JP2006052695A - Engine starting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically stop an engine under preset conditions for further improving fuel consumption and to reliably restart it after automatically stopped. <P>SOLUTION: This engine starting device comprises a stopping/restarting control means for automatically stopping/restarting the engine, a speed detecting means for detecting an engine speed, a predicting means for predicting a stroke of one cylinder during stopping the engine in accordance with the detection result of the speed detecting means in a stopping operation period before stopping the engine, and an intake flow amount adjusting means for adjusting an intake flow amount in each cylinder. The stopping/restarting control means controls the intake flow amount adjusting means in accordance with the prediction result of the predicting means so that the amount of air in a cylinder predicted to be in an expansion stroke during stop is greater than the amount of air in a cylinder predicted to be in a compression stroke during stop. Then, it stops a piston in the cylinder predicted to be in the expansion stroke during stopping the engine so as to be located in a predetermined adequate range for restart. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine starter, and in an engine that can be switched to a two-cylinder connection state in which a pair of cylinders are connected in series, an engine automatic stop condition set in advance in an idle operation state of the engine is established. The present invention relates to an engine starter configured to automatically stop the engine when the engine is started and to automatically restart the engine when a restart condition is satisfied in this state.

  Conventionally, in a spark ignition engine or the like, a technique for improving fuel efficiency by performing combustion in a state where 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 is known, The applicant of the present application also has a low load in a multi-cylinder engine that performs a cycle consisting of intake, compression, expansion, and exhaust strokes in order to reduce the economic burden required for the catalyst and improve fuel efficiency while improving emissions. In the low speed range, between the pair of cylinders in which the exhaust stroke and the intake stroke overlap, the burned gas discharged from the preceding cylinder which is the cylinder on the exhaust stroke side is introduced as it is into the subsequent cylinder which is the cylinder on the intake stroke side. The gas discharged from the cylinder is guided to the exhaust passage, and when the two cylinders are connected, the lean air that is larger than the stoichiometric air-fuel ratio by a predetermined amount in the preceding cylinder. The combustion state is controlled so that the combustion is performed in a state where the combustion is performed in a state where the stoichiometric air-fuel ratio is obtained by supplying fuel to the burned gas of the lean air-fuel ratio introduced from the preceding cylinder in the subsequent cylinder. (Special operation mode) On the other hand, in the high-load and high-rotation range, as usual, we propose a technology that controls the combustion state etc. (referred to as the normal operation mode) so that each cylinder performs combustion at the stoichiometric air-fuel ratio. (See Patent Document 1).

  According to this technique, the preceding cylinder can achieve the fuel efficiency improvement effect by the lean combustion and the fuel efficiency improvement by the reduction of the pumping loss, and the succeeding cylinder can the fuel efficiency improvement effect by the pumping loss reduction. Moreover, since the gas discharged from the succeeding cylinder to the exhaust passage can have a stoichiometric air-fuel ratio, even when lean combustion is performed in the preceding cylinder as will be described later, it is possible to sufficiently purify the exhaust gas using only the three-way catalyst. In addition, since a relatively expensive lean NOx catalyst is not required, the cost can be reduced.

  On the other hand, in recent years, in order to reduce fuel consumption, the engine is automatically stopped once during idling, etc., and then the engine is turned on when a restart condition is established such as when the driver starts the vehicle. A technology for automatic engine stop control (so-called idle stop control) that has been automatically restarted has been developed. The restart at the time of the idling stop control requires a quickness to start the engine immediately in accordance with the start operation of the vehicle, etc., but the output of the engine by a starter motor which has been generally performed conventionally. According to the method of restarting the engine through cranking that drives the shaft, there are problems that the starter motor is frequently operated and power is consumed, and that the life of the starter motor is shortened.

  Therefore, it is desirable to immediately start the engine with the combustion energy by injecting fuel into a cylinder that is in a stopped state in the expansion stroke to ignite and burn the cylinder. However, when the piston stop position of the cylinder that is in the stopped state in the expansion stroke as described above is inappropriate, for example, when the piston is stopped at a position very close to top dead center or bottom dead center, There is a possibility that the engine cannot be started normally due to the fact that the amount of air is so small that combustion energy cannot be obtained sufficiently or the stroke of the combustion energy acting on the piston is too short.

As a countermeasure against such a problem, for example, as shown in Patent Document 1 below, a braking device is provided for the crankshaft of the engine, and the piston of the cylinder that is stopped in the expansion stroke stops at an appropriate position during the stroke. If it is determined that the engine automatic stop condition is satisfied, as shown in Patent Document 2 below, the lean air-fuel ratio injection mode is selected and the intake pressure is increased as shown in Patent Document 2 below. The compression pressure is increased so that the piston of the cylinder that is stopped in the expansion stroke can be stopped at a predetermined position.
JP 2004-76617 A Japanese Utility Model Publication No. 60-128975 JP 2001-173473 A

  By the way, by incorporating the automatic stop control technique into the technique described in Patent Document 1 previously proposed by the applicant of the present application, a further improvement in fuel efficiency can be expected.

  However, according to the engine starting device disclosed in Patent Document 2, it is necessary to provide a device for braking the crankshaft of the engine in addition to the braking device of the vehicle, and the cylinder that is stopped in the expansion stroke is required. In order to stop the piston at an appropriate position, the braking device must be controlled with high accuracy, which is difficult to control.

  On the other hand, as disclosed in Patent Document 2 described above, even when a configuration is adopted in which the intake pressure is increased and the compression pressure is increased when the automatic engine stop condition is satisfied, the degree of decrease in the engine speed is also reduced. Changes, the piston stop position fluctuates, making it difficult to stop the piston properly at a position suitable for restarting the engine, and to improve the scavenging performance when the engine automatically stops. There is a problem that.

  In view of the above circumstances, the present invention relates to an improvement of a special engine that can be connected to two cylinders to improve emission performance and improve fuel efficiency, and further improves fuel efficiency by automatically stopping the engine under predetermined conditions. An engine starter that can be reliably restarted after this automatic stop is provided.

  The engine starter according to the present invention is a multi-cylinder four-cycle engine in which the combustion cycle of each cylinder is performed with a predetermined phase difference, and the engine is sucked at least in the low load side operation region of the engine. The control mode for the exhaust and combustion states is a special operation mode, and in this special operation mode, the burned gas discharged from the preceding cylinder in the exhaust stroke between a pair of cylinders in which the exhaust stroke and the intake stroke overlap is directly in the intake stroke In a starter for an engine that is introduced into the subsequent cylinder in the cylinder via the inter-cylinder gas passage and the gas discharged from the subsequent cylinder is led to the exhaust passage, the engine starter is set in advance. When the automatic stop condition is satisfied, stop the fuel supply to the engine and keep the engine When the restart condition of the engine in the automatic stop state is satisfied, the engine is automatically operated by injecting fuel into the cylinder in the expansion stroke at least when the engine is stopped to ignite and burn. A stop / restart control means for automatically restarting, a speed detection means for detecting the engine speed, and a stop operation period from when the fuel supply is stopped by the stop / restart control means until the engine stops. Predicting means for predicting the stroke of each cylinder when the engine is stopped based on the detection result of the speed detecting means, and intake air flow adjusting means for adjusting the intake air flow rate for each cylinder when control in the special operation mode is executed And the stop / restart control means is predicted to be in the stop-time expansion stroke based on the prediction result from the prediction means. By controlling the intake flow rate adjusting means so that the air amount of the cylinder is larger than the air amount of the cylinder predicted to be in the compression stroke at the time of stop, the cylinder of the cylinder predicted to be in the expansion stroke at the time of engine stop is controlled. The piston stop position is stopped within a predetermined appropriate range suitable for restart.

  According to the present invention, since the stop / restart control means for automatically stopping / restarting the engine when a predetermined automatic stop / restart condition is satisfied is provided, for example, wasteful fuel consumption is suppressed at the time of idle stop or the like. This makes it possible to obtain further fuel efficiency improvement effects while taking advantage of the characteristics of the engine that can be switched to the two-cylinder connected state. In other words, the special operation mode control is executed in the low load side operation region of the engine, and the combustion state control means is basically (at least after the engine is restarted) when the special operation mode control is executed. Except for a predetermined period), control is performed so that combustion is performed at a lean air-fuel ratio in the preceding cylinder, burned gas is introduced from the preceding cylinder, and combustion is performed in the subsequent cylinder together with newly supplied fuel. In the preceding cylinder, the thermal efficiency is improved by lean combustion, and in both the preceding and succeeding cylinders, the fuel efficiency is improved by reducing the pumping loss.

  Further, the stroke of each cylinder when the engine is stopped can be predicted by the prediction means, and the cylinders in the expansion stroke and the compression stroke when the engine is stopped can be predicted based on the prediction result. Then, in order to adjust the intake air flow rate of the cylinder that is predicted to be in the expansion stroke and the compression stroke when the engine is stopped, the intake flow rate adjusting means is adjusted by the stop / restart control means so that the expansion stroke at the engine stop time is reached. The piston of a certain cylinder can be stopped with a high probability in a predetermined appropriate range, that is, for example, at a position where the piston of the expansion stroke cylinder at the time of stoppage slightly approaches the bottom dead center side.

  In addition, the stop / restart control means automatically stops the engine while the two-cylinder connected state in which the intake flow rate to the subsequent cylinder is determined by the intake flow rate of the preceding cylinder that forms a pair with this, so that the compression and expansion strokes are performed when the engine is stopped. Each intake stroke that determines the intake flow rate to each cylinder has a longer interval than in the case where each cylinder is independent, so the intake flow rate can be reliably controlled regardless of the responsiveness of the intake flow adjustment means. The intake flow rate introduced into each cylinder can be adjusted effectively.

  Specifically, for example, the stop / restart control means predicts that the cylinder in the compression stroke when the engine is stopped is the preceding cylinder by the prediction means. In this case, the intake flow rate of the final intake stroke before the engine stop in the preceding cylinder predicted by the predicting means to be the stop-time compression stroke cylinder is the intake flow rate of the intake stroke immediately before the final intake stroke in the preceding cylinder. The intake flow rate adjusting means is controlled so as to be relatively smaller than (Claim 2), or the stop / restart control means is a cylinder that is in a compression stroke when the engine is stopped by the predicting means. If it is predicted that the burned gas is derived to the subsequent cylinder predicted to be the compression stroke cylinder at the time of stop by this predicting means through the inter-cylinder gas passage. The intake flow rate adjusting means is arranged so that the intake flow rate of the intake stroke immediately before the intake stroke when the engine is stopped in the cylinder is relatively smaller than the intake flow rate in the final intake stroke of the preceding cylinder that makes a different pair from the preceding cylinder. And can be controlled (Claim 3).

  Further, the control of the intake flow rate adjusting means by the stop / restart control means is not specifically limited. For example, the engine starter according to any one of claims 1 to 3 is provided. In the stop operation period after the fuel supply is stopped, the stop / restart control means increases the intake flow rate for the preceding cylinder and then throttles the intake flow rate for the preceding cylinder to reduce the cylinder in the compression stroke when the engine is stopped. Preferably, the intake flow rate adjusting means is controlled so as to change the air amount between the cylinder and the cylinder in the expansion stroke.

  According to this configuration, when the automatic engine stop condition is satisfied and the automatic engine stop control is executed, a sufficient intake air flow rate can be secured to the engine cylinder. It is possible to effectively improve the scavenging performance of the combustion gas by suppressing the rotational speed of the gas from excessively decreasing. In addition, when adjusting the intake air flow rate, it is better to decrease the intake flow rate than to increase it, and to adjust the intake flow rate of the stop-time expansion stroke and compression stroke cylinder with good responsiveness and accuracy. Can do.

  In the present invention, an external load adjusting means for adjusting an external load on the engine is further provided, and the stop / restart control means adjusts the external load adjusting means according to the engine rotation speed based on the detection result from the speed detecting means. (Claim 5).

  If comprised in this way, the piston of the cylinder in the expansion stroke at the time of a stop of this engine can be stopped in the predetermined appropriate range with higher probability by adjusting the amount of air charged into each cylinder.

