JP2005105974A - Controller of spark ignition engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel economy improvement effect by lean combustion and a reduction in pumping loss and a further increased fuel economy improvement effect by suppressing the occurrence of knocking. <P>SOLUTION: This controller of a spark ignition engine 1 comprises a special operation mode. In the special operation mode, the controller is brought into a two-cylinder connected state so that a gas discharged from a preceding cylinder 2A is led into a succeeding cylinder 2B and the exhaust gas is led into an exhaust gas passage 20, stratified combustion is performed at a lean air-fuel ratio in the preceding cylinder 2A, and the burned gas is led into the succeeding cylinder 2B and uniform combustion is performed together with the newly fed fuel. The controller comprises an air-fuel ratio control means, an ignition control means, and a knocking detection means. During the special operation mode, a compression self-ignition causing an assisted ignition is performed in the succeeding cylinder 2B to increase the EGR rate of the succeeding cylinder 2B in a high load side area. Also, an ignition assisted-retard is performed to increase knock resistance. When knocking is detected, the air-fuel ratio of the preceding cylinder 2A ia changed to a rich side. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a control device for a spark ignition engine, and more particularly to a control device for a spark ignition engine in which combustion is performed in each cylinder so as to improve fuel consumption and cost in a multi-cylinder engine. .

  Conventionally, in a spark ignition type engine, a technique for improving fuel efficiency has been studied by performing combustion in a state in which the air-fuel ratio of the air-fuel mixture in each cylinder is set to a lean air-fuel ratio larger than the stoichiometric air-fuel ratio. It is equipped with an injector (fuel injection valve) that directly injects fuel into the room, and stratified combustion is performed by injecting fuel in the compression stroke from the injector in a low rotation and low load range, thereby realizing super lean combustion (See, for example, Patent Document 1).

In such an engine, an ordinary three-way catalyst (a catalyst having a high purification performance in the vicinity of the theoretical air-fuel ratio with respect to HC, CO, and NOx) alone as an exhaust gas purification catalyst is sufficient for NOx during lean operation. Since the purification performance cannot be obtained, a lean NOx catalyst is provided that adsorbs NOx in an oxygen-excess atmosphere and separates and reduces NOx in an oxygen-concentrated atmosphere. When such a lean NOx catalyst is used, if the NOx adsorption amount of the lean NOx catalyst increases during the lean operation, for example, as shown in the above cited reference 1, additional fuel is added during the expansion stroke in addition to the main combustion. By injecting, the air-fuel ratio of the exhaust gas is enriched and CO is generated, thereby promoting the separation and reduction of NOx.
Japanese Patent Laid-Open No. 10-274085

  An engine that performs lean operation as described above requires the lean NOx catalyst in order to ensure NOx purification performance during lean operation. Further, a three-way catalyst is also required for exhaust purification in a region operated at a stoichiometric air-fuel ratio such as a high load region, the lean NOx catalyst is provided in addition to the three-way catalyst, and the lean A NOx catalyst requires a relatively large capacity in order to secure a certain amount of NOx adsorption, and is expensive compared to a three-way catalyst, which is disadvantageous in terms of cost.

  Moreover, in order to maintain the purification performance of the lean NOx catalyst, the NOx is temporarily removed by the removal of NOx, the supply of additional fuel for reduction, etc. at predetermined intervals such that the NOx adsorption amount increases as described above. It is necessary to enrich the air-fuel ratio, which reduces the fuel efficiency improvement effect due to lean combustion.

  In response to such a problem, the applicant of the present application is a control device for a multi-cylinder engine that performs a cycle including intake, compression, expansion, and exhaust strokes, and the exhaust stroke side between a pair of cylinders in which the exhaust stroke and the intake stroke overlap. The gas discharged from the preceding cylinder that is the cylinder of the cylinder 2 is introduced as it is into the subsequent cylinder that is the cylinder on the intake stroke side through the inter-cylinder gas passage, and the exhaust gas discharged from the subsequent cylinder is guided to the exhaust passage 2 A gas flow path that is in a cylinder connection state is configured, and the stratified combustion is performed in a state in which the gas flow path is in the two-cylinder connection state and a lean air-fuel ratio that is a predetermined amount larger than the theoretical air-fuel ratio in the preceding cylinder. The combustion state and the like are controlled so that the burned gas having a lean air-fuel ratio is introduced from the preceding cylinder to the succeeding cylinder and the succeeding cylinder performs homogeneous combustion together with the newly supplied fuel. The thought (Japanese Patent Application No. 2002-024548). Hereinafter, an operation mode in which such combustion is performed is referred to as a special operation mode.

  When the special operation mode is applied at least in the low-load and low-rotation range, combustion at a lean air-fuel ratio is performed in the preceding cylinder, and the heat efficiency is enhanced and the pumping loss is reduced, thereby obtaining a significant fuel efficiency improvement effect. In the succeeding cylinder, the homogeneous combustion is performed together with the burned gas having a lean air-fuel ratio introduced from the preceding cylinder and the newly supplied fuel, and the fuel efficiency improvement effect by reducing the pumping loss can be obtained. Moreover, if the air-fuel ratio in the succeeding cylinder is set to a substantial stoichiometric air-fuel ratio (the relationship between the amount of residual oxygen in the burned gas and the fuel used for combustion is the stoichiometric air-fuel ratio), The exhaust gas is sufficiently purified simply by providing a three-way catalyst, and the lean NOx catalyst, which has been conventionally required for combustion at a lean air-fuel ratio, is no longer necessary, thereby reducing costs and further improving fuel efficiency. .

  In particular, in the special operation mode, if combustion is performed by compression self-ignition in the subsequent cylinder, the fuel efficiency improvement effect is further enhanced. In compression self-ignition, forced ignition by the spark plug is not performed, and the fuel is self-ignited by setting the combustion chamber at a high temperature and high pressure in the latter half of the compression stroke. When the compression self-ignition is performed, the entire combustion chamber burns at a stretch, so that slow combustion that does not contribute to work is avoided, which is further advantageous in improving fuel consumption. In order to perform compression self-ignition in the succeeding cylinder, it is necessary to make the combustion chamber at a high temperature and high pressure, but in the special operation mode, high-temperature burned gas from the preceding cylinder is introduced into the succeeding cylinder, so compression self-ignition Is possible.

  The special operation mode is suitable for a low output (low load, low rotation) region because the amount of air (oxygen) consumed by the preceding cylinder and the succeeding cylinder is sucked only by the preceding cylinder. However, in order to obtain more fuel economy improvement effects, it is desired to expand the application range to a higher output (high load or high rotation) region. However, the higher the output, the higher the in-cylinder temperature of the succeeding cylinder and the more likely knocking occurs, so the application area of the special operation mode could not be expanded much.

  The present invention has been made in consideration of such problems, and it is possible to obtain a fuel efficiency improvement effect by lean combustion, reduction of pumping loss, etc., and a spark that can achieve a greater fuel efficiency improvement effect by suppressing the occurrence of knocking. A control device for an ignition engine is provided.

  According to a first aspect of the present invention, there is provided a control device for a multi-cylinder spark ignition engine in which each cylinder performs a cycle comprising intake, compression, expansion, and exhaust strokes with a predetermined phase difference. The gas discharged from the preceding cylinder, which is the cylinder on the exhaust stroke side, is introduced into the subsequent cylinder, which is the cylinder on the intake stroke side, through the inter-cylinder gas passage between the pair of cylinders where the intake strokes overlap. A gas flow path that is in a two-cylinder connection state is configured such that exhaust gas to be discharged is guided to the exhaust passage, and at least the gas flow path is in the two-cylinder connection state as an operation mode, Stratified combustion is performed in a state where the lean air-fuel ratio is also larger by a predetermined amount, and the newly supplied fuel is introduced from the preceding cylinder to the subsequent cylinder with burned gas having a lean air-fuel ratio. Both have a special operation mode in which homogeneous combustion is performed in the succeeding cylinder, and air-fuel ratio control means for setting the air-fuel ratio in each cylinder, and ignition control for setting the ignition timing of the spark plug provided in each cylinder Means for detecting knocking of the engine, and in the case of causing combustion by compression self-ignition with assist ignition in the subsequent cylinder during operation in the special operation mode, the relatively high load side In the operating region, the EGR rate in the succeeding cylinder is increased, and the ignition control means performs ignition assist retarding that delays the timing of assist ignition to improve knock resistance. Further, when knocking is detected by the knocking detection means The air-fuel ratio control means changes the air-fuel ratio of the preceding cylinder to a richer side.

