JP4577179B2 - Multi-cylinder engine starter - Google Patents

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 this second top dead center smoothly, it is preferable to output a larger kinetic energy when the expansion stroke cylinder is first ignited after reversing at the time of restart. In order to increase the output obtained by the first combustion in the expansion stroke cylinder, it is desirable to increase the combustion energy in the expansion stroke cylinder. However, if the in-cylinder air amount in the expansion stroke cylinder is increased too much, the in-cylinder air amount in the compression stroke cylinder decreases and the reverse energy due to combustion decreases, so that the in-cylinder air in the expansion stroke cylinder can be sufficiently compressed. become unable. On the other hand, if the combustion energy for reversing in the compression stroke cylinder is increased too much, the crankshaft of the engine may rotate backward, exceeding the bottom dead center, and the expansion stroke cylinder may exceed the top dead center. There is. Therefore, it is necessary to prevent the combustion energy for the reverse rotation in the compression stroke cylinder from increasing excessively, and therefore, the compression stroke of the in-cylinder air of the expansion stroke cylinder is limited (that is, the expansion stroke cylinder is reverse rotation). In-cylinder air cannot be compressed to the top dead center at the time). As a result, there is a limit in filling the expansion stroke cylinder with a large amount of air and performing stronger compression by reversing the engine due to combustion in the compression stroke cylinder, leaving a problem in startability.

  In view of the above circumstances, an object of the present invention is to provide a starter for a multi-cylinder engine that can increase the combustion energy of an expansion stroke cylinder at the time of restart and thereby improve the startability of the engine.

In order to solve the above-described problems, the present invention provides a method for combusting a compression stroke cylinder when the restart condition of a multi-cylinder engine is satisfied, reversing the crank stroke by a predetermined crank angle, and then combusting an expansion stroke cylinder. In a multi-cylinder engine starter that restarts an engine, the apparatus includes a piston position detection unit that detects a piston position of each cylinder, and a combustion rate control unit that controls a combustion rate of each cylinder, wherein the combustion rate control unit includes: A plurality of spark plugs are provided for each cylinder, and an ignition control unit capable of selectively controlling the spark plugs. The spark plugs are disposed at the center and the periphery of each cylinder. The ignition control unit ignites only some spark plugs at the time of initial combustion in the compression stroke cylinder at the time of restart, and at the center portion and the periphery at the time of initial combustion in the expansion stroke cylinder at the time of restart. A startup device for a multi-cylinder engine, characterized in controls to simultaneously ignite the spark plug. In this aspect, when the restart condition is satisfied and the restart control is started, first, the air-fuel mixture in the compression stroke cylinder is ignited and the predetermined crank angle is reversed. In this process, the piston of the expansion stroke cylinder moves to the top dead center side, and the combustion chamber is compressed by the kinetic energy from the compression stroke cylinder. However, in this reverse rotation operation, the expansion stroke cylinder does not reach top dead center, and the air-fuel mixture is ignited with a restricted piston stroke. This ignition causes the piston of the expansion stroke cylinder to normally rotate the engine by the combustion energy of the air-fuel mixture. This combustion energy is rapidly accelerated by the combustion speed control means, so that the piston stroke is limited under the restricted conditions. Even in such a case, the in-cylinder pressure can be rapidly increased to output a large kinetic energy.

The combustion speed control means includes a plurality of spark plugs arranged for each cylinder , and an ignition control unit capable of selectively controlling the ignition plug, and the spark plug includes a center portion and a peripheral portion of each cylinder. The ignition control unit ignites only some spark plugs at the time of initial combustion in the compression stroke cylinder at the time of restart, and at the center portion at the time of initial combustion in the expansion stroke cylinder at the time of restart. And the peripheral spark plug are simultaneously ignited, so at the time of initial combustion in the compression stroke cylinder at the time of restart, large kinetic energy is extracted from the compression stroke cylinder by slow combustion, and the expansion stroke cylinder The piston stroke can be increased within a limited range, and in the expansion stroke cylinder, due to rapid combustion in the limited piston stroke. It is possible to output a deal of kinetic energy.

