JP6358271B2 - Fuel injection device for internal combustion engine - Google Patents

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 valve including a pressure increasing device that increases a fuel injection pressure with a constant pressure increasing ratio. In this fuel injection valve, the fuel injection pressure can be set to either a reference pressure or a pressure obtained by multiplying the reference pressure by a pressure increase ratio (hereinafter also referred to as a reference increase pressure). Here, it is known that the fuel injection pressure at the start of fuel injection is set to a pressure between the reference pressure and the reference increase pressure by starting fuel injection in the middle of pressure increase (for example, Patent Documents). 1).

JP 2004-044494 A JP 2010-072122 A JP 2009-030490 A JP 2013-256916 A

  In the conventional technology, the fuel injection pressure at the start of fuel injection can be adjusted, but the fuel pressure continues until the fuel injection pressure reaches the reference increased pressure after the fuel injection starts. Pressure changes. For this reason, the fuel injection pressure during fuel injection cannot be maintained at an arbitrary pressure between the reference pressure and the reference increase pressure. If the fuel injection pressure cannot be adjusted to an appropriate value, combustion noise or smoke may occur. On the other hand, if the fuel injection pressure before fuel injection is maintained at a predetermined value, fluctuations in the fuel injection pressure during fuel injection can be suppressed.

  The present invention has been made in view of the above-described problems, and an object thereof is to maintain the fuel injection pressure at an arbitrary pressure between the reference pressure and the reference increase pressure.

  In order to solve the above problems, a fuel injection device for an internal combustion engine according to the present invention supplies a fuel injection valve that injects fuel by opening an injection hole by movement of a needle, and supplies fuel at a reference pressure to the fuel injection valve. A high pressure fuel reservoir, a fuel passage leading from the high pressure fuel reservoir to the nozzle hole, a control chamber connected to the fuel passage, and a fuel pressure in the control chamber from a fuel pressure in the fuel passage. An opening / closing mechanism that moves the needle in the direction of opening the nozzle hole when the pressure difference between the fuel pressure in the fuel passage and the fuel pressure in the control chamber exceeds a predetermined pressure difference. A pressure increasing device that is connected to the fuel passage and increases the pressure of the fuel in the fuel passage at a constant pressure increasing ratio, and the fuel pressure in the fuel passage required when fuel is injected from the fuel injection valve Is the standard When the pressure difference is higher than the force and lower than the reference increase pressure, which is a value obtained by multiplying the reference pressure by the increase ratio, the pressure difference after operation is smaller than the predetermined pressure difference. And a control device that increases the fuel pressure in the fuel passage by the pressure increasing device after the pressure reducing device is operated.

When the pressure reducing device is not in operation, the pressure in the control chamber is equal to the pressure of the fuel in the fuel passage. In this state, the nozzle hole is closed by the needle. At this time, the force in the valve closing direction is larger than the force in the valve opening direction applied to the needle. When the pressure reducing device is activated, the pressure in the control chamber is lower than the pressure in the fuel passage, thereby reducing the force in the valve closing direction applied to the needle. When the force in the valve opening direction becomes larger than the force in the valve closing direction applied to the needle, the needle moves and the injection hole is opened, so that fuel is injected. Here, when the pressure reducing device is operated, the pressure of the fuel in the control chamber is reduced in order to reduce the force in the valve closing direction applied to the needle. This drop in fuel pressure in the control chamber can occur even before fuel is actually injected from the fuel injection valve. Since the control chamber communicates with the fuel passage, the pressure reduction of the fuel in the control chamber subsequently reduces the fuel pressure in the fuel passage. For this reason, although the fuel pressure difference temporarily occurs, it is eliminated immediately. In this way, after the fuel pressure in the control chamber is reduced, the fuel pressure in the fuel passage is also reduced so that the fuel pressure difference is eliminated, so the fuel injection pressure is reduced. Therefore, the fuel injection pressure can be made lower than the reference pressure by operating the pressure reducing device in a range where fuel is not injected from the fuel injection valve. The predetermined pressure difference can be said to be a pressure difference at which fuel injection starts. Since the pressure increasing device increases the fuel injection pressure at a constant pressure increase ratio, the fuel injection pressure after the pressure has decreased below the reference pressure can be increased at a constant pressure increase ratio. Accordingly, the fuel injection pressure after the pressure increase is lower when the pressure reducing device is operated before pressure increase than when the pressure reducing device is not operated before pressure increase. That is, the fuel injection pressure can be maintained at an arbitrary pressure that is higher than the reference pressure and lower than the reference increase pressure. Since the fuel injection can be started in a state where the pressure increase is completed before the fuel injection is started, it is possible to suppress the pressure increase during the fuel injection and the fluctuation of the fuel injection pressure. In this way, the fuel injection pressure can be adjusted to an appropriate value, so that combustion noise can be suppressed or the amount of smoke generated can be reduced.

