JP2005163660A - Starting system of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely scavenge burnt gas from each cylinder of an engine 1 revolving by the inertia when automatic stop of the engine 1 and after fuel cut, to make a piston 13 of a cylinder 12 which is stopped in an expansion stroke stop in a predetermined range R suitable for restart, and to reduce fluctuation in revolution speed for a long period immediately before the stop of the engine and thereby to prevent generation of uncomfortable vibrations. <P>SOLUTION: For a predetermined period of time after the fuel cut, a throttle valve 23 is opened so that the scavenging is secured, and a power generation control of an alternator 28 and an opening control of the throttle valve 23 are performed, to control a degree of lowering in engine revolution speed. After exceeding a TDC last but one before the stop, fuel of a quantity depending on a TDC revolution speed at that time is injected into the cylinder 12 in a compression stroke (the cylinder is stopped in the expansion stroke), so that a compression reaction force is reduced by evaporation latent heat. Further, after exceeding the last TDC, the fuel of a quantity depending on the TDC revolution speed at that time is injected into the cylinder 12 in the compression stroke (the cylinder which is stopped in the compression stroke). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an engine starting device that starts an engine that has been automatically stopped when idle in response to a restart request, and more particularly to the field of control technology for automatically stopping an engine so as to be in a state suitable for restarting. Belongs.

_2. Description of the Related Art Conventionally, an engine control system (idle stop system) that automatically stops an engine during idling is known 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 the cranking and the engine blow-up give a sense of incongruity.

  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, in-cylinder direct-injection gasoline engines disclosed in Patent Documents 1 and 2, fuel is injected and supplied into a cylinder in an expansion stroke in a stopped state, and then started by ignition and combustion. The one that starts the engine with its own power without borrowing the power of the motor has been developed.

  When the cylinder in the expansion stroke is ignited and burned, the air filling amount of the cylinder is not so large, and the effective stroke is shortened, so that the starting torque obtained by combustion is intrinsic. It will not be too big. In addition, the amount of air in the cylinder changes depending on the stop position of the piston, and this affects the magnitude of the starting torque. Therefore, in order to ensure the startability of the engine, an expansion stroke occurs when the engine is stopped. There is a demand to control the piston stop position of a cylinder with high accuracy.

With respect to this point, in the Renoir start cycle type engine described in Patent Document 1, a braking force is applied to the rotation of the crankshaft using a mechanical braking mechanism. In the inertial rotation control method of the engine described, the operation of the intake / exhaust valve of the cylinder is stopped immediately before the rotation due to the inertia of the engine stops, and the piston is forcibly stopped by the compression reaction force.
Japanese Utility Model Publication No. 60-128975 Special table 2003-517134 gazette

  However, in the conventional idle stop system as described above, the engine is automatically stopped without depending on the operation of the ignition switch, and therefore vibrations caused by the vibration of the engine at the time of the stop may cause the driver to feel uncomfortable. There is. That is, in general, the engine is stopped after several revolutions due to inertia after the fuel supply is stopped, but immediately before the stop, the rotation speed decreases, and the fluctuation cycle of the rotation speed associated with the pump work of each cylinder is reduced. Because it becomes very long, low-frequency vibrations that are uncomfortable for humans occur.

  In particular, in the case where the startability is ensured as in the conventional example, after the fuel supply is stopped, for example, the throttle valve is opened to increase the intake flow rate to each cylinder, thereby scavenging the burned gas. However, in this case, the amount of air charged in each cylinder increases, and the compression reaction force increases. Therefore, fluctuations in the rotational speed of the engine increase, and the above-mentioned vibration tends to be a problem.

  The present invention has been made in view of such a point, and an object of the present invention is to automatically stop the engine when idling and to restart the engine in a cycle immediately before the engine stops. Focusing on long fluctuations in rotational speed, and reducing this is to suppress the occurrence of unpleasant shaking.

  In order to achieve the above object, in the present invention, fuel is injected and supplied into the cylinder immediately before the engine is stopped, and then in the compression stroke of the cylinder that does not reach the exhaust stroke until the engine is stopped. Air was cooled by latent heat to reduce the compression pressure.

  More specifically, the invention of claim 1 restarts without using a starting motor by injecting and supplying fuel into at least the cylinder in the expansion stroke of a stopped multi-cylinder engine, and igniting and burning it. For the engine starting device as described above, by stopping the fuel supply to each cylinder of the engine in operation, the engine stopping means for stopping the engine, and the engine from the stop of the fuel supply by the engine stopping means Stop cylinder estimation means for estimating at least one of cylinders that stop in the expansion stroke and compression stroke in the stop operation period until stop, and the cylinder estimated by the stop cylinder estimation means is the last compression stroke before the engine is stopped And a fuel injection control means for injecting fuel into the cylinder by the fuel injection valve.

  With the above configuration, during the operation of the engine, the fuel supply to each cylinder is stopped by the engine stop means, and in the stop operation period until the engine stops, first, the compression stroke is reached until the engine stops, In addition, a cylinder that does not reach the exhaust stroke, that is, a cylinder that is in either the expansion stroke or the compression stroke after the engine is stopped is estimated by the stop cylinder estimation means. When the cylinder is in the final compression stroke before the engine is stopped, the fuel injection valve of the cylinder is operated by the fuel injection control means, and fuel is injected into the cylinder. The air is cooled by the latent heat generated during vaporization in the compression stroke cylinder, and the compression pressure is reduced. As a result, fluctuations in the rotational speed of the engine are reduced, and vibration is suppressed.

  Since the cylinder into which the fuel is injected as described above does not reach the exhaust stroke until the subsequent engine stop, there is no fear that the fuel is discharged in an unburned state.

  In the invention of claim 2, the fuel injection control means injects fuel in the latter half of the compression stroke of the cylinder estimated by the stop cylinder estimating means. This is because by injecting the fuel after the temperature of the air in the cylinder has become sufficiently high by the compression operation, the fuel efficiently takes heat from the high-temperature air and vaporizes.

  Here, the cylinder estimation by the stopped cylinder estimation means can be performed based on, for example, the engine rotation speed or a decrease state thereof (at least one of the detection value of the engine rotation speed itself or the change state of the detection value). . That is, since cylinder identification is generally performed during operation of a multi-cylinder engine, it is possible to easily detect which stroke each cylinder is at a certain point in time, and stop from that point. It can be estimated how much the engine will rotate by inertia based on the engine speed, its reduced state, or the state of external load, etc. You can estimate whether to stop.

  According to a third aspect of the present invention, the stopped cylinder estimating means estimates the cylinder that stops in the expansion stroke after the engine stops, and the fuel injection control means determines that the estimated cylinder is the last cylinder before the engine is stopped. It is assumed that fuel is injected into this cylinder before the compression top dead center is exceeded.

  Thus, when the cylinder estimated to stop in the expansion stroke by the stop cylinder estimating means is in the compression stroke before exceeding the last compression top dead center, the fuel is injected into the cylinder, and the vaporization latent heat of the fuel is injected. As a result, the compression pressure decreases. As a result, the range of decrease in engine rotation speed when passing through the last top dead center is reduced, and fluctuations in engine rotation speed are reduced in the vicinity of the last top dead center where the fluctuation in rotation speed should be considerably large. Since it can be greatly reduced, engine shake can be effectively suppressed.

  According to a fourth aspect of the invention, in the third aspect of the invention, the intake air flow rate adjusting means for adjusting the intake air flow rate to each cylinder of the engine, and the intake air amount of each cylinder increases for a predetermined period in the engine stop operation period. And an intake flow rate control means for controlling the intake flow rate adjustment means. This makes it possible to scavenge the burned gas by increasing the intake air, fill each cylinder with fresh air, and improve the restartability thereafter.

  On the other hand, if the intake flow rate into the cylinder increases in this way, the compression pressure of the cylinder naturally increases, and the fluctuation of the engine rotation speed tends to increase. Therefore, in such a case, it is particularly effective to be able to suppress engine vibration as in the first to third aspects of the invention.

  According to a fifth aspect of the present invention, in the third aspect of the invention, an intake flow rate detecting means for detecting an intake flow rate to each cylinder of the engine is further provided, and the fuel injection control means is based on a detection value by the intake flow rate detecting means. Thus, the fuel injection amount is controlled so that the average air-fuel ratio in the cylinder is leaner than the rich flammability limit value. By doing so, the amount of fuel remaining in the expansion stroke cylinder at the time of stopping remains in the combustible range at the air-fuel ratio with respect to the air in the cylinder, and the ignition performance at the time of restart is ensured.

