third position corresponds to a minimum volumetric capacity of the pump. Fluid pressure within a control chamber urges the pump control ring toward the third position.

Description

MULTIPLE PRESSURE VARIABLE DISPLACEMENT PUMP WITH MECHANICAL

CONTROL

TECHNICAL FIELD

[0001] This disclosure relates to the field of variable displacement vane pumps, and more particularly, to a variable displacement vane pump having a biasing assembly that can provide multiple equilibrium pressures within a control chamber.

BACKGROUND

[0002] Variable displacement vane pumps are well-known and can include a displacement adjusting structure in the form of a pump control ring that can be moved to alter the rotor eccentricity of the pump and hence alter the volumetric capacity of the pump. If the pump is supplying a system with a substantially constant orifice size, such as an automobile engine lubrication system, changing the output volume of the pump is equivalent to changing the pressure produced by the pump.

[0003] Having the ability to alter the volumetric capacity of the pump to maintain an equilibrium pressure is important in environments in which the pump will be operated over a range of operating speeds, such as automobile lubrication pumps. In order to maintain an equilibrium pressure in such environments, it is known to utilize a feedback supply of the working fluid (e.g., lubricating oil) from the output of the pump to a control chamber adjacent the pump control ring, the pressure in the control chamber acting to move the control ring, typically against a biasing force from a return spring, to alter the capacity of the pump.

[0004] When the pressure at the output of the pump increases, such as when the operating speed of the pump increases, the increased pressure is applied to the control ring to overcome the bias of the return spring and to move the control ring to reduce the capacity of the pump, thus reducing the output volume and hence the pressure at the output of the pump. Conversely, as the pressure at the output of the pump drops, such as when the operating speed of the pump decreases, the decreased pressure applied to the control chamber adjacent the control ring allows the bias of the return spring to move the control ring to increase the capacity of the pump, raising the output volume and hence pressure of the pump. In this manner, an equilibrium pressure is obtained at the output of the pump. The equilibrium pressure is determined by the area of the control ring against which the working fluid and the control chamber acts, the pressure of the working fluid supplied to the chamber, and the bias force generated by the return spring.

[0005] Conventionally, the equilibrium pressure is selected to be a pressure which is acceptable for expected operating range of the engine and is thus somewhat of a compromise, as, for example, the engine may be able to operate acceptably at lower operating speeds with a lower working fluid pressure than is required at a higher operating engine speeds. To prevent undue wear or other damage to the engine, the engine designers will select an equilibrium pressure for the pump which meets the worst case (higher operating speeds) conditions. Thus, at lower speeds, the pump will be operating at a higher capacity than necessary for those speeds, wasting energy pumping the surplus, unnecessary working fluid.

[0006] It is known to utilize more than one control chamber in order that more than one equilibrium pressure can be established within the pump. However, by establishing multiple control chambers, the pump must take on a greater size physically, thereby requiring the pump to have a larger overall size. A larger sized pump can limit the applications by which the pump can be utilized within an automobile engine compartment. In addition, the multiple control chambers require additional machining and parts, such as seals, thereby increasing the cost of such designs as compared to single chamber designs. SUMMARY

[0007] Variable displacement vane pumps are described herein. One aspect of the disclosed embodiments is a variable displacement pump having a housing, a biasing assembly, and a control chamber. The housing has a pump chamber. The pump chamber has a fluid inlet, a fluid outlet, a pump control ring, and a vane pump rotor. The pump control ring is disposed within the housing for altering the displacement of the pump by rotating between a first position that corresponds to a maximum volumetric capacity of the pump, a second position that corresponds to an intermediary volumetric capacity of the pump, and a third position that corresponds to a minimum volumetric capacity of the pump. The vane pump rotor is rotatably mounted within the pump control ring and has a plurality of slidably mounted vanes engaging an inside surface of the pump control ring. The vane pump rotor also has an axis of rotation eccentric from a center of the pump control ring. The vane pump rotor rotates to pressurize fluid as the fluid moves from the fluid inlet to the fluid outlet. The biasing assembly urges the pump control ring toward the first position. The biasing assembly applies a first biasing force to the pump control ring when the pump control ring is located between the first position and the second position and applies a second biasing force to the pump control ring when the pump control ring is located between the second position and the third position. The control chamber is formed between the housing and the pump control ring. The fluid pressure within the control chamber urges the pump control ring toward the third position.