According to another aspect of the present invention, when the restart condition of the multi-cylinder engine is satisfied, the compression stroke cylinder is combusted and reversely rotated by a predetermined crank angle, and then the expansion stroke cylinder is combusted to restart the multi-cylinder engine. In a starter for a multi-cylinder engine to be started, a piston position detecting means for detecting a piston position of each cylinder and a combustion speed control means for controlling the combustion speed of each cylinder are provided, and the combustion speed control means is provided in a cylinder. A fuel supply system including a fuel injection valve that injects fuel; a fuel injection control unit that controls a fuel injection timing and a fuel injection amount of the fuel injection valve by the fuel supply system; and an ignition control unit that controls the ignition timing of the spark plug; the provided, the time interval between the ignition timing from the fuel injection during the first combustion in the expansion-stroke cylinder at the time of the restart, the first time the combustion of the compression stroke cylinder at the time of restart It is intended to shorten to the time interval from the fuel injection to the ignition timing. Also in this aspect, it is possible to achieve slow combustion in the compression stroke cylinder and rapid combustion in the expansion stroke cylinder according to the ignition timing. Accordingly, the kinetic energy from both cylinders can be increased.

  In a preferred embodiment, the time interval at the time of initial combustion of the expansion stroke cylinder at the time of restart is a predetermined time during which the in-cylinder turbulence induced by the injected fuel remains. In this aspect, during the initial combustion at the time of restart of the expansion stroke cylinder, a disturbance is caused by the fuel injection, and the spark plug ignites the air-fuel mixture while the disturbance remains, so the combustion speed is further promoted. It becomes possible to realize rapid combustion. The predetermined time can be determined experimentally by fuel or the like. For example, in a general gasoline engine, it can be set to about 0.03 seconds.

  As described above, according to the present invention, high kinetic energy can be output by rapidly burning the expansion stroke cylinder at the time of restart, so that the combustion energy of the expansion stroke cylinder at the time of restart is increased. As a result, the engine startability can be improved.

  1 and 2 show a schematic configuration of a four-cycle spark ignition engine 1 according to the present invention. 3 is an enlarged view of a main part of the engine 1. FIG. 3A is a partially enlarged view of FIG. 1, and FIG. 3B is a bottom view of the combustion chamber. 4A and 4B are bottom views of the combustion chamber of the engine 1. FIGS. 4A and 4B show examples of partial ignition, and FIG. 4C shows an example in which all the spark plugs 15 are ignited simultaneously.

  With reference to the drawings, 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 plurality of spark plugs 15 </ b> A to 15 </ b> C are installed in the combustion chamber 14 of each of the cylinders 12 </ b> A to 12 </ b> D so that the plug tip faces the combustion chamber 14. Each of the spark plugs 15A to 15C is provided with an ignition device 27 for generating an electric spark. Of the plurality (three in the illustrated example) of spark plugs 15 </ b> A to 15 </ b> C, the spark plug 15 </ b> A is disposed at the center of the combustion chamber 14, and the remaining spark plugs 15 </ b> B and 15 </ b> C are in the longitudinal direction of the crankshaft 3. (In the illustrated example, the front side of the engine 1 is a spark plug 15B and the rear side is a spark plug 15C).

  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 according to the amount is injected toward the vicinity of the electrodes of the spark plugs 15A to 15C. In the present embodiment, the fuel injection valve 16a is constituted by a multi-hole injector having a plurality of injection holes. Each fuel injection valve 16a is connected to a fuel supply system 16 capable of controlling its fuel pressure. Then, the fuel supply system 16 is controlled by the ECU 2, whereby each fuel injection valve 16a is configured to inject fuel at a predetermined timing and fuel pressure. As the multi-hole type injector, for example, an equivalent one disclosed in Japanese Patent Application Laid-Open No. 2005-98121 previously proposed by the present applicant can be adopted. Omitted.

  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.

  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 functionally includes a fuel injection control unit 41, an ignition control unit 42, an intake 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 an air density estimation unit 47. It is out.

  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. In the present embodiment, the spark plugs 15A to 15C of the cylinders 12A to 12D are configured to be selectively ignited, and as shown in FIG. 4A, or only one of the spark plugs 15B and 15C (in the illustrated example, the spark plug 15B) disposed at the peripheral edge of the combustion chamber 14, as shown in FIG. 4B. As shown in FIG. 4 (C), simultaneous ignition for selectively igniting the plurality of spark plugs 15A to 15C, and time for igniting the plurality of spark plugs 15A to 15C over time, as shown in FIG. Ignition is possible.

  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.

