JP6428592B2 - Fuel injection control device - Google Patents

Description

  The present invention relates to a fuel injection control device that controls fuel injection into a combustion chamber of an internal combustion engine by a fuel injection valve having a variable injection rate waveform.

  Since the diesel engine self-ignites the fuel by the compression in the cylinder, the compression ratio is higher than that of the gasoline engine, and the in-cylinder pressure generated by the combustion is also higher. In order to increase the output, it is necessary to increase the amount of combustion per cycle, which further increases the in-cylinder pressure.

  In Patent Document 1, the fuel injection amount is controlled so as not to exceed an allowable maximum in-cylinder pressure. Specifically, first, the gas density is calculated from the supply manifold pressure and temperature, and the maximum in-cylinder pressure is estimated from the relationship between the gas density and the maximum in-cylinder pressure. When the fuel injection amount exceeds the estimated maximum in-cylinder pressure, the fuel injection amount is reduced to reduce the in-cylinder pressure.

JP 2011-153579 A

  In the fuel injection control described in Patent Document 1, the fuel injection amount is only controlled so as not to exceed the maximum in-cylinder pressure, and the in-cylinder pressure cannot be increased to increase the output. Further, since the maximum in-cylinder pressure that the engine can tolerate is determined from the strength of the engine itself, it is necessary to increase the engine strength in order to increase the maximum in-cylinder pressure. However, there is a problem that the weight of the engine itself increases due to the strength increase and the manufacturing cost increases.

  Accordingly, the present invention has been made in view of the above-described problems, and an object of the present invention is to provide a fuel injection control device that can improve the output while suppressing the in-cylinder pressure below the maximum in-cylinder pressure.

  The present invention employs the following technical means in order to achieve the aforementioned object.

According to the present invention, fuel injection is performed by using any one injection rate waveform among a plurality of injection rate waveforms in accordance with an ignition acquisition unit (30) that acquires the degree of ignition delay in the cylinder and an output request to the internal combustion engine. comprising a control unit for controlling (30), and the plurality of injection rate waveform, the cylinder pressure in the combustion chamber a injection Iritsu waveform for controlling such that less than the maximum cylinder pressure, one injection This includes a two-time rising injection rate waveform that raises the injection rate twice. The injection that raises the injection rate for the first time in the two-time rising injection rate waveform is the pre-stage injection, and the injection that raises the injection rate the second time. , The injection rate waveform of the pre-injection has a part where the injection rate increases for the first time from the start of the pre-stage injection and reaches the maximum injection rate, and a part where the injection rate decreases from the maximum injection rate. The injection rate waveform is larger than 0 when the post injection is started. Ku, a portion reaches the maximum injection rate starts from the injection rate of the latter stage injection is increased for the second time, and a portion descending from the maximum injection rate, the rate of change of the increase in the injection rate at the first stage injection, More than the rate of change in the post-injection, the control unit increases twice when the degree of ignition delay acquired by the ignition acquisition unit is smaller than the threshold value and the output request to the internal combustion engine is high output It is a fuel injection control apparatus which controls to inject with an injection rate waveform.

According to the present invention as described above, when the degree of ignition delay is smaller than the threshold value and the output request to the internal combustion engine is a high output, control is performed so that the fuel is injected twice with a rising injection rate waveform. When the degree of ignition delay is small, it is easy to burn, so heat generation can be made to follow the injection rate. On the contrary, when the degree of ignition delay is large, it is difficult to burn, and heat generation does not follow the injection rate. Therefore, even if the injection rate is controlled, heat generation cannot be controlled. In the present invention, when it is easy to burn, it is controlled by the twice-increasing injection rate waveform, so that the in-cylinder pressure can be controlled with high accuracy. Further, when the output request to the internal combustion engine is high output, it is necessary to increase the in-cylinder pressure. Therefore, in the case of a high output demand, the cylinder pressure is controlled to be close to the maximum in-cylinder pressure while keeping the in-cylinder pressure below the maximum in-cylinder pressure using the twice-increase injection rate waveform.

Thus two rising injection rate waveform, Ri injection rate waveform der to control as the cylinder pressure in the combustion chamber becomes equal to or less than the maximum cylinder pressure, in the following description, also referred to as isobaric injection rate waveform. The two-time rising injection rate waveform ( isobaric injection rate waveform ) is injected in two stages, the front-stage injection and the rear-stage injection, and the ratio of the increase in the injection rate in the front-stage injection is larger than the ratio of the change in the rear-stage injection It is a rate waveform.

