JP4415841B2 - 4-cycle engine starter - Google Patents

Description

  The present invention relates to an engine starter configured to automatically stop an engine when a predetermined automatic stop condition is satisfied, and then restart when the predetermined restart condition is satisfied.

  In recent years, in order to enhance combustion performance and exhaust performance, engine exhaust gas recirculation control (so-called internal EGR control) in which an intake valve is opened during an exhaust stroke has been considered (for example, see Patent Document 1). According to such a method, a pumping loss can be reduced by a large amount of internal EGR, and fuel consumption can be improved by compression self-ignition.

Furthermore, in recent years, in order to reduce fuel consumption and reduce CO ₂ emissions, restart conditions such as when the engine is automatically stopped once during idle operation and then the vehicle is started by the driver. A technology for automatic engine stop control (so-called idle stop control) has been developed that automatically restarts the engine at the time when is established, and this idle stop control and the internal EGR control are used in combination. Has been proposed.
JP 2001-107759 A

  However, when the idle stop control and the internal EGR control are used in combination, the output (torque) may be reduced when the engine is restarted by the idle stop control.

  That is, when the internal EGR control is executed during the idle stop control, the temperature in the combustion chamber of the cylinder that becomes the compression stroke when the engine is restarted excessively rises, and as a result, the mixture before the compression top dead center is increased. This is because the compression self-ignition and the accompanying brake (force in the reverse direction) are likely to occur.

  Here, the temperature in the combustion chamber rises because when the engine is stopped, there is almost no gas flow in the engine, so that the heat of the engine itself (cylinder, etc.) heated during normal operation is heated in the combustion chamber and the exhaust system. Transmission to gas is a major factor.

  Specifically, in the internal EGR control of Patent Document 1, the exhaust system gas heated at the time of the automatic stop is sucked by the cylinder that becomes the intake stroke at the time of the restart, so that the combustion chamber during the subsequent compression stroke There was a possibility that the temperature would rise excessively, resulting in a decrease in output during restart.

  Therefore, it is conceivable that the internal EGR control is stopped until the restart of the engine is completed after the engine stop condition is satisfied, but in this case, a restart request is issued during the engine automatic stop operation period. It is necessary to repeat the stop and execution of the internal EGR control every time the engine stop condition and the restart condition are satisfied, including the case where the engine restart condition and the restart condition are executed. As a result, the deterioration of the switching mechanism has been accelerated.

  The present invention has been made in view of the above problems, and provides a starter for a four-cycle engine that can improve restart performance while reducing the frequency of exhaust recirculation execution or stop as much as possible. The purpose is that.

  In order to solve the above-mentioned problem, the present invention stops the fuel supply when the predetermined engine automatic stop condition is satisfied, stops the engine, and when the predetermined restart condition is satisfied after the fuel supply is stopped. In a four-cycle engine starter that performs automatic stop control that restarts the engine by performing combustion in a cylinder that is in an expansion stroke at least when the engine is stopped, the exhaust valve is opened in the exhaust stroke. In addition, a valve drive means that enables exhaust gas recirculation into the cylinder by a restart valve operation that opens again in the intake stroke, and a valve drive control unit that can switch execution or stop of the restart valve operation by the valve drive means; The engine automatic stop condition is satisfied, and the engine speed when the fuel supply is stopped is higher than the idle speed during normal operation. The valve drive control unit stops the restart valve operation in the middle of the engine automatic stop operation period after the fuel supply is stopped, and at least a predetermined time from the time when the restart condition is satisfied after the engine is stopped. It is characterized by restarting after elapses.

  According to the present invention, after the engine automatic stop condition is satisfied, when the restart condition is satisfied earlier than the stop of the restart valve operation, the engine is restarted while maintaining the state in which the restart valve operation is being performed. Since the engine can be started, the switching frequency of the restart valve operation can be reduced compared with the case where the stop or execution of the restart valve operation is switched every time the engine automatic stop condition and the restart condition are satisfied.

  Further, in the present invention, the restart valve operation is stopped until a predetermined time elapses after the restart condition is established after the engine is stopped, so that the cylinders in the intake stroke when the engine is stopped Since it is possible to suck in fresh air and stop the recirculation of the heated gas in the combustion chamber and exhaust system, the top dead center of compression is compared with the case of performing recirculation of exhaust during the automatic stop. Brake due to compression self-ignition of the previous air-fuel mixture can be suppressed, and restart performance can be improved.

  In the present invention, since the restart valve operation is executed until the middle of the engine automatic stop period as described above, the scavenging efficiency in the cylinder is reduced during this period, but the fuel supply is stopped. Since the engine speed of the engine is higher than the idling speed during normal operation, the number of piston operations can be increased more than when the engine speed is maintained as it is when the fuel supply is stopped. Can be supplemented.

  Therefore, according to the present invention, the restart performance can be improved while reducing the switching frequency of exhaust recirculation execution or stop as much as possible.

  The predetermined time is a time until the engine speed becomes relatively high, and can be set to a time until 3TDC (the third top dead center) elapses, for example.

  The four-cycle engine starter further includes an intake flow rate control unit that adjusts an intake flow rate flowing into the cylinder, and the intake flow rate control unit includes a cylinder that stops in an expansion stroke and a cylinder that stops in a compression stroke when the engine is stopped. For each of the above, the intake flow rate is reduced so that at least the intake amount in the last intake stroke before the stop is reduced, and the valve drive control unit performs the restart valve operation on the cylinder that stops in the expansion stroke when the engine is stopped. It is preferable to execute until the last intake stroke before stopping, and to stop the cylinder that stops in the compression stroke when the engine stops from the last intake stroke before stopping.

  According to this configuration, it is possible to increase the probability that the cylinder that is in the expansion stroke at the time of the automatic stop is set to a proper stop position having a relatively large volume, so that the restart performance can be further improved.

  That is, in the above configuration, although the intake air amount in the last intake stroke before the stop of each cylinder that stops in the expansion stroke and the compression stroke when the engine is stopped is reduced by the intake flow rate control unit, the expansion stroke when the engine is stopped is reduced by the valve drive control unit. Since the resuming valve operation is executed until the intake stroke of the cylinder, the intake air of the cylinder increases due to the intake air from the exhaust passage side, while the intake amount of the cylinder that becomes the compression stroke when the engine is stopped Less. Therefore, the compression resistance of the cylinder that is in the expansion stroke when the engine is stopped is larger in both cylinders. As a result, in the cylinder that is in the expansion stroke when the engine is stopped, the piston stop position is closer to the bottom dead center than the middle of the expansion stroke, and in the cylinder that is in the compression stroke when the engine is stopped, the piston stop position is higher than the middle of the stroke. The probability that such an engine stop state is obtained is increased.

  In this way, the intake air amount and the piston stop position can be adjusted by executing or stopping the restart valve operation, and in particular, the air amount entering the cylinder can be directly adjusted.

  In the four-cycle engine starter, the intake air amount adjusting means is a predetermined period of time from at least immediately after the fuel supply is stopped until the last intake stroke before the start of the cylinder that stops in the expansion stroke when the engine is stopped. It is preferable to increase the intake air flow rate.

  According to this configuration, since the intake air flow rate can be increased by the intake air amount adjusting means until the last intake stroke before the stop of the cylinder that becomes the expansion stroke when the engine is stopped is started, the restart valve operation is executed. The scavenging efficiency inside can be further supplemented.

  In the four-cycle engine starter, when the restart condition is satisfied immediately after the fuel supply is stopped, it is preferable to restart the fuel supply after executing the exhaust stroke or the intake stroke of all the cylinders at least once.

  According to this configuration, since the scavenging can be performed at least once immediately after the fuel supply is stopped, the combustion failure due to the residual gas can be suppressed and the restart performance can be further improved.