  In this case, by adjusting the external load adjusting means by the stop / restart control means, the piston of the cylinder in the expansion stroke when the engine is stopped is in a proper range suitable for restarting the engine, for example, slightly below the neutral point of the stroke. If it is stopped toward the dead center side, it does not matter whether the expansion stroke cylinder at the time of stop is the preceding cylinder or the succeeding cylinder, but for example, the stop / restart control means performs the compression stroke when the engine is stopped. When the external load adjusting means is controlled so that a certain cylinder becomes the preceding cylinder (Claim 6), the cylinder in the expansion stroke when the engine is stopped becomes the succeeding cylinder. It is possible to supply fuel in the higher succeeding cylinder and perform combustion for restarting the engine, which ensures the engine by combustion in the succeeding cylinder. It can be restarted. Moreover, even if the combustion in the subsequent cylinder is burned at a rich air / fuel ratio smaller than the stoichiometric air / fuel ratio when the engine is restarted, the burned gas due to the combustion in the subsequent cylinder is discharged through the exhaust passage, For example, compared with the case where the initial combustion is burned at the stoichiometric air-fuel ratio in the preceding cylinder and this burned gas is introduced into the succeeding cylinder, it continues continuously at the stoichiometric air-fuel ratio having a larger output than the lean air-fuel ratio at the initial stage of engine restart. And the engine can be restarted more reliably.

  In this case, it further includes an intake pressure detection means for detecting an intake pressure for each cylinder, and the stop / restart control means is configured to detect the external load based on the detection result by the intake pressure detection means and the detection result by the rotation speed detection means. It is preferable to control the adjusting means (claim 7).

  That is, if the intake air flow rate is simply adjusted by the intake air flow rate adjusting means, for example, when the intake air flow rate is increased, the responsiveness is worse than when the intake air flow rate is decreased. The external load adjusting means can be adjusted in consideration of the flow rate responsiveness. Therefore, the engine speed can be adjusted with a low degree of responsiveness for stopping the piston in an appropriate range.

  In the present invention, the restart condition in the stop / restart control means can be set as appropriate. For example, the restart condition includes a condition relating to an automatic stop duration which is an elapsed time from the time of the engine being automatically stopped. The stop / restart control means may be configured to restart the engine when a predetermined automatic stop duration has elapsed (claim 8).

  Furthermore, in the present invention, the engine may be restarted only by the combustion energy of the cylinder in the expansion stroke when the engine is stopped. For example, the engine may further include a starter motor that rotates the crankshaft in the forward direction. The control means may be configured to assist the starter motor when the engine starts normal rotation by combustion in the expansion stroke cylinder.

  Even in this case, since the restart of the engine is assisted by the starter motor, the restartability of the engine can be improved, and the burden on the starter motor can be reduced by the combustion energy in the cylinder.

  In the present invention, it is preferable that the stop / restart control means continuously operates the engine at a rotational speed higher than the idle rotational speed for a predetermined time before stopping the fuel supply.

  With this configuration, when the engine is automatically stopped, the fuel injection is stopped in a state where the engine rotation speed is increased to a value higher than a normal idle rotation speed that does not automatically stop the engine. Increase the engine speed (intake, compression, expansion and exhaust strokes) after stopping injection to reduce the engine speed along a preset reference line, and adjust the intake flow rate and external load adjusting means. By performing control to adjust the rotational resistance of the crankshaft, automatic stop control for stopping the piston at a position suitable for restarting the engine can be appropriately executed.

  According to the present invention, it is possible to suppress unnecessary fuel consumption at the time of idling stop, for example, and it is possible to obtain a further fuel efficiency improvement effect while taking advantage of the above-mentioned characteristics of the engine that can be switched to the two-cylinder connected state. There is. Moreover, the cylinders in the expansion stroke and the compression stroke can be predicted when the engine is stopped based on the prediction result by the prediction means, and the intake air flow rate of the cylinder predicted to be in the expansion stroke and the compression stroke when the engine is stopped is determined. In order to adjust, by adjusting the intake flow rate adjusting means by the stop / restart control means and adjusting the external load adjusting means, the pistons of the cylinders in the expansion stroke at the time of stop of the engine have a high probability within a predetermined appropriate range, for example, stop The piston of the time expansion stroke cylinder can be stopped at a position slightly close to the bottom dead center side. In addition, since each intake stroke that determines the intake flow rate to each cylinder in the compression and expansion strokes when the engine is stopped is more spaced than in the case of each cylinder independent state, the response by the intake flow rate adjusting means is improved. Regardless, the intake flow rate can be reliably controlled, and the intake flow rate introduced into each cylinder can be adjusted effectively.

  1 and 2 show a schematic configuration of a four-cycle spark ignition engine having an engine starter according to the present invention. The engine includes an engine main body 1 having a cylinder head 10 and a cylinder block 11 and an ECU 2 for engine control. The engine body 1 is provided with four cylinders 12A to 12D, and a piston 13 connected to the crankshaft 3 is fitted into each of the cylinders 12A to 12D so that a combustion chamber 14 is provided above the cylinder 13. Is formed.

  A spark plug 15 is installed at the top of the combustion chamber 14 of each of the cylinders 12 </ b> A to 12 </ b> D so that the plug tip faces the combustion chamber 14. An ignition device 27 capable of controlling the ignition timing by the ECU 2 is connected to the ignition plug 15. A fuel injection valve 16 that directly injects fuel into the combustion chamber 14 is provided on the side of the combustion chamber 14. This fuel injection valve 16 incorporates a needle valve and a solenoid (not shown), and is driven and opened for a time corresponding to the pulse width of the pulse signal input from the ECU 2, and has an amount corresponding to the valve opening time. The fuel is injected toward the vicinity of the electrode of the spark plug 15. In addition, fuel is supplied to the fuel injection valve 16 through a fuel supply system that includes a fuel pump, a fuel supply passage, and the like that are not shown, and that can apply a fuel pressure higher than the pressure in the combustion chamber during the compression stroke. It is configured as follows.

  In addition, intake ports 17, 17 a, 17 b that open toward the combustion chamber 14 and exhaust ports 18, 18 a, 18 b are provided above the combustion chambers 14 of the cylinders 12 </ b> A to 12 </ b> D. 18 are equipped with intake valves 19, 19a, 19b and exhaust valves 20, 20a, 20b, respectively. The intake valves 19, 19a, 19b and the exhaust valves 20, 20a, 20b are driven by a valve operating mechanism 29, which will be described later, so that each cylinder 12A-12D performs a combustion cycle with a predetermined phase difference. The opening / closing timings of the intake / exhaust valves 19 and 20 of 12A to 12D are set.

  An intake passage 21 and an exhaust passage 22 are connected to the intake port 17 and the exhaust port 18. As shown in FIG. 2, the downstream side of the intake passage 21 close to the intake port 17 is an independent branch intake passage 21a corresponding to each of the cylinders 12A to 12D. The upstream ends of the branch intake passages 21a are respectively It communicates with the surge tank 21b. A common intake passage 21c is provided upstream of the surge tank 21b, and an intake flow rate adjusting means including a throttle valve 23 driven by an actuator 24 is disposed in the common intake passage 21c. An air flow sensor 25 for detecting the intake flow rate and an intake pressure sensor 26 for detecting the intake pressure (negative pressure) are disposed on the upstream side and the downstream side of the throttle valve 23, respectively.

Further, an O ₂ sensor 38 that detects the air-fuel ratio by detecting the oxygen concentration in the exhaust gas is provided downstream of the collecting portion of the exhaust passage 22 where exhaust from each of the cylinders 12A to 12D collects. Further, an exhaust gas purification catalyst 37 is disposed in the exhaust passage 22 on the downstream side of the installation portion of the O ₂ sensor 38. The exhaust gas purification catalyst 37 is formed of, for example, a so-called three-way catalyst in which the purification rate of HC, CO, and NOx is extremely high when the air-fuel ratio of the exhaust is in the vicinity of the theoretical air-fuel ratio. As is generally known, the exhaust gas purification catalyst 37 composed of a three-way catalyst is used for HC, CO, and NOx when the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio (that is, the excess air ratio λ = 1). On the other hand, it is a catalyst that exhibits high purification performance.

  A combustion cycle including intake, compression, expansion, and exhaust strokes is performed with a predetermined phase difference for each of the cylinders 12A to 12D. In the case of a four-cylinder engine, from one end side in the cylinder row direction When referred to as the first cylinder 12A, the second cylinder 12B, the third cylinder 12C, and the fourth cylinder 12D, as shown in FIG. 5, the combustion cycle is the first cylinder 12A, the third cylinder 12C, the fourth cylinder 12D, 2 The operation is performed with a phase difference of 180 ° in crank angle in the order of the numbered cylinder 12B. In FIG. 5, EX is an exhaust stroke, IN is an intake stroke, F is fuel injection, S is forced ignition, and a star mark in the drawing indicates that compression self-ignition is performed.

  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 22a is provided so that the burned gas can be directly introduced to the subsequent cylinder). In the four-cylinder engine of this embodiment, as shown in FIG. 5, the exhaust stroke (EX) of the first cylinder 12A and the intake stroke (IN) of the second cylinder 12B overlap, and the exhaust stroke (EX) of the fourth cylinder 12D. ) And the intake stroke (IN) of the third cylinder 12C overlap, so that the first cylinder 12A and the second cylinder 12B, the fourth cylinder 12D and the third cylinder 12C form a pair, respectively, and the first cylinder 12A and the fourth cylinder The cylinder 12D is a preceding cylinder, and the second cylinder 12B and the third cylinder 12C are subsequent cylinders.

  The intake / exhaust ports of the cylinders 12A to 12D, the intake passage 21, the exhaust passage 22 and the inter-cylinder gas passage 22a connected thereto are specifically configured as follows.

  The first cylinder 12A and the fourth cylinder 12D, which are the preceding cylinders, respectively include an intake port 17 for introducing fresh air and a first exhaust port 18a for sending burned gas (exhaust gas) to the exhaust passage 22. And a second exhaust port 18b for leading the burned gas to the succeeding cylinder. Further, the second cylinder 12B and the third cylinder 12C, which are the subsequent cylinders, respectively, have a first intake port 17a for introducing fresh air and a second intake port 17b for introducing burned gas from the preceding cylinder. And an exhaust port 18 for sending the burned gas to the exhaust passage 22.

  In the example shown in FIGS. 1 and 2, the intake ports 17 in the first and fourth cylinders (preceding cylinders) 12A and 12D and the first intake ports 17a in the second and third cylinders (subsequent cylinders) 12B and 12C are 1 Two cylinders are provided in parallel on the left half side of the combustion chamber 14, while the first exhaust port 18a, the second exhaust port 18b and the second exhaust port in the first and fourth cylinders 12A and 12D (preceding cylinders). The second intake port 17b and the exhaust port 18 in the third cylinders (following cylinders) 12B and 12C are provided in parallel on the right half side of the combustion chamber 14.

  The intake port 17 in the first and fourth cylinders 12A and 12D and the first intake port 17a in the second and third cylinders 12B and 12C are connected to the downstream end of the branch intake passage 21a for each cylinder in the intake passage 21. Yes.

  The first exhaust port 18a in the first and fourth cylinders 12A and 12D and the exhaust port 18 in the second and third cylinders 12B and 12C are connected to the upstream ends of the branch exhaust passages 22b for each cylinder in the exhaust passage 22. Yes. An inter-cylinder gas passage 22a is provided between the first cylinder 12A and the second cylinder 12B and between the third cylinder 12C and the fourth cylinder 12D. The upstream end of the inter-cylinder gas passage 22a is connected to the second exhaust ports 18b of the first and fourth cylinders 12A and 12D as the preceding cylinders, and the second and third cylinders 12B as the subsequent cylinders. The downstream end of the inter-cylinder gas passage 22a is connected to the 12C second intake port 17b.

  The inter-cylinder gas passage 22a is a relatively short passage that connects adjacent cylinders so that the amount of heat released during the passage of gas discharged from the preceding cylinders 12A and 12D through the passage 22a can be kept relatively small. It has become.

  The intake / exhaust valves for opening and closing the intake / exhaust ports of the cylinders 12A to 12D and the valve operating mechanisms for these valves are as follows.