  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. 5A and 5B, 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 crank angle after the compression top dead center is 90 ° CA, that is, the crank angle after the compression top dead center, for example, the crank angle after the compression top dead center. If the piston 13 can be stopped within a range R in which the angle becomes 100 to 120 ° CA, a predetermined amount of air is secured in the compression stroke cylinder, and the crankshaft 3 can be slightly reversed by the initial combustion. Combustion energy can be obtained. In addition, by securing a large amount of air in the expansion stroke cylinder, it is possible to generate sufficient combustion energy for normal rotation of the crankshaft 3 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. 6 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. 7 is an enlarged view after the vicinity of time t1 in FIG. 6 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. 8 is a flowchart showing the piston stop position detection control operation, FIG. 9 is an explanatory diagram showing the output signal of the crank angle signal, and FIG. 10 is the relationship between the elapsed time from the engine automatic stop and the estimated cylinder temperature. It is a graph which shows.

  When the flag is ON at the time point t0 when the automatic stop condition of the engine 1 is satisfied, the ECU 2 sets the target speed of the engine 1 to a normal idle speed when the engine 1 is not automatically stopped (hereinafter referred to as a normal idle speed). For example, in the engine 1 in which the normal idle speed is set to 650 rpm (the automatic transmission is in the drive (D) range), the target speed (idle speed when the automatic stop condition is satisfied) is set to about 850 rpm. By setting the automatic transmission to the neutral (N) range, the engine rotational speed Ne is controlled 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). . 6 and 7 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. 7, 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 t1, the engine rotational speed Ne gradually decreases and eventually stops at the time 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. 7, 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. Here, in this embodiment, after the top dead center rotational speed ne of the engine 1 is decelerated within a predetermined range (specifically, 260 rpm to 400 rpm), fuel is injected into the intake stroke based on the atmospheric state. If the air density is less than a predetermined value (for example, 1.08 kg / m ³ ), the fuel injection F1 is executed in the final intake stroke for the compression stroke cylinder 12C. Yes. Thereby, even in an environment with an extremely low air density such as an altitude, a homogeneous air-fuel mixture is generated in the cylinder of the compression stroke cylinder 12C so that slow combustion can be realized at the time of restart.

  When the engine speed Ne further decreases and the final compression top dead center passage timing (time point t4 shown in FIG. 7) 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. 7 (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. 7) from before the stop is the starting 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. 7) 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. 8 is a flowchart showing the piston stop position detection control operation. 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. 9A or FIG. 9B. 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. 9A, 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 becomes Low when the signal CA1 rises, and the second crank angle signal CA2 becomes 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. 9B, 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).

  Further, in the present embodiment, immediately before the engine 1 stops, that is, after the timing t4 when each cylinder reaches the last stop stroke, the compression stroke cylinder 12C is changed to the compression stroke cylinder 12C as necessary based on the above-described piston position detection result. In contrast, an additional fuel injection F2 is performed. This fuel injection F2 is a compression stroke cylinder based on an additional fuel injection map (not shown) in which the fuel injection amount is set to a larger value as the stop position estimated based on the experiment is closer to the bottom dead center. For 12C, it is executed at the time of the last compression stroke (after time t4 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 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. 10 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. Note that the compression stroke cylinder 12C takes the characteristic of T _t3 when fuel is injected only after timing t3, and takes the characteristic of T _t4 when additional fuel is injected after timing t4. Such characteristics are 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.

  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 when the air conditioner is operated, it is determined whether or not the engine automatic stop time started after the automatic stop of the engine 1 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 interior of the compression stroke cylinder 12C has not been diluted, the air density in the atmosphere is further 1.08 kg / m. It is determined whether the number is ³ or more (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 this embodiment, after the automatic stop condition is satisfied and the vehicle speed = 0, until the engine 1 is forcibly stopped, the compression stroke cylinder 12C is placed on the top dead center side of the stroke center. In addition to executing the control for stopping within the proper stop range R, the control related to the fuel injection F2 in FIG. 7 is used to make the stop position of the piston 13 of the compression stroke cylinder 12C more precisely than the center of the stroke. Since the control to stop within the appropriate stop range R on the side is executed, 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). In this case, in this embodiment, partial ignition as shown in FIGS. 4 (A) and 4 (B) is performed. As a result, even when fuel is injected into the compression stroke cylinder 12C after restarting, it is possible to realize sufficient slow combustion. 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). If it is determined NO and it is confirmed that the piston 13 has not moved due to misfire, partial ignition is performed again on the compression stroke cylinder 12C (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 last time during the automatic stop control of the engine 1 as shown in FIG. Since the fuel injection F1 is executed in the compression stroke cylinder 12C in the intake stroke, 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. However, even in this case, the partial ignition shown in FIG. 4 (A) or (B) is executed. Thereby, even when the fuel for reverse rotation at the time of restart is injected into the compression stroke cylinder 12C at the time of automatic stop, it is configured to realize sufficient slow combustion.

