JP4123122B2 - Control device for spark ignition engine - Google Patents

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. .

  As described above, in the special operation mode, the fuel efficiency and cost can be significantly improved. Therefore, it is desirable to apply the special operation mode in the widest possible operation region including the idling operation. However, when the special operation mode is applied during idle operation, there arises a problem that it is difficult to ensure combustion stability as follows.

  In general, during idling, combustion stability decreases due to low rotation and low load. On the other hand, in the special operation mode, combustion in the succeeding cylinder is performed by introducing the burned gas, so that a large amount of EGR (exhaust gas recirculation) is achieved, which is disadvantageous for combustion stability. Therefore, when the special operation mode is applied during idle operation, conditions that are disadvantageous to combustion stability overlap, making it difficult to ensure.

  As a countermeasure against this problem, it is necessary to select conventional general combustion (hereinafter, an operation mode in which such combustion is performed is referred to as a normal operation mode) in which each cylinder independently burns during idle operation.

  Therefore, even during the special operation mode, it is necessary to switch to the normal operation mode every time the idle operation state is entered, and the frequency of switching the gas flow path is high. If the switching frequency of the gas flow path is high, the effect of improving the fuel efficiency is diminished due to a response delay associated with the switching, and the cost is increased in order to ensure the durability of each operating part, which is not desirable.

  The present invention has been made in consideration of such problems, and has an effect of improving fuel efficiency by reducing lean combustion and reducing pumping loss and the like, and switching frequency of the gas flow path while ensuring combustion stability during idle operation. It is an object of the present invention to provide a spark ignition type engine control device that can obtain a greater fuel efficiency improvement effect and cost reduction effect by reducing the fuel consumption.

  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 the special operation mode in which homogeneous combustion is performed in the succeeding cylinder and the non-combustion gas is introduced from the preceding cylinder to the succeeding cylinder without performing combustion in the preceding cylinder while the gas flow path is connected to the two cylinders. And a special idle operation mode in which homogeneous combustion is performed by spark ignition at the stoichiometric air-fuel ratio or richer air-fuel ratio in the succeeding cylinder, and the special operation mode is selected at least when operating in a low load and low rotation range. The special idle operation mode is selected during idle operation.

  According to this configuration, in the special operation mode selected at least in the low-load low-rotation region, the preceding cylinder performs combustion at a lean air-fuel ratio, thereby improving thermal efficiency and reducing pumping loss, thereby significantly improving fuel efficiency. In addition, in the subsequent cylinder, fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinder and homogeneous combustion is performed, so that a fuel efficiency effect by reducing pumping loss is obtained.

  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.

  In the special idle operation mode selected during the idle operation, the two-cylinder connection state in which the gas flow path is the same as in the special operation mode is obtained. For this reason, it is not necessary to switch the gas flow path every time the engine is in the idle operation state, and the frequency of switching the gas flow path can be reduced. Therefore, it is possible to prevent the fuel efficiency improvement effect from being reduced due to the response delay accompanying the switching, and the cost from being increased to ensure the durability of each operating part.

  Moreover, in the special idle operation mode, unburned gas that has passed through the preceding cylinder is guided to the subsequent cylinder. Since the preceding cylinder does not perform combustion, the unburned gas becomes fresh air passing through the preceding cylinder. Then, the air-fuel ratio with the fuel supplied for combustion in the succeeding cylinder (either directly injected into the succeeding cylinder or previously mixed with the burned gas) Since the air-fuel ratio is richer and homogeneous combustion is performed, sufficient combustion stability can be ensured.

  Further, in the special idle operation mode, the combustion in the subsequent cylinder is performed, so that the temperature of the subsequent cylinder is appropriately high. Therefore, when shifting to the special operation mode after that, it becomes easy to perform combustion by compression self-ignition in the succeeding cylinder. 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. As described above, the temperature of the subsequent cylinder is raised in advance in the special idle operation mode, so that the combustion by the compression self-ignition in the subsequent cylinder can be promptly performed after the transition to the special operation mode.

