JP2016094909A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine that can highly accurately detect generation of condensation water in EGR gas and can appropriately obtain an EGR gas flow rate by performing exhaust gas recirculation control on the basis of the detection result.SOLUTION: When an operating region of an engine is an EGR operating region, whether or not rotation fluctuation of a turbocharger occurs is detected, and when the rotation fluctuation continues for predetermined time (YES determination in Steps ST4, ST8), generation of condensation water in EGR gas is determined and an EGR gas flow rate is reduced (Step ST9). Thus, subsequent generation of condensation water is suppressed, so as to avoid failure such as generation of erosion of an impeller of a compressor caused by the condensation water. The generation of the condensation water can be detected highly accurately, and when the condensation water is generated, the EGR gas flow rate is reduced, so that the EGR gas flow rate can be obtained appropriately.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a control device for an internal combustion engine. In particular, the present invention relates to improvements in exhaust gas recirculation control.

  Conventionally, in an internal combustion engine (hereinafter sometimes referred to as an engine), exhaust gas recirculation in which a part of exhaust gas is recirculated to an intake passage by an exhaust gas recirculation passage in order to reduce NOx emissions and improve a fuel consumption rate. A device (EGR device) is known.

  When the exhaust gas is recirculated, condensed water may be generated due to cooling of the exhaust gas or the like. In an engine equipped with a supercharger, in the case of an LPL (Low Pressure Loop) -EGR device that recirculates exhaust gas to the upstream side of the compressor provided in the intake passage, this condensed water is caused by erosion of the impeller of the compressor, etc. Cause trouble.

  Patent Document 1 discloses a technique for preventing the generation of condensed water. Specifically, the dew point of the mixture of exhaust gas and intake air is obtained based on the atmospheric temperature, humidity, etc., and the exhaust gas recirculation is restricted when the temperature in the intake passage is below the dew point, etc. Condensate generation is prevented.

JP 2003-201903 A

  However, since the technique of Patent Document 1 estimates the possibility of condensed water generation based on the calculated dew point, condensed water is generated when the dew point calculation accuracy is not sufficiently obtained. In spite of this situation, exhaust gas recirculation may be limited. For this reason, the amount of exhaust gas recirculation is reduced more than necessary, and the effect of exhaust gas recirculation may not be sufficiently obtained.

  The present invention has been made in view of such a point, and an object of the present invention is to detect the generation of condensed water with high accuracy and perform exhaust gas recirculation control based on the detection, thereby appropriately adjusting the amount of exhaust gas recirculated. It is another object of the present invention to provide a control device for an internal combustion engine that can be obtained.

  In order to achieve the above object, the solution means of the present invention recirculates a part of the exhaust gas flowing through the exhaust passage into the cylinder through the exhaust recirculation passage and the supercharger provided in the intake passage. A control device for an internal combustion engine provided with an exhaust gas recirculation device is assumed. When the exhaust gas is being recirculated with respect to the control device for the internal combustion engine, when the state in which the rotational fluctuation of the supercharger has continued for a predetermined time, or the rotational fluctuation of the supercharger When the occurrence frequency exceeds a predetermined threshold, the amount of exhaust gas to be recirculated is reduced.

  When condensed water is generated in the recirculated exhaust gas, when the droplet collides with the impeller of the supercharger, rotation fluctuation of the supercharger occurs due to the impact. In addition, in a situation where condensed water is generated in the exhaust gas being recirculated, a relatively large number of droplets are generated, and these droplets continuously collide with the impeller of the turbocharger. The state in which the rotational fluctuation occurs continues for a predetermined time, or the frequency of occurrence of the rotational fluctuation of the supercharger increases. By utilizing this fact, in this solution, when the state in which the rotation fluctuation of the turbocharger has continued for a predetermined time, or when the occurrence frequency of the rotation fluctuation of the turbocharger exceeds a predetermined threshold value, Reduces the amount of exhaust gas to be recycled, assuming that condensed water is generated in the exhaust gas being recirculated. Thereby, generation | occurrence | production of subsequent condensed water can be suppressed and malfunctions, such as generation | occurrence | production of the erosion of the impeller of a supercharger resulting from this condensed water, can be avoided. In addition, it is possible to detect the occurrence of condensed water in the exhaust gas with high accuracy. When this condensed water is generated, the amount of exhaust gas to be recirculated is reduced, so that the amount of exhaust gas is reduced. A recirculation amount can be obtained appropriately.

