JP4293075B2 - 4-cycle multi-cylinder engine starter - Google Patents

Description

  The present invention relates to a starter for a four-cycle multi-cylinder engine, and automatically stops the engine when a preset automatic engine stop condition is satisfied in an idle operation state of the engine, and the restart condition in this state. The present invention relates to a starter for a four-cycle multi-cylinder engine configured to automatically restart the engine when the above is established.

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 that energy by injecting fuel into a cylinder that is in a stopped state during the expansion stroke, and igniting and burning the fuel. 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 sufficient energy cannot be obtained by combustion, or the stroke in which the energy from combustion acts 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. Thus, a technique for controlling the braking device is known. However, this configuration requires a braking device and is expensive. In order to prevent this, the applicant of the present application has proposed a stop control means for preventing inflow or exhaust of intake air into a cylinder of an engine at a predetermined timing, as shown in Patent Document 2. Furthermore, as shown in Patent Document 3, a technique has been proposed in which an exhaust valve of one or more cylinders of an internal combustion engine is closed after a predetermined timing has elapsed after the ignition switch is turned off.
Japanese Utility Model Publication No. 60-128975 JP-A-62-255557 WO 01/44636 A2

  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 Documents 2 and 3, the configuration in which the cylinder valve is closed at a predetermined timing is a type in which the cylinder stopped exclusively in the expansion stroke is ignited and restarted. It was not possible to perform precise stop control taking into account the relationship with the cylinder stopped at. In particular, since a method of applying a compression resistance to the cylinder that is in the compression stroke at the time of stopping, there is a tendency that NVH (engine vibration) when the engine is stopped tends to be high.

  In view of the above circumstances, the present invention has a four-cycle multi-cycle system that can reliably restart the engine by stopping the piston at an appropriate position while suppressing NVH (engine vibration) during automatic engine stop with a simple configuration. A starter for a cylinder engine is provided.

  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. A four-cycle multi-cylinder engine configured to restart the engine by injecting fuel into at least an automatically stopped cylinder in the expansion stroke to cause ignition and combustion when the engine restart condition is satisfied A variable valve timing system that is provided in each cylinder and that can change the opening and closing timing of a valve that opens and closes a port that opens to each cylinder according to the operating state of the engine, and the operation stroke of each cylinder A stroke detecting means for detecting, a rotational speed detecting means for detecting the rotational speed of the engine, and an engine rotational speed detected by the rotational speed detecting means; And a final top dead center grasping means for grasping the timing at which one of the cylinders reaches the final top dead center when the engine is stopped based on the stroke of each cylinder detected by the stroke detection means, and the engine is automatically stopped. The variable valve based on the timing grasped by the final top dead center grasping means, the rotational speed of the engine at the timing detected by the rotational speed detecting means, and the stroke of each cylinder detected by the stroke detecting means. Automatic stop control means for controlling the timing system, and the automatic stop control means includes a variable valve timing system that opens a port of a cylinder that becomes a compression stroke at the time of stop after each cylinder exceeds a final top dead center. A starter for a four-cycle multi-cylinder engine characterized by controlling.

  In this aspect, the automatic stop is started and the timing at which each cylinder reaches the final top dead center is grasped by the final top dead center grasping means. At this final top dead center, the automatic stop control means controls the variable valve timing system so as to open the cylinder port that is in the compression stroke when stopped. As a result, at the time of stopping, the amount of air in the cylinder that becomes the compression stroke is reduced and the compression reaction force is reduced, so that it is possible to stop while suppressing NVH (engine vibration). The “cylinder port” may be an intake port or an exhaust port of the cylinder, or may be both an intake port and an exhaust port. Or you may provide the port which can discharge | emit the air in a cylinder separately from an intake port and an exhaust port.

  According to a second aspect of the present invention, in the starter of the four-cycle multi-cylinder engine according to the first aspect, the automatic stop control means performs a compression stroke at the time of stop immediately after each cylinder exceeds the final top dead center. The variable valve timing system is controlled to open the cylinder port.

  In this aspect, since the pressure in the cylinder decreases when the cylinder that is in the compression stroke at the time of stopping first begins to compress, the compression reaction force received by the piston of the cylinder becomes small, and NVH (engine vibration) when the engine stops It is possible to stop the piston closer to the center at a desired stroke in a state in which is further suppressed.

  According to a third aspect of the present invention, in the starter of the four-cycle multi-cylinder engine according to the first or second aspect, the automatic stop control means is configured such that the engine rotates backward after each cylinder exceeds the final top dead center. When the engine rotational speed at the time of the final top dead center is higher than a predetermined value after performing the above, the variable valve timing system is controlled so as to open the port of the cylinder that becomes the expansion stroke when stopped. .

  In this mode, when the engine is automatically stopped, the intake amount of the cylinder that is in the compression stroke at the time of stop is reduced by opening the port of the cylinder that is in the compression stroke at the time of stop after each cylinder exceeds the final top dead center. As a result, the cylinders that are in the expansion stroke when stopped tend to stop toward the bottom dead center. At this time, when the rotational speed of the engine when each cylinder reaches the final top dead center is lower than a predetermined value (for example, 180 rpm), each cylinder is filled with sufficient air. Therefore, the stroke of each piston is closer to the center, but when it exceeds the final top dead center, the cylinder stroke that becomes the compression stroke at the time of stop is exhausted. The cylinder stop position may go too far to the bottom dead center side. Therefore, in this aspect, the engine speed at the time when the final top dead center is reached is used as a parameter, and the air in the cylinder that is in the expansion stroke is extracted so that the piston of the cylinder returns to the center side.

  According to a fourth aspect of the present invention, in the starter of the four-cycle multi-cylinder engine according to the first, second, or third aspect, the port of the cylinder is an intake port of a cylinder that is in the compression stroke.

  In this aspect, it is possible to reduce the compression reaction force while the intake valve remains open when the cylinder in the compression stroke shifts from the intake stroke to the compression stroke.