  According to this configuration, in the special operation mode, combustion at a lean air-fuel ratio is performed in the preceding cylinder, and the heat efficiency is increased and the pumping loss is reduced. Fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinder, and homogeneous combustion is performed, thereby obtaining a fuel efficiency effect by reducing pumping loss.

  Further, if the air-fuel ratio in the succeeding cylinder is set to a substantial stoichiometric air-fuel ratio, exhaust gas purification can be performed sufficiently only by providing a three-way catalyst in the exhaust passage, so that a lean NOx catalyst becomes unnecessary, further reducing costs. Fuel consumption can be improved.

  Further, when the combustion is performed by the compression self-ignition in the subsequent cylinder during the operation in the special operation mode, the fuel efficiency improvement effect can be further enhanced. In addition, if the ignition ignition that generates a spark with the spark plug is performed immediately before the compression self-ignition, the compression self-ignition can be stably performed and the ignition timing can be adjusted to ignite the compression self-ignition ignition. Timing can be controlled.

  According to the configuration of the present invention, during the operation in the special operation mode as described above, in the case of performing the combustion by the compression self-ignition accompanied by the assist ignition in the subsequent cylinder, the operation in the relatively high load side is performed in the subsequent cylinder. This increases the EGR (exhaust gas recirculation) rate, so that the amount of inert gas increases and the combustion temperature decreases. As a result, the occurrence of knocking can be suppressed.

  Unless otherwise specified, in this specification, the EGR rate is the ratio of the amount of EGR gas to the amount of fresh air sucked into the cylinder. Particularly, in the case of the subsequent cylinder in the special operation mode, the main EGR gas is equivalent to EGR (inert gas) in the burned gas sent from the preceding cylinder to the succeeding cylinder (this is particularly referred to as internal EGR). In addition, an EGR passage branched from the exhaust pipe leads the exhaust to the intake side (external EGR), and an exhaust recirculated by the gas flow during intake and exhaust (conventional general internal EGR) is added. May be.

  Further, the ignition control means performs ignition assist retard for delaying the timing of assist ignition. When ignition assist retard is performed, the timing of compression self-ignition is also delayed, so the combustion temperature is lowered and knock resistance is improved. This ignition assist retard may be performed when knocking occurs (when knocking is detected by the knocking detection means) (Claim 2), or in advance when knocking is likely to occur. Also good.

  When further knocking occurs, the air-fuel ratio control means changes the air-fuel ratio of the preceding cylinder to a richer side. When the air-fuel ratio of the preceding cylinder is changed to the rich side (however, leaner than the stoichiometric air-fuel ratio), the amount of fresh air consumed by the preceding cylinder increases and the amount of fresh air consumed by the subsequent cylinder decreases. That is, the internal EGR rate of the subsequent cylinder is increased. As a result, the combustion temperature is further reduced, and the occurrence of knocking can be further suppressed.

  If knocking still occurs, the air-fuel ratio of the preceding cylinder is set to the stoichiometric air-fuel ratio, and combustion in the subsequent cylinder is not performed (claim 2). By so doing, knocking in the succeeding cylinder can be reliably prevented.

  As described above, since the knock resistance is gradually enhanced according to the occurrence of knocking, the occurrence of knocking can be suppressed as much as possible even in a relatively high load range. . In other words, since the knock resistance is gradually increased, the operating range in which the special operation mode can be applied can be expanded to the high load side as much as possible, and the fuel consumption can be greatly reduced. it can.

  2. The gas flow path in which each cylinder is in an independent state in which fresh air is introduced from the intake passage to the intake port of each cylinder and exhaust gas discharged from the exhaust port of each cylinder is guided to the exhaust passage. The operation mode includes a normal operation mode in which combustion is performed in each cylinder with the gas flow path being in an independent state for each cylinder, and the ignition assist retard is detected when knocking is detected by the knocking detection means. When the ignition assist retard is started and further knocking is detected, control is performed to change the air-fuel ratio of the preceding cylinder to a richer side, and during control to change the air-fuel ratio of the preceding cylinder to a richer side, Further, when knocking is detected, the operation mode is switched from the special operation mode to the normal operation mode (Claim 3). It may be.

  According to this configuration, the operation mode is switched from the special operation mode to the normal operation mode as a means for obtaining the highest knock resistance. The normal operation mode is a conventional general engine combustion mode, in which each cylinder is inhaled with fresh air having an ambient temperature and burned. Therefore, the in-cylinder temperature of the succeeding cylinder is lower than that in the special operation mode, and the knock resistance can be sufficiently enhanced. Further, knocking can be reliably avoided by retarding the ignition timing in the normal operation mode.

  According to a fourth aspect of the present invention, there is provided a control device for a multi-cylinder spark ignition engine in which each cylinder performs a cycle consisting of intake, compression, expansion, and exhaust strokes with a predetermined phase difference. The gas discharged from the preceding cylinder, which is the cylinder on the exhaust stroke side, is introduced into the subsequent cylinder, which is the cylinder on the intake stroke side, through the inter-cylinder gas passage between the pair of cylinders where the intake strokes overlap. A gas flow path that is in a two-cylinder connection state is configured such that exhaust gas to be discharged is guided to the exhaust passage, and at least the gas flow path is in the two-cylinder connection state as an operation mode, Stratified combustion is performed in a state where the lean air-fuel ratio is also larger by a predetermined amount, and the newly supplied fuel is introduced from the preceding cylinder to the subsequent cylinder with burned gas having a lean air-fuel ratio. Both have a special operation mode in which homogeneous combustion is performed in the succeeding cylinder, and air-fuel ratio control means for setting the air-fuel ratio in each cylinder, and ignition control for setting the ignition timing of the spark plug provided in each cylinder Means for detecting knocking of the engine, and in the case of causing combustion by compression self-ignition with assist ignition in the subsequent cylinder during operation in the special operation mode, the relatively high load side In the operating region, the EGR rate in the succeeding cylinder is increased and the ignition control means performs ignition assist retard for delaying the timing of assist ignition. During the ignition assist retard, knocking is continuously performed a predetermined number of times or more by the knock detection means. Is detected, the air-fuel ratio of the preceding cylinder is set to the stoichiometric air-fuel ratio, and Characterized in that it is not performed baked.

  According to this configuration, as in the configuration of claim 1, in the special operation mode, a significant fuel efficiency improvement effect can be obtained by improving the thermal efficiency and reducing the pumping loss, and the air-fuel ratio in the succeeding cylinder can be substantially equal to the theoretical air-fuel ratio. By doing so, the lean NOx catalyst becomes unnecessary, and cost reduction and further improvement in fuel consumption can be achieved. Further, during operation in the special operation mode, combustion by compression self-ignition with assist ignition is performed in the subsequent cylinder, and the fuel efficiency improvement effect can be enhanced.

  During the operation in the special operation mode, when performing combustion by compression self-ignition with assist ignition in the subsequent cylinder, the EGR rate in the subsequent cylinder is increased and the ignition control is performed in the operation region on the relatively high load side. Knock resistance can be enhanced by the means performing ignition assist retard.

  By the way, as a form of knocking, there is one that occurs within one to several times (so-called one-shot knocking). One-shot knock is likely to occur when the load increases relatively abruptly. However, according to the above configuration, the air-fuel ratio of the preceding cylinder is set to the stoichiometric air-fuel ratio when knocking occurs continuously a predetermined number of times or more. The combustion in the subsequent cylinder is not performed. That is, since the response to one knock is suspended, the knocking suppression control is prevented from frequently switching. Then, when knocking occurs continuously a predetermined number of times or more, the air-fuel ratio of the preceding cylinder is set to the stoichiometric air-fuel ratio, and knocking is reliably prevented by not performing combustion in the succeeding cylinder.

