JP5126196B2 - Fuel injection control device - Google Patents

Description

  The present invention is applied to a fuel injection system that injects fuel supplied from a fuel supply pump and accumulated in a common rail from a fuel injection valve installed in each cylinder of the internal combustion engine, and is based on the common rail pressure detected by a pressure sensor. The present invention relates to a fuel injection control device that controls a fuel injection system.

  Conventionally, in a fuel injection system that injects fuel supplied from a fuel supply pump and accumulated in a common rail from a fuel injection valve installed in each cylinder of the internal combustion engine, the fuel injection system is controlled based on a common rail pressure detected by a pressure sensor (For example, refer to Patent Document 1).

  For example, the fuel injection amount from the fuel injection valve is set based on the accelerator opening and the rotational speed of the internal combustion engine, and the injection command signal for instructing the fuel injection valve to inject the set command injection amount is the command injection It is generated based on the amount and the common rail pressure at that time.

  Also, the target pressure of the common rail is set based on the operating state of the internal combustion engine, the discharge amount of the fuel supply pump is controlled based on the deviation between the actual pressure of the common rail detected by the pressure sensor and the target pressure, and the common rail pressure is set as the target Feedback control is performed to match the pressure.

JP 2007-309103 A

  By the way, when the output of the pressure sensor does not change due to disconnection or the like and becomes a constant value of “high” or “low”, an abnormality of the pressure sensor can be easily diagnosed. However, if the sensor output deviates due to gain deviation or offset deviation due to aging of the pressure sensor, etc., the output of the pressure sensor changes with the change of the common rail pressure, so the common rail pressure detected by the pressure sensor is abnormal. It is difficult to diagnose whether or not there is. The fuel injection system cannot be controlled with high accuracy by the common rail pressure detected by the pressure sensor in which the output deviation occurs.

  When an abnormality of the pressure sensor is detected, for example, the common rail pressure detected by the pressure sensor is not used, and the injection amount of the fuel injection valve and the discharge of the fuel supply pump are based on the physical model of the fuel injection valve and the fuel supply pump. It is conceivable to calculate the amount, the amount of fuel leak, etc., and adjust the discharge amount of the fuel supply pump based on the amount of fuel entering and exiting the common rail to open control the common rail pressure to the target pressure. An injection command signal for the fuel injection valve is generated based on the target pressure and command injection amount set by the open control.

  However, if open control is executed based on the physical model without using the common rail pressure detected by the pressure sensor, the fuel supply pump machine difference and time change, the fuel injection valve machine difference and time change, fuel leak amount, temperature The common rail pressure may not be accurately controlled to the target pressure due to a setting error of the physical model such as the fuel passage volume.

  Then, since errors generated when controlling the common rail pressure by open control are accumulated without being corrected, the common rail pressure becomes too high or too low as compared with the target common rail as shown in FIG. There is a fear.

  The present invention has been made to solve the above-described problem, and provides a fuel injection control device that controls a fuel injection system with high accuracy based on a common rail pressure even when an abnormality occurs in a pressure sensor. With the goal.

According to the first aspect of the present invention, when the internal combustion engine is in the idling operation state, the rotational speed fluctuation of each cylinder is detected when the fuel injection valve executes a predetermined amount of fuel injection according to a command from the injection command means. In addition, the injection amount of each cylinder is corrected so as to smooth the rotational speed fluctuation between the cylinders, and the fuel injection valves of all cylinders are injected so that the average rotational speed of the internal combustion engine matches the target rotational speed during idle operation. The idle injection amount correction means uniformly corrects the amount.

  Here, when the rotational speed fluctuation between the cylinders is smoothed by the command injection amount corrected by the idle injection amount correcting means, and the average rotational speed of the internal combustion engine matches the target rotational speed during idle operation, the fuel injection of each cylinder The actual injection amount of the valve should be a predetermined amount commanded to the fuel injection valve before correction.

  When the injection amount is corrected by the idle injection amount correction means so that the injection amount of the fuel injection valve becomes a predetermined amount, and the common rail pressure during idle operation is controlled to the predetermined pressure, the internal combustion engine The correction amount for correcting the injection amounts of the fuel injection valves of all the cylinders so as to make the average rotation speed of the engine coincide with the target rotation speed during idle operation should be zero.