  By the first half injection with a large change rate, the injection rate is rapidly increased to the maximum injection rate, and the in-cylinder pressure is increased to the maximum in-cylinder pressure in a short time. Thereafter, the in-cylinder pressure can be prevented from exceeding the maximum in-cylinder pressure by lowering the injection rate from the maximum injection rate. Furthermore, since the injection rate is greater than 0 at the start of the post-stage injection, it is possible to prevent the in-cylinder pressure from being lowered by excessively lowering the injection rate. In addition, it is possible to prevent the in-cylinder pressure from being increased or decreased excessively by the gradual increase in the rate of change of the injection rate in the subsequent injection. The injection rate is maintained at the maximum injection rate in order to reach a predetermined injection amount, and then the injection rate is lowered from the maximum injection rate.

With such a two-time rising injection rate waveform ( equal pressure injection rate waveform ) , the in-cylinder pressure can be controlled to be close to the maximum in-cylinder pressure below the maximum in-cylinder pressure without exceeding the maximum in-cylinder pressure. Therefore, it is possible to satisfy a high output requirement without increasing the strength of the internal combustion engine.

  In addition, the code | symbol in the bracket | parenthesis of each above-mentioned means is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

It is a figure which shows the outline | summary of an engine. It is a figure explaining operation | movement of a needle. It is a graph which shows the in-cylinder pressure of normal combustion mode. It is a graph which shows the injection rate of normal combustion mode. It is a graph which shows the in-cylinder pressure of an equal pressure combustion mode. It is a graph which shows the injection rate of an equal pressure combustion mode. It is a graph which shows the in-cylinder pressure of two combustion modes. It is a graph which shows the injection rate of two combustion modes. It is a flowchart which shows the switching control of 1st Embodiment. It is a graph which shows the relationship between an engine speed and injection quantity. It is a graph which shows the relationship between intake pressure and ignition delay. Flow chart showing supervisory control It is a flowchart which shows the switching control of 2nd Embodiment. It is a graph which shows the relationship between oxygen concentration and ignition delay.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described using a plurality of embodiments with reference to the drawings. In some embodiments, portions corresponding to the matters described in the preceding embodiments may be given the same reference numerals, or one letter may be added to the preceding reference numerals, and overlapping descriptions may be omitted. In addition, when a part of the configuration is described in each embodiment, the other parts of the configuration are the same as those of the embodiment described in advance. In addition to the combination of parts specifically described in each embodiment, the embodiments may be partially combined as long as the combination does not hinder the combination.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the fuel injection control device is applied to a multi-cylinder diesel engine equipped with a common rail fuel injection device.

  In the present embodiment, the engine 10 shown in FIG. 1 is mounted on a vehicle as an in-vehicle main engine, and is a four-cycle engine including intake, compression, expansion, and exhaust strokes. In an intake passage 11 of an engine 10 that is an internal combustion engine, an air flow meter 12 that detects an intake air amount, an intercooler 13 that cools intake air supercharged by a turbocharger 16, and a throttle valve device in order from the upstream side. 14 is provided. The throttle valve device 14 adjusts the opening degree of the throttle valve 14a by an actuator such as a DC motor.

  A combustion chamber 10 a of each cylinder of the engine 10 is connected to the downstream side of the throttle valve device 14 in the intake passage 11 via a surge tank 15. The combustion chamber 10 a is partitioned by a cylinder 10 b and a piston 17 of the engine 10. The engine 10 is provided with a fuel injection valve 18 having a tip projecting into the combustion chamber 10a. High pressure fuel, specifically light oil, is supplied to the fuel injection valve 18 from a common rail 19 serving as a pressure accumulator. Fuel is pumped from the fuel pump 20 to the common rail 19. In FIG. 1, only one cylinder is shown.

  As shown in FIG. 2, the fuel injection valve 18 includes a needle 39 that is a valve body, and a body 41 in which a plurality of circular injection holes 40 for injecting fuel are formed at the tip, and the needle 39 is accommodated therein. I have. Between the inner surface of the body 41 and the outer surface of the needle 39, an annular fuel passage 42 extending in the axial direction of the body 41 and through which the fuel supplied from the common rail 19 passes is formed. A seating surface 41 a on which the tip of the needle 39 is seated is formed on the inner surface of the tip of the body 41. In this configuration, when the needle 39 is seated on the seating surface 41a, the fuel passage 42 and the injection hole 40 are blocked, and fuel injection is stopped. On the other hand, the fuel passage 42 and the injection hole 40 are communicated with each other by separating the needle 39 from the seating surface 41a by energization operation. As a result, the fuel in the fuel passage 42 is directly injected and supplied from the nozzle hole 40 to the combustion chamber 10a.