  In the four-cycle engine starter, the intake valve opens near the top dead center and closes at a stage before the bottom dead center. It is preferable that the valve is opened during the intake stroke and is closed later than the intake valve.

  According to this configuration, the exhaust valve opens during the intake stroke and closes later than the intake valve. Therefore, in this valve opening operation, a relatively large amount of burned gas discharged during the exhaust stroke is used as internal EGR gas. Can be introduced into the cylinder. As a result, the fresh air introduced into the cylinder can be heated while ensuring the charging efficiency, and as a result, compression self-ignition in the subsequent compression stroke is ensured. Moreover, since the structure which opens an exhaust valve in the intake stroke is employ | adopted, internal EGR is realizable at the timing which an exhaust valve does not interfere with a piston. Therefore, the geometric compression ratio can be increased as much as possible.

  According to the present invention, the restart performance can be improved while reducing the switching frequency of exhaust recirculation execution or stop as much as possible.

  FIG. 1 and FIG. 2 show a schematic configuration of a four-cycle spark ignition type engine having an engine starter according to the present invention. The engine includes an engine body 1 having a cylinder head 3 and a cylinder block 4 and an ECU 2 for engine control.

  The engine body 1 is provided with four cylinders (# 1 cylinder 5A, # 2 cylinder 5B, # 3 cylinder 5C and # 4 cylinder 5D), and a crankshaft is provided in each cylinder 5A to 5D. By fitting the piston 7 connected to 6, a combustion chamber 8 is formed above the piston 7.

  At the top of the combustion chamber 8 of each of the cylinders 5A to 5D, an ignition plug 9 is installed so that the plug tip faces the combustion chamber 8. The spark plug 9 is provided with an ignition device 10 for generating an electric spark. A fuel injection valve 11 that directly injects fuel into the combustion chamber 8 is provided on the side of the combustion chamber 8.

  This fuel injection valve 11 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 combustion control unit 12 of the ECU 2. The fuel corresponding to the amount is injected toward the vicinity of the electrode of the spark plug 9.

  In addition, an intake port 13 and an exhaust port 14 that open toward the combustion chamber 8 are provided above the combustion chamber 8 of each of the cylinders 5A to 5D, and an intake valve 15 is connected to these ports 13 and 14. And an exhaust valve 16 respectively.

  The intake valve 15 is driven at a timing indicated by a symbol L1 in FIG. That is, the intake valve 15 is opened at a stage before the exhaust top dead center and closed at a stage before the intake bottom dead center.

  On the other hand, the exhaust valve 16 can be driven by a valve operating mechanism 17 for a normal valve opening operation performed during an exhaust stroke and a resuming valve operation performed during an intake stroke.

  FIGS. 3 and 4 are a perspective view and a side sectional view showing a specific configuration of the valve mechanism 17.

  Referring to FIGS. 1, 3 and 4, the valve mechanism 17 includes a first cam 19 for a normal valve opening operation provided on a camshaft 18 for driving the exhaust valve 16 and a relatively large lift amount, and a relatively lift. And a second cam 20 for resuming valve operation with a small amount, provided between the cams 19, 20 and the intake valve 15, the state in which the intake valve 15 is driven by the first cam 19 and the second cam 20. A switching mechanism 21 for switching to a state driven by the cam 20 is provided.

  The first cams 19 are paired in pairs, and the second cam 20 is disposed between the first cams 19 in the axial direction of the camshaft 18. Further, the first cam 19 and the second cam 20 are arranged so as to be displaced around the axis of the camshaft 18 so as to execute a valve opening operation (see FIG. 5) of the exhaust valve 16 described later. .

  The switching mechanism 21 includes a center tappet 22 installed at a position corresponding to the second cam 20 and a side tappet 24 including a pair of protrusions 23 installed at a position corresponding to the first cam 19. Between the bottom of the side tappet 24 and the bottom surface of the center tappet 22, a pair of compression coil springs 25 that urge the top surface of the center tappet 22 in the direction in which it presses against the second cam 20 are disposed. ing.

  Further, the corresponding projecting portions 23 of the center tappet 22 and the side tappet 24 are respectively formed with corresponding lock holes 26, 27, and when the center tappet 22 is in the raised position shown in FIG. 27 is configured to be in a communication state. Further, in the lock hole 26 of the center tappet 22, first and second lock pins 28 and 29 are disposed so as to be slidable in the axial direction. In the lock hole 27 provided in one of the two protrusions 23 of the side tappet 24, a first holder 30 having a recess into which the tip of the lock pin 29 is inserted is disposed, and the both protrusions A second holder 32 that holds the plunger 31 is disposed in the lock hole 27 provided on the other side of 23.

  In the lock hole 26 of the center tappet 22, a compression coil spring 33 that biases the first lock pin 28 toward the base end (plunger 31 side) and the second lock pin 29 are connected to the first lock pin 28. A compression coil spring 34 that is biased to the side is disposed.

  When the supply of hydraulic oil to the switching mechanism 21 is stopped via the hydraulic oil supply / discharge passage 35 formed in the side tappet 24, the compression coil spring 33, as shown in FIG. Due to the urging force of 34, the first lock pin 28 is accommodated in a state straddling the second holder 32 and the lock hole 26 of the center tappet 22, and the second lock pin 29 is accommodated in the first holder 30. By being accommodated, the center tappet 22 and the side tappet 24 are held in a connected state. Thereby, the exhaust valve 16 is operated by the first cam 19 and the second cam 20.

  On the other hand, when hydraulic fluid is supplied between the plunger 31 and the bottom of the second holder 32 from the hydraulic fluid supply / discharge passage 35, the first lock pin 28 pushed by the plunger 31 causes the center tappet 22 to move. When the second lock pin 29 is housed in the first holder 30, the center tappet 22 and the side tappet 24 are disconnected from each other. In this state, since the center tappet 22 is displaced relative to the side tappet 24 (up and down movement), the driving force of the center tappet 22 driven by the second cam 20 is applied to the intake valve 15 via the side tappet 24. While being transmitted, the exhaust valve 16 is actuated by the first cam 19.

  Then, by the valve operating mechanism 17, the exhaust valve 16 performs a normal valve opening operation indicated by a symbol L2 in FIG. 5 and a resuming valve operation indicated by a symbol L3. That is, the exhaust valve 16 is opened from immediately before the bottom dead center to immediately after the top dead center as indicated by reference numeral L2 by the first cam 19, and at the intake stroke as indicated by reference numeral L3 by the second cam 20. It is opened from the middle to the stage after the bottom dead center.

  In other words, in the present embodiment, the intake valve 15 is opened from before the top dead center to the stage before the bottom dead center as indicated by reference numeral L1, while the exhaust valve 16 is intaked as indicated by reference numeral L3. The valve is opened during the stroke and is closed later than the intake valve 15.

  By the restart valve operation of the exhaust valve 16, the burned gas discharged in the exhaust stroke can be introduced into the cylinder in a relatively large amount as internal EGR gas.

  In this embodiment, the camshaft 18 having the first cam 19 and the second cam 20, the switching mechanism 21, and hydraulic oil supply means (not shown) for supplying hydraulic oil to the switching mechanism 21 are provided. This constitutes an example of the valve driving means.

  Referring to FIGS. 1 and 2 again, an intake passage 36 and an exhaust passage 37 are connected to the intake port 13 and the exhaust port 14. A downstream side of the intake passage 36 close to the intake port 13 is an independent branch intake passage 36a corresponding to each of the cylinders 5A to 5D, and an upstream end of each branch intake passage 36a communicates with a surge tank 36b. Yes. A common intake passage 36c is provided upstream of the surge tank 36b, and a throttle valve 39 driven by an actuator 38 is provided in the common intake passage 36c. An airflow sensor 40 for detecting the intake air flow rate and an intake air temperature sensor 41 for detecting the intake air temperature are provided on the upstream side of the throttle valve 39, and the intake pressure (negative pressure) is detected on the downstream side of the throttle valve 39. An intake pressure sensor 42 is provided.

