JP4254607B2 - Engine starter - Google Patents

Description

  The present invention relates to an engine starter, and particularly to automatically stop an engine when a predetermined automatic stop condition is satisfied in an idle operation state of the engine, and then restart when a predetermined restart condition is satisfied. The present invention relates to an engine starter configured as described above.

In recent years, in order to reduce fuel consumption and reduce CO ₂ emissions, a restart condition has been established such that the engine is automatically stopped temporarily during idling and the vehicle is then started by the driver. At the time, a technology for automatic engine stop control (so-called idle stop control) that automatically restarts the engine has been developed. The restart at the time of the idle stop control requires a quickness to immediately start the engine in accordance with the start operation of the vehicle or the like, but the engine output by the starter motor is generally performed conventionally. According to the method of restarting the engine through cranking 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 the expansion stroke cylinder which is in a stopped state in the expansion stroke, and igniting and burning the fuel. However, when the engine is stopped, the in-cylinder pressure becomes approximately atmospheric pressure in a short time, so that sufficient output for restarting can be obtained even if fuel is supplied to the cylinder that is at approximately atmospheric pressure and burned. There is a risk of not being able to.

  As countermeasures, for example, engine starting devices such as Patent Document 1 and Patent Document 2 are known. When starting the engine, the engine starter disclosed in Patent Document 1 first injects fuel into a compression stroke cylinder that is stopped in the compression stroke to cause combustion, and temporarily reverses the engine. Thereafter, combustion is performed in the expansion stroke cylinder, and the engine is rotated in the normal direction to start. Similarly, in the engine starting device of Patent Document 2, when starting the engine, first, fuel is injected into the compression stroke cylinder which is stopped in the compression stroke, combustion is performed, and the engine is once reversely rotated. Then, the piston of the compression stroke cylinder is stopped before the bottom dead center, and thereafter, combustion is performed in the expansion stroke cylinder to start the engine by changing the rotation direction of the engine to normal rotation.

All of these engine starters reverse the engine once to raise the piston of the expansion stroke cylinder, increase its compression pressure, and then perform combustion in the cylinder. It is possible to obtain a sufficiently high output for the subsequent operation.
WO 01/38726 A1 WO 01/81759 A1

  According to the engine starting device disclosed in Patent Document 1 and Patent Document 2, the output obtained by the first combustion of the expansion stroke cylinder at the time of starting is increased. It is desirable that this output is high so that the subsequent operation can be performed continuously and smoothly. In order to increase the output obtained by the initial combustion of the expansion stroke cylinder, more in-cylinder air may be more strongly compressed by reversing the engine. However, there has been a limit in doing so in the past for the following reasons, and problems remain in improving startability.

  The first reason is that if the in-cylinder air amount of the expansion stroke cylinder is excessively increased, the in-cylinder air cannot be sufficiently compressed. Since the piston operating directions of the expansion stroke cylinder and the compression stroke cylinder are opposite directions, increasing the in-cylinder air amount of the expansion stroke cylinder (making the piston position at the time of stopping close to the bottom dead center) It is none other than reducing the air volume (making the piston position when stopped close to top dead center). In other words, if the in-cylinder air amount in the expansion stroke cylinder is increased too much, the in-cylinder air amount in the compression stroke cylinder decreases and the reverse energy due to combustion decreases, so that the in-cylinder air in the expansion stroke cylinder can be sufficiently compressed. It will disappear.

  The second reason is that if the combustion energy for reversal in the compression stroke cylinder is excessively increased in order to strongly compress the in-cylinder air of the expansion stroke cylinder, the engine (crankshaft) may be rotated in reverse. Is a point. The reverse rotation of the engine must be kept in a range where the piston of the compression stroke cylinder does not exceed the bottom dead center (the piston of the expansion stroke cylinder does not exceed the top dead center). If this is exceeded, the compression stroke cylinder returns to the intake stroke (the expansion stroke cylinder returns to the compression stroke), and smooth restart is no longer possible. Therefore, it is necessary to prevent the combustion energy for the reverse rotation in the compression stroke cylinder from increasing excessively, and therefore, the compression pressure of the in-cylinder air in the expansion stroke cylinder is limited.

  In view of the above circumstances, the present invention increases the initial combustion energy of the expansion stroke cylinder at the time of restart without excessively increasing the in-cylinder air amount of the expansion stroke cylinder and the engine reverse energy, thereby starting the engine. An engine starter capable of improving the performance is provided.