  The fuel injection valve 18 is configured to be able to variably control the injection rate waveform. The injection rate waveform is a waveform showing a change in the injection rate over time. In the present embodiment, the fuel injection valve 18 is configured to freely control the lift amount of the needle 39 so as to variably control the injection rate waveform. In other words, the fuel injection valve 18 is configured such that the injection rate waveform can be changed by speed control of the needle 39 that opens and closes the injection hole 40. For example, the fuel injection valve 18 adjusts the area of the fuel passage 42 by an actuator 43 having a piezo element to inject fuel. As a result, the fuel injection valve 18 can change the fuel injection rate waveform. For example, the fuel injection rate in the main injection can be varied over time.

  The actuator 43 of the fuel injection valve 18 includes, for example, a piezo stack. The piezo stack is a stacked body in which layers called PZT (PbZrTiO 3) and thin electrode layers are alternately stacked, and expands and contracts by applying a voltage due to the reverse piezoelectric effect which is a characteristic of the piezo element. The actuator 43 controls the position of the needle 39 using the displacement of the piezo stack.

  For example, when no voltage is applied to the piezo stack, the needle 39 is in a closed state and fuel injection is not performed. When a voltage is applied to the piezo stack, the piezo stack expands, and with the expansion as a motive power, the needle 39 is pushed up and fuel injection is started. When the voltage applied to the piezo stack is turned off, it discharges and the piezo stack contracts. As a result, the needle 39 is pushed down to stop fuel injection. By controlling the voltage supplied to the actuator 43, the amount of expansion of the piezo stack can be controlled. Therefore, by controlling the voltage, the valve opening speed of the needle 39 can be adjusted in a plurality of stages, so that the injection seal can be freely controlled.

  The intake port and the exhaust port of each cylinder of the engine 10 are opened and closed by an intake valve 21 and an exhaust valve 22, respectively. Here, the intake air cooled by the intercooler 13 by opening the intake valve 21 and the external EGR gas are introduced into the combustion chamber 10a. When fuel is injected from the fuel injection valve 18 into the combustion chamber 10a with intake air or the like introduced, the fuel self-ignites due to compression of the combustion chamber 10a, and energy is generated by combustion. This energy is taken out as rotational energy of the crankshaft 23 of the engine 10 via the piston 17. The gas used for combustion is discharged as exhaust into the exhaust passage 24 by opening the exhaust valve 22. A crank angle sensor 25 that detects the rotation angle of the crankshaft 23 is provided in the vicinity of the crankshaft 23.

  The vehicle is provided with a turbocharger 16. The turbocharger 16 includes an intake air compressor 16a provided in the intake passage 11, an exhaust turbine 16b provided in the exhaust passage 24, and a rotating shaft 16c that connects these. Specifically, the exhaust turbine 16b is rotated by the energy of the exhaust gas flowing through the exhaust passage 24, and the rotational energy is transmitted to the intake compressor 16a via the rotary shaft 16c, and the intake air is compressed by the intake compressor 16a. That is, the intake air is supercharged by the turbocharger 16. In the present embodiment, it is assumed that the turbocharger 16 can adjust the supercharging pressure of intake air by an energization operation.

  A purification device 26 that purifies the exhaust gas is provided on the downstream side of the turbocharger 16 in the exhaust passage 24. A part of the exhaust discharged to the exhaust passage 24 is returned to the intake passage 11 via the EGR passage 27. Specifically, the upstream side of the exhaust turbine 16 b in the exhaust passage 24 is connected to the surge tank 15 via the EGR passage 27. An EGR valve device 28 is provided in the EGR passage 27. The EGR valve device 28 adjusts the opening degree of the EGR valve 28a by an actuator such as a DC motor. Depending on the opening of the EGR valve 28a, a part of the exhaust discharged to the exhaust passage 24 is cooled by the EGR cooler 29 and then supplied to the surge tank 15 as external EGR gas.

  The ECU 30, which is an electronic control device that controls the engine system, executes a program stored in a storage medium and controls each part. The ECU includes at least one arithmetic processing unit (CPU) and a storage medium that stores programs and data. The ECU is realized, for example, by a microcomputer having a storage medium readable by a computer (hereinafter also referred to as “microcomputer”). The storage medium is a non-transitional physical storage medium that stores a computer-readable program and data in a non-temporary manner. The memory is realized by a semiconductor memory or a magnetic disk.

