Abstract:
Fuel-air mixture is supplied with stability to the neighboring area of an ignition plug without any effect on deflection of fuel spray due to the air flow (swirl/tumble) in a combustion chamber, and the deposition of fuel onto the side wall of a combustion chamber is reduced, leading to the prevention of occurrence of smoke. A fuel injection apparatus includes a fuel injection valve having a nozzle opening to a combustion chamber and an ignition plug. The fuel injection valve forms a fuel spray having different levels of average speed. The fuel spray has relatively high speed at least in half of a single cycle of a fuel injection, and after that, the fuel injection valve forms relatively low-speed fuel spray, and consequently, a fuel-air mixture including high-speed fuel spray is supplied to a neighboring area of the ignition plug.

Description:
This application is a division of application Ser. No. 09/053,518, filed Apr. 2, 1998, now U.S. Pat. No. 6,095,113. 

   FIELD OF THE INVENTION 
   The preset invention relates to a fuel injection apparatus and control method therefor. In particular, the present invention is suitable to a system for injecting fuel directly into the combustion chamber. 
   As for the apparatus in the prior art, an engine having a fuel injection valve having a nozzle opening to the combustion chamber is disclosed in Japanese Patent Application Laid-Open No. 2-169834 (1990). In this fuel injection valve, a swing force is applied to the fuel flow in order to improve the granularity of the fuel mist and reduce the spray speed, and consequently prevent the fuel from depositing on a wall of the combustion chamber. 
   In the fuel spray with its spray speed reduced as shown in the prior art, as the fuel spray is liable to be deflected due to the air turbulence (swirl/tumble) in the combustion chamber, and the fuel-air mixture can not be supplied stably to-the neighboring area of the ignition plug, there is such a problem that the fuel combustion tends to make unstable. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a fuel injection apparatus and control method therefor in which the fuel-air mixture can be supplied to the neighboring area of the ignition plug with out fuel splay deflection due to the air turbulence (swirl/tumble) in the combustion chamber and the fuel depletion on the combustion chamber wall is reduced as well, leading to the reduction of soot. 
   Another object of the present invention is to provide a fuel injection valve and a method of injecting fuel, by which the ignition can be improved, the production of soot can be reduced, and the stability of combustion can be improved when the engine speed is at high speed, even if the combustion is at a lean-burn state (an air/fuel ratio is about 20-50). 
   In order to achieve the above main object, a fuel injection valve having a nozzle opening to the combustion chamber inside and an ignition plug are provided so that the fuel injection valve may form fuel spray having different levels of average speed. 
   Preferably, the fuel injection valve forms relatively high-speed fuel spray at least in the half way of the single cycle of the fuel injection, and after that, it forms relatively low-speed fuel spray. Thus, the fuel-air mixture comprising high-speed fuel spray can be supplied to the neighboring area of the ignition plug. 
   In order to achieve the above another object, a fuel injection valve for an engine is provided with a valve body, a valve seat, a nozzle opening and a fuel guide in a nozzle portion. Further, the fuel guide forms a plurality of fuel swirling passages each of which has different strength of swirling. 
   Preferably, the fuel swirling passages which have less strength of swirling is formed at the nozzle opening side, compared with fuel swirling passage which have larger strength of swirling. 
   According to the present invention, the low-speed fuel spray does not deposit on the combustion chamber wall surface and the piston wall surface but diffuses in the combustion chamber and forms the fuel-air mixture. The fuel-air mixture formed with the fuel spray having high speed supplied to the neighboring area of the ignition plug is ignited, and the generated flame kernel is propagated as well as diffused by spray force and air flow into the fuel-air mixture formed by the low-speed fuel spray. Consequently, it will be appreciated that the stabilization of combustion and the prevention of soot generation by reducing the deposition of fuel spray onto the combustion chamber wall surface and the piston wall surface can be established together. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a structure of one embodiment of the present invention. 
       FIG. 2  is a descriptive diagram of the operation in the present invention. 
       FIG. 3  is a descriptive diagram of the operation in the present invention. 
       FIG. 4  is a descriptive diagram of the operation in the present invention. 
       FIG. 5  is a structure of fuel spray in the present invention. 
       FIG. 6  is a cross-section view of the injection valve in the present invention. 
       FIGS. 7A-7C , each is a structure of the fuel swirler according to a first embodiment of the present invention. 
       FIGS. 8A-8C , each is a structure of the fuel swirler according to a second embodiment of the present invention. 
