JP4259375B2 - Engine starter - Google Patents

Description

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

In recent years, in order to reduce fuel consumption and reduce CO ₂ emissions, a restart condition has been established such that the engine is automatically stopped temporarily during idling and the vehicle is then started by the driver. At the time, an automatic engine stop control (so-called idle stop control) technique that automatically restarts the engine has been developed. The restart at the time of the idle stop control requires a quickness to immediately start the engine in accordance with the vehicle starting operation or the like. According to the method of restarting the engine through cranking for driving the shaft, there is a problem that it takes a considerable time to complete the starting.

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

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

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

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

  In view of the above circumstances, the present invention can effectively improve the scavenging performance when the engine is automatically stopped, and can reliably restart the engine by stopping the piston at an appropriate position. Is to provide.

According to the first aspect of the present invention, when a preset automatic engine stop condition is satisfied, the fuel supply for continuing the engine operation is stopped to automatically stop the engine, and the automatic stop state is established. In an engine starter configured to restart an engine by injecting fuel into at least a cylinder that is stopped in an expansion stroke to cause ignition and combustion when a certain engine restart condition is satisfied A throttle valve that adjusts an intake flow rate sucked into the cylinder of the engine, an intake pressure detection means that detects an intake pressure downstream of the throttle valve, and an automatic stop operation when the engine is automatically stopped. An intake flow rate state that is a predetermined amount greater than the minimum intake flow rate required to continue engine operation at the first predetermined time in the initial stage; Set so that, and an automatic stop control means for controlling so as to reduce the intake air flow rate subsequently the second predetermined timing, the automatic stop control means after the second predetermined time, the second predetermined An intake pressure at a third predetermined timing provided from the timing to the last compression top dead center passage timing just before the stop is estimated based on the current output of the intake pressure detection means, and the estimated intake pressure is The opening degree of the throttle valve is adjusted by feedback control so as to be within a predetermined target intake pressure range.

  In this specification, “compression top dead center passage” means transition from the compression stroke to the expansion stroke via the top dead center. The last compression top dead center passage time just before the stop indicates the last compression top dead center passage time of all cylinders that have passed the compression top dead center immediately before the stop.

  Further, in this specification, a cylinder that is stopped in the expansion stroke during the automatic stop of the engine as described above, or any cylinder that eventually stops in that state is referred to as an expansion stroke cylinder. Similarly, cylinders corresponding to compression, intake and exhaust strokes are referred to as a compression stroke cylinder, an intake stroke cylinder and an exhaust stroke cylinder, respectively.

  Furthermore, in this specification, the simple term “intake pressure” refers to the pressure detected by the intake pressure detecting means (the pressure downstream of the throttle valve).

  According to a second aspect of the present invention, in the engine starter according to the first aspect, the third predetermined time is one time before the last compression top dead center passage time immediately before the stop (that is, from before the stop). (2) the compression top dead center passage time.

  According to a third aspect of the present invention, in the engine starter according to the second aspect, the target intake pressure range is in the vicinity of an intermediate point between the atmospheric pressure and the intake pressure during normal idle operation in which the engine is not automatically stopped. Or a range set closer to the atmospheric pressure than that.

  In the present specification, the term “normal idle operation (or idle rotation speed)” refers to normal idle operation (or idle rotation speed) when the engine is not automatically stopped as described above.

  According to a fourth aspect of the present invention, there is provided the engine starting device according to any one of the first to third aspects, wherein the automatic stop control means is based on a degree of change in the intake pressure accompanying a decrease in engine rotational speed. Then, a change in the intake pressure accompanying a subsequent decrease in the engine speed is predicted, and based on the prediction, the opening of the throttle valve is adjusted so that the intake pressure at the third predetermined time is within the target intake pressure range. It is characterized by adjusting.

  According to a fifth aspect of the present invention, in the engine starter according to the fourth aspect, the automatic stop control means is configured such that the predicted intake pressure at the third predetermined time deviates from the target intake pressure range. If so, the opening of the throttle valve is adjusted in a direction in which the intake flow rate increases.

  Here, adjusting the opening of the throttle valve in the direction in which the intake flow increases increases, for example, when the throttle valve is operated on and off, the opening is increased (the intake flow is temporarily reduced after the second predetermined time). (Including those performed after decreasing) and increasing the opening time (including those that delay the second predetermined time). In addition, when the opening is continuously changed as in feedback control or the like, it means that the average opening is increased so that the average intake flow rate is increased.

  According to a sixth aspect of the present invention, in the engine starting device according to the fourth or fifth aspect, the automatic stop control means is configured such that the predicted intake pressure at the third predetermined time is higher than the target intake pressure range. When it is off, the opening degree of the throttle valve is adjusted in the direction in which the intake flow rate decreases.

  Here, adjusting the opening degree of the throttle valve in a direction in which the intake flow rate decreases, for example, when the throttle valve is operated on and off, the opening degree is decreased (the intake flow rate is reduced after the second predetermined time). (Including those that are further reduced after the decrease) or the second predetermined time is advanced. In addition, when the opening is continuously changed as in feedback control or the like, it means that the average opening is decreased so that the intake flow rate is decreased.

  A seventh aspect of the present invention is the engine starting device according to any one of the first to sixth aspects, further comprising an alternator driven by the engine, wherein the automatic stop control means is provided at the third predetermined time. The power generation amount by the alternator is adjusted so that the engine rotation speed is within a predetermined target engine rotation speed range.

The present invention according to claim 8 is the engine starter according to any one of claims 1 to 7, wherein the engine is a naturally aspirated four-cycle four-cylinder having a compression ratio of 11 ± 2 (9 to 13). When the engine is automatically stopped, the intake pressure at the compression top dead center passage timing one time before the last compression top dead center passage timing immediately before the stop is −220 ± 40 (−260 to −180). The last compression top dead center so that it becomes mmHg (slightly closer to atmospheric pressure than the middle between the atmospheric pressure and the intake pressure during normal idling operation (generally -600 to -560 mmHg)). The engine rotational speed at the compression top dead center passage time one time before the passage time is configured to be 350 ± 50 (300 to 400) rpm.

According to a ninth aspect of the present invention, in the engine starting device according to any one of the first to eighth aspects, the throttle valve is provided in an independent intake passage for each of the cylinders. Features.

  According to the first aspect of the present invention, when the automatic engine stop condition is satisfied and the automatic engine stop control is executed, the intake air flow rate is the minimum necessary for continuing the engine operation at the first predetermined time. Therefore, it is possible to effectively improve the scavenging performance of the exhaust gas by sufficiently securing the intake air flow rate sucked into each cylinder of the engine. In addition, the intake resistance during this time is also reduced, and the engine speed is prevented from decreasing too quickly. This can increase the number of engine revolutions (intake, compression, expansion, and exhaust strokes) from when the fuel supply is stopped to when the engine is stopped. Can be easily stopped at the target position. Further, since the number of strokes until the engine is stopped increases, the scavenging performance of the exhaust gas can also be improved.

  Then, by reducing the intake air flow rate at the second predetermined time thereafter, the in-cylinder air amount of each cylinder during the automatic stop operation does not increase more than necessary, and the compression reaction force that the piston receives near the compression top dead center Increase is suppressed. By suppressing the increase in the compression reaction force, the rotational fluctuation (increase or decrease in minute rotational speed) is reduced, and vibration and noise can be reduced.