  According to a fifth aspect of the present invention, in the starter for a four-cycle multi-cylinder engine according to any one of the first to fourth aspects, the automatic stop control means is configured such that the cylinder that is in a compression stroke when stopped has a final top dead center. The variable valve timing system is controlled so that at least the intake port is maintained in the open state after the intake stroke is entered immediately before the intake.

  In this aspect, when opening the port of the cylinder that becomes the compression stroke, the phase immediately before the cylinder exceeds the final top dead center is the intake stroke, and at least the intake valve is open. Therefore, the compression reaction force is reduced. In addition, when the rotational speed when the final top dead center is exceeded is low (for example, less than 180 rpm), not only the intake valve but also the exhaust valve is opened in order to more actively reduce the compression reaction force. Also good.

  According to a sixth aspect of the present invention, in the starter of the four-cycle multi-cylinder engine according to any one of the first to fifth aspects, the engine is restarted after passing the last top dead center after executing the automatic stop control. When the condition is satisfied, the valve opening operation of the variable valve timing system by the automatic stop means is prohibited, and when the restartable condition is satisfied, the rotation of the engine is reversed from that of the cylinder that is in the expansion stroke. There is further provided restart control means for injecting fuel at the timing when the normal rotation is restored, and then igniting the cylinder at the timing when the engine changes from the reverse rotation to the normal rotation.

  In this aspect, when the engine restart request occurs after the engine has shifted to automatic engine stop control and passed the final top dead center, the valve opening operation of the variable valve timing system by the automatic stop means is prohibited. By performing fuel injection and ignition at a predetermined timing, it is possible to effectively use the reverse rotation operation of the engine immediately before the stop and to restart the engine immediately.

  According to the first aspect of the invention, at the final top dead center, the amount of air in the cylinder that becomes the compression stroke can be reduced and the compression reaction force can be reduced, so that NVH (engine vibration) is suppressed. Can be stopped. Therefore, according to the present invention, it is possible to reliably restart the engine by stopping the piston at an appropriate position while suppressing NVH (engine vibration) during automatic engine stop with a simple configuration. Play.

  According to the second aspect of the present invention, since the pressure in the cylinder decreases when the cylinder that is in the compression stroke at the start of the compression starts for the first time, the compression reaction force received by the piston of the cylinder decreases, and the engine stops when the engine is stopped. Since the piston can be stopped closer to the center at a desired stroke while NVH (engine vibration) is further suppressed, the positional accuracy when the piston is stopped is improved.

  According to the third aspect of the present invention, even if there is a variation in the braking of the piston related to the cylinder that reaches the compression stroke due to an individual difference of the engine or a variation in the rotational speed when passing through the final top dead center, this variation Can be absorbed by the cylinder in the expansion stroke, and more accurate braking control is possible.

  According to the fourth and fifth aspects of the present invention, it is possible to reduce the compression reaction force while the intake valve remains open when the cylinder that is in the compression stroke shifts from the intake stroke to the compression stroke. Therefore, there is an advantage that the control becomes simple and the operation accuracy of the valve becomes high.

  According to the sixth aspect of the present invention, after the shift to the automatic engine stop control, the reverse rotation of the engine immediately before the stop can be effectively used and the engine can be restarted immediately. It can be restarted.

  1 and 2 show a schematic configuration of a four-cycle spark ignition engine having an engine starter according to the present invention. This engine transmits power to an automatic transmission (not shown) mounted on a vehicle, and includes an engine 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 disposed above the cylinder 13. Is formed.

  In the present embodiment, a cylinder that is in the compression stroke when the engine is stopped is referred to as a compression stroke cylinder, and a cylinder that is in the expansion stroke is referred to as an expansion stroke cylinder. Is called an exhaust stroke cylinder). In the present embodiment, the cylinder 12A is an expansion stroke cylinder, the cylinder 12B is an exhaust stroke cylinder, the cylinder 12C is a compression stroke cylinder, and the cylinder 12D is an intake stroke cylinder.

  A spark plug 15 is fixed to the cylinder head 10 for each combustion chamber 14 of each of the cylinders 12A to 12D. Each spark plug 15 is installed such that its tip faces the corresponding combustion chamber 14 from the top. 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.

  An intake port 17 and an exhaust port 18 that open toward the combustion chamber 14 are provided above the combustion chamber 14 of each of the cylinders 12A to 12D, and an intake valve 19 and an exhaust valve 20 are connected to the ports 17 and 18, respectively. Are equipped.

  In the present embodiment, the intake valve 19 and the exhaust valve 20 are changed in opening / closing timing regardless of the phase of the crankshaft 3 by a variable valve timing system (VVTS: Variable Valve Timing System) 112 (see FIG. 2). It is configured to be possible. The timing at which the variable valve timing system 112 drives the intake valve 19 and the exhaust valve 20 of each cylinder 12A to 12D to open and close the intake port 17 and the exhaust port 18 is controlled by the ECU 2.

  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 (FIG. 1). 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.

  Further, an EGR valve 125 provided in the EGR passage 124 is connected to the common intake passage 21c on the downstream side of the throttle valve 23.

  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 for adjusting the target generated current Ge by controlling the rotation of the rotor (not shown) and adjusting the output voltage, and the control from the ECU 2 input to the regulator circuit 28a. Based on the signal, the control of the target generated current Ge corresponding to the electric load of the vehicle, the voltage of the vehicle-mounted battery, and the like 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 engine is based on a detection signal output from one crank angle sensor 30 (rotation speed detecting means). 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, 31 as described later. ing.

  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.

  Based on the rotational speed detected by the sensors 30 and 31 as the rotational speed detecting means and the stroke detecting means, and the stroke of each cylinder, the ECU 2 reaches the final top dead center when the engine is stopped. The final top dead center grasping means for grasping the timing is functionally configured.

  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 injection timing to the fuel injection valve 16, and an ignition plug 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, the first combustion is performed in the compression stroke cylinder 12C when the engine is automatically stopped, so that the piston 13 is pushed down to slightly reverse the crankshaft 3. As a result, the piston 13 of the expansion stroke cylinder 12A is once lifted, and the air-fuel mixture in the cylinder 12A is compressed and ignited and burned. And is configured to restart the engine.