  Further, when the pressure reducing device is operated so that the pressure difference after the operation is smaller than the predetermined pressure difference, the control device is required to perform a fuel pressure in the fuel passage during the fuel injection. Accordingly, the number of times of operating the pressure reducing device can be changed.

  When the pressure reducing device is operated in a range where fuel is not injected from the fuel injection valve, the pressure reducing device must be stopped before fuel is injected. Therefore, the amount of decrease in the fuel injection pressure per time when the pressure reducing device is operated in a range where fuel is not injected from the fuel injection valve is also limited. On the other hand, after the pressure difference of the fuel is generated by operating the pressure reducing device in a range where the fuel is not injected from the fuel injection valve, the pressure reducing device can be further operated if the pressure difference of the fuel is eliminated. Immediately after the fuel pressure difference is eliminated, the fuel injection pressure is lower than the reference pressure. At this time, the fuel injection pressure can be further reduced by operating the decompression device again. Thus, by operating the decompression device repeatedly a plurality of times, it is possible to increase the amount of decrease in the fuel injection pressure without injecting fuel. Therefore, the fuel injection pressure after the pressure increase can be adjusted in a wider range.

  Further, when the pressure reducing device is operated so that the pressure difference after the operation is smaller than the predetermined pressure difference, the control device is required to perform a fuel pressure in the fuel passage during the fuel injection. Accordingly, the period during which the decompression device is operated can be changed.

The amount of decrease in the fuel injection pressure varies depending on the length of the period in which the pressure reducing device is operated within a range where fuel is not injected from the fuel injection valve. Therefore, the amount of decrease in the fuel injection pressure can be adjusted by adjusting the length of the period during which the pressure reducing device is operated within a range in which fuel is not injected from the fuel injection valve. In this case, the longer the period during which the pressure reducing device is operated, the greater the amount of decrease in the pressure in the control chamber, and the greater the amount of decrease in the fuel injection pressure. Thus, since the amount of decrease in the fuel injection pressure can be adjusted, the fuel injection pressure after the pressure increase can also be adjusted. Furthermore, the fuel injection pressure is increased from the reference pressure to the reference increase pressure by increasing the fuel injection pressure after adjusting the number of times the pressure reduction device is operated and the period during which the pressure reduction device is operated to lower the fuel injection pressure. Can be adjusted to any pressure between.

  According to the present invention, the fuel injection pressure can be maintained at an arbitrary pressure between the reference pressure and the reference increase pressure.

It is a figure explaining schematic structure of a fuel injection valve which has a pressure increase unit. It is a time chart which showed change of various values when fuel is injected from a fuel injection valve. It is a time chart which showed transition of a command signal, an injection rate, and encircling pressure at the time of reducing pressure before pressure increase of fuel. It is the figure which showed the relationship between the fuel quantity which flows into drain piping, the pressure reduction amount, and a high pressure volume. 3 is a flowchart illustrating a flow for adjusting the fuel injection pressure according to the first embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified.

<Example>
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a schematic configuration of a fuel injection valve 10 having a pressure increasing unit 110. The fuel injection valve 10 according to the present embodiment is used for an internal combustion engine 1 mounted on a vehicle, for example. Although the internal combustion engine 1 according to this embodiment is a diesel engine, it can also be used in a gasoline engine. When the internal combustion engine 1 has a plurality of cylinders, a fuel injection valve 10 is provided in each cylinder.

  The internal combustion engine 1 is provided with a common rail 3 for storing high-pressure fuel. The common rail 3 is connected to a high-pressure fuel pump 5, and the common rail 3 stores fuel whose pressure has been increased by the high-pressure fuel pump 5. The common rail 3 is connected to a first fuel pipe 11A, a second fuel pipe 11B, and a third fuel pipe 11C that communicate with the fuel injection valve 10. In FIG. 1, the first fuel pipe 11 </ b> A, the second fuel pipe 11 </ b> B, and the third fuel pipe 11 </ b> C are shown separately. Instead, a single high-pressure pipe is connected to the common rail 3, One high-pressure pipe may be branched into three. In this embodiment, the common rail 3 corresponds to the high-pressure fuel storage part in the present invention.

