JP2007315228A - Internal combustion engine and method of burning in internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent knocking from occurring due to a difference in temperature between an intake side and an exhaust side in a combustion chamber in a three-point igniting internal combustion engine. <P>SOLUTION: In this internal combustion engine 1, a first ignition plug 11 is installed in the center area of the combustion chamber, and second and third ignition plugs 12, 13 are arranged in the peripheral areas of the combustion chamber on both sides of the intake and exhaust valves which are generally symmetric with respect to the first ignition plug 11. The internal combustion engine comprises a swirl generating means 23. When the area of the combustion chamber where the intake valve 6 is disposed and the area thereof where the exhaust valve 7 is disposed on the line extending through the ignition plugs 11 to 13 are defined as an intake side area and an exhaust side area, respectively, the swirl generating means can generate swirl flow from the intake side area toward the exhaust side area near the second ignition plug 12 and from the exhaust side area toward the intake side area near the third ignition plug 13. At least in the operating state of generating the swirl flow, the third ignition plug 13 is ignited before the first and second ignition plugs 11, 12 are ignited. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a multipoint ignition internal combustion engine having a plurality of ignition devices per cylinder, and more particularly to prevention of knocking.

  In order to improve the combustibility of the internal combustion engine, a multipoint ignition type internal combustion engine in which a plurality of spark plugs are provided in one cylinder is known. This multi-point ignition internal combustion engine is intended to be close to complete combustion by shortening the propagation distance of flames emitted from each spark plug.

  However, in a multipoint ignition type internal combustion engine, the combustion period is shortened and so-called rapid combustion occurs, so that the increase in in-cylinder pressure and in-cylinder temperature is steeper than in the case of one-point ignition, and knocking is likely to occur. There are harmful effects.

As a means for solving this problem, it is ignited by a plurality of spark plugs provided near the outer periphery of the cylinder bore, and the flame is placed on the swirl flow to propagate from the wide space of the cylinder bore to the narrow space, so that from the initial stage to the middle stage of combustion. Patent Document 1 describes a configuration that suppresses the spread of flame nuclei.
JP 2005-248840 A

  By the way, in the combustion chamber, the exhaust side region has a higher temperature than the intake side region. This is because the exhaust valve and its surroundings rise in temperature due to the passage of high-temperature burned gas, whereas the intake valve and its surroundings are cooled by being exposed to relatively low-temperature intake air during the intake stroke. This is because that. For this reason, the combustion speed of the air-fuel mixture is higher in the exhaust side region in the combustion chamber than in the intake side region, and even after the flame has propagated to the periphery of the combustion chamber in the exhaust side region, the flame still propagates to the intake side region. As a result, the mixture remains unburned. If this unburned air-fuel mixture is combusted by compression due to a rise in pressure in the combustion chamber before burning by flame propagation, so-called knocking occurs.

  In the multipoint ignition type internal combustion engine described in Patent Document 1, since the swirl flow is used, the propagation speed of the flame is increased. However, as described above, the combustion speeds of the exhaust side region and the intake side region are different. In addition, since a plurality of spark plugs are ignited simultaneously, there is a possibility that knocking may occur due to the above-described causes.

  Therefore, an object of the present invention is to suppress the occurrence of knocking in a multipoint ignition internal combustion engine.

  In the internal combustion engine of the present invention, a plurality of intake valves and exhaust valves are respectively disposed in the combustion chamber, a first spark plug is provided in a central region of the combustion chamber surrounded by the intake valve and the exhaust valve, and a first ignition valve is provided. In an internal combustion engine in which second and third ignition plugs are arranged in the combustion chamber peripheral region on both sides of the intake and exhaust valves, which are substantially symmetrical with respect to the plugs, the ignition timings of the first to third ignition plugs are brought into operation. And an ignition timing control means that controls the combustion chamber region on the side where the intake valve is disposed with respect to the line passing through each spark plug, and the combustion chamber region on the side where the exhaust valve is disposed. When the exhaust side region is defined, swirl flow from the intake side region toward the exhaust side region near the second spark plug and from the exhaust side region toward the intake side region near the third spark plug Occurrence of swirl that can occur in the combustion chamber It includes a stage, a. Then, at least in the operation state in which the swirl flow is caused, the third spark plug is ignited prior to the first and second spark plugs.