[0008] A second aspect of the disclosed embodiments is a variable displacement vane pump having a housing, a biasing assembly, a control chamber, a feedback path, and a spring chamber. The housing has a pump chamber. The pump chamber has a fluid inlet, a fluid outlet, a pump control ring, and a vane pump rotor. The pump control ring is disposed within the housing for altering the displacement of the pump by rotating between a first position that corresponds to a maximum volumetric capacity of the pump, a second position that corresponds to an intermediary volumetric capacity of the pump, and a third position that corresponds to a minimum volumetric capacity of the pump. The vane pump rotor is rotatably mounted within the pump control ring and has a plurality of slidably mounted vanes engaging an inside surface of the pump control ring. The vane pump rotor also has an axis of rotation eccentric from a center of the pump control ring. The vane pump rotor rotates to pressurize fluid as the fluid moves from the fluid inlet to the fluid outlet. The biasing assembly applies a first biasing force to the pump control ring when the pump control ring is located between the first position and the second position and applies a second biasing force to the pump control ring when the pump control ring is located between the second position and the third position. The control chamber is formed between the housing and the pump control ring. The fluid pressure within the control chamber urges the pump control ring toward the third position. The feedback path is in communication with the fluid outlet supplying a pressurized fluid to the control chamber. The spring chamber is formed between the housing and the pump control ring. The spring chamber has a maximum volume when the pump control ring is in the first position and a minimum volume when the pump control ring is in the third position. The biasing assembly is disposed within the spring chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The various features, advantages, and other uses of the present disclosure will become more apparent by referring to the following drawings, in which:

[0010] FIG. 1 is a perspective view showing a variable displacement vane pump and an automotive oil sump reservoir;

[0011] FIG. 2 is an exploded perspective view showing the variable displacement vane pump and the automotive oil sump reservoir of FIG. 1; [0012] FIG. 3 is an illustration showing a control ring of the variable displacement vane pump in a first position that corresponds to a maximum volumetric capacity of the variable displacement vane pump;

[0013] FIG. 4 is an illustration showing the control ring of the variable displacement vane pump in a second position that corresponds to an intermediary volumetric capacity of the variable displacement vane pump and a first stage equilibrium pressure;

[0014] FIG. 5 is an illustration showing the control ring of the variable displacement vane pump in a third position that corresponds to a minimum volumetric capacity of the variable displacement vane pump and a second stage equilibrium pressure;

[0015] FIG. 6 is a cross-sectional plain view of a biasing assembly of the variable displacement vane pump;

[0016] FIG. 7 is a diagram showing the variable displacement vane pump incorporated into a lubricating system of an automobile engine; and

[0017] FIG. 8 is a graph showing operation of the variable displacement vane pump with the biasing assembly.

DETAILED DESCRIPTION

[0018] The present invention provides a pump that may be utilized to pump a fluid, such as automotive engine lubricant. As illustrated in FIGS. 1-2, the pump 10 may be a variable displacement vane pump. In automobile engine applications, the pump 10 may be connected to an oil sump reservoir 12. A housing 14 of the pump 10 may include a back side 16, a midsection 18, a cover 20, and a plate 22. The midsection 18 forms the peripheral walls of the housing 14, in which pumping and control chambers are formed, as will be explained herein. The cover 20 is connected to and sealed to the midsection 18. The back side 16 of the housing defines fluid flow paths for the pump 10 to allow fluid to enter and exit the pump 10. The plate 22 is mounted between the back side 16 and the midsection 18 of the housing 14 and includes apertures that define locations where fluid can pass between the back side 16 of the housing 14 and the chambers defined within the midsection 18 of the housing.

[0019] A pump control ring 28 is pivotally connected to the housing 14 by a pivot pin 30 and, optionally, a needle bearing 32. In particular, the pivot pin 30 extends through an aperture 31 that is formed near an outer periphery of a generally circular portion 60 (shown in FIGS. 3-5) of the pump control ring 28. If present, the needle bearing 32 is mounted between the pivot pin 30 and the pump control ring 28 so as to provide easy pivoting of the pump control ring 28 relative to the pivot pin 30. A regulating member 62 (shown in FIGS. 3-5) extends outward from the circular portion 60 of the pump control ring 28. The vane pump rotor 34 and the pump control ring 28 are substantially circular in shape. The center of the pump control ring 28 is located eccentrically with respect to the center of a vane pump rotor 34 is mounted within the pump control ring 28.