  The high-pressure fuel pump 5 according to the present embodiment is, for example, a plunger type pump having a discharge amount adjusting mechanism, and boosts the fuel supplied from a fuel tank (not shown) to a predetermined pressure and supplies it to the common rail 3. The amount of fuel pumped from the high-pressure fuel pump 5 to the common rail 3 is feedback controlled by an ECU 20 described later so that the common rail pressure becomes the target pressure.

  The internal combustion engine 1 is provided with an ECU 20 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 20 is configured as a digital computer having a known configuration in which a read only memory (ROM), a random access memory (RAM), a microprocessor (CPU), and an input / output port are connected by a bidirectional bus. The ECU 20 controls the engine rotation speed and the like in addition to controlling the fuel injection timing and the fuel injection amount from the fuel injection valve 10. Therefore, the ECU 20 can also be said to be an electronic control unit for controlling the fuel injection valve 10.

  The common rail 3 is provided with a fuel pressure sensor 27 for detecting the pressure of the fuel in the common rail 3 (hereinafter referred to as common rail pressure). The fuel pressure sensor 27 is connected to the ECU 20 via electric wiring. In addition, the ECU 20 includes an accelerator opening sensor 21 that outputs an electrical signal corresponding to the amount of depression of the accelerator pedal by the driver and detects the engine load, and a crank position sensor 25 that detects the engine rotational speed via electrical wiring. Connected. Then, the output signals of these various sensors are input to the ECU 20. In this embodiment, the common rail pressure corresponds to the reference pressure in the present invention.

  The ECU 20 calculates the engine rotation speed from the frequency of the crank rotation angle pulse signal input from the crank position sensor 25, and the fuel injection valve 10 based on the accelerator opening signal input from the accelerator opening sensor 21 and the engine rotation speed. The fuel injection timing and the fuel injection amount are calculated.

  The fuel injection valve 10 is provided with a pressure increasing unit 110. The fuel injection valve 10 is provided with a nozzle 105 having an injection hole 116 formed therein. Further, the fuel injection valve 10 is provided with a needle 113 that opens and closes the injection hole 116, and a fuel reservoir 106 is formed around the needle 113 in the nozzle 105. Further, the fuel injection valve 10 receives a pressure of fuel in a control chamber 103 to be described later, and pushes the needle 113 downward in FIG. 1 (the direction in which the needle 113 moves toward the injection hole 116), and the command piston Independent of 112, a spring 112A is provided to push the needle in the valve closing direction.

  A control chamber 103 is formed adjacent to the command piston 112 in the upward direction of FIG. 1 (the direction in which the needle 113 is separated from the nozzle hole 116). The control chamber 103 is provided with an injection control valve 109 having a solenoid actuator 109A. The solenoid actuator 109A is controlled by the ECU 20. By operating the solenoid actuator 109A, the fuel in the control chamber 103 flows to the drain pipe 119A via the orifice 119. That is, operating the solenoid actuator 109A reduces the pressure in the control chamber 103. The control chamber 103 is connected to the pressure increasing path 108, the injection path 107, and the first fuel pipe 11A via the orifice 118. A check valve 117 is provided in the first fuel pipe 11A. The check valve 117 allows the fuel to flow only from the common rail 3 side to the fuel injection valve 10 side. In this embodiment, the injection passage 107 corresponds to the fuel passage in the present invention. In the present embodiment, the control chamber 103, the injection control valve 109, the orifice 118, and the orifice 119 correspond to the opening / closing device in the present invention. Furthermore, in this embodiment, the injection control valve 109 corresponds to the pressure reducing device in the present invention.

  The injection path 107 is connected to the fuel reservoir 106 of the nozzle 105. At the time of pressurized fuel injection, the fuel increased in pressure by the pressure increasing unit 110 flows through the pressure increasing path 108 and the injection path 107 and is supplied to the fuel reservoir 106. Since the fuel injection pressure is the fuel pressure in the fuel reservoir 106, the fuel pressure increased by the pressure increase unit 110 becomes the fuel injection pressure. On the other hand, during non-intensified fuel injection, fuel from the common rail 3 flows through the first fuel pipe 11 </ b> A and the injection path 107 and is supplied to the fuel reservoir 106. For this reason, the common rail pressure becomes the fuel injection pressure.