  According to a fifth aspect of the present invention, there is provided a control device for a multi-cylinder spark ignition engine in which each cylinder performs a cycle comprising intake, compression, expansion, and exhaust strokes with a predetermined phase difference. The gas discharged from the preceding cylinder, which is the cylinder on the exhaust stroke side, is introduced into the subsequent cylinder, which is the cylinder on the intake stroke side, through the inter-cylinder gas passage between the pair of cylinders where the intake strokes overlap. Gas flow path in which two exhaust cylinders are connected to each other so that exhaust gas to be exhausted is guided to the exhaust passage, and fresh air is introduced into the intake port of each cylinder from the intake passage and exhaust gas discharged from the exhaust port of each cylinder is A gas flow path that is in an independent state for each cylinder leading to the exhaust passage, and is selected as an operation mode in an operation region of low load and low rotation, and the gas flow path is in the above-described two-cylinder connection state However, stratified combustion is performed in the preceding cylinder with a lean air-fuel ratio that is a predetermined amount larger than the stoichiometric air-fuel ratio, and burned gas having a lean air-fuel ratio is introduced from the preceding cylinder to the succeeding cylinder and newly supplied. Special operation mode in which homogeneous combustion is performed in the subsequent cylinder together with the remaining fuel, and normal operation mode in which combustion is performed in each cylinder with the gas flow path being in an independent state for each cylinder selected in the operation region on the high load or high rotation side Air-fuel ratio control means for setting the air-fuel ratio in each cylinder, ignition control means for setting the ignition timing of a spark plug provided in each cylinder, and knocking detection means for detecting engine knocking And when performing combustion by compression self-ignition with assist ignition in the subsequent cylinder during operation in the special operation mode, in an operation region on a relatively high load side. When the EGR rate in the succeeding cylinder is increased and when the operation region is shifted to the operation region in which the normal operation mode is to be set with a load increase rate of a predetermined value or more, the air-fuel ratio of the preceding cylinder is set as the stoichiometric air-fuel ratio. The control is performed so as not to perform combustion in the succeeding cylinder, and then the normal operation mode is shifted to after the control is performed for a predetermined period.

  According to this configuration, as in the configuration of claim 1, in the special operation mode, a significant fuel efficiency improvement effect can be obtained by improving the thermal efficiency and reducing the pumping loss, and the air-fuel ratio in the succeeding cylinder can be substantially equal to the theoretical air-fuel ratio. By doing so, the lean NOx catalyst becomes unnecessary, and cost reduction and further improvement in fuel consumption can be achieved. Further, during operation in the special operation mode, combustion by compression self-ignition with assist ignition is performed in the subsequent cylinder, and the fuel efficiency improvement effect can be enhanced.

  During the operation in the special operation mode, when performing combustion by compression self-ignition with assist ignition in the subsequent cylinder, the EGR rate in the subsequent cylinder is increased and the ignition control is performed in the operation region on the relatively high load side. Knock resistance can be enhanced by the means performing ignition assist retard.

  Further, when the operation region shifts to the operation region to be set to the normal operation mode at a load increase rate of a predetermined value or more (a single knock is likely to occur), the air-fuel ratio of the preceding cylinder is set to the stoichiometric air-fuel ratio, and the succeeding cylinder After performing the control to prevent combustion in the engine for a predetermined period, it shifts to the normal operation mode, so it is possible to quickly suppress one knock without waiting for the time to switch to the normal operation mode. can do. The control for the predetermined period may be performed with the occurrence of knocking or may be performed regardless of the occurrence of knocking. In the latter case, since the transition to the normal operation mode when the load suddenly increases suddenly is temporarily suspended, the load decreases rapidly and then returns to the operation region where the special operation mode should be set. If there is a general change, the gas flow path can remain in the two-cylinder connection state. The predetermined period may be a predetermined time or may vary according to the degree of knocking, such as a period until knocking stops.

  As described above, the control device for the spark ignition type engine of the present invention is a multi-cylinder spark ignition type in which each cylinder performs a cycle consisting of intake, compression, expansion, and exhaust strokes with a predetermined phase difference. In an engine control apparatus, gas discharged from a preceding cylinder, which is a cylinder on the exhaust stroke side, between a pair of cylinders in which an exhaust stroke and an intake stroke overlap, is directly passed to a subsequent cylinder, which is a cylinder on the intake stroke side, via an inter-cylinder gas passage. In this way, a gas flow path is formed in which a two-cylinder connection state is established such that the exhaust gas discharged from the subsequent cylinder is guided to the exhaust passage. As an operation mode, at least the gas flow path is set to the two-cylinder connection state. Then, stratified combustion is performed in the preceding cylinder with a lean air-fuel ratio that is a predetermined amount larger than the stoichiometric air-fuel ratio, and the burned gas with a lean air-fuel ratio is transferred from the preceding cylinder to the succeeding cylinder. An air-fuel ratio control means for setting the air-fuel ratio in each of the cylinders, and a special operation mode in which homogeneous combustion is performed in the succeeding cylinders together with newly supplied fuel and An ignition control means for setting the ignition timing of the spark plug and a knocking detection means for detecting knocking of the engine are provided, and during the operation in the special operation mode, combustion by compression self-ignition with assist ignition is performed in the subsequent cylinder. In the operation region on the relatively high load side, the EGR rate in the succeeding cylinder is increased, and the ignition control means performs ignition assist retard that delays the timing of assist ignition to improve knock resistance, and further When knocking is detected by the knocking detection means, the air-fuel ratio control means makes the air-fuel ratio of the preceding cylinder more rich. Because and changes, together with obtaining a fuel economy improvement effect due to the lean combustion and pumping loss reduction, etc., by suppressing the occurrence of knocking, it is possible to obtain further significant fuel economy improvement effect.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic plan view of an entire engine equipped with a device according to an embodiment of the present invention, and FIG. 2 is a schematic view of the structure of one cylinder of an engine body 1 and intake / exhaust valves provided for the cylinder. FIG.

  In these drawings, the engine body 1 has a plurality of cylinders, and in the illustrated embodiment, has four cylinders 2A to 2D. A piston 3 is fitted into each of the cylinders 2 </ b> A to 2 </ b> D, and a combustion chamber 4 is formed above the piston 3.

  A spark plug 7 is provided at the top of the combustion chamber 4 of each cylinder 2A to 2D. The spark plug 7 has a plug tip facing the combustion chamber 4 and is connected to an ignition circuit 8 capable of controlling the ignition timing by electronic control. An injector 9 (fuel injection valve) that directly injects fuel into the combustion chamber 4 is provided at a side portion of the combustion chamber 4. The injector 9 includes a needle valve and a solenoid (not shown), and when a pulse signal is input, the injector 9 is driven for a time corresponding to the pulse width at the pulse input timing to open the valve, and according to the valve opening time. An amount of fuel is configured to be injected. The injector 9 is supplied with fuel by a fuel pump (not shown) via a fuel supply passage and the like, and a fuel supply system is provided so that a fuel pressure higher than the pressure in the combustion chamber in the compression stroke can be applied. It is configured.

  The intake ports 11, 11a, 11b and the exhaust ports 12, 12a, 12b open to the combustion chambers 4 of the respective cylinders 2A to 2D, and the intake passage 15 and the exhaust passage 20 are connected to these ports. Each port includes a preceding cylinder intake valve 31, a subsequent cylinder intake valve 31a, a burned gas introduction valve 31b, a subsequent cylinder exhaust valve 32, a preceding cylinder exhaust valve 32a, and a burned gas discharge valve 32b (these valves are intake valves of a conventional engine). Corresponding to an exhaust valve). Furthermore, camshafts 33 and 34 are provided above them. The engine main body 1 is provided with a knock sensor 27 made of a piezoelectric element that detects vibration when knocking occurs.

  Each cylinder performs a cycle consisting of intake, compression, expansion, and exhaust strokes with a predetermined phase difference. In the case of a four-cylinder engine, the first cylinder 2A, second cylinder from one end in the cylinder row direction When the cylinder 2B, the third cylinder 2C, and the fourth cylinder 2D are called, the above cycle has a phase difference of 180 ° in crank angle in the order of the first cylinder 2A, the third cylinder 2C, the fourth cylinder 2D, and the second cylinder 2B. (See FIG. 8).

