JP2004162532A - Intake air volume control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an intake air volume control device for further properly controlling the intake air volume when performing fuel cut control. <P>SOLUTION: This intake air volume control device of a vehicular internal combustion engine occasionally performs the fuel cut control, and has a cylinder pressure estimating means 26 for estimating cylinder pressure, a means 50 for estimating viscosity or a temperature of engine oil and a target minimum cylinder pressure determining means for determining target minimum cylinder pressure according to the estimated viscosity or temperature, and is characterized by controlling the intake air volume so that a minimum value of the cylinder pressure estimated by the cylinder pressure estimating means 26 becomes the target minimum cylinder pressure when performing the fuel cut control. This invention restrains oil consumption, reduces a catalyst temperature, restrains an increase in an oxygen storage quantity in a catalyst, and also restrains an increase in an exhaust NOx quantity when restored from the fuel cut control. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an intake air amount control device for an internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art In order to improve fuel efficiency and emission, a vehicular internal combustion engine is known which performs fuel cut control for stopping fuel supply to the internal combustion engine when the vehicle satisfies certain conditions, such as when decelerating or going downhill. is there. When the vehicle is decelerated or the like in which such fuel cut control is performed, the intake air amount is limited by intake air amount control means such as a throttle valve and an idle speed control valve (hereinafter, referred to as an "ISC valve"). As a result, the pressure in the intake port and in the cylinder is reduced, and so-called oil rise and oil fall are increased, so that oil consumption may be deteriorated.
[0003]
To cope with such a problem, Japanese Patent Application Laid-Open No. H11-157572 discloses that the opening degree of an ISC valve, which is an intake air amount control means, is controlled in accordance with the rotation speed of an internal combustion engine during the execution of the fuel cut control as described above. The oil consumption is improved by controlling the opening of the ISC valve to increase as the engine speed increases, and controlling the generated negative pressure to a constant value that is not so high. An intake air amount control device is disclosed.
[0004]
However, in this intake air amount control device, since the opening degree of the ISC valve is determined only by the engine speed, the amount of air actually sucked in at the determined opening degree is important for improving oil consumption and the like. Some cases may not be appropriate. That is, the opening degree determined only by the engine speed includes variations due to each internal combustion engine (for example, variations in the flow characteristic of each device of the ISC valve) and aging (for example, aging of the airflow resistance of the air cleaner). Since it is not considered, the amount of air actually taken in may be considerably different from the intended amount of air.
[0005]
If the actual intake air amount is smaller than the intended intake air amount, a higher negative pressure will be generated, and a sufficient oil consumption suppression effect cannot be obtained. Conversely, when the actual intake air amount is larger than the intended intake air amount, more air than necessary flows into the exhaust system catalyst during the fuel cut control, and the catalyst temperature decreases. This may lead to a decrease or an increase in the amount of oxygen stored in the catalyst. As a result, there is a possibility that a problem such as a decrease in the NOx purification capacity immediately after returning from the fuel cut control and an increase in the amount of exhausted NOx may occur.
[0006]
That is, when the catalyst temperature is lowered, the catalyst activity is reduced. Therefore, when heat is taken away by a large amount of inflow air and the catalyst temperature is lowered, the NOx purification ability may be lowered immediately after returning from the fuel cut control. There is. When the amount of oxygen stored in the catalyst increases, the amount of NOx that can be stored decreases, and the stored oxygen is released immediately after returning from the fuel cut control, thereby increasing the air-fuel ratio around the catalyst. It is also conceivable that the reduction effect of the catalyst is reduced and the NOx purification capability is reduced.
[0007]
Furthermore, it is known that the presence of oxygen when the catalyst temperature is high causes the catalyst particles to coarsen and accelerates the deterioration of the catalyst, and that the catalyst temperature may be high immediately after the start of the fuel cut control or the like. Therefore, when the intake air amount is larger than necessary, there is a concern that catalyst deterioration may be accelerated.