Here, the fuel pressure in the control chamber 103 is a fuel pressure applied in the direction of closing the nozzle hole 116 with respect to the needle 113, and the fuel pressure in the fuel reservoir 106 is a direction of opening the nozzle hole 116 with respect to the needle 113. This is the fuel pressure applied to. The control chamber 103 and the fuel reservoir 106 are communicated with each other via an orifice 118. For this reason, when the injection control valve 109 is closed, the fuel pressure in the control chamber 103 is substantially equal to the pressure in the injection passage 107 and the fuel reservoir 106. In this state, the needle 113 is pushed by the spring 112A and is in close contact with the sheet at the tip of the nozzle to close the nozzle hole 116.

  On the other hand, when the solenoid actuator 109A is energized and the injection control valve 109 is opened, the fuel in the control chamber 103 flows through the orifice 119 into the drain pipe 119A, and the pressure in the control chamber 103 decreases. As a result, the pressure in the control chamber 103 becomes lower than the pressure in the injection passage 107 and the fuel reservoir 106, so the needle 113 is pushed by the fuel pressure in the fuel reservoir 106, and the injection hole 116 resists the force of the spring 112A. Move away from. For this reason, the nozzle hole 116 is opened and the fuel in the fuel reservoir 106 is injected from the nozzle hole 116. Since the control chamber 103 and the fuel reservoir 106 communicate with each other via the orifice 118, when a sufficient time elapses after the injection control valve 109 is closed, the fuel pressure in the control chamber 103 and the fuel in the fuel reservoir 106 are increased. It becomes equal to pressure.

  Next, the pressure increasing unit 110 will be described. The pressure increasing unit 110 includes a pressure increasing piston 104 having a large diameter piston portion 104A and a small diameter piston portion 104B. A pressure increase control chamber 114B is provided on the small diameter piston portion 104B side of the large diameter piston portion 104A, and a common rail 3 is provided on the side opposite to the pressure increase control chamber 114B of the large diameter piston portion 104A via the second fuel pipe 11B. Communicating pressure chambers 114A are respectively formed. Further, a pressure increasing chamber 114 </ b> C communicating with the pressure increasing path 108 is formed at the end of the small diameter piston portion 104 </ b> B of the pressure increasing piston 104.

  The pressure increase unit 110 is provided with a pressure increase control valve 111. A pressure increase control valve 111 is connected to the pressure increase control chamber 114B. The pressure increase control valve 111 is a solenoid driven switching valve, and selectively connects the pressure increase control chamber 114B to the third fuel pipe 11C or the drain pipe 111A. The pressure increase control valve 111 (which may be the pressure increase unit 110) is controlled by the ECU 20.

  Since the energization of the solenoid actuator of the pressure increase control valve 111 is stopped when the pressure increase unit 110 is not operated, and the pressure increase control chamber 114B is connected to the third fuel pipe 11C via the pressure increase control valve 111, A common rail pressure acts in the pressure increase control chamber 114B. Further, since the common rail pressure acts on the pressure chamber 114A of the pressure increasing unit 110 via the second fuel pipe 11B, the pressures on both sides of the large diameter piston portion 104A of the pressure increasing piston 104 become equal.

  In this state, the pressure-increasing piston 104 is moved upward in FIG. 1 by the spring 115 that urges the large-diameter piston portion 104A toward the pressure chamber 114A side. Fuel flows from the common rail 3 through the one fuel pipe 11 </ b> A and the check valve 117. For this reason, the fuel pressure in the pressure increasing path 108 and the injection path 107 is equal to the common rail pressure. That is, when the pressure increasing unit 110 is not operated, the pressure of the fuel injected from the fuel injection valve 10 becomes the common rail pressure.

  On the other hand, when the solenoid of the pressure increase control valve 111 is energized, the pressure increase control chamber 114B is connected to the drain pipe 111A via the pressure increase control valve 111. Thereby, the fuel in the pressure increase control chamber 114B flows out from the pressure increase control valve 111 to the drain pipe 111A, and the pressure in the pressure increase control chamber 114B decreases. For this reason, the pressure increasing piston 104 is pushed by the pressure of the fuel in the pressure chamber 114A acting on the large diameter piston portion 104A, and the fuel in the pressure increasing chamber 114C is pressurized by the small diameter piston portion 104B. As a result, the fuel pressure in the pressure increasing chamber 114C becomes substantially equal to a value obtained by multiplying the common rail pressure in the pressure chamber 114A by the cross-sectional area ratio between the large diameter piston portion 104A and the small diameter piston portion 104B.