  Between a pair of cylinders in which the exhaust stroke and the intake stroke overlap, a cylinder on the intake stroke side (referred to herein as a preceding cylinder) from the cylinder on the exhaust stroke side when the exhaust stroke and the intake stroke overlap (this specification) The inter-cylinder gas passage 22 is provided so that the burned gas can be directly introduced to the subsequent cylinder). In the four-cylinder engine of this embodiment, the exhaust stroke (EX) of the first cylinder 2A and the intake stroke (IN) of the second cylinder 2B overlap, and the exhaust stroke (EX) of the fourth cylinder 2D and the third cylinder 2C. Since the intake strokes (IN) of the cylinders overlap (see FIG. 8), the first cylinder 2A and the second cylinder 2B, and the fourth cylinder 2D and the third cylinder 2C form a pair, respectively, and the first cylinder 2A and the fourth cylinder 2D is the preceding cylinder, the second cylinder 2B and the third cylinder 2C are the succeeding cylinders.

  The intake / exhaust port of each cylinder and the intake passage, exhaust passage, and inter-cylinder gas passage connected to the cylinder are specifically configured as follows.

  The first cylinder 2A and the fourth cylinder 2D, which are the preceding cylinders, respectively include an intake port 11 for introducing fresh air, and a first exhaust port 12a for sending burned gas (exhaust gas) to the exhaust passage. A second exhaust port 12b for leading the burned gas to the subsequent cylinder is provided. The second cylinder 2B and the third cylinder 2C, which are the subsequent cylinders, respectively, have a first intake port 11a for introducing fresh air and a second intake port for introducing burned gas from the preceding cylinder. 11b and an exhaust port 12 for sending burned gas to the exhaust passage.

  In the example shown in FIG. 1, there are two intake ports 11 for the first and fourth cylinders 2A and 2D and two first intake ports 11a for the second and third cylinders 2B and 2C, one for each cylinder. The first exhaust port 12a and the second exhaust port 12b in the first and fourth cylinders 2A and 2D and the second intake port 11b and the exhaust port in the second and third cylinders 2B and 2C are provided in parallel in the half. 12 is provided in parallel in the other half of the combustion chamber.

  The intake port 11 in the first and fourth cylinders 2A and 2D and the first intake port 11a in the second and third cylinders 2B and 2C are connected to the downstream ends of the branch intake passages 16 for each cylinder in the intake passage 15. Yes. In the vicinity of the downstream end of each branch intake passage 16, a multiple throttle valve 17 that is linked to each other via a common shaft is provided. This multiple throttle valve 17 is driven by an actuator 18 in accordance with a control signal, The intake air amount is adjusted. Note that an air flow sensor 19 that detects an intake air flow rate is provided in a common intake passage upstream of the collecting portion in the intake passage 15.

  An upstream end of a branch exhaust passage 21 for each cylinder in the exhaust passage 20 is connected to the first exhaust port 12a in the first and fourth cylinders 2A and 2D and the exhaust port 12 in the second and third cylinders 2B and 2C. Yes. Further, an inter-cylinder gas passage 22 is provided between the first cylinder 2A and the second cylinder 2B and between the third cylinder 2C and the fourth cylinder 2D, and the first, fourth cylinder 2A, The upstream end of the inter-cylinder gas passage 22 is connected to the 2D second exhaust port 12b, and the downstream end of the inter-cylinder gas passage 22 is connected to the second intake port 11b of the second and third cylinders 2B and 2C as the subsequent cylinders. Is connected.

The inter-cylinder gas passage 22 is provided with a linear O ₂ sensor 25 whose output changes linearly according to the oxygen concentration, and the fuel for the preceding cylinders 2A and 2D that has a predetermined lean air-fuel ratio according to the output. The injection amount is feedback controlled.

An O ₂ sensor 23 that detects the air-fuel ratio by detecting the oxygen concentration in the exhaust gas is provided at the downstream of the branch exhaust passage 21 in the exhaust passage 20. The O ₂ sensor 23 is a λO ₂ sensor whose output changes suddenly in the vicinity of the theoretical air-fuel ratio. Based on the output of the O ₂ sensor 23, the succeeding cylinders 2B and 2C (including cylinders 2A and 2D when each cylinder is in an independent state). ) Is feedback controlled. Furthermore, an exhaust purification three-way catalyst 24 is provided in the exhaust passage 20 downstream of the O ₂ sensor 23. As is generally known, the three-way catalyst 24 is highly purified against HC, CO, and NOx when the air-fuel ratio of the exhaust gas is close to the stoichiometric air-fuel ratio (that is, the excess air ratio λ is λ = 1). It is a catalyst showing performance.

  Although not shown in FIGS. 1 and 2, there are provided a rotation speed sensor 28 for detecting the engine speed and an accelerator opening sensor 29 (see FIG. 3 respectively) for detecting the accelerator opening (accelerator pedal depression amount). ing.

  The valves for opening and closing the intake / exhaust ports of each cylinder and the valve operating mechanism for these valves are as follows.

  The intake port 11, the first exhaust port 12a and the second exhaust port 12b in the first and fourth cylinders 2A and 2D are respectively provided with a preceding cylinder intake valve 31, a preceding cylinder exhaust valve 32a and a burned gas discharge valve 32b. Further, the first intake port 11a, the second intake port 11b, and the exhaust port 12 in the second and third cylinders 2B and 2C are respectively provided with a subsequent cylinder intake valve 31a, a burned gas introduction valve 31b, and a subsequent cylinder exhaust valve 32. It has been. Each of these valves opens by being pushed down by a cam integrally formed with the camshafts 33 and 34 when each cylinder is in the intake stroke or the exhaust stroke.

  The valve stop mechanism 35 switches each valve between an operating state and a stopped state, and is provided in the succeeding cylinder intake valve 31a, the burned gas introduction valve 31b, the preceding cylinder exhaust valve 32a, and the burned gas discharge valve 32b. . Since the mechanism is conventionally known and detailed illustration is omitted, for example, a hydraulic chamber capable of supplying and discharging hydraulic oil is provided in a tappet interposed between a cam and a valve shaft. When hydraulic oil is supplied to the valve, the cam operation is transmitted to the valve and the valve is opened and closed.When the hydraulic oil is discharged from the hydraulic chamber, the cam operation is not transmitted to the valve and the valve is stopped. It is something that has come to be. A first control valve 37 is provided in the hydraulic oil supply / discharge passage 36 to the valve stop mechanism 35 of the succeeding cylinder intake valve 31a and the preceding cylinder exhaust valve 32a, and the burned gas introduction valve 31b and the burned gas discharge are provided. A second control valve 39 is provided in the hydraulic oil supply / discharge passage 38 with respect to the valve 32b (see FIG. 3).

FIG. 3 is a block diagram of a control system in the present embodiment. In this figure, an ECU (control unit) 40 comprising an microcomputer for engine control includes an air flow sensor 19, an O ₂ sensor 23, a linear O ₂ sensor 25, a knock sensor 27, a rotation speed sensor 28, and an accelerator opening sensor. 29 is input. Control signals are output from the ECU 40 to the ignition circuit 8, the injectors 9, the actuator 18 of the multiple throttle valve 17, and the first and second control valves 37 and 39.

  The ECU 40 switches the operation mode according to the operation state, and performs switching of the gas flow path and combustion control so as to obtain an optimal combustion state. The ECU 40 includes an operation state determination unit 41, a valve stop mechanism control unit 42, Air-fuel ratio control means 43 and ignition control means 46 are provided.

  As shown in FIG. 4, the operating state determination means 41 is a control map in which the engine operating region is divided into a driving region A on the low load low rotation side and a driving region B on the high load side or high rotation side. The engine operating state (engine speed and engine load) checked by signals from the rotational speed sensor 28, the accelerator opening sensor 29, etc. is in which of the operating areas A and B. Is. Based on this determination, the operating state determining means 41, in the operating region A on the low-load and low-rotation side, the burned gas discharged from the preceding cylinders 2A, 2D in the exhaust stroke is used as it is in the succeeding cylinder 2B in the intake stroke. , 2C and a special operation mode for combustion is selected, and in a high load side or high rotation side operation region B, a normal operation mode in which each of the cylinders 2A to 2D is burned independently is selected. .

  In addition, when the operation state is in the special operation mode region A, the operation state determination means 41 is in any one of the low load side operation region A1, the medium load operation region A2, and the high load side operation region A3. It is to determine whether there is.