[0008]
[Patent Document 1]
JP-A-63-65153 [Patent Document 2]
JP 2001-164970 A
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and an object of the present invention is to provide an intake air amount control device that more appropriately controls an intake air amount during execution of the fuel cut control.
[0010]
[Means for Solving the Problems]
The present invention provides an intake air amount control device described in the claims as means for solving the above problems.
That is, the present invention is an intake air amount control device for an internal combustion engine for a vehicle, in which fuel cut control for stopping fuel supply may be performed even in a running state in which the vehicle speed is not zero. In-cylinder pressure estimating means, means for estimating the viscosity or temperature of engine oil, and target minimum in-cylinder pressure determining means for determining a target minimum in-cylinder pressure according to the estimated viscosity or temperature, During the execution of the fuel cut control, the intake air amount is controlled such that the minimum value of the in-cylinder pressure estimated by the in-cylinder pressure estimating means becomes the target minimum in-cylinder pressure. An air flow control device is provided.
[0011]
According to the present invention, when the fuel cut control is being performed, the intake air amount is controlled so that the minimum pressure in the cylinder becomes the target minimum cylinder pressure determined according to the engine oil viscosity or the temperature. Therefore, it is possible to prevent a high negative pressure from being generated in the intake port and the cylinder, and it is possible to suppress deterioration of oil consumption due to an increase in so-called oil rise and oil fall. In the present invention, in particular, the target minimum in-cylinder pressure is determined in accordance with the engine oil viscosity or temperature (the higher the temperature, the lower the viscosity), which is directly related to the actual oil rise or oil fall tendency. In addition, the intended suppression of oil consumption deterioration can be reliably achieved, and the amount of intake air can be minimized.
[0012]
By limiting the intake air amount to the minimum necessary in this way, it is possible to prevent more air than necessary from flowing into the exhaust system catalyst during the execution of the fuel cut control as described above. And the increase in the amount of oxygen stored in the catalyst can be suppressed, and the increase in the amount of exhaust NOx when returning from the fuel cut control can be suppressed. At the same time, the amount of oxygen flowing into the catalyst during the execution of the fuel cut control as described above can be minimized, so that deterioration of the catalyst can be reduced.
[0013]
That is, according to the present invention, the intake air amount during the execution of the fuel cut control as described above can be more appropriately controlled. Here, in order to control the intake air amount so that the minimum value of the in-cylinder pressure becomes the target minimum in-cylinder pressure, the target minimum in-cylinder pressure has a certain width, and a certain range is set. This includes the case where control is performed so that the minimum value of the in-cylinder pressure described above is entered.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a case where the intake air amount control device of the present invention is applied to a direct injection type spark ignition type internal combustion engine. Note that the present invention can be applied to other types of internal combustion engines such as a port injection type internal combustion engine and a compression ignition type internal combustion engine.
[0015]
Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a spark plug, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Denotes an exhaust valve, and 10 denotes an exhaust port.
The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11. The surge tank 12 is connected to an intake duct 13. A throttle valve 17 connected to an accelerator pedal 40 is disposed in the intake duct 13. A bypass path 24 is provided to bypass the throttle valve 17, and an ISC valve (idle speed control valve) 25 is provided in the bypass path 24. Further, an air cleaner 18 is arranged at an inlet of the intake duct 13.
[0016]
On the other hand, the exhaust port 10 is connected to an exhaust gas purification device 22 via an exhaust manifold 19 and an exhaust pipe 20. A catalyst 23 for purifying NOx and the like in the exhaust gas is arranged in the exhaust gas purifying device 22.
Each fuel injection valve 6 is connected to a fuel reservoir, a so-called delivery pipe 27, via a fuel supply pipe 6a. Fuel is supplied into the delivery pipe 27 from an electric control type variable discharge fuel pump 28. The fuel supplied into the delivery pipe 27 is supplied to the fuel injection valve 6 via each fuel supply pipe 6a. A fuel pressure sensor 29 for detecting the fuel pressure inside the delivery pipe 27 is attached to the delivery pipe 27. The discharge amount of the fuel pump 28 is controlled based on the output signal of the fuel pressure sensor 29 so that the fuel pressure in the delivery pipe 27 becomes the target fuel pressure.