  Next, referring to FIG. 12, 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).

  In this embodiment, when the expansion stroke cylinder 12A is ignited in step S127, rapid combustion is achieved by simultaneously igniting all the spark plugs 15A to 15C. Thereby, the expansion stroke cylinder 12A is not only given a large piston stroke within a range restricted by the slow combustion of the compression stroke cylinder 12C, but also generates a large combustion energy even in the restricted piston stroke, It is possible to output kinetic energy.

  Further, the delay time is obtained from an ignition map M15 for the expansion stroke cylinder 12A set in advance according to the stop position of the piston 13. In the present embodiment, this delay time is set within a time in which the turbulence in the cylinder caused by the second fuel injection remains, and specifically, 0.03 sec is preferable. 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. 13, 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 16a is functionally configured (see step S101 and the like). 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 this embodiment, as shown by F2 in FIG. 7, 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 stop, the fuel injection control means The fuel injection valve is controlled 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. 5A).

  14A and 14B are graphs for illustrating the effects of the above-described embodiment. FIG. 14A is a graph showing the transition of the in-cylinder pressure at the crank angle CA, and FIG. 14B is a graph showing the transition of the heat generation rate at the crank angle CA. The graph (C) is a graph showing the transition of the mass combustion ratio at the crank angle CA.

  With reference to FIGS. 14A to 14C, in each of the above-described embodiments, when the air density is less than a predetermined value, such as when the air density is relatively low during high altitude travel, automatic stop control is performed. The fuel injection valve is controlled so as to inject fuel into the initial combustion cylinder in the last intake stroke, so that the 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. 14A to 14C, a slow combustion characteristic can be obtained. The heat loss caused by the heat released from the cylinder inner wall surface 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. 14C).

  FIG. 15 is a graph showing a change in the in-cylinder pressure during the initial combustion of the expansion stroke cylinder during restart.

  PL11 in FIG. 15 is a case where control is performed so as to accelerate the combustion speed at the time of initial combustion of the expansion stroke cylinder, and PL12 shows a case where such combustion speed control is not executed. As is apparent from the solid line PL11 in FIG. 15, when the expansion stroke cylinder 12A is rapidly burned during the initial combustion, the in-cylinder pressure can be increased extremely quickly. For this reason, it is possible to output sufficient kinetic energy even during the first combustion where the piston stroke is restricted. On the other hand, when the combustion rate is not controlled, as shown in PL12, the peak of the in-cylinder pressure cannot be increased, and the kinetic energy also decreases.

  As described above, in this embodiment, when the restart condition is satisfied and the restart control is started, first, the air-fuel mixture in the compression stroke cylinder 12C is ignited and the crank angle is reversed. In this process, the piston 13 of the expansion stroke cylinder 12A moves to the top dead center side, and the combustion chamber is compressed by the kinetic energy from the compression stroke cylinder 12C. However, in this reverse rotation operation, the expansion stroke cylinder 12A does not reach the top dead center, and the air-fuel mixture is ignited with a restricted piston stroke. Due to this ignition, the piston 13 of the expansion stroke cylinder 12A causes the engine 1 to rotate normally by the combustion energy of the air-fuel mixture. This combustion energy is rapidly accelerated by a combustion speed control means such as multi-point ignition. Even under a condition in which the piston stroke is restricted, the in-cylinder pressure can be rapidly increased and a large kinetic energy can be output.

  In this embodiment, the combustion speed control means uses the combustion time that would have been required when the compression stroke cylinder 12C was reversely burned with the fuel injected immediately after the restart request as the reference combustion time, and the expansion stroke cylinder 12A. The initial combustion time (for example, 11 msec) is made shorter than the reference combustion time (for example, 15 msec). For this reason, in this embodiment, at the time of initial combustion in the expansion stroke cylinder 12A, rapid combustion characteristics with a shortened combustion time are obtained, so that it is possible to output large kinetic energy at the time of initial combustion with a restricted piston stroke. become.