  The valve stop mechanism control means 42 is in a two-cylinder connection state in which the burned gas of the preceding cylinders 2A and 2D is introduced into the succeeding cylinders 2B and 2C through the inter-cylinder gas passage 22 in the special operation mode, and each cylinder in the normal operation mode. The valve stop mechanism 35 is controlled to change the intake / exhaust flow state so that each cylinder is brought into an independent state for introducing fresh air into 2A to 2D. Specifically, the control mode is a special operation mode (operation region). A) Each valve stop mechanism 35 is controlled as follows by controlling each of the control valves 37 and 39 depending on whether the operation mode is in the normal operation mode (operation region B).

Special operation mode: Stops the first exhaust valve 32a and the first intake valve 31a
Second exhaust valve 32b and second intake valve 31b are in operating state Normal operation mode: first exhaust valve 32a and first intake valve 31a are in operating state
The second exhaust valve 32b and the second intake valve 31b are stopped. The air-fuel ratio control means 43 sets the air-fuel ratio of each of the cylinders 2A to 2D appropriately according to the operation mode and the operation state, and controls the intake air amount. Means 44 and fuel injection control means 45 are provided.

  The intake air amount control means 44 controls the opening degree (throttle opening degree) of the throttle valve 17 by controlling the actuator 18, and obtains the target intake air amount from a map or the like according to the operating state, and the target The throttle opening is controlled according to the intake air amount.

  That is, the intake air amount control means 44 controls the throttle opening according to the operating state so as to inhale a predetermined amount of fresh air (intake fresh air) into each cylinder. As shown in FIG. 5, the amount of fresh intake air (intake fresh air amount Vv) is the amount of fresh air consumed by combustion in the preceding cylinders 2A and 2D in the operation region A in the special operation mode (consumption). The fresh air amount Vf) is the sum of the fresh air amount consumed by combustion in the succeeding cylinders 2B and 2C (remaining fresh air amount Va), and the stroke volume of each cylinder (volume that the piston excludes in one stroke) Vs. Is set within the range. Further, the intake fresh air amount Vv is set so as to be the stoichiometric air-fuel ratio with respect to the total injection amount of fuel injected into the two cylinders of the preceding cylinders 2A and 2D and the succeeding cylinders 2B and 2C. This amount is necessary for the combustion of the fuel and is increased as the engine load increases.

  The fuel injection control means 45 controls the fuel injection amount and injection timing from the injectors 9 provided in the cylinders 2A to 2D according to the operating state of the engine. In the special operation mode, the fuel injection control means 45 responds to the total injection amount of the fuel injected into the two cylinders of the preceding cylinders 2A and 2D and the succeeding cylinders 2B and 2C according to the load as the engine load increases. In this special operation mode, the sum of the fuel injection amounts for both of the pair of cylinders is adjusted so that the stoichiometric air-fuel ratio becomes the amount of air introduced into the preceding cylinders 2A and 2D. At the same time, the fuel injected into the preceding cylinders 2A and 2D is adjusted by distributing the total fuel injection amount to the respective cylinders 2A to 2D to control the combustion ratio in the preceding and succeeding cylinders. That is, the fuel injection control means 45 controls the amount of fresh air consumed in the preceding cylinders 2A, 2D by controlling the fuel injected into the preceding cylinders 2A, 2D. As a result, the preceding cylinders 2A, 2D Therefore, the amount of fresh air (residual fresh air amount Va) contained in the burned gas introduced into the succeeding cylinders 2B and 2C is controlled. In the present embodiment, the amount of fresh air is expressed as a volume in a standard atmospheric state, and is obtained by dividing the weight of fresh air by the air density in the standard state.

  Then, the fuel injection control means 45 sets the air-fuel ratio in the preceding cylinders 2A, 2D so as to gradually shift to the rich side as the load increases as the load increases. That is, when it is determined that the engine operating state is in the low load side operation region A1, the lean air / fuel ratio is larger than the stoichiometric air / fuel ratio, preferably approximately three times the stoichiometric air / fuel ratio (air / fuel ratio A / F≈ 45, excess air ratio λ≈3) or more. When it is determined that the engine operating state is in the medium load operation region A2, the lean air-fuel ratio is smaller (rich side) than that in the low load side operation region A1, and preferably the stoichiometric air-fuel ratio. Is set to be approximately 2 to 3 times (A / F≈30 to 45, λ≈2 to 3). When it is determined that the operating state of the engine is in the high load side operation region A3, the lean air-fuel ratio is richer than that in the middle load operation region A2, and preferably about 2 of the theoretical air fuel ratio. It is set to be smaller than double (A / F≈30, λ≈2).

  By the way, enriching the air-fuel ratio of the preceding cylinders 2A, 2D increases the ratio of the preceding consumption fresh air amount Vf to the intake fresh air amount Vv. This is also to increase the ratio of the inert gas introduced to the succeeding cylinders 2B and 2C (increase the EGR rate). As described above, since there is a relationship of (intake fresh air amount Vv) = (preceding consumption fresh air amount Vf) + (remaining fresh air amount Va), if the air-fuel ratio of the preceding cylinders 2A and 2D is enriched, the preceding consumption new The ratio of the air volume Vf increases, and the ratio of the remaining fresh air Va decreases. In the present embodiment, the internal EGR rate of the subsequent cylinder in the special operation mode is the ratio of the preceding consumption fresh air amount Vf to the remaining fresh air amount Va. That is, (the internal EGR rate of the succeeding cylinder) = (preceding consumption fresh air amount Vf) / (remaining fresh air amount Va) × 100. If this relationship is expressed by the excess air ratio λ of the preceding cylinder, (the internal EGR ratio of the succeeding cylinder) = 1 / ((the excess air ratio λ of the preceding cylinder) −1) × 100.

  FIG. 6 is a graph showing the relationship between the internal EGR rate of the succeeding cylinder and the excess air ratio λ of the preceding cylinder. As indicated by the characteristic 70, the internal EGR rate of the subsequent cylinder increases in inverse proportion to the decrease (increase in load) of the excess air ratio λ of the preceding cylinder.

  In FIG. 6, when it is determined that the engine operating state is in the low load side operation region A1, the excess air ratio λ of the preceding cylinders 2A, 2D is set to be approximately 3 or more (for example, point 71). Therefore, the internal EGR rate of the succeeding cylinders 2B and 2C is approximately 50% or less. Further, when it is determined that the engine operating state is in the medium load operation region A2, the excess air ratio λ of the preceding cylinders 2A and 2D is set to be approximately 2 to 3 (for example, point 72). Therefore, the internal EGR rate of the succeeding cylinders 2B and 2C is approximately 50 to 100%. When it is determined that the engine operating state is in the high load side operation region A3, the excess air ratio λ of the preceding cylinders 2A and 2D is set to be approximately 2 or less (for example, point 73). The internal EGR rate of the succeeding cylinders 2B and 2C is approximately 100% or more.

  When the internal EGR rate of the succeeding cylinders 2B and 2C is increased, the amount of inert gas introduced into the succeeding cylinders 2B and 2C increases and the intake air temperature of the succeeding cylinders 2B and 2C rises, but as a result, it is difficult to self-ignite. Therefore, the occurrence of knocking can be suppressed. That is, in this embodiment, as the load increases, the internal EGR rate of the succeeding cylinders 2B and 2C is increased to improve the knock resistance.

  Further, when knocking occurs in the high load side operation region A3, the air-fuel ratio of the preceding cylinder is further changed to the rich side as necessary, and the internal EGR rate of the subsequent cylinder is increased (arrow shown in FIG. 6). By suppressing knocking. If knocking still does not stop, the excess air ratio λ of the preceding cylinders 2A and 2D is set to 1 (theoretical air-fuel ratio), and fuel injection in the succeeding cylinders 2B and 2C is stopped and combustion is performed. Do not.

  The timing of fuel injection in the special operation mode by the fuel injection control means 45 is set as follows. In the preceding cylinders 2A and 2D, fuel is injected in the compression stroke to stratify the air-fuel mixture, and the fuel is set to be unevenly distributed in the vicinity of the spark plug 7 at the ignition timing. The succeeding cylinders 2B and 2C are set so as to make the air-fuel mixture uniform by injecting fuel in the intake stroke in which the burned gas from the preceding cylinder is introduced.