       FIGS. 9A-9C , each is a structure of the fuel swirler according to a third embodiment of the present invention. 
       FIGS. 10A-10C , each is a structure of the fuel swirler according to a fourth embodiment of the present invention. 
       FIGS. 11A and 11B  are graphs showing the relationship between the fuel injection timing and the ignition timing. 
       FIGS. 12A-12D  are descriptive diagrams of the operation in the present invention. 
       FIG. 13  is a relationship among the spray amount of low speed component, the combustion stability and the smoke amount. 
       FIGS. 14A and 14B  are graphs showing the relationship among the fuel injection timing, the ignition timing, the combustion stability and the smoke amount. 
       FIGS. 15A-15D  show the structure of another embodiment of the present invention. 
       FIG. 16A  is a cross-sectional view of a fuel guide according to a fifth embodiment of the present invention. 
       FIG. 16B  is a vertical-sectional view showing a state of fuel spray. 
       FIG. 17A  is a cross-sectional view of a fuel guide according to a six embodiment of the present invention. 
       FIG. 17B  is a vertical-sectional view showing a state of fuel spray. 
       FIG. 17C  is a flow distribution of the fuel spray in a radial direction. 
       FIG. 18A  is a cross-sectional view of a fuel guide according to a seventh embodiment of the present invention. 
       FIG. 18B  is a vertical-sectional view showing a state of fuel spray in the fuel guide of FIG.  18 A. 
       FIG. 18C  is a flow distribution of the fuel spray in a radial direction in the fuel guide of FIG.  18 B. 
       FIG. 19A  is a cross-sectional view of a fuel guide according to another embodiment of the present invention, in which the valve body is changed to be conical in shape. 
       FIG. 19B  is a vertical section showing a state of fuel spray in the fuel guide of FIG.  19 A. 
       FIG. 19C  is a flow distribution of the fuel spray in a radial direction in the fuel guide of FIG.  19 A. 
       FIGS. 20A and 20B  are vertical sections showing a state of fuel spray in a fuel guide according to another embodiment of the present invention, in which the valve body is changed to be conical in shape. 
       FIG. 20C  is a vertical section showing an example of a state of fuel spray in the fuel guide of FIG.  20 A. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The structure of one embodiment of the present invention is shown in FIG.  1 . The fuel injection valve  1  and the ignition plug  2  are mounted on the engine head  50 . After the intake air is measured by the air flow meter  43 , the intake air passes through the throttle valve  41 , and reaches the combustion chamber  51  through the intake pipe and the intake valve  46 . The fuel spray  3  is injected from the fuel injection valve toward the cavity  6  formed on the piston  7 . The fuel injection valve is driven intermittently by the controller  45 . The signals of the air flow meter, the revolution speed N, the accelerator divergence angle a and the signal of the throttle valve divergence angle signal sensor  44  are read by the controller, and the fuel spray amount, the fuel spray timing, the ignition timing and the throttle valve divergence angle are controlled. The throttle valve may be controlled by the motor  42  independently of the accelerator. 
   Referring to  FIGS. 2 and 3 , the operation of the present invention will be explained.  FIG. 2  shows an example in which the fuel spray having high speed is supplied. The fuel spray is injected from the fuel injection valve toward the cavity  6  formed on the piston  7 . The duration time until the fuel injection is the period of time while the fuel spray can be captured in the cavity of the piston, for example, at the angle range between 30 degree and 60 degree before the top dead center in the compression stroke. The fuel spray colliding with the cavity is vaporized and forms the fuel vapor  4 , and the combustible gaseous mixture of the fuel vapor and the air is established near the ignition plug  2 . As the spray speed is larger, the gaseous mixture flows up toward the ignition plug due to the fuel spray energy and the air flow in the compression stroke. On the other hand. The residual fuel not vaporized makes liquid membrane in the combustion chamber, which leads to the reduction of the fuel-air mixture and consequently, the occurrence of sooty combustion. Therefore, it is well understood that the fuel spray having high speed can supply stable gaseous mixture of fuel and air near the ignition plug, but that the excess amount of fuel spray may cause the remained fuel not vaporized and the occurrence of sooty combustion. 
     FIG. 3  shows an example in which the low-speed fuel spray is supplied. As the fuel spray speed is low, the deposition of fuel on the piston is small and the fuel spray can be dispersed widely in the combustion chamber. The dispersed fuel evaporates and mixed with the air while the compression stroke, leading to soot-free combustion. However, as the energy of the fuel spray itself is small, the fuel spray tends to be deflected by the air flow in the combustion chamber, and hence, it is difficult to supply constantly the stable gaseous mixture to the neighboring area of the ignition plug. 