  In order to properly restart the engine by merely igniting the fuel injected into a specific cylinder without using a restart motor or the like in principle as described above, the mixture of the expansion stroke cylinder 12A is used. It is necessary to secure sufficient energy obtained by burning the fuel so that the compression stroke cylinder 12C overcomes the compression reaction force and exceeds the compression top dead center. For this purpose, it is necessary to ensure a sufficient amount of air in the expansion stroke cylinder 12A when the air-fuel mixture is burned.

  This mechanism will be described with reference to FIGS. 3 (a) and 3 (b). As shown in FIGS. 4A and 4B, the phases of the expansion stroke cylinder 12A and the compression stroke cylinder 12C are shifted by 180 ° CA when the engine is stopped. If the piston 13 of the expansion stroke cylinder 12A operates and is located on the bottom dead center side with respect to the stroke center, the amount of air in the cylinder increases and sufficient energy is obtained by combustion. However, when the piston 13 of the expansion stroke cylinder 12A is positioned extremely on the bottom dead center side, the air amount in the compression stroke cylinder 12C becomes too small as shown in FIG. At the time of combustion, sufficient energy for reversing the crankshaft 3 cannot be obtained.

  On the other hand, a predetermined range (for example, compression top dead center) slightly lower than the position where the crank angle becomes 90 ° CA when the compression top dead center is 0 ° CA, that is, the stroke center of the expansion stroke cylinder 12A. If the piston 13 can be stopped within a range of 100 ° CA to 120 ° CA from the point (hereinafter referred to as an appropriate range R), a large amount of air can be secured in the expansion stroke cylinder 12A and compression is performed. Since a predetermined amount of air is secured also in the stroke cylinder 12C, it is possible to obtain energy enough to reverse the crankshaft 3 a little, and the energy in the subsequent expansion stroke cylinder 12A is also sufficiently high. Thus, the engine can be reliably restarted.

  Therefore, the piston stop position control shown in FIG. 4 is performed by the automatic stop control means functionally provided in the ECU 2. In this control, at the timing t0 when the engine automatic stop condition is satisfied, a step of first setting and stabilizing the target rotational speed of the engine to a value higher than the normal idle rotational speed is executed. 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). ), And at a timing t1 when the engine rotation speed Ne is stabilized at the target rotation speed, the fuel injection is stopped and the engine rotation speed Ne is decreased.

  Further, the ECU 2 performs the intake flow rate at the normal idling time (minimum intake flow rate necessary for continuing the engine operation. For example, the air-fuel ratio in the cylinder has an excess air ratio λ = The variable valve timing system 112 is controlled to open so that the intake flow rate is larger than the intake flow rate of the engine cylinders 12A to 12D. ing.

  Next, the timing for controlling the alternator 28 will be described.

  The ECU 2 of the present embodiment stores a control condition for reducing the target generated current Ge of the alternator 28 from a preset initial value at the timing t1 when the fuel injection is stopped. As a result, the rotational resistance of the crankshaft 3 is reduced, and the rotational speed Ne of the engine can be maintained at a speed at which the piston 13 can be controlled to stop at an appropriate position. In the present embodiment, the target generated current Ge of the alternator 28 set at the fuel injection stop timing t1 is set to 0, for example.

  The ECU 2 also includes a timing t2 at which the target generated current Ge of the alternator 28 is temporarily increased from the initial value, and a timing t3 at which the target generated current Ge of the alternator 28 is adjusted in accordance with the degree of decrease in the engine rotational speed Ne. And are set. The timing t2 is set to a point in time after the combustion injection is stopped at the timing t1 described above, when it is detected that the engine rotation speed Ne has decreased to a reference speed (for example, 760 rpm) N2 that is set in advance. The timing t3 is set to a timing at which the engine top dead center rotational speed ne is within a predetermined range after the elapse of the timing t2. At this timing t3, by adjusting the target generated current Ge of the alternator 28 along the reference line set based on the results of experiments conducted in advance, it is possible to apply a load to the engine and reduce the rotational speed Ne. become.

  The timing t3 is a timing at which the compression top dead center that is fourth previous from the timing at which the engine is stopped is detected. Specifically, the top dead center rotational speed ne of the engine that is decelerating is detected. The top dead center rotational speed ne is determined by determining that the rotational speed ne is within, for example, 480 rpm to 540 rpm.

  FIG. 5 is a map in which the target generated current Ge is set to a larger value as the engine top dead center rotational speed ne is higher in order to set the target generated current of the alternator according to the engine rotational speed. The ECU 2 is configured to read out the target generated current Ge corresponding to the detected value of the top dead center rotational speed ne from the map of FIG. 5 at the timing t3 and to generate the target generated current Ge of the alternator 28 corresponding to this value. .

  The initial value when the target generated current Ge of the alternator 28 is increased at the timing t2 is set to a value larger than the maximum value of the target generated current Ge read from the map. For example, when the target generated current Ge read from the map shown in FIG. 5 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 60A at the timing t2, the amount of decrease in the target generated current Ge is set based on the value read from the map at the timing t3, and the alternator is set based on this value. It is set so that the control for reducing the target generated current 28 is executed.

  Further, the ECU 2 can detect the second compression top dead center before the engine is stopped as the timing t4 by detecting that the top dead center rotational speed ne is decelerated to a predetermined range after the timing t3 has elapsed. It is configured.

  By controlling the generated current of the alternator 28 as described above, at timing t4, the kinetic energy of the crankshaft 3, the flywheel, the piston 13, the connecting rod, etc., or the air compressed by the compression stroke cylinder 12C The potential energy, etc. of the cylinder is commensurate with the frictional resistance loss, etc. that acts thereafter, and the piston 13 of the cylinder 12A, which is in the expansion stroke when the engine is stopped, is stopped within a range R suitable for restarting the engine. It becomes possible.