  The ECU 30 includes an intake pressure sensor 31, an intake temperature sensor 32, an exhaust temperature sensor 33, an in-cylinder pressure sensor 34, an oxygen concentration sensor 38, a fuel pressure sensor 35, a water temperature sensor 36, an accelerator sensor 37, an air flow meter 12, and a crank angle sensor 25. The detected value is input. The intake pressure sensor 31 detects the gas pressure in the surge tank 15 as the intake pressure. The intake air temperature sensor 32 detects the gas temperature in the surge tank 15 as intake sound. The exhaust temperature sensor 33 detects the temperature of the exhaust discharged from the combustion chamber 10a as exhaust sound. The in-cylinder pressure sensor 34 detects the pressure in the combustion chamber 10a as the in-cylinder pressure. The oxygen concentration sensor 38 is attached to the intake passage 11 and detects the oxygen concentration in the intake air. The intake air to be detected is a mixture of fresh air and EGR gas. The fuel pressure sensor 35 detects the fuel pressure in the common rail 19. The water temperature sensor 36 detects the cooling water temperature of the engine 10. The crank angle sensor 25 detects the engine speed that is the rotational speed of the crankshaft 23 that is rotationally driven by the piston 17 and that is the rotational speed of the crankshaft 23 per unit time. The accelerator sensor 37 detects the accelerator operation amount of the accelerator operation member of the driver, and specifically detects the depression amount of the accelerator pedal.

  The ECU 30 includes a fuel injection control of the fuel injection valve 18, a drive control of the fuel pump 20, a drive control of the EGR valve device 28, and a supercharging pressure control by the turbocharger 16 based on detection values of various sensors. Combustion control is performed. With these controls, the combustion state in the engine 10 included in the combustion system is controlled to a desired state. Therefore, the ECU 30 functions as a control unit that controls the injection rate.

Next, the injection mode will be described with reference to FIGS. In this embodiment, there are two injection modes, a normal combustion mode and an isobaric combustion mode, and switching control for switching the injection mode under a predetermined condition is performed. The combustion mode is used in the same meaning as the injection rate waveform. 3 and 4, as the normal injection mode, respectively to the front advance by a broken line shows a later advance in solid lines. In the normal injection mode, the injection rate waveform is rectangular as shown in FIG. In such a normal injection mode, the maximum in-cylinder pressure may not exceed the maximum in-cylinder pressure before advance. However, since the maximum in-cylinder pressure exceeds the maximum in-cylinder pressure when advanced, injection control cannot be performed in the normal injection mode after advance.

The isobaric combustion mode is a two-time rising injection rate waveform ( isobaric injection rate waveform ) , and is an injection rate waveform for controlling the in-cylinder pressure in the combustion chamber 10a to be equal to or lower than the maximum in-cylinder pressure. When the isobaric combustion mode is performed, the in-cylinder pressure is not more than the maximum in-cylinder pressure, and the in-cylinder pressure is maintained for a longer time within a predetermined range that is not more than the maximum in-cylinder pressure. In the isobaric combustion mode, as shown in FIG. 6, the injection rate waveform is injected into two stages of the front injection and the rear injection, and the rate of change in the injection rate in the front injection is higher than the rate of change in the rear injection. large. In other words, the isobaric combustion mode has a front-stage injection that rises quickly to the maximum injection rate and a post-stage injection that rises slowly to the maximum injection rate.

  The injection rate waveform of the pre-stage injection consists of the part where the injection rate increases from the start of the pre-stage injection and reaches the maximum injection rate, the part that maintains the maximum injection rate for a predetermined time after reaching the maximum injection rate, and the maximum injection rate A descending portion.

  In the injection rate waveform of the post-injection, the injection rate at the start of the post-injection is greater than zero. In addition, the injection rate waveform of the post-injection includes a portion where the injection rate increases from the start of the post-injection and reaches the maximum injection rate, a portion that maintains the maximum injection rate for a predetermined period after reaching the maximum injection rate, And a portion descending from the rate. When comparing the front-stage injection and the rear-stage injection, the time during which the maximum injection rate is maintained is longer in the rear-stage injection.

  As shown in FIG. 5, the change in the in-cylinder pressure in the isobaric combustion mode is maintained at the maximum in-cylinder pressure for a predetermined period after reaching the maximum in-cylinder pressure without exceeding the maximum in-cylinder pressure. When comparing the normal combustion mode and the equal pressure combustion mode, as shown in FIG. 7 and FIG. 8, the constant pressure combustion mode may have a longer period during which the in-cylinder pressure is higher than the normal combustion mode before advancement. Recognize. In the normal combustion mode after advance, the maximum in-cylinder pressure is exceeded and cannot be used in actual injection control. Therefore, in the isobaric combustion mode, the output can be increased more than in the normal combustion mode before and after advance.

  Next, the injection mode switching control will be described with reference to FIGS. The switching control shown in FIG. 9 is control that is repeatedly performed when the internal combustion engine is driven.

