JP6332071B2 - Fuel injection control device - Google Patents

Description

  The present invention relates to a fuel injection control device that controls the state of fuel injection into an internal combustion engine.

  Generally, as a solution to the problems of smoke deterioration and unburned fuel deterioration caused by incomplete combustion of fuel that occurs when the amount of oxygen commensurate with the amount of fuel injected into the internal combustion engine does not remain in the cylinder The one disclosed in Patent Document 1 is known. The technique described in Patent Document 1 measures the oxygen concentration at the time of intake, and if the oxygen concentration is less than a predetermined reference concentration, the injection timing is advanced to suppress unburned fuel and smoke. .

JP 2011-99344 A

  Here, in general, combustion noise generated in the combustion process of the internal combustion engine has a correlation with the inclination of the heat generation rate, and the combustion noise can be reduced by reducing the inclination of the heat generation rate. As described in Patent Document 1, when the injection timing is advanced in order to suppress deterioration of unburned fuel and smoke, the inclination of the heat generation rate in combustion tends to increase. In this technique, the slope of the heat generation rate is not controlled at all. Therefore, there is a possibility that a large combustion noise is generated with respect to the target noise level.

  The present invention has been made in view of the above problems, and an object thereof is to provide a fuel injection control device capable of suppressing both deterioration of unburned fuel and smoke and deterioration of combustion noise.

  A fuel injection control apparatus according to one aspect of the present invention is a fuel injection control apparatus configured to control an injection state of fuel into an internal combustion engine (10), wherein the combustion noise of the internal combustion engine exceeds a target noise level. Based on target heat generation rate determining means (80) for determining the time transition of the target heat generation rate, the intake oxygen concentration supplied to the internal combustion engine in the intake stroke, and the oxygen consumption amount at each time in the combustion stroke The residual oxygen concentration estimating means (90) for estimating the time transition of the in-cylinder residual oxygen concentration during the combustion stroke when it is assumed that the combustion has reached the target heat generation rate, and the estimated in-cylinder residual oxygen Target injection rate determining means (100) for determining the time transition of the target injection rate based on the time transition of the concentration, and injection control so that the time transition of the fuel injection rate to the internal combustion engine becomes the time transition of the target injection rate First system to do Characterized in that it comprises a means (130).

  According to the fuel injection control device of the present invention, the time transition of the in-cylinder residual oxygen concentration is estimated such that the target heat generation rate does not exceed the target noise level over time. Further, the time transition of the target injection rate is determined based on the time transition of the in-cylinder residual oxygen concentration, and the injection control is executed so that the time transition of the injection rate becomes the time transition of the target injection rate. Therefore, it is possible to perform injection control so that the combustion noise does not exceed the target noise level. Further, the injection control is executed based on the time transition of the in-cylinder residual oxygen concentration during the combustion stroke. Therefore, it is possible to execute injection corresponding to the in-cylinder residual oxygen concentration every moment during the combustion stroke, and it is possible to avoid the situation where the in-cylinder residual oxygen amount is significantly less than the injected fuel amount, Deterioration of unburned fuel and smoke can be suppressed. As described above, according to the present invention, it is possible to suppress both deterioration of unburned fuel and smoke and deterioration of combustion noise.

  Note that the reference numerals in parentheses in the scope of claims are intended only to exemplify corresponding configurations in the embodiments described later in order to facilitate understanding of the description, and are not intended to limit the content of the invention. Absent.

System configuration diagram of fuel injection system Illustration of injection command signal and heat generation rate Processing flow of ECU in the first embodiment Map of engine speed, accelerator opening, and target heat release rate gradient Explanatory diagram of the definition of heat release rate slope Explanatory diagram of target heat generation rate determining means Map of oxygen concentration and burning rate Time transition of various parameters under arbitrary driving conditions

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the present embodiment, as shown in FIG. 1, a fuel injection system 11 in which a multi-cylinder diesel engine 10 (hereinafter referred to as the engine 10) is adopted as an internal combustion engine and an ECU 36 is applied to the engine 10 is illustrated. The engine 10 corresponds to the “internal combustion engine” in the claims.