  Further, by appropriately setting the second predetermined time, the intake air flow rate in the final intake stroke to the compression stroke cylinder (the final intake stroke in the cylinder before the engine is stopped) and the final intake air to the expansion stroke cylinder are set. The balance with the intake air flow rate of the stroke can be adjusted. The piston stop position greatly depends on the balance of the intake flow rate, and the piston with the larger intake flow rate tends to stop closer to the bottom dead center side than the piston with the smaller intake flow rate. By using this characteristic and setting the timing (second predetermined timing) for reducing the intake air flow rate to a suitable setting, the piston can be accurately stopped at the target appropriate position.

Further, the intake pressure at the third predetermined time (here, the predetermined time provided between the second predetermined time and the last compression top dead center passage time just before the stop) is within a predetermined target intake pressure range. Thus, the opening degree of the throttle valve is adjusted by feedback control . The intake pressure is closely related to the intake flow rate. If the other conditions are the same, the intake flow rate increases as the intake pressure increases (atmospheric pressure side). That is, by performing feedback control so that the intake pressure at the third predetermined timing closer to the engine stop timing falls within the target intake pressure range, the intake flow rate immediately before the stop can be controlled, and the intake flow rate balance adjustment can be performed. Can be performed with higher accuracy. In other words, the piston can be stopped with high accuracy by the appropriate target position.

  According to the invention which concerns on Claim 2, 3rd predetermined time is made into the 2nd compression top dead center passage time before a stop. The second compression top dead center before the stop is the start point of the final intake stroke in the compression stroke cylinder. Therefore, by setting this time point as the third predetermined time and adjusting the intake pressure to be within the target intake pressure range, the intake flow rate in the final intake stroke in the compression stroke cylinder is more directly controlled. Become. That is, the accuracy of the balance adjustment of the intake air flow rate can be further improved, and the piston can be stopped more accurately at the target proper position.

  According to the third aspect of the invention, the target intake pressure range is set near the middle of the intake air pressure during normal idling operation in which the engine is not automatically stopped or closer to the atmospheric pressure than that. The intake air flow rate in the final intake stroke in the compression stroke cylinder can be set to an appropriate size. For example, by appropriately setting the second predetermined time, the intake flow rate in the final intake stroke in the compression stroke cylinder can be made slightly smaller than that in the expansion stroke cylinder.

  As a result, the piston stop position of the compression stroke cylinder becomes slightly closer to the top dead center from the center (in the expansion stroke cylinder, slightly closer to the bottom dead center from the center). This is because when the engine is started, combustion is first performed in the compression stroke cylinder, and once the engine is reversely rotated, the in-cylinder air of the expansion stroke cylinder is compressed, where the combustion is performed in the expansion stroke cylinder in the forward rotation direction. The piston stop position is suitable when a starting method for rotation is adopted.

  According to the invention according to claim 4, when the intake pressure at the predicted third predetermined time is out of the target intake pressure range, the actual opening amount of the throttle valve is adjusted so as to swing to the opposite side. The intake pressure at the third predetermined time can be set within the target intake pressure range.

  Specifically, by making it as shown in claims 5 and 6 (including feedback control by intake pressure), the intake pressure at the third predetermined time can be more reliably set as the target intake pressure range. .

  Further, the stop position of the piston is also affected by a decrease in engine speed. Therefore, according to the seventh aspect of the present invention, the load applied to the engine (crankshaft) can be adjusted by adjusting the amount of power generated by the alternator, whereby the degree of decrease in engine rotation speed can be adjusted. . That is, the engine speed at the third predetermined time can be adjusted to be within a predetermined target engine speed range. By setting the target engine rotation speed range as a range in which the piston can easily stop at an appropriate position within the range, the piston can be stopped at the target appropriate position with higher accuracy.

According to the eighth aspect of the invention, in the engine starter described above, it is possible to obtain a specification that can specifically execute the control effectively.

According to the ninth aspect of the present invention, since the throttle valve is provided in the intake passage independent for each cylinder, the intake flow rate can be adjusted with higher accuracy and better responsiveness. In particular, such a throttle valve (multi-throttle valve) provided independently for each cylinder performs feedback control that adjusts the throttle opening so that the pressure is within the target pressure range while detecting the intake pressure. It is suitable for carrying out.

  1 and 2 show a schematic configuration of a naturally aspirated four-cycle four-cylinder spark ignition engine having an engine starter according to the present invention. The engine includes an engine main body 1 having a cylinder head 10 and a cylinder block 11 and an ECU 2 for engine control. The engine body 1 is provided with four cylinders (# 1 cylinder 12A, # 2 cylinder 12B, # 3 cylinder 12C, and # 4 cylinder 12D), and a crankshaft 3 is provided in each cylinder 12A-12D. By inserting the connected piston 13, a combustion chamber 14 is formed above the piston 13. The compression ratio is set within a range of 11 ± 2 (9 to 13).

  A spark plug 15 is installed at the top of the combustion chamber 14 of each of the cylinders 12 </ b> A to 12 </ b> D so that the plug tip faces the combustion chamber 14. The ignition plug 15 is provided with an ignition device 27 for generating an electric spark. A fuel injection valve 16 that directly injects fuel into the combustion chamber 14 is provided on the side of the combustion chamber 14. This fuel injection valve 16 incorporates a needle valve and a solenoid (not shown), and is driven and opened for a time corresponding to the pulse width of the pulse signal input from the ECU 2, and has an amount corresponding to the valve opening time. The fuel is injected toward the vicinity of the electrode of the spark plug 15.

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

  An intake passage 21 and an exhaust passage 22 are connected to the intake port 17 and the exhaust port 18. As shown in FIG. 2, the downstream side of the intake passage 21 close to the intake port 17 is an independent branch intake passage 21a corresponding to each of the cylinders 12A to 12D. A throttle valve 23 (multi-throttle valve) composed of a rotary valve of a type is provided and is driven by an actuator 24. An intake pressure sensor 26 (intake pressure detection means) that detects intake pressure (negative pressure) is provided immediately downstream of each throttle valve 23. The upstream end of the branch intake passage 21a communicates with the surge tank 21b. A common intake passage 21c is provided further upstream than the surge tank 21b, and an air flow sensor 25 for detecting the entire intake flow rate is provided there. Is provided.

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

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

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

  The ECU 2 receives detection signals from the sensors 25, 26, 30 to 34, and outputs a control signal for controlling the fuel injection amount and injection timing to the fuel injection valve 16. 15 is configured to output a control signal for controlling the ignition timing to the ignition device 27 attached to 15 and to output a control signal for controlling the throttle opening degree to the actuator 24 of the throttle valve 23. Has been. Further, as will be described later, when a preset automatic engine stop condition is satisfied, fuel injection to each of the cylinders 12A to 12D is stopped (fuel cut) at a predetermined timing to automatically stop the engine. Then, control (idle stop control) that automatically restarts the engine when a restart condition is satisfied, for example, when the driver performs an accelerator operation, is performed. In this idle stop control, the ECU 2 functionally includes automatic stop control means for performing control performed when the engine is automatically stopped.

  When the engine is restarted by the idle stop control, the first stroke is performed in the compression stroke cylinder, and the piston 13 is pushed down to slightly reverse the crankshaft 3. As a result, the piston 13 of the expansion stroke cylinder is once raised, and the air-fuel mixture in the cylinder is compressed, and the air-fuel mixture is ignited and burned to give the crankshaft 3 drive torque in the forward rotation direction. It is configured to restart the engine.

