JP2005188473A - Engine starter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a driver from feeling a sense of incompatibility by restraining sudden upwash, smoothly starting rotation of an engine in restarting, in an engine system E for automatically restarting the engine 1 by itself, by burning a cylinder 12 stopped in at least an expansion stroke, when a predetermined restarting condition is realized. <P>SOLUTION: When restarting the engine, after starting normal rotation by combustion of an expansion stroke cylinder 12B (a #2 cylinder), fuel is injected into a stopping time compression stroke cylinder 12A (a #1 cylinder) compressed by this normal rotation operation (a5), and compression pressure is reduced by the cooling effect by latent heat of vaporization. The fuel is injected into a stopping time intake stroke cylinder 12C (a #3 cylinder) on and after an intermediate period of a compression stroke (a6), and the temperature and pressure are reduced by the cooling effect by the latent heat of vaporization, and ignition is performed after exceeding TDC (a7). In that case, opening of a throttle valve 23 is kept in a state smaller than idle operation, until intake pressure of a branch intake passage 21a downstream of the throttle valve 23 is reduced to a preset value corresponding to the idle operation (t0 to t3). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to an engine starting device that automatically starts an engine that has been automatically stopped when idling in response to a restart request, and particularly relates to the technical field of intake air control at the time of starting.

2. Description of the Related Art Conventionally, an engine control system (idle stop system) is known in which an engine is automatically stopped during idling for the purpose of reducing fuel consumption and suppressing CO ₂ emission. In such a system, the engine must be started immediately in response to an engine restart request such as a start operation. However, in a general starting method in which the engine is started through cranking by the starting motor, the starting time is short. There is a tendency that it becomes a little longer, and there is also a problem that the noise accompanying cranking makes the driver feel uncomfortable.

  In addition, if the engine is stopped and restarted every time the engine is in an idle state, the number of times of starting is significantly increased compared to a normal system that starts only when the ignition switch is operated. The starter motor is required to have extremely high durability, and there is a problem that unnecessary cost increases.

Therefore, in recent years, for example, as in a direct injection engine disclosed in Patent Documents 1 and 2, fuel is injected and supplied into a cylinder that is in an expansion stroke in a stopped state, and is ignited and burned, thereby starting motor. The engine has been developed to start with its own power, that is, with its own power, without borrowing any other power.
Japanese Utility Model Publication No. 60-128975 Special table 2003-517134 gazette

  However, in the idle stop system, the engine is automatically started in response to an engine restart request such as a start operation without depending on the operation of the ignition switch. Even if the ranking is not performed, changes in the engine sound and vibrations may cause the driver to feel uncomfortable. In other words, in general, the engine has a particularly large intake charge amount in each cylinder at the time of start-up, so that it suddenly blows up.For example, when the driver depresses the accelerator pedal lightly to start the vehicle relatively slowly In addition, when the engine that starts automatically in response to this suddenly rises, the driver feels as if the vehicle has jumped forward and feels a strong sense of discomfort.

  The present invention has been made in view of such a point, and an object of the present invention is to provide an engine starter that automatically stops the engine when idling and then restarts automatically. The idea is to devise control of the flow rate of the intake air that is sometimes taken into each cylinder so that the engine rotation starts smoothly and the engine speed is suppressed to prevent the driver from feeling uncomfortable.

  In order to achieve the above object, according to the present invention, when the engine is started, the pressure of the intake passage, which usually decreases from the substantially atmospheric pressure state, is relatively high, and the intake charge amount of the cylinder increases as it is. During the possible period, the flow rate of the intake air sucked into each cylinder is made smaller than that during idling after warm-up.

  More specifically, according to the first aspect of the present invention, when a predetermined restart condition is satisfied, fuel is injected and supplied into at least the cylinder in the expansion stroke of the stopped multi-cylinder engine, and is ignited and burned. Therefore, for an engine starter that automatically restarts without using a starter motor, an intake flow rate adjusting means that can adjust the flow rate of intake air to each of the cylinders, and engine rotation when the engine is restarted. And an intake air amount control means for controlling the intake air flow rate adjusting means so that the intake air flow rate to each of the cylinders when starting up is smaller than that during idling after warm-up.

  With the above-described configuration, when the engine is automatically started, fuel is injected and supplied into the cylinder stopped at least in the expansion stroke, and the air-fuel mixture formed thereby is ignited and burned. Occur. As a result, when the engine starts normal rotation, intake of approximately atmospheric pressure is sequentially taken into each cylinder from the intake passage. At this time, until each engine starts up and stabilizes, each cylinder The intake air flow rate adjusting means is controlled by the intake air amount control means so that the intake air flow rate becomes smaller than that during idling after warm-up. As a result, even when the intake passage is close to atmospheric pressure, the amount of intake air charged into each cylinder does not increase so much that the engine does not blow up rapidly, and its rotation smoothly rotates at idle speed. Because it stands up to the vicinity, the driver will not feel uncomfortable.

  Here, when the downstream side of the intake passage of the engine is branched for each cylinder to be an independent branched intake passage, the intake flow rate adjusting means is individually provided in the branched intake passage. And an intake pressure detecting means for detecting the intake pressure state of the branch intake passage downstream of the valve body, and the intake air amount control means is an intake air pressure detected by the intake pressure detecting means. The opening of the intake flow rate adjustment valve is made smaller than that during the idling operation until the pressure state decreases from near atmospheric pressure until the set negative pressure state corresponding to the idling operation after the engine warms up. It is preferable to control (invention of claim 2).

  If such an intake flow rate adjusting valve is used, the volume of the branch intake passage downstream from the valve body becomes very small, so that the intake pressure state of this branch intake passage becomes a set negative pressure equivalent to the idling operation. In the meantime, by making the opening of the intake flow rate adjustment valve very small, it is possible to reliably prevent an increase in the intake charge amount of each cylinder and to obtain the effects of the invention sufficiently. In addition, since the volume of the branch intake passage downstream from the valve body is very small, the intake pressure quickly decreases and settles to the set negative pressure state at an early stage.

  Then, the intake air amount control means gradually opens the intake flow rate adjustment valve from fully closed in response to a change in the intake pressure state detected by the intake pressure detection means to the low pressure side. It is preferable (invention of claim 3). In this way, as the intake pressure in the branch intake passage decreases, the intake air flow rate increases so as to offset the decrease in the intake charge amount due to this. Engine rotation can be started more smoothly.

  Alternatively, instead of detecting the intake pressure state as described above, a rotation speed detection means for detecting the engine rotation speed is provided, and the intake air amount control means is configured to warm up the engine rotation speed detected by the rotation speed detection means. The intake air flow rate adjusting means may be controlled so that the intake air flow rate to each cylinder is smaller than that during the idling operation after the warm-up until it stabilizes in the vicinity of the subsequent idle rotation speed. invention).

  Note that the engine rotation speed is stabilized near the idle rotation speed. For example, after the engine rotation speed has increased to the vicinity of the idle rotation speed, the fluctuation range of the engine rotation speed due to combustion for each cylinder becomes a predetermined value or less. That means.

  Further, as the intake flow rate adjusting means, a variable valve mechanism capable of changing at least the lift amount of the intake valve of each cylinder is used instead of the intake flow rate adjusting valve, and the intake amount control means is provided with a lift of the intake valve. The variable valve mechanism may be controlled so that the amount becomes smaller than that during idle operation after warming up (invention of claim 5). By making the lift amount of the intake valve relatively small in this way, even if the intake passage is close to atmospheric pressure, the intake flow from there to each cylinder is throttled to prevent an increase in the intake charge amount. can do.

  Further, when the pressure in the intake passage is relatively high when the engine is restarted, instead of restricting the intake air sucked into the cylinder as described above, the closing timing of the intake valve is delayed to temporarily reduce the intake air sucked into the cylinder. An increase in the intake air filling amount may be suppressed by blowing a large amount back into the intake passage. That is, in the sixth aspect of the invention, in the same premise configuration as in the first to fifth aspects of the invention, the variable valve mechanism capable of changing at least the closing timing of the intake valve of each cylinder, and the engine rotation at the time of engine restart And a valve timing control means for controlling the variable valve mechanism so that the valve closing timing of the intake valve is retarded from that during idle operation after warming up.

