JP2011149313A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine, capable of accurately estimating a reduction amount of EGR (Exhaust Gas Recirculation) gas in occurrence of knocking with a simple structure, in the internal combustion engine equipped with an EGR system. <P>SOLUTION: The control device for the internal combustion engine includes an EGR control means having an EGR passage 46 and an EGR valve 48 and controlling an opening of the EGR valve 48 so that an EGR gas flow rate is a target flow rate, a variable valve means for varying close timing (IVC) of an intake valve 32 to the prescribed target timing, a knock sensor 38 for detecting knocking occurring in the internal combustion engine 10, a knock suppressing means for suppressing knocking by varying IVC to a delay side compared to the target timing when knocking is detected, and an estimating means for estimating a reduction amount from the target flow rate of the EGR gas based on a delay amount from the target timing in the knock suppressing means. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine having an EGR (Exhaust Gas Recirculation) system.

  Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2009-108759, there is known a system that realizes improvement of exhaust properties and fuel consumption in an internal combustion engine including an EGR device. More specifically, in this system, the control target flow rate of the recirculation gas is set according to the operating state of the engine, and the EGR valve is controlled according to the opening command value generated based on the control target flow rate. . Further, when the occurrence of a decrease in the flow rate of the EGR valve is detected based on the operation state at the time of occurrence of knocking, the actual opening degree of the EGR valve for securing the control target flow rate is learned. Furthermore, the learned actual opening as the opening command value in the engine operation state when knocking occurs, and as the opening command value in the engine operation state when knocking does not occur, the same engine operation state and the control target flow rate, It is reflected in EGR control.

JP 2009-108759 A JP 2007-16609 A JP 2004-346876 A

  In the conventional system, it can be determined that the EGR flow rate has decreased when knocking occurs, but the amount of decrease cannot be acquired. In this regard, as a method of obtaining the EGR flow rate, it is conceivable to provide a pressure sensor, a temperature sensor, or the like and estimate it from a behavior change between when the EGR valve is operating and when it is not operating. However, the addition of new sensors and their control systems has a problem of causing a significant cost increase, fuel consumption deterioration due to weight increase, and deterioration of mountability. For this reason, the construction of a system for accurately estimating the EGR flow rate with a simple configuration has been desired.

  The present invention has been made to solve the above-described problems. In an internal combustion engine equipped with an EGR system, an internal combustion engine capable of accurately estimating the amount of decrease in EGR gas when knocking occurs with a simple configuration. An object of the present invention is to provide an engine control device.

In order to achieve the above object, a first invention is a control device for an internal combustion engine,
An EGR passage connecting an exhaust passage and an intake passage of the internal combustion engine, and an EGR valve for adjusting a flow rate of the EGR gas flowing through the EGR passage, and the EGR gas flow rate is set to a target flow rate. EGR control means for controlling the opening of the EGR valve;
Variable valve operating means for changing the closing timing of the intake valve of the internal combustion engine to a predetermined target timing;
Knock detecting means for detecting knocking occurring in the internal combustion engine;
When knocking is detected by the knock detection means, knock suppression means for suppressing knocking by changing the closing timing of the intake valve to the retard side with respect to the target timing;
Estimating means for estimating a reduction amount of the EGR gas from the target flow rate based on a retard amount from the target time in the knock suppression means;
It is characterized by providing.

According to a second invention, in the first invention,
The knock suppression means gradually changes the closing timing of the intake valve to the retard side until knocking is no longer detected by the knock detection means.

According to a third invention, in the first or second invention,
The apparatus further comprises prohibiting means for prohibiting execution of the estimating means when the target flow rate is smaller than a predetermined value.

A fourth invention is any one of the first to third inventions,
The apparatus further comprises a second prohibiting unit that prohibits execution of the knock suppression unit when the target time is on the retard side of the predetermined time.

According to a fifth invention, in any one of the first to fourth inventions,
Ignition timing retarding means for retarding the ignition timing of the internal combustion engine when knocking is detected by the knock detection means;
Third prohibiting means for prohibiting execution of the ignition timing retarding means during execution of the knock suppressing means;
Is further provided.