  In order to properly restart the engine simply by igniting the fuel injected into a specific cylinder without using a restart motor or the like as described above, the air-fuel mixture in the expansion stroke cylinder is burned. By sufficiently securing the combustion energy obtained by the above, the cylinder that reaches the compression top dead center (compression stroke cylinder) must overcome the compression reaction force and exceed the compression top dead center. Therefore, it is necessary to ensure a sufficient amount of air in the expansion stroke cylinder.

  As shown in FIGS. 3A and 3B, the phases of the compression stroke cylinder and the expansion stroke cylinder are shifted by 180 ° CA, so that the pistons 13 operate in opposite directions. If the piston 13 of the expansion stroke cylinder is positioned on the bottom dead center side of the stroke center, the amount of air in the cylinder increases and sufficient combustion energy is obtained. However, when the piston 13 of the expansion stroke cylinder is extremely positioned on the bottom dead center side, the amount of air in the compression stroke cylinder becomes too small, and the crankshaft 3 is reversed by the initial combustion at the time of restart. Insufficient combustion energy can be obtained.

  On the other hand, a predetermined range R slightly lower than the position where the crank angle after the compression top dead center is 90 ° CA, for example, the crank angle after the compression top dead center, is the stroke center of the expansion stroke cylinder. If the piston 13 can be stopped within a range R of 100 ° to 120 ° CA, a predetermined amount of air is secured in the compression stroke cylinder, and the crankshaft 3 can be slightly reversed by the initial combustion. Combustion energy can be obtained. In addition, by securing a large amount of air in the expansion stroke cylinder, it is possible to generate sufficient combustion energy for normal rotation of the crankshaft 3 and reliably restart the engine.

  Therefore, the ECU 2 performs the following control to stop the piston 13 within the range R. FIG. 4 is a time chart when the engine is automatically stopped by this control, and shows the engine speed Ne, the boost pressure Bt (intake pressure), the opening K of the throttle valve 23, and the power generation amount Ge of the alternator 28. FIG. 5 is an enlarged view after the time t1 in FIG. 4 and shows a crank angle CA and a stroke transition chart of each cylinder in addition to FIG. For the sake of brevity, it is assumed that # 1 cylinder 12A is an expansion stroke cylinder, # 2 cylinder 12B is an exhaust stroke cylinder, # 3 cylinder 12C is a compression stroke cylinder, and # 4 cylinder 12D is an intake stroke cylinder. .

  The ECU 2 sets the target speed of the engine to a value higher than a normal idle rotation speed (hereinafter referred to as a normal idle rotation speed) when the engine is not automatically stopped at a time point t0 when the automatic engine stop condition is satisfied, for example, normal In an engine whose idle rotation speed is set to 650 rpm (the automatic transmission is in the drive (D) range), the target speed (idle rotation speed when the automatic stop condition is satisfied) is set to about 850 rpm (the automatic transmission is in the neutral (N) range). ) Is executed to stabilize the engine speed Ne at a slightly higher speed than the normal idle speed. Further, the opening K of the throttle valve 23 is adjusted so that the boost pressure Bt is stabilized at a relatively high predetermined value (about −400 mmHg).

  Then, the fuel injection is stopped at time t1 when the engine rotation speed Ne is stabilized at the target speed, and the engine rotation speed Ne is decreased. Further, at the fuel injection stop time t1 (first predetermined timing), which is the initial stage of the control operation for automatically stopping the engine, the opening degree K of the throttle valve 23 and the air-fuel ratio in the cylinder to the excess air ratio λ = 1. The intake air flow rate is set to be higher than the intake air flow rate during idling (minimum intake air flow rate necessary for continuing engine operation). That is, when the combustion state immediately before the time point t1 is set to an in-cylinder air-fuel ratio in the vicinity of the excess air ratio λ = 1 to near λ = 1 and homogeneous combustion is performed, the opening K of the throttle valve 23 is increased (for example, When the air-fuel ratio in the cylinder is set to lean and stratified combustion is performed, the opening K of the throttle valve 23 is maintained as it is (the relatively large opening during stratified combustion). . 4 and 5 show the former case.

  Further, the ECU 2 reduces the power generation of the alternator 28 at the time t1 from the time t0 when the automatic stop condition is satisfied. This reduces the rotational resistance of the crankshaft 3 so that the engine rotational speed Ne does not decrease too quickly.

  As a result of this control, the boost pressure Bt starts to increase slightly after time t1 (if the combustion just before time t1 is homogeneous combustion) or maintains a relatively high boost pressure Bt (if the time just before time t1 is stratified combustion) Exhaust gas scavenging is facilitated.

  When combustion injection is stopped at time t1, the engine rotational speed Ne begins to decrease, and at time t2 (second predetermined time) when it is confirmed that the engine speed Ne has become a preset reference speed, for example, 760 rpm or less, the throttle valve 23 is turned on. The opening is reduced (for example, opening K = about 15%). Then, the boost pressure Bt starts to decrease slightly after time t2, and the intake air flow rate sucked into each cylinder of the engine decreases. Air sucked between time t1 and time t2 when the throttle valve 23 is opened is guided to the branch intake passage 21a of each cylinder via the common intake passage 21c and the surge tank 21b. Then, the air is sucked in order from the cylinder that has reached the intake stroke. In the case shown in FIG. 5, the order is # 4 cylinder 12D, # 2 cylinder 12B, # 1 cylinder 12A, and # 3 cylinder 12C. Here, by setting the time point t1 and the time point t2 as described above, the # 1 cylinder 12A (expansion stroke cylinder) sucks more air than the # 3 cylinder 12C (compression stroke cylinder). become.

  Since the engine rotates by inertia after time t1, the rotational speed Ne of the engine gradually decreases and eventually stops at time t6. The decrease in the rotational speed Ne of the engine is as shown in FIG. 4 and FIG. Every time it goes up and down (around 10 times for a 4-cylinder 4-cycle engine), it goes down.

  In the time chart of the crank angle CA shown in FIG. 5, the solid line indicates the crank angle when the top dead center (TDC) of the # 1 cylinder 12A and the # 3 cylinder 12C is 0 ° CA, and the alternate long and short dash line indicates the # 2 cylinder 12B. The crank angle when the top dead center of the # 4 cylinder 12D is 0 ° CA is shown. The solid line and the alternate long and short dash line are in opposite phases with respect to 90 ° CA. In a four-cylinder four-cycle engine, one of the cylinders reaches compression top dead center every 180 ° CA. Therefore, this time chart shows either at the top of the waveform indicated by a solid line or one-dot chain line (crank angle = 0 ° CA). This indicates that the cylinder passes the compression top dead center.

