JP2010071187A - Fuel injection control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection control device learning injection quantity with high accuracy even if a cycle of pressure pulsation is changed according to fuel temperature when the injection quantity is learned by multi-stage injection. <P>SOLUTION: In this fuel injection control device, the cycle fp of the pressure pulsation generated in multi-stage injection for learning is calculated (S300) based on the length of a fuel pipe between a common rail and a fuel injection valve, fuel pressure, and fuel temperature, and any one of reference points (fp/2) made to be zero when the pressure pulsation is positively/negatively fluctuated is regarded as the optimum injection interval TINTopt (S302). In the fuel injection control device, injection intervals Tp1, Tp2, Tp3 between stages are calculated (S306) based on injection variation correction amounts Tc2, Tc3, Tc4 (S304) and the optimum injection interval TINTopt, multi-stage equal injection for learning is performed (S308) based on the injection intervals Tp1, Tp2, Tp3, and a learning value for a minute injection quantity is calculated (S310). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel injection control device that learns the injection amount of each stage by equally dividing the injection amount of a fuel injection valve that injects fuel into each cylinder of an internal combustion engine and performing multi-stage injection.

  In recent years, it has been required to control the injection amount of the fuel injection valve with high accuracy in order to cope with the tightening of exhaust gas regulations. For example, when a small amount of pilot injection is performed before the main injection that generates the main torque of the engine in one combustion cycle, such as a common rail type diesel engine, high-precision control of the injection amount is necessary. It is. For this reason, mechanical improvements have been made to processing errors and deterioration with time of the fuel injection valve.

  However, since there is a limit to the mechanical improvement, as disclosed in Patent Document 1, the injection amount is corrected by learning the minute injection amount, and the injection amount of the fuel injection valve is controlled with high accuracy. It has been known.

  In the injection amount learning of Patent Document 1, the learning control injection amount calculated based on the engine operating state is divided into n times substantially evenly and multistage injection is performed with a plurality of fuel pressures. Then, while performing multi-stage injection, the injection amount correction for smoothing the rotational speed fluctuation between the cylinders is performed, and the injection amount correction for maintaining the average engine rotational speed at the target rotational speed is performed to correct the injection amount for each cylinder. A correction value in which an amount is assigned to each stage is used as a learning value.

  However, when multistage injection is performed, pressure pulsation is generated by injection at each stage. Furthermore, the period of pressure pulsation changes according to the fuel temperature. As in Patent Document 1, when performing multistage injection for learning by dividing the injection amount evenly, if the period of pressure pulsation that occurs in multistage injection changes according to the fuel temperature, the injection amount of each stage varies, There arises a problem that the injection amount cannot be learned with high accuracy.

  In Patent Document 2, although it is not multistage injection for learning the injection amount, when fuel injection is performed at least twice during one combustion cycle, pressure pulsation occurs due to the first injection performed first, It is disclosed that the injection amount and the injection timing of the second injection to be performed later vary due to the pressure pulsation. Furthermore, it is disclosed that the propagation speed of pressure pulsation, in other words, the period of pressure pulsation changes depending on the length of the fuel pipe, the fuel pressure (common rail pressure), and the fuel temperature.

  And in patent document 2, the cycle of the pressure pulsation generated by the first injection is calculated based on the length of the fuel pipe, the fuel pressure, and the fuel temperature, and the first injection and the second in the calculated pressure pulsation cycle. The injection amount and the injection of the second injection so that the second injection is performed at the target injection amount and the target interval (target injection timing) based on the dimensionless interval obtained by dividing the injection interval between the injection and The time is corrected.

Therefore, even when the injection amount learning is performed by multi-stage injection, the period of pressure pulsation that changes according to the fuel temperature is calculated, and the injection of each stage after the first stage injection is the target injection amount based on this period of pressure pulsation. Further, it is conceivable to perform injection amount learning by correcting the injection amount and the injection timing so that the target injection timing is reached, thereby eliminating the influence of pressure pulsation.
JP 2003-254139 A JP 2003-314337 A

  However, depending on the injection timing of each stage after the first stage injection, the fuel injection may be performed at the injection timing when the variation in pressure pulsation amplitude, that is, the fuel pressure variation is large, so even if the injection amount is corrected, the injection amount May deviate from the target injection amount.

