CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 61/313,888 filed on March 15, 2010. The entire disclosure of the above application is incorporated herein by reference.

FIELD

[0002] The present disclosure relates to a pressure relief valve for a fluid pumping system. More specifically, the present disclosure relates to a low gain pressure relief valve for use in automotive applications.

BACKGROUND

[0003] A number of automotive fluid pumping system include a pressure relief valve to limit the downstream pressure output of the pump to establish an equilibrium operating pressure for the fluid pumping system. In some cases, the fluid pumping system and pressure relief valves are quite simple in design and include a cylindrical plunger positioned within a bore of the pump itself or the plunger may be externally mounted in a separate valve housing. The plunger is in fluid communication with a high side pressure output of the pump and is operable to open and close a waste passage that is in fluid communication with the low pressure side of the pump, a low pressure gallery or a sump. The plunger is biased by a spring to a first end of the bore corresponding to a closed position. The waste passage is blocked when the plunger is in the closed position. As the output pressure of the pump increases, the pressure of the working fluid on the end of the plunger acts against the bias of the spring and, when the pressure is sufficiently high, the plunger is moved from the closed position to expose the waste passage and allow pressurized working fluid from the high pressure side of the pump to enter the waste passage, thus reducing the output pressure produced by the pump. As the output pressure of the pump increases, the plunger is moved further into the bore, allowing more working fluid to enter the waste passage. As the output pressure of the pump decreases, the biasing force of the spring moves the plunger toward the closed position. An equilibrium level is reached based on the pump output, the geometry of the plunger, bore, and the mechanical characteristics of the spring.

[0004] Another more slightly complex lubrication system includes a pressure relief valve including a plunger having two spaced apart pistons of different diameters. Such configuration is the subject of patent application WO2006/032132, which is herein incorporated by reference in its entirety.

[0005] While the previously known relief valves have adequately performed in the past, they may suffer from certain disadvantages. For example, valve systems including moveable plungers in contact with pressurized fluid may be subject to receipt of feedback signals capable of sustaining the plunger in an undesirable oscillation. Furthermore, some pressure relief valves are more susceptible to jamming with debris that may be entrained in the working fluid and disrupting proper valve operation. In one instance, large particle contamination is a concern regarding restricting the plunger from returning to a completely closed position resulting in the pump producing insufficient output pressure and/or volume at a certain operating speed. In particular, the plunger may be restricted from completely closing the opening to the waste passage due to large particle contamination.

[0006] Other known pressure relief valves may include progressively shaped exit holes to vary the valve function. A progressively shaped exit hole includes one or more portions having a relatively small aperture through which pressurized fluid must pass. While these valves may function in certain environments, it is common for automotive components such as engine blocks to include residual casting sand retained within pockets or bores of the engine block. After the engine has been assembled and at initial engine operation, the casting sand or other small particle contaminants may break free and become entrained within the fluid to be pumped. The small particles may clog the progressively shaped exit hole and preclude proper operation. Accordingly, it may be desirable to provide a simple, inexpensive and improved pressure relief valve. SUMMARY

[0007] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0008] A pressure relief valve for a pump pressurizing a fluid includes a housing having a first aperture in communication with high pressure fluid, a second aperture in communication with low pressure fluid, a bore extending between the first and second apertures, and a conical seat formed at the end of the bore. A plunger is slidable between a first position where fluid is prevented from passing between the first and second apertures and a second position where fluid is allowed to flow between the first and second apertures. The plunger includes a conical surface. A biasing member urges the plunger toward the first position and engages the conical surface with the conical seat when the plunger is in the first position.

[0009] Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

[0010] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0011] Figure 1 is a fragmentary cross-sectional view of a prior art pressure relief valve;

[0012] Figure 2 is a fragmentary cross-sectional view of a low gain pressure relief valve constructed in accordance with the teachings of the present disclosure;

[0013] Figures 3a-3e depict enlarged fragmentary cross-sectional views of the valve shown in Figure 2 having a plunger at different axial positions;

[0014] Figure 4 is a graph depicting valve opening area versus valve position for the prior art and the valve of the present disclosure;

[0015] Figure 5 is an enlarged fragmentary cross-sectional view of the valve opening for a prior art valve; [0016] Figure 6 is an enlarged fragmentary cross-sectional view of the valve opening for a valve of the present disclosure;

[0017] Figure 7 is an enlarged fragmentary cross-sectional view depicting thin film fluid flow through an orifice of the prior art valve;

[0018] Figure 8 is an enlarged fragmentary cross-sectional view depicting thin film fluid flow through an orifice of the valve of the present disclosure;

[0019] Figure 9 is an enlarged fragmentary cross-sectional view depicting possible large particle jamming of the prior art valve;

[0020] Figure 10 is an enlarged fragmentary cross-sectional view depicting large particle retention within a recess of the valve of the present disclosure;

[0021] Figure 1 1 is a schematic of a fluid pumping system;

[0022] Figure 12 is a graph depicting discharge pressure versus discharge flow rate comparing a prior art valve to the valve of the present disclosure;

[0023] Figure 13 provides pressure distribution graphs for the prior art valve at open and closed positions; and

[0024] Figure 14 provides pressure distribution graphs for the valve of the present disclosure at open and closed positions.