[0020] The vane pump rotor 34 has a plurality of vanes 36 that are mounted for sliding within slots that are formed in the vane pump rotor 34. The vane pump rotor 34 includes a ring 35 (shown in FIGS. 3-5). The vanes 36 pass through openings formed in the ring 35 and are engaged by the ring 35 such that rotation of the ring 35 causes rotation of the vanes 36. Although a single ring 35 is shown, some implementations includes two or more rings to help keep the vanes 36 in contact with the pump control ring 28, especially at low speeds. The vanes 36 engage an inside surface (not shown) of the pump control ring 28, and the vanes 36 slide within the slots in response to movement of the pump control ring 28 with respect to the vane pump rotor 34. The vane pump rotor 34 has an axis of rotation that is eccentric from the center of the pump control ring 28, as will be described further herein. A drive shaft 38 is driven by any suitable means, such as an automotive engine or other mechanism that can supply working fluid to operation the pump 10. The drive shaft 38 engages the vane pump rotor 34 and rotates the vane pump rotor 34 as the drive shaft 38 is driven. [0021] As shown in FIGS. 3-5, the pump control ring 28, the vane pump rotor 34, and the vanes 36 cooperate to define working chambers 50 that are located between successive pairs of vanes 36. Pumping from a fluid inlet 42 of the pump 10 to the fluid outlet 44 of the pump 10 occurs because the volume of each working chamber 50 changes as it passes from the fluid inlet 42 to the fluid outlet 44, thereby increasing the pressure of the fluid. Thus, the fluid inlet 42 is the low pressure side of the pump 10, and the fluid outlet 44 is the high pressure side of the pump 10.

[0022] Pivoting of the pump control ring 28 is operable to vary the amount of volumetric change of each working chamber 50 during rotation, which in turn changes the volumetric displacement of the pump 10. In particular, the pump control ring 28 pivots between a first position (shown in FIG. 3), a second position (shown in FIG. 4), and a third position (shown in FIG. 5). The first position corresponds to a maximum volumetric capacity of the pump 10. In the first position, the pump control ring 28 has reached its end limit of travel in a clockwise direction with respect to the pivot pin 30 by engagement of the pump control ring 28 with the housing 14. The second position corresponds to an intermediary volumetric capacity of the pump 10. The third position corresponds to a minimum volumetric capacity of the pump 10. In the third position, the pump control ring 28 has reached its end limit of travel in a counter-clockwise direction with respect to the pivot pin 30. The volumetric capacity of the pump 10 varies as a function of the position of the pump control ring 28, which under working conditions, often will be disposed somewhere between the first position and the third position.

[0023] A spring chamber 40 and a control chamber 41 are defined within the housing 14 to regulate the position of the pump control ring 28. A first seal 46 and a second seal 48 are mounted within respective recesses in the pump control ring 28 and engage an inner surface of the housing 14 to define the control chamber 41. [0024] The control chamber 41 is formed within a space that is disposed outward of the pump control ring 28, between the pump control ring 28 and an interior surface of the housing 14. A second side 66 of the regulating member 62 faces the control chamber 41. The volume of the control chamber 41 changes based on the position of the pump control ring 28, given that the regulating member 62 moves with the pump control ring 28. The control chamber 41 is at a minimum volume when the pump control ring 28 is in the first position. The volume of the control chamber 41 increases as the pump control ring 28 moves toward the third position and reaches a maximum volume when the pump control ring 28 is in the third position.

[0025] The spring chamber 40 is formed within a space that is disposed outward of the pump control ring 28, between the pump control ring 28 and an interior surface of the housing 14. A first side 64 of a regulating member 62 faces the spring chamber 40. The volume of the spring chamber 40 is at a maximum volume when the pump control ring 28 is in the first position. The volume of the spring chamber 40 decreases as the pump control ring 28 moves toward the third position and reaches a minimum volume when the pump control ring 28 is in the third position.

