JP2006070859A - Spark ignition type gasoline engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve fuel economy performance and exhaust gas performance, by maintaining operation for performing compressed self-ignition in the widest load area by introducing burnt gas burnt in a lean state by a preceding cylinder into a succeeding cylinder. <P>SOLUTION: When controlling a special operation mode of performing the compressed self-ignition in the succeeding cylinder by introducing the burnt gas into the succeeding cylinder by performing lean combustion in the preceding cylinder, when the succeeding cylinder intake air temperature rises to the upper limit temperature T1 or more, the EGR ratio R is increased, or the air-fuel ratio of the preceding cylinder is corrected to the richer side than the air-fuel ratio corresponding to an initial set value. When the succeeding cylinder intake air temperature T is the lower limit temperature T2 or less, the EGR ratio R is reduced, or the air-fuel ratio of the preceding cylinder is corrected to the lean side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a spark ignition gasoline engine, and in particular, introduces burned gas burned lean in a preceding cylinder in an exhaust stroke between a pair of cylinders in which an exhaust stroke and an intake stroke overlap into a subsequent cylinder in an intake stroke as it is. In addition, the present invention relates to a spark-ignition gasoline engine having a special operation mode as an operation mode in which the subsequent cylinder performs premixed compression auto-ignition combustion (HCCI: Homogeneous-Charge Compression-Ignition Combustion. .

  As a technique for improving the fuel economy performance and exhaust gas performance of a spark ignition type gasoline engine, as shown in Patent Document 1, six cycles of two compressions and expansions are performed for one intake and exhaust, A structure in which subsequent combustion is performed and compression self-ignition is performed in a low speed, low load region, or, as described in Patent Document 2, an intake valve is opened after an exhaust valve is closed in a predetermined partial load region. In the meantime, by setting a minus overlap (period in which both the intake valve / exhaust valve are closed), the amount of internal EGR is increased, and the cylinder temperature is increased by this internal EGR to cause compression self-ignition. The configuration is known.

  However, the configuration of Patent Document 1 is a control technology that performs compression self-ignition in a low speed and low load region. However, since the configuration is switched to 6-cycle operation, torque fluctuation is likely to occur and compression self-ignition occurs in the same cylinder. As a result, the combustion control becomes difficult. On the other hand, in the configuration of Patent Document 2, compression self-ignition is effectively performed by the internal temperature rise action by the internal EGR in a relatively low speed / low load region, but in the extremely low load region, it is also good by the internal EGR. In-cylinder temperature may not reach the extent that compression self-ignition is performed. Further, there is a concern that the combustion chamber temperature will rise excessively on the relatively high speed / high load side, and knocking is likely to occur. In such a case, it is conceivable to reduce the in-cylinder temperature. Simply lowering the temperature will reduce the self-ignitability.

On the other hand, the applicant of the present invention, as disclosed in Patent Document 3, has an exhaust stroke in a partial load region of the engine in order to achieve a significant fuel efficiency improvement effect by using both lean combustion and compression self-ignition. Between the pair of cylinders where the intake stroke and the intake stroke overlap, the burned gas discharged from the preceding cylinder in the exhaust stroke is introduced into the subsequent cylinder in the intake stroke as it is through the inter-cylinder gas passage, In the cylinder, the air-fuel ratio is set to a lean air-fuel ratio larger than the stoichiometric air-fuel ratio, combustion is performed by forced ignition, and in the subsequent cylinder, fuel is supplied to the burned gas of the lean air-fuel ratio introduced from the preceding cylinder to compress the self We have applied for a technology related to a control device for a spark-ignition gasoline engine in which combustion is performed by ignition.
JP 2001-336435 A JP 2001-152919 A JP 2003-227377 A

  In the case of adopting the configuration of Patent Document 3, in addition to improving fuel efficiency by lean combustion of the preceding cylinder, by introducing high-temperature internal EGR gas by lean combustion into the succeeding cylinder, compression self-ignition becomes possible, and a wide operating range Therefore, the combustion efficiency close to that of a diesel engine can be realized, and the exhaust gas performance can be greatly improved.

  However, in order to improve fuel efficiency and exhaust gas performance with an engine of the type described in Patent Document 3 (stratified combustion is performed in the preceding cylinder and compression self-ignition is performed in the succeeding cylinder), a misfire occurs in the succeeding cylinder. Control to prevent knocking is required.

  Based on such a technique, the present invention introduces burned gas lean-burned in the preceding cylinder into the succeeding cylinder and maintains the operation of performing compression self-ignition in the widest possible load range. It is an object to provide a spark ignition gasoline engine that can improve the exhaust gas performance.

  As a result of earnest research, the inventor of the present invention has a ratio of EGR (exhaust gas recirculation) supplied to the subsequent cylinder from the viewpoint of preventing misfire and knocking during compression self-ignition when using both lean combustion and compression self-ignition. And found that there is a certain correlation between the intake air temperature and the subsequent cylinder intake air temperature, and completed the present invention.

  That is, the present invention relates to a multi-cylinder engine main body in which the combustion cycle of intake, compression, expansion, and exhaust of each cylinder is performed with a predetermined phase difference, and exhaust gas discharged to the exhaust passage to the EGR passage. A cold EGR device that recirculates to the intake passage, and an operating state control device that controls the operating state of the engine body and the cold EGR device. A normal operation mode in which burned gas is combusted after exhausted from the passage and exhausted to the exhaust passage, and burned gas lean burned in a preceding cylinder in the exhaust stroke between a pair of cylinders in which the exhaust stroke and the intake stroke overlap Is operated as it is in the succeeding cylinder in the intake stroke, and the subsequent cylinder is controlled to switch between the special operation mode in which compression self-ignition is performed. Conversion means, subsequent cylinder intake air temperature detecting means for detecting the subsequent cylinder intake air temperature when burned gas is introduced into the subsequent cylinder, and EGR recirculated by the cold EGR device among the gases introduced into the subsequent cylinder Means for obtaining an EGR ratio that combines the ratio of gas and the ratio of gas equivalent to EGR generated by combustion in the preceding cylinder, and the EGR ratio and the succeeding cylinder intake temperature when the burned gas is introduced into the succeeding cylinder Storage means for storing an appropriate range of the succeeding cylinder intake temperature in which the compression self-ignition operation is ensured in the succeeding cylinder based on the relationship, and the EGR rate and the succeeding cylinder intake temperature detected by the succeeding cylinder intake temperature detecting means, In the special operation mode, the subsequent cylinder intake air temperature is set to fall within an appropriate range lower than the upper limit temperature stored in the storage means and higher than the lower limit temperature. A spark-ignition gasoline engine characterized in that for controlling at least one of the air-fuel ratio of the EGR device and the preceding cylinders.

  In this aspect, when the special operation mode is set in the partial load region of the engine, the fuel efficiency improvement effect is obtained by improving the thermal efficiency by lean combustion in the preceding cylinder and reducing the pumping loss in each cylinder. Further, in the succeeding cylinder, fuel is supplied to the burned gas introduced from the preceding cylinder and combustion is performed, so that vaporization of the supplied fuel is promoted by the high-temperature burned gas and combustion is performed in the succeeding cylinder by compression self-ignition. Therefore, slow combustion that does not contribute to work by burning all over the combustion chamber is avoided, and a high fuel efficiency improvement effect is obtained. In addition, since the burned gas from the preceding cylinder is introduced into the succeeding cylinder, a state equivalent to that in which a large amount of EGR is performed is obtained, so that an effect of improving the exhaust gas performance can be obtained.

