JP2009191802A - Control device for compression ignition type internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To smoothly perform switching from diffuse combustion to premixed compression ignition combustion while reducing combustion noise. <P>SOLUTION: A combustion determination section 44 determines whether a combustion mode should be switched from diffuse combustion to premixed compression ignition combustion or not. When the combustion determination section 44 determines that the combustion mode should be switched from diffuse combustion to premixed compression combustion, an EGR control section 43 controls an EGR so as to increase an EGR gas amount supplied to an intake side. In the case that the EGR control section 43 controls the EGR so as to increase the EGR gas amount supplied to the intake side, a combustion noise prediction section 45 predicts combustion noise when switched to the premixed compression combustion based on an oxygen condensation in intake air, an engine load, a suction air amount or the supercharge pressure. A fuel injection control section 42 decides whether a fuel injection time should be controlled to an injection time for performing premixed compression ignition combustion or not based on the combustion noise predicted by the combustion noise prediction section 45. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for controlling a compression ignition type internal combustion engine that self-ignites by injecting fuel into a cylinder.

  The related art of this type of compression ignition type internal combustion engine control device is disclosed in Patent Documents 1 and 2 below. In Patent Document 1, a compression ignition internal combustion engine includes diffusion combustion in which fuel is directly injected into a cylinder near the compression top dead center and self-ignition of the fuel in the cylinder, and fuel and intake air formed in the cylinder Is operated by switching between premixed compression ignition combustion (PCCI combustion) for self-ignition of the premixed gas, and exhaust recirculation (EGR) for supplying a part of the exhaust gas after combustion to the intake side as EGR gas Do. Then, at the time of transition from diffusion combustion to premixed compression ignition combustion, a first intermediate combustion region is set, and the fuel injection timing in the first intermediate combustion region is changed between the fuel injection timing in diffusion combustion and the premixed compression ignition combustion. It is controlled to be retarded from an intermediate value with respect to the fuel injection timing. As a result, at the time of transition from diffusion combustion to premixed compression ignition combustion, the premixed gas is prevented from self-igniting at an early timing, thereby reducing combustion noise.

  Patent Document 2 discloses control for advancing the fuel injection timing in order to prevent misfire in diffusion combustion. More specifically, the basic misfire limit injection timing is obtained based on the relationship between the engine speed and the engine load as parameters, and the basic misfire limit injection timing is calculated based on the intake pressure advance angle correction value based on the intake pressure, the coolant temperature. The misfire limit injection timing is obtained by correcting with the cold advance angle correction value based on the intake air temperature and the intake air temperature advance angle correction value based on the intake air temperature, and further, the misfire limit injection timing is not advanced from the advance angle upper limit guard value. Restrict. When the misfire limit injection timing is advanced from the warm base injection timing based on the engine speed and the engine load, the fuel injection timing is controlled based on the misfire limit injection timing. When it is retarded from the warm base injection timing, the fuel injection timing is controlled based on the warm base injection timing. Accordingly, when the fuel injection timing is advanced in order to prevent the occurrence of misfire, the fuel injection timing is prevented from being excessively advanced, thereby reducing combustion noise.

JP 2007-2111596 A JP 2000-186598 A

  In a compression ignition type internal combustion engine, if the oxygen concentration in the intake air taken into the cylinder becomes excessive, combustion becomes steep and the combustion noise level increases. On the other hand, when the oxygen concentration in the intake air sucked into the cylinder becomes too low, combustion becomes slow, and torque shortage and misfire are likely to occur. At the time of transition from diffusion combustion to premixed compression ignition combustion, the EGR rate is increased in order to suppress the generation of nitrogen oxides (NOx), but because the responsiveness when supplying EGR gas to the intake side is low, Since the supply amount of EGR gas to the intake air is transiently insufficient and the oxygen concentration in the intake air becomes transiently excessive, the premixed gas is self-ignited at an early timing and combustion noise increases. In Patent Document 1, by setting the first intermediate combustion region at the time of transition from diffusion combustion to premixed compression ignition combustion, the premixed gas is supplied even if the supply amount of the EGR gas to the intake air is transiently insufficient. However, in order to sufficiently reduce the combustion noise, it is necessary to control the fuel injection timing in the first intermediate combustion region with high accuracy. For example, if the fuel injection timing is shifted to the retard side even a little, torque shortage tends to be caused. On the other hand, if the fuel injection timing is shifted to the advance side even a little, the effect of reducing the combustion noise cannot be obtained. As a result, it becomes difficult to smoothly transition from diffusion combustion to premixed compression ignition combustion.

  In addition, when the fuel injection timing is advanced to prevent misfire in diffusion combustion, if the fuel injection timing is excessively advanced, the fuel injected into the cylinder adheres to the cylinder inner wall and fuel consumption decreases. In addition, combustion noise increases. In Patent Document 2, combustion noise is reduced by limiting the fuel injection timing so that it does not advance from the advance angle upper limit guard value. However, when the fuel injection timing is advanced to the advance angle upper limit guard value and the oxygen concentration in the intake air is too low, the combustion becomes slow, and misfire is likely to occur.

  An object of the present invention is to provide a control device for a compression ignition type internal combustion engine that can smoothly shift from diffusion combustion to premixed compression ignition combustion while reducing combustion noise. Another object of the present invention is to provide a control device for a compression ignition internal combustion engine that can more reliably avoid the occurrence of misfire while reducing the adhesion of fuel to the cylinder inner wall.

  The control apparatus for a compression ignition type internal combustion engine according to the present invention employs the following means in order to achieve at least a part of the above-described object.

  The control apparatus for a compression ignition type internal combustion engine according to the present invention selectively performs either diffusion combustion or premixed compression ignition combustion, and supplies exhaust gas after combustion to the intake side as EGR gas. A device that controls a compression ignition type internal combustion engine that performs recirculation, a combustion determination unit that determines whether or not to shift from diffusion combustion to premixed compression ignition combustion, and a combustion determination unit that performs premix compression from diffusion combustion When it is determined to shift to ignition combustion, an EGR control unit that controls exhaust gas recirculation so as to increase the amount of EGR gas supplied to the intake side, and an amount of EGR gas that the EGR control unit supplies to the intake side Combustion that predicts combustion noise when shifting to premixed compression ignition combustion based on the oxygen concentration in the intake air, the engine load, the intake air amount or the supercharging pressure when controlling exhaust gas recirculation Noise prediction unit And a fuel injection control unit that determines whether or not to control the fuel injection timing to an injection timing for performing premixed compression ignition combustion based on the combustion noise predicted by the combustion noise prediction unit. .