  When the target timing of the intake valve closing timing (IVC) is changed to the advance side, the actual compression ratio increases due to the early closing action of the intake valve. For this reason, if a situation occurs in which the EGR gas amount falls below the target flow rate when the IVC advances, knocking is likely to occur. According to the first invention, when knocking is detected, the IVC is varied to the retard side. The retard amount of IVC at this time has a correlation with the amount of decrease in the EGR gas flow rate. Therefore, according to the present invention, the amount of decrease in the EGR gas flow rate can be accurately estimated based on the retardation amount.

  According to the second invention, when knocking is detected, the IVC is gradually changed to the retard side until the knocking is not detected. For this reason, according to the present invention, the amount of retardation of IVC up to the time when knocking is suppressed can be obtained with high accuracy.

  According to the third invention, when the target flow rate of the EGR gas is smaller than the predetermined value, the estimation of the decrease amount of the EGR gas flow rate is prohibited. In a region where the target flow rate of the EGR gas is small, knocking due to a decrease in the EGR gas flow rate is unlikely to occur, so there is no clear correlation between the decrease amount and the retard amount of the IVC. For this reason, according to the present invention, it is possible to effectively suppress estimation with low accuracy.

  According to the fourth aspect of the invention, when the IVC target time is behind the predetermined time, execution of the knock suppression means is prohibited. For this reason, according to the present invention, it is possible to effectively avoid the situation where the retard control of the IVC is executed when the retard amount of the IVC that only suppresses knocking cannot be secured.

  According to the fifth aspect, when the IVC is varied to the retard side by the knock suppression means, the retard control of the ignition timing is prohibited. Therefore, according to the present invention, it is possible to accurately acquire the amount of retardation of IVC that can suppress knocking, and therefore it is possible to accurately estimate the amount of decrease in the EGR gas flow rate based on the amount of retardation. it can.

It is a schematic block diagram for demonstrating the system configuration | structure of embodiment of this invention. It is a flowchart which shows the routine of this Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

Embodiment.
[Configuration of the embodiment]
FIG. 1 is a diagram for explaining the configuration of a system according to an embodiment of the present invention. The system shown in FIG. 1 includes an internal combustion engine 10 mounted on a vehicle. The internal combustion engine 10 of the present embodiment is assumed to be an in-line four cylinder type. FIG. 1 shows a cross section of one of the cylinders. A piston 12 is provided in each cylinder of the internal combustion engine 10. An intake passage 14 and an exhaust passage 16 communicate with each cylinder.

  In the middle of the intake passage 14, an electronically controlled throttle valve 18 and a surge tank 20 are provided. The surge tank 20 is disposed on the downstream side of the throttle valve 18. An air flow meter 22 that detects the intake air amount is installed on the upstream side of the throttle valve 18. An exhaust purification catalyst 26 that purifies exhaust gas is disposed in the exhaust passage 16.

  Each cylinder of the internal combustion engine 10 is provided with a fuel injector 28 for injecting fuel into the intake port, an ignition plug 30 for igniting an air-fuel mixture in the combustion chamber, an intake valve 32, and an exhaust valve 34. Yes. A crank angle sensor 36 for detecting the rotation angle (crank angle) of the crankshaft 24 is provided in the vicinity of the crankshaft 24 of the internal combustion engine 10. An accelerator position sensor 44 for detecting the accelerator pedal position is provided in the vicinity of the accelerator pedal.

  In addition, the internal combustion engine 10 includes an EGR passage 46 for performing so-called external EGR in which exhaust gas in the exhaust passage 16 is recirculated to the intake passage 14. One end of the EGR passage 46 is connected to the exhaust passage 16, and the other end of the EGR passage 46 is connected to the intake passage 14 on the downstream side of the surge tank 20. An EGR valve 48 for controlling the exhaust gas recirculation amount by opening and closing the EGR passage 46 is provided in the middle of the EGR passage 46.