  In other words, with the command injection amount corrected by the idle injection amount correction means, the injection amounts of the fuel injection valves of all cylinders are corrected so that the average rotation speed of the internal combustion engine matches the target rotation speed during idle operation. When the correction amount to be performed is not 0, it is considered that the common rail pressure deviates from the predetermined pressure according to the correction amount. There is a correlation between the correction amount at this time and the deviation amount of the common rail pressure.

  Therefore, the idle injection amount correction means is provided for the fuel injection valves for all cylinders so that the predetermined amount of injection commanded to the fuel injection valves by the injection command means and the average rotational speed of the internal combustion engine coincide with the target rotational speed during idle operation. The pressure estimation means can estimate the common rail pressure based on the corrected injection amount when the injection amount is uniformly corrected.

  For example, the corrected command injection amount can be calculated from a predetermined amount of injection commanded to the fuel injection valve by the injection command means and a correction amount for making the average rotation speed coincide with the target rotation speed during idle operation. Based on the corrected command injection amount, the fuel injection valve executes a predetermined amount of fuel injection according to a command from the injection command means. The command injection amount commanded by the injection command means so that the fuel injection valve injects a predetermined amount of fuel is determined by the actual pressure of the common rail.

  Therefore, based on a predetermined amount of injection commanded by the injection command means to the fuel injection valve and a corrected injection amount corrected by the idle injection amount correction means so that the average rotation speed matches the target rotation speed during idle operation, The pressure estimation means can estimate the common rail pressure.

Thus, with to smooth the rotation speed variations among the cylinders during idle operation, by using the injection amount learning method for matching the average rotational speed to the target rotational speed can be estimated common rail pressure at that time. Thus, even when an abnormality occurs in the pressure sensor, the fuel injection system can be controlled with high accuracy based on the estimated common rail pressure.

According to the second aspect of the present invention, when the pressure sensor is abnormal, the pressure control means replaces the actual pressure detected by the pressure sensor with the estimated common rail pressure estimated by the pressure estimating means and the common rail target pressure. The discharge amount of the fuel supply pump is feedback controlled based on the deviation.

Thereby, even when the pressure sensor is abnormal, the discharge amount of the fuel supply pump can be controlled with high accuracy based on the estimated common rail pressure.
According to the invention described in claim 3 , it is diagnosed whether the pressure sensor is abnormal by comparing the actual pressure of the common rail detected by the pressure sensor with the estimated pressure of the common rail estimated by the pressure estimating means.

  As a result, not only when the output of the pressure sensor does not change due to a disconnection or the like but is a constant value of “high” or “low”, the output of the pressure sensor varies depending on the common rail pressure. Even in this case, the abnormality of the pressure sensor can be easily diagnosed.

  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.

The block diagram which shows the fuel-injection system by 1st Embodiment. (A) is a block diagram of F / B control at the normal time, (B) is a block diagram of F / B control at the time of abnormal pressure sensor. A time chart which shows common rail pressure control by presumed common rail pressure. The flowchart which shows the common rail pressure estimation at the time of non-injection deceleration. The flowchart which shows F / B control of the common rail pressure based on an estimated pressure. The flowchart which shows the common rail pressure estimation at the time of idling by 2nd Embodiment. The characteristic view which shows the correction | amendment injection quantity at the time of idle driving | operation. The characteristic view which shows the common rail pressure estimation at the time of idle driving | operation. The time chart which shows the change of the common rail pressure at the time of the conventional pressure sensor failure.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
A fuel injection system according to a first embodiment of the present invention is shown in FIG.

(Fuel injection system 10)
The fuel injection system 10 of the present embodiment is for supplying fuel to a diesel engine (hereinafter also simply referred to as “engine”) 2 that is, for example, a four-cylinder internal combustion engine for automobiles. A fuel supply pump 14 that supplies fuel, a common rail 20 that stores high-pressure fuel, 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 device that controls the system A control device (Electronic Control Unit; ECU) 40 is provided.

