JP2010077909A - Method for controlling spark ignition type direct injection engine and device thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To satisfy combustion stability and reduction of pumping loss in a light load zone. <P>SOLUTION: Fuel is directly injected into a combustion chamber from a fuel injection valve and air fuel mixture in the combustion chamber is ignited by a spark plug. A prescribed period during which a piston moves to an intake stroke bottom dead center under a condition where an intake valve opens by opening the intake valve from an early stage of intake stroke and closing the same in a middle of the intake stroke in the light load zone, and fuel is injected during the prescribed period. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a control method and apparatus for a spark ignition direct injection engine.

  Engines, particularly spark-ignition engines for automobiles, have a strong tendency to be a direct injection type in which fuel is directly injected into a combustion chamber from the viewpoint of improving efficiency. As a fuel for a spark ignition direct injection engine, gasoline is generally used, but recently, a mixed fuel in which ethanol is mixed with gasoline, ethanol 100% (97% ethanol + 3% water, etc.) In many cases, fuels including those containing water are used. Examples of the mixed fuel obtained by mixing ethanol with gasoline include E10 (containing 10% ethanol), E25 (containing 25% ethanol), E85 (containing 85% ethanol), and the like, depending on the ethanol content.

  In Patent Document 1, when a plurality of types of fuels having different octane numbers, for example, gasoline, ethanol, and a mixed fuel of ethanol and gasoline are selectively used, a mirror having a low octane number is used at low load. A cycle is disclosed in which combustion is performed at a high compression ratio while using a high-octane fuel at high loads.

  Further, in Patent Document 2, a fuel containing alcohol such as ethanol has a low boiling point and poor ignitability. Therefore, when alcohol fuel or a mixed fuel of alcohol and gasoline is used, the fuel is used. It is disclosed that the engine is started by adding hydrogen.

Furthermore, Patent Document 3 is provided with variable valve means for changing the lift amount and the valve opening angle of the intake valve, and during idling, the intake valve is closed before the intake stroke bottom dead center to reduce pumping loss. It is disclosed that the intake valve is quickly closed.
JP 2008-031948 A JP 2007-278254 A JP 2006-348774 A

  By the way, when the engine is in a low load region, particularly when idling, there is a strong demand for improved fuel consumption by reducing pumping loss. It is also important how to ensure combustion stability in the low load region of the engine. In particular, when using a fuel with poor ignitability such as ethanol, or when using a mixture of fuel with poor ignitability and gasoline, how to ensure combustion stability in a low load region is a problem. Become.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a spark ignition direct injection engine control method capable of satisfying both reduction of pumping loss and combustion stability in a low load region. And providing an apparatus thereof.

In order to achieve the above object, the following solution is adopted in the control method of the present invention. That is, as described in claim 1 in the claims,
A control method for a spark ignition direct injection engine in which fuel is directly injected from a fuel injection valve into a combustion chamber, and an air-fuel mixture in the combustion chamber is ignited by an ignition plug,
In the low load region of the engine, the intake valve is opened from the beginning of the intake stroke and closed during the intake stroke to set a predetermined period during which the piston moves to the bottom dead center of the intake stroke with the intake valve closed Then, fuel is injected during the predetermined period.
It is like that.

  According to the above-described solution, the pumping loss can be reduced by quickly closing the intake air in a low load region of the engine. Also, during a predetermined period from when the intake valve is closed to the intake stroke bottom dead center, a very large negative pressure is generated in the cylinder as the piston moves toward the intake stroke bottom dead center. Therefore, by injecting fuel into this extremely negative pressure atmosphere, even if a fuel with poor ignitability such as ethanol is used, it is sufficiently vaporized and atomized (evaporated), and ignition is performed. Of course, stable combustion is performed as well as stable combustion.

A preferred mode based on the above solution is as described in claim 2 and the following claims. That is,
The fuel injected from the fuel injection valve contains at least ethanol (corresponding to claim 2). In this case, even when a fuel containing ethanol with poor vaporization and atomization is used, combustion stability can be sufficiently ensured in a low load region.

  The intake valve is controlled so that the valve closing timing is delayed as the engine speed and the engine load increase with the vicinity of the intake top dead center as the valve opening start timing. Correspondence). In this case, both the pumping loss reduction and the torque securing can be satisfied at a high level over the entire operation range.