  According to the first aspect of the present invention, when the predetermined engine automatic stop condition is satisfied, the fuel supply is stopped to stop the engine, and when the predetermined restart condition is satisfied after the engine is stopped, the engine is stopped. The fuel is supplied to the compression stroke cylinder in the compression stroke, ignited, and combustion is performed, whereby the engine is once operated in the reverse direction and the compression pressure is increased by the piston of the expansion stroke cylinder in the expansion stroke when the engine is stopped. In the engine starting device for starting the engine by operating it in the forward rotation direction by performing combustion in the expansion stroke cylinder after increasing the pressure, piston position detection means for detecting at least the piston position of the expansion stroke cylinder; Fuel injection for setting the fuel injection timing for the first combustion at the time of engine restart in at least the expansion stroke cylinder And a fuel injection controller for the first combustion in the expansion stroke cylinder when the piston position when the engine is stopped in the expansion stroke cylinder is closer to the bottom dead center than the center of the stroke. The timing is set to be a predetermined fuel injection timing during the reverse operation of the engine and after the piston of the expansion stroke cylinder moves closer to the top dead center than the center of the stroke.

  In this specification, a cylinder in the compression stroke while the engine is automatically stopped is referred to as a compression stroke cylinder, and a cylinder in the expansion stroke is referred to as an expansion stroke cylinder (similarly, a cylinder in the intake stroke is referred to as an intake stroke cylinder and an exhaust stroke). Each cylinder is referred to as an exhaust stroke cylinder). However, these are not specific cylinders, but when the engine is automatically stopped, for example, when the engine is completely stopped when the cylinder is in the compression stroke, the cylinder is referred to for convenience. Is referred to as a compression stroke cylinder (the same applies to an expansion stroke cylinder).

  According to a second aspect of the present invention, in the engine starter according to the first aspect of the present invention, the engine start device includes at least an in-cylinder temperature estimating means for estimating an in-cylinder air temperature of the expansion stroke cylinder, and the fuel injection control means The predetermined fuel injection timing is delayed when the estimated value of the in-cylinder air temperature of the stroke cylinder is high compared to when the estimated value is low.

  According to the third aspect of the present invention, when the predetermined engine automatic stop condition is satisfied, the fuel supply is stopped to stop the engine, and when the predetermined restart condition is satisfied after the engine is stopped, the engine is stopped. The fuel is supplied to the compression stroke cylinder in the compression stroke, ignited, and combustion is performed, whereby the engine is once operated in the reverse direction and the compression pressure is increased by the piston of the expansion stroke cylinder in the expansion stroke when the engine is stopped. In the engine starting device for starting the engine by operating in the normal rotation direction by performing combustion in the expansion stroke cylinder after increasing the engine, at least for the first combustion at the time of engine restart in the expansion stroke cylinder A fuel injection control means for setting a fuel injection timing and a fuel injection amount, wherein the fuel injection control means comprises the expansion stroke cylinder; The fuel for the first combustion is supplied by split injection, and at least the timing of fuel injection performed at the end of the split injection is set to be in reverse operation after the start of reverse operation of the engine. Features.

  Here, the divided injection means that the fuel supplied for one combustion (in this case, the first combustion in the expansion stroke cylinder) is divided and injected two or more times with a predetermined time difference. The fuel injection performed at the end of the divided injection is, for example, the second injection in the case of the two-part injection and the third injection in the case of the three-part injection.

  According to a fourth aspect of the present invention, in the engine starter according to the third aspect of the present invention, the engine start device further comprises piston position detecting means for detecting a piston position of the expansion stroke cylinder, and the fuel injection control means is provided in the expansion stroke cylinder. When the piston position when the engine is stopped is relatively close to the bottom dead center within a predetermined appropriate stop range suitable for restarting, compared to when the piston is relatively close to the top dead center, the subsequent injection amount in the above divided injection The ratio is increased relative to the injection amount ratio in the previous stage.

  According to a fifth aspect of the present invention, in the engine starter according to the third or fourth aspect of the present invention, the engine start device includes at least an in-cylinder temperature estimating means for estimating an in-cylinder air temperature of the expansion stroke cylinder, When the estimated value of the in-cylinder air temperature of the expansion stroke cylinder is high, the fuel injection timing at the latter stage of the divided injection is delayed as compared with when the estimated value is low.

  The fuel injection in the latter stage of the fuel injection described in claims 4 and 5 is the second fuel injection in the case of the two-part injection, and all the fuel injections are delayed from the earlier stage in the case of the three-part or more injection. It is classified as the latter stage of the term side, and the subsequent stage injection. The subsequent injection may be performed once (that is, fuel injection performed at the end of the divided injection), or may be performed twice or more including the end. When there are a plurality of subsequent fuel injections, the fuel injection amount and fuel injection timing can be determined by a reasonable method such as averaging (or averaging with weighting) the corresponding multiple injection amounts and injection timings. Define it.