  Moreover, when the engine body is operated in the special operation mode, at least of the cold EGR device and the air-fuel ratio of the preceding cylinder based on the relationship between the EGR rate and the succeeding cylinder intake temperature when the burned gas is introduced into the succeeding cylinder. By controlling one of them, it is possible to maintain a suitable EGR rate for each subsequent cylinder intake air temperature and to avoid both knocking and misfire. This is based on the knowledge about the relationship between the subsequent cylinder intake temperature and the EGR rate found by the present inventor. As will be described in detail later, if the subsequent cylinder intake temperature is the same in the subsequent cylinder, the EGR rate Knocking is likely to occur when the value is lower than a certain level, and misfire is likely to occur when the EGR rate is higher than a certain level. Further, when the intake temperature of the succeeding cylinder becomes low, the EGR rate at which misfire and knocking are likely to occur tends to decrease. Therefore, in this aspect, in the temperature of the intake air introduced into the succeeding cylinder and the EGR rate corresponding thereto, an area in which operation in an appropriate special operation mode can be performed is mapped and stored by experiment, and standard EGR is stored. The following cylinder intake air temperature suitable for this EGR rate is obtained using the rate as the initial set value, and the cold detection is performed so that the EGR rate measured by the measuring means becomes an appropriate value based on the subsequent cylinder intake air temperature detected by the temperature detecting means. At least one of the EGR device and the air-fuel ratio is controlled. Thereby, for example, by using an existing temperature sensor, it becomes possible to prevent misfire and knocking as much as possible.

  The “EGR rate” is defined by the following equation (1), for example.

However,
m _DISC : Mass of air burned in the preceding cylinder m _HCCI : Mass of air burned in the succeeding cylinder m _EGR-cold : Mass of EGR gas supplied to the preceding cylinder by the cold EGR device The spark ignition gasoline engine The operating state control device includes ignition assist control means for sparking a spark plug provided in the succeeding cylinder in order to assist the ignition in the succeeding cylinder in a mode in which the succeeding cylinder is operated by compression self-ignition. The proper range stored in the storage means preferably includes an ignition assist control region by the operation of the ignition assist control means.

  In this mode, even in the operation region where the compression self-ignition in the subsequent cylinder is difficult to be performed, the control for promoting the compression self-ignition of the subsequent cylinder is properly performed by the ignition assist control means, and the compression self-ignition is appropriately performed in the subsequent cylinder. As a result, the fuel efficiency can be significantly improved and the exhaust gas performance can be improved.

  In the above aspect, it is preferable that the ignition assist control means ignites the air-fuel mixture in the succeeding cylinder in the vicinity of the top dead center before the compression top dead center.

  According to this aspect, the control is executed to increase the pressure in the cylinder instantaneously by igniting the air-fuel mixture in the vicinity of the top dead center before the compression top dead center of the subsequent cylinder, so that the subsequent cylinder is reliably compressed at an appropriate time. Can be self-ignited.

  In the above aspect, it is preferable that the operating state control device has an EGR rate control means for increasing the EGR rate when the succeeding cylinder intake air temperature is equal to or higher than an upper limit temperature.

  In this aspect, since the knocking region is distributed on the low EGR rate side on the high temperature side of the subsequent cylinder intake temperature, which is generally on the high load side, the EGR rate is further improved to avoid knocking. Yes. As a result, even in the high load side, the operation in the special operation mode can be maintained and the fuel efficiency and the exhaust gas performance can be improved.

  In the above aspect, when the EGR rate cannot be increased by the cold EGR device, the operating state control device corrects the air-fuel ratio of the preceding cylinder to be richer than the air-fuel ratio corresponding to the initial set value. It is preferable to have.

  In this aspect, the amount of fresh air consumed in the preceding cylinder is increased by correcting the air / fuel ratio of the preceding cylinder to be richer than the air / fuel ratio corresponding to the initial set value, so that the succeeding cylinder intake temperature rises. However, as a result of the EGR rate defined by the equation (1) also increasing, the operation in the knocking region can be avoided. For this reason, even when it is difficult to increase the EGR rate on the high load side, the operation in the special operation mode can be maintained.

  In another aspect, the operating state control device includes fuel injection control means for controlling fuel injection, and the fuel injection control means is configured to make the air-fuel ratio of the preceding cylinder richer than the air-fuel ratio corresponding to the initial set value. After the correction, the fuel injection of the subsequent cylinder is preferably performed in the compression stroke of the subsequent cylinder.

  In this aspect, when the EGR rate cannot be increased by the cold EGR device, after correcting the air-fuel ratio of the preceding cylinder to be richer than the air-fuel ratio corresponding to the initial set value, fuel injection in the subsequent cylinder is further performed. Since it is performed in the compression stroke of the succeeding cylinder, the time during which the fuel is turned into a high-temperature gas is shortened and ignition is difficult. As a result, it is possible to effectively avoid the occurrence of knocking.

  In the above aspect, the operation state control device preferably opens the fresh air introduction valve of the subsequent cylinder when the air-fuel ratio of the preceding cylinder is corrected to a richer side than the air-fuel ratio corresponding to the initial set value. .

  In this aspect, when the EGR rate cannot be increased by the cold EGR device, when the air-fuel ratio of the preceding cylinder is corrected to be richer than the air-fuel ratio corresponding to the initial set value, fresh air is further introduced into the succeeding cylinder. Therefore, the subsequent cylinder intake air temperature of the subsequent cylinder is lowered by the introduced latent heat of vaporization of the fresh air, and the operation in the knocking region can be avoided. As a result, it is possible to effectively avoid the occurrence of knocking.

  In the above aspect, it is preferable that the operating state control device has an EGR rate control means for reducing the EGR rate when the succeeding cylinder intake air temperature is equal to or lower than a lower limit temperature.

  In this aspect, since the misfire region is distributed on the high EGR rate side on the low temperature side of the subsequent cylinder intake temperature, which is generally on the low load side, the EGR rate is reduced below this to avoid misfire. Yes. As a result, even in the low load side, the operation in the special operation mode can be maintained and the fuel efficiency and the exhaust gas performance can be improved.

  In the above aspect, when the EGR rate cannot be reduced by the cold EGR device, the operating state control device corrects the air-fuel ratio of the preceding cylinder to be leaner than the air-fuel ratio corresponding to the initial set value. It is preferable to have.

  In this aspect, by correcting the air-fuel ratio of the preceding cylinder to be leaner than the air-fuel ratio corresponding to the initial set value, the subsequent-cylinder intake air temperature decreases, but the EGR rate defined by Equation (1) also decreases. Driving in the misfire area can be avoided. As a result, even when it is difficult to reduce the EGR rate on the low load side, the operation in the special operation mode can be maintained.

  In a preferred aspect of the present invention, the operating state control device controls at least one of the cold EGR device and the air-fuel ratio of the preceding cylinder so as to fall within the appropriate range of the ignition assist region.

  In this aspect, it is difficult to knock, and by changing the ignition assist timing (ignition plug spark timing), the EGR rate (EGR rate in the ignition assist region) that can control the compression self-ignition timing is set, so that proper combustion is achieved. Compressive self-ignition that provides torque is possible.

  As described above, according to the present invention, the burned gas burned lean in the preceding cylinder by controlling the EGR or the air-fuel ratio based on the correlation between the intake cylinder temperature to the succeeding cylinder and the EGR rate. By maintaining the operation in the special operation mode in which the is introduced into the succeeding cylinder in a load range as wide as possible, the fuel consumption performance and the exhaust gas performance can be improved.

  Hereinafter, preferred embodiments of the present invention will be described.

  FIG. 1 shows a schematic configuration of an engine according to an embodiment of the present invention, and FIG. 2 schematically shows a structure of one cylinder of an engine main body 10 and intake and exhaust valves provided for the cylinder.

