JP2010090795A - Spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely prevent knocking in a spark ignition internal combustion engine and improve thermal efficiency. <P>SOLUTION: This internal combustion engine includes a pair of exhaust valves 8 and a pair of intake valves 7, a first spark plug 9 at roughly the center of a combustion chamber 1, and a tumble control valve variably controlling the intensity of tumble flow. Although ignition with the first ignition plug 9 is done at prescribed ignition timing, flame propagation 21 after spark ignition is distorted with a pair of vortexes T1, T2 due to a tumble flow, and an end gas zone 22 remains near the intake valve 7 of the combustion chamber 1. A second ignition plug 12 is arranged to correspond the end gas zone 22, and spark ignition combustion is done before knocking occurs by igniting at a suitable delay in phase difference with the first spark plug 9. Knocking is surely avoided by actively forming the end gas zone 22. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a spark ignition internal combustion engine represented by a gasoline engine, and more particularly to a knocking avoidance technique thereof.

  For example, in a spark ignition internal combustion engine that uses gasoline as fuel, as is well known, if the compression ratio is set high to increase the thermal efficiency, knocking is likely to occur in a high load range. In general, this knocking is avoided by retarding the ignition timing. However, if the ignition timing is retarded, the improvement in thermal efficiency due to the high compression ratio is impaired, and as a result, an improvement in fuel consumption can be achieved. Can not.

In Patent Document 1, two spark plugs are arranged in the combustion chamber to prevent misfire in lean combustion using a tumble flow, one spark plug is always ignited, and the other spark plug is misfired. A two-point ignition type spark ignition internal combustion engine is disclosed which is ignited only under easy operating conditions.
Japanese Utility Model Publication No. 4-125627

  Although the technique of Patent Document 1 has the advantage of shortening the flame propagation distance because ignition is simultaneously performed at two locations, knocking that occurs in a high load region cannot be avoided reliably. In particular, the location where knocking occurs in the combustion chamber is not necessarily constant, and the location where knocking occurs varies, so knocking cannot be sufficiently suppressed.

  The spark-ignition internal combustion engine of the present invention includes at least one exhaust valve and a pair of intake valves, and includes a first ignition plug at a substantially central position of the combustion chamber, and is combusted by the intake air flowing from the intake valve. A pair of tumble flows is generated in the room.

  The tumble flow is configured to distort flame propagation after spark ignition by the spark plug so as to leave an end gas region at the peripheral portion near the intake valve of the combustion chamber, and correspond to the end gas region. And a second spark plug. The second spark plug is basically ignited with a delay from the first spark plug, and sparks the end gas region before knocking.

  That is, in this spark ignition internal combustion engine, combustion is started by ignition by the first spark plug located substantially at the center of the combustion chamber. After ignition, the flame propagates from approximately the center of the combustion chamber to the outer peripheral side, but this flame propagation does not become a perfect circle due to a pair of tumble flows generated in the combustion chamber via a pair of intake valves. It will be distorted. The tumble flow generated in the combustion chamber becomes a pair of large symmetric vortices in a plan view of the combustion chamber as the combustion chamber becomes flat as the piston rises. The flame propagation is delayed at the outer periphery of the combustion chamber, and an unburned end gas region remains here. The size of the end gas region can be controlled by the strength of the tumble flow. When the tumble flow is increased, the end gas region is expanded, and when the tumble flow is decreased, the end gas region is reduced.

  The remaining unburned end gas region is ignited and burned by the spark of the second spark plug before knocking due to compression self-ignition. As a result, knocking is reliably avoided, the combustion period is shortened, and the thermal efficiency is excellent.

  According to the present invention, the end gas region is actively left in a specific part of the combustion chamber using the tumble flow, and the spark ignition is forcibly performed before the end of the knocking. Knocking can be avoided reliably and thermal efficiency can be improved.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an embodiment of a spark ignition internal combustion engine according to the present invention. In this internal combustion engine, a combustion chamber 1 is formed by a cylinder head 2, a cylinder block 3, and a piston 4, and an intake port 5 is formed. And a pair of exhaust valves 8 that open and close the exhaust port 6. A first spark plug 9 is disposed at the center position of the combustion chamber 1 surrounded by these four valves.

  The intake port 5 is substantially linear with an inclination angle suitable for generating a forward tumble flow in the combustion chamber 1, and has a cross section so that the intake port 5 is partitioned into upper and lower passages. A rectifying plate 11 is provided along the center of the tumble control valve 10, and a tumble control valve 10 that opens and closes a lower passage on the upstream side is provided. As is well known, when the tumble control valve 10 is closed, the intake air flows into the combustion chamber 1 only through the passage above the rectifying plate 11, so that the tumble flow (forward tumble flow) swirling in the vertical direction as shown by the arrow T in the figure. When the tumble control valve 10 is opened, the strength of the tumble flow decreases, and the strength of the tumble flow can be continuously variably controlled according to the opening degree of the tumble control valve 10. is there. On the top surface of the piston 4, a gently curved recess 4 a is formed so as not to disturb the tumble flow.