  Also, if the injection timing and injection amount of each stage after the first stage injection are corrected based on the pressure pulsation cycle that changes according to the fuel temperature, the correction based on the pressure pulsation cycle and the injection amount learning by multistage injection are combined. Thus, the injection amount is corrected twice. As a result, there is a problem that the injection amount learning cannot be performed with high accuracy.

  The present invention has been made in order to solve the above-described problem. When the injection amount is learned by multistage injection, the fuel that learns the injection amount with high accuracy even if the period of pressure pulsation changes according to the fuel temperature. An object is to provide an injection control device.

  According to the first to seventh aspects of the invention, when learning the injection amount by multistage injection, the injection timing of each stage after the first stage injection commanded to the fuel injection valve by the injection command means is adjusted based on the fuel temperature. Thus, the injection timing adjusting means sets the reference point that becomes 0 when the pressure pulsation generated in the multistage injection changes positively or negatively as the injection timing of each stage after the first stage injection.

  At the reference point that becomes 0 when the pressure pulsation fluctuates positively and negatively, the injection pressure of the fuel injection valve becomes the fuel pressure for learning the injection amount when there is no pressure pulsation. The fuel pressure variation is small at the pressure pulsation reference point. Therefore, by setting the reference point as the injection timing, it is possible to start injection at each stage after the first stage injection at the learning fuel pressure. Since the pressure pulsation does not occur at the start of the first stage injection, it is natural that the first stage injection can be started with the learning fuel pressure.

  Thus, by using the injection timing of each stage after the first stage injection as the reference point of pressure pulsation, the injection can be started at the injection timing with a small variation in fuel pressure. Thereby, the injection amount learning can be performed while eliminating the influence of the variation in the fuel pressure as much as possible. As a result, the injection amount of each stage of multistage injection can be learned with high accuracy.

  Furthermore, since the injection amount is not adjusted, and only the injection timing is adjusted to be the reference point for pressure pulsation, it is possible to prevent the injection amount from being corrected twice together with the correction at the time of learning. Thereby, the injection quantity of each stage of multistage injection can be learned with high accuracy.

According to the second aspect of the invention, the injection timing adjusting means retards the injection timing of each stage after the first stage injection as the fuel temperature increases.
As the fuel temperature increases, the pressure pulsation cycle becomes longer because the propagation speed of the pressure pulsation becomes slower. Therefore, as the fuel temperature increases and the period of pressure pulsation becomes longer, it is necessary to retard the injection timing in order to start fuel injection at the pressure pulsation reference point.

  By the way, there is a delay time depending on the valve opening characteristics of the fuel injection valve from when the fuel injection valve is commanded to fuel injection until the fuel injection valve actually starts fuel injection. This injection delay time is substantially the same in each stage of multistage injection if the fuel pressure is the same.

  However, even if the injection timing is adjusted based on the fuel temperature and fuel injection is started at the reference point of pressure pulsation, the actual injection timing may deviate from the reference point. Since the rate of change of the pressure pulsation amplitude before and after the reference point varies depending on the position of the number of injection stages, when the injection timing deviates from the reference point, the injection delay time of each stage after the first stage injection varies.

  Therefore, according to the third aspect of the invention, the injection timing adjusting means is an injection delay in which the fuel injection valve actually starts injection in each stage of injection after the initial stage injection commanded by the injection command means to the fuel injection valve. The injection timing is adjusted in consideration of time variations.

  In this manner, by adjusting the injection timing in consideration of the variation in the injection delay time, the injection timing can be adjusted based on the fuel temperature, and fuel injection can be started as close as possible to the reference point of pressure pulsation. As a result, the injection amount can be learned with high accuracy. Variations in the injection delay time can be obtained in advance by measurement or simulation of injection data.

  By the way, the period of pressure pulsation generated by the injection in each stage of the multi-stage injection is substantially constant unless the length of the pipe for supplying fuel to the fuel injection valve, the fuel pressure, and the fuel temperature are changed. The pipe length is the same as long as it is not replaced with a pipe having a different length. Therefore, when performing multistage injection for learning, if it is considered that the fuel pressure and the fuel temperature do not change during one multistage injection, the fuel pressure in each stage is set with the reference point of pressure pulsation caused by the first stage injection as the injection timing. If injection can be started, the period of pressure pulsation does not change during multistage injection.

Therefore, according to the invention described in claim 4, the injection timing adjusting means sets the reference point of the pressure pulsation generated by the first stage injection as the injection timing of each stage after the first stage injection in the multistage injection.
Accordingly, if the reference point of pressure pulsation generated by the first stage injection is set as the injection timing, fuel injection can be started at the reference point in each stage after the first stage injection.