  According to the first aspect of the invention, when the engine is restarted after being automatically stopped, the piston of the expansion stroke cylinder is raised by reversely rotating the engine once, and the combustion pressure in the cylinder is increased after the compression pressure is increased. Therefore, it is possible to obtain a high output for turning the engine in the forward rotation direction and performing the subsequent continuous operation.

  Moreover, when the piston position when the engine is stopped in the expansion stroke cylinder is closer to the bottom dead center than the center of the stroke, the fuel injection timing for the first combustion in the expansion stroke cylinder becomes the predetermined fuel injection timing. When the piston stop position of the expansion stroke cylinder is closer to the bottom dead center than the center of the stroke, the amount of in-cylinder air is relatively large and a large amount of combustion energy can be obtained. However, on the other hand, when the cylinder air is compressed during engine reverse rotation, the compression reaction force becomes large, and therefore, the compression cannot be sufficiently performed with limited reverse energy.

  Therefore, if the fuel injection timing is set as in the present invention and the fuel is injected after the reverse rotation operation of the engine and the piston of the expansion stroke cylinder moves closer to the top dead center than the center of the stroke, the fuel is injected to some extent. Since the fuel is injected into the cylinder in a state where the air is compressed, the compression pressure is reduced by the latent heat of vaporization. Therefore, the piston can move closer to top dead center (increase in piston stroke), and the density of compressed air can be further increased. The effect is much greater than when the fuel injection timing is set at the same time as or immediately after the start of the reverse operation of the engine, for example. As a result, more combustion energy can be obtained and startability can be improved.

  As described above, if the fuel injection timing is delayed, the density of compressed air in the cylinder can be increased. However, if the fuel injection timing is delayed too much, the time from fuel injection to ignition is shortened, and sufficient fuel vaporization time can be secured. There is a risk of disappearing. Therefore, according to the invention of claim 2, it is possible to obtain as much combustion energy as possible while properly balancing the balance. That is, when the in-cylinder air temperature is high and the fuel vaporization performance is relatively high, the density of the compressed air in the cylinder can be increased by delaying the fuel injection timing to obtain larger combustion energy. On the other hand, when the in-cylinder air temperature is low and the fuel vaporization performance is relatively low, the fuel vaporization time can be secured by advancing the fuel injection timing than when the in-cylinder air temperature is high.

  According to the third aspect of the invention, by dividing and injecting the fuel, it is possible to easily and more highly attain the fuel vaporization time and increase the density of the compressed air in the cylinder. That is, the fuel vaporization time is secured by the front injection, and the density of the compressed air in the cylinder can be increased by the latent heat of vaporization of the rear injection (including the last injection).

  According to the invention of claim 4, when the piston stop position of the expansion stroke cylinder is relatively close to the bottom dead center within a predetermined appropriate stop range suitable for restart (relatively large cylinder air amount), The fuel injection amount at the latter stage of the divided injection is increased as compared with the case where it is relatively near the top dead center (the amount of cylinder air is relatively small). That is, when the amount of air in the cylinder is relatively large, the compression reaction force also increases. Therefore, the compression pressure can be effectively reduced by increasing the fuel injection amount in the subsequent stage, and the density of the compressed air is increased. By making it, startability can be improved more.

  According to the invention of claim 5, as in the invention of claim 2, it is possible to obtain as much combustion energy as possible while appropriately balancing the securing of the fuel vaporization time and the increase in the density of compressed air in the cylinder. Can be. In addition, even if the subsequent fuel injection timing is delayed, the deterioration of the entire vaporization performance can be effectively prevented by setting the preceding fuel injection timing to a time at which a sufficient vaporization time can be secured.

  1 and 2 show a schematic configuration of a four-cycle spark ignition engine having an engine starter according to the present invention. The engine includes an engine main body 1 having a cylinder head 10 and a cylinder block 11 and an ECU 2 for engine control. The engine body 1 is provided with four cylinders (# 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.

  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. The fuel injection valve 16 incorporates a needle valve and a solenoid (not shown), and is driven for a time corresponding to the pulse width of the pulse signal input from the fuel injection control unit 41 of the ECU 2 to open the valve. An amount of fuel corresponding to the time is injected toward the vicinity of the electrode of the spark plug 15.

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

  An intake passage 21 and an exhaust passage 22 are connected to the intake port 17 and the exhaust port 18. As shown in FIG. 2, the downstream side of the intake passage 21 close to the intake port 17 is an independent branch intake passage 21a corresponding to each of the cylinders 12A to 12D. The upstream ends of the branch intake passages 21a are respectively It communicates with the surge tank 21b. A common intake passage 21c is provided upstream of the surge tank 21b, and a throttle valve 23 driven by an actuator 24 is provided in the common intake passage 21c. An air flow sensor 25 for detecting the intake air flow rate and an intake air temperature sensor 29 for detecting the intake air temperature are provided on the upstream side of the throttle valve 23, and the intake pressure (negative pressure) is detected on the downstream side of the throttle valve 23. An intake pressure sensor 26 is provided.