  In the present invention, when the state in which the rotation fluctuation of the turbocharger continues for a predetermined time, or when the occurrence frequency of the rotation fluctuation of the turbocharger exceeds a predetermined threshold, the exhaust gas to be recirculated I try to reduce the amount. Therefore, problems such as the occurrence of erosion of the impeller of the supercharger due to the condensed water can be avoided, and the recirculation amount of the exhaust gas can be appropriately obtained.

It is a figure showing a schematic structure of an engine concerning an embodiment. It is a block diagram which shows the structure of control systems, such as ECU. It is a flowchart figure which shows the procedure of EGR reduction control.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. This embodiment demonstrates the case where this invention is applied to the in-line 4 cylinder diesel engine mounted in the motor vehicle. The present invention can also be applied to a gasoline engine.

-Engine configuration-
FIG. 1 is a diagram showing a schematic configuration of an engine (internal combustion engine) 1 according to the present embodiment. 1 has four cylinders 11, 11,..., And each cylinder 11 is provided with an injector 2 (see FIG. 2).

  Each cylinder 11 is connected to an intake passage 3 constituting an intake system. An air cleaner 31 is provided at the upstream end of the intake passage 3. The intake passage 3 is provided with a compressor 41, an intercooler 32, and an intake throttle valve (diesel throttle) 33 of a turbocharger (supercharger) 4 in that order along the flow direction of the intake air. The compressor 41 includes an impeller 41a for compressing intake air. The intake air compressed by the compressor 41 in the intake system is guided into the cylinder 11 (see the arrow indicated by the solid line in FIG. 1), and then compressed in the compression stroke. The fuel is combusted by injecting fuel from the injector 2 into the cylinder 11. Engine output is obtained with the combustion of the fuel.

  Each cylinder 11 is connected to an exhaust passage 5 constituting an exhaust system. A turbine 42 of the turbocharger 4 is provided in the middle of the exhaust passage 5. The turbine 42 includes a wheel 42a that rotates in response to the exhaust flow. The wheel 42a is connected to the impeller 41a via the connecting shaft 4a. A catalyst 51 is provided downstream of the turbine 42. Moreover, a particulate filter (DPF) is provided as needed. Exhaust gas generated by combustion in each cylinder 11 is discharged to the exhaust passage 5, passes through the turbine 42, is purified by the catalyst 51, and is released into the atmosphere.

  The engine 1 according to the present embodiment is provided with an exhaust gas recirculation device 6. The exhaust gas recirculation device 6 includes an EGR passage that guides a part of exhaust gas (EGR gas) from the exhaust passage 5 downstream of the catalyst 51 (downstream of the turbine 42) to the intake passage 3 upstream of the compressor 41. (Exhaust gas recirculation passage) 61, an EGR valve 62 capable of changing the flow area of the EGR passage 61, and an EGR cooler 63 that cools the EGR gas. By this exhaust gas recirculation device 6, a part of the exhaust gas flowing through the exhaust passage 5 is recirculated into the cylinder 11 through the EGR passage 61 and the intake passage 3. The amount of exhaust gas (EGR gas) recirculated by the exhaust gas recirculation device 6 is adjusted by the opening degree of the EGR valve 62. This recirculation of EGR gas can reduce NOx emissions and improve the fuel consumption rate. In FIG. 1, the flow of exhaust gas (including EGR gas) is indicated by broken-line arrows.

-Control system-
As shown in FIG. 2, the injector 2, the intake throttle valve 33, and the EGR valve 62 are electrically connected to an ECU (Electronic Control Unit) 10.

  The ECU 10 includes an A / F sensor 80, an air flow meter 81, an intake air temperature sensor 82, an intake air pressure sensor 83, an exhaust air temperature sensor 84, a water temperature sensor 85, a crank position sensor 86, an accelerator opening sensor 87, and an intake throttle valve opening sensor 88. The EGR valve opening sensor 89 and the turbo rotation fluctuation sensor 8A are electrically connected to various sensors.

