JP2015209814A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently scavenge gas in a cylinder while suppressing an uncomfortable feeling that a driver and the like feels when stopping an internal combustion engine.SOLUTION: An ECU50 carries out scavenging control for scavenging gas in a combustion chamber 12 after detecting a command for stopping an engine 10. The ECU50 also estimates, while the engine is in operation, a valve tip temperature that is the temperature of a tip of a fuel injection valve 14, a head wall surface temperature that is the temperature of a lower surface of a cylinder head, a residual EGR quantity remaining in the combustion chamber 12 after the engine is stopped, and an air-intake system deposit amount adhered to an intake manifold 18. And then, the ECU50 variably sets, when the engine is stopped, the execution time of scavenging control based on a valve adhesion acid amount estimated based on the valve tip temperature, the head wall temperature, and the residual EGR quantity, and based on the air-intake system deposit amount.

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 a function of scavenging a cylinder after the engine is stopped.

  As a prior art, for example, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2007-066402), a control device for an internal combustion engine having a function of scavenging the cylinder after the engine is stopped is known. In the prior art, scavenging control is executed after a command to stop the internal combustion engine is issued. In the scavenging control, the fuel injection amount is increased to increase the engine speed, and then the fuel cut is executed and the throttle opening is increased. Thereby, the unburned fuel and exhaust gas remaining in the cylinder after the engine is stopped can be discharged.

Japanese Patent Laid-Open No. 2007-064032

  By the way, in the above-described prior art, after a command to stop the internal combustion engine is issued, scavenging control is executed to increase the engine speed. For this reason, in the prior art, it takes a long time until the internal combustion engine actually stops after a stop command such as turning off the ignition switch is issued, and there is a possibility of giving the driver a sense of incongruity. On the other hand, in order to suppress this uncomfortable feeling, if the execution time of the scavenging control is simply shortened, for example, sufficient acid generated by mixing exhaust gas and condensed water remaining at the tip of the fuel injection valve after the engine is stopped is sufficient. However, this acid causes a problem that the injection hole of the fuel injection valve is easily corroded.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to sufficiently scavenge a cylinder while suppressing a sense of incongruity of a driver or the like when stopping an internal combustion engine. An object of the present invention is to provide a control device for an internal combustion engine that can be performed.

A first invention is a fuel injection valve that injects fuel into a combustion chamber of an internal combustion engine;
An EGR mechanism that is provided between an intake passage and an exhaust passage of the internal combustion engine and recirculates EGR gas that is part of exhaust gas from the exhaust passage to the intake passage;
A valve tip temperature estimating means for estimating a valve tip temperature, which is a temperature of a tip portion of the fuel injection valve, based on an engine speed of the internal combustion engine, a fuel injection amount, and an intake air temperature;
A head wall surface temperature estimating means for estimating a head wall surface temperature that is a temperature of a lower surface portion facing the combustion chamber of the cylinder head based on a cooling water temperature of the internal combustion engine and the intake air temperature;
Residual EGR amount estimating means for estimating a residual EGR amount, which is an amount of the EGR gas remaining in the combustion chamber when the internal combustion engine is stopped, based on a recirculation amount of the EGR gas by the EGR mechanism and a temperature of the EGR gas. When,
Estimating the amount of acid adhering to the valve, which estimates the amount of acid adhering to the tip of the fuel injection valve when the internal combustion engine is stopped, based on the valve tip temperature, the head wall surface temperature, and the residual EGR amount Means,
The intake system deposit amount, which is the amount of deposit that adheres to the portion from the recirculation position of the EGR gas to the combustion chamber in the intake passage, is determined based on the engine speed, the fuel injection amount, and the recirculation amount of the EGR gas. Deposit amount estimating means for estimating
A means for executing scavenging control for scavenging the gas in the combustion chamber after detecting a stop command for the internal combustion engine, wherein the scavenging control execution time is determined based on the valve-attached acid amount and the intake system deposit amount; Scavenging control variable means for changing.

