JP2012241620A - Internal combustion engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine control device capable of executing valve timing variable control in engine cold time without spreading a range of a deterioration in drivability.SOLUTION: In the engine cold time, the valve timing variable control of an intake valve is prohibited in principle. Alternatively, the valve timing variable control in the engine cold time is allowed exceptionally on condition that AI control for increasing a fuel injection amount for raising a temperature of a catalyst is in execution.

Description

  The present invention relates to a control device for an internal combustion engine that performs variable valve timing control that varies the valve timing of an intake valve.

  As a mechanism mounted in an internal combustion engine such as a vehicle, a valve timing variable mechanism that varies the valve timing of an intake valve has been put into practical use. In an internal combustion engine equipped with such a variable valve timing mechanism, variable valve timing control is performed to vary the valve timing of the intake valve in accordance with the engine operating conditions.

  Conventionally, Patent Document 1 describes a control device for an internal combustion engine that permits variable valve timing control of an intake valve when the engine is cold, on condition that return to the initial position of valve timing is guaranteed. Has been.

JP 2010-223138 A

  If the valve timing variable control is performed even when the engine is cold and the valve overlap of the intake and exhaust valves is made by the advance of the valve timing, the intake port is warmed by the return of the combustion gas to the intake port, and the fuel As a result, the combustion is improved and the emission is improved. However, the following problems regarding drivability are involved in the variable valve timing control when the engine is cold.

  When the engine is cold from start to warm-up, the port wall surface is cold, so the amount of fuel injected from the injector on the port wall surface increases. In this state, when variable valve timing control is performed and the valve timing of the intake valve is advanced to increase the valve overlap of the intake and exhaust valves, the combustion gas blows back from the combustion chamber to the intake port. And since the fuel adhering to the port wall surface is vaporized by the combustion gas, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber becomes rich, and the idle stability is deteriorated.

  Further, depending on the variable valve timing control when the engine is cold, deterioration in acceleration (hegitation) occurs due to lean air-fuel ratio during acceleration. When the accelerator is stepped on and the amount of intake air increases, the fuel adhering to the wall surface of the port is vaporized by the air flow and introduced into the combustion chamber. The acceleration of the vehicle is ensured in view of the increase in combustion fuel due to vaporization from the port wall surface. On the other hand, if the valve timing of the intake valve is advanced before acceleration, the fuel adhering to the port wall surface is vaporized by the blow-back of the combustion gas, so the amount of fuel adhering to the port wall surface decreases. Therefore, if the valve timing of the intake valve is advanced before acceleration, the combustion fuel at the time of acceleration becomes less than expected, and sufficient torque cannot be increased.

  Therefore, if the return of the valve timing to the initial position is guaranteed when the engine is cold, if the variable valve timing control of the intake valve is permitted, the air-fuel ratio accompanying the advancement of the valve timing As a result, the drivability deteriorates due to the richness of the air and the lean air-fuel ratio during acceleration.

  The present invention has been made in view of such circumstances, and the problem to be solved is that it is possible to perform variable valve timing control when the engine is cold without expanding the range of deterioration of drivability. An object of the present invention is to provide a control device for an internal combustion engine.

  In order to solve the above-mentioned problem, the invention according to claim 1 as a control device for an internal combustion engine that performs variable valve timing control that varies the valve timing of the intake valve is a condition for performing variable valve timing control when the engine is cold. In addition, the fact that the increase control of the fuel injection amount is being implemented is included.

  If the variable valve timing control is performed unconditionally when the engine is cold, the drivability deteriorates due to the rich air-fuel ratio accompanying the advancement of the valve timing as described above and the lean air-fuel ratio during acceleration. I will. In order to avoid this, it is desirable to prohibit the variable valve timing control when the engine is cold.

  On the other hand, if the increase control of the fuel injection amount is performed, the air-fuel ratio is enriched by the increase control, and the drivability is deteriorated from the start. Therefore, if such increase control is being executed, the variable valve timing control can be performed without concern for deterioration in drivability. Further, since the fuel injection amount is increased, there is no shortage of combustion fuel during acceleration. Therefore, according to the above configuration, variable valve timing control when the engine is cold can be performed without expanding the range of deterioration of drivability.