  With the above configuration, as in the first aspect of the invention, since the amount of intake air charged into each cylinder does not increase so much until the engine rotation rises and stabilizes, the engine rotation is started smoothly. It is possible to prevent the engine from suddenly rising, so that the driver does not feel uncomfortable.

  As described above, according to the engine starting device according to the first to fifth aspects of the present invention, in the starting device that automatically stops the engine when idling and then restarts automatically and by itself. When the engine speed rises at the time of restart, the intake passage to each cylinder is throttled while the pressure in the intake passage is relatively high and it is considered that the intake charge amount of each cylinder will be excessive. Therefore, it is possible to prevent overfilling of the intake air, start up the engine rotation smoothly, and prevent a sudden rise. Thereby, even if it is a case where it starts automatically, a driver does not feel uncomfortable.

  According to the sixth aspect of the present invention, when the engine speed rises at the time of restart, the intake valve is brought into a predetermined delayed closing state to prevent overfilling of the intake air, and the same effect as described above can be obtained. .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.
-Schematic configuration of engine control system-
1 and 2 show an embodiment of an engine control system including an engine starter according to the present invention. The engine system E controls an engine 1 including a cylinder head 10 and a cylinder block 11, and controls the engine 1. ECU2 (engine controller) for carrying out. As shown in FIG. 2, the engine 1 is provided with four cylinders 12A to 12D. Inside each of the cylinders 12A to 12D, pistons connected to the crankshaft 3 as shown in FIG. Thus, a combustion chamber 14 is formed above the piston 13 in each of the cylinders 12A to 12D.

  Here, in general, in a multi-cylinder four-cycle engine, each cylinder performs a combustion cycle composed of intake, compression, expansion, and exhaust strokes with a predetermined phase difference. In the case of a cylinder engine, when referred to as the first cylinder 12A, the second cylinder 12B, the third cylinder 12C, and the fourth cylinder 12D from one end in the cylinder row direction, as shown in FIG. 5 (e), the first cylinder (# 1 ) Combustion is performed with a phase difference of 180 degrees in crank angle in the order of the third cylinder (# 3), the fourth cylinder (# 4), and the second cylinder (# 2).

  A spark plug 15 for igniting and burning the air-fuel mixture in the combustion chamber 14 is provided at the top of each combustion chamber 14 of each of the cylinders 12A to 12D. An electrode is disposed so as to face the combustion chamber 14. A fuel injection valve 16 for directly injecting fuel into the combustion chamber 14 is provided on the side of the combustion chamber 14 (right direction in FIG. 1). The injection direction is adjusted so that fuel is injected toward the vicinity of the electrode of the plug 15. The fuel injection valve 16 includes a needle valve and a solenoid (not shown). The fuel injection valve 16 is driven to open for a time corresponding to the pulse width in response to the input of a pulse signal from the ECU 2, and has an amount corresponding to the driving time. The fuel is injected into the cylinders 12A to 12D. The fuel injection valve 16 is supplied with fuel through a fuel supply passage or the like by a fuel pump (not shown), and the fuel supply pressure of the engine system E is combusted in the compression stroke. The fuel supply system is configured to be higher than the pressure in the chamber 14.

  Further, an intake port 17 and an exhaust port 18 opening toward the combustion chamber 14 are provided at the upper part of the combustion chamber 14 of each of the cylinders 12A to 12D. Exhaust valves 20 are respectively provided. These intake valve 19 and exhaust valve 20 are driven by a valve operating mechanism including a camshaft (not shown), and as described above, each of the cylinders 12A to 12D performs a combustion cycle with a predetermined phase difference. The opening / closing timing of the intake / exhaust valves 19 and 20 for each cylinder is set.

  Further, an intake passage 21 and an exhaust passage 22 are provided so as to communicate with the intake port 17 and the exhaust port 18, respectively. As shown in FIG. An independent branch intake passage 21a is provided for each of the cylinders 12A to 12D, and the upstream end of each branch intake passage 21a communicates with the surge tank 21b, and each of the branch intake passages 21a has a reduced sectional area. In addition, the valve body of the throttle valve 23 (intake flow rate adjusting valve) is individually provided. That is, the throttle valve 23 is a multi-rotary rotary valve (multi-throttle) whose valve body is driven by a common actuator 24 and throttles the branch intake passages 21a simultaneously.

  Further, as shown only in FIG. 2, an air flow sensor 25 for detecting the intake air amount is disposed in the common intake passage 21c upstream of the surge tank 21b in the intake passage 21, while the downstream of the surge tank 21b. In the branch intake passage 21a, intake pressure sensors 26, 26,... (Intake pressure detection means) for detecting intake pressure (intake pressure state) downstream of the valve body of the throttle valve 23 are disposed. ing. In the engine 1 of this embodiment, there is no passage for bypassing each valve body of the multi-throttle 23, and the intake air flow rate during idle operation is adjusted by the position of the valve body, that is, the throttle opening. It has become.

  On the other hand, a catalyst 29 for purifying the exhaust is disposed downstream of the collection portion of the exhaust passage 22 where exhaust from the cylinders 12A to 12D collects. This catalyst 29 is, for example, a so-called three-way catalyst in which the purification rate of HC, CO, and NOx is extremely high when the air-fuel ratio state of the exhaust is in the vicinity of the theoretical air-fuel ratio, and this is a relatively high oxygen concentration in the exhaust. It has an oxygen storage capacity for storing it in a high oxygen excess atmosphere. When the oxygen concentration is relatively low, the stored oxygen is released and reacted with HC, CO and the like. The catalyst 29 is not limited to a three-way catalyst, and may be any catalyst having an oxygen storage capacity as described above. For example, the catalyst 29 may be a so-called lean NOx catalyst that can purify NOx even in an oxygen-excess atmosphere.

  Further, the engine system E is provided with two crank angle sensors 30 and 31 for detecting the rotation angle of the crankshaft 3, and the engine rotation speed is mainly based on a signal from one crank angle sensor 30. As will be described in detail later, the rotation direction and the rotation angle of the crankshaft 3 are detected by the crank angle signals output from the two crank angle sensors 30 and 31 that are out of phase with each other. Yes. In addition, the engine system E includes a cam angle sensor 32 that detects a specific rotational position of the camshaft and outputs it as a cylinder identification signal, a water temperature sensor 33 that detects the temperature of the engine coolant (engine water temperature), an accelerator opening An accelerator opening sensor 34 and the like for detecting the degree (accelerator operation amount) are provided.

  The ECU 2 receives signals from the sensors 25, 26, 30 to 34 and outputs a signal for controlling the fuel injection amount and the injection timing to the fuel injection valve 16, and an ignition device for the ignition plug 15. 27 outputs a signal for controlling the ignition timing, and further outputs a signal for controlling the throttle opening to the actuator 24 of the throttle valve 23. As will be described in detail below, the ECU 2 stops the fuel supply to each cylinder 12A to 12D (fuel cut) and automatically stops the engine when a predetermined engine stop condition is satisfied during idling. After that, when a predetermined engine restart condition is satisfied by the driver's accelerator operation or the like, the engine 1 is automatically restarted.

  That is, when the engine 1 is restarted, the engine 1 is started only with its own power without borrowing the power of the starting motor. In this embodiment, as schematically shown in FIG. The first combustion is performed in the cylinder 12 in which the piston 13 is stopped in the middle of the compression stroke (# 1 cylinder 12A in the example in the figure, hereinafter also referred to as the compression stroke cylinder when stopped), and the piston 13 is pushed down. Thus, the crankshaft 3 is slightly rotated reversely ((a) in the figure), so that the cylinder 12 in the expansion stroke (# 2 cylinder 12B in the example in the figure, hereinafter also referred to as the stop expansion stroke cylinder). The piston 13 is raised to compress the air-fuel mixture in the cylinder 12B ((b) in the figure). Then, by igniting and burning the air-fuel mixture in the expansion stroke cylinder 12B that has been compressed and thus increased in temperature and pressure, a torque in the forward rotation direction is given to the crankshaft 3, and the engine 1 is I try to start it.