  The intake valve 32 and the exhaust valve 34 are provided with an intake valve timing control device 52 and an exhaust valve timing control device 54 that variably control their valve timing. In the present embodiment, the intake valve timing control device 52 and the exhaust valve timing control device 54 change the phase angle of the cam shaft (not shown) with respect to the crankshaft 24 so that the opening / closing timing is advanced while the operating angle remains constant. Alternatively, a retarded variable valve timing mechanism (VVT) is used. Hereinafter, the intake valve timing control device 52 and the exhaust valve timing control device 54 are referred to as “IN-VVT 52” and “EX-VVT 54”, respectively.

  The internal combustion engine system of the present embodiment includes an ECU (Electronic Control Unit) 50. In addition to the sensors described above, various sensors such as a water temperature sensor 40 for detecting the engine water temperature and a knock sensor 38 for detecting the occurrence of knocking are connected to the input side of the ECU 50. Various actuators such as the above-described actuator are connected to the output side of the ECU 50. The ECU 50 can control the operating state of the internal combustion engine 10 based on those sensor outputs.

[Operation of the embodiment]
In the internal combustion engine provided with the EGR system, external EGR can be performed in which a part of the exhaust gas (burned gas) flowing through the exhaust passage 16 is returned to the intake passage 14 via the EGR passage 46. Thereby, since a cold loss can be reduced, a fuel consumption rate (fuel consumption) can be improved effectively. Further, when the EGR gas is recirculated, combustion in the cylinder becomes slow. For this reason, the occurrence of knocking can be effectively suppressed by performing the external EGR in an operation region where knocking occurs.

  More specifically, in the system of the present embodiment, the EGR flow rate (hereinafter referred to as “required EGR flow rate”) required in the current operating state based on the operating state such as the engine speed and engine load factor of the internal combustion engine 10. And a target opening degree of the EGR valve 48 for realizing this is calculated. Then, when the opening degree of the EGR valve 48 is adjusted to the target opening degree, the EGR gas having the required EGR flow rate is recirculated to the intake passage 14.

  Here, it is preferable that the EGR flow rate is always controlled to the required EGR flow rate. However, when the EGR passage 46 is clogged, the recirculated EGR flow rate is assumed to be lower than the required EGR flow rate. In this case, knocking may occur depending on the operating state of the internal combustion engine 10. In particular, in the operation region where the advance angle control for advancing the IN-VVT 52 by a predetermined amount toward the intake BDC is performed for the purpose of improving the volumetric efficiency, the actual compression ratio is increased by the control. Knocking is more likely to occur.

  Therefore, in the system according to the present embodiment, KCS (Knock Control System) control that suppresses knocking by controlling the ignition timing of the internal combustion engine 10 is executed. More specifically, when the knock sensor 38 detects the occurrence of knocking, the ignition timing is retarded by a predetermined amount. Thereby, occurrence of knocking can be effectively suppressed.

(EGR flow reduction estimation operation)
Next, the estimation operation of the amount of decrease in EGR flow rate, which is a characteristic operation of the present embodiment, will be described. As described above, when the EGR flow rate is lower than the required EGR flow rate, unexpected knocking may occur. For this reason, it is preferable that the decrease in the EGR flow rate is detected early and reliably.

  Here, when the above-described advance control of the IN-VVT 52 is executed, the knocking can be suppressed by returning the IN-VVT 52 to the retard side instead of the knock suppression control by the KCS control. . That is, in the state where the IN-VVT 52 is advanced, the actual compression ratio is high due to the action of the intake valve 38 being quickly closed. For this reason, when the control for returning the IN-VVT 52 to the retarded angle side is executed, the actual compression ratio of the internal combustion engine 10 can be reduced to suppress knocking.

  In the retard control for the IN-VVT 52, the greater the amount of decrease in the EGR flow rate, the greater the retard amount required for suppressing knocking. That is, a certain correlation exists between the amount of decrease in the EGR flow rate and the amount of retardation of the IN-VVT 52. Therefore, in the present embodiment, when the IN-VVT 52 is returned to the retard side to suppress knocking, the amount of decrease in the EGR flow rate is estimated based on the retard amount. Thereby, it is possible to accurately estimate the amount of decrease in the EGR flow rate with a simple configuration without adding a new sensor or the like.

[Specific processing of the embodiment]
Next, specific processing executed in the present embodiment will be described with reference to FIG. FIG. 2 is a flowchart of a routine executed in the present embodiment.