  As shown in FIG. 1, the engine 10 is configured such that a piston (not shown) is accommodated in a cylinder block 12 so as to be able to reciprocate. A cylinder head (not shown) is provided on the upper end surface (front side of the paper surface) of the cylinder block 12. An intake port 20 and an exhaust port 22 that open to the combustion chamber 16 are formed in the cylinder head. The intake port 20 and the exhaust port 22 are respectively provided with an intake valve and an exhaust valve (not shown). The exhaust valve and the intake valve play a role of adjusting the intake air amount and the exhaust air amount.

  An intake pipe 28 for sucking outside air is connected to the intake port 20. During the intake stroke in which the intake valve opens the intake port 20, the piston descends in the cylinder and negative pressure is generated. As a result, the outside air sucked from the intake pipe 28 flows into the cylinder via the intake port 20.

  An exhaust pipe 30 for discharging combustion gas is connected to the exhaust port 22. During the exhaust stroke in which the exhaust valve opens the exhaust port 22, the exhaust gas pushed out of the combustion chamber 16 by the rise of the piston is discharged to the exhaust pipe 30 through the exhaust port 22.

  The ECU 36 controls the injection pressure, injection amount, and injection timing of the fuel (light oil) supplied to the engine 10.

  The fuel injection system 11 includes a common rail 32 capable of accumulating and holding fuel, a plurality of fuel injection valves 34 for injecting fuel pumped from the common rail 32 into the combustion chamber 16 of each cylinder of the engine 10, and the common rail 32 and the fuel injection valve. ECU 36 which controls 34 is provided.

  The fuel injection valve 34 is provided corresponding to each cylinder and is electronically controlled by the ECU 36. By the opening operation of the fuel injection valve 34, the fuel is injected into each cylinder.

  A fuel injection valve 34 for each cylinder is connected to the common rail 32 via a fuel pipe (not shown). The fuel in the common rail 32 is distributed and supplied to the fuel injection valve 34 through each fuel pipe.

  The ECU 36 includes a microcomputer 361 having a CPU, RAM, ROM and the like. The ECU 36 receives detection signals output from various sensors, and detects the operating state of the engine 10 based on these detection signals. The microcomputer 361 executes a control program stored in a storage medium such as a ROM, whereby a target heat generation rate inclination determining unit 60, a target heat generation amount determining unit 70, a target heat generation rate determining unit 80, a residual oxygen, which will be described later, are stored. It functions as a concentration estimating means 90, a target injection rate determining means 100, an injection command signal setting means 110, and a combustion speed determining means 120.

  The crank angle sensor 46 outputs a rotation angle signal that is a plurality of pulse signals to the ECU 36. The ECU 36 detects the rotation speed NE and the crank angle of the engine 10 based on the rotation angle signal. The accelerator opening sensor 47 outputs an accelerator opening signal to the ECU 36. The in-cylinder pressure sensor 55 is attached to one cylinder of the engine 10 and outputs an output signal corresponding to the in-cylinder pressure Pin in the combustion chamber 16 to the ECU 36.

  A supercharger 50 is provided in the intake pipe 28 and the exhaust pipe 30. The supercharger 50 recovers energy from the exhaust gas of the engine 10 and converts it into power, and pressurizes the intake air flowing through the intake pipe 28 of the engine 10 with the recovered power. The amount of air supplied to the engine 10 by the supercharger 50 can be increased, and the amount of combustible fuel is increased accordingly, so that the output of the engine 10 can be increased. In this embodiment, the supercharger 50 is provided in the exhaust pipe 30 and is driven by the energy of the exhaust gas, and is provided in the intake pipe 28 of the engine 10 and is driven by the rotational torque of the turbine wheel 51. A turbocharger having a compressor wheel 52 is employed. The turbine wheel 51 and the compressor wheel 52 are connected via a turbine shaft 53.

  The supercharging pressure sensor 54 is disposed on the downstream side of the intake pipe 28, detects the actual supercharging pressure Pb, and outputs an output signal corresponding to the actual supercharging pressure Pb.

