JP2010223143A - Fuel injection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly remove a foreign matter at the periphery of an injection hole of an injector. <P>SOLUTION: This fuel injection device has the injector 18 having a needle 34 capable of changing a valve closing speed, a detecting means 20 for detecting fuel leakage from a fuel injection hole 54 of the injector 18, and a control means 20 for increasing a valve closing speed of the needle 34 when the detecting means 20 detects the fuel leakage. When the fuel leakage is detected, a needle speed is increased when closing a valve, so that when the speed-increased needle 34 is seated on a needle body 50, the foreign matter is crushed. Thus, the fuel leakage caused by the sandwiching of the foreign matter between a tip of the needle 34 and the needle body 50 can be suppressed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel injection device for an internal combustion engine.

  2. Description of the Related Art There is known a fuel injection device that includes an injector for injecting fuel into a combustion chamber and a control unit that controls the injector. Inside the injector, a needle for opening and closing the injector is provided.

  Further, a technique is known in which an adsorption member including a magnet is disposed inside an injector, and foreign matter (metal powder) mixed in the fuel is adsorbed and removed by magnetic force (Patent Document 1).

JP 2007-32342 A

  When foreign matter is mixed in the fuel, the foreign matter may be caught between the tip of the needle and the needle body on which the needle is seated. As a result, the needle may not be seated correctly and fuel leakage may occur. In the above technique of removing the metal powder by magnetic force, the metal powder once captured may be detached by the fuel flow and may be caught between the needle and the needle body, which is insufficient to prevent fuel leakage. It was.

  The present invention has been made in view of the above problems, and in particular, a fuel injection device capable of effectively removing foreign matter sandwiched between the needle tip and the needle body and suppressing fuel leakage from the injector. The purpose is to provide.

  The fuel injection device includes: an injector provided with a needle that can change a valve closing speed; a detection unit that detects a fuel leak from a fuel injection hole of the injector; and when the detection unit detects a fuel leak, Control means for increasing the valve closing speed of the needle. According to this configuration, when a fuel leak is detected, the needle speed at the time of closing the valve is increased, so that the needle with the increased speed pulverizes the foreign matter when seated, and the crushed foreign matter is effectively removed by the fuel flow. Can be removed. As a result, it is possible to effectively suppress fuel leakage caused by foreign matter caught between the needle tip and the needle body.

  The said structure WHEREIN: The said detection means can be set as the structure which detects a fuel leak based on the output change of the combustion pressure sensor provided in the combustion chamber. According to this configuration, by using the combustion pressure sensor, fuel leakage can be detected at an early stage, so that foreign matter can be removed quickly.

  In the above configuration, a piezo element that expands and contracts according to the amount of applied charge, charge / discharge means that applies charge to the piezo element and removes charge from the piezo element, and expands and contracts the piezo element. Transmitting means for realizing opening and closing of the needle by transmitting to the needle, and the control means increases at least one of a charging speed and a discharging speed of the piezo element to increase the needle. The valve closing speed can be increased. According to this configuration, the needle speed can be easily changed by controlling the charging speed or discharging speed of the piezo element.

  In the above configuration, after the fuel leakage is detected, the control unit can increase the valve closing speed of the needle by a predetermined number of fuel injections to perform valve closing. According to this configuration, by limiting the number of times of increasing the needle speed, damage to the needle body when the needle is seated can be suppressed.

  According to the present invention, foreign matter sandwiched between the needle tip and the needle body can be effectively removed, and fuel leakage from the injector can be suppressed.

FIG. 1 is a diagram illustrating the configuration of the fuel injection device according to the first embodiment. FIG. 2 is a schematic cross-sectional view of a piezo injector. FIG. 3 is a flowchart illustrating the operation of the fuel injection device according to the first embodiment. FIG. 4 is a control circuit diagram of the piezo injector. FIG. 5 is a timing chart illustrating the operation of the fuel injection device according to the first embodiment.

  Embodiments according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration of a fuel injection device 100 according to the first embodiment. The fuel tank 10 stores fuel (for example, light oil) used in the internal combustion engine. The high-pressure pump 12 pumps fuel from the fuel tank 10 and supplies it to the common rail 14 in a high-pressure state. The common rail 14 stores the fuel supplied from the high-pressure pump 12 in a high-pressure state, and supplies the fuel to the piezo injector 18 through the high-pressure fuel passage 16. A part of the fuel stored in the common rail 14 is returned to the fuel tank 10 through the return passage 19.