  In the routine shown in FIG. 2, first, a required EGR flow rate is calculated (step 100). Here, specifically, the required requirements in the current operating state based on the engine speed and the engine load calculated based on the sensor signals of the crank angle sensor 36, the air flow meter 22, the accelerator position sensor 44, and the like. An EGR flow rate is calculated.

  Next, it is determined whether or not the required EGR flow rate is equal to or greater than a predetermined value (step 102). As the predetermined value, a preset value is used as a value for determining that a sufficient amount of EGR gas is recirculated. As a result, if establishment of the required EGR flow rate ≧ predetermined value is not required, it is determined that knocking due to a decrease in the EGR flow rate does not occur, the process proceeds to the next step, and normal KCS control is executed (step S1). 104). Here, specifically, the ignition retard prohibition flag exkcsih is set to OFF, and the knocking suppression control based on the retard of the ignition timing is executed.

  On the other hand, if it is determined in step 102 that the required EGR flow rate ≧ predetermined value is established, the process proceeds to the next step, and whether or not knocking has occurred is determined based on the detection signal of the knock sensor 38 (step 106). As a result, when the occurrence of knocking is detected, the process proceeds to the next step, and it is determined whether or not the operation region is the IN-VVT 52 (step 108). Specifically, it is determined whether or not the target advance amount evttb of the IN-VVT 52 is equal to or greater than a predetermined value EVTTGR. As the predetermined value RVTTGR, a preset value is read as a value for determining the operation region of the IN-VVT 52. As a result, when the establishment of evttb ≧ EVTTGR is not recognized, it is determined that the IVC early closing control is not executed, and the process proceeds to the above-described step 104, and the process of suppressing knocking by the normal KCS control is executed. Is done.

  On the other hand, if the establishment of evttb ≧ EVTTGR is recognized in step 108, it is determined that the IVC early closing control is being executed, and the process proceeds to the next step to determine whether the IN-VVT 52 can be retarded. It is determined whether or not (step 110). Specifically, it is determined whether or not the current target advance value evtt of the IN-VVT 52 is greater than zero. The target advance value evtt is a value obtained by subtracting a later-described retard amount evtkcs from the above-described target advance amount evttb, and is a value corresponding to the current advance amount. As a result, if the establishment of the target advance value evtt> 0 is not recognized, it is determined that the IN-VVT 52 cannot be further controlled to the retard side, and the routine proceeds to the above step 104, where the normal KCS is set. A process for suppressing knocking is executed by the control.

  On the other hand, when the establishment of the target advance value evtt> 0 is recognized in step 110, it is determined that the IN-VVT 52 can be controlled to the retard side, the process proceeds to the next step, and the KCS control is performed. Ignition retard is prohibited. (Step 112). Specifically, the ignition retard prohibition flag exkcsih is set to ON. Next, control for retarding the IN-VVT 52 by a predetermined amount is executed (step 114). Specifically, a value obtained by adding a predetermined retardation amount EVTRTDB to the previous value evtkcs (previous value) of the retardation amount is calculated as the current retardation amount evtkcs. Then, the IN-VVT 52 is controlled to be the target advance value evtt (= evttb-evtkcs).

  When the process of step 114 is repeatedly executed, the actual compression ratio gradually decreases due to the IVC early closing action. When the occurrence of knocking is no longer detected in step 106, the process proceeds to the next step, and it is determined whether or not the region is where knocking occurs in the base load (step 116). Specifically, it is determined whether or not the vehicle belongs to an operation region where knocking occurs when the external EGR is not executed and the IN-VVT 52 is operated at the target advance value evtt. As a result, when it is determined that it is not a region where knocking occurs in the base load, it is determined that knocking due to a decrease in the EGR flow rate does not occur, and this routine is immediately terminated.

  On the other hand, if it is determined in step 116 that the region is where knocking occurs at the base load, it is determined that knocking due to a decrease in the EGR flow rate has occurred, and the process proceeds to the next step to suppress knocking. It is determined whether or not the retard control of the IN-VVT 52 is being executed (step 118). Here, specifically, it is determined whether or not the retard angle control of the IN-VVT 52 in step 114 is being executed. As a result, when the retard control of the IN-VVT 52 is not executed, this routine is immediately terminated.