  An intake valve 19, a first exhaust valve 20a, and a second exhaust valve 20b are provided in the intake port 17, the first exhaust port 18a, and the second exhaust port 18b in the first and fourth cylinders (preceding cylinders) 12A and 12D, respectively. The first intake port 17a, the second intake port 17b, and the exhaust port 18 in the second and third cylinders (subsequent cylinders) 12B and 12C are respectively provided with a first intake valve 19a, a second intake valve 19b, and an exhaust valve 20. Is provided. These intake / exhaust valves are controlled at predetermined timings by a valve operating mechanism comprising camshafts 19a, 20a, etc. so that the intake strokes and exhaust strokes of the cylinders 12A to 12D are performed with the predetermined phase difference as described above. It is driven to open and close.

  Further, among these intake / exhaust valves, the first exhaust valve 19a, the second exhaust valve 20b, the first intake valve 19a, and the second intake valve 19b are switched between an operating state and a stopped state. A valve stop mechanism 29 is provided. The valve stop mechanism 29 has been known in the art and will not be shown in detail. For example, the hydraulic oil can be supplied to and discharged from a tappet interposed between the cams of the camshafts 19a and 20a and the valve shaft. When a hydraulic oil is supplied to the hydraulic chamber, the operation of the cam 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 performed. The valve is stopped by not being able to be transmitted to. The hydraulic oil is supplied by an oil pump driven by the drive while the engine is being driven, and is supplied by an electric oil pump driven by an electric motor while the engine is stopped.

  A first control valve 57 is provided in the hydraulic oil supply / discharge passage 56 for the valve stop mechanism 29 of the first exhaust valve 20a and the valve stop mechanism 29 of the first intake valve 19a, and the second exhaust valve 20b. A second control valve 59 is provided in the hydraulic oil supply / discharge passage 58 with respect to the valve stop mechanism 29 and the valve stop mechanism 29 of the second intake valve 19b (see FIG. 3).

  The engine body 1 is provided with an alternator (generator) 28 connected to the crankshaft 3 by a timing belt or the like. The alternator 28 includes a regulator circuit 28a that adjusts the target generated current by controlling the current of a field coil (not shown) and adjusting the output voltage, and the control from the ECU 2 that is input to the regulator circuit 28a. Based on the signal, the control of the target generated current corresponding to the electric load of the vehicle and the voltage of the vehicle-mounted battery is executed at normal times.

  Further, the engine is provided with two crank angle sensors 30 and 31 for detecting the rotation angle of the crankshaft 3, and the rotation speed of the engine is detected based on a detection signal output from one crank angle sensor 30. In addition, as will be described later, the rotation direction and the rotation angle of the crankshaft 3 are detected based on detection signals out of phase output from the crank angle sensors 30 and 31.

  Further, a cam angle sensor 32 for detecting a specific rotational position for cylinder identification provided on the camshafts 19a and 20a, a water temperature sensor 33 for detecting the coolant temperature of the engine, and an accelerator corresponding to the accelerator operation amount of the driver. Each detection signal output from the accelerator sensor 34 that detects the opening and the brake sensor 35 that detects that the driver has performed a brake operation is input to the ECU 2.

On the other hand, the ECU 2 is for engine control including a microcomputer or the like, and its drive and control systems are shown in FIGS. In this figure, the ECU 2 receives signals from detection signals from the sensors 25, 26, 30 to 36 and 38. That is, the ECU 2 receives signals from the air flow sensor 25 and the O ₂ sensor 38, and further detects crank speed sensors 30 and 31 for detecting the engine speed for determining the operating state and the accelerator opening (depressing the accelerator pedal). A signal from the accelerator sensor 34 or the like for detecting the amount) is also input. Further, the ECU 2 controls the ignition device 27 attached to the ignition plug 15, each fuel injection valve 16, the actuator 24 of the throttle valve 23, and the first and second control valves 57 and 59. A signal is output.

  The ECU 2 includes an operation state determination unit 41, a valve stop mechanism control unit 42, an intake flow rate control unit 43, a combustion state control unit 44, a generated current control unit 47, and a stop / restart control unit 48, and the engine combustion state and intake The control for switching the exhaust characteristics and the like is switched, and the fuel injection to each of the cylinders 12A to 12D is stopped (fuel cut) at a predetermined timing when a preset engine automatic stop condition is satisfied, and the engine Is automatically stopped, and the engine is automatically restarted when a restart condition is satisfied, for example, when an accelerator operation is performed by the driver.

  Specifically, as shown in FIG. 4, the operation state determination unit 41 includes an operation region A (partial load region) on the low load and low rotation side and an operation region on the high load side or high rotation side. The engine operating state (engine speed and engine load) examined by signals from the crank angle sensors 30, 31 and the accelerator sensor 34 has control maps divided into B and the operation regions A, B. It is discriminated in which area. Based on this determination, in the operation region A on the low load and low rotation side, the burned gas discharged from the preceding cylinders 12A and 12D in the exhaust stroke is introduced as it is into the subsequent cylinders 12B and 12C in the intake stroke. The special operation mode for combustion is selected, and in the operation region B on the high load side or high rotation side, the normal operation mode for independently burning each cylinder 12A to 12D is selected.

  The valve stop mechanism control means 42 is in a two-cylinder connection state in which the burned gas of the preceding cylinders 12A and 12D is introduced into the succeeding cylinders 12B and 12C via the inter-cylinder gas passage 22a in the special operation mode, and each cylinder in the normal operation mode. The valve stop mechanism 29 is 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 into each of 12A to 12D. In principle, each valve stop mechanism 29 is controlled as follows by controlling the control valves 57 and 59 depending on which one is present.

Operating region A: The first exhaust valve 20a and the first intake valve 19a are stopped.
The second exhaust valve 20b and the second intake valve 19b are in an operating state. Operation region B: the first exhaust valve 20a and the first intake valve 19a are in an operating state.
The second exhaust valve 20b and the second intake valve 19b are stopped. The intake flow rate control means 43 controls the opening degree (throttle opening degree) of the throttle valve 23 by controlling the actuator 24. Accordingly, a target intake air amount is obtained from a map or the like, and the throttle opening is controlled according to the target intake air amount. In this case, in the operation region A in the special operation mode, the subsequent cylinders (second and third cylinders 12B and 12C) are introduced from the preceding cylinders 12A and 12D in a state where the intake introduction from the branch intake passage 21a is blocked. Combustion is performed while the ratio of excess air in the gas to be supplied and the newly supplied fuel is a value corresponding to the stoichiometric air-fuel ratio, so that the combustion of fuel according to the required torque for the preceding and subsequent two cylinders The throttle opening is set so that the required amount of air (the amount of air that is the stoichiometric air-fuel ratio relative to the amount of fuel for two cylinders) is supplied to the preceding cylinders (first and fourth cylinders 12A and 12D). Is adjusted.

  The intake flow rate control means 43 controls the opening degree of the throttle valve 23 by controlling the actuator 24 in response to a signal from the stop / restart control means 46, and in the process of automatically stopping the engine, As well as ensuring the scavenging performance of each cylinder, the amount of air taken into the cylinders in the expansion stroke and compression stroke when the engine is stopped is adjusted.

  The combustion state control means 44 is composed of a fuel supply control means 45 and an ignition control means 46. The fuel supply control means 45 causes the fuel injection amount from the fuel injection valves 16 provided in the cylinders 12A to 12D and The injection timing is controlled according to the operating state of the engine, and ignition control means 46 controls ignition timing and ignition stop according to the operating state. In particular, the control of the combustion state (control of fuel injection and control of ignition) is changed depending on whether the operation state is in the operation region A in FIG. 4 or in the operation region B.

  That is, when the operation state is in the operation region A on the low load and low rotation side, the air-fuel ratio is set to the theoretical sky for the preceding cylinders (first and fourth cylinders) 12A and 12D as the control state in the special operation mode. The fuel injection amount is controlled so that the lean air-fuel ratio is larger than the fuel ratio, the injection timing is set so that fuel is injected in the compression stroke and the mixture is stratified, and near the compression top dead center The ignition timing is set so that the forced ignition is performed. On the other hand, for the succeeding cylinders (second and third cylinders) 12B and 12C, fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinder so that the stoichiometric air-fuel ratio is substantially achieved. In addition, the fuel injection amount is controlled, the injection timing is set so as to inject fuel in the intake stroke, and the forced ignition is stopped in order to perform compression self-ignition. It is not intended to exclude the combustion by forced ignition instead of the compression self-ignition of the succeeding cylinders 12B and 12C.

  Further, in the operation region A, the sum of the fuel injection amounts for the pair of cylinders including the preceding cylinder and the succeeding cylinder is adjusted to an amount that becomes the stoichiometric air-fuel ratio with respect to the fresh air amount introduced into the preceding cylinder. The fuel injection amount for the preceding cylinders (1st and 4th cylinders) 2A and 2D and the subsequent cylinders (2nd and 3rd cylinders) so that the compression self-ignition is satisfactorily performed while preventing knocking from occurring in the cylinders. The ratio of the fuel injection amount to the cylinders 2B and 2C is controlled according to the operating state.

  On the other hand, when the operating state of the engine is in the operating region B on the high load side or the high rotation side, the air-fuel ratio of the cylinders 12A to 12D is set to the stoichiometric air-fuel ratio or lower as control in the normal operation mode. For example, the fuel injection amount is controlled so that the stoichiometric air-fuel ratio is set in, for example, most of the operating region B, and richer than the stoichiometric air-fuel ratio in the fully-open load and the operating region in the vicinity thereof. In this case, the injection timing is set so that fuel is injected into each of the cylinders 12A to 12D in the intake stroke to make the air-fuel mixture uniform, and each cylinder 12A to 12D is forcedly ignited. To control.

  Further, the fuel state control means 44 receives input from the stop / restart control means 48 and controls fuel supply, ignition, etc. to the cylinders 12A to 12D at the time of automatic engine stop and subsequent restart. Has been made. These specific controls will be described later together with the stop / restart control means 48. However, when the engine is restarted after the engine is automatically stopped, it exceeds the compression top dead center at which the cylinder in the intake stroke first meets when the engine is stopped. Even when the restart instability period is up to the operation region A, the combustion in each cylinder is set to be a stoichiometric air-fuel ratio or a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio. In the stable period, the fuel injection timing for the subsequent cylinders 12B and 12C is set in the latter half of the compression stroke.

  Further, the combustion state control means 44, particularly the fuel supply control means 45, stops the fuel supply by the fuel injection valve 16 when the vehicle is decelerating and the engine rotational speed is higher than a predetermined rotational speed (hereinafter referred to as “the fuel injection valve 16”). The fuel cut during vehicle deceleration is referred to as “deceleration FC”).

  The generated current control means 47 receives the signal from the stop / restart control means 48 and sets the target generated current of the alternator 28, and in particular, from when an automatic stop condition described later is satisfied until the engine is stopped. The external load on the engine is adjusted by changing the target generated current by the alternator 28 in accordance with the engine rotation speed.

  On the other hand, the stop / restart control means 48 outputs a control signal to the various control means 43 to 47 and the like, and the fuel to each of the cylinders 12A to 12D is satisfied when a preset automatic engine stop condition is satisfied. Stops the injection at a predetermined timing (fuel cut), automatically stops the engine, and automatically restarts the engine when a restart condition is satisfied, such as when the driver performs an accelerator operation. It is comprised so that the control to perform may be performed. The stop / restart control means 48 of the present embodiment is configured to automatically stop and restart the engine while the control mode for the intake and exhaust of the engine and the combustion state remains in the special operation mode, that is, the two-cylinder connection state. ing.

  Specifically, the automatic stop condition includes, for example, a predetermined condition such as a vehicle speed of 0 km / h, a steering angle of a predetermined value or less, a battery voltage of a reference value or more, and an air conditioner being in an OFF state. The condition that the vehicle speed is after a predetermined value (for example, 10 km / h) or more after the stop is executed is included. The success / failure determination of the automatic stop condition by the stop / restart control means 48 may determine all the conditions included in the automatic stop condition at once. In this embodiment, each condition is distributed at a predetermined time. It is supposed to be judged.

  Then, if the stop / restart control means 48 determines that the automatic stop condition is satisfied as a result of the determination of success or failure of the automatic stop condition, each cylinder 12A by the fuel supply control means 45 at a predetermined time after stopping. The fuel supply to ˜12D and the ignition control means 46 are stopped.