  The fuel supply pump 14 incorporates a feed pump that pumps fuel from the fuel tank 12. The fuel supply pump 14 is a known pump that pressurizes the fuel sucked into the pressurizing chamber from the feed pump when the plunger reciprocates as the cam of the camshaft rotates. The metering valve 16 as a metering actuator is installed on the suction side of the fuel supply pump 14, and controls the amount of fuel sucked by the fuel supply pump 14 in the suction stroke by current control. By adjusting the fuel intake amount, the fuel discharge amount of the fuel supply pump 14 is adjusted.

  The common rail 20 is provided with a pressure sensor 22 for detecting the internal fuel pressure (common rail pressure), and a pressure reducing valve 24 for reducing the common rail pressure by overflowing the internal fuel to the fuel tank 12 side.

  The engine 2 is provided with a rotational speed sensor 32 that detects an engine rotational speed (NE) as a sensor that detects an operating state. Further, as other sensors for detecting the driving state, an accelerator sensor for detecting an accelerator opening (ACCP) that is an operation amount of an accelerator pedal by a driver, a temperature of cooling water (water temperature), a temperature of intake air (intake air temperature). The fuel injection system 10 is provided with a temperature sensor or the like for detecting each of these.

  The fuel injection valve 30 is, for example, a known electromagnetic valve that controls the lift of the nozzle needle that opens and closes the nozzle hole with the pressure in the control chamber. The injection amount of the fuel injection valve 30 is controlled by the pulse width of the injection command signal commanded from the ECU 40. As the pulse width of the injection command signal becomes longer, the injection amount increases.

  The ECU 40 as a fuel injection control device is mainly configured by a microcomputer centering on a CPU, RAM, ROM, flash memory and the like. The ECU 40 takes in output signals from various sensors including the pressure sensor 22 and the rotation speed sensor 32 and controls the engine operating state.

  For example, the ECU 40 controls the discharge amount of the fuel supply pump 14 so that the common rail pressure detected by the pressure sensor 22 becomes the target pressure. The ECU 40 sets a current value for controlling the metering valve 16 based on a characteristic map representing a correlation between the current value for controlling the metering valve 16 and the discharge amount.

Further, the ECU 40 controls the fuel injection amount of the fuel injection valve 30, the fuel injection timing, and the multi-stage injection pattern in which pilot injection, post injection, etc. are performed before and after the main injection.
The ECU 40 stores an injection characteristic map indicating the correlation between the pulse width of the injection command signal for instructing the fuel injection valve 30 and the injection amount in the ROM or flash memory for each predetermined pressure range of the common rail pressure. Then, when the injection amount of the fuel injection valve 30 is determined based on the engine speed and the accelerator opening, the ECU 40 refers to the injection characteristic map of the corresponding pressure range according to the common rail pressure detected by the pressure sensor 22. The pulse width of the injection command signal for commanding the determined injection amount to the fuel injection valve 30 is acquired.

  Next, feedback (F / B) control in the fuel injection system 10 of the first embodiment will be described based on the control block of FIG. In FIG. 2, the PI control unit 100, the physical model 102 of the fuel injection valve (INJ) 30, the physical model 104 of the fuel supply pump (S / P) 14, the common rail system (CRS) 110, and the common rail pressure prediction unit 120. The pressure estimation unit 130 is a control block in the ECU 40.

(When pressure sensor 22 is normal)
When the pressure (Pc) sensor 22 is normal, the PI control unit 100 feeds back the actual pressure of the common rail 20 detected from the output signal of the pressure sensor 22 as shown in FIG. The deviation from the pressure is obtained, and the discharge amount of the fuel supply pump 14 is calculated so that the actual pressure matches the target pressure. The target pressure for the common rail is set based on engine operating conditions such as engine speed and accelerator opening.

The physical model 102 of the fuel injection valve 30 calculates the injection amount of the fuel injection valve 30 based on the accelerator opening and the engine speed.
The sum of the discharge amount of the fuel supply pump 14 calculated by the PI control unit 100 and the injection amount calculated by the physical model 102 of the fuel injection valve 30 is used as the fuel amount to be discharged by the fuel supply pump 14. 14 physical models 104. Actually, the fuel leak amount of the fuel injection system 10 is also added to the discharge amount of the fuel supply pump 14 and the injection amount of the fuel injection valve 30 and input to the physical model 104 of the fuel supply pump 14.

