JPH11303717A - Cylinder injection internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce deterioration of durability of a spark plug easily generated by the side effect of self purifying operation, while keeping a wide range of ignition condition of an engine by using the spark plug of two-electrode type capable of preventing pollution of the plug by self purifying operation, in a cylinder injection internal combustion engine of spark ignition type. SOLUTION: This cylinder injection internal combustion engine is provided with a fuel injection valve 4 injecting fuel directly to a combustion chamber 1C, spark plug 5 provided so as to appear in the combustion chamber 1C to have a pair of side electrodes provided by interposing a center axial line of an insulator, and an ignition energy control means 23B decreasing ignition energy of the spark plug 5 in an operation region where air/fuel ratio of the engine is in the vicinity of theoretical air/fuel ratio or richer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection type internal combustion engine having an ignition plug having a pair of side poles (ie, two poles).

[0002]

2. Description of the Related Art In recent years, a spark ignition type direct injection type internal combustion engine for directly injecting fuel into a combustion chamber has been developed. In this direct injection type internal combustion engine, fuel injection mainly in a compression stroke is performed. The operation can be performed at a super-lean air-fuel ratio by the stratified combustion used.

[0003]

Incidentally, a spark ignition type internal combustion engine requires a spark plug (hereinafter referred to as a spark plug), and a single pole type as shown in FIG. 4 is usually used. I have. Also in the case of a spark ignition type direct injection internal combustion engine, a single-pole type spark plug is usually used. In this case, as shown in FIG. 32 parts carbon 33
In the case of an in-cylinder injection type internal combustion engine, the ignition condition range of the engine that can avoid contamination of the plug due to carbon adhesion or the like (FIG. 5)
) Must be performed.

That is, if the plug is not contaminated, stable combustion can be performed in a wide range (a range where the air-fuel ratio A / F and the EGR rate can be increased) as shown by a broken line A1 in FIG. When fouling occurs, the stable combustion region narrows as shown by a broken line A2. Therefore, unless the pollution status of the plug is known, the operation must be performed in a region surrounded by the broken line A2 to ensure stable combustion.

Therefore, the operation in the region where the air-fuel ratio A / F and the EGR rate are large is restricted, and the super-lean operation in which the air-fuel ratio is largely adjusted to the lean side and sufficient EGR introduction during this lean operation are performed. Therefore, a sufficient fuel efficiency improvement effect cannot be obtained. On the other hand, as shown in FIG. 6, a center axis of the insulator 34 (center pole 3
A two-pole plug (here, a two-pole semi-surface plug) having a pair of side poles 36 and 37 sandwiching the two center lines 35 has also been developed, and such a two-pole spark plug 31B has been developed.
In this case, since the ignition characteristics are stable, as shown by the solid line B in FIG. 5, the ignition condition range of the engine is larger than that of the single-pole type spark plug 31A (see the region enclosed by the broken line A2). , The ignition timing control range can be expanded, and a further improvement in fuel efficiency can be expected.

The reason why stable ignition characteristics are obtained by the bipolar ignition plug 31B is that contamination of the plug (that is, adhesion of carbon to the pole portion) is eliminated by the self-cleaning action. This self-purifying action means that the side electrodes 36, 37
Because of the positional relationship between the center electrode 32 and the center pole 32, sparks generated between the side poles 36 and 37 and the center pole 32 are generated around the center pole 32 where carbon is likely to adhere. Thus, the adhesion around the center pole 32 is prevented or eliminated.

However, in order to obtain this self-purifying action, it is necessary to increase the ignition energy by the spark plug to some extent. However, when the ignition energy of the spark plug is increased, as shown in FIG. 7, on the surface of the insulator 34 around the center pole 32, a region where a spark 39 occurs between the side poles 36 and 37 and the center pole 32 is generated. A problem that the insulator 34 is damaged or further cracked, such as being cut by the ignition energy of the spark to form the groove 38, and the spark does not fly sufficiently, thereby lowering the durability of the spark plug. There is.