That is, when the pressure increasing unit 110 is operated, the pressure increasing chamber 114C, the pressure increasing path 108, the injection path 1
07, the pressure in the fuel reservoir 106 and the control chamber 103 is increased to a pressure that is twice the cross-sectional area ratio between the large-diameter piston portion 104A and the small-diameter piston portion 104B of the booster piston 104. Therefore, before the pressure increasing unit 110 is operated, if the pressure in the pressure increasing chamber 114C, the pressure increasing path 108, the injection path 107, the fuel reservoir 106, and the control chamber 103 is a common rail pressure, fuel injection is performed when the pressure increasing unit 110 is operated. The pressure is increased to the reference increase pressure. Hereinafter, the cross-sectional area ratio is referred to as a pressure increase ratio. The pressure increasing ratio is a constant value determined by the shape of the pressure increasing piston.

  As described above, in the fuel injection valve 10 including the pressure increasing unit 110 of the present embodiment, the fuel injection pressure is changed from low pressure (that is, common rail pressure) to high pressure (that is, common rail pressure) by switching the operation of the pressure increasing unit 110. Reference increase pressure). In the present embodiment, the pressure increasing unit 110 that increases the pressure at a constant pressure increasing ratio corresponds to the pressure increasing device in the present invention.

  In a general fuel injection device that employs the pressure increasing unit 110 having the above structure, the fuel injection pressure is set to one of a common rail pressure and a reference increased pressure that is a pressure obtained by multiplying the common rail pressure by the pressure increasing ratio. Can do. However, since the optimum value of the fuel injection pressure varies depending on the operating state of the internal combustion engine 1, the required value of the fuel injection pressure (that is, the required pressure) may be higher than the common rail pressure and lower than the reference increase pressure. obtain. That is, the required pressure may be a pressure between the common rail pressure and the reference increase pressure.

  Therefore, in this embodiment, the fuel injection pressure is adjusted to match the required pressure. Here, FIG. 2 is a time chart showing transition of various values when fuel is injected from the fuel injection valve 10. The command signal is a signal input from the ECU 20 to the solenoid actuator 109A of the fuel injection valve 10 to inject fuel. This command signal is a signal for operating the solenoid actuator 109A. The needle lift amount indicates the lift amount of the needle 113 (may be the distance between the injection hole 116 in the central axis direction of the fuel injection valve 10 and the needle 113). The injection rate is the amount of fuel injected from the fuel injection valve 10 per unit time. The fuel injection pressure is the pressure of fuel in the fuel reservoir 106 and is the pressure of fuel injected from the fuel injection valve 10.

  There is a response delay (opening delay) from when the command signal is input to when the needle lift amount starts increasing. Similarly, there is a response delay (valve closing delay) from when the input of the command signal is stopped until the needle lift amount starts to decrease. Therefore, after the command signal is input, the injection rate increases after the time corresponding to the response delay elapses. However, the fuel injection pressure decreases even during a period from when the command signal is input until the needle lift amount starts increasing, that is, during a period when the needle lift amount is 0 and fuel is not injected.

When the command signal is input, the solenoid actuator 109A is activated, and the pressure in the control chamber 103 is released to the drain pipe 119A via the orifice 119. In order to move the needle 113 in the valve opening direction due to the difference between the fuel pressure in the fuel reservoir 106 and the fuel pressure in the control chamber 103, the force in the direction of raising the needle 113 due to this pressure difference is applied by the spring 112A. It must be greater than the force in the direction of lowering the needle 113. Until a pressure difference sufficient to raise the needle 113 between the fuel reservoir 106 and the control chamber 103 (hereinafter, also referred to as a predetermined pressure difference) is generated, the pressure in the control chamber 103 decreases, but fuel injection is performed. No fuel is injected from the valve 10. The time until the predetermined pressure difference is generated corresponds to the response delay. Here, since the fuel reservoir 106 communicates with the control chamber 103 via the orifice 118, if the pressure in the control chamber 103 decreases even during the response delay period, the pressure in the fuel reservoir 106 is delayed. Also decreases. Therefore, even if the fuel is not actually injected, the fuel pressure in the fuel reservoir 106 decreases. In the present embodiment, before the fuel injection pressure is increased by the pressure increasing unit 110, the fuel injection pressure is reduced using the fuel pressure drop during the response delay period. Even when the fuel is not depressurized according to the present embodiment, the pressure in the fuel reservoir 106 decreases as the pressure in the control chamber 103 decreases during fuel injection. Therefore, the fuel is actually injected from the nozzle hole 116 after the pressure in the fuel reservoir 106 has once decreased. For this reason, even when the pressure reduction of the fuel according to the present embodiment is not performed, the period in which the pressure in the control chamber 103 is decreased in consideration of the decrease in the pressure in the fuel reservoir 106 (that is, the command signal is input). Period) has been determined.