     FIG. 4  is a graph in which the horizontal axis represents the crank angle and the vertical axis represents the distance from the top dead center. The number  0  on the vertical axis means the top dead center in the compression stroke. In the spray pattern A in which the spray speed is high, the fuel spray reaches the cavity at the crank angle of about 40 degree, and after that, the gaseous mixture can be formed near the ignition plug by the piston action and the spray energy. On the other hand, in the spray pattern B in which the spray speed is low, the fuel spray reaches the cavity at the crank angle of about 35 degree, but the gaseous mixture can not blow up to the ignition plug because the spray energy is low. In this case, though the fuel spray reaches the cavity, the disposition of the fuel liquid onto the cavity is small. 
     FIG. 5  shows an example of the spray structure in the present invention. The spray  3   b  with high speed is formed inside the spray  3   a  with low speed. The spray angle for the spray with low speed is taken to be larger in order to promote the mixing action of the fuel and the air. In contrast, the spray angle for the spray with high speed is taken to be relatively small in order to increase the directivity in reflection to the ignition plug. As the high-speed spray generates negative pressure as it goes downstream, the low-speed spray  3   a  gets sucked in the spray  3   b , leading to the reduction of spray angle of the low-speed spray  3   a . This phenomena is distinguished in case that the circumference resistance is low and that the ambient pressure is high. For example, as the ambient pressure is between 0.3 MPa and 0.5 MPa when injecting the fuel while the compression stroke in order to establish lean-burn operation, the spray angle is smaller than the case of injecting the fuel while the intake stroke. This characteristic is preferable for direct fuel injection engines because the gaseous mixture in a lean-burn mode can be localized near the ignition plug and the spray angle can be taken to be large in order to increase the utilization ratio of the air, for example, when high intensity combustion. 
     FIG. 6  shows an example of the structure of the injection nozzle. The valve body  21  is linked to the plunger  24  and lifted by the coil  28 . The power voltage is applied intermittently through the connector  29  to the coil. When the power voltage is not applied, the valve body  21  is pressed to the valve seat  20  by the spring  30 . The fuel swirler  23  for swirling the fuel is arranged around the valve body, with which the fuel to be injected is swirled and the atomization of the fuel and its diffusion is facilitated. It is allowed to form the step part  24  at the plunger and limit the stroke of the valve body by the stopper  25 . 
     FIG. 7  shows the structure of the fuel swirler. In order to generate the swirling flow in the fuel, channels are defined to be extended from the center of the nozzle  31  and their offsets L 1  and L 2  are defined. In this example, the offset L 2  is larger than the offset L 1 , and hence, the rotating force applied to the fuel by the channel with offset L 2  is larger. Hence, the fuel spray tends to diffuse well and the spray speed in an axial direction is small. By placing the channel  34  with smaller offset at the downstream side of the channel  33  with larger offset, it is appreciated that the fuel spray having less rotating force, narrower spray angle and higher speed in the axial direction can be formed in advance and that the fuel spray having more rotating force, wider spray angle and lower speed in the axial direction can be formed later. 
     FIG. 8  shows another structure of the fuel swirler. In order to generate the swirling flow in the fuel, channels are defined to be extended from the center of the nozzle  31  and their offsets L 1  and L 2  are defined. In this example, the offset L 1  is larger than the offset L 2 , and hence, the rotating force applied to the fuel by the channel with offset L 1  is larger. Hence, the fuel spray tends to diffuse well and the spray speed in the axial direction is small. The channel  34  with smaller offset at the downstream side of the channel  33  with larger offset. In this example, As the channel  34  is formed in an oblique direction, compared with the structure shown in  FIG. 7 , it is appreciate that the fuel spray having less rotating force, more narrow spray angle and higher speed in the axial direction can be formed in advance. 
     FIG. 9  shows another structure of the fuel swirler. In order to generate the swirling flow in the fuel, channels are defined to be extended from the center of the nozzle  31  and their offsets L 1  and L 2  are defined. In this example, the offset L 1  is equal to the offset L 2 . Hence, the fuel spray tends to diffuse well and the spray speed in the axial direction is small. The enlarged volumetric parts  34  are defined at the outlet parts of the channels  33  and  34 . Thus, at the beginning of opening the valve, the fuel stored in the enlarged volumetric parts is injected at first. This configuration of the enlarged volumetric parts substantially makes smaller the offset of the channel with respect to the center of the nozzle, and thus, at the beginning of opening the valve, the fuel spray with narrower spray angle and higher speed in the axial direction can be injected at first. After that, the fuel spray with larger rotating force, wider spray angle and lower speed in the axial direction can be formed with the fuel flowing through the channels  33  and  34 . 