  In the present invention, when the amount of EGR gas supplied to the intake side in order to shift from diffusion combustion to premixed compression ignition combustion, the oxygen concentration in the intake air, the engine load, the intake air amount or the supercharging pressure are adjusted. Based on this, the combustion noise when shifting to premixed compression ignition combustion can be predicted more accurately by predicting the combustion noise when shifting to premixed compression ignition combustion. Then, by determining whether or not to control the fuel injection timing to the injection timing for performing the premixed compression ignition combustion based on the predicted combustion noise, the state shifts to the premixed compression ignition combustion in a state where the combustion noise becomes large. Can be avoided, and combustion noise when shifting to premixed compression ignition combustion can be sufficiently reduced. Therefore, according to the present invention, the transition from diffusion combustion to premixed compression ignition combustion can be performed smoothly while reducing combustion noise.

  In one aspect of the present invention, the fuel injection control unit may control the fuel injection timing to an injection timing for performing premixed compression ignition combustion when the combustion noise predicted by the combustion noise prediction unit is equal to or lower than an allowable level. Is preferred.

  In one aspect of the present invention, when the combustion noise predicted by the combustion noise prediction unit exceeds an allowable level, the fuel injection control unit further includes a misfire determination unit that determines the occurrence of misfire in combustion. If the combustion noise predicted in step (b) exceeds the allowable level, the fuel injection timing is controlled to be the injection timing for diffusive combustion, and if the misfire determination unit determines that misfiring will occur, it precedes the main fuel injection. Thus, by performing pilot injection, it is possible to avoid the occurrence of misfire. In this aspect, the fuel injection control unit more reliably avoids misfires by advancing the main injection timing when pilot injection is performed when the misfire determination unit determines that misfire occurs. can do. Further, in this aspect, the fuel injection control unit increases the pilot injection amount when the main injection timing is advanced to the advance limit time when the misfire determination unit determines that misfire occurs. Further, it is possible to more reliably avoid the occurrence of misfire while reducing the adhesion of the fuel to the cylinder inner wall due to the main injection.

  In one aspect of the present invention, the misfire determination unit determines the occurrence of misfire in combustion based on the oxygen concentration in the intake air, the engine load, the intake air amount, or the supercharging pressure, thereby more accurately detecting the occurrence of misfire. Can be judged well.

  In one aspect of the present invention, the combustion noise prediction unit includes the engine speed, the intake air temperature, the fuel injection timing, the engine coolant temperature, in addition to the oxygen concentration in the intake air, the engine load, the intake air amount or the supercharging pressure. By predicting the combustion noise when shifting to premixed compression ignition combustion based on any one or more of the above, the combustion noise when shifting to premixed compression ignition combustion can be predicted more accurately .

  In one aspect of the present invention, a combustion noise characteristic storage unit that stores a combustion noise characteristic representing a relationship of combustion noise in premixed compression ignition combustion with respect to oxygen concentration in intake air, engine load, intake air amount or supercharging pressure is provided. The combustion noise prediction unit further includes a combustion noise characteristic stored in the combustion noise characteristic storage unit in the premixed compression ignition combustion corresponding to the oxygen concentration in the intake air, the engine load, the intake air amount or the supercharging pressure. It is preferable to predict the combustion noise when shifting to premixed compression ignition combustion by calculating the combustion noise.

  In one aspect of the present invention, it is preferable that the combustion determination unit determines whether to shift from diffusion combustion to premixed compression ignition combustion based on the engine speed and the engine load.

  The control device for a compression ignition type internal combustion engine according to the present invention is a device that controls a compression ignition type internal combustion engine that injects fuel into a cylinder and self-ignites, and performs fuel injection control. And a misfire determination unit that determines the occurrence of misfire in combustion, and the fuel injection control unit performs pilot injection prior to the main fuel injection when it is determined by the misfire determination unit that misfire occurs. When not performing pilot injection, when pilot injection is being performed, the main injection timing is advanced, and when the main injection timing is advanced to the advance limit time, the pilot injection amount is increased. The gist is to make it.

  According to the present invention, when it is determined that misfiring occurs in combustion, pilot injection is performed prior to main fuel injection, pilot injection is performed, and pilot injection is performed when pilot injection is performed. When the injection timing is advanced and the main injection timing is advanced to the advance limit time, by increasing the pilot injection amount, the occurrence of misfire is more reliably generated while reducing the adhesion of fuel to the cylinder inner wall. Can be avoided.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a control device according to an embodiment of the present invention together with a compression ignition type internal combustion engine 10. The compression ignition type internal combustion engine 10 can be constituted by a known diesel engine using a piston-crank mechanism, for example. In the compression ignition type internal combustion engine 10 (diesel engine), intake air is sucked into the cylinder from the intake passage 14 during the intake stroke, and intake air sucked into the cylinder during the compression stroke is compressed by the piston 12. Here, the intake air into the cylinder can be pressurized by a supercharger such as a turbocharger (not shown). For example, when the piston 12 is located near the compression top dead center, the fuel is directly injected into the cylinder from the fuel injection valve 13 so that the fuel in the cylinder self-ignites and burns (diesel combustion). The exhaust gas after combustion is discharged into the exhaust passage 15 in the exhaust stroke. In the compression ignition type internal combustion engine 10, a recirculation passage 16 that connects the exhaust passage 15 and the intake passage 14 is provided, and a part of the exhaust gas after combustion passes through the recirculation passage 16 to the intake passage 14 (intake side). Exhaust gas recirculation (EGR) supplied as EGR gas is performed. The recirculation passage 16 is provided with an EGR control valve 17. By controlling the opening degree of the EGR control valve 17, the recirculation amount of the exhaust gas (EGR gas) from the exhaust passage 15 to the intake passage 14 is controlled, The amount of EGR gas (EGR rate) supplied to the intake side and sucked into the cylinder is controlled.