  The turbo rotation fluctuation sensor 8A is provided in the turbocharger 4 as shown in FIG. The turbo rotation fluctuation sensor 8A is for detecting the rotation fluctuation of the turbocharger 4, and is constituted by, for example, an acceleration sensor attached to the outer surface of the housing of the compressor 41. That is, the vibration amplitude of the housing of the compressor 41 is detected by the turbo rotation fluctuation sensor 8A, and the presence / absence of occurrence of the rotation fluctuation of the turbocharger 4 can be detected based on the detected value. Further, the mounting position of the turbo rotation fluctuation sensor 8A is not limited to the outer surface of the housing of the compressor 41. For example, you may attach to the outer surface of the housing of the turbine 42, or the outer surface of the center housing which supports the connection shaft 4a rotatably.

  Further, the turbo rotation fluctuation sensor 8A may detect the rotation speed of the compressor 41, the rotation speed of the turbine 42, or the rotation speed of the connecting shaft 4a. That is, the rotational speed may be detected by the turbo rotation fluctuation sensor 8A, and the presence / absence of the rotation fluctuation of the turbocharger 4 may be detected based on the detected value.

  Since the configuration and function of each sensor are well known, description thereof is omitted here.

  The ECU 10 controls the injector 2, the intake throttle valve 33, and the EGR valve 62 based on the detected values and measured values of the various sensors 80 to 89, 8A.

  Further, as will be described later, the ECU 10 executes EGR reduction control for controlling the EGR valve 62 based on the detection value of the turbo rotation fluctuation sensor 8A.

-Basic control of exhaust gas recirculation system-
Here, basic control of the exhaust gas recirculation device 6 will be described.

  When the EGR gas is recirculated using the exhaust gas recirculation device 6, a target EGR gas flow rate (hereinafter referred to as “target EGR gas flow rate”) and an estimated EGR gas flow rate (estimated value of the actual EGR gas flow rate). (Hereinafter referred to as “estimated EGR gas flow rate”), and the opening degree of the EGR valve 62 is feedback-controlled so that the estimated EGR gas flow rate approaches the target EGR gas flow rate. The target EGR gas flow rate in this case is set according to the operating state of the engine 1 (engine load or the like). The estimated EGR gas flow rate is stored in advance in the ROM of the ECU 10 using the opening of the EGR valve 62 detected by the EGR valve opening sensor 89, the temperature of the exhaust gas detected by the exhaust temperature sensor 84, and the like as parameters. It is obtained from a predetermined arithmetic expression or map.

-EGR weight loss control-
Next, the EGR reduction control that is the characteristic feature of this embodiment will be described. In this EGR reduction control, the opening degree of the EGR valve 62 is controlled based on the detection value of the turbo rotation fluctuation sensor 8A to reduce the EGR gas flow rate. Specifically, the detected value of the turbo rotation fluctuation sensor 8A in a state where the opening degree of the EGR valve 62 is controlled according to the basic control of the exhaust gas recirculation device 6 described above, that is, in a state where the EGR gas is recirculated. On the basis of this, the presence or absence of occurrence of rotational fluctuation of the turbocharger 4 is detected, and the EGR gas flow rate (the amount of exhaust gas to be recirculated) is reduced when this rotational fluctuation state continues for a predetermined time. I have to.

  When the EGR gas is cooled by the EGR cooler 63, cooled by mixing with fresh air, or compressed by the compressor 41, condensed water may be generated in the EGR gas. When the condensed water droplets collide with the impeller 41a of the compressor 41, the impact of the impact causes the rotational fluctuation of the turbocharger 4 to occur. Further, in the situation where condensed water is generated in the EGR gas, a relatively large number of droplets are generated, and these droplets continuously collide with the impeller 41a of the compressor 41. The state where the error occurs continues. By utilizing this fact, in the present embodiment, when the state in which the rotational fluctuation of the turbocharger 4 has occurred continues for a predetermined time, it is determined that condensed water is generated in the EGR gas, and this EGR Reduce gas flow. Thereby, generation | occurrence | production of subsequent condensate water is suppressed, and malfunctions, such as generation | occurrence | production of the erosion of the impeller 41a of the compressor 41 resulting from this condensate water, can be avoided now.