  The engine body 1 is also provided with an alternator 43 connected to the crankshaft 6 by a timing belt or the like. The alternator 43 has a built-in regulator circuit 43a that adjusts the output voltage by controlling the current of a field coil (not shown) and controls the control signal from the ECU 2 that is input to the regulator circuit 43a. The control of the amount of power generation corresponding to the electric load of the vehicle, the voltage of the vehicle-mounted battery, and the like is executed based on the above.

  Further, the engine is provided with two crank angle sensors 44 and 45 for detecting the rotation angle of the crankshaft 6, and the rotation speed of the engine is detected based on detection signals output from the respective crank sensors 44. In addition, as will be described later, the rotation direction and the rotation angle of the crankshaft 6 are detected based on detection signals out of phase output from the crank sensors 44 and 54 described above.

  The engine body 1 is provided with cam sensors 46 for detecting a specific rotational position for cylinder identification provided on the camshaft 18 and a water temperature sensor 47 for detecting the cooling water temperature of the engine. An accelerator opening sensor 48 that detects an accelerator opening corresponding to the driver's accelerator operation amount is provided on the vehicle body side.

  The ECU 2 is a control unit that comprehensively controls the operation of the engine. The engine of the present embodiment automatically stops the fuel supply by stopping fuel supply to each of the cylinders 5A to 5D (fuel cut) at a predetermined timing when a preset automatic engine stop condition is satisfied. Then, the engine is configured to perform control (idle stop control) that automatically restarts the engine when a restart condition is satisfied, for example, when an accelerator operation is performed by the driver. 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 airflow sensor 40, the intake pressure sensor 42, the crank angle sensors 44 and 45, the cam angle sensor 46, the water temperature sensor 47, and the accelerator opening sensor 48, and the fuel injection valve 11 and the throttle. The drive signals are output to the actuator 38 of the valve 39, the ignition device 10, the regulator circuit 43a of the alternator 43, and the starter motor (not shown). The ECU 2 functionally includes a combustion control unit 12, a power generation amount control unit 49, a piston position detection unit 50, an in-cylinder temperature estimation unit 51, and a VVL (Variable Valve Lift) control unit 52.

  The combustion control unit 41 mainly sets a fuel injection timing, a fuel injection amount in each injection, an ignition timing, an intake air flow rate, and the like, and controls combustion in each cylinder 5A to 5D.

  With respect to the fuel injection amount and the fuel injection timing, these are set appropriately, and the control signal is output to the fuel injection valve 11. 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 combustion control unit 41 also sets the divided injection timing and fuel distribution.

  As for the ignition timing, an appropriate ignition timing is set for each of the cylinders 5 </ b> A to 5 </ b> D, and an ignition signal is output to each ignition device 10.

  Regarding the intake flow rate, an appropriate intake flow rate is set for each of the cylinders 5A to 5D, and an opening degree signal of the throttle valve 39 corresponding to the intake flow rate is output to the actuator 38. In particular, in this embodiment, as will be described later, the opening of the throttle valve 39 is reduced during the engine automatic stop timing to reduce the intake air flow rate for each of the cylinders 5A to 5D.

  The power generation amount control unit 49 sets an appropriate power generation amount of the alternator 43 and outputs the drive signal to the regulator circuit 43a. In particular, in this embodiment, as will be described later, the load on the crankshaft 6 is changed by adjusting the amount of power generated by the alternator 43 when the engine is automatically stopped, and the piston 7 is stopped in an appropriate range suitable for restart. It is carried out. Also, at the time of restart, control is performed to increase the engine load by generating more power than usual, and to prevent the engine from blowing up (an increase in the engine speed more rapidly than necessary).

  The piston position detector 50 detects the piston position based on the detection signals of the crank sensors 44 and 45. 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 the present 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 5A to 5D at the time of restart is accordingly performed. It is carried out.

  The in-cylinder temperature estimation unit 51 uses each map 5A by using a map obtained in advance through experiments or the like based on the engine water temperature detected by the water temperature sensor 47, the intake air temperature detected by the intake air temperature sensor 41, or the like. The air temperature in the cylinder of ˜5D is estimated.

  The VVL control unit 52 controls the hydraulic oil supply means (not shown) to switch the supply or stop of the hydraulic oil to the switching mechanism 21, thereby turning ON or OFF the restart valve operation of the exhaust valve 16 by the switching mechanism 21 ( Hereinafter, the execution and stop of the VVL control are switched.

  Next, the idle stop control of this embodiment will be described below. In the idle stop control, the fuel supply is stopped to stop the engine when a predetermined engine automatic stop condition is satisfied, and the engine is restarted when the predetermined restart condition is satisfied after the engine is stopped. In the present embodiment, the restart valve operation is stopped during the engine automatic stop period after the fuel supply is stopped. As a result, when the restart condition is satisfied during the automatic stop period, the engine can be restarted with the restart valve operation being executed, so that the restart valve operation is stopped after stopping the fuel supply. Thus, an increase in the switching frequency of the restart valve operation can be suppressed.

  When restarting, combustion is first performed in the compression stroke cylinder, and the piston 7 is pushed down to reverse the crankshaft 6 slightly. As a result, the piston 7 of the expansion stroke cylinder is temporarily raised (closed to top dead center), and the air in the cylinder (which becomes the air-fuel mixture after fuel injection) is compressed and ignited and burned. ing. By this combustion, a driving torque in the normal rotation direction is applied to the crankshaft 6 to restart the engine.

  In order to properly restart the engine simply by igniting the fuel injected into a specific cylinder as described above, sufficient combustion energy is obtained by burning the air-fuel mixture in the expansion stroke cylinder. Accordingly, the cylinder that reaches the compression top dead center (in this embodiment, the compression stroke cylinder and the intake stroke cylinder) must overcome the compression reaction force and exceed the compression top dead center. Therefore, it is necessary to ensure a sufficient amount of air in the expansion stroke cylinder.

  As shown in FIGS. 6A and 6B, since the phases of the compression stroke cylinder and the expansion stroke cylinder are shifted by 180 ° CA, the pistons 7 operate in opposite directions. If the piston 7 of the expansion stroke cylinder is located on the bottom dead center side with respect to the stroke center, the amount of air in the cylinder increases and sufficient combustion energy is obtained. However, when the piston 7 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 6 is reversed by the initial combustion at the time of restart. Insufficient combustion energy can be obtained.

  On the other hand, a predetermined range R slightly above the top dead center side, for example, the crank angle after the compression top dead center, is located at the center of the stroke of the expansion stroke cylinder, that is, the crank angle after compression top dead center is 90 ° CA. If the piston 7 can be stopped within the range R of 100 to 120 ° CA, a predetermined amount of air is secured in the compression stroke cylinder, and the combustion is such that the crankshaft 6 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 6 and to reliably restart the engine (hereinafter referred to as “this”). The range R is set as the appropriate stop range R).

  The ECU 2 performs the following control so as to stop the piston 7 within the proper stop range R. FIG. 7 is a time chart when the engine is automatically stopped by this control, and shows engine speed Ne, crank angle CA, VVL control ON / OFF, throttle valve 39 opening degree K, and stroke transition of each cylinder. For the sake of brevity, it is assumed that # 1 cylinder 12A is an expansion stroke cylinder, # 2 cylinder 12B is an exhaust stroke cylinder, # 3 cylinder 12C is a compression stroke cylinder, and # 4 cylinder 12D is an intake stroke cylinder. .

