JP2006214317A - Fuel injection valve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make fuel hard to leak from a pressure chamber to a back pressure chamber formed by the end surface of a large-diameter proximal part of a nozzle valve element. <P>SOLUTION: A fuel injection valve raises fuel pressure in the pressure chamber 7 formed by a stepped surface of the large-diameter proximal part 6c of the nozzle valve element 6 more than injection fuel pressure by displacing a piston 9 with an actuator 11, pushes up the nozzle valve element 6 and brings an injection fuel pressure passage 5 and a nozzle 3 in communication. The back pressure chamber 8 formed by the end surface of the large-diameter proximal part is communicating with the injection fuel pressure passage 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel injection valve.

  In particular, in an internal combustion engine in which fuel is directly injected into a cylinder, it is desired to increase the fuel injection pressure of the fuel injection valve to promote atomization of the spray. In order to increase the fuel injection pressure, it has been proposed to drive the injection hole valve body using an electrostrictive actuator having a large driving force (see, for example, Patent Document 1).

  In the above-described fuel injection valve, the injection hole valve element is slidable in the axial direction within the fuel injection valve body, and a tip portion that can block communication between the injection fuel pressure passage and the injection hole; A large-diameter base that is located on the opposite side of the tip and has a larger diameter than the tip. An urging force in the valve closing direction by the atmospheric pressure and the valve closing spring acts on the end face of the large diameter base of the nozzle hole valve body. On the other hand, the injected fuel pressure acts on the valve hole for the injection hole in the valve opening direction. The valve closing direction force due to the valve closing spring and atmospheric pressure is set to be larger than the valve opening direction force due to the injected fuel pressure, and the injection hole valve element is closed.

  The ring-shaped pressure chamber formed by the stepped surface of the large-diameter base of the nozzle hole valve body communicates with the piston chamber formed by the tip surface of the piston displaced by the electrostrictive actuator. When the nozzle hole for the injection hole is closed, the pressure chamber and the piston chamber are set to the injected fuel pressure.

  When the electrostrictive actuator is extended by applying a voltage, the piston is displaced and the volume of the piston chamber is reduced, so that the fuel pressure in the piston chamber and the pressure chamber is made higher than the injected fuel pressure. When the valve opening direction force acting on the valve body increases and exceeds the valve closing direction force due to the valve closing spring and atmospheric pressure, the nozzle hole valve body is opened, that is, the nozzle hole valve body is pushed up. As a result, the seal portion at the tip is separated from the seat portion of the fuel injection valve body, and fuel injection is started.

  When the electrostrictive actuator is contracted by stopping the voltage application, the piston is returned to the initial position by the urging force of a spring or the like, and the volume of the piston chamber increases, so that the fuel pressure in the piston chamber and the pressure chamber decreases. Thus, when the valve opening direction force acting on the nozzle hole valve body decreases and falls below the valve closing direction force due to the valve closing spring and atmospheric pressure, the nozzle hole valve body is closed, that is, the nozzle hole The valve body is pushed down, the seal part at the tip of the injection hole valve element comes into contact with the seat part of the fuel injection valve body, the communication between the injection fuel pressure passage and the injection hole is cut off, and the fuel injection stops Is done.

Japanese Patent Laid-Open No. 11-200981 JP-T-2004-513278

  In the above-described fuel injection valve, a back pressure chamber is formed by the end face of the large diameter base portion of the nozzle hole valve body. Generally, the valve closing spring is disposed in the back pressure chamber. This back pressure chamber communicates with the fuel tank and is filled with fuel at atmospheric pressure.

  The back pressure chamber and the pressure chamber are separated by the large-diameter base of the nozzle hole, but the pressure chamber in which the injected fuel pressure and higher fuel pressure acts and the back pressure in which only atmospheric pressure acts The differential pressure between the pressure chamber and the chamber is large, and fuel leakage from the pressure chamber to the back pressure chamber is likely to occur along the large-diameter base sliding surface. When fuel leakage occurs, the amount of work of the high-pressure pump increases accordingly, leading to an increase in size of the high-pressure pump and deterioration of fuel consumption. In addition, when the pressurized fuel is released to atmospheric pressure, heat is generated, so that the leaked fuel becomes high temperature, and when it is returned to the fuel tank, the generation of vapor or the deterioration of the fuel accompanying the increase in the fuel tank temperature occurs. There is also a fear. Furthermore, if a large fuel leak occurs, the fuel pressure in the pressure chamber cannot be maintained high, and the valve opening for the nozzle hole becomes unstable.