  A throttle valve 7 is provided on the upstream side of the intake pipe 28, and an actuator 8 that drives the throttle valve 7 is connected to the throttle valve 7. The actuator 8 includes a motor, a gear mechanism (both not shown) and the like, and its operation is controlled by a control signal from the ECU 36, whereby the opening TH of the throttle valve 7 changes. The intake oxygen concentration Vo sucked into the combustion chamber 16 is controlled in accordance with the change in the throttle opening TH. The opening degree TH and the corresponding intake oxygen concentration Vo are detected by the throttle valve opening degree sensor 23.

  Next, fuel injection control from the fuel injection valve 34 by the ECU 36 will be described. The ECU 36 corresponds to the “fuel injection control device” in the claims.

  The injection control by the ECU 36 is performed by controlling the fuel injection amount and injection timing from the fuel injection valve 34. The ECU 36 calculates the optimal injection amount and injection timing based on the operating state of the engine 10 and controls the fuel injection of the fuel injection valve 34 based on the calculation result. Specifically, this injection control is performed by controlling the electric power supplied to the fuel injection valve 34 by a pulse signal (injection pulse) that defines the fuel injection amount and the injection timing.

  The injection control implemented in this embodiment is shown in FIG. The upper part of FIG. 2 shows the timing chart of the injection pulse, and the lower part of FIG. 2 shows the heat generation rate in the combustion chamber 16. The horizontal axis indicates the crank angle. As shown in FIG. 2, the ECU 36 causes the fuel injection valve 34 to execute pilot injection with an injection amount smaller than that of the main injection prior to main injection for generating torque. That is, the ECU 36 causes the fuel injection valve 34 to execute multi-stage injection of pilot injection and main injection in the combustion stroke of one combustion cycle. Note that, as shown in FIG. 2, the pilot injection has a smaller amount of fuel to be injected than the main injection, and therefore the peak value of the heat generation rate is also small. In the present embodiment, the injection amount required in the main injection (the injection amount based on the required torque) is divided into a plurality of times and injected at short intervals. For example, what is shown in FIG. 3 divides the injection amount required in the main injection into three times, and divides the first, second, and third injection amount ratios to be 2: 3: 5, The injection is performed with an extremely short interval between the three injections. The division ratio of the injection amount is determined by a desired injection condition.

  The ECU 36 performs injection control on the fuel injection valve 34 so that the combustion noise generated in the combustion chamber 16 becomes the target noise level. Hereinafter, specific processing contents will be described with reference to FIG.

  First, in S101, the current operating conditions (rotational speed NE, accelerator opening, etc.) are acquired. If an operating condition is acquired in S102, it will progress to S103.

  In S102, a target heat generation rate gradient θt corresponding to the obtained operating condition is determined based on a map stored in the ECU 36 in advance. Specifically, in the target heat generation rate inclination determining means 60 in the microcomputer 361, a map of the target heat generation rate inclination θt using the rotational speed NE and the accelerator opening as parameters as shown in FIG. 4 is stored in advance. . This map is created in correspondence with the target noise level of combustion noise using the rotational speed NE and the accelerator opening as parameters. When combustion is performed such that the target heat generation rate gradient θt is larger than the target heat generation rate gradient θt, combustion noise larger than the target noise level is generated. That is, if combustion is performed such that the target heat generation rate inclination θt is achieved, the combustion noise can be kept at the target noise level. When the target heat generation rate inclination θt is determined in S102, the target heat generation rate inclination determination means 60 transmits a signal relating to the determined target heat generation rate inclination θt to the target heat generation rate determination means 80. After transmitting a signal related to the target heat generation rate inclination θt, the process proceeds to S103.

  Here, the definition of the target heat generation rate inclination θt will be described. As shown in FIG. 5, the point of heat generation rate HRRO at the start of combustion associated with the first injection (hereinafter referred to as zero point) and the maximum heat generation rate HRRmax in the combustion associated with the third injection that is the last injection. The slope of the line segment L1 connecting these points is the target heat release rate slope θt.

  In S103, the target heat generation amount Qt is calculated according to the operation condition acquired in S101. Specifically, the target heat generation amount determination means 70 in the microcomputer 361 calculates the target heat generation amount Qt using the following equation (1).