  By the way, as described above, the estimation of the expansion stroke cylinder after the engine is stopped can be performed based on, for example, the engine rotational speed or a reduced state thereof. It means that the number of revolutions until the engine stops increases, and that the more the mechanical friction of the engine and the pump work are large and the faster the rotation falls, the fewer the number of revolutions until the engine stops. As with the inertia speed, the piston stop position in the cylinder that stops in the expansion stroke is also affected by the rotational inertia of the engine, mechanical friction, and the like. It can be estimated based on the lowered state.

  Here, as described above, the piston stop position of the expansion stroke cylinder is very important for ensuring the restartability of the engine, and normally the cylinder of the cylinder that is in the expansion stroke and the compression stroke when the engine is stopped. Due to the balance of the compression reaction force, the piston stops at a position relatively suitable for restarting in the vicinity of the center of the stroke. However, as in the first to fifth aspects of the present invention, when fuel injection is performed to suppress the vibration immediately before the engine is stopped, the piston stop position may change due to the fuel injection. is there.

  With respect to this point, the invention according to claim 6 is the piston stop position estimating means for estimating the piston stop position of the cylinder that stops in the expansion stroke based on the engine speed or the reduced state thereof in the invention of claims 3 to 5. The fuel injection control means corrects the fuel injection amount based on the estimated piston stop position.

  More specifically, the piston includes rotation speed detecting means for detecting engine rotation speed (top dead center rotation speed) when each cylinder sequentially passes through the compression top dead center during the engine stop operation period. The stop position estimation means estimates that the piston stop position is relatively close to the bottom dead center if the detection value by the rotation speed detection means is relatively high, while the detection value is relatively If it is on the low rotation side, it is assumed that the piston stop position is relatively close to the top dead center. The fuel injection control means corrects the fuel injection amount so as to be relatively small when the piston stop position estimating means estimates that the piston stop position is relatively close to bottom dead center. When it is estimated that the stop position is relatively close to the top dead center, the fuel injection amount is corrected to be relatively large (the invention of claim 7).

  Thus, based on the top dead center rotation speed detected immediately before the engine is stopped, the piston stop position of the cylinder that stops in the expansion stroke is shifted from the position suitable for restart to either the top dead center or the bottom dead center. When the amount of fuel injected into the cylinder is corrected in the final compression stroke before the engine stops, the degree of decrease in the compression pressure of the cylinder due to the latent heat of vaporization is changed. The engine rotation speed when the cylinder passes the final compression top dead center is corrected so that the position of the piston that stops in the subsequent expansion stroke approaches the position suitable for the restart.

  That is, when it is estimated that the piston stop position of the cylinder that stops in the expansion stroke is relatively shifted toward the bottom dead center from the position suitable for restart, the fuel injection amount is corrected to decrease and the cylinder is compressed by the latent heat of vaporization. The degree of pressure drop is reduced. As a result, the engine speed when the cylinder passes through the last compression top dead center is relatively low, and the piston stop position is corrected closer to the top dead center. On the other hand, when it is estimated that the piston stop position is relatively close to the top dead center, the degree of decrease in the compression pressure of the cylinder is increased by correcting the increase in the fuel injection amount. It will be corrected to the side.

  As described above, in the inventions of claims 6 and 7 in which the fuel injection amount is corrected based on the top dead center rotational speed, the invention of claim 8 includes the same piston stop position estimating means as those inventions, The fuel injection timing is corrected based on the piston stop position estimated by the piston stop position estimating means.

  That is, the engine is provided with a rotation speed detecting means for detecting the engine rotation speed when each cylinder sequentially passes the compression top dead center during the engine stop operation period, and the piston stop position estimation means is detected by the rotation speed detection means. If the value is on the relatively high rotation side, it is estimated that the piston stop position is relatively close to the bottom dead center. On the other hand, if the detection value is on the relatively low rotation side, the piston stop position is relatively It is assumed that it is close to top dead center. The fuel injection control means corrects the fuel injection timing to be relatively retarded when the piston stop position estimating means estimates that the piston stop position is relatively close to the bottom dead center. On the other hand, when it is estimated that the piston stop position is relatively close to top dead center, the fuel injection timing is corrected to be relatively advanced (invention of claim 9).

  By correcting the timing of injecting fuel into the compression stroke cylinder before passing through the last compression top dead center based on the top dead center rotation speed detected immediately before the engine is stopped, By adjusting the engine rotation speed when passing through the last compression top dead center, the stop position of the piston in the subsequent expansion stroke can be brought close to a position suitable for restart. In other words, if the fuel injection timing to the compression stroke cylinder is corrected to the advance side, the compression pressure of the cylinder that becomes the resistance of engine rotation can be reduced early, so that it passes the compression top dead center accordingly. When the engine speed increases, the piston stop position changes toward the bottom dead center. On the other hand, if the fuel injection timing is changed to the retard side, the engine rotation speed when passing through the compression top dead center becomes relatively low, so that the piston stop position changes closer to the top dead center.

  As described above, according to the engine starter according to the first to fifth aspects of the present invention, in the control system that automatically stops and restarts the engine when idling, immediately before the engine stops. Estimate at least one of the cylinders that will be in the compression stroke and will not reach the exhaust stroke, that is, the cylinder that will be in either the expansion stroke or the compression stroke after the engine is stopped, and inject the fuel in the compression stroke of this cylinder Since the compression pressure is reduced by the cooling effect due to the latent heat of vaporization, fluctuations in the rotational speed immediately before the engine is stopped can be reduced and the fluctuation can be suppressed. At that time, since the cylinder into which the fuel is injected does not reach the exhaust stroke before the engine is stopped, there is no fear that the fuel is discharged in an unburned state.

In addition, according to the inventions of claims 6 to 9, the piston stop position is suitable for restart by correcting the amount of fuel injected into the compression stroke cylinder immediately before engine stop and the injection timing thereof as described above. The restartability can be secured stably.

  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 valve for each cylinder is set.

  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. The intake passage 21 upstream of the surge tank 21b is a common intake passage 21c common to the cylinders 12A to 12D. The passage 21c is a throttle that restricts the intake flow by adjusting the cross-sectional area of the passage by a butterfly valve, for example. A valve 23 (intake flow rate adjusting means) and an actuator 24 for driving the valve 23 are provided. Further, as shown only in FIG. 2, the intake air amount is detected on the upstream side and the downstream side of the throttle valve 23, respectively. An air flow sensor 25 (intake flow rate detection means) for detecting the intake pressure (negative pressure) and an intake pressure sensor 26 for detecting intake pressure are provided.

  The engine 1 is provided with an alternator 28 that is drivingly connected to the crankshaft 3 by a belt or the like. Although not shown in detail, the alternator 28 includes a regulator circuit 28a that changes the output voltage by controlling the current of the field coil and thereby adjusts the amount of power generation, and the regulator circuit 28a includes the ECU 2. By inputting a control command (for example, voltage) from the vehicle, the amount of power generation is basically controlled in accordance with the electric load of the vehicle electrical component and the in-vehicle battery voltage. When the power generation amount of the alternator 28 is changed in this way, the driving force, that is, the magnitude of the external load of the engine 1 changes accordingly.

  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 is detected by a signal from one crank angle sensor 30 (rotation speed detecting means). The rotation speed is obtained and, 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. It has become. 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, first, the piston 13 stops in the middle of the compression stroke. The first combustion is performed in the cylinder 12, and the piston 13 is pushed down, so that the crankshaft 3 is slightly reversed. As a result, the piston 13 of the cylinder 12 in the expansion stroke is temporarily raised, and the cylinder 12 Compress the air-fuel mixture inside. Then, the engine 1 is started by applying a forward torque to the crankshaft 3 by igniting and burning the air-fuel mixture in the expansion stroke cylinder 12.

  As described above, in order to start the engine 1 only by its own power, the crankshaft 3 is given as much torque as possible in the normal rotation direction by the combustion of the expansion stroke cylinder 12 described above. The cylinder 12 that reaches a point (hereinafter abbreviated as TDC) must overcome the compression reaction force (compression pressure) and exceed the TDC. Therefore, in order to start the engine 1 reliably, it is necessary to ensure sufficient air for combustion in the cylinders 12 that are stopped during the expansion stroke.

  More specifically, in the cylinders 12 and 12 that are respectively in the expansion stroke and the compression stroke when the engine 1 is stopped (hereinafter also referred to as the stop expansion stroke cylinder and the stop compression stroke cylinder), as shown in FIG. Since the phase is shifted by 180 ° and the piston 13 operates in the opposite phase, if the piston 13 of the expansion stroke cylinder 12 stops closer to the bottom dead center (hereinafter abbreviated as BDC) than the center of the stroke, Although the amount of air in the cylinder 12 increases and a large torque is obtained by combustion, if the piston 13 is stopped too close to the BDC, the amount of air in the compression stroke cylinder 12 decreases, and the torque for reversing the engine 1 Cannot be obtained sufficiently.