  In the process of automatically stopping the engine as described above, from the fuel injection stop timing t1, the kinetic energy of the crankshaft 3, the flywheel, etc. is caused by mechanical loss due to frictional resistance or the pump work of each cylinder 12A-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 FIG. 4, after the engine rotational speed Ne temporarily drops each time the cylinders 12 </ b> A to 12 </ b> D reach compression top dead center, they again when the compression top dead center is exceeded. The engine rotation speed Ne gradually decreases while repeating up and down.

  In the time chart of the crank angle CA shown in FIG. 4, the solid line indicates the top dead center (TDC) of the first cylinder 12A (expansion stroke cylinder 12A) and the third cylinder 12C (compression stroke cylinder 12C) as the compression top dead center. The dashed line indicates the crank angle with 0 ° CA, and the alternate long and short dash line indicates the top dead center of the second cylinder 12B (exhaust stroke cylinder) and the fourth cylinder 12D (intake stroke cylinder) as 0 ° CA. In a four-cylinder four-cycle engine, there is a phase shift of 180 ° CA between the cylinders 12A and 12C indicated by the solid line and the cylinders 12B and 12C indicated by the alternate long and short dash line. The time chart indicates that compression top dead center is reached.

  The compression stroke cylinder 12C that reaches the compression stroke after the timing t5 after passing through the last compression top dead center (hereinafter referred to as the final compression top dead center) increases the air pressure as the piston 13 rises due to inertial force. The piston 13 is pushed back by the compression reaction force, and the crankshaft 3 is reversely rotated. 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 has exceeded the final compression top dead center due to the influence of the frictional resistance of the engine. It also changes depending on the rotational inertia of the engine at timing t5, that is, the level of the engine rotational speed Ne.

In this embodiment, when the final top dead center rotational speed ne is detected, the variable valve timing system 112 is controlled so that the port of the compression stroke cylinder 12C is opened for a certain valve opening time T _cls. (VTT3 in FIG. 4). By this control, the compression reaction force of the compression stroke cylinder 12C is reduced, so that the piston 13 of the compression stroke cylinder 12C stops at the center of the stroke, that is, at the top dead center side near 90 °. .

  This point will be described in detail with reference to FIG. 6 and FIG. 7. Normally, as described above, when the fuel injection is stopped from the timing t0 and the alternator 28 is driven to brake the engine while applying a load, Each cylinder stops approximately at the center of the stroke near 90 °. However, as described above, in order to perform a so-called automatic restart, as described with reference to FIG. 3A, the compression stroke cylinder 12C is slightly above the top dead center than the expansion stroke cylinder 12A. That is, it is preferable that the pistons of both cylinders stop within the range of R in FIG.

  In order to stop the piston 13 of the expansion stroke cylinder 12A, which becomes the expansion stroke when the engine automatically stops, within the appropriate range R suitable for restart, 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. Therefore, in the present embodiment, the compression reaction force of the compression stroke cylinder 12C is reduced by the control of the variable valve timing system 112, and the piston 13 of the compression stroke cylinder 12C is stopped at the top dead center side than the vicinity of the center of the stroke. It is doing so.

  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 when the variable valve timing system 112 is controlled as described above, a difference occurs in the frictional resistance of the engine due to the individual difference of the engine and the level of the engine temperature, and even if the variable valve timing system 112 is controlled as described above, 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, in the present invention, attention is paid to the fact that there is a clear correlation between the final top dead center rotational speed ne and the piston stop position of the expansion stroke cylinder 12A during the engine automatic stop period.

  FIG. 7 shows that the fuel injection is stopped at the timing t1 when the rotational speed Ne of the engine becomes a predetermined speed as described above, and each cylinder is maintained in the open state by the variable valve timing system 112 for a predetermined period thereafter. Thus, the top dead center rotational speed (final top dead center rotational speed) ne is measured when the pistons 13 provided in the cylinders 12A to 12D of the engine rotating due to inertia pass the final compression top dead center immediately before stopping. At the same time, the piston position of the expansion stroke cylinder 12A when the engine is stopped is examined, the piston position is taken on the vertical axis, and the top dead center rotational speed ne is taken on the horizontal axis, and the relationship between the two is graphed. It is a thing. When this operation was repeated and the correlation between the final top dead center rotational speed ne during the engine stop operation period and the piston stop position in the expansion stroke cylinder 12A was examined, the following results could be obtained. That is, the final top dead center rotational speed ne is within a range of 260 rpm or less, and on the low rotation side below about 180 rpm, as the final top dead center rotational speed ne decreases. The piston stop position is gradually changing closer to top dead center. On the other hand, on the high rotation side where the final top dead center rotational speed ne is 180 rpm or more, the stop position of the piston 13 is substantially constant regardless of the value, and is slightly distributed from the appropriate range R to the bottom dead center side. Yes.

  The characteristic distribution tendency as described above can be seen when the final top dead center rotational speed ne of the engine is on the high rotation side of 180 rpm or higher, and the expansion stroke cylinder 12A and the compression stroke cylinder 12C when the engine is stopped are respectively shown. This is considered to be because a sufficient amount of air is filled and the piston stop position is concentrated near 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 at the low rotation side of 180 rpm or less because the piston 13 reciprocating in each cylinder 12A to 12D exceeds the final top dead center and then is caused by frictional resistance or the like. It is thought that it is because the vehicle is decelerated and stops without reaching the center of the stroke.

  Therefore, in this embodiment, the valve opening time by the variable valve timing system 112 is set according to the value of the final top dead center rotational speed ne. Specifically, the map shown in FIG. 8 is stored in the ECU 2, and if the final top dead center rotational speed ne is less than 180 rpm, the valve opening time is set to be inversely proportional to the value. .