  According to the first aspect of the present invention, it is possible to appropriately change the execution time of the scavenging control based on the amount of acid adhering to the valve and the amount of intake system deposit that affects the ease of corrosion of the fuel injection valve. Thereby, discomfort by scavenging control can be suppressed while suppressing corrosion of the fuel injection valve. Further, it is possible to accurately estimate the acid adhesion amount (generated amount) after the internal combustion engine is stopped based on the operation state immediately before the internal combustion engine is stopped and the in-cylinder combustion state, and based on the estimation result, scavenging is performed. The execution time of control can be set accurately.

It is a block diagram for demonstrating the system configuration | structure of Embodiment 1 of this invention. 4 is a flowchart illustrating an example of scavenging time control executed by an ECU in the first embodiment of the present invention. It is a characteristic diagram which shows the relationship between valve tip temperature and head wall surface temperature, and the generation state of condensed water. In Embodiment 1 of this invention, it is explanatory drawing which shows an example of the data map which sets scavenging time. In Embodiment 2 of this invention, it is a flowchart which shows a part of scavenging time control. In Embodiment 3 of this invention, it is explanatory drawing which shows an example of the control performed for every area | region defined according to the valve adhesion acid amount and the intake system deposit amount.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
The first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a configuration diagram for explaining a system configuration according to the first embodiment of the present invention. The system of the present embodiment includes an engine 10 as an internal combustion engine configured by, for example, a diesel engine. Although FIG. 1 illustrates a four-cylinder engine, the present invention is applied to an internal combustion engine having an arbitrary number of cylinders. Each cylinder of the engine 10 includes a fuel injection valve 14 that injects fuel into the combustion chamber 12 (inside the cylinder). The engine 10 also includes an intake passage 16 that sucks air into the combustion chamber 12, an intake manifold 18 that is a part of the intake passage 16 and connected to the combustion chamber 12 of each cylinder, and an intake air that flows through the intake passage 16. An electronically controlled throttle valve 20 that adjusts the amount of air, an intercooler 22 that cools intake air flowing through the intake passage 16, an exhaust passage 24 that exhausts exhaust gas from each cylinder, and an exhaust gas that flows through the exhaust passage 24 And a catalyst 26 for purifying the gas.

  The engine 10 also includes an EGR mechanism 28 that recirculates EGR gas, which is part of the exhaust gas, from the exhaust passage 24 to the intake passage 16. The EGR mechanism 28 adjusts the EGR passage 30 that connects the intake passage 16 and the exhaust passage 24 and the recirculation amount (EGR amount) of EGR gas that is recirculated from the exhaust passage 24 to the intake passage 16 via the EGR passage 30. An EGR valve 32 for cooling, an EGR cooler 34 for cooling the EGR gas flowing through the EGR passage 30, and an EGR cooler bypass valve 36 for bypassing the EGR cooler 34 and circulating the EGR gas. The EGR gas is configured to return to the upstream side of the intake manifold 18 on the downstream side of the throttle valve 20.

Further, the engine 10 includes a supercharger 38 that is provided between the intake passage 16 and the exhaust passage 24 and supercharges intake air using the exhaust pressure. The supercharger 38 may be a variable capacity supercharger that can change the opening area of the turbine according to the opening of the turbo nozzle. In the present embodiment, the throttle valve 20, the EGR valve 32, and the turbo nozzle of the supercharger 38 are driven by, for example, an electric motor, so that the engine 10 is actually stopped after the engine stop command is detected. It is configured to be controllable during the period until.

  The system of the present embodiment includes a sensor system that detects the operating state of the engine 10 and an ECU (Electronic Control Unit) 50 that controls the engine 10 based on the output of the sensor system. The sensor system includes a crank angle sensor that outputs a signal for detecting the number of revolutions of the engine 10 (engine speed) and a crank angle, an airflow sensor that detects an intake air amount, and an engine coolant temperature (cooling water temperature). ), An intake air temperature sensor that detects the temperature of the intake air (intake air temperature), and an EGR temperature sensor that detects the temperature of the EGR gas.