  In step S11, an operating condition is acquired and it moves to step S12. The operating conditions are, for example, the engine speed Ne, the accelerator opening θac, and the intake pressure Pim. The ECU 30 acquires the accelerator opening degree θac from the accelerator sensor 37, acquires the engine speed Ne from the crank angle sensor 25, and acquires the intake pressure Pim that is the in-cylinder pressure from the in-cylinder pressure sensor 34. The intake pressure Pim has a correlation with the degree of ignition delay in the cylinder. Therefore, the ECU 30 functions as an ignition acquisition unit that acquires the degree of ignition delay in the cylinder. The ECU 30 functions as an intake pressure acquisition unit that acquires the intake pressure Pim.

  In step S12, it is determined whether or not there is a high output request from the acquired operating condition. If it is a high output request, the process proceeds to step S13, and if it is not a high output request, the process proceeds to step S16. Whether it is a high output request is determined by whether it is an output request higher than a predetermined output. Whether or not the request is a high output is determined from, for example, the engine speed Ne and the accelerator opening θac. When the required injection amount is obtained from the accelerator opening θac and the calculated injection amount exceeds the threshold indicated by the broken line in FIG.

  In step S13, it is determined whether or not the intake pressure Pim is greater than or equal to a predetermined intake pressure determination threshold value α. If the intake pressure determination threshold value α is greater than or equal to the intake pressure determination threshold value α, the process proceeds to step S14. Control goes to step S16. The intake pressure determination threshold value α is determined so that the ignition delay becomes smaller than a predetermined time as shown in FIG. If the ignition delay becomes longer, the maximum in-cylinder pressure Pmax may be exceeded at the time of initial combustion. Therefore, when the intake pressure is such that heat generation follows the injection rate, the process proceeds to step S14.

  In step S14, the target injection pressure and timing are set from the engine speed Ne, the accelerator opening θac, and the intake pressure Pim, and the process proceeds to step S15. In step S15, since it is a high output request and the intake pressure Pim is equal to or higher than the intake pressure determination threshold value α, the isobaric injection mode is set, and the process proceeds to step S17. In step S16, since it is not a high output request or the intake pressure Pim is not equal to or higher than the intake pressure determination threshold value α, the normal combustion mode is set, and the process proceeds to step S17. In step S17, injection is performed in the set injection mode, and this flow is terminated.

  Thus, in the case of a high output requirement and a condition in which ignition delay is small and combustion is easy, the isobaric combustion mode is set. Therefore, the high output requirement can be satisfied by the high output in the isobaric combustion mode. On the other hand, when it is not a high output requirement or when there are many ignition delays and it is difficult to burn, the normal combustion mode is set. Thus, the isobaric combustion mode is performed at a necessary timing, and the normal combustion mode is performed when it is not necessary.

In this embodiment, the variable injection rate is realized by speed control of the needle 39. When speed control is performed on the needle 39 in this manner, cavitation is likely to occur in the nozzle hole 40, and erosion, also called erosion, occurs in the nozzle hole 40 along with the collapse of the cavitation, which may cause excessive injection. Therefore, in order to detect an abnormality in the nozzle hole 40, the monitoring control shown in FIG. 12 is repeatedly performed when the internal combustion engine is driven.

In step S21 shown in FIG. 12, the injection amount at the time of injection according to a predetermined injection instruction is acquired, and the process proceeds to step S22. The injection amount is an injection amount when being injected into the cylinder from the injection hole 40 in a predetermined injection period, injection pressure, and injection rate waveform. The ECU 30 detects the fluctuation amount of the engine speed Ne when the fuel is injected according to a predetermined injection instruction, for example. The ECU 30 calculates engine torque from the fluctuation amount of the engine speed, and calculates the injection amount from the engine torque. Moreover, ECU30 may acquire the injection quantity from the injection quantity sensor which detects injection quantity, for example. Therefore, the ECU 30 functions as an injection amount acquisition unit that acquires the injection amount.

  In step S22, it is determined whether or not the injection amount has suddenly increased. If the injection amount has suddenly increased, the process proceeds to step S23. If the injection amount has not suddenly increased, the flow ends. The case of sudden increase is, for example, a value that exceeds the fluctuation range of the injection amount due to secular change, and the injection amount is increased from the previous injection amount.

  In step S24, assuming that an abnormality has occurred in the nozzle hole 40, control is performed so as to prohibit the isobaric combustion mode, and the process proceeds to step S25. When the isobaric combustion mode is prohibited, the normal combustion mode is set instead of the isobaric combustion mode even if the process proceeds to step S15 in FIG. If the constant pressure combustion mode is already set, the normal combustion mode is set.

  In step S25, assuming that an abnormality has occurred in the nozzle hole 40, output restriction is performed, and this flow is terminated. When the output restriction is performed, even when a high output is requested in the normal combustion mode, the control is performed so that the output is not a high output as required, but a predetermined limit output or less.

