Patent Application
20130312702
The present disclosure relates generally to low static leak common rail fuel systems, and more particularly to a shutdown pressure relief valve that releases high pressure from the common rail after shutdown.
Over the years, engineers have become more successful in reducing static leakage within common rail fuel systems. Reducing static leakage can improve performance, and efficiency, but is difficult to accomplish given the multitude of potential leak paths between the high pressure pump, common rail and valves within a plurality of fuel injectors for a common rail fuel system. While low static leakage is desirable, there is also a desire that all of the wetted volumes within a common rail fuel system return to atmospheric or tank pressure after the system is shutdown so that the risk of fuel spraying out of the system during servicing is reduced. While it is almost inconceivable that a common rail fuel system could be manufactured that had absolutely zero static leakage, the leakage in current systems may be so small that the decay of pressure in the high pressure volume can take an unacceptably long time to occur. Pressure decay times in excess of several minutes might be deemed unacceptable in the industry.
The present disclosure is directed toward one or more of the problems set forth above.
A common rail fuel system includes a common rail fluidly positioned between a high pressure pump and a plurality of fuel injectors. A transfer pump is fluidly positioned between a tank and the high pressure pump. A high pressure volume is fluidly positioned between the high pressure pump and a pair of valves in each of the plurality of fuel injectors. A medium pressure volume is fluidly positioned between the transfer pump and the high pressure pump. A low pressure volume is fluidly positioned between the plurality of fuel injectors and the transfer pump. The shutdown pressure relief valve has a first port fluidly connected to the low pressure volume, a second port fluidly connected to the medium pressure volume and a third port fluidly connected to the high pressure volume. The shutdown pressure relief valve is pressure actuated to open and close a fluid connection between the first port and the third port, responsive to fluid pressure in the second port.
In another aspect, a method of shutting down a common rail fuel system includes stopping the transfer pump and the high pressure pump. Pressure from a medium pressure volume is allowed to decay. A fluid connection between the high pressure volume and a low pressure volume is opened through a shutdown pressure relief valve responsive to the pressure decay from the medium pressure volume.
In still another aspect, a shutdown pressure relief valve includes a housing that defines a cavity fluidly connected to a first port, a second port and a third port. A piston is positioned to divide the cavity into a first chamber and a second chamber, and is movable along a centerline. The first chamber is fluidly connected to the first port and to the third port through a valve seat. The second chamber is fluidly connected to the second port. A valve member is positioned in the first chamber, and movable between a closed position in contact with the valve seat and an open position out of contact with the valve seat. The piston has a large area hydraulic surface exposed to fluid pressure in second port. The valve member has a small area hydraulic surface exposed to fluid pressure in the third port when in the closed position.
Referring to
Those skilled in the art will appreciate that when common rail fuel system 10 is in operation, the transfer pump 14 continuously draws low pressure fuel from tank 15 and provides medium pressure fuel to the inlet of high pressure pump 12 while the engine (not shown) is running The shut down pressure relief valve 30 utilizes the medium pressure that exists while the fuel system 10 is in operation to close the fluid connection between the first port 31 and the third port 33. At engine shut down, when the common rail fuel system 10 ceases operation, transfer pump 14 and high pressure pump 12 stop, and the medium pressure in medium pressure volume 21 decays back to tank 15. When this occurs, the residual high pressure in common rail 11 acts to open the third port to the first port to allow the residual pressure in the high pressure volume 20 to be released to the low pressure volume 22, which includes tank 15.
In
Referring now to
A valve member 43 is positioned in the first chamber 38, and is movable between a closed position in contact with valve seat 40, and an open position out of contact with valve seat 40. In the illustrated embodiment, valve member 43 is a spherically shaped ball that contacts a conical valve seat 40. However, those skilled in the art will appreciate that other designs would fall within the scope of the present disclosure. For instance, one might substitute a known flat seat and counterpart valve member often associated with control valves of the type utilized in fuel injectors 13 in certain common rail applications. The piston 42 has a large area hydraulic surface 51 exposed to fluid pressure in second chamber 39 and hence to second port 32. The valve member 43 has a small area hydraulic surface 52 exposed to fluid pressure in the third port 33 when valve member 43 is in the closed position in contact with valve seat 40. Piston 42 includes an intermediate hydraulic surface 53 exposed to fluid pressure in second port 32. The small area hydraulic surface 52 and the intermediate hydraulic surface 53 are oriented in opposition to the large area hydraulic surface 51.
Housing 35 may include a hollow body 44, a valve seat component 45 and a banjo fitting 46. The valve seat component 45 may define an orifice 55 fluidly positioned between valve seat 40 and the third port 33. The flow area of orifice 55 may define the rate at which fluid pressure in the high pressure volume 20 is released toward first port 31 when valve member 43 is lifted off of valve seat 40. Also shown as optional is the inclusion of a possible edge filter 78 in the third port 33. The banjo fitting 46 defines first port 31 and has one of a continuum of neutral orientations around centerline 37. This structure allows free rotation of banjo fitting 46 and may ease in installation and make shut down pressure relief valve 30 versatile for use across several different common rail fuel systems with different geometries and spatial constraints. In order to allow for some misalignment between valve seat 40 and the movement line of piston 42, the piston may contact the valve member 43 at an alignment neutral location of a planar surface 56 oriented perpendicular to centerline 37. Thus, the centerline 32 of valve seat 40 may be slightly off center with the line along which piston 42 moves, such that one or both are slightly displaced from centerline 37. However, by choosing the structure shown, the operation of shut down pressure relief valve 30 can be desensitized to any minor misalignments in this regard.