As a technique for controlling the ignition energy, there is a technique disclosed in Japanese Utility Model Laid-Open Publication No. 61-12760, but this technique is required because the battery voltage increases as the engine speed increases. Since the ignition energy also increases, it is a technique for increasing the ignition energy in accordance with the integrated value of the engine speed, and cannot solve the above-described problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problem, and it is possible to extend the range of ignition conditions of an engine by using a two-pole type spark plug capable of preventing the plug from being soiled by a self-cleaning action. It is another object of the present invention to provide an in-cylinder injection type internal combustion engine capable of reducing a decrease in durability of an ignition plug which is likely to occur as a side effect of a self-cleaning action.

[0010]

According to a first aspect of the present invention, there is provided an in-cylinder injection type internal combustion engine according to the present invention, wherein a fuel injection valve directly injects fuel into a combustion chamber, and a fuel injection valve is provided by an ignition plug facing the combustion chamber. Combustion is performed by igniting the injected fuel. At this time, the ignition plug has a pair of side poles provided so as to sandwich the central axis of the insulator, so that stable ignition characteristics are obtained,
The range of possible ignition timings is expanded, and appropriate ignition timing control can be performed.

In the case of such an ignition plug having a pair of side poles, if the ignition energy of the ignition plug is increased, the self-cleaning effect can be obtained, but the insulator may be damaged. In an operation region in which the air-fuel ratio of the engine is near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, the ignition energy control means reduces the ignition energy of the spark plug while ensuring reliable ignition performance. In addition, the insulator can be prevented from being damaged while obtaining.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIGS. 1 to 3 show a direct injection internal combustion engine as an embodiment of the present invention.
A spark ignition type direct injection internal combustion engine according to the present embodiment (hereinafter also referred to as a direct injection engine or simply an engine)
Are configured for each cylinder 1A of the engine body as shown in FIG.

That is, the combustion chamber 1C formed above the piston 1B of each cylinder 1A is connected to an intake port 2A communicating with the intake passage 2 and an exhaust port 3A communicating with an exhaust passage (not shown). The port 2A and the exhaust port 3A are provided with an intake valve 2B and an exhaust valve 3B that open and close with the combustion chamber 1C. In particular, the intake port 2 is directed vertically downward along the axis of the cylinder 1A (not shown).
The intake air flowing into C is guided to a curved portion 1D formed on the upper surface of the piston 1B, so that a tumble flow F can be formed.

A fuel injection valve (injector) 4 is provided above the cylinder 1A, and a spark plug (spark plug) 5 is provided above the center of the cylinder 1A so as to face the combustion chamber 1C. A fuel-air mixture is created by injecting fuel from the injector 4 into the tumble flow F of intake air formed in the combustion chamber 1C, and the fuel-air mixture is ignited by a spark plug 5 to perform combustion.

In particular, the spark plug 5 has a stable ignition characteristic and has a small pollution (for example, adhesion of carbon to the pole portion) due to the self-cleaning action. A plug 31B is used. That is, as shown in FIG. 6, the spark plug 5 is a bipolar plug (in this case, a pair of side poles 36 and 37) sandwiching the center axis (the axis of the center pole 32) 35 of the insulator 34. Bipolar creepage plug).

The intake passage 2 is connected to the intake pipe 2C, the surge tank 7, and the intake manifold 2D in this order from the upstream side, and is provided upstream of the surge tank 7 with a throttle valve 6 for controlling the amount of intake air. Further, an exhaust gas recirculation passage (EGR passage) 8A and an exhaust gas recirculation amount control valve (EGR) for opening and closing the EGR passage 8A are provided between the exhaust port 3A and the intake pipe 2C immediately above the surge tank 7 in the intake passage 2.
An exhaust gas recirculation device (EGR) 8 including a valve 8B is interposed.

