JP2017218910A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine capable of implementing requests of EGR at the maximum extent while preventing a backflow of EGR gas.SOLUTION: A control device switches between normal EGR control for controlling an opening of an EGR valve to an opening corresponding to an operating state of an internal combustion engine and fully closing control for maintaining the opening of the EGR valve in a fully closed state. The control device calculates estimated differential pressure that is an estimated value of differential pressure between gas pressure on the downstream side of the EGR valve and gas pressure on the upstream side, and EGR gas amount that is gas amount flowing in an EGR passage. The control device determines whether or not the opening of the EGR valve is fully closed, and when it is determined that the EGR valve is opened, it decides whether or not the normal EGR control is switched to the fully closing control on the basis of the calculated EGR gas amount. When it is determined that the opening of the EGR valve is fully closed, the control device decides whether or not the fully closing control is switched to the normal EGR control on the basis of the calculated estimated differential pressure.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a control device for an internal combustion engine.

  Conventionally, for example, Japanese Patent Application Laid-Open No. 2008-101498 discloses a technique related to exhaust gas recirculation (EGR) for circulating exhaust gas to the intake side. In this technique, in order to prevent the backflow of EGR gas, the difference between the detection value of the intake pressure sensor and the detection value of the exhaust pressure sensor is calculated to determine the flow direction of the EGR gas, and this flow direction is the backflow direction. In this case, the EGR valve is closed.

JP 2008-101498 A JP 2004-100508 A Japanese Patent Laying-Open No. 2015-010591

  In the configuration in which the gas pressure on the upstream side and the gas pressure on the downstream side of the EGR valve in the EGR passage are directly detected by the pressure sensors, the differential pressure between these gas pressures can be accurately calculated. However, in the configuration in which any gas pressure is estimated without using a pressure sensor, an error occurs in the calculated estimated differential pressure. For this reason, in the configuration in which the backflow of the EGR gas is determined based on the calculated estimated differential pressure, the EGR valve is not closed and the backflow of the EGR gas is caused even though the EGR gas is actually in a backflow condition. It is assumed that the EGR request cannot be satisfied without the EGR valve being opened even though the EGR gas does not flow back in practice.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a control device for an internal combustion engine that can realize EGR requirements to the maximum while preventing backflow of EGR gas. .

  The present invention is directed to an internal combustion engine control device having an EGR passage connecting an intake passage and an exhaust passage, and an EGR valve arranged in the EGR passage. Based on the opening degree of the EGR valve, the control device calculates an estimated differential pressure calculating means that calculates an estimated differential pressure that is an estimated value of a differential pressure between the gas pressure downstream of the EGR valve and the upstream gas pressure in the EGR passage. And an EGR gas amount calculating means for calculating an EGR gas amount that is an amount of gas flowing through the EGR passage without being based on the opening degree of the EGR valve, and the opening degree of the EGR valve according to the operating state of the internal combustion engine. And EGR valve control means for switching between normal EGR control and full-closed control for maintaining the opening of the EGR valve fully closed. The EGR valve control means includes determination means for determining whether or not the opening degree of the EGR valve is fully closed. When the determination means determines that the EGR valve is open, the EGR gas amount calculation means Whether or not to switch from normal EGR control to full-closed control is determined based on the EGR gas amount calculated by, and when the determination means determines that the opening of the EGR valve is fully closed, an estimated difference Whether or not to switch from the fully closed control to the normal EGR control is determined based on the estimated differential pressure calculated by the pressure calculating means.

When the EGR valve is fully closed, it is not possible to determine whether or not to switch from normal EGR control to fully closed control based on the amount of EGR gas flowing through the EGR passage. On the other hand, when the EGR valve is open, the accuracy of the estimated differential pressure between the gas pressure downstream of the EGR valve and the gas pressure upstream of the EGR passage is low. According to the present invention, when the EGR valve is open,
Whether or not to switch from normal EGR control to fully closed control is determined based on the calculated EGR gas amount. As a result, it is determined whether or not to switch to the fully closed control after eliminating the influence of the error in the estimated differential pressure, so that the backflow of EGR gas can be reliably prevented. Further, according to the present invention, when the opening degree of the EGR valve is fully closed, it is determined whether to switch from the fully closed control to the normal EGR control based on the calculated estimated differential pressure. As a result, it is possible to prevent the fully closed control from being maintained even though it is not a condition for the backflow of the EGR gas, so that it is possible to satisfy the EGR request to the maximum and reduce the NOx emission amount. Become.