  Further, in the above configuration, a gas flow path is formed 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 has 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 when the engine is in a predetermined engine state, the prohibition condition for the special operation mode is established, and the prohibition condition It is also effective to select the normal operation mode instead of the special operation mode and the special idle operation mode when it is established (claim 2).

  In this way, when the special operation mode is prohibited, the special idle operation mode during the idle operation is also prohibited and the normal operation mode is set. Also in this case, it is not necessary to switch the gas flow path every time the idle operation state is entered, and the frequency of switching the gas flow path can be reduced. Further, since the normal operation mode is the same as the conventional general combustion mode of the engine, combustion stability during idle operation can be ensured.

  The special operation mode prohibition condition includes engine temperature detection means for detecting the temperature state of the engine, and the special operation mode prohibition condition is when the temperature detected by the engine temperature detection means is lower than a predetermined value. (Claim 3).

  In this way, the special operation mode is prohibited and the normal operation mode is selected when the engine has low combustion stability and the combustion stability at the low temperature of the engine can be ensured.

  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 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, via the inter-cylinder gas passage between the pair of cylinders where the stroke and the intake stroke overlap. A gas flow path is formed in which a two-cylinder connection state is established such that the exhaust gas discharged from the exhaust gas is guided to an exhaust passage provided with a catalyst for purification, and provided with catalyst temperature detection means for detecting the temperature state of the catalyst As an operation mode, stratified combustion is performed with at least a lean air-fuel ratio that is a predetermined amount larger than the stoichiometric air-fuel ratio in the preceding cylinder while the gas flow path is in the two-cylinder connected state. In addition, a special operation mode in which 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 newly supplied fuel, and the gas flow path is connected to the two cylinders. However, without performing combustion in the preceding cylinder, unburned gas is directly introduced from the preceding cylinder to the succeeding cylinder, and homogeneous combustion is performed by spark ignition at the stoichiometric or richer air-fuel ratio in the succeeding cylinder. A special idle operation mode, and the special operation mode is selected at least when operating in a low-load low-rotation range, and the temperature detected by the catalyst temperature detecting means is lower than a predetermined value during idle operation. The special idle operation mode is sometimes selected.

  In this way, the fuel efficiency can be improved by improving the thermal efficiency and the pumping loss as in the configuration of the first aspect, and the cost can be reduced by eliminating the need for the lean NOx catalyst.

  Further, when the catalyst temperature is low (when it is in an inactive state), the temperature increase of the catalyst can be promoted more than in the special operation mode by setting the special idle operation mode. The special operation mode and the special idle operation mode are both in the two-cylinder connection state, but when comparing the exhaust temperatures when performing the same work (equivalent torque generation) in the special operation mode and the special idle operation mode during idling. In the special operation mode, the preceding cylinder performs stratified lean combustion, and the subsequent cylinder introduces hot burned gas from the preceding cylinder to become compression self-ignition combustion, and both stratified lean combustion and compression self-ignition combustion are in the form of low-temperature combustion. The temperature of the exhaust discharged from the subsequent cylinder is in a relatively low temperature state. On the other hand, in the special idle operation mode, only the succeeding cylinders are forcedly ignited and burned at the stoichiometric air-fuel ratio or richer air-fuel ratio (because the combustion range gradually expands due to flame propagation), the exhaust temperature Becomes higher. Therefore, the exhaust temperature can be increased in the special idle operation mode than in the special operation mode, so that the catalyst temperature can be increased.

  Therefore, since the catalyst temperature rise can be promoted while the two cylinders are connected without switching to the normal operation mode during idle operation, the frequency of switching the gas flow path can be reduced. That is, it is possible to prevent the fuel efficiency improvement effect from being reduced due to the response delay accompanying the switching, and the cost from being increased to ensure the durability of each operating part.