  In this regard, if the piston 13 of the expansion stroke cylinder 12 is stopped within a predetermined range R (ATDC 100 to 120 ° CA in the illustrated example) slightly close to the BDC from the center of the stroke, an appropriate amount of air is supplied to the compression stroke cylinder 12. It is possible to perform reverse operation by the first combustion here, and the amount of air in the expansion stroke cylinder 12 is increased, so that the torque by the combustion here is sufficiently increased to ensure startability. It can be done.

  Therefore, when the engine 1 is automatically stopped during idling, first, the fuel is cut at a predetermined rotational speed slightly higher than the idle rotational speed so that the scavenging of each of the cylinders 12A to 12D is sufficiently performed, and the throttle is throttled for a predetermined period. The valve 23 is opened and controlled so as to have a preset opening. By appropriately setting the timing for closing the throttle valve 23 thus opened, the amount of air sucked into the stop expansion stroke cylinder 12 and the stop compression stroke cylinder 12 is sufficiently increased, and the expansion is performed. The air amount of the stroke cylinder 12 can be made larger than that of the compression stroke cylinder 12. By doing so, the probability that the piston 13 of the expansion stroke cylinder 12 stops somewhat within the predetermined range R near the bottom dead center (BDC) from the center of the stroke increases due to the balance of the compression pressures of the two cylinders 12. .

  On the other hand, by opening the throttle valve 23 in this way, if the amount of intake air into each cylinder 12A-12D increases, naturally the compression reaction force of each cylinder 12A-12D also increases. The shaking may increase and the driver may feel uncomfortable. That is, in a state where the engine rotational speed immediately before the stop is very low, the fluctuation cycle of the rotational speed derived from the pump work of the cylinders 12A to 12D becomes very long and low frequency fluctuations occur. Since the backlash accompanying the reverse operation of the engine 1 is also low frequency, the driver feels uncomfortable when these swings become large.

  In this embodiment, as will be described in detail later, in this embodiment, when the stop expansion stroke cylinder 12 and the stop compression stroke cylinder 12 are respectively in the compression stroke immediately before the engine 1 is stopped, By injecting fuel into the air and cooling the air by its vaporization latent heat, thereby reducing the compression pressure, the fluctuation of the rotational speed when the stop-time expansion stroke cylinder 12 passes through the last TDC is reduced, While suppressing the swing of the engine 1, the swing due to the subsequent reverse operation is also suppressed.

-Engine stop control-
Next, engine stop control by the ECU 2 will be described with reference to FIGS. 4 and 5 are flowcharts showing the procedure of the stop control, and FIG. 6 shows the engine rotation during the period from the fuel cut to the inertial rotation of the engine 1 (hereinafter also referred to as a stop operation period). Changes in speed, crank angle, and stroke of each cylinder 12A to 12D are shown in association with each other, and the control of the throttle opening performed during that time and the change in intake pressure (intake pipe negative pressure) thereby are schematically shown. It is explanatory drawing shown.

  FIG. 7 is a diagram showing the 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. FIG. 8 is an explanatory diagram showing a state in which the fluctuation state of the engine speed changes due to fuel injection into the compression stroke cylinder 12 immediately before the engine is stopped.

  First, as shown in FIG. 6 (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 and 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. Therefore, in this embodiment, as shown in FIG. 6 (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. 7, 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. Note that there is a clear correlation between (the top dead center rotational speed described in the claims and 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. Then, as shown in FIG. 6 (a), the TDC rotational speed for each 180 ° CA is detected in the process of decreasing the engine rotational speed, and the power generation amount of the alternator 28 and the throttle valve 23 are detected according to the detected value. By controlling the opening, the degree of decrease in the engine speed is adjusted.

  Specifically, FIG. 7 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. Is within the range R (ATDC 100 to 120 ° CA) suitable for restarting.

  As described above, the specific range of the TDC rotational speed at which the piston 13 of the expansion stroke cylinder 12 stops in the predetermined range R suitable for restarting the engine 1 is hereinafter referred to as an appropriate rotational speed range in this specification. Shall. In this embodiment, as will be described in detail below, when the engine speed decreases while repeating up and down as shown in FIG. 6 (a), the TDC rotation speed for each cylinder 12A to 12D is detected. Then, the detected value is compared with the appropriate rotational speed range, and the power generation amount of the alternator 28 and the opening degree of the throttle valve 23 are controlled according to the speed deviation between them.

  That is, first, during a predetermined period immediately after the fuel cut, as described above, the throttle valve 23 is opened relatively large for scavenging of each of the cylinders 12A to 12D. Even if the throttle opening is further adjusted, the cylinder Since the pump work of 12 does not change so much, it is difficult to adjust the engine speed. Therefore, during this time, the alternator 28 is intentionally operated to generate power, and the amount of power generation is controlled by changing the magnitude of the power generation driving force for that purpose, thereby adjusting the degree of decrease in the engine rotation speed. At this time, the power generation amount of the alternator 28 is controlled to be large so that the TDC rotation speed is close to the lower limit of the appropriate rotation speed range, that is, the engine rotation is slightly lowered.

  Further, after the predetermined period has elapsed, the degree of decrease in the engine rotation speed is adjusted by adjusting the pump work amount of the engine 1 by controlling the opening degree of the throttle valve 23. However, in the case of the throttle valve 23 arranged upstream of the surge tank 21b, the change in the intake air amount of each of the cylinders 12A to 12D is slow even if the throttle valve 23 is controlled to close, so that the engine is previously controlled by the alternator 28 as described above. Only when the TDC rotational speed is lower than the appropriate rotational speed range, the throttle opening is controlled to the open side so that the decrease in the engine rotational speed is moderated. ing.

  As described above, the degree of decrease in the engine rotation speed is adjusted by the power generation control of the alternator 28 and the control of the opening degree of the throttle valve 23, and the TDC rotation speed is within the proper rotation speed range before passing the last TDC at the latest. If so, the kinetic energy of the moving parts such as the crankshaft 3, the flywheel, or the piston 13 and the connecting rod at this time, or the potential energy of the high pressure air of the compression stroke cylinder 12 acts thereafter. It becomes commensurate with friction or the like, and the piston 13 of the cylinder 12 in the expansion stroke when the engine 1 is stopped can be stopped within the predetermined range R suitable for the restart.

  By the way, as shown in FIG. 6 (a) and FIG. 8, the rotational speed fluctuation (up / down) of the engine 1 gradually increases as the engine rotational speed decreases and the fluctuation period becomes longer. In the state immediately before the stop as shown in FIG. 8, the vibration of the engine 1 caused by a large rotational speed fluctuation before and after passing through the last TDC becomes a low frequency objectionable for humans. The same applies to the swaying that occurs with the subsequent reverse rotation of the engine 1.

  In addition, as described above, when the engine 1 is automatically stopped, the throttle valve 23 is opened for scavenging and the like, and in particular, the intake amount of the stop expansion stroke cylinder 12 and the stop compression stroke cylinder 12 is thereby reduced. Since the compression reaction force increases, the fluctuation range of the rotational speed at the last TDC increases, the fluctuation of the engine 1 increases, and the subsequent fluctuation also increases, causing the driver to feel uncomfortable. There is a strong fear of feeling.

  In this embodiment, as shown in FIG. 8 with reference numerals Inj1 and Inj2, first, the cylinder 12 in the compression stroke before passing through the last TDC before the engine is stopped, that is, the last of them, A predetermined amount of fuel is injected at an appropriate timing (Inj1) into the stop-time expansion stroke cylinder 12 (# 2 cylinder 12B in the example shown in the figure) that shifts to the expansion stroke beyond the TDC of the cylinder, and the cylinder is caused by the latent heat of vaporization. The air in 12 is cooled to reduce the compression reaction force (compression pressure). By doing this, as shown by the wavy line in the figure. The fluctuation of the engine rotation speed when passing through the last TDC is effectively reduced, and the fluctuation of the engine 1 is reduced.

  Further, a predetermined amount of fuel is also applied to the compression stroke cylinder 12 at the time of stop (the # 1 cylinder 12A in the example shown in the figure) after the engine 1 is reversely rotated without exceeding the next TDC. Is injected (Inj2), and the air in the cylinder 12 is cooled by the latent heat of vaporization, thereby reducing the compression pressure of the cylinder 12. As a result, the compression pressure of the air in the stop compression stroke cylinder 12 becomes sufficiently high, and the pressure of the air can be reduced in a state where the engine 1 is hardly moving. The force applied to the engine in the reverse direction of the engine is reduced, and the backlash can be suppressed.

