JP2015075069A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To curb adhesion of deposit to a fuel injection valve or remove the adhered deposit.SOLUTION: A control device is applied to an internal combustion engine which can be operated by fuel with alcohol mixed with hydrocarbon fuel. When adhesion of deposit to a fuel injection valve of the internal combustion engine is expected, the control device executes inhibitory control to curb the adhesion of the deposit to the fuel injection valve or to remove the adhered deposit during a period after a stop request of the internal combustion engine till a stop thereof. An execution amount of the inhibitory control is set in accordance with an alcohol concentration in the fuel supplied to the internal combustion engine and an exhaust air-fuel ratio thereof.

Description

  The present invention relates to a control device for an internal combustion engine. More specifically, the present invention relates to a control device for an internal combustion engine that can use a mixture of alcohol and hydrocarbon fuel.

  Patent Document 1 discloses a system that executes control for removing deposits adhering to a fuel injection valve of an internal combustion engine. Specifically, in this system, deposit adhesion to the tip of the fuel injection valve is detected based on, for example, the resistance value or temperature of the nozzle tip of the fuel injection valve. When deposit adhesion is detected, residual fuel remaining at the tip of the fuel injection valve is removed by increasing the fuel pressure, closing the intake valve or heating the tip of the fuel injection valve, or the like.

JP 2006-183469 A JP 2002-285895 A JP 2006-242084 A JP 2003-106192 A

  By the way, the factor which produces | generates the deposit adhering to a fuel injection valve changes with alcohol concentration of a fuel. However, the control of Patent Document 1 is based on a fuel injection valve of a gasoline engine, and does not use a fuel mixture of alcohol and hydrocarbon fuel. In this regard, a system is desired that can more appropriately suppress or eliminate deposit adhesion in accordance with changes in the amount of deposit adhesion due to the alcohol concentration of the fuel.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to suppress or prevent the deposit from adhering to a fuel injection valve installed in an internal combustion engine that can use a mixed fuel of hydrocarbon fuel and alcohol. It is an object of the present invention to provide an internal combustion engine control apparatus improved so as to be eliminated.

In order to achieve the above object, the present invention is a control device for an internal combustion engine capable of using a fuel in which alcohol and hydrocarbon fuel are mixed,
When deposits are expected to adhere to the fuel injection valves of the internal combustion engine, deposits are suppressed or removed from the fuel injection valves during a period from when the internal combustion engine is requested to stop until the internal combustion engine is stopped. Means for executing suppression control for
Means for detecting or estimating the alcohol concentration of fuel supplied to the internal combustion engine;
Means for detecting or estimating the exhaust air-fuel ratio of the internal combustion engine;
Means for setting the execution amount of the suppression control according to the alcohol concentration and the exhaust air-fuel ratio;
A control device for an internal combustion engine, comprising:

  Various factors that affect the amount of deposit generated on the fuel injection valve vary depending on the alcohol concentration and also vary depending on the amount of carbonyl compound produced by combustion. The amount of carbonyl compound produced can be estimated according to the alcohol concentration and the exhaust air / fuel ratio. Therefore, in the present invention, the execution amount of the suppression control is set according to the alcohol concentration and the exhaust air-fuel ratio, so that the execution amount of the suppression control is set to an appropriate execution amount with respect to the deposit generation amount. Can do. Thereby, it is possible to minimize the demerits such as the deterioration of fuel consumption due to excessive execution of the suppression control while reliably suppressing or removing the deposit.