  It is more effective to select the special operation mode when the engine is in an idling operation and the temperature detected by the catalyst temperature detecting means is equal to or higher than a predetermined value.

  In this case, since the special operation mode is applied when the temperature of the catalyst is already high and is in an active state and it is not necessary to actively promote the temperature rise, further improvement in fuel consumption can be achieved. In this case, it is desirable to ensure combustion stability even when the special operation mode is applied during idle operation (for example, the engine has such characteristics or is in such an operation state). Or any other means for improving combustion stability).

  In the special operation mode, ignition assist means for igniting for ignition assist is provided before the appropriate timing of compression self-ignition so as to promote compression self-ignition in the succeeding cylinder. Is preferred.

  In this way, even in the relatively low load operation region where the special operation mode is selected, the compression self-ignition in the subsequent cylinder is promoted, and combustion by compression self-ignition can be surely performed. Generation is further suppressed, and fuel consumption can be further improved.

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 the engine control apparatus, the gas discharged from the preceding cylinder, which is the cylinder on the exhaust stroke side, between the pair of cylinders where the exhaust stroke and the intake stroke overlap is directly passed through the intercylinder gas passage to the subsequent cylinder which is the cylinder on the intake stroke side. 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. A special operation mode in which homogeneous combustion is performed in the succeeding cylinder together with newly supplied fuel and a gas flow path in the connected state of the two cylinders, and combustion in the preceding cylinder is not performed. A special idle operation mode in which unburned gas is introduced into the subsequent cylinder as it is, and homogeneous combustion is performed by spark ignition at a theoretical air-fuel ratio or richer air-fuel ratio in the subsequent cylinder,
The special operation mode is selected at least when operating in the low-load and low-speed range, and the special idle mode is selected during idle operation, or at least when the special-operation mode is selected when operating in the low-load and low-speed range. Since the special idle operation mode is selected when the idling operation is selected and the catalyst temperature is lower than a predetermined value, the fuel efficiency improvement effect by lean combustion, pumping loss reduction, etc. is obtained. By reducing the frequency of switching the gas flow path while ensuring the combustion stability during idling and promoting the temperature rise of the catalyst, it is possible to obtain a greater fuel efficiency improvement effect and cost reduction 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.

  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. 7).

  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. (See FIG. 7), 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. Further, 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, a water temperature sensor 27 (engine temperature detecting means) for detecting the temperature of the engine cooling water, a rotational speed sensor 47 for detecting the engine rotational speed, and an accelerator opening (accelerator pedal depression amount). ) For detecting an accelerator opening degree 48 (see FIG. 3 respectively).

  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, to an ECU (control unit) 40 for engine control comprising a microcomputer or the like, an air flow sensor 19, O ₂ sensor 23, the linear O ₂ sensor 25, water temperature sensor 27, speed sensor 47 and accelerator opening sensor The signals from 48 are respectively input. Control signals are output from the ECU 40 to the ignition circuit 8, the fuel injection valves 9, the actuator 18 of the multiple throttle valve 17, and the first and second control valves 37 and 39, respectively.

  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, Intake air amount control means 43 and combustion control means 44 are provided.

  The operating state discriminating means 41 examines the operating state of the engine based on signals from the catalyst temperature sensor 26, the water temperature sensor 27, the rotation speed sensor 47, the accelerator opening sensor 48, etc., and selects an operating mode. Specifically, when the engine coolant temperature by the water temperature sensor 27 is lower than a predetermined value (unwarmed air), or when the operation region is in the high load side or high rotation side operation region B shown in FIG. Select a mode. When the engine coolant temperature is equal to or higher than a predetermined value (warm-up completion) and the operation region is in the operation region A on the low load / low rotation side shown in FIG. 4, the special operation mode is selected. When the engine coolant temperature is equal to or higher than a predetermined value (warm-up completion) and the idling operation is being performed, the special idling operation mode is selected.