[0017]
In the internal combustion engine shown in FIG. 1, a water temperature sensor 50 for detecting the temperature of cooling water for cooling the internal combustion engine is attached to the cylinder block 2, and an in-cylinder pressure sensor for detecting the pressure in the cylinder at the cylinder head 3. 26 are provided.
The electronic control unit (ECU) 30 is a known type of digital computer in which a CPU (central processing unit), a RAM (random access memory), a ROM (read only memory), and an input / output port are connected by a bidirectional bus. In addition to performing basic control of the engine such as fuel injection amount control by exchanging signals with the components of the engine, it also controls intake air amount during execution of fuel cut control as described below. The above-described in-cylinder pressure sensor 26, fuel pressure sensor 29, and water temperature sensor 50 are connected to the ECU 30, and their output signals are supplied to the ECU 30.
[0018]
A load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40. The load sensor 41 is connected to the ECU 30, and the output voltage is input to the ECU 30. The ECU 30 is also connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. Further, the ignition plug 5, the fuel injection valve 6, the ISC valve 25, the fuel pump 28, and the like are also connected to the ECU 30. These components can be controlled by signals from the ECU 30. I have.
[0019]
In the internal combustion engine having the above-described configuration, in order to improve fuel efficiency and emission, the vehicle speed is not zero when the vehicle satisfies predetermined conditions, such as during deceleration or downhill. Also, the so-called fuel cut control for stopping the fuel supply is performed. While the fuel cut control is being performed, the throttle valve 17 is almost fully closed. However, in the internal combustion engine, as described below, the ISC valve 25 is controlled to control the intake air amount. The in-cylinder pressure is adjusted.
[0020]
Hereinafter, the intake air amount control during the fuel cut control performed in the internal combustion engine will be described with reference to the flowchart of FIG. The flowchart of FIG. 2 shows a control routine of intake air amount control performed in the internal combustion engine during the execution of the fuel cut control. This control routine is executed by the ECU 30 by interruption every predetermined time.
[0021]
When the control routine starts, first, at step 101, it is determined whether or not the fuel cut control is being performed. If it is determined in step 101 that the fuel cut control is not being performed, the control routine ends. If it is determined that the fuel cut control is being performed, the process proceeds to step 103.
[0022]
In step 103, the engine oil temperature (hereinafter, referred to as "oil temperature") To is estimated. In the present embodiment, the oil temperature To is estimated from the engine cooling water temperature detected by the water temperature sensor 50. That is, the relationship between the detected engine coolant temperature and the oil temperature To is obtained in advance through experiments or the like and is made into a map, and the oil temperature To is estimated from the engine coolant temperature based on this map. The map is stored in the ROM of the ECU 30.
[0023]
The oil temperature To may be estimated by another method. For example, the estimation may be made based on the history of the engine operation state (required torque, engine speed, etc.) within a predetermined time up to that time. Also in this case, a corresponding map is created in advance and stored in the ROM of the ECU 30. Alternatively, a temperature sensor for detecting the oil temperature To may be provided to directly detect the oil temperature To.
[0024]
When the oil temperature To is estimated in step 103, the target minimum in-cylinder pressure Pmo is determined based on the oil temperature To in a succeeding step 105. The target minimum in-cylinder pressure Pmo is the minimum in-cylinder pressure at which oil consumption can be suppressed to an intended level, and depends on the oil temperature To.
That is, the oil consumption is deteriorated due to the decrease in the pressure in the cylinder because the oil rises in the combustion chamber from the gap between the piston 4 and the cylinder block 2 and the oil rise and fall between the intake and exhaust valves 7 and 9 and the valve guide. The main cause is that the so-called oil drop that leaks oil into the combustion chamber from the gap increases. Here, if the viscosity of the oil is low, the oil easily passes through the gap, and if the pressure in the cylinder is the same, the lower the viscosity of the oil, the more the oil rises or falls, and the oil consumption becomes worse.