Determine the ethanol content in the total fuel injected from the fuel injection valve,
In the low load region of the engine, when the content ratio of ethanol in the total fuel is determined to be greater than or equal to a predetermined value, fuel injection is performed during the predetermined period, while the content ratio of ethanol is determined to be less than the predetermined amount When performing fuel injection during the opening period of the intake valve,
(Corresponding to claim 4). In this case, in the low load region of the engine, a fuel that has low ethanol content and good combustibility was used while ensuring combustion stability when using fuel containing a large amount of ethanol that deteriorates combustibility. When injecting fuel during the opening period of the intake valve (that is, prohibiting fuel injection during a predetermined period when the in-cylinder negative pressure is extremely high), the injected fuel may fly too much under a large negative pressure. By preventing or suppressing, a situation where a large amount of fuel adheres to the wall surface of the combustion chamber can be prevented or suppressed.

In order to achieve the above object, the following solution is adopted in the control device of the present invention. That is, as described in claim 5 in the claims,
A control device for a spark ignition direct injection engine that directly injects fuel into a combustion chamber from a fuel injection valve and ignites an air-fuel mixture in the combustion chamber with an ignition plug,
Variable valve means for changing the closing timing of the intake valve while opening the intake valve from the beginning of the intake stroke;
In a low load region of the engine, the variable valve means is controlled to close the intake valve in the middle of the intake stroke, thereby setting a predetermined period during which the piston moves to the intake stroke bottom dead center with the intake valve closed. Valve control means for
Injection control means for performing fuel injection from the fuel injection valve in the predetermined period in a low load region of the engine;
It is supposed to be equipped with. According to the said solution technique, the control apparatus for performing the control method of Claim 1 is provided.

  According to the present invention, it is possible to satisfy both the pumping loss reduction and the combustion stability in the engine low load region.

  In FIG. 1, E is an engine, particularly an automobile engine. In the embodiment, E is an in-line four-cylinder engine. In FIG. 1, one cylinder is representatively shown, and a combustion chamber 4 is defined by a cylinder 1, a cylinder head 2, and a piston 3 slidably fitted in the cylinder 1. A fuel injection valve 5 and a spark plug 6 are disposed facing the combustion chamber 4.

  In the combustion chamber 4, two intake ports 10 and two exhaust ports 11 formed in the cylinder head 2 are opened. In FIG. 1, one of the two intake ports 10 and the two exhaust ports 11 is disposed in a direction perpendicular to the paper surface and is not depicted in FIG. 1. The intake port 10 is opened and closed by an intake valve 12, and the exhaust port 11 is opened and closed by an exhaust valve 13. A camshaft for driving the intake valve 12 to open and close is indicated by reference numeral 14, and a camshaft for driving the exhaust valve 13 to open and close is indicated by reference numeral 15. Each of the camshafts 14 and 15 is interlocked with a crankshaft (that is, the piston 3) (not shown). A lift adjusting mechanism 16 is incorporated in the interlocking mechanism between the crankshaft and the camshaft 14 for the intake valve 12. The lift adjustment mechanism 16 changes the valve opening characteristics of the intake valve 12 as will be described later.

  The intake port 10 in each cylinder is connected to a surge tank 21 via a branch intake passage 20. A common intake passage 22 is connected to the surge tank 21. An air cleaner 23 is disposed at the upstream end of the common intake passage 22, and a throttle valve 24 is disposed downstream of the air cleaner 23. On the other hand, the exhaust gas from the exhaust port 11 is discharged to the atmosphere through the exhaust passage 30. An exhaust gas purification device 31 such as a three-way catalyst is disposed in the exhaust passage 30. An air-fuel ratio sensor S4 is disposed in the exhaust passage 30 upstream of the exhaust gas purification device 31. The air-fuel ratio sensor S4 may be one that turns on and off at the theoretical air-fuel ratio, and may be one that can detect the air-fuel ratio continuously.

  In FIG. 2, U is a controller (control unit) configured using a microcomputer. The controller U controls the fuel injection valve 5, the spark plug 6, and the lift adjustment mechanism 16 described above. The controller U receives signals from various sensors S1 to S4. The sensor S1 detects an engine load. In the embodiment, the sensor S1 detects an intake air amount. The sensor S2 detects the engine speed. Sensor S3 is the air-fuel ratio sensor described above. The sensor S4 detects the rotational position of the crankshaft, that is, the crank angle.