  The valve stop mechanism control means 42 controls the valve stop mechanism 35 by the control valves 37 and 39 to switch the gas flow path. The switching is performed according to the operation mode. Specifically, the two-cylinder connected state is set in the special operation mode and the special idle operation mode, and the individual cylinders are set in the normal operation mode. The operating state of each valve is controlled as follows.

Two-cylinder connection state: the leading cylinder exhaust valve 32a and the trailing cylinder intake valve 31a are stopped.
The burned gas discharge valve 32b and the burned gas introduction valve 31b are activated. Each cylinder is independent: the preceding cylinder exhaust valve 32a and the succeeding cylinder intake valve 31a are activated.
The burned gas discharge valve 32b and the burned gas introduction valve 31b are stopped. The intake air amount control means 43 controls the opening degree (throttle opening degree) of the throttle valve 17 by controlling the actuator 18, and operates. A target intake air amount is obtained from a map or the like according to the state, and the throttle opening is controlled according to the target intake air amount. In this case, in the special operation mode, as will be described later, in the succeeding cylinders (second and third cylinders 2B and 2C), in the gas introduced from the preceding cylinder in a state where the intake introduction from the branch intake passage 16 is blocked. Combustion is performed so that the ratio of the residual oxygen amount to the newly supplied fuel has a theoretical air-fuel ratio relationship (hereinafter referred to as a substantial stoichiometric air-fuel ratio). An amount of air necessary for the combustion of fuel according to torque (the amount of air that is the stoichiometric air-fuel ratio with respect to the amount of fuel for two cylinders) is supplied to the preceding cylinders (first and fourth cylinders 2A and 2D). Thus, the throttle opening is adjusted.

  Further, in the special idle operation mode, the throttle opening degree is set so that the amount of air is supplied to the preceding cylinders 2A and 2D so that the air-fuel ratio becomes the stoichiometric air-fuel ratio or slightly richer in the combustion in the succeeding cylinders 2B and 2C. Is adjusted.

  The combustion control unit 44 includes a fuel injection control unit 45 and an ignition control unit 46. The fuel injection control unit 45 causes the fuel injection amount and the injection timing from the fuel injection valves 9 provided in the respective cylinders 2A to 2D. Is controlled according to the operating state of the engine, and the ignition control means 46 controls the ignition timing and the ignition stop according to the operating state. In particular, the combustion control (fuel injection control and ignition control) is changed according to the operation mode.

  That is, in the normal operation mode, the fuel injection amount is controlled so that the air-fuel ratio of each of the cylinders 2A to 2D becomes the stoichiometric air-fuel ratio or richer, for example, in the most region of the normal operation mode. The air-fuel ratio is set to be richer than the stoichiometric air-fuel ratio in the fully open load and the operation region in the vicinity thereof. In this case, the injection timing is set so as to homogenize the air-fuel mixture by injecting fuel to each of the cylinders 2A to 2D in the intake stroke, and each cylinder 2A to 2D is forcedly ignited and homogenized. Burn.

  In the special operation mode, fuel injection is performed for the preceding cylinders 2A and 2D so that the air-fuel ratio is a lean air-fuel ratio larger than the stoichiometric air-fuel ratio, preferably approximately twice or more than the stoichiometric air-fuel ratio. In addition to controlling the amount, the injection timing is set so that fuel is injected in the compression stroke and the mixture is stratified, and the ignition timing is set so that forced ignition is performed near the compression top dead center . On the other hand, for the succeeding cylinders 2B and 2C, fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinder, and the fuel injection amount is controlled so as to obtain a substantial stoichiometric air-fuel ratio. The injection timing is set so that fuel is injected in the intake stroke. And combustion by compression self-ignition is performed without performing forced ignition. At this time, assist ignition is performed before the timing of compression self-ignition (near the compression top dead center). Therefore, the ignition control means 46 also functions as an ignition assist means. However, depending on conditions (for example, when the in-cylinder temperature of the succeeding cylinder is low), forced ignition may be performed without performing compression self-ignition.

