Patent Publication Number: US-7896262-B2

Title: Fuel injection valve for internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application 2007-332574 filed on Dec. 25, 2007, so that the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fuel injection valve which injects fuel into a combustion chamber of an internal combustion engine or the like. 
     2. Description of Related Art 
     An internal combustion engine has a fuel injection valve for injecting fuel into each of a plurality of combustion chambers. This injection valve has a valve guide formed in a cylindrical shape and a valve member. The valve guide has nozzle holes. The valve member is disposed in a center opening of the guide. The valve member is reciprocated to be seated on a valve seat of the guide and to leave the seat. Therefore, the holes are repeatedly opened and closed. A fuel passage is formed between the valve guide and the valve member. When the valve member leaves the seat, fuel flows through the fuel passage and is injected into the chamber through the holes. 
     Because each hole is formed in a small size, a portion of the fuel injected through the hole easily remains as residues on a surface of the valve guide placed around fuel outlets of the holes. These fuel residues are exposed to combustion products (e.g., CO 2 , CO, H 2 O, NO, and the like) having high temperatures during the operation of the engine. Further, when the operation of the engine is stopped, the residues are cooled down. Therefore, the residues are solidified or caked as deposits on the valve guide around the fuel outlets of the holes. These deposits placed around the holes change the spray angle of the injected fuel and/or the shape of the spray formed by the injected fuel. In this case, it is difficult to maintain the fuel injection performance of the injection valve at a superior level. 
     To solve this problem, Published Japanese Patent First Publication No. 2001-90638 discloses a fuel injection valve wherein an organic layer made of perfluoropolyether compound such as FAS (fluoro-alkyl-silane) or the like is attached to the surface of a valve guide around nozzle holes of the guide. FAS has water repellency. The FAS layer prevents fuel from being attached to the surface of the valve guide as deposits, or the deposits attached to the surface of the valve guide are easily detached due to the FAS layer. 
     However, this injection valve in the Publication No. 2001-90638 has the problem that FAS thermally decomposed is attached to the surface of the valve guide More specifically, a portion of the valve guide on the downstream side of the holes is heated by combustion products. Therefore, FAS attached to the surface of the valve guide is thermally decomposed and reacts with P, Zn, Si, compounds of carboxylic acids and base components, and the like contained in the fuel to produce low melting amorphous glass. Therefore, PAS thermally decomposed has no water repellent performance. Further, the low melting amorphous glass derived from thermally decomposed FAS and fuel residues containing non-burned carbon forms deposits, and these deposits become fixed and attached to the surface of the valve guide around the holes. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide, with due consideration to the drawbacks of the conventional valve, a fuel injection valve which prevents deposits from being attached to the surface of a valve guide around a nozzle hole of the guide. 
     According to an aspect of this invention, the object is achieved by the provision of a fuel injection valve comprising a valve guide with a valve seat placed on an inner surface of the valve guide and a nozzle hole from which fuel is injected, a valve member movable along an axial direction of the valve guide to be seated on the valve seat of the valve guide and to leave the valve seat, and a covering layer disposed on a surface of the valve guide around an outlet opening of the nozzle hole. The valve member seated on the valve seat closes the nozzle hole of the valve guide. The valve member leaving the valve seat opens the nozzle hole. The covering layer has a hydrophilic property higher than that of the surface of the valve guide. 
     With this structure of the injection valve, when the nozzle hole is opened, fuel is injected through the nozzle hole. In this case, a portion of the injected fuel remains on the covering layer disposed on the outer surface of the valve guide. Because the covering layer has a hydrophilic property higher than that of the surface of the valve guide, the covering layer prevents the fuel remaining on the layer from being solidified or caked as deposits on the layer around the outlet opening of the nozzle hole. 
     More specifically, the covering layer having a high hydrophilic property successively collects water contained in the fuel and forms a film of the water on the layer. When a portion of fuel injected from the hole remains on the covering layer as residues containing non-burned carbons, P, Zn, Si, compounds of carboxylic acids and base components, and the like, the fuel residues float on the water film. In this case, the injection flow of the fuel easily removes the fuel residues from the water film successively formed. Therefore, the covering layer prevents a portion of fuel from being remaining as residues on the layer. That is, the covering layer prevents the generation of deposits from fuel residues and the deposition of the deposits on the layer. 
