JP3772891B2 - Engine starter - Google Patents

Description

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

In recent years, in order to reduce fuel consumption and reduce CO ₂ emissions, a restart condition has been established such that the engine is automatically stopped temporarily 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. The restart at the time of the idle stop control requires a quickness to immediately start the engine in accordance with the start operation of the vehicle or the like, but the engine output by the starter motor is generally performed conventionally. According to the method of restarting the engine through cranking that drives the shaft, there are problems that the starter motor is frequently operated and power is consumed, and that the life of the starter motor is shortened.

  Therefore, it is desirable to immediately start the engine with the combustion energy by injecting fuel into a cylinder that is in a stopped state in the expansion stroke to ignite and burn the cylinder. However, when the piston stop position of the cylinder that is in the stopped state in the expansion stroke as described above is inappropriate, for example, when the piston is stopped at a position very close to top dead center or bottom dead center, There is a possibility that the engine cannot be started normally due to the fact that the amount of air is so small that combustion energy cannot be obtained sufficiently or the stroke of the combustion energy acting on the piston is too short.

As a countermeasure against such a problem, for example, as shown in Patent Document 1 below, a braking device is provided for the crankshaft of the engine, and the piston of the cylinder that is stopped in the expansion stroke stops at an appropriate position during the stroke. If it is determined that the engine automatic stop condition is satisfied, as shown in Patent Document 2 below, the lean air-fuel ratio injection mode is selected and the intake pressure is increased as shown in Patent Document 2 below. The compression pressure is increased so that the piston of the cylinder that is stopped in the expansion stroke can be stopped at a predetermined position.
Japanese Utility Model Publication No. 60-128975 JP 2001-173473 A

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

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

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

According to the first aspect of the present invention, when a preset automatic engine stop condition is satisfied, the fuel supply for continuing the operation of the engine is stopped and the engine is automatically stopped. 4 cycles configured to automatically restart the engine by injecting fuel into at least the cylinders automatically stopped in the expansion stroke to cause ignition and combustion when the engine restart condition is established A multi-cylinder engine starter, which is driven by the engine and has an alternator that has a short characteristic with respect to an increase time when the generated current value of a certain width is changed, and when the engine is automatically stopped to, after temporarily increasing the target generated current of the alternator to advance large value set initial value, the rotation of the crankshaft And an automatic stop control means for performing control to reduce the target generated current value to adjust anti-a, reduction of the engine rotational speed decrease amount from the initial value of the target generated current is generated after the stop fuel injection The engine rotation speed is detected when the crank angle of the engine reaches a preset detection angle in the process of decreasing the engine rotation speed so that the value corresponds to the state. Compared with the case where it is high, the amount of decrease in the target generated current from the initial value is set to a large value .

The present invention according to claim 2, in the starting device of the engine according to the claim 1, the piston controlling the amount of decrease in the target generated current based on an engine rotational speed detected at the time of passing through the compression top dead center To do.

According to a third aspect of the present invention, in the engine starting device according to the first or second aspect , the intake throttle amount is increased in the direction of increasing the intake flow rate introduced into the cylinder at the initial stage of the operation of automatically stopping the engine. Is adjusted, and the target generated current of the alternator is increased to a preset initial value.

According to a fourth aspect of the present invention, in the engine starting device according to the third aspect , the intake throttle amount is adjusted in the direction of increasing the intake flow rate introduced into the cylinder at the initial stage of the operation of automatically stopping the engine. At the same time, the target generated current of the alternator is temporarily set to a low value.

According to a fifth aspect of the present invention, in the engine starting device according to any one of the first to fourth aspects, the shift state of the automatic transmission is changed from the drive state to the neutral state at the initial stage of the operation of automatically stopping the engine. as well as changes to one in which increasing to a preset initial value target generated current of the alternator.

According to a sixth aspect of the present invention, in the engine starter according to any one of the first to fifth aspects, the engine rotational speed when stopping fuel injection when the engine is automatically stopped is set to a normal idle speed. The value is set higher than the speed.

According to the first aspect of the present invention, when the engine automatic stop condition is established and the engine is automatically stopped, the target generator current of the alternator is temporarily increased to the initial value to sufficiently increase the power generation function of the alternator. The engine rotation speed is detected when the engine rotation speed decreases and the crank angle reaches a preset detection angle, and is set according to the engine rotation speed decrease state. Based on the reduced amount of the target generated current, control is performed to reduce the target generated current of the alternator , and when the engine speed is low, the reduced amount of the target generated current is set to a large value. by controlling so as to reduce the rotational resistance of the crankshaft, position of the piston of the cylinder as the expansion stroke at the stop time of the engine is suitable for restarting the engine To stop, it is possible to adjust the rotational resistance of the crankshaft to an appropriate value corresponding to the degraded state of the engine rotational speed.

According to the second aspect of the present invention, the generated current of the alternator is calculated based on the rotational speed of the engine detected when the piston passes the compression top dead center and the rotational speed of the engine is temporarily stabilized. By performing the control, it is possible to effectively improve the accuracy of the control for adjusting the rotational resistance of the crankshaft to an appropriate value in response to a state where the engine rotational speed is reduced.

According to the third aspect of the present invention, a sufficient amount of intake air is introduced into the cylinder by reducing the intake throttle amount in a region where the engine rotation speed is sufficiently high at the initial stage of the operation of automatically stopping the engine. By effectively improving the scavenging performance of each cylinder and reducing the pumping loss, the target power generation current of the alternator is increased to the initial value, so that the power generation function of the alternator can be demonstrated quickly and sufficiently, and the crankshaft Can be adjusted to an appropriate value.

According to the fourth aspect of the present invention, the intake throttle amount is reduced to introduce a sufficient amount of intake air into the cylinder in a region where the engine rotation speed is sufficiently high at the initial stage of the operation of automatically stopping the engine. By temporarily reducing the target generator current of the alternator, the scavenging performance of each cylinder can be effectively improved, and after reducing both the rotational resistance of the crankshaft and the pumping loss, the target power generation of the alternator By raising the current to the initial value, there is an advantage that the power generation function of the alternator can be quickly and sufficiently exhibited and the external load of the engine can be adjusted to an appropriate value.

According to the fifth aspect of the present invention, at the initial stage of the operation for automatically stopping the engine, the automatic transmission is set to the neutral state, and the fuel injection is stopped in a state in which the fluctuation of the engine rotational speed due to the disturbance is suppressed, so By reducing it, there is an advantage that automatic stop control for stopping the piston at a position suitable for restarting the engine can be properly executed.

According to the invention of claim 6 , when the engine is automatically stopped, the fuel injection is stopped in a state where the rotation speed of the engine is increased to a value higher than a normal idle rotation speed that does not automatically stop the engine. As a result, the engine speed (the number of intake, compression, expansion, and exhaust strokes) from when the fuel injection is stopped to when the engine is stopped can be sufficiently secured, and the target generator current of the alternator can be controlled. By adjusting the rotational resistance of the crankshaft, there is an advantage that automatic stop control for stopping the piston at a position suitable for restarting the engine can be appropriately executed.