  Referring to FIG. 3 again, the ignition control means 46 performs control such as ignition timing control and ignition stop of each of the cylinders 2A to 2D in accordance with the operating state. In the special operation mode, control is performed as follows. In the preceding cylinders 2A and 2D, forced ignition is performed in the vicinity of the compression top dead center, and the fuel unevenly distributed in the vicinity of the spark plug 7 is stratified. Then, in the succeeding cylinders 2B and 2C, the compression ignition is performed, so that the forced ignition is stopped. However, in order to stably perform compression self-ignition and to adjust the ignition timing, assist ignition is performed immediately before ignition.

  It should be noted that a means for discriminating the temperature and the like in the succeeding cylinders 2B and 2C is provided, the status such as the temperature in the succeeding cylinders 2B and 2C is discriminated in the special operation mode, and the temperature in the succeeding cylinders 2B and 2C is determined. When it is determined that compression self-ignition is possible due to a relatively high level, control is performed to execute compression self-ignition as described above, while the temperature in the succeeding cylinders 2B and 2C is relatively low and compression self-ignition does not occur If it is possible, the ignition timing may be set so that forced ignition is performed at a predetermined timing near the compression top dead center.

  In order to set the assist ignition timing, the ignition control means 46 includes an ignition assist ignition control means 47 and a knock determination means 48. The ignition assist ignition control means 47 sets the assist ignition timing so that the compression self-ignition is performed at the optimum timing. Usually, for example, it is set to 15 ° CA (crank angle) before compression top dead center (TDC). When the operation state is in the high load side operation region A3 and knocking occurs, ignition assist retard (ignition timing is delayed) is performed.

  FIG. 7 is a diagram showing the in-cylinder pressure characteristics of the succeeding cylinders 2B and 2C when performing compression self-ignition with assist ignition. The horizontal axis shows the crank angle (° CA) of the succeeding cylinders 2B and 2C. 0 ° CA is the compression top dead center (TDC). The vertical axis shows the in-cylinder pressure of the succeeding cylinders 2B and 2C. A characteristic 81 indicates an in-cylinder pressure when the assist ignition SA1 (−15 ° CA) is performed. Similarly, characteristic 82 indicates the case of assist ignition SA2 (−10 ° CA), and characteristic 83 indicates the case of assist ignition SA2 (−5 ° CA). As shown in this figure, as the assist ignition timing is delayed, the timing at which the in-cylinder pressure becomes maximum (peak) is also delayed. After the TDC, the volume of the combustion chamber 4 starts to increase (expansion stroke), so that the combustion becomes more moderate as the peak of the in-cylinder pressure is delayed. Accordingly, the in-cylinder temperature decreases and knocking is less likely to occur. That is, knock resistance is improved by performing ignition assist retard. However, on the other hand, as the assist ignition timing is delayed, the peak value of the in-cylinder pressure decreases and the output decreases. Therefore, the delay amount (retard amount) is set to a value that can suppress the output decrease to the minimum while improving the knock resistance according to the characteristics of the engine.

  Based on the signal from knock sensor 27, knock determination means 48 determines whether knock has occurred or has stopped.

  Next, the operation of the engine 1 of this embodiment will be described. In the special operation mode, the combustion cycle of each cylinder is as shown in FIG. FIG. 8 is a diagram showing an exhaust stroke, an intake stroke, a fuel injection timing, an ignition timing, and the like of each cylinder in the special operation mode. Each stage of FIG. 8 shows a combustion cycle of each cylinder 2A to 2D. EX is an exhaust stroke, IN is an intake stroke, F is fuel injection, S is forced ignition, SA is assist ignition, and a star mark in the figure indicates that compression self-ignition is performed. As shown in FIG. 8, the exhaust stroke EX of the preceding cylinders 2A and 2D and the intake stroke IN of the succeeding cylinders 2B and 2C are made at the same time. The fuel gas is guided to the succeeding cylinders 2B and 2C (indicated by white arrows).

  As described above, as the gas flow path, the preceding cylinder exhaust valve 32a and the succeeding cylinder intake valve 31a are stopped, and the burned gas discharge valve 32b and the burned gas introduction valve 31b are activated, so that a substantial new The flow path of gas and gas is as shown in FIG. 9, and the burned gas discharged from the preceding cylinders 2A and 2D is directly introduced into the succeeding cylinders 2B and 2C via the inter-cylinder gas passage 22, and the subsequent A two-cylinder connection state is established in which only the gas discharged from the cylinders 2B and 2C is guided to the exhaust passage 20.

In this state, fresh air is introduced into the preceding cylinders 2A and 2D from the intake passage 15 during the intake stroke (arrow a in FIG. 9), and the air-fuel ratio detected by the linear O ₂ sensor 25 is detected in the preceding cylinders 2A and 2D. While the fuel injection amount is feedback controlled so that the air-fuel ratio set by the air-fuel ratio control means 43 is achieved, fuel is injected in the compression stroke, and ignition is performed at a predetermined ignition timing, so that the stratification at the super lean air-fuel ratio is performed. Combustion is performed (see FIG. 8).

  Thereafter, burned gas discharged from the preceding cylinders 2A and 2D is introduced into the succeeding cylinders 2B and 2C through the gas passage 22 during a period in which the intake strokes of the preceding cylinders 2A and 2D overlap with the exhaust strokes of the succeeding cylinders 2B and 2C. (The white arrow in FIG. 8 and the arrow b in FIG. 9). In the succeeding cylinders 2B and 2C, fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinders 2A and 2D, and the fuel injection amount is controlled so as to obtain a substantial stoichiometric air-fuel ratio. Fuel is injected during the intake stroke. Then, the spray is homogenized during the period from the intake stroke to the compression stroke, and assist ignition is performed before the top dead center of the compression stroke to perform compression self-ignition (see FIG. 8).

  When compression self-ignition is performed in the succeeding cylinders 2B and 2C, the combustion is performed all over the combustion chamber 4, so that slow combustion that does not contribute to work is avoided, which is further advantageous in improving fuel consumption. In order to perform compression self-ignition in the succeeding cylinders 2B and 2C, the inside of the combustion chamber 4 needs to be at a high temperature and a high pressure. However, by setting the two cylinders in a connected state, the succeeding cylinders 2B and 2C have a preceding cylinder 2A. , 2D, since high-temperature burned gas is introduced, compression self-ignition is possible.

  As described above, the preceding cylinders 2A and 2D increase the thermal efficiency and reduce the pumping loss by stratified combustion in the ultra-lean state, while the succeeding cylinders 2B and 2C have the effect of reducing the pumping loss similarly to the preceding cylinders 2A and 2D. In addition to being obtained, thermal efficiency is enhanced by combustion by compression self-ignition, and fuel efficiency is greatly improved by these actions.

  The preceding cylinders 2A and 2D have a very lean air-fuel ratio, so that the amount of NOx generated is relatively small. In the succeeding cylinders 2B and 2C, the burned gas is introduced from the preceding cylinders 2A and 2D. Is sufficiently suppressed. This is also advantageous for improving emissions.

  Moreover, since only the stoichiometric burned gas discharged from the succeeding cylinders 2B and 2C is guided to the exhaust passage 20, exhaust gas purification can be carried out sufficiently only by providing the exhaust passage 20 with the three-way catalyst 24. The lean NOx catalyst, which was necessary when performing combustion at the air-fuel ratio, is not necessary, and the cost can be reduced.

  FIG. 10 is a schematic flowchart of control mainly related to knocking suppression in the special operation mode. When the control starts, first, each sensor signal is read in step S1, and if it is determined that the operation state is in the operation region A (YES in step S3), the process proceeds to step S5, and the special operation mode is controlled. If it is further determined that the operation state is in the high load side operation region A3 (YES in step S9), the process proceeds to step S13, and the presence / absence of knocking is determined. If YES in step S13, that is, if it is determined that knocking has occurred, the process proceeds to step S15, the knocking suppression request level F is incremented by 1, and then the process proceeds to step S21. Here, the knocking suppression request level F is an index indicating the degree of request for knocking suppression. The knocking suppression request level F takes a value of 0 to 3, and the larger this value is, the higher the knocking suppression request level is, that is, the control that makes knocking less likely to occur is required. At normal time when no knocking occurs, F = 0 (initial value).