     Because deposits are not substantially formed around the outlet opening of the nozzle hole, a flow rate of the injected fuel and a spray angle of the injected fuel can be maintained at adequate values even when an engine with the injection valve is intermittently operated for a long time. 
     Accordingly, because the covering layer having a high hydrophilic property is disposed on the surface of the valve guide around the outlet opening of the nozzle hole, the injection valve can prevent deposits of fuel from being solidified or caked on the surface of the valve guide around the outlet openings of the holes. As a result, the injection valve can maintain the fuel injection performance such as a flow rate of fuel and a spray angle of fuel at superior levels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal sectional view of a fuel injection valve according to the first embodiment of the present invention; 
         FIG. 2  is an enlarged view of a covering layer attached to a surface of a nozzle body in the injection valve shown in  FIG. 1 ; 
         FIG. 3  is an explanatory view showing an angle of water repellence in the covering layer and an angle of water repellence in a nozzle hole plate; 
         FIG. 4  is an enlarged view of a covering layer attached to a surface of a nozzle body according to a modification of the first embodiment; 
         FIG. 5  is an enlarged view of a covering layer attached to surfaces of a nozzle body according to the second embodiment; 
         FIG. 6  is an explanatory view of deposits formed on the surface of the nozzle body; 
         FIG. 7  is an explanatory view showing a change in a flow rate of sprayed fuel; and 
         FIG. 8  is an explanatory view showing a change in a spray angle of fuel. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described with reference to the accompanying drawings, in which like reference numerals indicate like parts, members or elements throughout the specification unless otherwise indicated. 
     Embodiment 1 
       FIG. 1  is a longitudinal sectional view of a fuel injection valve according to the first embodiment, while  FIG. 2  is an enlarged view of a covering layer attached to a surface of a nozzle body in the injection valve shown in  FIG. 1 . 
     A fuel injection valve (hereinafter, called an injector)  1  shown in  FIG. 1  is, for example, attached to each of engine heads of a direct injection type gasoline engine (not shown) to inject gasoline into a combustion chamber of the engine. This injector  1  may be used for a pre-mixed type gasoline engine or a diesel engine. As a type of fuel injection valve, a fuel adding valve is used for a NOx reducing process or a particulate matter regeneration process. This fuel adding valve adds fuel into an exhaust gas passage to regenerate the exhaust catalyst and prevent lowering the performance of exhaust emission control. 
     As shown in  FIG. 1  and  FIG. 2 , the injector  1  has a cylindrical housing  10  composed of a first magnetic member  11 , a non-magnetic member  12  disposed on the front side of the member  11  and a second magnetic member  13  disposed on the front side of the member  12 . The members  11  to  13  are attached to one another by laser welding or the like to be aligned along the axial direction of the injector  1 . Each of the members  11  and  13  is made of a magnetic material. The member  12  is made of anon-magnetic material to prevent the members  11  and  13  from magnetically interacting with each other. 
     The injector  1  further has a cylindrical external connector  19  tightly fitted to the inner circumferential surface of the housing  10  at a rear end portion  102  of the housing  10 , a nozzle holder  14  of which a rear end portion is attached to the outer circumferential surface of the member  13 , a cylindrical nozzle body (or a valve guide)  30  fixed to the inner circumferential surface of a front end portion  141  of the holder  14 , a cylindrical fixed core  21  fixedly attached to the inner circumferential surfaces of the members  11  and  12  to be disposed in the center opening of the housing  10 , a cylindrical movable core  22  disposed in the center opening of the housing  10  on the front side of the core  21  to be reciprocated along the axial direction, and a needle valve (or a valve member)  40  of which a rear portion is attached to a front portion of the core  22  to be disposed in the center openings of the housing  10 , the holder  14  and the body  30 . 