  In the special idle operation mode, fresh air is sucked in the preceding cylinders 2A and 2D, but fuel injection is not performed here. That is, combustion is not performed. Accordingly, the fresh air is introduced as it is into the subsequent cylinder. In the succeeding cylinders 2B and 2C, the fuel injection amount is determined so that the fresh air becomes the stoichiometric air fuel ratio or a slightly richer air fuel ratio. The injection timing is set so that the fuel is injected during the intake stroke to homogenize the air-fuel mixture, and homogeneous combustion is performed by forced ignition.

  Table 1 below summarizes the characteristics of the gas flow path, the air-fuel ratio, and the ignition method for each of the above operation modes.

  As shown in Table 1, in the normal operation mode, the gas flow path is in an independent state for each cylinder, and the air-fuel ratio is the stoichiometric air-fuel ratio or richer (excess air ratio λ ≦ 1). Then, the preceding cylinders 2A, 2D and the succeeding cylinders 2B, 2C are subjected to forced ignition to perform homogeneous combustion.

  In the special operation mode, the gas flow path is set to the two-cylinder connection state, the air-fuel ratio of the preceding cylinders 2A and 2D is lean (excess air ratio λ> 1), and the fuel is injected so that the fuel is unevenly distributed near the spark plug at the time of ignition. . Then, stratified combustion is performed by forced ignition. On the other hand, in the succeeding cylinders 2B and 2C, the air-fuel ratio is set to a substantial stoichiometric air-fuel ratio (excess air ratio λ = 1), and homogeneous combustion is performed by compression self-ignition (in some cases, ignition assist ignition).

  In the special idle operation mode, the gas flow path is in a two-cylinder connection state, but in the preceding cylinders 2A and 2D, only intake is performed and combustion is not performed. In the succeeding cylinders 2B and 2C, the air-fuel ratio is set to the stoichiometric air-fuel ratio or richer than the fresh air introduced from the preceding cylinder (excess air ratio λ ≦ 1). Then, forced ignition is performed to perform homogeneous combustion.

  Next, the operation of the engine 1 of this embodiment will be described. First, the operation mode is selected according to the operation state. FIG. 5 is a flowchart for selecting an operation mode. When this control starts, first, the operating state is determined in step S1. Then, it is determined whether or not the coolant temperature detected by the water temperature sensor 27 is equal to or higher than a predetermined value (step S3). If NO, the process proceeds to step S13 and the normal operation mode is selected. If YES in step S3, it is next determined whether or not the operation region is operation region B shown in FIG. 4 (step S5). If YES, the process proceeds to step S13 and the normal operation mode is selected. . If NO in step S5, it is further determined whether or not the engine is idling (step S7). If YES, the process proceeds to step S9 to select the special idle operation mode. If NO, the process proceeds to step S11. Transition to the special idle operation mode is selected.

  When the normal operation mode is selected, 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 substantial fresh air and gas flow paths are as shown in FIG. 6, and the intake ports 11 and 11 a and the exhaust ports 12 a and 12 of each cylinder 2 </ b> A to 2 </ b> D are substantially independent of each other, and each cylinder 2 </ b> A from the intake passage 15. Fresh air is introduced into the ~ 2D intake ports 11 and 11a, and burned gas is discharged from the exhaust ports 12a and 12 of the cylinders 2A to 2D into the exhaust passage 20.

  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, high output is obtained in the operation region B of high rotation or high load, and combustion stability can be ensured even in the state of unwarmed air where the cooling water temperature is low.