(Equation 1)
Qt = α × Qinj
α is the combustion amount per unit fuel, and Qinj is the target injection amount determined based on the operating conditions. When the target heat generation amount Qt is calculated in S103, the target heat generation amount determination means 70 transmits a signal related to the determined target heat generation amount Qt to the target heat generation rate determination means 80. After transmitting a signal related to the target heat generation amount Qt, the process proceeds to S104.

  In S104, the time transition HRRt (t) of the target heat generation rate is determined based on the target heat generation rate gradient θt determined in S102 and the target heat generation amount Qt calculated in S103. The process of S104 is executed by the target heat generation rate determining means 80. A specific determination method will be described with reference to FIG. The time transition of the target heat generation rate during the combustion period is a line segment in FIG. This line segment is uniquely determined by the target heat generation rate inclination θt, which is the inclination of the line segment, and the target heat generation amount Qt represented by the area surrounded by the horizontal axis and the line segment. That is, the time transition HRRt (t) of the target heat generation rate at each time during the combustion stroke is determined by the target heat generation rate inclination θt, and the time transition HRRt of the target heat generation rate during the combustion stroke is determined by the target heat generation amount Qt. Time tmax and HRRtmax that are the maximum values of (t) are determined. Thereby, the time transition HRRt (t) of the target heat generation rate during the combustion stroke is determined. When the time transition HRRt (t) of the target heat generation rate is determined in S104, the target heat generation rate determination means 80 instructs the residual oxygen concentration estimation means 90 over time transition HRRt (t) of the determined target heat generation rate. Send a signal about. After transmitting a signal regarding the time transition HRRt (t) of the target heat generation rate, the process proceeds to S105.

  In S105, based on the intake oxygen concentration Vo detected by the throttle valve opening sensor 23 and the time transition HRRt (t) of the target heat generation rate determined by the target heat generation rate determining means 80, the cylinder in the combustion stroke Estimate the time transition of oxygen concentration remaining in the inside. Specifically, with the initial value of the intake oxygen concentration Vo, the time transition of the instantaneous oxygen consumption consumed in the cylinder when it is assumed that combustion is performed so as to become the time transition HRRt (t) of the target heat generation rate From Ouse (t), the time transition Vrem (t) of the in-cylinder residual oxygen concentration during the combustion stroke is estimated. The process of S105 is executed by the residual oxygen concentration estimation means 90.

Next, a specific principle of estimating the time transition Vrem (t) of the in-cylinder residual oxygen concentration will be described. Assuming that the fuel injected in the combustion chamber 16 is completely burned, CO ₂ (carbon dioxide) and H ₂ O (water) according to the ratio of carbon (C) and oxygen (H), which are elements in the fuel, by combustion. Is generated. At this time, since the CO ₂ concentration in the atmosphere is small compared with the CO ₂ concentration generated by the combustion of the fuel, it is ignored, so the CO ₂ contained in the exhaust is consumed by the combustion of the fuel with the O _{2 in the} intake air. It can be considered that it was generated. That is, it can be considered that the decrease amount of O ₂ from the O ₂ concentration of intake air and the increase amount of CO ₂ have a proportional relationship. Similarly, H ₂ O generated by fuel combustion can be considered. The chemical reaction equation when it is assumed that the injected fuel is completely burned can be expressed by the following equation (2).

(Equation 2)
CmHn + (m + n / 4) O ₂ → mCO ₂ + (n / 2) H ₂ O
Here, m is a constant determined based on the fuel C ratio, and n is a constant determined based on the fuel H ratio. The number of moles of fuel A and the number of moles of oxygen B required for complete combustion of one mole of fuel are calculated by the following formulas 3 and 4.

(Equation 3)
Number of fuel moles A = (number of moles of carbon 12) × m + (number of moles of hydrogen 1) × n

(Equation 4)
Number of moles of oxygen necessary for complete combustion of 1 mole of fuel B = (number of moles of oxygen 16) × (m + n / 4)
Here, the ratio of the oxygen amount (oxygen consumption amount) necessary to burn all of the injected fuel amount is represented by B / A. The target instantaneous injection amount Qinj (t) is expressed by Qt (t) / α from Equation 1. Therefore, the time transition Ouse (t) of the instantaneous oxygen consumption, which is the amount of oxygen consumed by combustion in the cylinder, is obtained by the following equation 5 based on the time transition Qt (t) of the target heat generation amount. . The time transition Ouse (t) of the instantaneous oxygen consumption corresponds to “oxygen consumption” in the claims.