  1 and 2 show a schematic configuration of a four-cycle spark ignition engine having an engine starter according to the present invention. The engine includes an engine main body 1 having a cylinder head 10 and a cylinder block 11 and an ECU 2 for engine control. The engine body 1 is provided with four cylinders 12A to 12D, and a piston 13 connected to the crankshaft 3 is fitted into each of the cylinders 12A to 12D so that a combustion chamber 14 is provided above the cylinder 13. Is formed.

  A spark plug 15 is installed at the top of the combustion chamber 14 of each of the cylinders 12 </ b> A to 12 </ b> D so that the plug tip faces the combustion chamber 14. A fuel injection valve 16 that directly injects fuel into the combustion chamber 14 is provided on the side of the combustion chamber 14. This fuel injection valve 16 incorporates a needle valve and a solenoid (not shown), and is driven and opened for a time corresponding to the pulse width of the pulse signal input from the ECU 2, and has an amount corresponding to the valve opening time. The fuel is injected toward the vicinity of the electrode of the spark plug 15.

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

  An intake passage 21 and an exhaust passage 22 are connected to the intake port 17 and the exhaust port 18. As shown in FIG. 2, the downstream side of the intake passage 21 close to the intake port 17 is an independent branch intake passage 21a corresponding to each of the cylinders 12A to 12D. The upstream ends of the branch intake passages 21a are respectively It communicates with the surge tank 21b. A common intake passage 21c is provided upstream of the surge tank 21b, and a throttle valve 23 driven by an actuator 24 is provided in the common intake passage 21c. An air flow sensor 25 for detecting the intake flow rate and an intake pressure sensor 26 for detecting the intake pressure (negative pressure) are disposed on the upstream side and the downstream side of the throttle valve 23, respectively.

  The engine body 1 is provided with an alternator (generator) 28 connected to the crankshaft 3 by a timing belt or the like. The alternator 28 includes a regulator circuit 28a that adjusts the target generated current by controlling the current of a field coil (not shown) and adjusting the output voltage, and the control from the ECU 2 that is input to the regulator circuit 28a. Based on the signal, the control of the target generated current corresponding to the electric load of the vehicle and the voltage of the vehicle-mounted battery is executed at normal times.

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

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

  The ECU 2 receives the detection signals from the sensors 25, 26, 30 to 35, and outputs a control signal for controlling the fuel injection amount and the injection timing to the fuel injection valve 16. 15 is configured to output a control signal for controlling the ignition timing to the ignition device 27 attached to 15 and to output a control signal for controlling the throttle opening degree to the actuator 24 of the throttle valve 23. Has been. Further, as will be described later, when a preset automatic engine stop condition is satisfied, fuel injection to each of the cylinders 12A to 12D is stopped (fuel cut) at a predetermined timing to automatically stop the engine. At the same time, control for automatically restarting the engine is executed when a restart condition is satisfied, for example, when an accelerator operation is performed by the driver.

  Specifically, when the engine is automatically stopped, the first combustion is performed in the compression stroke cylinder in which the piston 13 is stopped in the middle of the compression stroke, so that the piston 13 is pushed down to slightly reverse the crankshaft 3. As a result, when the engine is automatically stopped, the piston 13 of the expansion stroke cylinder in which the piston 13 is stopped in the middle of the expansion stroke is temporarily raised, and the air-fuel mixture in the cylinder is compressed and ignited and burned. Thus, a drive torque in the normal rotation direction is applied to the crankshaft 3 to restart the engine.

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

  That is, as shown in FIGS. 3A and 3B, in the cylinders that are in the expansion stroke and the compression stroke when the engine is stopped, the phases are shifted by 180 ° CA. If the piston 13 of the expansion stroke cylinder is positioned on the bottom dead center side of the stroke center, the amount of air in the cylinder increases and sufficient combustion energy is obtained. However, when the piston 13 of the expansion stroke cylinder is extremely positioned on the bottom dead center side, the amount of air in the compression stroke cylinder becomes too small and sufficient combustion energy for reversing the crankshaft 3 is obtained. Disappear.

  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, for example, the crank angle after the compression top dead center, is the stroke center of the expansion stroke cylinder. If the piston 13 can be stopped within an appropriate range of 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 and reliably restart the engine.

  Therefore, as shown in FIG. 4, the automatic stop control means provided in the ECU 2 sets the target rotational speed of the engine to the normal idle speed when the engine is not automatically stopped at the time t0 when the automatic engine stop condition is satisfied. Control is performed to stabilize by setting a value higher than the rotational speed. For example, in an engine in which a normal idle rotation speed is set to 650 rpm (the automatic transmission is in the drive range), the target rotation speed (idle rotation speed when the automatic stop condition is satisfied) is set to about 810 rpm (the automatic transmission is in the neutral range). ) Is executed to stabilize the engine rotational speed Ne at a rotational speed slightly higher than the normal idle rotational speed, and fuel injection is performed at time t1 when the engine rotational speed Ne is stabilized at the target rotational speed. The engine speed Ne is stopped to decrease the engine speed Ne.

  In addition, at the fuel injection stop time t1, which is the initial stage of the control operation for automatically stopping the engine, the air-fuel ratio in the cylinder is set to, for example, λ (excess air ratio) = 1, for example, the intake air flow rate during normal idling By setting the opening degree K of the throttle valve 23 so that the intake air flow rate becomes larger than (the minimum intake air flow rate necessary for continuing the engine operation), the intake air throttle amount is reduced, thereby reducing the cylinder 12A of the engine. The intake flow rate sucked into -12D is sufficiently secured. That is, when the combustion state immediately before the time point t1 is uniform combustion with the air-fuel ratio in the cylinder set to λ = 1 or in the vicinity thereof, the opening degree of the throttle valve 23 at the fuel injection stop time point t1. For example, by setting K to an opening of about 30% of the fully open position and increasing the boost pressure (intake pressure) Bt, the intake flow rate sucked into the cylinders 12A to 12D of the engine is necessary for continuing the engine operation. The fuel gas scavenging is ensured by setting it to a state larger by a predetermined amount than the minimum intake flow rate, and the target power generation current Ge of the alternator 28 is set to the time when the automatic stop condition is satisfied at the fuel injection stop time t1. The rotational resistance of the crankshaft 3 is reduced by lowering than t0.