     FIG. 10  shows another structure of the fuel swirler. In order to generate the swirling flow in the fuel, channels are defined to be extended from the center of the nozzle  31  and their offsets L 1  and L 2  are defined. In this example, the offset L 1  is equal to the offset L 2 . Hence, the fuel spray tends to diffuse well and the spray speed in the axial direction is small. The enlarged volumetric part  36  is defined at the outlet part of the channels  33  and  34 . Thus, at the beginning of opening the valve, the fuel stored in the enlarged volumetric part is injected at first. This configuration of the enlarged volumetric part substantially makes smaller the offset of the channel with respect to the center of the nozzle, and thus, at the beginning of opening the valve, the fuel spray with narrower spray angle and higher speed in the axial direction can be injected at first. After that, the fuel spray with larger rotating force, wider spray angle and lower speed in the axial direction can be formed with the fuel flowing through the channels  33  and  34 . In comparison with the structure shown in  FIG. 9 , as the enlarged volumetric part  36  is shaped uniformly and continuously in a circumferential direction, the fabrication of the structure is easy. 
   The relationship between the fuel injection timing and the ignition timing is shown in FIG.  11 . In  FIG. 11A , the fuel is injected in the intake stroke, and after that, the gaseous mixture of fuel and air is ignited at the intake and compression strokes before the crank angle reaches the top dead center. In such an operation condition that the torque generated by the engine is larger and the amount of injected fuel is larger, the pre-mixed air is formed.  FIG. 11B  shows an example of stratified combustion for lean-burn combustion. When the fuel injection is completed near the top dead center in the compression stroke, for example, before 40 degree, the fuel spray of high speed component comes at first after delay in transportation for the position of the ignition plug, and then, the fuel spray of low speed component is initiated. As described above, as the high speed component is unaffected by the air flow inside the combustion chamber, stable gaseous mixture can be established near the ignition plug. It is preferable to ignite the gaseous mixture when the high speed component reaches the ignition plug. 
   The fuel injection operation is described in  FIG. 12  in relationship to the engine operation. In FIG.  12 ( a ), the fuel spray of high speed component is injected from the fuel injection valve  1  toward the piston cavity. The injected fuel collided with the piston cavity and evaporated blows up to the ignition plug due to the energy of the fuel spray itself and the air flow inside the combustion chamber. (FIG.  12 ( a )) After that, while the air spray of slow speed component is diffused inside the combustion chamber, the fuel spray of high speed component is ignited, and then, the flame kernel so formed is propagated to the gaseous mixture formed with the fuel spray of slow speed component as well as the flame kernel is diffused due to the fuel spray and the air flow. 
     FIG. 13  shows an example of the relationship between the spray. amount for low speed component and the stability of combustion and the concentration of smoke. As the spray amount of low speed component increases, the stability of combustion increases. However, in case that the spray amount of low speed component is too excess, the disposition of fuel onto the piston top surface increases and thus, the amount of smoke increase as well as the stability of combustion decreases. In this example, as the overall spray amount is about 15 mm 3 /pulse, if 50% of the overall spray amount is occupied by the fuel spray with narrow spray angle and high speed, the amount of smoke increases. In this condition that the fuel pressure is 10 MPa, the average speed of the fuel spray of high speed component is about 12 m/s under ambient pressure 0.3 MPa, and the average speed of the fuel spray of low speed component is about 6 m/s. In considering the diffusion of the fuel spray inside the combustion chamber, the spray angle is preferably between 60 degree and 90 degree for low speed component, and between 20 degree and 50 degree for high speed component. 
     FIGS. 14A and 14B , the combustion stability (fluctuation in the average effective pressure or engine torque) and the smoke discharge amount is shown in responsive to parameters of the fuel injection timing and the ignition timing. In this example, it is understood that the combustion is stable if the ignition timing is set to be about 30 degree after the fuel injection timing. The duration time for keeping the gaseous mixture of fuel and air is longer and the utilization ratio of air becomes higher by making earlier the fuel injection timing, and consequently, the amount of discharged smoke decreases. Therefore, the fuel injection timing and the ignition timing for optimizing the combustion stability can be selected so that the amount of discharged smoke may not increase. 
