JP2007092719A - Starter of multicylinder engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the startability of an engine by effectively utilizing a compression stroke cylinder after reversal. <P>SOLUTION: Fuel for restarting is injected in advance into the compression stroke cylinder 12C when the engine automatically stops. Next, fresh air is introduced into the compression stroke cylinder 12C by opening an intake valve of the compression stroke cylinder 12C when the engine reversely rotates when beginning restarting, and the fuel is also injected. When meeting with the first top dead center, compressed self-ignition is performed by the compression stroke cylinder 12C. Thus, a pumping loss in the compression stroke cylinder 12C is eliminated, and high starting torque can be outputted. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multi-cylinder engine starter, and in particular, automatically stops an engine when a predetermined automatic stop condition is satisfied in an engine idling state or the like, and then restarts when a predetermined restart condition is satisfied. The present invention relates to a starter for a multi-cylinder engine that is configured to be

In recent years, in order to reduce fuel consumption and reduce CO ₂ emissions, a restart condition has been established such that the engine is automatically stopped once during idling and the vehicle is then started by the driver. At the time, a technology for automatic engine stop control (so-called idle stop control) that automatically restarts the engine has been developed.

As a restarting method at the time of this idle stop control, as in the prior art disclosed in Patent Documents 1 and 2, when the restarting condition of the engine in the automatic stop state is satisfied, the cylinder stopped in the compression stroke ( In this specification, an air-fuel mixture (referred to as “compression stroke cylinder”) is ignited, the engine is once reversed, and then fuel is injected into a cylinder stopped in the expansion stroke (referred to as “expansion stroke cylinder” in this specification). There is known a so-called reverse restart system that is configured to ignite and automatically restart the engine.
JP 2004-124753 A Japanese Patent Laid-Open No. 2005-90498

  In order to make the above-described reverse restart system effective and to put the idle stop control into practical use, it is essential to secure at the restart control a kinetic energy sufficient to exceed the second top dead center after the restart. In order to overcome the second top dead center smoothly, the kinetic energy output from the expansion stroke cylinder reversed from the reverse rotation to the normal rotation is increased, and the compression stroke is shifted again to the compression stroke due to the normal rotation of the expansion stroke cylinder. It is preferable to obtain kinetic energy also from the cylinder. However, since the compression stroke cylinder after the reverse rotation contains only burned gas, conventionally, the compression stroke cylinder after the reverse rotation has not been effectively used. For this reason, a pumping loss occurs in the compression stroke cylinder, and it has become clear from the study of the present inventors that this is a major obstacle in overcoming the second top dead center.

  In view of the above circumstances, an object of the present invention is to provide a starter for a multi-cylinder engine that can improve the startability of the engine by effectively using the compression stroke cylinder after inversion.