  An outline of the control of the controller U will be described with reference to FIGS. First, FIG. 3 shows a change state of the valve opening characteristic of the intake valve 12 by the lift changing mechanism 16. As is apparent from FIG. 3, the opening timing of the intake valve 12 is always set to the beginning of the intake stroke (near the intake top dead center). On the other hand, the closing timing of the intake valve 12 is greatly changed. This will be described in detail below. First, what is indicated by the α line is the earliest, with the lift amount being the smallest and the valve closing timing being at an approximately intermediate position of the intake stroke. Further, as indicated by the β line, the lift amount is the largest, the valve closing timing is the latest, and the valve closing timing is a time that is considerably late after the bottom dead center of the intake stroke. Then, between the α line and the β line, the valve closing timing is set to be delayed as the lift amount increases.

  The valve opening characteristics of the intake valve 12 are continuously variable or changed step by step between the α ray and the β ray. In this case, as shown in FIG. 4, the closer to the β-ray, the higher the engine speed and the higher the engine load. The α line corresponds to the idle time, and the β line corresponds to the full load or the maximum allowable rotational speed. In the low load region, particularly when idling, the α ray is set so that the pumping loss can be reduced most effectively. Then, as the engine load increases or the engine speed increases, the closing timing of the intake valve 12 is gradually delayed so that the effect of reducing the pumping loss is gradually reduced. The period during which the valve 12 is opened and the valve opening lift amount are increased, which is advantageous for securing torque). Note that the lift changing mechanism 16 for obtaining the valve opening characteristics as shown in FIG. 3 can be realized by using various conventionally proposed mechanisms such as the one shown in Patent Document 3, for example. Further, if the variable lift mechanism 16 is selected to open and close the intake valve 12 with an electromagnetic coil, for example, an arbitrary lift amount and an arbitrary valve opening angle (crank angle during the valve opening period) can be obtained. Is possible.

  When the valve opening characteristic indicated by the α line is set, for example, when the intake valve is quickly closed, the crank angle from when the intake valve 12 is closed to the bottom dead center of the intake stroke becomes considerably large. At this time, the piston 3 moves toward the bottom dead center of the intake stroke during a predetermined period T between the time when the intake valve 12 is closed and the bottom dead center of the intake stroke. A large negative pressure is generated. Therefore, by performing fuel injection during the predetermined period T (the fuel injected during the predetermined period T is indicated by hatching in FIG. 3), the fuel is vaporized, that is, vaporized and atomized well. Therefore, even if the fuel is poorly vaporized or atomized, it is ignited satisfactorily and stable combustion is ensured thereafter. More specifically, for example, a fuel that is poorly vaporized and atomized is injected in a predetermined period T, such as a mixed fuel of ethanol fuel or a mixture of ethanol and gasoline and containing a large amount of ethanol (for example, 10% or more). Thus, good ignition and subsequent stable combustion can be ensured. On the other hand, in the medium load and high load regions, fuel injection is performed during a period in which the intake valve 12 is open during the intake stroke. As a result, fuel injection is performed when the combustion chamber is not at a large negative pressure, and the injected fuel flies too much and adheres to the top surface of the piston 3 and the inner wall surface of the combustion chamber 4 in large quantities. The situation will be prevented or suppressed.

  FIG. 5 is a flowchart showing an example of control performed by the controller U. This flowchart will be described below. In the following description, Q indicates a step. First, in Q1, signals from various sensors S1 to S4 are read. Thereafter, in Q2, the valve opening characteristic of the intake valve 12 is set to the valve opening characteristic corresponding to the current engine load and engine speed according to the map shown in FIG.

  After Q2, at Q3, it is determined whether or not the stoichiometric air-fuel ratio is detected by the air-fuel ratio sensor S3. If the determination in Q3 is YES, the content ratio of ethanol is determined in Q4 based on the current fuel injection amount. That is, in the embodiment, it is assumed that a mixed fuel of gasoline and ethanol (including the case where ethanol is 100% or gasoline 100%) is used, and the determination of Q4 is the content ratio of ethanol to gasoline It becomes discrimination of. This determination is made based on the difference in the theoretical air-fuel ratio between ethanol and gasoline. Specifically, the theoretical air-fuel ratio of gasoline is 14.7, whereas the theoretical air-fuel ratio of ethanol is 9, so that the value of the theoretical air-fuel ratio is greatly different. This means that the larger the fuel injection amount at the stoichiometric air-fuel ratio, the higher the ethanol content ratio. Therefore, based on the fuel injection amount at the stoichiometric air-fuel ratio, the ethanol in all fuels The content ratio can be known. If an air-fuel ratio sensor S3 that can detect the air-fuel ratio in a continuously variable manner is used, the content ratio of ethanol can be known even when the detected air-fuel ratio is other than the stoichiometric air-fuel ratio. In addition, the content ratio of ethanol is changed at the time of refueling. If the content ratio of ethanol immediately after refueling is determined, the process of determining the content ratio of ethanol is substantially unnecessary until the next refueling. It becomes.