The compression ignition internal combustion engine 10 includes an intake air amount sensor 25 that detects an intake air amount IA into the cylinder, and an oxygen concentration sensor 26 that detects an oxygen (O ₂ ) concentration AO in the intake air that is drawn into the cylinder. A rotational speed sensor 27 for detecting the engine rotational speed Ne, an intake air temperature sensor 28 for detecting the temperature TI of the intake air sucked into the cylinder, and a temperature Tw of the cooling water (coolant) of the compression ignition internal combustion engine 10 And a coolant temperature sensor 29 for detecting the above. The intake air amount sensor 25 detects the intake air amount IA at a position upstream of the position where exhaust gas (EGR gas) is supplied in the intake passage 14. On the other hand, the intake air temperature sensor 28 detects the intake air temperature (intake air temperature) TI at a position downstream of the position where the EGR gas is supplied in the intake passage 14 (inside the cylinder). The oxygen concentration sensor 26 detects the oxygen concentration AO in the intake air at a position downstream of the position where the EGR gas is supplied in the intake passage 14 (inside the cylinder). Therefore, as the EGR gas concentration (EGR rate) supplied to the intake side increases, the oxygen concentration AO in the intake air detected by the oxygen concentration sensor 26 decreases. A signal indicating the intake air amount IA detected by the intake air amount sensor 25, a signal indicating the oxygen concentration AO in the intake air detected by the oxygen concentration sensor 26, and a signal indicating the engine speed Ne detected by the rotational speed sensor 27 The signal indicating the intake air temperature (intake air temperature) TI detected by the intake air temperature sensor 28 and the signal indicating the coolant temperature Tw detected by the coolant temperature sensor 29 are input to an electronic control unit (ECU) 40. The It is also possible to detect the supercharging pressure (when the intake air is pressurized by the supercharger) instead of the intake air amount IA.

  The electronic control unit 40 can be configured to include, for example, the functional blocks shown in FIG. The fuel injection control unit 42 that performs fuel injection control of the compression ignition type internal combustion engine 10 sends an injection control signal generated based on the operation state of the compression ignition type internal combustion engine 10 such as the rotational speed Ne and load to the fuel injection valve 13. By outputting, the fuel injection timing (fuel injection start timing) Tinj and the fuel injection amount Fu are controlled. In the compression ignition type internal combustion engine 10, not only normal diesel combustion (diffusion combustion) in which fuel is directly injected into the cylinder near the compression top dead center to self-ignite the fuel in the cylinder, but also fuel formed in the cylinder It is also possible to perform premixed compression ignition combustion (PCCI combustion) in which the premixed air and intake air are self-ignited. By performing this premixed compression ignition combustion, it is possible to suppress the generation of black smoke. When performing premix compression ignition combustion, fuel is directly injected into the cylinder from the fuel injection valve 13 in the intake stroke or compression stroke to form a premixed mixture of fuel and intake air in the cylinder. The premixed gas is compressed by the piston 12 and self-ignited.

  The EGR control unit 43 controls the opening degree of the EGR control valve 17 by outputting an EGR control signal generated based on the operating state such as the rotational speed Ne and the load of the compression ignition type internal combustion engine 10 to the EGR control valve 17. Then, the amount of EGR gas (EGR rate) supplied to the intake side is controlled. Thus, EGR (exhaust gas recirculation) is controlled. When premixed compression ignition combustion is performed, the EGR control unit 43 preferably increases the amount of EGR gas (EGR rate) supplied to the intake side by EGR as compared with the case where diffusion combustion (normal combustion) is performed. A large amount of EGR gas, which has a larger heat capacity than air (fresh air), is mixed in the intake air to reduce the concentration of fuel and oxygen in the premixed gas, thereby extending the autoignition delay time and The self-ignition timing can be controlled near the compression top dead center. Moreover, in the premixed gas, the inert EGR gas is dispersed almost uniformly around the fuel and oxygen, and this absorbs the heat of combustion, so the generation of nitrogen oxides (NOx) is greatly suppressed. Is done.

  The combustion determination unit 44 determines whether to perform diffusion combustion or premixed compression ignition combustion. Here, it is possible to determine whether to perform diffusion combustion or premixed compression ignition combustion based on the rotational speed Ne and torque Te (load) of the compression ignition type internal combustion engine 10. For example, when the rotational speed Ne and the torque Te of the compression ignition type internal combustion engine 10 are in the low speed / low load region that is a region that does not exceed the characteristic line A shown in FIG. 2, the combustion determination unit 44 performs the premixed compression ignition. Choose the way to burn. On the other hand, when the rotational speed Ne and the torque Te of the compression ignition type internal combustion engine 10 are in the high speed / high load region that exceeds the characteristic line A shown in FIG. 2, the combustion determination unit 44 performs the diffusion combustion. Select. Further, when the rotational speed Ne of the compression ignition type internal combustion engine 10 is lower than the predetermined value Ne1 and the torque Te is lower than the predetermined value Te1, the combustion determination unit 44 selects a method of performing premixed compression ignition combustion. Is also possible. On the other hand, when one or more of the condition where the rotational speed Ne of the compression ignition internal combustion engine 10 is higher than the predetermined value Ne1 and the condition where the torque Te of the compression ignition internal combustion engine 10 is higher than the predetermined value Te1 are satisfied. The combustion determination unit 44 can also select a method for performing diffusion combustion. Depending on whether the fuel injection control unit 42 controls the fuel injection timing near the compression top dead center or the intake stroke (or the compression stroke) based on the determination result of the combustion determination unit 44, the compression ignition type internal combustion engine 10 is controlled. As the combustion, either diffusion combustion or premixed compression ignition combustion can be selectively performed. The torque Te (load) of the compression ignition type internal combustion engine 10 can be calculated from, for example, the fuel injection amount Fu, and the fuel injection amount Fu is calculated by the electronic control unit 40 (fuel injection control unit 42). (The target value of the fuel injection amount) can be used.