  A second spark plug 12 is disposed at the peripheral edge of the combustion chamber 1 on the intake valve 7 side, specifically, at a position between the pair of intake valves 7 and below the intake port 5.

  Although the fuel injection valve is not shown, in the present invention, the fuel may be injected and supplied in the intake port 5 or the fuel may be directly injected into the cylinder. As this fuel, ordinary gasoline fuel is used.

  Next, the operation of the spark ignition internal combustion engine of the present invention configured as described above will be described.

  The strength of the tumble flow that is variably controlled by the tumble control valve 10 is basically controlled so that the tumble flow becomes stronger as the engine load increases, as shown in FIG. In the high load range, a strong tumble flow is given.

  FIG. 3 shows a state of flame propagation of the air-fuel mixture ignited by the first spark plug 9 in the combustion chamber 1, and a certain percentage of the fuel in the combustion chamber 1, for example, 50% of the fuel is produced by the flame propagation combustion. The position of the peripheral edge 21 of the flame propagation at the stage of combustion is shown. FIG. 3 (a) shows a state when the strength of the tumble flow is relatively high, but this is caused by a pair of forward tumble flows generated in the combustion chamber 1 via the pair of intake valves 7. The flame propagation is not a perfect circle but a distorted shape. That is, as a result of the pair of tumble flows in the combustion chamber 1, the combustion chamber 1 becomes flat as the piston 4 rises, and a pair of large along the cylinder outer circumference as indicated by arrows T 1 and T 2 in plan view of the combustion chamber 1. A vortex is generated symmetrically. Since the flame is likely to travel along the vortices T1 and T2, the flame propagation is relatively delayed at the outer peripheral portion of the combustion chamber 1 near the intake valve 7 where the two vortices T1 and T2 meet. The end gas region 22 of the fuel remains. The size of the end gas region 22 can be controlled by the strength of the tumble flow. When the tumble flow is strengthened, the end gas region 22 is enlarged as shown in FIG. 3A, and when the tumble flow is weakened, the size of FIG. Thus, the end gas region 22 is reduced. As described above, since the tumble flow intensity is controlled according to the load, FIG. 3A corresponds to a high load region where knocking is a problem.

  The unburned end gas region 22 remaining in a specific region as shown in FIG. 3A is ignited with a delay from the first spark plug 9 before being ignited, that is, knocked as the piston 4 rises. The second spark plug 12 is forcibly ignited and ignited and burned quickly. Therefore, knocking due to unauthorized ignition is reliably avoided, and the thermal efficiency is improved. Since the end gas region 22 is formed away from the exhaust valve 8 serving as a heat spot and close to the intake valve 7, knocking due to self-ignition hardly occurs.

  FIG. 4 shows heat generation in combustion in one cycle of the present invention compared with heat generation (a chain line) of a general spark ignition type internal combustion engine, and FIG. (B) shows the heat generation in the low load region. As indicated by the alternate long and short dash line in FIG. 1 (a), in a high load region, generally, unburned fuel remaining at various positions in the combustion chamber as end gas undergoes rapid self-ignition combustion before combustion by flame propagation, It becomes knocking. In the present invention, the end gas region 22 is positively formed at a specific portion where the second spark plug 12 is disposed by using the tumble flow, and the end gas region 22 is spark-ignited. No knocking occurs and knocking can be avoided reliably.

  On the other hand, the second spark plug 12 is ignited substantially simultaneously with the first spark plug 9 in a low load region where knocking is not a problem. At this time, the tumble flow is weak and the clear end gas region 22 is not formed as shown in FIG. Therefore, since the flame propagation distance is shortened by simultaneously igniting both the first spark plug 9 and the second spark plug 12, the combustion period is shortened as shown in FIG. In a general spark ignition type internal combustion engine, when combustion is performed particularly in a lean condition in a low load range, the combustion becomes slow and the combustion period becomes longer as shown by the one-dot chain line, which causes an increase in unburned HC. In the present invention, by shortening the combustion period as two-point ignition as described above, unburned HC is reduced, and thermal efficiency is improved by shortening the heat generation period.

  FIG. 5 shows the characteristics of the phase difference between the ignition timing of the first spark plug 9 and the ignition timing of the second spark plug 12, and FIG. 5 (a) shows the relationship between the phase difference and the load. FIG. (B) shows the relationship between the phase difference and the tumble flow intensity (tumble ratio). Note that the ignition timing of the first spark plug 9 is basically set along a general MBT point, and the second spark plug 12 has an ignition timing delayed by a phase difference from this. As shown in FIG. 1A, the phase difference of the ignition timing is increased as the load is higher. In the high load region, the ignition timing phase difference 22 is sufficiently large so that the end gas region 22 is sparked immediately before knocking. On the other hand, the phase difference becomes minimum or zero in the low load range, and is ignited at two points at the same time. As for the tumble flow strength, as the tumble flow strength is higher, a larger phase difference is given as shown in FIG.