  The pressure increasing unit 110 increases the fuel injection pressure at a predetermined pressure increasing ratio. For this reason, when the fuel injection pressure is reduced using the pressure drop of the fuel during the response delay period, the fuel injection pressure after the pressure increase is multiplied by the pressure increase ratio after the fuel injection pressure is reduced during the response delay period. It becomes the value. Therefore, when the fuel pressure is reduced, the fuel injection pressure after the pressure increase becomes lower than when the fuel pressure is not reduced. By adjusting the number of times the fuel is depressurized and the length of the period during which the fuel is depressurized, the fuel injection pressure after depressurization can be adjusted in a wide range, so the fuel injection pressure after pressure increase is also adjusted in a wide range be able to. For example, the lower the required pressure, the greater the number of times the fuel is decompressed or the longer the period during which the fuel is decompressed.

  FIG. 3 is a time chart showing changes in the command signal, the injection rate, and the fuel injection pressure when the pressure is reduced before the fuel pressure is increased. In the injection rate and the fuel injection pressure, the solid line indicates a case where pressure reduction is performed before the fuel pressure is increased, and the alternate long and short dash line indicates a case where pressure reduction is not performed before the fuel pressure is increased. PA is a value obtained by multiplying the common rail pressure by the pressure increase ratio (ie, the reference increase pressure), PB is the required pressure, PC is the common rail pressure (ie, the reference pressure), and PD is the pressure after the pressure reduction. The value of PA is the largest, and the value decreases in the order of PB, PC, PD. The value obtained by dividing the reference increased pressure PA by the common rail pressure PC (PA / PC) and the value obtained by dividing the required pressure PB by the pressure PD after depressurization (PB / PD) are both the above pressure increase ratio. Note that, when the required pressure PB is higher than the reference increase pressure PA or when the required pressure PB is lower than the common rail pressure PC, the common rail pressure PC needs to be adjusted, and thus is not dealt with in the present application. The first command signal is a command signal for reducing the fuel injection pressure, and the second command signal is a command signal for injecting fuel. Therefore, when the pressure is not reduced before the fuel pressure is increased, only the second command signal shown in FIG. 3 is input. When the pressure is reduced before the fuel pressure is increased, the first command signal is input within a range where the injection rate becomes zero. As a result, the fuel injection pressure once becomes lower than the common rail pressure. The lower the required pressure PB, the greater the amount of pressure reduction. As the amount of decompression increases, the number of times the command signal is input within a range where fuel is not injected is increased, or the time during which the command signal is input within a range where fuel is not injected (that is, the length of the command signal) is increased. Thereafter, pressure increase of the fuel is started, and when the fuel injection pressure rises, a command signal for fuel injection is input. In addition, even when a command signal for fuel injection is input as described above, a pressure drop may actually occur, but this pressure drop is omitted in FIG.

Here, the amount of pressure reduction (may be a pressure drop amount) when the fuel injection pressure is reduced within a range where fuel is not injected can be expressed by the following equation.
dP = k (dV / V)
However, dP is the amount of decompression, k is the bulk modulus, dV is the amount of fuel flowing through the drain pipe 119A, and V is the volume in the range affected by the decompression of the fuel (hereinafter also referred to as decompressed volume). The decompression volume is a volume within the fuel injection valve 10 and a range in which the fuel injection pressure after the pressure is increased (hereinafter also referred to as a high pressure volume), a volume of the common rail 3, and a common rail 3 other than the high pressure volume. The total value of the volume of each pipe (the first fuel pipe 11A, the second fuel pipe 11B, the third fuel pipe 11C, and the pipe between the high pressure fuel pump 5 and the common rail 3) that is connected and has the same pressure as the common rail pressure. is there. The high pressure volume is the volume of the first fuel pipe 11 </ b> A, the injection path 107, the fuel reservoir 106, and the control chamber 103 on the injection path 107 side of the pressure increase chamber 114 </ b> C, the pressure increase path 108, and the check valve 117.