Then, the injector 4, the spark plug 5,
To control the throttle valve 6 and the EGR valve 8B,
Various sensors (operating state detecting means) 10 and an electronic control unit (ECU) 20 are provided. In this engine, fuel is directly injected from the injector 4 into the cylinder (inside the combustion chamber 1C), so that fuel injection can be performed at any timing regardless of the opening and closing of the intake valve 2B. For this reason, the present engine has a late lean mode in which fuel is injected during a compression stroke to perform stratified combustion as a fuel injection mode. In this late lean mode, the engine tumbles at a stage very close to the ignition timing as in the latter stage of the compression stroke. The fuel is injected toward the flow F, and the fuel is collected near the spark plug, the air-fuel ratio is partially rich, and the overall combustion is significantly lean, so that the ignitability and the combustion stability can be ensured. Efficient saving operation can be performed.

There are a lean mode, a stoichiometric feedback mode, and an open loop mode as modes mainly for injecting fuel during the intake stroke to perform premix combustion.
Among them, in the first lean mode, the fuel is injected before the second lean mode, the fuel is premixed, and the air-fuel ratio is generally leaner than the stoichiometric air-fuel ratio, and the ignitability is improved.
A certain saving operation can be performed while obtaining a certain output while ensuring combustion stability.

In the stoichiometric feedback mode, by performing feedback control based on the output of the O ₂ sensor so that the air-fuel ratio maintains the stoichiometric state, a sufficient engine while exhibiting an exhaust gas purifying action by a three-way catalyst (not shown) or the like is provided. Output can be obtained efficiently. In the open loop mode, combustion is performed by controlling the air-fuel ratio to stoichiometric or rich open loop so that a sufficient output can be obtained at the time of acceleration, starting, and the like.

In the present engine, one of these various operation modes is selected, and in each mode, fuel injection control (ie, injection control of the injector 4) and ignition control (ie, drive control of the ignition plug 5) are performed. , Intake air amount control (that is, control of the throttle valve 6) and exhaust gas recirculation amount control (that is, control of the EGR valve 8B).

Each of these controls is performed by the operating state detecting means 10.
ECU based on the operating state detected (or calculated) by
20. For this reason, the ECU 20
As shown in FIG. 1, a mode selection unit 21 for selecting an operation mode, a fuel injection control unit 22 for controlling the driving of the injector 4, an ignition control unit 23 for controlling the driving of the spark plug 5, and a throttle valve 6 are provided. An intake control unit 24 for controlling the exhaust gas and an exhaust gas recirculation control unit 25 for controlling the EGR valve 8B are provided.

[0022] Note that the operating condition detecting means 10, engine speed sensor 11, a throttle opening sensor 12, an accelerator position sensor (APS) 13, other air flow sensor 14 includes a O ₂ sensor or the like (not shown) .
Further, a battery voltage sensor 15 for detecting a voltage of a battery (not shown) as a driving power source for the ignition plug 5 and the like is provided.

The ECU 20 includes an effective pressure calculating means for calculating an average effective pressure Pe from each information of the engine speed Ne detected by the engine speed sensor 11 and the accelerator opening θ detected by the accelerator position sensor 13. (Pe calculating means) 27 is provided, and the average effective pressure (engine load state) Pe calculated by the effective pressure calculating means 27 is used together with the engine speed Ne as the operating state of the engine. It is used for control.

The mode selection means 21 selects a mode based on the operating state of the engine, that is, the load state Pe of the engine and the engine speed Ne, for example, with the characteristics shown in the map of FIG. . That is, in the low-load / low-speed region, the latter-stage lean mode is selected, and as the load or the rotational speed further increases, the first-stage lean mode, the stoichiometric feedback mode, and the open-loop mode are sequentially selected. ing. In FIG. 2, the boundary between the late lean mode and the early lean mode, and the boundary between the stoichiometric feedback mode and the open loop mode are indicated by a dashed line, and the boundary between the early lean mode and the stoichiometric feedback mode is a solid line. , Respectively.