  Hereinafter, a specific procedure of the EGR reduction control will be described with reference to the flowchart of FIG. This flowchart is executed at predetermined intervals in the ECU 10 after the engine 1 is started.

  First, in step ST1, it is determined whether or not the operating state of the engine 1 is in the EGR operating region. This determination is well known and is performed based on the coolant temperature of the engine 1, the engine speed, the engine load, and the like. For example, the cooling water temperature detected by the water temperature sensor 85, the engine rotational speed calculated based on the signal from the crank position sensor 86, and the engine load determined based on the signal from the accelerator opening sensor 87 are previously set. When the set threshold value is exceeded, it is determined that it is in the EGR operating region.

  When the operating state of the engine 1 is not in the EGR operating region but NO is determined in step ST1, the process proceeds to step ST2, and EGR (exhaust gas recirculation) is stopped. That is, the exhaust gas recirculation is not performed with the EGR valve 62 fully closed. In step ST3, each flag described later is set to “0” and the process returns.

  On the other hand, when the operating state of the engine 1 is in the EGR operating region and a YES determination is made in step ST1, the process proceeds to step ST4, where it is determined whether or not the rotational fluctuation of the turbocharger 4 has occurred. This determination is made based on the detection value of the turbo rotation fluctuation sensor 8A. Specifically, when the amplitude of vibration of the housing of the compressor 41 detected by the turbo rotation fluctuation sensor 8A exceeds a predetermined value, it is determined that the rotation fluctuation of the turbocharger 4 has occurred. The predetermined value in this case is preset by experiment or simulation.

  If the rotational fluctuation of the turbocharger 4 has occurred, and if YES is determined in step ST4, the process proceeds to step ST5, and it is determined whether or not the fluctuation detection flag is “1”. This fluctuation detection flag is a flag that is set to “1” (ie, set to “1” in step ST6 described later) when the rotation fluctuation of the turbocharger 4 is detected.

  Since the fluctuation detection flag is “0” at the start of this control, NO is determined in step ST5, and the process proceeds to step ST6.

  In step ST6, the fluctuation detection flag is set to “1”.

  Then, it moves to step ST7 and starts the 1st timer with which ECU10 was equipped beforehand. The first timer is timed up when a predetermined time (for example, 1 sec) elapses. This value is not limited to this and is set as appropriate.

  In step ST8, it is determined whether or not the first timer has expired. If the first timer has not yet timed out and a NO determination is made in step ST8, the process returns to step ST4 to determine whether or not the rotation fluctuation of the turbocharger 4 has occurred, that is, the rotation fluctuation of the turbocharger 4. It is determined whether or not the state in which the occurrence has occurred continues.

  When the rotational fluctuation of the turbocharger 4 continues, and if YES is determined in step ST4, the process proceeds to step ST5 to determine whether or not the fluctuation detection flag is “1”. . Since the fluctuation detection flag is already “1” in step ST6, a YES determination is made here, and the process proceeds to step ST8 to determine whether or not the first timer has timed out.

  If the rotational fluctuation of the turbocharger 4 is resolved before the first timer expires, a NO determination is made in step ST4 and the process proceeds to step ST10. As described above, as an example of a situation in which the rotational fluctuation of the turbocharger 4 is eliminated before the first timer expires (a situation in which the rotational fluctuation of the turbocharger 4 is eliminated without reducing the EGR gas flow rate) It is assumed that the foreign matter has flowed into the system and the foreign matter collided with the impeller 41a of the compressor 41 to temporarily cause the rotational fluctuation of the turbocharger 4 and then the rotational fluctuation of the turbocharger 4 is eliminated. .

  On the other hand, if the first timer has timed out without eliminating the rotational fluctuation of the turbocharger 4, a YES determination is made in step ST8, and the process proceeds to step ST9. In step ST9, the EGR reduction operation is executed and the fluctuation detection flag is set to “0”. Further, the reduction operation execution flag is set to “1”. The reduction operation execution flag is a flag that is set to “1” when the EGR reduction operation is executed.