  In order to solve the above-mentioned 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 supplies a fuel spray into the cylinder at a predetermined timing from the fuel injection valve. And when the restart condition is satisfied, the compression stroke cylinder is combusted, the multi-cylinder engine is reversed by a predetermined crank angle, and then the expansion stroke cylinder is combusted to restart the multi-cylinder engine. In this starting device, a piston position detecting means for detecting the piston position of each cylinder, and the fuel injection timing by the fuel supply system is controlled so as to execute fuel injection to each cylinder based on the detection by the piston position detecting means. A fuel injection control means for igniting, and an ignition means for igniting the air-fuel mixture in the cylinder, and at least during the reverse operation period at the start of restart In order to open the intake valve of the cylinder, the intake valve closing timing during the reverse rotation period is delayed to a timing that is a predetermined crank angle later than the bottom dead center, and the fuel injection control means During the automatic stop operation, the fuel for restarting is injected after the compression stroke cylinder reaches the last intake stroke, and the forward rotation is performed while the intake valve of the compression stroke cylinder is opened during the reverse rotation operation. The fuel supply system is controlled so as to inject fuel, and the ignition means executes re-combustion near the first compression top dead center of the compression stroke cylinder that has turned to normal rotation after restarting. Is a starter for a multi-cylinder engine. In this aspect, by injecting fuel into the compression stroke cylinder after the last intake stroke before the automatic stop, it becomes possible to homogenize the air-fuel mixture in the compression stroke cylinder at the time of restart. In addition, for the following reasons, the in-cylinder temperature drop when the compression stroke cylinder is changed from reverse rotation to normal rotation can be effectively suppressed. That is, during the reverse rotation operation at the time of restart, since the compression stroke cylinder has no uneven distribution of fuel, it becomes a slow homogeneous combustion and avoids in-cylinder temperature change due to cooling loss. Thereafter, when turning from reverse rotation to normal rotation, the piston of the compression stroke cylinder moves to the top dead center relatively slowly. At this time, the in-cylinder temperature rises as the air in the cylinder is compressed, but the heat is absorbed by the wall surface in the cylinder, causing a cold loss. As a result of the slow operation of the piston, the cooling loss also increases. As a result, the in-cylinder pressure due to this cooling loss is also greatly reduced, and conventionally, the compression stroke cylinder could not be sufficiently heated to a high temperature and pressure. On the other hand, in the present invention, it is possible to realize a slow homogeneous combustion during the reverse rotation operation, so even when moving to the top dead center at a relatively slow speed when turning to normal rotation. Thus, it becomes difficult for the temperature in the cylinder to decrease as in the conventional case, and it becomes possible to move to the top dead center while maintaining relatively high heat energy. In this state, when the closing timing of the intake valve is retarded, fresh air is introduced into the compression stroke cylinder, fuel is then injected into the compression stroke cylinder, and the air-fuel mixture is top dead in the compression stroke cylinder. It is ignited near the point. In the combustion after the forward compression, a considerable amount of burnt gas remains, so the combustion tends to be slow. In the present invention, the in-cylinder temperature of the compression stroke cylinder is compared by the combustion at the time of reverse rotation. Therefore, combustion is promoted during the first forward rotation after reversing from the reverse rotation, and a large kinetic energy can be output from the piston. Further, in the slow combustion at the time of reverse rotation, there is no fear that the in-cylinder temperature will rise excessively and knocking is less likely to occur. In the present invention, the “ignition means” may be not only a spark plug but also means for realizing compression self-ignition. Therefore, by using the heavy EGR of the compression stroke cylinder at the time of the first forward rotation, the fuel injection amount and the injection timing so that the compression self-ignition occurs near the compression top dead center (preferably just before the compression top dead center). Etc. may be controlled.

  In a preferred aspect, the fuel injection control means controls the fuel injection amount so that the air-fuel ratio at the time of fuel injection becomes λ ≦ 1 during the automatic stop operation of the multi-cylinder engine. In this aspect, since the compression stroke cylinder is in a relatively homogeneous and rich state, it is possible to ensure slow combustion at the time of restart and prevent cold loss. Further, since the reverse rotation amount is also increased, the compression force of the expansion stroke cylinder is also increased, so that it is possible to increase the compression amount and the intake valve opening period in the expansion stroke cylinder.

  In a preferred aspect, the ignition means performs compression self-ignition when the compression stroke cylinder first reaches top dead center after restarting, and is fuel injection injected during reverse operation at restart This is because the fuel injection control means controls the fuel injection amount so that the amount becomes smaller than the fuel injection amount for the reverse operation injected into the compression stroke cylinder during the automatic stop operation. In this aspect, the air-fuel mixture is combusted in an entirely homogeneous state at the time of reversing at the time of restart, so that the cooling loss is prevented and the compression amount and the intake valve opening period in the expansion stroke cylinder are increased. In addition, when turning from reverse rotation to normal rotation, it is possible to suppress a decrease in the in-cylinder temperature and to ensure combustion by compression self-ignition as much as possible in a fresh air state. .

  In a preferred aspect, the ignition means performs ignition by a spark plug near the top dead center at the time of the first forward rotation of the restarted compression stroke cylinder. In this aspect, it is possible to assist the ignition of the compression self-ignition by the burned gas at the time of reverse rotation at the most suitable timing at the time of normal rotation, and it is possible to obtain high kinetic energy from the compression stroke cylinder.