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

  In the compression stroke cylinder 12C that reaches the compression top dead center after the time t5 when the last compression top dead center is passed, the air pressure increases as the piston 13 rises due to the inertial force, and the piston 13 is top dead due to the compression reaction force. The crankshaft 3 is reversed without being pushed back beyond the point. Since the air pressure of the expansion stroke cylinder 12A increases due to the reverse rotation of the crankshaft 3, the piston 13 of the expansion stroke cylinder 12A is pushed back to the bottom dead center side according to the compression reaction force, and the crankshaft 3 rotates forward again. First, the reverse rotation and forward rotation of the crankshaft 3 are repeated several times, and the piston 13 stops after reciprocating. The stop position of the piston 13 is substantially determined by the balance of the compression reaction force in the compression stroke cylinder 12C and the expansion stroke cylinder 12A, and is influenced by the intake resistance of the intake stroke cylinder 12D, the friction of the engine, and the like. It also changes depending on the rotational inertia of the engine at the time t5 when the compression top dead center is exceeded, that is, the level of the engine rotational speed Ne.

  Therefore, in order to stop the piston 13 of the expansion stroke cylinder 12A within the predetermined range R suitable for restarting, first, the compression reaction force of the expansion stroke cylinder 12A and the compression stroke cylinder 12C is sufficiently increased, and the expansion stroke cylinder 12A is expanded. It is necessary to adjust the intake air flow rates for both cylinders so that the compression reaction force of the stroke cylinder 12A is larger than the compression reaction force of the compression stroke cylinder 12C by a predetermined value or more. For this purpose, the throttle valve 23 is opened at the fuel injection stop time t1 and its opening K is increased so that a predetermined amount of air is sucked into both the expansion stroke cylinder 12A and the compression stroke cylinder 12C. The intake air amount is adjusted by reducing the opening of the throttle valve 23 at time t2 when the time has elapsed.

  However, in an actual engine, because there are individual differences in the shape of the throttle valve 23, the intake port 17, the branch intake passage 21a, etc., the behavior of the air flowing through them changes, so that each cylinder during the automatic engine stop period Variations occur in the intake air flow rate sucked into 12A to 12D and the intake resistance of the intake stroke cylinder 12D, and the engine frictional resistance also varies depending on individual engine differences and engine temperature. Even if the opening / closing control of the valve 23 is performed, it is difficult to keep the piston stop position of the cylinder in the expansion stroke and the cylinder in the compression stroke within the appropriate range R when the engine is stopped.

  Therefore, in the present embodiment, the engine rotation speed when each of the cylinders 12A to 12D passes through the compression top dead center as shown in an example in FIG. 6 in the process in which the engine rotation speed decreases during the automatic engine stop period. Control is performed using the fact that there is a clear correlation between (top dead center rotational speed) ne and the piston stop position of the expansion stroke cylinder 12A.

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

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

  In particular, when looking at the second top dead center rotational speed ne (corresponding to the engine rotational speed Ne at time t4 in FIG. 5) before the engine is stopped, as shown in FIG. The speed ne is in the range of about 280 rpm to 380 rpm, and on the low rotation side below about 320 rpm, the piston stop position gradually becomes top dead as the top dead center rotational speed ne decreases. It is changing to a point. On the other hand, on the high rotation side where the top dead center rotational speed ne is 320 rpm or higher, the stop position of the piston 13 becomes substantially constant and falls within the substantially appropriate range R regardless of the top dead center rotational speed ne. I understand.

  The characteristic distribution tendency as described above is observed when the engine top dead center rotational speed ne is on the high rotation side of 320 rpm or more, a sufficient amount of air in each of the expansion stroke cylinder 12A and the compression stroke cylinder 12C. This is considered to be because the piston stop position is concentrated toward the center of the stroke due to the compression reaction force of the air. It should be noted that the piston stop position is distributed to the lower left on the low rotation side of 320 rpm or lower because the piston 13 reciprocating in each cylinder is reversed on the compression top dead center side and then decelerated by friction or the like. This is thought to be due to stopping without being able to return to the center of the process.

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

  FIG. 8 conceptually represents the distribution diagram shown in FIG. 7 as a general characteristic diagram. As in FIG. 7, the horizontal axis indicates the second top dead center rotational speed from before the stop, and the vertical axis indicates the piston stop position of the expansion stroke cylinder. As shown in this characteristic diagram, the piston stop position of the expansion stroke cylinder is closer to the bottom dead center (180 °) as the second top dead center rotational speed (hereinafter referred to as the top dead center rotational speed ne2) before the stop as a whole increases. The side closer to CA). However, when the top dead center rotational speed ne2 is within the range of 350 ± 50 rpm (300 to 400 rpm), it is likely to stop in the proper range R (100 to 120 ° CA) relatively stably.

  The characteristic diagram of FIG. 8 shows the characteristic when the boost pressure Bt (hereinafter referred to as boost pressure Bt2) at the second compression top dead center passage timing t4 (third predetermined timing) from before stop is around −220 mmHg. Yes. When the boost pressure Bt2 is lower (vacuum side), this characteristic moves as a whole to the bottom dead center side when the piston stop position is high, and when the boost pressure Bt2 is higher (atmospheric pressure side).

  Therefore, at the third predetermined time t4, the piston 13 can be adjusted so that the top dead center rotational speed ne2 is 350 ± 50 rpm and the boost pressure Bt2 is around −220 mmHg (preferably −220 ± 40 mmHg). This is a very effective measure for stopping within the appropriate range R. Therefore, in the present embodiment, as shown in a flowchart described later, the power generation amount of the alternator 28 is adjusted so that the top dead center rotational speed ne2 at the third predetermined time t4 is within the target engine rotational speed range (350 ± 50 rpm). In addition to performing control, feedback control is performed to adjust the opening of the throttle valve 23 so that the boost pressure Bt2 at the third predetermined time t4 is within the target intake pressure range (−220 ± 40 mmHg).

  Note that when the final compression top dead center passage time (time point t5 shown in FIG. 5) has passed, none of the cylinders passes through the top dead center, and the stroke is not changed. The piston 13 tries to stop at the target proper position while being damped and oscillated within the stroke (when the crank 13 moves in the opposite direction, the crankshaft 3 reverses and the engine speed Ne becomes negative). However, at this time, the intake stroke cylinder 12D performs an intake operation, and if the intake resistance is large, the stop position of the piston 13 tends to vary. In particular, the intake resistance acts so as to increase when the piston 13 moves to the bottom dead center side, so that the piston 13 is likely to stop closer to the top dead center than intended. Since the piston 13 of the intake stroke cylinder 12D and the piston 13 of the expansion stroke cylinder 12A move in the same phase, the piston 13 of the expansion stroke cylinder 12A tends to stop near the top dead center rather than the target.

  Therefore, in the present embodiment, the opening degree K of the throttle valve 23 is increased to the first predetermined opening degree (the opening degree K1 shown in FIG. 5, for example, K1 = about 40%) substantially simultaneously with the time point t5 (may be slightly delayed). Thus, the intake resistance of the intake stroke cylinder 12D is reduced. This makes it easier for the piston 13 to stop at a target position corresponding to the balance without affecting the intake flow rate balance in the expansion stroke cylinder 12A and the compression stroke cylinder 12C.

  Further, when the top dead center rotational speed ne is high at the last top dead center passage time (time t5) and the boost pressure Bt2 is low at the third predetermined time t4, the piston 13 of the expansion stroke cylinder 12A stops near the end of the stroke. Conditions that are easy to do overlap (see FIG. 8), and there is a high possibility of stopping at a target stop position (100 to 120 ° CA after top dead center). Under such conditions, if control is performed to increase the opening K of the throttle valve 23 to the first predetermined opening K1 at time t5, the piston stop position becomes closer to the latter stage of the stroke, and instead the target stop position. There is a risk that it will come off. Therefore, in this embodiment, in such a case, the opening K of the throttle valve 23 at the time point t5 is a second predetermined opening (in FIG. 5) that is lower (or closed) than the first predetermined opening K1. The opening degree K2) is set to suppress the increase of the intake flow rate so that the piston stop position of the expansion stroke cylinder 12A does not become too close to the bottom dead center.