[0026] A feedback path 82 supplies pressurized fluid to the control chamber 41 from a fluid outlet 44 of the pump 10. This can be done directly, by routing the feedback path 82 directly to the control chamber 41 from the fluid outlet 44, or indirectly, by routing the feedback path 82 to another portion of the pump 10 that is in fluid communication with the fluid outlet 44 and is at equilibrium with the fluid outlet 44. Because the feedback path 82 is in fluid communication with the fluid outlet 44 of the pump 10, the feedback path 82 receives pressurized fluid at the outlet pressure of the pump 10. In some implementations, a restrictor (not shown) is formed along the feedback path 82 to control the amount of pressure provided via the feedback path 82. In the illustrated example, the feedback path 82 is formed in housing 14 and is fluid communication with the control chamber 41 and the fluid outlet 44. [0027] A biasing assembly 90 may be formed within the spring chamber 40 to control the position of the pump control ring 28 and the volume of the control chamber 41. The biasing assembly 90 urges the pump control ring 28 toward the first position by applying a first biasing force to the pump control ring 28 when the pump control ring 28 is located between the first position and the second position. As the pressure increases within the control chamber 41, the pressure will eventually be able to overcome the first biasing force and move the pump control ring 28 toward the second position. As the pump control ring 28 pivots toward the second position, the pressure within the control chamber 41 will remain substantially constant, resulting in a first equilibrium pressure. Once the pump control ring 28 reaches the second position, a second biasing force is activated and applied to urge the pump control ring 28 toward the second position. If the pressure continues to increase within the control chamber 41, the pressure will eventually be sufficient to overcome the second biasing force and the pump control ring 28 will pivot toward the third position. As the pump control ring 28 pivots toward the third position, the pressure within the control chamber 41 will remain substantially constant, resulting in a second equilibrium pressure. Although two biasing forces are described, it will be obvious to one skilled in the art that the number of biasing forces acting on the pump control ring 28 could be varied to alter the number of equilibrium pressures that the pump 10 can maintain.

[0028] In the illustrated example, the biasing assembly 90 has a first compression spring 51, a second compression spring 52, and a control pin 53. As shown in FIG. 6, the first compression spring 51 and the second compression spring 52 are substantially coaxially aligned with the first compression spring 51 positioned closer to the regulating member 62. When engaged, the first compression spring 51 applies a first spring load to the pump control ring 28 and the second compression spring 52 applies a second spring load to the pump control ring 28. In some implementations, the second spring load is greater than the first spring load. The control pin 53 has a substantially T-shaped configuration with a first leg 54 extending through the radial center of the first compression spring 51 and a second leg 55 located between the first compression spring 51 and the second compression spring 52. The spring chamber 40 may an annular shoulder 43 that the second leg 55 of the control pin 53 may abut to prevent the first leg 54 of the control pin 53 from engaging the regulating member 62 of the pump control ring 28 when the first compression spring 51 is not compressed. As the pressure increases within the control chamber 41, the first side 64 of the regulating member 62 engages a first end 56 of the first compression spring 51 and compresses the first compression spring 51 toward the second leg 55 of the control pin 53. Once the first compression spring 51 has compressed to a distance that allows the first side 64 of the regulating member 62 to engage the first leg 54 of the control pin 53, the second leg 55 of the control pin 53 will compress the second compression spring 52 toward the housing 14.

[0029] Although the first compression spring 51 and the second compression spring 52 act independently in the illustrated example, it is anticipated that the first compression spring 51 and the second compression spring 52 could combine to provide the second biasing force. In this embodiment, the first compression spring 51 may have substantially the diameter as the width of the spring chamber 40. Once the first side 64 of the regulating member 62 is able to engage the first leg 54 of the control pin 53, the first compression spring 51 continues compressing and the second compression spring 52 begins compressing due to force of the pressure in the control chamber 41.

[0030] The biasing assembly is not limited to being housed within the spring chamber 40 or utilizing compression springs. Other biasing assemblies could be utilized. For example, there could be two tension springs or two compression springs could be used in a location other than the spring chamber 40. In some implementations, the first compression spring 51 and the second compression spring 52 have the same spring rate. In other implementations, the first compressions spring 51 and the second compression spring 52 have different spring rates. For example, the first compression spring 51 can have a first spring rate and the second compression spring 52 can have a second spring rate that is greater than the first spring rate 51.