  Going back, if NO is determined in step S13, it is subsequently determined in step S17 whether F = 0 or not. If YES, the process directly proceeds to step S21. When it is determined NO in step S17, it indicates that knocking has not occurred at the present time, but the knocking suppression request level F is not zero. As will be described later, when the knocking suppression request level F is not 0, knocking suppression control is performed in accordance with the value. Therefore, for example, when knocking is stopped by the control, NO is determined in step S13 and NO is determined in step S17. Is done. At this time, the process proceeds to step S19, and the value of the knocking suppression request level F is decremented by 1, and the process proceeds to step S21.

  In step S21 (and step S29), the knocking suppression request level F is determined. When it is determined that F = 0 (0 in step S21), normal control is performed. That is, the ignition assist retard is not performed (step S23), and the normal preceding cylinder air-fuel ratio (step S31) in the high load side operation region A3 is set. When it is determined that F = 1 (1 or 2 in step S21 and YES in step S29), ignition assist is retarded (step S25), and the normal preceding cylinder air-fuel ratio in the high load side operation region A3 (step S31). ). By performing the ignition assist retard in this manner, knock resistance is improved. When it is determined that F = 2 (1 or 2 in step S21 and NO in step S29), ignition assist is retarded (step S25), and the air-fuel ratio of the preceding cylinders 2A and 2D is further reduced (excess air ratio). λ approaches 1). As a result, the internal EGR rate of the succeeding cylinders 2B and 2C increases, so that the knock resistance is further improved. When it is determined that F = 3 (3 in step S21), the preceding cylinders 2A and 2D perform combustion at the stoichiometric air-fuel ratio (excess air ratio λ = 1), and the subsequent cylinders 2B and 2C perform combustion. Not performed. Accordingly, the fuel injection in the succeeding cylinders 2B and 2C is stopped, and the ignition assist is not performed (steps S27 and S35). Thus, since combustion is not performed in the succeeding cylinders 2B and 2C, occurrence of knocking is reliably suppressed.

  As described above, the knock resistance is gradually strengthened according to the occurrence of knocking, so that knocking occurrence is suppressed as much as possible while always selecting the minimum knock resistance improvement measures. be able to. By doing so, the operation range to which the special operation mode is applied can be expanded to the high load side as much as possible, and the fuel consumption can be greatly reduced.

  Going back, if NO is determined in step S3, the process proceeds to step S7, the normal operation mode is controlled, and the process returns. At that time, the knocking suppression request level F is set to the initial value 0 (step S11). When it is determined NO in step S9, the process returns via step S11.

  In the normal operation mode, as described above, the preceding cylinder exhaust valve 32a and the succeeding cylinder intake valve 31a are activated, and the burned gas discharge valve 32b and the burned gas introduction valve 31b are stopped. The air and gas flow paths are as shown in FIG. 11, and the intake ports 11, 11 a and the exhaust ports 12 a, 12 of each cylinder 2 </ b> A to 2 </ b> D are substantially independent, and the intake air of each cylinder 2 </ b> A to 2 </ b> D from the intake passage 15. Fresh air is introduced into the ports 11 and 11a, and burned gas is discharged into the exhaust passage 20 from the exhaust ports 12a and 12 of the cylinders 2A to 2D.

  In the normal operation mode, the intake / exhaust timing is controlled in accordance with the load, the intake air amount and the fuel injection amount are controlled so that the stoichiometric air-fuel ratio or richer, and homogeneous combustion is performed by forced ignition. . Accordingly, a high output can be obtained in the operation region B of high load or high rotation.

  By the way, as a mode for switching from the special operation mode to the normal operation mode, the operation state may shift from the high load side operation region A3 to the operation region B at a relatively high load increase rate (quick depression of the accelerator) (for example, FIG. 4 to the driving state 56). Even in such a case, temporary knocking (one-shot knocking) is likely to occur during the time lag until switching to the normal operation mode. Therefore, in this embodiment, when the high load side operation region A3 is shifted to the operation region B at a load increase rate of a predetermined value or more, the air-fuel ratio of the preceding cylinders 2A, 2D is set to the stoichiometric air-fuel ratio and the subsequent cylinders 2B, 2C. After performing control for preventing combustion in the predetermined period, the operation mode is shifted to the normal operation mode. By doing so, it is possible to quickly suppress a single knock without waiting for a time to switch to the normal operation mode.

  The control for the predetermined period may be performed with the occurrence of knocking or may be performed regardless of the occurrence of knocking. In the latter case, since the transition to the normal operation mode when the load suddenly increases suddenly is temporarily suspended, the load is suddenly decreased (accelerator return) and then returned to the operation region A. When there is a spike-like change, the gas flow path can be kept in the 2-cylinder connected state. The predetermined period may be a predetermined time or may vary according to the degree of knocking, such as a period until knocking stops.

  Next, a modified example of control related to knocking suppression in the special operation mode will be described. FIG. 12 is a schematic flowchart of the control. When the control starts, first, each sensor signal is read in step S51, and if it is determined that the operation state is in the operation region A (YES in step S53), the process proceeds to step S55, and the special operation mode is controlled. If it is further determined that the operation state is in the high load side operation region A3 (YES in step S59), the process proceeds to step S61, and the presence / absence of knocking is determined. If YES in step S61, that is, if it is determined that knocking has occurred, the process further proceeds to step S63, and the number of times of knocking is counted. When knocking occurs a plurality of times continuously (the number of times is appropriately set in advance) (YES in step S65), combustion at the theoretical air fuel ratio (excess air ratio λ = 1) is performed in the preceding cylinders 2A and 2D. The combustion is not performed in the succeeding cylinders 2B and 2C. Therefore, the fuel injection in the succeeding cylinders 2B and 2C is stopped, and the ignition assist is not performed (steps S67 and S69). Thus, since combustion is not performed in the succeeding cylinders 2B and 2C, occurrence of knocking is reliably suppressed. Going back, when knocking has not occurred (NO in step S61), or when it is determined that the knocking has occurred immediately after occurrence (NO in step S65), ignition assist retard is performed. Is performed (step S71), and the normal preceding cylinder air-fuel ratio in the high load side operation region A3 is set (step S73). That is, by performing ignition assist retard, knock resistance is improved in advance, and the occurrence of knocking is suppressed.

  According to this modification, since the response to the one-shot knock is suspended, the knocking suppression control is prevented from being frequently switched. And when knocking occurs continuously a predetermined number of times or more, knocking can be reliably suppressed.

  Further, if NO is determined in step S53, the process proceeds to step S57, the normal mode is controlled, and the process returns. If NO is determined in step S59, the process returns without performing knocking suppression control.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to the said embodiment and its modification, A various deformation | transformation is possible within the range described in the claim. For example, in the control shown in FIG. 10, when the knocking suppression request level F is determined to be F = 3 in step S21, the normal operation mode may be switched. In the normal operation mode, each cylinder 2 </ b> A to 2 </ b> D is inhaled with fresh air having an ambient temperature and burns. Accordingly, the in-cylinder temperatures of the succeeding cylinders 2B and 2C are lower than in the normal operation mode, and the knock resistance can be sufficiently increased.

  In the above embodiment, the ratio of the inert gas in the burned gas introduced from the preceding cylinders 2A, 2D is increased to increase the internal EGR rate of the succeeding cylinders 2B, 2C. The internal EGR rate may be further increased by recirculating the exhaust gas with this gas flow. In addition, an EGR passage that connects the branch exhaust passage 21 or the exhaust passage 20 and the inter-cylinder gas passage 22 is provided, and an EGR valve is provided in the EGR passage to perform external EGR in the subsequent cylinders 2B and 2C. Alternatively, this and this internal EGR rate increase measure may be used in combination to increase the EGR rate of the succeeding cylinders 2B and 2C.

  The operation mode is not necessarily limited to the normal operation mode and the special operation mode, and other modes may be provided. Also, in the special operation mode, the operation region may not be divided into three stages as in the above embodiment, but may be divided into two stages or four or more stages. Alternatively, the air-fuel ratio of the preceding cylinders 2A, 2D and the like may be continuously changed according to the operation state in the operation region A without providing a clearly separated operation region (A1 to A3, etc.).