[0025]
On the other hand, the oil viscosity depends on the oil temperature To, and decreases as the oil temperature To increases. Therefore, the higher the oil temperature To is, the more likely the oil rises and falls, and the worse the oil consumption becomes.
From the above, in order to suppress the oil consumption to the same level, the higher the oil temperature To, the higher the minimum in-cylinder pressure Pm needs to be maintained, so the target minimum in-cylinder pressure Pmo determined in step 105 is determined. Becomes higher as the oil temperature To estimated at step 103 is higher.
[0026]
In the present embodiment, the minimum in-cylinder pressure Pm at which the intended oil consumption suppressing effect can be obtained at each oil temperature To is obtained in advance through experiments or the like to form a map, and the map is obtained in step 103 based on this map. The target minimum in-cylinder pressure Pmo according to the determined oil temperature To is determined. As is clear from the above description, since the oil temperature To is used as an index indicating the oil viscosity in the present embodiment, a map in which the oil temperature To corresponds to the target minimum in-cylinder pressure Pmo. Similarly to the above, a map in which the target minimum in-cylinder pressure Pmo is determined according to the oil viscosity can be created. Based on this map, the oil viscosity is determined instead of the oil temperature To to determine the target minimum in-cylinder pressure Pmo. Pmo may be determined.
[0027]
When the target minimum in-cylinder pressure Pmo is determined in step 105, first, in step 107, the target intake air amount Svo is determined based on the engine speed NE and the target minimum in-cylinder pressure Pmo. The target intake air amount Svo is an intake air amount such that the minimum in-cylinder pressure Pm becomes the target minimum in-cylinder pressure Pmo at the time of the engine speed NE, and increases as the engine speed NE increases. It increases as the in-cylinder pressure Pmo increases. In the present embodiment, a map of the target intake air amount Svo with respect to the engine speed NE and the target minimum in-cylinder pressure Pmo is created in advance and stored in the ROM of the ECU 30, and based on this, the target intake air amount Svo is determined. It is determined.
[0028]
Subsequently, in step 107, the target opening Vao of the ISC valve 25 corresponding to the target intake air amount Svo is further determined. During the execution of the fuel cut control, the throttle valve 17 is almost fully closed, and thus the target opening Vao is an opening at which the intake air amount via the ISC valve 25 becomes the target intake air amount Svo. In the present embodiment, the relationship between the amount of intake air via the ISC valve 25 and the opening degree Va of the ISC valve 25 is determined in advance by experiments or the like, and the target intake air amount Svo previously determined based on this relationship is determined. The corresponding target opening Vao is determined.
[0029]
In the above description of step 107, first, the target intake air amount Svo is determined from the engine speed NE and the target minimum in-cylinder pressure Pmo, and then the target opening degree Vao is determined from the target intake air amount Svo. As described above, the target opening degree Vao may be directly determined from the engine speed NE and the target minimum in-cylinder pressure Pmo. That is, by incorporating the relationship between the intake air amount via the ISC valve 25 and the opening Va of the ISC valve 25 into the map for determining the target intake air amount Svo, the engine speed NE and the target minimum in-cylinder pressure Pmo can be reduced. The target opening Vao can be determined directly from the engine speed NE and the target minimum in-cylinder pressure Pmo using this map.
[0030]
When the target opening Vao of the ISC valve 25 is determined in step 107, in step 109, the ISC valve 25 is controlled such that the opening Va becomes the target opening Vao. Then, in step 111, the minimum value of the in-cylinder pressure detected by the in-cylinder pressure sensor 26 (that is, the in-cylinder pressure detected in one cycle when the four strokes of intake, compression, expansion, and exhaust are defined as one cycle) Is determined to be equal to the target minimum in-cylinder pressure Pmo determined in step 105. The minimum value Pm of the in-cylinder pressure is usually detected during the intake stroke.