  As described above, according to the present invention, fuel is injected into the compression stroke cylinder during the automatic stop operation, the intake valve of the compression stroke cylinder is opened during the reverse operation of the restart control, and fresh air is supplied to the compression stroke cylinder. When the first top dead center is reached after reversing, the fuel mixture in the compression stroke cylinder is burned again to prevent the pumping loss in the compression stroke cylinder. The reversible compression stroke cylinder can be used effectively, and the engine startability can be improved.

  1 and 2 show a schematic configuration of a four-cycle spark ignition type multi-cylinder engine according to the present invention. (A) is the whole structure, (B) has shown the structure which shows the principal part.

  Referring to FIGS. 1 (A), 1 (B), and 2, this engine 1 has a cylinder head 10 and a cylinder block 11, and is configured to be controlled by an 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 of the cylinders 12A to 12D. By inserting the 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.

  Referring to FIG. 1B, the intake valve 19 has a tappet 19a at the top of the stem. The tappet 19a is driven by an intake cam 19b that is rotationally driven by a camshaft 191, and the intake valve 19 is configured to open and close when the intake cam 19b drives the tappet 19a. Yes. Here, the camshaft 191 in the present embodiment is provided with a VVT (Valable Valve Timing Mechanism) 190, and is configured to be able to change the valve opening timing by the control of the ECU 2, as will be described later. On the other hand, the exhaust valve 20 is configured such that its tappet 20a is driven by an exhaust cam 20b fixed to the camshaft 201. The valve operating mechanisms such as the camshafts 191 and 201, the intake cam 19b, and the exhaust cam 20b are configured such that each cylinder 12A to 12D performs a combustion cycle with a predetermined phase difference.

  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 air flow sensor 25 for detecting the intake air flow rate and an intake air temperature sensor 29 for detecting the intake air temperature are provided on the upstream side of the throttle valve 23, and the intake pressure (negative pressure) is detected on the downstream side of the throttle valve 23. An intake pressure sensor 26 is provided.

  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.

  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 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 receives detection signals from the air flow sensor 25, the intake pressure sensor 26, the intake air temperature sensor 29, the crank angle sensors 30, 31, the cam angle sensor 32, the water temperature sensor 33, and the accelerator opening sensor 34, The drive signals are output to the 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 functionally 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, and a VVT control unit 47. Yes.

  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, during the automatic stop control operation, the fuel is supplied after the compression stroke cylinder reaches the last compression stroke. Further, in the present embodiment, in the stroke in which the compression stroke cylinder is reversed, the fuel burned at the first top dead center after the reverse rotation is reversed is also injected. The fuel injection control unit 41 also sets the fuel injection timing and the fuel injection amount.

  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. In the present embodiment, as will be described later, the ignition control unit 42 controls the ignition device 27 to constitute assist means for assisting compression self-ignition of the compression stroke cylinder 12C at the first top dead center at the time of restart. Is set to

  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 detection unit 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 estimation unit 46 uses each map 12A based on an engine water temperature detected by the water temperature sensor 33, an intake air temperature detected by the intake air temperature sensor 29, etc., using a map obtained in advance through experiments or the like. In-cylinder temperature estimation means for estimating the air temperature in the cylinder of -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 VVT control unit 47 normally determines the opening timing of the intake valve 19 according to the operating state based on a control map (not shown), and at the time of restart, based on the retard control map M3. The intake valve closing timing during the reverse operation period is retarded to a timing that is a predetermined crank angle later than the bottom dead center. By this control, the intake valve 19 of the compression stroke cylinder that has changed from reverse rotation to normal rotation is opened, and fresh air can be introduced.

  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 position where the center of the stroke of the expansion stroke cylinder, that is, 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 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.

