JP2015151913A - Control device of spark ignition type internal combustion engine - Google Patents

Abstract

An object of the present invention is to suppress a decrease in tumble ratio at a high engine speed using a partial load region in which a lean burn operation is performed in a spark ignition internal combustion engine having a variable intake mechanism. An ignition plug 24 disposed near the center of the upper wall surface of a combustion chamber 14 for igniting an air-fuel mixture, and an intake manifold 16b having a mechanism for changing the length of each intake branch pipe 16b2. Prepare. Above the combustion chamber 14, a tumble flow is generated in which an air flow from the intake side to the exhaust side is generated. In the partial load region where the lean burn operation is performed, when the engine speed is high, each intake branch pipe 16b2 is made longer than when the engine speed is low. [Selection] Figure 10

Description

  The present invention relates to a control device for a spark ignition type internal combustion engine.

  Conventionally, for example, Patent Document 1 discloses an internal combustion engine including an intake variable mechanism that can change the length of an intake passage (more specifically, an intake manifold). In this conventional internal combustion engine, the intake manifold is shortened as the engine speed increases.

JP 2009-215963 A Japanese Patent Laid-Open No. 4-183928 JP 2010-174463 A

  As the engine rotational speed is higher as in the internal combustion engine described in Patent Document 1, the intake passage efficiency is shortened by using the inertia pulsation effect of intake air by shortening the intake passage. However, in a spark ignition internal combustion engine in which a tumble flow is generated in the upper part of the combustion chamber to generate an air flow from the intake side to the exhaust side, and a lean burn operation is performed in the partial load region, the inertia pulsation effect is positively generated at a high engine speed. If used, the following problems occur. That is, when a high inertia pulsation effect is exhibited at a high engine speed, the tumble ratio decreases, and as a result, the gas flow velocity around the spark plug may decrease during ignition. If the gas flow velocity is not properly ensured during the lean burn operation, there is a concern that the ignitability will deteriorate.

  The present invention has been made to solve the above-described problems, and in a spark ignition internal combustion engine having a variable intake mechanism, a tumble ratio at a high engine speed using a partial load region where lean burn operation is performed. An object of the present invention is to provide a control device for a spark ignition type internal combustion engine that can suppress a decrease in the engine.

The first invention is
A spark plug disposed near the center of the upper wall of the combustion chamber for igniting the air-fuel mixture;
A variable intake mechanism that makes the length of the intake passage variable,
A control device for a spark ignition internal combustion engine in which a tumble flow is generated in which an air flow from the intake side to the exhaust side is generated above the combustion chamber, and a lean burn operation is performed in a partial load region,
In the partial load region where the lean burn operation is performed, the engine includes a control unit that controls the variable intake mechanism so that the intake passage becomes longer when the engine speed is high than when the engine speed is low. To do.

  According to the first aspect of the present invention, it is possible to suppress a decrease in the tumble ratio by increasing the intake pipe length at the time of high engine speed using the partial load region where the lean burn operation is performed. Thereby, the fall of the gas flow rate around a spark plug can be suppressed at the time of ignition. As a result, the ignitability of the air-fuel mixture during lean burn operation can be improved.

It is a figure for demonstrating the system configuration | structure of the spark ignition type internal combustion engine which concerns on Embodiment 1 of this invention. It is a figure which shows the structure around the combustion chamber of the internal combustion engine shown in FIG. FIG. 2 is a cross-sectional view illustrating a configuration of an intake manifold illustrated in FIG. 1. It is a figure which shows each component of the tumble flow produced | generated in a cylinder. It is a figure for demonstrating the problem at the time of applying the control of the conventional intake pipe length to lean burn operation. It is a figure for demonstrating the reason that a tumble ratio falls in a high rotation area | region. It is a figure showing the relationship between a spark plug part flow velocity and a tumble ratio. It is a figure which compares and shows the state of the gas flow in the combustion chamber at the time of ignition by the level of tumble ratio. It is a figure for demonstrating the inertia pulsation effect of intake. It is a figure showing the operating range of the internal combustion engine when the control of the intake pipe length concerning Embodiment 1 of the present invention is applied, and the effect of the control concerned. It is a time chart for demonstrating the difference between the control of Embodiment 1 of this invention at the time of use of a partial load area | region, and the conventional control. It is a flowchart of the control routine performed in Embodiment 1 of the present invention.