  When the special operation mode is selected, the combustion cycle of each cylinder is as shown in FIG. FIG. 7 is a diagram showing the exhaust stroke, intake stroke, fuel injection timing, ignition timing, and the like of each cylinder in the special operation mode. Each stage of FIG. 7 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, and a star mark in the figure indicates that compression self-ignition is performed. As shown in FIG. 7, 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. 8, 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 in the intake stroke (arrow a in FIG. 8), and the air-fuel ratio detected by the linear O ₂ sensor 25 is detected in the preceding cylinders 2A and 2D. Fuel is injected in the compression stroke while the fuel injection amount is feedback controlled so that the super lean air / fuel ratio is approximately twice or more than the theoretical air / fuel ratio, and ignition is performed at a predetermined ignition timing. Stratified combustion is performed at the fuel ratio (see FIG. 7).

  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. 7 and the arrow b in FIG. 8). 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 compression self-ignition is performed by increasing the pressure and temperature in the combustion chamber near the top dead center of the compression stroke (see FIG. 7).

  When compression auto-ignition is performed in the succeeding cylinders 2B and 2C, the entire combustion chamber is burned at a time, 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. In order to promote the compression self-ignition, it is better to ignite as an ignition assist before the compression self-ignition timing (in the vicinity of compression top dead center).

  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 lean air-fuel ratio that is approximately twice or more than the stoichiometric air-fuel ratio, so that the amount of NOx generated is relatively small. In the succeeding cylinders 2B and 2C, the preceding cylinders 2A and 2D By introducing the burned gas, a state equivalent to that in which a large amount of EGR is performed is achieved, and low temperature combustion by compression self-ignition is executed, so that the generation of NOx is sufficiently suppressed. This is also advantageous for improving emissions.

  Moreover, since only the stoichiometric burned gas discharged from the succeeding cylinder is guided to the exhaust passage, exhaust purification is sufficiently performed by simply providing a three-way catalyst in the exhaust passage, and combustion at a lean air-fuel ratio is conventionally performed. The lean NOx catalyst that is required in the case of carrying out is unnecessary and the cost can be reduced.

  When the special idle operation mode is selected, the same control as in the special operation mode is performed as the gas flow path as shown in FIG. At this time, intake is performed in the preceding cylinders 2A and 2D (arrow a in FIG. 9), but fuel injection and ignition are not performed, and the fresh air is then introduced into the intake stroke of the preceding cylinders 2A and 2D and the subsequent cylinders 2B and 2B. In the period in which the exhaust strokes of 2C overlap, they are directly introduced into the succeeding cylinders 2B and 2C through the inter-cylinder gas passage 22 (arrow b in FIG. 9). In the succeeding cylinders 2B and 2C, fuel is supplied to the fresh air introduced from the preceding cylinders 2A and 2D, and the fuel injection amount is controlled so as to become the stoichiometric air-fuel ratio or an air-fuel ratio richer than that. Fuel is injected. Then, the spray is homogenized during the period from the intake stroke to the compression stroke, and forced ignition is performed near the top dead center of the compression stroke to perform homogeneous combustion.

  In this way, in the special idle operation mode, the gas flow path is in the same two-cylinder connection state as in the special operation mode, so there is no need to switch the gas flow path every time the idle operation state is entered, and the frequency of switching the gas flow path is increased. Can be reduced. Therefore, it is possible to prevent the fuel efficiency improvement effect from being reduced due to the response delay accompanying the switching, and the cost from being increased to ensure the durability of each operating part. In addition, since homogeneous combustion is performed at a stoichiometric air-fuel ratio or richer air-fuel ratio while introducing fresh air, combustion stability can be sufficiently ensured even during idling, where combustion stability tends to decrease.

  Further, since the combustion is performed in the succeeding cylinders 2B and 2C, the temperatures of the succeeding cylinders 2B and 2C are appropriately high. Therefore, when shifting to the special operation mode after that, it becomes easy to perform combustion by compression self-ignition in the succeeding cylinders 2B and 2C.

  As shown in the flowchart of FIG. 5, the special operation mode is not selected even in the operation region A, that is, the prohibition is determined as NO in step S3, that is, the cooling water temperature is less than a predetermined value. Is the case. At this time, even during the idling operation, the process proceeds to step S13 and the normal operation mode is selected. As a result, the special idling operation mode is also prohibited. Also in this case, it is not necessary to switch the gas flow path every time the idle operation state is entered, and the frequency of switching the gas flow path can be reduced.

