Abstract:
A tubular debris shield and diverter mounted in a high pressure flow passage within a fuel injector, provide the dual functions of passing the main flow of high pressure fuel with large debris particles to relatively large discharge openings, such as the injector spray holes, while allowing some high pressure fuel to flow through a multitude of very small transverse holes to a sensitive hydraulic component, such an injector control valve circuit. In one embodiment, the tube has a wall thickness in the range of about 0.1 to 0.5 mm at least about 2000 holes with a diameter in the range of about 20 to 30 microns.

Description:
BACKGROUND  
       [0001]    The present invention relates to fuel injectors, particularly for vehicle internal combustion engines. 
         [0002]    In a well-known type of fuel injector, an injection valve is hydraulically opened and closed by the opening and closing of a solenoid actuated control valve. Both valves are subject to highly pressurized fuel from a supply pump or common rail. To reduce engine emissions, fuel systems are being designed for injection at higher and higher pressure. To seal high pressure fuel during closure of the control valve, it is necessary to increase the hold-down force and thereby avoid seat leakage at these higher pressures. 
         [0003]    The higher control valve seating force increases the potential for seat damage when debris gets trapped or crushed in the opening and closing control valve. To meet more stringent emissions regulations it has been found that injecting fuel multiple times during one combustion event is required. To achieve fast opening and closing of the fuel injectors, faster opening and closing control valves with less valve lift are being adopted. Control valve lifts under 50 microns are common. Ideally, debris should to be small enough to pass through the valve seat area. 
         [0004]    Debris that gets trapped in the seat area will continue to damage that seat as it opens and closes. This significantly reduces the life of the injectors. When damaged, control valve seats no longer seal properly. Fuel delivered by the fuel injector tends to increase when control valve seats leak. This performance change results in unintended fuel delivery increases which can cause engine damage due to over fueling and also rough engine operation due to uneven fuel delivery into the various engine cylinders. As a consequence, the most common reason for replacing fuel injectors is performance problems caused by control valve seat damage. 
         [0005]    Techniques are known for addressing this problem to some extent. The fuel from the fuel tank is filtered through multiple filters prior to reaching the fuel injector but some debris gets through these filters. Primary and secondary filters are located between the fuel tank and the entrance to the high pressure fuel pump. At the entrance to the fuel injector a third, small filter functions at the high pressures produced by the high pressure pump. The primary and secondary filters trap about 99% of the debris in the fuel prior to entering the high pressure fuel pump. The remaining debris in the fuel and additional debris from components such as the high pressure pump become trapped in the small filter (typically an edge filter or laser drilled filter). 
         [0006]    Filters used to capture debris at the entrance of the injector are challenging to design at a reasonable cost. These filters typically are not serviced over the life of the injector and to avoid plugging, are theoretically designed to allow debris particles smaller than 30 microns to 60 microns in diameter to pass. In general, however, the filter at the entrance to the injector typically will permit particles smaller than about 50 microns to pass. This does not present a plugging problem with respect to the discharge holes for fuel injection, which are typically larger than 100 microns, but does present a problem for the durability of the control valve. Rod-shaped particles that have a diameter under 60 microns but a length of up to 150 to 200 microns can still pass through the entrance filters. These particles cause damage if they pass into the control valve. 
         [0007]    Even if the edge region of an entrance edge filter is designed with a 50 micron passage, larger particles are not permanently trapped but, rather, extrude through the passage as rods or flakes with an effective diameter of about 50 microns. Thus, the overall volume of debris reaching the control valve is not reduced by the typical entrance filter. The control valve must hammer the extruded debris down to a size that will pass through the control valve. 
       SUMMARY  
       [0008]    The object of the present invention is to avoid debris damage to a hydraulic component within a fuel injector, particularly a control valve for a needle injection valve, by limiting the debris that reaches the component to a size that can readily pass through the component. 
         [0009]    In the case of such control valve, the debris is preferably limited to an effective diameter of less than 50 microns, especially less than 25 microns. 
         [0010]    This object is achieved by providing a simple, low-cost filter-type device in a small space inside the injector, which remains in place during the life of the injector without plugging. 
         [0011]    The device is in essence a tubular debris shield and diverter in a high pressure flow passage within the injector, providing the dual function of passing the main flow of high pressure fuel with large particles that get through the entrance filter down to relatively large discharge openings, such as the injector spray holes, while allowing some high pressure fuel to flow through a multitude of very small transverse holes to the hydraulic component, such as into the injector control valve circuit. 
