JP2005337184A - Engine starter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stop a piston at a proper position when an engine stops automatically to restart the engine securely by a simple configuration. <P>SOLUTION: This engine starter constituted to stop the engine automatically when automatic stop conditions set in advance of the engine are satisfied and restart the engine automatically when restart conditions of the engine are satisfied is provided with an automatic stop control means 43 for setting target rotation speed of the engine when stopping fuel injection to a value higher than usual idle rotation speed to stop the engine automatically in a uniform combustion form of the engine and setting target rotation speed of the engine when stopping fuel injection to a value lower than the target rotation speed in the uniform combustion form to stop fuel injection after the target rotation speed is continued for a fixed period of time and stop the engine automatically in a stratified combustion form of the engine. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an engine starting device, and when an engine automatic stop condition set in advance in an engine idling state or the like is satisfied, the engine is automatically stopped and a restart condition is satisfied in this state. The present invention relates to an engine starter configured to automatically restart the engine.

Recently, in order to reduce fuel consumption and CO ₂ emissions, the engine is automatically stopped once during idle operation, etc., and then restart conditions such as starting the vehicle are established. A technology for automatic engine stop control (so-called idle stop control) that automatically restarts the engine has been developed. The restart during the idle stop control requires a smooth start of the engine in accordance with the vehicle starting operation or the like, but the engine output shaft is driven by a starter motor as is generally done conventionally. According to the method of restarting the engine through cranking for driving the motor, there are problems that the starter motor is frequently operated and a large noise is generated and 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.
Japanese Utility Model Publication No. 60-128975 JP 2001-173473 A

  According to the engine starting device disclosed in Patent Document 1, it is necessary to provide a device for braking the crankshaft of the engine separately from the braking device for the vehicle, and the piston of the cylinder that is stopped in the expansion stroke is provided. In order to stop at an appropriate position, the braking device must be controlled with high accuracy, and there is a problem that this control is difficult.

  On the other hand, as disclosed in Patent Document 2 described above, even when the configuration is such that the intake pressure is increased and the compression pressure is increased when the engine automatic stop condition is satisfied, When the degree of decrease in the engine rotation speed changes, there is a problem that the stop position of the piston fluctuates and it is difficult to properly stop the piston at a position suitable for restarting the engine.

  In view of the above circumstances, the present invention provides an engine starter capable of reliably restarting an engine by stopping a piston at an appropriate position when the engine is automatically stopped with a simple configuration.

  According to the first aspect of the present invention, when a preset engine automatic stop condition is satisfied, the fuel supply for continuing the operation of the engine is stopped and the engine is automatically stopped. Engine start configured to automatically restart the engine by injecting fuel into at least the cylinder stopped in the expansion stroke to cause ignition and combustion when the engine restart condition is established When the engine is automatically stopped in the uniform combustion mode of the engine, the target rotational speed of the engine when stopping fuel injection is set to a value higher than the normal idle rotational speed, and this target rotational speed is set. When the fuel injection is stopped after a certain period of time is continued and the engine is automatically stopped in the stratified combustion mode of the engine, the fuel injection is The target rotational speed of the engine at the time of stop is set to a value lower than the target rotational speed of the uniform combustion mode, it is intended to stop the fuel injection after the target rotational speed is continued over a certain time.

  According to a second aspect of the present invention, in the engine starting device according to the first aspect, when the engine automatic stop condition is satisfied in the stratified combustion mode of the engine, the engine is stratified until the fuel injection is stopped. Switching from the combustion mode to the uniform combustion mode is prohibited.

  According to a third aspect of the present invention, in the engine starter according to the first or second aspect, when the engine is automatically stopped in the stratified combustion mode of the engine, the target rotational speed of the engine at the time of stopping the fuel injection Is set to a value higher than the normal idling speed.

  According to a fourth aspect of the present invention, when a preset automatic engine stop condition is satisfied, the fuel supply for continuing the operation of the engine is stopped to automatically stop the engine, and the automatic stop state. Engine start configured to automatically restart the engine by injecting fuel into at least the cylinder stopped in the expansion stroke to cause ignition and combustion when the engine restart condition is established A determination means for determining whether or not an automatic engine stop condition is satisfied when the engine rotational speed is higher than a normal idle rotational speed, and the engine automatic stop condition in the stratified combustion mode of the engine. If it is determined that the fuel injection has been established, the target engine speed when stopping fuel injection is set to a value lower than the target engine speed in the uniform combustion mode. Rutotomoni engine until the fuel injection is stopped is that a prohibition means for prohibiting from being switched to the homogeneous combustion mode from the stratified combustion mode.

  According to a fifth aspect of the present invention, in the engine starting device according to any one of the first to fourth aspects, the operation region in which the engine is automatically stopped is provided with a stratified combustion mode and provided in the exhaust passage. In addition, when it is necessary to improve the purification performance of the exhaust gas purification catalyst, there is provided combustion control means for making the engine a uniform combustion form.

  According to a sixth aspect of the present invention, in the engine starting device according to any one of the first to fifth aspects, an intake flow rate adjusting means for adjusting an intake flow rate introduced into the cylinder, and an engine automatically When stopping, the intake flow rate adjusting means is operated in a direction to increase the intake flow rate until the engine rotation speed decreases to a predetermined speed or less after the fuel injection is stopped, and the engine rotation speed is decreased to a predetermined speed or less. And an intake air flow rate control means for operating the intake air flow rate adjusting means in a direction to decrease the intake air flow rate at the time when the intake air flow rate decreases. It is to set.

  According to the first aspect of the present invention, when the engine automatic stop condition is satisfied and the engine is automatically stopped, the target engine speed set according to the operating state of the engine is continued for a certain period of time. Therefore, the fuel injection is stopped in a state where the engine rotational speed is stable. Therefore, after the fuel injection is stopped, the control for reducing the engine rotational speed is properly executed, The piston of the cylinder to be stopped can be stopped at a position suitable for restarting the engine, and before the target engine speed set according to the operating state of the engine is continued for a certain period of time, When the automatic stop condition is canceled, the response to the start request can be improved by stopping the automatic engine stop control.

  When the engine is automatically stopped in a uniform combustion mode of the engine, the target rotational speed of the engine is set to a value higher than a normal idle rotational speed at which the engine is not automatically stopped, and the target rotational speed is set at a constant time. Since the fuel injection is stopped for a long time, the control for reducing the rotational speed of the engine is properly executed after the fuel injection is stopped. The engine can be stopped at a position suitable for starting, and the burned gas in each cylinder can be reliably discharged until the engine is stopped. In addition, when the engine is automatically stopped in a stratified combustion mode in which the intake air flow introduced into the cylinder of the engine is large and the scavenging performance when the engine is automatically stopped can be sufficiently secured, the engine when the fuel injection is stopped Is set to a value lower than the target rotational speed of the uniform combustion mode, thereby ensuring the scavenging performance of each cylinder and improving the fuel consumption until the fuel injection is stopped. There is an advantage that generation of noise can be effectively suppressed.

  According to the second aspect of the present invention, when the engine automatic stop control is started in the stratified combustion mode of the engine that can sufficiently ensure the scavenging performance of each cylinder during the automatic engine stop, the fuel injection is stopped. By prohibiting the engine from switching from the stratified combustion mode to the uniform combustion mode, the fuel efficiency is effectively improved and the engine noise is generated without impairing the scavenging performance of each cylinder when the engine is automatically stopped. There is an advantage that can be suppressed.

  In the invention according to claim 3, even when the engine is automatically stopped in the stratified combustion mode of the engine that can secure a sufficient scavenging performance of each cylinder when the engine is automatically stopped because the intake air flow introduced into the cylinder of the engine is large. Since the fuel injection is stopped in a state where the engine rotation speed becomes a target rotation speed set to a value higher than the normal idle rotation speed, while scavenging of each cylinder is ensured at the time of automatic engine stop, It is possible to appropriately execute control for decreasing the engine speed after stopping the fuel injection, and to stop the piston of the cylinder that is in the expansion stroke at the time of stopping the engine at a position suitable for restarting the engine.

  According to the fourth aspect of the present invention, it is determined whether or not the engine automatic stop condition is satisfied in a state where the engine speed is higher than the normal idle speed, and the engine speed is reduced after the fuel injection is stopped. By appropriately executing the control to decrease, the piston of the cylinder that becomes the expansion stroke at the time of stopping the engine can be stopped at a position suitable for restarting the engine. In addition, the intake air flow introduced into the engine cylinder is large, the scavenging performance of each cylinder can be sufficiently secured when the engine is automatically stopped, and the target rotation speed is set to a higher value than the uniform combustion mode. When the engine is automatically stopped in the combustion mode, since switching to the uniform combustion mode is prohibited, there are advantages that fuel consumption is improved and generation of engine noise is effectively suppressed.