  Next, a modified example of the control for selecting the operation mode will be described. In this modification, combustion stability can be ensured even when the special operation mode is applied during idle operation (for example, an engine with such characteristics, or some other means for improving combustion stability are provided). Etc.), it is suitable.

  FIG. 10 is a flowchart for this modification. When this control is started, first, the operating state is determined in step S21. Then, it is determined whether or not the operation region is the operation region B shown in FIG. 4 (step S23). If YES, the process proceeds to step S35 and the normal operation mode is selected. If NO in step S23, it is next determined whether or not the engine is idling (step S25). If YES, the temperature of the three-way catalyst 24 detected by the catalyst temperature sensor 26 is more than a predetermined value. It is determined whether or not there is (step S27). And if it is NO at Step S27, it will shift to Step S31 and will select special idle operation mode.

  Going back, if NO is determined in step S25 and if YES is determined in step S27, the process proceeds to step S29, and whether or not the coolant temperature detected by the water temperature sensor 27 is equal to or higher than a predetermined value. Is made. If YES in step S29, the process proceeds to step S33 and the special operation mode is selected. If NO, the process proceeds to step S35 and the normal operation mode is selected.

  In this modification, when the temperature of the three-way catalyst 24 is low (when inactive), the special idle operation mode is set. The special idle operation mode is a two-cylinder connection state as in the special operation mode, but in the special operation mode, the preceding cylinders 2A and 2D are stratified lean combustion, and the succeeding cylinders 2B and 2C are hot burned of the preceding cylinders 2A and 2D. Since gas is introduced and compression self-ignition combustion is performed, and both stratified lean combustion and compression self-ignition combustion are in the form of low-temperature combustion, the temperature of exhaust discharged from the succeeding cylinders 2B and 2C becomes a relatively low temperature state. On the other hand, in the special idle operation mode, only the following cylinders 2B and 2C are forcibly ignited and burned at the stoichiometric air-fuel ratio or richer air-fuel ratio (because the combustion range is gradually expanded by flame propagation). The exhaust temperature becomes higher. Therefore, the exhaust temperature is higher in the special idle operation mode than in the special operation mode. Therefore, by applying the special idle operation mode, the temperature increase of the three-way catalyst 24 can be promoted more than when the special operation mode is set.

  In this way, the catalyst temperature rise can be promoted while the two-cylinder connection state is maintained without switching to the normal operation mode during idle operation, so the frequency of switching the gas flow path can be reduced. That is, it is possible to prevent the fuel efficiency improvement effect from being reduced due to the response delay accompanying the switching, and the cost from being increased to ensure the durability of each operating part.

  Since the special operation mode is applied when the temperature of the three-way catalyst 24 is equal to or higher than a predetermined value and is in an active state and it is not necessary to positively promote the temperature rise, further improvement in fuel consumption can be achieved. . However, even in this case, when the cooling water temperature is low (YES in step S27 and NO in step S29), the normal operation mode is selected, but the catalyst temperature and the cooling water temperature have a strong correlation. The frequency is low.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to the said embodiment, A various deformation | transformation is possible within the range described in the claim. For example, the engine body 1 is not limited to a four-cylinder engine, and can be applied to an engine having a larger number of cylinders. Even if the preceding cylinder and the succeeding cylinder are set in a pair of cylinders in which the exhaust stroke and the intake stroke overlap each other, good.

  Further, the operation mode is not necessarily limited to the normal operation mode, the special operation mode, and the special operation mode, and may have other modes.

  The fuel injection into the subsequent cylinder does not necessarily have to be performed by the injector 9 that injects the fuel into the combustion chamber 4. For example, some fuel supply mechanism may be provided in the inter-cylinder gas passage 22, and in the special idle operation mode. May be supplied with fuel by the injectors 9 of the preceding cylinders 2A and 2D (however, ignition in the preceding cylinders 2A and 2D is not performed).