  When performing EGR, since the responsiveness when supplying EGR gas to the intake side is low, the operation state in which the EGR rate deviates from the target value and the oxygen concentration AO in the intake gas deviates from the target value AOT is transient. Will occur. If the EGR rate is lower than the target value and the oxygen concentration AO in the intake air is excessive with respect to the target value AOT, the fuel self-ignition timing is too early, and the combustion becomes steep and the combustion noise level is likely to increase. Become. In particular, when the combustion of the compression ignition type internal combustion engine 10 is shifted from diffusion combustion to premixed compression ignition combustion, the EGR rate is increased in order to retard the combustion peak and suppress noise. Therefore, the supply amount of EGR gas to the intake air is transiently insufficient, and the oxygen concentration AO in the intake air becomes excessively large relative to the target value AOT. The air-fuel mixture is ignited at an early timing and the combustion noise level is likely to increase. On the other hand, if the EGR rate is higher than the target value and the oxygen concentration AO in the intake air is too small with respect to the target value AOT, the fuel self-ignition timing is too late, and the combustion becomes slow, resulting in insufficient torque and misfire. It becomes easy to invite. Therefore, in the present embodiment, a combustion noise prediction unit 45 that predicts a combustion noise level NL during premixed compression ignition combustion and a misfire determination unit 47 that determines the occurrence of misfire in combustion (diffusion combustion) are provided. .

  The combustion noise level NL at the time of premixed compression ignition combustion generally changes in accordance with the oxygen concentration AO in the intake air. For example, as shown in FIG. Thus, the combustion noise level NL increases, and the combustion noise level NL decreases as the oxygen concentration AO in the intake air decreases. The combustion noise level NL changes according to the engine torque Te (engine load, fuel injection amount Fu) even if the oxygen concentration AO in the intake air is constant, for example, as shown in FIG. The combustion noise level NL increases as the engine torque Te increases, and the combustion noise level NL decreases as the engine torque Te decreases. Further, the combustion noise level NL changes according to the intake air amount (supercharging pressure) IA even if the oxygen concentration AO in the intake air is constant, and for example, as shown in FIG. The level of the air amount (supercharging pressure) IA is peaked, and the combustion noise level NL decreases regardless of whether it increases or decreases. Therefore, the combustion noise prediction unit 45 determines the combustion noise level NL during premixed compression ignition combustion based on the oxygen concentration AO in the intake air, the engine torque Te (engine load), and the intake air amount (or supercharging pressure) IA. Can be predicted. At that time, combustion representing the relationship of the combustion noise level NL during premixed compression ignition combustion with respect to the oxygen concentration AO in the intake air, the engine torque Te (fuel injection amount Fu), and the intake air amount (or supercharging pressure) IA. A noise characteristic map is created in advance and stored in the combustion noise characteristic storage unit 46 (storage device) in the electronic control unit 40. In the combustion noise characteristic map stored in the combustion noise characteristic storage unit 46, the combustion noise prediction unit 45 gives the supplied oxygen concentration AO, engine torque Te (fuel injection amount Fu), and intake air amount (or supercharging). The combustion noise level NL at the time of premixed compression ignition combustion is predicted by calculating the combustion noise level NL corresponding to (pressure) IA.

  Further, the combustion noise level NL includes not only the oxygen concentration AO in the intake air, the engine torque Te, and the intake air amount (supercharging pressure) IA, but also the engine speed Ne, the intake air temperature TI, the fuel injection timing Tinj, and the coolant temperature. Also affected by Tw. For example, as shown in FIG. 3D, the combustion noise level NL increases with an increase in the engine speed Ne and decreases with a decrease in the engine speed Ne. In addition to the oxygen concentration AO, engine torque Te, and intake air amount (supercharging pressure) IA, the combustion noise level NL during premixed compression ignition combustion can also be predicted based on the engine speed Ne. . Further, for example, as shown in FIG. 3E, the combustion noise level NL increases with an increase in the intake air temperature TI, has a peak at a certain intake air temperature TI, and below that level, the intake air temperature. Decrease relative to decrease in TI. Therefore, the combustion noise predicting unit 45 performs the premixed compression ignition combustion based on the intake air temperature TI in addition to the oxygen concentration AO in the intake air, the engine torque Te, and the intake air amount (supercharging pressure) IA. It is also possible to predict the combustion noise level NL. Further, when considering both premixed compression ignition combustion and normal combustion, the combustion noise level NL has a peak at a certain fuel injection timing Tinj and is advanced from that timing, for example, as shown in FIG. Even if retarded, the combustion noise level NL decreases. Therefore, the combustion noise predicting unit 45 performs the premixed compression ignition combustion based on the fuel injection timing Tinj in addition to the oxygen concentration AO in the intake air, the engine torque Te, and the intake air amount (supercharging pressure) IA. It is also possible to predict the combustion noise level NL. Further, for example, as shown in FIG. 3G, the combustion noise level NL increases with an increase in the coolant temperature Tw, has a peak at a certain coolant temperature Tw level, and below that level the coolant temperature. Decrease with respect to decrease in Tw. For this reason, the combustion noise predicting unit 45 performs the premixed compression ignition combustion based on the coolant temperature Tw in addition to the oxygen concentration AO in the intake air, the engine torque Te, and the intake air amount (supercharging pressure) IA. It is also possible to predict the combustion noise level NL. In this way, the combustion noise predicting unit 45, in addition to the oxygen concentration AO in the intake air, the engine torque Te, and the intake air amount (or supercharging pressure) IA, the engine speed Ne, the intake air temperature TI, and the fuel injection timing. The combustion noise level NL at the time of premixed compression ignition combustion can also be predicted based on one or more of Tinj and the coolant temperature Tw. At that time, the combustion noise level NL calculated using the combustion noise characteristic map with the oxygen concentration AO in the intake air, the engine torque Te, and the intake air amount IA as parameters is used as the engine speed Ne and the intake air temperature TI. The correction can be made based on one or more of the fuel injection timing Tinj and the coolant temperature Tw. It is also possible to calculate the combustion noise level NL by adding any one or more of the engine speed Ne, the intake air temperature TI, the fuel injection timing Tinj, and the coolant temperature Tw to the parameters of the combustion noise characteristic map.