  On the other hand, a catalyst 37 for purifying the exhaust is disposed downstream of the collection portion of the exhaust passage 22 where exhaust from each of the cylinders 12A to 12D collects. This catalyst 37 is, for example, a so-called three-way catalyst in which the purification rate of HC, CO and NOx is extremely high when the air-fuel ratio state of the exhaust is in the vicinity of the theoretical air-fuel ratio, and this is a relatively high oxygen concentration in the exhaust. It has an oxygen storage capacity for storing it in a high oxygen excess atmosphere. When the oxygen concentration is relatively low, the stored oxygen is released and reacted with HC, CO and the like. Note that the catalyst 37 is not limited to a three-way catalyst, and may be any catalyst that has the above-described oxygen storage ability. For example, the catalyst 37 may be a so-called lean NOx catalyst that can purify NOx even in an oxygen-excess atmosphere.

  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.

  Furthermore, the engine body 1 is provided with a cam angle sensor 32 for detecting a specific rotational position for cylinder identification provided on the camshaft, and a water temperature sensor 33 for detecting the cooling water temperature of the engine. An accelerator opening sensor 34 for detecting an accelerator opening corresponding to the driver's accelerator operation amount is provided.

  The ECU 2 is a control unit that comprehensively controls the operation of the engine. The engine of the present embodiment automatically stops fuel injection by stopping fuel injection into each cylinder 12A to 12D at a predetermined timing when a preset automatic engine stop condition is satisfied. Then, the engine is configured to perform control (idle stop control) that automatically restarts the engine when a restart condition is satisfied, for example, when an accelerator operation is performed by the driver. Hereinafter, in the description of the ECU 2, the portion related to the idle stop control will be mainly described.

  The ECU 2 receives detection signals from the air flow sensor 25, the intake pressure sensor 26, the intake air temperature sensor 29, the crank angle sensors 30, 31, the cam angle sensor 32, the water temperature sensor 33, and the accelerator opening sensor 34, and The drive signals are output to the fuel injection valve 16, the actuator 24 of the throttle valve 23, the ignition device 27, and the regulator circuit 28a of the alternator 28, respectively. The ECU 2 functionally includes a fuel injection control unit 41, an ignition control unit 42, an intake air flow rate control unit 43, a power generation amount control unit 44, a piston position detection unit 45, and an in-cylinder temperature estimation unit 46.

  The fuel injection control unit 41 is fuel injection control means for setting the fuel injection timing and the fuel injection amount for each injection and outputting the signal to the fuel injection valve 16. In particular, in the present embodiment, as will be described later, fuel for the first combustion in the expansion stroke cylinder at the time of restart is supplied by split injection. The fuel injection control unit 41 also performs setting of the divided injection timing and fuel distribution.

  The ignition control unit 42 sets an appropriate ignition timing for each of the cylinders 12 </ b> A to 12 </ b> D and outputs an ignition signal to each ignition device 27.

  The intake flow rate control unit 43 sets an appropriate intake flow rate for each of the cylinders 12 </ b> A to 12 </ b> D, and outputs an opening degree signal of the throttle valve 23 corresponding to the intake flow rate to the actuator 24. In particular, in this embodiment, as will be described later, the opening degree of the throttle valve 23 is adjusted when the engine is automatically stopped, and control is performed so that the piston 13 stops in an appropriate stop range suitable for restart. The intake flow rate control unit 43 also adjusts the opening of the throttle valve 23 at that time.

  The power generation amount control unit 44 sets an appropriate power generation amount of the alternator 28 and outputs the drive signal to the regulator circuit 28a. In particular, in this embodiment, as will be described later, the load on the crankshaft 3 is changed by adjusting the power generation amount of the alternator 28 when the engine is automatically stopped, and the piston 13 is stopped in an appropriate range suitable for restart. It is carried out. The power generation amount control unit 44 also adjusts the power generation amount of the alternator 28 at that time. Further, at the time of restarting, control is performed to increase the engine load by generating more power than usual, and to prevent the engine from blowing up (raising the engine speed more rapidly than necessary).

  The piston position detector 45 detects the piston position based on the detection signals of the crank angle sensors 30 and 31. Since the piston position and the crank angle (° CA) have a one-to-one correspondence, the piston position is represented by the crank angle in this specification as is generally done. In this embodiment, as will be described later, the in-cylinder air amount is calculated based on the piston positions during the automatic stop of the expansion stroke cylinder and the compression stroke cylinder, and the combustion control of each cylinder at the time of restart is performed accordingly. Yes.