[0031] FIG. 7 is a diagram showing the pump 10 incorporated in a lubricating system of an automobile engine 100. The pump 10 receives fluid, such as oil, from the oil sump reservoir 12 at an inlet pressure PI via the fluid inlet 42 of the pump 10. The pump 10 increases the pressure of the fluid to an outlet pressure P2, and the fluid exits the pump 10 at the fluid outlet 44. The fluid travels from the fluid outlet 44 of the pump 10 to the automobile engine 100 via a supply circuit 102 and is subsequently returned to the oil sump reservoir 12 via a return circuit 104. A portion of the fluid at the outlet pressure P2 is diverted from the fluid outlet 44 of the pump 10 to the control chamber 41 via the feedback path 82. As the pressure within the control chamber 41 increases, the pump control ring 28 is rotated toward the third position, thereby decreasing the volumetric output of the pump 10.

[0032] The use of the biasing assembly 90 allows the pump 10 to provide multiple equilibrium pressures in the control chamber 41, as shown in FIG. 8. Initially, the pump control ring 28 is in the first position as the pressure in the control chamber 41 is not sufficient to overcome the first biasing force of the first compression spring 51 to compress the first compression spring 51, which is shown as segment 701. During segment 701, the pump 10 will have the maximum per- rotation volumetric capacity. Once the pressure increases within the control chamber 41 to a point where it is able to overcome the first biasing force of the first compression spring 51 and the regulating member 62 is able to compress the first compression spring 51, the pump control ring 28 will move toward the second position, which is shown as segment 702. The movement of the pump control ring 28 toward the second position linearly decreases the per-rotation volumetric capacity of the pump 10 and allows the pressure within the control chamber 41 to remain substantially constant at the first equilibrium pressure. [0033] As the pressure in the control chamber 41 continues to rise, there will be a point where the regulating member 62 will engage the control pin 53, preventing the first compression spring 51 from compressing further. As shown in segment 703, the per-rotation volumetric capacity of the pump 10 will remain constant because the pressure within the control chamber 41 is unable to overcome the second biasing force of the second compression spring 52 to compress the second compression spring 52. As a result, the pump control ring 28 remains in the second position. Once the pressure increases within the control chamber 41 to a point where it is able to overcome the second biasing force of the second compression spring 52 and the second leg 55 of the control pin 53 is able to compress the second compression spring 52 toward the housing 14, the pump control ring 28 will move toward the third position, which is shown as segment 704. The movement of the pump control ring 28 toward the third position linearly decreases the per-rotation volumetric capacity of the pump 10 and allows the pressure within the control chamber 41 to remain substantially constant at the second equilibrium pressure. Once the pump control ring 28 reaches the third position, the pump 10 will have the minimum volumetric capacity.

[0034] While the description has been made in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments, but to the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is performed under the law.

Claims

CLAIMS What is claimed is:

1. A variable displacement vane pump having a housing with a pump chamber, the pump chamber having a fluid inlet, a fluid outlet, a pump control ring, and a vane pump rotor, the pump control ring disposed within the housing for altering the displacement of the pump by rotating between a first position that corresponds to a maximum volumetric capacity of the pump, a second position that corresponds to an intermediary volumetric capacity of the pump, and a third position that corresponds to a minimum volumetric capacity of the pump, the vane pump rotor rotatably mounted within the pump control ring and having a plurality of slidably mounted vanes engaging an inside surface of the pump control ring, the vane pump rotor having an axis of rotation eccentric from a center of the pump control ring, the vane pump rotor rotating to pressurize fluid as the fluid moves from the fluid inlet to the fluid outlet, comprising:

a biasing assembly for urging the pump control ring toward the first position, wherein the biasing assembly applies a first biasing force to the pump control ring when the pump control ring is located between the first position and the second position and applies a second biasing force to the pump control ring when the pump control ring is located between the second position and the third position; and

a control chamber formed between the housing and the pump control ring, wherein fluid pressure within the control chamber urges the pump control ring toward the third position.