  As an increase control of the fuel injection amount as a condition for performing the variable valve timing control when the engine is cold, for example, an increase control of the fuel injection amount performed for increasing the temperature of the catalyst can be cited. Of course, the increase control of the fuel injection amount other than the temperature increase of the catalyst can also be a condition for performing the variable valve timing control when the engine is cold.

  If the fuel injection amount increase control and the valve timing variable control are started at the same time, the air-fuel ratio enrichment due to the increase in the fuel injection amount and the air-fuel ratio enrichment due to the advance of the valve timing occur at the same time. There is a risk that a significant torque increase will occur. Therefore, according to claim 3, if the condition for performing the variable control of the valve timing when the engine is cold is to include that a prescribed time has elapsed since the start of the fuel injection amount increase control, A time difference can be added between the start of the fuel injection amount increase control and the start of variable valve timing control. Therefore, a rapid torque increase can be suppressed.

  On the other hand, if the internal combustion engine is repeatedly started without a sufficient engine stop time to evaporate the fuel adhering to the intake port, the amount of fuel adhering to the intake port increases each time the engine is started. If the variable valve timing control is performed in a state where an excessive amount of fuel is attached to the intake port when the engine is cold, the air-fuel ratio is significantly enriched, which may cause a combustion failure. In that respect, if the condition for performing the variable valve timing control when the engine is cold is included in the condition for executing the variable valve timing control according to the fourth aspect of the invention, an excessively large intake port may be caused. When the amount of fuel is attached, the variable valve timing control is not permitted. For this reason, it is possible to avoid a substantial enrichment of the air-fuel ratio associated with the variable valve timing control when the engine is cold.

1 is a schematic diagram schematically showing the configuration of an internal combustion engine to which an embodiment of the present invention is applied. The flowchart which shows the process sequence of cold VVT control precondition establishment determination routine employ | adopted as the same embodiment. The time chart which shows an example of the control mode at the time of engine starting in the embodiment. The time chart which shows an example of the control aspect before and behind AI control implementation in the embodiment. The time chart which shows an example of the control aspect in the some trip of the embodiment.

Hereinafter, an embodiment of a control device for an internal combustion engine according to the present invention will be described in detail with reference to FIGS.
As shown in FIG. 1, in an intake passage 1 of an internal combustion engine to which the control device of the present embodiment is applied, an air cleaner 2 for purifying intake air, an air flow meter 3 for detecting intake air, A throttle valve 4 for adjusting the amount and an injector 5 for injecting fuel during intake are provided. The intake passage 1 is connected to the combustion chamber 8 via an intake valve 6. The internal combustion engine is provided with a variable valve timing mechanism (VVT mechanism) 7 that makes the valve timing of the intake valve 6 variable.

  A spark plug 9 for igniting the air-fuel mixture is installed in the combustion chamber 8 where the air-fuel mixture of intake air and fuel is combusted. The combustion chamber 8 is connected to the exhaust passage 11 via the exhaust valve 10.

  An exhaust passage 11 through which exhaust exhausted from the combustion chamber 8 flows is provided with an air-fuel ratio sensor 12 for detecting the oxygen concentration in the exhaust and a catalyst 13 for purifying the exhaust. The exhaust passage 11 is connected to a secondary air supply path 14 for supplying secondary air during exhaust. The secondary air supply path 14 is provided with an air pump 15 that pressurizes and discharges air, and an air switching valve 16 that turns on and off the supply of secondary air.

  Such an internal combustion engine is controlled by an electronic control unit 17. The electronic control unit 17 includes a central processing unit (CPU) that performs various arithmetic processes related to engine control, a read-only memory (ROM) in which programs and data for engine control are stored, CPU calculation results and sensor A random access memory (RAM) for temporarily storing detection results and the like is provided.