  The ECU 2 sets a target speed of the engine 1 higher than a normal idle speed (hereinafter referred to as a normal idle speed) when the engine 1 is not automatically stopped at the time t0 when the automatic stop condition of the engine 1 is established. For example, in the engine 1 in which the normal idle rotation speed is set to 650 rpm (the automatic transmission is in the drive (D) range), the target speed (idle rotation speed when the automatic stop condition is satisfied) is set to about 850 rpm (the automatic transmission is neutral). By setting (N) range), control is performed to stabilize the engine rotational speed Ne at a rotational speed that is 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 higher 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 decreases while repeating up and down (around 10 times in the 4-cylinder 4-cycle engine 1).

  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 third cylinder 12C 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 fourth cylinder 12D 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, since any cylinder reaches compression top dead center every 180 ° CA, this time chart is 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 reversed without being pushed back beyond 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 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 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 is started, 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 stopping the engine, the piston stop position is obtained by examining the measured value of the CA counter (step S44).

  Further, in the present embodiment, the fuel injection F1 is performed on the compression stroke cylinder 12C immediately before the engine 1 stops, that is, after the timing t3 when each cylinder reaches the last stop stroke (see FIG. 5). ). The fuel injection amount at this time is determined by the fuel injection control unit 41 so that the air-fuel ratio in the compression stroke cylinder 12C becomes λ ≦ 1. By this fuel injection, vaporization atomization in the compression stroke cylinder 12C can be promoted, and a homogeneous air-fuel mixture can be generated as a whole.

  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 since the engine stop and the in-cylinder temperature. is there.

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, 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. Note that, regarding the compression stroke cylinder 12C, since the fuel is injected after the timing t3, the characteristic of _T12C is taken, and such a characteristic is stored in the control map corresponding to this graph.

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

  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.

Next, the control operation when the engine 1 is restarted will be described based on the flowcharts shown in FIGS. First, it is determined whether or not a predetermined engine restart condition (e.g., when an accelerator operation for starting is performed from a stopped state, when the battery voltage is reduced, or when the air conditioner is activated, etc.) ( In step S101), when it is determined NO and it is confirmed that the restart condition of the engine 1 is not satisfied, the process waits as it is. If it is determined YES in step S101 and it is confirmed that the restart condition of the engine 1 is satisfied, the in-cylinder temperature estimating unit 46 determines that the engine water temperature, the stop time (elapsed time from the automatic stop), the intake air temperature. The in-cylinder temperature is estimated from the above (step S102). Then, based on the stop position of the piston 13 detected by the piston position detector 45, the amount of air in the compression stroke cylinder 12C and the expansion stroke cylinder 12A is calculated (step S103). That is, the combustion chamber volumes of the compression stroke cylinder 12C and the expansion stroke cylinder 12A are obtained from the stop position of the piston 13, and when the engine is stopped, the engine 1 is stopped after several revolutions after the fuel injection is stopped. The expansion stroke cylinder 12A is also filled with fresh air, and the inside of the compression stroke cylinder 12C and the expansion stroke cylinder 12A is substantially atmospheric pressure while the engine is stopped. Will be required. However, at the time of this calculation, the restart fuel is injected during the automatic stop operation in the compression stroke cylinder 12C. Therefore, the compression stroke cylinder 12C is new based on the characteristics of _T12C in FIG. The volume is calculated.

  Next, the VVT control unit 47 calculates the retard amount of the intake valve 19 from the stop position of the compression stroke cylinder or the like while referring to the retard control map M3 (step S104), and based on the calculated retard amount. Then, the VVT 190 is driven to retard the valve closing timing of the intake valve 19 (step S105). By operating this VVT 190, the intake valve 19 of the compression stroke cylinder 12C is opened on the predetermined bottom dead center side during the reverse rotation operation, and fresh air is introduced.

  Next, the spark plug 15 of the compression stroke cylinder 12C is ignited (step S106). 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 (rise or fall of the crank angle signal) have been detected within a predetermined time after ignition (step S107). If it is determined NO and it is confirmed that the piston 13 has not moved due to misfire, re-ignition is repeatedly performed on the compression stroke cylinder 12C (step S108). By the ignition in step S106 or step S108, the homogeneous air-fuel mixture in the compression stroke cylinder 12C burns relatively slowly, and the combustion energy is converted into kinetic energy, so that the engine 1 falls within a predetermined stroke range. Reverse.