2. The variable displacement vane pump of claim 1, further comprising:

a needle bearing mounted between the pump control ring and the housing to allow the pump control ring to pivot relative to the needle bearing.

3. The variable displacement vane pump of claim 1, further comprising a feedbath path in communication with the fluid outlet supplying a pressurized fluid to the control chamber.

4. The variable displacement vane pump of claim 1, further comprising:

a spring chamber formed between the housing and the pump control ring, wherein the spring chamber has a maximum volume when the pump control ring is in the first position and a minimum volume when the pump control ring is in the third position.

5. The variable displacement vane pump of claim 4, wherein the biasing assembly is

disposed within the spring chamber.

6. The variable displacement vane pump of claim 1, wherein the biasing assembly further comprises:

a first spring having a first spring load;

a second spring having a second spring load; and

a control pin having a substantially T-shaped configuration with a first leg extending through the radial center of the first spring and a second leg located between the first spring and the second spring.

7. The variable displacement vane pump of claim 6, wherein the first spring and the second spring are substantially coaxially aligned.

8. The variable displacement vane pump of claim 6, wherein the second spring load of the second spring is greater than the first spring load of the first spring.

9. The variable displacement vane pump of claim 6, wherein the pump control ring engages the first spring and the second spring engages the housing.

10. The variable displacement vane pump of claim 6, further comprising:

11. The variable displacement vane pump of claim 10, wherein the first spring, the second spring, and the control pin are disposed within the spring chamber.

12. The variable displacement vane pump of claim 11, wherein the second spring engages the spring chamber.

13. The variable displacement vane pump of claim 6, wherein the first spring and the second spring are compression springs.

14. The variable displacement vane pump of claim 13, wherein the first compression spring and the second compression spring are substantially coaxially aligned, and the second spring load of the second compression spring is greater than the first spring load of the first compression spring.

15. The variable displacement vane pump of claim 14, wherein the second leg of the control pin compresses the second compression spring when the pump control ring engages the first leg of the control pin.

16. The variable displacement vane pump of claim 15, further comprising:

17. The variable displacement vane pump of claim 16, wherein the first compression spring, the second compression spring, and the control pin are disposed within the spring chamber.

18. The variable displacement vane pump of claim 17, wherein the second compression spring engages the spring chamber.

19. A variable displacement vane pump having a housing with a pump chamber, the pump chamber having a fluid inlet, a fluid outlet, a pump control ring, and a vane pump rotor, the pump control ring disposed within the housing for altering the displacement of the pump by rotating between a first position that corresponds to a maximum volumetric capacity of the pump, a second position that corresponds to an intermediary volumetric capacity of the pump, and a third position that corresponds to a minimum volumetric capacity of the pump, the vane pump rotor rotatably mounted within the pump control ring and having a plurality of slidably mounted vanes engaging an inside surface of the pump control ring, the vane pump rotor having an axis of rotation eccentric from a center of the pump control ring, the vane pump rotor rotating to pressurize fluid as the fluid moves from the fluid inlet to the fluid outlet, comprising:

a biasing assembly for urging the pump control ring toward the first position, wherein the biasing assembly applies a first biasing force to the pump control ring when the pump control ring is located between the first position and the second position and applies a second biasing force to the pump control ring when the pump control ring is located between the second position and the third position;

a control chamber formed between the housing and the pump control ring, wherein fluid pressure within the control chamber urges the pump control ring toward the third position; a feedback path in communication with the fluid outlet supplying a pressurized fluid to the control chamber; and

a spring chamber formed between the housing and the pump control ring, wherein the spring chamber has a maximum volume when the pump control ring is in the first position and a minimum volume when the pump control ring is in the third position, and the biasing assembly is disposed within the spring chamber.

20. The variable displacement vane pump of claim 19, wherein the biasing assembly further comprises:

a first compression spring having a first spring load;

a second compression spring having a second spring load, wherein the second spring load of the second compression spring is greater than the first spring load of the first compression spring; and

a control pin having a substantially T-shaped configuration with a first leg extending through the radial center of the first compression spring and a second leg located between the first compression spring and the second compression spring, wherein the second leg of the control pin compresses the second compression spring when the pump control ring engages the first leg of the control pin.