  In addition to the air flow meter 3 and the air-fuel ratio sensor 12 described above, detection signals from various sensors that detect engine operating conditions are input to the electronic control unit 17. The electronic control unit 17 controls the throttle valve 4, the injector 5, the VVT mechanism 7, the spark plug 9, the air pump 15, the air switching valve 16, and the like based on the detection results of such sensors, thereby implementing engine control. .

  Further, as part of engine control, the electronic control unit 17 performs air injection (AI) control for raising the temperature of the catalyst 13 through the supply of secondary air to the exhaust when the engine is started. In the AI control, the fuel injection amount of the injector 5 is increased along with the supply of secondary air to the exhaust. The unburned fuel component in the exhaust gas is increased by enriching the air-fuel ratio by increasing the fuel injection amount, and the secondary air is supplied into the exhaust gas so that the unburned fuel component is burned in the exhaust passage 11. The temperature of the catalyst 13 is increased.

  More specifically, the AI control is performed in the following manner. That is, the electronic control unit 17 activates the air pump 15 and starts counting up the AI counter when the AI control execution condition is satisfied. The AI counter is a counter for measuring the time from the start of operation of the air pump 15, and the value is counted up every specified control cycle after the operation of the air pump 15. The electronic control unit 17 opens the air switching valve 16 to start supplying the secondary air to the exhaust gas and starts increasing the fuel injection amount when the value of the AI counter becomes equal to or greater than the prescribed AI increase determination value. . The supply of the secondary air and the increase in the fuel injection amount here are continued until the temperature of the catalyst 13 rises to its activation temperature.

  Further, the electronic control unit 17 performs valve timing variable control (VVT control) of the intake valve by driving the VVT mechanism 7 during engine operation. When the engine is cold, the air-fuel ratio is rich and hesitation may occur due to the advance of the valve timing of the intake valve, and drivability may deteriorate. Therefore, VVT control when the engine is cold (cold VVT control) Are prohibited in principle, and the valve timing of the intake valve is kept at the most retarded angle. However, in the present embodiment, cold VVT control is permitted only when the following cold VVT control precondition is satisfied.

  The success or failure of the cold VVT control precondition is determined through the processing of the cold VVT control precondition establishment determination routine shown in FIG. The processing of this routine is repeatedly executed by the electronic control unit 17 at regular control cycles during engine operation.

  In this routine, it is determined that the cold VVT control precondition is satisfied when all of the following conditions (A) to (G) are satisfied (YES in all of S100 to S106) (S107). On the other hand, if one or more of the conditions (A) to (G) are not satisfied (determined as NO in any of S100 to S106), it is determined that the cold VVT control precondition is not satisfied (S108). .

  (A) The condition for calculating the target displacement angle is satisfied (S100: YES). The calculation conditions for the target displacement angle are that the rotational phase of the intake camshaft is fixed, that the engine coolant temperature can be detected normally, and that the hydraulic pressure for driving the VVT mechanism 7 is not insufficient. This is true when all the conditions are satisfied and the engine oil pressure has been increased, or when the VVT most retarded angle control is executed after the cold start.

(B) The integrated intake air amount is not more than a predetermined value (S101: YES).
(C) No failure (abnormality) of the VVT mechanism 7 (S102: YES).
(D) The deviation between the target rotational speed of the internal combustion engine and the actual rotational speed is not so large (S103: YES).

(E) The AI control is being executed (S104: YES).
(F) A specified time has elapsed since the start of AI control (S105: YES). More specifically, the value of the above-described AI counter is equal to or greater than a specified cold VVT control execution determination value (> AI increase determination value).

  (G) The number of repeated starting operations is not more than a specified value (S106: YES). The number of repeated startings is counted by a repeated starting number counter. The value of the repeated starting frequency counter is counted up when the engine is started, and is cleared if the amount of decrease in the engine cooling water temperature from the previous trip is greater than or equal to a predetermined value when the ignition switch is turned on. In the present embodiment, the predetermined value is set to “2”, and the cold VVT control precondition is not satisfied when the number of repeated startings is 3 or more.