  As described above, in the monitoring control, the increase in the injection amount under the same injection instruction condition is monitored, and when the sudden increase in the injection amount is confirmed, the implementation of the isobaric combustion mode is prohibited and the output is limited. .

  As described above, the fuel injection control device according to the present embodiment has the constant pressure combustion mode when the intake pressure Pim is equal to or higher than the predetermined intake pressure determination threshold value α and the output request to the engine 10 is a high output. It is controlled to inject at. When the intake pressure Pim is higher than the intake pressure determination threshold value α, the degree of ignition delay is small, and heat generation can be made to follow the injection rate. Conversely, if the degree of ignition delay is large and heat generation cannot follow the injection rate, heat generation cannot be controlled with high accuracy even if the injection rate is controlled with high accuracy. In the present embodiment, since the isobaric combustion mode is performed when it is easy to burn, the in-cylinder pressure can be controlled with high accuracy by the isobaric combustion mode. When the output request to the engine 10 is a high output request higher than the predetermined output request, it is necessary to increase the in-cylinder pressure. Therefore, by injecting in the isobaric combustion mode, the in-cylinder pressure can be made close to the maximum in-cylinder pressure while keeping the in-cylinder pressure below the maximum in-cylinder pressure Pmax.

  Thus, the isobaric combustion mode is an injection rate waveform for controlling the in-cylinder pressure in the combustion chamber 10a to be equal to or less than the maximum in-cylinder pressure Pmax. The isobaric combustion mode is an injection rate waveform in which injection is performed in two stages, upstream injection and downstream injection, and the rate of change in the injection rate increase in upstream injection is greater than the rate of change in downstream injection.

  By the first half injection with a large change rate, the injection rate is rapidly increased to the maximum injection rate, and the in-cylinder pressure is increased to the maximum in-cylinder pressure Pmax in a short time. Thereafter, the in-cylinder pressure can be prevented from exceeding the maximum in-cylinder pressure Pmax by lowering the injection rate from the maximum injection rate. Furthermore, since the injection rate is greater than 0 at the start of the post-stage injection, it is possible to prevent the in-cylinder pressure from being lowered by excessively lowering the injection rate. In addition, it is possible to prevent the in-cylinder pressure from being increased or decreased excessively by the gradual increase in the rate of change of the injection rate in the subsequent injection. The injection rate is maintained at the maximum injection rate in order to reach a predetermined injection amount, and then the injection rate is lowered from the maximum injection rate.

  By such an equal pressure combustion mode, the in-cylinder pressure can be controlled to be close to the maximum in-cylinder pressure Pmax that is equal to or less than the maximum in-cylinder pressure Pmax without exceeding the maximum in-cylinder pressure Pmax. This ensures maximum work. Therefore, the high output requirement can be satisfied without increasing the strength of the engine 10.

  Thus, the isobaric combustion mode is effective in order to maximize the output performance in the engine 10 in which the maximum in-cylinder pressure Pmax is determined. In such an equal pressure combustion mode, the injection rate waveform is set so that the target in-cylinder pressure profile preset in the engine 10 matches the actual in-cylinder pressure profile. The target in-cylinder pressure profile is a profile that can maintain the maximum in-cylinder pressure at the maximum in-cylinder pressure Pmax and has a large output. The injection rate waveform is determined so as to obtain such a target in-cylinder pressure profile.

  In the isobaric combustion mode, the front injection and the rear injection are performed, and the injection rate is larger than 0 at the start of the rear injection. In the case of simple multi-injection, poor spray due to the influence of the throttle generated when the valve is closed occurs. However, since the injection rate at the start of the subsequent stage is larger than 0 as in the present embodiment, the influence of the throttle generated when the valve is closed can be reduced to prevent the smoke from getting worse. The injection rate at the time of subsequent disclosure is preferably such that the flow area of the throttle generated when the needle 39 is opened is larger than the flow area of the nozzle hole 40.

Further, in this embodiment, when the injection amount increases rapidly , the injection in the isobaric combustion mode is prohibited, and the injection is controlled in the normal combustion mode, which is another injection rate waveform. Accordingly, when the injection amount changes suddenly and an abnormality occurs in the nozzle hole 40, it is possible to prevent the isobaric combustion mode from being performed. When an abnormality occurs in the nozzle hole 40, when the isobaric combustion mode is performed, the time during which the maximum in-cylinder pressure is reached is long, so that the influence on the injection amount due to the abnormality in the nozzle hole 40 may be increased. Therefore, by implementing the normal combustion mode in which the in-cylinder pressure is lower than the isobaric combustion mode, it is possible to suppress the influence caused by the abnormality of the nozzle hole 40. Further, when an abnormality occurs in the nozzle hole 40, the user may be notified that the abnormality has occurred.