(Equation 5)
Ouse (t) = (Qt (t) / α) × (B / A)
Therefore, the in-cylinder residual oxygen amount O ₂ (t) at each hour is obtained by the following equation (6).

(Equation 6)
O ₂ (t) = O ₂ (t−1) −Ouse (t)
Based on the in-cylinder residual oxygen amount O ₂ (t) obtained every time, the time transition Vrem (t) of the in-cylinder residual oxygen concentration is calculated.

  When the time transition Vrem (t) of the in-cylinder residual oxygen concentration is estimated in S105, the residual oxygen concentration estimation means 90 sends the estimated in-cylinder residual oxygen concentration time transition Vrem (t) to the combustion speed determination means 120. Send a signal about. After transmitting a signal relating to the time transition Vrem (t) of the in-cylinder residual oxygen concentration, the process proceeds to S106.

  In S106, the time transition K (t) of the combustion speed is determined based on the time transition Vrem (t) of the in-cylinder residual oxygen concentration estimated in S105. Specifically, in the combustion rate determining means 120 in the microcomputer 361, a map of the combustion rate with the oxygen concentration as a parameter as shown in FIG. 7 is stored in advance. Based on this map, the time transition K (t) of the combustion speed corresponding to the time transition Vrem (t) of the in-cylinder residual oxygen concentration at each time is uniquely determined. When the time transition K (t) of the combustion speed is estimated in S106, the combustion speed determination means 120 transmits a signal related to the determined time transition K (t) of the combustion speed to the target injection rate determination means 100. After transmitting a signal related to the time transition K (t) of the combustion speed, the process proceeds to S107.

  In S107, the time transition Rinj (t) of the target injection rate based on the target instantaneous injection amount Qinj (t) and the time transition K (t) of the combustion speed obtained from the time transition HRRt (t) of the target heat generation rate. ). The process of S107 is executed by the target injection rate determination means 100. The target instantaneous injection amount Qinj (t) is obtained from Equation 1. Specifically, the time transition Rinj (t) of the target injection rate is calculated based on the following Equation 7.

(Equation 7)
Rinj (t) = Qinj (t) / K (t)
The time transition Rinj (t) of the target injection rate is calculated by Equation 7 based on the time transition K (t) of the combustion speed for each combustion cycle. The injection end timing is uniquely determined from the target injection amount Qinj determined based on the driving situation.

  FIG. 8 shows the processing results from S104 to S107. If it is assumed that combustion for realizing the time transition HRRt (t) of the target heat generation rate is performed under an arbitrary operating condition (pattern 1), the in-cylinder residual oxygen concentration decreases with the passage of time. Further, the time transition K (t) of the combustion speed also decreases with time according to the time transition Vrem (t) of the in-cylinder residual oxygen concentration. The difference between the end time t1 of the time transition Rinj (t) of the target injection rate and the end time t2 of the time transition HRRt (t) of the target heat generation rate is due to the ignition delay period from injection to combustion. Is.

  Here, as shown in FIG. 8, in comparison with the first intake oxygen concentration Voref1, which is the intake oxygen concentration (initial value of the time transition of the in-cylinder oxygen concentration) under an arbitrary operating condition (first pattern), When the second intake oxygen concentration Voref2 in the operating state (second pattern) decreases, the time transition Rinj (t) of the target injection rate is controlled to the advance side after a predetermined time t3 that is in the middle of the combustion period. Become so. Further, after the predetermined time t3, the advance angle increases as time elapses. This is because when the oxygen concentration is equal to or lower than the predetermined value C, the rate of decrease in the combustion speed is larger than when the oxygen concentration is equal to or higher than the predetermined value C (see FIG. 7). In the period in which the residual oxygen concentration is smaller than the predetermined value C, the rate of decrease in the combustion rate with respect to the rate of decrease in the in-cylinder residual oxygen concentration with time elapses, and the time required from the injection of fuel to the combustion becomes longer. It is to become. It should be noted that the first pattern and the second pattern are respectively “first operating condition” and “second operating condition” in the claims, and the first intake oxygen concentration Voref1 and the second intake oxygen concentration Voref2 are respectively “first intake condition”. It corresponds to “oxygen concentration” and “second intake oxygen concentration”. Further, the target injection rate of the first pattern and the target injection rate of the second pattern correspond to “first target injection rate” and “second target injection rate” in the claims, respectively.