  In the present embodiment, the combustion speed control means makes the initial combustion time (for example, 28 msec) in the compression stroke cylinder 12C longer than the reference combustion time. For this reason, in this embodiment, the combustion in the compression stroke cylinder 12C for reversing the engine 1 at the time of restart is relatively slow combustion. For this reason, during the reverse rotation operation at the time of restart, heat loss caused by heat released from the combustion of the air-fuel mixture in the compression stroke cylinder 12C from the inner wall surface of the cylinder becomes moderate, and a relatively large amount of combustion energy is moved. Since the energy can be converted into energy, the piston stroke in the expansion stroke cylinder 12A also increases within a limited range.

  In the present embodiment, the combustion speed control means includes a plurality of ignition plugs 15A to 15C arranged for each cylinder, and an ignition control unit 42 that can selectively control the ignition plugs 15A to 15C. The ignition control unit 42 simultaneously ignites a plurality of spark plugs 15A to 15C during the initial combustion of the expansion stroke cylinder 12A at the time of restart (see FIG. 4C). For this reason, in the present embodiment, the combustion speed of the air-fuel mixture is controlled to a desired speed by ignition control, and rapid combustion in the expansion stroke cylinder 12A can be easily realized.

  Further, in the present embodiment, the spark plugs 15A to 15C are disposed at the central portion and the peripheral portion of each of the cylinders 12A to 12D, and the ignition control unit 42 is the first in the compression stroke cylinder 12C at the time of restart. At the time of combustion, only a part of the center and peripheral spark plugs 15A to 15C is ignited, and at the time of initial combustion in the expansion stroke cylinder 12A at the time of restart, the spark plugs 15A to 15C are simultaneously ignited. It is something to control. For this reason, in the present embodiment, during the initial combustion in the compression stroke cylinder 12C at the time of restart, a large kinetic energy is extracted from the compression stroke cylinder 12C by slow combustion, and the piston stroke of the expansion stroke cylinder 12A is within a limited range. In addition, the expansion stroke cylinder 12A can output large kinetic energy due to rapid combustion in a restricted piston stroke.

  Further, in the present embodiment, the combustion speed control means includes a fuel supply system 16 including a fuel injection valve 16 a that injects fuel into the cylinder, and a fuel injection timing and a fuel injection amount of the fuel injection valve 16 a by the fuel supply system 16. A fuel injection control unit 41 for controlling and an ignition control unit 42 for controlling the ignition timing of the spark plugs 15A to 15C, and the time from when the fuel injection valve 16a injects fuel until the spark plugs 15A to 15C are ignited The interval is increased at the time of initial combustion of the compression stroke cylinder 12C at the time of restart, and is shortened at the time of initial combustion of the expansion stroke cylinder 12A at the time of restart. Also in this aspect, it is possible to achieve slow combustion in the compression stroke cylinder 12C and rapid combustion in the expansion stroke cylinder 12A according to the ignition timing. Accordingly, the kinetic energy from both cylinders 12A and 12D can be increased.

  Further, in the present embodiment, the time interval (ignition delay time defined in the map M15 in FIG. 12) at the time of initial combustion of the compression stroke cylinder 12C at the time of restart is in the cylinder induced by the injected fuel. This is a predetermined time during which the disturbance remains. For this reason, in this embodiment, during the initial combustion when the expansion stroke cylinder 12A is restarted, the fuel injection causes a disturbance, and the spark plugs 15A to 15C ignite the air-fuel mixture while the disturbance remains. The combustion rate is further promoted, and rapid combustion can be realized. The predetermined time can be determined experimentally by fuel or the like. For example, in a general gasoline engine 1 as in this embodiment, it can be set to about 0.03 seconds.

  As described above, the combustion speed control means includes a plurality of ignition plugs 15A to 15C, an ignition control unit that selectively controls ignition of these ignition plugs 15A to 15C, and an expansion stroke cylinder set in the control map M15. It can be realized by setting the ignition delay time of 12A to be shorter than that during normal operation.

  Further, as shown in FIGS. 16 and 17, a hydrogen injection injector 160 may be employed in addition to the fuel injection valve 16a.