  Referring to FIG. 10, when engine 1 (that is, crankshaft 3) reverses, intake valve 19 of compression stroke cylinder 12C opens as VVT 190 delays the valve closing timing, and fresh air is introduced. Will be. The ECU 2 calculates the amount of air flowing into the intake valve opening period of the compression stroke cylinder 12C in the reverse rotation period from the number of reverse rotations of the engine 1, the intake air temperature, and the engine water temperature (step S121). This calculation is executed by referring to the inflow air amount map M4. Next, the fuel is set so that the air-fuel ratio becomes λ ≦ 1 with respect to the calculated air amount, and the fuel is injected into the compression stroke cylinder 12C during the intake valve opening period of the reverse rotation period (step S122). On the other hand, the ECU 2 calculates the fuel injection amount and fuel injection timing for the expansion stroke cylinder 12A in parallel with the processes of steps S121 and S122, and injects fuel to the expansion stroke cylinder 12A based on the calculation results. (Step S123). Such parallel processing can be realized, for example, by configuring the ECU 2 with a plurality of CPUs or programming interrupt control.

  After the fuel injection into the expansion stroke cylinder 12A, ignition is performed after a predetermined delay time has elapsed (step S124). The predetermined delay time is obtained from an expansion stroke cylinder ignition delay map M5 set in advance according to the stop position of the piston. By the initial combustion in the expansion stroke cylinder 12A by this ignition, the engine 1 turns from reverse rotation to normal rotation. Accordingly, the piston 13 of the compression stroke cylinder 12C moves to the top dead center side, and starts to compress the internal gas (the air-fuel mixture injected with the fuel in step S122). In this embodiment, the compression stroke cylinder 12C operates the ignition plug 15 in the vicinity of the top dead center (more specifically, several degrees before the top dead center CA) to execute the ignition assist (step S125). As a result, the air-fuel mixture in the compression stroke cylinder 12C burns relatively rapidly despite containing a large amount of burned gas, and can output a large kinetic energy.

  Next, referring to FIG. 11, the following steps S140 to S144 are controls for reducing as much as possible the energy for exceeding the compression top dead center when performing combustion in the intake stroke cylinder 12D. .

  First, in step S140, the in-cylinder air density is estimated, and the air amount of the intake stroke cylinder 12D is calculated from the estimated value. Next, an air-fuel ratio correction value for preventing self-ignition is calculated based on the in-cylinder temperature estimated in step S102 (step S141). That is, when self-ignition occurs, a force (reverse torque) that pushes the piston 13 back to the bottom dead center before the compression top dead center is generated by the combustion. This is undesirable because it consumes a lot of energy for exceeding the compression top dead center. Therefore, in order to suppress this reverse torque, the air-fuel ratio is corrected to the lean side so that self-ignition does not occur.

  Next, the fuel injection amount to the intake stroke cylinder 12D is calculated from 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. This fuel injection is performed so that the compression pressure is reduced by the latent heat of vaporization (that is, the energy required for exceeding the compression top dead center is reduced). This is delayed until later (step S143). 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.

  Next, in order to suppress the occurrence of the reverse torque, the ignition timing is delayed after top dead center and ignited (step S144). With the above control, in the intake stroke cylinder 12D, the compression pressure is reduced to easily exceed the top dead center until the compression top dead center, and a torque in the forward direction is generated by the combustion energy when the top dead center is passed. To come.

  After step S144, normal control may be performed, but in this embodiment, blow-up suppression control is further performed. The term “air-up” as used herein means that the engine speed rapidly increases more than necessary after the initial combustion in the intake stroke cylinder 12D, which may cause an acceleration shock or give the driver a sense of incongruity. Absent. Ascending, since the intake pressure (pressure downstream of the throttle valve 23) during the automatic stop period is substantially atmospheric pressure, the combustion in each cylinder immediately after the start (after the initial combustion in the intake stroke cylinder 12D) This is caused by a temporary increase in energy compared to the combustion energy during normal idle operation. Therefore, in subsequent steps S145 to S158, control for suppressing this blow-up is performed.

