JP4483822B2 - Fuel injection control device - Google Patents

Description

  The present invention relates to a fuel injection valve that is opened and closed by displacing a piston through a fluid filled in a transmission chamber by extension and contraction of the actuator, and performs fuel injection control by expanding and contracting the actuator. The present invention relates to a fuel injection control device for an internal combustion engine.

  As this type of fuel injection valve, for example, a piezo injector mounted on a common rail diesel engine has been proposed, as can be seen in Patent Document 1 below. The piezo injector includes a large-diameter piston pushed by the piezo-injector, a small-diameter piston having a smaller diameter than the large-diameter piston, and a nozzle needle. The transmission chamber defined by the large-diameter piston, the small-diameter piston, and the inner wall is filled with fuel. Further, the pressure of the high-pressure fuel supplied from the common rail is applied to the nozzle needle both on the injection opening side and on the opposite side, whereby the nozzle needle is closed.

  The piezoelectric element that functions as an actuator extends, whereby power is transmitted to the small-diameter piston via the large-diameter piston and the fluid in the transmission chamber. Fuel that applies pressure to the opposite side of the injection opening flows out to the fuel tank side. Thereby, the nozzle needle is opened by the pressure of the high-pressure fuel from the injection opening side. According to such a configuration, a small displacement amount of the piezo element can be converted into a large displacement amount by the large-diameter piston, the transmission chamber, and the small-diameter piston. As a result, the piezo injector can be opened and closed using the piezo element as an actuator. Can be done appropriately.

  However, it has been found by the inventors that in the above-described piezo injector, the responsiveness to the valve opening command is lowered under a situation where the valve opening time of the piezo injector is long.

In addition to the above-described piezo injector, in a fuel injection valve that is opened and closed by displacing a piston through a fluid filled in the transmission chamber by extension and contraction of an actuator, These facts that can reduce responsiveness are generally common.
JP 2002-136156 A

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to open and close a valve by displacing a piston through a fluid filled in a transmission chamber by extension and contraction of an actuator. It is an object of the present invention to provide a fuel injection valve that can maintain a high responsiveness even when a fuel injection valve is used.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

In the first aspect of the present invention, it is determined whether or not a condition is satisfied that an amount of fluid leakage from the transmission chamber due to the extension operation of the actuator is larger than an amount of fluid filling the transmission chamber due to the contraction operation of the actuator. And a changing means for advancing the output timing of an operation signal for extending the actuator when it is determined that the condition is satisfied, and the determining means includes a fuel injection period by the fuel injection valve. Is equal to or longer than a predetermined time, it is determined that the condition is satisfied .

  In the above configuration, when the outflow amount of the fluid in the transmission chamber by the extension operation of the actuator is larger than the fluid filling amount in the transmission chamber by the contraction operation of the actuator, the power is transmitted through the fluid regardless of the extension of the actuator. It will not be possible to sufficiently transmit to the piston. For this reason, the delay amount from the output of the operation signal for extending the actuator to the actual opening of the fuel injection valve may be longer than that when the leakage amount and the filling amount are balanced. There is.

  In this regard, in the above-described configuration, it is possible to favorably compensate for an increase in the delay amount by advancing the output timing of the operation signal in such a situation, and as a result, it is possible to maintain a high valve opening response. .

Here, in the above configuration, when the fuel injection period is long, the extension period of the actuator is long, and as a result, the period during which the actuator pushes the piston through the fluid becomes long. When the piston is pushed through the fluid due to the extension of the actuator, the pressure of the fluid rises compared to the contraction period of the actuator, and the fluid is likely to leak from the transmission chamber. For this reason, the amount of fluid leaking from the transmission chamber increases as the extension time of the actuator increases.

  In the above configuration, paying attention to such a property, it is possible to appropriately determine whether the above condition is satisfied based on the fact that the fuel injection period is equal to or longer than a predetermined time.

According to a second aspect of the present invention, whether or not a condition is satisfied that an amount of fluid leakage from the transmission chamber due to the extension operation of the actuator is greater than an amount of fluid filling the transmission chamber due to the contraction operation of the actuator. And determining means for advancing the output timing of an operation signal for extending the actuator when it is determined that the condition is satisfied, the determining means injecting fuel by the fuel injection valve When the cycle time is equal to or shorter than a predetermined time, it is determined that the condition is satisfied.

In the above configuration, when the outflow amount of the fluid in the transmission chamber by the extension operation of the actuator is larger than the fluid filling amount in the transmission chamber by the contraction operation of the actuator, the power is transmitted through the fluid regardless of the extension of the actuator. It will not be possible to sufficiently transmit to the piston. For this reason, the delay amount from the output of the operation signal for extending the actuator to the actual opening of the fuel injection valve may be longer than that when the leakage amount and the filling amount are balanced. There is.
In this regard, in the above-described configuration, it is possible to favorably compensate for an increase in the delay amount by advancing the output timing of the operation signal in such a situation, and as a result, it is possible to maintain a high valve opening response. .
Here, in the above configuration, when the actuator is in the contracted state, the fluid pressure in the transmission chamber is low, so that the fluid easily flows into the transmission chamber. On the other hand, the shorter the fuel injection cycle time by the fuel injection valve, the shorter the time during which the actuator is in the contracted state. For this reason, it means that the filling amount of the fluid into the transmission chamber decreases as the ejection cycle time becomes shorter. In the above configuration, paying attention to such a property, it is possible to appropriately determine whether or not the above condition is satisfied based on the fact that the injection cycle time is equal to or shorter than a predetermined time.