  Next, the control operation of the ECU 2 when the engine is automatically stopped will be described based on the flowcharts shown in FIGS. These flowcharts are flowcharts of engine automatic stop control from uniform combustion in which the air-fuel ratio in the cylinder is set to the stoichiometric air-fuel ratio or near the stoichiometric air-fuel ratio. When this control operation starts, it is first determined whether or not an automatic engine stop condition is satisfied based on detection signals output from various sensors (step S1). Specifically, the brake switch remains on for a predetermined time, the remaining battery level is equal to or higher than a preset reference value, and the vehicle speed is equal to or lower than a predetermined value (for example, 10 km / h). Is confirmed, it is determined that the engine automatic stop condition is satisfied. If any of the above requirements is not satisfied, it is determined that the engine automatic stop condition is not satisfied.

  If it is determined YES in step S1 and it is confirmed that the engine automatic stop condition is satisfied, the shift range of the automatic transmission is set to neutral to make it unloaded (step S2) and EGR. The EGR valve (not shown) provided in the passage is closed to stop the exhaust gas recirculation (step S31), and the target value (target speed) of the engine rotational speed Ne is a value N1 higher than the normal idle rotational speed. (For example, about 850 rpm) is set (step S3). Further, the opening K of the throttle valve 23 is adjusted (the throttle valve 23 is operated in the valve opening direction) so that the boost pressure Bt becomes a target pressure P1 set to about −400 mmHg, for example (step S4), and the engine The ignition timing retard amount is calculated so that the rotational speed Ne becomes the target speed N1 (step S5). Thus, the throttle opening K is fed back in order to set the boost pressure Bt to the target pressure P1, and the retard amount of the ignition timing is fed back in order to set the engine rotational speed Ne to the target speed N1 (engine (Rotational speed feedback control is executed).

  In step S1, the determination of the automatic engine stop condition is executed when the vehicle speed is reduced to 10 km / h or less. It can be set to a value (850 rpm) higher than the normal idle rotation speed (for example, 650 rpm in the D range state of the automatic transmission) when automatic stop is not performed, and before the engine rotation speed decreases to the normal idle rotation speed (650 rpm) In addition, the above steps S2 and S3 can be executed. Therefore, there is no need to increase the engine rotational speed once reduced to the normal idle rotational speed to the target rotational speed N1 (850 rpm), and the driver will not be uncomfortable with the increased engine rotational speed. .

  At time t0 when the engine automatic stop condition is satisfied, the shift range of the automatic transmission in step S2 is shifted from the drive state (D range) to the neutral state (N range) so that the load on the automatic transmission is reduced. Since the target engine speed of the engine is set to N1 in step S3, the engine speed Ne increases slightly from time t0 and becomes stable as shown in FIG.

  Next, it is determined whether or not a fuel injection stop condition (fuel cut condition) is satisfied, specifically, whether or not the engine speed Ne is the target speed N1 and the boost pressure Bt is the target pressure P1. If it is determined NO (step S6), the process returns to step S4 and the above control operation is repeated. Then, at the time when YES is determined in step S6 (time t1 in FIGS. 4 and 5), the throttle valve 23 is opened to a relatively large opening (about 30%) (step S7), and the alternator 28 is turned on. The power generation amount is set to 0 to stop power generation (step S8), and fuel injection is stopped (step S9).

  Thereafter, after the fuel injection stop time t1, whether or not the engine rotational speed Ne has become equal to or lower than a reference speed N2 set in advance to about 760 rpm in order to determine that the engine rotational speed Ne has started to decrease. Is determined (step S10). Then, when the determination is YES in step S10 (time t2), the opening of the throttle valve 23 is reduced (set to about 15%) (step S11). As a result, the boost pressure Bt that opens the throttle valve 23 and approaches the atmospheric pressure in step S7 starts to decrease with a predetermined time difference in accordance with the closing operation of the throttle valve 23.

  Note that, instead of the above-described embodiment in which the throttle valve 23 is closed at the time t2 when it is determined in step S10 that the engine rotational speed Ne has become equal to or less than the reference speed N2, the piston 13 is compression dead. The throttle valve 23 may be closed when it is determined that the engine speed when passing the point, that is, the engine top dead center speed ne is equal to or lower than the reference speed N2.

  Next, it is determined whether or not the engine top dead center rotational speed ne is equal to or lower than a preset reference speed N2 set to about 760 rpm (step S12). If YES is determined here, the engine rotational speed Ne is decreased along a reference line set based on experiments performed in advance, and the top dead center rotational speed ne2 at the third predetermined time t4 is determined. The power generation amount of the alternator 28 is adjusted so as to be within the target engine speed range (350 ± 50 rpm), and the boost pressure Bt2 at the third predetermined time t4 is within the target intake pressure range (−220 ± 40 mmHg). Feedback control for adjusting the opening of the throttle valve 23 is performed.

  Specifically, first, the power generation amount of the alternator 28 is set to an initial value set to about 60 A in advance, and initial control of the power generation amount Ge for operating the alternator 28 over a period of about 300 ms is executed (step S13). ). As a result, the rotational resistance of the crankshaft 3 temporarily increases, so that the rotational speed Ne of the engine can be quickly reduced so as to follow the reference line.

  Next, based on the deviation between the reference line where the top dead center rotational speed ne is set and the actual and the current boost pressure Bt, the second compression top dead center passage time (third predetermined time t4) from before the stop. An estimated value (Bt9) of the boost pressure Bt is calculated (step S15). Next, the opening degree of the throttle valve 23 is adjusted according to the deviation of the estimated value Bt9 from the target intake pressure range (−220 ± 40 mmHg). That is, when the estimated value Bt9 is lower than the target intake pressure range (vacuum side), the opening degree K of the throttle valve 23 is increased by a predetermined amount, and conversely when it is higher (at atmospheric pressure side), the opening degree K is decreased by a predetermined amount. Feedback control is performed (step S17).

  Then, in the process in which the engine rotational speed Ne decreases along the preset reference line, for example, when the engine passes the fourth compression top dead center before the engine is stopped (time shown in FIG. 5). It is determined whether the top dead center rotational speed ne4 of the engine at t3) is within a predetermined first range α (step S20). The first range α is set to, for example, 480 rpm to 540 rpm. If it is determined YES in step S20 and the top dead center rotational speed ne4 is confirmed to be within the first range α (480 rpm to 540 rpm), it corresponds to the top dead center rotational speed ne at that time t3. The generated power Ge of the alternator 28 is controlled (step S21). That is, as shown in FIG. 11, as the engine top dead center rotational speed ne increases, the power generation amount Ge corresponding to the top dead center rotational speed ne is read from the map in which the power generation amount Ge is set to a larger value. By setting the amount Ge as a target value and operating the alternator 28 for a period of about 300 ms, the power generation amount Ge of the alternator 28 is controlled.