  The ECU 2 sets the target speed of the engine to a value higher than a normal idle speed when the engine is not automatically stopped (hereinafter referred to as an idle speed during normal operation) at a time t0 when the automatic engine stop condition is satisfied. For example, in an engine 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 (N)). By setting to (range), control for stabilizing the engine rotational speed Ne at a rotational speed slightly higher than the normal idle rotational speed is executed. Further, during the normal operation up to the time point t0, the VVL control is executed (ON). Further, the opening K of the throttle valve 39 is adjusted so that the boost pressure Bt is stabilized at a relatively high predetermined value (about −400 mmHg).

  Then, fuel injection is stopped at time t1 when the engine speed Ne is stabilized at the target speed, and the engine speed Ne is decreased. Further, at the fuel injection stop time t1, which is the initial stage of the control operation for automatically stopping the engine, the opening K of the throttle valve 39 is set at the idling time when the air-fuel ratio in the cylinder is set to the excess air ratio λ = 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 engine operation). That is, when the combustion state immediately before the time point t1 is that the in-cylinder air-fuel ratio is set to an excess air ratio λ = 1 to near λ = 1 and the combustion is homogeneously performed, the opening K of the throttle valve 39 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 39 is maintained as it is (the relatively large opening during stratified combustion). . FIG. 7 shows the former case.

  Because of this control, the boost pressure Bt starts to increase slightly after time t1 (when the combustion just before time t1 is homogeneous combustion) or maintains a relatively high boost pressure Bt (when just before time t1 is stratified combustion), At this time point t1, the restart valve operation is executed to reduce the exhaust gas scavenging performance, but the exhaust gas scavenging performance can be supplemented by increasing the boost pressure Bt or maintaining a relatively high boost pressure Bt.

  Further, the ECU 2 temporarily stops the power generation of the alternator 43 at time t1. This reduces the rotational resistance of the crankshaft 6 and prevents the engine rotational speed Ne from stopping too quickly.

  Since the engine rotates by inertia after time t1, the engine speed Ne gradually decreases and eventually stops at time t6, but this decrease in engine speed Ne is slightly increased as shown in FIG. It decreases while repeating down (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 # 1 cylinder 5A and the # 3 cylinder 5C is 0 ° CA, and the alternate long and short dash line indicates the # 2 cylinder 5B. And the crank angle when the top dead center of the # 4 cylinder 5D is 0 ° CA. The solid line and the alternate long and short dash line are in opposite phases with respect to 90 ° CA. In a four-cylinder four-cycle engine, one of the cylinders reaches compression top dead center every 180 ° CA. Therefore, this time chart shows either at the top of the waveform indicated by a solid line or a one-dot chain line (crank angle = 0 ° CA). This indicates that the cylinder passes the compression top dead center.

  The timing at which any one of the cylinders becomes the compression top dead center coincides with the timing of the up-down valley of the engine rotational speed Ne. In other words, the rotational speed Ne of the engine gradually declines every time each cylinder reaches compression top dead center, and then gradually rises up and down again when it exceeds the compression top dead center, gradually repeating up and down. It goes down.

  Then, in the compression stroke cylinder 5C that reaches the compression top dead center after the time t5 when the last compression top dead center is passed, the air pressure increases as the piston 7 rises due to the inertial force, and the piston 7 rises due to the compression reaction force. The crankshaft 6 is reversely rotated without exceeding the dead point. Since the air pressure of the expansion stroke cylinder 5A increases due to the reverse rotation of the crankshaft 6, the piston 7 of the expansion stroke cylinder 5A is pushed back to the bottom dead center side according to the compression reaction force, and the crankshaft 6 rotates forward again. First, the reverse rotation and the normal rotation of the crankshaft 6 are repeated several times, and the piston 7 stops after reciprocating. The stop position of the piston 7 is substantially determined by the balance of the compression reaction force in the compression stroke cylinder 5C and the expansion stroke cylinder 5A, and is influenced by the intake resistance of the intake stroke cylinder 5D, the friction of the engine, and the like. This also changes depending on the rotational inertia of the engine at the time t5 when the compression top dead center is exceeded, that is, the level of the engine rotational speed Ne.

  Therefore, in order to stop the piston 7 of the expansion stroke cylinder 5A within the proper stop range R, first, the compression reaction forces of the expansion stroke cylinder 5A and the compression height cylinder 5C are sufficiently increased, respectively, and the compression of the expansion stroke cylinder 5A 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 high / low cylinder 5C by a predetermined value or more.

  For this purpose, the throttle valve 39 is closed at a time t2 when a predetermined time has elapsed from the stop of the fuel injection and the opening K is reduced to lower the boost pressure Bt, so that the expansion stroke cylinder 5A and the compression stroke cylinder 5C For each, the intake amount in the last intake stroke before the engine is stopped is reduced.

  In addition to this, in the present embodiment, the VVL control is stopped at time t4 when the intake bottom dead center in the final intake stroke of the expansion stroke cylinder 5A is exceeded. Thus, in the final intake stroke, the expansion stroke cylinder 5A can be sucked air from the intake valve and the exhaust valve, while the compression stroke cylinder 5C is sucked air only from the intake valve. In combination with the adjustment of the opening degree K of the throttle valve 39, the intake flow rate of the expansion stroke cylinder 5A can be increased more reliably than the compression stroke cylinder 5C.

  In particular, when the opening degree K of the throttle valve 39 is adjusted, the opening degree is caused by the distance to the combustion chamber 8 (that is, the passage lengths of the common intake passage 36c, the surge tank 36b, and the branch intake passage 36a). While there is a time lag from the adjustment of K to the change of the intake flow rate, in the VVL control, the gas communication path into the combustion chamber 8 is blocked by opening and closing the exhaust valve 16, so that the VVL control is stopped. As a result of having immediacy before the change of the intake flow rate, it is possible to reliably reduce the intake flow rate to the compression stroke cylinder 5C at the time point t4.

  By the way, in the process in which the engine is automatically stopped in this way and the engine rotational speed decreases, the engine rotational speed (top dead center rotational speed) ne and the expansion when each cylinder 5A to 5D passes through the compression top dead center. There is a clear correlation with the piston stop position of the stroke cylinder 5A. That is, the piston stop position of the expansion stroke cylinder 5A 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.

  By utilizing 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 t4]) is within a certain speed range. Such control is performed so that the piston 7 of the expansion stroke cylinder 5A is more reliably stopped within the appropriate stop range R. Specifically, the load (engine load) of the crankshaft 6 is adjusted by increasing / decreasing the power generation amount of the alternator 43, and the second top dead center rotational speed ne (time t4) from before stop is 350 ± 50 rpm. It is within the range.

  When the engine rotational speed Ne further decreases and the final compression top dead center passage time (time t5 shown in FIG. 7) has passed, none of the cylinders passes the top dead center, and the stroke is not changed. The piston 7 tries to stop within the target proper stop range R while being damped and oscillated within the stroke (when the piston 7 moves in the opposite direction, the crankshaft 6 is reversed and the engine rotational speed Ne becomes negative). However, at this time, the intake stroke cylinder 5D performs an intake operation, and if the intake resistance is large, the stop position of the piston 7 tends to vary. In particular, the intake resistance acts so as to increase when the piston 7 moves toward the bottom dead center, so that the piston 7 is more likely to stop than the top dead center rather than the target. Since the piston 7 of the intake stroke cylinder 5D and the piston 7 of the expansion stroke cylinder 5A move in the same phase, the piston 7 of the expansion stroke cylinder 5A tends to stop more than the top dead center rather than the target.

  Therefore, in this embodiment, the opening degree K of the throttle valve 39 is increased to the opening degree K1 shown in FIG. 7 (for example, about K1 = about 40%) almost simultaneously with the time point t5 (may be slightly delayed), and the intake stroke is performed. The intake resistance of the cylinder 5D is reduced. This makes it easier for the piston 7 to stop at a target position corresponding to the balance without affecting the intake flow rate balance in the expansion stroke cylinder 5A and the compression stroke cylinder 5C.