  In these drawings, the engine of the present embodiment is a spark ignition type four-cylinder four-cycle engine, and includes an engine body 10 and an ECU 100 that controls the engine body 10.

  The engine body 10 includes a cylinder block 11A and a cylinder head 11B integrated with the upper portion of the cylinder block 11A. A crankshaft 12 is disposed in the cylinder block 11A. Around the crankshaft 12, a pair of crank angle sensors 13A and 13B having a phase difference in the circumferential direction are arranged, and respective detection signals are input to the ECU 100. As will be described later, the ECU 100 detects the engine speed from the detection signal of one of the crank angle sensors 13A, and can identify the rotational direction of the crankshaft 12 from the detection signals of both the crank angle sensors 13A, 13B. It has become.

  Four cylinders 14A to 14D arranged in the longitudinal direction of the crankshaft 12 are formed in the cylinder block 11A.

  Four pistons 15 connected to the crankshaft 12 are fitted in each of the cylinders 14A to 14D. In this embodiment, when the first cylinder 14A, the second cylinder 14B, the third cylinder 14C, and the fourth cylinder 14D are called from one end side in the cylinder row direction, the stroke in which the piston 15 moves up and down in each of the cylinders 14A to 14D. As shown in Table 1, the crank angle is 180 ° in order so that the combustion cycle of the cylinders 14A to 14D is in the order of the first cylinder 14A, the third cylinder 14C, the fourth cylinder 14D, and the second cylinder 14B. The phase difference is set.

  A combustion chamber 16 is formed above each piston 15.

  A spark plug 17 fixed to the cylinder head 11 </ b> B is provided at the top of the combustion chamber 16 of each cylinder 14 </ b> A to 14 </ b> D, and the tip of the plug faces the combustion chamber 16. An ignition circuit 18 capable of controlling the ignition timing by electronic control is connected to the ignition plug 17.

  A fuel injection valve 19 that directly injects fuel into the combustion chamber 16 is provided at a side portion of the combustion chamber 16. This fuel injection valve 19 incorporates a needle valve and a solenoid (not shown), and when a pulse signal is input from a fuel injection control means described later, the fuel injection valve 19 is driven and opened for a time corresponding to the pulse width at the pulse input timing. The fuel is injected and an amount of fuel corresponding to the valve opening time is injected. The fuel injection valve 19 is supplied with fuel via a fuel supply passage or the like by a fuel pump (not shown), and the fuel pressure is higher than the pressure in the combustion chamber 16 during the compression stroke. A supply system is configured.

  An intake passage 22 is provided in the engine body 10 in order to introduce fresh air into each of the cylinders 14A to 14D. A throttle valve 23 is provided in the intake passage 22. Further, on the upstream side of the throttle valve 23, a temperature sensor 24 for detecting the temperature of the supplied air and an air flow sensor 25 for measuring the flow rate are provided. An intake manifold 22a is connected downstream of the throttle valve 23 in the intake passage 22 and an independent pipe 22b is connected to the intake ports 40A and 40B of the cylinders 14A to 14D.

On the other hand, in order to discharge burnt gas from each of the cylinders 14A to 14D, the engine body 10 is connected to an exhaust passage 27 via a branch exhaust passage 26. An upstream end portion of the exhaust passage 27 is provided with an O ₂ sensor 28 that detects the oxygen concentration in the exhaust gas. Further, a three-way catalyst 29 is provided downstream of the O ₂ sensor 28 in the exhaust passage 27 for exhaust gas purification. As is generally known, the three-way catalyst 29 has high purification performance for HC, CO, and NOx when the air-fuel ratio of the exhaust gas is in the vicinity of the stoichiometric air-fuel ratio (that is, the excess air ratio λ = 1). It is the catalyst shown.

  Further, as shown in FIG. 1, the engine body 10 is provided with a cold EGR device 30 that connects the exhaust passage 27 and the intake passage 22 in order to return the cooled EGR gas to the intake passage 22. In the cold EGR passage 30a of the apparatus 30, an EGR cooler 31 is provided as a cooling means for cooling the EGR gas, and a cold EGR valve 32 for controlling the amount of EGR gas is provided.

  Next, the piping structure of each of the cylinders 14A to 14D, the intake passage 22, and the exhaust passage 27 will be described.

  As described above, in the four-cylinder engine of this embodiment, the combustion strokes of the cylinders 14A to 14D are performed in the order shown in Table 1. At this time, between a pair of cylinders in which the exhaust stroke and the intake stroke overlap, a cylinder on the exhaust stroke side (referred to as a preceding cylinder in this specification) to a cylinder on the intake stroke side (referred to as a subsequent cylinder in this specification). By directing the burnt gas as it is, the preceding cylinder performs lean combustion, and the succeeding cylinder can be operated in a special operation mode in which compression self-ignition is performed. Therefore, in order to enable operation in such a special operation mode, each cylinder 14A to 14D has the following piping structure.

  First, in the cylinder head 11B in this embodiment, two sets of ports 40A, 40B, 41A, and 41B are formed in pairs for each combustion chamber 16 of each cylinder 14A to 14D.

  One set of ports 40 </ b> A and 40 </ b> B is an intake port communicating with the intake passage 22. One (port 41A) of the other pair of ports 41A and 41B is an exhaust port connected to the exhaust passage 27 via the branch exhaust passage 26. The other (port 41B) is a cylinder that communicates with each other in the longitudinal direction of the crankshaft 12 (in the example shown, the first cylinder 14A and the second cylinder 14B, and the third cylinder 14C and the fourth cylinder 14D). It is a hot EGR port connected so as to be able to communicate with the intermediate gas passage 42.

  The intake ports 40A and 40B, the exhaust port 41A, and the hot EGR port 41B are provided with on-off valves 43 to 45 attached to the cylinder head 11B. Each on-off valve 43 to 45 is driven so as to open and close at a predetermined timing by a known valve operating mechanism including camshafts 46, 47 and the like. Thereby, one on-off valve 43 functions as an intake valve, and the other one of the on-off valves 44 and 45 disposed on the exhaust port 41A (the on-off valve 44) is connected to the hot EGR port 41B as an exhaust valve. The arranged one (open / close valve 45) functions as a hot EGR valve.

  Further, among these on-off valves 43 to 45, those arranged in the intake ports 40A, 40B of the second and third cylinders 14B, 14C and those in the exhaust ports 41A of the first, fourth cylinders 14A, 14D. Further, valve stop mechanisms 48 and 49 are provided for switching the valves 43 to 45 between the operation state and the stop state for the ones disposed in the hot EGR ports 41B. The structure of the valve stop mechanisms 48 and 49 is known in the art and will not be shown in detail. For example, the hydraulic oil is applied to the tappet interposed between the cams of the camshafts 46 and 47 and the valve shaft. In the state where hydraulic oil is supplied to the hydraulic chamber, and the hydraulic oil is supplied to the hydraulic chamber, the cam operation is transmitted to the valve to open and close the valve, and when the hydraulic oil is discharged from the hydraulic chamber, the cam This is realized by configuring the valve to stop when the operation of is not transmitted to the valve.

  As will be described later, the valve stop mechanisms 48 and 49 are configured to selectively open and close the corresponding on-off valves 43 to 45 by the ECU 100. As a result, the ECU 100 can operate the engine body 10 in a plurality of operation modes (special operation mode and normal operation mode). Further, the engine body 10 is provided with a water temperature sensor 50 that detects the water temperature of the engine cooling water.

The ECU (control unit) 100 includes a crank angle sensor 13A, 13B, a temperature sensor 24, an air flow sensor 25, an O ₂ sensor 28, a water temperature sensor 50, and an accelerator opening (accelerator pedal depression amount) for determining the operation state. An accelerator opening sensor 51 is connected to detect each of the detected signals. The ECU 100 is connected to actuators (not shown) provided in the fuel injection valves 19 and the valve stop mechanisms 48 and 49, and these mechanisms can be driven and controlled based on input signals. Has been.