  Thereafter, by determining whether or not the engine top dead center rotational speed ne is within the second range β set in advance to about 470 rpm to 480 rpm (step S22), the engine rotational speed Ne is significantly reduced. If it is determined YES, the power generation amount Ge of the alternator 28 is set to a large value of about 100 A as shown by the broken lines in FIGS. 4 and 5, and about 300 ms. By controlling the alternator 28 over the period of time, control is executed to temporarily increase the power generation amount Ge of the alternator 28 (step S23). This is because, when the degree of decrease in the rotational speed Ne of the engine is significant, it is difficult to mitigate it (applying rotational energy to the crankshaft 3). And the number of elapsed times of compression top dead center is reduced by about once to restore the reference line set in advance.

  If it is determined NO in step S20 and it is confirmed that the engine top dead center rotational speed ne4 is not within the first range α (482 rpm to 540 rpm), the top dead center rotational speed ne is set to the top dead center rotational speed ne. The process proceeds to step S22 without executing the power generation amount control of the corresponding alternator 28. Further, when it is determined NO in step S22 and it is confirmed that the engine top dead center rotational speed ne is not within the second range β, the control for temporarily increasing the power generation amount Ge of the alternator 28 is performed. Without moving to step S24 below.

  Then, it is determined whether or not the engine top dead center rotational speed ne is equal to or less than a predetermined value N3 (step S24). The predetermined value N3 is a value corresponding to the engine rotational speed when passing through the last compression top dead center in the process in which the engine rotational speed Ne is decreasing along a preset reference line. Is set to about. Further, the boost pressure Bt at each time when each cylinder sequentially passes the compression top dead center is detected, and the value is stored.

  When it is determined YES in step S24 and it is confirmed that the engine top dead center rotational speed ne is equal to or lower than the predetermined value N3 (t5), it is determined that the last top dead center has been passed. Further, at this time t5, the boost pressure Bt at the previous compression top dead center passage time (third predetermined time t4) is read, and it is the boost pressure Bt2 at the second compression top dead center before the stop. Determine (step S25).

  Then, based on the top dead center rotational speed ne (hereinafter referred to as the final top dead center rotational speed ne1) when passing through the last compression top dead center and the boost pressure Bt2 at the second compression top dead center before the stop, A determination is made as to whether or not there is a large tendency to stop near the latter period (close to the bottom dead center in the expansion stroke cylinder 12A) (step S26). Specifically, when the final top dead center rotational speed ne1 is equal to or higher than a predetermined rotational speed N4 (for example, N4 = 200 rpm) and the boost pressure Bt2 is equal to or lower than a predetermined pressure P2 (for example, P2 = −200 mmHg) (vacuum side). It is determined that there is a large tendency to stop near the end of the stroke (the piston stop position in the expansion stroke cylinder 12A is close to 120 ° CA with respect to the appropriate range R in the range of 100 to 120 ° CA after compression top dead center). (YES in step S26).

  If it is determined NO in this step S19, the tendency to stop near the latter half of the stroke is not so large, and relatively close to the first half of the stroke (the piston stop position in the expansion stroke cylinder 12A is 100 with respect to the appropriate range R). There is a tendency to stop at a position close to ° CA or 100 ° CA or less. Therefore, the throttle valve 23 is opened so that it can be stopped within the proper range more reliably. That is, for example, the opening degree K of the throttle valve 23 is increased so as to be the first predetermined opening degree K1 set to about 40%, and the intake air flow rate is increased (step S27). By doing so, the intake resistance of the intake stroke cylinder 12D is reduced, and it becomes easier to stop at a later stage of the stroke. As a result, the stopping position of the piston 13 in the expansion stroke cylinder 12A is prevented as much as possible from falling below the lower limit (100 ° CA) of the appropriate range R, and the stopping accuracy within the appropriate range R can be further improved. it can.

  On the other hand, if it is determined YES in step S26, the piston 13 is in the latter stage of the stroke, in which the rotational inertia of the engine is large, the intake flow rate in the final intake stroke to the compression stroke cylinder 12C is small, and the compression reaction force is small. There are already conditions that make it easy to stop by the side. Therefore, the opening degree K of the throttle valve 23 is adjusted so that the opening degree K of the throttle valve 23 becomes the second predetermined opening degree K2 (for example, K2 = about 5%) (step S28). This second opening may be further reduced or closed depending on the engine characteristics and the like. By so doing, an intake resistance of an appropriate size is generated in the intake stroke cylinder 12D, and it is less likely that the intake stroke will be moved further toward the later stage than at the later stage of the target stroke. As a result, the stopping position of the piston 13 in the expansion stroke cylinder 12A is prevented as much as possible from exceeding the upper limit (120 ° CA) of the appropriate range R, and the stopping accuracy within the appropriate range R can be further improved. it can.

  Thus, as the engine speed Ne further decreases, it is determined whether or not the engine has been stopped (step S29). When the determination is YES, detection of the crank angle sensors 30, 31 is performed as described later. After executing the control for detecting the stop position of the piston 13 based on the signal (step S30), the control operation is terminated.

  FIG. 12 shows the piston stop position detection control operation executed in step S30 of the flowchart. When this detection control is started, based on the first crank angle signal CA1 (signal from the crank angle sensor 30) and the second crank angle signal CA2 (signal from the crank angle sensor 31), when the first crank angle signal CA1 rises. It is determined whether or not the second crank angle signal CA2 is Low, or whether or not the second crank angle signal CA2 is High when the first crank angle signal CA1 falls (Step S41). As a result, it is determined whether the phase relationship between the signals CA1 and CA2 during the engine stop operation is as shown in FIG. 13A or FIG. Whether it is in a state or a reverse state is determined.

  That is, at the time of forward rotation of the engine, as shown in FIG. 13A, the second crank angle signal CA2 is generated with a phase delay of about a half pulse width with respect to the first crank angle signal CA1, thereby the first crank angle signal. The second crank angle signal CA2 becomes Low when 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. 13B, the second crank angle signal CA2 is generated with a phase advance of about a half pulse width with respect to the first crank angle signal CA1, thereby On the contrary, the second crank angle signal CA2 becomes High when the first crank angle signal CA1 rises, and the second crank angle signal CA2 becomes Low when the first crank angle signal CA1 falls.

  Therefore, if the determination in step S41 is YES, the CA counter for measuring the crank angle change in the forward rotation direction of the engine is increased (step S42). If the determination in step S41 is NO, the CA counter is increased. Down (step S43). Then, after stopping the engine, the piston stop position is obtained by examining the measured value of the CA counter (step S44).

  A control operation when the engine that has been automatically stopped as described above is restarted will be described with reference to the flowchart shown in FIG. First, it is determined whether or not a preset engine restart condition is satisfied (step S101). If it is determined NO and it is confirmed that the engine restart condition is not satisfied, the process is continued. Wait in the state. Then, when an accelerator operation or the like for starting from the stop state is performed, or when the battery voltage decreases, it is determined YES in Step S101 and it is confirmed that the engine restart condition is satisfied. In this case, the amount of air in the compression stroke cylinder 12C and the expansion stroke cylinder 12A is calculated based on the stop position of the piston 13 (step S102). That is, the combustion chamber volumes of the compression stroke cylinder 12C and the expansion stroke cylinder 12A are obtained from the stop position of the piston 13, and when the engine is stopped, the engine is stopped after several revolutions after the fuel injection is stopped. Since the stroke cylinder 12A is also filled with fresh air, and the inside of the compression stroke cylinder 12C and the expansion stroke cylinder 12A is substantially atmospheric pressure while the engine is stopped, the amount of fresh air is calculated from the combustion chamber volume. It will be required.