  As the EGR reduction operation, the current opening degree of the EGR valve 62 is reduced by a predetermined amount to reduce the EGR gas flow rate. For example, the opening degree is decreased by 10% with respect to the current opening degree of the EGR valve 62. This value is not limited to this and can be set as appropriate. By reducing the EGR gas flow rate in this way, the amount of moisture in the gas flowing through the EGR passage 61 and the intake passage 3 is reduced, so that the generation of condensed water can be suppressed.

  After performing the EGR reduction operation in this way, the process returns to step ST1 again, and when the operating state of the engine 1 is in the EGR operating region, the operations of steps ST4 to ST9 described above are repeated. That is, when the rotation fluctuation of the turbocharger 4 continues and the first timer expires, an EGR reduction operation for further reducing the EGR gas flow rate is executed in step ST9. As described above, when the EGR reduction operation is executed a plurality of times, the EGR gas flow rate is significantly reduced, and the generation of condensed water is eliminated.

  On the other hand, when the rotation fluctuation of the turbocharger 4 is eliminated by executing the EGR reduction operation, the rotation fluctuation of the turbocharger 4 is eliminated before the first timer expires, or the turbocharger 4 from the beginning of the control. If the rotational fluctuation is not generated, NO is determined in step ST4, and the process proceeds to step ST10.

  In step ST10, it is determined whether or not the weight reduction operation execution flag is “1”. In the state in which the operation in step ST9 is executed (the state in which the EGR reduction operation is executed), when the rotational fluctuation of the turbocharger 4 is resolved and the process proceeds to step ST10, the reduction operation execution flag is “1”. Therefore, YES is determined in step ST10, and the process proceeds to step ST11. On the other hand, when the process proceeds to step ST10 without executing the operation of step ST9 described above (without executing the EGR reduction operation), the reduction operation execution flag is “0”, so step ST10 Is NO and the process proceeds to step ST14.

  In step ST11, a second timer provided in advance in the ECU 10 is started. The second timer is timed up when a predetermined time (for example, 100 msec) elapses. This value is not limited to this and is set as appropriate.

  After the start of the second timer, in step ST12, it is determined whether or not the rotational fluctuation of the turbocharger 4 has occurred. If YES in step ST12 due to the occurrence of rotational fluctuation of the turbocharger 4, the process proceeds to step ST6, where the first timer is started as described above, and the rotational fluctuation of the turbocharger 4 is occurring. If the first timer expires, an EGR reduction operation for decreasing the EGR gas flow rate is executed in step ST9. On the other hand, if the rotation fluctuation of the turbocharger 4 is resolved before the first timer expires, NO is determined in step ST4, and the process proceeds to step ST10 without executing the EGR reduction operation.

  On the other hand, if the rotation fluctuation of the turbocharger 4 has not occurred after the start of the second timer, a NO determination is made in step ST12 and the process proceeds to step ST13 to determine whether or not the second timer has timed out. If the second timer has not yet timed up and a NO determination is made in step ST13, the process returns to step ST12, and it is determined whether or not a rotational fluctuation of the turbocharger 4 has occurred.

  When the state in which the rotation fluctuation of the turbocharger 4 has not occurred continues and the second timer has timed up, a YES determination is made in step ST13, and the process proceeds to step ST14. In step ST14, each flag is set to “0”. Thereafter, the process proceeds to step ST15, and normal EGR control is performed by the basic control of the exhaust gas recirculation device 6 described above.

  Further, when NO is determined in step ST10 and the process proceeds to step ST14, each flag is set to “0”, and then normal EGR control based on the basic control of the exhaust gas recirculation device 6 described above is executed.

  Since such EGR reduction control is performed, the ECU 10 constitutes a control device for an internal combustion engine according to the present invention. This control device is configured to receive signals from the turbo rotation fluctuation sensor 8A, the water temperature sensor 85, the crank position sensor 86, and the accelerator opening sensor 87 as input signals. In addition, this control device is configured to output an opening command signal to the EGR valve 62 as an output signal.