  The engine temperature detecting means is not limited to the water temperature sensor, and for example, the catalyst temperature sensor 26 may be used, or a means for separately measuring or predicting may be used.

  As a prohibition condition for the special operation mode, a condition other than the engine coolant temperature (for example, an elapsed time from the engine start) may be set or combined.

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 a flowchart for an operation mode selection. It is explanatory drawing which shows the substantial combustion state in normal operation mode. 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 explanatory drawing which shows the substantial combustion state in special idle operation mode. It is a flowchart for the modification of an operation mode selection.

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 24 (Three-way) catalyst 26 Catalyst temperature sensor (catalyst temperature detection means)
27 Water temperature sensor (engine temperature detection means)
40 ECU
44 Combustion control means 46 Ignition control means (ignition assist means)

Claims (6)

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 which is the cylinder on the exhaust stroke side is directly introduced into the subsequent cylinder which is the cylinder on the intake stroke side via the inter-cylinder gas passage, A gas flow path is formed in which a two-cylinder connection state is established such that 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. A special operation mode in which burned gas having a lean air-fuel ratio is introduced to perform homogeneous combustion in the succeeding cylinder together with newly supplied fuel;
While the gas flow path is in the connected state of the two cylinders, combustion in the preceding cylinder is not performed, unburned gas is directly introduced from the preceding cylinder to the succeeding cylinder, and the stoichiometric air-fuel ratio or a richer air in the succeeding cylinder is obtained. A special idle operation mode in which homogeneous combustion is performed by spark ignition at a fuel ratio,
A control device for a spark ignition engine, wherein the special operation mode is selected at least during operation in a low load and low rotation range, and the special idle operation mode is selected during idle operation. 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 special operation mode prohibition condition is satisfied when the engine is in a predetermined engine state, and the normal operation mode is selected instead of the special operation mode and the special idle operation mode when the prohibition condition is satisfied. Item 2. A spark ignition engine control device according to Item 1. Engine temperature detecting means for detecting the temperature state of the engine,
The spark ignition engine control device according to claim 2, wherein the prohibition condition of the special operation mode is satisfied when a temperature detected by the engine temperature detecting means is lower than a predetermined value. 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 which is the cylinder on the exhaust stroke side is directly introduced into the subsequent cylinder which is the cylinder on the intake stroke side via the inter-cylinder gas passage, A gas flow path is formed in which the exhaust gas discharged from the cylinder is connected to a two-cylinder state in which the exhaust gas is guided to an exhaust passage provided with a catalyst for purification.
A catalyst temperature detecting means for detecting the temperature state of the catalyst;
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. A special operation mode in which burned gas having a lean air-fuel ratio is introduced to perform homogeneous combustion in the succeeding cylinder together with newly supplied fuel;
While the gas flow path is in the connected state of the two cylinders, combustion in the preceding cylinder is not performed, unburned gas is directly introduced from the preceding cylinder to the succeeding cylinder, and the stoichiometric air-fuel ratio or a richer air in the succeeding cylinder is obtained. A special idle operation mode in which homogeneous combustion is performed by spark ignition at a fuel ratio,
When operating at least in the low load and low speed range, the above special operation mode is selected,
The control apparatus for a spark ignition engine, wherein the special idle operation mode is selected during idling and when the temperature detected by the catalyst temperature detecting means is lower than a predetermined value. 5. The spark ignition engine control device according to claim 4, wherein the special operation mode is selected when the engine is in an idling operation and the temperature detected by the catalyst temperature detecting means is equal to or higher than a predetermined value.   An ignition assist means for igniting for ignition assistance is provided before an appropriate timing of compression self-ignition so as to promote compression self-ignition in the subsequent cylinder in the special operation mode. The control device for a spark ignition engine according to any one of 1 to 5.

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