  The in-cylinder temperature estimation unit 46 uses each map 12A based on an engine water temperature detected by the water temperature sensor 33, an intake air temperature detected by the intake air temperature sensor 29, or the like using a map obtained in advance through experiments or the like. In-cylinder temperature estimation means for estimating the air temperature in the cylinder of -12D. In particular, in this embodiment, as will be described later, in-cylinder temperature estimation is performed in consideration of the engine stop time when the engine is restarted, and combustion control is performed based on the estimated value.

  In performing the idle stop control by the ECU 2 having the above-described configuration, when the engine is restarted, the combustion is first performed in the compression stroke cylinder, so that the piston 13 is pushed down to slightly reverse the crankshaft 3. As a result, the piston 13 of the expansion stroke cylinder is once raised (closed to top dead center), and the air-fuel mixture (which becomes the air-fuel mixture after fuel injection) is compressed and ignited and burned. Thus, the engine is restarted by applying a driving torque in the forward direction to the crankshaft 3.

  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 ensuring the combustion energy obtained by the above, the cylinder that reaches the compression top dead center (in this embodiment, the compression stroke cylinder and the intake stroke cylinder) overcomes the compression reaction force and overcomes the compression top dead center. It must be exceeded. 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 located on the bottom dead center side with respect to 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. The sufficient combustion energy cannot 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 the range R of 100 to 120 ° CA, a predetermined amount of air is secured in the compression stroke cylinder, and the combustion is such that the crankshaft 3 can be slightly reversed by the initial combustion. Energy will be obtained. Moreover, 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 (hereinafter referred to as this range). R is an appropriate stop range R).

  Therefore, the ECU 2 performs the following control to stop the piston 13 within the proper stop range R. FIG. 4 is a time chart when the engine is automatically stopped by this control, and shows the rotational speed Ne of the engine, the boost pressure Bt (intake pressure), and the opening degree K of the throttle valve 23. 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, which is the initial stage of the control operation for automatically stopping the engine, the opening K of the throttle valve 23 is set at the idling time when the cylinder air-fuel ratio is set to the excess air ratio λ = 1. The intake air flow rate is set to be higher than the intake air flow rate (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.

  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.

  Further, the ECU 2 temporarily stops the power generation of the alternator 28 at time t1. This reduces the rotational resistance of the crankshaft 3 so that the engine rotational speed Ne does not decrease too quickly.

  When the combustion injection is stopped at time t1, the engine rotational speed Ne starts to decrease, and the throttle valve 23 is closed at time t2 when it is confirmed that the engine speed has become a preset reference speed, for example, 760 rpm or less. 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 engine speed Ne gradually decreases and eventually stops at time t5. As shown in FIGS. 4 and 5, the engine speed Ne decreases. 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 t4 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 t4 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 proper stop range R, first, the compression reaction forces of the expansion stroke cylinder 12A and the compression stroke cylinder 12C are sufficiently increased, and the compression of the expansion stroke cylinder 12A is performed. It is necessary to adjust the intake air flow rates for both cylinders so that the reaction force is greater 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 closing the throttle valve 23 and reducing its opening K at time t2 when the time has elapsed.

  By the way, in the process in which the engine is automatically stopped in this way and the engine rotational speed decreases, the engine rotational speed (top dead center rotational speed) ne when each cylinder 12A to 12D passes through the compression top dead center, and the expansion There is a clear correlation between the piston stop position of the stroke cylinder 12A. That is, the piston stop position of the expansion stroke cylinder 12A is in the proper stop range when the top dead center rotational speed ne in each stage (second, third, fourth from the stop) is within a certain speed range. The probability of being in R increases.

  Using this characteristic, in this embodiment, the top dead center rotational speed ne in a predetermined stage (particularly important is the second before the stop (time point t3)) in the process of decreasing the engine rotational speed Ne is within a certain speed range. Such control is performed so that the piston 13 of the expansion stroke cylinder 12A is more reliably stopped within the proper stop range R. Specifically, the load (engine load) of the crankshaft 3 is adjusted by increasing or decreasing the power generation amount of the alternator 28, and the second top dead center rotational speed ne (time point t3) from before the stop is 350 ± 50 rpm. It is within the range.

  When the engine speed Ne further decreases and the final compression top dead center passage time (time point t4 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 within the target proper stop range R while being damped and oscillated within the stroke (when the crank 13 moves in the opposite direction, the crankshaft 3 is reversed and the engine rotational 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 this embodiment, the opening degree K of the throttle valve 23 is increased to the opening degree K1 shown in FIG. 5 (for example, about K1 = about 40%) almost simultaneously with the time point t4 (may be slightly delayed), and the intake stroke cylinder 12D. The intake resistance 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.