  As described above, according to the present embodiment, when the state in which the rotation fluctuation of the turbocharger 4 has occurred continues for a predetermined time, it is assumed that condensed water is generated in the EGR gas. The flow rate is reduced. Thereby, generation | occurrence | production of subsequent condensed water can be suppressed and malfunctions, such as generation | occurrence | production of the erosion of the impeller 41a of the compressor 41 resulting from this condensed water, can be avoided. The condensed water generated in the EGR gas causes corrosion of the pipes constituting the EGR path, corrosion in the cylinder 11, and causes of water hammer phenomenon in the cylinder 11 in addition to erosion of the impeller 41 a. However, according to the present embodiment, the occurrence of condensed water can be suppressed, so that these problems can also be avoided.

  Further, in the present embodiment, it is possible to directly detect whether or not condensed water is generated in the EGR gas based on the presence or absence of rotational fluctuation of the turbocharger 4, so that the condensed water is generated with high accuracy. It can be detected. When condensed water is generated, the EGR gas flow rate is reduced. For this reason, the EGR gas flow rate can be appropriately obtained as compared with the conventional technique (which estimates the possibility of the occurrence of condensed water based on the calculated dew point).

(Modification)
Next, a modified example will be described. In the above-described embodiment, the EGR reduction operation is performed when the rotation fluctuation of the turbocharger 4 continues for a predetermined period (a period until the first timer expires).

  In this modification, instead, the EGR reduction operation (the operation of step ST9 in FIG. 3) is executed when the frequency of occurrence of rotational fluctuations of the turbocharger 4 exceeds a predetermined threshold. That is, in a situation where the rotational fluctuation of the turbocharger 4 is intermittently generated, the EGR reduction operation is executed when the frequency of occurrence exceeds a predetermined threshold value.

  Specifically, the number of occurrences of rotation fluctuations of the turbocharger 4 during a predetermined period (the number of times the amplitude of vibration of the housing of the compressor 41 detected by the turbo rotation fluctuation sensor 8A exceeds a predetermined value) is set in advance. When the threshold value is exceeded, the EGR reduction operation is executed. For example, when the number of occurrences of rotational fluctuations of the turbocharger 4 during 3 seconds exceeds 10, EGR reduction operation is executed assuming that condensed water is generated in the EGR gas. These values are not limited to this, and can be appropriately set by experiment or simulation.

  Other configurations and operations are the same as those of the above-described embodiment.

-Other embodiments-
In the embodiment described above, the case where the present invention is applied to the in-line four-cylinder diesel engine 1 mounted on an automobile has been described. The present invention is applicable not only to automobiles but also to engines used for other purposes. Further, the number of cylinders and the engine type (separate type engine, V-type engine, horizontally opposed engine, etc.) are not particularly limited.

  Further, when the rotational fluctuation of the turbocharger 4 is still not resolved despite the EGR gas flow rate being “0” by the EGR reduction control described above, the cause of the rotational fluctuation of the turbocharger 4 is other than condensed water. It is assumed that For example, the impeller 41a of the turbocharger 4 is damaged or the exhaust system parts are damaged. In this case, it is preferable that the MIL (warning lamp) on the meter panel in the passenger compartment is lit to urge the driver to warn and the abnormality information is written in the diagnosis provided in the ECU 10. It is also preferable to limit the engine output.

  The present invention is applicable to exhaust gas recirculation control in an LPL-EGR device mounted on a diesel engine.

1 engine (internal combustion engine)
11 Cylinder 3 Intake passage 4 Turbocharger (supercharger)
5 Exhaust passage 6 Exhaust gas recirculation device 61 EGR passage (exhaust gas recirculation passage)
62 EGR valve 8A Turbo rotation fluctuation sensor 10 ECU

Claims (1)

In a control device for an internal combustion engine provided with an exhaust gas recirculation device that recirculates a part of exhaust gas flowing through an exhaust passage into a cylinder through a supercharger provided in an intake passage through an exhaust gas recirculation passage,
In a state where the exhaust gas is recirculated, a state in which the rotation fluctuation of the turbocharger continues for a predetermined time, or the occurrence frequency of the rotation fluctuation of the turbocharger exceeds a predetermined threshold In this case, the control device for the internal combustion engine is configured to reduce the amount of the exhaust gas to be recirculated.

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