  Further, the likelihood of misfire changes depending on the oxygen concentration AO in the intake air, and as shown in FIG. 4A, for example, the misfire is less likely to occur as the oxygen concentration AO in the intake air increases. Misfires are likely to occur as the oxygen concentration AO in the intake air decreases. The likelihood of misfire changes even when the oxygen concentration AO in the intake air is constant, and changes according to the engine torque Te (engine load, fuel injection amount Fu). For example, as shown in FIG. Furthermore, misfires are less likely to occur as the engine torque Te increases, and misfires more likely to occur as the engine torque Te decreases. Further, the likelihood of misfiring changes according to the intake air amount (supercharging pressure) IA even if the oxygen concentration AO in the intake air is constant. For example, as shown in FIG. Misfires are less likely to occur as the air amount (supercharging pressure) IA increases, and misfires are more likely to occur as the intake air amount (supercharging pressure) IA decreases. Therefore, the misfire determination unit 47 can determine the occurrence of misfire based on the oxygen concentration AO in the intake air, the engine torque Te (engine load), and the intake air amount (or supercharging pressure) IA. At that time, a misfire characteristic map representing the relationship between the normal combustion region and the misfire occurrence region with respect to the oxygen concentration AO in the intake air, the engine torque Te (fuel injection amount Fu), and the intake air amount (or supercharging pressure) IA is previously stored. Created and stored in the misfire characteristic storage unit 48 (storage device) in the electronic control unit 40. The misfire determination unit 47 uses the misfire characteristic map stored in the misfire characteristic storage unit 48 to provide the supplied oxygen concentration AO, engine torque Te (fuel injection amount Fu), and intake air amount (or supercharging pressure) IA. The occurrence of misfire is determined by determining whether the region corresponding to and is a normal combustion region or a misfire occurrence region.

  Further, misfires are more likely to occur in addition to the oxygen concentration AO, the engine torque Te, and the intake air amount (supercharging pressure) IA in the intake air, as well as the engine speed Ne, the intake air temperature TI, the fuel injection timing Tinj, and the cooling. It is also affected by the liquid temperature Tw. For example, as shown in FIG. 4 (d), misfire is more likely to occur as the engine speed Ne increases, and less likely to occur as the engine speed Ne decreases. In addition to the oxygen concentration AO, the engine torque Te, and the intake air amount (supercharging pressure) IA, the occurrence of misfire can also be determined based on the engine speed Ne. Further, for example, as shown in FIG. 4E, misfire is less likely to occur as the intake air temperature TI increases, and is more likely to occur as the intake air temperature TI decreases. The occurrence of misfire can also be determined based on the intake air temperature TI in addition to the oxygen concentration AO, the engine torque Te, and the intake air amount (supercharging pressure) IA. Further, for example, as shown in FIG. 4F, misfire is less likely to occur as the fuel injection timing Tinj is advanced, and is more likely to occur as the fuel injection timing Tinj is retarded. The occurrence of misfire can also be determined based on the fuel injection timing Tinj in addition to the oxygen concentration AO in the intake air, the engine torque Te, and the intake air amount (supercharging pressure) IA. Further, for example, as shown in FIG. 4G, misfires are less likely to occur as the coolant temperature Tw increases, and are more likely to occur as the coolant temperature Tw decreases. The occurrence of misfire can also be determined based on the coolant temperature Tw in addition to the oxygen concentration AO, the engine torque Te, and the intake air amount (supercharging pressure) IA. As described above, the misfire determination unit 47 determines the engine speed Ne, the intake air temperature TI, and the fuel injection timing Tinj in addition to the oxygen concentration AO in the intake air, the engine torque Te, and the intake air amount (or supercharging pressure) IA. The occurrence of misfire can also be determined based on one or more of the coolant temperature Tw.

  Next, processing executed by the electronic control unit 40 when the combustion of the compression ignition type internal combustion engine 10 is shifted from diffusion combustion to premixed compression ignition combustion will be described with reference to the flowchart of FIG. The process according to the flowchart of FIG. 5 is repeatedly executed at predetermined intervals when diffusion combustion is performed.

  In step S101, the engine speed Ne and the engine torque Te (engine load) are acquired. The engine torque Te here can be calculated from the fuel injection amount Fu, and the fuel injection amount Fu is a value calculated by the electronic control device 40 (fuel injection control unit 42) (target value of the fuel injection amount). ) Can be used. In step S102, the combustion determination unit 44 determines whether or not to shift from diffusion combustion to premixed compression ignition combustion (PCCI combustion). Here, based on the engine speed Ne and torque Te (load) acquired in step S101, it is determined whether or not to shift from diffusion combustion to premixed compression ignition combustion. For example, when the engine speed Ne and the torque Te shift from the high speed / high load region to the low speed / low load region in FIG. 2, it is determined that the condition for shifting from diffusion combustion to premixed compression ignition combustion is satisfied. be able to. On the other hand, when the engine speed Ne and the torque Te are within the high speed / high load region of FIG. 2, it can be determined that the condition for shifting from diffusion combustion to premixed compression ignition combustion is not satisfied. When the condition for shifting from diffusion combustion to premixed compression ignition combustion is not satisfied (when the determination result of step S102 is NO), the execution of this process is temporarily terminated, and this process is executed again after a predetermined time. On the other hand, when it is determined to shift from diffusion combustion to premixed compression ignition combustion (when the determination result in step S102 is YES), the process proceeds to step S103.

  In step S103, EGR control is performed by the EGR control unit 43 so as to increase the amount of EGR gas (EGR rate) supplied to the intake side by increasing the opening of the EGR control valve 17. In step S104, the oxygen concentration AO in the intake air, the intake air amount (or supercharging pressure) IA, the intake air temperature TI, the fuel injection timing Tinj, and the coolant temperature Tw are acquired. As the fuel injection timing Tinj here, a value (target value of the fuel injection timing) calculated by the electronic control unit 40 (fuel injection control unit 42) can be used. Further, the oxygen concentration AO in the intake air can be detected by the oxygen concentration sensor 26, but it is also possible to estimate the oxygen concentration AO in the intake air sucked into the cylinder. In that case, the oxygen concentration in the exhaust gas is estimated from the air-fuel ratio (A / F), the EGR rate is estimated from the opening of the EGR control valve 17 (EGR control signal to the EGR control valve 17), and the EGR gas in the EGR gas It is possible to estimate the oxygen concentration AO in the intake air from the oxygen concentration (= the oxygen concentration in the exhaust), the oxygen concentration in the air, and the EGR rate. In step S105, the combustion noise level prediction unit 45 predicts the combustion noise level NL when the premixed compression ignition combustion is started. Here, based on the oxygen concentration AO in the intake air, the engine torque Te (fuel injection amount Fu), and the intake air amount (supercharging pressure) IA, the combustion noise level NL when shifting to premixed compression ignition combustion is predicted. can do. In addition to the oxygen concentration AO in the intake air, the engine torque Te (fuel injection amount Fu), and the intake air amount (supercharging pressure) IA, the engine speed Ne, the intake air temperature TI, the fuel injection timing Tinj, and the coolant Based on any one or more of the temperature Tw, the combustion noise level NL when shifting to the premixed compression ignition combustion can also be predicted.