  However, even if the reference point of pressure pulsation is used as the injection timing, as described above, the actual injection timing may deviate from the reference point. As a result, the cycle of the combined wave of pressure pulsations generated in multi-stage injection is not constant and may vary from injection stage to injection stage.

Therefore, according to the invention described in claim 5, the injection timing adjusting means sets the reference point of the combined wave of the pressure pulsation generated in the multistage injection as the injection timing of each stage after the first stage injection.
By taking into account that the actual injection timing deviates from the reference point and the period of pressure pulsation changes, the pressure pulsation is obtained by setting the reference point of the combined wave of pressure pulsation as the injection timing of each stage after the first stage injection. The fuel injection can be started more accurately at the reference point. The reference point in the combined wave of pressure pulsation can be obtained in advance by measurement of injection data or simulation.

  According to the invention described in claim 6, the injection timing adjusting means is configured such that the injection interval between the front stage injection and the rear stage injection following the front stage injection in the multi-stage injection is greater than or equal to the minimum interval determined by the valve opening characteristics of the fuel injection valve. The reference point of the interval area is the injection timing of each stage after the first stage injection.

  From the time when the injection command means commands fuel injection to the fuel injection valve until the time when the fuel injection valve opens and starts fuel injection, the valve opening characteristic determined by the mechanical and electrical characteristics of the fuel injection valve Accordingly, a delay time occurs. Therefore, the injection interval between the front stage injection and the rear stage injection needs to be longer than the minimum interval determined by the valve opening characteristic of the fuel injection valve.

  By the way, since the pressure pulsation attenuates with time, the longer the injection interval from the preceding injection, the smaller the deviation amount of the subsequent injection amount due to the pressure pulsation when the actual injection timing deviates from the reference point. However, if the injection interval is too long, there is a risk of causing poor combustion or abnormal combustion noise in multistage injection. Therefore, a maximum value is set for the injection interval.

  Therefore, according to the invention described in claim 7, the injection timing adjusting means sets the reference point at which the injection interval is maximum between the maximum interval and the minimum interval allowed between the front-stage injection and the rear-stage injection as the first-stage injection. The injection timing for each subsequent stage is used.

As a result, multistage injection can be performed within a range that does not inhibit combustion, and even if the injection timing deviates from the reference point, the deviation in the injection amount due to pressure pulsation can be minimized.
The functions of the plurality of means provided in the present invention are realized by hardware resources whose functions are specified by the configuration itself, hardware resources whose functions are specified by a program, or a combination thereof. The functions of the plurality of means are not limited to those realized by hardware resources that are physically independent of each other.

Embodiments of the present invention will be described below with reference to the drawings.
(Fuel injection system)
FIG. 1 shows a fuel injection system 10 of the present embodiment. The fuel injection system 10 is for, for example, injecting fuel into each cylinder of a four-cylinder diesel engine (hereinafter also simply referred to as “engine”) 2 for an automobile. The fuel injection system 10 includes a high-pressure pump 14 that supplies fuel to a common rail 20, a common rail 20 that stores high-pressure fuel, and a fuel injection valve 30 that injects high-pressure fuel supplied from the common rail 20 into the combustion chamber of each cylinder of the engine 2. And an electronic control unit (ECU) 40 for controlling the system.

  The high-pressure pump 14 as a fuel supply pump incorporates a feed pump that pumps fuel from the fuel tank 12. The high-pressure pump 14 is a known pump that pressurizes fuel sucked from the feed pump into the pressurizing chamber by reciprocating the plunger as the cam of the camshaft rotates. Plural plungers of the high pressure pump 14 are installed around one cam.

  The metering valve 16 serving as a metering actuator is installed on the suction side of the high-pressure pump 14 and regulates the amount of fuel sucked by the high-pressure pump 14 during the suction stroke by current control. Then, by adjusting the fuel intake amount, the fuel discharge amount of the high-pressure pump 14 is adjusted.

  The common rail 20 is provided with a pressure sensor 22 that detects internal fuel pressure (common rail pressure). The pressure limiter 24 discharges the fuel in the common rail 20 when the common rail pressure exceeds a preset upper limit value, and restricts the common rail pressure so as not to exceed the upper limit value.