     FIG. 15  shows an example that the fuel is injected from the top of the combustion chamber and the injected fuel is ignited sideways. The high speed component of the fuel spray collides with the top surface of the piston, and by drifting the evaporated fuel toward the neighboring area of the ignition plug by the air flow marked with an arrow as well as diffusing the fuel spray of slow speed component inside the combustion chamber, the occurrence of smoke can be prevented. In this example, as the high speed component of the fuel spray is certainly made to be collided with the piston and evaporated, the combustible gaseous mixture can be stably supplied toward the ignition plug by the air flow, for example, tumble flow. 
   As the fifth embodiment of the fuel guide  23  shown in  FIG. 23 , by making an area of a bypass passage  55   a  at a particular portion in a bypass passage  55  to be unequal to an area of other bypass passage  55 , a speed distribution in the nozzle is controlled to form fuel spray in a direction different from a nozzle axis. Under a condition where a mounting layout of the fuel injection valve  1  is restricted, it is advantageous to permit setting of the fuel injecting direction freely. Also, it becomes unnecessary to perform a process for bending the nozzle in a particular direction. 
     FIG. 17  shows the sixth embodiment of the fuel guide  23  of the fuel injection valve  20 . The fuel guide  23  is provided on perpendicularly intersecting imaginary lines X—X and Y—Y extending through the center of the fuel guide  23  without providing an offset in a fuel swirl aperture  34   b  to flow the fuel from the opposing fuel swirl aperture  34   b  for collision. Since the collided fuel has a speed component directed to the center direction, a filled-core fuel spray, in which the fuel spray is present even in the center, can be formed. 
     FIG. 18  shows the ninth embodiment of the fuel guide  23  of the fuel injection valve  20 . A cone-shaped fuel spray is formed by a fuel swirl groove  33   a  and the fuel guide aperture  34   b , and fuel pray is formed within the cone-shaped fuel spray by collision. By offsetting the fuel swirl groove  33   a , fuel is sprayed in swirl lo fashion, and the fuel guide  23  is provided on perpendicularly intersecting imaginary lines X—X and Y—Y extending through the center of the fuel guide  23  without providing an offset in a fuel swirl aperture  34   b ,  34   b  to flow the fuel from the opposing fuel swirl. aperture  34   b  for collision. In order to avoid excessive concentration of the fuel toward the center of fuel spray, total sectional area of the groove, to which the fuel collides can be made smaller than total sectional area of the guide groove. 
     FIG. 19  shows an embodiment, in which the valve body  21  of the fuel injection valve  1  is modified. In the shown embodiment, the valve body  21  is formed into cone-shaped configuration. By cone-shape of the valve body  21 , it makes difficult to form a cavity on the downstream side of the valve body  21  to prevent formation of hollow fuel spray. Smaller cone angle a form smaller spray angle to increase degree of filling. In the shown embodiment, with respect to the embodiment of  FIG. 7 , the valve body  21  modifies into a cone-shaped valve. In conjunction therewith, the fuel guide apertures  33   a  and  34   a  are offset for L 1  and L 2  in X direction and Y direction in the same plane. 
     FIG. 20  shows the embodiment, in which the first embodiment of the fuel guide  23  of the fuel injection valve  20  is modified into the cone-shaped configuration as shown in FIG.  12 . As shown in FIG.  20 ( a ), a gap  50  between the valve body  21  and the valve seat  25  is designed to be smaller at closer position to the nozzle  31 . As shown in FIG.  20 ( c ), when the gap  50  is set to be greater at closer position to the nozzle, expanding flow is established to easily form cavity. Once cavity is formed, a hollow portion having no fuel on the downstream side of the valve body  25  is cased to easily make the fuel spray hollow shaped configuration. When the gap defined with the valve body  25  is formed to be further contracting flow, fuel flow becomes stable and occurrence of cavity can be avoided to establish filled-core fuel spray. Restriction of formation of cavity may also be effective for stabilization of the fuel amount. Also, measuring precision can be improved. 
   According to the present invention, by forming the fuel spray having different levels of average speed and injecting the fuel spray into the combustion chamber, it will be appreciated that the stabilization of combustion and the prevention of soot generation by reducing the deposition of fuel spray onto the combustion chamber wall surface and the piston wall surface can be established together.