         [0012]    The small holes prevent debris from passing through the wall of the tube and the flow through the center of the tube carries debris that attempts to plug these small holes to the injector spray holes. The main flow washes away the particles and helps prevent the small holes from plugging. 
         [0013]    In one aspect, the disclosure is directed to a debris shield in the high pressure fuel supply passage upstream of a branch line leading to the control valve, comprising a tube fixed to the injector body, with a central passage aligned with the main fuel supply passage and a multiplicity of transverse holes through which high pressure fuel is delivered to the branch line. In this way, high pressure fuel for injection passes axially through the tube and high pressure fuel to the upstream side of the control valve passes radially through the holes in the tube. 
         [0014]    Damaging debris has higher density than fuel, so the debris is more likely to travel past the small holes, which are preferably 90 degrees to the main flow. The small holes (approximately 20-25 microns) are less likely to plug due to the 90 degree change in particle direction required for the particles to enter the small holes. 
         [0015]    The debris at the entrance to the holes is not subject to a significant pressure drop across the holes so, unlike in edge filters, no extrusion forces arise that would otherwise force larger particles through the holes. The transverse entrance to the holes acts like a shield to minimize the penetration of debris into the holes. Furthermore, larger particles at the entrance to the holes are flushed away (i.e., diverted) from the holes in the main axial flow through the tube. 
         [0016]    Thus, an important advantage of the present invention is that large particles are neither accumulated nor extruded, and particles that do pass through the diverter shield have an effective size that enables them to pass readily through the control valve without being hammered to a smaller size. 
         [0017]    In the preferred embodiment, the injector body comprises an upper portion containing the control valve and an upper portion of the fuel supply passage, a lower portion containing the injector valve and a lower portion of the fuel supply passage, and a distinct central plate portion having upper and lower surfaces rigidly trapped between the upper and lower portions of the body and a debris shield chamber fluidly connecting the upper and lower portions of the fuel supply passage. The debris shield is situated in the shield chamber, with opposed ends extending from the upper to the lower surface of the central portion of the body. The tube is fixed to the body in longitudinal compression between the upper and lower portions of the body. 
         [0018]    The placement of the debris shield in a central plate with slight protrusions of the tube above the plate, allows the tube to be crushed a controlled amount. The plate thickness is easy to control to close dimensions. The unique configuration of the tube into the plate is very beneficial as a low cost modification and for ease of manufacturing. Because the tube is made of material that can yield without cracking, the dimensional control of the tube length is relaxed, which helps reduce cost. The tube is crushed and slightly yielded to assure that it seals against the upper and lower portions of the body. It is important to seal the tube on both ends to assure that no leakage occurs that would allow large particles to enter the control valve fluid passages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING  
         [0019]    Embodiments of the invention will be described below with reference to the accompanying drawing, in which: 
           [0020]      FIG. 1  is a longitudinal section view of a fuel injector that incorporates a first embodiment; 
           [0021]      FIG. 2  is a detailed section view of the first embodiment; and 
           [0022]      FIG. 3  is a detailed section view of a second embodiment. 
       
    
    
     DETAILED DESCRIPTION  
       [0023]      FIG. 1  shows an injector  10  that embodies one aspect of the present invention. The injector has a body  12  including a central bore  14  in which a needle valve  16  reciprocates axially to selectively seal against and lift off seat  18  in the lower portion near tip  20  of the body. A plurality of injection holes or orifices  22  are formed in the tip below the valve seat  18 . The needle valve  16  has an upper end  24  situated in a needle control chamber  26  whereby a combination of hydraulic and spring forces selectively close the nose of valve  16  against seat  18  or lift the valve  16  from the seat  18 , depending on the pressure in chamber  26 . 
         [0024]    After passing through a high pressure filter (not shown), high pressure fuel is supplied to the injector through port  28  into main passage  30 , having upper portion  30   a,  which leads to the valve body  12 , and lower portion  30   b,  which is in fluid communication with the bore  14 . In a well-known manner, differential area profiles and fluid volumes on and around needle  16  achieve the desired hydraulic balances such that high pressure fuel is selectively discharged through orifices  22 . When the needle valve  16  is to be closed, high pressure fuel in the needle control chamber  26  urges the injector valve  16  against the injector valve seat  18  to prevent flow of high pressure fuel from the bore  14  to the orifices  22  and when the needle valve is to be opened the needle control chamber  26  is fluidly connected to low a pressure sump, thereby reducing the fluid pressure in the control chamber  26  and on the upper end  24  of the needle valve  16 , lifting the needle valve off the injector seat  18  and discharging fuel through the orifices  22 . 