     Each of the cores  21  and  22  is made of a magnetic material. The cores  21  and  22  face each other in the axial direction. The core  22  is brought into contact with the core  21  in response to a magnetic attracting force induced between the cores  21  and  22 . The body  30  is pressed into the holder  14  and is fixedly attached to the holder  14  by welding or the like. The needle valve  40  and the body  30  are coaxially disposed. The needle valve  40  is reciprocated with the core  22  along the axial direction of the body  30  (i.e., the axial direction of the injector  1 ). 
     The nozzle body  30  has a cylindrical nozzle body wall  31  fitted to the portion  141  of the holder  14 , a valve seat  32  disposed on the inner circumferential surface of a conically-shaped front end portion of the wall  31 , and a nozzle hole plate  33  fixedly disposed between the front end portion of the wall  31  and the holder  14  so as to cover the valve seat  32 . The inner diameter of the valve seat  32  is gradually reduced toward the front side, and the valve seat  32  has a circular opening facing the front end of the needle valve  40  in the axial direction and communicating with the opening between the needle valve  40  and the holder  14 . The hole plate  33  has a plurality of nozzle holes  34  through which the opening of the seat  32  communicates with the chamber of the engine head. The plate  33  may have a single nozzle hole. 
     The needle valve  40  has a sealing portion  42  at its front end. This sealing portion  42  can be seated on the valve seat  32  of the nozzle body  30  in response to the needle valve  40  moving toward the front side. 
     The injector  1  further has a spring  26  disposed in the center openings of the cores  21  and  22  while one end of the spring  26  is in contact with the rear end of the needle valve  40 , a cylindrical adjusting pipe  28  fixedly attached to the inner circumferential surface of the core  21  to be disposed in the center opening of the core  21  and being in contact with the other end of the spring  26 , and a fuel filter  18  fixedly disposed in the center opening of the connector  19 . 
     The spring  26  acts as an elastic member to produce an elastic force biasing the needle valve  40  toward the front side. The spring  26  pushes the sealing portion  42  of the needle valve  40  toward the valve seat  32  of the nozzle body  30 . Therefore, when the core  22  is not attracted to the core  21 , the sealing portion  42  can be stably seated on the valve seat  32 . A load applied to the spring  26  is adjusted by adjusting the length of the pipe  28  pressed into the core  21 . The elastic member is not limited to the spring  26 . For example, a blade spring or a damper using gas or liquid may be used as the elastic member. 
     Fuel of a fuel tank (not shown) is supplied from a fuel inlet  191  placed at the rear end of the connector  19  and flows into the opening of the housing  10  through the filter  18 . The filter  18  removes foreign matters contained in the fuel. 
     The injector  1  further has a coil assembly  50  disposed on the outer circumferential surface of the housing  10  and a plate housing  15 . The coil assembly  50  has a coil  51  inducing a magnetic attracting force between the cores  21  and  22 , a molding member  52  covering the coil  51 , and an electric connector  53  through which the coil  51  receives electric power. The coil  51  is formed in the cylindrical shape so as to surround the housing  10  along the circumferential direction of the injector  1 . The molding member  52  is made of resin. The molding member  52  is disposed on both the inner and outer circumferential surfaces of the coil  51  to electrically insulate the coil  51  from the housing  10 . The connector  53  has a connector body attached to the molding member  52 , a wire  54  connected with the coil  51  while penetrating through the body, and a terminal  55  connected with the wire  54  outside the body. The connector body is made of resin. 
     The plate housing  15  is attached to the housing  10  and the nozzle holder  14  to cover the outer circumferential surface and the rear surface of the coil  51  through the molding member  52 . The plate housing  15  holds the coil  51 . The plate housing  15  is made of a magnetic material. 
     The injector  1  further has a covering layer  5  attached to a surface  331  of the nozzle hole plate  33  of the nozzle body  30 . The covering layer  5  is located around a plurality of outlet openings  341  of the respective holes  34 . The covering layer  5  is made of a non-organic material having a hydrophilic property higher than that of the surface  331  of the plate  33 . The degree of hydrophilic property is indicated by an angle of water repellence. The water repellence angle denotes a contact angle of a water drop indicating the degree of wetting. 