  First, power generation by the alternator 28 is started (step S145). The target current value is set higher than usual by the power generation amount control unit 44 of the ECU 2. Since the load (engine load) of the crankshaft 3 is increased by the power generation of the alternator 28, the blow-up is suppressed.

  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 idling stop is not performed (step S150). If YES is determined here, it is in a state in which the engine is likely to blow up. Therefore, the opening of the throttle valve 23 is made smaller than the throttle opening during normal idling operation (step S151), and the combustion energy is reduced. Reduce the amount generated.

  Next, it is determined whether or not the temperature of the catalyst 37 provided in the exhaust passage 22 is equal to or lower than the activation temperature (step S152). If YES is determined, the target air-fuel ratio is set to a rich air-fuel ratio satisfying λ ≦ 1. At the same time (step S153), the ignition timing is delayed after top dead center (step S154). By doing so, the temperature increase of the catalyst 37 is promoted, and the amount of combustion energy generated is suppressed by the delay of the ignition timing.

  Going back, if NO is determined in step S152, the target air-fuel ratio is set to a lean air-fuel ratio satisfying λ> 1 (step S158) and combustion is performed. This lean combustion can suppress the amount of combustion energy generated while suppressing fuel consumption.

  After step S154 or step S158, the process returns to step S150, and the control is repeated until it is determined NO. If it is determined as NO in step S150, there is no longer a possibility that the engine will blow up, and the routine proceeds to normal control including the power generation amount of the alternator 28 (step S160).

  FIG. 12 shows the behavior of the engine based on the above-described control. (A) is a timing chart of the compression stroke cylinder 12C, the expansion stroke cylinder 12A, and the intake stroke cylinder 12D, and (B) corresponds to (A). It is a graph which shows the change of a pressure, a heat release rate, and cylinder temperature. In FIG. 12B, the solid line is according to the present embodiment, and the phantom line is a comparative example in which fuel is injected into the compression stroke cylinder 12C at the start of restart and ignited at the first top dead center.

  As described above, in this embodiment, fuel is injected into the compression stroke cylinder 12C after the last intake stroke before the automatic stop, thereby homogenizing the air-fuel mixture in the compression stroke cylinder 12C at the time of restart. It becomes possible to plan. Further, since the fuel is injected so that the air-fuel ratio becomes λ ≧ 1 during the automatic stop operation, it is possible to suppress a decrease in the in-cylinder temperature at the time of restart. That is, as shown in FIG. 12 (B), when fuel is injected and the air-fuel mixture is combusted at the time of restart, not only the uneven distribution of fuel increases, but also the rapid disturbance due to the disturbance of the spray accompanying the fuel injection. Stratified combustion occurs. On the other hand, since the in-cylinder temperature is lowered at the time of restart, the heat is absorbed by the wall surface of the compression stroke cylinder 12C, and a large cooling loss occurs. Sufficient kinetic energy cannot be extracted. On the other hand, in the present embodiment, the rich air-fuel mixture injected before the automatic stop can be slowly burned, so that the in-cylinder temperature drop when the compression stroke cylinder 12C is reversed is effectively suppressed. In addition, a pressure drop due to cooling loss can be avoided.