  Next, the specific procedure of the engine stop control described above will be described with reference to the flowcharts of FIGS. 4 and 5. This flow starts at a predetermined timing during engine operation (START), and in step SA1, idle stop is performed. Whether or not the condition (IDL Stop condition) is satisfied is determined. 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 idle stop condition is satisfied in step SA1 (in the case of YES), in the subsequent step SA2, a predetermined condition for specifying any one cylinder 12 (for example, the first cylinder 12A) and stopping the engine is set. Judgment is made as to whether or not established. 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 increases, and sufficient scavenging is performed.

  Subsequently, in step SA5, it is determined whether or not the TDC rotational speed obtained from the signal from the crank angle sensor 30 is within an appropriate rotational speed range (is the rotational speed at TDC within a predetermined range?). If this determination is YES and the TDC rotational speed is in the appropriate rotational speed range, the process proceeds to step SA6, where it is determined whether the engine rotational speed is equal to or lower than the predetermined rotational speed. This predetermined rotational speed takes into account the intake transport delay, and as shown in FIGS. 6 (c) and 6 (d), the intake amount to the stop expansion stroke cylinder 12 (# 2 cylinder 12B in the example) is compressed when stopped. This is for closing the throttle valve 23 at a timing higher than that of the stroke cylinder 12 (# 1 cylinder 12A in the figure), and corresponds to the time t2 in the figure, and in this embodiment, for example, about 500 to 600 rpm. Is set in the range. If the engine rotational speed is equal to or lower than the predetermined rotational speed (YES in step SA6), the process proceeds to step SA9 described later. On the other hand, if the engine rotational speed is higher than the predetermined rotational speed (in the case of NO), the process proceeds to step SA5. Return.

  If it is determined in step S5 that the TDC rotational speed is not within the proper rotational speed range (in the case of NO), the process proceeds to step SA7, and based on the rotational speed deviation between the TDC rotational speed and the proper rotational speed range. The power generation amount of the alternator 28 is calculated. This power generation amount is read from, for example, a map set in advance according to the engine rotation speed, the speed deviation from the appropriate rotation speed range, and the current power generation amount. For example, the TDC rotation speed is higher than the upper limit of the appropriate rotation speed range. Sometimes, the power generation amount of the alternator 28 is increased so that the load on the engine 1 is increased, while when the TDC rotational speed is lower than the lower limit of the appropriate rotational speed range, the power generation amount is decreased so that the load on the engine 1 is decreased. is there. In the map, the target value of the power generation amount is set to be large so that the TDC rotational speed is near the lower limit of the appropriate rotational speed range.

  In step SA8 following step SA7, a control command is output to the regulator circuit 28a of the alternator 28 according to the calculation result (alternator power generation). By adjusting the load of the engine 1 by the power generation operation of the alternator 28, the trajectory of the rotational speed of the engine 1 rotating by inertia is shifted to either the high rotation side or the low rotation side, and gradually becomes the target. Approach the trail. If the engine rotational speed becomes equal to or lower than the predetermined rotational speed in step SA6 (YES), the process proceeds to step SA9 and the throttle valve 23 is closed (throttle close).

  Subsequently, in step SA10, it is determined whether the TDC rotational speed is in the appropriate rotational speed range as in step SA5. If the determination is YES and the TDC rotational speed is in the appropriate rotational speed range, the process proceeds to step SA11. If it is determined that the TDC rotational speed is not within the proper rotational speed range (in the case of NO), the process proceeds to step SA12, and the opening of the throttle valve 23 is calculated based on the deviation of the TDC rotational speed from the proper rotational speed range. To do. The throttle opening is read from a map set in advance according to, for example, the engine speed, the speed deviation from the appropriate speed range, and the current opening, and the TDC speed is lower than the lower limit of the proper speed range. In some cases, the throttle opening is increased so that the pump work of the engine 1 is decreased, while the throttle control is set not to be performed when the TDC rotational speed is higher than the upper limit of the appropriate rotational speed range.

  In other words, when the throttle valve 23 upstream of the surge tank 21b is used, the response delay toward the throttle side of the intake air becomes large and sufficient controllability cannot be obtained. Is increased, the degree of decrease in engine rotational speed is increased (lower rotational speed), and the throttle valve 23 is driven to open only when the TDC rotational speed is lower than the lower limit of the appropriate rotational speed range. As a result, the degree of decrease in engine speed is moderated. In step SA13, the actuator 24 of the throttle valve 23 is driven (throttle driving), and the process proceeds to step SA11.

  By controlling the alternator 28 and the throttle valve 23 as described above, the degree of decrease in the engine speed after the fuel cut is adjusted to gradually decrease while repeating up and down as shown in FIG. 6 (a) and FIG. It is possible to gradually correct the engine rotational speed trajectory to be within the appropriate rotational speed range by the last TDC at the latest.

  In step SA11, it is determined whether or not the detected TDC rotational speed is equal to or less than a predetermined value A. This predetermined value A is set in association with the TDC rotational speed from the last before the engine stop determined experimentally in advance. If the TDC rotational speed determined in step SA10 is equal to or smaller than the predetermined value A, (If the determination is YES), it is determined that the engine 1 has passed the second TDC from the end and may pass the next TDC, but will not pass the next TDC. The process proceeds to step SA14 in FIG. On the other hand, if the TDC rotational speed is higher than the predetermined value A (when the determination is NO), the engine 1 has not yet passed through the second TDC from the last, so the control of the throttle valve 23 described above should be continued. Return to step SA10.

  On the other hand, in step SA14 of FIG. 5 which proceeds with a determination of YES in step SA11, it is determined whether or not the TDC rotation speed (detection value) is equal to or smaller than a predetermined value B. This predetermined value B is experimentally obtained in advance in the same manner as the predetermined value A and is set in association with the last TDC rotational speed before the engine is stopped. If the TDC rotational speed is equal to or lower than the predetermined value B ( If the determination is YES), the engine 1 has already passed the last TDC, so the process proceeds to step SA17 described later. If the TDC rotational speed is higher than the predetermined value B (if the determination is NO), then Since the TDC to be greeted is the last TDC, the process proceeds to steps SA15 and SA16, and before the cylinder 12 (# 2 cylinder 12B shown in FIG. 8) in the compression stroke exceeds the last TDC, The fuel is injected into the fuel (injecting fuel into the compression stroke cylinder), and the process returns to step SA14.

  That is, fuel is injected and supplied to the compression stroke cylinder 12 that reaches the final TDC before the engine is stopped (the expansion stroke cylinder at the time of stopping after the TDC is stopped in the expansion stroke). By cooling the air and reducing the compression pressure, it is possible to greatly reduce the rotational speed fluctuation at the last TDC where the rotational speed fluctuation should be the largest during normal rotation. Unpleasant shaking of the engine 1 can be suppressed.

  Here, the calculation of the fuel injection amount to the stop-time expansion stroke cylinder 12 is set in advance in association with the flow rate of the intake air detected by the air flow sensor 25 and the TDC rotational speed in step SA15. This is done by reading the fuel injection amount from the map. In this map, the target value of the fuel injection amount is set so that the air-fuel ratio in the cylinder 12 does not become excessively rich even if fuel is injected into the stop-time expansion stroke cylinder 12 at the time of restart to be described later. Basically, it is set to be leaner than the theoretical air-fuel ratio.

  In the map, the target value of the fuel injection amount is corrected to decrease when the TDC rotational speed is relatively high within the range of the predetermined values A to B (close to the predetermined value A). On the other hand, when the TDC rotational speed is relatively low (close to the predetermined value B), an increase correction is made accordingly, and even when such an increase correction is performed, The air-fuel ratio in the cylinder 12 is set to be leaner than the rich flammability limit (for example, A / F = 7 to 8).

  The reason for correcting the fuel injection amount according to the TDC rotational speed as described above is that the piston stop position changes due to the fuel injection to the compression stroke cylinder 12 immediately before the engine is stopped. That is, when the expansion stroke cylinder 12 at the time of stop is in the compression stroke before exceeding the last TDC, if the fuel is injected into the cylinder 12 to reduce the compression reaction force, the final TDC is obtained as a result. When the engine speed exceeds the value, the rotational inertia force at that time increases, and the stop position of the piston 13 in the stop expansion stroke cylinder 12 is considered to change relatively toward the BDC (however, the compression reaction If the force decreases, the increase in engine rotation speed during the expansion stroke after passing through the TDC also slows down, so the change in the piston stop position does not become too large).