  The fuel injection valve 30 is, for example, a known injection valve that controls the lift of the nozzle needle that opens and closes the injection hole with the pressure in the control chamber. When fuel is injected from the fuel injection valve 30, the high pressure fuel supplied from the common rail 20 to the control chamber overflows to the low pressure side by communicating the control chamber with the low pressure side. As a result, the fuel pressure in the control chamber decreases and the nozzle needle lifts. The fuel overflowing from the control chamber of the fuel injection valve 30 to the low pressure side is returned to the fuel tank 12.

  The engine 2 is provided with a rotation speed sensor 32 that detects the rotation speed of the engine 2 as a sensor that detects the operating state. Further, as other sensors for detecting the driving state, an accelerator sensor for detecting an accelerator opening that is an operation amount of an accelerator pedal, a temperature sensor for detecting an intake air temperature (intake air temperature), and a fuel temperature (fuel temperature), respectively. Is provided in the fuel injection system 10.

  The ECU 40 constituting the fuel injection control device is constituted by a microcomputer centering on a CPU, ROM, RAM, flash memory, input / output interface and the like. Then, the ECU 40 detects output signals from various sensors including the pressure sensor 22, the rotation speed sensor 32, the accelerator sensor, the intake air temperature sensor, and the fuel temperature sensor to detect the engine operating state, and the engine is based on the detected engine operating state. Control the operating state.

  The ECU 40 stores the relationship between the duty ratio of the current supplied to the metering valve 16 and the discharge amount of the high-pressure pump 14 in a storage device such as a ROM or a flash memory as a discharge amount characteristic map. The ECU 40 performs feedback control of energization to the metering valve 16 so that the common rail pressure acquired from the pressure sensor 22 becomes the target common rail pressure.

Further, the ECU 40 controls the injection timing and the injection amount of the fuel injection valve 30 based on the engine operating state obtained from various sensors including the pressure sensor 22.
When performing multi-stage injection including pilot injection and post-injection before and after the main injection that causes the engine 2 to generate main torque during one combustion cycle, the ECU 40 performs the injection amount and injection timing in each stage of fuel injection, and Control the pattern of multi-stage injection.

  The ECU 40 functions as an injection command unit, an injection amount learning unit, and an injection timing adjustment unit by executing a control program stored in the ROM or flash memory.

(Injection command means)
The ECU 40 outputs an injection pulse signal as an injection command signal for controlling the injection timing and the injection amount of the fuel injection valve 30. The ECU 40 stores the injection amount characteristic of the injection amount with respect to the pulse width of the injection pulse signal in the storage device described above as a map for each common rail pressure that is the injection pressure. As the pulse width of the injection pulse signal becomes longer, the injection amount increases. Further, the ECU 40 controls the injection timing at which the fuel injection valve 30 starts injection based on the rising timing of the injection pulse signal.

(Injection amount learning means)
The ECU 40 performs minute injection amount learning when the load applied to the engine 2, the engine speed, the water temperature, and the like satisfy predetermined learning conditions during idle operation.

When the learning condition is satisfied, the ECU 40 equally divides the injection amount into n times, and commands the fuel injection valve 30 to perform n-stage multi-stage injection in one combustion cycle.
Then, the ECU 40 corrects the injection amount with respect to the fuel injection valve 30 of each cylinder so that the rotational speed fluctuation amount between the cylinders is smoothed. In this case, in each cylinder, the ECU 40 sets a value obtained by dividing the correction amount of the injection amount into n equal parts as the first injection amount correction amount of each stage.

  Next, the ECU 40 uniformly corrects the injection amount so that the average engine rotation speed of each cylinder becomes the target engine rotation speed. In this case, in each cylinder, the ECU 40 sets a value obtained by dividing the correction amount of the injection amount into n equal parts as the second injection amount correction amount of each stage.

  The ECU 40 smoothes the rotational speed fluctuation amount between the cylinders, and corrects the average engine rotational speed of each cylinder so as to become the target engine rotational speed, and corrects the first injection amount correction amount and the second injection amount correction of each stage in the multi-stage injection. The sum of the amount and the injection amount learning value learned by multi-stage injection in the same manner up to the previous time is taken as the learning value for the current minute injection amount learning.

  When the small injection amount learning is completed at one learning fuel pressure, the ECU 40 adjusts the discharge amount of the high-pressure pump 14 to adjust the common rail pressure to a different learning fuel pressure. The learned fuel pressure is a fuel pressure representing each pressure range obtained by dividing the entire range of the common rail pressure used as the injection pressure into a plurality of pressure ranges.