  By stopping the combustion injection at the time point t1, the throttle valve 23 is closed at the time point t2 when it is confirmed that the engine rotational speed Ne has decreased to a preset reference speed (for example, 760 rpm) or less. . The boost pressure Bt begins to decrease from the time t2 when the throttle valve 23 is closed, and the intake flow rate introduced into each cylinder of the engine decreases, so that the common intake air between the opening time t1 and the closing time t2 of the throttle valve 23 is reduced. As the air introduced into the passage 21c passes through the surge tank 21b and the branch intake passage 21a, as shown in FIG. 5, the fourth cylinder 12D, the second cylinder 12B, the first cylinder 12A, and the The cylinders are introduced in the order of the three cylinders 12C with a predetermined transport delay. By setting the opening time t1 and the closing time t2 of the throttle valve 23 at appropriate times in consideration of the transport delay of the intake air, the expansion stroke becomes more than the third cylinder 12C that is in the compression stroke when the engine is stopped. More air is introduced into the first cylinder 12A.

  Further, at the time t2 when it is confirmed that the engine rotational speed Ne has decreased below the reference speed N2, the target generated current Ge of the alternator 28 is temporarily increased, and the engine top dead center rotational speed as will be described later. At the time t3 when ne is within the predetermined range, the reference line set based on the results of experiments, etc. performed in advance by adjusting the target generated current Ge of the alternator 28 in accordance with the degree of decrease in the engine speed Ne. A control for reducing the rotational speed Ne of the engine is executed.

  When the engine is automatically stopped as described above, the kinetic energy of the crankshaft 3, the flywheel, etc. from the fuel injection stop time t1 is caused by mechanical loss due to frictional resistance or pump work of each cylinder 12A to 12D. When consumed, the crankshaft 3 of the engine is rotated several times by inertia, and in a 4-cylinder 4-cycle engine, it stops after reaching the compression top dead center of about 10 times. Specifically, as shown in FIGS. 4 and 5, the engine rotational speed Ne temporarily drops each time the cylinders 12 </ b> A to 12 </ b> D reach the compression top dead center, and then exceed the compression top dead center. The engine rotational speed Ne gradually decreases while repeating the up-down that rises again at the time.

  In the time chart of the crank angle CA shown in FIG. 5, the solid line indicates the top dead center (TDC) of the first cylinder 12A and the third cylinder 12C as 0 ° CA, and the alternate long and short dash line indicates the second cylinder 12B and the fourth cylinder 12D. The crank angle with the top dead center at 0 ° CA is shown. In a four-cylinder, four-cycle engine, there is a phase shift of 180 ° CA between the cylinders 12A, 12C indicated by the solid line and the cylinders 12B, 12C indicated by the alternate long and short dash line. The time chart indicates that compression top dead center is reached.

Then, the cylinder 12C greet compression top dead center after the time t 5 to the front stop of the engine exceeds the last compression TDC, increased air pressure with the rise of the piston 13 by inertial force, by the compression reaction force The piston 13 is pushed back to reverse the crankshaft 3. 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 frictional resistance of the engine and exceeds the last compression top dead center. rotational inertia of time t 5 of the engine, i.e. also vary according to the level of the engine rotational speed Ne.

  Therefore, in order to stop the piston 13 of the expansion stroke cylinder 12A in the expansion stroke within the appropriate range R suitable for restart when the engine automatically stops, first, the expansion stroke cylinder 12A and the compression stroke cylinder 12C It is necessary to adjust the intake air flow rates for both cylinders 12A and 12C so that the compression reaction force becomes sufficiently large and the compression reaction force of the expansion stroke cylinder 12A is larger than the compression reaction force of the compression stroke cylinder 12C by a predetermined value or more. There is. For this reason, in the present embodiment, a predetermined amount of air is supplied to both the expansion stroke cylinder 12A and the compression stroke cylinder 12C by setting the opening K of the throttle valve 23 to a large value at the fuel injection stop time t1. After the intake, the throttle valve 23 is closed at a time t2 when a predetermined time has elapsed, and the opening K is reduced to adjust the intake air amount.

  However, in an actual engine, because there are individual differences in the shapes of the throttle valve 23, the intake port 17, the branch intake passage 21a, and the like, the behavior of the air flowing through them changes, so that during each automatic stop period of the engine Variations occur in the intake air flow rate sucked into the cylinders 12A to 12D. Further, even if the opening / closing control of the throttle valve 23 is performed as described above due to differences in engine friction resistance due to individual engine differences and engine temperature, the cylinder 12A and the cylinder 12A that are in the expansion stroke when the engine is stopped In some cases, the piston stop position of the cylinder 12C in the compression stroke cannot be within the appropriate range R.

  In this regard, according to the present invention, when the engine speed Ne decreases during the automatic engine stop period, the cylinders 12A to 12D pass through the compression top dead center as shown in an example in FIG. It was noted that there is a clear correlation between the engine rotational speed (top dead center rotational speed) ne and the piston stop position of the cylinder 12A in the expansion stroke at the time of engine stop. As shown in FIGS. 4 and 5, the piston 13 of each cylinder 12 </ b> A to 12 </ b> D passes through the compression top dead center in the process in which the engine speed Ne decreases after the time t <b> 1 when the fuel injection is stopped. The engine rotational speed, that is, the top dead center rotational speed ne is detected, and the target generated current Ge of the alternator 28 is controlled in accordance with the detected value of the top dead center rotational speed ne, thereby reducing the degree of decrease in the engine rotational speed Ne. I try to adjust it.

  That is, in FIG. 6, as described above, the fuel injection is stopped at the time t1 when the rotational speed Ne of the engine becomes a predetermined speed, and the throttle valve 23 is kept open for a predetermined period thereafter. The piston 13 provided in each cylinder 12A to 12D of the engine that rotates due to inertia measures the top dead center rotational speed ne when the piston 13 passes through the compression top dead center, and the piston position of the expansion stroke cylinder 12A when the engine is stopped. The piston position is plotted on the vertical axis, and the top dead center rotational speed ne of the engine is plotted on the horizontal axis, and the relationship between the two is graphed. By repeating this operation, a distribution map showing the correlation between the top dead center rotational speed ne during the engine stop operation period and the piston stop position in the expansion stroke cylinder 12A is obtained.

  From the above distribution chart, a predetermined correlation is found between the top dead center rotational speed ne during the engine stop operation period and the piston stop position in the expansion stroke cylinder 12A. In the example shown in FIG. If the top dead center rotation speed ne in the sixth to second before the range is within the range indicated by hatching, the stop position of the piston 13 is within a range R suitable for engine restart (100 after the compression top dead center). It can be seen that it falls within the range of (° to 120 ° CA).

  Particularly, regarding the second top dead center rotational speed ne before the engine is stopped, the top dead center rotational speed ne is within the range of about 280 rpm to 380 rpm as shown in FIG. On the low rotation side below 320 rpm, the piston stop position gradually changes closer to the top dead center as the top dead center rotation speed ne decreases. On the other hand, on the high rotation side where the top dead center rotational speed ne is 320 rpm or higher, the stop position of the piston 13 becomes substantially constant and falls within the substantially appropriate range R regardless of the top dead center rotational speed ne. I understand.