  In order to perform such control, it is necessary to immediately determine that the time point t5 is the last compression top dead center passage timing, and the next compression top dead center (in the compression stroke cylinder 5C) is It must be predicted at time t5 that it will not pass. Therefore, in this embodiment, the ECU 2 determines the last top dead center passage time. The ECU 2 compares the engine speed when passing through each top dead center with a predetermined rotational speed (for example, 260 rpm) obtained in advance through experiments or the like, and when the former becomes lower than the latter, It is determined that it is a compression top dead center time. Note that the higher the top dead center rotational speed ne in the final compression top dead center passage time, the closer to the latter stage of the stroke (the piston stop position of the expansion stroke cylinder 5A is closer to the bottom dead center, and the compression stroke cylinder 5C is closer to the top dead center). It becomes easy to stop.

  Further, the ECU 2 determines the second top dead center passage time before the stop (the time t4). Specifically, the ECU 2 determines a range of the third top dead center rotational speed range N3 (for example, 420 to 470 rpm: see FIG. 7) in which the engine rotational speed when passing through each top dead center is obtained in advance through experiments or the like. When it is determined that the top dead center is reached, it is determined that the next top dead center is the second top dead center passage time before the stop. The restart valve operation is stopped based on the second top dead center passage time (time t4) before the stop obtained here.

  Next, the control operation of the ECU 2 when the engine is automatically stopped will be described based on the flowcharts shown in FIGS. These flowcharts are flowcharts of engine automatic stop control from uniform combustion in which the air-fuel ratio in the cylinder is set to the stoichiometric air-fuel ratio or near the stoichiometric air-fuel ratio.

  When this control operation starts, it is first determined whether or not an automatic engine stop condition is satisfied based on detection signals output from various sensors (step S1). Specifically, the cooling water temperature is equal to or higher than a predetermined automatic stop permission temperature (for example, 60 ° C.), the brake switch remains on for a predetermined time, and the remaining battery level is equal to or higher than a preset reference value. Yes, when it is confirmed that the vehicle speed is in a state equal to or lower than a predetermined value (for example, 10 km / h), it is determined that the automatic engine stop condition is satisfied, and one of the above requirements is not satisfied. In this case, it is determined that the automatic engine stop condition is not satisfied.

  If it is determined as YES in step S1 and it is confirmed that the engine automatic stop condition is satisfied, the shift of the automatic transmission is set to neutral so as to be in a no-load state (step S2), and the engine rotation The target value (target speed) of the speed Ne is set to a predetermined speed N1 (for example, about 850 rpm) higher than the normal idle rotation speed (step S3). Further, the opening K of the throttle valve 39 is adjusted (the throttle valve 39 is operated in the valve opening direction) so that the boost pressure Bt becomes a target pressure P1 set to, for example, about −400 mmHg (step S4), and the engine The retard amount of the ignition timing is calculated so that the rotational speed Ne becomes the target predetermined speed N1 (step S5). Thereby, the throttle opening K is fed back in order to set the boost pressure Bt to the target pressure P1, and the retard amount of the ignition timing is fed back in order to set the engine rotation speed Ne to the predetermined speed N1 (engine rotation). Speed feedback control is executed).

  In step S1, the determination of the automatic engine stop condition is executed when the vehicle speed is reduced to 10 km / h or less. Therefore, the idle rotation speed (predetermined speed N1 when the automatic engine stop condition is satisfied) is determined. ) Can be set to a value (850 rpm) higher than the normal idle rotation speed when the engine is not automatically stopped (for example, 650 rpm in the D range state of the automatic transmission), and the engine rotation speed is set to the normal idle rotation speed (650 rpm). ), The above steps S2 to S5 can be executed. Therefore, there is no need to increase the engine rotational speed once reduced to the normal idle rotational speed to the target rotational speed N1 (850 rpm), and the driver will not be uncomfortable with the increased engine rotational speed. .

  Further, as described above, by setting the idle rotation speed when the automatic stop condition is satisfied to a value higher than the normal idle rotation speed, the value decreases with the restart valve operation executed for a while after the automatic stop condition is satisfied. This scavenging performance can be supplemented after stopping the fuel supply described later.

  Next, it is determined whether or not the fuel injection stop condition is satisfied, specifically, whether or not the engine rotational speed Ne has reached the target predetermined speed N1 and the boost pressure Bt has reached the target pressure P1 (step). S6) If NO is determined, the process returns to step S4 to repeat the control operation. Then, when YES is determined in step S6 (time t1 in FIG. 7), the throttle valve 39 is opened to a relatively large opening (about 30%) (step S7), and the amount of power generated by the alternator 43 is increased. The power generation is stopped by setting to 0 (step S8), and the fuel injection is stopped (step S9). Note that by opening the throttle valve 39 in step S7, the intake flow rate to each cylinder can be increased to compensate for the scavenging performance that decreases with the restart valve operation.

  Thereafter, after the fuel injection stop timing t1, whether or not the engine rotational speed Ne has become equal to or lower than a predetermined speed N2 set in advance to about 760 rpm in order to determine that the engine rotational speed Ne has started to decrease. Is determined (step S10). Then, the throttle valve 39 is closed when it is determined as YES in step S10 (time t2 in FIG. 7) (step S11). As a result, the boost pressure Bt that is opened to approach the atmospheric pressure by opening the throttle valve 39 in step S7 starts to decrease with a predetermined time difference according to the closing operation of the throttle valve 39. As will be described in detail later, due to the boost pressure Bt thus reduced, the intake amount in the last intake stroke before engine stop is reduced for each of the expansion stroke cylinder 5A and the compression stroke cylinder 5C.

  It should be noted that, instead of the above-described embodiment in which the throttle valve 39 is closed at the time t2 when it is determined in step S10 that the engine rotational speed Ne has become equal to or less than the predetermined speed N2, the compression dead of the piston 7 The throttle valve 39 may be closed when it is determined that the engine speed when passing the point, that is, the engine top dead center speed ne is equal to or lower than the predetermined speed N2.

  Next, it is determined whether or not the engine top dead center rotational speed ne is equal to or lower than a predetermined speed N2 set to a preset value of about 760 rpm (step S12). If YES is determined here, the engine speed Ne is controlled to decrease along a preset reference line thereafter. In the present embodiment, the power generation amount of the alternator 43 is adjusted so that the top dead center rotational speed ne at the time of each compression top dead center passing sequentially falls within the appropriate rotational speed range (step S13). Specifically, when the top dead center rotational speed ne is high, the power generation amount is increased so that the next top dead center rotational speed ne approaches a preset reference line. Conversely, when the top dead center rotational speed ne is low, the power generation amount is decreased.

  Then, each time each cylinder sequentially passes through the compression top dead center, it is determined whether or not the engine top dead center rotational speed ne is within a predetermined value range N3 (420 to 470 rpm) (step S14). This predetermined value N3 is an engine rotational speed that can be taken by the third top dead center rotational speed ne before the engine stops in the process in which the rotational speed Ne of the engine is decreasing along a preset reference line, This is a range measured in advance by experiments or the like.

  While the determination in step S14 is NO, the process returns to step S14 and the control is repeated. When the determination in step S14 is YES, it is then determined whether or not the second top dead center before stopping the engine has been reached ( Step S15). While the determination of step S15 is NO, step S15 is repeatedly executed. When the determination of step S15 is YES, the VVL control is stopped (step S16).

  That is, in this step S16, the VVL control is stopped at time t4 in FIG. As a result, since the VVL control is stopped after the intake stroke of the expansion stroke cylinder 5A and before the intake stroke of the compression stroke cylinder 5C, the intake flow rate of the expansion stroke cylinder 5A is large when the engine is stopped, and the intake air of the compression stroke cylinder 5C The flow rate is reduced. Therefore, since the compression reaction force of the expansion stroke cylinder 5A increases and the compression reaction force of the compression stroke cylinder 5C decreases, the probability of stopping the piston 7 of the expansion stroke cylinder 5A within the appropriate stop range R when the engine is stopped is increased. be able to.