It is a figure which shows the structure of the engine system to which the control apparatus of Embodiment 1 of this invention is applied. It is a figure for demonstrating the problem of the full-closed control using an estimated differential pressure. It is a figure for demonstrating how to determine a suitable value. It is a figure for demonstrating how to determine a suitable value. It is a flowchart which shows the routine performed by ECU of Embodiment 1 of this invention. It is a figure which shows an example of the driving | running pattern containing the conditions which EGR reverse flow generate | occur | produces. It is a time chart for demonstrating the effect of the control performed in the system of Embodiment 1 of this invention. It is various modifications of the control block diagram which extracted the functional block for calculating the opening degree of an EGR valve in normal EGR control.

  Embodiments of the present invention will be described below with reference to the drawings. However, in the embodiment shown below, when referring to the number of each element, quantity, quantity, range, etc., unless otherwise specified or clearly specified in principle, the reference However, the present invention is not limited to these numbers. In addition, structures, steps, and the like described in the following embodiments are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a diagram showing a configuration of an engine system to which a control device according to Embodiment 1 of the present invention is applied. The internal combustion engine according to the present embodiment is a diesel engine with a turbocharger (hereinafter simply referred to as “engine”). The engine body 2 is provided with four cylinders in series. An intake manifold 4 and an exhaust manifold 6 are attached to the engine body 2. An intake passage 10 through which fresh air taken from an air cleaner (not shown) flows is connected to the intake manifold 4. A turbocharger compressor 14 is attached to the intake passage 10. A diesel throttle valve 24 is provided downstream of the compressor 14 in the intake passage 10. An intercooler 22 is provided between the compressor 14 and the diesel throttle valve 24 in the intake passage 10. The exhaust manifold 6 is connected to an exhaust passage 12 for releasing the exhaust gas emitted from the engine body 2 into the atmosphere. A turbocharger turbine 16 is attached to the exhaust passage 12. A catalyst device 26 for purifying exhaust gas is provided downstream of the turbine 16 in the exhaust passage 12.

  The engine according to the present embodiment includes an EGR device that recirculates exhaust gas from the exhaust system to the intake system. In the EGR device, a position downstream of the diesel throttle valve 24 in the intake passage 10 and the exhaust manifold 6 are connected by an EGR passage 30. An EGR valve 32 is disposed in the EGR passage 30. An EGR cooler 34 is provided on the exhaust side of the EGR valve 32 in the EGR passage 30. The EGR passage 30 is provided with a bypass passage 36 that bypasses the EGR cooler 34.

  The engine system according to the present embodiment includes an ECU (Electronic Control Unit) 50. The ECU 50 is a control device that comprehensively controls the entire engine system, and the control device according to the present invention is embodied as one function of the ECU 50.

  The ECU 50 captures and processes a sensor signal provided in the engine system. Sensors are installed in various parts of the engine system. An air flow meter 52 for detecting the actual amount of fresh air is attached to the intake passage 10 downstream of the air cleaner. An intake pressure sensor 54 for detecting the intake pressure is attached to the intake passage 10 downstream of the diesel throttle valve 24. Further, a temperature sensor 56 for detecting the intake manifold gas temperature is attached to the intake manifold 4. The EGR valve 32 is provided with an opening sensor 58 for detecting the actual opening of the EGR valve. Further, a rotation speed sensor 60 that detects the rotation speed of the crankshaft, an accelerator opening sensor 62 that outputs a signal corresponding to the opening of the accelerator pedal, and the like are also attached. The ECU 50 processes the signals of the acquired sensors and operates the actuators according to a predetermined control program. The actuator operated by the ECU 50 includes an EGR valve 32, a diesel throttle valve 24, and the like. There are many actuators and sensors connected to the ECU 50 other than those shown in the figure, but the description thereof is omitted in this specification.

[Operation of Embodiment 1]
The engine control executed by the ECU 50 usually includes EGR control. In the normal EGR control of the present embodiment, an EGR corresponding to the input engine rotation speed and injection amount is used by using a characteristic map that defines the characteristics of the opening degree of the EGR valve with respect to the operating state such as the engine rotation speed and the injection amount. The valve opening is calculated.

  Here, in the normal EGR control, for example, in the low rotation and high load region, the gas pressure downstream of the diesel throttle valve 24 in the intake passage 10 becomes larger than the gas pressure in the exhaust manifold 6, whereby the gas in the EGR passage 30 is taken into the intake air. There is a case where a phenomenon of backflow in the direction from the passage 10 toward the exhaust manifold 6 (hereinafter referred to as EGR backflow) occurs. As a means for preventing the EGR reverse flow, it is conceivable to perform a fully closed control for keeping the EGR valve 32 fully closed. More specifically, for example, the gas pressure obtained by subtracting the downstream gas pressure from the gas pressure upstream of the EGR valve 32 in the EGR passage 30 is estimated, and the estimated gas pressure (hereinafter, estimated differential pressure) becomes a negative value. When this happens, switching from the normal EGR control to the fully closed control can be considered.