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

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

  Therefore, as shown in FIG. 4 and FIG. 5, until a predetermined time elapses from the time point t1 when the fuel injection is stopped, that is, until the time point t2 when the engine speed Ne drops below the reference speed (for example, about 760 rpm), In order to sufficiently secure the scavenging performance of each cylinder 12A to 12D while suppressing the effects of rotational inertia and frictional resistance, the opening degree K of the throttle valve 23 is a relatively large value (for example, 30% opening degree of full opening). It is preferable to set to. Further, in order to maintain the engine speed Ne at a speed at which the piston 13 can be stopped at an appropriate position, the target generated current Ge of the alternator 28 is set to 0, for example, at the fuel injection stop time t1. It is like that.

  Then, at the time t2 when the engine speed Ne is decreased to the reference speed N2 or less, the opening K of the throttle valve 23 is reduced, and the target power generation current Ge of the alternator 28 is increased to a preset initial value. After the execution, at the time t3 when the engine top dead center rotational speed ne is within the predetermined range, the target generated current Ge of the alternator 28 is decreased to a value corresponding to the decreased state of the engine rotational speed Ne, and the crankshaft 3 By adjusting the rotational resistance and changing the external load of the engine in accordance with the degree of decrease in the engine rotational speed Ne, the engine rotational speed Ne is decreased along a reference line set based on experiments conducted in advance. I am doing so.

  Specifically, the engine top dead center rotational speed ne is detected in the process in which the engine rotational speed Ne decreases along the reference line, and the top dead center rotational speed ne falls within, for example, 480 rpm to 540 rpm. Based on the top dead center rotational speed ne at the time point t3 when it is determined that the engine has passed through the fourth compression top dead center before the engine is stopped, as shown in FIG. As described above, the higher the engine top dead center rotational speed ne is, the larger the value of the target generated current Ge is read from the map where the target generated current Ge corresponding to the detected value of the top dead center rotational speed ne is read. The alternator 28 has a target generated current Ge corresponding to the value.

  Further, the initial value when the target generated current Ge of the alternator 28 is increased at the time point t2 when the engine rotation speed Ne is reduced to the reference N2 speed or less is larger than the maximum value of the target generated current Ge read from the map. The target generated current Ge of the alternator 28 is controlled based on the detected value of the top dead center rotational speed ne by lowering the target generated current Ge that has been set and increased to the initial value at the time t2 at the time t3. It is configured as follows. For example, when the target generated current Ge read from the map is set to 0 to 50A, the initial value is set to a value higher than 50A that is the maximum value, for example, 60A. Then, after the target generated current Ge is set to 60 A at the time t2, the amount of decrease in the target generated current Ge is set based on the value read from the map at the time t3, and the alternator is set based on this value. Control for reducing the target generated current 28 is executed.

By controlling the power generation current of the alternator 28 as described above is executed at the time t 5 that has passed through the last compression TDC, the crank shaft 3, flywheel, the kinetic energy of the piston 13 and a connecting rod or the like has In addition, the potential energy of the air compressed in the compression stroke cylinder 12C is commensurate with the frictional resistance loss that is applied thereafter, and the piston 13 of the cylinder 12A that is in the expansion stroke when the engine is stopped is used to restart the engine. It becomes possible to stop within a suitable range R.

  A control operation when the engine is automatically stopped by the automatic stop control means of the ECU 2 will be described based on the flowcharts shown in FIGS. When this control operation starts, it is determined whether or not an automatic stop permission flag F for determining whether or not the engine is in an operating state capable of executing the automatic stop control is ON (step S1). This automatic stop permission flag F is satisfied when the vehicle speed is a predetermined value (for example, 10 km / h) or more, the steering angle is not more than a predetermined value, the battery voltage is not less than a reference value, and the air conditioner is in an OFF state. In addition, it is determined that the engine can be automatically stopped and is turned on.

  If YES is determined in step S1, it is determined whether the accelerator sensor 34 is in an OFF state and the brake sensor 35 is in an ON state (step S2). When it is confirmed that the engine is in a state, it is determined whether or not the engine speed Ne is larger than a reference value F / C · ON for fuel cut during deceleration that is set in advance to about 1100 rpm (step S1). S3) If NO is determined, the process proceeds to the following step S7.

  If it is determined YES in step S3 and it is confirmed that the engine speed Ne is larger than the determination reference value F / C · ON for fuel cut during deceleration, the fuel cut (FC) during deceleration is determined. Execute (step S4). Next, it is determined whether or not the engine rotational speed Ne has dropped below a fuel return determination reference value F / C · OFF that is set to about 900 rpm in advance (step S5). When it is determined YES, The fuel cut (FC) at the time of deceleration is terminated and the normal fuel injection state is restored (step S6).

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

  Then, it is determined whether or not the accelerator sensor 34 is in the ON state or the brake sensor 35 is in the OFF state, that is, whether or not the deceleration state is released (step S10). Returning to step S1, the above control operation is repeated. If it is determined NO in step S10 and it is confirmed that the deceleration state is not released, it is determined whether or not the vehicle speed is 0, that is, whether or not the vehicle is stopped and the automatic stop condition is satisfied. Determination is made (step S11).

  If it is determined as YES in step S11 and it is confirmed that the vehicle is stopped, the lean combustion state in which the air-fuel ratio in the cylinder is set to a value considerably larger than the stoichiometric air-fuel ratio at this time t0, that is, It is determined whether or not the engine is in a stratified combustion state (step S12). If it is determined YES and it is confirmed that the engine is currently in an operation state of stratified lean combustion, the target rotational speed N1 of the engine is A value higher than the normal idle rotation speed (650 rpm) by a predetermined amount, for example, about 810 rpm (step S13), and an EGR valve (provided in the EGR passage) for improving the scavenging performance of each cylinder 12A to 12D ( The exhaust gas recirculation is stopped by closing (not shown) (step S14).

  When it is determined NO in step S12 and it is confirmed that the engine is not in the stratified lean combustion operation state, for example, in order to lower the catalyst temperature or refresh the NOx catalyst, the air-fuel ratio in the cylinder Is the stoichiometric air-fuel ratio or the uniform combustion state set near the stoichiometric air-fuel ratio, the target engine speed N1 of the engine is set to a value higher than the above-mentioned 810 rpm, for example, about 860 rpm (step S15), and the throttle valve 23 is operated in the valve opening direction so that the opening degree K of the throttle valve 23 is feedback-controlled so that the boost pressure Bt becomes the target pressure P1 set to about −400 mmHg, for example (step S16). Then, the shift range of the automatic transmission is set to neutral and is set to a no-load state (step S17).

  As described above, in step S1, it is confirmed that the engine automatic stop permission flag F is in the ON state when the vehicle speed is higher than 10 km / h, and in step S2, the vehicle is decelerating (the brake sensor is turned on by 35 ON). When it is confirmed that the target engine speed N1 is stabilized at a predetermined value corresponding to the combustion state of the engine, the engine speed Ne is set to the normal idle speed. Before the speed drops to (650 rpm), the engine automatic stop control can be executed. Accordingly, the driver feels uncomfortable with the increase in the engine rotational speed Ne as in the case where the engine rotational speed Ne once decreased to the normal idle rotational speed is increased to the target rotational speed N1. It is possible to prevent the occurrence of a bad effect such as the time until the engine is automatically stopped or the time until the engine is automatically stopped longer than necessary.