         [0025]    With reference to  FIGS. 1 and 2 , the invention provides a debris shield  32  within the injector, where some of the high pressure fuel is delivered from the high pressure supply passage (e.g.,  30   a ) via auxiliary passage or branch  34  to control valve  36 . Control valve  36  is in fluid communication with and controls the pressure in the needle control chamber  26 , thereby closing and opening the needle valve  16 . An actuator body  38  is connected to the valve body  12  by threading to a substantially tubular body connector  40 , and contains a solenoid actuator  42  for a pintle  44   a  or the like that seals against and lifts from seat  44   b.  Seat  44   b  is located such that an upstream region  46  of the control valve chamber is in fluid communication with high pressure passage  34  and a downstream region  48  is in fluid communication with a low pressure sump, such as the fuel tank or low pressure fuel delivery line to the high pressure supply pump. 
         [0026]    In the illustrated embodiment, the auxiliary flow from high pressure supply passage  30   a  enters passage  50  via passage  52 , the former being in direct fluid communication with the needle control chamber  26  and with passage  34 . Preferably, the auxiliary passage  52  includes an orifice  54  leading to passage  50 , and another orifice  56  is situated between passage  50  and passage  34 . 
         [0027]    The debris shield  32  is in the intermediate portion  30   c  of the high pressure fuel supply passage  30 , between portions  30   a  and  30   b.  The debris shield comprises a tube  58  with a central axial passage  60  and a multiplicity of radial holes  62  through the tube wall. High pressure fuel for injection passes axially into and out of the tube  58  and high pressure fuel to the upstream side  46  of the control valve  36  passes radially through the holes  62  in the tube. In the illustrated embodiment, the debris shield is in the high pressure fuel supply passage  30   c  upstream of branch passage  52 , whereby radial flow through the debris shield enters the passage  50  and passage  34 . However, inasmuch as the main purpose of the debris shield is to prevent debris from entering the control valve  36 , the upstream flow path  34  can be directly fluidly connected to the fluid volume where the radial flow exits the debris shield. 
         [0028]    It should thus be appreciated that the debris shield  32  is in the main high pressure fuel supply passage  30 , upstream of the branch line  34  leading to the control valve  36 , and comprises a tube or the like  58  fixed to the body  12 , with a central passage  60  aligned with the fuel supply passage and a multiplicity of transverse holes  62  through which high pressure fuel is delivered to the branch line  34 . 
         [0029]    The debris shield  32  is preferably situated in a shield chamber  64  in the body, defined by a shield chamber wall spaced radially from the tube. The tube has opposed ends  66 ,  68  and the tube is fixed to the body at the ends. Preferably the valve body  12  comprises an upper portion  70  containing a vertical portion of high pressure supply passage  30   a,  control valve seat  44   b,  and upstream entry point  46  of passage  34  to the seat  44   b.  The valve body  12  also includes a lower portion  72  containing the injector valve  16 , needle control chamber  26 , and the lower portion  30   b  of the fuel supply passage  30 . A distinct central portion  74  of the valve body  12  in the form of a plate having upper and lower surfaces  76 ,  78  is rigidly trapped between the upper and lower portions  70 ,  72  of the body. The shield chamber  64  fluidly connects the upper and lower portions  30   a,    30   b  of the fuel supply passage. Auxiliary passage  52 , passage  50  to the needle control chamber  26 , and orifices  54  and  56  are also preferably located in the central plate  74 . 
         [0030]    The nominal distance between opposed ends  66 ,  68  of the tube  58  is preferably greater than the distance between the upper surface  76  and the lower surface  78  of the central portion  74  of the body, However, in the assembled condition of the injector, the body portions  70 ,  72 , and  74  are pulled tightly together by the body connector  40  (See  FIG. 1 ) so that tube  58  is fixed to the body in longitudinal compression between the upper and lower portions  70 ,  72  of the body. 
         [0031]    The shield chamber  64  preferably includes a collection gallery  80  at the intersection with the auxiliary passage  52 . All the fuel supplied to the passage  34  must pass through the holes  62  and gallery  80 . Preferably, the gallery extends to the lower surface  78  of the central portion  74  of the body, and auxiliary passage  52  extends from the lower surface of the central portion of the body from the gallery at an oblique upward angle toward the axis of the bore  14 . Passage  50  terminates within the central portion  74  of the body between the first and second orifices  54 ,  56  and is oriented along an axis from the injector control chamber obliquely upward toward the first portion  30   a  of the fuel supply passage. 