     The layer  5  is, for example, made of boron nitride (hereinafter, called h-BN) in the hexagonal crystal system. This h-BN is superior in heat resistance, Therefore, the layer  5  is hardly reacted with fuel residues such as non-burned carbons, P, Zn, Si, compounds of carboxylic acids and base components, and the like. The h-BN is, for example, deposited on the surface  331  of the plate  33  according to a plasma chemical vapor deposition (CVD) to form the covering layer  5 . The thickness of the layer  5  ranges from 20 nm (2×10 −8  m) to 10 μm (1×10 −5  m). Assuming that the thickness of the layer  5  is smaller than 20 nm, the layer  5  insufficiently prevents fuel residues from being deposited on the plate  33 . Assuming that the thickness of the layer  5  exceeds 10 μm, the layer  5  is easily detached from the plate  33  by the injected fuel. In this embodiment, the layer  5  has the thickness of approximately 0.2 μm. 
     As shown in  FIG. 3 , the covering layer  5  made of h-BN has an angle of water repellence equal to approximately 70 degrees. In contrast, the plate  33  is, for example, made of a type of stainless steel such as SUS 304. SUS 304 contains Ni ranging from 8.00 to 10.50 wt %, Cr ranging from 18.00 to 20.00 wt %, C (C≦0.08 wt %), Si (≦1.00 wt %), Mn (≦2.00 wt %), P (≦0.045 wt %) ands (≦0.030 wt %). The surface  331  of the plate  33  made of SUS 304 has an angle of water repellence equal to approximately 90 degrees. Because the water repellence angle of the covering layer  5  is smaller than that of the surface  331  of the plate  33 , the covering layer  5  has the hydrophilic property higher than that of the surface  331  of the plate  33 . 
     The inventors of this application actually measured the angle of water repellence. In this measurement, a drop of water from a micro syringe was dropped on the surface of the covering layer  5 . Then, light was emitted to the water drop from one side of the layer  5 , a camera located on the other side of the layer  5  received the light, and an image indicating the shape of the water drop was obtained. Then, the contact angle of the water drop located on the surface of the layer  5  was measured to obtain the water repellence angle of h-BN. In the same manner, the inventors measured the water repellence angle of SUS 304. 
     Next, an operation of the injector  1  will be described below. 
     During the stoppage of electric power to the coil  51 , no magnetic attracting force is induced between the cores  21  and  22 . Therefore, the core  22  is placed due to the pushing force of the spring  26  to be away from the core  21 , and the sealing portion  42  of the needle valve  40  is seated on the valve seat  32  of the nozzle body  30 . Therefore, the injector  1  is set in the valve closing state, and fuel is not injected from any nozzle hole  34 . 
     When electric power is supplied to the coil  51 , the coil  51  induces a magnetic field, and magnetic fluxes flow through a magnetic circuit formed of the housing plate  14 , the magnetic members  11  and  13 , the cores  21  and  22  and the cover  15 . Therefore, a magnetic attracting force is induced between the cores  21  and  22  placed away from each other. When this magnetic attracting force exceeds the pushing force of the spring  26 , the core  22  and the needle valve  40  attached to each other are moved toward the rear side to approach the core  21 . As a result, the sealing portion  42  of the needle valve  40  leaves the valve seat  32 , so that the injector  1  is set to the valve opening state. 
     During the valve opening state, fuel entering the fuel inlet  191  of the connector  19  flows through the filter  18 , the inner opening of the adjusting pipe  28  placed on the inner side of the housing  10 , the inner opening of the core  21 , the inner opening of the core  22 , and the inner opening of the needle valve  40  in that order. Then, the fuel flows outside the valve  40  through a fuel hole  45 . This hole  45  communicates the inner opening of the valve  40  and the outside of the valve  40 . Then, the fuel flows through an opening between the housing  10  and the valve  40  and an opening between the valve  40  and the holder  14 . Then, the fuel passes through an opening between the valve  40  and the nozzle body  30  and an opening between the sealing portion  42  and the valve seat  32 . Then, the fuel is injected from the nozzle holes  34  into a chamber of the engine head. 