  Therefore, if it is estimated that the piston stop position is slightly deviated from the predetermined range R toward the TDC based on the TDC rotational speed detected in the penultimate TDC, the fuel injected into the compression stroke cylinder 12 To increase the engine speed so that the engine speed when the final TDC is exceeded is relatively high. On the other hand, when it is estimated that the piston stop position is deviated toward the BDC, the fuel injection amount is decreased. The engine speed when the final TDC is exceeded is relatively low.

  That is, in the above flow, the piston stop position of the cylinder 12 that becomes the expansion stroke after the stop is estimated on the basis of the second TDC rotational speed from the end before the engine stop, and according to this, the last stop in the cylinder 12 is estimated. The piston stop position is corrected by correcting the amount of fuel injected in the compression stroke. The fuel injection timing is preferably in the second half of the compression stroke. This is because by injecting the fuel after the temperature of the air in the cylinder 12 has become sufficiently high by the compression operation, the fuel efficiently takes heat from the high-temperature air and vaporizes.

  As described above, if the engine 1 passes through the last TDC, the TDC rotational speed detected in the last TDC is equal to or less than the predetermined value B. Therefore, it is determined YES in the returned step SA14, Proceed to step SA17. In this step SA17, it is determined whether the engine 1 has been reversed based on the crank angle signals output from the two crank angle sensors 30, 31 by a subroutine described later (see FIGS. 9 and 10). . If the determination is NO, the process waits until the engine is reversely rotated. If the determination is YES when the engine 1 is reversely rotated, in step SA18, the cylinder 12 in the compression stroke at that time (the compression stroke cylinder at the time of stop). : It is determined whether or not # 1 cylinder 12A shown in FIG. 8 is in a predetermined crank angle range before TDC (predetermined crank angle range?).

  The determination of the crank angle is based on the fact that the piston 13 of the compression stroke cylinder 12 that is separated from the TDC toward the BDC by the reverse rotation operation of the engine 1 is more than a certain distance, and the fuel injected from the fuel injection valve 16 is separated from the TDC. It is for judging that it was in the state which did not adhere so much to the crown surface of. Therefore, if it is determined in step SA18 that the crank angle is within the predetermined crank angle range (if the determination is YES), the process immediately proceeds to steps SA19 and SA20 to inject fuel into the stop-time compression stroke cylinder 12 during reverse rotation. Thereafter, the process proceeds to step SA21.

  That is, after the stop expansion stroke cylinder 12 has shifted to the expansion stroke beyond the last TDC as described above, the compression of the cylinder 12 that has shifted to the compression stroke (stop compression stroke cylinder stopped in the compression stroke as it is). After the pressure is increased and thus the engine 1 starts the reverse operation, the fuel is also injected into the cylinder 12 to cool the high-temperature and high-pressure air, thereby reducing the pressure. As a result, the compression pressure in the engine reverse direction applied to the piston 13 in the compression stroke cylinder 12 can be reduced, and the backlash of the engine 1 can be reduced.

  In other words, the compressed air is cooled by the latent heat of vaporization of the injected fuel in a state where almost all the kinetic energy of the engine that rotates by inertia is converted into the potential energy of the air in the compression stroke cylinder 12, and the pressure is reduced. By doing so, the kinetic energy of the engine 1 is absorbed very efficiently, and the swinging immediately before stopping is suppressed.

  At this time, also in the step SA19, the fuel injection amount is read from the map based on the intake air flow rate and the TDC rotational speed as in the case of the expansion stroke cylinder 12 at the time of stop (step SA15). Also in this map, the basic target value of the fuel injection amount is set so that the air-fuel ratio becomes lean in accordance with the intake air flow rate. The air-fuel ratio in the cylinder 12 does not become excessively rich even when the fuel is injected, so that the fuel injection forms a highly combustible air-fuel mixture in the vicinity of the spark plug 15 to improve the ignitability. it can.

  Also in the above map, taking into account that the stop position of the piston 13 changes due to fuel injection immediately before the engine 1 is stopped, as in the case of the compression stroke cylinder 12 at the time of stop, the fuel corresponding to the TDC rotational speed is used. The injection amount is corrected. More specifically, the target value of the fuel injection amount in this map becomes 0 if the TDC rotational speed is equal to or higher than a predetermined value (a value smaller than the predetermined value B) set in advance. While the fuel injection is not performed, the fuel injection amount is set to increase as the TDC rotational speed is lower than the predetermined value.

  That is, when the engine rotational speed at the final TDC is lower than the predetermined value, the piston 13 of the expansion stroke cylinder 12 stops closer to the TDC than the predetermined range R suitable for restarting or remains within the range R. In this embodiment, the fuel injection amount to the compression stroke cylinder 12 is changed in accordance with the deviation of the TDC rotational speed from the predetermined value. Then, the compression pressure of the cylinder 12 is appropriately reduced, and thereby the stop position of the piston 13 in the compression stroke cylinder 12 is appropriately changed closer to TDC. As a result, the stop position of the piston 13 in the expansion stroke cylinder 12 changes moderately toward BDC, and is corrected so as to fall within the predetermined range R.

  On the other hand, if the final TDC rotational speed is equal to or higher than the predetermined value, it is estimated that the piston 13 of the expansion stroke cylinder 12 stops at a position relatively close to the BDC in the predetermined range R suitable for restarting. At this time, fuel injection into the compression stroke cylinder 12 is not performed.

  That is, in the step SA19, the piston stop position of the cylinder 12 that becomes the expansion stroke after the stop is estimated based on the last TDC rotational speed before the engine stop, and the compression stroke next to the cylinder 12 is correspondingly estimated. The stop position of the piston 13 in the stop-time expansion stroke cylinder 12 is corrected by correcting the amount of fuel injected to the cylinder 12 (stop-time compression stroke cylinder) that has been shifted.

  As described above, even when fuel is injected when the stop expansion stroke cylinder 12 and the stop compression stroke cylinder 12 are in the compression stroke, the cylinders 12 and 12 are exhausted before the engine stops thereafter. There is no worry that the fuel will be released in an unburned state. Further, the fuel injected into the cylinder 12 in this way is sufficiently vaporized and remains in a state of being mixed with air, and is burned when the engine is restarted, which will be described later.

  In step SA21 following step SA20, the signal from the crank angle sensors 30, 31 indicates that the engine 1 has been stopped several times on the forward rotation side and the reverse rotation side, as described above. Judgment based on. If this determination is YES and it is confirmed that the engine 1 is stopped, the process proceeds to step SA22, and the piston stop position of the cylinder 12 in the expansion stroke is detected by a subroutine described later, and this is stored in the memory of the ECU 2. Thus, 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. 9 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. 10A or FIG. 10B, and the normal rotation and inversion of the engine 1 are thereby performed. Determine.

  More specifically, during forward rotation of the engine, as shown in FIG. 10A, the second crank angle signal CA2 causes a phase delay of about a half pulse width with respect to the first crank angle signal CA1, and the first 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. 10B, 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.

  In the engine stop control flow shown in FIGS. 4 and 5, the engine stop that stops the engine 1 by stopping the fuel supply to the cylinders 12 </ b> A to 12 </ b> D of the operating engine 1 in step SA <b> 3 of FIG. 4. The means 2a is configured, and in steps SA4, SA6 and SA9, the throttle valve 23 is set so that the intake air amount of each cylinder 12A to 12D increases during a predetermined period in the stop operation period after the fuel cut by the engine stop means 2a. An intake flow rate control means 2b for opening the valve is configured.

  Further, in steps SA2, SA5, and SA10 in the figure, in the engine stop operation period after the fuel cut, the stop cylinder estimation that estimates the cylinder 12 (stop expansion stroke cylinder) that stops in the middle of the expansion stroke when the engine stops thereafter. Means 2c is configured. That is, in this embodiment, first, in step SA2, the fuel cut is executed when the specific cylinder 12 (for example, the first cylinder 12A in this embodiment) is in a predetermined stroke (for example, the intake stroke). Thus, it can be estimated that the immediately preceding ignition order cylinder 12 (for example, the second cylinder 12B) stops in the expansion stroke. If the TDC rotational speed for each of the cylinders 12A to 12D is in the vicinity of the appropriate rotational speed range in the course of further decreasing the engine rotational speed, the cylinder (second cylinder 12B) expands at the time of stop as initially estimated. It becomes a stroke cylinder.