  The ECU 100 includes a storage unit 110 that stores programs and data necessary for control, an operation mode switching unit 120 that is functionally configured by a program stored in the storage unit 110, a subsequent cylinder intake air temperature estimation unit 130, an EGR rate. An operation state control device including a control unit 140, an air-fuel ratio control unit 150, an ignition assist control unit 160, a fuel injection control unit 170, and an ignition control unit 180 is configured.

  The storage unit 110 stores a special operation mode and a normal operation mode.

  The normal operation mode is an operation mode in which the cylinders 14A to 14D are burned in the order of No. 1, No. 3, No. 4, and No. 2, and the burned gas of each of the cylinders 14A to 14D is discharged to the exhaust passage 27 as it is. When this operation mode is selected, the ECU 100 as the operation state control device controls the on-off valves 43 to 45 as will be described later.

  On the other hand, in the special operation mode, basically, the burned gas burned in the preceding cylinder (1st cylinder 14A, 4th cylinder 14D) is introduced into the succeeding cylinder (2nd cylinder 14B, 3rd cylinder 14C). In addition to the intake / exhaust path, lean combustion is performed in the preceding cylinder, and compression self-ignition is performed in the succeeding cylinder.

  3 and 4 are examples showing the operation of the valve in the operation state in the special operation mode, FIG. 3 is a special operation mode at low and medium loads, and FIG. 4 is a high load side in the special operation mode region. Each time is shown. 3 and 4, EX is an exhaust stroke, IN is an intake stroke, F is fuel injection, S is forced ignition, and a star mark in the drawings indicates that compression self-ignition is performed. ing. SA virtually indicates ignition assist in compression self-ignition.

  Referring to these drawings, in the four-cylinder engine of this embodiment, the exhaust stroke (EX) of the first cylinder 14A and the intake stroke (IN) of the second cylinder 14B overlap, and the exhaust stroke of the fourth cylinder 14D. (EX) and the intake stroke (IN) of the third cylinder 14C overlap each other, so that the first cylinder 14A and the second cylinder 14B and the fourth cylinder 14D and the third cylinder 14C form a pair, respectively. The fourth cylinder 14D is the preceding cylinder, the second cylinder 14B, and the third cylinder 14C are the subsequent cylinders.

  Next, in order to control the operating state of the engine, the storage means 110 stores an engine load / rotational speed control map divided for each operating region.

  FIG. 5 is a graph showing an example of division for each operation region.

  With reference to the figure, in the present embodiment, the engine operating region is divided into a low-load low-rotation side operation region A and a high-load side or high-rotation side operation region B. Further, in the operation region A, the low load side operation region A1, the medium load operation region A2, and the high load side operation region A3 are divided according to the engine load situation.

  Next, the storage unit 110 stores a control map that divides the operation region in the special operation mode based on the relationship between the subsequent cylinder intake air temperature T and the EGR rate R.

  FIG. 6 is a schematic diagram for explaining the definition of the EGR rate R, and FIG. 7 is a graph showing an example of the control map.

  First, referring to FIG. 6, the EGR rate R in the present embodiment is defined as in equation (1).

However,
m _DISC : mass of air combusted in the preceding cylinder (gas equivalent to EGR: hereinafter referred to as “preceding combustion air mass”)
m _HCCI : Mass of air used for combustion in the succeeding cylinder (hereinafter referred to as “subsequent combustion air mass”)
m _EGR-cold : Mass of EGR gas supplied to the preceding cylinder by the cold EGR device (hereinafter referred to as “cold EGR gas mass”)
In the equation (1) and FIG. 6, the EGR rate R in the present specification represents the cold EGR gas mass m _EGR-cold by the cold EGR device 30 and the gas mass equivalent to EGR generated by the combustion in the preceding cylinders 14A and 14D ( This is the ratio of both the pre-combustion air mass m _DISC ) to the fresh air.

  There is a certain correlation in the operation region between the EGR rate R and the subsequent cylinder intake air temperature T. That is, as shown in FIG. 7, in the operation region Z1 in which misfire is likely to occur, the EGR rate R is distributed to about 180% or more in the high temperature (high load) state where the subsequent cylinder intake air temperature T is 300 ° C. or higher. As the cylinder intake air temperature T decreases, it is distributed in a region where the EGR rate R is low. When the subsequent cylinder intake air temperature T is 150 ° C., the EGR rate R decreases to about 65% or more. On the other hand, even in the operation region Z2 where knocking is likely to occur, the EGR rate R is distributed in a range up to about 120% in the high temperature (high load) state where the subsequent cylinder intake temperature T is 300 ° C. or higher. As T decreases, it is distributed in a region where the EGR rate R is low, and terminates when the EGR rate R is 0 when the succeeding cylinder intake air temperature T is about 180 ° C.

  The region Z3 with good compression self-ignition exists between these regions Z1 and Z2. Further, even in the compression self-ignition, there is a region Z4 that requires ignition assist, and it is necessary to perform the ignition assist in that region. Therefore, in this embodiment, a control map is created by experiments and the like, and the EGR rate R is controlled according to the subsequent cylinder intake air temperature T, thereby avoiding both misfire and knocking.

  Next, the operation mode switching means 120 is based on the control map of FIG. 5 stored in the storage means 110, and the engine operation is examined by signals from the crank angle sensors 13A and 13B, the accelerator opening sensor 51, and the like. It is determined whether the state (engine speed and engine load) is in the operation region A or B, and in the operation region A on the low load low rotation side, the exhaust gas discharged from the preceding cylinder in the exhaust stroke is already detected. A special operation mode in which the fuel gas is directly introduced into the subsequent cylinder in the intake stroke and burned is selected, and in a high load side or high rotation side operation region B, a normal operation mode in which each cylinder is independently burned is selected. It is like that.

  In addition, when the operation state is in the special operation mode region A, the operation mode switching means 120 is set to any one of the low load side operation region A1, the medium load operation region A2, and the high load side operation region A3. As will be described later, in the low / medium load side operation areas A1 and A2, the low / medium load special operation mode is selected (see FIG. 3), and in the high load operation area A3, the high The load special operation mode (see FIG. 4) is selected.

  When the operation mode switching means 120 selects the special operation mode, the ECU 100 enters a two-cylinder connection state in which the burned gas of the preceding cylinder is introduced into the succeeding cylinder via the inter-cylinder gas passage 42, and each cylinder is in the normal operation mode. The valve stop mechanisms 48 and 49 are controlled so as to change the intake / exhaust flow state so that each cylinder is brought into an independent state where fresh air is introduced. Specifically, the control mode is a special operation mode (operation region A), The on-off valves 40A, 40B, 41A, 41B are opened and closed as shown in Table 2 by controlling the valve stop mechanisms 48, 49 depending on which of the operation modes (operation region B) is in effect.

  In this embodiment, the succeeding cylinder intake air temperature estimating means 130 constitutes temperature detecting means for detecting the succeeding cylinder intake air temperature to the succeeding cylinder, and the outside air temperature or engine based on the detected values of the temperature sensor 24 or the water temperature sensor 50 is used. The succeeding cylinder intake air temperature T is indirectly detected based on the water temperature, the operating state of the engine (engine speed and engine load), and the like. The succeeding cylinder intake air temperature estimating means 130 estimates the temperature of burned gas introduced from the preceding cylinders 14A and 14D to the succeeding cylinders 14B and 14C.