  In particular, in the present embodiment, the throttle valve 39 is closed in step S10, so that the intake amount in the last intake stroke before engine stop is reduced for each of the expansion stroke cylinder 5A and the compression stroke cylinder 5C. By executing the VVL control, the intake air amount for each of the cylinders 5A and 5C can be supplemented.

  Next, it is determined whether or not the top dead center speed ne is equal to or lower than the last top dead center rotational speed N4 before stopping (step S17). The predetermined value N4 is a value corresponding to the engine rotational speed when passing through the last compression top dead center in the process in which the engine rotational speed Ne is decreasing along a preset reference line. Is set to about.

  While the determination of step S17 is NO, step S17 is repeatedly executed. When the determination of step S17 is YES, the throttle valve 39 is opened to a predetermined large opening (for example, 40%) (step S18). ).

  Thereafter, as the engine speed Ne further decreases, it is determined whether or not the engine has stopped (step S19), and when it is determined YES (t7 in FIG. 7), as will be described later. After executing the control for detecting the stop position of the piston 7 based on the detection signals of the crank angle sensors 44 and 45 (step S20), the control operation is terminated.

  According to the above automatic stop control, the probability that the piston stop position is within the proper stop range R is increased.

  That is, as shown in FIG. 7, the throttle valve 39 is opened to the opening K1 for scavenging at the beginning of the automatic engine stop operation, but then the throttle valve 39 is once closed to reduce the intake flow rate. Thereafter, the restart valve operation is stopped at the timing t4 when the piston 7 of the expansion stroke cylinder 5A passes the last top dead center before the engine stops, so that the intake air amount is reduced in the final intake stroke before the expansion stroke cylinder 5A is stopped. In many cases, the intake air amount decreases in the last intake stroke before the compression stroke cylinder 5C is stopped. Accordingly, the expansion stroke cylinder 5A has a relatively high compression resistance, and the compression stroke cylinder 5C has a low compression resistance.

  Combined with this, since the intake resistance of the intake stroke cylinder 5D is reduced by opening the throttle valve 39 at the time t5 (step S19) when the last top dead center before the stop is exceeded, the piston of the expansion stroke cylinder 5A is reduced. The probability that 7 stops within the position of the bottom dead center side from the middle of the expansion stroke, that is, within the appropriate stop range R (see FIG. 6) increases.

  By stopping the piston 7 of the expansion stroke cylinder 5A at such a position, as will be described later, the starting performance is improved when the engine is restarted.

  FIG. 10 shows the piston stop position detection control operation executed in step S20 of the flowchart. When this detection control is started, based on the first crank angle signal CA1 (signal from the crank angle sensor 44), whether or not the second crank angle signal CA2 is Low when the first crank angle signal CA1 rises, or It is determined whether or not the second crank angle signal CA2 is High when the first crank angle signal CA1 falls (step S21). Thereby, it is determined whether the phase relationship between the signals CA1 and CA2 during the engine stop operation is as shown in FIG. 11A or FIG. Whether it is in a state or a reverse state is determined.

  That is, at the time of forward rotation of the engine, as shown in FIG. 11A, 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, thereby the first crank angle. The second crank angle signal CA2 becomes High when the signal CA1 rises. On the other hand, at the time of reverse rotation of the engine, as shown in FIG. 11B, 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 On the contrary, 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 CA1 falls.

  Therefore, if the determination in step S21 is YES, the CA counter for measuring the crank angle change in the forward rotation direction of the engine is increased (step S22). If the determination in step S21 is NO, the CA counter is increased. Down (step S23). Then, after stopping the engine, the piston stop position is obtained by examining the measured value of the CA counter (step S24).

  In parallel with the automatic stop control described above, it is always determined whether or not the restart condition is satisfied. If it is determined that the restart condition is satisfied, for example, an accelerator operation or the like is performed. If the battery voltage drops or the air conditioner is activated, the pre-stop restart control shown in FIG. 12 is executed.

  In the restart control before stop, first, it is determined whether or not the top dead center rotational speed ne is equal to or lower than the top dead center speed Ne4 (step S71). That is, in step S71, it is determined whether or not a restart condition is satisfied at a time point after time t4. If YES is determined here, the VVL control is restarted (step S72). Next, the shift of the automatic transmission is changed from neutral (N range) to drive (D range) (step S73), and fuel injection is resumed (step S74), and normal control is performed.

  On the other hand, if it is determined as NO in step S71, it is determined whether or not the top dead center speed ne is equal to or lower than the top dead center speed N2 (step S75). If YES is determined, the processes after step S73 are executed. If NO is determined, the crank angle at the original time point is detected and stored (step S76).

  At the time of this step S76, the engine is rotating by inertia. Next, whether or not the crankshaft 6 has passed 720 ° CA from the crank angle stored in step S76, that is, the stroke of each cylinder 5A to 5D is determined. It is determined whether or not one round has been made (step S77). Here, if it determines with NO, while repeatedly performing step S77, if it determines with YES, the process after the said step S73 will be performed.

  As described above, in this embodiment, when the restart condition is satisfied between the stop of fuel injection (time t1) and the predetermined time (time t4 in this embodiment), the normal control is performed while the VVL control is executed. Therefore, the switching frequency of the switching mechanism 21 can be reduced, and as a result, consumption of the outside switching mechanism 21 can be suppressed.

  Further, in the restart control before stop, after the restart condition is satisfied immediately after the fuel stop (in the present embodiment, until time t2), after one stroke of the stroke of each cylinder 5A to 5D, Since the fuel injection is resumed, the gas remaining in each of the cylinders 5A to 5D is discharged during one round immediately after the fuel injection is stopped, and the combustion failure caused by the residual gas is suppressed. As a result, the restart performance can be improved.

  On the other hand, the control operation at the time of restarting the engine that has entered the automatic stop state without executing the restart control before stop will be described based on the time chart shown in FIG. 12 and the flowcharts shown in FIGS. To do. First, it is determined whether or not a predetermined engine restart condition is satisfied (step S101). If YES is determined, for example, if an accelerator operation for starting from a stopped state is performed, the battery voltage is When the air temperature decreases or when the air conditioner is activated, the in-cylinder temperature is estimated based on the engine water temperature, the elapsed time since the automatic stop, the intake air temperature, and the like (step S102).

  Based on the stop position of the piston 7 detected when the engine is automatically stopped, the amount of air in the compression stroke 5C and the expansion stroke cylinder 5A is calculated (step S103). That is, the combustion chamber volumes of the compression stroke cylinder 5C and the expansion stroke cylinder 5A are obtained from the stop position of the piston 7. When the engine is automatically stopped, the engine is stopped after several revolutions after the fuel injection is stopped, so that the expansion stroke cylinder 5A is also filled with fresh air, and the compression stroke cylinder 5C is in the engine automatic stop period. And since the inside of the expansion stroke cylinder 5A is at substantially atmospheric pressure, the amount of fresh air is obtained from the combustion chamber volume.

  Next, the stop position of the piston 7 detected in accordance with the output signals of the crank angle sensors 44 and 45 is within the appropriate stop range R (BTDC 60 ° CA to 80 ° CA before top dead center) in the compression stroke cylinder 5C. It is then determined whether or not the vehicle is near the bottom dead center BDC (step S104). If YES is determined in step S104 and it is confirmed that the amount of air in the compression stroke cylinder 5C is relatively large, the air amount in the compression stroke cylinder 5C calculated in step S103 is λ ( The first fuel injection is performed so that the air-fuel ratio (excess air ratio)> 1 (for example, air-fuel ratio = about 20) (step S105). This air-fuel ratio is obtained from the first air-fuel ratio map M1 for the first time of the compression stroke cylinder 5C set in advance according to the stop position of the piston 7, 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 5C is relatively large.