On the other hand, in the region where the final top dead center rotational speed ne is 180 rpm or higher, the piston 13 of the expansion stroke cylinder 12A tends to fall to the bottom dead center side by opening the compression stroke cylinder 12C. Therefore, in the present embodiment, as shown in FIGS. 4 and 6, after the final top dead center rotational speed has elapsed, when the final top dead center rotational speed is equal to or higher than a predetermined speed (ie, 180 rpm), The variable valve timing system 112 of the expansion stroke cylinder 12A is controlled so that the expansion stroke cylinder 12A is opened and the air of the expansion stroke cylinder 12A is released for a predetermined valve opening time _Topen (FIG. 4). Displayed as VTT1). By this control, the piston stop position of the expansion stroke cylinder 12A slightly shifts to the top dead center side, and can finally be stopped at a desired position.

  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, the system waits for an automatic stop permission flag F that determines whether or not the engine is in an operating state in which automatic engine stop control can be executed (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. Are set to be ON.

  If YES is determined in step S1, the ECU 2 waits until an AND condition is established in which the accelerator sensor 34 is in the OFF state and the brake sensor 35 is in the ON state (step S2). When it is determined YES and it is confirmed that the vehicle is in a deceleration state, the ECU 2 performs the F / C execution rotation speed that is the determination reference value for fuel cut during deceleration in which the engine rotation speed Ne is set to about 1100 rpm in advance. Or greater (step S3). If NO is determined, the process proceeds to the following step S7.

  On the other hand, when it determines with YES by the said step S3, ECU2 performs the fuel cut (FC) at the time of deceleration (step S4). Next, it waits for the engine speed Ne to fall below the F / C stop rotational speed that is a reference value for fuel return that is set to about 900 rpm in advance (step S5), and when YES is determined. Then, the fuel cut (FC) at the time of deceleration is terminated and the normal fuel injection state is restored (step S6).

  Next, the target rotational speed of the engine is set to about 800 rpm, for example, and this speed is maintained (step S7). Thereafter, it is determined whether or not the accelerator sensor 34 is in an ON state and the brake sensor 35 is in an OFF state (step S8). If YES is determined, the process returns to step S1 to decelerate the vehicle. In step S8, when it is determined No and it is confirmed that the vehicle is in a decelerating state, the engine control operation shown in FIG. 10 is performed.

  Referring to FIG. 10, when it is confirmed in step S8 that the vehicle is in a decelerating state, the vehicle speed is set to 0, and the process waits for the automatic stop condition to be satisfied (step S11).

  When the automatic stop condition is satisfied in step S11, the ECU 2 sets the target rotation speed to 860 rpm. As a result, the rotational speed Ne of the engine is set to a value higher than the idle rotational speed (650 rpm) by a predetermined amount. At the same time, the EGR valve 125 is closed to stop the exhaust gas recirculation, and the shift range is switched to neutral so that the engine is in a no-load state (step S12).

  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 decelerated (the brake sensor 35 is When it is confirmed that the engine target rotational speed N1 is stabilized at a predetermined value corresponding to the combustion state of the engine, the engine rotational speed Ne is set to a normal idle speed. Before the speed is reduced to 650 rpm, automatic engine stop control can be performed. Therefore, the driver feels uncomfortable with the increase in the engine rotational speed Ne as in the case where the engine rotational speed Ne once decreased to the normal idle rotational speed is increased to the target rotational speed N1. It is possible to prevent the occurrence of a bad effect such as the time until the engine is automatically stopped or the time until the engine is automatically stopped longer than necessary.

  Further, at the timing t0 when it is confirmed that the engine automatic stop condition is satisfied in step S11, the target rotational speed N1 of the engine is set to a predetermined value in step S12, and the shift range of the automatic transmission is driven. Since the load of the automatic transmission is reduced by shifting from the state (D range) to the neutral state (N range), as shown in FIG. It will rise slightly from t0.

  Next, the ECU 2 waits for the elapse of a predetermined time set in advance to about 1 sec (seconds) after the timing t0 (step S13). When it is determined YES in step S13, the ECU 2 waits until a fuel injection stop condition (FC condition) is satisfied (step S14). Specifically, in this step S14, it is awaited that an AND condition that the engine rotational speed Ne becomes the target rotational speed N1 and the boost pressure Bt becomes the predetermined target pressure is satisfied. 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 S14 and it is confirmed that the engine rotational speed Ne and the boost pressure Bt are stable (timing t1 in FIGS. 4 and 6), the fuel injection is stopped. Thereafter (step S15), the target power generation current Ge of the alternator 28 is set to 0 to stop power generation (step S16), and the variable valve timing system 112 is operated to open the valves of the respective cylinders (step S17).

  Next, referring to FIG. 11, after step S17, ECU 2 waits for timing t2 from timing t1 (step S18), and stops ignition by ignition device 27 when determined YES. (Step S19). By this step S19, it is possible to burn the fuel remaining in the cylinder after the fuel stop, and to prevent the fuel injected just before the stop from burning.

  Next, the system waits for the engine rotational speed Ne to become equal to or lower than the reference speed N2 set in advance to about 760 rpm (step S20). This step S20 is for counting the timing t3.

  In step S20, at the timing determined as YES (that is, timing t3), the target generated current Ge of the alternator 28 is set to an initial value (about 60A) (step S21), and the alternator 28 is operated (step S22). That is, as shown in FIG. 5, the higher the top dead center rotational speed ne of the engine, the more the target generated current Ge corresponding to the top dead center rotational speed ne is read from the map in which the target generated 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.

  Next, it waits for the top dead center rotational speed ne to decelerate within a predetermined range (step S23). This step S23 is for detecting the timing t4, and the predetermined range is set within a range of 260 rpm to 400 rpm, for example. If YES is determined in the step S23, it is confirmed at that timing that the second compression top dead center before the engine stop is passed.

  In step S23, the fuel injection amount for the cylinder 12C, which becomes the compression stroke when the engine is stopped, is set from the map (not shown) at the timing determined as YES (that is, the timing t4). Injection is performed (step S24). This map is set so that the fuel injection amount becomes larger as the engine top dead center rotational speed ne is higher, and is stored in the ECU 2 in advance. 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.

  Next, it waits for the engine top dead center rotational speed ne to decelerate to a predetermined value N or less (step S25). This step S25 is for detecting the timing t5, and the predetermined value N is set to about 260 rpm, for example.