  The EGR rate control means 140 is for determining the EGR rate R based on the control map set in the range of the areas Z3 and Z4 based on the data shown in FIG. Based on the control map (FIG. 7), the opening (throttle opening) of the throttle valve 23 and the cold are adjusted so that the EGR rate R corresponding to the subsequent cylinder intake temperature T estimated by the subsequent cylinder intake temperature estimation means 130 is obtained. It controls the cold throttle valve 32 of the EGR device 30.

The air-fuel ratio control means 150 increases the total injection amount of fuel injected into the two cylinders of the preceding cylinders 14A and 14D and the succeeding cylinders 14B and 14C according to the load as the engine load increases. While adjusting, the sum of the fuel injection amounts for both the pair of cylinders having the preceding / following relationship in this special operation mode becomes the stoichiometric air-fuel ratio with respect to the mass of fresh air introduced into the preceding cylinders 14A and 14D. While calculating the amount, the fuel injection amount distributed to each of the cylinders 14A to 14D is calculated to control the air-fuel ratio in each of the preceding / following cylinders 14A to 14D. That is, the air-fuel ratio control means 150 calculates the mass of fresh air consumed in the preceding cylinders 14A and 14D by calculating the mass m _EGR-cold of the _{cold EGR} and the fuel injected into the preceding cylinders 14A and 14D. The new air mass (subsequent combustion air mass m _HCCI ) included in the burned gas introduced from the preceding cylinders 14A and 14D to the succeeding cylinders 14B and 14C is calculated. The air-fuel ratio control means 150 determines the intake mass m introduced into each cylinder 14A to 14D. As shown in FIG. 6, in the operation region A that is in the special operation mode, the intake mass m is equal to the mass of burned gas introduced by the cold EGR (cold EGR gas mass m _EGR-cold ) and the preceding cylinder 14A. , The sum of the fresh air mass burned at 14D (preceding combustion air mass m _DISC ) and the fresh air mass burned (subsequent combustion air mass m _HCCI ) among the gases supplied to the succeeding cylinders 14B and 14C is there. Further, in this embodiment, the intake mass m 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 14A and 14D and the succeeding cylinders 14B and 14C. It is an amount necessary for the combustion of the fuel according to the output, and is increased as the engine load increases.

  In the special operation mode region A, the ignition assist control means 160 drives the ignition circuit 18 so that ignition is performed before compression top dead center based on a control flow described later in order to promote compression self-ignition.

  Further, the fuel injection control means 170 controls the injection amount and the injection timing from the fuel injection valve 19 according to the operating state determined by the ECU 100. Then, the air-fuel ratio of the preceding cylinders 14A and 14D in the special operation mode region A is controlled by the control of the fuel injection amount by the fuel injection control means 170 and the control of the intake air amount by the control of the throttle valve drive motor etc. (not shown). However, the air-fuel ratio is leaner than the stoichiometric air-fuel ratio (excess air ratio λ> 1).

  The ignition control means 180 cooperates with the ignition assist control means 160 and the fuel injection control means 170 to control the ignition circuit 18 and to ignite plugs in the preceding cylinders 14A, 14D or the succeeding cylinders 14B, 14C depending on the operating state. 17 ignition timing, ignition stop timing, and the like are controlled.

  Next, the control flow in the above-described embodiment will be described with reference to FIGS.

  FIG. 8 is a flowchart showing a main flow of operation state control according to the embodiment of FIG.

  Referring to FIG. 4, when engine operation is started, operation mode switching means 120 of ECU 100 selects an operation mode (step S1). In step S1, the engine load / rotation speed control map is read from the storage means 110, and the operating state of the engine is determined based on detection signals output from the crank angle sensors 13A, 13B, the accelerator opening sensor 51, and the like. . If it is determined that the operation state is a high load state in which the special operation mode cannot be selected, the operation mode is switched to the normal operation mode (step S2), and if it is determined that it is possible, Switch to special operation mode (step S3 and below).

  In the special operation mode, first, as shown in Table 2, the valve stop mechanisms 48 and 49 are controlled so that the intake air from the intake passage 22 is supplied only to the preceding cylinders 14A and 14D. At the same time, by closing the exhaust ports 41A of the preceding cylinders 14A and 14D and opening the EGR port 41B, the burned gas burned in the preceding cylinders 14A and 14D is introduced into the succeeding cylinders 14B and 14C, and the succeeding cylinders 14B and 14C. An intake / exhaust path is configured so that the burned gas is discharged from the branch exhaust path 26 to the exhaust path 27 (step S3).

Next, based on the control map described in FIG. 7, the initial set value is read, and the excess air ratio λ _DISC of the preceding cylinders 14A and 14D and the throttle valve 23 are obtained so that the EGR rate R corresponding to the initial set value is obtained. The valve opening amount of the cold EGR valve 32 is set (step S4).

  Further, in the special operation mode, the fuel injection control of FIGS. 3 and 4 is performed according to the operation region of FIG.

  When the operating region is the low load region A1, the ECU 100 for the preceding cylinders 14A, 14D is a super lean air fuel ratio in which the air fuel ratio is larger than the stoichiometric air fuel ratio, preferably approximately three times the stoichiometric air fuel ratio (A / F The fuel injection amount is controlled so that it becomes approximately 45) or more. In this case, 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 near the compression top dead center. Further, for the subsequent cylinders 14B and 14C, fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinders 14A and 14D, and the combustion is substantially performed in the subsequent cylinders 14B and 14C. The fuel injection amount is controlled so that the theoretical air / fuel ratio is obtained. Then, the injection timing is set so as to make the air-fuel mixture uniform by injecting fuel in the intake stroke, and compression self-ignition is performed.

  When the operation region is the medium load region A2, the lean air-fuel ratio is smaller (rich side) than the air-fuel ratio in the low-load side operation region A1 for the preceding cylinders 14A, 14D, and preferably the theoretical The fuel injection amount is controlled to be approximately twice the air-fuel ratio (A / F≈30) or more.

  When the operation range is the low / medium load range A1, A2, the fuel injection timing and ignition timing are set so that the fuel is injected in the compression stroke and the mixture is stratified, and the compression is performed. The ignition timing is set near the top dead center (see FIG. 3).

On the other hand, when the operation region is the high load region A3, the preceding air cylinder 14A, 14D has a lean air-fuel ratio that is smaller (rich side) than the air-fuel ratio in the middle load operation region A2, and preferably The fuel injection amount is controlled to be smaller than about twice the theoretical air-fuel ratio (A / F≈30), and the fuel is injected during the intake stroke so that the air-fuel mixture is uniformly dispersed and homogenized. And the ignition timing is set so that forced ignition is performed near the compression top dead center (see FIG. 4). Further, regarding the fuel injection amount for the preceding cylinders 14A, 14D, in addition to the above control, the preceding cylinders 14A, 14D reduce the subsequent combustion air mass m _HCCI introduced into the succeeding cylinders 14B, 14C as the load increases. The fuel injection amount is adjusted. In other words, by increasing the rate of combustion in the preceding cylinders 14A and 14D and increasing the rate of increase in the preceding combustion air mass m _DISC , the preceding combustion air mass m _HCCI is reduced in proportion to the load. The fuel injection amount for the cylinders 14A and 14D is controlled. By controlling in this way, the difference between the air mass m sucked into the preceding cylinders 14A and 14D and the preceding combustion air mass m _DISC consumed by combustion in the preceding cylinders 14A and 14D is reduced.

  Next, the ECU 100 estimates the subsequent cylinder intake air temperature T (step S5). If the subsequent cylinder intake air temperature T is equal to or higher than the upper limit temperature T1 set in the map of FIG. 7, the control shifts to an upper limit temperature handling process (steps S6 and S10).