It is a figure for demonstrating the relationship between the production | generation factor of the deposit adhering to an injector, and the alcohol concentration of a fuel. It is a figure for demonstrating the relationship between a deposit generation | occurrence | production risk and alcohol concentration. It is a figure which shows an example of the ratio of each component in the emission at the time of using the fuel from which alcohol concentration differs. It is a figure for demonstrating the execution amount of the suppression control of a deposit in embodiment of this invention. It is a figure for demonstrating the relationship between the exhaust air-fuel ratio and the increase correction amount with respect to the execution amount of suppression control in embodiment of this invention. It is a figure for demonstrating the relationship between the alcohol concentration of a fuel and the increase correction amount with respect to the execution amount of suppression control in embodiment of this invention. It is a timing chart for demonstrating the outline | summary of the suppression control in embodiment of this invention. It is a flowchart for demonstrating the routine of control which a control apparatus performs in embodiment of this invention. It is a flowchart for demonstrating the routine of the other control which a control apparatus performs in embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

Embodiment.
The system of the embodiment of the present invention has an internal combustion engine for FFV (Flexible Fuel Vehicle) that can use an alcohol mixed fuel in which alcohol and hydrocarbon fuel are mixed as fuel. An air flow meter is installed in the intake passage of the internal combustion engine. The internal combustion engine includes a water temperature sensor for detecting the temperature of the cooling water, a fuel pressure sensor for detecting the pressure (fuel pressure) of the supplied fuel, an alcohol concentration sensor for detecting the alcohol concentration of the fuel, and an exhaust air Various sensors such as an exhaust gas sensor for detecting the fuel ratio are installed.

  The system of the embodiment of the present invention has an ECU (Electronic Control Unit). The ECU is a control device that controls the operation of the internal combustion engine. The ECU captures and processes signals from various sensors including an air flow meter, a water temperature sensor, a fuel pressure sensor, an alcohol sensor, and an exhaust gas sensor. The ECU processes each acquired sensor signal and operates each actuator or device in accordance with a predetermined control program. The actuator or device operated by the ECU includes a port injection injector (hereinafter also referred to as “injector”) as a fuel injection valve, an electric cooling fan for a radiator, and a water pump. There are many actuators, devices, and sensors connected to the ECU in addition to the above, but the description thereof is omitted in this specification.

  The control executed by the ECU in the present embodiment includes a control (hereinafter also referred to as “suppression control”) for predicting deposit adhesion to the injector, suppressing deposit adhesion, or removing the deposited deposit.

  First, a mechanism for generating a deposit that adheres to an injector of an internal combustion engine will be described. The fuel injected during operation of the internal combustion engine remains in the injector nozzle hole after the internal combustion engine is stopped. Residual fuel is oxidized and polymerized by the ambient heat around the injector and NOx in the blown-back gas, and is gummed in the vicinity of the injector nozzle hole. When the operation of the internal combustion engine is resumed and fuel injection is performed again, the fuel in the blown-back gas adheres to the gummed fuel, and the deposit further increases.

The following factors affect the formation of deposits deposited in this way.
(A) Residual fuel amount remaining in the nozzle hole (B) Atmospheric heat around the injector, that is, tip temperature near the injector nozzle hole (C) Residual NOx concentration in the port (D) Blow-back PM amount

  By the way, the physical values of the factors (A) to (D) change depending on the alcohol concentration of the injected fuel. In other words, the amount of deposit generated varies depending on the alcohol concentration. Therefore, if the suppression control executed in the internal combustion engine using gasoline as fuel is applied as it is, there may be a case where excessive countermeasure control is executed, for example, the control execution time becomes long. Such excessive countermeasure control is not preferable from the viewpoint of improving fuel consumption. Therefore, in the present embodiment, the execution amount of the suppression control is determined based on the change of the factor according to the alcohol concentration of the fuel.

  FIG. 1 is a diagram for explaining the relationship between the deposit generation factor adhering to the injector and the alcohol concentration of the fuel. In FIG. 1, the horizontal axis represents the alcohol concentration, and the vertical axis represents the physical value of each of the factors (A) to (D). As shown in FIG. 1, each of the above factors (A) to (D) decreases or decreases as the alcohol concentration increases. That is, as a whole, the higher the alcohol concentration, the lower the risk of depositing. The change of each factor will be specifically described.