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

  Further, at the time t0 when it is determined in step S11 that the vehicle speed is 0 and it is confirmed that the engine automatic stop condition is satisfied, the target engine speed N1 of the engine is set to a predetermined value in steps S13 and S15. In addition, since the shift range of the automatic transmission is shifted from the drive state (D range) to the neutral state (N range) in step S17, the load on the automatic transmission is reduced, which is shown in FIG. Thus, the engine rotation speed Ne slightly increases from the time point t0 when the automatic stop condition is satisfied.

  Next, it is determined whether or not a predetermined time set in advance to about 1 sec (seconds) has elapsed after a time point t0 when it is determined YES in step S11 and it is confirmed that the automatic engine stop condition is satisfied. (Step S18). If it is determined NO in step S18, this determination operation is repeated, and if it is determined YES, whether or not the fuel injection stop condition (FC condition) is satisfied, specifically, the engine speed. It is determined whether or not Ne becomes the target rotational speed N1 and the boost pressure Bt is stabilized in a state where the target pressure P1 is reached (step S19). If the accelerator sensor 34 is turned off or the brake sensor 35 is turned on during the determination operation, the process returns without stopping the fuel injection. Thereby, it is possible to prevent an inappropriate automatic stop of the engine from being performed in a case where the vehicle speed is shifted to 0 immediately after the vehicle speed becomes zero.

  Then, when it is determined YES in step S19 and it is confirmed that the engine speed Ne and the boost pressure Bt are stable (time t1 in FIGS. 4 and 5), the fuel injection is stopped. After (step S20), the target power generation current Ge of the alternator 28 is set to 0 to stop power generation (step S21), and the throttle valve 23 is opened to set the opening degree K to about 30%, for example. (Step S22).

  Thereafter, whether or not a predetermined time has elapsed from the time point t1 when the fuel injection is stopped in the above step S20, that is, the combustion of the fuel injected before reaching the two compression top dead centers after the fuel injection is stopped is performed. It is determined whether or not the process has been completed (step S23), and when it is determined YES, the ignition by the ignition device 27 is stopped (step S24). Next, by determining whether or not the engine rotational speed Ne has become equal to or lower than the reference speed N2 set to about 760 rpm in advance (step S25), the engine rotation is stopped after the fuel injection stop time t1 shown in FIG. It is determined whether or not the speed Ne has started to decrease. At a time t2 when it is determined YES, the throttle valve 23 is closed and its opening degree K is set to 0% (step S26). As a result, the boost pressure Bt that has risen so as to approach the atmospheric pressure when the throttle valve 23 is opened in step S22 starts to decrease with a predetermined time difference in accordance with the closing operation of the throttle valve 23.

  Further, the power generation control for operating the alternator 28 is started by setting the target power generation current Ge of the alternator 28 to an initial value set to about 60 A in advance (step S27). Note that the engine top dead center is replaced with the above embodiment in which the throttle valve 23 is closed at the time t2 when it is determined in step S25 that the engine rotational speed Ne is equal to or lower than the reference speed N2. For example, when it is determined that the rotational speed ne is equal to or lower than the reference speed N2 set to about 760 rpm, for example, the throttle valve 23 is closed and power generation control of the alternator 28 is started. Good.

  Next, it is determined whether or not the engine top dead center rotational speed ne is within the first predetermined range (step S28). This first predetermined range is a time point t3 when the engine passes through the fourth compression top dead center before the engine is stopped, for example, in the process in which the rotational speed Ne of the engine decreases along a preset reference line. Is a value set based on the top dead center rotational speed ne, and specifically, is set within the range of 480 rpm to 540 rpm.

  When it is determined YES in step S28 and it is confirmed that the engine top dead center rotational speed ne is within the predetermined range (480 rpm to 540 rpm), it corresponds to the top dead center rotational speed ne at that time t3. The target generated current Ge of the generated alternator 28 is set (step S29). That is, as shown in FIG. 11, the higher the engine top dead center rotational speed ne is, the higher the engine top dead center rotational speed ne is read from the map where the target power generation current Ge is set to a larger value. Based on this value, control is performed to reduce the target generated current Ge of the alternator 28 from the initial value (60A) to the value read from the map.

Then, dead center rotational speed ne on the engine, the second predetermined range set based on the TDC engine speed ne at the time t 4 when passing through the second compression top dead center before the engine stop, for example 260rpm It is determined whether it is within the range of -400 rpm (step S30). The fuel injection amount increases as the engine top dead center rotational speed ne increases at time t4 when it is determined as YES in this step S30 and it is confirmed that the second compression top dead center before the engine stop is passed. From the map (not shown) set to (2), the fuel injection amount for the cylinder 12C that is in the compression stroke when the engine is stopped is set, and fuel is injected in the latter half of the compression stroke of the cylinder 12C (step S31). When the fuel injected into the cylinder 12C is vaporized, the temperature in the cylinder is lowered, and the increase in the internal pressure is suppressed.

  Then, it is determined whether or not the engine top dead center rotational speed ne is equal to or less than a predetermined value N3 (step S32). This predetermined value N3 is a value corresponding to the top dead center rotational speed ne when exceeding the last compression top dead center in the process in which the engine rotational speed Ne is decreasing along a preset reference line, For example, it is set to about 260 rpm. Further, the boost pressure Bt at each time point when each of the cylinders 12A to 12C sequentially passes the compression top dead center is detected, and the value is stored.

  If it is determined YES in step S32 and it is confirmed that the engine top dead center rotational speed ne is equal to or lower than the predetermined value N3, that is, the engine has passed the last compression top dead center, At time t5, the boost pressure Bt at the time of passing through the previous compression top dead center is read, and this value is set as the boost pressure Bt at the second compression top dead center (TDC) before engine stop (step). S33).

  The top dead center rotational speed ne at the time t5 when the engine reaches the final compression top dead center (hereinafter referred to as the final top dead center rotational speed ne1) and the boost pressure Bt at the second compression top dead center before the engine stops. Based on (hereinafter referred to as boost pressure Bt2), it is determined whether or not the piston 13 tends to stop at a later position in each stroke (a position closer to the bottom dead center in the expansion stroke cylinder 12A) (step S34). . Specifically, when the final top dead center rotational speed ne1 is equal to or higher than a predetermined rotational speed N4 (for example, N4 = 200 rpm) and the boost pressure Bt2 is equal to or lower than a predetermined pressure P2 (for example, P2 = −200 mmHg) (vacuum side) ), The piston stop position in the expansion stroke cylinder 12A is 100 ° to 120 ° CA after the compression top dead center with respect to the appropriate range R. Since there is a large tendency to stop at a position close to 120 ° CA, YES is determined in step S34.