  The ECU 50 calculates the engine speed, the engine load, the fuel injection amount, the target EGR amount, etc. based on the output of the sensor system, and the fuel injection valve 14, the throttle valve 20, the EGR valve 32, EGR based on these calculation results. Actuators such as the cooler bypass valve 36 are driven. Thereby, the ECU 50 controls the operating state of the engine 10 while burning the air-fuel mixture in the cylinder. Further, the ECU 50 executes EGR control for controlling the EGR amount by changing the opening degree of the EGR valve 32 according to the operating state of the engine 10.

[Features of Embodiment 1]
(Scavenging control)
After detecting a stop command for stopping the engine 10 (engine stop), the ECU 50 executes scavenging control for scavenging the gas in the cylinder. For example, in the scavenging control, the fuel injection amount is increased to increase the engine speed, and then the fuel cut is executed and the opening of the throttle valve 20 is increased. Thereby, the unburned fuel and exhaust gas remaining in the cylinder after the engine is stopped can be discharged. Further, when the engine is stopped, the exhaust gas remaining in the cylinder and the condensed water react with each other at the tip of the fuel injection valve 14 to generate an acid, and this acid corrodes the fuel injection hole of the fuel injection valve 14. Sometimes.

  According to the scavenging control, exhaust gas and condensed water remaining in the cylinder can be discharged to the outside, and corrosion of the fuel injection holes can be suppressed. The scavenging control is an example, and the present invention is not limited to this scavenging control. That is, the present invention is applied to any scavenging control for scavenging the gas in the cylinder after detecting a stop command for the internal combustion engine.

  However, if the execution time (scavenging time) of the scavenging control is long, it takes time until the engine 10 is actually stopped after the ignition switch is turned OFF, which may give the driver a sense of incongruity. On the other hand, when the scavenging time is too short, corrosion of the fuel injection holes cannot be sufficiently suppressed. For this reason, in the present embodiment, the scavenging time control for changing the scavenging time is executed based on the in-cylinder situation immediately before the engine is stopped. Hereinafter, scavenging time control will be described.

(Scavenging time control)
FIG. 2 is a flowchart showing an example of scavenging time control executed by the ECU in the first embodiment of the present invention. In the scavenging time control, first, during the operation of the engine 10, the processing of steps 100 to 108 is executed. More specifically, in step 100, a time average value of the valve tip temperature is estimated based on the engine speed, the fuel injection amount, and the intake air temperature. The valve tip temperature means the temperature of the tip of the fuel injection valve 14 exposed to the gas in the cylinder. In step 100, for example, an average value of the valve tip temperature at a certain time is calculated as a time average value.

  On the other hand, in step 102, the time average value of the head wall surface temperature is estimated based on the cooling water temperature and the intake air temperature. The head wall surface temperature means the temperature of the lower surface portion facing the inside of the combustion chamber 12 in the cylinder head. Next, in step 104, the amount of condensed water adhering to the tip of the fuel injection valve 14 when the engine is stopped is estimated based on the valve tip temperature and the head wall surface temperature. Here, FIG. 3 is a characteristic diagram showing the relationship between the valve tip temperature and the head wall surface temperature, and the condensed water generation state. As shown in this figure, when the valve tip temperature is lower than the head wall surface temperature, condensation occurs at the tip of the fuel injection valve 14.

  For this reason, in step 104, the amount of condensed water is estimated based on, for example, the characteristic data shown in FIG. 3, the valve tip temperature, and the head wall surface temperature. More specifically, first, an estimated value (time average value) of the valve tip temperature and the head wall surface temperature immediately before the engine stop, and a temperature decrease curve after the engine stop obtained by experiments or the like (for example, the characteristic data of FIG. 3). ) To estimate an actual temperature decrease curve with the estimated value as an initial value. Then, the amount of condensed water generated (condensation amount) may be estimated based on the valve tip temperature and the head wall surface temperature obtained from the estimation result.