  Although not shown in FIG. 1, in the present invention, a known sensor for detecting knocking can be provided, and control can be performed to increase the strength of the tumble flow when the occurrence of knocking is detected. By increasing the tumble flow strength in this way, the end gas region 22 can be brought together in one place as shown in FIG. 3A and can be reliably ignited and burned, and knocking can be suppressed. Similarly, when occurrence of knocking is detected, unauthorized ignition of the end gas region 22 can be more reliably avoided by reducing the phase difference between the ignition timing of the first spark plug 9 and the ignition timing of the second spark plug 12. .

  In the present invention, correction according to the octane number (in other words, self-ignitability) of the supplied fuel can also be performed. It is to be noted that a device for detecting the octane number of the fuel is known, and it is possible to automatically determine the octane number of the fuel using such a device, or whether so-called high-octane gasoline or regular gasoline is used. The driver may input. FIG. 6 shows an example of correction for the self-ignitability of the fuel. The tumble flow intensity basically increases according to the load as described above. However, the higher the fuel self-ignitability, the more the tumble flow intensity becomes. Correct the flow strength to be higher. Thereby, for example, knocking when using low octane gasoline is reliably avoided.

  FIG. 7 shows a different embodiment of the tumble flow generating means. A sub-intake passage 31 for generating a tumble flow is added to the intake port 5 in place of the tumble control valve 10 and the rectifying plate 11 described above. The auxiliary intake passage 31 is open at the front end in the vicinity of the pair of intake valves 7, and the flow rate of the auxiliary intake passage 31 can be continuously changed upstream in order to continuously change the tumble flow intensity. A flow control valve 32 is provided.

  In the examples of FIGS. 1 and 7, the tumble flow strength is variably controlled. However, in order to avoid knocking in a high load range, variable control of the tumble flow strength is not always essential, and at least knocking is a problem. It is sufficient that a tumble flow with sufficient strength exists in the high load range.

  FIG. 8 shows an example in which the shape of the concave portion 4a on the top surface of the piston 4 is changed so that the pair of large vortices T1 and T2 along the outer periphery of the cylinder due to the tumble flow are generated more reliably. As shown in the drawing, the concave portion 4a of the piston 4 has a planar shape in which two ellipses are connected so as to smoothly guide the two symmetric vortices T1 and T2, and the two vortices T1 and T2 are branched. Further, apex portions 51 and 52 for merging are provided between the pair of intake valves 7 and between the pair of exhaust valves 8.

1 is a cross-sectional view showing an embodiment of a spark ignition internal combustion engine according to the present invention. The characteristic view which shows the relationship between load and tumble flow strength. Explanatory drawing which shows the mode of flame propagation in a combustion chamber when (a) tumble flow intensity | strength is high and (b) tumble flow intensity | strength is low. The characteristic view which showed the heat generation in a cycle about (a) high load and (b) low load. The characteristic view which showed the relationship between ignition timing phase difference, (a) load, and (b) tumble ratio. The characteristic view which showed the relationship between the self-ignition property of fuel, load, and tumble flow intensity. Sectional drawing which shows the Example which provided the sub intake passage for tumble flow production | generation. The (a) top view and (b) sectional view showing an example of the crevice of a piston.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Combustion chamber 4 ... Piston 5 ... Intake port 7 ... Intake valve 8 ... Exhaust valve 9 ... 1st spark plug 10 ... Tumble control valve 12 ... 2nd spark plug

Claims (6)

At least one exhaust valve and a pair of intake valves are provided, a first spark plug is provided at a substantially central position of the combustion chamber, and a pair of tumble flows are generated in the combustion chamber by the intake air flowing from the intake valve. A spark ignition internal combustion engine,
The tumble flow distorts the flame propagation after the spark ignition by the spark plug so that the end gas region remains in the peripheral portion near the intake valve of the combustion chamber, and the second ignition corresponding to the end gas region. With a plug,
A spark ignition internal combustion engine characterized in that the second ignition plug is ignited with a delay from the first ignition plug, and the end gas region is ignited before knocking.   2. The spark ignition internal combustion engine according to claim 1, further comprising means for variably controlling the intensity of the tumble flow, and providing a stronger tumble flow in a high load region than in a middle load region.   2. The spark ignition internal combustion engine according to claim 1, further comprising means for variably controlling the strength of the tumble flow and a knocking detection means, wherein the strength of the tumble flow is increased when occurrence of knocking is detected.   The spark ignition internal combustion engine according to any one of claims 1 to 3, wherein the higher the load, the larger the phase difference between the ignition timing of the first spark plug and the ignition timing of the second spark plug. .   The spark ignition internal combustion engine according to claim 4, wherein the first spark plug and the second spark plug ignite simultaneously in the low load range.   2. A knock detection means is provided, and the phase difference between the ignition timing of the first spark plug and the ignition timing of the second spark plug is reduced when the occurrence of knocking is detected. The spark ignition internal combustion engine in any one of -5.

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