  When it is determined NO in step S34, the engine does not tend to stop at a position near the latter stage of the stroke as described above, and the position at a relatively earlier stage of the stroke, that is, in the expansion stroke cylinder 12A. There is a possibility that the piston stop position stops at a position close to 100 ° CA or 100 ° CA or less with respect to an appropriate range R of 100 ° to 120 ° CA after compression top dead center. Therefore, in order to stop the piston 13 within the proper range R more reliably, the throttle valve 23 is opened. For example, the throttle valve 23 is opened so that the opening degree K of the throttle valve 23 is set to the first opening degree K1 set to about 40% of full opening (step S35), and the intake air flow rate is increased to thereby increase the intake stroke. The intake resistance of the cylinder 12D is reduced. As a result, the engine is likely to stop at a later position in the stroke, and as a result, the stop position of the piston 13 in the expansion stroke cylinder 12A is prevented from exceeding the lower limit (100 ° CA) within the appropriate range R. become.

  On the other hand, if it is determined YES in step S34, the rotational inertia of the engine is large, the intake air flow rate in the final intake stroke to the compression stroke cylinder 12C is small, and the compression reaction force is small. There is already a condition where 13 is likely to stop at a later position in the stroke. Therefore, the throttle valve 23 is operated so that the opening degree K of the throttle valve 23 becomes the second opening degree K2 set to, for example, about 5% (step S36). The second opening K2 may be a smaller opening or a closed state according to engine characteristics and the like. In this way, an appropriate intake resistance is generated in the intake stroke cylinder 12D, and the occurrence of a situation in which the stop position of the piston 13 exceeds the appropriate range R and becomes further late is effectively prevented.

  Next, it is determined whether or not the engine is stopped (step S37). When it is determined YES, the shift range of the automatic transmission is returned from the neutral state to the drive state (D range) (step S38). ) After turning off the automatic stop permission flag F (step S39), the control operation is terminated.

  A control operation for restarting the engine that has been automatically stopped as described above will be described based on the flowcharts shown in FIGS. 12 to 14 and the time charts shown in FIGS. 15 and 16. First, it is determined whether or not a predetermined engine restart condition is satisfied (step S101). If YES is determined, for example, if an accelerator operation for starting from a stopped state is performed, the battery voltage is When the air temperature decreases or when the air conditioner is activated, the in-cylinder temperature is estimated based on the engine water temperature, the elapsed time since automatic stop, the intake air temperature, and the like (step S102).

  Based on the stop position of the piston 13 detected when the engine is automatically stopped, the amount of air in the compression stroke cylinder 12C and the expansion stroke cylinder 12A is calculated (step S103). That is, the combustion chamber volumes of the compression stroke cylinder 12C and the expansion stroke cylinder 12A are obtained from the stop position of the piston 13. When the engine is automatically stopped, the engine is stopped after several revolutions after the fuel injection is stopped. Therefore, the expansion stroke cylinder 12A is also filled with fresh air, and the compression stroke cylinder 12C and the expansion cylinder 12C are expanded while the engine is stopped. Since the inside of the stroke cylinder 12A is at substantially atmospheric pressure, the amount of fresh air is obtained from the combustion chamber volume.

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

  On the other hand, when it is determined NO in step S104 and the air amount in the compression stroke cylinder 12C is relatively small, the air-fuel ratio satisfying λ ≦ 1 with respect to the air amount in the compression stroke cylinder 12C calculated in step S103. The first fuel injection is performed so as to become (step S106). This air-fuel ratio is obtained from the first second air-fuel ratio map M2 of the compression stroke cylinder 12C set in advance according to the stop position of the piston 13, and satisfies λ ≦ 1 (theoretical air-fuel ratio or richer air-fuel ratio). By setting, even when the amount of air in the compression stroke cylinder 12C is small, sufficient combustion energy for reverse rotation can be obtained.

  Next, the cylinder 12C is ignited after the elapse of a predetermined time set in consideration of the vaporization time from the first fuel injection to the compression stroke cylinder 12C (step S107). Then, it is determined whether or not the piston 13 has moved based on whether or not the edges of the crank angle sensors 30 and 31, that is, the rising or falling edge of the crank angle signal are detected within a certain time after ignition (step S 108). When it is determined NO and it is confirmed that the piston 13 has not moved due to misfire, the compression stroke cylinder 12C is re-ignited (step S109).

  If it is determined YES in step S108 and it is confirmed that the piston 13 has moved, the split ratio of split fuel injection to the expansion stroke cylinder 12A (based on the piston stop position and the in-cylinder temperature estimated in step S102) The ratio of the first stage injection and the second 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 S103 (step S122). The air-fuel ratio at this time is obtained from an air-fuel ratio map M3 for the expansion stroke cylinder 12A set in advance according to the stop position of the piston 13. Further, 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. Step S123).

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

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

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

  Next, taking into account the fuel vaporization time, the second time fuel is injected into the compression stroke cylinder 12C (step S128). The fuel injection amount at this time is such that the entire air-fuel ratio based on the total injection amount with the first injection amount becomes richer (for example, about 6) than the combustible air-fuel ratio (lower limit is 7 to 8). It is obtained from the second air-fuel ratio map M5 for the compression stroke cylinder 12C set in advance according to the stop position of the piston 13. The compression top dead center can be easily exceeded by reducing the compression pressure in the vicinity of the compression top dead center of the compression stroke cylinder 12C according to the latent heat of vaporization caused by the second injection fuel in the compression stroke cylinder 12C. It becomes.

  Note that the second fuel injection into the compression stroke cylinder 12C is performed 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.

  Since the fuel injected for the second time in the compression stroke cylinder 12C does not burn as described above, the next combustion following the first combustion in the expansion stroke cylinder 12A is the intake stroke cylinder 12D, that is, as shown in FIG. This is the first combustion in the fourth cylinder that was in the intake stroke when stopped. As energy for the piston 13 of the intake stroke cylinder 12D to exceed the compression top dead center, a part of the initial combustion energy in the expansion stroke cylinder 12A is used, and the initial combustion energy in the expansion stroke cylinder 12A is compressed. The stroke cylinder 12C is used both for overcoming the compression top dead center and for the intake stroke cylinder 12D for exceeding the compression top dead center.

  Therefore, for smooth start-up, it is desirable that the energy required for the intake stroke cylinder 12D to exceed the compression top dead center is small. For this purpose, the air density in the cylinder 12D is estimated, and the intake stroke cylinder is estimated from the estimated value. After calculating the 12D 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 S102 (step S141). That is, when self-ignition occurs, a force (reverse torque) that pushes the piston 13 back to the bottom dead center before the compression top dead center is generated by the combustion, and much energy is required to exceed the compression top dead center. Since it is consumed, it is not desirable. Therefore, in order to suppress the reverse torque, the air-fuel ratio is corrected to the lean side so that compression self-ignition does not occur.