  On the other hand, when the succeeding cylinder intake air temperature T is equal to or lower than the lower limit temperature T2 set in the map, the control shifts to a lower limit temperature handling process (steps S7 and S20). Here, the upper limit temperature T1 refers to a temperature that requires countermeasures against knocking in the subsequent cylinder when the EGR rate R is at the initial set value, and the lower limit temperature T2 refers to the temperature that follows when the EGR rate R is at the initial set value. This is the temperature at which it is necessary to take measures against misfire in a cylinder. These are determined by the experiment when the control map based on FIG. 7 is created by the experiment or the like.

  When the succeeding cylinder intake air temperature T is lower than the upper limit temperature T1 and higher than the lower limit temperature T2, it is determined whether or not the ignition assist control is necessary (step S8). While the ignition assist control subroutine is executed (step S9), if it is determined that it is not necessary, the operation state is monitored by returning to step S1, and the above-described flow is repeated.

  Next, the ignition assist control will be described with reference to FIG.

  FIG. 9 is a flowchart showing a subroutine of ignition assist control.

Referring to the figure, in the ignition assist control, the crank angle sensors 13A and 13B detect the phase of the target subsequent cylinder 14B (or 14C) (step S91), and in parallel, inject into the subsequent cylinder. The calculated fuel is calculated (step S92). As described above, in the present embodiment, the EGR rate R is determined based on the subsequent cylinder intake air temperature T, and the preceding cylinder is determined based on the EGR rate R and the intake mass m detected by the air flow sensor 25. Therefore, the fuel injection amount is determined so that the excess air ratio λ _HCCI becomes 1 based on the mass of the subsequent combustion air included in the burned gas burned at the air-fuel ratio.

  Next, the fuel injection control means 170 of the ECU 100 determines whether or not the target subsequent cylinder 14B (or 14C) is in the intake stroke (step S93), and the subsequent cylinder 14B (or subsequent cylinder 14C) is in the intake stroke. If there is, the fuel injection valve 19 is driven to inject the calculated amount of fuel (step S94).

  Next, the ignition assist control means 160 of the ECU 100 waits for the piston 15 to reach the compression top dead center of the target subsequent cylinder 14B (or 14C) (step S95), and immediately after reaching the compression top dead center. The ignition circuit 18 is driven so that the spark plug 17 sparks (step S96). As a result, in the region Z4 where compression self-ignition is difficult, as shown by the phantom line SA in FIGS. 3 and 4, compression self-ignition is reliably realized by the ignition assist, and misfire can be prevented.

  Next, a flow when the upper limit temperature handling process S10 is adopted will be described with reference to FIG. FIG. 10 is a flowchart showing a subroutine of the upper limit temperature handling process S10.

  In this state, in the upper limit temperature handling process S10, first, a measure is taken to avoid knocking by increasing the EGR rate R as much as possible. First, the EGR rate control means 140 of the ECU 100 calculates an EGR rate R that falls within an appropriate range at the subsequent cylinder intake air temperature T based on the control map (FIG. 7) (step S11).

Next, in order to obtain the calculated EGR rate R, it is determined whether or not the cold EGR gas mass m _EGR-cold can be increased by the cold EGR device 30 (step S12). If it is determined that the cold EGR gas mass m _EGR-cold can be increased, that is, there is room for opening the cold EGR valve 32 of the cold EGR device 30, and the boost pressures of the preceding cylinders 14A and 14D are cold. When the EGR gas mass m _EGR-cold is a value that can be introduced, the open amount of the cold EGR valve 32 is increased to increase the cold EGR gas mass m _EGR-cold , which is indicated by the circled numeral 1 in FIG. Control is executed (step S13). As a result, as is apparent from the equation (1), the overall EGR rate R increases, and the engine operating state can be moved away from the knocking region Z2.

On the other hand, if it is determined in step S12 that the cold EGR gas mass m _EGR-cold cannot be increased, the ECU 100 calculates the fuel injection amount by the fuel injection control means 170 (step S14), and the preceding cylinder 14A. , 14D is corrected to the rich side, and the control indicated by the circled number 2 in FIG. 7 is executed (step S15). As a result, the overall EGR rate R increases while the subsequent cylinder intake air temperature T rises. As a result, the engine operation in the knocking region Z2 can be avoided.

  Furthermore, in this embodiment, an ignition assist promotion process for effectively avoiding the occurrence of knocking in the subsequent cylinders 14B and 14C is performed (step S16), and the process returns to the main routine of the original special operation mode.

  Next, a subroutine of the ignition assist promotion process S16 in the subsequent cylinder will be described.

  FIG. 11 is a flowchart showing a subroutine of the ignition assist promotion process S16.

  Referring to the figure, when the succeeding cylinder intake temperature T of the succeeding cylinders 14B and 14C exceeds the upper limit temperature T1, processing for suppressing ignition is performed in this subroutine in order to maintain the special operation mode. . Specifically, the ECU 100 detects the strokes of the subsequent cylinders 14B and 14C from the crank angle sensors 13A and 13B (step S161) and calculates the fuel injection amount in the subsequent cylinders (step S162). Next, the ECU 100 waits for the succeeding cylinders 14B and 14C to reach the latter half of the compression stroke (for example, 50 ° to 85 ° CA from the BDC) (step S163), and the ECU 100 injects fuel when reaching the latter half of the compression stroke. The fuel injection control means 170 is activated (step S164). By injecting the fuel at this timing, the time for which the injected fuel is turned into a high-temperature gas is shortened, and ignition is difficult. As a result, compression self-ignition by the ignition assist in the succeeding cylinders 14B and 14C is ensured.

  Thus, it is difficult to knock, and by changing the ignition assist timing (ignition plug spark timing), the EGR rate (EGR rate of the ignition assist region Z4) R that can control the compression self-ignition timing is set appropriately. Compressive self-ignition that provides a good combustion torque is possible.

  Next, the flow of the lower limit temperature handling process S20 when the subsequent cylinder intake air temperature T is equal to or lower than the lower limit temperature T2 will be described.

  FIG. 12 is a flowchart showing a subroutine of the lower limit temperature handling process S20.

  Referring to FIG. 7, when the lower limit temperature handling process S20 is adopted, in order to reduce the EGR rate R as much as possible and to avoid misfire, the EGR rate control means 140 of the ECU 100 is controlled by a control map (FIG. 7). ), The EGR rate R that falls within an appropriate range at the subsequent cylinder intake air temperature T is calculated (step S21).

Next, in order to obtain the calculated EGR rate R, it is determined whether or not the cold EGR gas mass m _EGR-cold can be reduced by the cold EGR device 30 (step S22). If it is determined that the cold EGR gas mass m _EGR-cold can be reduced, that is, if there is room to close the cold EGR valve 32 of the cold EGR device 30, the open amount of the cold EGR valve 32 is reduced. Then, the control indicated by the circled number 3 in FIG. 7 is executed by reducing the EGR gas (step S23). As a result, as is apparent from the equation (1), the overall EGR rate R is reduced, and the operating state of the engine can be moved away from the misfire region Z1.

On the other hand, when it is determined in step S22 that the cold EGR gas mass m _EGR-cold cannot be reduced, the ECU 100 calculates the fuel injection amount by the fuel injection control means 170 (step S24), and the preceding cylinder 14A. , 14D is further corrected to the lean side, and the control indicated by the circled numeral 4 in FIG. 7 is executed (step S25). As a result, although the succeeding cylinder intake air temperature T decreases, the overall EGR rate R also decreases, so that the engine operating state can be kept away from the misfire region.