  According to the fifth aspect of the present invention, the engine automatic stop control is executed in the stratified combustion mode of the engine at normal times, so that the fuel efficiency is effectively improved and the generation of engine noise is suppressed. There are advantages. Further, when it is necessary to improve the purification performance of the exhaust gas purification catalyst, for example, when it is necessary to maintain the activation temperature by preventing the temperature of the exhaust gas purification catalyst from decreasing, or the NOx adsorption of the exhaust gas purification catalyst When the NOx adsorbed on the material is separated, the exhaust purification performance can be sufficiently ensured by setting the engine to a uniform combustion mode.

  According to the sixth aspect of the present invention, when the engine is automatically stopped, the intake air flow rate is increased from the time when the fuel injection is stopped until the engine rotational speed decreases to a predetermined speed or less, thereby scavenging each cylinder. After executing the control to reduce the pumping loss effectively, the engine speed is below a preset constant value regardless of whether the engine is in stratified combustion mode or uniform combustion mode. When the flow rate is reduced to the minimum, the intake flow rate introduced into the engine cylinder is reduced, so that the control of stopping the piston of the cylinder that is in the expansion stroke when the engine stops is stopped at a position suitable for restarting the engine. There is an advantage that it can be executed.

  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. 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, an intake port 17 and an exhaust port 18 that open toward the combustion chamber 14 are provided above the combustion chamber 14 of each of the cylinders 12A to 12D, and an intake valve 19 and an exhaust gas are connected to these ports 17 and 18, respectively. Each valve 20 is equipped. The intake valve 19 and the exhaust valve 20 are driven by a valve operating mechanism having a camshaft (not shown), so that each cylinder 12A to 12D performs a combustion cycle with a predetermined phase difference. The opening / closing timings of the 12D intake / exhaust valves 19, 20 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 (boost pressure) are disposed on the upstream side and the downstream side of the throttle valve 23, respectively.

  Further, an exhaust gas purification catalyst 37 is disposed downstream of the collection portion of the exhaust passage 22 where exhaust from each of the cylinders 12A to 12D collects. 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, and the oxygen concentration in the exhaust gas Has an oxygen storage capacity for storing it in a relatively high oxygen-excess atmosphere, and releases the stored oxygen to react with HC, CO, etc. when the oxygen concentration is relatively low. The exhaust gas purification catalyst 37 is not limited to a three-way catalyst, and may be any catalyst that has the above-described oxygen storage capability. For example, the exhaust gas purification catalyst 37 is a so-called lean NOx catalyst that can purify NOx even in an oxygen-excess atmosphere. Also good.

  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.

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

  The ECU 2 receives detection signals from the sensors 25, 26, 30 to 35, and outputs a control signal for controlling the fuel injection amount and injection timing to the fuel injection valve 16, as well as ignition. By controlling the ignition timing with respect to the ignition device 27 attached to the plug 15, the combustion control means 41 for executing the combustion control corresponding to the operating state of the engine and the actuator 24 of the throttle valve 23 with the throttle open. An intake flow rate control means 42 for controlling the intake flow rate by outputting a control signal for controlling the degree of fuel, and predetermined fuel injection to each cylinder 12A-12D when a predetermined automatic engine stop condition is satisfied Stop at the timing (fuel cut), automatically stop the engine, and then the accelerator operation by the driver, etc. An automatic stop control means 43 for performing an automatic control to restart the engine when the start condition is satisfied, the power generation current control means 46 for setting a target generated current of the alternator 28 is provided.

  The combustion control means 41 and the intake flow rate control means 42 are provided in the cylinders 12A to 12D in a low load low rotation idle operation region (normal idle operation region) and a high rotation high load full load region in which the engine is not automatically stopped. Combustion control in a uniform combustion mode in which the air-fuel ratio is set to a substantially stoichiometric air-fuel ratio is executed, and the air-fuel ratio in the cylinders 12A to 12D is considerably larger than the stoichiometric air-fuel ratio, for example, the The stratified combustion mode combustion control in which the fuel ratio is set to 30 to 40 is executed. Further, when it is necessary to improve the purification performance of the exhaust gas purification catalyst 37 in the normal operation region where the combustion control of the stratified combustion mode is executed, for example, the temperature of the exhaust gas purification catalyst 37 is prevented from decreasing. When it is necessary to maintain the activation temperature, or when the NOx adsorbed on the NOx adsorbent of the exhaust gas purification catalyst 37 is released, the air-fuel ratio in the cylinders 12A to 12D is set to a substantially stoichiometric air-fuel ratio. The combustion control in the uniform combustion mode is executed.

  The automatic stop control means 43 causes the first combustion in the compression stroke cylinder in which the piston 13 is stopped in the middle of the compression stroke when the engine is automatically stopped, so that the piston 13 is pushed down to slightly reverse the crankshaft 3. When the engine is automatically stopped, the piston 13 of the expansion stroke cylinder in which the piston 13 is stopped in the middle of the expansion stroke is temporarily raised, and the air-fuel mixture in the cylinder is compressed and ignited and burned. Thus, a control for applying a forward driving torque to the crankshaft 3 to restart the engine is executed.

  In order to ignite the fuel injected into a specific cylinder and restart the engine properly without using a restart motor or the like as described above, the air-fuel mixture in the expansion stroke cylinder is burned. The obtained combustion energy must be sufficiently secured, and the cylinder that reaches the compression top dead center must overcome the compression reaction force and exceed the compression top dead center. Therefore, it is necessary to ensure a sufficient amount of air in the expansion stroke cylinder in which the piston 13 is in the middle of the expansion stroke when the engine is automatically stopped.

  That is, as shown in FIGS. 3A and 3B, in the cylinders that are in the expansion stroke and the compression stroke when the engine is stopped, the phases are shifted by 180 ° CA. If the piston 13 of the expansion stroke cylinder is positioned on the bottom dead center side of the stroke center, the amount of air in the cylinder increases and sufficient combustion energy is 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, as shown in FIG. 4, the automatic stop control means 43 provided in the ECU 2 sets the target rotational speed of the engine to the normal speed when the engine is not automatically stopped at the time t0 when the automatic engine stop condition is satisfied. Control is performed to stabilize by setting a value higher than the idle rotation speed. 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), when the engine is automatically stopped in the stratified combustion mode, the target rotation speed is set to about 810 rpm (the automatic transmission is neutral). The range is set so that the engine rotational speed Ne is stabilized at a slightly higher rotational speed than the normal idle rotational speed, and fuel injection is performed at time t1 when the engine rotational speed Ne is stabilized at the target rotational speed. Is stopped, and the rotational speed Ne of the engine is reduced.

  When the engine is automatically stopped in a uniform combustion mode, the engine rotational speed Ne is set to the above normal idle rotational speed by setting the target rotational speed of the engine to, for example, about 860 rpm (the automatic transmission is in the neutral range). The fuel injection is stopped in a state that is higher and is stabilized at a higher rotational speed than when the engine is stopped in the stratified combustion mode.

  Further, the automatic stop control means 43 determines whether or not the engine automatic stop condition is satisfied in a state where the engine rotational speed Ne is controlled to a value higher than a normal idle rotational speed at which the engine is not automatically stopped. Determining means 44 and prohibiting means 45 for prohibiting the engine from switching from the stratified combustion mode to the uniform combustion mode until the fuel injection is stopped when the engine automatic stop condition is satisfied in the stratified combustion mode of the engine. Is provided.

  As shown in FIGS. 4 and 5, the opening degree K of the throttle valve 23 is increased to, for example, about 30% of full opening at the fuel injection stop time t1, which is the initial stage of the control operation for automatically stopping the engine. By increasing the boost pressure (intake pressure) Bt, the intake flow rate drawn into each cylinder 12A to 12D of the engine is increased by a predetermined amount from the minimum intake flow rate necessary for continuing the engine operation. Control for setting and ensuring scavenging of the cylinders 12A to 12D is executed in the intake flow rate control means 42, and the target power generation current Ge of the alternator 28 is established at the time point t1 when the fuel injection is stopped. The power generation current control means 46 is configured to execute control for reducing the rotational resistance of the crankshaft 3 by lowering it from the time point t0. That.