  The physical model 104 of the fuel supply pump 14 calculates a current value for controlling the metering valve 16 of the fuel supply pump 14 based on the input fuel amount. The fuel supply pump 14 discharges a fuel amount corresponding to the current value when the metering valve 16 is controlled by the current value calculated by the physical model 104.

  The common rail system 110 includes a common rail 20 and a fuel injection valve 30. The fuel discharged from the fuel supply pump 14 is accumulated in the common rail 20 and injected from the fuel injection valve 30.

  Then, based on the deviation between the actual pressure of the common rail detected by the pressure sensor 22 and the target pressure, the PI control unit 100 feedback-controls the discharge amount of the fuel supply pump 14 so that the actual pressure matches the target pressure.

The pressure prediction unit 120 calculates a predicted pressure at which the common rail pressure changes next based on the following equation (1).
P (i + 1) = (Qpump + Qinj + Qleak) × bulk elastic modulus / high pressure part volume + Px (1)
Here, P (i + 1): the predicted pressure next to the common rail, Px: the current common rail pressure, Qpump: the discharge amount of the fuel supply pump 14, Qinj: the injection amount of the fuel injection valve 30, Qleak: fuel injection from the fuel supply pump 14 The amount of fuel leakage of the fuel injection system 10 reaching the valve 30 and the volume of the high pressure part: the volume of the high pressure part of the fuel injection system 10 extending from the fuel supply pump 14 to the fuel injection valve 30. Qinj is acquired from the physical model 102 of the fuel injection valve 30, and Qpump is acquired from the physical model 104 of the fuel supply pump 14.

  When the pressure sensor 22 is normal, the detected pressure of the pressure sensor 22 is substituted for Px. When the pressure sensor 22 is abnormal, the estimated pressure of the common rail estimated by the pressure estimation unit 130 or the predicted pressure predicted by the pressure prediction unit 120 last time is substituted as will be described later.

  When the actual common rail pressure approaches the target pressure, the ECU 40 switches the input of the PI control unit 100 from the pressure detected by the pressure sensor 22 to the pressure predicted by the pressure prediction unit 120. Then, the discharge amount of the fuel supply pump 14 is controlled based on the deviation between the predicted pressure calculated by the equation (1) and the target pressure so that the common rail pressure does not overshoot the target pressure, and the common rail pressure is set to the target pressure. Move closer to.

(When pressure sensor 22 is abnormal)
When the pressure sensor 22 is abnormal, feedback control based on the output signal of the pressure sensor 22 cannot be executed. In this case, the pressure estimation unit 130 of the ECU 40 instructs the fuel injection valve 30 to perform a predetermined amount of minute injection during the non-injection deceleration operation. The fuel injection at this time may be combined with the fuel injection for learning the minute injection amount, or may be executed for estimating the common rail pressure in this embodiment separately from the learning of the minute injection amount.

  The pressure estimator 130 detects, from the output signal of the rotational speed sensor 32, a fluctuation amount (Δω) of the engine rotational speed that is caused by the minute injection performed during the non-injection deceleration operation. Then, the engine torque is calculated from the fluctuation amount of the engine speed, and the actual injection amount actually injected from the fuel injection valve 30 is calculated from the engine torque.

  When the minute injection amount learning has already been performed and the actual injection amount calculated this time is correct, the common rail pressure is calculated from the injection characteristic map 132 of the pulse width of the injection command signal that commands the minute amount injection and the actual injection amount. Can be estimated.

  As shown in FIG. 2B, when the pressure sensor 22 is abnormal, the ECU 40 estimates the common rail 20 estimated by the PI control unit 100 when the pressure estimation unit 130 estimates the common rail pressure during no-injection deceleration. The pressure is used instead of the pressure detected by the pressure sensor 22, and the discharge amount of the fuel supply pump 14 is feedback controlled based on the deviation between the estimated pressure and the target pressure.

  When the engine operating state is no longer the non-injection deceleration state, as shown by the dotted line in FIG. 2B, the ECU 40 calculates the common rail predicted pressure and target pressure predicted by the pressure prediction unit 120 instead of the estimated pressure. Based on the deviation, the discharge amount of the fuel supply pump 14 is controlled to control the common rail pressure.

  In Formula (1), when the predicted pressure is calculated first after the engine operating state is no longer the non-injection deceleration state, the estimated pressure Pp of the common rail pressure that is estimated last in the non-injection deceleration state is used as Px. .