  FIG. 4 is a diagram showing the relationship between the amount of fuel flowing in the drain pipe 119A (horizontal axis), the reduced pressure amount (vertical axis), and the reduced pressure volume. The amount of fuel flowing through the drain pipe 119A can be adjusted by the number of times the fuel flows through the drain pipe 119A and the time during which the fuel flows. In FIG. 4, the points indicated by circles and squares indicate the respective times when the number of times of flowing the fuel into the drain pipe 119 </ b> A (the number of times of lifting the injection control valve 109) is overlapped without fuel being injected from the fuel injection valve 10. The amount of decompression at. As described above, the amount of pressure reduction increases as the amount of fuel flowing through the drain pipe 119A increases. In addition, the smaller the decompression volume, the greater the amount of decompression when the same amount of fuel flows through the drain pipe 119A. Here, when the fuel injection pressure is lowered, the input of the command signal must be finished before the needle 113 moves. For this reason, the amount of pressure reduction by one command signal is limited, but if the fuel pressure in the control chamber 103 and the fuel pressure in the fuel reservoir 106 become equal thereafter, the command signal can be input again. . The fuel injection pressure can be further reduced by inputting the command signal again. That is, by inputting the command signal a plurality of times within a range where fuel is not injected from the fuel injection valve 10, the amount of pressure reduction can be increased without injecting fuel. Furthermore, the fuel injection pressure can be adjusted to an arbitrary pressure between the common rail pressure and the reference increase pressure by adjusting the number of command signal inputs and the length of the command signal input period. Further, even if the number of command signal inputs is the same, the fuel injection pressure can be adjusted by adjusting the length of the command signal input period, and the number of command signal inputs is one. Even so, the fuel injection pressure can be adjusted by adjusting the length of the command signal input period. That is, the fuel injection pressure can be adjusted by adjusting at least one of the number of command signal inputs or the length of the command signal input period.

  In the case where a plurality of fuel injections such as pilot injection, main injection, and after injection are performed during one cycle, the fuel injection pressure can be changed for each injection. However, when multiple injections such as pilot injection, main injection, and after injection are performed at the same pressure, the common rail pressure is not increased by the pressure increasing unit 110. In the present embodiment, in the case where a plurality of fuel injections such as pilot injection, main injection, and after injection are performed, the pressure increasing unit 110 is used only when the pressure needs to be increased in any one of the injections. Increase fuel pressure by

  FIG. 5 is a flowchart showing a flow for adjusting the fuel injection pressure according to the present embodiment. This flowchart is executed by the ECU 20 for each fuel injection. When a plurality of fuel injections such as pilot injection, main injection, and after injection are performed during one cycle, the fuel injection is performed for each injection. This flowchart is for controlling the fuel injection pressure, and the control for injecting the fuel is separately performed by the ECU 20. In this embodiment, the ECU 20 that executes the flowchart shown in FIG. 5 corresponds to the control device according to the present invention.

  In step S101, the operating state of the internal combustion engine 1 is detected. In this step, the engine speed and the fuel injection amount are detected. Since the fuel injection amount is correlated with the accelerator opening, the accelerator opening may be detected instead of the fuel injection amount. The fuel injection amount here is the total amount of fuel injected per cycle by one cylinder in order to generate torque in the internal combustion engine 1.

  In step S102, the required pressure is calculated. When fuel injection is performed a plurality of times such as pilot injection, main injection, and after injection, the required pressure in the injection that is the target of this flowchart. Since the required pressure in each fuel injection is related to the engine rotational speed and the fuel injection amount, the relationship between the required pressure, the engine rotational speed and the fuel injection amount is obtained in advance through experiments or the like, mapped, and stored in the ECU 20. Let me.

  In step S103, it is determined whether or not the required pressure is higher than the reference pressure (common rail pressure in this embodiment) and lower than the reference increase pressure. In this step, it is determined whether or not the pressure needs to be reduced before the fuel pressure is increased. If an affirmative determination is made in step S103, the process proceeds to step S104. On the other hand, if a negative determination is made, the process proceeds to step S107.

  In step S104, the pressure reduction amount of the fuel is calculated. The amount of pressure reduction is calculated based on the common rail pressure, the pressure increase ratio, and the required pressure. That is, the required fuel injection pressure after pressure reduction is calculated by dividing the required pressure by the pressure increase ratio. Then, the pressure reduction amount of the fuel can be calculated by subtracting the required fuel injection pressure after the pressure reduction from the common rail pressure.