[0025] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

[0026] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0027] Figure 1 depicts a prior art pressure relief valve generally indicated at reference numeral 10. Valve 10 includes a housing 12 defining a bore 14 in receipt of a plunger 16. A compression spring 18 biases plunger 16 into engagement with housing 12 to define a closed valve position. Plunger 16 includes a first piston portion 20 substantially shaped as a right circular cylinder having an outer cylindrical surface 22 and a substantially planar end face 24. A passageway 26 is in receipt of pressurized fluid output from a pump (not shown). A waste passage 28 may be selectively placed in communication with passageway 26 when plunger 16 is moved away from its closed position and end face 24 translates past a lip 30 of bore 14.

[0028] Figure 2 depicts a pressure relief valve 40 constructed in accordance with the teachings of the present disclosure. Valve 40 includes a plunger 42 axially translatable within a bore 44 in a housing 46. A spring 48 urges plunger 42 toward a closed position shown in Figure 2. Housing 46 includes a high pressure passage 50 in receipt of fluid output from a pump (not shown). A waste passage 52 may be selectively placed in fluid communication with passage 50 when plunger 42 is axially translated away from its closed position. Housing 46 also includes an intermediate bore 54 having an inner diameter smaller than bore 44. A further reduced diameter bore 56 is in receipt of a first piston portion 58 of plunger 42.

[0029] Plunger 42 also includes a second piston portion 60 having an outer cylindrical surface 62 sized to slide within bore 44. Second piston portion 60 also includes a pocket 64 in receipt of spring 48. A stem portion 66 interconnects first piston portion 58 and second piston portion 60.

[0030] Figures 3a-3e provide enlarged fragmentary cross-sectional views of a portion of pressure relief valve 40 having plunger 42 at a number of different positions including a closed position shown in Figure 3a and an open position shown at Figure 3e. A conical valve seat 70 is formed at one end of bore 54 in communication with passage 52. Conical seat 70 terminates at a wall 73 of housing 46 to define a circular opening having a first size. A mating conical surface 72 is formed at an end 74 of second piston 60. Outer cylindrical surface 62 has a diameter greater than the size of the circular opening at wall 73. As shown in Figure 3a, when plunger 42 is at the closed position, conical surface 72 engages conical seat 70 along the majority of the length of conical seat 70.

[0031] A recess 78 is formed in second piston 60 at end 74 to retain debris therein. Recess 78 includes a conically shaped wall 80 intersecting conical surface 72 at an edge 82. Edge 82 defines a circle at the intersection of conical surface 72 and wall 80. [0032] As previously mentioned, one of the concerns with the prior art valve system is that certain feedback conditions existed that were capable of self sustaining unstable oscillations of plunger 16. The plunger oscillations may cause undesirable noise, vibration or harshness. To prevent this type of instability, it may be desirable to reduce the gain of critical components in the system. As part of the solution to the prior problem, the present disclosure provides a method to reduce the gain of a fluid pressure relief valve.

Input Applied_ Pressure Hydraulic_ Resistance

Accordingly, reduced gain is realized by increasing hydraulic resistance. The hydraulic resistance through pressure relief valve 40 is due to a combination of turbulent and laminar flow coefficients. These coefficients are non-linear functions of temperature, fluid properties and the three dimensional fluid path geometry. Fluid path geometry is a function of plunger shape, housing shape and plunger position. Plunger position is a function of fluid pressure, plunger effective area and biasing spring rate. It should be appreciated that this expression is simplified and intended only to illustrate the principle of valve gain and not necessarily to provide a numerical means for quantifying valve gain.

[0033] It is contemplated that hydraulic resistance is proportional to valve opening area. Figure 4 depicts a comparison of valve gain based on valve opening area for the prior art design of Figure 1 and the inventive design of Figure 2. As is evident from the graph, the rate of change of opening area per change in valve position is substantially lower for pressure relief valve 40 than pressure relief valve 10. Figures 5 and 6 depict plunger 16 and plunger 42 axially displaced the same amount. An opening area between housing 12 and plunger 16 is substantially greater than the opening area between housing 46 and plunger 42.