  In order to perform such control, it is necessary to immediately determine that the time point t4 is the last compression top dead center passage timing, and the next compression top dead center (in the compression stroke cylinder 12C) is It must be predicted at time t4 that it will not pass. Therefore, in the present embodiment, the ECU 2 determines the last top dead center passage time. The ECU 2 compares the engine rotation speed when passing through each top dead center with a predetermined rotation speed (for example, 260 rpm) obtained in advance through experiments or the like, and when the former becomes equal to or lower than the latter, It is determined that it is time to pass top dead center. Note that the higher the top dead center rotational speed ne at the last compression top dead center passage time, the closer to the latter stage of the stroke (the piston stop position of the expansion stroke cylinder 12A is closer to the bottom dead center, and closer to the top dead center in the compression stroke cylinder 12C). It becomes easy to stop.

  Incidentally, the intake flow rate balance in the final intake stroke of the expansion stroke cylinder 12A and the compression stroke cylinder 12C immediately before the engine is stopped is also affected by the boost pressure Bt. In particular, the second compression top dead center passage timing (time point t3 in FIG. 5) from before the stop is the start point of the final intake stroke in the compression stroke cylinder 12C, and the influence of the boost pressure Bt at this point is large. That is, when the boost pressure Bt is low (vacuum side), the intake flow rate to the compression stroke cylinder 12C decreases, and as a result, the stop position of the piston 13 of the compression stroke cylinder 12C is close to top dead center (in the expansion stroke cylinder 12A). It tends to be near the bottom dead center). The reverse is true when the boost pressure Bt is high (atmospheric pressure side).

  Therefore, when the top dead center rotational speed ne at the last top dead center passage timing is high and the boost pressure Bt at the second compression top dead center passage timing before the stop is low, the piston 13 of the expansion stroke cylinder 12A is in the stroke. Conditions that are likely to stop at the later stage overlap, and there is a high possibility of stopping at the target stop position (100 to 120 ° CA after top dead center). Under such conditions, if the control is performed to increase the opening of the throttle valve 23 to K1 at the time t3, the piston stop position may be closer to the end of the stroke, and may be deviated from the target stop position. is there. Therefore, in this embodiment, in such a case, the opening degree of the throttle valve 23 at the time point t3 is set to an opening degree K2 (see FIG. 5) that is lower (or closed) than K1, and the intake flow rate is reduced. By suppressing the increase, the piston stop position of the expansion stroke cylinder 12A is prevented from becoming too close to the bottom dead center.

  Thus, the piston 13 is completely stopped at the time point t5. By detecting the operation of the piston 13 from immediately before the stop to the stop by the crank angle sensors 30, 31, the piston position detection unit 45 of the ECU 2 detects the stop position of the piston 13. Is detected. FIG. 6 is a flowchart showing the detection control operation of the piston stop position. 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). Accordingly, it is determined whether the phase relationship between the signals CA1 and CA2 during the engine stop operation is as shown in FIG. 7A or 7B, and the engine is rotated forward. 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. 7A, 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, during reverse rotation of the engine, as shown in FIG. 7B, 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, so 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).

  When the engine is completely stopped, the in-cylinder temperatures of the cylinders 12A to 12D change as shown in the temperature characteristics of FIG. FIG. 8 is a graph showing the relationship between the elapsed time from the engine stop and the in-cylinder temperature, and is an estimated value of the in-cylinder temperature change when the in-cylinder temperature is 80 ° C. when the engine is stopped (time point t5). is there.

  As shown in this characteristic, when the engine is completely stopped, the flow of the cooling water is stopped, so that the in-cylinder temperature rapidly rises immediately after the stop. Then, it peaks at about 10 seconds after the engine stops, and then gradually decreases. This characteristic varies depending on the temperature of the cooling water (engine water temperature), the outside air temperature (intake air temperature), and the like, and the in-cylinder temperature estimation unit 46 of the ECU 2 stores data in which the characteristic is mapped.

  Since scavenging is promoted by increasing the opening K of the throttle valve 23 during the engine stop operation period, a sufficient amount of fresh air is supplied to the catalyst 37. Therefore, the oxygen storage amount of the catalyst 37 is sufficiently large while the engine is stopped.

  Next, control during engine restart will be described. When restarting, the combustion is first performed in the compression stroke cylinder 12C as described above, and the engine is once reversely rotated, and then the combustion is performed in the expansion stroke cylinder 12A, so that the engine rotates in the forward rotation direction. That is, once the engine is reversely rotated, the piston 13 of the expansion stroke cylinder 12A is raised, and after the compression pressure is increased, combustion in the cylinder is performed. The piston stop position of the expansion stroke cylinder 12A is in the proper stop range R and a sufficient amount of air for combustion is secured, and the air is compressed by the reverse rotation of the engine, so that large combustion energy is obtained. . That is, the engine can be reliably rotated in the normal rotation direction and smoothly shifted to the subsequent continuous operation.