  By the way, the stop / restart control means 48 may execute the first combustion in the cylinder in the expansion stroke at the time of stop when the engine is restarted to cause the engine to perform forward rotation. When the engine is restarted, the cylinder in the compression stroke when the engine is stopped is first burned to depress the piston, and the cylinder pressure in the expansion stroke is raised to increase the in-cylinder pressure. Fuel is injected into the stroke cylinder for ignition and combustion, combustion air is present in the combustion chamber after the initial combustion in the compression stroke cylinder, and fuel corresponding to the amount of air is injected after the initial combustion. By supplying the fuel at an appropriate time, the cylinder is controlled so as to perform re-combustion when the cylinder turns up and exceeds the compression top dead center. That is, at the time of automatic restart of the engine, control is performed such that the engine is once reversely operated at the initial stage of the start and then the normal rotation is started.

  In order to properly restart the engine by igniting the fuel injected into a specific cylinder without using a restart motor in principle as described above, the air-fuel mixture in the expansion stroke cylinder is combusted. It is necessary to ensure sufficient combustion energy to be obtained so that the subsequent cylinders exceed the compression top dead center. Therefore, it is necessary to ensure a sufficient amount of air in the expansion stroke cylinder where the piston 13 is in the middle of the expansion stroke when the engine is automatically stopped.

  That is, as shown in FIGS. 6A and 6B, in the cylinder that is in the expansion stroke and the compression stroke when the engine is stopped, the pistons 13 operate in opposite directions, and the piston 13 of the expansion stroke cylinder is in the stroke. If it is located on the bottom dead center side from the center, the amount of air in the cylinder increases and sufficient combustion energy can be obtained. However, when the piston 13 of the expansion stroke cylinder is extremely positioned on the bottom dead center side, the amount of air in the compression stroke cylinder becomes too small and sufficient combustion energy for reversing the crankshaft 3 is obtained. Disappear.

  In contrast, the center of the stroke of the expansion stroke cylinder, that is, a predetermined range slightly lower than the position where the crank angle after compression top dead center is 90 ° CA, for example, the crank angle after compression top dead center is 100 If the piston 13 can be stopped within an appropriate range R of ° to 120 ° CA, a predetermined amount of air is secured in the compression stroke cylinder, and the crankshaft 3 can be slightly reversed by the initial combustion. Combustion energy can be obtained. In addition, by securing a large amount of air in the expansion stroke cylinder, it is possible to generate sufficient combustion energy for normal rotation of the crankshaft 3 and reliably restart the engine.

  Therefore, the stop / restart control means 48 provided in the ECU 2 controls the intake flow rate control means 43, the combustion state control means 44, and the generated current control means 47 to stop the piston 13 within the appropriate range R. Yes.

  Further, the stop / restart control means 48 executes any one of the preceding cylinders 12A and 12D and the succeeding cylinders 12B and 12C when the engine is automatically stopped in the special operation mode. Based on this prediction, the intake air flow control means 43 adjusts the amount of air taken into the preceding cylinders 12A and 12D and stops it within the appropriate range R. Therefore, in the present embodiment, the stop / restart control means 48 also serves as the prediction means described in the claims.

  Specifically, as shown in FIG. 7, the automatic stop control means provided in the ECU 2 causes the preceding cylinders 12A, 12D and the subsequent cylinders 12B, 12C to be cylinders at the time t0 when the automatic engine stop condition is satisfied. While maintaining the two-cylinder connection state in which communication is performed by the inter-gas passage 22a, control is performed to set the engine target rotational speed to a value higher than the normal idle rotational speed when the engine is not automatically stopped. For example, in an engine in which the normal idle rotation speed is set to 650 rpm (the automatic transmission is in the drive range), the target rotation speed (idle rotation speed when the automatic stop condition is satisfied) is set to about 800 rpm (the automatic transmission is in the neutral range). ) Is executed to stabilize the engine rotational speed Ne at a rotational speed slightly higher than the idle rotational speed in the normal mode, and fuel injection is performed at time t1 when the engine rotational speed Ne is stabilized at the target rotational speed. Is stopped to reduce the engine speed Ne.

  Further, at the fuel injection stop time t1, which is the initial stage of the control operation for automatically stopping the engine, the air-fuel ratio in the succeeding cylinders 12B, 12C is the intake air flow rate during idling in the normal mode (in order to continue engine operation). The intake air that is drawn into the cylinders 12A to 12D of the engine is reduced by setting the opening K of the throttle valve 23 so that the intake air flow rate is larger than the minimum intake air flow rate required for the engine). A sufficient flow rate is ensured. That is, when the combustion state immediately before the time point t1 is uniform combustion in which the air-fuel ratio in the succeeding cylinders 12B and 12C is set to λ (excess air ratio) = 1 or in the vicinity thereof, the fuel injection is stopped. At the time t1, the opening K of the throttle valve 23 is increased to, for example, about 30% of full opening, and the boost pressure (intake pressure) Bt is increased, whereby the intake air flow sucked into the cylinders 12A to 12D of the engine. Is set to a state larger by a predetermined amount than the minimum intake flow rate required for continuing the engine operation to ensure scavenging of the combustion gas, and the target generated current of the alternator 28 at the fuel injection stop time t1. The rotation resistance of the crankshaft 3 is reduced by lowering Ge from the time point t0 when the automatic stop condition is satisfied.

  By stopping the combustion injection at the time point t1, the throttle valve 23 is closed at the time point t2 when it is confirmed that the engine rotational speed Ne has decreased to a preset reference speed (for example, 790 rpm) or less. . The boost pressure Bt begins to decrease from the time t2 when the throttle valve 23 is closed, and the intake flow rate introduced into each cylinder of the engine decreases, so that the common intake air between the opening time t1 and the closing time t2 of the throttle valve 23 is reduced. As the air introduced into the passage 21c passes through the surge tank 21b and the branch intake passage 21a, as shown in FIG. 8, the fourth cylinder 12D, which is the preceding cylinder that reaches the intake stroke, and the first cylinder 12A in this order. It is introduced with a predetermined transport delay. At this time, the burned gas of the preceding cylinders 12A and 12D is introduced into the second cylinder 12B and the third cylinder 12C, which are the succeeding cylinders.

  In this embodiment, at this time t2, which of the preceding and succeeding cylinders is in the expansion stroke when the engine is stopped based on the engine rotation speed by the crank angle sensors 30 and 31, the engine temperature by the water temperature sensor 33, and the like. Is output to the intake flow rate control means 43, and the intake flow rate control means 43 opens and closes the opening and period of the throttle valve 23 while taking into account the prediction and the intake air delay. By setting the control at an appropriate time, the intake air amount to the preceding cylinders 12A and 12D, and hence the intake air amount to the subsequent cylinders 12B and 12C into which the gas from the preceding cylinders 12A and 12D is introduced is adjusted, and the engine is stopped. More air is introduced into the cylinder that is in the expansion stroke than in the cylinder that is sometimes in the compression stroke.

  In the example of FIG. 8, the opening degree of the throttle valve 23 is set to 30% at the time point t1, and the opening degree is set to 0% at the time point t2, and the stop-time expansion stroke cylinder is the preceding cylinder 12A at the time point t2. It is predicted that there is, and the opening degree of the throttle valve 23 is increased to 20% at the time t4 when it passes through the three compression top dead centers by counting from the engine stop state based on this prediction. Control is performed so that the intake air amount of a certain preceding cylinder 12A increases. At this time, the air amount of the succeeding cylinder 12C in the compression stroke at the time of the stop is determined by the intake amount of the fourth cylinder 12D indicated by hatching in FIG. 8, but the opening degree of the throttle valve 23 at this time becomes 0%. Therefore, the intake amount of the compression stroke cylinder at the time of stop is relatively small. In this way, more air is introduced into the cylinder that is in the expansion stroke than in the cylinder that is in the compression stroke when the engine is stopped.

  Further, at the time t2 when it is confirmed that the engine rotational speed Ne has decreased below the reference speed N2, the target generated current Ge of the alternator 28 is temporarily increased, and the engine top dead center rotational speed as will be described later. At time t3 when ne is within the predetermined range, the target power generation current Ge of the alternator 28 is reduced to a value corresponding to the reduced state of the engine rotational speed Ne, so that a reference set based on experimental results conducted in advance Control is performed to reduce the rotational speed Ne of the engine along the line.

  When the engine is automatically stopped as described above, the kinetic energy of the crankshaft 3, the flywheel, etc. from the fuel injection stop time t1 is caused by mechanical loss due to frictional resistance or pump work of each cylinder 12A to 12D. When consumed, the crankshaft 3 of the engine is rotated several times by inertia, and in a 4-cylinder 4-cycle engine, it stops after reaching the compression top dead center of about 10 times. Specifically, as shown in FIGS. 7 and 8, after each of the cylinders 12 </ b> A to 12 </ b> D reaches compression top dead center, the engine rotational speed Ne drops temporarily and then exceeds compression top dead center. The engine rotational speed Ne gradually decreases while repeating the up-down that rises again at the time.

  In the cylinder 12C that reaches the compression top dead center after the time t6 when the last compression top dead center is exceeded before the engine is stopped, the air pressure increases as the piston 13 rises due to the inertial force, and the compression reaction force causes the piston to rise. 13 is pushed back, and the crankshaft 3 is reversely rotated. Since the air pressure of the expansion stroke cylinder 12A increases due to the reverse rotation of the crankshaft 3, the piston 13 of the expansion stroke cylinder 12A is pushed back to the bottom dead center side according to the compression reaction force, and the crankshaft 3 rotates forward again. First, the reverse rotation and forward rotation of the crankshaft 3 are repeated several times, and the piston 13 stops after reciprocating. The stop position of the piston 13 is substantially determined by the balance of the compression reaction force in the compression stroke cylinder 12C and the expansion stroke cylinder 12A, and is influenced by the frictional resistance of the engine and exceeds the last compression top dead center. It also changes depending on the rotational inertia of the engine at time t6, that is, the level of the engine rotational speed Ne.

  Therefore, in order to stop the piston 13 of the expansion stroke cylinder 12A in the expansion stroke within the appropriate range R suitable for restart when the engine automatically stops, first, the expansion stroke cylinder 12A and the compression stroke cylinder 12C are used. The intake flow rates for both cylinders 12A and 12C are adjusted so that the compression reaction force of each of the cylinders 12A and 12C is sufficiently large and the compression reaction force of the expansion stroke cylinder 12A is greater than the compression reaction force of the compression stroke cylinder 12C by a predetermined value or more. There is a need. For this reason, in the present embodiment, a predetermined amount of air is supplied to both the expansion stroke cylinder 12A and the compression stroke cylinder 12C by setting the opening K of the throttle valve 23 to a large value at the fuel injection stop time t1. After the intake, the throttle valve 23 is closed at a time t2 when a predetermined time elapses and the opening K is reduced to adjust the intake air amount, and the stop expansion stroke cylinder is the preceding cylinder 12A. , 12D or the succeeding cylinders 12B, 12C, the opening degree of the throttle valve 23 at the time 2TDC (compression top dead center) t4 before engine stop is adjusted.

  However, in an actual engine, because there are individual differences in the shapes of the throttle valve 23, the intake port 17, the branch intake passage 21a, and the like, the behavior of the air flowing through them changes, so that during each automatic stop period of the engine Variations occur in the intake air flow rate sucked into the cylinders 12A to 12D. Further, even if the opening / closing control of the throttle valve 23 is performed as described above due to differences in engine friction resistance due to individual engine differences and engine temperature, the cylinder 12A and the cylinder 12A that are in the expansion stroke when the engine is stopped In some cases, the piston stop position of the cylinder 12C in the compression stroke cannot be within the appropriate range R.

  In this regard, according to the present invention, when the engine speed Ne decreases during the automatic engine stop period, the cylinders 12A to 12D pass through the compression top dead center as shown in an example in FIG. It was noted that there is a clear correlation between the engine rotational speed (top dead center rotational speed) ne and the piston stop position of the cylinder 12A in the expansion stroke at the time of engine stop. As shown in FIGS. 7 and 8, the piston 13 of each cylinder 12 </ b> A to 12 </ b> D passes through the compression top dead center in the process in which the engine rotational speed Ne decreases after the time t <b> 1 when the fuel injection is stopped. The engine rotational speed, that is, the top dead center rotational speed ne is detected, and the target generated current Ge of the alternator 28 is controlled in accordance with the detected value of the top dead center rotational speed ne, thereby reducing the degree of decrease in the engine rotational speed Ne. I try to adjust it.