  Then, the above-described minute injection amount learning is performed by the multistage injection in which the injection amount is equally divided into n times at the adjusted learning fuel pressure. When the learning condition is satisfied, the ECU 40 changes the learning fuel pressure and performs the minute injection amount learning at the unlearned learning fuel pressure.

(Injection timing adjustment means)
When the minute injection amount learning is performed by the multi-stage injection, pressure pulsation is generated in the fuel pipe between the fuel injection valve 30 and the common rail 20 of each cylinder by the fuel injection in each stage. If pressure pulsation occurs in the fuel pipe between the fuel injection valve 30 and the common rail 20, the fuel pressure when the fuel injection valve 30 starts fuel injection varies, and there is a possibility that the injection amount of each stage after the first stage injection may vary. is there.

  Further, the pressure pulsation period fp is determined by the length of the fuel pipe between the fuel injection valve 30 and the common rail 20 and the propagation speed of the pressure pulsation, as shown in the following equation (1). As shown in the following equation (2), the propagation speed of the pressure pulsation is determined by the bulk modulus of the fuel and the fuel density.

Pressure pulsation period fp = fuel pipe length / pressure pulsation propagation speed (1)
Pressure pulsation propagation speed = (bulk elastic modulus of fuel / fuel density) ^1/2 (2)
The bulk modulus of fuel is a function of fuel pressure and fuel temperature, and the fuel density is a function of fuel temperature. The length of the fuel pipe is basically fixed in the fuel injection system 10. Therefore, the period of pressure pulsation changes with fuel pressure and fuel temperature.

  Therefore, as shown in FIG. 2, when the reference injection interval (TINT) of the learning multi-stage injection 202 is fixed based on the pressure pulsation 200 at the reference fuel temperature at a predetermined fuel pressure, for example, the fuel temperature Increases from the reference temperature, and as shown in FIG. 2, when the period of the pressure pulsation 210 becomes longer than the period of the pressure pulsation 200, the fuel pressure at the injection timing of each stage after the first stage injection may change. . As a result, the injection amount of each stage varies in the multistage injection 212 when the fuel is injected with the pressure pulsation 210 as compared to the multistage injection 202 when the fuel is injected with the pressure pulsation 200. If the injection amount at each stage varies due to a change in the fuel temperature, the minute injection amount cannot be learned with high accuracy by the multi-stage injection in which the injection amount is equally divided into n.

  Therefore, when performing multistage injection for learning, the present inventor adjusts the injection timing of each stage according to the fuel temperature so that the injection amount of each stage does not vary even if the period of pressure pulsation changes. Thought to do. Then, the inventor of the present application, based on the pressure pulsation period that changes according to the fuel temperature in addition to the fuel pressure, the injection timing of each stage after the first stage injection, in other words, the subsequent stage injection and the subsequent stage injection following the preceding stage injection, In the pressure pulsation 220 shown in FIG. 3, the reference point 222 that becomes 0 when the pressure pulsation 220 fluctuates positively and negatively is found as the injection timing of each stage. The reference point 222 is a point corresponding to ½ of the period of the pressure pulsation 220.

  At the reference point 222, the fuel pressure of the pressure pulsation 220 becomes the fuel pressure of the common rail pressure when the injection amount learning is performed, that is, the learning fuel pressure. Since the pressure pulsation due to the multistage injection is not generated when the first stage injection is started, the fuel pressure when the first stage injection is performed is the learning fuel pressure. Therefore, by adjusting the injection timing of each stage after the first stage injection based on the change of the fuel temperature and starting the fuel injection at the reference point 222 of the pressure pulsation 220, the fuel is obtained at the same learning fuel pressure in each stage of the multistage injection. Injection can be started. Thus, even if the period of the pressure pulsation changes according to the change in the fuel temperature, the injection timing is adjusted without adjusting the injection amount, and the reference point 222 of the pressure pulsation 220 is set as the injection timing. In each stage of the multistage injection in which the quantity is divided into n, variation in the injection quantity can be prevented and fuel can be injected evenly.

  Further, as shown in FIG. 4, the ECU 40 commands the fuel injection valve 30 to inject fuel, and after the drive current 230 is supplied to the fuel injection valve 30, the fuel injection valve 30 actually performs the fuel in each stage of the multistage injection 240. Before the injection is started, there is a delay time ΔT according to the valve opening characteristics determined by the mechanical characteristics and electrical characteristics of the fuel injection valve 30. Then, including this delay time ΔT, the fuel injection valve 30 is set with a minimum interval that needs to be secured at least between the front-stage injection and the rear-stage injection based on the valve opening characteristics of the fuel injection valve 30. .