  On the other hand, when it is determined NO in step S104 and the air amount in the compression stroke cylinder 5C is relatively small, the air-fuel ratio satisfying λ ≦ 1 with respect to the air amount in the compression stroke cylinder 5C calculated in step S103. The first fuel injection is performed so as to become (step S106). This air-fuel ratio is obtained from the second air-fuel ratio map M2 for the first time of the compression stroke cylinder 5C set in advance according to the stop position of the piston 7, 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 5C is small, sufficient combustion energy for reverse rotation can be obtained.

  Next, the cylinder 5C is ignited at a time point t7 (see FIG. 13) after the elapse of a predetermined time set in consideration of the vaporization time from the first fuel injection to the compression stroke cylinder 5C (step S107: Symbol E0 in FIG. Then, it is determined whether or not the edges of the crank angle sensors 44 and 45, that is, the rising or falling edge of the crank angle signal has been detected within a certain time after ignition, that is, whether or not the crankshaft 6 has been reversed. If it is determined NO and it is confirmed that a misfire has occurred and the piston 7 has not moved, re-ignition is performed on the compression stroke cylinder 5C (step S109).

  If it is determined YES in step S108 and it is confirmed that the piston 7 has moved, the split fuel injection split for the expansion stroke cylinder 5A is based on the stop position of the piston 7 and the in-cylinder temperature estimated in step S102. The ratio (the ratio between the first pre-injection and the second post-injection) is calculated (step S121). The latter injection ratio is set to a larger value as the piston stop position in the expansion stroke cylinder 5A is closer to the bottom dead center and 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 5A calculated in step S103 (step S122). The air-fuel ratio at this time is obtained from an air-fuel ratio map M3 for the expansion stroke cylinder 5A set in advance according to the stop position of the piston 7. Further, based on the fuel injection amount to the expansion stroke cylinder 5A calculated in step S122 and the split ratio calculated in step S121, the first stage fuel injection amount for the expansion stroke cylinder 5A is calculated, and the fuel is Injecting (step S123).

  Next, the subsequent (second) fuel injection timing for the expansion stroke cylinder 5A is calculated based on the in-cylinder temperature estimated in step S102 (step S124). This second injection timing is the time when the air in the cylinder is compressed after the piston 7 starts moving toward the top dead center (reverse rotation of the engine), and the latent heat of vaporization of the injected fuel is compressed. It is set so that the pressure is effectively reduced, that is, the piston 7 is set close to top dead center, and the time for the second injected fuel to evaporate by the ignition timing is set as long as possible. Is done.

  Next, the subsequent (second) fuel injection amount for the expansion stroke cylinder 5A is calculated based on the fuel injection to the expansion stroke cylinder 5A calculated in step S122 and the split ratio calculated in step S121 (step S125). The injection is performed at the second injection timing calculated in step S124 (step S126).

  After the second fuel injection into the expansion stroke cylinder 5A, ignition is performed at a time point t8 (see FIG. 13) when a predetermined delay time has elapsed (step S127: symbol E1 in FIG. 13). This delay time is obtained from the ignition map M4 for the expansion stroke cylinder 5A set in advance according to the stop position of the piston 7. By the initial combustion in the expansion stroke cylinder 5A by the ignition, the engine turns from reverse rotation to normal rotation. Therefore, the piston 7 of the compression stroke cylinder 5C moves to the top dead center side, and the gas in the cylinder (burned gas combusted by ignition in step S107) starts to be compressed.

  Next, taking into account the fuel vaporization time, the second time fuel is injected into the compression stroke cylinder 5C (step S128). The fuel injection amount at this time is such that the entire air-fuel ratio based on the injection amount obtained by adding up the first injection amount becomes richer (for example, about 6) than the combustible air-fuel ratio (lower limit is 7 to 8). It is obtained from the second air-fuel ratio map M5 for the compression stroke cylinder 5C set in advance according to the stop position of the piston 7. 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 5C in accordance with the latent heat of vaporization caused by the second injection fuel in the compression stroke cylinder 5C. It becomes.

  Note that the second fuel injection into the compression stroke cylinder 5C is performed exclusively to reduce the compression pressure in the cylinder, and ignition and combustion are not performed on this, and it is richer than the combustible air-fuel ratio. Therefore, compression self-ignition does not occur, and the incombustible fuel is made harmless by a purification catalyst (not shown) provided in the exhaust passage 37 thereafter.

  Since the fuel injected for the second time in the compression stroke cylinder 5C does not burn as described above, as shown in FIG. 13, the next combustion following the first combustion E1 in the expansion stroke cylinder 5A is the intake stroke cylinder 5D, That is, it is the first combustion E2 in the # 4 cylinder 5D that was in the intake stroke at the time of stop. As energy for the piston 7 of the intake stroke cylinder 5D to exceed the compression top dead center, a part of the energy of the initial combustion E1 in the expansion stroke cylinder 5A is charged, and the energy of the initial combustion E1 in the expansion stroke cylinder 5A is The compression stroke cylinder 5C is used both for overcoming the compression top dead center and for the intake stroke cylinder 5D exceeding the compression top dead center.

  Therefore, for smooth start-up, it is desirable that the energy required for the intake stroke cylinder 5D to exceed the compression top dead center is small. For this purpose, the air density in the intake stroke cylinder 5D is estimated, and the intake air is estimated from the estimated value. After calculating the air amount of the stroke cylinder 5D (step S140), an air-fuel ratio correction value for preventing compression self-ignition is calculated based on the in-cylinder temperature estimated in step S102 (step S141). That is, when compression self-ignition occurs, a force (brake) is generated that pushes the piston 7 back to the bottom dead center before reaching the compression top dead center due to the combustion, and energy for exceeding the compression top dead center by that amount. It is not desirable because it consumes a lot. Therefore, in order to suppress the brake, 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 5D is calculated based on the air amount of the intake stroke cylinder 5D 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 5D. In this fuel injection, the compression pressure is reduced by the latent heat of vaporization, that is, the energy necessary for exceeding 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 engine stop period, the intake air temperature, the engine water temperature, and the like.

  Further, in order to suppress the occurrence of the brake, the ignition timing is delayed after top dead center and ignited (step S144). By executing the control described above, in the intake stroke cylinder 5D, the compression reaction force becomes small until the compression top dead center and easily exceeds the top dead center, and the combustion E2 at the time when the top dead center is exceeded. Torque in the forward direction due to the combustion energy is generated.

  Next, power generation by the alternator 43 is started (step S145), and it is determined whether or not the piston 7 of the exhaust stroke cylinder 5B has reached the compression top dead center (time t9 in FIG. 13) (step S146). If NO is determined, step S146 is repeatedly executed. If YES is determined, execution of the VVL control is started (step S147), and the process proceeds to normal control.

  As described above, in the restart control after the engine is stopped, the VVL control is stopped until the time t9 (3TDC elapsed time in the embodiment) after the predetermined time has elapsed after the restart. Since the recirculation of the gas in the combustion chamber 8 and the exhaust passage 37 heated by the heat of the cylinder block 4 itself can be stopped, compression top dead as compared with the case where the exhaust gas recirculation is executed at the time of the automatic stop. Brake due to compression self-ignition of the air-fuel mixture before the point can be suppressed, and as a result, restart performance can be improved.

  As described above, according to the above embodiment, after the automatic engine stop condition is satisfied, when the restart condition is satisfied at an earlier time (before time t4) than when the VVL control (restart valve operation) is stopped. Since the engine can be restarted while maintaining the state where the restart valve operation is being executed, it is compared with the case where the stop or execution of the restart valve operation is switched each time the automatic engine stop condition and the restart condition are satisfied. Thus, the switching frequency of the restart valve operation can be reduced.