The fuel injection control means 22 controls the fuel injection amount (fuel injection period) and fuel injection timing in accordance with the operating state of the engine such as the engine load state Pe and the engine speed Ne based on the selected operation mode. Specifically, the injection end timing and the injection start timing are set, and the driving of the injector 4 is controlled based on these settings. As for the fuel injection amount, the fuel injection amount is set based on the target air-fuel ratio A / F set by the air-fuel ratio setting means 26 and the intake flow rate detected by the air flow sensor 14. Further, the air-fuel ratio setting means 26 sets the target air-fuel ratio A / F according to the operating state of the engine such as the engine load state Pe and the engine speed Ne based on the selected operation mode.

The ignition control means 23 sets the fuel ignition timing in accordance with the operating state of the engine such as the engine load state Pe and the engine speed Ne based on the selected operation mode, and sets the ignition plug 5 based on this setting. Energy control means 23A for controlling the ignition energy of the spark plug 5 together with the fuel ignition timing control means 23A for controlling the driving of the
B is provided. The present engine is characterized by this ignition energy control means 23B. Here, controlling the ignition energy means, for example, changing the power supply time to the primary coil in a general ignition system electric circuit (not shown) through the ECU 20.

The ignition energy control means 23B reduces the ignition energy of the ignition plug 5 in a specific operation region of the engine based on the selected operation mode, and increases the ignition energy of the ignition plug 5 in other operation regions.
This specific operation region is an operation region where the air-fuel ratio of the engine is near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio,
As shown by hatching in FIG. 2, the stoichiometric feedback mode and the open loop mode correspond to this.

That is, the ignition energy control means 23B reduces the ignition energy of the ignition plug 5 in the stoichiometric feedback mode or the open loop mode.
That is, the energization time of the ignition plug 5 is shortened. In operation modes other than the stoichiometric feedback mode and the open loop mode, that is, in the lean mode (late lean mode or early lean mode), the ignition energy of the ignition plug 5 is increased, that is, the energizing time to the primary coil is extended. I do.

It should be noted that the ignition energy of the ignition plug 5 varies not only according to the energizing time to the primary coil in the electric circuit of the ignition system (not shown) but also according to the battery voltage (not shown). That is, even if the energization times are equal, if the battery voltage is low, the ignition energy decreases. Therefore, the lower the battery voltage, the longer the energizing time. For this reason, the ignition energy control means 23B sets the basic energization time using, for example, a map in which the energization time is made to correspond to the ignition energy, and responds to the battery voltage value detected by the battery voltage sensor 15 during the basic energization time. Correction is performed to set the final energization time.

In such ignition energy control, the self-cleaning action and durability of the ignition plug 5 using such a two-pole type ignition plug 31B are intended to be compatible while ensuring a good operating condition of the engine. Is what you do. In other words, when a two-pole type spark plug 31B is used as the spark plug 5, the spark passes through the vicinity of the surface of the insulator 34 around the center pole 32. The surface of the insulator 34 can be prevented from adhering carbon, and the adhering carbon can be easily removed, and a self-cleaning action for preventing contamination of the plug can be expected.

To obtain this self-cleaning action, it is necessary to increase the ignition energy by the spark plug to some extent. However, when the ignition energy by the spark plug is increased, the surface of the insulator 34 is shaved by the ignition energy of the spark to form the groove 38. (See FIG. 7), the insulator 34 is damaged or cracked, and the durability of the spark plug is reduced. Therefore, the ignition energy of the spark plug 5 is reduced in a specific operation region of the engine, and the ignition plug 5 is reduced in other operation regions.
By increasing the ignition energy of the ignition plug 5, the self-cleaning action and durability of the ignition plug 5 are both made compatible.

In selecting the specific operation region in this case, reducing the ignition energy must not adversely affect the combustion. In the lean mode (late lean mode or early lean mode), it is difficult to secure combustion stability unless reliable ignition is performed. Therefore, during operation in the lean mode (during lean operation), the ignition energy of the ignition plug 5 is increased. That is, it is necessary to lengthen the energization time to the primary coil, and here, the ignition energy during the lean operation is made almost maximum. On the other hand, in the operation region where the air-fuel ratio is near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, that is, in the stoichiometric feedback mode and the open loop mode,
Even if the ignition energy is reduced, the ignition can be surely performed. Therefore, in such an operation region, the ignition energy of the ignition plug 5 is reduced, that is, the energization time is shortened.