  Thereafter, when turning from reverse rotation to normal rotation, the piston 13 of the compression stroke cylinder 12C moves to the top dead center relatively slowly. At this time, as the air in the cylinder is compressed, the in-cylinder temperature rises. However, as is apparent from the change in the in-cylinder temperature shown in FIG. It will be absorbed by the inner wall surface and cause a cold loss. As the piston 13 moves slowly, the cooling loss also increases. As a result, the in-cylinder pressure due to the cooling loss also greatly decreases, and the first combustion at the top dead center tends to be slow. On the other hand, in the present embodiment, it is possible to realize a slow homogeneous combustion during the reverse rotation operation, and therefore when moving to the normal rotation, it is moving to the top dead center at a relatively slow speed. However, the in-cylinder temperature drop is less likely to occur as in the comparative example, and it is possible to move to the top dead center while maintaining relatively high thermal energy. In this state, when the closing timing of the intake valve 19 is retarded, fresh air is introduced into the compression stroke cylinder 12C, and then fuel is injected into the compression stroke cylinder 12C, and the mixture is compressed into the compression stroke cylinder. It is ignited near the top dead center of 12C. In the combustion after the forward compression, a considerable amount of burned gas remains, and as is apparent from the heat generation rate in FIG. 12B, the combustion in the comparative example tends to be slow. In the embodiment, since the in-cylinder temperature of the compression stroke cylinder 12C is maintained at a relatively high temperature by the combustion at the time of reverse rotation, the combustion is promoted at the time of the first normal rotation after the reverse rotation from the reverse rotation. It becomes possible to output kinetic energy. Further, in the slow combustion at the time of reverse rotation, there is no fear that the in-cylinder temperature will rise excessively and knocking is less likely to occur.

  In the present embodiment, the fuel injection control unit 41 as fuel injection control means controls the fuel injection amount so that the air-fuel ratio at the time of fuel injection becomes λ ≦ 1 during the automatic engine stop operation. It is. For this reason, in this embodiment, since the compression stroke cylinder 12C is relatively homogeneous and rich, it is possible to ensure slow combustion at the time of restart and to prevent cold loss. Further, since the reverse rotation amount is also increased, the compression force of the expansion stroke cylinder 12A is also increased, so that it is possible to increase the compression amount and the intake valve opening period in the expansion stroke cylinder 12A.

  In the present embodiment, the fuel injection control is performed such that the fuel injection amount injected during the reverse rotation operation at the time of restart is smaller than the fuel injection amount for the reverse rotation operation injected into the compression stroke cylinder 12C during the automatic stop operation. The ignition means is realized by the part 41 controlling the fuel injection amount. For this reason, in the present embodiment, the air-fuel mixture is combusted in an entirely homogeneous state at the time of reversal at the time of restarting, so that cooling loss is prevented and the amount of compression in the expansion stroke cylinder 12A and the intake valve opening period In addition to being able to achieve an increase, in the event of a change from reverse rotation to normal rotation, the decrease in the in-cylinder temperature will be suppressed, and combustion by compression self-ignition will be as reliable as possible with fresh air. can do.

  FIG. 13 is a combustion cycle diagram at the time of restart of the compression stroke cylinder, (A) is the present embodiment, and (B) is the prior art.

  When restarting as described above is started with reference to FIGS. 13A and 13B, in this embodiment, when the compression stroke cylinder that has changed from reverse rotation to normal rotation exceeds the first top dead center, Since the air-fuel mixture supplied with fresh air and fuel is ignited at the time of reverse rotation, there is no pumping loss and positive work can be performed as indicated by + W in FIG. As a result, it is possible to output torque for sufficiently exceeding the second top dead center until the intake stroke cylinder 12D and the exhaust stroke cylinder 12B are subsequently ignited. On the other hand, in the conventional apparatus, when the first top dead center is exceeded after restart, the compression stroke cylinder 12C is not ignited, so that a pumping loss occurs as shown by -W in FIG. 13B. And it is difficult to cross the second top dead center.

  As described above, in the present embodiment, fuel is injected into the compression stroke cylinder 12C during the automatic stop operation and is slowly burned at the time of reverse rotation, and then the intake valve 19 of the compression stroke cylinder 12C is opened to fresh air into the compression stroke cylinder 12C. When the first top dead center is reached after reversing and fuel is injected again, the pumping loss in the compression stroke cylinder 12C is prevented by burning again in the compression stroke cylinder 12C. The compression stroke cylinder 12 </ b> C after the reverse rotation can be effectively used, and the startability of the engine 1 can be improved.

  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, the ignition means is a spark plug 15 that ignites near the top dead center during the first forward rotation of the restarted compression stroke cylinder 12C, and executes spark ignition instead of step S125 in FIG. Also good. In this case, the compression self-ignition by the burned gas at the time of reverse rotation can be assisted with ignition at the most suitable timing at the time of normal rotation, and high kinetic energy can be obtained from the compression stroke cylinder 12C.