  Further, in the present embodiment, when the intake pressure Pim is equal to or higher than the intake pressure determination threshold value α and the output request to the engine 10 is a high output, control is performed to inject in the isobaric combustion mode. When the intake pressure Pim is equal to or higher than the intake pressure determination threshold value α, the ignition delay is small and combustion is easy. When it is easy to burn, heat generation can follow the injection rate waveform. As a result, when the isobaric combustion mode is performed, the actual in-cylinder pressure profile can be brought close to the target in-cylinder pressure profile.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS. The present embodiment is characterized in that not the intake pressure Pim but the oxygen concentration O2im is used to determine the inflammability in the cylinder. The injection mode switching control of this embodiment will be described. The switching control shown in FIG. 13 is control that is repeatedly performed when the internal combustion engine is driven.

  In step S31, operation conditions are acquired similarly to step S11, and the process proceeds to step S32. The operating conditions include the oxygen concentration O2im. Therefore, the ECU 30 functions as an oxygen concentration acquisition unit that acquires the oxygen concentration of the intake air. In step S32, similarly to step S12, it is determined whether or not a high output request is made based on the obtained operating condition. If the request is a high output request, the process proceeds to step S33, and if not, the process proceeds to step S36. .

  In step S33, it is determined whether or not the oxygen concentration O2im is equal to or greater than a predetermined oxygen concentration determination threshold β. If the oxygen concentration determination threshold β is equal to or greater than step S34, the process proceeds to step S34. Control goes to step S36. The oxygen concentration determination threshold value β is determined so that the ignition delay becomes smaller than a predetermined time as shown in FIG.

  In step S34, similarly to step S14, the target injection pressure and timing are set from the engine speed Ne, the accelerator opening θac, and the intake pressure Pim, and the process proceeds to step S35. In step S35, since it is a high output request and the oxygen concentration O2im is equal to or higher than the oxygen concentration determination threshold value β, the isobaric injection mode is set, and the process proceeds to step S37. In step S36, it is not a high output request or the oxygen concentration O2im is not equal to or higher than the oxygen concentration determination threshold value β, so the normal combustion mode is set, and the process proceeds to step S37. In step S37, as in step S17, injection is performed in the set injection mode, and this flow ends.

  As described above, in the present embodiment, in the case of a high output requirement, a condition where the oxygen concentration is high, the ignition delay is small, and combustion is easy, the isobaric combustion mode is set. As a result, as in the first embodiment described above, the high output requirement can be satisfied by the high output in the isobaric combustion mode. On the other hand, when it is not a high output requirement or when the oxygen concentration is low and the ignition delay is large and it is difficult to burn, the normal combustion mode is set. Thus, the isobaric combustion mode is performed at a necessary timing, and the normal combustion mode is performed when it is not necessary.

  In the present embodiment, the oxygen concentration of the intake air is acquired by the oxygen concentration sensor 38, but is not limited to the oxygen concentration sensor 38, and the oxygen concentration is estimated from a correlated numerical value, for example, an EGR rate. Also good.

  In the present embodiment, the oxygen concentration O2im is used to determine the ignition delay, but without determining only the oxygen concentration O2im, the degree of ignition delay is acquired by both the intake pressure Pim and the oxygen concentration O2im, You may judge the flammability. This makes it possible to determine the easiness of burning with higher accuracy.

(Other embodiments)
The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  The structure of the above-described embodiment is merely an example, and the scope of the present invention is not limited to the scope of these descriptions. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  In the first embodiment described above, two injection rate waveforms are switched. However, the present invention is not limited to two injection rate waveforms, and three or more injection rate waveforms may be switched. The control is not limited to switching between the isobaric combustion mode and the normal combustion mode, but may be control switching between the isobaric combustion mode and another injection mode. Other injection modes include, for example, an injection rate waveform having a boot shape, a Δ shape, a trapezoidal shape, and a staircase shape.

  In the first embodiment described above, the actuator 43 of the fuel injection valve 18 uses a piezo element, but is not limited to such a configuration. Any configuration capable of adjusting the valve opening speed may be used. For example, a configuration may be adopted in which a plurality of pressure chambers having different pressures are provided and the valve opening speed is adjusted by switching these chambers.

  Further, in each of the above-described embodiments, using the detected values correlated with the ignition delay such as the intake pressure Pim and the oxygen concentration O2im, it is determined that the combustion is likely to occur when the degree of the ignition delay is smaller than the threshold value. However, it is not limited to the intake pressure Pim and the oxygen concentration O2im. The EGR rate may be used, or may be determined using other values.