  That is, FIG. 9 shows that the fuel injection is stopped at the time t1 when the rotational speed Ne of the engine becomes a predetermined speed as described above, and the throttle valve 23 is kept open for a predetermined period thereafter. The piston 13 provided in each cylinder 12A to 12D of the engine that rotates due to inertia measures the top dead center rotational speed ne when the piston 13 passes through the compression top dead center, and the piston position of the expansion stroke cylinder 12A when the engine is stopped. The piston position is plotted on the vertical axis, and the top dead center rotational speed ne of the engine is plotted on the horizontal axis, and the relationship between the two is graphed. By repeating this operation, a distribution map showing the correlation between the top dead center rotational speed ne during the engine stop operation period and the piston stop position in the expansion stroke cylinder 12A is obtained.

  From the above distribution diagram, a predetermined correlation is found between the top dead center rotational speed ne during the engine stop operation period and the piston stop position in the expansion stroke cylinder 12A. In the example shown in FIG. 9, the engine is stopped. If the top dead center rotational speed ne at the sixth to second before the state is within the range indicated by hatching, the stop position of the piston 13 is within a range R suitable for restarting the engine (after the compression top dead center). 100 ° to 120 ° CA).

  Therefore, as shown in FIG. 7 and FIG. 8, until a predetermined time elapses from the time point t1 when the fuel injection is stopped, that is, until the time point t2 when the engine rotational speed Ne drops below the reference speed (for example, about 760 rpm). In order to sufficiently secure the scavenging performance of each cylinder 12A to 12D while suppressing the effects of rotational inertia and frictional resistance, the opening degree K of the throttle valve 23 is a relatively large value (for example, 30% opening degree of full opening). It is preferable to set to. Further, in order to maintain the engine speed Ne at a speed at which the piston 13 can be stopped at an appropriate position, the target generated current Ge of the alternator 28 is set to 0, for example, at the fuel injection stop time t1. It is like that.

  Then, at the time t2 when the engine speed Ne is decreased to the reference speed N2 or less, the opening K of the throttle valve 23 is reduced, and the target power generation current Ge of the alternator 28 is increased to a preset initial value. After the execution, at the time t3 when the engine top dead center rotational speed ne falls within the predetermined range, the target power generation current Ge of the alternator 28 is decreased to a value corresponding to the decreased state of the engine rotational speed Ne, and the crankshaft 3 By adjusting the rotational resistance of the engine and changing the engine external load in accordance with the degree of decrease in the engine rotational speed Ne, the engine rotational speed Ne is decreased along a reference line set based on experiments conducted in advance. I try to let them.

  Specifically, the engine top dead center rotational speed ne is detected in the process in which the engine rotational speed Ne decreases along the reference line, and the top dead center rotational speed ne falls within, for example, 480 rpm to 540 rpm. When it is determined that the engine has passed through the fourth compression top dead center before the engine is stopped, the top dead center of the engine is determined based on the top dead center rotational speed ne at time t3. The target generated current Ge corresponding to the detected value of the top dead center rotational speed ne is read from the map shown in FIG. 10 in which the target generated current Ge is set to a larger value as the point rotational speed ne is higher, and this value is read as an alternator. It is configured to set as 28 target generated current Ge. As a result, before the engine rotational speed Ne decreases below the predetermined value, that is, before the engine rotational speed Ne decreases below the rotational speed at which the power generation function of the alternator 28 can be sufficiently exerted (for example, 420 rpm), the alternator 28 described above. Becomes an operating state, and control for adjusting the degree of decrease in the engine rotational speed Ne is executed.

  Further, the initial value when the target generated current Ge of the alternator 28 is increased at the time point t2 when the engine speed Ne is decreased to the reference speed N2 or less is larger than the maximum value of the target generated current Ge read from the map. The target generated current Ge of the alternator 28 is controlled based on the detected value of the top dead center rotational speed ne by lowering the target generated current Ge that has been set and increased to the initial value at the time t2 at the time t3. It is configured as follows. For example, when the target generated current Ge read from the map is set to 0 to 50A, the initial value is set to a value higher than 50A that is the maximum value, for example, 60A. Then, after the target generated current Ge is set to 60 A at the time t2, the amount of decrease in the target generated current Ge is set based on the value read from the map at the time t3, and the alternator is set based on this value. Control for lowering the 28 target power generation current Ge is performed.

  By controlling the generated current of the alternator 28 as described above, the kinetic energy and compression stroke cylinder of the crankshaft 3, the flywheel, the piston 13, and the connecting rod, etc. at the time t6 when the final compression top dead center is passed. The potential energy etc. of the air compressed in 12C is commensurate with the frictional resistance loss and the like acting thereafter, and the range R suitable for restarting the engine of the piston 13 of the cylinder 12A that is in the expansion stroke when the engine is stopped. It becomes possible to stop within.

  A control operation when the engine is automatically stopped by the stop / restart control means 48 of the ECU 2 will be described based on flowcharts shown in FIGS. When this control operation starts, it is determined whether or not an automatic stop permission flag F for determining whether or not the engine is in an operating state capable of executing the automatic stop control is ON (step S1). This automatic stop permission flag F indicates that the vehicle speed is not less than a predetermined value (for example, 10 km / h), the steering angle is not more than a predetermined value, the battery voltage is not less than a reference value, and the air conditioner is in an OFF state after the vehicle speed is 0. When the above condition is satisfied, it is determined that the engine can be automatically stopped and is turned on.

  If YES is determined in step S1, it is determined whether the accelerator sensor 34 is in an OFF state and the brake sensor 35 is in an ON state (step S2). When it is confirmed that the engine is in the state, it is determined whether or not the engine rotational speed Ne is larger than the reference value for fuel cut during deceleration that is set in advance to about 1100 rpm (step S3). If determined, the process proceeds to the following step S7.

  When it is determined YES in step S3 and it is confirmed that the engine speed Ne is larger than the reference value for fuel cut during deceleration, fuel cut during deceleration (FC) is executed (step S4). ). Next, it is determined whether or not the engine rotational speed Ne has decreased below a fuel recovery determination reference value that has been set to about 900 rpm in advance (step S5). The cut (FC) is terminated and the normal fuel injection state is restored (step S6).

  Next, the target rotational speed of the engine is set to a value higher than the normal idle rotational speed (about 650 rpm) by a predetermined amount, for example, about 800 rpm, and this speed is maintained (step S7).

  Then, it is determined whether or not the accelerator sensor 34 is turned on or the brake sensor 35 is turned off, that is, whether or not the deceleration state is released (step S8). Returning to step S1, the above control operation is repeated. If it is determined NO in step S8 and it is confirmed that the deceleration state is not released, it is determined whether or not the vehicle speed is 0, that is, whether or not the vehicle is stopped and the automatic stop condition is satisfied. Determine (step S9).

  When it is determined YES in step S9 and it is confirmed that the vehicle is stopped, the engine target rotational speed N1 is set to a value higher than 810 rpm, for example, about 860 rpm (step S10). Then, the shift range of the automatic transmission is set to neutral and is set to a no-load state (step S11).

  Here, at the time t0 when it is determined in step S9 that the vehicle speed is 0 and it is confirmed that all the automatic engine stop conditions are satisfied, the target engine speed N1 of the engine is set to a predetermined value in step S10. In addition, since the shift range of the automatic transmission is shifted from the drive state (D range) to the neutral state (N range) in step S11, the load on the automatic transmission is reduced, which is shown in FIG. Thus, the engine rotation speed Ne slightly increases from the time point t0 when the automatic stop condition is satisfied.

  Next, it is determined whether or not a predetermined time (for example, about 1 second) has passed after a time point t0 when it is determined as YES in step S11 and it is confirmed that the automatic engine stop condition is satisfied. (Step S12). If NO is determined in step S12, the process waits until a predetermined time elapses, and whether or not the fuel injection stop condition (FC condition) is satisfied when YES is determined. Specifically, it is determined whether or not the engine rotational speed Ne becomes the target rotational speed N1 and the boost pressure Bt is stabilized in the state where the target pressure P1 is reached (step S13). If the accelerator sensor 34 is turned on or the brake sensor 35 is turned off during the determination operation, the process returns without stopping the fuel injection. Thereby, it is possible to prevent an inappropriate automatic stop of the engine from being performed in a case where the vehicle speed is shifted to 0 immediately after the vehicle speed becomes zero.

  Then, when it is determined YES in step S13 and it is confirmed that the engine speed Ne and the boost pressure Bt are in a stable state (time t1 in FIGS. 7 and 8), the fuel injection is stopped. After (step S14), the target power generation current Ge of the alternator 28 is set to 0 to stop power generation (step S15), and the throttle valve 23 is opened to set the opening K to about 30%, for example. (Step S16).

  Thereafter, whether or not a predetermined time has elapsed from the time point t1 when the fuel injection is stopped in step S14, that is, the combustion of the fuel injected before reaching the two compression top dead centers after the fuel injection is stopped. It is determined whether or not the process has been completed (step S17), and when the determination is YES, ignition by the ignition device 27 is stopped (step S18). Next, by determining whether or not the engine rotational speed Ne has become equal to or lower than a reference speed N2 set to about 790 rpm in advance (step S19), after the fuel injection stop time t1 shown in FIGS. 7 and 8, It is determined whether or not the engine rotational speed Ne has started to decrease. At a time t2 when it is determined YES, the throttle valve 23 is closed and its opening K is set to 0% (step S20). As a result, the boost pressure Bt that has risen so as to approach the atmospheric pressure when the throttle valve 23 is opened in step S17 starts to decrease with a predetermined time difference according to the closing operation of the throttle valve 23.

  Then, the target power generation current Ge of the alternator 28 is set to an initial value set to about 60 A in advance, and power generation control for operating the alternator 28 is started (step S21). The engine top dead center is replaced with the above-described embodiment in which the throttle valve 23 is closed at the time t2 when it is determined in step S19 that the engine speed Ne is equal to or lower than the reference speed N2. For example, when it is determined that the rotational speed ne is equal to or lower than the reference speed N2 set to about 790 rpm, for example, the throttle valve 23 is closed and power generation control of the alternator 28 is started. Good.

  Further, at this time, that is, at the time t2 when it is determined that the reference speed N2 or less is reached, the cylinder in the expansion stroke is predicted when the engine is stopped based on the engine speed, the engine temperature, etc., and the predicted stop It is determined whether the time expansion stroke cylinder is the preceding cylinder 12A, 12D or the succeeding cylinder 12B, 12C, and the determination result is stored (step S22). In the present embodiment, this prediction is made based on data collected in advance through experiments or the like.

  Next, it is determined whether or not the engine top dead center rotational speed ne is within the first predetermined range (step S23). This first predetermined range is a time point t3 when the engine passes through the fourth compression top dead center before the engine is stopped, for example, in the process in which the rotational speed Ne of the engine decreases along a preset reference line. Is a value set based on the top dead center rotational speed ne, and specifically, is set within the range of 480 rpm to 540 rpm.

  When it is determined YES in step S23 and it is confirmed that the engine top dead center rotational speed ne is within the predetermined range (480 rpm to 540 rpm), it corresponds to the top dead center rotational speed ne at that time t3. The target generated current Ge of the generated alternator 28 is set (step S24). That is, as shown in FIG. 10, the higher the engine top dead center rotational speed ne is, the higher the engine top dead center rotational speed ne is read from the map where the target power generation current Ge is set to a larger value, and the target power generation current Ge corresponding to the top dead center rotational speed ne is read. Based on this value, control is performed to reduce the target generated current Ge of the alternator 28 from the initial value (60A) to the value read from the map.

  Next, the engine top dead center rotational speed ne is within a second predetermined range set based on the top dead center rotational speed ne at the time t4 when the engine passes the third compression top dead center before the engine stops, for example, 380 rpm to It is determined whether it is within the range of 480 rpm (step S25). At the time t4 when it is determined as YES in this step S25 and it is confirmed that the third compression top dead center before the engine stop is passed, the cylinder in the expansion stroke when the engine is stopped is preceded by the prediction in the step S22. It is determined whether or not the cylinders are 12A and 12D (step S26), and the throttle valve 23 is opened by the intake flow rate control means 43 only when the cylinders are the preceding cylinders 12A and 12D. The degree is set (step S27).