  Further, when the stop-time expansion stroke cylinder 12 estimated by the stop cylinder estimating means 2c is in the last compression stroke before the engine is stopped, that is, before the engine is stopped, by steps SA14 to SA16, SA19, SA20 in FIG. Before the final TDC of the cylinder 12 is exceeded, fuel is injected by the fuel injection valve 16 in the latter half of the compression stroke of the cylinder 12, and after the stop-time expansion stroke cylinder 12 has shifted to the expansion stroke beyond the final TDC, the step After the reverse rotation operation of the engine 1 is detected in SA17, the fuel injection control means 2d for injecting fuel by the fuel injection valve 16 is also configured in the cylinder 12 (compression stroke cylinder at the time of stop) in the compression stroke.

  The fuel injection control means 2d corrects the fuel injection amount to the stop-time expansion stroke cylinder 12 in the compression stroke before the last TDC passage according to the TDC rotational speed detected in the second TDC from the last. At the same time, the fuel injection amount to the compression stroke cylinder 12 after passing through this is corrected according to the TDC rotational speed detected in the last TDC (including the case where the fuel injection amount = 0) (including the case where the fuel injection amount = 0). Steps SA15 and SA19).

  In other words, the steps SA15 and SA19 correspond to the piston stop position estimating means 2e for estimating the piston stop position of the stop expansion stroke cylinder 12 based on the TDC rotational speed, and the fuel injection control. The means 2d corrects the fuel injection amount to the compression stroke cylinder 12 before exceeding the last TDC according to the estimation result of the piston stop position based on the second TDC rotation speed from the last, and the last TDC rotation speed. When it is estimated that the piston stop position is relatively close to TDC based on the above, fuel is injected into the compression stroke cylinder 12 after the reverse rotation of the engine 1.

  Further, the fuel injection control means 2d performs the fuel injection to the compression stroke cylinder 12 after exceeding the last TDC as described above after the reverse operation of the engine 1, and this reverse operation is performed by the crank angle sensor. Step SA17 detected based on signals from 30, 31 corresponds to the reverse operation detecting means 2f for detecting the reverse operation before the engine 1 is stopped.

  As described above, according to the engine stop control described in detail, when the engine 1 is automatically stopped by the fuel cut at the time of idling, the throttle valve 23 is opened for the first predetermined period, and after the stop, the cylinders 12 and 12 that are respectively in the expansion stroke and the intake stroke are provided. Each of the required amounts of air is inhaled, and the degree of decrease in engine speed is adjusted by controlling the alternator 28 and the throttle valve 23, so that the piston 13 is reactivated in the expansion stroke cylinder 12 after the engine 1 is stopped. It can be stopped within a predetermined range R suitable for starting.

  In addition, by injecting fuel into the cylinders 12 and 12 in the compression stroke before and after the passage of the last TDC immediately before the engine stop, and reducing the compression pressure of the cylinder 12, fluctuations in the engine rotation speed immediately before the stop are reduced. Thus, the vibration of the engine 1 can be effectively suppressed, and the swinging of the crankshaft 3 due to normal / reverse rotation can also be suppressed. In addition, by correcting the fuel injection amount at that time in accordance with the TDC rotational speed, the stop position of the piston 13 in the stop expansion stroke cylinder 12 can be finally corrected so as to fall within the predetermined range R.

  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, but the engine 1 is stopped. After that, 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, the air in the cylinder 12 leaks immediately. Each of the stroke cylinders 12 is in a state in which fresh air (air) at substantially atmospheric pressure exists in the volume corresponding to the piston stop position.

-Engine start control-
Next, the case of restarting the engine 1 that has been automatically stopped during idling as described above will be described with reference to FIGS. 11 and 12 are flowcharts showing the procedure of start control. FIG. 13 shows the fuel injection and ignition timing for each cylinder 12A to 12D at the time of start and the change of the stroke of each cylinder 12A to 12D. FIG. 4 is a stroke diagram corresponding to an open operation state of an intake / exhaust valve. FIG. 14 is a time series showing how the in-cylinder pressure, generated torque, and engine speed of each cylinder 12A to 12D change due to fuel injection and ignition for each cylinder 12A to 12D at the time of starting. It is a chart.

  First, the specific procedure of the start control will be described based on the flowchart of FIG. 11. This flow starts from the engine stop state (START), and whether or not a predetermined engine restart condition is satisfied in step SB1. judge. 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, based on the stop position of the piston 13 obtained by counting the crank angle signal as described above, the compression stroke cylinder 12 when the engine is stopped (compression cylinder when stopped: cylinder # 1 in FIGS. 13 and 14). 12A) and the expansion stroke cylinder 12 (stop expansion stroke cylinder: # 2 cylinder 12B in FIGS. 13 and 14) are calculated. That is, assuming that the combustion chamber volumes of the cylinders 12A to 12D are obtained from the stop position of the piston 13, and that the cylinders 12A to 12D are almost filled with fresh air at atmospheric pressure as described above, The amount of air in each of the cylinders 12 is calculated.

  Subsequently, in step SB3, the compression stroke cylinder 12 is set to have a predetermined air-fuel ratio (A / F for the first compression stroke cylinder) with respect to the air amount of the compression stroke cylinder 12 at the time of stop calculated in step SB2. Inject fuel. In this case, 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. (A / F ranges from approximately 11 to 14). Since the fuel is injected into the stop-time compression stroke cylinder 12 immediately before the engine 1 is stopped by the engine stop control described above, the actual fuel injection amount is corrected to be reduced accordingly.

  Next, in step SB4, after elapse of a predetermined time set in consideration of fuel vaporization time from fuel injection to the stop compression stroke cylinder 12, the ignition plug 15 of the cylinder 12 is energized to ignite the air-fuel mixture. To do. 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 and the compression is performed. The stroke cylinder 12 is repeatedly ignited.

  On the other hand, when the edge of the crank angle signal is detected in the step SB5 (in the case of YES) and it is determined that the piston 13 has moved, that is, the engine 1 has rotated in the reverse direction, in the subsequent step SB7, the step SB2 The 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 S2. 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. Or, a slightly richer value is set. Note that, as with the stop compression stroke cylinder 12, fuel is injected just before the engine is stopped in the stop expansion stroke cylinder 12, so that the actual fuel injection amount is corrected to decrease accordingly.

  In the following step SB8, the air-fuel mixture in the expansion stroke cylinder 12 at the time of stop is sufficiently compressed by the rise of the piston 13 accompanying the reverse rotation of the engine 1, and a predetermined time until the piston 13 is almost stopped by this compression reaction force. After the elapse of (ignition delay), the expansion stroke cylinder 12 is ignited. By igniting and burning the compressed air-fuel mixture in the expansion stroke cylinder 12 in this way, the engine 1 starts to rotate in the forward rotation direction with a sufficiently large torque. The ignition delay time is roughly the time until the piston 13 of the expansion stroke cylinder 12 reaches the vicinity of TDC after the engine 1 rotates in reverse, and is set in advance in association with the piston stop position when the engine is stopped. Is obtained from the generated map.

  Subsequently, in step SB9, fuel is injected at a timing in consideration of the fuel vaporization time into the compression stroke cylinder 12 at the time of stop when the engine 1 rotates in the forward direction and then reaches TDC. Thereby, the temperature in the compression stroke cylinder 12 is lowered by the latent heat of vaporization of the injected fuel, and the in-cylinder pressure is lowered. Therefore, the compression reaction force of the cylinder 12 accompanying the forward rotation of the engine 1 is reduced, and the piston 13 Can easily exceed TDC. Therefore, the forward rotation operation of the engine 1 started by the combustion of the stop expansion stroke cylinder 12 in step SB8 is continued, the stop compression stroke cylinder 12 exceeds TDC, and each of the cylinders 12A to 12D has the next stroke. It will go on.

  Subsequently, in step SB10 of FIG. 12, the intake stroke cylinder 12 at the time of stop by the forward rotation operation of the engine 1 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 density (in-cylinder air density) of the air charged in (# 3 cylinder 12C in FIGS. 13 and 14) is estimated, and the air amount of the intake stroke cylinder 12 is calculated based on this estimated value. In step SB11, an air-fuel ratio correction value for preventing self-ignition is calculated mainly from the estimated value of the in-cylinder temperature of the intake stroke cylinder 12, and in the subsequent step SB12, the correction value is taken into consideration. Based on the air-fuel ratio and the air amount in the intake stroke cylinder 12 calculated in step SB10, the fuel injection amount to the intake stroke cylinder 12 is calculated. In other words, the intake stroke cylinder 12 at the time of stoppage is prevented from self-ignition due to the compression pressure, the in-cylinder temperature, etc. in the compression stroke that comes first after the engine is started, and the air-fuel ratio is set to minimize the compression reaction force. Correction is performed, and the corrected air-fuel ratio becomes slightly rich, for example, about A / F = 13.