  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 restartability, 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 (in the compression stroke cylinder 12C, slightly closer to the top dead center than the center of the stroke). Control is desirable.

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

1 shows a schematic configuration of a four-cycle spark-ignition multi-cylinder engine according to the present invention, (A) shows the overall configuration, and (B) shows a configuration showing the main part. 1 is a schematic configuration diagram of a four-cycle spark ignition type multi-cylinder engine according to the present invention. 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 further 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 (1/3) which shows the control action at the time of engine restart. It is a flowchart (2/3) which shows the control action at the time of engine restart. It is a flowchart (3/3) which shows the control action at the time of engine restart. The behavior of the engine based on the restart control of the present embodiment is shown. (A) is a timing chart of the compression stroke cylinder 12C, the expansion stroke cylinder 12A, and the intake stroke cylinder 12D, and (B) corresponds to (A). It is a graph which shows the change of a pressure, a heat release rate, and cylinder temperature. It is a combustion cycle figure at the time of restart of a compression stroke cylinder, (A) is this embodiment and (B) is a prior art.

Explanation of symbols

F1 fuel injection M3 retard control map 1 multi-cylinder engine 3 crankshaft 12A expansion stroke cylinder 12B exhaust stroke cylinder 12C compression stroke cylinder 13 piston 14 combustion chamber 15 spark plug 16 fuel supply system 16a fuel injection valve 19 intake valve 41 fuel injection control Unit 42 Ignition control unit 43 Intake flow rate control unit 44 Power generation amount control unit 45 Piston position detection unit 46 In-cylinder temperature estimation unit 47 VVT control unit 190 VVT

Claims (4)

Including a direct injection type fuel injection valve that injects fuel into the combustion chamber of a multi-cylinder engine, and a fuel supply system that supplies fuel spray into the cylinder at a predetermined timing from the fuel injection valve, and when a restart condition is satisfied, In a multi-cylinder engine starter that burns a compression stroke cylinder, reverses the multi-cylinder engine by a predetermined crank angle, then burns an expansion stroke cylinder to restart the multi-cylinder engine.
Piston position detecting means for detecting the piston position of each cylinder;
Fuel injection control means for controlling fuel injection timing by the fuel supply system so as to execute fuel injection to each cylinder based on detection of the piston position detection means;
Ignition means for igniting the air-fuel mixture in the cylinder, and at least the intake valve closing timing during the reverse operation period so that the intake valve of the compression stroke cylinder opens at the reverse operation period at the start of restart. Retard the crank angle later than the bottom dead center
The fuel injection control means injects fuel for restart after the compression stroke cylinder reaches the final intake stroke during the automatic stop operation of the multi-cylinder engine, and the compression stroke during the reverse rotation operation. The fuel supply system is controlled so as to inject fuel for forward rotation while the intake valve of the cylinder is open.
The starter for a multi-cylinder engine, wherein the ignition means executes re-combustion in the vicinity of the first compression top dead center of the compression stroke cylinder that has turned to normal rotation after restarting. The starter for a multi-cylinder engine according to claim 1,
The multi-cylinder characterized in that the fuel injection control means controls the fuel injection amount so that the air-fuel ratio at the time of fuel injection becomes λ ≦ 1 during the automatic stop operation of the multi-cylinder engine. Engine starter. The multi-cylinder engine starter according to claim 1 or 2,
The ignition means performs compression self-ignition when the compression stroke cylinder first reaches top dead center after restart is started, and the fuel injection amount injected during the reverse rotation operation at the time of restart is automatically Start of a multi-cylinder engine characterized in that the fuel injection control means controls the fuel injection amount so as to be smaller than the fuel injection amount for reverse operation injected into the compression stroke cylinder during the stop operation. apparatus. The multi-cylinder engine starter according to any one of claims 1 to 3,
The multi-cylinder engine starter characterized in that the ignition means executes ignition by a spark plug in the vicinity of the top dead center at the time of the first forward rotation of the restarted compression stroke cylinder.

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