  In step S106, the fuel injection control unit 42 determines whether or not the combustion noise level NL predicted in step S105 is an allowable level NL0 or less. When the predicted combustion noise level NL is equal to or lower than the allowable level NL0 (when the determination result in step S106 is YES), in step S107, the fuel injection timing Tinj is set to the injection timing (near compression top dead center) for performing diffusion combustion. ) Is advanced by the fuel injection control unit 42 to advance to the injection timing (intake stroke or compression stroke) at which premixed compression ignition combustion is performed. As a result, the transition from diffusion combustion to premixed compression ignition combustion is completed, and the execution of this process ends. On the other hand, when the predicted combustion noise level NL exceeds the allowable level NL0 (when the determination result of step S106 is NO), the fuel injection timing Tinj is maintained at the injection timing for performing diffusion combustion, and the process proceeds to step S108.

  In step S108, the misfire determination unit 47 determines the occurrence of misfire in diffusion combustion (whether there is a possibility of misfire). Here, the occurrence of misfire can be determined based on the oxygen concentration AO in the intake air, the engine torque Te (fuel injection amount Fu), and the intake air amount (supercharging pressure) IA. In addition to the oxygen concentration AO in the intake air, the engine torque Te (fuel injection amount Fu), and the intake air amount (supercharging pressure) IA, the engine speed Ne, the intake air temperature TI, the fuel injection timing Tinj, and the coolant The occurrence of misfire can also be determined based on any one or more of the temperature Tw. If it is determined that no misfire has occurred (no possibility of misfire), the execution of this process is temporarily terminated, and this process is executed again after a predetermined time. On the other hand, if it is determined that misfire occurs (possibility of misfire), the process proceeds to step S109.

  In step S109, the fuel injection control unit 42 determines whether pilot injection is performed prior to the main fuel injection. When pilot injection is not performed (when the determination result of step S109 is NO), in step S110, fuel injection timing (pilot injection timing Tinjp and main injection timing) is set so that pilot injection is performed prior to the main injection of fuel. Tinjm) is controlled by the fuel injection control unit 42. Then, the execution of this process is temporarily terminated, and this process is executed again after a predetermined time. On the other hand, when pilot injection has already been performed (when the determination result of step S109 is YES), the process proceeds to step S111.

  In step S111, the fuel injection control unit 42 determines whether or not the main injection timing Tinjm is retarded from the advance limit time Tinjm0. When the main injection timing Tinjm is retarded from the advance limit time Tinjm0 (when the determination result in step S111 is YES), in step S112, the control for advancing the main injection timing Tinjm is performed by the fuel injection control unit 42. Is done. Here, the main injection timing Tinjm is advanced to the advance angle limit timing Tinjm0. The advance angle limiting time Tinjm0 is set to a time that deviates from the misfire occurrence region based on, for example, the oxygen concentration AO in the intake air. Further, both the pilot injection timing Tinjp and the main injection timing Tinjm can be advanced, or only the main injection timing Tinjm can be advanced without the pilot injection timing Tinjp being advanced. When both the pilot injection timing Tinjp and the main injection timing Tinjm are advanced, the interval between the pilot injection timing Tinjp and the main injection timing Tinjm can be kept constant. For example, the advance amount of the main injection timing Tinjm It is also possible to change the interval between the pilot injection timing Tinjp and the main injection timing Tinjm by making it larger than the advance amount of the injection timing Tinjp. Then, the execution of this process is temporarily terminated, and this process is executed again after a predetermined time.

  On the other hand, when the main injection timing Tinjm has already advanced to the advance angle limit timing Tinjm0 (when the determination result in step S111 is NO), in step S113, control for increasing the pilot injection amount Fup is performed. 42. Then, the execution of this process is temporarily terminated, and this process is executed again after a predetermined time.

  As described above, when the combustion of the compression ignition type internal combustion engine 10 is shifted from the diffusion combustion to the premixed compression ignition combustion, the EGR rate is increased in order to suppress the generation of NOx, but the EGR gas is supplied to the intake side. Since the responsiveness at the time is low, the supply amount of the EGR gas to the intake air becomes transiently insufficient, and the oxygen concentration AO in the intake air becomes transiently excessive with respect to the target value AOT. If the fuel injection timing Tinj is advanced to the injection timing at which premixed compression ignition combustion is performed in a state where the oxygen concentration AO in the intake air is excessive (a state where the EGR gas is insufficient), the premixed gas is automatically detected at an early timing. It ignites and the combustion noise level NL increases. On the other hand, in the process of the flowchart of FIG. 5, when the EGR rate is increased in order to shift from diffusion combustion to premixed compression ignition combustion, the combustion noise level NL when shifting to premixed compression ignition combustion is predicted. Whether or not to advance the fuel injection timing Tinj to the injection timing for performing the premixed compression ignition combustion is determined based on the predicted combustion noise level NL. When the predicted combustion noise level NL is larger than the allowable level NL0, the fuel injection timing Tinj is maintained at the injection timing for performing the diffusion combustion (the advance to the injection timing for performing the premixed compression ignition combustion is prohibited). Thus, it is possible to avoid the transition to the premixed compression ignition combustion in the state where the combustion noise level NL exceeds the allowable level NL0. On the other hand, when the predicted combustion noise level NL is equal to or lower than the allowable level NL0, the combustion noise when the fuel injection timing Tinj is advanced to the injection timing for performing the premixed compression ignition combustion is shifted to the premixed compression ignition combustion. The level NL can be sufficiently reduced. Therefore, according to the present embodiment, the transition from diffusion combustion to premixed compression ignition combustion can be performed smoothly while reducing the combustion noise level NL.