According to a third aspect of the present invention, whether or not a condition is satisfied in which a fluid leakage amount from the transmission chamber due to the extension operation of the actuator is larger than a fluid filling amount into the transmission chamber due to the contraction operation of the actuator. And a changing means for advancing the output timing of an operation signal for extending the actuator when it is determined that the condition is satisfied, and the determining means includes the actuator for the contraction time of the actuator. It is determined that the condition is satisfied when the ratio of the extension times of the two is equal to or greater than a threshold value.

In the above configuration, when the outflow amount of the fluid in the transmission chamber by the extension operation of the actuator is larger than the fluid filling amount in the transmission chamber by the contraction operation of the actuator, the power is transmitted through the fluid regardless of the extension of the actuator. It will not be possible to sufficiently transmit to the piston. For this reason, the delay amount from the output of the operation signal for extending the actuator to the actual opening of the fuel injection valve may be longer than that when the leakage amount and the filling amount are balanced. There is.
In this regard, in the above-described configuration, it is possible to favorably compensate for an increase in the delay amount by advancing the output timing of the operation signal in such a situation, and as a result, it is possible to maintain a high valve opening response. .
Here, in the above configuration, when the extension period of the actuator is long, the period during which the actuator pushes the piston through the fluid becomes long. When the piston is pushed through the fluid due to the extension of the actuator, the pressure of the fluid rises compared to the contraction period of the actuator, and the fluid is likely to leak from the transmission chamber. For this reason, the amount of fluid leaking from the transmission chamber increases as the extension time of the actuator increases. On the other hand, when the actuator is in a contracted state, the pressure of the fluid in the transmission chamber is low, so that the fluid tends to flow into the transmission chamber. For this reason, it means that the filling amount of the fluid into the transmission chamber decreases as the time during which the actuator is in the contracted state is shorter.

  In the above configuration, paying attention to such properties, it is possible to appropriately determine whether the above condition is satisfied based on the ratio of the extension time to the contraction time of the actuator being equal to or greater than a threshold value.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the determination means decreases the threshold value as the pressure of the fuel supplied to the fuel injection valve increases.

  In general, the higher the fuel pressure supplied to the fuel injection valve, the greater the force required when the piston is displaced with the extension of the actuator. This means that the higher the fuel pressure, the higher the pressure of the fluid when the piston is displaced by the extension of the actuator. And the higher the fluid pressure, the easier it is for fluid to leak from the transmission chamber. In this regard, in the above configuration, it is possible to more appropriately determine whether or not the condition that the leakage amount is larger than the filling amount is satisfied by lowering the threshold value as the fuel pressure is higher.

According to a fifth aspect of the present invention, in the third aspect of the invention, the actuator is a piezo element, and the determination unit decreases the threshold value as the voltage of the piezo element is higher .

  Since the piezoelectric element has a higher expansion amount as its voltage is higher, it is considered that the pressure applied to the fluid in the transmission chamber is higher as the voltage is higher. Further, since the voltage of the piezo element increases as the force applied to the piezo element increases, it is considered that the pressure of the fluid in the transmission chamber that determines the force applied to the piezo element increases as the voltage of the piezo element increases. And the higher the fluid pressure, the easier it is for fluid to leak from the transmission chamber. In this regard, in the above configuration, it is possible to appropriately determine whether or not the above condition is satisfied based on the voltage of the piezoelectric element.

  The invention according to claim 7 is the invention according to any one of claims 1 to 6, wherein the fuel injection valve is provided with an elastic member that applies an elastic force in an extension direction of the actuator to the piston. A fluid having a predetermined pressure can flow into the transmission chamber from the outside.

  In the above configuration, since the elastic force in the extension direction of the actuator is applied to the piston, the pressure in the transmission chamber is reduced when the actuator is contracted. For this reason, when the actuator is contracted, the fluid flows into the transmission chamber, so that the leakage of the fluid from the transmission chamber when the actuator is extended can be compensated.

  The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the fuel injection valve is supplied with fuel from a pressure accumulating chamber for storing high-pressure fuel, and the fuel injection valve is connected to the piston. A nozzle needle provided closer to the injection opening, and the nozzle needle is applied with a pressure of high-pressure fuel directed toward the injection opening and the opposite side, and applies pressure toward the injection opening. The fuel is configured to flow out to a fuel tank that supplies fuel to the pressure accumulating chamber when the piston is displaced toward the injection opening.

  In the above configuration, when the piston is displaced to the injection opening side due to the extension of the actuator, the high-pressure fuel that pushes the nozzle needle toward the injection opening side flows out to the fuel tank side. For this reason, the force which pushes a nozzle needle to the reverse side of an injection opening part becomes dominant, and a fuel injection valve opens because a nozzle needle is displaced toward the reverse side.

(First embodiment)
Hereinafter, a first embodiment in which a fuel injection control device according to the present invention is applied to a fuel injection control device mounted on a diesel engine will be described with reference to the drawings.

  FIG. 1 shows the overall configuration of the engine system according to the present embodiment. As shown in the drawing, the fuel in the fuel tank 2 is pumped up by the high-pressure fuel supply pump 4 and pressurized and supplied to the common rail 6. The fuel stored in the high pressure state in the common rail 6 is supplied to a piezo injector PI provided in each cylinder of a four-cylinder diesel engine through a high pressure fuel passage 8. Further, each of the piezo injectors PI is connected to a low pressure fuel passage 10 for returning the fuel supplied via the high pressure fuel passage 8 to the fuel tank 2 as leak fuel. Note that a check valve 12 is provided in the low pressure fuel passage 10 and is opened when the pressure in the low pressure fuel passage 10 becomes equal to or higher than a predetermined pressure, and the fuel in the low pressure fuel passage 10 is transferred to the fuel tank 2. Returned.