In the ignition control means 23, the ignition timing set by the fuel ignition timing control means 23A is determined by the ignition plug 5
And the energizing is performed for the energizing time set by the ignition energy control means 23B from this starting timing.
Stop energization. The intake control means 24 sets the intake air amount according to the operating state of the engine such as the engine load state Pe and the engine speed Ne based on the selected operation mode, and based on the setting, sets the throttle valve 6.
Control.

The exhaust gas recirculation control means 25 sets the amount of exhaust gas recirculation (reflux rate) in accordance with the operating state of the engine, such as the engine load state Pe and the engine speed Ne, based on the selected operation mode. EG based
The R valve 8B is controlled. Here, EGR is introduced only when the engine is in the late lean mode or the stoichiometric feedback mode, but is not introduced in the first lean mode or open loop mode. This is because the introduction of EGR in the lean mode in the previous period deteriorates combustion, but the effect of reducing NOx and improving fuel efficiency is extremely small. Also,
In the open loop mode, the priority is given to securing the engine output. In addition, in the stoichiometric feedback mode, EGR is introduced mainly for the purpose of improving fuel efficiency. However, if a large amount of EGR is introduced, the combustion deteriorates. Set less than mode.

Since the in-cylinder injection type internal combustion engine according to one embodiment of the present invention is constructed as described above, the control of the ignition energy control means 23B of the ignition control means 23 will be mainly described. It operates as shown in the flowchart. That is, first, in the ECU 20, the operating state detected by the operating state detecting means 10 based on the engine speed Ne, the throttle opening θth, the accelerator position APS, the intake air flow rate, and the average effective pressure calculated by the effective pressure calculating means 27. (Engine load state) Pe is read (step S10), and this operation state (particularly, engine speed N)
The operating mode selecting means 21 selects an operating mode from the latter lean mode, the earlier lean mode, the stoichiometric feedback mode, and the open loop mode based on e and the engine load state Pe).

Next, the value of the battery voltage detected by the battery voltage sensor 15 is read (step S20).
The ignition energy control means 23 of the ignition control means 23
In B, it is determined whether or not the selected operation mode is the lean mode (the latter lean mode or the earlier lean mode) (step S30). If it is the lean mode, the ignition energy is increased to a large value (a value stored in advance). Set (Step S
40) If the mode is not the lean mode, that is, if the mode is the stoichiometric feedback mode or the open loop mode, the ignition energy is set to a small value (a value stored in advance) (step S50).

Then, based on the battery voltage value read in step S20 and the ignition energy set in step S40 or S50, the time for energizing the primary coil is set. For example, the basic energizing time is set using a map in which the energizing time of the primary coil is associated with the ignition energy, and the basic energizing time is set to the basic energizing time.
A correction is made according to the battery voltage value detected in step (1) to set a final power-on time.

By such ignition energy control, the ignition plug 5 using the bipolar ignition plug 31B can secure both the self-cleaning action and the durability while ensuring the good operating condition of the engine. Is there an advantage that comes to mind. That is, the bipolar plug 3 is used as the spark plug 5.
When the ignition energy of the ignition plug is increased to some extent using the ignition plug 1B, a spark of a certain energy is generated at the center pole 3
2, the carbon is prevented from adhering to the periphery of the center pole 32 itself or to the surface of the insulator 34 around the center pole 32, and the adhering carbon is removed.

With such a self-purifying action, the plug 5
Is prevented, and deterioration of the plug performance due to the contamination is prevented. As a result, as shown by the solid line B in FIG. 5, a wider region (air-fuel ratio A /
F and the EGR rate can be stabilized), the super-lean operation in which the air-fuel ratio is largely adjusted to the lean side can be performed, and sufficient EGR is performed during the lean operation.
The fuel cell system can be introduced, and a sufficient fuel efficiency improvement effect can be obtained.