  Further, by stopping the restart valve operation until a predetermined time elapses after the restart condition is satisfied after the engine is stopped (until time t9), the intake stroke cylinder 5D is inhaled when the engine is stopped. Since fresh air can be sucked from the system (intake passage 36) and the recirculation of the heated gas in the combustion chamber 8 and the exhaust passage 37 can be stopped, the recirculation of exhaust is executed during the automatic stop. Compared to the case, braking due to compression self-ignition of the air-fuel mixture before compression top dead center can be suppressed, and restart performance can be improved.

  In the above embodiment, the restart valve operation is executed until the middle of the engine automatic stop period (time point t4) as described above, so that the scavenging efficiency in each of the cylinders 5A to 5D decreases during this period. However, since the engine speed when the fuel supply is stopped is set higher than the idle speed during the normal operation, the operation of the piston 7 is performed more than when the engine speed is maintained as it is when the fuel supply is stopped. The number of times can be increased, and the scavenging performance can be supplemented.

  Therefore, according to the present embodiment, the restart performance can be improved while reducing the switching frequency of exhaust recirculation execution or stop as much as possible.

  In the above embodiment, the throttle valve 39 is closed at time t2 after the fuel cut condition is satisfied (step S11 in FIG. 8), so that the last intake before the engine stop for the expansion stroke cylinder 5A and the compression stroke cylinder 5C. The intake amount in the stroke is reduced.

  According to this embodiment, for each of the cylinders 5A to 5C, although the intake amount in the final intake stroke before engine stop decreases, the restart valve operation is executed until the time t4, so the compression stroke cylinder 5C While the intake amount is small and the compression resistance of the cylinder 5C is low, the intake amount of the expansion stroke cylinder 5A is large, and the compression resistance of the cylinder 5A is large. As a result, the engine stop state is such that the piston stop position is closer to the bottom dead center than the middle of the expansion stroke cylinder in the expansion stroke cylinder 5A, and the piston stop position is closer to the top dead center side than the middle of the stroke in the compression stroke cylinder 5C. The probability of getting higher.

  Here, the reason why the intake air amount can be adjusted by executing or stopping the resumption valve operation is that the exhaust valve 16 is opened during the intake stroke by the switching mechanism 21. This is because the intake air can be taken in through both the exhaust port 13 and the exhaust port 14.

  In the above embodiment, since the throttle valve 39 is opened between the time points t1 and t2 in FIG. 8, the decrease in the scavenging performance due to the execution of the restart valve operation is compensated by opening the throttle valve 39. be able to.

  Further, in the above embodiment, when the restart condition is satisfied from the time point t1 to the time point t2, that is, immediately after the fuel injection is stopped, the process waits for one cycle of the stroke of each cylinder 5A to 5D. (Step S77 in FIG. 12), the fuel injection is resumed.

  According to this embodiment, immediately after fuel injection, the gas remaining in the cylinders 5A to 5D can be discharged during a single stroke, and the combustion failure due to the residual gas can be suppressed. As a result, the restart performance can be improved.

  Further, in the above embodiment, as shown in FIG. 5, the intake valve 15 is opened from before the top dead center to the stage before the bottom dead center (reference numeral L1), while the exhaust valve 16 is opened to the intake stroke. The valve is opened later than the intake valve 15 (restart valve operation) (reference L2).

  According to this embodiment, by the restart valve operation of the exhaust valve 16, the burned gas discharged in the exhaust stroke can be introduced into the cylinder in a relatively large amount as the internal EGR. As a result, the fresh air introduced into the cylinder can be heated while ensuring the charging efficiency, and as a result, compression self-ignition in the subsequent compression stroke is ensured. Moreover, since the structure which opens the exhaust valve 16 in the intake stroke is employ | adopted, internal EGR is realizable at the timing which the exhaust valve 16 does not interfere with the piston 7. FIG. Therefore, the geometric compression ratio can be increased as much as possible.

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 exploded sectional view showing a switching mechanism of the engine of FIG. 1. It is front sectional drawing of the switching mechanism of the engine of FIG. (A) is a schematic diagram showing the piston stop position, and (b) is a graph showing the relationship between the piston stop position and the air amount. It is a chart which shows the valve opening operation | movement for every process of an intake valve and an exhaust valve. It is a time chart which shows change states, such as ON or OFF of engine speed, throttle opening, and restart valve operation at the time of an engine automatic stop. It is a flowchart which shows the first half of the engine automatic stop control operation. It is a flowchart which shows the second half part of the engine automatic stop operation | movement. It is explanatory drawing 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 flowchart which shows the restart control before a stop when the restart conditions are satisfied before an engine stops. It is a time chart which shows change states, such as engine speed at the time of an engine restart, and ON or OFF of a restart valve operation. It is a flowchart (1/3) which shows restart control when the restart conditions are satisfied after an engine stop. It is a flowchart (2/3) which shows the restart control when the restart conditions are satisfied after an engine stop. It is a flowchart (3/3) which shows the restart control when restart conditions are satisfied after an engine stop.

Explanation of symbols

1 Engine body 2 ECU
5A-5D cylinder 18 camshaft (an example of valve drive means)
19 1st cam 20 2nd cam 21 Switching mechanism (an example of valve drive means)
39 Throttle valve (an example of intake flow control unit)
52 VVL control part (an example of a valve drive control part)

Claims (5)

When the predetermined engine automatic stop condition is satisfied, the fuel supply is stopped to stop the engine, and when the predetermined restart condition is satisfied after the fuel supply is stopped, combustion is performed at least in the cylinder in the expansion stroke when the engine is stopped. In a four-cycle engine starter configured to execute automatic stop control for restarting the engine by performing
Valve drive means for enabling exhaust gas recirculation into the cylinder by a resumption valve operation that opens the exhaust valve again in the intake stroke in addition to the valve opening operation in the exhaust stroke;
A valve drive control unit capable of switching execution or stop of the restart valve operation by the valve drive means,
When the engine automatic stop condition is satisfied and the fuel supply is stopped, the engine speed is set higher than the idle speed during normal operation
The valve drive control unit stops the restart valve operation in the middle of the engine automatic stop operation period after the fuel supply is stopped, and at least a predetermined time elapses after the restart condition is satisfied after the engine is stopped. A starter for a four-cycle engine, which is restarted after starting. An intake air flow rate control unit for adjusting the intake air flow rate flowing into the cylinder;
The intake flow rate control unit reduces the intake flow rate so that the intake amount at least in the last intake stroke before the stop is reduced for each of the cylinder that stops in the expansion stroke and the cylinder that stops in the compression stroke when the engine is stopped.
The valve drive control unit executes the resumption valve operation until the last intake stroke before the stop for the cylinder that stops in the expansion stroke when the engine is stopped, and the last before the stop for the cylinder that stops in the compression stroke when the engine is stopped. The starter for a four-cycle engine according to claim 1, wherein the starting device is stopped from the intake stroke.   The intake air amount adjusting means increases the intake air flow rate over a predetermined time period from at least immediately after the fuel supply is stopped until the last intake stroke before the stop of the cylinder that stops in the expansion stroke when the engine is stopped. The starter for a 4-cycle engine according to claim 2.   The fuel supply is restarted after the exhaust stroke or the intake stroke of all the cylinders is executed at least once when the restart condition is satisfied immediately after the fuel supply is stopped. 4. A starter for a 4-cycle engine according to the item.   The intake valve opens near the top dead center and closes before the bottom dead center, and the valve drive means opens the exhaust valve in the middle of the intake stroke. The starter for a 4-cycle engine according to any one of claims 1 to 4, wherein the valve is closed later than the intake valve.

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