  The engine system further includes various sensors that detect the operating state of the diesel engine, such as a fuel pressure sensor 14 that detects the fuel pressure in the common rail 6 and a crank angle sensor 16 that detects the rotation angle of the crankshaft of the diesel engine. Yes. The engine system also includes an accelerator sensor 18 that detects an operation amount of an accelerator pedal by a user.

  Further, the engine system includes a control device 20. The control device 20 controls the output of the diesel engine by operating various actuators of the diesel engine such as the piezo injector PI based on the detection values of the various sensors.

  Here, the configuration of the piezo injector PI will be described with reference to FIG.

  An injection opening 32 is formed at the tip of the body 30 of the piezo injector PI. In addition, a cylindrical needle storage portion 34 is provided at the distal end portion of the body 30. The needle storage portion 34 stores a nozzle needle 36 that can be displaced in the axial direction. The nozzle needle 36 is seated on an annular needle seat portion 38 formed at the distal end portion of the body 30, thereby blocking the needle storage portion 34 from the outside (combustion chamber of the diesel engine), while from the needle seat portion 38. By separating, the needle storage portion 34 is communicated with the outside. Further, the high-pressure fuel supplied to the high-pressure fuel passage 8 is supplied to the needle storage portion 34.

  The back side of the nozzle needle 36 (the side opposite to the side facing the needle seat portion 38) faces the back pressure chamber 40. Fuel from the high-pressure fuel passage 8 is supplied to the back pressure chamber 40 via the needle storage portion 34. The nozzle needle 36 is pushed toward the needle seat portion 38 by the spring 42.

  The back pressure chamber 40 can communicate with the low pressure fuel passage 10 through a valve 44. The valve 44 is seated on the annular valve seat 46 on the back side, so that the low pressure fuel passage 10 and the back pressure chamber 40 are shut off and displaced toward the front end side of the body 30. The pressure chamber 40 is communicated. An elastic force on the valve seat 46 side is applied to the valve 44 by a spring 48.

  The valve seat 46 side of the valve 44 faces the needle-side piston 49. The rear side of the needle side piston 49 faces the tip of the piezo side piston 52 having a larger diameter than the needle side piston 49. A transmission chamber 54 is defined by the needle-side piston 49, the piezo-side piston 52, and the inner peripheral surface of the body 30. The transmission chamber 54 is filled with fuel.

  On the other hand, the piezo-side piston 52 is connected to the piezo element PE on the rear side of the body 30. Incidentally, the back surface of the piezo element PE facing the piezo-side piston 52 is fixed to the body 30.

  The piezo element PE includes a laminate (piezo stack) formed by laminating a plurality of piezoelectric elements, and functions as an actuator by expanding and contracting due to a reverse piezoelectric effect. Specifically, the piezo element PE is a capacitive load, and expands when charged and contracts when discharged. The piezoelectric element PE according to this embodiment uses a piezoelectric element made of a piezoelectric material such as PZT.

  When no current is supplied to the piezo element PE and the piezo element PE is in a contracted state, a force is exerted by the high pressure fuel in the high pressure fuel passage 8, so that the valve 44 is positioned behind the body 30. At this time, the back pressure chamber 40 and the low pressure fuel passage 10 are blocked by the valve 44. For this reason, the nozzle needle 36 is pushed toward the distal end side of the body 30 by the pressure of the fuel in the back pressure chamber 40 and the needle spring 42 and is in a state of being seated on the needle seat portion 38 (valve closed state).

  On the other hand, when current is supplied to the piezo element PE and the piezo element PE is in the extended state, the valve 44 moves to the tip side of the body 30. As a result, the back pressure chamber 40 communicates with the low pressure fuel passage 10. As a result, the pressure of the fuel in the back pressure chamber 40 is reduced, and the force that the high pressure fuel in the needle housing portion 34 pushes the nozzle needle 36 toward the rear of the body 30 causes the fuel in the back pressure chamber 40 and the needle spring 42 to move. If it becomes larger than the force which pushes the nozzle needle 36 to the front of the body 30 more than predetermined, the nozzle needle 36 will be in the state (valve open state) separated from the needle seat part 38. FIG.

  FIG. 3 shows the configuration of the control device 20.

  As shown in the drawing, the electric power supplied from the battery B to the ECU 20 is first supplied to a DC / DC converter 21 which is a booster circuit. The DC / DC converter 21 boosts the voltage of the battery B (for example, “12 V”) to a high voltage (for example, “200 to 300 V”) for charging the piezo element PE.

  The boosted voltage of the DC / DC converter 21 is applied to the capacitor 22. One terminal of the capacitor 22 is connected to the DC / DC converter 21 side, and the other terminal is grounded. Then, when the boosted voltage of the DC / DC converter 21 is applied to the capacitor 22, the capacitor 22 stores electric charge to be supplied to the piezo element PE. Incidentally, it is desirable that the capacitor 22 has a capacitance (for example, about “several hundred μF”) such that the voltage hardly changes by a single charging process to the piezo element PE.

  The terminal side of the capacitor 22 that becomes a high potential, that is, the DC / DC converter 21 side is connected to the terminal side that becomes a high potential of the piezo element PE via a series connection body of the charge switch 23 and the charge / discharge coil 24. It is connected. And the terminal side which becomes the low electric potential of the piezo element PE is grounded.

  One terminal of a discharge switch 25 is connected between the charge switch 23 and the charge / discharge coil 24, and the other terminal of the discharge switch 25 is grounded.

  A diode 26 is connected in parallel to the discharge switch 25. The cathode of the diode 26 is connected between the capacitor 22 and the charge / discharge coil 24, and the anode thereof is connected to the ground side. The diode 26, together with the capacitor 22, the charge switch 23, and the charge / discharge coil 24, constitutes a chopper circuit that charges the piezo element PE, and functions as a freewheeling diode.