  FIG. 16 shows an example in which a direct injection type hydrogen injection injector 160 is employed in a port injection type gasoline engine. FIG. 17 shows only a hydrogen injection injector 160 (FIG. 17B) in the combustion chamber 17 of the direct injection type gasoline engine. The example which employ | adopted is shown.

  In any form, when hydrogen is used in combination, the combustion speed of the fuel is increased. Hydrogen has a wide flame range and is easy to ignite, and also has a high combustion speed. By mixing hydrogen with gasoline and using it as a fuel, the ignition speed and combustion speed are increased, and the expansion stroke cylinder 12A at the time of restart is used. It is possible to output a large kinetic energy by accelerating the initial combustion.

  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 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 can reduce the compression pressure due to the latent heat of vaporization and ensure the vaporization performance as much as possible. A compatible timing (predetermined fuel injection timing) may be determined by experiments or the like, and one fuel injection may be performed at the predetermined fuel injection timing.

  Further, 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 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. FIG. 2 is an enlarged view of a main part of the engine, in which (A) is a partially enlarged view of FIG. 1 and (B) is a bottom view of a combustion chamber. It is a bottom view of the combustion chamber of the engine, (A) (B) shows an example of partial ignition, (C) shows an example in which all of the spark plugs ignited simultaneously. 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. 7 is a partially enlarged view of FIG. 6, 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 graph for showing an effect of an embodiment mentioned above, (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. It is a graph which shows the change of the cylinder pressure at the time of the first combustion of the expansion stroke cylinder at the time of restart. It is a fragmentary sectional view which shows the example which employ | adopted the direct injection type hydrogen injection injector for the port injection type gasoline engine. The example which employ | adopted the injector for hydrogen injection as the combustion chamber of a direct injection type gasoline engine is shown, (A) is a fragmentary sectional view, (B) is a bottom view of a combustion chamber.

Explanation of symbols

1 4-cycle multi-cylinder engine 2 ECU
3 Crankshaft 12A Expansion stroke cylinder 12C Compression stroke cylinder 13 Piston 14 Combustion chamber 15 Spark plug 16 Fuel supply system 16a Fuel injection valve 29 Intake air 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 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 Air density estimation unit CA Crank angle CA _P piston stop position R Proper stop range SW1 Large Barometric pressure sensor 160 Hydrogen injector

Claims (3)

A multi-cylinder engine starter that, when a multi-cylinder engine restart condition is satisfied, burns the compression stroke cylinder, reverses it by a predetermined crank angle, and then burns the expansion stroke cylinder to restart the multi-cylinder engine. In
Piston position detecting means for detecting the piston position of each cylinder;
Combustion speed control means for controlling the combustion speed of each cylinder, wherein the combustion speed control means includes a plurality of ignition plugs arranged for each cylinder, and an ignition control unit capable of selectively controlling the ignition plugs. The spark plugs are disposed at the center and the periphery of each cylinder, and the ignition control unit ignites only some spark plugs at the time of initial combustion in the compression stroke cylinder at the time of restart. A starting device for a multi-cylinder engine is characterized in that, at the time of initial combustion in the expansion stroke cylinder at the time of restart, control is performed so that the center and peripheral spark plugs are simultaneously ignited . A multi-cylinder engine starter that, when a multi-cylinder engine restart condition is satisfied, burns the compression stroke cylinder, reverses it by a predetermined crank angle, and then burns the expansion stroke cylinder to restart the multi-cylinder engine. In
Piston position detecting means for detecting the piston position of each cylinder;
Combustion speed control means for controlling the combustion speed of each cylinder;
With
The combustion speed control means includes a fuel supply system including a fuel injection valve that injects fuel into the cylinder, a fuel injection control unit that controls fuel injection timing and fuel injection amount of the fuel injection valve by the fuel supply system, and an ignition plug An ignition control unit that controls the ignition timing of the expansion stroke cylinder at the time of restart, and the time interval from the fuel injection at the time of initial combustion of the expansion stroke cylinder to the ignition timing at the time of restart, A starter for a multi-cylinder engine characterized by being shortened with respect to a time interval from ignition to ignition timing . The starter for a multi-cylinder engine according to claim 2 ,
The multi-cylinder engine starter characterized in that the time interval at the time of initial combustion of the expansion stroke cylinder at the time of restart is a predetermined time during which the turbulence in the cylinder induced by the injected fuel remains .

Images