  In order to start the engine 1 only with its own force in this way, the torque in the forward rotation direction as much as possible is given to the crankshaft 3 by the combustion of the expansion stroke cylinder 12B at the time of stop, and thereby (c) in FIG. As shown in FIG. 6, the cylinder 12A that reaches compression top dead center (hereinafter abbreviated as TDC) must overcome the compression reaction force (compression pressure) and exceed TDC. Therefore, in order to start the engine 1 reliably, it is necessary to ensure sufficient air for combustion in the stop-time expansion stroke cylinder 12B.

  Therefore, in this embodiment, when the engine 1 is automatically stopped during idling, first, the fuel is cut at a predetermined rotational speed slightly higher than the idling rotational speed so that the scavenging of each cylinder 12A to 12D is sufficiently performed. At the same time, the throttle valve 23 is opened for a predetermined period of time to control the opening degree to be set in advance. Then, by closing the throttle valve 23 at an appropriate preset timing, the amount of air sucked into the stop expansion stroke cylinder 12B and the stop compression stroke cylinder 12A is sufficiently increased, and the expansion stroke cylinder The air amount of 12B is set to be slightly larger than that of the compression stroke cylinder 12A.

By doing so, the piston 13 of the expansion stroke cylinder 12B is somewhat suitable for restarting closer to the bottom dead center (BDC) from the center of the stroke due to the balance of the compression pressure of the air in the two cylinders 12A and 12B. It stops within a range R (described later).
-Engine stop control-
Next, engine stop control by the ECU 2 will be described mainly with reference to FIGS. FIG. 4 is a flowchart showing the procedure of the stop control, and FIG. 5 shows the engine speed and crank during the period from the fuel cut to the inertial rotation of the engine 1 (hereinafter also referred to as a stop operation period). An explanatory view schematically showing the change in the angle and the stroke of each cylinder 12A to 12D in association with each other, and schematically showing the control of the throttle opening performed during that time and the change in the intake pressure (intake pipe negative pressure) caused thereby. It is.

  FIG. 6 is a diagram showing a correlation between the TDC rotational speed (described later) of the engine 1 whose rotation gradually decreases during the stop operation period and the piston stop position in the expansion stroke cylinder 12 after the stop.

  First, as shown in FIG. 5 (a), when a fuel cut is performed at a predetermined set rotational speed (800 rpm in the illustrated example) during operation of the engine 1 (time t0), the crankshaft 3 or fly The kinetic energy of a moving part such as a wheel is consumed by mechanical friction and pumping work of each cylinder 12A to 12D, so that the engine rotation speed gradually decreases, and the engine 1 stops after several revolutions due to inertia. It will be. In detail, while the engine 1 rotates by inertia, the engine rotation speed temporarily decreases greatly every time the compression top dead center (TDC) of each of the cylinders 12A to 12D is reached. When it exceeds, it rises again, and it goes down while repeating up and down. For example, when the fuel is cut at about 800 rpm as shown in the figure, the TDC is usually exceeded 8 or 9 times, and after the last TDC (time t3), the next TDC cannot be exceeded. To stop (time t4 to t6).

  That is, as described above, in the cylinder 12 (# 1 cylinder 12A in the figure) that cannot exceed TDC and remains in the compression stroke, the air pressure increases as the piston 13 rises due to inertial force, and the compression reaction force causes the piston 13 to move. Once stopped (time t4), it is pushed back toward the BDC. As a result, the crankshaft 3 reverses and the engine speed becomes a negative value as shown in FIG. 5A. Then, this time, the cylinder 12 in the expansion stroke (transition to the expansion stroke beyond the last TDC) is performed. In this example, the air pressure of the # 2 cylinder 12B) rises, and a compression reaction force to the BDC side acts on the piston 13, and the piston 13 of the expansion stroke cylinder 12 is temporarily caused by this compression reaction force. After stopping (time t5), it is pushed back toward the BDC. Thus, the crankshaft 3 rotates forward again, and the engine speed returns to a positive value.

  As described above, the pistons 13 of the cylinders 12 </ b> A to 12 </ b> D are reciprocated several times and stopped after the compression reaction forces acting in the opposite directions on the pistons 13 of the compression stroke cylinder 12 and the expansion stroke cylinder 12. (Time t6), the stop position is roughly determined by the balance between the compression reaction forces of the compression and expansion stroke cylinders 12, and finally exceeds TDC before the stop due to the influence of the friction of the engine 1 and the like. It changes according to the rotational inertia of the engine 1 at the time, that is, the level of the engine speed when the TDC is finally exceeded.

  Therefore, in order to stop the piston 13 of the cylinder 12 in the expansion stroke when the engine is stopped within the predetermined range R suitable for restarting, first, the compression reaction of the expansion stroke cylinder 12 at the stop time and the compression stroke cylinder 12 at the stop time is first. It is necessary to adjust the amount of intake air to both cylinders 12 so that the force is sufficiently large and the compression reaction force of the expansion stroke cylinder 12 is in a suitable balance larger than the compression stroke cylinder 12 by a predetermined amount or more. There is. For this reason, in this embodiment, as shown in FIG. 5 (c), the throttle valve 23 (time t1) opened immediately after the fuel cut is closed after the lapse of a predetermined period (time t2). As shown, the intake pipe negative pressure is temporarily reduced (intake amount is increased), so that the required amount of air is sucked into the compression and expansion stroke cylinders 12 when stopped.

  However, the actual engine 1 has individual variations in the shape of the throttle valve 23 itself, the intake port 17, the branch intake passage 21a, and the like, and the behavior of the air flow that circulates there may change. Since the amount of air flowing into each of the cylinders 12A to 12D varies to some extent during the period, even if the opening / closing control of the throttle valve 23 as described above is performed, it is only that when the engine is stopped, the compression stroke or the expansion stroke It is difficult to accurately set the piston stop position of the cylinder 12 to be within the target range R.

  In this regard, in this embodiment, as shown in an example in FIG. 6, the engine rotation speed when each of the cylinders 12 </ b> A to 12 </ b> D sequentially passes TDC in the process of gradually decreasing the engine rotation speed during the stop operation period. Focusing on the fact that there is a clear correlation between (hereinafter also referred to as TDC rotational speed) and the piston stop position of the cylinder 12 in the expansion stroke after the engine is stopped, as shown in FIG. By detecting the TDC rotational speed at every 180 ° CA in the process of decreasing the engine rotational speed and controlling the opening degree of the throttle valve 23 according to the detected value, the degree of decrease in the engine rotational speed is adjusted. Yes.

  Specifically, FIG. 6 shows that the engine 1 that rotates by inertia is cut off when the engine speed is approximately 800 rpm as described above and the throttle valve 23 is kept open for a predetermined period thereafter. Each time the cylinders 12A to 12D exceed TDC, the engine rotational speed (TDC rotational speed) at that time is measured, and the piston position of the expansion stroke cylinder 12 after being stopped is examined, and this piston position is determined. The relationship between the two is shown with the vertical axis and the TDC rotational speed on the horizontal axis. By repeating such an operation a predetermined number of times, a distribution diagram showing a correlation between the TDC rotational speed during the engine stop operation period and the piston stop position in the expansion stroke cylinder 12 after the stop is obtained.

  In the example in the figure, the rotation speed when the last TDC before the engine stop is not shown, but the last one from the TDC rotation speed immediately after the fuel cut (the ninth in the example counted from the end) is not shown. Data up to the previous TDC rotational speed (second one from the end) is shown. The 9th to 2nd TDC rotation speeds from the last are distributed in a lump, and as is apparent in the 6th to 2nd ones shown in the figure, the TDC rotation speed is within a certain range (see FIG. If it is within a range indicated by hatching, it can be seen that the piston stop position falls within a range R suitable for restart (ATDC 100 to 120 ° CA in the example in the figure).