  On the other hand, a diode 27 is connected to the charging switch 23 in parallel. The diode 27 has a cathode side connected to the capacitor 22 side and an anode side connected to the discharge switch 25 side. The diode 27, together with the capacitor 22, the charge / discharge coil 24, and the discharge switch 25, constitutes a chopper circuit that discharges the electric charge of the piezo element PE, and functions as a freewheeling diode.

  The drive circuit having the above configuration is driven by the microcomputer 28. Specifically, the microcomputer 28 operates the charge switch 23 and the discharge switch 25 based on the detection values of various sensors that detect the operating state of the diesel engine. Each of these operations is performed in the manner shown in FIG.

  FIG. 4A shows the transition of the operation mode of the charge switch 23, FIG. 4B shows the transition of the operation mode of the discharge switch 25, and FIG. 4C shows the current flowing through the piezo element PE (operation). The transition of the operation voltage of the piezo element PE is shown in FIG. 4 (d).

  As shown in the figure, the piezo element PE is charged while increasing / decreasing the operation current by the chopper control by turning on / off the charging switch 23. Specifically, when the charging switch 23 is turned on, a closed loop circuit including the capacitor 22, the charging switch 23, the charging / discharging coil 24, and the piezo element PE is formed. Thereby, the electric charge of the capacitor 22 is charged into the piezo element PE. At this time, the amount of current flowing through the piezo element PE increases. On the other hand, after the charging switch 23 is turned on, the charging switch 23 is turned off, thereby forming a closed loop circuit including the charging / discharging coil 24, the piezoelectric element PE, and the diode 26. Thereby, the flywheel energy of the charging / discharging coil 24 is charged in the piezo element PE. At this time, the amount of current flowing through the piezo element PE decreases.

  By performing the step-down chopper control in which the charging switch 23 is operated in the above-described manner, the piezo element PE is charged, and the potential on the terminal side that becomes the high potential of the piezo element PE rises. As a result, the piezo element PE extends and the piezo injector PI opens.

  On the other hand, the piezo element PE is discharged while increasing / decreasing the operation current by the chopper control by the on / off operation of the discharge switch 25. Specifically, when the discharge switch 25 is turned on, a closed loop circuit is formed by the discharge switch 25, the charge / discharge coil 24, and the piezoelectric element PE. Thereby, the piezo element PE is discharged. At this time, the amount of current flowing through the piezo element PE increases. Furthermore, after the discharge switch 25 is turned on, the discharge switch 25 is turned off, whereby a closed loop circuit is formed by the capacitor 22, the diode 27, the charge / discharge coil 24, and the piezoelectric element PE. Thereby, the flywheel energy of the charge / discharge coil 24 is recovered by the capacitor 22.

  By performing the step-up chopper control in which the discharge switch 25 is operated in the above-described manner, the piezo element PE is discharged, and the potential on the terminal side that becomes the high potential of the piezo element PE is lowered. Thereby, the piezo element PE contracts and the piezo injector PI is closed.

  By the way, in the fuel injection control by the piezo injector PI, the inventors have found that the responsiveness of opening the piezo injector PI is lowered depending on the operation state of the diesel engine. Hereinafter, this will be described in detail with reference to FIG.

  5A shows a cross-sectional structure around the needle-side piston 49 in the piezo injector PI, FIG. 5B shows a command value (command injection period) of the injection period, and FIG. ) And FIG. 5D show the injection rate.

  As shown in the figure, the piezo element PE is in a contracted state before the start of fuel injection, and the valve 44 is seated on the valve seat portion 46. Here, when the piezo element PE extends, the piezo element PE pushes the needle side piston 49 through the fuel in the piezo side piston 52 and the transmission chamber 54, so that the valve 44 is separated from the valve seat portion 46. In this state, the pressure of the fuel in the transmission chamber 54 increases, so that the fuel leaks from the transmission chamber 54 although it is a very small amount.

  On the other hand, when the piezo element PE contracts, the needle side piston 49 is displaced to the piezo element PE side, so that the valve 44 is seated on the valve seat portion 46. However, since the elastic force on the injection opening 32 side is applied to the needle side piston 49 by the spring 50, the fuel pressure in the transmission chamber 54 can be lower than that on the low pressure fuel passage 10 side. For this reason, the fuel is filled into the transmission chamber 54 from the low pressure fuel passage 10 side.

  Then, when the force due to the pressure of the fuel filled in the transmission chamber 54 and the elastic force due to the spring 50 are balanced, the fuel filling is completed, and the needle-side piston 49 is in a steady and stable state. However, when fuel injection is performed again before the fuel filling is completed and the needle-side piston 49 is steadily stabilized, the fuel in the transmission chamber 54 is reduced, so the needle-side piston The displacement of the needle side piston 49 is started from the state where the valve 49 is not in contact with the valve 44.

  Therefore, when the fuel filling amount in the transmission chamber 54 shown in FIG. 5C is insufficient as compared with the case where the fuel filling amount in the transmission chamber 54 shown in FIG. 5C is sufficient. The actual injection start timing is delayed. In this case, since the maximum lift amount of the nozzle needle 36 is reduced, the actual fuel injection end timing is advanced. The relationship between the injection period, the lift amount of the nozzle needle 36 and the injection rate for the cases shown in FIGS. 5C and 5D is shown in FIGS. As shown in the figure, the start timing of the increase in the lift amount is when the fuel filling amount in the transmission chamber 54 is insufficient (solid line in the figure) and short (dotted line in the figure). There is a delay. For this reason, the lift amount at the discharge start timing of the piezo element PE, which is the decrease start timing of the lift amount, is different in these two cases, so the timing at which the actual injection rate becomes zero is also different. For this reason, when the filling amount is insufficient, the actual injection start timing is delayed and the actual injection end timing is advanced as compared with a sufficient case, so that the fuel injection amount is reduced.