Embodiment 1 FIG.
[System Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining a system configuration of a spark ignition type internal combustion engine 10 according to Embodiment 1 of the present invention. FIG. 2 is a diagram showing a configuration around the combustion chamber 14 of the internal combustion engine 10 shown in FIG. The system of this embodiment includes a spark ignition type internal combustion engine 10. Each cylinder of the internal combustion engine 10 is provided with a piston 12 that reciprocates within the cylinder. A combustion chamber 14 is formed on the top side of the piston 12 in the cylinder. An intake passage 16 and an exhaust passage 18 communicate with the combustion chamber 14.

  As shown in FIG. 2, the intake port 16a of the intake passage 16 is provided with an intake valve 20 that opens and closes the intake port 16a. The exhaust port 18a of the exhaust passage 18 opens and closes the exhaust port 18a. An exhaust valve 22 is provided. A spark plug 24 for igniting the air-fuel mixture is provided in each cylinder. More specifically, the spark plug 24 is disposed near the center of the upper wall surface of the combustion chamber 14.

  As shown in FIG. 1, an air cleaner 26 is installed near the inlet of the intake passage 16. The air cleaner 26 is provided with an air flow meter 28 that outputs a signal corresponding to the flow rate of air sucked into the intake passage 16. An electronically controlled throttle valve 30 is provided downstream of the air flow meter 28.

  The intake passage 16 on the downstream side of the throttle valve 30 is configured as an intake manifold 16b connected to each intake port 16a. The intake manifold 16b includes a collecting portion that functions as a surge tank 16b1, and an intake branch pipe 16b2 that connects the surge tank 16b1 and each intake port 16a. The intake manifold 16b of this embodiment is configured to be able to change the intake manifold length (more specifically, the length of each intake branch pipe 16b2).

  FIG. 3 is a cross-sectional view showing the configuration of the intake manifold 16b shown in FIG. As shown in FIG. 3, each intake branch pipe 16b2 is formed to surround the surge tank 16b1. The surge tank 16b1 and each intake branch pipe 16b2 can communicate with each other at two locations, the first connection port 16b3 and the second connection port 16b4. The first connection port 16b3 is provided at the end of each intake branch pipe 16b2 on the surge tank 16b1 side. The second connection port 16b4 allows the surge tank 16b1 and each intake branch pipe 16b2 to communicate with each other at a site downstream of the first connection port 16b3. The intake manifold 16b includes an opening / closing valve 16b5 that opens and closes the second connection port 16b4.

  According to the intake manifold 16b configured as described above, when the second connection port 16b4 is closed by the on-off valve 16b5, the intake air flows through the first connection port 16b3 as shown in FIG. The entire intake branch pipe 16b2 is directed toward each intake port 16a. On the other hand, when the second connection port 16b4 is opened by the opening / closing valve 16b5, the intake air passes through the second connection port 16b4 and part of each intake branch pipe 16b2 as shown in FIG. It goes to port 16a. As described above, the “variable intake mechanism” is realized in which the intake branch pipe 16b2 having the above-described configuration is provided to open and close the opening / closing valve 16b5 so that the length of each intake branch pipe 16b2 through which intake air actually flows is variable. .

  The system shown in FIG. 1 further includes an ECU (Electronic Control Unit) 40. In addition to the air flow meter 28 described above, various sensors for detecting the operation state of the internal combustion engine 10 such as a crank angle sensor 42 for detecting the engine rotation speed are connected to the input portion of the ECU 40. Further, the output portion of the ECU 40 operates the internal combustion engine 10 such as the on-off valve 16b5, the throttle valve 30, the ignition device 44 including the ignition plug 24, and the fuel injection valve 46 that supplies fuel to the internal combustion engine 10. Various actuators for control are connected. The ECU 40 performs predetermined engine control such as fuel injection control and ignition control by operating various actuators in accordance with the above-described various sensors and a predetermined program. In particular, in the internal combustion engine 10 of the present embodiment, in the partial load region, lean burn operation (more specifically, lean burn operation using homogeneous lean burn combustion in which a lean mixture is uniformly formed in the entire cylinder) ) Is performed. However, the lean burn operation in the present invention is performed by diluting the air-fuel mixture in the cylinder by introducing EGR gas, in addition to the lean burn operation performed by controlling the air fuel ratio to be leaner than the stoichiometric air fuel ratio as in the above embodiment. Burn operation is also included.

  FIG. 4 is a diagram showing each component of the tumble flow generated in the cylinder. As shown in FIG. 3, the internal combustion engine 10 of the present embodiment is configured such that a tumble flow (vertical vortex flow) is generated in a manner in which an air flow from the intake side to the exhaust side is generated above the combustion chamber 14. Yes. More specifically, the tumble flow shown in FIG. 3 is decomposed into a normal tumble flow component and a reverse tumble flow component shown in FIG.