  According to the present invention, since the flame generated by the third spark plug propagates to the intake side region by swirl flow, combustion is started early in the intake side region where the combustion speed is slow. Therefore, when combustion in the exhaust side region is started, it is possible to prevent the unburned air-fuel mixture from undergoing compression self-ignition before the flame propagation in the intake side region and causing knocking.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration diagram of an internal combustion engine to which the present invention is applicable. In the figure, 1 is a main body of a multi-cylinder internal combustion engine having a cylinder array in which a plurality of cylinders are arranged in the main axis direction, 2 is an intake passage thereof, 3 is an intake port portion, 4 is a throttle valve, 5 is an exhaust port portion, 6 Is an intake valve, 7 is an exhaust valve, 8 is a combustion injection valve, 9 is a combustion chamber, 10 is a piston, and 11 to 13 are ignition plugs. Reference numeral 20 denotes a control unit, 21 denotes an intake air amount sensor, and 22 denotes a crank angle sensor. Reference numeral 23 denotes a swirl control valve (hereinafter referred to as SCV) as a swirl generating means for causing swirl flow in the cylinder, which will be described later under relatively low load operating conditions based on a command from the control unit 20. The intake swirl is generated by narrowing the flow passage area of the intake passage 2 and increasing the intake flow velocity to the cylinder.

  The control unit 20 is composed of a microcomputer comprising a CPU and its peripheral devices. The control unit 20 determines the operating state of the internal combustion engine based on the inputs from the sensors 21 and 22 as the operating state detecting device, and injects fuel. The operation of the fuel injection valve 8 and the SCV 23 is controlled so that the timing, the injection amount, and the opening degree of the SCV 23 described later coincide with a predetermined target value. Similarly, the operation of the spark plugs 11 to 13 is controlled as an ignition timing control means.

  FIG. 2 shows details of the arrangement of the three spark plugs 11-13. The internal combustion engine of this embodiment is a four-valve type in which two intake valves 6 (6A, 6B) and two exhaust valves 7 (7A, 7B) are arranged per cylinder as shown in plan view in FIG. It has become. Of the three spark plugs, the first spark plug 11 located in the center is called a main plug, and is located in the central region of the combustion chamber 9 surrounded by the four intake valves 6 or the exhaust valves 7. On the other hand, the second and third spark plugs 12 and 13 are referred to as sub-plugs, and are located around the combustion chamber 9 on both sides of the intake valve 6 and the exhaust valve 7 that are substantially symmetrical with respect to the first spark plug 11. Located in the area.

  The SCV 20 is a valve capable of adjusting the flow passage area of one intake port 6B. For example, as shown in FIG. 2, a butterfly valve that opens and closes around the shaft 23a can be used. In the case where the swirl flow is increased as in the case of operation at a relatively low load, the SCV 20 is controlled so that the valve opening is reduced to narrow the flow passage area of the intake port 3B, thereby both the intake ports 3A, The amount of intake air flowing from 3B into the combustion chamber 9 is biased, and a clockwise intake swirl is generated as shown by an arrow in FIG. When the swirl flow is weakened, such as during operation at a relatively high load, control is performed so that the valve opening is increased, thereby reducing the deviation of the intake air amount between the intake ports 3A and 3B.

  The shape of the combustion chamber on the cylinder head 1a side is a so-called pent roof shape in which the vicinity of the line passing through the discharge electrode portions 11g to 13g of each spark plug 11 to 13 is a ridge line.

  Next, the ignition timing of each of the spark plugs 11 to 13 in the operation state in which the swirl flow is caused with a relatively low load will be described.

  In the present embodiment, when the piston 10 rises to the vicinity of the compression top dead center, first, ignition by the third spark plug 13 is performed. Note that the ignition timing is advanced or retarded according to the operating state, as in general ignition timing control.

  Since the swirl flow is generated in the combustion chamber 9, the air-fuel mixture in the vicinity of the third spark plug 13 is directed to the region on the intake valve 6 side. Therefore, the flame emitted from the third spark plug 13 spreads from the intake valve 6B toward the intake valve 6A by swirl flow, as indicated by an arrow 14 in FIG. That is, first, ignition is performed by a third spark plug (an intake swirl upstream spark plug located in the vicinity of the upstream portion on the intake side when viewed from the swirl flow direction) 13, so that the combustion speed is relatively low at a relatively low temperature. Combustion is started from the region on the intake valve 6 side.