  As described above, in the first embodiment, even when the pressure sensor 22 is abnormal, not only the common rail pressure is predicted by the pressure prediction unit 120 but also the actual value of the fuel injection valve 30 from the minute injection executed in the non-injection deceleration state. The injection amount is detected, and the common rail pressure is estimated based on the actual injection amount and the injection command signal.

  Therefore, as shown in FIG. 3, even when the actual common rail pressure 202 is shifted as shown by the dotted line with respect to the common rail pressure 200 assumed when feedback control is performed only by the common rail pressure predicted by the pressure prediction unit 120. The common rail pressure can be prevented from greatly deviating from the target pressure by feedback control of the discharge amount of the fuel supply pump 14 based on the common rail pressure estimated in the non-injection deceleration state.

(Common rail pressure estimation routine)
FIG. 4 shows a common rail pressure estimation routine. The common rail pressure estimation routine of FIG. 4 is always executed. In FIG. 4, “S” represents a step.

  In S400, the ECU 40 determines whether or not a learning condition for the minute injection amount is satisfied. The ECU 40 determines that the learning condition is satisfied if it is a non-injection deceleration state in which the vehicle speed is reduced and fuel injection is cut when the accelerator is off. When the learning condition is not satisfied (S400: No), the ECU 40 ends this routine.

  When the learning condition is satisfied (S400: Yes), the ECU 40 instructs the fuel injection valve 30 to perform single injection for learning the small injection amount (S402), and from the fluctuation amount (Δω) of the engine speed at that time The engine torque is calculated, and the actual injection amount of the fuel injection valve 30 is calculated from the engine torque (S404).

In S406, the ECU 40 acquires the common rail pressure at that time as the estimated pressure from the injection characteristic map 132 of the pulse width of the injection command signal and the injection amount.
In S408, the ECU 40 determines based on the flag F whether or not the pressure sensor 22 has already been diagnosed as abnormal. If the pressure sensor 22 has already been diagnosed as abnormal, the flag F is set to 1. If the pressure sensor 22 has not been diagnosed as abnormal, the flag F is set to 0. ing. If the flag F is not 0 and the pressure sensor 22 has already been diagnosed as abnormal (S408: No), the ECU 40 proceeds to S418.

  If the flag F is 0 and the pressure sensor 22 has not yet been diagnosed as being abnormal (S408: Yes), in S410, the ECU 40 calculates the estimated common rail pressure estimated in S406 and the detected common rail pressure by the pressure sensor 22. It is determined whether or not the absolute value of the difference exceeds a predetermined value. If the absolute value of the difference between the estimated pressure and the detected pressure is equal to or less than the predetermined value (S410: No), the ECU 40 determines that the pressure sensor 22 is normal and ends this routine.

  When the absolute value of the difference between the estimated pressure and the detected pressure exceeds a predetermined value (S410: Yes), the ECU 40 determines that the pressure sensor 22 is abnormal and increments (+1) the abnormal counter in S412. . In S414, the ECU 40 determines whether or not an abnormality has occurred in the pressure sensor 22 continuously n times from the value of the abnormality counter. If the abnormality of the pressure sensor 22 has not occurred continuously n times (S414: No), the ECU 40 does not determine that the pressure sensor 22 is abnormal and ends this routine.

  When the abnormality of the pressure sensor 22 has occurred n times continuously (S414: Yes), in S416, the ECU 40 determines that the pressure sensor 22 is abnormal and sets the flag F to 1.

  In S418, the ECU 40 sets the flag C to 1 and ends this routine. If the flag C is 1, it indicates that the common rail pressure is estimated, and if it is 0, the common rail pressure is not estimated.

(Pressure feedback routine)
FIG. 5 shows a common rail pressure feedback routine. The pressure feedback routine of FIG. 5 is always executed. In FIG. 5, “S” represents a step.

  In S420, the ECU 40 determines whether or not the flag F is 1. As described above, the flag F is set to 1 when the abnormality of the pressure sensor 22 has already been diagnosed, and is set to 0 when the pressure sensor 22 has not been diagnosed as abnormal.