  The positive tumble flow component is a component due to the action of the gas flow A flowing in from the opening of the intake valve 20 above the combustion chamber 14, and the tumble flow in the same direction as the final tumble flow shown in FIG. It is a component to be generated. On the other hand, the reverse tumble flow component is a component due to the action of the gas flow B flowing in from the opening of the intake valve 20 on the lower side (piston 12 side) of the combustion chamber 14, and the tumble flow in the direction opposite to the normal tumble flow. It is a component which is going to produce. The direction and strength of the tumble flow finally generated in the cylinder is determined by the balance between the strengths of these two tumble flow components. Therefore, it can be said that the intake system of the internal combustion engine 10 is configured such that the forward tumble flow component is stronger than the reverse tumble flow component.

[Control of Embodiment 1]
In an internal combustion engine in which a lean burn operation is performed in a partial load region, such as the internal combustion engine 10 having the above-described configuration, a gas flow velocity around the spark plug 24 at the time of ignition (hereinafter, referred to as “tumble flow”) It is important to improve the fuel efficiency (referred to as “ignition plug flow velocity”). However, when trying to utilize a tumble flow that is strong in lean burn operation, the spark plug flow velocity decreases in the high rotation range due to the influence of the inertia pulsation of the intake air, and the ignitability of the air-fuel mixture deteriorates. There is. The deterioration of ignitability deteriorates the lean burn combustion resistance (that is, makes it difficult to establish combustion at a certain lean air-fuel ratio). In order to deal with this problem, in the present embodiment, the variable intake mechanism (intake manifold 16b) is used to prevent the spark plug portion flow velocity from decreasing in the high rotation region. Hereinafter, the control of the intake pipe length of the present embodiment will be described while explaining the difference from the conventional control of the intake pipe length.

  FIG. 5 is a diagram for explaining a problem when the conventional control of the intake pipe length is applied to the lean burn operation. In the conventional example shown in FIG. 5, it is assumed that lean burn operation using a tumble flow is performed in the partial load region as in the present embodiment. In the conventional control of the intake pipe length, in order to obtain an improvement in the volumetric efficiency of the intake air over the entire operation region, as shown in FIG. 5A, the low rotation region (the engine rotation speed region is low, medium and high When captured, a long intake pipe length is used in a high load area and a short intake pipe length is used in other operation areas including a high rotation high load area. However, when such intake pipe length control is applied to lean burn operation, as shown in FIG. 5 (B), the tumble ratio decreases in the high rotation region, and as a result, the spark plug flow velocity decreases. .

  With reference to FIG. 6, the reason why the tumble ratio decreases in the high rotation region will be described. FIG. 6A shows test results obtained by measuring the tumble ratio of the flow generated when air is introduced into the cylinder with the IN valve lift amount (lift amount of the intake valve 20) fixed at an arbitrary value. FIG. From the test results shown in FIG. 6A, it can be seen that when air is introduced at a low lift amount, the tumble ratio decreases, and the tumble ratio increases as the lift amount increases. This is because as the lift amount increases, the upper flow A shown in FIG. 4 increases, and the forward tumble flow component becomes relatively stronger than the reverse tumble flow component.

  FIG. 6B is a diagram comparing the change in the intake air ratio with respect to the change in the lift amount during the opening period of the intake valve 20 at the engine rotation speed level. The intake air ratio here means the ratio of the inflow air amount at each lift amount with respect to the entire air amount flowing into the cylinder during one valve opening period, and the intake air ratio is during the valve opening period. 6B changes in the direction indicated by the arrow in FIG. From FIG. 6 (B), it can be seen that a large amount of air is introduced into the cylinder at the time of high rotation in a low lift amount state compared to at the time of low rotation. In the low lift amount state, the ratio of the upper flow A shown in FIG. 4 decreases and the ratio of the lower flow B increases in comparison with the high lift amount state. As a result, the reverse tumble flow component is stronger in the low lift amount state than in the high lift amount state. For this reason, in the high rotation region, the tumble ratio decreases as shown in FIG.

  FIG. 7 is a diagram showing the relationship between the spark plug flow velocity and the tumble ratio. FIG. 8 is a diagram showing the state of the gas flow in the combustion chamber 14 at the time of ignition by comparing the tumble ratio with the level. As shown in FIG. 7, the relationship between the spark plug flow velocity and the tumble ratio is not linear, and when the spark plug flow velocity falls below a certain value C, the air flow formation in the cylinder changes rapidly. In response, it drops rapidly. The reason why such characteristics are obtained is as follows.