(A) Residual fuel amount in nozzle hole Generally, the higher the alcohol concentration of the fuel, the higher the viscosity of the fuel. Accordingly, the amount of fuel dripping into the nozzle hole is reduced. For this reason, it is considered that the residual amount of fuel in the nozzle hole decreases as the alcohol concentration increases.

(B) Injector tip temperature The higher the concentration alcohol, the higher the latent heat of vaporization and the lower the intake air temperature. Further, if the alcohol concentration is increased, the amount of water generated correspondingly increases, so that the specific heat increases and the combustion gas temperature decreases. Therefore, the higher the alcohol concentration, the lower the injector tip temperature.

一方、エタノール１００％の燃料を燃焼させた場合の反応式は次式（２）に示される。

上記式（１）及び（２）から、エタノール１００％の場合、ガソリンの場合と比べて生成される水分量が約１．５倍増加することがわかる。 As an example, the latent heat of vaporization of gasoline is about 100 [kcal / kg], and in the case of 100% ethanol, the latent heat of vaporization is about 216 [kcal / kg].
The reaction when gasoline is burned is shown in the following formula (1).

On the other hand, the reaction formula when fuel of 100% ethanol is burned is shown in the following formula (2).

From the above formulas (1) and (2), it can be seen that in the case of 100% ethanol, the amount of water produced is increased by about 1.5 times compared to the case of gasoline.

(C) Residual NOx concentration In the case of an equal air fuel ratio, the lower the combustion temperature, the lower the NOx. Further, the higher the alcohol concentration of the fuel, the lower the combustion gas temperature. Therefore, the higher the alcohol concentration, the lower the residual NOx concentration.

(D) Blow-back PM amount The higher the alcohol concentration of the fuel, the lower the content of higher carbon that is a precursor of particulate matter (PM). Therefore, the higher the alcohol concentration, the smaller the amount of PM generated by combustion.

  FIG. 2 is a diagram for explaining the relationship between deposit generation risk and alcohol concentration. As shown in FIG. 2, the risk of deposit generation decreases in a quadratic function as the alcohol concentration of the fuel increases due to the combined effect of the change of each factor of deposit generation according to the alcohol concentration. Accordingly, the execution amount of the suppression control can be set smaller than the case of gasoline fuel because the risk of deposit generation is reduced.

Next, the influence of the carbonyl compound produced when alcohol fuel is used on the production of deposit will be described. First, the reaction mechanism when ethanol is burned is shown in the following formula (3).

As shown in Formula (3), the oxidation reaction of ethanol is started by a hydrogen abstraction reaction with OH, and CH ₃ CH ₂ O is generated. From CH ₃ CH ₂ O, formaldehyde (HCHO) and acetaldehyde are competitively formed. (CH ₃ CHO) is generated.

Thus, when alcohol is burned, carbonyl compounds such as formaldehyde (HCHO) and acetaldehyde (CH ₃ CHO) are generated. When a high-concentration alcohol fuel is used, a larger amount of carbonyl compound is generated during combustion than when gasoline is used, and increases as the alcohol concentration is higher. FIG. 3 is a diagram showing an example of the ratio of each component during emission when fuels having different alcohol concentrations are used. In FIG. 3, the right side of the bar graph is for gasoline (ethanol concentration 0%), and the left side is for fuel with 85% ethanol. FIG. 3 also shows that the amount of carbonyl compound discharged is higher when the alcohol concentration of the fuel is higher.

  Incidentally, as described above, the amount of carbonyl compound produced increases as the alcohol concentration increases. Moreover, the reaction of carbonyl compound formation as shown in Formula (3) occurs in the state of incomplete combustion due to oxygen deficiency. Therefore, the amount of carbonyl compound produced can be estimated from the alcohol concentration and the exhaust air / fuel ratio (A / F) monitored by the exhaust gas sensor.