  The piezo injector 18 injects fuel into the combustion chamber 22 based on a drive signal output from an ECU 20 (Engine Control Unit) via an EDU 21 (Electronic Driving Unit). The combustion pressure in the combustion chamber 22 is measured by a CPS sensor 24 (CPS: Constriction Pressure Sensor) that is a combustion pressure sensor, and is output to the ECU 20. The fuel that has not been used for the injection is returned to the fuel tank 10 by a return passage 19 connected to the piezo injector 18.

  The ECU 20 includes a microcomputer and a memory. In this embodiment, the ECU 20 functions as detection means for detecting fuel leakage from the fuel injection hole of the injector and control means for increasing the valve closing speed of the needle 34 when the fuel leakage is detected.

  FIG. 2 is a schematic cross-sectional view of the piezo injector 18 of FIG. The piezo injector 18 includes a piezo stack 30 as a piezo element, a piston 32, and a needle 34. Further, the piezo injector 18 is provided with a high-pressure fuel passage 36, a return passage 38, and an oil tight chamber 40 as fuel passages. A fuel chamber 42 is provided at the distal end portion of the needle 34 and a back pressure chamber 44 is provided at the proximal end portion, and fuel is supplied from the high pressure fuel passage 36 respectively. The horizontal section of the central portion 34a of the needle 34 has a larger diameter than the other portions, and the distal end side sandwiching the central portion 34a of the needle 34 is connected to the oil tight chamber 40 and the proximal end side is connected to the return passage 38.

  The EDU 21 is connected between the ECU 20 and the piezo stack 30 and functions as charge / discharge means for applying charge to the piezo stack 30 and removing charge from the piezo stack 30. The piezo stack 30 expands when the amount of stored charge increases and contracts when it decreases. The expansion and contraction of the piezo stack 30 is transmitted to the center portion 34a of the needle by the piston 32 functioning as a transmission means and the fuel in the oil-tight chamber 40.

  The operation of the piezo injector 18 will be described with reference to FIG. In the injection stop state, the push-down force due to the rail pressure acting on the proximal end portion of the needle 34 and the spring force are larger than the push-up force due to the pressure acting on the distal end portion of the needle, and the high pressure fuel is at the distal end portion of the needle 34. It is sealed. When an electric charge is applied from the EDU 21 to the piezo stack 30 according to a command from the ECU 20, the piezo element expands and the piston 32 is pushed down. When the piston 32 is pushed down, the check ball 52 delayed in operation due to inertia closes the passage 53 between the return passage 38 and the oil tight chamber 40, and the oil tight chamber 40 becomes a closed space.

  When the piezo stack 30 further expands, the fuel in the oil-tight chamber 40 is compressed, and the fuel whose pressure has increased tends to lift the needle 34 from the distal end side to the proximal end side. When the pressure in the oil-tight chamber 40 exceeds a certain level, the pressing force acting on the proximal end portion of the needle 34 (pressing force due to the rail pressure of the back pressure chamber 44 + spring force) acts on the central portion and the distal end portion of the needle. The pushing force (the pushing force caused by the rail pressure in the fuel chamber 42 + the pushing force caused by the rail pressure in the oil tight chamber 40) increases, and the injection hole 54 opens. Even after the injection hole 54 is opened, the pressure in the oil tight chamber rises while the piezo stack 30 continues to expand, so that the valve opening speed of the needle 34 increases.

  The speed at which the pressure in the oil-tight chamber 40 increases is determined by the speed at which charges are applied to the piezoelectric stack 30. Therefore, in the fuel injection device 100 of the present embodiment, the valve opening speed of the needle can be changed by changing the charge application speed to the piezo stack 30.

  The nozzle is closed by removing the electric charge from the piezo stack 30. As the electric charge is removed, the piezo stack 30 contracts, and the piston 32 is pushed up to increase the volume of the oil tight chamber 40. As a result, the pressure in the oil-tight chamber 40 is reduced and the force for pushing up the needle 34 is also lowered, so that the force for pushing down the needle 34 is relatively increased and the needle 34 is pressed against the needle body 50. Thereby, the fuel injection is completed. Here again, the valve closing speed of the needle 34 can be changed by changing the charge removal rate from the piezo stack 30 in the same manner as when the needle 34 is raised.

  In the injector 18 described above, high-pressure fuel is injected from the injection hole 54 when the needle 34 is raised. Here, if foreign matter such as metal powder is mixed in the fuel, the foreign matter may be caught between the tip of the needle 34 and the needle body 50. As a result, the needle 34 may not be properly seated on the needle body 50, the high-pressure fuel seal may be insufficient, and fuel leakage may occur.