     When the electric power supplied to the coil  51  is stopped, the magnetic attracting force between the cores  21  and  22  disappears. Therefore, the core  22  and the needle valve  40  attached to each other are moved due to the pushing force of the spring  26  toward the front side and is placed away from the core  21 . As a result, the sealing portion  42  of the needle valve  40  is again seated on the valve seat  32 . Therefore, the injector  1  is returned to the valve closing state, and the fuel injection from the holes  34  is stopped. 
     Next, the action of the covering layer  5  will be described. 
     During the fuel injection, a portion of the fuel outputted from the outlet openings  341  of the holes  34  remains on the covering layer  5  attached to the surface  331  of the plate  33  around the outlet openings  341  of the holes  34 . Assuming that the surface  331  of the plate  33  is directly exposed to the fuel, fuel remaining on the surface  331  will be solidified or caked as deposits on the surface  331 . However, in this embodiment, the covering layer  5  having a high hydrophilic property exists on the surface  331  of the plate  33 . This covering layer  5  prevents fuel remaining on the layer  5  from being solidified or caked as deposits on the layer  5 . 
     More specifically, the covering layer  5  having a high hydrophilic property successively collects water contained in the fuel to form a film of the water on the layer  5 . When a portion of fuel injected from the holes  34  remains on the covering layer  5  as residues containing non-burned carbons, P, Zn, Si, compounds of carboxylic acids and base components, and the like, the fuel residues float on the water film. In this case, the injection flow of the fuel easily removes the fuel residues from the water film successively formed. Therefore, the covering layer  5  prevents a portion of fuel from being remaining as residues on the layer  5 , so that the covering layer  5  prevents the generation of deposits from fuel residues and the deposition of the deposits on the layer  5 . 
     Accordingly, because the covering layer  5  having a high hydrophilic property is placed on the surface  331  of the plate  33 , the injector  1  can prevent deposits of fuel from being solidified or caked on the surface of the nozzle body  30  around the outlet openings  341  of the holes  34 . 
     Modification of Embodiment 1 
       FIG. 4  is an enlarged view of the covering layer  5  attached to surfaces of the nozzle body  30  according to a modification of the first embodiment. In the injector  1  according to the first embodiment, the covering layer  5  having a high hydrophilic property is attached to only the surface  331  of the nozzle hole plate  33  of the nozzle body  30  around the outlet openings  341  of the respective holes  34 . However, as shown in  FIG. 4 , because fuel injected from the holes  34  passes across inner circumferential surfaces  342  of the holes  34 , the covering layer  5  may be attached to the inner circumferential surfaces  332  of the holes  34  as well as the surface  331  of the plate  33 . Further, because fuel sprayed from the holes  34  comes in contact with surfaces  142  of the front end portion  141  of the nozzle holder  14 , the covering layer  5  may be attached to the surfaces  142  of the nozzle holder  14 . 
     Accordingly, the injector  1  can prevent deposits of fuel from being solidified or caked on the inner circumferential surfaces  332  of the holes  34  and/or the surfaces  142  of the nozzle holder  14 . 
     The covering layer  5  may be attached to a surface of the needle valve  40  around the sealing portion  42 . In this case, the injector  1  can prevent deposits of fuel from being solidified or caked on the surface of the needle valve  40  around the sealing portion  42 . Further, the covering layer  5  attached to the surface of the needle valve  40  can reduce the sliding frictional resistance between the needle valve  40  and the nozzle body  30 . 
     Embodiment 2 
     In the first embodiment, the nozzle body  30  has the nozzle body wall  31  and the nozzle hole plate  33  which are separately formed and are attached to each other as one unit in the injector  1 . However, the nozzle body wall  31  and the nozzle hole plate  33  may be integrally formed. 
       FIG. 5  is an enlarged view of the covering layer  5  attached to surfaces of a nozzle body according to the second embodiment. 