  When the time transition Rinj (t) of the target injection rate is estimated in S107, the target injection rate determination means 100 sends a signal related to the determined time transition Rinj (t) of the target injection rate to the injection command signal setting means 110. Send. After transmitting a signal related to the time transition Rinj (t) of the target injection rate, the process proceeds to S108.

  In S108, the target injection condition is determined by the injection command signal setting means 110 so that the time transition of the injection rate in the main combustion accompanying the main injection becomes the time transition Rinj (t) of the target injection rate determined in S107. The Here, the target injection condition may be any of a target injection pressure in each injection divided in the main combustion, a target division ratio that is a division ratio of the injection amount of each injection, and an injection interval of each injection.

  The determination of various injection conditions may use a map stored in advance in the ECU 36 or may be calculated each time using a mathematical formula. For example, when the injection control is performed so that the injection amount of the first injection is increased by a predetermined amount without changing the injection amount of the main injection, the third injection amount is controlled to be decreased accordingly, so the third injection The maximum value of the heat generation rate in the combustion associated with is small. That is, the inclination of heat generation rate during main combustion can be reduced. On the other hand, when the injection control is performed so as to increase the injection amount of the third injection, the maximum value of the heat generation rate in the combustion accompanying the third injection becomes large. That is, the slope of the heat release rate during main combustion can be increased. When the injection condition is determined in S108, the injection command signal setting means 110 transmits an injection command signal based on the determined injection condition to the drive circuit 130 to drive the drive circuit 130 (S109). The drive circuit 130 controls the fuel injection valve 34 to execute injection corresponding to the target injection condition. When the injection command signal is transmitted to the drive circuit 130, the process in FIG. 3 ends.

  Next, the effect in this embodiment is demonstrated.

  (1) Time transition Ouse () of the instantaneous oxygen consumption consumed in the cylinder when it is assumed that combustion is performed such that the target heat generation rate becomes the time transition HRRt (t) with the intake oxygen concentration Vo as an initial value. From time t), the time transition Vrem (t) of the in-cylinder residual oxygen concentration during the combustion stroke is estimated. Further, the time transition Rinj (t) of the target injection rate of the fuel to be injected is determined based on the time transition Vrem (t) of the in-cylinder residual oxygen concentration, and the time transition of the injection rate is the time transition Rinj ( The injection condition from the fuel injection valve 34 is determined so that t). That is, in order to realize combustion in which the time transition of the heat generation rate becomes the time transition HRRt (t) of the target heat generation rate, the injection conditions (injection amount, injection timing, etc.) corresponding to the in-cylinder residual oxygen concentration every moment Can be determined. For this reason, it is possible to realize the combustion with the time transition HRRt (t) of the target heat generation rate, and it is possible to keep the combustion noise at the target noise level. Further, since the injection condition is determined based on the in-cylinder residual oxygen concentration, the fuel amount corresponding to the in-cylinder residual oxygen concentration can be injected. Therefore, the situation where the injected fuel does not burn can be avoided, and the unburned fuel and smoke can be reduced. As described above, according to the present embodiment, it is possible to keep the combustion noise at the target noise level and reduce both unburned fuel and smoke.

  (2) The time transition HRRt (t) of the target heat generation rate is uniquely determined based on the two parameters of the target heat generation rate inclination θt and the target heat generation amount. Therefore, the calculation load of the ECU 36 can be reduced as compared with the case where the target heat generation rate at each time is calculated one by one.