  As described above, the specific range of the TDC rotational speed at which the piston 13 of the expansion stroke cylinder 12 stops within the predetermined range R suitable for restarting the engine 1 is hereinafter referred to as an appropriate rotational speed range in this specification. And In this embodiment, as will be described in detail below, the TDC rotational speed for each of the cylinders 12A to 12D is detected when the engine rotational speed decreases while repeating up / down as shown in FIG. 5 (a). The detected value is compared with the appropriate rotational speed range, and the throttle valve 23 is controlled to open and close according to the speed deviation between the two. That is, for example, when the TDC rotational speed is lower than the appropriate rotational speed range, the throttle opening is controlled to the open side to reduce the pump work of each of the cylinders 12A to 12D, thereby slowing down the engine rotational speed. To do so.

  As described above, if the degree of decrease in the engine rotational speed is adjusted by controlling the opening degree of the throttle valve 23 so that the TDC rotational speed is within the appropriate rotational speed range before passing the last TDC at the latest, At this time, the kinetic energy possessed by the moving parts such as the crankshaft 3, the flywheel, the piston 13 and the connecting rod, the potential energy possessed by the high-pressure air of the compression stroke cylinder 12, etc. are commensurate with the friction acting thereafter. Thus, when the engine 1 is stopped, the piston 13 of the cylinder 12 in the expansion stroke can be stopped within the predetermined range R suitable for the restart.

  Next, the specific procedure of the engine stop control described above will be described with reference to the flowchart of FIG. 4. This flow starts at a predetermined timing during engine operation (START), and in step SA1, the condition of the idle stop is determined. It is determined whether or not it is established. This determination is made based on the vehicle speed, the operating condition of the brake, the engine water temperature, etc. For example, the vehicle speed is smaller than a predetermined speed, the brake is operating, the engine water temperature is within a predetermined range, and the engine 1 is If there is no particular inconvenience for stopping, it is assumed that the idle stop condition is satisfied.

  When the idling stop condition is satisfied in the step SA1 (in the case of YES), any one cylinder 12 (the first cylinder 12A or the fourth cylinder 12D in the flow of FIG. 4) is specified in the subsequent step SA2. Then, it is determined whether or not a predetermined condition for stopping the engine is satisfied. That is, it is determined whether or not the engine rotation speed is a fuel cut set rotation speed (approximately 800 rpm in this embodiment), whether or not the specified cylinder 12 is in a preset stroke (for example, an intake stroke).

  If all the conditions are satisfied and it is determined YES, the process proceeds to step SA3 to stop the fuel injection to each cylinder 12A to 12D (fuel cut), and in the subsequent step SA4, the throttle valve 23 is set to the set opening degree. Open (throttle open). As a result, as shown in FIGS. 6C and 6D, the amount of intake air to each of the cylinders 12A to 12D is increased, sufficient scavenging is performed, and the catalyst 29 disposed in the exhaust passage 22 has a large amount. As fresh air is supplied, the amount of oxygen stored in the catalyst 29 is sufficiently increased.

  In the subsequent step SA5, the throttle valve 23 is kept open until it is determined that the engine rotational speed is equal to or lower than the predetermined rotational speed (engine rotational speed at time t2 in FIG. 5). If YES, the process proceeds to step SA6 to close the throttle valve 23 (throttle close). By opening and closing the throttle valve 23 in this manner, as shown in FIGS. 5 (c) and 5 (d), the stop expansion stroke cylinder 12 (# 2 cylinder 12B in the illustrated example) and the stop compression stroke cylinder 12 (in the illustrated example). # 1 cylinder 12A) is increased in intake air amount, and the intake air amount into the stop expansion stroke cylinder 12 is larger than that in the stop compression stroke cylinder 12, so that the piston of the stop expansion stroke 12 is approximately at the center of the stroke. It can be stopped closer to the BDC than the part.

  Subsequently, in step SA7, it is determined whether or not the TDC rotational speed obtained from the signal from the crank angle sensor 30 is within the appropriate rotational speed range (is the rotational speed at TDC within a predetermined range?), And the determination is YES and TDC rotation is performed. If the speed is within the appropriate rotational speed range, the process proceeds to step SA8, where it is determined whether the TDC rotational speed is equal to or less than a predetermined value A. This predetermined value A is experimentally set in advance in association with the last TDC rotational speed before the engine is stopped. If the TDC rotational speed obtained in step SA7 is equal to or lower than the predetermined value A (determination is YES) In this case, the engine 1 cannot exceed the next TDC and stops, so the process proceeds to Step SA11 described later, and if the TDC rotational speed is higher than the predetermined value A (when the determination is NO). Since the engine 1 exceeds the next TDC, the process returns to step SA7.

  If it is determined in step SA7 that the TDC rotational speed is not in the appropriate rotational speed range (NO), the process proceeds to step SA9, where the rotational speed between the TDC rotational speed and the appropriate rotational speed range is set. Based on the deviation, the opening of the throttle valve 23 is calculated. Then, in step SA10, the actuator 24 of the throttle valve 23 is driven (throttle drive) so that the opening degree is reached, and the process proceeds to step SA8. That is, for example, when the TDC rotational speed is higher than the upper limit of the appropriate rotational speed range, the degree of decrease in the engine rotational speed is achieved by driving the throttle valve 23 toward the closing side and increasing the pump work of each cylinder 12A to 12D. Increase On the other hand, when the TDC rotational speed is lower than the lower limit of the appropriate rotational speed range, the degree of decrease in engine rotational speed is reduced by driving the throttle valve 23 to reduce the pump work of each cylinder 12A to 12D. Relax.

  By correcting the opening degree of the throttle valve 23 in this way, as shown in FIG. 5 (a), the locus of the engine speed that gradually decreases while repeating up and down is shifted to either the high speed side or the low speed side. Thus, it can gradually approach the desired trajectory, and can be within the proper rotational speed range by the last TDC at the latest. If it carries out like this, in the expansion stroke cylinder 12 of the engine 1 which stops naturally after that, the piston 13 will stop in the predetermined range suitable for restart.

  Then, if the engine 1 exceeds the last TDC and the TDC rotation speed at that time becomes equal to or less than the predetermined value A, the engine 1 has already passed the last TDC. The two cylinders 12 and 12 in the compression stroke and the expansion stroke are rotated several times on the forward rotation side and the reverse rotation side by the compression reaction force of the two cylinders 12 and 12, respectively, and then stopped. Therefore, the process proceeds to step SA11, where the stop (complete stop) of the engine 1 is confirmed based on the signals from the crank angle sensors 30, 31, and if the stop of the engine 1 is confirmed as YES, the process proceeds to step SA12. A piston stop position of the cylinder 12 in the expansion stroke is detected based on the crank angle signals output from the two crank angle sensors 30 and 31 by the subroutine described later (see FIGS. 7 and 8). This is stored in the memory of the ECU 2 and the engine stop control is completed (END).

  That is, as described above, the crankshaft 3 is rotated several times in both forward and reverse directions just before the engine 1 is stopped. Therefore, the piston stop position is detected only by counting the signal from the crank angle sensor 30. I can't. Therefore, in this embodiment, the rotation direction and the rotation angle of the crankshaft 3 are detected as follows based on the crank angle signals output from the two crank angle sensors 30 and 31 and shifted from each other. A crank angle with respect to TDC or BDC of each cylinder 12A to 12D, that is, a piston stop position is detected.

  Specifically, FIG. 7 is a flowchart showing a subroutine for detecting the stop position of the piston. When this flow starts, in step SC1, the first crank angle signal CA1 (the output signal from the first crank angle sensor 30) is shown. ) And the second crank angle signal CA2 (output signal from the second crank angle sensor 31), when the ECU 2 rises the first crank angle signal CA1, the second crank angle signal CA2 is either Low or High. It is also determined whether the second crank angle signal CA2 is High or Low when the first crank angle signal CA1 falls. That is, it is determined whether the phase relationship between these signals CA1 and CA2 is as shown in FIG. 8 (a) or FIG. 8 (b). Determine.

  More specifically, during forward rotation of the engine, as shown in FIG. 8A, the second crank angle signal CA2 has a phase delay of about a half pulse width with respect to the first crank angle signal CA1. The second crank angle signal CA2 becomes Low when the first crank angle signal CA1 rises, and the second crank angle signal CA2 becomes High when the first crank angle signal CA1 falls. On the other hand, at the time of reverse rotation of the engine, as shown in FIG. 8B, the second crank angle signal CA2 has a phase advance of about a half pulse width with respect to the first crank angle signal CA1. Contrary to the forward rotation, the second crank angle signal CA2 becomes High when the first crank angle signal CA1 rises, and the second crank angle signal CA2 becomes Low when the first crank signals CA1 fall. It is.