  The fuel injection device according to the present embodiment solves such a problem, effectively removes the foreign matter sandwiched between the tip of the needle 34 and the needle body 50, and suppresses fuel leakage from the injector 18. It is intended.

  FIG. 3 is a flowchart showing the operation of the fuel injection device 100 when removing foreign matter. First, the ECU 20 detects a fuel leak from the injection hole 54 of the injector 18 (step S10). In this embodiment, the ECU 20 determines the presence or absence of fuel leakage based on the output signal from the CPS sensor 24 provided in the combustion chamber 22. Specifically, when fuel leakage occurs, an abnormal increase in combustion pressure occurs in the combustion chamber 22. Accordingly, the pressure in the combustion chamber 22 is measured by the CPS sensor 24, and when the sensor output exceeds a predetermined threshold (for example, the maximum pressure during normal combustion), it is determined that the fuel leaks, thereby detecting the fuel leak. It can be performed.

  When fuel leakage is detected, the ECU 20 performs control to increase the valve closing speed of the needle 34 when the injector 18 is closed (step S12). As a result, the needle 34 is seated on the needle body 50 at a higher speed than normal, and if foreign matter is attached, it is crushed by impact. Since the crushed foreign matter is discharged to the outside along with the fuel flow at the time of fuel injection, fuel leakage is eliminated. Thereafter, the fuel leakage is again detected by the CPS sensor 24 (step S10), and the piezo injector 18 is closed at a higher needle speed than normal until the fuel leakage is eliminated.

  FIG. 4 is a control circuit of the piezo injector 18 according to the present embodiment. A capacitor 60 and a resistor 62 are connected in parallel to the piezo injector 18. The resistor 62 is for consuming the electric charge accumulated in the piezo injector 18, and a capacitor can be used instead. A switch SW1 is connected in series between the capacitor 60 and the piezo injector 18, and a switch SW2 is connected in series between the resistor 62 and the piezo injector 18, and opens and closes according to commands from the ECU 20. The capacitor 60 stores an electric charge to be added to the piezo injector 18 and is previously boosted to a predetermined voltage by a boosting mechanism (not shown) in the EDU 21. As illustrated, the capacitor 60, the resistor 62, and the two switches SW1 and SW2 are part of the EDU 21. The capacitor 60 and the switch SW1 function as charging means for the piezo ejector 18, and the resistor 62 and the switch SW2 function as discharging means.

  FIG. 5 is a timing chart showing the operation of the control circuit of FIG. 4 during fuel injection. The chart at the normal time is indicated by a solid line, and the chart at the time when the needle speed is increased in Step S12 in FIG. First, when the energization command from the ECU 20 is turned ON, the switch SW1 on the capacitor 60 side where the electric charge is accumulated is connected, and the switch SW2 is opened. As a result, a current flows from the capacitor 60 to the piezo injector 18 and the voltage of the piezo injector 18 rises. If the switch SW1 is left connected, the current value becomes excessive, so that the switch SW1 is disconnected for T1off time after T1on time. Thereafter, until the voltage of the piezo injector 18 reaches a predetermined value (a preset maximum voltage), the switch SW1 repeats connection for the T1 on time and disconnection for the T1 off time. As the voltage of the piezo injector 18 increases, the needle 34 rises and the rising speed continues to increase.

  When the voltage of the piezo ejector 18 reaches a predetermined value, the switch SW1 is maintained in an open state, and the voltage of the piezo injector 18 is maintained at a constant value. For a while after charging of the piezo injector 18 is stopped, the pressure of the oil-tight chamber 40 continues to be higher than the back pressure, so the needle 34 continues to rise. When the pressure in the oil-tight chamber 40 becomes equal to the back pressure, the needle speed becomes zero and the needle 34 stops rising.

  When the energization command from the ECU 20 is turned off, the switch SW2 on the resistor 62 side is connected for a predetermined time T2on. Thereby, the electric charge stored in the piezo injector 18 is consumed in the resistor 62, and the voltage of the piezo injector 18 drops. Also in this case, the switch SW2 is disconnected for T2off time after T2on time so that the current does not become excessive. Thereafter, until the voltage of the piezo injector 18 returns to the initial value, the switch SW1 repeats connection for T2 on time and disconnection for T2 off time. The needle 34 begins to descend as the voltage of the piezo injector 18 drops, and is seated on the needle body 50 and stops. The needle speed increases greatly at the start of the descent and then gradually decreases and becomes zero as the needle is seated.