In the illustrating embodiment, a load nut 47 and the banjo fitting 46 are trapped between a shoulder 57 of hollow body 44 and a shoulder 58 of valve seat component 45. O-rings 75 and 76 may seal against leakage between banjo fitting 46 and load nut 47 and hollow body 44, respectively. Load nut 47 may include a set of external threads 72 that interact with the mounting location in common rail fuel system 10 (e.g., end of common rail 11 or junction block associated with high pressure pump 12) to avoid the inclusion of threads on valve seat component 45. Thus, when a tool is used to engage tool engagement surface 71 of load nut 47, the resulting force can push down on shoulder 58 and allow a rounded end 70 to be pushed into a counterpart seat of the mounting location (not shown) to form a fluid tight seal of a type well known in the art. Shut down pressure relief valve 30 may also include an o-ring 73 to provide a seal between valve seat component 45 and load nut 47. In addition, an o-ring 74 might also be included to provide a seal where shut down pressure relief valve 30 interacts with a mounting feature in common rail fuel system 10. Finally, shut down pressure relief valve 30 may include a port fitting 48 that defines second port 32. In the illustrated embodiment, depending upon whether edge filter 78 and/or o-ring seal 50 are included, the shut down pressure relief valve 30 includes exactly twelve to fourteen parts. Because of the interaction between valve member 43 and piston 42 is desensitized to misalignments, and for other reasons known in the art, shut down pressure relief valve 30 may not need to include any category parts. Those skilled in the art will appreciate that a category part is one that comes in several different sizes to compensate for different tolerance build ups in different assemblies. In the illustrated structure, further flexibility is provided by the ability of the load nut 47 to be free to rotate with respect to hollow body 44 and banjo fitting 46 about centerline 37.
The load nut 47 and the banjo fitting 46 are free to rotate and slide slightly up and down between the valve seat component 45 and the hollow body 44 in the illustrated embodiment. Outlet fitting 48 and valve seat component 45 may be threadably attached to hollow body 44. The illustrated structure allows the shut down pressure relief valve 30 to be connected to a high pressure port in common rail fuel system 10 without rotating the sealing surfaces against each other during tightening. In addition, the low pressure port 31 may then be oriented in any direction around centerline 37.
The present disclosure finds potential application in any common rail fuel system. The present disclosure finds particular application in common rail fuel systems with low static leakage. The present disclosure finds specific application in high pressure common rail fuel systems with low static leakage associated with compression ignition engines.
When common rail fuel system 10 is in operation, medium pressure from medium pressure volume 21 is transmitted to second port 32 and acts upon large area hydraulic surface 51 of piston 42. By appropriately sizing the small area hydraulic surface 52 of valve member 43, and taking in to account the expected pressure in high pressure volume 20 during normal operation, the medium pressure acting on piston 42 should be sufficient to hold valve member 43 in its closed position in contact with valve seat 40 to close the fluid connection between third port 33 and first port 31. As such, no significant leakage should occur through shut down pressure relief valve 30 when the common rail fuel system is in normal operation. When the associated engine is shut down and the common rail fuel system 10 is also shut down, the transfer pump 14 and the high pressure pump 12 will be stopped. Pressure in the medium pressure volume 21 will then quickly decay back to tank 15 (low pressure volume 22), such as through transfer pump 14. When this pressure drop occurs, the pressure force acting on large area hydraulic surface 51 is relieved. Eventually, the pressure will drop low enough that the residual high pressure in high pressure volume 20 will hydraulically push on the small area hydraulic surface 52 of valve member 43 causing it to move upward along centerline 37 out of contact with valve seat 40 to open the fluid connection between third port 33 and first port 31. This allows the residual high pressure and high pressure volume 20 to escape to low pressure volume 22. Depending upon the sizing of orifice 55, engineers can control the rate at which this pressure release occurs. For instance, it might be desirable for the residual high pressure, which may be in excess of 250 MPa to occur over a duration less than maybe two minutes. However, this time period is clearly a matter of design choice. For instance, one could expect that the medium pressure output from transfer pump 14 to be on the order of maybe 550 KPa, and pressure in the low pressure volume 22 to be on the order of 0 to maybe 50 KPa greater than atmospheric pressure. When transfer pump 14 stops, one could expect the medium pressure to decay back toward tank 15 in a matter measured in seconds rather than minutes.
The structure of the shut down pressure relief valve 30 illustrated allows great flexibility for use of one valve across many different common rail fuel systems 10. In addition, the structure allows for mounting valve 30 at virtually any location around or in common rail fuel system 10 that facilitates the necessary fluid connections to the first, second and third ports 31-33. For instance, the shut down pressure relief valve could be mounted at one end of a conventional common rail, in one of the blocks that comprise a daisy chain type common rail fuel system, attached to an accumulator in a common rail fuel system or even in a junction block associated with or in proximity to high pressure pump 12. In the illustrated design, valve 30 is passive such that as long as an engine is turning and the common rail fuel system 10 is operating, the transfer pump 14 can generate enough pressure to keep valve member 43 in its closed position. Once the engine stops rotating, the transfer pump 14 stops and the pressure on top of the piston 42 is relieved, allowing the valve member 43 and piston 42 to be pushed upward by the high pressure fuel in high pressure volume 20 to release the residual fuel pressure. Thus, provided a service technician waits some minimum prescribed time, determined by the size of orifice 55, the fuel system 10 can be serviced and opened without residual high pressure fuel being sprayed when system 10 is being serviced after an engine and common rail fuel system 10 has been shut down.
It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present disclosure in any way. Thus, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims.