[0031]
If it is determined in step 111 that the minimum value Pm of the in-cylinder pressure is equal to the target minimum in-cylinder pressure Pmo, the present control routine ends. If it is determined that they are not equal, step 113 is executed. Proceed to. In the determination in step 111, the target minimum in-cylinder pressure Pmo has a certain width, and if the minimum value Pm of the in-cylinder pressure falls within the range, the minimum value Pm of the in-cylinder pressure is set to the target value. It may be determined that it is equal to the minimum in-cylinder pressure Pmo.
[0032]
In step 113, it is determined whether the minimum value Pm of the in-cylinder pressure is larger than the target minimum in-cylinder pressure Pmo. If it is determined in step 113 that the minimum value Pm of the in-cylinder pressure is larger than the target minimum in-cylinder pressure Pmo, the process proceeds to step 115, in which the opening Va of the ISC valve 25 is shifted in the closing direction by a predetermined opening ΔVa. Controlled. As a result, the amount of intake air via the ISC valve 25 is reduced, and the minimum value Pm of the in-cylinder pressure is reduced.
[0033]
On the other hand, if it is determined in step 113 that the minimum value Pm of the in-cylinder pressure is smaller than the target minimum in-cylinder pressure Pmo, the process proceeds to step 117, and the opening Va of the ISC valve 25 is opened by a predetermined opening ΔVa. Controlled in the direction. As a result, the amount of intake air via the ISC valve 25 increases, and the minimum value Pm of the in-cylinder pressure increases. When the opening of the ISC valve 25 is controlled in step 115 or step 117, the process returns to step 111 and the control therefrom is repeated.
[0034]
As described above, in the present embodiment, in the control from step 111 to step 117, the opening Va of the ISC valve 25 is determined by a map or the like in step 107 in accordance with the minimum value Pm of the actual in-cylinder pressure. The target opening degree Vao is corrected. For this reason, the opening degree Va of the ISC valve 25 is set to the above-mentioned value due to a variation (for example, a variation in the flow characteristic of each device of the ISC valve 25) or a variation with the passage of time (for example, a variation with time in the ventilation resistance of the air cleaner 18). Even when the amount of air actually taken in when the target opening degree Vao is set is considerably different from the intended amount of air, the minimum value Pm of the in-cylinder pressure is appropriately adjusted so as to become the target minimum in-cylinder pressure Pmo. The amount of intake air can be controlled. Further, since the minimum value of the pressure in the intake port 8 is considered to be substantially the same as the minimum value Pm of the in-cylinder pressure detected during the intake stroke, when the control routine shown in FIG. It is considered that the minimum value of the pressure in the port 8 is also controlled to be substantially equal to the target minimum in-cylinder pressure Pmo.
[0035]
As described above, according to the present embodiment, during execution of the fuel cut control, the target minimum in-cylinder pressure Pmo in which the intake air amount is controlled and the minimum pressure Pm in the cylinder is determined according to the oil temperature To. Therefore, a high negative pressure is prevented from being generated in the intake port 8 and the cylinder, and deterioration of oil consumption due to so-called oil rise and oil fall can be suppressed. In particular, the target minimum in-cylinder pressure Pmo is determined according to the oil temperature To (the higher the temperature, the lower the viscosity), which is related to the actual tendency of the oil to rise or drop. It is possible to reliably suppress the deterioration of the oil consumption and to minimize the intake air amount.
[0036]
By keeping the intake air amount to the minimum necessary in this way, it is possible to prevent more air than necessary from flowing into the catalyst 23 of the exhaust system during the execution of the fuel cut control. The increase in the amount of oxygen stored in the catalyst 23 is suppressed, and the increase in the amount of exhaust NOx when returning from the fuel cut control can be suppressed. Further, for example, immediately after the cold start, it is necessary to quickly raise the catalyst temperature. However, when the catalyst temperature is low, the oil temperature To is usually low. Accordingly, the target minimum in-cylinder pressure Pmo is set to be low, and the amount of intake air is suppressed to a small value. As described above, according to the above-described intake air amount control, the intake air amount is reduced when the catalyst temperature is low, such as shortly after the cold start, so that the catalyst temperature decrease is suppressed, and the subsequent rise of the catalyst temperature is suppressed. It is advantageous in terms of warmth.