  As described above, as described with reference to FIG. 7, the operation in the appropriate special operation mode is performed at the intake air temperature (following cylinder intake air temperature) T introduced into the succeeding cylinders 14B and 14C and the EGR rate R corresponding thereto. A region where the engine can be operated is mapped and stored in an experiment, and an EGR rate R suitable for the succeeding cylinder intake air temperature T is obtained using a standard succeeding cylinder intake air temperature T as an initial set value, and the succeeding detected by the temperature detecting means. Based on the cylinder intake temperature T, at least one of the cold EGR device 30 and the air-fuel ratio is controlled so that the EGR rate R measured by the measuring means becomes an appropriate value. Thereby, in this embodiment, it becomes possible to maintain a suitable EGR rate R for each subsequent cylinder intake air temperature T, and to avoid both knocking and misfire.

  Further, when the special operation mode is set in the partial load region of the engine, a fuel efficiency improvement effect can be obtained by improving thermal efficiency by lean combustion in the preceding cylinders 14A and 14D and reducing pumping loss in each of the cylinders 14A to 14D. Further, in the succeeding cylinders 14B and 14C, fuel is supplied to the burned gas introduced from the preceding cylinders 14A and 14D and combustion is performed, so that vaporization of the supplied fuel is promoted by the high-temperature burned gas, and the succeeding cylinders Since combustion is performed by compression self-ignition at 14B and 14C, slow combustion that does not contribute to work by burning all over the combustion chamber is avoided, and a high fuel efficiency improvement effect is obtained. In addition, the succeeding cylinders 14B and 14C are in a state equivalent to the case where a large amount of EGR is performed by introducing the burned gas from the preceding cylinders 14A and 14D, so that an effect of improving exhaust gas performance is obtained. It is done.

  Further, in the present embodiment, in a mode in which the subsequent cylinders 14B and 14C are operated by compression self-ignition, ignition is performed by sparking spark plugs provided in the subsequent cylinders 14B and 14C in order to assist ignition in the subsequent cylinders 14B and 14C. An assist control means 160 is provided, and an appropriate range of the control map includes an ignition assist area Z4. The ignition assist control means 160 determines that the succeeding cylinder 14B when the EGR rate R is controlled to the ignition assist area Z4. , 14C is configured to spark the spark plug. Therefore, even when the compression cylinders 14B and 14C are in an operation region (ignition assist region Z4) that is assumed to be difficult to perform compression self-ignition, the ignition assist control means 160 performs compression self-ignition of the subsequent cylinders 14B and 14C. The promoting control is properly executed, and the subsequent cylinders 14B and 14C are appropriately compressed and ignited to obtain a remarkable fuel efficiency improvement effect and an exhaust gas performance improvement effect.

  Further, in the present embodiment, the ignition assist control means 160 controls the ignition control means 180 so as to ignite the air-fuel mixture in the succeeding cylinders 14B and 14C near the top dead center before the compression top dead center. By executing the control to instantly increase the in-cylinder pressure by igniting the air-fuel mixture in the vicinity of the top dead center before the compression top dead center of the succeeding cylinders 14B and 14C, the succeeding cylinders 14B and 14C can be surely timely Compression self-ignition can be done.

  Further, since the EGR rate control means 140 in this embodiment is set so as to increase the EGR rate R as the subsequent cylinder intake temperature T rises, generally the high temperature of the subsequent cylinder intake temperature T on the high load side is high. On the side, since the knocking region is distributed on the side where the EGR rate R is low, the EGR rate R is further improved to avoid knocking. As a result, even in the high load side, the operation in the special operation mode can be maintained and the fuel efficiency and the exhaust gas performance can be improved.

  Further, when the EGR rate R cannot be increased by the cold EGR device 30, the air-fuel ratio control means 150 in the present embodiment corrects the air-fuel ratio of the preceding cylinders 14A and 14D to the rich side, so that the succeeding cylinder intake air temperature T is As a result of the increase, the EGR rate R defined by the equation (1) also increases. As a result, the operation in the knocking region Z2 can be avoided. As a result, even when it is difficult to increase the EGR rate R on the high load side, the operation in the special operation mode can be maintained.

  Further, in this embodiment, the ECU 100 corrects the air-fuel ratio of the preceding cylinders 14A and 14D to the rich side, and then performs fuel injection of the subsequent cylinders 14B and 14C in the compression stroke of the subsequent cylinders 14B and 14C. When the EGR rate R cannot be increased by the cold EGR device 30, after the air-fuel ratio of the preceding cylinders 14A and 14D is corrected to the rich side, fuel injection in the subsequent cylinders 14B and 14C is further performed in the subsequent cylinders 14B and 14C. Performed in the compression stroke. As a result, the time for which the fuel is turned into a high-temperature gas is shortened, and it becomes difficult to ignite, and it becomes possible to effectively avoid the occurrence of knocking, so that the occurrence of knocking can be effectively avoided. It becomes possible.

  Further, in the present embodiment, the EGR rate control means 140 controls the EGR rate R to decrease as the succeeding cylinder intake air temperature T decreases, so that the EGR rate R is reduced to avoid misfire. ing. As a result, even in the low load side, the operation in the special operation mode can be maintained and the fuel efficiency and the exhaust gas performance can be improved.

  Further, in the present embodiment, when the EGR rate R cannot be reduced by the cold EGR device 30, the air-fuel ratio control means 150 makes the air-fuel ratio of the preceding cylinders 14A, 14D leaner than the air-fuel ratio corresponding to the initial set value. Therefore, although the subsequent cylinder intake air temperature T is decreased, the EGR rate R defined by the equation (1) is also reduced, and the operation in the misfire region Z1 can be avoided. Therefore, even when it is difficult to lower the EGR rate R on the low load side, it is possible to maintain the operation in the special operation mode.

  Thus, according to the present embodiment, by controlling the EGR or the air-fuel ratio based on the correlation between the subsequent cylinder intake air temperature T to the subsequent cylinders 14B and 14C and the EGR rate R, the preceding cylinders 14A and 14D By maintaining the operation in the special operation mode in which the burned gas burned lean is introduced into the succeeding cylinders 14B and 14C in as wide a load range as possible, it is possible to improve the fuel consumption performance and the exhaust gas performance. There is a remarkable effect.

  The above-described embodiments are merely preferred specific examples of the present invention, and the present invention is not limited to the above-described embodiments.

  For example, in the upper limit temperature handling process described with reference to FIG. 10, the control flow of FIG. 13 can be employed as the ignition assist promotion process.

  FIG. 13 is a flowchart showing a subroutine of ignition assist promotion processing in another embodiment of the present invention.

  Referring to the figure, in this embodiment, in order to lower the succeeding cylinder intake temperature T in the upper limit temperature handling process, the stroke of the succeeding cylinder is detected (step S161), and the valve opening amount is calculated (step S162). Then, after waiting for the intake stroke (step S163), the intake ports 40A and 40B of the subsequent cylinders 14B and 14C are selectively opened during the intake stroke to introduce fresh air (step S164). This step S164 is realized by changing the intake / exhaust flow state as shown in Table 3 by the operation mode switching means 120 of the valve stop mechanisms 48, 49 and closing the valve after a predetermined time has elapsed. (Steps S165 and S166).

  As described above, when the air-fuel ratio of the preceding cylinders 14A and 14D is corrected to the rich side, in the configuration in which the fresh air introduction valves (open / close valves 40A and 40B) of the succeeding cylinders 14B and 14C are opened, the cold EGR device 30 performs the EGR rate. When R cannot be increased, when the air-fuel ratio of the preceding cylinders 14A and 14D is corrected to the rich side, fresh air is further introduced into the succeeding cylinders 14B and 14C. The subsequent cylinder intake air temperature T of 14B and 14C decreases, and the operation in the misfire region Z1 can be avoided. As a result, the occurrence of misfire can be effectively avoided.

  In addition, the following modifications are possible in the present invention.

  In addition, the specific structure of the apparatus of this invention is not limited to the said embodiment, A various change is possible. Other embodiments are described below.