  In step SB13, when the stop-time intake stroke cylinder 12 is in the compression stroke, fuel injection is performed in the middle of the compression stroke. That is, fuel is injected in the intake stroke at the time of starting by a normal starter motor, but in this embodiment, the engine stop time, intake air temperature, and so on are effectively reduced by the latent heat of vaporization of the fuel. In consideration of the cooling water temperature and the like, the fuel is injected in the middle of the compression stroke. As a result, the compression pressure of the stop-time intake stroke cylinder 12 is effectively reduced, and this also prevents self-ignition. Thereafter, the process proceeds to step SB14, and after the stop-time intake stroke cylinder 12 exceeds TDC and shifts to the expansion stroke, the spark plug 15 is energized and ignited. This ignition timing is set to an advance side (compression stroke) with respect to the TDC when the engine is normally started. However, if the starting motor is not used as in this embodiment, the ignition timing is set before the TDC. When ignited, the reverse torque acting on the piston 13 may hinder starting, so that the ignition is performed in the expansion stroke after passing through the TDC.

  Subsequently, in step SB15, it is determined whether or not the intake pressure (intake pipe negative pressure) in the branch intake passage 21a downstream of the throttle valve 23 is higher than that during normal idling operation of the engine 1. If it is determined that this is higher than that during idling (in the case of YES), the process proceeds to step SB16, and the throttle valve 23 is driven so as to be smaller than the throttle opening during idling according to the intake pressure. Then, the amount of air taken into the combustion chamber 14 of the cylinder 12 from the upstream side of the throttle valve 23 is reduced, and the process returns to step SB15. Then, the control of the throttle valve 23 is repeated until the intake pressure becomes the same as that during idle operation. On the other hand, if the intake pressure becomes equal to or less than during idle operation and NO is determined in step SB15, the process proceeds to step SB17. Transition to engine control.

  In the above steps SB15 and SB16, when the air in the surge tank 21b, which is in a state close to the atmospheric pressure while the engine is stopped, is sucked into the cylinder 12 at the time of start-up and becomes fully charged, the engine speed increases rapidly. In consideration of the problem that large vibrations are generated, the intake of air into each of the cylinders 12A to 12D is limited by the throttle valve 23.

  According to the above-described flow, the engine 1 automatically stopped at the time of idling can be restarted without using a starting motor or the like in response to a restart request. That is, as shown in FIGS. 13 and 14, when an engine restart request is made when the engine is stopped when idling (time 0.0 in FIG. 14), first, the cylinder 12 (# 1 in the compression stroke) Fuel is injected into the cylinder 12A) (shown as a1 in both figures. The same applies to the following fuel injection and ignition), thereby igniting the air-fuel mixture formed in the cylinder 12 (a2) The crankshaft 3 is once rotated in the reverse rotation direction (left direction in FIG. 13). As a result, the air in the stop expansion stroke cylinder 12 (# 2 cylinder 12B) is compressed and fuel is injected into the cylinder 12 (a3) to form an air-fuel mixture in the cylinder 12, and this air-fuel mixture is ignited. By doing so (a4), the engine 1 starts to rotate in the normal rotation direction (right direction in FIG. 13).

  Subsequently, before the stop compression stroke cylinder 12 (# 1 cylinder 12A) exceeds TDC, fuel is again injected into the cylinder (a5), thereby reducing the compression pressure of the cylinder 12 and the piston 13 In addition, fuel is injected to the intake stroke cylinder 12 (# 3 cylinder 12C) at the time of stop, which reaches TDC, so that the air-fuel ratio becomes rich, and the fuel By delaying the injection timing from the normal timing (intake stroke) to the middle of the compression stroke (a6), self-ignition is prevented, and in addition to this, the ignition timing is retarded until after TDC ( a7) No reverse torque is generated at all. By burning the intake stroke cylinder 12 at the time of stopping in this way, it is possible to reliably apply the torque in the normal rotation direction to the engine 1, sufficiently increase the engine rotation speed, and ensure startability.

At this time, the throttle valve 23 is controlled to be closed more than in the normal idling operation, so that the stop exhaust stroke cylinder 12 (# 3 cylinder) is ignited and burned following the stop intake stroke cylinder 12 (# 3 cylinder). # 4 Cylinder 12D) is restricted from being charged with intake air, and also in this cylinder, fuel injection and ignition are performed in the same manner as in the above-described stop intake stroke cylinder 12 (a8, a9). The torque applied to the engine 1 due to the combustion of the cylinder 12 is not so great that the engine rotation is prevented from abruptly rising or large vibrations being generated at the start.
-Effect-
Therefore, according to the engine system E (engine starter) of this embodiment, as described above, when the engine 1 automatically stops at the time of idling, first, the fuel of each cylinder 12A to 12D according to the establishment of the stop condition. As the cut is performed, the throttle valve 23 is opened for a predetermined period to increase the intake flow rate of each of the cylinders 12A to 12D, so that the burned gas is sufficiently scavenged, and the expansion stroke and The amount of air in the cylinders 12 and 12 in the compression stroke is sufficiently increased. Further, when the throttle valve 23 is closed at an appropriate timing, the air amount in the expansion stroke cylinder 12 after the stop is larger than the compression stroke cylinder 12 by a predetermined amount, and thus, the piston 13 in the expansion stroke 12 is increased. Stops slightly closer to the BDC than the center of the stroke.

  Further, while the rotational speed of the engine 1 that rotates by inertia is gradually decreased, the engine rotational speed when each of the cylinders 12A to 12D sequentially passes through the TDC is detected, and according to the TDC rotational speed. During the predetermined period, the magnitude of the external load of the engine 1 is adjusted by controlling the power generation amount of the alternator 28, and after the predetermined period, the pumps of the cylinders 12A to 12D of the engine 1 are controlled by controlling the opening degree of the throttle valve 23. The degree of decrease in engine rotation speed is adjusted by adjusting the work amount. As a result, the degree of decrease in the engine rotational speed is corrected so that the TDC rotational speed is generally within the appropriate rotational speed range, and the piston 13 of the expansion stroke cylinder 12 stops in a predetermined range R suitable for restart. Become.

  Further, as shown in FIG. 8, when any one of the cylinders 12 (# 4 cylinder in FIG. 8) passes through the second TDC from the last, the cylinder 12 (in FIG. # 2 cylinder) is injected with fuel in the latter half of the compression stroke (Inj1), and the compression pressure is reduced by the cooling effect of the latent heat of vaporization. As a result, in the vicinity of the last TDC where the rotational speed fluctuation should be considerably large, the amount of decrease in the engine rotational speed, that is, the rotational speed fluctuation is greatly reduced as shown by the wavy line in the figure, and the engine 1 is shaken. Is suppressed.

  Subsequently, the compression stroke cylinder 12 (# 2 cylinder) has shifted to the expansion stroke beyond the last TDC, and the cylinder 12 (# 1 cylinder in the figure) in the next ignition sequence has shifted to the compression stroke. Later, if the engine 1 is reversely operated by the compression reaction force of the compression stroke cylinder 12, fuel is also injected into the cylinder 12 (Inj2). Then, the compressed air in the cylinder 12 is cooled by the latent heat of vaporization of the fuel, and the pressure is reduced, whereby the force in the engine reverse direction applied from the compressed air to the piston 13 is reduced, and the engine 1 is shaken. Return is effectively suppressed.

  In this way, by suppressing the low-frequency vibrations and rebounds of the engine 1 immediately before stopping, the driver can feel uncomfortable even when the engine automatically stops without depending on the ignition operation. Disappear.

  In addition, in this embodiment, as described above, the amount of fuel injected into the cylinders 12 and 12 in the compression stroke before and after the passage of the last TDC is set to the latest TDC rotational speed, that is, the second from the last. Correction is made in accordance with the TDC rotational speed detected at the TDC and the last TDC. For this reason, the TDC rotational speed is deviated from the appropriate rotational speed range at the time of passing through the TDC immediately before the engine is stopped. Even when it is estimated that the piston stop position of the time expansion stroke cylinder 12 deviates from the predetermined range R, the final correction of the piston stop position can be performed by correcting the fuel injection amount.

Thereby, the piston 13 of the expansion stroke cylinder 12 at the time of stop can be more reliably stopped within the predetermined range R, and the good startability as described above can be stably ensured at the time of subsequent engine restart. It is.
-Other embodiments-
In the engine system E of this embodiment, as described above, the amount of fuel injected into the cylinder 12 in the compression stroke immediately before the stop of the engine 1 is corrected according to the most recently detected TDC rotational speed. Although the final correction of the piston stop position is performed, the present invention is not necessarily limited to this.