  When it is determined in step SC1 of the flow that the engine 1 is in the normal rotation state (in the case of YES), the count number of the CA counter for measuring the crank angle change in the normal rotation direction of the engine 1 is set. On the contrary, when it is determined that the reverse rotation state is established (in the case of NO), the count number of the CA counter is decreased. Here, the rise and fall of the first crank angle signal CA1 and the second crank angle signal CA2 are caused by rotation of the crankshaft 3 for each predetermined angle (in this embodiment, the interval between the rise and fall is approximately 10 degrees). Therefore, the forward / reverse rotation of the engine 1 is determined as described above according to the state of the second crank angle signal CA2 when the first crank angle signal CA1 rises and falls. In addition, the rotation angle of the crankshaft 3 can be obtained from the number of rising or falling edges of the first crank angle signal CA1 and the second crank angle signal CA2. In this way, even when the crankshaft 3 rotates in the forward and reverse directions as described above when the engine is stopped, the crank angle can be accurately detected regardless of this and the piston stop position can be obtained.

  As described above, according to the engine stop control described in detail, when the engine 1 is automatically stopped by the fuel cut during idling, the throttle valve 23 is opened for the first predetermined period, and the cylinders 12 and 12 that respectively become the expansion stroke and the intake stroke after the stop. In addition, the required amount of air is inhaled at the same time, and thereafter, the throttle valve 23 is controlled to open and close according to the deviation of the TDC rotational speed from the appropriate rotational speed range, thereby adjusting the degree of decrease in the engine rotational speed. Thus, the piston 13 can be stopped in a predetermined range R suitable for restarting in the expansion stroke cylinder 12 after the engine is stopped.

Further, as described above, when the throttle valve 23 is opened for a predetermined period in the engine stop operation period, almost all the burned gas in each of the cylinders 12A to 12D is scavenged out of the cylinder and filled with fresh air. A large amount of oxygen is stored in the catalyst 29 in the exhaust passage 22. However, after the engine 1 is stopped, the air pressure leaks immediately even in the expansion stroke cylinder 12 and the compression stroke cylinder 12 in which the intake and exhaust valves 19 and 20 are closed, so that each cylinder 12A to 12D has a piston. There is a state where fresh air (air) at approximately atmospheric pressure exists in the volume corresponding to the stop position.
-Engine start control-
Next, restart of the engine 1 that has been automatically stopped at the time of idling as described above will be described with reference to FIGS. 3 and 9 to 12. 9 and 10 are flowcharts showing the procedure of start control, and FIG. 11 shows the fuel injection and ignition timing of each cylinder 12A to 12D at the start, and the change of the stroke of each cylinder 12A to 12D. FIG. 3 is a stroke diagram corresponding to open / close states of intake and exhaust valves. FIG. 12 shows that the in-cylinder pressure of each of the cylinders 12A to 12D rises due to the fuel injection and ignition for each of the cylinders 12A to 12D at the time of starting, thereby increasing the starting torque of the engine 1 and increasing the engine speed. It is the time chart which showed a mode that it stood up with the fall of the throttle valve opening degree and intake pressure at that time.

  As described above, the engine start control of this embodiment is to start the engine 1 by itself, and as shown in FIG. 3 and FIG. 11 as an example, first, the stop compression stroke cylinder 12A (# 1 cylinder) ), The engine 1 is temporarily operated in reverse (FIG. 3 (a), a1 and a2 in FIG. 11), thereby compressing the expansion stroke cylinder 12B (# 2 cylinder) at the stop, Then, the air-fuel mixture in the expansion stroke cylinder 12B whose pressure has increased is ignited and burned (FIG. 3 (b), a3, a4 in FIG. 11). By doing so, the combustion pressure of the expansion stroke cylinder 12B becomes sufficiently high, and the effective stroke becomes long, so that a large starting torque can be obtained.

  However, when combustion is initially performed in the compression stroke cylinder 12A at the time of stop as described above, the burned gas resulting from this combustion is filled in the cylinder 12A, so that the cylinder 12A is started as shown in FIG. 3 (c). When the first TDC of the time is reached, the compression reaction force acting on the piston 13 becomes considerably large, and there is a possibility that the start fails because the compression reaction force cannot be exceeded. Even if the compression reaction force can be overcome and TDC can be exceeded, the engine rotational speed at that time becomes large, and the starting torque cannot be obtained by combustion in the cylinder 12A filled with burned gas. It is difficult to increase the engine speed smoothly.

  The # 3 cylinder 12C in the next ignition order of the # 1 cylinder 12A is stopped in the intake stroke (hereinafter also referred to as a stop-time intake stroke cylinder), and the air in the cylinder 12C is stopped in the engine. In addition to being warmed by heat radiation from the cylinder wall surface, the temperature is considerably high, and the air warmed in this passage is drawn from the branch intake passage 21a downstream of the throttle valve 23 to be fully filled. Thus, in the compression stroke, the temperature and pressure in the cylinder 12C become considerably high, the engine rotation is greatly reduced by the compression reaction force, and the auto-ignition is very likely to occur.

  Further, the # 4 cylinder 12D, which reaches the ignition order following the # 3 cylinder 12C, is stopped in the exhaust stroke (hereinafter also referred to as a stop exhaust stroke cylinder). Therefore, if the throttle valve 23 is opened to the opening corresponding to the normal idling operation at the time of starting, the branch downstream of the throttle valve 23 is taken. The intake pressure from the intake passage 21a to the intake port 17 does not readily decrease to the intake pressure during idle operation, and remains close to atmospheric pressure, so that the intake charge amount is considerably large as in the case of the # 3 cylinder 12C. Become.

  In addition to this, when the # 4 cylinder 12D reaches the ignition order, the rotational inertia of the engine 1 increases to some extent. Therefore, if the intake charge amount becomes large as described above, The torque increases excessively, the starting torque rises steeply, and the engine blows up suddenly (temporarily rises higher than the idle speed). Such a sudden rise of the engine may cause a strong sense of discomfort to the driver when the engine 1 is automatically started as in this embodiment.

  In view of the above problems, in the start control of this embodiment, first, the reverse rotation torque of the engine 1 due to the combustion of the stop-time compression stroke cylinder 12A is secured, and the stop-time expansion stroke cylinder 12B is sufficiently compressed. By doing so, the starting torque in the forward rotation direction due to the combustion of the cylinder 12B is greatly increased. Then, additional fuel injection is performed when the stop-time compression stroke cylinder 12A is compressed in accordance with the forward rotation operation of the engine 1 (a5 in FIG. 11), and the compression pressure is reduced by the cooling effect due to the latent heat of vaporization. Thus, as shown in FIG. 3 (c), the rotation of the engine 1 in the forward rotation direction is maintained so as to surely exceed the TDC that the cylinder 12A first meets when starting.

  Further, with respect to the stop-time intake stroke cylinder 12C (# 3 cylinder) in the next ignition sequence of the stop-time compression stroke cylinder 12A, the cylinder 12C is shifted to the compression stroke and the temperature and pressure are increased. The fuel is injected (a6 in FIG. 11), and the compression pressure is lowered by the cooling effect due to the latent heat of vaporization, and the occurrence of self-ignition is prevented. Further, by retarding the ignition timing of the cylinder 12C after the TDC (a7 in FIG. 11), it is avoided that the cylinder internal pressure increases due to the combustion before the TDC, and the drop in the engine rotation is reduced. After passing through the second TDC at the start as shown in d), the engine rotation is started by igniting and burning.

  If the engine speed rises and the engine starts successfully, the stop exhaust stroke cylinder 12D (# 4 cylinder), which subsequently reaches the ignition order, and the cylinders 12B, 12A, 12C,. On the other hand, as in the case of starting with a normal starting motor, fuel is injected in the intake stroke, ignited and burned at the end of the compression stroke, and the throttle valve 23 is opened immediately at that time. However, while the intake pressure detected by the intake pressure sensors 26, 26,... Is high, the opening operation of the throttle valve 23 is delayed to suppress the increase in the intake charge amount to each of the cylinders 12A to 12D. It is.