Furthermore, by keeping the intake air amount to the minimum necessary amount, the amount of oxygen flowing into the catalyst during the fuel cut control can be minimized at the same time, so that deterioration of the catalyst can be suppressed.
[0037]
In the control routine shown in FIG. 2, the target intake air amount Svo is determined from the engine speed NE and the target minimum in-cylinder pressure Pmo, and the target opening Vao of the ISC valve 25 is determined from the target intake air amount. However, the present invention is not limited to this, and the target opening degree Vao may be determined by another method.
[0038]
That is, for example, the target opening degree Vao is set to a predetermined opening degree or an opening degree determined only by the engine speed NE (in this case, a map of the target opening degree Vao with respect to the engine speed NE is created in advance. The opening Va of the ISC valve 25 is determined so that the minimum pressure Pm in the cylinder becomes the target minimum cylinder pressure Pmo determined in step 105 in the subsequent steps 111 to 117. You may make it control. In such a case, the control corresponding to step 107 can be simplified, but the control accuracy of the in-cylinder pressure immediately after the start of the fuel cut control is reduced.
[0039]
In the above description, the case where the intake air amount control means during the fuel cut control is the ISC valve 25 has been described. However, the present invention is not limited to this, and the intake air amount control means during the fuel cut control is performed. May be other means. For example, if the throttle valve is an electronic throttle valve and does not have an ISC valve, the intake air amount control means during the fuel cut control is an electronic throttle valve. In this case, see the flowchart of FIG. By controlling the electronic throttle valve instead of the ISC valve 25 according to the procedure described above, substantially the same operation and effect as in the above-described embodiment can be obtained.
[0040]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an intake air amount control device that more appropriately controls an intake air amount during execution of fuel cut control. According to the intake air amount control device, oil consumption can be reliably suppressed, and the intake air amount during the execution of the fuel cut control can be kept to a minimum, thereby lowering the catalyst temperature and storing oxygen in the catalyst. The increase in the amount is suppressed, and the increase in the amount of exhaust NOx when returning from the fuel cut control can be suppressed. At the same time, deterioration of the catalyst can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a case where an intake air amount control device of the present invention is applied to a direct injection type spark ignition type internal combustion engine.
FIG. 2 is a flowchart illustrating a control routine of intake air amount control during execution of fuel cut control.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine body 2 ... Cylinder block 3 ... Cylinder head 4 ... Piston 5 ... Spark plug 6 ... Electric control type fuel injection valve 7 ... Intake valve 8 ... Intake port 9 ... Exhaust valve 10 ... Exhaust port 11 ... Intake branch pipe 12 ... Surge tank 13 Intake duct 17 Throttle valve 18 Air cleaner 22 Exhaust gas purifying device 23 Catalyst 24 Bypass path 25 Idle speed control valve (ISC valve)
26 ... in-cylinder pressure sensor 30 ... electronic control unit (ECU)
40 ... accelerator pedal 50 ... water temperature sensor

Claims (1)

An intake air amount control device for a vehicle internal combustion engine in which fuel cut control for stopping fuel supply may be performed even in a running state in which the vehicle speed is not zero,
In-cylinder pressure estimating means for estimating in-cylinder pressure;
Means for estimating the viscosity or temperature of the engine oil;
Having a target minimum in-cylinder pressure determining means for determining a target minimum in-cylinder pressure according to the estimated viscosity or temperature,
During the execution of the fuel cut control, the intake air amount is controlled such that the minimum value of the in-cylinder pressure estimated by the in-cylinder pressure estimating means becomes the target minimum in-cylinder pressure. Air flow control device.

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