  On the other hand, if the retard control of the IN-VVT 52 is being executed in step 118, it is determined that knocking has been suppressed by the retard of the IN-VVT 52, and the process proceeds to the next step to estimate the amount of EGR decrease. (Step 120). Specifically, the engine speed, the engine load, and the EGR reduction amount corresponding to the retard amount evtkcs of the IN-VVT 52 executed in step 114 are specified from the map.

  As described above, according to the system of the present embodiment, when knocking is suppressed by the retard control of the IN-VVT 52, the EGR reduction amount is estimated based on the retard amount. As a result, the amount of decrease in the EGR flow rate can be accurately estimated without adding a new sensor or the like.

  By the way, in this embodiment, the IN-VVT 52 is used to advance or retard the opening / closing timing of the intake valve 32 with a constant operating angle. However, the internal combustion engine further includes an operating angle variable mechanism for the intake valve 32. In the engine, the operating angle may be varied so that only the closing timing (IVC) of the intake valve 32 is advanced or retarded.

  In the above-described embodiment, the ECU 50 executes the process of step 106, and the “knock detection means” in the first invention executes the process of step 114, whereby the first step is performed. The “knock suppression means” according to the first aspect of the invention executes the processing of step 120, thereby realizing the “estimation means” according to the first aspect of the invention.

  Further, in the embodiment described above, the “prohibiting means” in the third aspect of the present invention is realized by the ECU 50 executing the processing of step 102 described above.

  Further, in the above-described embodiment, the “second prohibiting means” in the fourth aspect of the present invention is realized by the ECU 50 executing the process of step 108.

  In the embodiment described above, the “third prohibiting means” according to the fifth aspect of the present invention is realized by the ECU 50 executing the process of step 112.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Piston 14 Intake passage 16 Exhaust passage 18 Throttle valve 20 Surge tank 22 Air flow meter 24 Crankshaft 26 Exhaust purification catalyst 28 Fuel injector 30 Spark plug 32 Intake valve 34 Exhaust valve 36 Crank angle sensor 38 Knock sensor 40 Water temperature sensor 44 Accelerator position sensor 46 EGR passage 48 EGR valve 50 ECU (Electronic Control Unit)
52 Intake valve timing controller (IN-VVT)
54 Exhaust valve timing control device (EX-VVT)

Claims (5)

An EGR passage connecting an exhaust passage and an intake passage of the internal combustion engine, and an EGR valve for adjusting a flow rate of the EGR gas flowing through the EGR passage, and the EGR gas flow rate is set to a target flow rate. EGR control means for controlling the opening of the EGR valve;
Variable valve operating means for changing the closing timing of the intake valve of the internal combustion engine to a predetermined target timing;
Knock detecting means for detecting knocking occurring in the internal combustion engine;
When knocking is detected by the knock detection means, knock suppression means for suppressing knocking by changing the closing timing of the intake valve to the retard side with respect to the target timing;
Estimating means for estimating a reduction amount of the EGR gas from the target flow rate based on a retard amount from the target time in the knock suppression means;
A control device for an internal combustion engine, comprising:   2. The control device for an internal combustion engine according to claim 1, wherein the knock suppression means gradually changes the closing timing of the intake valve to the retard side until knocking is no longer detected by the knock detection means.   3. The control device for an internal combustion engine according to claim 1, further comprising prohibiting means for prohibiting execution of the estimating means when the target flow rate is smaller than a predetermined value.   4. The apparatus according to claim 1, further comprising: a second prohibiting unit that prohibits execution of the knock suppression unit when the target timing is on the retard side with respect to a predetermined timing. 5. Control device for internal combustion engine. Ignition timing retarding means for retarding the ignition timing of the internal combustion engine when knocking is detected by the knock detection means;
Third prohibiting means for prohibiting execution of the ignition timing retarding means during execution of the knock suppressing means;
The control device for an internal combustion engine according to any one of claims 1 to 4, further comprising:

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