  Carbonyl compounds are active species. Therefore, the polymerization reaction with the residual NOx and the fuel adhering to the tip of the injector is promoted. For this reason, when there is much quantity of a carbonyl compound, the production amount (namely, deposit generation | occurrence | production risk) of a deposit will increase. Therefore, it is necessary to set the execution amount of the suppression control to be large for the amount that the deposit generation risk is increased by the carbonyl compound.

  FIG. 4 is a diagram for explaining the execution amount of deposit suppression control in the embodiment of the present invention. From the viewpoint described above, the execution amount when the suppression control is executed in the present embodiment is set according to the alcohol concentration and the exhaust air-fuel ratio A / F. Specifically, first, the amount of reduction due to the factors (A) to (D) is set to be lower than the execution amount in the case of gasoline. The amount of deposit generated due to the factors (A) to (D) decreases in a quadratic function as the alcohol concentration increases. Accordingly, as shown in FIG. 4 (a), the execution amount is set to be a quadratic function smaller than the execution amount in the case of gasoline as the alcohol concentration increases.

  On the other hand, as shown in FIG. 4B, the execution amount is corrected to be increased by the amount of carbonyl compound generation that increases depending on the alcohol concentration and the operating conditions (here, the exhaust air-fuel ratio). FIG. 5 is a view for explaining the relationship between the exhaust air-fuel ratio and the increase correction amount with respect to the execution amount of the suppression control in the embodiment of the present invention, and FIG. 6 shows the alcohol concentration and the concentration in the embodiment of the present invention. It is a figure for demonstrating the relationship with the increase correction amount with respect to the execution amount of suppression control.

  As described above, carbonyl compounds increase due to incomplete combustion due to oxygen deficiency. Therefore, as shown in FIG. 5, when compared with fuels having the same alcohol concentration, the increase correction amount is set to be larger as the air-fuel ratio is richer. In addition, the carbonyl compound increases as the alcohol concentration of the fuel increases. Therefore, as shown in FIG. 6, when comparing the same exhaust air-fuel ratio, the increase correction amount is set to be larger as the alcohol concentration is higher.

  FIG. 7 is a timing chart for explaining the suppression control in the embodiment of the present invention. In each of (a) to (i) of FIG. 7, the horizontal axis represents a common time. In the example of FIG. 7, control for driving the electric cooling fan is executed as the deposit suppression control. In this case, the execution amount of the suppression control that is set is the time (hereinafter referred to as “execution time”) for driving the electric cooling fan to suppress deposits.

  As shown in FIG. 7, when there is a request to stop the internal combustion engine from the driver at time t1, the IG (ignition) -OFF request flag is turned ON. In the example of FIG. 7, at this time, the intake air temperature exceeds the reference value Ref1, and the water temperature exceeds the reference value Ref2. Here, the reference values Ref1 and Ref2 are criteria for the intake air temperature and the water temperature for determining deposit generation. In other words, when the intake air temperature is higher than the reference value Ref1 and the water temperature is higher than the reference value Ref2, it is determined that the deposit is at a high temperature and a warm state where deposits are expected to adhere to the injector. The

  As shown in FIG. 7, when the intake air temperature exceeds the reference value Ref1 and the water temperature exceeds the reference value Ref2, suppression control is executed. In this case, as shown in FIG. 7, at time t1 when the IG-OFF flag is turned on, the suppression control execution flag is also turned on.

  When the suppression control execution flag is turned ON, the drive duty of the electric cooling fan is maintained at 100. That is, the electric cooling fan is driven as it is. In response to the driver's request to stop the internal combustion engine, the injection flag and the ignition flag are turned OFF at time t1. This stops fuel injection and ignition.

  From time t1 when the suppression control execution flag is turned ON, at time t2 when the integrated value of the drive time of the electric cooling fan reaches the execution time of suppression control, the IG-OFF execution flag is turned ON. At the same time, the ignition switch (IG-SW) is turned off.