  Accordingly, an object of the present invention is to increase the fuel pressure in the pressure chamber formed by the step surface of the large-diameter base portion of the injection hole valve body by displacing the piston by the actuator to increase the injection hole valve body. In the fuel injection valve to be opened, it is difficult to cause fuel leakage from the pressure chamber to the back pressure chamber formed by the large-diameter base end face of the nozzle hole.

  According to a first aspect of the present invention, there is provided a fuel injection valve according to a first aspect of the present invention, wherein a front end portion capable of interrupting communication between an injected fuel pressure passage and an injection hole and a large diameter positioned opposite to the front end portion and having a larger diameter than the front end side A fuel pressure in a pressure chamber formed by a step surface of the large-diameter base by displacing a piston by an actuator, having an injection hole valve body that has a base and slides in the axial direction in the fuel injection valve body In the fuel injection valve that raises the injection valve pressure and pushes up the injection hole valve body to connect the injection fuel pressure passage and the injection hole, the back pressure chamber formed by the end surface of the large-diameter base is It is characterized by communicating with the injected fuel pressure passage.

  According to a second aspect of the present invention, there is provided the fuel injection valve according to the first aspect, wherein the piston chamber formed by the front end surface of the piston communicates with the pressure chamber, and the piston is An intermediate chamber having a small-diameter base portion smaller in diameter than the distal end side and having the small-diameter base portion provided between the actuator chamber in which the actuator is located and the piston chamber is provided, and the intermediate chamber communicates with the injected fuel pressure passage. It is characterized by that.

  According to the fuel injection valve of the first aspect of the present invention, when the injection hole valve body is opened, the fuel pressure in the pressure chamber is higher than the injection fuel pressure. The back pressure chamber separated through the large-diameter base is connected to the injected fuel pressure passage to apply the injected fuel pressure, so that the back pressure chamber is compared with the case where atmospheric pressure is applied to the back pressure chamber. The pressure difference between the chamber and the pressure chamber is reduced, and it is possible to make it difficult for fuel leakage from the pressure chamber to the back pressure chamber.

  When the injection hole valve body is lifted, the fuel pressure in the piston chamber communicating with the pressure chamber is made higher than the injected fuel pressure. If such a piston chamber is adjacent to a low-pressure actuator chamber such as atmospheric pressure via a piston, fuel leakage from the piston chamber to the actuator chamber is likely to occur. However, according to the fuel injection valve according to claim 2 of the present invention, the intermediate chamber communicating with the injected fuel pressure passage is provided between the actuator chamber and the piston chamber. Therefore, it is adjacent to the intermediate chamber that has only the injected fuel pressure through the small diameter base of the piston, rather than the piston chamber where the injected fuel pressure is exceeded, and the differential pressure with the actuator chamber is reduced, causing fuel leakage to the actuator chamber. It can be made difficult to occur. Further, the differential pressure between the piston chamber and the intermediate chamber is small, and fuel leakage from the piston chamber to the intermediate chamber hardly occurs.

  FIG. 1 is a sectional view showing a fuel injection valve according to the present invention. This fuel injection valve, for example, injects high-pressure fuel pressurized in a pressure accumulation chamber common to each cylinder in order to inject fuel directly into a cylinder of a diesel engine or a cylinder-injection spark ignition internal combustion engine It is. Of course, this fuel injection valve can also be used to inject fuel, for example, into an intake port other than in the cylinder. Reference numeral 1 denotes a main body of the fuel injection valve.

  A sac chamber 2 is formed at the tip of the main body 1, and a plurality of nozzle holes 3 are formed in communication with the sac chamber 2. A frustoconical surface 4 is formed immediately upstream of the sac chamber 2, and an injected fuel pressure passage 5 is formed immediately upstream of the frustoconical surface 4.

  Reference numeral 6 denotes a nozzle hole, which has a small-diameter tip 6a, an intermediate-diameter intermediate 6b, and a large-diameter base 6c. The diameter of the base portion 6c is larger than the distal end side (the distal end portion 6a and the intermediate portion 6b), and the diameter of the intermediate portion 6b is larger than the distal end side (the distal end portion 6a). It is good also as the same diameter. The tip portion 6a is located in the injected fuel pressure passage 5, two tapered surfaces are formed at the tip, and a corner portion between the two tapered surfaces becomes a seal portion. The communication between the injection fuel pressure passage 5 and the injection hole 3 is blocked by pushing down the injection hole valve body 6 and bringing the seal part into contact with the seat part on the frustoconical surface 4.