  Thereafter, the engine top dead center rotational speed ne is within a third predetermined range set based on the top dead center rotational speed ne at the time t5 when the engine passes the second compression top dead center before stopping the engine, for example, 260 rpm to It is determined whether or not it is within the range of 400 rpm (step S28). In this step S28, YES is determined, and the fuel injection amount is set to a larger value as the engine top dead center rotational speed ne is higher. From this map, the fuel injection amount for the cylinder 12C that is in the compression stroke when the engine is stopped is set, and the fuel is injected in the latter half of the compression stroke of the cylinder 12C (step S29). When the fuel injected into the cylinder 12C is vaporized, the temperature in the cylinder is lowered, and the increase in the internal pressure is suppressed.

  Then, it is determined whether or not the engine top dead center rotational speed ne is equal to or less than a predetermined value N3 (step S30). This predetermined value N3 is a value corresponding to the top dead center rotational speed ne when exceeding the last compression top dead center in the process in which the engine rotational speed Ne is decreasing along a preset reference line, For example, it is set to about 260 rpm.

  Next, it is determined whether or not the engine is stopped (step S31). When it is determined YES, the shift range of the automatic transmission is returned from the neutral state to the drive state (D range) (step S32). ) After turning off the automatic stop permission flag F (step S33), the control operation is terminated.

  7 and 8 of the present embodiment are described on the assumption that the cylinder in the expansion stroke when the engine is stopped is the preceding cylinder 12A. However, this expansion stroke cylinder at the time of stop is the subsequent cylinders 12B and 12C. It may be the case. For example, as shown in FIG. 14, even when the stop expansion stroke cylinder is the second cylinder 2B (subsequent cylinder), the opening degree of the throttle valve 23 is set to 30% at the time point t1, and the opening is opened at the time point t2. The degree is set to 0%, and at this time t2, it is predicted that the expansion stroke cylinder at the time of stop is the succeeding cylinder 12B. The amount of air charged in the stop-time expansion stroke cylinder 12B is determined by the intake amount of the first cylinder 12A immediately after time t2, and the opening amount of the throttle valve 23 is set to 30% as the intake amount of the preceding cylinder 12A. This is the intake amount when the boost pressure rises. On the other hand, in the first cylinder 12A in the compression stroke at the time of stop, the air amount at the time of engine stop is determined in the intake stroke immediately after time t5. At this time, the throttle valve 23 is closed and the boost pressure is reduced, and therefore the intake air amount introduced into the preceding cylinder 12A is relatively small. In this way, more air is introduced into the cylinder that is in the expansion stroke than in the cylinder that is in the compression stroke when the engine is stopped.

  According to the above apparatus, based on the output from the crank angle sensors 30, 31 and the water temperature sensor 33, the stop / restart control means 48 predicts the stroke of each cylinder when the engine is stopped, and based on this prediction result, The cylinders in the expansion stroke and the compression stroke can be predicted when the engine is stopped. The engine is adjusted by adjusting the throttle valve 23 through the intake flow rate control means 43 by the stop / restart control means 48 in order to adjust the intake flow rate of the cylinder that is predicted to be in the expansion stroke and the compression stroke when the engine is stopped. The piston of the cylinder in the expansion stroke at the time of the stop can be stopped within a proper range R where the piston of the expansion stroke cylinder at the time of the stop slightly approaches the bottom dead center side with a high probability.

  In addition, the stop / restart control means 48 automatically stops the engine while the two-cylinder connected state in which the intake air flow rate to the succeeding cylinders 12B and 12C is determined by the intake air flow rate of the preceding cylinder that forms a pair with the succeeding cylinders 12B and 12C. In addition, since each intake stroke for determining the intake flow rate to each cylinder in the expansion stroke is longer than that in each cylinder independent state, the intake flow rate control is surely performed regardless of the responsiveness by the throttle valve 23. And the intake flow rate introduced into each cylinder can be adjusted effectively.

  A control operation for restarting the engine that has been automatically stopped as described above will be described based on the flowcharts shown in FIGS. 15 to 17 and the time charts shown in FIGS. First, it is determined whether or not a predetermined engine restart condition is satisfied (step S101). If YES is determined, for example, if an accelerator operation for starting from a stopped state is performed, the battery voltage is When the air temperature decreases or when the air conditioner is activated, the in-cylinder temperature is estimated based on the engine water temperature, the elapsed time since the automatic stop, the intake air temperature, and the like (step S102).

  Based on the stop position of the piston 13 detected when the engine is automatically stopped, the amount of air in the compression stroke cylinder 12C and the expansion stroke cylinder 12A is calculated (step S103). That is, the combustion chamber volumes of the compression stroke cylinder 12C and the expansion stroke cylinder 12A are obtained from the stop position of the piston 13. When the engine is automatically stopped, the engine is stopped after several revolutions after the fuel injection is stopped. Therefore, the expansion stroke cylinder 12A is also filled with fresh air, and the compression stroke cylinder 12C and the expansion cylinder 12C are expanded while the engine is stopped. Since the inside of the stroke cylinder 12A is at substantially atmospheric pressure, the amount of fresh air is obtained from the combustion chamber volume.

  Next, the first fuel injection is performed so that the air-fuel ratio (theoretical air-fuel ratio or richer air-fuel ratio) satisfies λ ≦ 1 with respect to the air amount of the compression stroke cylinder 12C calculated in step S103 (step S103). S104). This air-fuel ratio is obtained from the first-time second air-fuel ratio map M1 of the compression stroke cylinder 12C set in advance according to the stop position of the piston 13, and satisfies λ ≦ 1 (theoretical air-fuel ratio or richer air-fuel ratio). By setting, the combustion energy for reversal can be sufficiently obtained.

  Next, the cylinder 12C is ignited after a predetermined time set in consideration of the vaporization time from the first fuel injection to the compression stroke cylinder 12C (step S105). Then, it is determined whether or not the piston 13 has moved based on whether or not the edges of the crank angle sensors 30 and 31, that is, the rising or falling edge of the crank angle signal, have been detected within a certain time after ignition (step S106). If it is determined NO and it is confirmed that the misfire has occurred and the piston 13 has not moved, the compression stroke cylinder 12C is re-ignited (step S107).

  If it is determined YES in step S106 and it is confirmed that the piston 13 has moved, the air-fuel ratio in the expansion stroke cylinder 12A calculated in step S103 becomes a predetermined air-fuel ratio (near λ = 1). Next, the fuel injection amount is calculated (step S108). The air-fuel ratio at this time is obtained from the air-fuel ratio map M2 for the expansion stroke cylinder 12A set in advance according to the stop position of the piston 13.

  Then, after the fuel injection to the expansion stroke cylinder 12A, ignition is performed in the expansion stroke cylinder 12A when a predetermined delay time has elapsed (step S109). This delay time is obtained from the ignition map M3 for the expansion stroke cylinder 12A set in advance according to the stop position of the piston 13. By the combustion in the expansion stroke cylinder 12A by the ignition, the engine turns from reverse rotation to normal rotation. Accordingly, the piston 13 of the compression stroke cylinder 12C moves to the top dead center side, and the gas in the cylinder (burned gas combusted by ignition in step S105) starts to be compressed.

  Next, taking into account the fuel vaporization time, the second fuel is injected into the compression stroke cylinder 12C (step S110). The fuel injection amount at this time is such that the entire air-fuel ratio based on the total injection amount with the first injection amount becomes richer (for example, about 6) than the combustible air-fuel ratio (lower limit is 7 to 8). It is obtained from the second air-fuel ratio map M4 for the compression stroke cylinder 12C set in advance according to the stop position of the piston 13. The compression top dead center can be easily exceeded by reducing the compression pressure in the vicinity of the compression top dead center of the compression stroke cylinder 12C according to the latent heat of vaporization caused by the second injection fuel in the compression stroke cylinder 12C. It becomes.

  Note that the second fuel injection into the compression stroke cylinder 12C is performed only to reduce the compression pressure in the cylinder, and ignition and combustion are not performed on this, and it is richer than the combustible air-fuel ratio. Therefore, self-ignition does not occur, and the non-combustible fuel is made harmless by reacting with oxygen stored in the exhaust gas purification catalyst 37 in the exhaust passage 22 thereafter.

  As described above, since the fuel injected for the second time in the compression stroke cylinder 12C does not burn, the next combustion following the first combustion in the expansion stroke cylinder 12A was in the intake stroke cylinder 12D, that is, the intake stroke when stopped. Combustion in the fourth cylinder. As energy for the piston 13 of the intake stroke cylinder 12D to exceed the compression top dead center, a part of the initial combustion energy in the expansion stroke cylinder 12A is used, and the initial combustion energy in the expansion stroke cylinder 12A is compressed. The stroke cylinder 12C is used both for overcoming the compression top dead center and for the intake stroke cylinder 12D for exceeding the compression top dead center.

  Therefore, for smooth start-up, it is desirable that the energy required for the intake stroke cylinder 12D to exceed the compression top dead center is small. For this reason, the air density in the intake stroke cylinder 12D is estimated, and the intake air is estimated from the estimated value. After calculating the air amount of the stroke cylinder 12D (step S111), an air-fuel ratio correction value for preventing self-ignition is calculated based on the in-cylinder temperature estimated in step S102 (step S112). That is, when self-ignition occurs, a force (reverse torque) that pushes the piston 13 back to the bottom dead center before the compression top dead center is generated by the combustion, and much energy is required to exceed the compression top dead center. Since it is consumed, it is not desirable. Therefore, in order to suppress the reverse torque, the air-fuel ratio is corrected to the lean side so that compression self-ignition does not occur.

  Next, the fuel injection amount to the intake stroke cylinder 12D is calculated based on the air amount of the intake stroke cylinder 12D calculated in step S111 and the air-fuel ratio considering the air-fuel ratio correction value calculated in step S112 ( Step S113). Then, fuel is injected into the intake stroke cylinder 12D. In this fuel injection, the compression pressure is reduced by the latent heat of vaporization, that is, the energy required to exceed the compression top dead center is reduced. The process is delayed until the later stage of the compression stroke (step S114), and the delay amount is calculated based on the automatic engine stop period, the intake air temperature, the engine water temperature, and the like.

  Further, in order to suppress the occurrence of the reverse torque, ignition is delayed after the top dead center (step S115). By executing the control described above, in the intake stroke cylinder 12D, the compression pressure is reduced to the compression top dead center and easily exceeds the top dead center. Directional torque will be generated.

  And after this step S115 is performed, the electric power generation by the alternator 28 is started (step S116). Here, the target power generation amount by the alternator 28 is not particularly limited, but is set higher than the target power generation amount in the normal control in this embodiment.

  Subsequently, in step S117, it is determined whether the cylinder having the expansion stroke when the engine is stopped is the preceding cylinder 12A, 12D or the succeeding cylinder 12B, 12C, and the expansion stroke cylinder at the stop is the preceding cylinder 12A, 12D. Is determined, the combustion in the stop exhaust stroke cylinder into which the burned gas is introduced in the stop expansion stroke cylinder 12A is thinned out (step S118), and the subsequent stop exhaust stroke cylinder is Fuel is injected so that the air-fuel ratio becomes a lean air-fuel ratio (step S119), and the expansion stroke cylinder at the time of stop is ignited at a normal timing (step S120), and control is performed so as to shift to normal control.

  That is, when the cylinders in the expansion stroke when the engine is stopped are the preceding cylinders 12A and 12D, fresh air is consumed by the combustion in step S109, and the burned gas generated by this combustion passes through the inter-cylinder gas passage 22a. This is introduced into the stop-time exhaust stroke cylinder 12B, which is the subsequent cylinder. Since no fresh air remains in the burned gas, combustion cannot be executed in (5) shown in FIG. 18 (a). Therefore, the exhaust stroke cylinder 12B at the time of stoppage is the first after the restart. In the compression stroke to be greeted, fuel injection and ignition are stopped. In addition, there is an advantage that excessive blow-up at the time of restart can be prevented by thinning out the combustion immediately after passing through the compression top dead center at which the intake stroke cylinder at the time of stop first reaches after the restart. In the stop expansion stroke cylinder 12A, which is the preceding preceding cylinder, control is performed in the special operation mode. Therefore, fuel is injected so that the air-fuel ratio becomes a lean air-fuel ratio larger than the stoichiometric air-fuel ratio, and ignition and combustion are performed. It is supposed to run.