  However, the presence of sufficient air in the expansion stroke cylinder 12A hinders strong compression of the air. This is because the compression reaction force of the compressed air acts in the direction of pushing back the piston 13 of the expansion stroke cylinder 12A.

  Therefore, in the present embodiment, control is performed to increase the compression amount (increase the density) of the air in the expansion stroke cylinder 12A by delaying the fuel injection timing to the expansion stroke cylinder 12A. If the fuel injection timing is delayed, the fuel is injected into the cylinder in which the cylinder air is compressed to some extent, and the compression pressure is reduced by the latent heat of vaporization. Therefore, if the energy is the same as that of the reverse engine rotation, the piston 13 can move closer to the top dead center (increase in piston stroke), and the density of compressed air can be further increased.

  FIG. 9 is a graph showing the relationship between the fuel injection timing to the expansion stroke cylinder 12A and the corresponding piston arrival point (the position closest to the top dead center when not ignited), by delaying the fuel injection. Represents the effect. The horizontal axis of FIG. 9 represents the fuel injection timing for the first combustion of the expansion stroke cylinder 12A in terms of the crank angle (ATDC after top dead center), and the vertical axis represents the piston arrival point of the expansion stroke cylinder 12A corresponding thereto. This is expressed in terms of crank angle (ATDC after top dead center). The smaller the crank angle at the piston arrival point (closer to the top dead center TDC), the smaller the in-cylinder volume at the time of maximum compression (the higher the air density), and the larger energy can be obtained during combustion. The characteristics shown in FIG. 9 are obtained when the piston stop position of the expansion stroke cylinder 12A is 110 ° CA (ATDC). As shown in this characteristic, the piston reaching point when injected at the beginning of the reverse rotation operation (crank angle = 110 ° CA (ATDC)) is about 36.5 ° CA (ATDC), whereas the reverse rotation starts. When the piston 13 is injected when moving to the top dead center side up to 70 ° CA (ATDC), the piston reaching point is about 33.5 ° CA (ATDC), and the compressed air density of about 3 ° CA is obtained. Increase can be achieved.

  However, if the fuel injection timing is delayed too much, the vaporization is delayed, and the piston 13 reaches the reaching point before the compression pressure is sufficiently lowered by the latent heat of vaporization. That is, the piston reaching point starts to decrease (in the example of FIG. 9, after 70 ° CA (ATDC)). After all, in order to obtain the maximum air density increasing effect, it is preferable to perform the fuel injection timing from the middle stage of the compression stroke of the expansion stroke cylinder 12A to the first half of the latter stage.

  On the other hand, delaying the fuel injection timing also shortens the time from fuel injection to ignition, which may result in insufficient vaporization during ignition. In order to sufficiently promote vaporization by the time of ignition, it is desirable to perform fuel injection at an early stage (for example, at the beginning of the reverse operation). That is, the increase in the air density and the promotion of vaporization at the time of ignition have conflicting requirements regarding the fuel injection timing.

  Therefore, in this embodiment, the fuel is dividedly injected (divided into two parts), the first stage fuel injection is performed at the beginning of the reverse rotation operation, and the second stage fuel injection is performed during the reverse rotation operation (preferably more than 90 ° CA (ATDC) at the center of the stroke Near the top dead center, which is performed at an injection timing of 70 ° CA (ATDC) in FIG. That is, vaporization is promoted by the first stage fuel injection that takes a relatively long time until the ignition timing, and the compressed air density is increased by the second stage fuel injection.

  The fuel injection control unit 41 of the ECU 2 determines the ratio (split ratio) of the injected fuel between the front stage and the rear stage and the fuel injection timing of the rear stage based on the piston stop position of the expansion stroke cylinder 12A and the in-cylinder air temperature at the start of reverse rotation ( The combustion energy can be increased as much as possible while ensuring the vaporization performance. That is, when the piston stop position of the expansion stroke cylinder 12A is relatively close to the bottom dead center within the appropriate stop range R (relatively large in-cylinder air amount), it is relatively close to top dead center (relatively). The fuel injection amount ratio at the subsequent stage is increased as compared with the case where the in-cylinder air amount is small. This is because when the amount of air in the cylinder is relatively large, the compression reaction force also becomes large. Therefore, by increasing the fuel injection amount in the subsequent stage, the compression pressure is effectively reduced and the density of the compressed air is increased. It is. Further, the fuel injection amount ratio in the subsequent stage is also increased when the in-cylinder air temperature is relatively high. This is because when the in-cylinder air temperature is high, the fuel vaporization performance is high, so that it is not necessary to perform fuel injection in the previous stage to ensure the vaporization performance.