         [0032]    The holes  62  of the debris shield have a diameter less than 30 microns, preferably about 20 microns. The control valve pintle  44   a  is actuated by solenoid  42  to seal against and lift from a seat  44   a  with a minimum lift, and the diameter of the holes  62  in the tube should be smaller than this minimum lift. The material composition and wall thickness of the tube  58  should be such that the tube compresses during installation without excessive strain that would affect the diameter of the holes  62 . 
         [0033]      FIG. 3  shows a second embodiment in which the debris diverter shield  32  is in a different location within the injector, and the associated passages for achieving control of the injector differ from those shown in  FIG. 2  In  FIG. 3 , components which are identical to those shown in  FIG. 2  carry the same numeric identifier, whereas components that are not identical but provide the same or similar functionality are indicated with a prime (′). In this embodiment, the debris shield  32  is located in the upper portion  30   a ′ of the high pressure passage within the upper block  70 ′, and the lower portion  30   b  in block  72  and intermediate portion  30   c ′ in block  74 ′ are straight bores. 
         [0034]    The lower portion of passage  30   a ′ has a counter bore  82  defining an internal shoulder  84 . The upper end  66  of the diverter shield  32  bears against the shoulder  84  and the lower end  68  of the diverter shield  32  bears against the upper surface  76 ′ of the intermediate block  74 ′. As with the embodiment of  FIGS. 1 and 2 , the diverter shield  32  is thereby compressed and rigidly held in position. 
         [0035]    High pressure fuel in passage  30   a ′ enters the debris diverter  32 , with some flow passing through the transverse holes into gallery  64 ′, branch line  52 ′ and into the needle control chamber  26 . While the control valve  36  is closed, high pressure is maintained in the needle control chamber  26 , passage  50 ′ and passage  34 ′. Upon lifting of the control valve  36 , this pressurized fuel is exposed to the low pressure at  48 , thereby inducing the lifting of the needle valve within chamber  26 . 
         [0036]    It should be appreciated that a tubular, perforated debris diverter shield can be located anywhere within the injector whereby a main high pressure fuel flow passes axially through the tube and a secondary or auxiliary flow passes transversely through the perforations to a component within the injector that is vulnerable to the presence of small particles of debris. Particularly in the illustrated and analogous embodiments, the pressure drop across the perforations or holes is relatively small. For example, while the control valve  36  is closed, there is substantially no pressure drop because the passages to the control valve are at the pressure of the fuel in supply line  30 . When the control valve  36  opens, the orifices such as at  54  and  56  maintain a relatively high pressure in the gallery  64 . Even with pressure in the main passage  30  above 20,000 psi, the pressure drop across the holes can be as low as about 30 psi. One can trade off the lower cost of laser drilling fewer holes against the increase in pressure drop to, e.g., about 100 psi. 
         [0037]    The combination of robust main flow axially through the tube, transverse orientation of the perforations, and small pressure drop across the perforations, avoids substantial transverse forces on the particles so they do not even begin extruding through the holes. Due to the low transverse forces on the particles they tend to remain near the entrances to the perforations and are immediately flushed by the main flow to the region of the injector where they can easily pass through the injection orifices. 
         [0038]    It should be appreciated that in a typical implementation for a passenger vehicle, the debris diverter shield  32  would have a length in the range of about 3-4 mm, an OD of about 2.5 mm, and an ID of about 1.5 mm (e.g., with a wall thickness in the range of about 0.1 to 0.5 mm), and at least about 2000 holes with a diameter in the range of about 20 to 30 microns. However, the dimensions of the diverted shield and the number of holes would be correspondingly larger for heavier end uses, but the size of the holes should remain in the same range for use with the same type of fuel having similar debris characteristics. 
         [0039]    The present invention has exhibited a remarkable reduction in the effects of debris contamination in the typical fuel flow to an injector control valve. Raw fuel contains debris having a size up to 1000 microns. Typical filters upstream of the injector permit debris of up to 60 microns effective diameter to pass through to the injector and additional debris may be introduced into the fuel by hardware components in the fuel line downstream of the filters. Typical edge filters at the injector cannot filter debris smaller than 30-50 microns and debris of larger size is extruded and thereby reduced in size in the range of 30-50 microns before entering the main passage in the injector. Typical fuels have so much debris that even if large particles were diverted within the injector to an accumulation chamber or the like, the capacity would not be large enough to handle the diverted debris accumulated over only a fraction of the desired service life of the injector. The extent of debris reduction according to the invention can vary with particle size distribution in the fuel. However, a comparison of total debris reaching the control valve as between a conventional fuel system with fuel line filter and edge filter at the entrance to the injector, and the same system but with the addition of a debris diverter shield as shown and described herein, showed a reduction by a factor of over 10.