  (3) The time transition Rinj (t) of the target injection rate is not determined by a map stored in advance in the ECU 36, but is calculated by a mathematical formula based on the time transition K (t) of the combustion speed for each combustion cycle. I have to. Here, the number of patterns of the combustion speed time transition K (t) depends on the number of patterns of the time transition Vrem (t) of the in-cylinder residual oxygen concentration, and the number of combinations of parameters such as the engine speed NE and the accelerator opening. Therefore, it is an infinite number. Therefore, in general, as a method for determining the control amount using the map, only a few typical patterns are stored in the ECU, and the control amount is approximately determined according to the input parameters in many cases. Therefore, when the time transition Rinj (t) of the target injection rate is determined by a map using the combustion speed as an input parameter, the optimal target injection rate time corresponding to the time transition HRRt (t) of the target heat generation rate It is difficult to say that the transition Rinj (t) is obtained. On the other hand, as in the present embodiment, by calculating the time transition Rinj (t) of the target injection rate by a mathematical formula based on the time transition K (t) of the combustion speed for each combustion cycle, Compared with the case of determining the time transition Rinj (t), the time transition Rinj (t) of the optimum target injection rate can be calculated. Therefore, the combustion which becomes the time transition HRRt (t) of the target heat generation rate can be realized with high accuracy. In this embodiment, the combustion speed is determined based on the map when determining the combustion speed from the in-cylinder oxygen concentration. However, since the combustion speed is uniquely determined with respect to the in-cylinder oxygen concentration, the time transition of the target injection rate Rinj (t) is calculated by calculation.

  (4) Compared with the first intake oxygen concentration Voref1, which is the intake oxygen concentration (initial value of the time transition of the in-cylinder oxygen concentration) under an arbitrary operation condition (first pattern) (second pattern) ), The time transition Rinj (t) of the target injection rate is controlled to the advance side after a predetermined time t3 in the middle of the combustion period. Therefore, even if the time required from fuel injection to combustion becomes longer as the combustion speed decreases with the passage of time, the injection timing can be set earlier, so that In addition, combustion for realizing the time transition HRRt (t) of the target heat generation rate can be caused.

(Other embodiments)
The present invention is not limited to the above embodiment, and may be modified as follows as long as it belongs to the technical scope of the present invention.

  In the above embodiment, the intake oxygen concentration Vo is detected by the throttle valve opening sensor 23. For example, the pressure Po in the intake manifold and the intake manifold detected by an intake pressure sensor and an intake temperature sensor (not shown) It may be calculated or determined by the temperature To.

  In the above embodiment, the time transition Qt of the target heat generation amount is calculated by a mathematical formula, but it is determined using a map based on the engine speed NE and the accelerator opening similarly to the target heat generation rate gradient θt. You may make it do.

  In the above embodiment, the time transition K (t) of the combustion speed is determined based on the time transition Vrem (t) of the in-cylinder residual oxygen concentration, and the target injection is performed based on the time transition K (t) of the combustion speed. The rate time transition Rinj (t) is determined. However, based on the relational expression of the time transition Vrem (t) of the in-cylinder residual oxygen concentration and the time transition Rinj (t) of the target injection rate, or the map stored in advance in the ECU 36, the time transition K (t ) May be determined without determining the time transition Rinj (t) of the target injection rate.

  In the above embodiment, the time transition Vrem (t) of the in-cylinder residual oxygen concentration is estimated by the residual oxygen concentration estimation means 90, but the estimated physical quantity is not an oxygen concentration, but an oxygen amount such as an oxygen amount, for example. Any physical quantity having a correlation with the concentration may be used. The wording “cylinder residual oxygen concentration” in the claims is also defined as including these physical quantities. Further, although the combustion speed determination means 120 determines the time transition K (t) of the combustion speed, the physical quantity to be determined may be a physical quantity correlated with the combustion speed, such as a combustion speed coefficient.

  In the above embodiment, the injection amount required for the main injection is divided into a plurality of injections. However, the injection may be a single injection that injects the required injection amount at a time.

  In the above embodiment, the time transition HRRt (t) of the target heat generation rate is determined based on the target heat generation rate gradient θt and the target heat generation amount Qt, but the target heat generation at every time during the combustion stroke The time transition HRRt (t) of the target heat generation rate may be determined by calculating the rate one by one.

  In the above-described embodiment, the target heat generation amount Qt is calculated by using Formula 1, but it can also be determined using a map corresponding to the driving situation stored in the ECU 36 in advance.