  Further, by stopping the fuel injection at the time t1, the throttle valve 23 is closed at the time t2 when it is confirmed that the engine rotational speed Ne has decreased to a preset reference speed (for example, 790 rpm) or less. To do. From the time t2 when the throttle valve 23 is closed, the boost pressure Bt starts to decrease, and the intake flow rate introduced into the cylinders 12A to 12D of the engine decreases, and from the opening time t1 to the closing time t2 of the throttle valve 23. The air introduced into the common intake passage 21c passes through the surge tank 21b and the branch intake passage 21a, and thereby reaches the intake stroke of the fourth cylinder 12D, the second cylinder 12B, the first cylinder 12A, and the third cylinder 12C. Introduced in sequence with a predetermined transport delay. In consideration of the intake transport delay, the opening time t1 and the closing time t2 of the throttle valve 23 are set to appropriate times, so that more air expands than the third cylinder 12C, which is in the compression stroke when the engine is stopped. It will be introduced into the first cylinder 12A, which is the stroke.

  Next, at the time t2 when it is confirmed that the engine rotational speed Ne has decreased to the reference speed N2 or less, the target generated current Ge of the alternator 28 is temporarily increased, and the engine top dead center rotation is performed as described later. At the time t3 when the speed ne is within the predetermined range, the target generated current Ge of the alternator 28 is adjusted to a value corresponding to the degree of decrease in the engine rotational speed Ne, and is set based on the results of experiments conducted in advance. Control is performed to reduce the engine speed Ne along the reference 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. 4 and 5, the engine rotational speed Ne temporarily drops each time the cylinders 12 </ b> A to 12 </ b> D reach the compression top dead center, and then exceed the 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 t5 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 13 is pushed back, and the crankshaft 3 is reversely rotated. Due to the reverse rotation of the crankshaft 3, the air pressure of the expansion stroke cylinder 12 </ b> A that becomes the expansion stroke when the engine is stopped increases, so that the piston 13 of the expansion stroke cylinder 12 </ b> A is pushed back toward the bottom dead center according to the compression reaction force. Thus, the crankshaft 3 starts to rotate forward again, and the reverse rotation and forward rotation of the crankshaft 3 are repeated several times to stop the piston 13 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 the time t5, 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 compression of the expansion stroke cylinder 12A and the compression stroke cylinder 12C is performed. It is necessary to adjust the intake air flow rates for both cylinders 12A and 12C so that the reaction force becomes sufficiently large and the compression reaction force of the expansion stroke cylinder 12A is larger than the compression reaction force of the compression stroke cylinder 12C by a predetermined value or more. is there. For this reason, in this embodiment, by setting the opening K of the throttle valve 23 to a large value at the time t1 when the fuel injection is stopped, a predetermined amount of air is supplied to both the expansion stroke cylinder 12A and the compression stroke cylinder 12C. After the inhalation, the throttle valve 23 is closed to reduce its opening K at a time t2 when it is confirmed that the engine rotational speed Ne has decreased to a preset reference speed (for example, 790 rpm) or less. Thus, the intake air amount is adjusted.

  That is, in FIG. 6, as described above, the fuel injection is stopped at the time t1 when the rotational speed Ne of the engine becomes a predetermined speed, and the throttle valve 23 is maintained in the open state 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 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 chart, 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. 6, 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). Particularly, regarding the second top dead center rotational speed ne before the engine is stopped, the top dead center rotational speed ne is within the range of about 280 rpm to 380 rpm as shown in FIG. On the low rotation side below 320 rpm, the piston stop position gradually changes closer to the top dead center as the top dead center rotation speed ne decreases. On the other hand, on the high rotation side where the top dead center rotational speed ne is 320 rpm or higher, the stop position of the piston 13 becomes substantially constant and falls within the substantially appropriate range R regardless of the top dead center rotational speed ne. I understand.

  The characteristic distribution tendency as described above can be seen when the engine top dead center rotational speed ne is on the high rotation side of 320 rpm or more, which is sufficient for the expansion stroke cylinder 12A and the compression stroke cylinder 12C when the engine is stopped. It is considered that this is because a large amount of air is filled and the piston stop position is concentrated toward the center of the stroke due to the compression reaction force of the air. It should be noted that the piston stop position is distributed to the lower left side at the low rotation side of 320 rpm or less, after the piston 13 reciprocating in each cylinder 12A to 12D is reversed on the compression top dead center side, and then the frictional resistance, etc. This is considered to be because the vehicle cannot be returned to the center of the stroke by being decelerated by the stop and stops.

  On the other hand, when the throttle valve 23 is kept closed without opening the fuel injection after the fuel injection is stopped, as shown by the broken line in FIG. The stop position of the piston 13 changes according to the height of the top dead center rotational speed ne. This is because if the throttle valve 23 is kept closed, the intake negative pressure is maintained at a high level (the intake pressure is low), and the compression reaction of the cylinders that become the expansion stroke cylinder 12A and the compression stroke cylinder 12C after the engine is stopped. This is because the influence of the rotational speed (rotational inertia) of the engine and the frictional resistance becomes relatively large because the force becomes small.

  Therefore, in order to sufficiently secure the scavenging performance of each of the cylinders 12A to 12D while suppressing the effects of the rotational inertia and the frictional resistance, as shown in FIGS. 4 and 5, the fuel injection is stopped at a predetermined time t1. Until the time elapses, that is, until the time point t2 when the engine speed Ne drops below the reference speed N2 (for example, about 790 rpm), the opening K of the throttle valve 23 is set to a relatively large value (for example, 30% of the fully opened position). ) Must be set. 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 preferable.

  Then, at the time t2 when the engine rotational speed Ne is reduced below the reference speed N2, 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 external load of the engine corresponding to the degree of decrease in the engine rotational speed Ne, the engine rotational speed Ne is reduced along the reference line set based on experiments conducted in advance. It becomes possible to make it.

  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. Based on the top dead center rotational speed ne at the time point t3 when it is determined that the engine has passed through the fourth compression top dead center before the engine is stopped, as shown in FIG. As described above, the higher the engine top dead center rotational speed ne is, the larger the value of the target generated current Ge is read from the map where the target generated current Ge corresponding to the detected value of the top dead center rotational speed ne is read. The alternator 28 has a target generated current Ge corresponding to the value.

  Further, the initial value when the target generated current Ge of the alternator 28 is increased at the time point t2 when the engine rotation speed Ne is reduced to the reference N2 speed 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 reducing the target generated current 28 is executed.

  By controlling the generated current of the alternator 28 as described above, the kinetic energy of the crankshaft 3, the flywheel, the piston 13, the connecting rod, etc. at the time t5 when the final compression top dead center is passed. The potential energy, etc., of the air compressed in the compression stroke cylinder 12C is commensurate with the frictional resistance loss, etc. that acts thereafter, and the piston 13 of the cylinder 12A that is in the expansion stroke when the engine is stopped is suitable for restarting the engine. It is possible to stop within the range R.

  A control operation when the engine is automatically stopped by the automatic stop control means of the ECU 2 will be described based on the flowcharts shown in FIGS. When this control operation is started, it is determined whether or not an automatic stop permission flag F indicating 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 satisfies all the conditions such as the vehicle speed is a predetermined value (for example, 10 km / h) or more, 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. In such a case, it is determined that the engine can be automatically stopped and is turned on.

  If it is determined YES in step S1, it is determined whether or not 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 deceleration state, it is determined whether or not the engine rotational speed Ne is larger than a reference value FC · ON for deceleration fuel cut that is set in advance to about 1100 rpm (step S1). S3) If NO is determined, the process proceeds to the following step S7.

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

  Next, it is determined whether or not the air-fuel ratio in the cylinders 12A to 12D is in the operation state of the stratified combustion mode in which the air-fuel ratio in the cylinders 12A to 12D is set to a value considerably larger than the stoichiometric air-fuel ratio (step S7). Determines whether the uniform combustion prohibition flag that prohibits the engine from being in the uniform combustion mode is in the ON state (step S8). If it is determined NO in step S8, after the uniform combustion prohibition flag is turned on (step S9), the engine target rotational speed is set to a predetermined amount higher than the normal idle rotational speed (about 650 rpm). A high value is set, for example, about 750 rpm, and this speed is maintained (step S10).

  When it is determined as NO in step S7 and it is confirmed that the air-fuel ratio in the cylinder is in the operation state of the uniform combustion mode in which the air-fuel ratio in the cylinder is set to the stoichiometric air-fuel ratio or near the stoichiometric air-fuel ratio, the target engine speed is set to A value higher than the above 750 rpm, for example, about 800 rpm is set, and this speed is maintained (step S11). Then, it is determined whether or not the accelerator sensor 34 is in the ON state or the brake sensor 35 is in the OFF state, that is, whether or not the deceleration state is released (step S12). Returning to step S1, the above control operation is repeated. If it is determined NO in step S12 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. Determination is made (step S13).

  If it is determined YES in step S13 and it is confirmed that the vehicle is stopped, the stratified combustion mode operation state in which the air-fuel ratio in the cylinder is set to a value considerably larger than the stoichiometric air-fuel ratio at this time t0. (YES in step S14), if the determination is YES, the engine target rotational speed N1 is set to a value higher than the normal idle rotational speed (650 rpm) by a predetermined amount, for example, about 810 rpm. The stratified lean combustion state is set to set (step S15), and the exhaust gas recirculation is stopped by closing the EGR valve (not shown) provided in the EGR passage in order to improve the scavenging performance of each cylinder 12A to 12D. (Step S16).

  When it is determined NO in step S13 and it is confirmed that the engine is not in the stratified combustion mode, the air-fuel ratio in the cylinder is reduced to reduce the catalyst temperature or to refresh the NOx catalyst. If it is confirmed that the engine is in the operation state of the uniform combustion mode set to the stoichiometric air fuel ratio or near the stoichiometric air fuel ratio, whether or not the uniform combustion prohibition flag for prohibiting the engine from being in the uniform combustion mode is ON (YES in step S17), if YES is determined, the process proceeds to step S15 to execute control of the stratified combustion mode.

  If it is determined NO in step S17 and it is confirmed that the uniform combustion prohibition flag is in the OFF state, the target rotational speed N1 of the engine is set to a value higher than 810 rpm, for example, about 860 rpm, and uniform. The control of the combustion mode is executed (step S18), and the throttle valve 23 is operated in the valve opening direction so that the boost pressure Bt becomes the target pressure P1 set to, for example, about -400 mmHg. (Step S19), the shift range of the automatic transmission is set to neutral, and no load is applied (step S20).

  As described above, it is confirmed in step S1 that the vehicle is running at a speed greater than 10 km / h and the engine automatic stop permission flag F is in the ON state. In step S2, the vehicle is decelerated (the brake sensor 35 is When the engine rotational speed Ne is confirmed to be in the ON state), the engine rotational speed Ne is set to a predetermined value corresponding to the combustion state of the engine. Before the speed is reduced to 650 rpm, automatic engine stop control is executed.

  Further, at the time t0 when it is determined in step S13 that the vehicle speed is 0 and it is confirmed that the engine automatic stop condition is satisfied, the target engine speed N1 of the engine is set to a predetermined value in steps S15 and S18. 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 S17, the load on the automatic transmission is reduced, which is shown in FIG. Thus, the engine speed Ne slightly increases from the time point t0 when the engine automatic stop condition is satisfied.

  Next, it is determined whether or not a predetermined time set in advance in about 1 sec (seconds) has elapsed after time t0 when it is determined as YES in step S13 and it is confirmed that the automatic engine stop condition is satisfied. (Step S21) When it is determined NO, it is determined whether or not the accelerator sensor 34 is turned on, that is, whether or not the driver has performed a start operation (Step S22). If YES is determined in step S22, the process proceeds to step S1 without automatically stopping the engine. As a result, when the driver performs a start operation immediately after the vehicle speed becomes zero, that is, when a re-acceleration request is made for the vehicle, the automatic engine stop control is prohibited and re-acceleration responsiveness is ensured. It will be.

  Then, when it is determined YES in step S21, whether or not the fuel injection stop condition (FC condition) is satisfied, specifically, the engine speed Ne becomes the target speed N1 and the boost pressure Bt Is determined to be stable in a state where the target pressure P1 is reached (step S23). After determining YES in step S23 and confirming that the engine speed Ne and the boost pressure Bt are stable (time t1 in FIG. 4), after stopping the fuel injection (step S24) Then, it is determined whether or not a uniform combustion prohibition flag that prohibits the engine from being in a uniform combustion mode is in an ON state (step S25). If YES in step S25, the uniform combustion prohibition flag is turned OFF (step S26), and then the target power generation current Ge of the alternator 28 is set to 0 to stop power generation (step S27). ), The throttle valve 23 is opened, and the opening degree K is set to about 30%, for example (step S28).

  Thereafter, whether or not a predetermined time has elapsed from the time point t1 when the fuel injection is stopped in step S20, 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 S29), and when the determination is YES, ignition by the ignition device 27 is stopped (step S30). 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 S31), after the fuel injection stop time t1 shown in FIG. 4 and FIG. It is determined whether or not the engine speed Ne has started to decrease. At a time t2 when it is determined YES, the throttle valve 23 is closed and its opening degree K is set to 0% (step S32). 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 S28 starts to decrease with a predetermined time difference in accordance with the closing operation of the throttle valve 23.

  Further, the power generation control for operating the alternator 28 is started by setting the target power generation current Ge of the alternator 28 to an initial value set to about 60 A in advance (step S33). Note that the engine top dead center is replaced with the above embodiment in which the throttle valve 23 is closed at the time t2 when it is determined in step S31 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, for example, about 790 rpm, the throttle valve 23 is closed and power generation control of the alternator 28 is started. Good.

  Next, it is determined whether or not the engine top dead center rotational speed ne is within the first predetermined range (step S34). 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.

  If it is determined YES in step S34 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 S35). That is, as shown in FIG. 11, 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. 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 a time point t4 when the engine passes the second compression top dead center before the engine stops, for example, 260 rpm to It is determined whether it is within the range of 400 rpm (step S36). The fuel injection amount increases as the engine top dead center rotational speed ne increases at time t4 when it is determined YES in step S36 and it has been confirmed that the second compression top dead center before the engine stop has passed. From the map (not shown) set to, the fuel injection amount for the cylinder 12C that is in the compression stroke when the engine is stopped is set, and fuel is injected in the latter half of the compression stroke of the cylinder 12C (step S37). 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 S38). 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. Further, the boost pressure Bt at each time when each of the cylinders 12A to 12D sequentially passes the compression top dead center is detected, and the value is stored.

  If it is determined YES in step S38 and the engine top dead center rotational speed ne is equal to or lower than the predetermined value N3, that is, if it is confirmed that the engine has passed the last compression top dead center, At time t5, the boost pressure Bt at the time of passing through the previous compression top dead center is read, and this value is set as the boost pressure Bt at the second compression top dead center (TDC) before engine stop (step). S39).

  The top dead center rotational speed ne at the time t5 when the engine reaches the final compression top dead center (hereinafter referred to as the final top dead center rotational speed ne1) and the boost pressure Bt at the second compression top dead center before the engine stops. Based on (hereinafter referred to as boost pressure Bt2), it is determined whether or not the piston 13 tends to stop at a later position in each stroke (a position near the bottom dead center in the expansion stroke cylinder 12A) (step S41). . Specifically, when the final top dead center rotational speed ne1 is equal to or higher than a predetermined rotational speed N4 (for example, N4 = 200 rpm) and the boost pressure Bt2 is equal to or lower than a predetermined pressure P2 (for example, P2 = −200 mmHg) (vacuum side) ), The piston stop position in the expansion stroke cylinder 12A is 100 ° to 120 ° CA after the compression top dead center with respect to the appropriate range R. Since there is a large tendency to stop at a position close to 120 ° CA, YES is determined in step S40.

  If it is determined NO in step S40, the engine does not tend to stop at a position near the latter stage of the stroke as described above, and the position at a relatively earlier stage of the stroke, that is, in the expansion stroke cylinder 12A. There is a possibility that the piston stop position may stop at a position close to 100 ° CA or 100 ° CA or less with respect to an appropriate range R of 100 ° to 120 ° CA after compression top dead center. Therefore, in order to stop the piston 13 within the proper range R more reliably, the throttle valve 23 is opened. For example, the throttle valve 23 is opened so that the opening degree K of the throttle valve 23 is set to the first opening degree K1 that is set to about 40% of full opening (step S41), and the intake air flow is increased to thereby increase the intake stroke. The intake resistance of the cylinder 12D is decreased. As a result, the engine is likely to stop at a later position in the stroke, and as a result, the stop position of the piston 13 in the expansion stroke cylinder 12A is prevented from exceeding the lower limit (100 ° CA) within the appropriate range R. become.

  On the other hand, if YES is determined in step S40, the rotational inertia of the engine is large, the intake air flow rate in the final intake stroke to the compression stroke cylinder 12C is small, and the compression reaction force is small. There is already a condition where 13 is likely to stop at a later stage of the stroke. Therefore, the throttle valve 23 is operated so that the opening degree K of the throttle valve 23 becomes the second opening degree K2 set to about 5%, for example (step S42). The second opening K2 may be a smaller opening or a closed state according to engine characteristics and the like. In this way, an appropriate intake resistance is generated in the intake stroke cylinder 12D, and the occurrence of a situation where the stop position of the piston 13 exceeds the appropriate range R and is further on the late stage is effectively prevented.

  Next, it is determined whether or not the engine is stopped (step S43). 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 S44). ) After turning off the automatic stop permission flag F (step S45), the control operation is terminated.

  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. 12 to 14 and the time charts shown in FIGS. 15 and 16. 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 stop position of the piston 13 detected according to the output signals of the crank angle sensors 30 and 31 is within the proper stop range R (before BTDC 60 ° CA to 80 ° CA) in the compression stroke cylinder 12C. Then, it is determined whether or not it is close to the bottom dead center BDC (step S104). When it is determined YES in step S104 and it is confirmed that the air amount in the compression stroke cylinder 12C is relatively large, the air amount in the compression stroke cylinder 12C calculated in step S103 is λ ( The first fuel injection is performed such that the air / fuel ratio (excess air ratio)> 1 (for example, air / fuel ratio = about 20) (step S105). This air-fuel ratio is obtained from the first air-fuel ratio map M1 for the first time of the compression stroke cylinder 12C set in advance according to the stop position of the piston 13, and is set to a lean air-fuel ratio of λ> 1. This prevents excessive combustion energy for reverse rotation even when the amount of air in the compression stroke cylinder 12C is relatively large.

  On the other hand, when it is determined NO in step S104 and the air amount in the compression stroke cylinder 12C is relatively small, the air-fuel ratio satisfying λ ≦ 1 with respect to the air amount in the compression stroke cylinder 12C calculated in step S103. The first fuel injection is performed so as to become (step S106). This air-fuel ratio is obtained from the first second air-fuel ratio map M2 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, even when the amount of air in the compression stroke cylinder 12C is small, sufficient combustion energy for reverse rotation can be obtained.

  Next, the cylinder 12C is ignited after the elapse of a predetermined time set in consideration of the vaporization time from the first fuel injection to the compression stroke cylinder 12C (step S107). 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 S108). If it is determined NO and it is confirmed that misfire has occurred and the piston 13 has not moved, the compression stroke cylinder 12C is re-ignited (step S109).

  If it is determined YES in step S108 and it is confirmed that the piston 13 has moved, the split fuel injection split for the expansion stroke cylinder 12A is based on the stop position of the piston 13 and the in-cylinder temperature estimated in step S102. The ratio (the ratio between the first pre-injection and the second post-injection) is calculated (step S121). The latter injection ratio is set to a larger value as the piston stop position in the expansion stroke cylinder 12A is closer to the bottom dead center or as the in-cylinder temperature is higher.

  Next, the fuel injection amount is calculated so that a predetermined air-fuel ratio (λ ≦ 1) is obtained with respect to the air amount of the expansion stroke cylinder 12A calculated in step S103 (step S122). The air-fuel ratio at this time is obtained from an air-fuel ratio map M3 for the expansion stroke cylinder 12A set in advance according to the stop position of the piston 13. Further, based on the fuel injection amount to the expansion stroke cylinder 12A calculated in step S122 and the division ratio calculated in step S121, the first stage fuel injection amount for the expansion stroke cylinder 12A is calculated, and the fuel is Injecting (step S123).

  Next, based on the in-cylinder temperature estimated in step S102, the subsequent (second) fuel injection timing for the expansion stroke cylinder 12A is calculated (step S124). This second injection timing is a timing when the air in the cylinder is compressed after the piston 13 starts moving toward the top dead center (reverse rotation of the engine), and the latent heat of vaporization of the injected fuel is compressed. The pressure is set to be reduced effectively, that is, the piston 13 is set to approach the top dead center, and the time for the second injected fuel to evaporate by the ignition timing is set to be as long as possible. The

  Next, the subsequent (second) fuel injection amount for the expansion stroke cylinder 12A is calculated based on the fuel injection amount for the expansion stroke cylinder 12A calculated in step S122 and the split ratio calculated in step S121 (step S125). ), And is injected at the second injection timing calculated in step S124 (step S126).

  After the second fuel injection into the expansion stroke cylinder 12A, ignition is performed when a predetermined delay time has elapsed (step S127). This delay time is obtained from the ignition map M4 for the expansion stroke cylinder 12A set in advance according to the stop position of the piston 13. Due to the initial combustion in the expansion stroke cylinder 12A by the ignition, the engine turns from reverse rotation to normal rotation. Therefore, 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 the ignition in step S107) starts to be compressed.

  Next, taking into account the fuel vaporization time, the second time fuel is injected into the compression stroke cylinder 12C (step S128). 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 M5 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 exclusively 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.

  Since the fuel injected for the second time in the compression stroke cylinder 12C does not burn as described above, the next combustion following the first combustion in the expansion stroke cylinder 12A is the intake stroke cylinder 12D, that is, as shown in FIG. This is the first combustion in the fourth cylinder that was in the intake stroke when stopped. 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 purpose, 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 S140), an air-fuel ratio correction value for preventing self-ignition is calculated based on the in-cylinder temperature estimated in step S102 (step S141). That is, when self-ignition occurs, a force (reverse torque) that pushes the piston 13 back to the bottom dead center side is generated before reaching the compression top dead center due to 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 S140 and the air-fuel ratio in consideration of the air-fuel ratio correction value calculated in step S141 ( Step S142). 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 S143), 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 performed with a delay after the top dead center (step S144). 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.

  After step S144, the control state may be shifted to a normal control state. However, in this embodiment, control for further suppressing the increase in engine speed is performed. This increase in engine rotation speed means that the engine rotation speed suddenly increases more than necessary after the initial combustion in the intake stroke cylinder 12D, and causes an acceleration shock or a feeling of strangeness to the driver. This is not desirable. The increase in the engine rotation speed is immediately after starting (after the first combustion in the intake stroke cylinder 12D) because the intake pressure (pressure downstream of the throttle valve 23) during the automatic stop period is substantially atmospheric pressure. It is generated when the combustion energy in each of the cylinders 12A to 12D temporarily becomes larger than the combustion energy during normal idle operation. For this purpose, in steps S145 to S158 described below, control for suppressing the engine speed from rising is performed.

  First, power generation is started by setting the target current value of the alternator 28 higher than usual (step S145), and the rotational resistance (external load of the engine) of the crankshaft 3 is increased by the power generation of the alternator 28, thereby rotating the engine speed. Suppresses the rising of. Next, it is determined whether or not the intake pressure detected by the intake pressure sensor 26 is higher than the intake pressure during normal idling when the engine is not automatically stopped (step S150). Since the engine speed is likely to rise, the amount of combustion energy generated is reduced by making the opening of the throttle valve 23 smaller than the throttle opening during normal idle operation (step S151). Suppress.

  Then, it is determined whether or not the temperature of the exhaust gas purification catalyst 37 provided in the exhaust passage 22 is equal to or lower than the activation temperature (step S152). If YES is determined, the target air-fuel ratio in the cylinder is set to λ ≦ The rich air-fuel ratio is set to 1 (step S153), and the ignition timing is delayed after top dead center (step S154). Thereby, the temperature increase of the catalyst 37 is promoted, and the amount of combustion energy generated is suppressed by the delay of the ignition timing.

  On the other hand, if it is determined NO in step S152 and it is confirmed that the temperature of the exhaust gas purification catalyst 37 is higher than the activation temperature, the target air-fuel ratio in the cylinder is set to a lean air-fuel ratio with λ> 1. The stratified lean combustion state is set (step S158). This lean combustion suppresses fuel consumption and suppresses the amount of combustion energy generated.

  The process returns to step S150 through step S154 or step S158, and it is determined that the intake pressure has decreased even during normal idling when it is determined NO in step S150 and the engine is not automatically stopped. The control operation is repeated. If it is determined NO in step S150, there is no possibility that the engine speed will increase any more, so that the normal control state including the generated current of the alternator 28 is entered (step S160).

  When the restart control is executed, as shown in FIGS. 15 and 16, first, the first fuel injection J3 is performed in the compression stroke cylinder 12C (third cylinder), and combustion is performed by the ignition (FIG. 15). (1)) is performed. With the combustion pressure (part a in FIG. 16) due to this 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, the first fuel injection J3 of the compression stroke cylinder 12C becomes a lean air-fuel ratio (λ> 1) when the air amount is relatively large, and a stoichiometric air-fuel ratio or a rich air-fuel ratio (λ ≦ 1) when it is small. Therefore, an appropriate combustion energy for reversing the engine, that is, a combustion energy that does not excessively reverse the compression top dead center while sufficiently compressing the air in the expansion stroke cylinder 12A. Can be obtained.

  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, the first fuel injection J1 in the expansion stroke cylinder 12A is performed and vaporization starts. Then, when the piston 13 of the expansion stroke cylinder 12A moves to the top dead center side (preferably closer to the top dead center from the stroke center) and the air in the cylinder 12A is compressed, the second (rear stage) fuel injection J2 is performed. Is done. The compression pressure is reduced by the latent heat of vaporization of the injected fuel, and the piston 13 comes closer to the top dead center, so that the density of the compressed air (air mixture) increases (part b in FIG. 16).

  When the piston 13 of the expansion stroke cylinder 12A is sufficiently close to top dead center, the cylinder 12A is ignited, and the first injected fuel (J1) and the second injected fuel (J2) whose vaporization is promoted are promoted. ) Are combusted ((2) in FIG. 15), and the engine is driven in the forward rotation direction by the combustion pressure (c portion in FIG. 16).

  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. 15), but the compression stroke cylinder 12C is not combusted, 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. 16), 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. 15) for reducing the temperature in the cylinder and the compression pressure by the latent heat of vaporization of the fuel. As shown in the figure, since, for example, the middle stage of the compression stroke is set, 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. 16). 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.

  Thus, the first compression top dead center ((3) in FIG. 15) after the start of restart and the second compression by the energy of the first combustion ((2) in FIG. 15) in the expansion stroke cylinder 12A. The top dead center ((4) in FIG. 15) can be exceeded, and smooth and reliable startability can be ensured, and thereafter ((5), (6) in FIG. ) Makes the air-fuel ratio lean (λ> 1) according to the temperature of the catalyst 37, or delays the ignition timing, thereby shifting to normal operation while preventing the engine speed from rising.

  When the engine automatic stop condition set in advance as described above is satisfied, the fuel injection for continuing the operation of the engine is stopped to automatically stop the engine, and the engine restart condition in the automatic stop state. In the engine starter configured to restart the engine by injecting fuel into the cylinder 12A that is stopped in at least the expansion stroke to cause ignition and combustion when When the engine is automatically stopped in the form, the target rotational speed N1 of the engine at the time of stopping the fuel injection is set to a value higher than the normal idle rotational speed, and the target rotational speed N1 is continued for a certain time. If you want to stop the fuel injection after the engine and stop the engine automatically in the stratified combustion mode of the engine, stop the fuel injection. When the target rotational speed N1 of the engine is set to a value lower than the target rotational speed N1 of the uniform combustion mode, the fuel injection is stopped after the target rotational speed N1 is continued for a predetermined time. Since it is configured to execute in the means 43, the piston 13 of the cylinder 12A, which is in the expansion stroke when the engine is stopped, is stopped at a position suitable for restarting the engine, that is, a position slightly offset toward the bottom dead center side from the stroke center. Can be appropriately executed.

  That is, when the engine automatic stop condition is satisfied and the engine is automatically stopped, the target engine speed N1 set according to the engine operating state is continued for a certain time, for example, 1 second. Since the fuel injection is stopped in a state where the engine rotational speed is stable, the control for lowering the engine rotational speed is appropriately executed after the fuel injection is stopped, and the cylinder 12A that is in the expansion stroke when the engine is stopped. The piston can be stopped at a position suitable for restarting the engine. Further, before the target engine speed N1 set in accordance with the engine operating state is continued for a certain period of time, the engine automatic stop condition is canceled by the accelerator sensor 34 being turned on. In this case, the response to the start request can be improved by stopping the automatic engine stop control.

  When the engine is automatically stopped in the uniform combustion mode of the engine, the target rotational speed N1 of the engine is set to a value higher than the normal idle rotational speed (650 rpm), for example, 860 rpm, and the target rotational speed N1 is By stopping the fuel injection while continuing for a certain period of time, the engine rotation speed (the number of intake, compression, expansion, and exhaust strokes) from this fuel injection stop time t1 until the engine is stopped. Can be secured sufficiently. Therefore, by reducing the engine rotational speed Ne along a preset reference line, the amount of air introduced into the cylinder 12A that is in the expansion stroke when the engine is stopped becomes larger than the cylinder 12C that is in the compression stroke. The piston 13 of the expansion stroke cylinder 12A can be stopped in a range R suitable for restarting the engine, that is, at a position slightly offset toward the bottom dead center side from the stroke center, Before the engine is stopped, burnt gas can be reliably discharged to ensure scavenging performance.

  Further, when the engine is automatically stopped in the stratified combustion mode in which the intake air flow rate introduced into the cylinders 12A to 12D of the engine is large and the scavenging performance at the time of automatic engine stop can be sufficiently secured, the fuel injection is stopped. Since the target engine speed N1 of the engine is set to a value (810 rpm) lower than the target engine speed N1 (860 rpm) of the uniform combustion mode, the fuel injection is stopped without impairing the scavenging performance of each cylinder 12A to 12D. There is an advantage that the fuel consumption can be improved and the generation of engine noise can be effectively suppressed.

  In the above embodiment, when the engine automatic stop condition is satisfied in the stratified combustion mode of the engine that can sufficiently ensure scavenging at the time of the automatic engine stop, the engine is uniform from the stratified combustion mode until the fuel injection is stopped. Since the switching to the combustion mode is prohibited, the scavenging performance of each of the cylinders 12A to 12D is caused by switching from the stratified combustion mode to the uniform combustion mode with a small intake flow rate during the engine stop operation. It is possible to prevent a decrease in fuel efficiency and fuel consumption, and to effectively suppress the occurrence of a situation in which engine noise increases due to the target engine speed N1 being set to a large value. There are advantages.

  In particular, as shown in the above-described embodiment, when the engine is automatically stopped in the stratified combustion mode of the engine that can secure a sufficient scavenging performance when the engine is automatically stopped because of a large intake flow rate introduced into the cylinders 12A to 12D of the engine. However, the fuel injection is stopped by setting the target engine speed N1 of the engine to a value (810 rpm) higher than the normal idle speed (650 rpm) that does not automatically stop the engine. While ensuring the scavenging performance of -12D, the control of lowering the engine speed after the fuel injection is stopped is properly executed, and the piston 13 of the cylinder 12A that is in the expansion stroke when the engine is stopped is used to restart the engine. It can be stopped at a suitable position.

  Further, as described above, the determination means 44 for determining whether or not the engine automatic stop condition is satisfied in a state where the engine rotational speed Ne is higher than the normal idle rotational speed, and the engine automatic operation in the stratified combustion mode of the engine. When it is determined that the stop condition is satisfied, the target rotational speed N1 of the engine when stopping fuel injection is set to a value (810 rpm) lower than the target rotational speed N1 (860 rpm) of the uniform combustion mode, and the fuel In the case where the automatic stop control means 44 is provided with the prohibition means 45 for prohibiting the engine from being switched from the stratified combustion mode to the uniform combustion mode until the injection is stopped, the cylinder 12A which is in the expansion stroke when the engine is stopped is provided. Automatic stop control for stopping the piston 13 at a position suitable for restarting the engine can be appropriately executed.

  That is, since the engine automatic stop control is executed when the engine automatic stop condition is satisfied when the engine rotational speed Ne is higher than the normal idle rotational speed, the engine that has once decreased to the normal idle rotational speed. As in the case where the rotational speed Ne is increased to the target rotational speed N1, it takes time for the driver to feel uncomfortable with the increase in the engine rotational speed Ne or to automatically stop the engine. It is possible to stop the piston 13 of the cylinder 12A, which is in the expansion stroke at the time of stopping the engine, at a position suitable for restarting the engine while preventing the adverse effects such as becoming longer. When the engine automatic stop condition is satisfied in the stratified combustion mode of the engine that can ensure sufficient scavenging at the time of automatic engine stop because the intake air flow rate introduced into the cylinders 12A to 12D of the engine is large, uniform combustion Since switching to the engine is prohibited and the engine is stopped in the stratified combustion mode, the effect of increasing the frequency with which the engine automatic stop control is executed from the stratified combustion mode of the engine, which has a high effect of improving fuel efficiency, is effective. Thus, there is an advantage that the fuel consumption can be improved and the engine speed can be prevented from being increased and the engine noise can be prevented.

  In the above-described embodiment, the combustion control means 41 controls the engine so that the operation region in which the engine is automatically stopped is in the stratified combustion mode and the engine is in the uniform combustion mode when the purification performance of the exhaust gas purification catalyst 37 needs to be improved. Since the engine is configured to be executed, there is an advantage in that the fuel consumption is effectively improved and the generation of engine noise is suppressed by executing the engine automatic stop control in the stratified combustion mode of the engine at normal times. Further, when it is necessary to improve the purification performance of the exhaust gas purification catalyst, for example, when it is necessary to maintain the activation temperature by preventing the temperature of the exhaust gas purification catalyst 37 from decreasing, or the exhaust gas purification catalyst 37 When the NOx adsorbed by the NOx adsorbent is separated, the exhaust purification performance can be sufficiently ensured by setting the engine to a uniform combustion mode.

  In addition, after the engine automatic stop condition was established in the stratified combustion state of the engine, it became necessary to remove NOx adsorbed on the NOx adsorbent of the exhaust gas purification catalyst, and the engine was in an operation state in which the engine is in a uniform combustion mode. In this case, the prohibition means 45 prohibits the switching to the uniform combustion mode, and the switching to the uniform combustion mode is performed at a predetermined time after the engine restart, whereby the purification performance of the exhaust gas purification catalyst 37. Thus, the control for improving the value is executed.

  Further, as shown in the above embodiment, when the intake air flow rate is configured to increase from the fuel injection stop time t1 until the engine rotational speed Ne drops below a predetermined speed, the engine is automatically stopped. By increasing the intake air flow rate at the initial stage of the operation, the scavenging performance of each of the cylinders 12A to 12D can be effectively improved, and the engine can be automatically stopped with the pumping loss reduced. Moreover, regardless of whether the engine is in a stratified combustion mode or a uniform combustion mode, when the engine speed Ne drops below a predetermined value (for example, 790 rpm), the engine cylinders 12A to 12D By reducing the intake flow rate introduced into the engine, there is an advantage that the control for stopping the piston 13 of the cylinder 12A, which is in the expansion stroke when the engine is stopped, at a position suitable for restarting the engine can be properly executed.

  That is, as shown in FIG. 17, when the engine is in the uniform combustion mode, the target rotational speed N1 of the engine at the fuel injection stop time t1 is set to a higher value than in the stratified combustion mode. There is a tendency that the engine speed (the number of intake, compression, expansion, and exhaust strokes) from the injection stop time t1 to when the engine is stopped tends to increase, but the engine rotational speed Ne is constant and preset. The number of strokes after time t2, t2 'when the value drops below the value (790 rpm) is substantially the same number of strokes. Therefore, in both the case where the engine is in the stratified combustion mode and the case where the engine is in the uniform combustion mode, the engine cylinders 12A to 12D are in the engine cylinders 12A to 12D at the time points t2 and t2 ′ when the engine rotational speed Ne drops below the predetermined value. By reducing the intake flow rate introduced into the engine, the piston of the cylinder 12A, which is in the expansion stroke at the time of stopping the engine, can be stopped at a position suitable for restarting the engine.

  Furthermore, in the above embodiment, at the time t0 when the engine automatic stop condition is satisfied, the target engine speed N1 is set to a value higher than the normal idle engine speed, and feedback control of the engine engine speed Ne is performed. The fuel injection is stopped while the engine operating state is stabilized by controlling the intake flow rate adjusting means including the throttle valve 23 so that the intake negative pressure Bt becomes a constant value. The engine automatic stop control for reducing the engine rotation speed Ne along the reference line can be executed more appropriately.

  In the above embodiment, when the engine is automatically stopped, after the fuel injection is stopped after the engine rotational speed Ne becomes the preset reference speed N2, for example, the fourth time before the engine stop is passed. At the time t3 when it is confirmed that the compression top dead center is reached, the top dead center rotational speed ne is detected, and the target generated current Ge corresponding to the top dead center rotational speed ne is determined from the map shown in FIG. When the top dead center rotational speed ne is low, the reduction amount of the target generated current Ge of the alternator 28 is set to a larger value than when the top dead center rotational speed ne is high. Therefore, the engine is set along a preset reference line. The target generated current Ge of the alternator 28 can be appropriately controlled so as to decrease the rotational speed Ne. Thus, the fourth top dead center before the engine is stopped so that the second top dead center speed ne before the engine is stopped is within the range indicated by hatching in FIG. The target generated current Ge of the alternator 28 is adjusted based on the number of times speed ne, and the rotational resistance of the engine is changed, so that the piston 13 of the cylinder that is in the expansion stroke when the engine is stopped is brought into a position suitable for restarting the engine. Can be stopped.

  Further, in order to stop the piston 13 of the cylinder 12A, which is in the expansion stroke when the engine is stopped, at a position suitable for restarting the engine, the generated current of the alternator 28 is controlled immediately before the engine is stopped. It is desirable to adjust the rotational resistance of the crankshaft 3. However, immediately before the engine is stopped, the engine rotational speed Ne becomes low, and the power generation function of the alternator 28 is not fully exhibited. Even if the target power generation current Ge is changed, the rotational resistance of the crankshaft 3 Therefore, it is difficult to accurately adjust the reduced state of the engine rotational speed Ne. Therefore, in order to stop the piston 13 of the cylinder 12A, which is in the expansion stroke when the engine is stopped, at an appropriate position, the target generated current Ge of the alternator 28 is increased to a preset initial value after the fuel injection is stopped. The target of the alternator 28 is set to a value corresponding to the degree of decrease in the engine speed at the middle stage of the process in which the engine speed Ne decreases (for example, when the fourth to sixth compression top dead centers before the engine stops). It is desirable to execute control for reducing the generated current Ge.

  That is, the alternator 28 can accurately adjust the rotational resistance of the crankshaft 3 over a wide range by adjusting the target generated current Ge to an arbitrary value, for example, from about 0 A to about 60 A, as shown in FIG. Thus, it is known that when the target power generation current Ge is set from a small current value of about 10 A to a large current value of about 60 A, for example, it takes about 0.1 sec. On the other hand, when the target generated current Ge of the alternator 28 is set to a small current value of about 10 A from a large current value of about 60 A, for example, the generated current can be instantaneously changed. .

  Therefore, at the initial stage of the operation for automatically stopping the engine, the target power generation current Ge of the alternator 28 is increased to an initial value of about 60 A so that the power generation function of the alternator 28 can be sufficiently exhibited. The engine top dead center rotational speed ne when passing through the compression top dead center is detected, and when the top dead center rotational speed ne is low, the amount of decrease in the target generated current Ge is set to a larger value than when it is high. By performing the setting, control is performed to adjust the rotational resistance of the crankshaft 3 in accordance with the reduced state of the engine rotational speed Ne and stop the piston 13 of the expansion stroke cylinder 12A at a position suitable for restarting the engine. Is desirable.

  In addition, while detecting the top dead center rotational speed ne when the piston 13 passes through the compression top dead center, the reduction amount of the target generated current Ge is controlled based on the top dead center rotational speed ne. Instead of the above-described embodiment, the crank angle at the time when the piston 13 passes the center position of the stroke is set as the detection angle, and the target power generation is performed based on the engine speed Ne detected at the time when the detection angle is reached. It is also possible to set a reduction amount of the current Ge. However, when the piston 13 passes through the center position of the stroke, the engine rotational speed Ne is in a significantly fluctuating state, and it is difficult to accurately determine the reduced state of the engine rotational speed Ne. As shown in the embodiment, based on the engine top dead center rotational speed ne when the piston 13 in which the engine rotational speed Ne is temporarily stabilized passes the compression top dead center, the target generated current Ge of the alternator 28 is It is desirable to set the amount of decrease.

  In particular, in the above-described embodiment, the intake flow rate introduced into the cylinders 12A to 12D is sufficiently ensured by reducing the intake throttle amount in a region where the engine rotational speed Ne is sufficiently high at the initial stage of the operation for automatically stopping the engine. At the same time, the target power generation current Ge of the alternator 28 is set to 0, for example, so that the target power generation current Ge is temporarily reduced, so that the scavenging performance of each cylinder 12A to 12D is effectively improved. In addition, both the rotational resistance of the crankshaft 3 and the pumping loss can be reduced. Therefore, at the initial stage of the operation of automatically stopping the engine, while preventing the engine speed Ne from significantly decreasing, the target generated current Ge of the alternator 28 is increased to the initial value at a predetermined timing thereafter. There is an advantage that the power generation function of the alternator 28 can be exhibited quickly and sufficiently to adjust the external load of the engine to an appropriate value.

  Further, as shown in the above-described embodiment, at the initial stage of the operation of automatically stopping the engine, the automatic transmission is set to the neutral state and the fuel injection is stopped to suppress the rotation of the engine while the fluctuation of the engine rotational speed Ne due to the disturbance is suppressed. When it is configured to reduce the speed Ne, there is an advantage that automatic stop control for stopping the piston 13 at a position suitable for restarting the engine can be appropriately executed.

  Further, in the above embodiment, it is determined whether or not the piston 13 tends to stop at a position near the latter half of the stroke based on the top dead center rotational speed ne1 at the time t5 when the piston 13 reaches the last compression top dead center. Since the opening degree K of the throttle valve 23 is adjusted according to the determination result, the stroke amount of the piston 13 immediately before the engine is stopped is appropriately adjusted to be within a range R suitable for restarting the engine. The automatic stop control for stopping the piston 13 can be appropriately executed.

  For example, does the piston 13 tend to stop at a position near the latter half of the stroke depending on whether or not the final top dead center rotational speed ne1 is 200 rpm or more and the boost pressure Bt2 satisfies the condition that P2 = −200 mmHg or less? If NO is determined, the opening degree K of the throttle valve 23 is set to a first opening degree set in advance to about 40% to reduce the intake resistance of the intake stroke cylinder 12D. Thus, it is possible to effectively prevent the position of the piston 13 of the expansion stroke cylinder 12A from exceeding the lower limit of the appropriate range R. On the other hand, if the determination result is YES, the opening degree K of the throttle valve 23 is set to a second opening degree of about 5%, and an appropriate intake resistance is generated in the intake stroke cylinder 12D, whereby the piston 13 There is an advantage that it is possible to prevent the stop position from exceeding the appropriate range R and further toward the later stage.

  In the above-described embodiment, the example in which the intake flow rate to the cylinders 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 has been described. The present invention is not limited to this, and a known variable valve mechanism that changes the lift amount of the intake valve 19 provided in each of the cylinders 12A to 12D is provided to adjust the intake flow rate to each of the cylinders 12A to 12D. Alternatively, the intake flow rate to each of the cylinders 12A to 12D is adjusted using a multiple throttle valve in which a valve body is individually provided in the branch intake passage 21a connected to each of the cylinders 12A to 12D. You may comprise as follows.

  Further, in the above-described embodiment, at the time t2 when the engine rotational speed Ne is lower than the reference speed N2 set in advance to about 790 rpm after the fuel injection is stopped, the operation of decreasing the opening K of the throttle valve 23; Although the operation of increasing the target generated current Ge of the alternator 28 is performed at the same time, it is not always necessary to match the operation point of both, and the opening time of the throttle valve 23 is decreased according to the increase timing of the target generated current Ge of the alternator 28. It may be shifted slightly before and after time t2.

  Further, in the engine starter in the above embodiment, when the engine in the automatic stop state is restarted, the crankshaft 3 is slightly reversed first by causing the compression stroke cylinder 12C to perform the first combustion. Although the ignition is performed after rotating and compressing the air-fuel mixture in the expansion stroke cylinder 12A, the engine starter according to the present invention is not limited to this, and the expansion stroke cylinder 12A is first ignited. May be configured to restart the engine.

  Furthermore, in the above embodiment, when the engine is restarted, the fuel injection for the initial combustion in the expansion stroke cylinder 12A is divided injection (J1 + J2). This is achieved by reducing the compression pressure due to the latent heat of vaporization and ensuring the vaporization performance. It is also possible to formulate a timing (predetermined fuel injection timing) that can be compatible with the above as much as possible through experiments or the like, and to perform one fuel injection at the predetermined fuel injection timing. Further, the divided fuel injection performed for the first combustion in the expansion stroke cylinder 12A when the engine is restarted may be divided into three or more as required.

  Although omitted in the above embodiment, when the engine is restarted, when the 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 increased by the predetermined time after the start. You may make it perform control accompanied by the assist by a starter motor, when it does not reach a predetermined value.

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 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 etc. of the engine speed at the time of an engine stop. It is a time chart which shows change states, such as a throttle opening and a target generated current at the time of an engine stop. 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 distribution map which shows the correlation with the top dead center rotational speed and piston stop position in the 2nd before an engine stop. 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. 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 control action at the time of engine restart. It is a flowchart which shows the middle part of control action at the time of restart of an engine. 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. It is a time chart which shows the change state etc. of the engine speed at the time of an engine stop. It is a time chart which shows the change state of the electric power generation current of an alternator.

Explanation of symbols

12A to 12D Cylinder 22 Exhaust passage 23 Throttle valve (intake flow rate adjusting means)
37 Exhaust gas purification catalyst 41 Combustion control means 42 Intake flow rate control means 43 Automatic stop control means 44 Judging means 45 Inhibiting means

Claims (6)

  When the preset automatic engine stop condition is satisfied, the fuel supply for continuing the engine operation is stopped to automatically stop the engine, and the restart condition for the engine in the automatic stop state is satisfied. An engine starter configured to automatically restart the engine by injecting fuel into at least the cylinder stopped in the expansion stroke and causing ignition and combustion to occur, and uniform combustion of the engine In the case of automatically stopping the engine in the form, after setting the target rotational speed of the engine at the time of stopping the fuel injection to a value higher than the normal idle rotational speed, the target rotational speed is continued for a certain period of time. When stopping the fuel injection and automatically stopping the engine in the stratified combustion mode of the engine, the engine at the time of stopping the fuel injection Characterized in that it comprises an automatic stop control means for stopping the fuel injection after the target rotational speed is set to a value lower than the target rotational speed of the uniform combustion mode and the target rotational speed is continued for a predetermined time. The engine starter.   2. The engine according to claim 1, wherein when the engine automatic stop condition is satisfied in the stratified combustion mode of the engine, the engine is prohibited from being switched from the stratified combustion mode to the uniform combustion mode until the fuel injection is stopped. The engine starting device as described.   3. When the engine is automatically stopped in the stratified combustion mode of the engine, the target rotational speed of the engine when stopping fuel injection is set to a value higher than a normal idle rotational speed. The engine starting device as described.   When the preset automatic engine stop condition is satisfied, the fuel supply for continuing the engine operation is stopped to automatically stop the engine, and the restart condition for the engine in the automatic stop state is satisfied. An engine starter configured to automatically restart the engine by injecting fuel into at least the cylinder stopped in the expansion stroke and causing ignition and combustion to occur. When determining that the engine automatic stop condition is satisfied in a state where the engine is higher than the normal idle speed, and when it is determined that the engine automatic stop condition is satisfied in the stratified combustion mode of the engine The target rotational speed of the engine when stopping the fuel injection is set to a value lower than the target rotational speed of the uniform combustion mode, and the fuel injection is Engine starting system in which the engine until the locked is characterized in that a prohibition means for prohibiting from being switched to the homogeneous combustion mode from the stratified combustion mode.   Combustion control means for making the engine into a uniform combustion mode when it is necessary to improve the purification performance of the exhaust gas purification catalyst provided in the exhaust passage while making the operation region for automatically stopping the engine a stratified combustion mode The engine starting device according to any one of claims 1 to 4.   Intake flow rate adjusting means for adjusting the intake flow rate introduced into the cylinder, and when the engine is automatically stopped, the intake flow rate is increased from when the fuel injection stops until the engine rotational speed drops below a predetermined speed. And the intake flow rate control means for operating the intake flow rate adjustment means in a direction to decrease the intake flow rate when the engine rotational speed drops below a predetermined speed. The engine starting device according to any one of claims 1 to 5, wherein the engine rotation speed at the time of reduction is set to a constant value regardless of the combustion mode of the engine.

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