  In the suppression control, the specific relationship between the required amount of suppression control and the alcohol concentration, and the relationship between the increase correction amount with respect to the required amount, the exhaust air-fuel ratio, and the alcohol concentration are obtained by, for example, experiments or simulations. The obtained relationship is stored in the ECU as a map that defines the relationship between the required amount and the alcohol concentration, a three-dimensional map that defines the relationship between the exhaust air-fuel ratio, the alcohol concentration, and the increase correction amount. In actual control, a required amount (“required time” in the present embodiment) corresponding to the exhaust air-fuel ratio and alcohol concentration is obtained according to this map.

  FIG. 8 is a flowchart for illustrating a control routine executed by the ECU in the embodiment of the present invention. The routine of FIG. 8 is a routine that is repeatedly executed during operation of the internal combustion engine.

  In the routine of FIG. 8, first, an alcohol concentration learning value is acquired (S100). The alcohol concentration of the fuel is estimated by alcohol concentration learning during normal operation of the internal combustion engine. In step S100, this alcohol concentration learning value is acquired and used as the alcohol concentration when the internal combustion engine is stopped.

  Next, it is determined whether or not there is an IG-OFF request (S102). That is, it is determined whether or not the IG-OFF request flag is turned on. If the IG-OFF request is not accepted, the current process is temporarily terminated as it is.

  On the other hand, when the request for IG-OFF is recognized in step S102, the intake air temperature and the water temperature are acquired in step S104. Here, the intake air temperature is detected based on the output of the air flow meter, and the water temperature is detected based on the output of the water temperature sensor.

  Next, it is determined whether or not the intake air temperature is higher than the reference value Ref1 and the water temperature is higher than the reference value Ref2. Here, if the establishment of the intake air temperature> the reference value Ref1 and the water temperature> the reference value Ref2 is not recognized, it can be determined that the risk of depositing is low, so the internal combustion engine is stopped this time (S108).

  On the other hand, if it is determined in step S106 that intake air temperature> reference value Ref1 and water temperature> reference value Ref2 are established, it is determined that the current state is in a region where there is a risk of deposit occurrence to the injector. Therefore, in this case, the process proceeds to step S110, and the suppression control execution flag is turned ON.

  Next, the execution time of the suppression control is calculated in step S112 (S112). Here, the execution time is obtained by correcting the time obtained according to the alcohol concentration with the increase correction amount obtained according to the alcohol concentration and the exhaust air / fuel ratio. Thereafter, the internal combustion engine is stopped (S114).

  Next, suppression control is executed (S116). That is, when the electric cooling fan is driven or is driven, the driving is continued as it is. Next, it is determined whether or not the driving time of the electric cooling fan from the start of the suppression control has exceeded the execution time (S118). In step S118, when it is not recognized that the drive time has exceeded the execution time, the process returns to step S116, and the electric cooling fan is maintained in the drive state. Until it is recognized in step S118 that the drive time has exceeded the execution time, the processes in steps S116 and S118 are repeated.

  If it is determined in step S118 that the drive time has exceeded the execution time, or if the internal combustion engine is stopped in step S108, then the ignition is turned off in step S120. As a result, energization to the ECU is terminated and the vehicle soak is made. Thereafter, the current process is temporarily terminated.

  As described above, according to the present embodiment, the execution amount of the deposit suppression control is set according to the alcohol concentration of the fuel and the carbonyl compound generation amount estimated from the alcohol concentration and the exhaust air-fuel ratio. . Thus, necessary and sufficient suppression control is executed on the generated deposit in accordance with the alcohol concentration of the fuel and the operating state. Therefore, the surplus can suppress the execution of the control while suppressing the deposit.

  In the routine of FIG. 8, the processing of step S112 is executed to realize the “means for setting the execution amount” of the present invention, and the processing of steps S116 and S118 is executed to execute “suppression control. "Means to execute" are realized.