  Therefore, in the present embodiment, when the amount of fuel leakage from the transmission chamber 54 due to the expansion of the piezo element PE is larger than the amount of fuel charged into the transmission chamber 54 due to the contraction of the piezo element PE, a broken line in FIG. As shown by, a process for advancing the charge start timing is performed. Hereinafter, this will be described in detail with reference to FIG.

  FIG. 7 shows a processing procedure of fuel injection control according to the present embodiment. This process is repeatedly executed by the control device 20 at a predetermined cycle, for example.

  In this series of processing, first, in step S10, the accelerator pedal operation is performed based on the operation amount of the accelerator pedal detected by the accelerator sensor 18 and the rotational speed of the output shaft of the diesel engine based on the detected value of the crank angle sensor 16. An injection amount (requested injection amount) for generating output torque required according to the amount is calculated.

  In the subsequent step S12, the number of stages of fuel injection is calculated based on the required injection amount and the rotational speed. In other words, in the present embodiment, several stages are selected from pilot injection, main injection, and after injection within one cycle of the combustion cycle, and multistage injection control for performing these selected injections is performed. Here, in pilot injection, a very small amount of fuel is injected to promote the mixing of fuel and air immediately before ignition, and the ignition timing delay after main injection is shortened to generate nitrogen oxides (NOx). To reduce combustion noise and vibration. The main injection contributes to the generation of output torque of the diesel engine and has the maximum injection amount during multi-stage injection. After-injection recombusts particulate matter (PM). Here, for example, when the number of injection stages is “2”, one stage of pilot injection and one stage of main injection are performed, and when the number of injection stages is “4”, two stages of pilot injection and one stage of main injection are performed. And one-stage after injection.

  In subsequent step S14, a command value (command injection start time) and a command value (command injection period) of the injection period for each of the plurality of injections determined by the number of injection stages are calculated. In the subsequent step S16, a ratio kt between the total injection period (elongation time of the piezo element PE) in one fuel cycle and the time during which injection is not performed (contraction time of the piezo element PE) in a single cylinder is calculated. That is, as illustrated in FIG. 8A for the case where the number of injection stages is four, the total time of the command injection periods t1 to t4 is set as the total injection period ton. Then, the ratio kt is calculated by “kt = ton / toff = ton / {(2 × 60 × 1000 / NE) −ton}” using the rotational speed NE. Here, the rotational speed NE is defined as the number of revolutions per minute, the injection period ton is in units of 1 millisecond, and two rotations of the output shaft correspond to one combustion cycle. I am considering.

  The ratio kt is a parameter for determining whether or not the condition that the amount of fuel leakage from the transmission chamber 54 is larger than the amount of fuel filling the transmission chamber 54 is satisfied. That is, the larger the ratio kt, the longer the period in which the fuel leaks from the transmission chamber 54 and the shorter the time during which the fuel is filled in the transmission chamber 54. Therefore, whether or not the above condition is satisfied is determined based on this ratio kt. be able to.

  Specifically, in the present embodiment, as shown in FIG. 8B, the amount of fuel leakage from the transmission chamber 54 is filled with the fuel into the transmission chamber 54 by the ratio kt and the fuel pressure NPC in the common rail 6. A region that exceeds the amount is specified as an “injection start delay generation region”. Here, the reason why the fuel pressure is used to specify this region is that the fuel pressure applied to the transmission chamber 54 when the piezo element PE is extended increases as the fuel pressure increases, so that the fuel easily leaks from the transmission chamber 54.

  In view of the above properties, when the processing in step S16 in FIG. 7 is completed, it is determined in step S18 whether the ratio kt is equal to or greater than the threshold value α. Here, the threshold value α is a value for determining whether or not a condition that the amount of fuel leakage from the transmission chamber 54 is larger than the amount of fuel filling the transmission chamber 54 is satisfied. This threshold value α is variably set according to the fuel pressure in the common rail 6 detected by the fuel pressure sensor 14. Specifically, from the relationship shown in FIG. 8B, the threshold value α is decreased as the fuel pressure increases.

  If it is determined that the threshold value α is equal to or greater than the threshold value α, it is determined that the condition is satisfied, and the process proceeds to step S20. In step S20, as shown by the broken line in FIG. 6A, the timing for starting charging the piezo element PE is corrected to the advance side. At this time, the advance side correction amount may be variably set according to the ratio kt or the fuel pressure. That is, for example, the advance side correction amount may be increased as the ratio kt increases or as the fuel pressure increases.

  When a negative determination is made in step S18 or when the process of step S20 is completed, the process proceeds to step S22. In step S22, the piezo element PE is charged and discharged. Here, when the process of step S20 is not performed, charging of the piezo element may be started at the command injection start time calculated in step S14. When the process of step S14 is performed, The charging of the piezo element PE may be started at a timing advanced from the command injection start timing. Further, the discharge start timing may be set when the command injection period has elapsed from the command injection start timing calculated in step S14. That is, the discharge start timing is the same regardless of the presence or absence of the process in step S20.

  When the process of step S22 is completed, this series of processes is temporarily terminated.

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) When the condition that the amount of fuel leakage from the transmission chamber 54 due to the expansion operation of the piezo element PE is larger than the amount of fuel filling the transmission chamber 54 due to the contraction operation of the piezo element PE is satisfied. Faster charge start. Thereby, the responsiveness of valve opening of the piezo injector PI can be maintained high.