  In step S105, the length of the command signal input period and the number of command signal inputs are calculated. The relationship between the length of the command signal input period, the number of times the command signal is input, and the amount of decompression of the fuel is obtained in advance through experiments or simulations. If the amount of decompression is insufficient with one decompression, the decompression is performed a plurality of times. For example, the decompression is performed a plurality of times at a constant decompression amount, and the decompression amount at the time of the final decompression is adjusted, thereby adjusting the total decompression amount to the required decompression amount. Moreover, you may set the pressure reduction amount per time so that the pressure reduction amount of each time may become equal. In step S106, the fuel is depressurized. In step S106, a command signal is input according to the length of the input period of the command signal calculated in step S105 and the number of input command signals. A sensor for detecting the fuel injection pressure may be provided in the fuel injection valve 10, and the fuel injection pressure may be feedback controlled when the fuel is depressurized.

  On the other hand, in step S107, it is determined whether the required pressure is equal to the reference increase pressure. In this step, it is determined whether or not the fuel pressure needs to be increased. That is, when a negative determination is made in step S103, it is considered that the required pressure is equal to either the reference increase pressure or the common rail pressure. When the required pressure is the reference increase pressure, it is necessary to increase the fuel pressure. If an affirmative determination is made in step S107, the process proceeds to step S108. On the other hand, if a negative determination is made, this flowchart is terminated. In step S108, fuel pressure is increased. Here, the fuel injection pressure is increased at a preset pressure increase ratio.

  As described above, according to the present embodiment, the fuel injection pressure after the pressure increase can be adjusted by adjusting the amount of pressure reduction before increasing the fuel at a predetermined pressure increase ratio. Therefore, even when the required pressure is higher than the common rail pressure and lower than the reference increase pressure, the actual fuel injection pressure can be matched with the required pressure. And when the fuel is actually injected, since the pressure increase of the fuel by the pressure increase unit 110 is completed, it can suppress that a fuel injection pressure fluctuates during fuel injection. Thus, since the fuel injection pressure can be maintained at an appropriate value, combustion noise can be suppressed or the amount of smoke generated can be reduced.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 3 Common rail 5 High pressure fuel pump 10 Fuel injection valve 11A First fuel piping 11B Second fuel piping 11C Third fuel piping 20 ECU
27 Fuel pressure sensor 103 Control chamber 104 Pressure increasing piston 104A Large diameter piston portion 104B Small diameter piston portion 105 Nozzle 107 Injection path 108 Pressure increasing path 109 Injection control valve 109A Solenoid actuator 110 Pressure increasing unit 111 Pressure increasing control valve 111A Drain piping 112 Command Piston 112A Spring 113 Needle 114A Pressure chamber 114B Pressure increase control chamber 114C Pressure increase chamber 115 Spring 116 Injection hole 117 Check valve 118 Orifice 119 Orifice 119A Drain piping

Claims (3)

A fuel injection valve that injects fuel by opening a nozzle hole by moving the needle;
A high-pressure fuel reservoir for supplying fuel at a reference pressure to the fuel injection valve;
A fuel passage leading from the high-pressure fuel reservoir to the nozzle hole;
A control chamber connected to the fuel passage, and a pressure reducing device that lowers the pressure of the fuel in the control chamber to be lower than the pressure of the fuel in the fuel passage, and the pressure of the fuel in the fuel passage and the pressure in the control chamber An opening and closing device that moves the needle in a direction to open the nozzle hole when the pressure difference with the fuel pressure is equal to or greater than a predetermined pressure difference;
A pressure increasing device connected to the fuel passage and increasing the pressure of the fuel in the fuel passage at a constant pressure increasing ratio;
The fuel pressure in the fuel passage required at the time of fuel injection from the fuel injection valve is higher than the reference pressure and lower than a reference increase pressure that is a value obtained by multiplying the reference pressure by the increase ratio. A control device that increases the fuel pressure in the fuel passage by the pressure increasing device after operating the pressure reducing device so that the pressure difference after operation is smaller than the predetermined pressure difference;
A fuel injection device for an internal combustion engine.   When the pressure reducing device is operated so that the pressure difference after operation is smaller than the predetermined pressure difference, the control device responds to the fuel pressure in the fuel passage required at the time of fuel injection. The fuel injection device for an internal combustion engine according to claim 1, wherein the number of times of operating the pressure reducing device is changed.   When the pressure reducing device is operated so that the pressure difference after operation is smaller than the predetermined pressure difference, the control device responds to the fuel pressure in the fuel passage required at the time of fuel injection. The fuel injection device for an internal combustion engine according to claim 1, wherein a period during which the pressure reducing device is operated is changed.

Images