  In addition, the combustion noise level NL is influenced not only by the oxygen concentration AO (EGR rate) in the intake air but also by the engine torque Te (fuel injection amount Fu) and the intake air amount (supercharging pressure) IA. Even if the concentration AO (EGR rate) is constant, it changes according to changes in the engine torque Te and the intake air amount IA. In contrast, in this embodiment, not only the oxygen concentration AO in the intake air but also the engine torque Te and the intake air amount (supercharging pressure) IA are used to predict the combustion noise level NL when shifting to premixed compression ignition combustion. Therefore, the prediction accuracy of the combustion noise level NL when shifting to premixed compression ignition combustion can be improved. Further, the combustion noise level NL is also affected by the engine speed Ne, the intake air temperature TI, the fuel injection timing Tinj, and the coolant temperature Tw. Therefore, not only the oxygen concentration AO in the intake air, the engine torque Te, the intake air amount (supercharging pressure) IA, but also any one of the engine speed Ne, the intake air temperature TI, the fuel injection timing Tinj, and the coolant temperature Tw. By predicting the combustion noise level NL using at least two, the prediction accuracy of the combustion noise level NL can be further increased.

  Further, when the predicted combustion noise level NL is larger than the allowable level NL0 and the fuel injection timing Tinj is maintained at the injection timing for performing diffusion combustion, the transiently insufficient EGR rate gradually increases. The oxygen concentration AO during intake gradually decreases. If the oxygen concentration AO in the intake air is insufficient, the self-ignition timing of the fuel is retarded, and misfire is likely to occur. On the other hand, in the process of the flowchart of FIG. 5, when the predicted combustion noise level NL is larger than the allowable level NL0, the occurrence of misfire is determined, and when it is determined that misfire occurs, the pilot injection is performed as the main injection. By performing before this, the combustion of the main injection can be activated by the pilot injection and the occurrence of misfire can be avoided. If it is determined that misfire occurs and pilot injection has already been performed, the occurrence of misfire can be more reliably avoided by advancing the main injection timing Tinjm.

  However, if the main injection timing Tinjm is excessively advanced, the fuel from the main injection adheres to the inner wall of the cylinder and causes a reduction in fuel consumption, and the combustion noise level NL increases. On the other hand, in the process of the flowchart of FIG. 5, when it is determined that misfire occurs, if the main injection timing Tinjm is already advanced to the advance limit time Tinjm0, the pilot injection amount Fup is increased. Further, while reducing the adhesion of fuel to the cylinder inner wall and the combustion noise level NL due to the main injection, the combustion of the main injection can be activated by the pilot injection and the occurrence of misfire can be avoided more reliably. Since pilot injection has a smaller injection amount than main injection, the influence of fuel adhering to the cylinder inner wall due to an increase in pilot injection amount Fup is small.

  In addition, the likelihood of misfire is affected not only by the oxygen concentration AO (EGR rate) in the intake air but also by the engine torque Te (fuel injection amount Fu) and the intake air amount (supercharging pressure) IA. Even if the oxygen concentration AO (EGR rate) is constant, it changes according to changes in the engine torque Te and the intake air amount IA. On the other hand, in this embodiment, since the occurrence of misfire is determined using not only the oxygen concentration AO in the intake air but also the engine torque Te and the intake air amount (supercharging pressure) IA, the misfire determination accuracy is improved. be able to. Further, the likelihood of misfire is also affected by the engine speed Ne, the intake air temperature TI, the fuel injection timing Tinj, and the coolant temperature Tw. Therefore, not only the oxygen concentration AO in the intake air, the engine torque Te, the intake air amount (supercharging pressure) IA, but also any one of the engine speed Ne, the intake air temperature TI, the fuel injection timing Tinj, and the coolant temperature Tw. The determination accuracy of misfire can be further increased by determining the occurrence of misfire by using more than one.

  In this embodiment, the determination of the occurrence of misfire and the fuel injection control for avoiding the occurrence of misfire can be performed not only at the time of transition from diffusion combustion to premixed compression ignition combustion. Hereinafter, the process executed by the electronic control unit 40 when performing fuel injection control for avoiding the occurrence of misfire will be described with reference to the flowchart of FIG. 6. The process according to the flowchart of FIG. 6 is repeatedly executed at predetermined time intervals.

  In step S201, the oxygen concentration AO in the intake air, the engine torque Te (engine load), the intake air amount (or supercharging pressure) IA, the engine speed Ne, the intake air temperature TI, the fuel injection timing Tinj, and the coolant temperature Tw. Is acquired. In step S202, the occurrence of misfire in combustion (whether there is a possibility of misfire) is determined by the misfire determination unit 47 as in step S108 of the flowchart of FIG. If it is determined that no misfire has occurred (no possibility of misfire), the execution of this process is temporarily terminated, and this process is executed again after a predetermined time. On the other hand, if it is determined that misfire occurs (there is a possibility of misfire), the process proceeds to step S203.

  In step S203, as in step S109 in the flowchart of FIG. 5, the fuel injection control unit 42 determines whether pilot injection is performed prior to the main fuel injection. When the pilot injection is not performed (when the determination result of step S203 is NO), in step S204, the fuel is injected so that the pilot injection is performed prior to the main fuel injection as in step S110 of the flowchart of FIG. The fuel injection control unit 42 controls the injection timing (the pilot injection timing Tinjp and the main injection timing Tinjm). Then, the execution of this process is temporarily terminated, and this process is executed again after a predetermined time. On the other hand, when pilot injection has already been performed (when the determination result of step S203 is YES), the process proceeds to step S205.

  In step S205, as in step S111 of the flowchart of FIG. 5, the fuel injection control unit 42 determines whether or not the main injection timing Tinjm is retarded from the advance limit time Tinjm0. When the main injection timing Tinjm is retarded from the advance limit time Tinjm0 (when the determination result in step S205 is YES), in step S206, the pilot injection timing Tinjp is similar to step S112 in the flowchart of FIG. The fuel injection control unit 42 performs control to advance at least the main injection timing Tinjm among the main injection timing Tinjm. Then, the execution of this process is temporarily terminated, and this process is executed again after a predetermined time.

  On the other hand, when the main injection timing Tinjm has already advanced to the advance angle limit timing Tinjm0 (when the determination result in step S205 is NO), in step S207, pilot injection is performed as in step S113 of the flowchart of FIG. The fuel injection control unit 42 performs control to increase the amount Fup. Then, the execution of this process is temporarily terminated, and this process is executed again after a predetermined time.