[0034] Figures 7 and 8 provide further explanation for a difference in hydraulic resistance between the prior art design of valve 10 and presently disclosed valve 40. As is shown in Figure 7, once plunger 16 is moved from the closed position to open a path to waste passage 28, fluid flows from passage 26 to waste passage 28. It should be noted that a relatively large open area exists to either side of an orifice defined between end face 24 and a wall 88 of passage 28. Based on this geometrical configuration, the length of the orifice is very small.

[0035] Figure 8 depicts plunger 42 axially displaced from the closed position to provide an annular orifice between conical seat 70 and conical surface 72. As shown in Figure 4, for the same magnitude of axial displacement, not only is the opening area between plunger 42 and housing 46 less than the opening area between plunger 16 and housing 12, but the length of the orifice is substantially greater. Hydraulic resistance increases as the path length of a thin film of fluid increases. After valve 40 opens, a thin film of fluid has a significant path length through which the fluid must pass in valve 40 as compared to valve 10. A higher hydraulic resistance results.

[0036] Figures 9 and 10 illustrate a contamination resistance feature of valve 40. Figure 9 depicts prior art valve 10 while Figure 10 depicts valve 40. Based on the geometry of housing 12 and the interface of surfaces 24 and 22 with bore 14, large particles may collect at the opening between plunger 16 and housing 12. During a closing action of plunger 16, the large particles may jam the valve in the open position.

[0037] Based on the shape of conical seat 70, conical surface 72 and recess 78, large particles do not collect near the valve opening. Small particles are washed through the gap between conical seat 70 and conical surface 72 at relatively high velocity.

[0038] To evaluate the theoretical differences between valve 10 and valve 40, a test fluid pumping system 1 10 was constructed as shown in Figure 1 1 . A fixed displacement pump 1 12 includes an inlet 1 14 in communication with a low pressure fluid reservoir 6. An outlet 1 18 of pump 12 discharges pressurized fluid to a variable hydraulic load 120. Fluid may exit variable hydraulic load 120 and enter a low pressure fluid reservoir 122. The pressure relief valve to be tested is plumbed in communication with outlet 1 18. Figure 1 1 depicts valve 40 where passage 50 is in receipt of pressurized fluid output from pump 1 12 and waste passage 52 is in communication with fluid reservoir 1 16. Plunger 42 is biased toward a closed position by spring 48. [0039] To evaluate the gain of the different relief valves, variable hydraulic load 120 is first configured to provide a minimum load. At this time, fixed displacement pump 1 12 is driven at constant speed. Figure 12 depicts discharge pressure versus discharge flow rate for valve 10 and valve 40. At minimum hydraulic load, the discharge flow rate is at a maximum and is substantially the same for both valves because both of the valves are in the closed position. As the hydraulic load 120 is increased, the discharge pressure increases. Initially, the effective surface area of plunger 16 and plunger 42 are the same. Similarly, the force applied by spring 18 and spring 48 is the same. As such, the valve opening pressure for each valve is the same.

[0040] As the variable hydraulic load is further increased, the traces of discharge pressure versus discharge pressure flow rate for each pump diverge. Valve 10 exhibits a relatively high gradient due to a reduction of static pressure acting on the effective end surface of plunger 16 once the valve opens. This phenomenon is illustrated at Figures 13 and 14 where the upper portions of Figures 13 and 14 relate to valves 10 and 40 being closed and where a uniform static pressure distribution is applied to each plunger.

[0041] An open position is shown at the lower portion of Figure 13 where relatively high fluid velocity exists near plunger face 24. A reduction in static pressure results and is depicted by the pressure distribution graph above each plunger. The gradient of discharge pressure versus discharge flow rate for valve 40 is substantially less. The reduced gain or gradient is due at least in part to a less drastic change in pressure distribution acting on plunger 42 as the plunger moves from the closed position to the open position. The lower portion of Figure 14 depicts this arrangement. When plunger 42 is in the open position, the zone of high fluid velocity is not directly adjacent to the upper surface of plunger 42. The shape of conical annulus between conical seat 70 and conical surface 72, as well as the shape of recess 78, define the flow path of fluid.

[0042] Furthermore, the effective area on which pressurized fluid may act is increased by the provision of conical surface 72. By limiting the reduction in static pressure and increasing the surface area on which the pressure may act, the discharge pressure versus discharge flow rate gradient of valve 40 is reduced.

[0043] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.