  On the other hand, if the stop expansion stroke cylinder is not the preceding cylinder in step S117 (NO in step S117), in other words, if the cylinders in the expansion stroke when the engine is stopped are the succeeding cylinders 12B and 12C, the stop expansion stroke is performed. Unlike the case where the cylinder is the preceding cylinder, the burned gas from the initial combustion in the expansion stroke cylinder for the forward rotation start of the engine is discharged to the exhaust passage 22, while the stop-time exhaust stroke cylinders 12A and 12D which are the preceding cylinders Since fresh air is introduced into the exhaust stroke cylinder, fuel is injected into the stop-time exhaust stroke cylinder so that the air-fuel ratio becomes a lean air-fuel ratio larger than the stoichiometric air-fuel ratio (step S121), ignition, Combustion is performed (see (5) in FIG. 18B). Then, the compression stroke cylinder becomes the preceding cylinder, and the burned gas after the fresh air is consumed by the combustion for the reverse operation in step S105 is introduced into the stop expansion stroke cylinder that continues, FIG. As shown in (6) of (b), the second combustion for the forward rotation operation of the stop-time expansion stroke cylinder is thinned out (fuel injection and ignition are stopped), and the normal control is started. It has become.

  When the restart control is executed, as shown in FIGS. 18 and 19, first, the first fuel injection J3 is performed in the compression stroke cylinder 12C (third cylinder), and combustion is performed by the ignition (FIG. 18). (1)) is performed. With the combustion pressure (part a in FIG. 19) due to the combustion (1), the piston 13 of the compression stroke cylinder 12C is pushed down to the bottom dead center side, and the engine is driven in the reverse direction. Here, since the first fuel injection J3 of the compression stroke cylinder 12C is injected so as to have a stoichiometric air-fuel ratio or a richer air-fuel ratio (λ ≦ 1) than that, an appropriate combustion energy for engine reverse rotation, that is, While sufficiently compressing the air in the expansion stroke cylinder 12 </ b> A, it is possible to obtain combustion energy that is not excessively reversed beyond its compression top dead center. FIG. 18A shows a time chart when the stop expansion stroke cylinder is the preceding cylinder, and FIG. 18B shows a time chart when the stop expansion stroke cylinder is the succeeding cylinder. However, in the case of FIG. 18, it refers to both cases of FIG. (A) and FIG. (B).

  As the engine starts reverse rotation, the piston 13 of the expansion stroke cylinder 12A (first cylinder) starts to move in the direction of the top dead center. Immediately thereafter, fuel injection J1 is performed in the expansion stroke cylinder 12A, and vaporization starts. This fuel injection J1 is also set to have a stoichiometric air-fuel ratio or a richer air-fuel ratio (λ ≦ 1) than that (b portion in FIG. 19).

  When the piston 13 of the expansion stroke cylinder 12A is sufficiently close to the top dead center, the cylinder 12A is ignited and the injected fuel (J1) whose vaporization is promoted is combusted ((2) in FIG. 18). ), The engine is driven in the forward rotation direction by the combustion pressure (c portion in FIG. 19).

  In addition, fuel richer than the combustible air-fuel ratio is injected into the compression stroke cylinder 12C at an appropriate timing (J4) ((3) in FIG. 18), but the compression stroke cylinder 12C does not burn. The compression pressure of the compression stroke cylinder 12C is reduced by the latent heat of vaporization caused by fuel injection (part d in FIG. 19), and accordingly, the compression top dead center (the first compression top dead center from the start of starting) is exceeded. The initial combustion energy of the consumed expansion stroke cylinder 12A is reduced.

  Furthermore, the timing of fuel injection (J5) in the intake stroke cylinder 12D, which is the next combustion cylinder, is set to an appropriate timing ((4) in FIG. 18) for reducing the temperature in the cylinder and the compression pressure by the latent heat of vaporization of the fuel. As shown, for example, after the middle stage of the compression stroke), self-ignition before the compression top dead center is prevented in the compression stroke of the intake stroke cylinder 12D. Further, in combination with the ignition timing of the intake stroke cylinder 12D being set after the compression top dead center, combustion before the compression top dead center is prevented (part e in FIG. 19). That is, by reducing the compression pressure by the fuel injection (J5) and not performing the combustion before the compression top dead center, the energy of the first combustion in the expansion stroke cylinder 12A becomes the compression top dead center (the second compression from the engine start start time). It is possible to suppress consumption to exceed the top dead center.

  Moreover, since the fuel injection (J5) in the intake stroke cylinder 12D is injected so as to have a stoichiometric air-fuel ratio or a rich air-fuel ratio (λ ≦ 1), combustion for restarting the engine (in FIG. 18) Since (1), (2), and (4)) can be executed substantially continuously and with the output secured, the engine can be reliably restarted.

  Thus, the first compression top dead center ((3) in FIG. 17) after the start of restart and the second compression by the energy of the first combustion ((2) in FIG. 18) in the expansion stroke cylinder 12A. The top dead center ((4) in FIG. 17) can be exceeded, and smooth and reliable startability can be ensured. And immediately after that ((5) in FIG. 18), the combustion is stopped depending on whether the expansion stroke cylinder is the preceding cylinder 12A, 12D or the succeeding cylinder 12B, 12C, or is larger than the stoichiometric air-fuel ratio. By executing the control at a lean air-fuel ratio, switching control is performed to suppress fuel consumption and ensure reliable restartability (see FIGS. 18A and 18B). From then on ((6) in FIG. 18), the air-fuel ratio is made lean (λ> 1) according to the temperature of the catalyst, or the ignition timing is delayed to increase the engine speed. To prevent normal operation.

  As described above, in the apparatus of this embodiment, when the engine is automatically stopped, the two cylinders are connected and stopped until the piston of the cylinder in the intake stroke reaches the compression top dead center for the first time when the engine is stopped. The fuel that is injected during this period is injected not at the lean air-fuel ratio but at the stoichiometric air-fuel ratio or the rich air-fuel ratio, so that the output required for restarting the engine can be reliably obtained. The engine can be restarted properly and reliably without switching the flow path in the cylinder.

  The operation during normal operation of the engine will be described with reference to FIGS. In the operation region A on the low-load and low-rotation side, the special operation mode is controlled by the operation mode control means including the valve stop mechanism control means 42 and the intake flow rate control means 43. In principle, the first operation mode is as described above. When the exhaust valve 20a and the first intake valve 19a are in the stopped state and the second exhaust valve 20b and the second intake valve 19b are in the activated state, the substantial fresh air and gas flow paths are as shown in FIG. Thus, the burned gas discharged from the preceding cylinders (first and fourth cylinders) 12A and 12D is directly introduced into the subsequent cylinders (second and third cylinders) 12B and 12C through the inter-cylinder gas passage 22a ( Along with the arrow b) in FIG. 20, only the gas discharged from the succeeding cylinders 12B and 12C is guided to the exhaust passage 22 (arrow c in FIG. 20), and the two-cylinder connection state is established.

  In this state, fresh air is introduced into the preceding cylinders 12A and 12D from the intake passage 21 during the intake stroke (arrow a in FIG. 20), and the air-fuel ratio in the preceding cylinders 12A and 12D is larger than the stoichiometric air-fuel ratio. Fuel is injected in the compression stroke while the fuel injection amount is controlled to be approximately twice or less than the air-fuel ratio, and ignition is performed at a predetermined ignition timing, so that stratified combustion at the lean air-fuel ratio is performed. Done.

  Further, burned gas derived from the preceding cylinders 12A and 12D is introduced into the succeeding cylinders 12B and 12C through the gas passage 22a during a period in which the intake strokes of the preceding cylinders 12A and 12D overlap with the exhaust strokes of the succeeding cylinders 12B and 12C. (The white arrow in FIG. 5 and the arrow b in FIG. 20). In the succeeding cylinders 12B and 12C, fuel is supplied to the burned gas having a lean air-fuel ratio introduced from the preceding cylinders 12A and 12D, and the fuel injection amount is controlled so as to be the stoichiometric air-fuel ratio. After the fuel is injected, compression self-ignition is performed near the top dead center of the compression stroke due to an increase in pressure and temperature in the combustion chamber.

  In this case, since the high-temperature burned gas discharged from the preceding cylinders 12A and 12D is immediately introduced into the succeeding cylinders 12B and 12C through the short inter-cylinder gas passage 22a, the succeeding cylinders 12B and 12C are in the combustion chamber during the intake stroke. The temperature in the combustion chamber 14 rises to the extent that the air-fuel mixture can self-ignite near the top dead center at the end of the compression stroke. Moreover, the burned gas is sufficiently mixed and evenly distributed until it is introduced into the succeeding cylinders 12B and 12C, and the fuel injected in the intake stroke is also completely combusted by the end of the compression stroke. Therefore, a uniform mixture distribution state that satisfies the ideal simultaneous compression self-ignition condition can be obtained. And combustion is rapidly performed by simultaneous compression self-ignition, and, thereby, thermal efficiency is improved significantly.

  As described above, in the preceding cylinders 12A and 12D, the thermal efficiency is improved by the stratified combustion in lean, and the pumping loss is reduced by reducing the intake negative pressure as compared with a normal engine that does not perform the stratified combustion, In the succeeding cylinders 12B and 12C, while the air-fuel ratio is substantially the stoichiometric air-fuel ratio, the compression self-ignition is performed in a uniform air-fuel mixture distribution state, and the thermal efficiency is improved, and the burned fuel extruded from the preceding cylinders 12A and 12D. Since gas is fed, the pumping loss is further reduced as compared with the preceding cylinders 12A and 12D. These effects greatly improve fuel efficiency.

  In addition, the preceding cylinders 12A and 12D have a lean air-fuel ratio that is approximately twice or close to the theoretical air-fuel ratio, so that the amount of NOx generated can be suppressed to a relatively small value. On the other hand, in the succeeding cylinders 12B and 12C, the burned gas is introduced from the preceding cylinders 12A and 12D so that a large amount of EGR is performed, and rapid combustion by simultaneous compression self-ignition is performed. Therefore, the reaction between oxygen and nitrogen is avoided as much as possible, so that the generation of NOx is sufficiently suppressed. This is also advantageous for improving emissions.

  Further, at least in the compression self-ignition region A of the succeeding cylinders 12B and 12C, the succeeding cylinder 12B so that the oxygen concentration in the exhaust gas discharged from the succeeding cylinders 12B and 12C becomes a value corresponding to the combustion state of the stoichiometric air-fuel ratio. , 12C is configured to control the air-fuel ratio of the preceding cylinders 12A, 12D, the combustion is performed at a lean air-fuel ratio, and only the burned gas of the subsequent cylinders 12B, 12C burned at the stoichiometric air-fuel ratio. It is led out to the exhaust passage 22. Therefore, it is not necessary to provide a lean NOx catalyst as in the conventional lean burn engine, and the exhaust purification performance is sufficiently ensured by the three-way catalyst 37 alone. Since there is no need to provide a lean NOx catalyst, there is no need to temporarily enrich the air-fuel ratio for NOx release and reduction when the NOx storage amount of the lean NOx catalyst is increased, thereby reducing fuel consumption improvement. can avoid. Furthermore, the problem of sulfur poisoning of the lean NOx catalyst does not occur.

  On the other hand, in the operation region B on the high load side or the high rotation side, the normal operation mode is set. As described above, the first exhaust valve 20a and the first intake valve 19a are in the operating state, and the second exhaust valve 20b and the second intake valve 19b. 21 is brought into a stopped state, the actual flow path of fresh air and gas becomes as shown in FIG. 21, the intake ports 17, 17a and exhaust ports 18a, 18 of each cylinder 12A-12D become independent, and the intake air Fresh air is introduced from the passage 21 to the intake ports 18 and 18a of the cylinders 12A to 12D, and burned gas is discharged from the exhaust ports 18 and 18a of the cylinders 12A to 12D to the exhaust passage 22. In this case, the output performance is ensured by controlling the intake air amount and the fuel injection amount so that the stoichiometric air-fuel ratio or richer.

  The engine starting device described above is an embodiment of the device to which the starting device according to the present invention is applied, and the specific configuration of the device is appropriately changed without departing from the gist of the present invention. This is possible, and modifications will be described below.