  Next, in step 106, the residual EGR amount is estimated based on the EGR amount and the temperature of the EGR gas. The residual EGR amount means the amount of EGR gas remaining in the cylinder when the engine is stopped. The residual EGR amount is calculated, for example, as a time average value when the engine is stopped. The residual EGR amount is estimated based on the EGR amount, the temperature of the EGR gas, the opening degree of the throttle valve 20, and the opening degree of the turbo nozzle (when the supercharger 38 is a variable displacement type). Also good.

  Next, in step 108, the amount of acid adhering to the valve is estimated based on the amount of condensed water estimated in step 104 and the residual EGR amount estimated in step 106. That is, the valve adhesion acid amount is estimated based on the valve tip temperature, the head wall surface temperature, and the residual EGR amount. The amount of acid attached to the valve means the amount of acid generated by the reaction between the condensed water and the residual EGR gas after the engine is stopped and attached to the tip of the fuel injection valve 14.

  Next, in step 110, it is determined whether or not a stop command for the engine 10 has been detected by an operation such as the driver turning off the ignition switch. If a stop command is detected, the process proceeds to step 112. When the stop command is not detected, that is, when the operation of the engine 10 is continued, the estimation processing in steps 100 to 108 is repeated until the stop command is detected. In FIG. 2, this iterative process is represented by an arrow returning to step 108.

  Next, in step 112, the amount of acid adhering to the valve after engine stop is estimated based on the estimation result in step 108. Specifically, for example, the last valve adhesion acid amount calculated in step 108 immediately before the stop command is detected is adopted as the valve adhesion acid amount after the engine is stopped. On the other hand, in step 114, the intake system deposit amount is estimated based on the engine speed, the fuel injection amount, and the EGR amount. The intake system deposit amount is defined as the amount of deposit that adheres to the portion from the recirculation position of the EGR gas to the combustion chamber 12 in the intake passage 16, that is, the portion from the intake manifold 18 to the combustion chamber 12. As the intake system deposit amount, for example, a cumulative value (cumulative deposit amount) obtained by accumulating the intake system deposit amount per cycle may be used.

  Next, in step 116, the scavenging time is set by referring to, for example, the data map shown in FIG. 4 on the basis of the valve attached acid amount and the intake system deposit amount after the engine is stopped. In step 118, the above-described scavenging control is executed for the set scavenging time. FIG. 4 is an explanatory diagram showing an example of a data map for setting the scavenging time in the first embodiment of the present invention. In this figure, for example, from the scavenging time setting map which is a data map of 3 rows × 3 columns, the amount of valve adhesion acid divided into three ranges X1, X2, and X3 and the three ranges Y1, Y2, and Y3 are divided. In this example, one of the scavenging times A, B, and C is set based on the intake system deposit amount. The scavenging times A, B, and C are set such that A> B> C. Further, the scavenging time C may be set to a value when the scavenging control is not executed (for example, C = 0).

  The characteristics of the scavenging time setting map will be described. First, when the engine is stopped, the more the amount of acid adhering to the valve, the higher the risk of corrosion of the fuel injection holes. Therefore, it is necessary to sufficiently perform the scavenging control. For this reason, the scavenging time setting map is set so that the scavenging time becomes longer as the valve-attached acid amount increases. Further, according to the research of the present inventor, it has been confirmed that the deposit state in the intake system greatly affects the progress of corrosion. More specifically, when the intake system deposit amount is small (for example, when the travel distance is less than 1000 km), the corrosion of the fuel injection holes is more likely to proceed than when the intake system deposit amount is large. For this reason, the scavenging time setting map is set so that the scavenging time becomes shorter as the intake system deposit amount increases.