  The engine body 1 is not limited to a four-cylinder engine but can be applied to an engine having a larger number of cylinders, and the preceding cylinder and the succeeding cylinder may be set in a pair of cylinders in which the exhaust stroke and the intake stroke overlap. Further, the fuel injection into the subsequent cylinder is not necessarily performed by the injector 9 that injects the fuel into the combustion chamber 4. For example, a fuel supply mechanism may be provided in the inter-cylinder gas passage 22.

It is a schematic plan view of the whole engine provided with the apparatus by one Embodiment of this invention. It is a schematic sectional drawing, such as an engine main body. It is a block diagram of a control system. It is explanatory drawing which shows an operation area | region. It is explanatory drawing which shows the relationship between the amount of intake fresh air, the amount of fresh air consumption, and the amount of residual fresh air. It is a characteristic view showing the relationship between the internal EGR rate of the subsequent cylinder and the excess air ratio of the preceding cylinder. It is a figure which shows the in-cylinder pressure characteristic of the subsequent cylinder in the case of performing the compression self-ignition accompanying assist ignition. It is a figure which shows the exhaust stroke of each cylinder in special operation mode, an intake stroke, fuel injection timing, ignition timing, etc. FIG. It is explanatory drawing which shows the substantial combustion state in special operation mode. It is a schematic flowchart of the control regarding knocking suppression mainly in special operation mode. It is explanatory drawing which shows the substantial combustion state in normal operation mode. It is a modification of the flowchart shown in FIG.

Explanation of symbols

1 Engine body 2A, 2D 1st and 4th cylinders (preceding cylinder)
2B, 2C 2nd and 3rd cylinders (following cylinders)
11, 11a, 11b Intake port 12, 12a, 12b Exhaust port 20 Exhaust passage 22 Inter-cylinder gas passage 27 Knock sensor (knocking detection means)
40 ECU
43 Air-fuel ratio control means 46 Ignition control means

Claims (5)

In a control device for a multi-cylinder spark ignition engine in which each cylinder performs a cycle consisting of intake, compression, expansion, and exhaust strokes with a predetermined phase difference,
Between a pair of cylinders in which the exhaust stroke and the intake stroke overlap, the gas discharged from the preceding cylinder that is the cylinder on the exhaust stroke side is directly introduced into the subsequent cylinder that is the cylinder on the intake stroke side via the inter-cylinder gas passage. A gas flow path is formed that is in a two-cylinder connection state in which exhaust gas discharged from the cylinder is guided to the exhaust passage,
As an operation mode, stratified combustion is performed at least in a state in which the gas flow path is in the two-cylinder connected state and the preceding cylinder has a lean air-fuel ratio that is a predetermined amount larger than the stoichiometric air-fuel ratio. It has a special operation mode in which homogeneous combustion is performed in the succeeding cylinder together with newly supplied fuel by introducing burned gas having a lean air-fuel ratio,
Air-fuel ratio control means for setting the air-fuel ratio in each cylinder,
Ignition control means for setting the ignition timing of a spark plug provided in each cylinder;
A knocking detection means for detecting engine knocking,
During operation in the special operation mode, in the case of performing combustion by compression self-ignition with assist ignition in the subsequent cylinder, the EGR rate in the subsequent cylinder is increased in the operation region on the relatively high load side,
The ignition control means performs ignition assist retarding that delays the timing of assist ignition to improve knock resistance,
Furthermore, when knocking is detected by the knocking detection means, the air-fuel ratio control means changes the air-fuel ratio of the preceding cylinder to a richer side. The ignition assist retard starts as knocking is detected by the knocking detection means,
When knocking is further detected during this ignition assist retard, control is performed to change the air-fuel ratio of the preceding cylinder to a richer side,
During the control for changing the air-fuel ratio of the preceding cylinder to a richer side, when knocking is further detected, the air-fuel ratio of the preceding cylinder is set to the stoichiometric air-fuel ratio and combustion in the subsequent cylinder is not performed. The control device for a spark ignition engine according to claim 1. A gas flow path is formed that introduces fresh air from the intake passage to the intake port of each cylinder and guides the exhaust gas discharged from the exhaust port of each cylinder to the exhaust passage, so that each cylinder becomes independent.
As an operation mode, it has a normal operation mode in which combustion is performed in each cylinder with the gas flow path being in an independent state of each cylinder,
The ignition assist retard starts as knocking is detected by the knocking detection means,
When knocking is further detected during this ignition assist retard, control is performed to change the air-fuel ratio of the preceding cylinder to a richer side,
2. The spark ignition according to claim 1, wherein during the control for changing the air-fuel ratio of the preceding cylinder to a richer side, when knocking is further detected, the operation mode is switched from the special operation mode to the normal operation mode. Type engine control device. In a control device for a multi-cylinder spark ignition engine in which each cylinder performs a cycle consisting of intake, compression, expansion, and exhaust strokes with a predetermined phase difference,
Between a pair of cylinders in which the exhaust stroke and the intake stroke overlap, the gas discharged from the preceding cylinder that is the cylinder on the exhaust stroke side is directly introduced into the subsequent cylinder that is the cylinder on the intake stroke side via the inter-cylinder gas passage. A gas flow path is formed that is in a two-cylinder connection state in which exhaust gas discharged from the cylinder is guided to the exhaust passage,
As an operation mode, stratified combustion is performed at least in a state in which the gas flow path is in the two-cylinder connected state and the preceding cylinder has a lean air-fuel ratio that is a predetermined amount larger than the stoichiometric air-fuel ratio. It has a special operation mode in which homogeneous combustion is performed in the succeeding cylinder together with newly supplied fuel by introducing burned gas having a lean air-fuel ratio,
Air-fuel ratio control means for setting the air-fuel ratio in each cylinder,
Ignition control means for setting the ignition timing of a spark plug provided in each cylinder;
A knocking detection means for detecting engine knocking,
During the operation in the special operation mode, when performing combustion by compression self-ignition with assist ignition in the subsequent cylinder, the EGR rate in the subsequent cylinder is increased in the operation region on the relatively high load side, and The ignition control means performs an ignition assist retard that delays the timing of the assist ignition,
During this ignition assist retard, when knocking is detected continuously for a predetermined number of times or more by the knocking detection means, the air-fuel ratio of the preceding cylinder is set to the stoichiometric air-fuel ratio, and combustion in the subsequent cylinder is not performed. A control device for a spark ignition type engine. In a control device for a multi-cylinder spark ignition engine in which each cylinder performs a cycle consisting of intake, compression, expansion, and exhaust strokes with a predetermined phase difference,
Between a pair of cylinders in which the exhaust stroke and the intake stroke overlap, the gas discharged from the preceding cylinder that is the cylinder on the exhaust stroke side is directly introduced into the subsequent cylinder that is the cylinder on the intake stroke side via the inter-cylinder gas passage. A gas flow path that is in a two-cylinder connection state in which exhaust gas discharged from the cylinder is guided to the exhaust passage;
A gas flow path is formed that introduces fresh air from the intake passage to the intake port of each cylinder and guides the exhaust gas discharged from the exhaust port of each cylinder to the exhaust passage.
The operation mode is selected in the low load and low rotation operation region, and the stratified charge combustion is performed in a state where the gas flow path is in the above-described two-cylinder connected state and the preceding cylinder has a lean air-fuel ratio that is a predetermined amount larger than the theoretical air-fuel ratio. A special operation mode in which the burned gas having a lean air-fuel ratio is introduced from the preceding cylinder to the succeeding cylinder, and homogeneous combustion is performed in the succeeding cylinder together with the newly supplied fuel,
A normal operation mode that is selected in an operation region on a high load or high rotation side, and in which the gas flow path is in an independent state of each cylinder and combustion is performed in each cylinder;
Air-fuel ratio control means for setting the air-fuel ratio in each cylinder,
Ignition control means for setting the ignition timing of a spark plug provided in each cylinder;
A knocking detection means for detecting engine knocking,
During the operation in the special operation mode, when performing combustion by compression self-ignition with assist ignition in the subsequent cylinder, the EGR rate in the subsequent cylinder is increased in the operation region on the relatively high load side, and When the operation region shifts to the operation region in which the normal operation mode is to be set at a load increase rate of a predetermined value or more, the air-fuel ratio of the preceding cylinder is set to the stoichiometric air-fuel ratio and combustion in the subsequent cylinder is not performed. A control device for a spark ignition engine, wherein control is performed for a predetermined period, and then the operation mode is shifted to the normal operation mode.

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