  Next, the specific procedure of the start control will be described with reference to the flowcharts of FIGS. 9 and 10. This flow starts from the engine stop state (START), and first, predetermined engine restart is performed at step SB1 of FIG. It is determined whether the condition is satisfied. This restart condition is when the brake is released to start from the stop state, when the accelerator operation is performed, when the engine is required to operate the air conditioner, etc. If such a condition is not satisfied, the process waits until the condition is satisfied. If the restart condition is satisfied (YES in step SB1), the process proceeds to step SB2.

  In step SB2, the stop compression stroke cylinder 12 (# 1 cylinder 12A in FIG. 3) and the stop expansion stroke cylinder 12 (see FIG. 3) are determined based on the stop position of the piston 13 obtained by the above-described subroutine (see FIGS. 8 and 9). In FIG. 3, the amount of air in the # 2 cylinder 12B) is calculated. That is, the volumes in the stop compression stroke cylinder 12 and the stop expansion stroke cylinder 12 are determined from the stop position of the piston 13, and the cylinders 12A to 12D of the engine 1 are almost in the atmospheric pressure state as described above. Assuming that the above is satisfied, the air amounts of the cylinders 12 and 12 are calculated.

  Subsequently, in step SB3, a fuel injection amount is calculated such that a predetermined air-fuel ratio (A / F for the first compression stroke cylinder) is obtained with respect to the air amount of the compression stroke cylinder 12 at the time of stop calculated in step SB2. The fuel is injected into the compression stroke cylinder 12. Specifically, the air-fuel ratio is obtained from a map set in advance in association with the piston stop position or the like when the engine is stopped, whereby the air-fuel ratio of the compression stroke cylinder 12 is richer than the stoichiometric air-fuel ratio. It is set to a value (A / F is preferably in the range of about 11 to 14, more preferably about 13). In order to prevent misfire, it is necessary to control the fuel injection amount so that the air-fuel ratio becomes leaner than the rich-side flammability limit value (approximately 7 in A / F).

  Next, in step SB4, after elapse of a predetermined time set in consideration of the fuel vaporization time from the fuel injection to the stop-time compression stroke cylinder 12, the spark plug 15 of the cylinder 12 is energized to become the air-fuel mixture. Ignite. In step SB5, whether or not the piston 13 has moved depending on whether or not the edge of the signal from the crank angle sensors 30 and 31 (rising or falling of the crank angle signal) is detected within a predetermined time from the ignition in step SB4. If the piston 13 does not move due to misfire or the like (in the case of NO), the process returns to step SB6 to the compression stroke cylinder 12. Repetitively ignite.

  On the other hand, when the edge of the crank angle signal is detected in step SB5 (in the case of YES) and it is determined that the piston 13 has moved, that is, the engine 1 has started reverse rotation, the routine proceeds to step SB7, where Fuel is injected into the expansion stroke cylinder 12 so as to be a predetermined air-fuel ratio (A / F for the expansion stroke cylinder 12) with respect to the air amount of the expansion stroke cylinder 12 at the time of stop calculated in step SB2. Also in this case, the air-fuel ratio for the expansion stroke cylinder 12 is obtained from a map set in advance in association with the piston stop position or the like when the engine is stopped, as in step SB3. Alternatively, it is set to a slightly richer value (A / F is preferably approximately 13).

  In the subsequent step SB8, after a predetermined time (ignition delay) has elapsed since the reverse rotation operation of the engine 1 was detected, the expansion stroke cylinder 12 is ignited and combusted. During this ignition delay time, the piston 13 of the expansion stroke cylinder 12 at the time of stop rises due to the reverse rotation operation of the engine 1, the air-fuel mixture in the cylinder 12 is sufficiently compressed, and the piston 13 is almost stopped by the compression reaction force. This corresponds to the time until the engine is stopped, and is obtained from a map set in advance in association with the piston stop position when the engine is stopped. By igniting and burning the air-fuel mixture sufficiently compressed in the expansion stroke cylinder 12 in this way, the engine 1 starts to rotate in the forward direction with a sufficiently large torque.

  Subsequently, at step SB9, the second-time fuel injection (additional fuel injection) for the cylinder 12 is performed on the compression stroke cylinder 12 at the time of stopping when the engine 1 reaches the first TDC as the engine 1 rotates forward. It is executed at a predetermined timing considering the vaporization time. When the fuel injected in this way is vaporized, it takes heat from the surrounding gas (vaporization latent heat), thereby lowering the temperature in the compression stroke cylinder 12 and lowering the in-cylinder pressure. Even if is filled, the compression reaction force can be reduced, and the piston 13 can reliably exceed TDC. Thus, the forward rotation operation of the engine 1 started by the combustion of the stop-time expansion stroke cylinder 12 in step SB8 is continued, the stop-time compression stroke cylinder 12 exceeds TDC, and each of the cylinders 12A to 12D follows. It will proceed to the process of.

  Here, the timing of the additional injection to the compression stroke cylinder 12 at the time of stop is after the middle period when the compression stroke during the forward rotation of the cylinder 12 is roughly divided into three parts of the first period, the middle period, and the second period by the crank angle. It is preferable to do this. This is because the correlation between the fuel injection timing and the effect of reducing the cylinder internal pressure due to this is taken into account. If fuel injection is performed in the first half of the compression stroke, the gas temperature in the cylinder 12 is prematurely determined. As a result, the amount of heat received by the gas from the cylinder wall surface increases, and the gas density is increased by the vaporized fuel, so that the effect of reducing the temperature and pressure in the cylinder 12 is diminished. is there.

  Note that if the timing of the additional injection becomes too late, the fuel vaporization is delayed and a sufficient cooling effect cannot be obtained. Therefore, the fuel additional injection is performed from the middle stage of the compression stroke of the cylinder 12 to the first half of the latter stage. It can be said that it is preferable.

  Subsequent to step SB9, in step SB10 of FIG. 10, the air charged in the intake stroke cylinder 12 (# 3 cylinder 12C in FIG. 3) at the time of stop by the forward rotation operation of the engine 1 started as described above. Calculate the amount of In other words, the intake stroke cylinder 12 at the time of stop is the second TDC at the start time following the compression stroke cylinder 12 at the time of stop, but as described above, relatively high temperature air is present in the cylinder 12. Is fully filled at approximately atmospheric pressure and is very prone to self-ignition.

  Therefore, in step SB10, the air density in the intake stroke cylinder 12 at the time of stop is estimated based on the in-cylinder temperature and the atmospheric pressure estimated from the engine water temperature, the engine stop time, the intake air temperature, and the like. The air filling amount in the cylinder 12 is calculated based on the value. In the subsequent step SB11, a correction value to the rich side of the air-fuel ratio for preventing self-ignition is calculated mainly based on the estimated value of the in-cylinder temperature, and in the subsequent step SB12, the correction value is considered. Based on the air-fuel ratio determined in this way and the air charge amount in the cylinder 12 calculated in step SB10, the fuel injection amount to the stop-time intake stroke cylinder 12 is calculated.

  Subsequently, in step SB13, after the stop-time intake stroke cylinder 12 shifts to the compression stroke, fuel is injected into the cylinder 12 after the middle stage of the compression stroke. By doing so, the temperature and pressure in the cylinder 12 are reduced due to the latent heat of vaporization of the fuel, as in the case of the compression stroke cylinder 12 at the time of stop, so that the cylinder 12 is filled with relatively high temperature air as described above. Even if it is, it can suppress the raise of the temperature and pressure accompanying compression, and can prevent generation | occurrence | production of self-ignition. In addition, since the compression pressure of the cylinder 12 is also reduced, the drop in engine rotation during TDC ignition is reduced accordingly.