On the other hand, when the ignition energy of the spark plug is increased to obtain the self-cleaning action of the bipolar ignition plug 31B, the surface of the insulator 34 is shaved by the ignition energy of the spark to form a groove 38 (see FIG. 7). In this case, the ignition energy of the spark plug 5 is reduced in a specific operating region of the engine. It is possible to prevent a decrease in durability while securing the self-cleaning action of the plug 5.

In this case, the specific operation region in which the ignition energy is reduced is in the stoichiometric feedback mode or the open loop mode in which the reduction of the ignition energy does not adversely affect the ignition and combustion. Therefore, both the self-cleaning action of the spark plug 5 and the securing of durability can be achieved without inducing.

In this embodiment, the ignition energy is selected from two values, large and small. However, the ignition energy may be set in a plurality of steps from high to low. For example, if the ignition energy is E1
E3 (E1 <E2 <E3) is set in three stages, and is set to E3 in the latter lean mode, to E2 in the former lean mode,
In the stoichiometric feedback mode or the open loop mode, various configurations such as setting to E1 are possible.

Further, the ignition energy is used to control the operating state of the engine (for example, the engine speed Ne) regardless of the operating mode.
Or according to the engine load condition Pe). However, in this case as well, it is preferable that the ignition energy is relatively large in the lean mode region and the ignition energy is reduced mainly in the stoichiometric feedback mode or the open loop mode in which ignition and combustion are stable.

Further, the control for reducing the ignition energy in the specific operation region (such as the stoichiometric feedback mode or the open loop mode) in which the ignition and the combustion are stable is not always performed in the specific operation region. The operation may be partially performed in the specific operation region. For example, during a specific operation region, a certain time T
If the ignition energy is reduced by 1, the next fixed time T2
May increase the ignition energy.

[0045]

As described in detail above, according to the in-cylinder injection type internal combustion engine of the present invention, the spark plug has a pair of side poles provided so as to sandwich the center axis of the insulator. As a result, the range of possible ignition timing is expanded, appropriate ignition timing control can be performed, and the ignition energy control means reduces the ignition energy of the ignition plug in a specific operation region of the engine. In addition, it is possible to prevent the insulator from being damaged due to excessive ignition energy while obtaining the self-cleaning action. Therefore, by appropriate ignition timing control, the durability of the spark plug can be ensured while improving the performance of the engine such as improvement of fuel efficiency.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a direct injection internal combustion engine as one embodiment of the present invention.

FIG. 2 is a diagram illustrating ignition energy control of a direct injection internal combustion engine as one embodiment of the present invention.

FIG. 3 is a flowchart illustrating ignition energy control of a direct injection internal combustion engine as one embodiment of the present invention.

FIG. 4 is a side view showing a general unipolar ignition plug.

FIG. 5 shows the range of ignition conditions of a conventional in-cylinder injection type internal combustion engine using a general unipolar ignition plug, and the use of a bipolar ignition plug considered in the process of devising the present invention. It is a figure which shows the ignition condition range of a direct injection internal combustion engine.

FIG. 6 is a side view showing a general bipolar ignition plug.

FIG. 7 is a front view (a sectional view taken along the line AA of FIG. 6) of the ignition plug showing a problem when a bipolar ignition plug is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1C Combustion chamber 4 Fuel injection valve 5 Spark plug (ignition plug) 20 ECU 23 Ignition control means 23A Ignition energy control means 34 Insulator 36,37 Side pole

Claims (1)

[Claims] 1. A fuel injection valve for injecting fuel directly into a combustion chamber, an ignition plug provided so as to face the combustion chamber and having a pair of side poles provided across a central axis of an insulator; An in-cylinder injection type internal combustion engine, comprising: an ignition energy control means for reducing the ignition energy of the ignition plug in an operation range where the air-fuel ratio is near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio.