JP4604948B2 - Multi-cylinder engine starter - Google Patents

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.

In recent years, in order to reduce fuel consumption and reduce CO ₂ emissions, etc., when a restart condition is established such as when the engine is automatically stopped once during idle operation or the like, and then the vehicle is started. Technology for automatic engine stop control (so-called idle stop control) that automatically restarts the engine has been developed. As a restart method at the time of this idle stop control, as in the prior art disclosed in Patent Document 1, when the restart condition of the engine in the automatic stop state is satisfied, the cylinder stopped in the compression stroke (this cylinder In the specification, the air-fuel mixture is ignited, the engine is once reversed, and then fuel is injected into the cylinder stopped in the expansion stroke (referred to as “expansion stroke cylinder” in this specification). In other words, a so-called reverse restart system configured to automatically restart the engine and a cylinder stopped simply in the expansion stroke as disclosed in Patent Documents 2 and 3 are used. There is a so-called forward restart type that ignites. In particular, Patent Document 3 discloses a starter and a combustion starter in a forward rotation restart system.
JP 2004-324479 A JP 2004-324479 A JP 2004-316455 A

  In any of the restart methods described above, the load when the restarted engine reaches two compression strokes is the largest. In order to smoothly overcome this second compression stroke, the piston position during the first combustion is a very important factor. However, the conventional starter merely estimates the position of the piston that automatically stops, and the cylinder in which the air-fuel mixture is first ignited positively at the time of restart (referred to as “initial combustion cylinder” in this specification). It did not increase kinetic energy. Therefore, the variation in the starting torque at the time of restarting becomes large, and it is difficult to increase the success rate of restarting without the assistance of the starter.

  The present invention has been made in view of the above problems, and provides an engine starter that can be restarted as much as possible only by combustion of an air-fuel mixture by slow combustion in an initial combustion cylinder. It is an issue.

  In order to solve the above-described problems, the present invention includes a direct injection type fuel injection valve that injects fuel into a combustion chamber of a multi-cylinder engine, and when the preset automatic stop condition for the multi-cylinder engine is satisfied, The fuel supply for continuing the operation of the cylinder engine is stopped to automatically stop the multi-cylinder engine, and when the restart condition is satisfied, at least the air-fuel mixture of the expansion stroke cylinder is burned, and the multi-cylinder In a multi-cylinder engine starter that restarts an engine, an initial combustion cylinder prediction means that predicts an initial combustion cylinder that first combusts an air-fuel mixture during restart during an automatic stop operation of the multi-cylinder engine, and an air density estimation And when the air density estimated by the air density estimating means is less than a predetermined value during the automatic stop operation of the multi-cylinder engine. And a fuel injection control means for controlling the fuel injection valve so as to inject fuel into the first combustion cylinder in the last intake stroke during the automatic stop control. . In this aspect, during the process of automatically stopping the engine, the initial combustion cylinder (expansion stroke cylinder in the case of the forward rotation restart method, compression stroke cylinder in the case of the reverse rotation restart method) is estimated, and at least the air density is estimated. When the air density estimated by the means is less than a predetermined value, the fuel injection valve is controlled to inject fuel into the first combustion cylinder in the last intake stroke during the automatic stop control. When the air density is relatively low, homogenization of the air-fuel mixture is promoted in the first combustion cylinder, and turbulence due to spraying does not occur. Thereby, for example, when the initial combustion cylinder is a compression stroke cylinder, not only the stop position of the compression stroke cylinder is controlled near the top dead center, but also when the mixture of the compression stroke cylinder is ignited at the time of restart, Slow combustion characteristics can be obtained even when a considerable amount of time has passed from automatic stop to restart, or even in an environment with low air density, so heat from combustion of the mixture is released from the cylinder inner wall surface. The heat loss caused by this also becomes moderate, and it becomes possible to convert a relatively large amount of combustion energy into kinetic energy. Therefore, a relatively large reverse kinetic energy can be secured by the slow combustion with a small air weight, and the kinetic energy of the expansion stroke cylinder can be further increased by the relatively large reverse kinetic energy by the slow combustion. As a result, it is possible to secure sufficient kinetic energy to exceed the second compression stroke.

In a preferred aspect, there is provided stop position control means for performing position control so that the piston stop position of the first combustion cylinder to be automatically stopped is within a predetermined crank angle range on the top dead center side with respect to the stroke center. In this aspect, when the initial combustion cylinder is stopped near the top dead center, the piston stroke of the initial combustion cylinder can be set large, and the kinetic energy at the time of restart can be increased.

  In a preferred embodiment, a stop time measuring means for measuring a stop time is provided, and the fuel injection control means is configured to provide fuel to the first combustion cylinder after the restart condition is satisfied when the measured stop time has exceeded a predetermined value. The fuel injection valve is controlled so as to execute injection. In this aspect, even when the cylinder is diluted by a long-term automatic stop, it is possible to reliably ensure the combustion energy for restart and to secure the reverse rotation torque at the time of restart.

In a preferred embodiment, the first combustion cylinder is a compression stroke cylinder that is ignited to temporarily reverse the multi-cylinder engine that has been automatically stopped, and the fuel injection control means has a top dead center when the engine passes the top dead center. When it is estimated that the compression stroke cylinder stops at the bottom dead center side from the predetermined crank angle range when the multi-cylinder engine is automatically stopped based on the point rotation speed and the boost pressure , The fuel injection valve is controlled so that additional fuel is injected during the stop control. In this aspect, in the reverse rotation start method, in the compression stroke cylinder as the initial combustion cylinder estimated by the cylinder stop position control means, the in-cylinder pressure decreases due to cooling by the vaporization latent heat of the fuel injected in the compression stroke, It is possible to finely adjust the piston stop position from the middle of the operation stroke toward the top dead center. As a result, the cylinder volume of the expansion stroke cylinder in the automatic stop state can be controlled to be larger than the cylinder volume of the compression stroke cylinder in the automatic stop state.

  As described above, according to the present invention, the fuel injected into the initial combustion cylinder during the automatic stop control under a predetermined condition is vaporized and atomized, thereby homogenizing the air-fuel mixture in the initial combustion cylinder. Therefore, rapid combustion at the time of restart can be prevented and kinetic energy due to slow combustion can be ensured, so that sufficient kinetic energy to exceed the second compression stroke can be obtained. As a result, it is possible to ensure that the engine can be restarted as much as possible only by the combustion of the air-fuel mixture due to the slow combustion in the first combustion cylinder.

  1 and 2 show a schematic configuration of a four-cycle spark ignition engine 1 according to the present invention. The engine 1 has a cylinder head 10 and a cylinder block 11 and is configured to be controlled by the ECU 2. The engine 1 is provided with four cylinders (a first cylinder 12A, a second cylinder 12B, a third cylinder 12C, and a fourth cylinder 12D), and is connected to the crankshaft 3 inside each cylinder 12A to 12D. By inserting the inserted piston 13, a combustion chamber 14 is formed above the piston 13.

  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 such that the plug tip faces the combustion chamber 14. The ignition plug 15 is provided with an ignition device 27 for generating an electric spark. Further, the engine 1 is provided with a fuel supply system 16 that is disposed on the side of the combustion chamber 14 and includes a fuel injection valve 16 a that directly injects fuel into the combustion chamber 14. The fuel supply system 16 is provided with an electric high-pressure pump (not shown). The fuel in the fuel tank discharged from the electric high-pressure pump is injected into the fuel injection valve 16a through a distribution pipe. Yes. The electric high-pressure pump is configured so that the fuel pressure can be adjusted by the ECU 2 according to the operating state of the engine 1, for example, in a range from 3 MPa to 13 MPa. As the fuel supply system, for example, an equivalent one disclosed in Japanese Patent Application Laid-Open No. 2002-242738 previously proposed by the applicant of the present application can be applied. To do.

  The fuel injection valve 16a 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 fuel injection control unit 41 of the ECU 2. The valve opening time The fuel corresponding to the amount is injected toward the vicinity of the electrode of the spark plug 15.

  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 valve 20 are connected to the ports 17 and 18, respectively. Are equipped. The intake valve 19 and the exhaust valve 20 are driven by a valve mechanism having a camshaft or the like (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 and 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 a throttle valve 23 driven by an actuator 24 is provided in the common intake passage 21c. An upstream side of the throttle valve 23 is provided with an air flow sensor 25 for detecting the intake air flow rate, an intake air temperature sensor 29 for detecting the temperature of the intake air, and an atmospheric pressure sensor SW1 for detecting the air density in the atmosphere. An intake pressure sensor 26 for detecting intake pressure (negative pressure) is provided on the downstream side.

  On the other hand, a catalyst 37 for purifying the exhaust is disposed downstream of the collection portion of the exhaust passage 22 where exhaust from each of the cylinders 12A to 12D collects. This catalyst 37 is, 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 state of the exhaust is in the vicinity of the theoretical air-fuel ratio, and this is a relatively high oxygen concentration in the exhaust. It has an oxygen storage capacity for storing it in a high oxygen excess atmosphere. When the oxygen concentration is relatively low, the stored oxygen is released and reacted with HC, CO and the like. The catalyst 37 is not limited to a three-way catalyst, and may be any catalyst as long as it has an oxygen storage capacity as described above. For example, the catalyst 37 may be a so-called lean NOx catalyst that can purify NOx even in an oxygen-excess atmosphere.

  In FIG. 2, reference numeral 38 denotes an exhaust gas recirculation passage for recirculating the exhaust gas led out to the exhaust passage 22 to the intake air passage 21. The exhaust gas recirculation passage 38 has an EGR valve 39 for adjusting the recirculation amount of the exhaust gas. Is provided.

  The engine 1 is also provided with an alternator 28 connected to the crankshaft 3 by a timing belt or the like. The alternator 28 includes a regulator circuit 28a for adjusting the amount of power generation by controlling the current of a field coil (not shown) and adjusting the output voltage, and the control signal from the ECU 2 input to the regulator circuit 28a. Based on the above, control of the amount of power generation corresponding to the electric load of the vehicle, the voltage of the on-vehicle battery, and the like is executed.

  Further, the engine 1 is provided with two crank angle sensors 30 and 31 for detecting the rotation angle of the crankshaft 3, and the engine rotation speed Ne is detected based on a detection signal output from one crank angle sensor 30. In addition, as will be described later, the rotation direction and the rotation angle of the crankshaft 3 are detected based on detection signals out of phase output from the crank angle sensors 30 and 31.

  Further, the engine 1 is provided with a cam angle sensor 32 that detects a specific rotational position for cylinder identification provided on the camshaft, and a water temperature sensor 33 that detects the cooling water temperature of the engine 1. Is provided with an accelerator opening sensor 34 for detecting the accelerator opening corresponding to the accelerator operation amount of the driver.

  The ECU 2 is a control unit that comprehensively controls the operation of the engine 1. The ECU 2 according to the present embodiment automatically stops the engine 1 by stopping fuel injection to each cylinder 12A to 12D at a predetermined timing (fuel cut) when a preset automatic stop condition of the engine 1 is satisfied. In addition, the engine 1 is configured to perform control (idle stop control) that automatically restarts the engine 1 when a restart condition is satisfied, for example, when the driver performs an accelerator operation. Hereinafter, in the description of the ECU 2, the portion related to the idle stop control will be mainly described.

  The ECU 2 includes detection signals from an air flow sensor 25, an intake pressure sensor 26, an intake temperature sensor 29, crank angle sensors 30, 31, a cam angle sensor 32, a water temperature sensor 33, an accelerator opening sensor 34, and an atmospheric pressure sensor SW1. Are input to the fuel supply system 16 (fuel injection valve 16a), the actuator 24 of the throttle valve 23, the ignition device 27, and the regulator circuit 28a of the alternator 28, respectively. The ECU 2 includes a fuel injection control unit 41, an ignition control unit 42, an intake air flow rate control unit 43, a power generation amount control unit 44, a piston position detection unit 45, an in-cylinder temperature estimation unit 46, an air density estimation unit 47, and an exhaust gas recirculation control unit. 48 is functionally included.

  The fuel injection control unit 41 is a fuel injection control unit that sets fuel injection timing, a fuel injection amount in each injection, and a fuel pressure, and outputs a signal to the fuel supply system 16. In particular, in the present embodiment, as will be described later, fuel for the first combustion in the expansion stroke cylinder at the time of restart is supplied by split injection. The fuel injection control unit 41 also performs setting of the divided injection timing and fuel distribution.

  The ignition control unit 42 sets an appropriate ignition timing for each of the cylinders 12 </ b> A to 12 </ b> D and outputs an ignition signal to each ignition device 27.

  The intake flow rate control unit 43 sets an appropriate intake flow rate for each of the cylinders 12 </ b> A to 12 </ b> D, and outputs an opening degree signal of the throttle valve 23 corresponding to the intake flow rate to the actuator 24. In particular, in this embodiment, as will be described later, the opening degree of the throttle valve 23 is adjusted when the engine 1 is automatically stopped, and control is performed so that the piston 13 stops in an appropriate stop range suitable for restart. The intake flow rate control unit 43 also adjusts the opening of the throttle valve 23 at that time.

  The power generation amount control unit 44 sets an appropriate power generation amount of the alternator 28 and outputs the drive signal to the regulator circuit 28a. In particular, in this embodiment, as will be described later, the load on the crankshaft 3 is changed by adjusting the power generation amount of the alternator 28 when the engine 1 is automatically stopped, and the piston 13 is stopped in an appropriate range suitable for restart. Control is in progress. At that time, the power generation amount control unit 44 also adjusts the power generation amount of the alternator 28. Further, at the time of restart, control is performed to increase the load of the engine 1 by generating more power than usual and to prevent the engine from blowing up (an increase in engine speed that is more rapid than necessary).

  The piston position detector 45 detects the piston position based on the detection signals of the crank angle sensors 30 and 31. Since the piston position and the crank angle (° CA) have a one-to-one correspondence, the piston position is represented by the crank angle in this specification as is generally done. In this embodiment, as will be described later, the in-cylinder air amount is calculated based on the piston positions during the automatic stop of the expansion stroke cylinder and the compression stroke cylinder, and the combustion control of each cylinder at the time of restart is performed accordingly. Yes.

  The in-cylinder temperature estimator 46 uses a map obtained by experiments in advance based on the engine 1 water temperature detected by the water temperature sensor 33, the intake air temperature detected by the intake air temperature sensor 29, and the like. In-cylinder temperature estimation means for estimating the air temperature in the cylinders 12A to 12D. In particular, in the present embodiment, as will be described later, in-cylinder temperature estimation is performed in consideration of the stop time of the engine 1 when the engine 1 is restarted, and combustion control is performed based on the estimated value.

  The air density estimation unit 47 estimates the air density of the atmosphere from the outputs of the intake air temperature sensor 29 and the atmospheric pressure sensor SW1, and outputs a fuel injection timing parameter when the engine 1 is automatically controlled.

  The exhaust gas recirculation controller 48 is for driving the EGR valve 39 to open and close the exhaust gas recirculation passage 38.

  In performing the idle stop control by the ECU 2 having the above-described configuration, when the engine 1 is restarted, the combustion is first performed in the compression stroke cylinder, so that the piston 13 is pushed down to slightly reverse the crankshaft 3. As a result, the piston 13 of the expansion stroke cylinder is once raised (closed to top dead center), and the air-fuel mixture (which becomes the air-fuel mixture after fuel injection) is compressed and ignited and burned. Accordingly, the engine 1 is restarted by applying a driving torque in the forward rotation direction to the crankshaft 3.

  In order to properly restart the engine 1 simply by igniting the fuel injected into a specific cylinder without using a restart motor or the like as described above, the air-fuel mixture in the expansion stroke cylinder is burned. By sufficiently securing the combustion energy obtained in this way, the cylinder that reaches the compression top dead center (in this embodiment, the compression stroke cylinder and the intake stroke cylinder) overcomes the compression reaction force, and the top dead center is reached. It must be exceeded. Therefore, it is necessary to secure a sufficient amount of air in the expansion stroke cylinder, and to realize rapid combustion to speed up the conversion from thermal energy to kinetic energy.

  As shown in FIGS. 3A and 3B, since the phases of the compression stroke cylinder and the expansion stroke cylinder are shifted by 180 ° CA, the pistons 13 operate in opposite directions. 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 the crankshaft 3 is reversed in the initial combustion at the time of restart. Insufficient combustion energy can be obtained.

  On the other hand, a predetermined range R slightly lower than the center of the expansion stroke cylinder, that is, a position where the crank angle after compression top dead center is 90 ° CA, for example, the crank angle after compression top dead center is If the piston 13 can be stopped within a range R of 100 to 120 ° CA, a predetermined amount of air is ensured in the compression stroke cylinder, and the combustion is such that the crankshaft 3 can be slightly reversed by the initial combustion. Energy will 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 to reliably restart the engine 1 (hereinafter referred to as “this”). The range R is set as the appropriate stop range R).

  Therefore, the ECU 2 performs the following control to stop the piston 13 within the proper stop range R.

  FIG. 4 is a time chart when the engine is automatically stopped by this control, and shows the engine speed Ne, the boost pressure Bt (intake pressure), and the opening degree K of the throttle valve 23. FIG. 5 is an enlarged view after the vicinity of time t1 in FIG. 4, and shows a crank angle CA and a stroke transition chart of each cylinder in addition to FIG.

  Hereinafter, for the sake of brevity, it is assumed that the first cylinder 12A is an expansion stroke cylinder, the second cylinder 12B is an exhaust stroke cylinder, the third cylinder 12C is a compression stroke cylinder, and the fourth cylinder 12D is an intake stroke cylinder.

  FIG. 7 is an explanatory diagram showing the output signal of the crank angle signal, and FIG. 8 is a graph showing the relationship between the elapsed time from the engine automatic stop and the estimated in-cylinder temperature.

  The ECU 2 sets the target speed of the engine 1 to the normal idle speed when the engine 1 is not automatically stopped when the flag is ON at the time t0 when the automatic stop condition of the engine 1 is satisfied, that is, in step S1 of FIG. In the engine 1 in which a value higher than (hereinafter, referred to as a normal idle speed), for example, a normal idle speed is set to 650 rpm (the automatic transmission is in the drive (D) range), the target speed (when the automatic stop condition is satisfied) is set. Is set to about 850 rpm (the automatic transmission is in the neutral (N) range), so that the engine rotational speed Ne is stabilized at a rotational speed slightly higher than the normal idle rotational speed. Further, the opening K of the throttle valve 23 is adjusted so that the boost pressure Bt is stabilized at a relatively high predetermined value (about −400 mmHg).

  Then, the fuel injection is stopped at the time t1 when the engine speed Ne is stabilized at the target speed, and the engine speed Ne is decreased. Also, at the time of idling when the opening degree K of the throttle valve 23 is set to the excess air ratio λ = 1 in the cylinder at the fuel injection stop time t1, which is the initial stage of the control operation for automatically stopping the engine 1. The intake air flow rate is set to be larger than the intake air flow rate (minimum intake air flow rate necessary for continuing the operation of the engine 1). That is, when the combustion state immediately before the time t1 is set to an in-cylinder air-fuel ratio in the vicinity of the excess air ratio λ = 1 to near λ = 1 and homogeneous combustion is performed, the opening K of the throttle valve 23 is increased (for example, When the air-fuel ratio in the cylinder is set to lean and stratified combustion is performed, the opening K of the throttle valve 23 is maintained as it is (the relatively large opening during stratified combustion). . 4 and 5 show the former case.

  As a result of this control, the boost pressure Bt starts to increase slightly after time t1 (if the combustion just before time t1 is homogeneous combustion) or maintains a relatively high boost pressure Bt (if the time just before time t1 is stratified combustion) Exhaust gas scavenging is facilitated.

  Further, the ECU 2 temporarily stops the power generation of the alternator 28 at time t1. This reduces the rotational resistance of the crankshaft 3 so that the engine rotational speed Ne does not decrease too quickly.

  Thus, when combustion injection is stopped at time t1, the engine rotational speed Ne starts to decrease, and the throttle valve 23 is closed at time t2 when it is confirmed that the engine speed has become a preset reference speed, for example, 760 rpm or less. Then, the boost pressure Bt starts to decrease slightly after time t2, and the intake flow rate sucked into each cylinder of the engine 1 decreases. Air sucked between time t1 and time t2 when the throttle valve 23 is opened is guided to the branch intake passage 21a of each cylinder via the common intake passage 21c and the surge tank 21b. Then, the air is sucked in order from the cylinder that has reached the intake stroke. In the case shown in FIG. 5, the order is the fourth cylinder 12D, the second cylinder 12B, the first cylinder 12A, and the third cylinder 12C. Here, by setting the time point t1 and the time point t2 as described above, the first cylinder 12A (expansion stroke cylinder) sucks more air than the third cylinder 12C (compression stroke cylinder). become.

  Since the engine 1 rotates inertially after the time point t1, the engine rotational speed Ne gradually decreases and eventually stops at the time point t5. The decrease in the engine rotational speed Ne is small in increments as shown in FIGS. It goes down while repeating ups and downs (around 10 times for a 4 cylinder 4 cycle engine).

  In the time chart of the crank angle CA shown in FIG. 5, the solid line indicates the crank angle when the top dead center (TDC) of the first cylinder 12A and the fourth cylinder 12D is 0 ° CA, and the alternate long and short dash line indicates the second cylinder 12B. The crank angle when the top dead center of the third cylinder 12C is 0 ° CA is shown. The solid line and the alternate long and short dash line are in opposite phases with respect to 90 ° CA. In the four-cylinder four-cycle engine 1, any cylinder reaches compression top dead center every 180 ° CA. Therefore, this time chart is shown at the top of the waveform (crank angle = 0 ° CA) indicated by a solid line or a one-dot chain line. It shows that any cylinder passes the compression top dead center.

  The timing at which any one of these cylinders becomes the compression top dead center coincides with the timing of the up-down valley of the engine rotation speed Ne. In other words, the engine rotational speed Ne gradually decreases every time each cylinder reaches compression top dead center, and then gradually rises and falls again when the compression top dead center is exceeded. To do.

  In the compression stroke cylinder 12C that reaches the compression top dead center after the time t4 when the last compression top dead center is passed, the air pressure increases as the piston 13 rises due to the inertial force, and the piston 13 is top dead due to the compression reaction force. The crankshaft 3 is reversely pushed back without exceeding the point. Since the air pressure of the expansion stroke cylinder 12A increases due to the reverse rotation of the crankshaft 3, the piston 13 of the expansion stroke cylinder 12A is pushed back to the bottom dead center side according to the compression reaction force, and the crankshaft 3 rotates forward again. First, the reverse rotation and forward rotation of the crankshaft 3 are repeated several times, and the piston 13 stops after reciprocating. The stop position of the piston 13 is substantially determined by the balance of the compression reaction force in the compression stroke cylinder 12C and the expansion stroke cylinder 12A, and is influenced by the intake resistance of the intake stroke cylinder 12D, the friction of the engine 1, and the like. This also changes depending on the rotational inertia of the engine 1 at the time t4 when the compression top dead center is exceeded, that is, the engine rotational speed Ne.

  Therefore, in order to stop the piston 13 of the expansion stroke cylinder 12A within the proper stop range R, first, the compression reaction forces of the expansion stroke cylinder 12A and the compression stroke cylinder 12C are sufficiently increased, and the compression of the expansion stroke cylinder 12A is performed. It is necessary to adjust the intake air flow rates for both cylinders so that the reaction force is greater than the compression reaction force of the compression stroke cylinder 12C by a predetermined value or more. For this purpose, the throttle valve 23 is opened at the fuel injection stop time t1 and its opening K is increased so that a predetermined amount of air is sucked into both the expansion stroke cylinder 12A and the compression stroke cylinder 12C. The intake air amount is adjusted by closing the throttle valve 23 and reducing its opening K at time t2 when the time has elapsed.

  By the way, in the process in which the engine 1 is automatically stopped in this way and the engine rotational speed decreases, the engine rotational speed (top dead center rotational speed) ne when each of the cylinders 12A to 12D passes through the compression top dead center, There is a clear correlation with the piston stop position of the expansion stroke cylinder 12A. That is, the piston stop position of the expansion stroke cylinder 12A is in the proper stop range when the top dead center rotational speed ne in each stage (second, third, fourth from the stop) is within a certain speed range. The probability of being in R increases.

  Using this characteristic, in this embodiment, the top dead center rotational speed ne in a predetermined stage in the process of decreasing the engine rotational speed Ne (especially the second before the stop (time point t3)) is within a certain speed range. Such control is performed so that the piston 13 of the expansion stroke cylinder 12A is more reliably stopped within the proper stop range R. Specifically, the load (engine load) of the crankshaft 3 is adjusted by increasing or decreasing the power generation amount of the alternator 28, and the second top dead center rotational speed ne (time point t3) from before the stop is 350 ± 50 rpm. It is within the range.

  When the engine speed Ne further decreases and the final compression top dead center passage timing (time point t4 shown in FIG. 5) is passed, none of the cylinders passes through the top dead center, and the stroke is not changed. The piston 13 tries to stop within the target proper stop range R while performing damped vibration (when the piston 13 moves in the opposite direction, the crankshaft 3 reverses and the engine rotational speed Ne becomes negative) within the stroke. However, at this time, the intake stroke cylinder 12D performs an intake operation, and if the intake resistance is large, the stop position of the piston 13 tends to vary. In particular, since the intake resistance acts so as to increase when the piston 13 moves toward the bottom dead center, the piston 13 tends to stop closer to the top dead center than the target. Since the piston 13 of the intake stroke cylinder 12D and the piston 13 of the expansion stroke cylinder 12A move in the same phase, the piston 13 of the expansion stroke cylinder 12A tends to stop near the top dead center rather than the target.

  Therefore, in this embodiment, the opening degree K of the throttle valve 23 is increased to the opening degree K1 shown in FIG. 5 (for example, about K1 = 40%) almost simultaneously with the time point t4 (may be slightly delayed), and the intake stroke cylinder 12D. The intake resistance is reduced. This makes it easier for the piston 13 to stop at a target position corresponding to the balance without affecting the intake flow rate balance in the expansion stroke cylinder 12A and the compression stroke cylinder 12C.

  In order to perform such control, it is necessary to immediately determine that the time t4 is the last compression top dead center passage timing, and the next compression top dead center (in the compression stroke cylinder 12C) is It must be predicted at time t4 that it will not pass. Therefore, in the present embodiment, the ECU 2 determines the last top dead center passage timing. The ECU 2 compares the engine rotation speed when passing through each top dead center with a predetermined rotation speed (for example, 260 rpm) obtained in advance through experiments or the like, and when the former becomes equal to or lower than the latter, It is determined that it is the top dead center passage timing. The higher the top dead center rotational speed ne at the final compression top dead center passage timing, the closer to the latter stage of the stroke (the piston stop position of the expansion stroke cylinder 12A is closer to the bottom dead center, and closer to the top dead center in the compression stroke cylinder 12C). It becomes easy to stop.

  Incidentally, the intake flow rate balance in the final intake stroke of the expansion stroke cylinder 12A and the compression stroke cylinder 12C immediately before the engine is automatically stopped is also affected by the boost pressure Bt. In particular, the second compression top dead center passage timing (time point t3 in FIG. 5) from before the stop is the start point of the final intake stroke in the compression stroke cylinder 12C, and the influence of the boost pressure Bt at this point is large. That is, when the boost pressure Bt is low (vacuum side), the intake flow rate to the compression stroke cylinder 12C decreases, and as a result, the stop position of the piston 13 of the compression stroke cylinder 12C is close to top dead center (in the expansion stroke cylinder 12A). It tends to be near the bottom dead center). The reverse is true when the boost pressure Bt is high (atmospheric pressure side).

  Therefore, when the top dead center rotational speed ne at the last top dead center passage timing is high and the boost pressure Bt at the second compression top dead center passage timing before the stop is low, the piston 13 of the expansion stroke cylinder 12A is in the stroke. Conditions that are likely to stop at the later stage overlap, and there is a high possibility of stopping at the target stop position (100 to 120 ° CA after top dead center). Under such conditions, if the control is performed to increase the opening of the throttle valve 23 to K1 at the time t3, the piston stop position may be closer to the end of the stroke, and may be deviated from the target stop position. is there. Therefore, in this embodiment, in such a case, the opening degree of the throttle valve 23 at the time point t3 is set to an opening degree K2 (see FIG. 5) that is lower (or closed) than K1. By suppressing the increase, the piston stop position of the expansion stroke cylinder 12A is prevented from becoming too close to the bottom dead center.

  Thus, the piston 13 is completely stopped at the time point t5. By detecting the operation of the piston 13 immediately before the stop by the crank angle sensors 30 and 31, the piston position detection unit 45 of the ECU 2 detects the stop position of the piston 13. Is detected. FIG. 6 is a flowchart showing the detection control operation of the piston stop position. When this detection control starts, based on the first crank angle signal CA1 (signal from the crank angle sensor 30) and the second crank angle signal CA2 (signal from the crank angle sensor 31), when the first crank angle signal CA1 rises. It is determined whether or not the second crank angle signal CA2 is low, or whether or not the second crank angle signal CA2 is high when the first crank angle signal CA1 falls (step S41). Thus, the engine 1 determines whether the phase relationship between the signals CA1 and CA2 during the stop operation of the engine 1 is as shown in FIG. 7A or 7B. It is determined whether the vehicle is in the normal rotation state or the reverse rotation state.

  That is, during forward rotation of the engine 1, as shown in FIG. 7A, the second crank angle signal CA2 is generated with a phase delay of about a half pulse width with respect to the first crank angle signal CA1, so that the first crank angle The second crank angle signal CA2 is low when the signal CA1 rises, and the second crank angle signal CA2 is high when the first crank angle signal CA1 falls. On the other hand, at the time of reverse rotation of the engine 1, as shown in FIG. 7B, the second crank angle signal CA2 is generated with a phase advance of about a half pulse width with respect to the first crank angle signal CA1, thereby Contrary to the rotation, the second crank angle signal CA2 becomes High when the first crank angle signal CA1 rises, and the second crank angle signal CA2 becomes Low when the first crank angle signal CA1 falls.

  Therefore, if the determination in step S41 is YES, the CA counter for measuring the crank angle change in the forward rotation direction of the engine 1 is increased (step S42). If the determination in step S41 is NO, the CA counter (Step S43). Then, after the engine is automatically stopped, the piston stop position is obtained by examining the measured value of the CA counter (step S44).

  When the engine 1 is completely stopped, the in-cylinder temperatures of the cylinders 12A to 12D change as shown in the temperature characteristics of FIG. FIG. 8 is a graph showing the relationship between the elapsed time from the engine automatic stop and the in-cylinder temperature, and the estimation of the in-cylinder temperature change when the in-cylinder temperature at the time of the engine automatic stop (time t5) is 80 ° C. Value.

As shown in this characteristic, when the engine 1 is completely stopped, the flow of the cooling water is stopped, so that the in-cylinder temperature rapidly rises immediately after the stop. Then, it peaks at about 10 seconds after the engine stops automatically, and then gradually decreases. This characteristic varies depending on the temperature of the cooling water (engine water temperature), the outside air temperature (intake air temperature), and the like, and the in-cylinder temperature estimation unit 46 of the ECU 2 stores data in which the characteristic is mapped. Regarding the initial combustion cylinder (the compression stroke cylinder 12C in the case of the reverse rotation restart method and the expansion stroke cylinder 12A in the case of the forward rotation restart method), fuel is injected after timing t3 in a predetermined case. Therefore, in this case, the characteristic of _T12C is taken, and such a characteristic is stored in the control map corresponding to this graph.

  Note that scavenging is promoted by increasing the opening K of the throttle valve 23 during the automatic engine stop operation period, so that a sufficient amount of fresh air is supplied to the catalyst 37. Therefore, the oxygen storage amount of the catalyst 37 is sufficiently large during the automatic engine stop.

  Next, control when the engine 1 is restarted will be described. When restarting, the combustion is first performed in the compression stroke cylinder 12C as described above, and the engine 1 is once reversely rotated, and then the combustion is performed in the expansion stroke cylinder 12A, so that the forward rotation direction is changed. That is, once the engine 1 is reversely rotated, the piston 13 of the expansion stroke cylinder 12A is raised, and after the compression pressure is increased, combustion in the cylinder is performed. When the piston stop position of the expansion stroke cylinder 12A is within the proper stop range R and a sufficient amount of air for combustion is secured, and the air is compressed by the reverse rotation of the engine 1, large combustion energy is obtained. It is done. That is, the engine 1 can be reliably rotated in the forward direction and smoothly shifted to the subsequent continuous operation.

  However, the presence of sufficient air in the expansion stroke cylinder 12A hinders strong compression of the air. This is because the compression reaction force of the compressed air acts in the direction of pushing back the piston 13 of the expansion stroke cylinder 12A.

  Therefore, in the present embodiment, control is performed to increase the compression amount (increase the density) of the air in the expansion stroke cylinder 12A by delaying the fuel injection timing to the expansion stroke cylinder 12A. When the fuel injection timing is delayed, the fuel is injected into the cylinder in which the cylinder air is compressed to some extent, and the compression pressure is reduced by the latent heat of vaporization. Therefore, if the energy of the reverse rotation of the engine 1 is the same, the piston 13 can move closer to the top dead center (increase in piston stroke), and the density of compressed air can be further increased.

  The control operation when the engine 1 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 starts, it is determined whether or not an automatic stop permission flag indicating whether or not the engine 1 is in an operation state in which automatic stop control can be executed is ON (step S1). This automatic stop permission flag is satisfied when 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 addition, it is determined that the automatic stop control of the engine 1 can be executed, and the ON state is set.

  If YES is determined in step S1, it is determined whether or not the accelerator opening sensor 34 is in an OFF state (step S2), and YES is determined and the vehicle is in a predetermined deceleration state. If so, it is determined whether or not the brake is further depressed (step S3). In the present embodiment, the process proceeds to the next step S4 only when both the determinations of steps S2 and S3 are YES, and in other cases, the process returns to step S2 to substantially satisfy the automatic stop condition. Wait to do.

  When steps S2 and S3 are both established, it is determined whether or not the engine rotational speed Ne is larger than a determination reference value FC • ON for determination of fuel cut execution during deceleration that is set to about 1100 rpm in advance (step S4). ) If YES, the fuel cut during deceleration is executed (step S5). Next, it is determined whether or not the engine rotational speed Ne has decreased to a fuel recovery determination reference value F / C · OFF that is set to about 900 rpm in advance (step S6). When it is determined YES, The fuel cut (FC) at the time of deceleration is terminated and the normal fuel injection state is restored (step S7), and the process proceeds to step S8. On the other hand, when it is determined in step S4 that the engine rotational speed Ne is equal to or less than the determination reference value FC · ON for deceleration fuel cut execution determination, the fuel cut control (steps S5 to S7) is bypassed, Immediately the process proceeds to step S8.

  In step S8, it is determined whether or not the air-fuel ratio in each of the cylinders 12A to 12D is currently set to a lean combustion state in which the air-fuel ratio is set to a value considerably larger than the stoichiometric air-fuel ratio, that is, an operation state of stratified lean combustion. Is determined, the target rotational speed of the engine 1 is set to a value higher than the normal idle rotational speed (about 650 rpm) by a predetermined amount, for example, about 750 rpm, and this speed is maintained (step S9). . If it is determined NO in step S7 and it is confirmed that the air-fuel ratio in the cylinder is in a uniform combustion operation state in which the air-fuel ratio in the cylinder is set at or near the stoichiometric air-fuel ratio, the target rotation of the engine 1 is The speed is set to a value higher than 750 rpm, for example, about 800 rpm, and this speed is maintained (step S10).

  Thereafter, it is determined again at this point whether the accelerator opening sensor 34 is OFF and the brake sensor 35 is ON (steps S11 and S12). If both are determined to be YES If the accelerator position sensor 34 is ON or the brake sensor 35 is OFF, the process returns to step S1 to repeat the control operation.

  Referring to FIG. 10, when the accelerator opening sensor 34 is OFF and the brake sensor 35 is ON, whether the vehicle speed is 0, that is, whether the vehicle has stopped. Is determined (step S20).

  If it is determined YES in step S20 and it is confirmed that the vehicle is stopped, the combustion state in which the air-fuel ratio in the cylinders 12A to 12D is leaner than the stoichiometric air-fuel ratio at this time t0, that is, the stratified combustion state (Step S21). If it is determined YES and it is confirmed that the engine 1 is currently in the stratified lean combustion operation state, the target rotational speed N1 of the engine 1 is The EGR valve provided in the exhaust gas recirculation passage 38 is set to a value higher by a predetermined amount than the idle rotation speed (650 rpm), for example, about 810 rpm (step S22), and the scavenging performance of each of the cylinders 12A to 12D is improved. 39 is closed to stop the exhaust gas recirculation (step S23).

  On the other hand, when it is determined NO in step S21 and it is confirmed that the engine 1 is not in the stratified lean combustion operation state, for example, in order to lower the catalyst temperature or refresh the NOx catalyst, When it is confirmed that the fuel ratio is in the uniform combustion state set at the stoichiometric air fuel ratio or near the stoichiometric air fuel ratio, the target rotational speed N1 of the engine 1 is set to a value higher than the above 810 rpm, for example, about 860 rpm. (Step S24) And the throttle valve 23 is operated in the valve opening direction, and the opening degree K of the throttle valve 23 is feedback-controlled so that the boost pressure Bt becomes the target pressure P1 set to, for example, about -400 mmHg (Step S25). ).

  When Steps S22 to S23 or Steps S24 to S25 are completed, the ECU 2 sets the shift range of the automatic transmission to neutral and sets it to a no-load state (Step S26).

  As described above, it is confirmed in step S1 that the vehicle speed is higher than 10 km / h and the automatic stop permission flag of the engine 1 is in the ON state, and 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 control is performed to stabilize the target rotational speed N1 of the engine 1 as a predetermined value corresponding to the combustion state of the engine 1. The automatic stop control of the engine 1 can be executed before the engine speed decreases to the idle rotation speed (650 rpm). Therefore, the driver feels uncomfortable with the increase in the engine rotational speed Ne as in the case where the engine rotational speed Ne once decreased to the normal idle rotational speed is increased to the target rotational speed N1. It is possible to prevent the occurrence of a bad effect such as the time until the engine 1 is automatically stopped or the time until the engine 1 is automatically stopped longer than necessary.

  Further, as described above, when the amount of air introduced into each cylinder 12A to 12D is large and the cylinder 12A to 12D is in a stratified lean combustion state in which the scavenging performance of each cylinder 12A to 12D can be sufficiently ensured, each cylinder 12A to 12D. The target rotational speed N1 is set to a lower value than in a uniform combustion state in which the amount of air introduced into the cylinder is small and it is difficult to sufficiently secure the scavenging performance of the cylinders 12A to 12D. As a result, while scavenging performance is ensured in the stratified lean combustion state, adverse effects such as deterioration of fuel consumption and generation of unpleasant combustion noise occur due to the engine rotational speed Ne becoming higher than necessary. There is an advantage that can be prevented.

  Further, at the time t0 when the vehicle speed is determined to be 0 in step S20, the target rotational speed N1 of the engine 1 is set to a predetermined value in steps S22 and S24, and the automatic transmission shift is performed in step S26. Since the load of the automatic transmission is reduced by shifting the range from the drive state (D range) to the neutral state (N range), as shown in FIG. Will rise slightly from the time t0 established.

  Next, it is determined whether or not a predetermined time set in advance in about 1 sec has elapsed after time t0 when it is determined as YES in Step S29 and it is confirmed that the automatic stop condition of the engine 1 is satisfied (Step S29). S27). If it is determined NO in step S27, this determination operation is repeated, and if it is determined YES, whether or not the fuel injection stop condition (FC condition) is satisfied, specifically, the engine speed. It is determined whether Ne is the target rotational speed N1 and whether the boost pressure Bt is stable in a state where the target pressure P1 is reached (step S28). When the accelerator opening sensor 34 is turned off or the brake sensor 35 is turned on during the determination operation, the process returns without stopping the fuel injection. Thereby, it is possible to prevent an inappropriate automatic stop of the engine 1 from being performed when the vehicle state is shifted to the traveling state immediately after the vehicle speed becomes zero.

  Then, when it is determined YES in step S28 and it is confirmed that the engine speed Ne and the boost pressure Bt are in a stable state (time t1 in FIGS. 4 and 5), the fuel injection is stopped. After (step S29), the target power generation current Ge of the alternator 28 is set to 0A to stop power generation (step S30), and the throttle valve 23 is opened to set its opening K to about 30%, for example. (Step S31).

  Referring to FIG. 11, thereafter, whether or not a predetermined time has elapsed from time t1 when the fuel injection is stopped in step S29, that is, before the fuel injection is stopped, before two compression top dead centers are reached. It is determined whether or not the combustion of the injected fuel has been completed (step S32), and when the determination is YES, the ignition by the ignition device 27 is stopped (step S33). Next, by determining whether or not the engine rotational speed Ne has become equal to or less than the reference speed N2 set to about 760 rpm in advance, the engine rotational speed Ne starts to decrease after the fuel injection stop time t1 shown in FIG. (Step S34), and when it is determined YES, the throttle valve 23 is closed and the opening degree K is set to 0% (step S35). 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 S31 starts to decrease with a predetermined time difference according to 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 S36). Note that the top dead center of the engine 1 is replaced with the above embodiment in which the throttle valve 23 is closed at the time t2 when it is determined in step S34 that the engine rotational speed Ne is equal to or lower than the reference speed N2. For example, when it is determined that the rotational speed ne is equal to or lower than the reference speed N2 set to about 760 rpm, for example, 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 top dead center rotational speed ne of the engine 1 is within a first predetermined range (step S37). This first predetermined range is, for example, a time point t3 when the engine 1 passes through the fourth compression top dead center before the engine 1 is stopped in the process in which the engine rotational speed Ne decreases along the preset reference line. Is a value set based on the top dead center rotational speed ne, and specifically, is set within the range of 480 rpm to 540 rpm.

  When it is determined YES in step S37 and it is confirmed that the top dead center rotational speed ne of the engine 1 is within the predetermined range (480 rpm to 540 rpm), the top dead center rotational speed ne at that time t3 is set. The target generated current Ge of the corresponding alternator 28 is set (step S38). That is, as the top dead center rotational speed ne of the engine 1 is higher, the target generated current Ge corresponding to the top dead center rotational speed ne is read from the map M1 in which the target generated current Ge is set to a larger value, and 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 top dead center rotational speed ne of the engine 1 is within a second predetermined range set based on the top dead center rotational speed ne at the time t3 when the second compression top dead center before the engine automatic stop is passed, for example, It is determined whether it is within the range of 260 rpm to 400 rpm (step S39).

Referring to FIG. 12, if it is determined as YES in step S39, ECU 2 determines whether the air density is less than a predetermined value (step S50). In this determination, for example, when the automatic stop control is executed at a high altitude (1500 m in Japan, 1800 m or more in EU countries), the combustion at the time of restart becomes too rapid, so the startability is deteriorated. Since there is a case, in order to change the fuel injection timing according to the air density, the determination is made at this time. For example, when the air density is 1.08 kg / m ³ , in the present embodiment, the fuel injection map M2 in which the fuel injection amount is set to a larger value as the top dead center rotational speed ne of the engine 1 is higher based on the experiment. Based on the above, restart fuel is injected into the compression stroke cylinder 12C in the intake stroke (between time points t3 and t4 shown in FIG. 4) (step S51). As a result, the restart fuel is vaporized and atomized in the compression stroke cylinder 12C, and a homogeneous air-fuel mixture is generated during the automatic stop period. Further, the fuel injected into the cylinder 12C is vaporized, so that the temperature in the cylinder is lowered.

  And it is determined whether the top dead center rotational speed ne of the engine 1 is below predetermined value N3 (step S52). 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. It is set to about 260 rpm. Further, the boost pressure Bt at each time point when each of the cylinders 12A to 12C sequentially passes the compression top dead center is detected, and the value is stored.

  When it is determined YES in step S52 and it is confirmed that the top dead center rotational speed ne of the engine 1 has become the predetermined value N3 or less, that is, the engine 1 has passed the last compression top dead center. At this time t5, the boost pressure Bt when 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 the engine automatic stop. (Step S53).

  The top dead center rotational speed ne at the time t5 when the engine 1 reaches the final compression top dead center (hereinafter referred to as the final top dead center rotational speed ne1) and the compression top dead center two times before the engine 1 stops. Based on the boost pressure Bt (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 closer to the bottom dead center in the expansion stroke cylinder 12A) ( Steps S54 and S55). Specifically, the final top dead center rotational speed ne1 is equal to or higher than a predetermined rotational speed N4 (for example, N4 = 200 rpm) (when step S54 is YES), and the boost pressure Bt2 is the predetermined pressure P2 (for example, P2 = −200 mmHg). ) When it is below (when it is on the vacuum side) (when step S55 is YES), there is a large tendency to stop at a position closer to the latter stage of the stroke. Therefore, in the present embodiment, when steps S54 and S55 are used as determination criteria and the above-described conditions are satisfied, the piston stop position in the expansion stroke cylinder 12A is 100 ° to 120 ° CA after compression top dead center. It is assumed that the vehicle stops at a position close to 120 ° CA with respect to the stop range R.

  If YES is determined in steps S54 and S55, the rotational inertia of the engine 1 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. Thus, there is already a condition in which the piston 13 is likely to stop at a later position in 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 S56). The second opening K2 may be a smaller opening or a closed state according to the characteristics of the engine 1 or the like. In this way, an appropriate intake resistance is generated in the intake stroke cylinder 12D, and the occurrence of a situation in which the stop position of the piston 13 exceeds the appropriate stop range R and becomes further late is effectively prevented.

  On the other hand, when it is determined NO in any of the above steps S54 and S55, the tendency of the engine 1 to stop at a position near the latter stage of the stroke as described above is not remarkable, and the stroke is relatively closer to the previous period. The position, that is, the piston stop position in the expansion stroke cylinder 12A may stop at a position close to 100 ° CA or less than 100 ° CA with respect to an appropriate stop range R that becomes 100 ° to 120 ° CA after compression top dead center. is there. Therefore, in order to stop the piston 13 more reliably within the proper stop range R, 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 set to about 40% of full opening (step S35), and the intake air flow rate is increased to thereby increase the intake stroke. The intake resistance of the cylinder 12D is reduced. As a result, the engine 1 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 stop range R. Will be.

Referring to FIG. 13, in the present embodiment, the throttle opening K is adjusted by the determinations in steps S54 and S55, so that the compression stroke cylinder 12C can move toward the top dead center in the stroke center. , after the adjustment of the throttle opening K, executes the process of estimating the piston stop position CA _P of the compression stroke cylinder (step S60) whether CA _P is within the appropriate stop range R is determined (step S61) . In a case where if the piston stop position CA _P in this determination is determined to be proper stop range R out, set the estimated as the stop position is closer to the bottom dead center is, the fuel injection amount is a large value on the basis of experimental Based on the added fuel injection map M3, additional fuel is injected into the compression stroke cylinder 12C in the final compression stroke (after the time point t5 has elapsed). As a result, the in-cylinder pressure of the compression stroke cylinder 12C is reduced as much as possible, and the piston 13 of the compression stroke cylinder 12C is more precisely stopped within the appropriate stop range R (preferably at the top dead center side). It becomes possible.

  When it is determined in step S61 that the stop position of the compression stroke cylinder 12C is within the proper stop range R, or after step S62 is executed, it is determined whether or not the engine 1 has been stopped ( (Step S63) When the determination is YES, counting of the engine automatic stop time is started (Step S64). Next, the shift range of the automatic transmission is returned from the neutral state to the drive state (D range) (step S65), and after the automatic stop permission flag is turned OFF (step S66), the control operation is terminated.

  A control operation when restarting the engine 1 that has been in the automatic stop state as described above will be described based on the flowcharts shown in FIGS. First, it is determined whether or not a predetermined engine restart condition is satisfied (step S100). If YES is determined, for example, if an accelerator operation for starting from a stopped state is performed, the battery voltage is When the engine speed is lowered or the air conditioner is activated, it is determined whether or not the engine automatic stop time started in step S64 is within a preset reference time (step S101). When the automatic stop time of the engine 1 is relatively long, even if the fuel is injected during the automatic stop control, the inside of the compression stroke cylinder 12C is diluted and desired combustion characteristics can be obtained. There is a risk that it will not be possible. Therefore, in this determination, it is determined again whether or not fuel injection is necessary according to the stop time of the engine 1.

  If the determination in step S101 is YES, that is, if it is determined that the engine automatic stop time is relatively short and the cylinder of the compression stroke cylinder 12C has not been diluted, the air density in the atmosphere is further within a predetermined range. It is determined whether or not (step S102). On the other hand, if the determination in step S101 is NO, the flow proceeds to a flow (steps S103 to S110) for igniting the compression stroke cylinder 12C, as in the case of YES in step S102.

  As a flow for igniting the compression stroke cylinder 12C, first, 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 S103).

  Next, the amount of air in the compression stroke cylinder 12C and the expansion stroke cylinder 12A is calculated based on the stop position of the piston 13 detected when the engine 1 is automatically stopped (step S104). 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 1 is automatically stopped, the engine 1 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 is stopped during the automatic engine stop. Since the inside of 12C and the expansion stroke cylinder 12A is substantially at atmospheric pressure, the amount of fresh air is obtained from the combustion chamber volume.

  Next, the piston stop position detected according to the output signals of the crank angle sensors 30 and 31 is the bottom dead center in the proper stop range R (BTDC 60 to 80 ° CA before top dead center) in the compression stroke cylinder 12C. It is determined whether or not the vehicle is near the BDC (step S105). As described above, in the present embodiment, the control for stopping the compression stroke cylinder 12C within the appropriate stop range R on the top dead center side with respect to the stroke center from step S20 to step S57 where the automatic stop condition is satisfied is performed. In addition to being executed, the stop position of the piston 13 of the compression stroke cylinder 12C is further precisely stopped within the proper stop range R on the top dead center side of the stroke center by the control from step S60 to step S62 in FIG. Therefore, the compression stroke cylinder 12C moves to the top dead center side with a very high probability. However, since it is difficult to say that there is no stop at the bottom dead center side than the intended position for some reason, the piston stop position of the compression stroke cylinder 12C is confirmed in step S105 as a precaution. is there.

  If it is determined as YES in this step S105 (though such a determination is very rare) and it is confirmed that the amount of air in the compression stroke cylinder 12C is relatively large, in step S104 described above. The first fuel injection is performed with respect to the calculated air amount of the compression stroke cylinder 12C so that the air-fuel ratio becomes λ (excess air ratio)> 1 (for example, air-fuel ratio = about 20) (step S106). The air-fuel ratio is obtained from the first air-fuel ratio map M11 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 S105 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 S104. The first fuel injection is performed so as to become (step S107). This air-fuel ratio is obtained from the first second air-fuel ratio map M12 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 a predetermined time set in consideration of the vaporization time from the first fuel injection into the compression stroke cylinder 12C (step S108). 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 is detected within a certain time after ignition (step S 109). When it is determined NO and it is confirmed that the piston 13 has not moved due to misfire, the compression stroke cylinder 12C is re-ignited (step S110).

  On the other hand, if the engine automatic stop time is relatively short in step S101 described above and the air density is less than the predetermined value in step S102, the fuel has already been injected into the compression stroke cylinder 12C in step S62 of FIG. Therefore, a homogeneous air-fuel mixture is generated in the compression stroke cylinder 12C. Therefore, in that case, the compression stroke cylinder 12C is immediately ignited (step S111), and thereafter, after step S109, the reverse rotation operation is executed.

  Next, referring to FIG. 15, when it is determined YES in step S109 and it is confirmed that the piston 13 has moved, the expansion stroke is determined based on the piston stop position and the in-cylinder temperature estimated in step S103. A division ratio of the divided fuel injection to the cylinder 12A (a ratio between the first pre-stage injection and the second post-stage 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 S104 (step S122). The air-fuel ratio at this time is obtained from an air-fuel ratio map M14 for the expansion stroke cylinder 12A set in advance according to the stop position of the piston 13. Further, the first stage fuel injection amount for the expansion stroke cylinder 12A is calculated and injected based on the fuel injection amount to the expansion stroke cylinder 12A calculated in step S122 and the split ratio calculated in step S121 (in FIG. Step S123).

  Next, based on the in-cylinder temperature estimated in step S103, a subsequent (second) fuel injection timing for the expansion stroke cylinder 12A is calculated (step S124). This second injection timing is a time when the air in the cylinder is compressed after the piston 13 starts moving toward the top dead center (reverse rotation of the engine 1), and the vaporization latent heat of the injected fuel is compressed. It is set so that the pressure is effectively reduced, that is, the piston 13 is set close to top dead center, and the time for the second injected fuel to evaporate by the ignition timing is secured as much 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 M15 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 1 changes from reverse rotation to normal rotation. Therefore, the piston 13 of the compression stroke cylinder 12C moves to the top dead center side and starts to compress the gas in the cylinder (burned gas burned by ignition in step S108).

  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 M16 for the compression stroke cylinder 12C set in advance according to the stop position of the piston 13. The compression top dead center can be easily exceeded by reducing the compression pressure in the vicinity of the compression top dead center of the compression stroke cylinder 12C according to the latent heat of vaporization caused by the second injection fuel in the compression stroke cylinder 12C. It becomes.

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

  Next, referring to FIG. 16, 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. In other words, 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, it is desirable that the energy required for the intake stroke cylinder 12D to exceed the compression top dead center is small for a smooth start. For this purpose, the air density in the cylinder 12D is estimated, and the intake stroke cylinder 12D is estimated from the estimated value. After calculating the air amount (step S140), an air-fuel ratio correction value for preventing self-ignition is calculated based on the in-cylinder temperature estimated in step S103 (step S141). That is, when self-ignition occurs, a force (reverse torque) that pushes the piston 13 back to the bottom dead center before the compression top dead center is generated by the combustion, and much energy is required to exceed the compression top dead center. Since it is consumed, it is not desirable. Therefore, in order to suppress the reverse torque, the air-fuel ratio is corrected to the lean side so that compression self-ignition does not occur.

  Next, the fuel injection amount to the intake stroke cylinder 12D is calculated based on the air amount of the intake stroke cylinder 12D calculated in step 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 delay is delayed until the later stage of the compression stroke (step S143), and the delay amount is calculated based on the automatic stop period of the engine 1, 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, but 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, which causes an acceleration shock or gives the driver a feeling of strangeness. 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 of the crankshaft 3 (external load of the engine 1) is increased by the power generation of the alternator 28 to rotate the engine. Suppresses speed increase.

  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 1 is not automatically stopped (step S150). Since the engine speed is likely to increase, the opening of the throttle valve 23 is made smaller than the throttle opening during normal idle operation (step S151), thereby generating combustion energy. Reduce the amount.

  Then, it is determined whether or not the temperature of the exhaust gas purification catalyst 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 rise of the catalyst 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 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. A stratified lean combustion state is set (step S158). This lean combustion suppresses fuel consumption and suppresses the amount of combustion energy generated.

  After returning to step S150 through step S154 or step S158, it is determined NO in step S150, and it is confirmed that the intake pressure has decreased even during normal idling when the engine 1 is not automatically stopped. The above control operation is repeated. If it is determined NO in step S150, there is no possibility that the engine speed will be increased any more, and therefore the normal control state including the generated current of the alternator 28 is entered (step S160).

  As described above, in this embodiment, the compression stroke cylinder 12C as the initial combustion cylinder is estimated in the process of automatically stopping the engine 1, and at least when the air density is less than the predetermined value, the automatic stop control is performed. Since the fuel is injected into the compression stroke cylinder 12C in the last intake stroke at, when the air density is relatively low, such as when traveling at high altitude, the injected fuel is introduced into the cylinder on the intake air and quickly Vaporization and atomization can promote homogenization of the air-fuel mixture, prevent rapid combustion during restart, and ensure kinetic energy due to slow combustion, resulting in the second compression It becomes possible to secure sufficient kinetic energy to exceed the stroke.

  In addition, the ECU 2 of the present embodiment measures the stop time, and when the measured stop time has exceeded a predetermined value, the fuel is injected so that fuel injection is performed on the compression stroke cylinder 12C after the restart condition is satisfied. The stop time measuring means for controlling the injection valve is functionally configured (see steps S64, S101, etc.). For this reason, in the present embodiment, even when the cylinder is diluted by a long-term automatic stop, it is possible to reliably ensure the combustion energy for restart and ensure the reverse torque at the time of restart.

  Further, in the present embodiment, the fuel injection control means, as shown in steps S60 to S62 in FIG. 13, when the compression stroke cylinder 12C is likely to stop at the bottom dead center side from the predetermined crank angle range at the time of stopping. Is for controlling the fuel injection valve so that fuel is dividedly injected into the compression stroke cylinder 12C during the stop control. For this reason, in this embodiment, in the reverse rotation start method, the compression stroke cylinder 12C estimated by the ECU 2 by the piston position detection unit 45 as the cylinder stop position control means can be stopped from the middle of the operation stroke toward the top dead center. become. As a result, the cylinder volume of the expansion stroke cylinder 12A in the automatic stop state can be controlled to be larger than the cylinder volume of the compression stroke cylinder 12C in the automatic stop state (see FIG. 3A).

  Next, control in the case of the normal rotation restart method will be described with reference to FIGS. 17 and 18.

  First, referring to FIG. 17, even when the engine 1 is automatically stopped in the normal rotation restart method, the same processing (steps S1 to S31) as in FIG. 9 and FIG. Is done.

  Thereafter, it is determined whether or not the air density is less than a predetermined value (step S200). If the air density is less than the predetermined value, the top dead center rotational speed ne of the engine 1 is higher for the expansion stroke cylinder 12A based on experiments. The fuel for restarting is injected into the expansion stroke cylinder 12A in the intake stroke (during the stroke immediately before time t3 shown in FIG. 4) based on the fuel injection map M21 in which the fuel injection amount is set to a large value. (Step S201). As a result, the restart fuel is vaporized and atomized in the expansion stroke cylinder 12A, and a homogeneous air-fuel mixture is generated during the automatic stop period. Further, the fuel injected into the expansion stroke cylinder 12A is vaporized, whereby the in-cylinder temperature is lowered. Thereafter, processing similar to steps S52 to S56 (steps S202 to S207) in FIG. 12 is executed.

  On the other hand, in the forward rotation restart method, the processing of steps S60 to S62 shown in FIG. 13 is omitted, and the same processing (steps S208 to S211) as that of steps S63 to S66 of FIG. Exit.

  Next, referring to FIG. 18, when the establishment of the restart condition is detected after the automatic stop (step S220), the engine whose count is started in step S209 is the same as in the case of the normal rotation restart method. It is determined whether or not the automatic stop time is within a preset reference time (step S221).

  If the determination in step S221 is YES, it is further determined whether the air density in the atmosphere is within a predetermined range (step S222). On the other hand, if the determination in step S221 is NO, the flow proceeds to a flow (steps S223 to S227) for igniting the expansion stroke cylinder 12A, as in the case of YES in step S222. Thereafter, after the processing similar to steps S103 and S104 in FIG. 14 (steps S223 and S224, only the expansion stroke cylinder is performed in step S224), the vaporization time from fuel injection to the expansion stroke cylinder 12A is executed. After a predetermined time set in consideration of the above, the cylinder 12A is ignited (step S225). Then, it is determined whether or not the piston 13 has moved according to 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 predetermined time after ignition (step S226). If it is determined as NO and it is confirmed that the piston 13 has not moved due to misfire, re-ignition is performed on the expansion stroke cylinder 12A (step S227).

  On the other hand, if the engine automatic stop time is relatively short in step S221 and the air density is less than the predetermined value in step S222, the fuel has already been injected into the expansion stroke cylinder 12A in step S201 of FIG. Therefore, a homogeneous air-fuel mixture is generated in the expansion stroke cylinder 12A. Therefore, in that case, the expansion stroke cylinder 12A is immediately ignited (step S228), and thereafter, after step S226, the reverse rotation operation is executed.

  When the engine 1 is started by this ignition and the edge of the crank angle sensor 30 is detected, the same processing as the flow after FIG. 16 in the normal rotation restart system is executed, and the routine shifts to normal control.

  FIG. 19 is a graph for illustrating the effects of the above-described embodiments. FIG. 19A is a graph showing the transition of the in-cylinder pressure at the crank angle CA, and FIG. 19B is the graph showing the transition of the heat generation rate at the crank angle CA. (C) is a graph showing the transition of the mass combustion ratio at the crank angle CA.

  With reference to FIGS. 19A to 19C, in each of the above-described embodiments, automatic stop control is performed when the air density is less than a predetermined value, such as when the air density is relatively low during high altitude travel. The fuel injection valve is controlled so as to inject fuel into the initial combustion cylinder in the last intake stroke, so that homogenization of the air-fuel mixture is promoted in the compression stroke cylinder 12C or the expansion stroke cylinder 12A due to spraying. Disturbances are no longer occurring. As a result, even when a considerable amount of time has passed from the automatic stop to the restart, or even in an environment where the air density is low, not only the stop position of the compression stroke cylinder is controlled closer to the top dead center, but also the restart Sometimes, when the air-fuel mixture in the compression stroke cylinder is ignited, as shown by the solid lines PL1, J1, and Q1 in FIGS. 19A to 19C, slow combustion characteristics can be obtained. Heat loss caused by heat absorbed in the cylinder also becomes moderate, and a relatively large amount of combustion energy can be converted into kinetic energy. Therefore, a relatively large reverse kinetic energy can be secured by the slow combustion with a small air weight, and the kinetic energy of the expansion stroke cylinder can be further increased by the relatively large reverse kinetic energy by the slow combustion. On the other hand, when fuel is injected at the time of restart without considering the air density, rapid combustion occurs as shown by virtual lines PL2, J2, and Q2 in FIGS. The kinetic energy cannot be extracted sufficiently (see FIG. 19C).

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various deformation | transformation is possible within the range of the invention described in the claim. For example, in the reverse restart system, in the above embodiment, the fuel injection for the initial combustion in the expansion stroke cylinder 12A at the time of restart is divided injection, but this is reduced in compression pressure by latent heat of vaporization and ensuring 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, in the reverse rotation restart method, the divided fuel injection performed for the first combustion of the expansion stroke cylinder 12A at the time of restart may be divided into three or more as required.

  Although omitted in the above-described 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 speed is increased by the predetermined timing after the start). Control with assistance by a starter motor may be performed.

  The control for automatically stopping the engine 1 is not limited to the above embodiment, and may be set as appropriate. However, in order to improve the restartability, control is performed such that the stop position of the piston 13 in the expansion stroke cylinder 12A is slightly closer to the bottom dead center than the center of the stroke (slightly closer to the top dead center in the compression stroke cylinder 12C). It is desirable that

  It goes without saying that various modifications can be made within the scope of the claims of the present invention.

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. FIG. 5 is a partially enlarged view of FIG. 4, and is a time chart showing a crank angle and a stroke transition of each cylinder. It is a flowchart which shows detection control operation | movement of a piston stop position. It is explanatory drawing which shows the output signal of a crank angle signal. It is a graph which shows the relationship between the elapsed time from an engine stop, and a cylinder temperature estimated value. It is a flowchart which shows the control content in embodiment which employ | adopted the reverse rotation restart system. It is a flowchart which shows the control content in embodiment which employ | adopted the reverse rotation restart system. It is a flowchart which shows the control content in embodiment which employ | adopted the reverse rotation restart system. It is a flowchart which shows the control content in embodiment which employ | adopted the reverse rotation restart system. It is a flowchart which shows the control content in embodiment which employ | adopted the reverse rotation restart system. It is a flowchart which shows the control content in embodiment which employ | adopted the reverse rotation restart system. It is a flowchart which shows the control content in embodiment which employ | adopted the reverse rotation restart system. It is a flowchart which shows the control content in embodiment which employ | adopted the reverse rotation restart system. It is a flowchart which shows the control content in embodiment which employ | adopted the normal rotation restart system. It is a flowchart which shows the control content in embodiment which employ | adopted the normal rotation restart system. It is a graph for showing the effect of each embodiment, (A) is a graph which looked at change of in-cylinder pressure at crank angle CA, (B) is a graph which looked at change of heat release rate at crank angle CA, (C) Is a graph showing the transition of the mass combustion ratio at the crank angle CA.

Explanation of symbols

1 4-cycle multi-cylinder engine 2 ECU
3 Crankshaft 12A Expansion stroke cylinder (example of first combustion cylinder in forward rotation system)
12C compression stroke cylinder (an example of the first combustion cylinder in the reverse rotation mode)
DESCRIPTION OF SYMBOLS 13 Piston 14 Combustion chamber 15 Spark plug 16 Fuel supply system 16a Fuel injection valve 29 Intake temperature sensor 30 Crank angle sensor 31 Crank angle sensor 32 Cam angle sensor 33 Water temperature sensor 34 Accelerator opening sensor 41 Fuel injection control part 42 Ignition control part 43 Intake flow rate control unit 44 Power generation amount control unit 45 Piston position detection unit 46 In-cylinder temperature estimation unit 47 Air density estimation unit 48 Exhaust gas recirculation control unit CA crank angle CA _P piston stop position R Appropriate stop range SW1 Atmospheric pressure sensor

Claims (4)

Provided with a direct injection type fuel injection valve that injects fuel into the combustion chamber of a multi-cylinder engine, and a fuel supply for continuing operation of the multi-cylinder engine when a preset automatic stop condition of the multi-cylinder engine is satisfied The multi-cylinder engine is restarted by automatically stopping the multi-cylinder engine and restarting the multi-cylinder engine by burning the air-fuel mixture of at least the expansion stroke cylinder when the restart condition is satisfied. In
An initial combustion cylinder predicting means for predicting an initial combustion cylinder that first combusts an air-fuel mixture during restart during an automatic stop operation of the multi-cylinder engine;
Air density estimation means for estimating air density;
During the automatic stop operation of the multi-cylinder engine, if at least the air density estimated by the air density estimation means is less than a predetermined value, fuel is injected into the initial combustion cylinder in the final intake stroke during the automatic stop control. And a fuel injection control means for controlling the fuel injection valve. The starter for a multi-cylinder engine according to claim 1,
Start of a multi-cylinder engine characterized by comprising stop position control means for controlling the position of the piston of the first combustion cylinder to be automatically stopped so that the piston stop position is within a predetermined crank angle range on the top dead center side of the stroke center. apparatus. A starter for a multi-cylinder engine according to claim 1 or 2, further comprising stop time measuring means for measuring a stop time,
The fuel injection control means controls the fuel injection valve so that the fuel injection is performed on the first combustion cylinder after the restart condition is satisfied when the measured stop time has exceeded a predetermined value. A starter for a multi-cylinder engine. The multi-cylinder engine starter according to any one of claims 1 to 3,
The first combustion cylinder is a compression stroke cylinder that is ignited in order to reverse the once stopped multi-cylinder engine.
The fuel injection control means is configured such that when the multi-cylinder engine is automatically stopped based on the top dead center rotational speed and the boost pressure when the engine passes through the top dead center , the compression stroke cylinder is located on the lower dead center side than the predetermined crank angle range. If it is estimated to stop in the relative said compression stroke cylinder, multi-cylinder engine, characterized in that to inject additional fuel into the stop control, and controls the fuel injection valve Starter.

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