  According to the process of the flowchart of FIG. 6, when it is determined that misfire occurs and pilot injection is not performed, the pilot injection is performed before the main injection, so that the combustion of the main injection is activated by the pilot injection. The occurrence of misfire can be avoided. If it is determined that misfire occurs and pilot injection has already been performed, the occurrence of misfire can be more reliably avoided by advancing the main injection timing Tinjm. Further, when it is determined that misfire occurs, if the main injection timing Tinjm is already advanced to the advance limit time Tinjm0, the pilot injection amount Fup is increased to increase the amount of fuel from the main injection to the cylinder inner wall. While reducing the adhesion and combustion noise level NL, the combustion of the main injection can be activated by the pilot injection and the occurrence of misfire can be avoided more reliably.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to such embodiment at all, and it can implement with a various form in the range which does not deviate from the summary of this invention. Of course.

It is a figure which shows schematic structure of the control apparatus which concerns on embodiment of this invention with a compression ignition type internal combustion engine. It is a figure explaining an example of the conditions which switch between diffusion combustion and premixed compression ignition combustion. It is a figure which shows an example of the characteristic of the combustion noise level NL. It is a figure which shows an example of the characteristic of misfire. It is a flowchart explaining the process which an electronic controller performs. It is a flowchart explaining the other process which an electronic controller performs.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Compression ignition type internal combustion engine, 12 Piston, 13 Fuel injection valve, 14 Intake passage, 15 Exhaust passage, 16 Recirculation passage, 17 EGR control valve, 25 Intake air amount sensor, 26 Oxygen concentration sensor, 27 Rotation speed sensor, 28 Intake Temperature sensor, 29 Coolant temperature sensor, 40 Electronic control unit, 42 Fuel injection control unit, 43 EGR control unit, 44 Combustion determination unit, 45 Combustion noise prediction unit, 46 Combustion noise characteristic storage unit, 47 Misfire determination unit, 48 Misfire Characteristic storage unit.

Claims (10)

An apparatus for controlling a compression ignition type internal combustion engine that selectively performs either diffusion combustion or premixed compression ignition combustion, and performs exhaust gas recirculation for supplying a part of the exhaust gas after combustion to the intake side as EGR gas Because
A combustion determination unit that determines whether or not to shift from diffusion combustion to premixed compression ignition combustion;
An EGR control unit that controls exhaust gas recirculation so as to increase the amount of EGR gas supplied to the intake side when it is determined by the combustion determination unit to shift from diffusion combustion to premixed compression ignition combustion;
When the exhaust gas recirculation control is performed so as to increase the amount of EGR gas supplied to the intake side by the EGR control unit, premixing is performed based on the oxygen concentration in the intake air, the engine load, the intake air amount or the supercharging pressure. A combustion noise prediction unit for predicting combustion noise when shifting to compression ignition combustion;
A fuel injection control unit that determines whether to control the fuel injection timing to an injection timing for performing premixed compression ignition combustion based on the combustion noise predicted by the combustion noise prediction unit;
A control device for a compression ignition type internal combustion engine. A control device for a compression ignition internal combustion engine according to claim 1,
A control device for a compression ignition internal combustion engine that controls the fuel injection timing to an injection timing for performing premixed compression ignition combustion when the combustion noise predicted by the combustion noise prediction unit is below an allowable level . A control device for a compression ignition internal combustion engine according to claim 1 or 2,
A misfire determination unit for determining the occurrence of misfire in combustion when the combustion noise predicted by the combustion noise prediction unit exceeds an allowable level;
The fuel injection control unit
If the combustion noise predicted by the combustion noise prediction unit exceeds the allowable level, control the fuel injection timing to the injection timing for diffusion combustion,
Furthermore, when the misfire determination unit determines that misfire occurs, a control device for a compression ignition type internal combustion engine that performs pilot injection prior to main injection of fuel. A control device for a compression ignition internal combustion engine according to claim 3,
A control device for a compression ignition type internal combustion engine, wherein the fuel injection control unit advances the main injection timing when pilot injection is performed when it is determined by the misfire determination unit that misfire occurs. A control device for a compression ignition internal combustion engine according to claim 4,
The fuel injection control unit controls the compression ignition type internal combustion engine to increase the pilot injection amount when the main injection timing is advanced to the advance limit time when the misfire determination unit determines that misfire occurs. apparatus. A control device for a compression ignition type internal combustion engine according to any one of claims 3 to 5,
The misfire determination unit is a control device for a compression ignition internal combustion engine that determines the occurrence of misfire in combustion based on the oxygen concentration in intake air, the engine load, the intake air amount, or the supercharging pressure. A control device for a compression ignition type internal combustion engine according to any one of claims 1 to 6,
In addition to the oxygen concentration in the intake air, the engine load, the intake air amount, or the supercharging pressure, the combustion noise prediction unit sets any one or more of the engine speed, the intake air temperature, the fuel injection timing, and the engine coolant temperature. And a control device for a compression ignition type internal combustion engine that predicts combustion noise when shifting to premixed compression ignition combustion. A control device for a compression ignition type internal combustion engine according to any one of claims 1 to 7,
A combustion noise characteristic storage unit for storing combustion noise characteristics representing a relationship of combustion noise during premixed compression ignition combustion with respect to oxygen concentration in intake air, engine load, intake air amount or supercharging pressure;
The combustion noise prediction unit calculates the combustion noise during premixed compression ignition combustion corresponding to the oxygen concentration in the intake air, the engine load, the intake air amount or the supercharging pressure in the combustion noise characteristic stored in the combustion noise characteristic storage unit. A control device for a compression ignition type internal combustion engine that predicts combustion noise when shifting to premixed compression ignition combustion by calculation. A control device for a compression ignition type internal combustion engine according to any one of claims 1 to 8,
The combustion determination unit is a control device for a compression ignition type internal combustion engine that determines whether to shift from diffusion combustion to premixed compression ignition combustion based on the engine speed and the engine load. A device for controlling a compression ignition type internal combustion engine that self-ignites by injecting fuel into a cylinder,
A fuel injection control unit for performing fuel injection control;
A misfire determination unit that determines the occurrence of misfire in combustion; and
With
When the fuel injection control unit determines that misfire occurs in the misfire determination unit,
When pilot injection is not performed prior to main fuel injection, pilot injection is performed,
When pilot injection is in progress, advance the main injection timing,
A control device for a compression ignition internal combustion engine that increases a pilot injection amount when the main injection timing is advanced to an advance limit time.

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