  Subsequently, fuel is injected so that the predetermined first air-fuel ratio is obtained with respect to the air amount of the compression stroke cylinder 12C calculated in step S102 (step S103), and then the expansion calculated in step S102 is performed. Fuel is injected so that the air / fuel ratio in the stroke cylinder 12A becomes a predetermined air / fuel ratio (step S104). In this case, the first air-fuel ratio of the compression stroke cylinder 12C and the air-fuel ratio for the expansion stroke cylinder 12A are obtained from the maps M1 and M2 according to the stop position of the piston. The first-time air-fuel ratio of the compression stroke cylinder 12C is richer than the stoichiometric air-fuel ratio (range of air-fuel ratios 11 to 14), and the air-fuel ratio of the expansion stroke cylinder 12A is substantially the stoichiometric air-fuel ratio or slightly richer than that. The maps M1 and M2 are set in advance so that the fuel ratio becomes the same.

  Next, after the time set in consideration of the fuel vaporization time after the fuel injection of the compression stroke cylinder 12C, the cylinder is ignited (step S105). Then, it is determined whether or not the piston has moved based on whether or not an edge of the crank angle sensor (rise or fall of the crank angle signal) has been detected within a certain time after ignition (step S106), and NO is determined. If it is confirmed that the piston has not moved due to misfire, re-ignition is repeatedly performed on the compression stroke cylinder 12C (step S107).

  If it is determined as YES in step S106 and the edge of the crank angle sensor is detected, the time from when the predetermined delay time elapses after the edge detection, that is, the time until the reverse rotation of the engine ends is elapsed. Thereafter, the expansion stroke cylinder 12A is ignited (step S108). The delay time is obtained from the map M3 according to the stop position of the piston 13. Further, when the predetermined crank angle (second injection timing of the compression stroke cylinder 12C) is reached, fuel is injected again into the compression stroke cylinder 12C (step S109). In this case, the second air-fuel ratio of the compression stroke cylinder 12C is obtained from the map M4 in accordance with the stop position, the fuel injection amount is calculated based on these, and the appropriate fuel injection of the compression stroke cylinder 12C is calculated from the map M5. Timing, ie, the action of latent heat of vaporization due to fuel injection (lowering the gas temperature in the cylinder due to fuel vaporization) contributes to an appropriate injection timing that contributes to a decrease in compression pressure (for example, from the middle to the first half of the compression stroke) Time).

  The air-fuel ratio for the second time of the compression stroke cylinder 12C is set to an appropriate rich air-fuel ratio at which the effect of latent heat of vaporization is increased, and the compression of the compression stroke cylinder 12C is performed by re-injecting fuel in the compression stroke cylinder 12C. The compression reaction force in the vicinity of the top dead center is reduced, and it is possible to sufficiently overcome the compression top dead center by the combustion of the expansion stroke cylinder 12A (combustion brought about by the ignition in step S108). When such control at the start is completed, the control shifts to normal control (step S110).

  By executing the restart control described above, as shown in FIGS. 15 and 16, the combustion air-fuel ratio is first made slightly richer than the stoichiometric air-fuel ratio in the compression stroke cylinder 12C (# 3 cylinder) (see FIG. 15). 15 (1)) is performed, and the combustion pressure (part a in FIG. 16) by this combustion (1) pushes down the piston 13 of the compression stroke cylinder 12C to the bottom dead center side, so that the engine rotates in the reverse direction. When driven, the piston 13 of the expansion stroke cylinder 12A (# 1 cylinder) approaches top dead center, whereby the air in the cylinder is compressed and the in-cylinder pressure rises (portion b in FIG. 16). When the piston 13 of the expansion stroke cylinder 12A is sufficiently close to the top dead center, the cylinder is ignited and the fuel previously injected into the cylinder burns ((2) in FIG. 15). The engine is driven in the forward rotation direction by the combustion pressure (c portion in FIG. 16). Further, when fuel is injected into the compression stroke cylinder 12C at an appropriate timing ((3) in FIG. 15), the compression stroke cylinder 12C is not combusted, but the compression stroke is caused by the latent heat of vaporization caused by fuel injection. The compression pressure of the cylinder 12C is reduced (d portion in FIG. 16). Thus, until the second compression top dead center is exceeded by the combustion in the expansion stroke cylinder 12A, that is, until the combustion is performed in the intake stroke cylinder 12D (# 4 cylinder) and the engine driving force is applied. The engine driving force is ensured.

  In this case, since the air-fuel ratio of the compression stroke cylinder 12C is made somewhat rich, the driving force of the engine is increased and the reverse rotation operation is sufficiently performed, and the pressure in the cylinder of the expansion stroke cylinder 12A is increased, which is sufficient. It is possible to generate a large combustion torque (engine driving force).

  In addition, by performing fuel injection for reducing the compression pressure in the compression stroke cylinder 12C, it is possible to reliably start the expansion stroke cylinder 12A by combustion.

  Further, the fuel injection timing in the intake stroke cylinder 12D is set to an appropriate timing (for example, after the middle stage of the compression stroke) at which the temperature in the cylinder and the compression pressure are reduced by the latent heat of vaporization of the fuel (in FIG. 15). (4)) self-ignition (before the compression top dead center) in the compression stroke of the intake stroke cylinder 12D is prevented, and the ignition timing of the intake stroke cylinder 12D is set after the compression top dead center. Therefore, combustion before the compression top dead center is prevented, and in the intake stroke cylinder 12D, it is possible to increase the engine drive efficiency in the forward rotation direction while reducing the compression reaction force.

  Thereafter, combustion is sequentially performed in each cylinder ((5) and (6) in FIG. 15) under normal control, and the restart of the engine is completed.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to said embodiment, A various deformation | transformation is possible within the range of the invention described in the claim. For example, in the above-described embodiment, the intake flow rate to each of the cylinders 12A to 12D is adjusted using the multiple throttle valve 23 in which the valve body is individually disposed in the branch intake passage 21a connected to each of the cylinders 12A to 12D. However, the present invention is not limited to this, and the intake flow rate to each of the cylinders 12A to 12D is adjusted by the common (single) throttle valve 23 disposed in the common intake passage 21c upstream of the surge tank 21b. You may comprise so that it may do.

  In that case, on-off control is suitable for adjusting the opening of the throttle valve 23. For example, at the second predetermined time t2, the throttle valve 23 is temporarily closed to a substantially closed state, and thereafter, until the third predetermined time t4, the opening time of the throttle valve 23 and its opening according to the required correction amount of the boost pressure Bt. You may make it open by setting. The second predetermined time t2 itself may be adjusted back and forth. In particular, when it is necessary to correct the boost pressure Bt to the low pressure side, there is a possibility that the effect cannot be sufficiently obtained even if the opening degree of the throttle valve 23 that has already been closed to a substantially closed state is further reduced. In such a case, it is effective to reduce the overall intake flow rate by advancing the second predetermined time t2.

  The flowcharts shown in FIGS. 9 and 10 of the above embodiment show the case where the combustion state immediately before the automatic stop is uniform combustion, but the combustion state immediately before the automatic stop is stratified combustion with a lean air-fuel ratio. There may be. In that case, the opening degree K of the throttle valve 23 has already been set to a large value at the time of step S7 in FIG. Therefore, what is necessary is just to control so that the opening degree K may be maintained.