  When the timing t5 is detected, in this embodiment, immediately after the detection, the variable valve timing system 112 is controlled to open the intake port 17 and the exhaust port 18 of the compression stroke cylinder 12C (step S26). In this control, the air amount of the compression stroke cylinder 12C is reduced and the compression reaction force is reduced at the time of stop, so that the stop can be performed while suppressing NVH (engine vibration). Note that, as an aspect of the present embodiment, when the compression stroke cylinder 12C transitions to the intake stroke at the timing t4, the intake port 17 may be continuously maintained in an open state.

  In particular, in this embodiment, when the final top dead center rotational speed ne is determined, the intake port 17 and the exhaust port 18 of the compression stroke cylinder 12C are immediately opened, so that the compression stroke cylinder 12C is first compressed when stopped. As a result, the compression reaction force received by the piston of the compression stroke cylinder 12C is reduced as a result of the pressure in the cylinder being reduced, and the piston is moved to a desired stroke while NVH (engine vibration) when the engine is stopped is further suppressed. It can be stopped near the center.

Then, ECU 2, the variable valve timing system 112 calculates the time T _cls for releasing the compression stroke cylinder 12C, to calculate the closing timing (step S27). In this calculation, the valve opening time T _cls is determined based on the table of FIG. 8 described above.

Next, the ECU 2 measures the calculated valve opening time T _cls (step S28), and closes the intake port 17 and the exhaust port 18 of the compression stroke cylinder 12C at the timing when the valve opening time T _cls has elapsed (step S29).

Next, with reference to FIG. 12, the ECU 2 calculates the valve opening timing of the expansion stroke cylinder 12A (step S30). Specifically, the valve opening time T _open of the expansion stroke cylinder 12A is determined based on the crank angle detected by the crank angle sensors 30 and 31 and the rotational speed output from the crank angle sensor 30.

When T _open is determined, the ECU 2 waits for a timing t6 when the engine first turns from normal rotation to reverse rotation after the final top dead center rotation speed has elapsed (step S31). When the timing t6 is detected, ECU 2 is discriminated whether exceeds the valve opening time T _open is 0 calculated in step S30 (step S32), if it exceeds 0, the expansion stroke by the time The intake port 17 and the exhaust port 18 of the cylinder 12A are opened (steps S33 to S35), and if it is 0 or less, the valve opening of the expansion stroke cylinder 12A is omitted.

The valve opening time T _open depends on the final top dead center rotational speed ne. As described above, when the final top dead center rotational speed ne is less than 180 rpm, the piston of the expansion stroke cylinder 12A tends to be biased toward the top dead center. On the other hand, when the final top dead center rotational speed ne is 180 rpm or more, since a considerable amount of air is also contained in the expansion stroke cylinder 12A, it is necessary to remove it. From this point of view, in step S30, based on the unillustrated map, the valve opening time _Topen is determined based on the final top dead center rotational speed ne, and when the final top dead center rotational speed ne is 180 rpm or more, , Steps S32 to S35 are executed, the air in the expansion stroke cylinder 12A is extracted, the piston of the expansion stroke cylinder 12A is moved to the top dead center side, and the final top dead center rotational speed ne is less than 180 rpm. Is that the stop position of the piston is controlled by the valve opening control of the compression stroke cylinder 12C in steps S26 to S29, and the expansion stroke cylinder 12A is not opened.

  Next, the system waits for timing t7 when the engine is stopped (step S36). 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 S37). Then, after setting the automatic stop permission flag F to OFF (step S38), the control operation is terminated.

  Next, interrupt control when there is a request to restart the engine while the above-described automatic stop control is being executed will be described with reference to FIGS. 13 and 14.

  Referring to FIG. 13, ECU 2 monitors whether there is a restart request in the whole process of automatic stop control (the control shown in the flowcharts shown in FIGS. 9 to 12) and determines an interrupt request. When the engine is in a stop operation (step S40) and it is detected that the brake is OFF or the accelerator is ON (step S41), it is set to determine that there is a restart request. Yes.

  When these requirements (steps S40 and S41) are satisfied, the ECU 2 determines whether or not the timing at which the restart request has been made has elapsed t5 (step S42). As described above, the timing t5 is a point at which each cylinder passes the final compression top dead center, and the engine speed has dropped to about 280 rpm or less.

  If the engine has passed the timing t5, the ECU 2 determines whether or not the crankshaft is in the first forward rotation (step S43). If it is the first forward rotation, the ECU 2 further determines whether or not it is immediately after passing through the compression top dead center (step S44). If it is immediately after passing, the ECU 2 injects fuel into the expansion stroke cylinder 12A (step S45), and then immediately ignites the expansion stroke cylinder 12A (step S46). As a result, the engine that has been decelerated while rotating forward is energized by the energy generated by the combustion of the expansion stroke cylinder 12A, and thereafter, the routine proceeds to normal control (step S47). In this embodiment, in this step S47, in order to prevent the engine from accelerating rapidly, the ignition timing is retarded in the same manner as the restart control described later.

  On the other hand, if the restart request is before the timing t5 has elapsed in step S42, the ECU 2 further determines whether or not it is immediately after passing through the compression top dead center (step S48). In this step S48, if it is immediately after passing through the compression top dead center, the flow is returned to step S45. On the other hand, if it is not immediately after passing through the compression top dead center, fuel is injected into the cylinder in the compression stroke (step S49). It waits for this cylinder to exceed the compression top dead center (step S50). Then, at the timing when the cylinder in the compression stroke exceeds the top dead center (that is, when the cylinder into which the fuel has been injected enters the expansion stroke), this cylinder (the cylinder into which the fuel has been injected) is ignited (step S51). Thereafter, the process proceeds to step S47.

  Next, the case where the conditions are not met in step S43 and step S44 will be described with reference to FIG.