  (2) The ratio of the expansion time to the contraction time of the piezo element PE, in other words, the ratio kt between the total injection time in one fuel cycle and the time during which no injection is performed in a single cylinder is greater than or equal to the threshold value α. Based on the above, it is possible to appropriately determine whether or not the above condition is satisfied.

  (3) By reducing the threshold value α as the pressure increases, it is possible to appropriately determine whether or not the condition that the leakage amount is larger than the filling amount is satisfied.

  (4) The piezo injector PI is provided with a spring 50 that pushes the needle-side piston 49 in the extending direction of the piezo element PE, and fuel of a predetermined pressure can flow into the transmission chamber 54 from the outside. As a result, when the piezo element PE is contracted, fuel flows into the transmission chamber 54, so that the fuel leaking from the transmission chamber 54 can be replenished.

  (5) The pressure of the high pressure fuel applied to the injection opening 32 side and the opposite side is applied to the nozzle needle 36 of the piezo injector PI. Is displaced to the injection opening 32 side, and flows out to the fuel tank 2 side for supplying fuel to the common rail 6. Thereby, when the piezo element PE extends and the needle-side piston 49 is displaced toward the injection opening 32, the high-pressure fuel that pushes the nozzle needle 36 toward the injection opening 32 flows out to the fuel tank 2 side. . For this reason, the force which pushes the nozzle needle 36 to the reverse side of the injection opening 32 becomes dominant, and the piezo injector PI is opened by the nozzle needle 36 being displaced toward the reverse side.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  FIG. 9 shows a processing procedure of fuel injection control according to the present embodiment. This process is repeatedly executed by the control device 20 at a predetermined cycle, for example. In FIG. 9, the same processes as those in FIG. 7 are given the same reference numerals for the sake of convenience.

  In the present embodiment, in step S18a, the threshold value α is variably set according to the voltage of the piezo element PE when the piezo element PE is in the expanded state. Specifically, the threshold value α is decreased as the voltage of the piezo element PE increases. Here, the voltage of the piezo element PE is used as a parameter having a correlation with the fuel pressure in the transmission chamber 54.

  That is, the voltage of the piezo element PE is determined by the extension amount of the piezo element PE and the force applied to the piezo element PE. Here, the higher the voltage of the piezo element PE, the longer the extension amount of the piezo element PE. And as the extension amount is longer, the transmission chamber 54 is compressed, so the fuel pressure in the transmission chamber 54 increases. For this reason, the higher the voltage of the piezo element PE, the higher the fuel pressure in the transmission chamber 54. Further, the greater the force applied to the piezo element PE, the higher the voltage of the piezo element PE due to the piezoelectric effect. The force applied to the piezo element PE is determined by the fuel pressure in the transmission chamber 54. For this reason, it is considered that the higher the voltage of the piezo element PE, the higher the fuel pressure in the transmission chamber 54.

  For this reason, it is considered that the higher the voltage of the piezo element PE, the greater the amount of fuel leakage from the transmission chamber 54 than the amount of fuel filling the transmission chamber 54. For this reason, the threshold value α is set to a smaller value as the voltage of the piezo element PE is higher.

  Note that the voltage of the piezo element PE, that is, the voltage between the terminal side of the piezo element PE, which is at a high potential, and the ground is divided by two resistors so that the microcomputer 28 in the control device 20 and the like. It may be detected by converting to a voltage that can be handled by

  According to the present embodiment described above, in addition to the effects (1), (2), (4), and (5) of the first embodiment, the following effects can be obtained. .

  (6) By decreasing the threshold value α as the voltage of the piezo element PE is higher, it is possible to appropriately determine whether or not the condition that the leakage amount is larger than the filling amount is satisfied.

(Third embodiment)
Hereinafter, the third embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  The capacitance C of the piezo element PE (the apparent capacitance that relates the electric charge stored in the piezo element PE and the voltage of the piezo element PE) C has temperature dependence. Specifically, the capacity C increases as the temperature increases. Thus, since the electrical characteristics of the piezo element PE change according to the temperature, it is difficult to control the displacement amount of the piezo element PE based on the electrical state quantity. Actually, the piezoelectric rate d defined by the ratio of the displacement amount to the voltage of the piezo element PE increases as the temperature increases. For this reason, when the displacement amount of the piezo element PE is controlled by the voltage of the piezo element PE, it is difficult to maintain high control accuracy.

Therefore, in the present embodiment, the amount of energy supplied to the piezo element PE is determined when the piezo element PE is extended and controlled by charging the piezo element PE. This is because, if the energy of the piezo element PE is the same, the displacement amount of the piezo element PE can be made substantially constant regardless of the temperature variation of the piezo element PE. This is simply explained as follows. That is, when the energy E of the piezo element PE is constant, the voltage V decreases from the relationship “E = ½ CV ² ” when the capacity increases from the above relationship as the temperature increases. For this reason, the effect of increasing the piezoelectric ratio d as the temperature rises is offset by the effect of the voltage drop accompanying the temperature rise. Note that details of the amount of displacement of the piezo element PE being substantially constant when the energy is constant are described in, for example, JP-A-2005-130561.

  In the present embodiment, the charge switch 23 and the discharge switch 25 are operated in the manner shown in FIG. 10 in order to control the energy to be constant. Hereinafter, the charging switch 23 will be described as an example. As shown in the figure, the time for turning on the charging switch 23 is constant throughout the charging process, and the time for turning off the charging switch 23 is the time until the current flowing through the piezo element PE becomes zero. In other words, the timing for switching from the current increasing operation to the decreasing operation is set as the time when the increasing operation time becomes a predetermined time, and the timing for switching from the current decreasing operation to the increasing operation is set when the current becomes zero. To do. As a result, the amount of energy supplied to the piezo element PE per unit time can be made substantially constant regardless of the temperature of the piezo element PE, so the energy supplied to the piezo element PE can be easily controlled by the charging time. can do. For example, Patent Document 1 discloses that the amount of energy supplied to the piezo element PE per unit time can be made constant by the chopper control of the above aspect.