  Here, the amount of fuel injected in the compression stroke in the intake stroke cylinder 12 at the time of stop is a predetermined range in which the average air-fuel ratio in the cylinder 12 is close to the theoretical air-fuel ratio (for example, approximately 12 to 16 in A / F). More preferably, the control is performed so that it is slightly richer than the stoichiometric air-fuel ratio (for example, about 13 in A / F). This is in consideration of the correlation between the air-fuel ratio and the cylinder internal pressure reduction effect. When the air-fuel ratio is too lean, the fuel injection amount is too small, and the temperature and pressure decrease due to the latent heat of vaporization described above. When the air-fuel ratio becomes too rich, the work required for restart will be affected by the increase in fuel and the density of the air-fuel mixture. This is because it increases. The fuel injection timing in the compression stroke of the stop-time intake stroke cylinder 12 is preferably after the middle of the compression stroke for the same reason as in the case of the stop-time compression stroke cylinder 12.

  In step SB14, after the stop-time intake stroke cylinder 12 exceeds the TDC from the compression stroke and shifts to the expansion stroke, the spark plug 15 is energized to ignite the air-fuel mixture in the cylinder 12. If this ignition timing is also at the time of engine start using a normal starter motor, it is set to an advance side from TDC (for example, about 6 ° CA before TDC). If the engine is started without being used, ignition before TDC and an increase in the cylinder internal pressure due to combustion may become a torque in the reverse direction, which may hinder engine start. Is delayed until after TDC. In addition, if there is no increase in the cylinder pressure due to combustion before TDC, the engine rotation drop can be reduced.

  Subsequently, at step SB15, the intake pressure (intake pipe negative pressure) of the branch intake passage 21a for each of the cylinders 12A to 12D is warmed up by the engine 1 based on the signals from the intake pressure sensors 26, 26,. It is determined whether or not it is equal to or higher than the set value corresponding to the subsequent idle operation. Here, before the engine 1 is started, the intake pressure of each branch intake passage 21a (the air pressure downstream of the valve body of the throttle valve 23) is substantially atmospheric pressure, and the determination is YES. If the throttle valve 23 is opened at this time, the engine 12 will be increased due to overfilling of the intake air into the cylinder 12, and at this time, the routine proceeds to step SB16 where the throttle valve 23 has a smaller opening ( For example, it is kept in a fully closed state).

  On the other hand, when the cylinders 12A to 12D perform intake in the intake stroke in accordance with the forward rotation operation of the engine 1 described above, the volume downstream of the valve body in the branch intake passage 21a for each of the cylinders 12A to 12D is small. The intake pressure at this part immediately decreases and corresponds to the idling operation. In this way, when the intake pressure detected by all the intake pressure sensors 26, 26,... Is lower than the set value, NO is determined in step SA15, and the process proceeds to step SB17 to shift to normal engine control. That is, the throttle valve 23 is controlled to have an opening corresponding to the idling operation.

  That is, in this flow, if the throttle valve 23 is opened at the start of engine start, the stop-time exhaust stroke cylinder 12D that first shifts to the intake stroke, and the cylinders 12B, 12A, .., And the intake pressure sensor 26 for each of the cylinders 12A to 12D detects that the air in the state close to atmospheric pressure is sucked from the intake passage 21 and the intake charge amount becomes excessive. The opening of the throttle valve 23 is delayed until all of the intake pressure drops to a considerable extent during idle operation, thereby preventing problems such as a sudden rise of the engine 1 due to overfilling of the intake air. Yes.

  The throttle valve 23 is not kept in the fully closed state until the intake pressure is reduced to a value corresponding to the idling operation as described above, but the throttle valve 23 is slightly opened smaller than that in the idling operation. You may make it keep to.

  In step SB15 of the engine start control flow shown in FIG. 10, the throttle valve 23 is controlled based on signals from the intake pressure sensors 26, 26,. An intake pressure detecting means 2a for detecting an intake pressure state downstream from the valve body is configured, and when the engine speed rises when the engine 1 is restarted by step SB16, the detected intake pressure is detected after the engine is warmed up. Intake amount control for controlling the opening degree of the throttle valve 23 so that the intake air flow rate to each of the cylinders 12A to 12D becomes smaller than that during the idling operation after the warm-up until the set value corresponding to the idling operation is reached. Means 2b is configured.

-Effect-
Therefore, according to the engine system E (engine starter) of this embodiment, first, when the engine 1 automatically stops during idling, the above-described stop control (FIGS. 4 to 6 and the like) causes the cylinders 12A to 12D to be stopped. The piston stop position of the cylinder 12 that scavenges the burned gas and becomes the expansion stroke after the engine is stopped can be within a predetermined range R suitable for restarting slightly closer to the BDC than the center of the stroke. In addition, a sufficient amount of fresh air can be supplied to the exhaust purification catalyst 29 during the stop operation period of the engine 1, whereby the oxygen storage amount of the catalyst 29 becomes sufficiently large.

  On the other hand, when the engine 1 is restarted, the engine 1 is automatically and self-started in response to the restart request by using the above-described start control (FIGS. 9 to 12 and the like) without using a start motor. That is, referring to FIG. 11, the description will be given mainly in time series based on FIG. 12. When a restart request is made while the engine 1 is stopped (time t 0), first, reference numeral a 1 is shown in FIG. As shown, the fuel injection valve 16 of the # 1 cylinder 12A stopped in the compression stroke is actuated to inject fuel into the cylinder 12A, whereby the air-fuel ratio rich air-fuel mixture is injected into the cylinder 12. Is formed. When the rich air-fuel mixture is ignited by the spark plug 17 and burned (a2), a negative torque (reverse torque) is generated as indicated by T1 in FIG. It rotates in the left direction of FIG. 11 (time t1). For this reason, the engine speed temporarily becomes a negative value as shown in FIG.

  When the reverse rotation operation of the engine 1 is detected by signals from the crank angle sensors 30, 31, the fuel injection valve 16 of the stop expansion stroke cylinder 12 (# 2 cylinder 12B) is operated as shown in FIG. (A3), an air-fuel mixture is formed in the cylinder 12B, and the air-fuel mixture is compressed by the upward movement of the piston 13 due to the reverse operation. At this time, since the reverse torque T1 is sufficiently large, the piston 13 of the expansion stroke cylinder 12B at the time of stop rises to the vicinity of the TDC, and the air-fuel mixture in the cylinder 12B is sufficiently compressed so that the temperature and pressure are high. become. When the engine 1 is rotated from the reverse direction to the normal direction by the compression pressure, that is, immediately after the engine speed returns from the negative value to zero as shown in FIG. (A4 in FIG. 4B), a large combustion pressure is generated thereby, the starting torque rises as shown by T2 in FIG. 4E, and the engine speed increases as shown in FIG. Time t2: Forward rotation start).

  When the inside of the stop compression stroke cylinder 12A is compressed along with the forward rotation operation, fuel injection (additional addition) into the cylinder 12A again after the middle stage of the compression stroke, as shown in FIG. Fuel injection) is performed (a5), and the inside of the cylinder 12A is cooled by the latent heat of vaporization of the fuel, so that the temperature in the cylinder 12A is higher than that in the case where this additional fuel injection is not performed (shown by a broken line in the figure) And the increase in pressure is greatly suppressed. As a result, the engine 1 can surely exceed the first TDC (first TDC) that is first met at the time of start-up, and the drop in engine rotation at that time is reduced (f). Further, the fuel injected for cooling the compression stroke cylinder 12A subsequently reacts with oxygen stored in the catalyst 29 in the exhaust passage 22 and is rendered harmless, so that no problem occurs. .

  FIG. 6 (c) shows the stop-time intake stroke cylinder 12C (# 3 cylinder) that has shifted to the compression stroke after the stop-time compression stroke cylinder 12A has exceeded the initial first TDC at the start as described above. As shown in FIG. 4, fuel is injected after the middle of the compression stroke (a6), and the inside of the cylinder 12 is cooled by the latent heat of vaporization. As a result, an increase in temperature and pressure due to compression is suppressed, the occurrence of self-ignition is prevented, and the compression reaction force of the cylinder 12C is reduced. In addition, the ignition timing for the cylinder 12C is until after TDC. By retarding, an increase in cylinder pressure due to ignition and combustion before TDC is avoided. As a result, the drop in engine rotation is reduced, and the engine 1 can reliably exceed the second TDC.