  When the flag F is not 1 (S420: No), since the pressure sensor 22 is normal, the ECU 40 executes normal feedback control in S422 and ends this routine. That is, the ECU 40 feedback-controls the discharge amount of the fuel supply pump 14 so that the common rail pressure detected by the pressure sensor 22 matches the target pressure.

  When the flag F is 1, that is, when the pressure sensor 22 is abnormal (S420: Yes), the ECU 40 determines whether or not the flag C is 1 in S424. As described above, if the flag C is 1, it indicates that the common rail pressure is estimated, and if it is 0, the common rail pressure is not estimated.

  When the flag C is 1, that is, when the common rail pressure is estimated in the common rail pressure estimation routine of FIG. 4 (S424: Yes), the ECU 40 substitutes the estimated pressure Pp into Px (S426), and sets the flag C to 0. Setting is made (S428). Then, the predicted pressure P (i + 1) is calculated based on the formula (1) (S430), the discharge amount of the fuel supply pump 14 is feedback-controlled based on the estimated pressure Pp (S432), and this routine ends.

  When the flag C is not 1, that is, when the common rail pressure is not estimated (S424: No), the ECU 40 substitutes the predicted pressure P (i + 1) predicted last time in the equation (1) as P (i) for Px. (S434) The predicted pressure P (i + 1) is calculated (S436). Then, the discharge amount of the fuel supply pump 14 is controlled based on the predicted pressure P (i + 1) to control the common rail pressure (S438), and this routine is terminated.

  In the first embodiment, the ECU 40 corresponds to the fuel injection control device of the present invention, and the pressure estimation unit 130 corresponds to the pressure estimation means of the present invention. 4 corresponds to the function executed by the injection command means of the present invention, the process of S404 corresponds to the function executed by the injection amount detection means of the present invention, and the process of S406 corresponds to the present invention. The pressure estimation means corresponds to the function executed by the pressure estimation means, and the processing of S408 to S416 corresponds to the function executed by the abnormality diagnosis means of the present invention. 5 corresponds to the function executed by the pressure control means of the present invention.

  In the first embodiment described above, in the non-injection deceleration operation state, the learning method of the minute injection amount is applied to detect the actual injection amount from the fluctuation amount of the rotation speed, and the common rail pressure is estimated from the actual injection amount. . As a result, the estimated pressure of the common rail and the detected pressure of the pressure sensor 22 can be compared, so that not only when the output of the pressure sensor does not change due to a disconnection or the like and is a constant value of “high” or “low”. Even when the output of the pressure sensor 22 changes according to the common rail pressure, an abnormality of the pressure sensor 22 can be easily diagnosed even when the output is shifted due to a gain shift or an offset shift.

Even when an abnormality occurs in the pressure sensor 22, the discharge amount of the fuel supply pump 14 can be controlled based on the estimated pressure, and the common rail pressure can be controlled to the target pressure with high accuracy.
An appropriate injection command signal for instructing the fuel injection valve 30 to inject an injection amount set from the engine speed and the accelerator opening based on the estimated pressure even when an abnormality occurs in the pressure sensor 22. Can be generated.

[Second Embodiment]
A second embodiment of the present invention is shown in FIG. In the second embodiment, the common rail pressure is estimated by executing FCCB correction and ISC correction during idle operation.

(Common rail pressure estimation routine)
FIG. 6 shows a common rail pressure estimation routine according to the second embodiment. The common rail pressure estimation routine of FIG. 6 is always executed. In FIG. 6, “S” represents a step. Note that the processing in S448 to S458 in FIG. 6 is substantially the same as the processing in S408 to S418 in FIG.

  In S440, the ECU 40 determines whether or not a learning condition for the minute injection amount is satisfied. If the accelerator is turned off and the vehicle speed is 0, the engine speed is stable within a predetermined range, and the water temperature, intake air temperature, intake pressure, etc. are within a predetermined range for executing injection amount learning, the ECU 40 It is determined that the learning condition for the minute injection amount at the time is satisfied.

When the learning condition is not satisfied (S440: No), the ECU 40 ends this routine.
When the learning condition is satisfied (S440: Yes), in S442, as shown in FIG. 7, the ECU 40 equally divides the command injection amount Qtotal of a predetermined amount set for learning the minute injection amount during idle operation into n equal parts. Then, the fuel injection valve 30 is commanded n times. In FIG. 7, for example, Qtotal is set to 5 mm ³ , Qtotal is divided into five, and five fuel injections are commanded to the fuel injection valve 30 by Qtotal / 5 = 1 mm ³ .

In addition, what is necessary is just to set suitably the number which divides | segments instruction | command injection amount in each cylinder according to instruction | command injection amount and the micro injection amount to learn. For example, if the command injection amount is 6 mm ³ , if divided into 6, the divided injection amount is 1 mm ³ , and if divided into 3, the divided injection amount is 2 mm ³ .

Further, the pulse width of the injection command signal for commanding the fuel injection valve 30 to inject Qtotal / 5 = 1 mm ³ is the common rail pressure set to a predetermined pressure and the command injection amount Qtotal / 5 = 1 mm ³ during idling operation. And based on the injection characteristic map. In this case, the FCCB correction and ISC correction, which will be described later, are reflected in the pulse width of the injection command signal for instructing the injection of Qtotal / 5 = 1 mm ³ .

  In S444, the ECU 40 executes inter-cylinder rotational speed fluctuation correction (FCCB correction) and idle average rotational speed correction (ISC correction). The engine speed used here is the same as or different from the engine speed detected from the above-described speed sensor 32.

  In the FCCB correction, the ECU 40 detects the rotational speed fluctuation of each cylinder from the rotational speed sensor 32, and adds the FCCB correction amount (ΔQc) to Qtotal in each cylinder so as to smooth the rotational speed fluctuation between the cylinders. In this case, ΔQc / 5 is added to the injection amount Qtotal / 5 of each injection divided into five times.

  Further, in the ISC correction, the ECU 40 uniformly adds an ISC correction amount (QISC) to all the cylinders in order to make the engine rotation speed coincide with the target rotation speed during idle operation. In this case, QISC / 5 is further added to ΔQc / 5 added by FCCB correction to the injection amount Qtotal / 5 of each injection divided into five times. Here, ΔQc / 5 and QISC / 5 are corrected as the pulse width of the injection command signal for the fuel injection valve 30.

  Thus, by adding ΔQc / 5 by FCCB correction and QISC / 5 by ISC correction to Qtotal / 5, the rotational speed fluctuation between the cylinders is smoothed, and the average engine speed becomes the target idle speed. Match the speed.

  By the way, if the common rail pressure is a predetermined pressure assumed from the engine operating state during the idling operation and the fuel injection valve 30 is injecting the predetermined amount of fuel commanded by the injection command signal, the ISC correction which is the correction injection amount is corrected. The amount will be zero and the average engine speed should be the target speed.

  Conversely, as shown in FIG. 8, when the average engine speed is deviated from the target engine speed and the current ISC correction amount for making the average engine speed equal to the target engine speed is not zero, the injection command This indicates that the injection amount of the fuel injection valve 30 is deviated from the injection amount in the injection characteristic map at the predetermined pressure assumed with respect to the signal, or that the common rail pressure is deviated from the predetermined pressure assumed during idle operation.

  In addition, the ISC correction amount is not zero even though the fuel injection valve 30 injects a predetermined amount of fuel during the idling operation and the injection command signal has already been corrected so that the average rotational speed matches the target rotational speed. In this case, it is considered that the actual pressure of the common rail is deviated from the predetermined pressure. At this time, there is a correlation between the deviation amount of the common rail pressure and the ISC correction amount.

  Here, since the ISC correction amount is the correction amount of the pulse width of the injection command signal as described above, the average rotational speed during idle operation is based on the ISC correction amount, that is, the correction amount of the pulse width of the injection command signal. The pulse width of the corrected injection command signal corrected to coincide with the target rotation speed can be calculated. The fuel injection valve 30 injects a predetermined amount of fuel by the corrected injection command signal. Therefore, the corresponding common rail pressure in the injection characteristic map can be estimated based on the predetermined amount of command injection and the pulse width of the corrected injection command signal. That is, the common rail pressure can be estimated based on a predetermined amount of command injection and an ISC correction amount.

Therefore, in S446, the ECU 40 estimates the common rail pressure based on the ISC correction amount.
Hereinafter, the processing of S448 to S458 is substantially the same as the processing of S408 to S418 in FIG.