  Subsequently, before the relatively low temperature air-fuel mixture in the vicinity of the intake valves 6A and 6B is combusted, for example, at a timing advanced about 15 degrees in crank angle after the third spark plug 13 is ignited, (Neutral spark plugs located in areas where there is no upstream or downstream relationship in the swirl flow direction when the swirl flow is not substantially determined in one direction) 11, and a second spark plug (swirl plug) When viewed from the flow direction, ignition by the exhaust swirl upstream spark plug (12) located near the upstream portion on the exhaust side is performed substantially simultaneously.

  As a result, a flame generated by the ignition of the third ignition plug 13 and a flame generated by the ignition of the first and second ignition plugs 11 and 12 exist in the combustion chamber 9. Since the propagation distance of flames emitted from ˜13 is shorter than that in the case of single point ignition, the combustion period can be shortened and time loss can be reduced.

  The optimum crank angle from the ignition of the third spark plug 13 to the ignition of the first and second spark plugs 11 and 12 is a swirl determined by the bore diameter, piston crown shape, and other intake port 6 shapes. Since it depends on the strength of the flow, etc., it is set according to the engine specifications. Further, since the strength of the swirl flow and the flame propagation speed fluctuate depending on the engine operating state, the crank angle from the ignition of the third ignition plug 13 to the ignition of the first and second ignition plugs 11 and 12 is determined as the engine operation. You may make it control variably according to a state.

  Then, after the air-fuel mixture in the vicinity of the intake valves 6A and 6B is combusted by the ignition of the first and second ignition plugs 11 and 12, the first ignition plug 11 is ignited again, and the intake valve 6 side by swirl flow The unburned air-fuel mixture toward the region is burned. The region on the intake valve 6 side in the combustion chamber 9 is relatively low in temperature as described above, and further, there is a cooling loss from the cylinder wall surface in the vicinity of the periphery of the combustion chamber 9, so that the flame is easily extinguished during propagation, There is a possibility that an unburned air-fuel mixture may remain in the vicinity of the peripheral edge of the combustion chamber 9 (end zone) after the end of the combustion period. The unburned air-fuel mixture remaining in the end zone in this way may cause so-called knocking by compression self-ignition due to the pressure increase in the combustion chamber before the flame propagates in the expansion stroke of the next cycle. Therefore, as described above, after ignition by the first and second spark plugs 11 and 12, ignition is performed again by the first spark plug 11 to leave unburned in the region on the intake valve 6 side. Reduce the amount of air-fuel mixture and suppress the occurrence of knocking.

  Here, the behavior of the combustion pressure when the first to third ignition plugs 11 to 13 are ignited at the above ignition timing will be described with reference to FIG. FIG. 4 shows the relationship between the combustion pressure and the crank angle. In the figure, the solid line shows the behavior when the control of this embodiment is executed, and the broken line shows the conventional control for igniting the three spark plugs almost simultaneously (hereinafter referred to as the control). , The behavior when the conventional three-point ignition is executed), and the chain line show the case of ignition by one spark plug.

  In the case of the conventional three-point ignition, the combustion period can be drastically shortened compared with the case of the one-point ignition, but the combustion pressure rises sharply as shown in the figure because the combustion is too early. As a result, the knocking limit is lowered. On the other hand, in the case of one-point ignition, the time required for flame propagation is longer than in the case of three-point ignition, so the increase in the combustion pressure becomes slow. However, since the efficiency of flame propagation to the region on the intake valve side where the temperature is relatively low is poor, the unburned mixture tends to remain near the end zone on the intake valve side. And since this unburned air-fuel mixture may cause compression self-ignition due to pressure rise before propagating flame in the next cycle, it cannot be said that the knocking limit is high.

  On the other hand, in the ignition timing control of the present embodiment, the ignition is first performed only by the third spark plug 13, so that the rise of the combustion pressure is slow as in the case of one-point ignition. However, by performing ignition with the first and second spark plugs 11 and 12 thereafter, the combustion period is shortened compared to the one-point ignition when the combustion pressure is increased. Further, by performing the ignition with the first spark plug 11 again, the amount of air-fuel mixture remaining in the combustion chamber without being burned can be reduced. That is, the occurrence of knocking can be suppressed while shortening the combustion period.

  FIG. 5 shows the relationship between knock intensity and ignition timing in the conventional three-point ignition and the present embodiment. The solid line in the figure is the present embodiment, the chain line is the conventional three-point ignition, and the broken line is acceptable. Knock strength (hereinafter referred to as allowable knock strength) is shown. As described above, the present embodiment suppresses the occurrence of knocking by slowing the increase in the combustion pressure more slowly than the conventional three-point ignition. Therefore, as shown in FIG. The ignition timing at which the knock intensity exceeds the allowable knock intensity as compared with the three-point ignition becomes the advance side. That is, the output can be improved by advancing the ignition timing.