  In the above embodiment, the extension amount of the piezo element PE can be controlled with high accuracy. Specifically, in the present embodiment, the amount of extension is controlled as desired by charging the amount of energy corresponding to the fuel pressure in the common rail 6 detected by the fuel pressure sensor 14. Here, the amount of energy is made variable according to the fuel pressure because the displacement amount of the piezo element PE changes according to the force applied from the outside in the direction opposite to the displacement direction of the piezo element PE. On the other hand, in order to open the piezo injector PI, in other words, in order to displace the nozzle needle 36 shown in FIG. 2 to the rear of the body 30, the fuel supplied via the high-pressure fuel passage 8 is used. Must overcome the force that pushes the valve 44 toward the valve seat 46 by the piezo element PE. For this reason, the force applied in the direction opposite to the displacement direction of the piezo element PE changes according to the fuel pressure.

  In the present embodiment, the map shown in FIG. 11 is provided in the control device 20, and the energy supplied to the piezo element PE is set according to the fuel pressure. The map shown in FIG. 11 instructs to increase the amount of energy supplied to the piezo element PE as the fuel pressure increases. The control device 20 sets an energy amount according to the fuel pressure based on the map, and variably sets a charging period (discharge period) for turning on / off the charging switch 23 and the like accordingly.

  By managing the energy in this way, the amount of expansion of the piezo element PE can be controlled easily and with high accuracy regardless of the temperature. This means that the fuel pressure in the transmission chamber 54 can be grasped with high accuracy by the amount of energy set according to the fuel pressure. That is, it is considered that the pressure of the transmission chamber 54 in the extended state is high because the amount of expansion of the piezo element PE increases as the amount of energy supplied to the piezo element PE increases. Further, the higher the fuel pressure in the common rail 6 is, the larger the amount of energy supplied to the piezo element PE is set. Therefore, the greater the amount of energy supplied to the piezo element PE, the longer the extension operation (charging process) of the piezo element PE. It is considered that the pressure in the transmission chamber 54 is high when it is made. Therefore, in the present embodiment, the threshold value α is variably set according to the amount of energy supplied to the piezo element PE.

  FIG. 12 shows a processing procedure of fuel injection control according to the present embodiment. This process is repeatedly executed by the control device 20 at a predetermined cycle, for example. In FIG. 12, the same processes as those in FIG. 7 are given the same reference numerals for the sake of convenience.

  In the present embodiment, in step S18b, the threshold value α is variably set according to the amount of energy supplied to the piezo element PE in order to extend the piezo element PE. Specifically, the threshold value α is reduced as the amount of energy supplied to the piezo element PE increases.

  According to the present embodiment described above, in addition to the effects (1), (2), (4), and (5) of the first embodiment, the following effects can be obtained. .

  (7) By reducing the threshold value α as the amount of energy supplied to the piezo element PE is higher, it is possible to appropriately determine whether or not the condition that the leakage amount is larger than the filling amount is satisfied. In addition, by using the amount of energy supplied to the piezo element PE, it is possible to suitably suppress a change in the appropriate threshold value α due to fluctuations in the extension amount of the piezo element PE due to the temperature of the piezo element PE, and thus the above determination. It can be done more appropriately.

(Other embodiments)
Each of the above embodiments may be modified as follows.

  In each of the above embodiments, the period Toff in which fuel injection is not performed may be set as the period from the end of the last stage fuel injection in the previous combustion cycle to the start of the first stage fuel injection in the current combustion cycle.

  In the second embodiment, when the threshold value α is variably set according to the voltage of the piezo element PE, the threshold value α may be further corrected by the temperature of the piezo element PE. Thereby, the fluctuation of the voltage due to the temperature of the piezo element PE can be preferably removed, and as a result, the fuel pressure in the transmission chamber 54 can be grasped with higher accuracy by the voltage of the piezo element PE. Here, the temperature of the cooling water of the diesel engine may be simply used as the temperature of the piezo element PE here. For example, the capacitance of the piezo element PE is calculated by detecting the charge amount and voltage of the piezo element PE. Thus, the temperature of the piezo element PE may be estimated. Incidentally, details of this method focusing on the fact that the apparent capacitance defined by the change in voltage with respect to the change in charge changes according to the temperature are described in, for example, Japanese Patent Application Laid-Open No. 2002-21620.

  In view of the fact that the larger the rotational speed of the output shaft of the diesel engine, the shorter the time between injections, the higher the rotational speed, the more difficult it is to compensate for fuel leakage from the transmission chamber 54. The charging start time may be advanced when is equal to or greater than a predetermined threshold.

  In view of the fact that the higher the fuel pressure in the common rail 6, the greater the force applied to the transmission chamber 54 when the valve 44 is opened, the higher the fuel pressure, the greater the amount of fuel leakage from the transmission chamber 54. Therefore, when the fuel pressure is equal to or higher than a predetermined pressure, the charging start time may be advanced.

  Considering that the fuel injection period becomes longer as the required injection amount increases, it is considered that the condition that the amount of fuel leakage from the transmission chamber 54 becomes larger than the filling amount as the required injection amount increases. Therefore, when the required injection amount is larger than a predetermined amount, the charging start timing may be advanced.

  In view of the tendency that the injection period tends to become longer as the number of injection stages in the multi-stage injection control increases, the condition that the amount of fuel leakage from the transmission chamber 54 becomes larger than the filling amount as the number of injection stages increases. Therefore, the charging start timing may be advanced when the number of injection stages is larger than the predetermined number of stages.

  The structure of the piezo injector PI is not limited to that illustrated in FIG. At this time, not only the binary operation of valve opening and closing according to the displacement of the piezo element PE, but the displacement of the piezo element PE as described in, for example, U.S. Pat. No. 6,520,423. The injector may be capable of continuously adjusting the lift amount of the nozzle needle according to the above. Even in this case, if the configuration is such that the power of the piezo element PE is transmitted to the member (piston) that displaces the nozzle needle via the fluid in the transmission chamber, the fluid from the transmission chamber by the extension operation of the piezo element PE It is effective to advance the charging start timing of the piezo element PE when the condition that the amount of leakage of the piezo element PE is larger than the amount of fluid filled into the transmission chamber by the contraction operation of the piezo element PE is satisfied.

  The fuel injection valve is not limited to one that uses the piezo element PE as an actuator, but may be one that uses, for example, an electromagnetic solenoid as an actuator. Even in this case, the application of the present invention is effective if the valve is opened and closed by displacing the piston through the fluid filled in the transmission chamber by the expansion and contraction of the actuator. .

  In addition, the internal combustion engine is not limited to a diesel engine, and may be, for example, a direct injection gasoline engine.

The figure which shows the whole structure of the engine system concerning 1st Embodiment. Sectional drawing which shows the cross-section of the piezo injector in the same embodiment. The figure which shows the structure of the control apparatus in the embodiment. The time chart which shows the aspect of the charge process and discharge process of a piezo element in the embodiment. The figure explaining the cause which the response delay of the valve opening of a piezo injector arises. The figure explaining the cause which valve closing of a piezo injector is accelerated. The flowchart which shows the process sequence of the fuel-injection control concerning the said embodiment. The figure explaining the method of determining whether the charge start time in the said process is advanced. The flowchart which shows the process sequence of the fuel-injection control concerning 2nd Embodiment. The time chart which shows the aspect of the charge process and discharge process of a piezoelectric element in 3rd Embodiment. The figure which shows the map for determining the energy supply amount to the piezo element in the embodiment. The flowchart which shows the process sequence of the fuel-injection control concerning the embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Control apparatus (one Embodiment of a fuel injection control apparatus), 32 ... Injection opening part, 34 ... Needle accommodating part, 36 ... Nozzle needle, 48 ... Needle side piston, 54 ... Transmission chamber, PE ... Piezo element.

Claims (8)

An internal combustion engine that performs fuel injection control by operating the actuator to expand and contract with respect to a fuel injection valve that is opened and closed by displacing a piston via a fluid filled in a transmission chamber by extension and contraction of the actuator In the fuel injection control device of
Determining means for determining whether or not a condition is satisfied in which an amount of fluid leakage from the transmission chamber due to the extension operation of the actuator is greater than an amount of fluid filling the transmission chamber due to a contraction operation of the actuator;
Changing means for advancing the output timing of an operation signal for extending the actuator when it is determined that the condition is satisfied;
The determination unit determines that the condition is satisfied when a fuel injection period by the fuel injection valve is equal to or longer than a predetermined time . An internal combustion engine that performs fuel injection control by operating the actuator to expand and contract with respect to a fuel injection valve that is opened and closed by displacing a piston via a fluid filled in a transmission chamber by extension and contraction of the actuator In the fuel injection control device of
Determining means for determining whether or not a condition is satisfied in which an amount of fluid leakage from the transmission chamber due to the extension operation of the actuator is greater than an amount of fluid filling the transmission chamber due to a contraction operation of the actuator;
Changing means for advancing the output timing of an operation signal for extending the actuator when it is determined that the condition is satisfied;
The determination means determines that the condition is satisfied when a fuel injection cycle time by the fuel injection valve is equal to or shorter than a predetermined time . An internal combustion engine that performs fuel injection control by operating the actuator to expand and contract with respect to a fuel injection valve that is opened and closed by displacing a piston via a fluid filled in a transmission chamber by extension and contraction of the actuator In the fuel injection control device of
Determining means for determining whether or not a condition is satisfied in which an amount of fluid leakage from the transmission chamber due to the extension operation of the actuator is greater than an amount of fluid filling the transmission chamber due to a contraction operation of the actuator;
Changing means for advancing the output timing of an operation signal for extending the actuator when it is determined that the condition is satisfied;
The determination unit determines that the condition is satisfied when a ratio of an extension time of the actuator to a contraction time of the actuator is equal to or greater than a threshold value . 4. The fuel injection control apparatus according to claim 3, wherein the determination means decreases the threshold value as the pressure of fuel supplied to the fuel injection valve increases . The actuator is a piezo element;
4. The fuel injection control apparatus according to claim 3, wherein the determination unit decreases the threshold value as the voltage of the piezo element increases . The actuator is a piezo element;
4. The fuel injection control apparatus according to claim 3, wherein the determination unit decreases the threshold value as the amount of energy supplied to the piezo element increases . The fuel injection valve is provided with an elastic member that applies an elastic force in an extension direction of the actuator to the piston.
The fuel injection control device according to claim 1, wherein a fluid having a predetermined pressure can flow into the transmission chamber from the outside. The fuel injection valve is supplied with fuel from an accumulator that stores high-pressure fuel,
The fuel injection valve includes a nozzle needle that is provided closer to the injection opening than the piston, and the nozzle needle is applied with pressure of high-pressure fuel toward the injection opening and the opposite side, and the injection opening The high-pressure fuel that applies pressure toward the portion side is configured to flow out toward the fuel tank that supplies fuel to the pressure accumulating chamber when the piston is displaced toward the injection opening. Item 8. The fuel injection control device according to any one of Items 1 to 7.