  Next, the fuel injection amount to the intake stroke cylinder 12D is calculated based on the air amount of the intake stroke cylinder 12D calculated in step S140 and the air-fuel ratio in consideration of the air-fuel ratio correction value calculated in step S141 ( Step S142). Then, fuel is injected into the intake stroke cylinder 12D. In this fuel injection, the compression pressure is reduced by the latent heat of vaporization, that is, the energy required to exceed the compression top dead center is reduced. The process is delayed until the later stage of the compression stroke (step S143), and the delay amount is calculated based on the automatic engine stop period, the intake air temperature, the engine water temperature, and the like.

  Further, in order to suppress the occurrence of the reverse torque, ignition is performed with a delay after the top dead center (step S144). By executing the control described above, in the intake stroke cylinder 12D, the compression pressure is reduced to the compression top dead center and easily exceeds the top dead center. Directional torque will be generated.

  After step S144, the control state may be shifted to a normal control state, 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 (external load of the engine) of the crankshaft 3 is increased by the power generation of the alternator 28, thereby rotating the engine speed. Suppresses the rising of.

  Next, it is determined whether or not the intake pressure detected by the intake pressure sensor 26 is higher than the intake pressure during normal idling when the engine is not automatically stopped (step S150). Since the engine speed is likely to rise, the amount of combustion energy generated is reduced by making the opening of the throttle valve 23 smaller than the throttle opening during normal idle operation (step S151). Suppress.

  Then, it is determined whether or not the temperature of the exhaust gas purification catalyst 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 λ ≦ 1. The rich air-fuel ratio is set (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.

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

  By executing the restart control, as shown in FIGS. 15 and 16, first, the first fuel injection J3 is performed in the compression stroke cylinder 12C (third cylinder), and combustion is performed by the ignition (FIG. 15). (1)) is performed. With the combustion pressure (part a in FIG. 16) due to this combustion (1), the piston 13 of the compression stroke cylinder 12C is pushed down to the bottom dead center side, and the engine is driven in the reverse direction. Here, the first fuel injection J3 of the compression stroke cylinder 12C becomes a lean air-fuel ratio (λ> 1) when the air amount is relatively large, and a stoichiometric air-fuel ratio or a rich air-fuel ratio (λ ≦ 1) when it is small. Therefore, an appropriate combustion energy for reversing the engine, that is, a combustion energy that does not excessively reverse the compression top dead center while sufficiently compressing the air in the expansion stroke cylinder 12A. Obtainable.

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

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

  In addition, fuel richer than the combustible air-fuel ratio is injected into the compression stroke cylinder 12C at an appropriate timing (J4) ((3) in FIG. 15), but the compression stroke cylinder 12C is not combusted, The compression pressure of the compression stroke cylinder 12C is reduced by the latent heat of vaporization caused by fuel injection (part d in FIG. 16), and accordingly, the compression top dead center (the first compression top dead center from the start of starting) is exceeded. The initial combustion energy of the consumed expansion stroke cylinder 12A is reduced.

  Furthermore, the timing of fuel injection (J5) in the intake stroke cylinder 12D, which is the next combustion cylinder, is set to an appropriate timing ((4) in FIG. 15) for reducing the temperature in the cylinder and the compression pressure by the vaporization latent heat of the fuel. As shown, for example, after the middle stage of the compression stroke), self-ignition before the compression top dead center is prevented in the compression stroke of the intake stroke cylinder 12D. Further, in combination with the ignition timing of the intake stroke cylinder 12D being set after the compression top dead center, combustion before the compression top dead center is prevented (part e in FIG. 16). That is, by reducing the compression pressure by the fuel injection (J5) and not performing the combustion before the compression top dead center, the energy of the first combustion in the expansion stroke cylinder 12A becomes the compression top dead center (the second compression from the engine start start time). It is possible to suppress consumption to exceed the top dead center.

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

  When the preset engine automatic stop condition is satisfied as described above, the fuel injection for continuing the operation of the engine is stopped to automatically stop the engine, and the engine restart condition in the automatic stop state. In the engine starter configured to restart the engine by injecting fuel into the cylinder 12A that is in a stopped state at least in the expansion stroke to cause ignition and combustion, the engine is driven by the engine. And an automatic stop control means for lowering the target generated current Ge of the alternator 28 after raising it to an initial value set in advance to a large value when the engine is automatically stopped. The decrease amount of the engine is set to a value corresponding to the decrease state of the engine speed Ne generated after the fuel injection is stopped. Therefore, by adjusting the rotational resistance of the crankshaft 3 to a value corresponding to the reduced state of the engine rotational speed Ne, the piston 13 of the cylinder 12A that is in the expansion stroke when the engine is stopped is in a range R suitable for restarting the engine. It can be stopped at a position that is slightly offset from the center of the stroke to the bottom dead center side.

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

  Therefore, after the target power generation current Ge of the alternator 28 is increased to the initial value in the initial stage of the operation for automatically stopping the engine, the piston 13 is compressed and compressed after the power generation function of the alternator 28 can be sufficiently exerted. The engine top dead center rotational speed ne when passing through the dead center is detected, and when the top dead center rotational speed ne is low, the reduction amount of the target generated current Ge is set to a larger value than when the top dead center rotational speed ne is high. Thus, the control for adjusting the rotational resistance of the crankshaft 3 in response to the reduced state of the engine rotational speed Ne can be executed quickly and accurately. Therefore, the piston 13 of the cylinder 12A that is in the expansion stroke when the engine is stopped is operated. It can be stopped at a position suitable for restarting the engine.

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

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

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

  Further, as shown in the above embodiment, at the initial stage of the operation of automatically stopping the engine, the opening K of the throttle valve 23 is set to about 30% to sufficiently secure the intake flow rate introduced into the cylinders 12A to 12D. After that, when the target generated current Ge of the alternator 28 is increased to a preset initial value at a predetermined timing, the intake throttle amount is set at the initial stage of the automatic stop operation where the engine speed Ne is sufficiently high. Is reduced, and a sufficient amount of intake air is introduced into the cylinders 12A to 12D to effectively improve the scavenging performance of the cylinders 12A to 12D, and after reducing the pumping loss, the power generation function of the alternator 28 is improved. By adjusting the rotational resistance of the crankshaft 3 to an appropriate value quickly and sufficiently, the piston 1 of the cylinder that becomes the expansion stroke when the engine is stopped is used. The control for stopping the position suitable for restart of the engine, there is an advantage that can be more appropriately performed.

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

  Further, in the above-described embodiment, at the time t2 when the engine rotation speed Ne drops below the reference speed N2 set in advance to about 760 rpm after the stop of fuel injection, that is, at the beginning of the operation for automatically stopping the engine. Since the control for increasing the target generated current Ge of the alternator 28 to the initial value is performed in the automatic stop control means while reducing the opening K of the engine 23 to reduce the intake air flow rate, the throttle valve 23 is set appropriately. By closing at the timing, the amount of air introduced into the cylinder 12A that is in the expansion stroke when the engine is stopped can be adjusted to be larger than the cylinder 12C that is in the compression stroke, and the power generation of the alternator 28 is also performed. By effectively exhibiting the function at an appropriate timing, the piston of the expansion stroke cylinder 12A is Ton 13 within R suitable for restart of the engine, i.e. can be stopped at a position slightly leaning the bottom dead center side from the stroke center.