  As described above in detail, according to the scavenging time control, it is possible to appropriately change the scavenging time based on the amount of acid adhering to the valve and the amount of intake system deposit that affects the ease of corrosion of the fuel injection hole. That is, when the amount of acid adhering to the valve is small and the amount of intake system deposit is large, the risk of corrosion of the fuel injection hole is low, so the scavenging time is shortened and the uncomfortable feeling experienced by the driver etc. by the scavenging control is minimized It can be suppressed to the limit. In addition, when the amount of acid adhering to the valve is large and when the amount of intake system deposit is small, the risk of corrosion of the fuel injection holes is high. Scavenging can be performed sufficiently.

  Therefore, according to the present embodiment, it is possible to suppress the uncomfortable feeling due to the scavenging control while suppressing the corrosion of the fuel injection valve 14. Further, in the present embodiment, it is possible to accurately estimate the acid adhesion amount (generated amount) after the engine is stopped based on the operating state immediately before the engine is stopped and the in-cylinder combustion state, and based on the estimation result. The scavenging time can be set accurately.

  In the first embodiment, step 100 in FIG. 2 shows a specific example of the valve tip temperature estimating means, and step 102 shows a specific example of the head wall surface temperature estimating means. Step 104 shows a specific example of the condensed water amount estimation means, Step 106 shows a specific example of the residual EGR amount estimation means, Step 108 shows a specific example of the valve adhesion acid amount estimation means, and Step 114 shows a deposit amount estimation. Specific examples of the means are shown, and steps 116 and 118 show specific examples of the scavenging control variable means.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. In addition to the same configuration as that of the first embodiment, the present embodiment is characterized in that the amount of EGR gas supplied to the combustion chamber during engine operation decreases as the intake system deposit amount decreases. Yes. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  FIG. 5 is a flowchart showing a part of scavenging time control in Embodiment 2 of the present invention. As shown in this figure, in the present embodiment, first, in step 200, processing similar to that in step 114 described in the first embodiment (FIG. 2) is executed to estimate the intake system deposit amount. Next, in step 202, the corrosion correction EGR amount is calculated by referring to the EGR correction map based on the estimated intake system deposit amount. The corrosion correction EGR amount is an EGR amount considering the influence of the intake system deposit amount on the corrosion of the fuel injection hole.

  As described above, the corrosion of the fuel injection hole is more likely to proceed as the intake system deposit amount is smaller. Therefore, when the intake system deposit amount is small, it is preferable to reduce the EGR gas that is a cause of acid generation. Therefore, the EGR correction map is set so that the corrosion correction EGR amount decreases as the intake system deposit amount decreases, and is stored in the ECU 50 in advance. When the corrosion correction EGR amount is calculated in step 202, in the EGR control, the opening degree of the EGR valve 32 is controlled so that the actual EGR amount coincides with the corrosion correction EGR amount. On the other hand, in the scavenging time control, in step 106, the residual EGR amount is estimated using the corrosion correction EGR amount. Further, the intake system deposit amount calculated in step 200 is also used in step 116 (see FIG. 1).

  In the present embodiment configured as described above, it is possible to obtain substantially the same operational effects as in the first embodiment. In particular, in the present embodiment, the EGR amount during engine operation can be reduced as the intake system deposit amount is smaller. Thus, even when the intake system deposit amount is small, it is possible to suppress the generation of acid when the engine is stopped and to protect the fuel injection hole from corrosion.

Embodiment 3 FIG.
Next, a third embodiment of the present invention will be described with reference to FIG. The present embodiment is characterized in that the scavenging time is set in consideration of the EGR amount immediately before the engine is stopped in addition to the same configuration as in the first embodiment. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the present embodiment, the EGR amount is constantly monitored during operation of the engine. For example, when the time average value of the EGR amount immediately before the engine is stopped is larger than a predetermined determination value, the estimated value of the valve-attached acid amount Increase scavenging time based on As a result, the residual EGR gas can be efficiently reduced and the scavenging time can be minimized.