  Then, when the stationary intake stroke cylinder 12C, which has shifted to the expansion stroke beyond the second TDC, is ignited (a7) and combustion is performed, torque in the forward rotation direction is applied to the engine 1, and the same figure is obtained. The starting torque rises as indicated by T3 in (e), and as a result, the engine speed increases to near the idle speed (650 rpm in this example) as shown in FIG. However, since the ignition timing is retarded until TDC as described above and combustion starts in the expansion stroke, the start-up torque rise is suppressed so as not to become excessively large, and the increase in engine rotation is moderate. It will be a thing.

  Subsequently, as shown in FIG. 4D, fuel is injected into the exhaust stroke cylinder 12D at the time of stop in the intake stroke (a8) and ignited before TDC (third TDC) (a9). Similarly, as shown in FIGS. 2B and 2A, fuel injection and ignition are performed on the stop expansion stroke cylinder 12B and the stop compression stroke cylinder 12A (a10 to a13), By burning, the engine speed further increases and gradually approaches the idle speed as shown in FIG.

  At this time, since the throttle valve 23 is fully closed as shown in FIG. 5G, the air downstream of the throttle valve 23 in the branch intake passage 21a is sucked into the cylinders 12D, 12B, and 12A. However, the inflow of intake air from the upstream side of the valve 23 is limited, and the intake charge amount of each of the cylinders 12A to 12D does not increase so much. For this reason, the engine 1 does not blow up suddenly, and its rotation starts up smoothly. Even when the engine 1 is automatically started, the driver does not feel uncomfortable.

  As described above, when the four cylinders 12C, 12D, 12B, and 12A perform the intake stroke once in order, the intake pressure of the branch intake passage 21a for each of the cylinders 12A to 12D is shown in FIG. h), as shown by the phantom line, both become the set negative pressure state corresponding to the idling operation (time t3). In response to this, the throttle valve 23 opens as shown in FIG. It is actuated and enters a state corresponding to idle operation.

-Other embodiments-
In the above-described embodiment, the opening degree of the throttle valve 23 is controlled based on the detection values by the intake pressure sensors 26, 26,... Disposed in the intake passage 21, but the present invention is not limited to this. Control is performed so that the opening degree of the throttle valve 23 becomes smaller than that during idling until the engine speed determined based on signals from the crank angle sensors 30 and 31 is stabilized in the vicinity of the idle speed after warm-up. Alternatively, the opening operation of the throttle valve 23 is delayed only for a predetermined number of times (for example, 2 to 3 times) set in advance from the start of normal rotation of the engine 1 until the crankshaft 3 rotates. You may do it.

  Further, in the above-described embodiment, as an intake flow rate adjusting means for adjusting the intake flow rate to each of the cylinders 12A to 12D, the throttle valve 23 in which the valve body is individually disposed in the branch intake passage 21a for each of the cylinders 12A to 12D. However, the present invention is not limited to this, and as the intake flow rate adjusting means, for example, a known variable valve mechanism that can change at least the closing timing and the lift amount of the intake valve 19 for each of the cylinders 12A to 12D is adopted. May be.

  In other words, when the lift amount of the intake valve 19 is changed, the intake charge amount can be reduced by controlling the lift amount to be smaller than that during idling after warming up and narrowing the intake flow. Further, when changing the valve closing timing, the valve closing timing is controlled so as to be retarded from the idling operation after the warm-up, so that the intake passage 21 of the intake air once sucked into the cylinder 12 is temporarily returned. The amount of intake air can be reduced by increasing the amount of air blown back. The operation procedure of the ECU 2 that controls the variable valve mechanism in this way constitutes the valve timing control means.

  Furthermore, in the above-described embodiment, when the engine is restarted, the crankshaft 3 is first slightly reversed to ignite after the air-fuel mixture in the stop expansion stroke cylinder 12 is compressed. Instead, the stop-time expansion stroke cylinder 12 may be ignited first, thereby restarting the engine.

1 is a schematic configuration diagram of an engine control system according to an embodiment of the present invention. It is a schematic diagram which shows the structure of the intake system and exhaust system of an engine. It is explanatory drawing which shows typically the procedure of reverse rotation start of an engine. It is a flowchart which shows the control procedure of an engine automatic stop. It is explanatory drawing which shows the change of the engine speed in the engine stop operation period, a crank angle, the throttle opening, and the intake pipe negative pressure with the change of the stroke of each cylinder. It is a distribution map which shows correlation with the TDC rotational speed in an engine stop operation period, and the piston stop position after an engine stop. It is a flowchart of the subroutine for detecting the piston position at the time of an engine stop. It is explanatory drawing which shows the crank angle signal output from two crank angle sensors, (a) is an engine normal rotation, (b) is a crank angle signal at the time of engine reverse rotation. It is a flowchart which shows the control procedure of the first half of an engine automatic start. It is a flowchart which shows the control procedure of the second half of an engine automatic start. FIG. 5 is a stroke diagram showing fuel injection and ignition timing for each cylinder at the start, together with stroke change of each cylinder and the open / closed state of the intake and exhaust valves. 4 is a time chart showing changes in in-cylinder pressure, engine torque, and rotational speed for each cylinder at the time of starting, together with changes in throttle opening and intake pressure.

Explanation of symbols

E Engine system (engine starter)
1 Engine 2 ECU (Engine Controller)
2a Intake pressure detection means 2b Intake amount control means 12A to 12D Cylinder 21 Intake passage 21a Branch intake passage 23 Throttle valve (intake flow rate adjustment valve)
26 Intake pressure sensor (intake pressure detection means)

Claims (6)

When a predetermined restart condition is satisfied, fuel is injected and supplied into at least the cylinder in the expansion stroke of the stopped multi-cylinder engine, and is ignited and burned. An engine starter designed to start,
An intake air flow rate adjusting means capable of adjusting an intake air flow rate to each of the cylinders;
An intake air amount control means for controlling the intake air flow rate adjusting means so that the intake air flow rate to each cylinder is less than that during idling after warm-up when the engine speed rises at the time of engine restart;
An engine starting device comprising: The downstream side of the intake passage of the engine is branched for each cylinder to be a branch intake passage independent of each other,
The intake flow rate adjusting means is an intake flow rate adjustment valve in which a valve body is individually disposed in the branch intake passage.
Intake pressure detection means for detecting the intake pressure state of the branch intake passage downstream from the valve body of the intake flow rate adjustment valve,
The intake air flow rate control means is configured to reduce the intake air flow rate until the intake pressure state detected by the intake pressure detection means decreases from the vicinity of the atmospheric pressure and reaches a set negative pressure state corresponding to idle operation after engine warm-up. 2. The engine starting device according to claim 1, wherein the opening of the adjusting valve is controlled to be smaller than that during the idling operation.   The intake air amount control means is a valve that gradually opens the intake air flow rate adjustment valve from fully closed in response to a change in the intake pressure state detected by the intake pressure detection means toward the low pressure side. The engine starting device as described. A rotation speed detecting means for detecting the engine rotation speed;
The intake air amount control means is configured so that the intake air flow rate to each cylinder is higher than that during idle operation after the warm-up until the engine speed detected by the rotational speed detection means stabilizes in the vicinity of the idle speed after the warm-up. 2. The engine starting device according to claim 1, wherein the intake air flow rate adjusting means is controlled so as to be reduced. The intake flow rate adjusting means is a variable valve mechanism that can change at least the lift amount of the intake valve of each cylinder,
The intake air amount control means controls the variable valve mechanism so that the lift amount of the intake valve is smaller than that during idle operation after warming up. The engine starting device as described. When a predetermined restart condition is satisfied, fuel is injected and supplied into at least the cylinder in the expansion stroke of the stopped multi-cylinder engine, and is ignited and burned. An engine starter designed to start,
A variable valve mechanism capable of changing at least the closing timing of the intake valve of each cylinder;
A valve timing control means for controlling the variable valve mechanism so that the closing timing of the intake valve is retarded from the idling operation after warm-up when the engine rotation rises at the time of engine restart;
An engine starting device comprising:

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