  That is, in a cycle in which a tumble flow having a high tumble ratio is generated, the flow in the initial tumble flow direction (the flow direction of the normal tumble flow component) is well maintained even during ignition. As a result, as shown in FIG. 8A corresponding to when the tumble ratio becomes a value D higher than the value C, the flow velocity of the gas on the upper wall surface side of the combustion chamber 14 is higher than the flow velocity of the gas on the piston 12 side. Thus, the spark plug flow velocity is increased. Thereby, the lean combustion resistance is ensured satisfactorily. On the other hand, in a cycle in which a tumble flow having a low tumble ratio is generated, the tumble flow cannot be formed at the time of ignition, or at least the initial tumble flow is difficult to maintain well. As a result, as shown in FIG. 8B corresponding to when the tumble ratio becomes a value E lower than the value C, the gas flow rate on the piston 12 side is higher than the gas flow rate on the upper wall surface side of the combustion chamber 14. Increases, and the spark plug flow velocity decreases. Thereby, the lean burn combustion resistance deteriorates.

  FIG. 9 is a diagram for explaining the inertia pulsation effect of intake air, and shows the relationship between the transition of the intake port pressure during one cycle and the valve opening period of the intake valve 20. At the time of low rotation, the amplitude of the intake port pressure is small as shown by the broken line in FIG. 9, and as a result, no large pressure wave is generated in each intake port 16a. On the other hand, when the engine speed increases, a large negative pressure wave is generated in the intake port 16a in the early stage of opening of the intake valve 20. The phase of the generated negative pressure wave is reversed when it reaches the surge tank 16b1, which is the open end, and returns to each intake port 16a as a positive pressure wave. The conventional intake pipe length control is configured such that when a short intake pipe length is selected, the peak of the positive pressure wave reaches each intake port 16a just before the intake valve 20 is closed at the time of high rotation. Thereby, the volumetric efficiency of intake air can be improved. For this reason, it can be said that such a configuration is preferable for a high load high rotation region. However, when such a configuration is adopted in the partial load region where the lean burn operation is performed, the intake air ratio increases immediately before the closing timing of the intake valve 20 (that is, in the low lift amount state). . As a result, as already described with reference to FIG. 6, the tumble ratio is lowered.

  Therefore, in the present embodiment, in the partial load region where the lean burn operation is performed, the opening / closing valve 16b5 is closed so that a long intake pipe length is obtained at a high rotation speed higher than the predetermined engine rotation speed F. As the intake pipe length increases, the time required for a sonic pressure wave to move from each intake port 16a to the surge tank 16b1 and to return to each intake port 16a as a positive pressure wave from the surge tank 16b1 increases. As a result, as shown in FIG. 9, the timing at which the peak of the positive pressure wave arrives can be delayed as compared to when a short intake pipe length is used. For this reason, introduction of air in a low lift amount state can be suppressed as compared with the case of using a short intake pipe length. Thus, the intake system of the internal combustion engine 10 uses a long intake pipe length when the engine rotation speed reaches the engine rotation speed F, so that the timing when the positive pressure wave peaks in the intake port 16a is the intake valve 20. The timing is later than the closing timing.

  FIG. 10 is a diagram showing the operating range of the internal combustion engine 10 and the effect of the control when the intake pipe length control according to the first embodiment of the present invention is applied. As shown in FIG. 10 (A), the control of the intake pipe length of the present embodiment is a partial load region (low to medium load region) where lean burn operation is performed, and the engine rotational speed is higher than the predetermined engine rotational speed F. This is different from the conventional control shown in FIG. 5A in that a long intake pipe length is used in a high high rotation region. The engine rotation speed F is when the tumble ratio reaches the value C (that is, when the tumble ratio rapidly decreases due to a decrease in the air introduction ratio in the low lift amount state while using a short intake pipe length). The value is lower than the engine speed G by a predetermined value. Due to this difference, as shown in FIG. 10B, in the high rotation region, it is possible to prevent the tumble ratio from being lowered by suppressing the introduction of air in the low lift amount state.

  FIG. 11 is a time chart for explaining the difference between the control of the present embodiment and the conventional control when the partial load region is used. This time chart is a situation in which the engine speed increases as time passes as shown in FIG. According to the conventional control in which a short intake pipe length is used regardless of changes in the engine speed, as shown by the broken line in FIG. 11C, as the engine speed increases, the inertia pulsation effect decreases. The air introduction rate in the lift amount state increases. Along with this, as indicated by the broken line in FIG. 11D, the spark plug portion flow velocity gradually decreases as the engine speed increases. The spark plug portion flow velocity is determined at a certain timing (in this example, when the engine rotation speed reaches a predetermined engine rotation speed G) due to the change in the in-cylinder airflow described above with reference to FIGS. 7 and 8. Decreases rapidly. Note that the spark plug flow velocity after the sudden drop gradually decreases again.