  FIG. 6 is an explanatory diagram showing an example of control executed for each region determined according to the valve adhesion acid amount and the intake system deposit amount in the third embodiment of the present invention. In the control shown in this figure, the EGR control during engine operation is stopped in the regions P and P ′ where the intake system deposit amount is small or the valve-attached acid amount is large, and among these regions, the valve-attached acid amount is large In P ′, the scavenging time is made longer than in other areas P, Q, and R. On the other hand, in the region R in which the intake system deposit amount is large and the valve adhesion acid amount is small, the scavenging time is shortened or the scavenging control is not performed compared to the other regions P, P ′, and Q. In the present embodiment configured as described above, it is possible to obtain substantially the same operational effects as in the first embodiment.

  In the present invention, the configurations of the second and third embodiments may be combined. In the first and third embodiments, the data map of 3 rows × 3 columns in which the amount of valve adhesion acid and the amount of intake system deposit is divided into three stages is illustrated, but the present invention is not limited to this, and the amount of valve adhesion acid In addition, a data map in which the intake system deposit amount is divided into an arbitrary number of stages can be used. In the first embodiment, the diesel engine has been described as an example. However, the present invention is not limited to this, and the present invention may be applied to a gasoline engine provided with an in-cylinder fuel injection valve.

  As described above, the present invention may be configured such that the smaller the intake system deposit amount estimated by the deposit amount estimating means, the smaller the recirculation amount of EGR gas during the operation of the internal combustion engine. According to this configuration, the EGR amount during operation can be reduced as the intake system deposit amount is smaller. Thus, even when the intake system deposit amount is small, it is possible to suppress the generation of acid when the internal combustion engine is stopped, and to protect the fuel injection valve from corrosion.

10 Engine (Internal combustion engine)
12 Combustion chamber 14 Fuel injection valve 16 Intake passage 18 Intake manifold 20 Throttle valve 24 Exhaust passage 28 EGR mechanism 30 EGR passage 32 EGR valve 34 EGR cooler 36 EGR cooler bypass valve 38 Supercharger 50 ECU

Claims (1)

A fuel injection valve for injecting fuel into the combustion chamber of the internal combustion engine;
An EGR mechanism that is provided between an intake passage and an exhaust passage of the internal combustion engine and recirculates EGR gas that is part of exhaust gas from the exhaust passage to the intake passage;
A valve tip temperature estimating means for estimating a valve tip temperature, which is a temperature of a tip portion of the fuel injection valve, based on an engine speed of the internal combustion engine, a fuel injection amount, and an intake air temperature;
A head wall surface temperature estimating means for estimating a head wall surface temperature that is a temperature of a lower surface portion facing the combustion chamber of the cylinder head based on a cooling water temperature of the internal combustion engine and the intake air temperature;
Residual EGR amount estimating means for estimating a residual EGR amount, which is an amount of the EGR gas remaining in the combustion chamber when the internal combustion engine is stopped, based on a recirculation amount of the EGR gas by the EGR mechanism and a temperature of the EGR gas. When,
Estimating the amount of acid adhering to the valve, which estimates the amount of acid adhering to the tip of the fuel injection valve when the internal combustion engine is stopped, based on the valve tip temperature, the head wall surface temperature, and the residual EGR amount Means,
The intake system deposit amount, which is the amount of deposit that adheres to the portion from the recirculation position of the EGR gas to the combustion chamber in the intake passage, is determined based on the engine speed, the fuel injection amount, and the recirculation amount of the EGR gas. Deposit amount estimating means for estimating
A means for executing scavenging control for scavenging the gas in the combustion chamber after detecting a stop command for the internal combustion engine, wherein the scavenging control execution time is determined based on the valve-attached acid amount and the intake system deposit amount; A scavenging control variable means to change;
The control apparatus of the internal combustion engine provided with.

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