     As shown in  FIG. 5 , the nozzle body  30  has a wall portion fixed to the inner circumferential surface of the holder  14  and a conical portion  301  extending from the front end of the wall portion. These portions are integrally formed with each other. The valve seat  32  is disposed on the inner circumferential surface of the conical portion  301 . The nozzle holes  34  are disposed at the front end of the conical portion  301  of the body  30 . The conical portion  301  of the body  30  is protruded from the holder  14 . 
     The covering layer  5  is attached to an outer circumferential surface  300  of the conical portion  301  of the body  30  around the outlet openings  341  of the holes  34  and the inner circumferential surfaces  342  of the holes  34 . 
     Because the outlet openings  341  of the holes  34  are placed at the front end of the conical portion  301 , the water film formed on the covering layer  5  is easily gathered around the outlet openings  341  while containing residues of fuel. Accordingly, the fuel injected from the holes  34  can efficiently remove the fuel residues gathered around the holes  34  from the water film. 
     Experimental Results for Estimating Deposits 
     The injector  1  with the covering layer  5  coated on the surface  331  of the plate  33  of the nozzle body  30  around the outlet openings  341  of the holes  34  was prepared as an inventive sample. Another injector with no covering layer was prepared as a comparative sample. Each of the samples were mounted in an engine, and the engine was operated for a predetermined time. Thereafter, fuel deposits attached to the surface  331  of the plate  33  in the comparative sample and fuel deposits attached to the covering layer  5  in the inventive sample were observed to measure a change in the flow rate of fuel sprayed into a chamber of the engine head and to measure a change in the spray angle of the fuel. 
     Each sample was mounted at the center of the engine. The temperature at the front end of the sample was approximately 250° C. The engine speed was approximately 2000 rpm. The fuel pressure was approximately 12 Mpa. The driving torque of the engine was approximately SON/m. The operation time of the engine was four hours. 
     Experimental results will be described with reference to  FIG. 6  to  FIG. 8 .  FIG. 6  is an explanatory view of deposits on the covering layer  5  and deposits on the surface  331  of the plate  33 . Deposits shown in  FIG. 6  were observed by using a scanning electron microscope (SEM). 
     As shown in  FIG. 6 , no deposits are formed at a start time of the engine operation. However, in the comparative sample, a large quantity of deposits are formed on the surface  331  of the plate  33  after the operation of the engine. In contrast, in the inventive sample, a quantity of deposits formed on the covering layer  5  after the operation of the engine is very small. 
     Accordingly, it will be realized that the covering layer  5  coated on the surface  331  of the plate  33  can effectively prevent fuel deposits from being formed on the layer  5 . 
       FIG. 7  is an explanatory view showing a change in a flow rate of the sprayed fuel, while  FIG. 8  is an explanatory view showing a change in a spray angle of the fuel. 
     A first flowrate of the injected fuel in each sample was measured at the operation start time, and a second flow rate of the injected fuel in each sample was measured after the operation of the engine. Then, a flow rate difference was obtained by subtracting the first flow rate from the second flow rate, and a ratio (%) of the flow rate difference to the first flow rate was calculated. This experiment was performed twice for each sample. 
     Further, a first spray angle of the injected fuel in each sample was measured at the operation start time, and a second spray angle of the injected fuel in each sample was measured after the operation of the engine. Then, an angle difference was obtained by subtracting the first spray angle from the second spray angle, and a ratio (%) of the angle difference to the first spray angle was calculated. This experiment was performed twice for each sample. 
     As shown in  FIG. 7  and  FIG. 8 , in the comparative sample having no h-BN, the ratios are largely lower than 0.0%. Therefore, the flow rate of the injected fuel and the spray angle of the injected fuel are reduced together in the comparative sample. In contrast, in the inventive sample coated with h-BN, the ratios are substantially equal to 0.0%. Therefore, none of the flow rate of the injected fuel and the spray angle of the injected fuel are changed during the engine operation in the injector  1 . 
     Accordingly, it will be realized that the covering layer  5  coated on the surface  331  of the plate  33  can effectively maintain the fuel injecting performance such as the flow rate of the injected fuel and the spray angle of the injected fuel. 
     These embodiments should not be construed as limiting the present invention to structures of those embodiments, and the structure of this invention may be combined with that based on the prior art.