  (1) In the above embodiment, regardless of whether the cylinder in the compression stroke (expansion stroke, etc.) when the engine is stopped is the preceding cylinder or the succeeding cylinder, the throttle valve 23 that is the cylinder intake flow rate adjusting means and the external load The alternator 28, which is an adjusting means, is used to stop the piston 13 of the cylinder in the expansion stroke and the compression stroke within an appropriate range when the engine is stopped. The external load adjusting means such as the alternator 28 is used to stop the piston. In addition to stopping the piston 13 in an appropriate range, the cylinder in the compression stroke (expansion stroke) may be intentionally stopped in either the preceding cylinder or the succeeding cylinder when the engine is stopped.

  In this case, for example, by changing the target power generation current of the alternator 28 in the stop operation period from when the fuel supply is stopped until the engine stops so that the stop compression stroke cylinder becomes the preceding cylinder. You may control so that a compression stroke cylinder at the time of a stop may become a preceding cylinder. With this configuration, the cylinder that is in the expansion stroke when the engine is stopped (expansion stroke cylinder when the engine is stopped) becomes the succeeding cylinder. Therefore, when the engine is restarted, fuel is supplied to the succeeding cylinder that is relatively hot compared to the preceding cylinder. Thus, combustion for restarting the engine can be performed, and thus the engine can be reliably restarted by combustion in the subsequent cylinder. Moreover, even if the combustion in the subsequent cylinder is burned at the stoichiometric air-fuel ratio or a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio when the engine is restarted, the burned gas due to the combustion in the subsequent cylinder is discharged through the exhaust passage 22. For example, compared with the case where the initial combustion is burned at the stoichiometric air-fuel ratio in the preceding cylinder and this burned gas is introduced into the succeeding cylinder, the engine is continuously operated at the stoichiometric air-fuel ratio having a larger output than the lean air-fuel ratio at the initial stage of engine restart And the engine can be restarted more reliably.

  In this case, the stop / restart control means 48 controls the target generated current of the alternator 28 based on the detection result by the intake pressure sensor 27 for detecting the intake pressure for each cylinder and the detection results by the crank angle sensors 30 and 31. May be.

  The external load adjusting means is not limited to the alternator 28. For example, the crankshaft 3 can be changed by changing the number of torque converters and frictional engagement elements rotated by the crankshaft 3 using an automatic transmission mechanism including a torque converter. The load may be changed, or a resistance mechanism specialized for adjusting the external load may be used.

  (2) In the above embodiment, when the engine is restarted, the stop / restart control means 48 performs fuel so that the stoichiometric air-fuel ratio or a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio is reduced with respect to the cylinder in the compression stroke when the engine is stopped. Is controlled so that the engine rotates in the reverse direction after being ignited and combusted, so that the engine is operated in the normal direction. Fuel cannot be injected and ignited and burned in the vicinity of this compression top dead center, but by omitting the initial combustion in the compression stroke cylinder at the stop for the reverse operation of the engine, or for this initial combustion By setting the lean air-fuel ratio larger than the stoichiometric air-fuel ratio to the fuel supplied to the engine, fuel for normal operation of the engine is injected in the corresponding stroke of the compression stroke cylinder. Ignited in the vicinity of dead center, it can be controlled so as to burn. In this way, combustion can be executed even in the compression stroke cylinder that reaches the compression top dead center immediately after the initial combustion in the compression stroke cylinder at the time of stop, and as a result, the forward rotation operation is continuously performed at the initial stage of engine restart. For combustion.

  In particular, when the combustion for the reverse operation is omitted, the fuel injected into the compression stroke cylinder for the normal operation of the engine is set to be the stoichiometric air fuel ratio or a rich air fuel ratio. Thus, the output is secured, and the ignition timing is set immediately after the compression top dead center, thereby effectively preventing the generation of negative torque.

  (3) In the above embodiment, the valve stopping mechanism 29 is used as the valve operating mechanism. However, this valve operating mechanism is not particularly limited, and other known techniques such as an electromagnetic valve are used for electrical operation. And a plurality of cams including cams having no cam nose, and a plurality of rocker arms driven by the cams. The arm may be integrated so that the opening / closing drive or opening / closing timing of the intake valve (exhaust valve) may be changed.

  (4) In the above-described embodiment, an example in which the intake flow rate to each cylinder 12A to 12D is adjusted by the intake flow rate adjusting means including the throttle valve 23 disposed on the upstream side of the surge tank 21b will be described. However, the present invention is not limited thereto, and the intake flow rate to each of the cylinders 12A to 12D is adjusted by providing a known variable valve mechanism that changes the lift amount of the intake valve 19 provided in each of the cylinders 12A to 12D. Alternatively, the flow rate of intake air to each of the cylinders 12A to 12D using a multiple throttle valve in which a valve body is individually disposed in the branch intake passage 21a connected to each of the cylinders 12A to 12D. You may comprise so that it may adjust.

  (5) In the above embodiment, the fuel injection for the initial combustion in the expansion stroke cylinder 12A at the time of restarting the engine is batch injection (J1), but this is divided into two or more divided injections. There may be.

  (6) Although omitted in the above embodiment, when the engine is restarted, when a predetermined condition is satisfied, for example, when the piston stop position is not within the proper stop range R, or when the engine rotation speed is reached by a predetermined time after the start. When the engine does not reach a predetermined value, or when the engine is first burned in the expansion stroke at the time of stopping without reversely operating the engine, the control with the assist by the starter motor may be performed. Even in this case, the burden on the starter motor can be reduced by the energy generated by the combustion of the engine.

1 is a schematic cross-sectional view of an engine provided with a starter according to the present invention. It is explanatory drawing which shows the structure of the intake system and exhaust system of an engine. It is a block diagram of a control system. It is explanatory drawing which shows an example of the driving | operation area | region setting for performing control according to a driving | running state. It is explanatory drawing which shows the combustion cycle, valve opening timing, etc. of a preceding cylinder and a succeeding cylinder. It is explanatory drawing which shows the relationship between the piston stop position and air quantity of the cylinder which becomes an expansion stroke and a compression stroke at the time of an engine stop. It is a time chart which shows the change state of the engine speed at the time of an engine stop. 6 is a time chart showing a change state of a throttle valve opening, a target generated current, and the like when the engine is stopped when an expansion stroke cylinder at the time of stop is a preceding cylinder. It is a distribution map which shows the correlation with the engine speed at the time of an engine stop, and a piston stop position. It is a graph which shows an example of the map for setting the target electric power generation current of an alternator according to the rotational speed of an engine. It is a flowchart which shows the first half of the engine automatic stop control operation. It is a flowchart which shows the middle part of an engine automatic stop control operation | movement. It is a flowchart which shows the second half part of the engine automatic stop control operation. 6 is a time chart showing a change state of a throttle valve opening, a target generated current, and the like when the engine is stopped when an expansion stroke cylinder at the time of stop is a subsequent cylinder. It is a flowchart which shows the first half of the control action at the time of engine restart. It is a flowchart which shows the middle part of control action at the time of engine restart. It is a flowchart which shows the latter half part of the control action at the time of engine restart. It is a time chart which shows the combustion operation etc. at the time of engine restart. It is a time chart which shows the change state etc. of the engine speed at the time of engine restart. Fig. (A) shows the case where the stop expansion stroke cylinder is the preceding cylinder, and Fig. (B) shows the case where the stop expansion stroke cylinder is the subsequent cylinder. It is explanatory drawing which shows the distribution path | route of substantial fresh air and gas at the time of low load low rotation. It is explanatory drawing which shows the distribution path | route of substantial fresh air and gas at the time of high load high rotation.

Explanation of symbols

1 Engine body 2 ECU
12A Predecessor cylinder 12B Subsequent cylinder 12C Subsequent cylinder 12D Predecessor cylinder 22a Inter-cylinder gas passage 23 Throttle valve (intake flow rate adjusting means)
28 Alternator (External load adjusting means)
30, 31 Crank angle sensor 42 Valve stop mechanism control means 43 Intake flow rate control means 44 Fuel state control means 45 Fuel supply control means 46 Stop / restart control means (also serves as prediction means)
46 Ignition control means 47 Power generation current control means 48 Stop / restart control means

Claims (10)

A multi-cylinder four-cycle engine in which the combustion cycle of each cylinder is performed with a predetermined phase difference, and control modes for intake / exhaust and combustion states of the engine at least in the low-load operation region of the engine. In this special operation mode, the burned gas discharged from the preceding cylinder in the exhaust stroke between the pair of cylinders in which the exhaust stroke and the intake stroke overlap is directly connected to the subsequent cylinder in the intake stroke. In an engine starter that is in a two-cylinder connection state in which gas introduced from the subsequent cylinder is led to the exhaust passage,
When a preset engine automatic stop condition is satisfied, the engine is automatically stopped with the two-cylinder connected state by stopping the fuel supply to the engine, and the engine restart condition in this automatic stop state When the engine is established, stop / restart control means that automatically restarts the engine by injecting fuel into the cylinders that are in the expansion stroke when the engine is stopped and causing ignition and combustion, and engine speed is detected And when the engine of each cylinder is stopped based on the detection result of the speed detection means during the stop operation period from when the fuel supply is stopped by the stop / restart control means until the engine stops. Predicting means for predicting the stroke and the intake flow rate for each cylinder when the control in the special operation mode is being executed. And a suction flow rate adjusting means for integer,
The stop / restart control means is configured such that the air amount of the cylinder predicted to be in the stop expansion stroke is greater than the air amount of the cylinder predicted to be in the stop compression stroke based on the prediction result from the prediction means. By controlling the intake flow rate adjusting means so as to increase, the piston stop position of the cylinder predicted to be in the expansion stroke when the engine is stopped is stopped within a predetermined appropriate range suitable for restart. Engine starter.   The stop / restart control means, when the predicting means predicts that the cylinder in the compression stroke when the engine is stopped is the preceding cylinder, the predicting cylinder predicted to be the stop compression stroke cylinder by the predicting means. The intake air flow rate adjusting means is controlled so that the intake air flow rate in the final intake stroke before the engine stop in the engine is relatively smaller than the intake air flow rate in the preceding cylinder immediately before the final intake stroke. The engine starting device according to claim 1.   The stop / restart control means, when the predicting means predicts that the cylinder in the compression stroke when the engine is stopped is the succeeding cylinder, the succeeding cylinder predicted to be the stop compression stroke cylinder by the predicting means. The intake air flow rate in the preceding intake cylinder in the preceding cylinder in which the intake air flow rate immediately before the stop stroke of the engine in the preceding cylinder that derives burned gas through the inter-cylinder gas passage is different from the preceding cylinder. 2. The engine starting device according to claim 1, wherein the intake flow rate adjusting means is controlled so as to be relatively smaller.   The stop / restart control means expands the cylinders in the compression stroke when the engine is stopped by reducing the intake flow rate for the preceding cylinder after increasing the intake flow rate for the preceding cylinder in the stop operation period after stopping the fuel supply. 3. The engine starting device according to claim 1, wherein the intake flow rate adjusting means is controlled so as to change an air amount with a cylinder in a stroke.   The apparatus further comprises external load adjusting means for adjusting an external load on the engine, and the stop / restart control means adjusts the external load adjusting means according to the engine rotation speed based on the detection result from the speed detecting means. The engine starting device according to any one of claims 1 to 4.   6. The engine starter according to claim 5, wherein the stop / restart control means controls the external load adjusting means so that a cylinder in a compression stroke becomes a preceding cylinder when the engine is stopped. Intake pressure detection means for detecting the intake pressure for each cylinder is further provided,
The said stop / restart control means controls the said external load adjustment means based on the detection result by this intake pressure detection means and the detection result by the said rotational speed detection means, The said load control means is characterized by the above-mentioned. Engine starter.   The stop / restart control means includes a condition relating to an automatic stop duration, which is an elapsed time from the time of automatic engine stop, as the restart condition, and restarts the engine when a predetermined automatic stop duration has elapsed. The engine starter according to any one of claims 1 to 7, wherein start control is performed. A starter motor that rotates the crankshaft in a forward direction;
The engine according to any one of claims 1 to 8, wherein the stop / restart control means assists the starter motor when the engine starts normal rotation by combustion in the expansion stroke cylinder. Starting device.   The stop / restart control means performs a continuous operation for a predetermined time at an engine speed higher than an idle speed before the fuel supply is stopped. The engine starting device according to the item.

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