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

In the above embodiment, for example, in an engine in which the normal idle rotation speed when the engine is not automatically stopped is set to 650 rpm (the automatic transmission is the drive range), the target rotation speed of the engine (the automatic transmission is set to the neutral range). set) N1 is, because of the structure so as to stop the normal idle rotational speed higher than the fuel injection at the time t 1 it becomes about 860rpm in the example the homogeneous combustion state, the engine is stopped from the stop time t1 of the fuel injection The engine speed (the number of intake, compression, expansion, and exhaust strokes) until the state is reached can be sufficiently secured. Therefore, the engine rotational speed Ne is reduced along a preset reference line, and the target power generation current Ge of the alternator 28 is controlled in the process to adjust the rotational resistance of the crankshaft 3, so that the engine is restarted. There is an advantage that the automatic stop control for stopping the piston 13 within the range R suitable for starting can be properly executed.

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

In the above embodiment, based on the TDC engine speed ne1 at the time t 5 the piston 13 reaches its end of compression top dead center, whether the piston 13 tends to stop at the position of the second half side of the stroke Since the determination is made and the opening degree K of the throttle valve 23 is adjusted according to the determination result, the stroke amount of the piston 13 immediately before the engine is stopped is appropriately adjusted to be within a range R suitable for restarting the engine. Thus, the automatic stop control for stopping the piston 13 can be properly executed.

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

  In the above embodiment, an example in which the intake flow rate adjusting means including the throttle valve 23 disposed on the upstream side of the surge tank 21b is used to adjust the intake flow rate to each of the cylinders 12A to 12D has been described. The present invention is not limited to this, and a known variable valve mechanism that changes the lift amount of the intake valve 19 provided in each of the cylinders 12A to 12D is provided to adjust the intake flow rate to each of the cylinders 12A to 12D. Alternatively, the intake flow rate to each of the cylinders 12A to 12D is adjusted using a multiple throttle valve in which a valve body is individually provided in the branch intake passage 21a connected to each of the cylinders 12A to 12D. You may comprise as follows.

  Further, in the above embodiment, at the time t2 when the engine rotational speed Ne is lower than the reference speed N2 set in advance to about 760 rpm after the fuel injection is stopped, the operation of decreasing the opening K of the throttle valve 23; Although the operation of increasing the target generated current Ge of the alternator 28 is simultaneously performed, it is not always necessary to match the operation time points of the two, and the opening time of the throttle valve 23 is decreased according to the increase timing of the target generated current Ge of the alternator 28. You may make it shift slightly back and forth from the time t2.

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

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

  Although omitted in the above embodiment, when the engine is restarted, when the predetermined condition is satisfied, for example, when the piston stop position is not within the proper stop range R, or when the engine rotation speed is increased by the predetermined time after the start. You may make it perform control accompanied by the assist by a starter motor, when it does not reach a predetermined value.

1 is a schematic cross-sectional view of an engine provided with a starter according to the present invention. It is explanatory drawing which shows the structure of the intake system and exhaust system of an engine. It is explanatory drawing which shows the relationship between the piston stop position and air quantity of the cylinder which becomes an expansion stroke and a compression stroke at the time of an engine stop. It is a time chart which shows the change state etc. of the engine speed at the time of an engine stop. It is a time chart which shows the change state etc. of the throttle opening degree and the target generated current when the engine is stopped. It is a distribution map which shows the correlation with the engine speed at the time of an engine stop, and a piston stop position. It is a distribution map which shows the correlation with the top dead center rotational speed and piston stop position in the 2nd before an engine stop. It is a flowchart which shows the first half of the engine automatic stop control operation. It is a flowchart which shows the middle part of an engine automatic stop control operation | movement. It is a flowchart which shows the second half part of the engine automatic stop control operation. It is a graph which shows an example of the map for setting the target electric power generation current of an alternator according to the rotational speed of an engine. It is a flowchart which shows the first half of the control action at the time of engine restart. It is a flowchart which shows the middle part of control action at the time of engine restart. It is a flowchart which shows the latter half part of the control action at the time of engine restart. It is a time chart which shows the combustion operation etc. at the time of engine restart. It is a time chart which shows the change state etc. of the engine speed at the time of engine restart. It is a time chart which shows the change state of the electric power generation current of an alternator.

Explanation of symbols

2 ECU (automatic stop control means)
3 Crankshaft 13 Piston 16 Fuel Injection Valve 23 Throttle Valve 28 Alternator

Claims (6)

When the preset automatic engine stop condition is satisfied, the fuel supply for continuing the engine operation is stopped to automatically stop the engine, and the restart condition for the engine in the automatic stop state is satisfied. The engine is a four-cycle multi-cylinder engine starter configured to automatically restart the engine by injecting fuel and igniting and burning at least the cylinders automatically stopped in the expansion stroke. And
An alternator that is driven by the engine and has a short characteristic with respect to the time to increase when changing the generated current value of a certain width ;
Control that when the engine is automatically stopped, the target generator current of the alternator is temporarily increased to an initial value set to a large value in advance , and then reduced to the target generator current value for adjusting the rotation resistance of the crankshaft. And an automatic stop control means for executing
To a value which amounts decrease corresponding to the degraded state of the engine rotational speed that occurred after stopping the fuel injection from the initial value of the target generated current, setting the crank angle of the engine in the process of the engine rotational speed is lowered in advance When the detected angle is reached, the engine speed is detected, and when the engine speed is low, the amount of decrease in the target generated current from the initial value is set to a larger value than when the engine speed is high. An engine starting device. 2. The engine starter according to claim 1, wherein a reduction amount of the target generated current is controlled based on an engine rotational speed detected when the piston passes through the compression top dead center. In the initial stage of the operation of automatically stopping the engine, after adjusting the intake throttle amount in a direction to increase the intake flow rate introduced into the cylinder, the target generated current of the alternator is increased to a preset initial value. The engine starting device according to claim 1 or 2. In the initial stage of the operation for automatically stopping the engine, the intake throttle amount is adjusted in a direction to increase the intake flow rate introduced into the cylinder, and the target generator current of the alternator is temporarily set to a low value. The engine starting device according to claim 3. 2. The shift state of the automatic transmission is changed from the drive state to the neutral state at the initial stage of the operation for automatically stopping the engine, and the target generator current of the alternator is increased to a preset initial value. The engine starter according to any one of -4. The engine start according to any one of claims 1 to 5, wherein the engine rotation speed when stopping fuel injection when the engine is automatically stopped is set to a value higher than a normal idle rotation speed. apparatus.

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