  As described above, in the present embodiment, the third spark plug 13 is ignited first, and the flame generated thereby is propagated to the intake side region using swirl flow. Thus, combustion is performed at an early stage, and knocking due to compression self-ignition in the intake side region can be prevented.

  Further, after ignition by the third spark plug 13, a predetermined period, for example, a period longer than the period in which the flame generated by the third spark plug propagates to the vicinity of the first and second spark plugs 11 and 12 has elapsed. Later, since the first and second spark plugs 11 and 12 are ignited substantially simultaneously, the combustion time can be shortened and the time loss can be reduced.

  Furthermore, since the first ignition plug 11 is ignited again after the first and second ignition plugs 11 and 12 are ignited, it is possible to prevent the unburned mixture from remaining in the combustion chamber.

  Further, by slowing the increase in the combustion pressure after the start of combustion, it is possible to suppress the hitting sound (combustion noise) resulting from the combustion.

  The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims.

1 is an overall configuration diagram of an internal combustion engine to which the present embodiment is applied. It is a top view which shows the outline of the combustion chamber structure of this embodiment. It is a figure for demonstrating the swirl flow in a combustion chamber. It is a figure for demonstrating the characteristic of a combustion pressure. It is a figure for demonstrating the characteristic of knock intensity | strength.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Main body of internal combustion engine 2 Intake passage 3 Intake port part 4 Throttle valve 5 Exhaust port part 6 Intake valve 7 Exhaust valve 8 Combustion injection valve 9 Combustion chamber 10 Piston 11 1st spark plug 12 2nd spark plug 13 3rd spark plug 13 Spark plug

Claims (6)

A plurality of intake valves and exhaust valves are arranged in the combustion chamber, a first spark plug is provided in the central region of the combustion chamber surrounded by the intake valve and the exhaust valve, and the position is substantially symmetrical with respect to the first spark plug. In the internal combustion engine in which the second and third spark plugs are arranged in the combustion chamber peripheral region on both sides of the intake and exhaust valves,
Ignition timing control means for controlling the ignition timing of the first to third spark plugs according to the operating state;
When the combustion chamber region on the side where the intake valve is disposed with respect to the line passing through each spark plug is defined as the intake side region, and the combustion chamber region on the side where the exhaust valve is disposed is defined as the exhaust side region, Swirl generation that can cause swirl flow in the combustion chamber in the vicinity of the second spark plug from the intake side region toward the exhaust side region, and in the vicinity of the third spark plug from the exhaust side region toward the intake side region. Means, and
The internal combustion engine characterized in that the ignition timing control means ignites the third spark plug prior to the first and second spark plugs at least in an operation state in which a swirl flow is caused by the swirl generating means. .   2. The internal combustion engine according to claim 1, wherein the first and second ignition plugs are ignited after a predetermined period elapses after the third ignition plug is ignited.   The said predetermined period is a period longer than the period required for the flame produced | generated at least by the ignition of the said 3rd spark plug to propagate to the said 2nd spark plug vicinity. Internal combustion engine.   The internal combustion engine according to claim 2 or 3, wherein the first and second spark plugs are ignited substantially simultaneously.   5. The internal combustion engine according to claim 2, wherein after the first and second ignition plugs are ignited, the first ignition plug is ignited again after a predetermined period of time elapses. . In a combustion method of an internal combustion engine having a swirl generating means,
The internal combustion engine
When the side of the combustion chamber area where the intake valve is located is defined as the intake side and the side where the exhaust valve is located is defined as the exhaust side,
An intake swirl upstream spark plug located in the vicinity of the swirl flow upstream portion of the combustion chamber region on the intake side when viewed in the flow direction of the swirl; and
In the swirl flow direction, the exhaust swirl upstream spark plug located in the vicinity of the swirl flow upstream portion of the exhaust-side combustion chamber region or the swirl flow region in the vicinity of the combustion chamber central region is not substantially determined in one direction. Having at least one of the neutral spark plugs located,
A combustion method for an internal combustion engine, characterized in that when a swirl is generated by a swirl generating means, an intake swirl upstream spark plug is ignited at an early timing with respect to another spark plug.