  However, the above-described fully closed control has the following problems. FIG. 2 is a diagram for explaining a problem of the fully closed control using the estimated differential pressure. As shown in this figure, the estimated differential pressure varies with respect to the actual value of the differential pressure. This variation is due to an error occurring in the opening degree of the EGR valve 32 and the like, and some variation beyond the estimated value cannot be avoided. For this reason, for example, when the actual value of the differential pressure is a negative value and the estimated differential pressure varies to the positive value side, it is a condition that the EGR valve 32 should be closed by the fully closed control. Regardless, the EGR valve 32 may be opened by mistake. In particular, in the state where the EGR valve 32 is open, the variation in the estimated differential pressure further increases, so that the possibility that the EGR valve 32 cannot be closed further increases.

  As another means for preventing the EGR reverse flow, for example, a gas amount [g / s] per unit time (hereinafter referred to as an EGR gas amount) in which the gas in the EGR passage 30 flows in the direction from the exhaust manifold 6 to the intake passage 10 is used. It is conceivable that the fully closed control is executed when the detected EGR gas amount is 0 or less. However, since the EGR gas amount is 0 during the fully closed control, it is not possible to determine the return from the fully closed control to the normal EGR control based on the EGR gas amount.

  Therefore, in the system according to the first embodiment of the present invention, whether or not the execution of the fully closed control is necessary is determined by a different method depending on whether the opening degree of the EGR valve 32 is fully closed or opened. More specifically, when the EGR valve 32 is opened, it is determined whether or not the fully closed control is to be executed based on whether or not the EGR gas amount is 0 or less. As described above, when the EGR valve 32 is opened, the variation range of the estimated differential pressure is large. According to the above control, when the EGR valve 32 is opened, whether or not the execution of the fully closed control is necessary is determined without using the estimated value of the differential pressure before and after the EGR valve. Can do.

  Further, when the opening degree of the EGR valve 32 is fully closed, it is determined whether or not the execution of the fully closed control is necessary depending on whether or not the estimated differential pressure is larger than the appropriate value. Note that the adaptive value is a threshold value of the estimated differential pressure for determining whether or not a condition for causing EGR backflow is satisfied, and is determined by the following method, for example. FIG. 3 and FIG. 4 are diagrams for explaining how to determine the fitness value. As shown in these figures, the conforming value is preferably the upper limit variation width of the estimated differential pressure with respect to the actual differential pressure. The variation range of the estimated differential pressure varies depending on the intake pressure, the engine speed, the injection amount, the fresh air amount, the opening of the variable nozzle, the opening of the exhaust control valve (ECV), and the like. For this reason, by using any of these as an input and using a characteristic map that specifies a suitable value, it is possible to calculate a suitable value that has the same value as the upper limit variation width of the estimated differential pressure with respect to the actual differential pressure.

  According to such a conforming value, for example, when the actual differential pressure ≦ 0 (when the condition for the occurrence of EGR backflow is satisfied), even if the estimated differential pressure varies to the upper limit, the estimated differential pressure is the conforming value. It becomes a smaller value. Therefore, by determining whether or not the estimated differential pressure is greater than the appropriate value, it is possible to reliably determine the case where the condition for generating the EGR backflow is satisfied. Further, when the actual differential pressure> 0 (when the condition for generating EGR reverse flow is not satisfied), if the estimated differential pressure is larger than the conforming value, at least the condition for generating EGR reverse flow is satisfied. It can be determined that it has not been established. For this reason, when the estimated differential pressure is a value larger than the conforming value, the EGR request can be satisfied by opening the EGR valve 32, whereby the NOx emission amount can be reduced.

[Specific Processing in First Embodiment]
Next, specific processing executed in the system of the first embodiment described above will be described in detail using a flowchart. FIG. 5 is a flowchart showing a routine executed by ECU 50 of the first embodiment of the present invention.

  In the routine shown in FIG. 5, first, as the various detected values and estimated values, the actual fresh air amount, the intake pressure, the opening degree of the EGR valve 32, the intake manifold gas temperature, the exhaust manifold gas pressure, the EGR gas amount, and the estimated differential pressure are used. Etc. are acquired (step S2). Specifically, the actual fresh air amount is detected from a signal from the air flow meter 52. The intake pressure is detected from a signal from the intake pressure sensor 54. The opening degree of the EGR valve 32 is detected from the signal of the opening degree sensor 58. The intake manifold gas temperature is detected from a signal from the temperature sensor 56. The gas pressure in the exhaust manifold is estimated using the opening degree of the EGR valve 32 and the like. The EGR gas amount is calculated by subtracting the actual fresh air amount from the actual in-cylinder inflow air amount. At this time, the actual in-cylinder inflow air amount can be calculated by a function using the detected intake pressure and intake manifold gas temperature. The estimated differential pressure is calculated by subtracting the intake pressure from the gas pressure (estimated value) of the exhaust manifold.

  Next, it is determined whether or not the opening degree of the EGR valve 32 acquired in step S2 is fully closed (step S4). As a result, when it is determined that the EGR valve 32 is opened, it is determined that the EGR backflow cannot be determined using the estimated differential pressure, and the process proceeds to the next step, which is acquired in step S2 above. It is determined whether or not the EGR gas amount is 0 or less (step S6). As a result, when the establishment of EGR gas amount ≦ 0 is not recognized, it is determined that the condition for generating the EGR backflow is not established, and the routine proceeds to the next step, where the normal EGR control is executed ( Step S8). On the other hand, when the establishment of EGR gas amount ≦ 0 is recognized in step S6, it is determined that the condition for the occurrence of EGR reverse flow is established, the process proceeds to the next step, and the opening degree of the EGR valve 32 is determined. Is fully closed (step S10).

  If it is determined in step S4 that the opening degree of the EGR valve 32 is fully closed, it can be determined that no gas flow is generated in the EGR passage 30. In this case, in order to determine whether or not the condition for generating the EGR backflow is satisfied, it is determined whether or not the estimated differential pressure is larger than the adaptive value (step S12). As a result, if the establishment of the estimated differential pressure> the adaptive value is not recognized, it is determined that the condition for generating the EGR backflow is still established, and the fully closed control is maintained (step S14). On the other hand, when it is recognized that the estimated differential pressure> the adaptive value is satisfied, it is determined that the condition for generating the EGR backflow is not satisfied, and the normal EGR control is executed (step S16).

  By switching between normal EGR control and full-closed control according to the routine described above, EGR backflow is prevented and NOx emission is reduced by normal EGR control when the conditions for generating EGR backflow are not satisfied It becomes possible to do.

  Next, the effect by the control of the system according to the first embodiment of the present invention will be described in comparison with a comparative example. FIG. 6 is a diagram illustrating an example of an operation pattern including a condition in which EGR backflow occurs. In FIG. 6, a condition for generating an EGR backflow is satisfied in the operation region where the differential pressure ≦ 0 [kPa]. FIG. 7 is a time chart for explaining the effect of the control executed in the system of the first embodiment. In addition, the time chart shown in FIG. 7 has shown the time chart at the time of implement | achieving the driving | running pattern shown in FIG. Further, the time chart shown in FIG. 7 illustrates a case where the estimated differential pressure varies on the large side with respect to the actual differential pressure.

  Comparative example 1 shown in the time chart of FIG. 7 shows an example of control for determining whether or not the EGR valve full-closed control needs to be executed based on whether the estimated differential pressure is 0 or more. In Comparative Example 1, at the time t1 when the operation pattern shifts to the region where the differential pressure ≦ 0, the estimated differential pressure is still a value of 0 or more, so the opening degree of the EGR valve is not controlled to be fully closed. For this reason, in Comparative Example 1, an EGR backflow occurs after time t1.

  Further, Comparative Example 2 shown in the time chart of FIG. 7 shows an example of control for determining whether or not the EGR valve full-closed control needs to be executed based on whether or not the EGR gas amount is 0 or less. In the comparative example 2, the opening degree of the EGR valve is controlled to be fully closed in response to the EGR gas amount becoming 0 or less at the time t1 when the operation pattern shifts to the region where the actual differential pressure ≦ 0. For this reason, in Comparative Example 2, EGR backflow can be prevented after time t1. However, in Comparative Example 2, since the EGR gas amount is maintained at 0 after time t1, the opening degree of the EGR valve is maintained fully closed after time t2 when the operation pattern shifts to a region where the actual differential pressure> 0. End up. For this reason, in Comparative Example 2, the amount of NOx emission after time t2 cannot be reduced.

  In contrast, in the system according to the first embodiment of the present invention, the full-closed control is performed in response to the EGR gas amount becoming 0 or less at the time t1 when the operation pattern shifts to the region where the actual differential pressure ≦ 0. Is executed to control the opening of the EGR valve to be fully closed. Thereby, EGR backflow can be prevented after time t1. Further, in the system according to the first embodiment of the present invention, at time t3 when the estimated differential pressure becomes larger than the appropriate value, the normal EGR control is restored and the EGR valve is opened. Thereby, since the request | requirement of EGR can be implement | achieved to the maximum, it becomes possible to reduce the NOx discharge | emission amount after time t3 effectively.

  By the way, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the following modifications may be made.

  The normal EGR control that can be executed in the system of the first embodiment described above is not limited to the control that calculates the opening degree of the EGR valve using the characteristic map. FIG. 8 shows various modified examples of the control block diagram in which functional blocks for calculating the opening degree of the EGR valve in the normal EGR control are extracted. In the system of the first embodiment described above, the opening degree of the EGR valve is calculated using the characteristic map as shown in (A) in the figure, but the target EGR rate is shown in (B) in the figure. Alternatively, the opening degree of the EGR valve may be calculated by feeding back the estimated EGR rate. Further, as shown in (C) of the figure, the opening degree of the EGR valve may be calculated by combining the characteristic map shown in (A) and the feedback shown in (B).

  In the first embodiment, the estimated differential pressure is calculated based on the detected value of the intake pressure and the estimated value of the exhaust manifold gas pressure. However, the method of calculating the estimated differential pressure is limited to this. Absent. That is, when calculating the estimated differential pressure, at least one of the upstream gas pressure and the downstream gas pressure of the EGR valve 32 is not directly detected by the pressure sensor, and at least the EGR valve is opened. What is necessary is just to set it as the structure estimated using a degree. Further, the gas pressure upstream of the EGR valve 32 is not limited to the exhaust manifold gas pressure, and the gas pressure upstream of the EGR valve 32 in the EGR passage 30 may be directly detected by a pressure sensor or estimated by a known method. . Similarly, the gas pressure on the downstream side of the EGR valve 32 is not limited to the intake pressure, and the gas pressure on the downstream side of the EGR valve 32 in the EGR passage 30 may be directly detected by a pressure sensor or estimated by a known method. Further, the EGR gas amount is not limited as long as it is calculated without using the opening degree of the EGR valve. For example, the EGR gas amount may be directly detected from a sensor signal such as a flow rate sensor.

  In the first embodiment described above, the ECU 50 executes the process of step S2, thereby realizing the “estimated differential pressure calculating means” and the “EGR gas amount calculating means” in the first invention. By executing the processing of step S4, the “determination means” in the first invention is realized, and when the ECU 50 executes the processing of steps S4 to S16, the “EGR valve control means” in the first invention is realized. It has been realized.

2 Engine body 4 Intake manifold 6 Exhaust manifold 10 Intake passage 12 Exhaust passage 14 Compressor 16 Turbine 22 Intercooler 24 Diesel throttle valve 26 Catalytic device 30 EGR passage 32 EGR valve 34 EGR cooler 36 Bypass passage 50 ECU (Electronic Control Unit)
52 Air Flow Meter 54 Intake Pressure Sensor 56 Temperature Sensor 58 Opening Sensor 60 Rotation Speed Sensor 62 Accelerator Opening Sensor

Claims (1)

An internal combustion engine control device comprising an EGR passage connecting an intake passage and an exhaust passage, and an EGR valve disposed in the EGR passage,
An estimated differential pressure calculating means for calculating an estimated differential pressure that is an estimated value of a differential pressure between the gas pressure on the downstream side of the EGR valve and the gas pressure on the upstream side in the EGR passage based on the opening degree of the EGR valve; ,
EGR gas amount calculation means for calculating an EGR gas amount that is an amount of gas flowing through the EGR passage without being based on the opening degree of the EGR valve;
EGR valve control means for switching between normal EGR control in which the opening degree of the EGR valve is set in accordance with the operating state of the internal combustion engine and full-closed control in which the opening degree of the EGR valve is maintained in a fully closed state With
The EGR valve control means includes determination means for determining whether or not the opening degree of the EGR valve is fully closed, and when the determination means determines that the EGR valve is open, the EGR gas amount Whether to switch from the normal EGR control to the fully closed control is determined based on the amount of EGR gas calculated by the calculating means, and the opening of the EGR valve is determined to be fully closed by the determining means. When it is done, it is configured to determine whether or not to switch from the fully closed control to the normal EGR control based on the estimated differential pressure calculated by the estimated differential pressure calculating means. A control device for an internal combustion engine.

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