  In the first embodiment described above, the functions realized by the ECU 30 may be realized by hardware and software different from those described above, or a combination thereof. The ECU 30 may realize each functional block such as a control unit that performs injection control by one processor. The ECU 30 may communicate with, for example, another control device, and the other control device may execute part or all of the processing. When the ECU 30 is realized by an electronic circuit, it can be realized by a digital circuit including a large number of logic circuits or an analog circuit.

DESCRIPTION OF SYMBOLS 10 ... Engine (internal combustion engine) 10a ... Combustion chamber 10b ... Cylinder 18 ... Fuel injection valve 25 ... Crank angle sensor 30 ... ECU (Ignition acquisition part, control part, injection amount acquisition part, intake pressure acquisition part, oxygen concentration acquisition part)
31 ... Intake pressure sensor 32 ... Intake temperature sensor 33 ... Exhaust temperature sensor 34 ... In-cylinder pressure sensor 35 ... Fuel pressure sensor 36 ... Water temperature sensor 37 ... Accelerator sensor 38 ... Oxygen concentration sensor 39 ... Needle 40 ... Injection hole 43 ... Actuator

Claims (7)

A fuel injection control device that controls injection of fuel from a fuel injection valve (18) having a variable injection rate waveform into a combustion chamber (10a) of an internal combustion engine (10),
An ignition acquisition unit (30) for acquiring the degree of ignition delay in the cylinder;
A control unit (30) for controlling fuel injection using any one of the plurality of injection rate waveforms according to an output request to the internal combustion engine,
The plurality of the injection rate waveform, an injection Iritsu waveform for cylinder pressure in the combustion chamber is controlled to be less than the maximum cylinder pressure, thereby increasing the injection rate twice during a single injection 2 Including the rising injection rate waveform,
In the second-time rising injection rate waveform, the first injection is the first-stage injection, and the second injection is the second-stage injection.
The injection rate waveform of the pre-stage injection has a portion where the injection rate increases for the first time from the start of the pre-stage injection and reaches the maximum injection rate, and a portion where the injection rate decreases from the maximum injection rate,
The injection rate waveform of the post-stage injection is such that the injection rate at the start of the post-stage injection is greater than 0, the injection rate rises for the second time from the start of the post-stage injection, and reaches the maximum injection rate, A portion descending from the maximum injection rate,
The rate of change in the injection rate increase in the front injection is greater than the rate of change in the post injection,
When the degree of ignition delay acquired by the ignition acquisition unit is smaller than a threshold value and the output request to the internal combustion engine is a high output request higher than a predetermined output, the control unit performs the two times. A fuel injection control device that controls to inject with a rising injection rate waveform. The fuel injection valve is configured such that the injection rate waveform can be changed by speed control of a valve body that opens and closes an injection hole,
It further includes an injection amount acquisition unit (30) for acquiring the injection amount,
Wherein the control unit, the injection amount of currently obtained by the injection quantity obtaining section, than the previous injection amount, when increased beyond the range of variation due to aging is injected in the two rising injection rate waveform The fuel injection control device according to claim 1, wherein the control is performed so as to prohibit the fuel injection and perform the injection with the other injection rate waveform. The ignition acquisition unit, the intake pressure, obtained as a value representing the degree of the ignition delay,
When the intake pressure acquired by the ignition acquisition unit is equal to or higher than a predetermined intake pressure, and the output request to the internal combustion engine is the high output request, the control unit uses the two-time rising injection rate waveform. The fuel injection control device according to claim 1, wherein the fuel injection control device controls the fuel injection. The ignition acquisition unit, the oxygen concentration of the intake air, obtained as a value representing the degree of the ignition delay,
When the oxygen concentration acquired by the ignition acquisition unit is equal to or higher than a predetermined oxygen concentration and the output request to the internal combustion engine is the high output request, the control unit uses the twice-increasing injection rate waveform. The fuel injection control device according to claim 1, wherein the fuel injection control device controls the fuel injection. The said injection rate waveform of the said back | latter stage injection has a part maintained at the said maximum injection rate over predetermined time after an injection rate raises and it reaches | attains the said maximum injection rate. Fuel injection control device. The injection rate waveform of the pre-stage injection has a portion that is maintained at the maximum injection rate for a predetermined time after the injection rate increases and reaches the maximum injection rate,
6. The fuel injection control device according to claim 5, wherein a predetermined time maintained at the maximum injection rate in the rear-stage injection is longer than a predetermined time maintained at the maximum injection ratio in the front-stage injection. The said injection rate waveform of the said front | former stage injection has a part maintained by the said maximum injection rate over predetermined time after an injection rate raises and it reaches | attains the said maximum injection rate. Fuel injection control device.

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