  As shown in the figure, when the restart request is after the timing t5 has elapsed and the crankshaft 3 is in the first forward rotation operation (when the determination in step S43 is Yes and the determination in step S44 is NO) The ECU 2 closes the intake port 17 and the exhaust port 18 of the compression stroke cylinder 12C (step S60), and waits for the crankshaft 3 to reversely rotate in this state (step S61). When the crankshaft 3 rotates in the reverse direction, fuel is injected into the closed expansion stroke cylinder 12A (step S62), and the crankshaft 3 waits for normal rotation (step S63). The timing from step S60 to step S63 is the timing at which the compression stroke cylinder 12C is opened and then the expansion stroke cylinder 12A is opened when the automatic stop control described above is executed. When there is a start request, the valve opening operation of the compression stroke cylinder 12C and the expansion stroke cylinder 12A is prohibited.

  Next, when the crankshaft rotates forward, the ECU 2 ignites the expansion stroke cylinder 12A (step S64), and then proceeds to step S47. As a result, combustion can occur in the cylinder that is stopping in the expansion stroke, and the torque can be increased with the energy.

  Next, when the restart request is after the timing t5 has elapsed and the crankshaft 3 is not in the first forward rotation operation (when the determination in step S43 is NO), the ECU 2 It is determined whether or not it is during the first reverse rotation of the shaft 3 (step S65). If it is determined in step S65 that the crankshaft 3 is in the first reverse rotation, the intake port 17 and the exhaust port 18 of the expansion stroke cylinder 12A are set regardless of the control in steps S30 to S35 described above. The air is closed to secure air in the expansion stroke cylinder 12A (step S66), and thereafter, the process proceeds to step S62. On the other hand, if it is not the first reverse rotation in step S65, it is considered that there is no longer enough torque to restart the engine. In this case, the engine is stopped after the engine is stopped. Yes.

  Next, the control operation when the engine is restarted will be described based on the flowcharts shown in FIGS. 15 to 17 and the time charts shown in FIGS. 18 and 19. First, it is determined whether or not a predetermined engine restart condition is satisfied (step S101). In this determination, for example, when the accelerator operation for starting from the stop state is performed, when the battery voltage is lowered, or when the air conditioner is activated, the restart condition is set as the establishment factor. If YES is determined in step 101, the ECU 2 estimates the in-cylinder temperature based on the engine water temperature, the elapsed time since the automatic stop, the intake air temperature, and the like (step S102).

  Then, based on the stop position of the piston 13 detected when the engine is automatically stopped, the ECU 2 calculates the amount of air in the compression stroke cylinder 12C and the expansion stroke cylinder 12A (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. Thereby, even when the amount of air in the compression stroke cylinder 12C is relatively large, it is possible to prevent excessive energy due to combustion for reverse rotation.

  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 satisfy (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 energy can be obtained by combustion for reverse rotation.

  Next, the cylinder 12C is ignited after 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, have been detected within a certain time after ignition (step S108). If 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 (in FIG. 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. Accordingly, the piston 13 of the compression stroke cylinder 12C moves to the top dead center side and starts to compress the gas in the cylinder (burned gas burned by ignition in step 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 above control, in the intake stroke cylinder 12D, the compression pressure becomes small until the compression top dead center and easily exceeds the top dead center. A torque in the rolling direction is 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 energy due to combustion in each of the cylinders 12A to 12D temporarily becomes larger than the energy due to combustion 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 increase, the opening of the throttle valve 23 is made smaller than the throttle opening during normal idle operation (step S151), thereby generating energy due to combustion. Reduce the amount.

  Then, it is determined whether or not the temperature of the exhaust gas purification catalyst provided in the exhaust passage 22 is equal to or lower than the activation temperature (step S152). If YES is determined, the target air-fuel ratio in the cylinder is λ ≦ 1. The rich air-fuel ratio is set (step S153), and the ignition timing is delayed after top dead center (step S154). As a result, the temperature rise of the catalyst is promoted, and the amount of energy generated by combustion 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 energy generated by combustion.

  The process returns to step S150 through step S154 or step S158, and until it is determined NO in step S150 and it is confirmed that the intake pressure is lower than that during normal idling when 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. 18 and 19, first, the first fuel injection J3 is performed in the compression stroke cylinder 12C (third cylinder), and combustion is performed by ignition (FIG. 18). (1)) is performed. With the combustion pressure (part a in FIG. 19) due to the 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, the energy by moderate combustion for reversing the engine, that is, by the combustion to such an extent that the air in the expansion stroke cylinder 12A is sufficiently compressed but does not excessively reverse beyond its compression top dead center. You can get energy.

  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 is closer to the top dead center, so the density of the compressed air (air mixture) increases (part b in FIG. 19).

  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. 18), and the engine is driven in the forward rotation direction by the combustion pressure (c portion in FIG. 19).

  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. 18), but the compression stroke cylinder 12C does not burn. 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. 19), and accordingly, the compression top dead center (the first compression top dead center from the start of starting) is exceeded. The energy by the first combustion of the expansion stroke cylinder 12A to be consumed 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. 18) for reducing the temperature in the cylinder and the compression pressure by the latent heat of vaporization 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. 19). 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. 18) after the start of restart and the second compression by the energy of the first combustion ((2) in FIG. 18) in the expansion stroke cylinder 12A. It is possible to exceed the top dead center ((4) in FIG. 18), ensuring a smooth and reliable startability, 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 stopped in at least the expansion stroke to cause ignition and combustion when 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. Is set to a value corresponding to the reduced 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 suitable for restarting the engine. It can be stopped in R, that is, at a position slightly offset toward the bottom dead center side from the center of the stroke.

  That is, the alternator 28 can accurately adjust the rotational resistance of the crankshaft 3 over a wide range by adjusting the target generated current Ge to an arbitrary value, for example, from about 0 A to about 60 A, 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, in the initial stage of the operation for automatically stopping the engine, the target power generation current Ge of the alternator 28 is increased to an initial value, so that the power generation function of the alternator 28 can be sufficiently exerted, and then the piston 13 is compressed. 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 it 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.