  That is, for example, for fuel injection performed on the stop-time expansion stroke cylinder 12 before passing through the final TDC, the timing of fuel injection is corrected instead of or in addition to the correction of the fuel injection amount as described above. You may make it do. That is, when the stop-time expansion stroke cylinder 12 is in the compression stroke, if the timing of fuel injection into the cylinder 12 is corrected to the advance side, the compression pressure of the cylinder 12 that becomes the resistance of engine rotation is advanced. Therefore, the engine rotational speed when passing through the TDC becomes relatively high, and the piston stop position can be changed closer to the BDC. Conversely, the fuel injection timing is retarded. If it is changed to the side, the engine rotation speed when passing through the TDC becomes relatively low, so the piston stop position can be changed closer to the TDC.

  On the other hand, with respect to the fuel injection performed to the compression stroke cylinder 12 at the time of stop after passing through the last TDC, in the embodiment, the piston 13 is actually moved relative to the estimated result of the piston stop position based on the last TDC rotational speed. However, the fuel injection is performed only when stopping near the TDC. However, the present invention is not limited to this, and the fuel injection may be performed even when the piston 13 stops relatively close to the BDC.

  Further, when the fuel injection is performed only when the piston stop position is estimated to be relatively close to TDC as in the above-described embodiment, as shown in FIG. The timing can be set before the reverse rotation of the engine 1, that is, before the engine speed becomes negative (Inj2 ').

  Further, in the above-described embodiment, the fuel is injected into the cylinders 12 and 12 in the compression stroke before and after the passage of the last TDC immediately before the engine 1 is stopped. Only the stop expansion stroke cylinder 12 in the compression stroke before the passage may be injected just before the stop, and conversely, only the stop compression stroke cylinder 12 that shifts to the compression stroke after the last TDC passes. Alternatively, fuel injection may be performed.

  Furthermore, in the above embodiment, as shown in steps SA4 to SA9 of the engine stop control flow of FIG. 4, after the fuel cut, the throttle valve 23 that has been opened to a predetermined opening degree is once closed (the predetermined rotational speed in step SA6). Until the following), power generation control of the alternator 28 is performed (steps SA7 and SA8), but power generation control is not performed thereafter. However, the present invention is not limited to this. The end of the predetermined period is determined by one of the time elapsed from the time point, and even after the throttle valve 23 is closed in accordance with this determination, the engine speed is equal to or lower than the predetermined rotation speed at which the alternator 28 can effectively generate power (for example, about The power generation control of the alternator 28 is continued by steps SA5 to SA7 until the pressure reaches 350 rpm or less). It may be.

  In addition, in the engine 1 of the above-described embodiment, the throttle valve 23 upstream of the surge tank 21b is used as the intake flow rate adjusting means for adjusting the intake flow rate to each of the cylinders 12A to 12D. As the flow rate adjusting means, a known variable valve mechanism that changes the lift amount of the intake valve 19 for each cylinder 12A to 12D may be adopted, or the branch intake passage 21a for each cylinder 12A to 12D may be used. It is also possible to use a multiple throttle valve in which valve bodies are individually arranged.

  In the case of using a multiple throttle valve arranged on the downstream side of the intake passage 21 as described above, the intake can be throttled with good responsiveness by controlling the throttle valve to the closed side. It is possible to increase the degree of decrease in engine speed by controlling not only on the opening side as in the case of the side throttle valve 23 but also on the closing side.

  Further, in the start control of the engine 1 in the above embodiment, 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 engine stop control according to the present invention can also be applied to an engine system that first ignites the stop-stroke expansion stroke cylinder 12 and thereby restarts 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 the relationship between the piston stop position of the cylinder which becomes an expansion stroke and a compression stroke, respectively, and an air quantity at the time of an engine stop. It is a flowchart which shows the procedure of the first half of control of an engine automatic stop. It is a flowchart which shows the procedure of the second half of control of 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 explanatory drawing which shows a mode that the fluctuation range of an engine speed changes by the fuel injection to the cylinder in a compression stroke immediately before 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 of the first half of the engine restart at the time of idling. It is a flowchart which shows the control of the second half of the engine restart at the time of idling. FIG. 4 is a stroke diagram showing the fuel injection and ignition timing for each cylinder at the time of engine restart in association with the stroke change of each cylinder and the open operation state of the intake and exhaust valves. 3 is a time chart showing changes in in-cylinder pressure, generated torque, and engine rotation speed for each cylinder when the engine is restarted. FIG. 9 is a view corresponding to FIG. 8 according to another embodiment in which fuel injection into the compression stroke cylinder at the time of stop is performed before the reverse rotation operation of the engine.

Explanation of symbols

E Engine system (engine starter)
1 Engine 2 ECU (Engine Controller)
2a Engine stop means 2b Intake flow rate control means 2c Stop cylinder estimation means 2d Fuel injection control means 2e Piston stop position estimation means 2f Reverse rotation detection means 12A to 12D Cylinder 13 Piston 16 Fuel injection valve 23 Throttle valve (Intake flow rate adjustment means)
25 Air flow sensor (intake flow rate detection means)
30 Crank angle sensor (rotational speed detection means)

Claims (9)

An engine starter that restarts without using a starter motor by injecting fuel into a cylinder at least in the expansion stroke of a stopped multi-cylinder engine by means of a fuel injection valve and igniting and burning it. Because
Engine stop means for stopping the engine by stopping fuel supply to each cylinder of the engine in operation;
Stop cylinder estimation means for estimating at least one of cylinders that stop in the expansion stroke and the compression stroke in a stop operation period from the stop of fuel supply by the engine stop means until the engine stops;
Fuel injection control means for injecting fuel into the cylinder by the fuel injection valve when the cylinder estimated by the stop cylinder estimation means is in the last compression stroke before engine stop;
An engine starting device comprising:   2. The engine starter according to claim 1, wherein the fuel injection control means injects fuel in the latter half of the compression stroke of the cylinder estimated by the stopped cylinder estimation means. The stop cylinder estimation means estimates the cylinder that stops in the expansion stroke,
3. The engine starting device according to claim 2, wherein the fuel injection control means is configured to inject fuel into the cylinder before the cylinder exceeds the last compression top dead center before the engine is stopped. . An intake flow rate adjusting means for adjusting the intake flow rate to each cylinder of the engine;
An intake air flow rate control means for controlling the intake air flow rate adjusting means so that the intake air amount of each cylinder increases during a predetermined period in the engine stop operation period;
The engine starter according to claim 3, further comprising: Intake flow rate detection means for detecting the intake flow rate to each cylinder of the engine,
The fuel injection control means controls the fuel injection amount so that the average air-fuel ratio in the cylinder is leaner than the rich flammability limit value based on the detection value by the intake flow rate detection means. The engine starting device according to claim 3. A piston stop position estimating means for estimating a piston stop position of a cylinder that stops in the expansion stroke based on the engine rotation speed or a decrease state of the engine rotation speed;
The engine starter according to any one of claims 3 to 5, wherein the fuel injection control means corrects a fuel injection amount based on the estimated piston stop position. Rotational speed detection means for detecting the engine rotational speed when each cylinder sequentially passes the compression top dead center during the engine stop operation period,
The piston stop position estimating means estimates that the piston stop position is relatively close to the bottom dead center if the detection value by the rotational speed detection means is relatively high, while the detection value is relatively If it is on the low rotation side, it is estimated that the piston stop position is relatively close to the top dead center,
The fuel injection control means corrects the fuel injection amount to be relatively small when the piston stop position is estimated to be relatively close to bottom dead center by the piston stop position estimation means, while the piston stop position 7. The engine starting device according to claim 6, wherein the fuel injection amount is corrected so as to be relatively increased when it is estimated that is relatively close to top dead center. A piston stop position estimating means for estimating a piston stop position of a cylinder that stops in the expansion stroke based on the engine rotation speed or a decrease state of the engine rotation speed;
The engine according to any one of claims 3 to 5, wherein the fuel injection control means corrects the fuel injection timing based on the piston stop position estimated by the piston stop position estimation means. Starting device. Rotational speed detection means for detecting the engine rotational speed when each cylinder sequentially passes the compression top dead center during the engine stop operation period,
The piston stop position estimating means estimates that the piston stop position is relatively close to the bottom dead center if the detection value by the rotational speed detection means is relatively high, while the detection value is relatively If it is on the low rotation side, it is estimated that the piston stop position is relatively close to the top dead center,
The fuel injection control means corrects the fuel injection timing to be relatively retarded when the piston stop position estimating means estimates that the piston stop position is relatively close to bottom dead center, The engine according to claim 8, wherein when the piston stop position is estimated to be relatively close to top dead center, the fuel injection timing is corrected to be relatively advanced. Starter.

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