Then, the effect | action of this Embodiment comprised as mentioned above is demonstrated.
As shown in FIG. 3, when the AI control execution condition is satisfied at time t <b> 1, the AI counter starts to be counted up as the air pump 15 is operated. At time t2, when the value of the AI counter becomes equal to or greater than the AI increase determination value, the air switching valve 16 is opened to start supplying secondary air to the exhaust gas, and the increase in fuel injection amount (AI increase) is increased. Done.

  When the value of the AI counter becomes equal to or higher than the cold VVT control execution determination value at time t3 thereafter, the cold VVT control execution condition is satisfied and the cold VVT control is started. When the cold VVT control is started, the target VVT advance amount is increased from “0”, and the valve timing of the intake valve is advanced.

  As shown in FIG. 4, when AI control is started, the fuel injection amount is increased by AI, and the air-fuel ratio becomes rich. In the present embodiment, cold VVT control is permitted in a state where the air-fuel ratio becomes rich due to such an AI increase.

  In the present embodiment, the cold VVT control is started after a specified time has elapsed after the start of the AI control. Therefore, a time difference is added between the time of enrichment of the air-fuel ratio by increasing the fuel injection amount in AI control and the time of enrichment of the air-fuel ratio by performing cold VVT control, and the air-fuel ratio by the two controls It is possible to suppress the occurrence of a sudden torque increase due to the overlapping of the enrichment.

  Further, in the present embodiment, as shown in FIG. 5, if the value of the repetitive start frequency counter that is counted up every time the start flag indicating that the engine start is completed is 2 or less, the cold VVT The control precondition can be established, and if other conditions are satisfied, the cold VVT control is permitted. On the other hand, when the value of the repetitive start number counter becomes 3 or more, the cold VVT control precondition is not satisfied, and the cold VVT control is prohibited.

  The value of the repeated start counter is cleared if the time from engine stop to restart is sufficiently long and the engine cooling water temperature has decreased by more than a predetermined value from the end of the previous trip when the ignition switch is turned on. The Therefore, after the clearing, the cold VVT control is allowed again.

  As described above, in the present embodiment, the cold VVT control is limited by the number of repeated startings, for the following reason. When the engine is started, a large amount of fuel adheres to the wall surface of the intake port. For this reason, if the internal combustion engine is repeatedly started without a sufficient engine stop time to evaporate the fuel adhering to the intake port, the amount of fuel adhering to the intake port increases each time the engine is started. If the cold VVT control is performed in a state where an excessive amount of fuel is attached to the intake port when the engine is cold, the air-fuel ratio is significantly enriched, which may cause a combustion failure. Therefore, in the present embodiment, the cold VVT control is prohibited when the number of repeated starts increases.

According to the control apparatus for an internal combustion engine of the present embodiment as described above, the following effects can be obtained.
(1) In the present embodiment, the condition that the VVVT control that is prohibited in principle when the engine is cold is exceptionally performed includes that the fuel injection amount increase control by the AI control is being performed. If the cold VVT control is performed when the AI control is not being performed, the drivability deteriorates due to the rich air-fuel ratio and the occurrence of hesitation. However, during the execution of the AI control, the air-fuel ratio is enriched by the AI increase in the fuel injection amount, and the drivability is deteriorated from the start. Therefore, during the execution of the AI control, the cold VVT control can be performed without worrying about deterioration of drivability. In addition, since the fuel injection amount is increased by the AI control, combustion fuel is not insufficient during acceleration and no hesitation occurs. Therefore, according to the present embodiment, variable valve timing control when the engine is cold can be performed without expanding the range of deterioration of drivability.

  (2) In the present embodiment, the condition for performing the variable valve timing control when the engine is cold includes that a specified time has elapsed since the start of the fuel injection amount increase control. Therefore, a time difference can be given between the start of the fuel injection amount increase control and the start of the variable valve timing control, and a rapid torque increase can be suppressed.

  (3) In the present embodiment, the condition for performing the variable valve timing control when the engine is cold includes that the number of repeated startings of the internal combustion engine is equal to or less than a specified value. Therefore, when an excessive amount of fuel adheres to the intake port as a result of repeated starting, the cold VVT control is prohibited, and the air / fuel ratio is not significantly enriched by the cold VVT control. be able to.