  On the other hand, if the injection interval of each stage is too long in multistage injection, the latter half of the multistage injection is delayed, causing a problem of poor ignition or abnormal combustion noise. In this embodiment, the final stage injection timing of the multistage injection is set to the top dead center (TDC) of the compression stroke. Note that the final stage injection timing may be set variably in consideration of combustion noise, exhaust gas, and the like. In addition, the degree of occurrence of poor ignition or abnormal combustion noise also increases or decreases depending on the common rail pressure. Therefore, the maximum interval of the injection intervals is set based on the number of stages of multistage injection and the common rail pressure.

  Then, as shown in FIG. 5, a reference point 222 that is the injection timing of each stage is set in the interval region 254 between the set minimum interval 250 and maximum interval 252. If there are a plurality of reference points 222 in the interval region 254, any reference point 222 may be used as the injection timing.

  Here, since the pressure pulsation attenuates with time, in order to minimize the influence of the pressure pulsation generated by the fuel injection up to the previous stage, the minimum interval 250 and the maximum interval are used as the injection timing of each stage after the first stage injection. It is desirable to select a reference point 222 that is as close as possible to the maximum interval 252 with respect to 252.

  From the above, assuming that the minimum interval is fmin, the maximum interval is fmax, and the period of pressure pulsation is fp, the injection timing of each stage after the first stage injection is calculated based on the following equation (3) in the multistage injection for learning. Determined by the optimum injection interval TINTopt.

TINTopt = max (fmin <k × fp / 2 <fmax) (3)
In Expression (3), k is a natural number that satisfies (fmin <k × fp / 2 <fmax). When the reference point 222 as close as possible to the maximum interval 252 is used as the injection timing, the maximum value of k that satisfies Equation (3) is selected.

  By the way, in multistage injection, the pressure pulsation generated when the current injection is performed is a combination of pressure pulsations generated by the injection of each stage before the current injection. However, it is considered that the conrail pressure and the fuel temperature are constant in one multistage injection. From the formulas (1) and (2), if the Conrail pressure as the fuel pressure and the fuel temperature are constant without change, the period of the pressure pulsation does not change and is constant. Therefore, if each stage of injection is performed at the reference point 262 of the pressure pulsation 260 shown in FIG. 6, the amplitude of the pressure pulsation 260 is a combination of the stages, but the period of the pressure pulsation 260 is the first stage injection. This is the same as the period of pressure pulsation that occurs when

  Therefore, if the reference point 262 of the pressure pulsation 260 is set to the injection timing of each stage, the fuel injection of each stage can be performed at any reference point 262 of the pressure pulsation 260 in the multistage injection.

  However, as described above, after the drive current 230 is supplied to the fuel injection valve 30, the fuel injection valve 30 is not opened until the fuel injection valve 30 actually starts fuel injection at each stage of the multi-stage injection 260. A delay time ΔT occurs depending on the characteristics. This delay time ΔT varies depending on the learned fuel pressure when the injection amount learning is performed. Therefore, in order to set the reference point 262 to the injection timing in each stage after the first stage injection, it is naturally necessary to consider this delay time ΔT.

  Here, even if the reference point 262 is set as the injection timing in consideration of the delay time ΔT, it is difficult to accurately start the fuel injection at the reference point 262, and the actual injection timing may deviate from the reference point 262. . When the actual injection timing shifts from the reference point 262 to the position indicated by reference numeral 272 as indicated by the multistage injection 242 in FIG. 6, the period of the pressure pulsation 260 changes as indicated by the dotted pressure pulsation 270. Thus, when the injection timing deviates from the reference point 262, the injection amount at each stage after the first stage injection varies.

  Furthermore, the rate of change of pressure pulsation when deviating from the reference point 262 differs depending on the position of the number of injection stages and which reference point 262 between the minimum interval and the maximum interval is the injection timing, that is, the injection interval. In this case, as shown by the multi-stage injection 242 in FIG. 6, if the injection timing deviates from the reference point 262, the injection quantity at each stage varies and the injection quantity cannot be learned with high accuracy.

  Therefore, it is desirable to set the injection timing of each stage after the first stage injection, in other words, the injection interval of each stage in consideration of the injection delay variation in which the actual injection timing deviates from the reference point 262.

  In this embodiment, the injection variation correction amount for each stage for correcting the injection delay variation is stored in a storage device such as a ROM or a flash memory for each stage number position of the multistage injection as a map using the common rail pressure and the injection interval as parameters. ing. For example, when performing four-stage multi-stage injection, the second stage, third stage, and fourth stage injection variation correction amounts are set to Tc2, Tc3, Tc4, first stage and second stage, second stage and third stage, respectively. Assuming that the injection intervals between the third stage and the fourth stage are Tp1, Tp2, and Tp3, respectively, Tp1, Tp2, and Tp3 are expressed by the following equations (4), (5), and (6).

Tp1 = INTTop-Tc2 (4)
Tp2 = TINTop + Tc2-Tc3 (5)
Tp3 = TINTop + TC3-Tc4 (6)
In this way, by adjusting the injection interval in multi-stage injection, that is, the injection timing in consideration of the injection delay variation, the injection of each stage after the initial stage injection can be started more accurately at the reference point of pressure pulsation.

(Micro injection amount learning routine)
FIG. 7 shows a minute injection amount learning routine. The routine of FIG. 7 is executed when the load applied to the engine 2, the engine speed, the water temperature, and the like satisfy predetermined learning conditions during idle operation. In FIG. 7, “S” represents a step. When this routine is executed, the ECU 40 adjusts the common rail pressure to the learned fuel pressure that has not yet been learned in the minute injection amount learning, for example, by adjusting the discharge amount of the high-pressure pump 14. In addition, the multi-stage injection is exemplified by a four-stage injection.

  In S300, the ECU 40 reads the length of the fuel pipe between the common rail 20 and the fuel injection valve 30 from a storage device such as a ROM or a flash memory. Further, the ECU 40 detects the common rail pressure as the fuel pressure from the output signal of the pressure sensor 22, and detects the fuel temperature from the output signal of the fuel temperature sensor. Then, the ECU 40 calculates the pressure pulsation period fp by substituting the length of the fuel pipe, the fuel pressure, and the fuel temperature into the equations (1) and (2).

In S302, the ECU 40 calculates the optimal injection interval TINTopt between the respective stages based on the equation (3).
In S304, the ECU 40 determines the injection variation correction amounts Tc2, Tc3, and Tc4 for correcting the injection delay variation in each stage of injection after the first stage injection, the common rail pressure, the stage number position, and the optimum injection interval TINTopt calculated in S302. Calculate based on

  In S306, the ECU 40 substitutes the optimum injection interval TINTopt calculated in this way and the correction amounts Tc2, Tc3, and Tc4 into the equations (4) to (6), and the injection intervals Tp1, Tp2, Tp3 between the respective stages. Is calculated.

  In S308, the ECU 40 calculates the learning injection amount based on the engine speed and the accelerator opening, and based on the learning injection amount, each injection amount in each of the four stages of multistage injection is equalized. Sets the stage injection amount. Then, based on the injection intervals Tp1, Tp2, and Tp3 between the respective stages calculated in S306 and the injection quantity of each stage obtained by equally dividing the learning injection quantity into four parts, the ECU 40 performs the learning multi-stage uniform injection. To do. In this learning multi-stage injection, the ECU 40 smoothes fluctuations in the rotation speed between the cylinders and maintains the average engine rotation speed at the target rotation speed for each stage of the multi-stage injection that is injected for learning in each cylinder. Correct the injection amount.

In S310, the ECU 40 calculates the sum of the learned injection correction amount and the injection correction amount learned up to the previous time as the current learning value.
When the calculation of the learned value is completed in S310, the ECU 40 repeatedly executes this routine until the entire range of the working pressure range of the common rail pressure is learned.

  According to the present embodiment described above, when the multi-stage injection for learning is performed by equally dividing the injection amount by n, the injection at each stage after the initial stage injection is performed based on the fuel temperature, the common rail pressure, and the fuel pipe length. The timing is adjusted, and fuel injection is started in each stage after the first stage injection at the reference point of pressure pulsation. Thereby, the amplitude of the pressure pulsation generated in each stage of injection becomes a composite wave of the pressure pulsation generated by each stage of injection, but the period of the pressure pulsation does not change and is constant. Therefore, by starting the injection of each stage at the reference point of pressure pulsation, even if the period of pressure pulsation changes according to the fuel temperature, it is possible to reduce as much as possible that the injection amount in each stage varies due to the pressure pulsation. Thereby, multistage injection can be implemented and the minute injection amount can be learned with high accuracy.

  In addition, variations in the injection amount caused by the change in the pressure pulsation period according to the fuel temperature are prevented by adjusting the injection timing without adjusting the injection amount. Thus, it is possible to prevent the injection amount from being corrected twice. Thereby, multistage injection can be implemented and the minute injection amount can be learned with high accuracy.

[Other Embodiments]
In the above-described embodiment, the pressure pulsation amplitude is obtained by performing the injection at each stage with the pressure pulsation reference point as the injection timing of each stage after the first stage injection with respect to the pressure pulsation whose cycle changes according to the fuel temperature. Although it is a composite wave of pressure pulsations generated by each stage of injection, its period is assumed to be constant. On the other hand, although the reference point of the pressure pulsation is set as the injection timing, the actual injection timing is deviated from the reference point, so that the period of the combined wave of pressure pulsation, that is, the reference point may be considered. The deviation of the reference point in the combined wave of pressure pulsation can be obtained in advance by measurement of injection data or simulation.

  In the above embodiment, the functions of the injection command means and the injection timing adjustment means are realized by the ECU 40 whose functions are specified by the control program. On the other hand, at least some of the functions of the plurality of means may be realized by hardware whose functions are specified by the circuit configuration itself.

  As described above, the present invention is not limited to the above-described embodiment, and can be applied to various embodiments without departing from the gist thereof.

The block diagram which shows the fuel-injection system by this embodiment. The time chart which shows the shift | offset | difference of the period of pressure pulsation by the change of fuel temperature, and injection amount. The time chart which shows the period of pressure pulsation. The time chart which shows the injection delay of the fuel injection valve with respect to a drive current. The time chart which shows the setting of the injection interval of each step | level. The time chart which shows the synthesis | combination of a pressure pulsation, and the dispersion | variation in the injection delay of a fuel injection valve. The flowchart which shows a micro injection amount learning routine.

Explanation of symbols

2: diesel engine (internal combustion engine), 10: fuel injection system, 20: common rail, 30: fuel injection valve, 40: ECU (fuel injection control device, injection command means, injection timing adjustment means)

Claims (7)

In the fuel injection control device that learns the injection amount of each stage by equally dividing the injection amount of the fuel injection valve that is injected into each cylinder of the internal combustion engine and performing multi-stage injection,
Injection command means for commanding fuel injection to the fuel injection valve;
When the injection amount is learned by the multi-stage injection, the injection command means generates the multi-stage injection by adjusting the injection timing of each stage after the first stage injection commanded to the fuel injection valve based on the fuel temperature. Injection timing adjusting means for setting the reference point that becomes 0 when the pressure pulsation fluctuates positively and negatively as the injection timing of each stage after the first stage injection;
A fuel injection control device comprising:   2. The fuel injection control device according to claim 1, wherein the injection timing adjusting means retards the injection timing of each stage after the initial stage injection as the fuel temperature increases.   The injection timing adjustment means takes into account the variation in the injection delay time from when the injection command means commands fuel injection to the fuel injection valve until the fuel injection valve actually starts fuel injection. The fuel injection control device according to claim 1, wherein the injection timing of each subsequent stage is adjusted.   4. The fuel according to claim 1, wherein the injection timing adjusting unit sets the reference point of the pressure pulsation generated by the first-stage injection as the injection timing of each stage after the first-stage injection. 5. Injection control device.   The fuel injection according to any one of claims 1 to 3, wherein the injection timing adjusting means sets the reference point of the combined wave of the pressure pulsation as an injection timing of each stage after the first stage injection. Control device.   The injection timing adjusting means is configured to determine the reference in the interval region in which the injection interval between the pre-stage injection in the multi-stage injection and the post-stage injection following the pre-stage injection is equal to or greater than the minimum interval determined by the valve opening characteristic of the fuel injection valve. The fuel injection control device according to any one of claims 1 to 5, wherein the point is an injection timing of each stage after the initial stage injection.   The injection timing adjustment means sets the reference point at which the injection interval becomes maximum in the interval region between the maximum interval and the minimum interval allowed between the preceding stage injection and the following stage injection after the first stage injection. The fuel injection control device according to claim 6, wherein the injection timing is set for each stage.