  On the other hand, according to the control of the present embodiment, the intake pipe length is lengthened when reaching the engine rotation speed F that is a value on the lower rotation side than the engine rotation speed G. Thus, by suppressing the inertia pulsation effect in the high rotation region, the air introduction ratio in the low lift amount state can be lowered as shown by the solid line in FIG. More specifically, in the high speed region, as the engine rotational speed increases, the peak timing of the positive pressure wave is delayed and the inertia pulsation effect is less used. For this reason, as the engine speed increases, the air introduction ratio in the low lift amount state decreases. Therefore, as shown by a solid line in FIG. 11D, the spark plug flow velocity in the high rotation region can be kept high. More specifically, the characteristic that the spark plug flow velocity gradually increases as the engine speed increases is obtained. Note that the reduction in the intake air amount accompanying the suppression of the inertia pulsation effect in the high rotation region can be compensated by increasing the throttle opening.

  FIG. 12 is a flowchart showing a control routine executed by the ECU 40 in order to realize the control of the first embodiment described above. In addition, this routine shall be repeatedly performed for every predetermined | prescribed control period.

  In step 100, the ECU 40 determines whether or not the operation region of the internal combustion engine 10 is a predetermined partial load region in which the lean burn operation is performed. The ECU 40 stores a partial load region in which the lean burn operation is performed, and the current operation region determined based on the intake air amount and the engine rotational speed respectively acquired using the air flow meter 28 and the crank angle sensor 42 is a partial. It is determined whether or not the load area is satisfied.

  When the operation region is the partial load region, the ECU 40 proceeds to step 102 and determines whether or not the engine rotation speed is higher than the engine rotation speed F. As described above, the engine rotation speed F is a value that has a margin for a predetermined value with respect to the engine rotation speed G when the tumble ratio suddenly decreases. The engine rotation speed F is known in advance by experiments or the like and is stored in the ECU 40.

  If it is determined in step 102 that the current engine speed is equal to or lower than the predetermined engine speed F, the ECU 40 proceeds to step 104 and opens the opening / closing valve 16b5 in order to obtain a short intake pipe length. Or keep it open. On the other hand, if it is determined that the current engine rotation speed is higher than the predetermined engine rotation speed F, the ECU 40 proceeds to step 106 and closes the opening / closing valve 16b5 in order to obtain a long intake pipe length, Or keep it closed.

  According to the routine shown in FIG. 12 described above, it is possible to suppress a decrease in the tumble ratio by increasing the length of the intake pipe when using the high load region which is the partial load region where the lean burn operation is performed. Thereby, the fall of the spark plug part flow velocity at the time of ignition can be suppressed. As a result, the ignitability of the air-fuel mixture during lean burn operation can be improved.

  By the way, in Embodiment 1 described above, when using the partial load region where the lean burn operation is performed, a short intake pipe length is selected when the engine rotational speed is equal to or lower than the predetermined engine rotational speed F, and the engine rotational speed is the predetermined engine. When the rotational speed is higher than F, a long intake pipe length is selected. However, the control of the variable intake mechanism in the present invention is not limited to the above aspect. That is, for example, in the partial load region where the lean burn operation is performed, the length of the intake passage may be increased continuously or stepwise as the engine speed increases.

  In the first embodiment described above, the “control means” in the present invention is realized by the ECU 40 executing a series of processes of the control routine shown in FIG.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Piston 14 Combustion chamber 16 Intake passage 16a Intake port 16b Intake manifold 16b1 Surge tank 16b2 Intake branch pipe 16b3 First connection port 16b4 Second connection port 16b5 On-off valve 18 Exhaust passage 18a Exhaust port 20 Intake valve 22 Exhaust valve 24 Spark plug 26 Air cleaner 28 Air flow meter 30 Throttle valve 40 ECU (Electronic Control Unit)
42 Crank angle sensor 44 Ignition device 46 Fuel injection valve

Claims (1)

A spark plug disposed near the center of the upper wall of the combustion chamber for igniting the air-fuel mixture;
A variable intake mechanism that makes the length of the intake passage variable,
A control device for a spark ignition internal combustion engine in which a tumble flow is generated in which an air flow from the intake side to the exhaust side is generated above the combustion chamber, and a lean burn operation is performed in a partial load region,
In the partial load region where the lean burn operation is performed, the engine includes a control unit that controls the variable intake mechanism so that the intake passage becomes longer when the engine speed is high than when the engine speed is low. Control device for spark ignition type internal combustion engine.

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