  After Q4 or when NO is determined in Q3, it is determined in Q5 whether or not the ethanol content ratio is determined. If YES in Q5, it is determined in Q6 whether the ethanol content is equal to or greater than a predetermined value (for example, 10%). If the determination in Q6 is YES, it is determined whether or not the current load range is a low load region (for example, a load region of 20% or less of the total load). When the determination in Q7 is YES, fuel injection is performed during a predetermined period T in which a large negative pressure is generated in the combustion chamber 4.

  If NO in the determination of Q7 or NO in the determination of Q6, fuel injection is performed in Q9 while the intake valve 12 is open. If the determination in Q5 is NO, the process proceeds to Q7.

  Although the embodiment has been described above, the present invention is not limited to the embodiment, and can be appropriately changed within the scope described in the scope of claims. For example, the invention includes the following cases. . The engine E may be of an appropriate type such as a supercharged type, three cylinders, six cylinders or more. Of course, the object of the present invention is not limited to what is explicitly stated, but also implicitly includes providing what is substantially preferred or expressed as an advantage.

The simplified system diagram which shows an example of the engine to which this invention was applied. The block diagram which shows the example of a control system of this invention. The characteristic view which shows a mode that the valve opening characteristic of an intake valve is changed. The map for changing the valve opening characteristic of FIG. 3 according to an engine load and an engine speed. The flowchart which shows the example of control of this invention.

Explanation of symbols

U: Controller E: Engine 4: Combustion chamber 5: Fuel injection valve 6: Spark plug 11: Intake valve 12: Exhaust valve 16: Lift adjustment mechanism S1: Sensor (engine load)
S2: Sensor (engine speed)
S3: Sensor (air-fuel ratio sensor)
S4: Sensor (crank angle)

Claims (5)

A control method for a spark ignition direct injection engine in which fuel is directly injected from a fuel injection valve into a combustion chamber, and an air-fuel mixture in the combustion chamber is ignited by an ignition plug,
In the low load region of the engine, the intake valve is opened from the beginning of the intake stroke and closed during the intake stroke to set a predetermined period during which the piston moves to the bottom dead center of the intake stroke with the intake valve closed Then, fuel is injected during the predetermined period.
A control method for a spark ignition direct injection engine. In claim 1,
A control method for a spark ignition direct injection engine, wherein the fuel injected from the fuel injection valve contains at least ethanol. In claim 1,
The intake valve is controlled so that the valve closing timing is delayed as the engine speed and the engine load increase with the vicinity of the intake top dead center as the valve opening start timing.
A control method for a spark ignition direct injection engine. In claim 2,
Determine the ethanol content in the total fuel injected from the fuel injection valve,
In the low load region of the engine, when the content ratio of ethanol in the total fuel is determined to be greater than or equal to a predetermined value, fuel injection is performed during the predetermined period, while the content ratio of ethanol is determined to be less than the predetermined amount When performing fuel injection during the opening period of the intake valve,
A control method for a spark ignition direct injection engine. A control device for a spark ignition direct injection engine that directly injects fuel into a combustion chamber from a fuel injection valve and ignites an air-fuel mixture in the combustion chamber with an ignition plug,
Variable valve means for changing the closing timing of the intake valve while opening the intake valve from the beginning of the intake stroke;
In a low load region of the engine, the variable valve means is controlled to close the intake valve in the middle of the intake stroke, thereby setting a predetermined period during which the piston moves to the intake stroke bottom dead center with the intake valve closed. Valve control means for
Injection control means for performing fuel injection from the fuel injection valve in the predetermined period in a low load region of the engine;
A control device for a spark-ignition direct-injection engine.

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