  Comparing charts at normal time and high-speed valve closing, the connection time (T2on: B) of the switch SW2 when the needle descends at high-speed valve closing is longer than that at normal time (T2on: A) (A < B). As a result, the charge removal rate from the piezo injector 18 at the time of high-speed valve closing can be increased compared to the normal time. As a result, the needle speed at the time of high-speed valve closing can be increased compared to the normal time.

  As described above, according to the fuel injection device 100 according to this embodiment, when the ECU 20 detects a fuel leak from the injection hole 54 of the injector, the valve closing speed of the needle 34 is increased. Thereby, the foreign material contained in the fuel can be crushed and removed by the impact when the needle is seated. As a result, foreign matter sandwiched between the tip of the needle 34 and the needle body 50 can be effectively removed, and fuel leakage from the injector 18 can be suppressed.

  In a conventional fuel injection device, the valve closing speed of the needle is limited in order to reduce fatigue damage at the tip of the needle and noise during seating. Therefore, it has been difficult to obtain a valve closing speed necessary to destroy the foreign matter. Further, in the injector in which the needle speed is determined in advance by the hydraulic circuit, the needle speed cannot be changed. As in the fuel injection device 100 of the present embodiment, the valve closing speed is increased only when fuel leakage is detected, thereby effectively removing foreign matter while suppressing damage to the needle 34 and the needle body 50. Can do.

  In this embodiment, the ECU 20 detects fuel leakage based on the output of the CPS sensor 24 provided in the combustion chamber 22. In the conventional fuel leak logic, several cycles may be required to avoid a determination error. However, since the fuel leak can be detected at an early stage by using the CPS sensor 24, the foreign matter is quickly removed. be able to.

  Further, in this embodiment, a direct-acting piezo injector 18 is employed as the injector, and the ECU 20 increases the discharge speed from the piezo stack 30, thereby increasing the contraction speed of the piezo stack 30 and the needle 34. The valve closing speed is increased. Thereby, the needle speed can be easily changed. In contrast to the piezoelectric injector shown in FIG. 2, a piezoelectric injector may be opened by contracting (discharging) the piezo stack and closing by expanding (charging). In such a piezo injector, a circuit equivalent to the control circuit shown in FIG. 4 is used, and charging and discharging may be reversed in the current control of the piezo injector shown in FIG. Also in this case, at the time of charging the piezo stack (when the valve is closed), it is possible to increase the charging speed and increase the valve closing speed by increasing the time to turn on the capacitor (charging means) side switch. it can. In this way, any type of injector may be used as long as the valve closing speed of the needle can be changed.

  Further, as described with reference to FIG. 3, it is preferable to detect the fuel leakage (step S10) every time the control for increasing the needle speed at the time of valve closing (step S12) is performed. When 24 is not used, another method may be used. For example, when several cycles are required to detect a fuel leak as in the prior art, the valve may be closed by increasing the needle speed by a predetermined number of injections after the fuel leak is detected. Thereby, even if it takes a certain amount of time to detect the fuel leakage, the foreign matter can be removed quickly. Moreover, damage to the needle body 50 can be suppressed by limiting the valve closing operation in a state where the needle speed is increased to a certain number of times.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

18 Piezo injector 20 ECU
30 Piezo stack 34 Needle 50 Needle body 54 Injection hole

Claims (4)

An injector with a needle whose valve closing speed can be changed;
Detecting means for detecting fuel leakage from the fuel injection hole of the injector;
Control means for increasing the valve closing speed of the needle when the detection means detects fuel leakage;
A fuel injection device comprising:   2. The fuel injection device according to claim 1, wherein the detection means detects a fuel leak based on an output of a combustion pressure sensor provided in the combustion chamber. A piezo element that expands and contracts according to the amount of charge applied;
Charge / discharge means for applying charge to the piezo element and removing charge from the piezo element;
A transmission means for realizing the opening and closing of the needle by transmitting expansion and contraction of the piezo element to the needle;
Have
3. The fuel injection device according to claim 1, wherein the control unit increases the valve closing speed of the needle by increasing at least one of a charging speed and a discharging speed of the piezo element. 4.   The said control means increases the valve closing speed of the said needle by the predetermined frequency | count of fuel injection after a fuel leak is detected, and performs valve closing. The fuel injection device described.

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