  In the present embodiment, the case where the control for driving the electric cooling fan for the requested execution time after the internal combustion engine is stopped has been described as the deposit suppression control. Thereby, since the injector front-end | tip is cooled, adhesion of a deposit can be suppressed. However, the deposit suppression control in the present invention is not limited to this. For example, the water pump may be driven instead of driving the electric cooling fan. The suppression control for driving the water pump can be realized according to the timing chart of FIG. 7 and the flowchart of FIG.

  Further, for example, as another suppression control, in the final injection cycle of each cylinder immediately before the stop of the internal combustion engine, there is a control in which the fuel injection pressure is increased to inject the fuel, and the fuel at the tip of the injector is blown off. Also in this case, the injection pressure (execution amount of suppression control) required to suppress the deposit adhesion is set according to the deposit amount estimated from the alcohol concentration and the operating conditions such as the exhaust air-fuel ratio. In the final injection cycle of each cylinder immediately before the internal combustion engine is stopped, fuel is injected at the injection pressure. Alternatively, the fuel injection amount may be controlled instead of the injection pressure or together with the injection pressure control. The injection pressure can be increased using a variable feed pressure system.

  FIG. 9 is a flowchart for illustrating another control routine executed by the ECU in the embodiment of the present invention. The routine shown in FIG. 9 is executed in place of the routine shown in FIG. 8, and includes the processes of steps S202 to S210 instead of the processes of steps S112 to S118 between the processes of steps S110 and S120. Except for this, it is the same as the routine of FIG.

  Specifically, after the suppression control execution flag is turned on in step S110, the required injection pressure is calculated (S202). The required fuel pressure is calculated by correcting the required injection pressure that is set according to the alcohol concentration, according to the alcohol concentration and the exhaust air / fuel ratio. That is, here again, the required injection pressure corresponding to the alcohol concentration is increased and corrected according to the concentration of the residual carbonyl compound estimated from the alcohol concentration, the water temperature immediately before stopping the internal combustion engine, and the exhaust air / fuel ratio, and the required fuel pressure is calculated. The

  Next, the injection pressure is increased (S204). The injection pressure is increased by using a variable feed pressure system and increasing the feed pressure to the required value. Next, it is determined whether or not the feed pressure has reached a required value (S206). When it is not recognized in step S206 that the feed pressure has reached the required value, the process returns to step S204, and the feed pressure is increased. Until it is recognized in step S206 that the feed pressure has reached the required value, the processes in steps S204 and S206 are repeated.

  When it is determined in step S206 that the feed pressure has reached the required value, suppression control is executed (S208). That is, here, fuel is injected at the set required injection pressure (feed pressure) for the final injection cycle of each cylinder. Thereafter, the internal combustion engine is stopped (S210).

  In the routine of FIG. 9, the processing of step S202 is executed to realize the “means for setting the execution amount” of the present invention, and the processing of step S208 is executed to execute “suppression control”. Means "are realized.

  In the above embodiment, when referring to the number of each element, quantity, quantity, range, etc., the reference is made unless otherwise specified or the number is clearly specified in principle. The invention is not limited to the numbers. The structures, steps, and the like described in this embodiment are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

Claims (1)

A control device for an internal combustion engine capable of using a fuel in which alcohol and hydrocarbon fuel are mixed,
When deposits are expected to adhere to the fuel injection valves of the internal combustion engine, deposits are suppressed or removed from the fuel injection valves during a period from when the internal combustion engine is requested to stop until the internal combustion engine is stopped. Means for executing suppression control for
Means for detecting or estimating the alcohol concentration of fuel supplied to the internal combustion engine;
Means for detecting or estimating the exhaust air-fuel ratio of the internal combustion engine;
Means for setting the execution amount of the suppression control according to the alcohol concentration and the exhaust air-fuel ratio;
A control device for an internal combustion engine, comprising:

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