  In the above-described embodiment, an example in which the first air-fuel ratio is set to a rich air-fuel ratio equal to or lower than the theoretical air-fuel ratio for the compression stroke cylinder 12C at the time of engine restart has been described. The second air-fuel ratio is set immediately after the compression top dead center in the original compression stroke after setting the lean air-fuel ratio to a predetermined amount leaner than the stoichiometric air-fuel ratio, leaving excess oxygen in the cylinder, and the engine turning in the forward rotation direction. Fuel may be injected so that combustion can be performed, and ignition may be performed immediately after compression top dead center.

  In particular, when the piston position of the expansion stroke cylinder 12A when the engine is stopped is close to the top dead center side within the appropriate starting range, this is preferable.

  That is, when the piston position of the expansion stroke cylinder 12A when the engine is stopped is close to the top dead center side within the appropriate starting range, the air volume of the expansion stroke cylinder 12A is swung to the side where the air volume is small. On the other hand, in the compression stroke cylinder 12C that is in a phase opposite to that of the expansion stroke cylinder 12A, the fuel injection amount corresponding to the amount of air is swung to the side with the larger air volume. Since the amount can be increased, in the compression stroke cylinder 12C, the first air-fuel ratio is made lean so that combustion is performed both in the reverse operation (air compression of the expansion stroke cylinder 12A) and in the normal operation. The second air-fuel ratio may be set to be equal to or lower than the stoichiometric air-fuel ratio, and the combustion may be performed in the compression stroke cylinder 12C following the combustion in the expansion stroke cylinder 12A during the forward rotation operation.

  Further, in the engine starter in the above-described embodiment, when restarting the engine in the automatic stop state, the crankshaft 3 is slightly reversed first by causing the compression stroke cylinder 12C to perform the first combustion. Although the ignition is performed after the air-fuel mixture in the expansion stroke cylinder 12A is compressed by rotating it, the engine starter according to the present invention is not limited to this, and the initial combustion is performed in the expansion stroke cylinder 12A. The engine may be restarted without being reversed once.

  The appropriate range R of the piston stop position in the above embodiment, various engine rotational speeds Ne, various top dead center rotational speeds ne, each opening K of the throttle valve 23, various boost pressures Bt, target intake pressure range, and target engine rotational speed. Each set value such as the range may be appropriately changed according to engine characteristics or the like.

1 is a schematic cross-sectional view of an engine provided with a starter according to the present invention. It is explanatory drawing which shows the structure of the intake system and exhaust system of an engine. It is explanatory drawing which shows the relationship between the piston stop position and air quantity of the cylinder which becomes an expansion stroke and a compression stroke at the time of an engine stop. It is a time chart which shows the change state etc. of the engine speed at the time of an engine stop. FIG. 5 is a partially enlarged view of FIG. 4 and a time chart showing a crank angle and a stroke transition of each cylinder. It is a distribution map which shows the correlation with the engine speed at the time of an engine stop, and a piston stop position. It is a distribution map which shows the correlation with the top dead center rotational speed and piston stop position in the 2nd before an engine stop. It is a characteristic view which shows notionally the general relationship between the top dead center rotational speed second before the engine stop and the intake pressure at that time and the piston stop position. It is a flowchart which shows the first half of the engine automatic stop control operation. It is a flowchart which shows the second half part of the engine automatic stop control operation. It is a graph which shows an example of the map for setting the electric power generation amount of an alternator according to the rotational speed of an engine. It is a flowchart which shows detection control operation | movement of a piston stop position. It is explanatory drawing which shows an output signal in a crank angle signal. It is a flowchart which shows the control action at the time of engine restart. It is a time chart which shows the combustion operation etc. at the time of engine restart. It is a time chart which shows the change state etc. of the engine speed at the time of engine restart.

Explanation of symbols

2 ECU (automatic stop control means)
12A, 12B, 12C, 12D Cylinder 23 Throttle valve 26 Intake pressure sensor (Intake pressure detection means)
t1 First predetermined time t2 Second predetermined time t4 Third predetermined time

Claims (9)

When the preset automatic engine stop condition is satisfied, the fuel supply for continuing the engine operation is stopped to automatically stop the engine, and the restart condition for the engine in the automatic stop state is satisfied. Sometimes, in an engine starter configured to restart the engine by injecting fuel into a cylinder that is in a stopped state at least in the expansion stroke to cause ignition and combustion,
A throttle valve that adjusts the intake air flow rate sucked into the engine cylinder;
An intake pressure detecting means for detecting an intake pressure downstream of the throttle valve;
When the engine is automatically stopped, the throttle valve is set to an intake flow rate state that is a predetermined amount greater than the minimum intake flow rate required to continue the engine operation at the first predetermined time in the initial stage of the automatic stop operation. And an automatic stop control means for controlling to reduce the intake flow rate at the second predetermined time thereafter,
The automatic stop control means uses the intake pressure at a third predetermined time provided between the second predetermined time and the last compression top dead center passage time immediately before the stop , after the second predetermined time. An engine start characterized in that the throttle valve opening is adjusted by feedback control so that the estimated intake pressure is within a predetermined target intake pressure range, estimated based on the current output of the pressure detection means apparatus.   2. The engine starter according to claim 1, wherein the third predetermined time is a compression top dead center passage time one time before the last compression top dead center passage time immediately before the stop.   3. The target intake pressure range is a range set in the vicinity of an intermediate point between the atmospheric pressure and the intake pressure during normal idling operation without automatically stopping the engine or closer to the atmospheric pressure than that. The engine starter described.   The automatic stop control means predicts a change in intake pressure accompanying a subsequent decrease in engine rotation speed from a degree of change in the intake pressure accompanying a decrease in engine rotation speed, and based on the prediction, at the third predetermined time The engine starter according to any one of claims 1 to 3, wherein an opening of the throttle valve is adjusted so that the intake pressure is within the target intake pressure range.   The automatic stop control means adjusts the opening degree of the throttle valve in a direction in which the intake flow rate increases when the predicted intake pressure at the third predetermined time is out of the target intake pressure range. The engine starter according to claim 4, wherein   The automatic stop control means adjusts the opening degree of the throttle valve in a direction in which the intake flow rate decreases when the predicted intake pressure at the third predetermined time is out of the target intake pressure range. 6. The engine starting device according to claim 4 or 5, wherein the engine starting device is an engine starting device. With an alternator driven by the engine,
The automatic stop control means adjusts the amount of power generated by the alternator so that the engine rotation speed at the third predetermined time falls within a predetermined target engine rotation speed range. The engine starting device according to claim 1. The engine is a naturally aspirated 4-cycle 4-cylinder gasoline engine with a compression ratio of 11 ± 2.
When the engine is automatically stopped, the intake pressure at the compression top dead center passage timing one time before the last compression top dead center passage time immediately before the stop is −220 ± 40 mmHg and The engine rotational speed at the compression top dead center passage time one time before the compression top dead center passage time is configured to be 350 ± 50 rpm, according to any one of claims 1 to 7, Engine starter.   9. The engine starter according to claim 1, wherein the throttle valve is provided in an independent intake passage for each of the cylinders. 10.

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