  In the above embodiment, the time transition K (t) of the combustion speed is determined by a map using the oxygen concentration as an input parameter, but may be calculated by calculation. As a means for calculating by calculation, it is conceivable to derive from a relational expression between time and equivalence ratio based on the momentum theory. A specific calculation method will be described in detail. First, the elapsed time t (φ) from the injection with respect to the specified equivalence ratio φ is calculated using the following equations 8 to 10.

なお、ｔ（φ）は指定当量比φに対する噴射からの経過時間、φｔｈは理論当量比、ρａは筒内ガス密度、ρｆは燃料密度、θｓｐは噴霧角、ｄは噴孔径、Ｐｃは噴射圧、Ｐｃｙｌは筒内圧、ｃは収縮係数である。

Note that t (φ) is the elapsed time from injection with respect to the specified equivalence ratio φ, φth is the theoretical equivalence ratio, ρa is the in-cylinder gas density, ρf is the fuel density, θsp is the spray angle, d is the nozzle hole diameter, and Pc is the injection pressure. , Pcyl is the in-cylinder pressure, and c is the contraction coefficient.

なお、Ｃ_Ｏ２は酸素濃度である。

Note that _CO2 is the oxygen concentration.

次に、噴射からの経過時間ｔ（φ）においてφが１となる時間ｔｃｍｂを求め、その逆数１／ｔｃｍｂを所定の酸素濃度に対する燃焼速度として決定する。

Next, a time tcmb at which φ becomes 1 in the elapsed time t (φ) from the injection is obtained, and its reciprocal 1 / tcmb is determined as a combustion rate for a predetermined oxygen concentration.

DESCRIPTION OF SYMBOLS 10 Engine, 11 Fuel injection system, 16 Combustion chamber, 32 Common rail, 34 Fuel injection valve, 36 ECU, 50 Supercharger, 52 Cylinder pressure sensor, 54 Supercharging pressure sensor, 23 Throttle valve opening sensor, 60 Target heat generation Rate slope determination means, 70 Target heat generation amount determination means, 80 Target heat generation rate determination means, 90 Residual oxygen concentration estimation means, 100 Target injection rate determination means, 110 Injection command signal setting means, 120 Combustion speed determination means, 130 Drive circuit

Claims (4)

A fuel injection control device configured to control an injection state of fuel to an internal combustion engine (10),
Target heat generation rate determining means (80) for determining the time transition of the target heat generation rate so that the combustion noise of the internal combustion engine does not exceed the target noise level;
Based on the intake oxygen concentration supplied to the internal combustion engine in the intake stroke and the time transition of the oxygen consumption during the combustion stroke, it is assumed that the combustion is performed so as to achieve the target heat generation rate. Residual oxygen concentration estimating means (90) for estimating the time transition of the in-cylinder residual oxygen concentration,
Target injection rate determination means (100) for determining a time transition of the target injection rate based on the estimated time transition of the in-cylinder residual oxygen concentration;
A fuel injection control device comprising: control means (130) for performing injection control so that the time transition of the fuel injection rate to the internal combustion engine becomes the time transition of the target injection rate.   2. The fuel injection control device according to claim 1, wherein the target injection rate determining means calculates the time transition of the target injection rate by calculation based on the estimated time transition of the in-cylinder residual oxygen concentration. When the second intake oxygen concentration, which is the intake oxygen concentration in another second operation condition, is smaller than the first intake oxygen concentration, which is the intake oxygen concentration, in any first operation condition,
The target injection rate determining means is configured to advance the second target injection rate in the second operating condition after the predetermined time during the combustion stroke from the first target injection rate in the first operating condition. 3. The fuel injection control device according to claim 1, wherein the fuel injection control device is determined so that the advance angle gradually increases as time elapses. A target heat generation rate gradient determining means (60) for determining a target heat generation rate gradient so that combustion noise does not exceed the target noise level based on the operating state of the internal combustion engine;
A target heat generation amount determining means (70) for determining a target heat generation amount capable of obtaining a desired torque based on the operating state of the internal combustion engine;
The target heat generation rate determining means determines a time transition of the target heat generation rate based on the target heat generation rate gradient and the target heat generation amount. A fuel injection control device according to claim 1.

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