  (1) In the above embodiment, the exhaust gas discharged from the succeeding cylinders 14B and 14C to the exhaust passage 27 is controlled by the air-fuel ratio control means 150 so as to be the stoichiometric air-fuel ratio, but this is limited to such control. Instead, the air-fuel ratio of the exhaust gas may be a lean air-fuel ratio. Even in this case, since the combustion in the succeeding cylinders 14B and 14C is performed by compression self-ignition, the exhaust gas performance can be improved, and even if a NOx catalyst is provided, a relatively compact one should be adopted. This is economically advantageous.

  (2) Although the preceding cylinders 14A and 14D are configured to perform combustion by forced ignition in the above-described embodiment, combustion by compression self-ignition and combustion by forced ignition are also performed in the preceding cylinders 14A and 14D. It may be switched according to the state or the like.

  (3) The device of the present invention can also be applied to multi-cylinder engines other than four-cylinder engines. For example, in the case of six cylinders, the exhaust stroke of one cylinder and the intake stroke of another cylinder do not completely overlap. In such a case, the exhaust stroke of one cylinder precedes the intake stroke of the other cylinder. In addition, two cylinders in which both strokes partially overlap may be used as a pair of preceding and succeeding cylinders.

It is a figure showing the schematic structure of the engine by one embodiment of the present invention. FIG. 2 is a diagram schematically showing a structure of one cylinder of an engine body and intake and exhaust valves provided for the cylinder. It is an example which shows operation | movement of the valve | bulb in the driving | running state in special operation mode. It is an example which shows operation | movement of the valve | bulb in the driving | running state in special operation mode. It is a graph which shows an example divided into every operation area. It is a schematic diagram for demonstrating the definition of an EGR rate. It is a graph which shows an example of a control map. It is a flowchart which shows the main flow of the driving | running state control which concerns on embodiment of FIG. It is a flowchart which shows the subroutine of ignition assistance control. It is a flowchart which shows the subroutine of an upper limit temperature response process. It is a flowchart which shows the subroutine of an ignition assistance promotion process. It is a flowchart which shows the subroutine of a minimum temperature response process. It is a flowchart which shows the subroutine of the ignition assistance promotion process in another embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine main body 15 Piston 22 Intake passage 23 Throttle valve 24 Temperature sensor 27 Exhaust passage 100 ECU (an example of operation state control device)
110 Storage unit 120 Operation mode switching unit 130 Subsequent cylinder intake air temperature estimation unit (an example of a subsequent cylinder intake air temperature detection unit)
140 EGR rate control means 150 Air-fuel ratio control means 160 Ignition assist control means 170 Fuel injection control means 180 Ignition control means A3 High load operation area A2 Medium load operation area A1 Low load side operation area m Intake mass m _DISC preceding combustion air mass m _EGR-cold Cold EGR gas mass m _HCCI Subsequent combustion air mass T Subsequent cylinder intake temperature T1 Upper limit temperature T2 Lower limit temperature Z1 Misfire region Z2 Knocking region Z3 Compression self-ignition region Z4 Ignition assist region λ Excess air ratio λ _DISC Special operation mode Cylinder excess air ratio λ _HCCI special operation mode excess air ratio of subsequent cylinders

Claims (10)

A multi-cylinder engine body in which intake, compression, expansion, and exhaust combustion cycles of each cylinder are performed with a predetermined phase difference;
A cold EGR device that recirculates exhaust gas discharged to the exhaust passage to the intake passage via the EGR passage;
An operation state control device that controls the operation state of the engine body and the cold EGR device, and the operation state control device comprises:
Each cylinder is in an exhaust stroke between a normal operation mode in which the gas sucked from the intake passage in accordance with the combustion cycle is burned and then exhausted burned gas to the exhaust passage, and a pair of cylinders in which the exhaust stroke and the intake stroke overlap. An operation mode switching means for switching and controlling a special operation mode in which the burned gas burned lean in the preceding cylinder is directly introduced into the succeeding cylinder in the intake stroke and compression auto-ignition is performed in the succeeding cylinder;
Subsequent cylinder intake air temperature detection means for detecting the subsequent cylinder intake air temperature when burned gas is introduced into the subsequent cylinder;
Means for obtaining an EGR rate by combining a ratio of EGR gas recirculated by the cold EGR device among gases introduced into the succeeding cylinder and a ratio of gas equivalent to EGR generated by combustion in the preceding cylinder;
Storage means for storing an appropriate range of the succeeding cylinder intake temperature at which the compression self-ignition operation is ensured in the succeeding cylinder based on the relationship between the EGR rate and the succeeding cylinder intake temperature when the burned gas is introduced into the succeeding cylinder; And the following cylinder intake air temperature is lower than the upper limit temperature stored in the storage means and lower than the lower limit temperature in the special operation mode based on the EGR rate and the subsequent cylinder intake temperature detected by the subsequent cylinder intake temperature detection means. A spark ignition type gasoline engine characterized by controlling at least one of a cold EGR device and an air-fuel ratio of a preceding cylinder so as to fall within a high appropriate range. The spark ignition gasoline engine according to claim 1,
The operating state control device includes ignition assist control means for sparking a spark plug provided in the succeeding cylinder in order to assist the ignition in the succeeding cylinder in a mode in which the succeeding cylinder is operated by compression self-ignition,
The appropriate range stored in the storage means includes an ignition assist control region by the operation of the ignition assist control means. A spark ignition gasoline engine. The spark ignition gasoline engine according to claim 2,
The spark ignition type gasoline engine characterized in that the ignition assist control means ignites an air-fuel mixture in a succeeding cylinder in the vicinity of top dead center before compression top dead center. The spark ignition type gasoline engine according to any one of claims 1 to 3,
The spark ignition gasoline engine characterized in that the operating state control device has an EGR rate control means for increasing the EGR rate when the succeeding cylinder intake air temperature is equal to or higher than an upper limit temperature. The spark ignition gasoline engine according to claim 4,
The operating state control device has air-fuel ratio control means for correcting the air-fuel ratio of the preceding cylinder to a richer side than the air-fuel ratio corresponding to the initial set value when the EGR rate cannot be increased by the cold EGR device. This is a spark ignition gasoline engine. The spark ignition gasoline engine according to claim 5,
The operating state control device has fuel injection control means for controlling fuel injection, and the fuel injection control means corrects the air-fuel ratio of the preceding cylinder to a richer side than the air-fuel ratio corresponding to the initial set value, A spark ignition gasoline engine characterized in that fuel injection of a subsequent cylinder is performed in a compression stroke of the subsequent cylinder. The spark ignition gasoline engine according to claim 5,
The spark ignition is characterized in that the operation mode switching means opens the fresh air introduction valve of the subsequent cylinder when the air-fuel ratio of the preceding cylinder is corrected to a richer side than the air-fuel ratio corresponding to the initial set value. Type gasoline engine. The spark ignition gasoline engine according to any one of claims 1 to 7,
The spark-ignition gasoline engine characterized in that the operating state control device has EGR rate control means for reducing the EGR rate when the succeeding cylinder intake air temperature is equal to or lower than a lower limit temperature. The spark ignition gasoline engine according to claim 8,
The operating state control device has air-fuel ratio control means for correcting the air-fuel ratio of the preceding cylinder to be leaner than the air-fuel ratio corresponding to the initial set value when the EGR rate cannot be reduced by the cold EGR device. This is a spark ignition gasoline engine. The spark ignition gasoline engine according to any one of claims 2 to 9,
The spark-ignition gasoline engine characterized in that the operating state control device controls at least one of the air-fuel ratio of the cold EGR device and the preceding cylinder so as to fall within the appropriate range of the ignition assist region.

Images