  The outer peripheral surface of the intermediate portion 6b of the injection hole valve body 6 is a sliding surface, and the intermediate portion 6b separates the injected fuel pressure passage 5 and the ring-shaped pressure chamber 7 formed by the step surface of the base portion 6c. The Further, the outer peripheral surface of the base portion 6c of the nozzle hole valve body 6 is also a sliding surface, and the pressure chamber 7 and the back pressure chamber 8 formed by the end surface of the base portion 6c are separated by the base portion 6c. The back pressure chamber 8 communicates with the injected fuel pressure passage 5.

  9 is a piston, and the piston chamber 10 and the pressure chamber 7 formed by the front end surface of the piston 9 communicate with each other. The piston chamber 10 also communicates with the injected fuel pressure passage 5 via a check valve 15 that allows only the fuel flow to the piston chamber 10. An electrostrictive actuator 11 is housed in the actuator chamber 12. The piston 9 has a base portion 9 a having a smaller diameter than the distal end side, and the base portion 9 a enters the actuator chamber 12 and contacts the electrostrictive actuator 11. An intermediate chamber 13 is formed around the base 9 a of the piston 9. The intermediate chamber 13 is in communication with the injected fuel pressure passage 5. A part of the base portion 9a of the piston 9 is a sliding surface with respect to the partition wall through-hole of the actuator chamber 12, and a circumferential groove is formed in the sliding surface, and a seal ring 17 is disposed in the groove. ing.

  In the actuator chamber 12, a spring 14 for urging the base portion 9a of the piston 9 toward the electrostrictive actuator 11 side is disposed. As a result, the piston 9 follows the expansion and contraction of the electrostrictive actuator 11. A valve closing spring 16 is disposed in the back pressure chamber 8, and the injection hole valve element 6 is always urged in the valve closing direction by the valve closing spring 16.

  Thus, a constant valve closing direction force generated by the valve closing spring 16 and the injected fuel pressure in the back pressure chamber 8 acts on the nozzle hole valve body 6. When the electrostrictive actuator 11 is extended by applying a voltage, the piston 9 is displaced to reduce the volume of the piston chamber 10, and the pressure in the pressure chamber 7 communicating with the piston chamber 10 and the piston chamber 10 is the injected fuel pressure. Fuel pressure is increased. Accordingly, the valve opening direction force acting on the nozzle hole valve body 6 by the fuel pressure in the pressure chamber 7 is increased, and the valve opening direction force acting on the nozzle hole valve body 6 by the fuel pressure in the injection fuel pressure passage 5 is increased. When the force in the valve closing direction is exceeded, the injection hole valve element 6 is pushed up, and the injected fuel pressure passage 5 and the injection hole 3 communicate with each other by separating the tip seal portion from the frustoconical surface 4. Then, fuel injection is started. At the moment when the seal part at the tip of the nozzle hole 6 is separated from the frustoconical surface 4, the injected fuel pressure also acts on the inner side of the seal part of the nozzle hole, and the valve opening direction force accordingly. Becomes higher.

  On the other hand, when the voltage application is stopped and the electrostrictive actuator 11 is contracted, the piston 9 is returned to the initial position by the action of the spring 14 to increase the volume of the piston chamber 10 and the fuel in the piston chamber 10 and the pressure chamber 7. Reduce pressure. At this time, since the piston chamber 10 communicates with the injected fuel pressure passage 5 via the check valve 15, the fuel pressure in the piston chamber 10 and the pressure chamber 7 does not drop below the injected fuel pressure.

  Thus, the valve opening direction force acting on the nozzle hole valve body 6 due to the fuel pressure in the pressure chamber 7 decreases, and the valve opening direction force acting on the nozzle hole valve body 6 due to the fuel pressure in the injection fuel pressure passage 5. When the force in the valve closing direction is reduced, the injection hole valve body 6 is pushed down, the tip seal portion comes into contact with the frustoconical surface 4, and the injection fuel pressure passage 5 and the injection hole 3 communicate with each other. It is shut off and fuel injection is stopped. At the moment when the seal portion at the tip of the injection hole valve body 6 comes into contact with the frustoconical surface 4, only a pressure lower than the injected fuel pressure acts on the inner side of the seal portion of the injection hole valve body. The valve opening direction force is reduced.

  In the fuel injection valve configured as described above, the fuel pressure in the back pressure chamber 8 is always injected with respect to the pressure chamber 7 which is higher than the injected fuel pressure when the injection hole valve body 6 is opened. Since the fuel pressure is set, the differential pressure between the pressure chamber 7 and the back pressure chamber 8 becomes smaller than when the back pressure chamber 8 is set to the atmospheric pressure. It is possible to make it difficult for fuel leakage to 8 to occur. If a large fuel leak occurs, the inside of the pressure chamber 7 cannot be maintained at a pressure higher than the injected fuel pressure, and the opening of the injection hole valve body 6 becomes unstable. Can do.