  In the second embodiment, the processing of S440 and S442 in FIG. 6 corresponds to the function executed by the injection command means of the present invention, the processing of S444 corresponds to the function executed by the idle injection amount correction means, and the processing of S446 is performed. This corresponds to the function executed by the pressure estimation means.

  In the plurality of embodiments described above, in the non-injection deceleration operation state or the idle operation state where the learning condition is satisfied, the injection amount is learned from the fluctuation amount of the rotation speed (rotation speed) by applying the small injection amount learning method. Then, the common rail pressure was estimated from the fluctuation amount of the rotation speed on the assumption that the injection amount was corrected normally in the previous learning.

Thereby, even when the pressure sensor 22 for detecting the common rail pressure is abnormal, the discharge amount of the fuel supply pump 14 can be feedback-controlled based on the estimated common rail pressure.
As a result, the common rail pressure can be prevented from becoming too high or too low with respect to the target pressure, and the common rail pressure can be controlled with high accuracy. Therefore, it is possible to omit a pressure limiter that opens when the common rail pressure rises excessively.

  Moreover, since the estimated pressure of the common rail can be used instead of the pressure sensor 22, it is not necessary to install two pressure sensors 22 for fail-safe when an abnormality occurs in the pressure sensor 22.

[Other Embodiments]
In the above embodiment, the injection amount is learned by applying the learning method of the minute injection amount, and the estimated common rail pressure estimated based on the learned injection amount is applied to the discharge amount control of the fuel supply pump 14 and the fuel injection valve 30. Used to generate injection command signal. In addition, when the pressure sensor 22 is abnormal, the estimated pressure of the common rail may be used for other control of the fuel injection system 10.

  In the above embodiment, the functions of the injection command means, the injection amount detection means, the pressure estimation means, the idle injection amount correction means, the pressure control means, and the abnormality diagnosis means are realized by the ECU 40 whose functions are specified by the control program. On the other hand, at least a part of the functions of the above means may be realized by hardware whose function is 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.

2: diesel engine (internal combustion engine), 14: fuel supply pump, 20: common rail, 22: pressure sensor, 30: fuel injection valve, 40: ECU (fuel injection control device, injection command means, injection amount detection means, pressure estimation) Means, idle injection amount correction means, pressure control means, abnormality diagnosis means)

Claims (3)

The fuel injection system is applied to a fuel injection system that injects fuel supplied from a fuel supply pump and accumulated in a common rail from a fuel injection valve installed in each cylinder of the internal combustion engine, and is based on a common rail pressure detected by a pressure sensor. In the fuel injection control device to control,
Injection command means for commanding a predetermined amount of fuel injection to the fuel injection valve when the internal combustion engine is in an idle operation state;
A variation in the rotation speed of each cylinder when the fuel injection valve performs fuel injection is detected by an injection command signal from the injection command means, and the injection amount of each cylinder is set so as to smooth the rotation speed variation between the cylinders. Idle injection amount correction means for correcting the injection amounts of the fuel injection valves of all the cylinders uniformly so as to make the average rotation speed of the internal combustion engine coincide with the target rotation speed during idle operation,
The idle injection amount correcting means is provided for all cylinders so that a predetermined injection amount commanded to the fuel injection valve by the injection command means and an average rotational speed of the internal combustion engine coincide with a target rotational speed during idle operation. Pressure estimating means for estimating the common rail pressure based on a corrected injection amount when the injection amount of the fuel injection valve is uniformly corrected;
A fuel injection control device comprising: Pressure control means for feedback-controlling the common rail pressure by controlling a discharge amount of the fuel supply pump based on a deviation between an actual pressure of the common rail detected by the pressure sensor and a target pressure of the common rail;
When the pressure sensor is abnormal, the pressure control means is based on a deviation between the estimated pressure of the common rail estimated by the pressure estimating means and the target pressure of the common rail, instead of the actual pressure detected by the pressure sensor. Feedback control of the discharge amount of the fuel supply pump
The fuel injection control device according to claim 1 . Comparing an actual pressure of the common rail detected by the pressure sensor with an estimated pressure of the common rail estimated by the pressure estimating means, an abnormality diagnosis means for diagnosing whether or not the pressure sensor is abnormal is provided. The fuel injection control device according to claim 1 , wherein the fuel injection control device is a fuel injection control device.

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