  As described above, according to this embodiment, at the final compression top dead center, the amount of air in the compression stroke cylinder 12C can be reduced and the compression reaction force can be reduced, so that NVH (engine vibration) can be reduced. It is possible to stop while suppressing. Therefore, according to the present embodiment, the piston 13 can be stopped at an appropriate position and the engine can be restarted reliably while suppressing NVH (engine vibration) during automatic engine stop with a simple configuration. Has an effect.

  In particular, in this embodiment, the variable valve timing system is controlled to open the port of the cylinder that becomes the compression stroke at the time of stopping immediately after each cylinder exceeds the final top dead center. Since the pressure in the cylinder decreases when the cylinder 12C starts to compress for the first time, the compression reaction force received by the piston 13 of the cylinder becomes small, and the desired state is achieved in a state where NVH (engine vibration) at the time of engine stop is further suppressed. Since the piston 13 can be stopped closer to the center during the stroke, the positional accuracy when the piston 13 is stopped is improved.

  Further, in the present embodiment, after each cylinder exceeds the final top dead center, after the engine performs a reverse rotation operation, the engine rotation speed at the final top dead center is higher than a predetermined value. Is to open the port of the expansion stroke cylinder 12A. Therefore, the braking of the piston 13 related to the cylinder that reaches the compression stroke varies due to the individual difference of the engine and the variation of the rotational speed when passing through the final compression top dead center. Even if this occurs, this variation can be absorbed by the cylinder that reaches the expansion stroke, and more accurate braking control is possible.

  Further, according to the present embodiment, when the engine restart condition is satisfied after passing the final compression top dead center (timing t5) after executing the automatic stop control, the variable valve timing system 112 of the ECU 2 When the valve opening operation is prohibited and the restartable condition as described with reference to FIGS. 13 to 14 is satisfied, the fuel is returned to the expansion stroke cylinder 12A at the timing when the rotation of the engine returns from the reverse rotation to the normal rotation. After that, by igniting the cylinder at the timing when the engine changes from reverse rotation to normal rotation, it becomes possible to effectively use the reverse rotation operation of the engine immediately before the stop and restart the engine immediately. It becomes possible to restart the engine more quickly.

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 throttle opening degree and the target generated current when the engine is stopped. 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 timing chart which shows valve opening control of the variable valve timing system at the time of an engine stop. It is a distribution map which shows the correlation with the last top dead center rotational speed before an engine stop, and a piston stop position. It is a graph which shows an example of the map for setting the valve opening time of a variable valve timing system according to the last top dead center rotational speed of an engine. It is a flowchart which shows the first half of the engine automatic stop control operation. It is a flowchart which shows the second half part of the engine automatic stop control operation. It is a flowchart which shows the second half part of the engine automatic stop control operation. It is a flowchart which shows the second half part of the engine automatic stop control operation. It is a flowchart which shows the control operation | movement when there exists a restart request | requirement in the middle of the engine automatic stop control operation | movement. It is a flowchart which shows the control operation | movement when there exists a restart request | requirement in the middle of the engine automatic stop control operation | movement. 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 (an example of top dead center grasping means and automatic stop control means)
3 Crankshaft 13 Piston 17 Intake port 18 Exhaust port 30, 31 Crank angle sensor (an example of rotational speed detection means and stroke detection means)
112 Variable valve timing system

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. And a starting device for a four-cycle multi-cylinder engine configured to restart the engine by injecting fuel into at least an automatically stopped cylinder in an expansion stroke to cause ignition and combustion.
A variable valve timing system that is provided in each cylinder and that can change the opening and closing timing of a valve that opens and closes a port that opens to each cylinder according to the operating state of the engine;
Stroke detecting means for detecting the operating stroke of each cylinder;
A rotational speed detecting means for detecting the rotational speed of the engine;
Based on the rotation speed of the engine detected by the rotation speed detection means and the stroke of each cylinder detected by the stroke detection means, the final determination of when any cylinder reaches the final top dead center when the engine is stopped. Top dead center grasping means,
When the engine is automatically stopped, based on the timing grasped by the final top dead center grasping means, the rotation speed of the engine at the timing detected by the rotation speed detecting means, and the stroke of each cylinder detected by the stroke detecting means. And an automatic stop control means for controlling the variable valve timing system,
The automatic stop control means controls the variable valve timing system so as to open a port of a cylinder which becomes a compression stroke when stopping after each cylinder exceeds the final top dead center. Starter. The starter for a four-cycle multi-cylinder engine according to claim 1,
The automatic stop control means controls the variable valve timing system so as to open a port of a cylinder that becomes a compression stroke at the time of stop immediately after each cylinder exceeds a final top dead center. Cycle multi-cylinder engine starter. The starter for a 4-cycle multi-cylinder engine according to claim 1 or 2,
The automatic stop control means is used when the engine speed at the final top dead center is higher than a predetermined value after the engine performs reverse rotation after each cylinder exceeds the final top dead center. Is a four-cycle multi-cylinder engine starter that controls a variable valve timing system so as to open a cylinder port that is in an expansion stroke when stopped. The starter for a 4-cycle multi-cylinder engine according to claim 1, 2, or 3,
4. A starter for a four-cycle multi-cylinder engine, wherein the port of the cylinder is an intake port of a cylinder in the compression stroke. The starter for a four-cycle multi-cylinder engine according to any one of claims 1 to 4,
The automatic stop control means controls the variable valve timing system so that at least the intake port is kept open after shifting to the intake stroke immediately before the cylinder that becomes the compression stroke at the time of stoppage reaches the final top dead center. A starter for a four-cycle multi-cylinder engine, The starter for a 4-cycle multi-cylinder engine according to any one of claims 1 to 5,
If the engine restart condition is satisfied after passing the last top dead center after executing the automatic stop control, the valve opening operation of the variable valve timing system by the automatic stop means is prohibited and the restartable condition Is established, fuel is injected into the cylinder in the expansion stroke at the timing when the engine rotation returns from the reverse rotation to the normal rotation, and then the cylinder is ignited at the timing when the engine changes from the reverse rotation to the normal rotation. A starter for a four-cycle multi-cylinder engine, further comprising restart control means for performing the operation.

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