  When the back pressure chamber 8 is at atmospheric pressure, the back pressure material 8 is communicated with a fuel tank (not shown). The back pressure chamber 8 is filled with fuel leaking from the pressure chamber 7, and the leaked fuel into the back pressure chamber 8 is hot.

  Thus, when the fuel in the back pressure chamber 8 is returned to the fuel tank, the fuel temperature in the fuel tank increases, and the fuel supplied from the fuel tank to the pressure accumulating chamber is likely to become vapor in the pressure accumulating chamber. In this fuel injection valve, the fuel in the back pressure chamber 8 is not discharged to the fuel tank, and such a problem does not occur.

  In the fuel injection valve, an intermediate chamber 13 is provided between the piston chamber 10 and the actuator chamber 12. If the piston chamber 10 and the actuator chamber 12 are made adjacent to each other via the sliding surface of the piston 9 without providing such an intermediate chamber 13, the fuel pressure in the piston chamber 10 becomes equal to or higher than the injected fuel pressure. Moreover, a large differential pressure is generated between the actuator chamber 12 and the atmospheric pressure, and fuel leakage from the piston chamber 10 to the actuator chamber 12 is likely to occur. If a large fuel leak occurs, the inside of the piston chamber 10 cannot be maintained at a pressure higher than the injected fuel pressure, and the opening of the injection hole valve element 6 becomes unstable.

  In this fuel injection valve, since the intermediate chamber 13 adjacent to the piston chamber 10 through the sliding surface of the piston 9 is set to the injected fuel pressure, the differential pressure between the piston chamber 10 and the piston chamber 10 is small. The fuel leakage from 10 to the intermediate chamber 13 hardly occurs, and the problem that the valve opening of the nozzle hole 6 becomes unstable can be sufficiently suppressed. The intermediate chamber 13 and the actuator chamber 12 are adjacent to each other through the sliding surface of the small-diameter base portion 9a of the piston 9, but the fuel pressure in the intermediate chamber 13 does not become higher than the injected fuel pressure. Compared with the case where the piston chamber 10 that is equal to or higher than the pressure is adjacent to the actuator chamber 12, the differential pressure with the actuator chamber 12 becomes smaller, and it is possible to make it difficult for fuel leakage to occur. Further, in this fuel injection valve, the seal member 17 is disposed on the sliding surface of the small-diameter base 9a of the piston 9, thereby making it difficult for fuel leakage to occur.

  The actuator chamber 12 communicates with the fuel tank. If fuel leaks from the intermediate chamber 13 to the actuator chamber 12, the leaked fuel is returned to the fuel tank. As a result, the actuator chamber 12 is not filled with the fuel of the injected fuel pressure, and the electrostrictive actuator 11 is not damaged. The fuel injection valve uses the electrostrictive actuator 11 as an actuator. However, the electrostrictive actuator 11 can be any actuator that can instantaneously displace the piston 9 to increase the fuel pressure in the piston chamber 10 and the pressure chamber 7. Can be used instead.

It is sectional drawing of the fuel injection valve by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main body 3 Injection hole 5 Injection fuel pressure passage 6 Valve body for injection hole 7 Pressure chamber 8 Back pressure chamber 9 Piston 10 Piston chamber 11 Electrostrictive actuator 12 Actuator chamber 13 Intermediate chamber

Claims (2)

  A tip portion capable of blocking communication between the injected fuel pressure passage and the injection hole, and a large-diameter base portion located on the opposite side of the tip portion and having a larger diameter than the tip side, and the inside of the fuel injection valve body in the axial direction A sliding nozzle hole body is provided, and the piston is displaced by an actuator to raise the fuel pressure in the pressure chamber formed by the stepped surface of the large-diameter base from the injected fuel pressure. In the fuel injection valve that pushes up and communicates the injected fuel pressure passage with the injection hole, a back pressure chamber formed by the end face of the large-diameter base is in communication with the injected fuel pressure passage. Fuel injection valve.   The piston chamber formed by the front end surface of the piston communicates with the pressure chamber, the piston has a small diameter base portion having a smaller diameter than the front end side, and between the actuator chamber where the actuator is located and the piston chamber, The fuel injection valve according to claim 1, wherein an intermediate chamber in which the small-diameter base is located is provided, and the intermediate chamber communicates with the injected fuel pressure passage.

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