In addition, the said embodiment can also be changed and implemented as follows.
In the above embodiment, the number of repeated startings for prohibiting the cold VVT control is set to 3 or more. However, the number may be changed as appropriate according to the state of fuel adhesion on the intake port wall surface of the internal combustion engine. .

  In the above embodiment, when the number of repeated start of the internal combustion engine increases, the cold VVT control is prohibited, but when the amount of fuel adhesion on the intake port wall surface according to the repeated start is not so large, The cold VVT control may not be limited according to the number of repeated starts.

  In the above embodiment, the cold VVT control is permitted after a specified time has elapsed since the start of the increase in the fuel injection amount by the AI control. However, if drastic deterioration in drivability does not occur even if the enrichment of the air-fuel ratio by increasing the fuel injection amount and the enrichment of the air-fuel ratio by the cold VVT control do not occur, the AI control is performed. The cold VVT control may be started simultaneously with the increase of the fuel injection amount.

  In the above embodiment, the cold VVT control is permitted on the condition that the fuel injection amount increase by the AI control for increasing the temperature of the catalyst is being executed. However, the fuel injection is performed in the control other than the AI control. Even when the amount is increased, the cold VVT control may be permitted. For example, the fuel injection amount may be increased in accordance with a shift change of the transmission, and the fact that the increase in the fuel injection amount at this time is being executed is also a condition for executing the cold VVT control. As long as the engine is cold, variable valve timing control can be performed.

Next, the technical idea that can be grasped from the above embodiment and its modifications will be described below.
(B) The control apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the valve timing of the intake valve is set to a most retarded angle while the variable valve timing control is prohibited when the engine is cold. .

  If the valve timing of the intake valve is set to the most retarded angle while the variable valve timing control is prohibited, the valve timing of the intake valve is advanced depending on the execution of the variable valve timing control. If the valve timing of the intake valve is advanced, the valve overlap of the intake / exhaust valve increases, the return of combustion gas to the intake port increases, the vaporization of the fuel adhering to the port wall surface is increased, and the air is exhausted. The fuel ratio becomes richer. Therefore, when the valve timing of the intake valve is set to the most retarded angle while the variable control is prohibited, there is a concern that the drivability deteriorates due to the variable valve timing control of the intake valve when the engine is cold. It is desirable to prohibit execution in principle. If the present invention is applied to such a configuration, variable valve timing control of the intake valve when the engine is cold can be permitted under a certain condition without expanding the range of deterioration of drivability.

  DESCRIPTION OF SYMBOLS 1 ... Intake passage, 2 ... Air cleaner, 3 ... Air flow meter, 4 ... Throttle valve, 5 ... Injector, 6 ... Intake valve, 7 ... Valve timing variable mechanism (VVT mechanism), 8 ... Combustion chamber, 9 ... Spark plug, DESCRIPTION OF SYMBOLS 10 ... Exhaust valve, 11 ... Exhaust passage, 12 ... Air-fuel ratio sensor, 13 ... Catalyst, 14 ... Secondary air supply path, 15 ... Air pump, 16 ... Air switching valve, 17 ... Electronic control unit

Claims (4)

In a control device for an internal combustion engine that performs variable valve timing control that varies the valve timing of an intake valve,
The control device for an internal combustion engine, characterized in that the condition for performing the variable valve timing control when the engine is cold includes that the fuel injection amount increase control is being performed. The control device for an internal combustion engine according to claim 1, wherein the increase control of the fuel injection amount is performed to raise the catalyst temperature. The internal combustion engine control according to claim 1 or 2, wherein a condition for performing the variable valve timing control when the engine is cold includes that a predetermined time has elapsed since the start of the fuel injection amount increase control. apparatus. The control of the internal combustion engine according to any one of claims 1 to 3, wherein the condition for performing the variable valve timing control when the engine is cold includes that the number of repeated startings of the internal combustion engine is not more than a specified value. apparatus.

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