  Regarding the subsequent fuel injection timing, the later fuel injection timing is delayed when the in-cylinder air temperature is relatively high (however, the timing corresponding to the injection timing of 70 ° CA in FIG. 9 is set as the upper limit). In other words, when the in-cylinder air temperature is high, the fuel vaporization performance is high, so even if the subsequent fuel injection timing is delayed, it is easy to vaporize until ignition, and the fuel injection timing is delayed accordingly. Therefore, the compressed air density is further increased.

  The control operation at the time of engine restart including the above control will be described based on the flowcharts shown in FIGS. First, it is determined whether or not a predetermined engine restart condition (e.g., when an accelerator operation for starting is performed from a stopped state, when the battery voltage is reduced, or when the air conditioner is activated, etc.) ( In step S101), when it is determined NO and it is confirmed that the engine restart condition is not satisfied, the process waits as it is. If it is determined YES in step S101 and it is confirmed that the engine restart condition is satisfied, the in-cylinder temperature estimation unit 46 determines the engine water temperature, the stop time (elapsed time from the automatic stop), the intake air temperature, and the like. From this, the in-cylinder temperature is estimated (step S102). Then, based on the stop position of the piston 13 detected by the piston position detector 45, the amount of air in the compression stroke cylinder 12C and the expansion stroke cylinder 12A is calculated (step S103). That is, the combustion chamber volumes of the compression stroke cylinder 12C and the expansion stroke cylinder 12A are obtained from the stop position of the piston 13, 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.

  Next, it is determined whether or not the piston stop position is relatively at the bottom dead center BDC side within the proper stop range R (before the top dead center BTDC 60 to 80 ° CA) in the compression stroke cylinder 12C (step). S104).

  If YES is determined in step S104 and the air amount is relatively large, the process proceeds to step S105, where λ (excess air ratio)> 1 with respect to the air amount of the compression stroke cylinder 12C calculated in step S103. The fuel is injected so that the air-fuel ratio (for example, air-fuel ratio = about 20) is reached (first fuel injection). This air-fuel ratio is obtained from the compression stroke cylinder first-time air-fuel ratio map M1 set in advance according to the stop position of the piston. By setting the lean air-fuel ratio such that λ> 1, even when the amount of air in the compression stroke cylinder 12C is relatively large, the combustion energy for the reverse rotation does not become excessive, and the reverse rotation is excessive (the compression stroke cylinder). At 12C, the piston 13 that has moved to the bottom dead center side passes through the bottom dead center and reverses to the intake stroke).

  On the other hand, if NO is determined in step S104 and the air amount is relatively small, the process proceeds to step S106, where the air-fuel ratio becomes λ ≦ 1 with respect to the air amount of the compression stroke cylinder 12C calculated in step S103. The fuel is injected as described above (first fuel injection). This air-fuel ratio is obtained from a compression stroke cylinder first-time air-fuel ratio map M2 set in advance according to the stop position of the piston. By setting the stoichiometric air-fuel ratio of λ ≦ 1 or a richer air-fuel ratio than that, sufficient combustion energy for reverse rotation can be obtained even when the amount of air in the compression stroke cylinder 12C is relatively small.

  Next, the process proceeds to step S107, and after the time set in consideration of the vaporization time from the first fuel injection to the compression stroke cylinder 12C, the cylinder is ignited. Then, it is determined whether or not the piston 13 has moved based on whether or not the edges of the crank angle sensors 30 and 31 (rise or fall of the crank angle signal) have been detected within a predetermined time after ignition (step S108). If it is determined NO and it is confirmed that the piston 13 has not moved due to misfire, re-ignition is repeatedly performed on the compression stroke cylinder 12C (step S109).

  If the edges of the crank angle sensors 30, 31 are detected and it is determined that the piston 13 has moved (YES in step S108), the expansion stroke cylinder 12A is detected based on the piston stop position and the in-cylinder temperature estimated in step S102. A split ratio of split fuel injection (ratio between the front stage injection (first time) and the rear stage injection (second time)) is calculated (step S121). The later-stage injection ratio is increased as the piston stop position in the expansion stroke cylinder 12A is closer to the bottom dead center and as the in-cylinder temperature is higher.

  Next, the fuel injection amount is calculated so that a predetermined air-fuel ratio (λ ≦ 1) is obtained with respect to the air amount of the expansion stroke cylinder 12A calculated in step S103 (step S122). The air-fuel ratio at this time is obtained from the expansion stroke cylinder air-fuel ratio map M3 set in advance according to the stop position of the piston.

  Next, based on the fuel injection amount to the expansion stroke cylinder 12A calculated in step S122 and the split ratio calculated in step S121, the first stage fuel injection amount for the expansion stroke cylinder 12A is calculated and injected. (Step S123).

  Next, based on the in-cylinder temperature estimated in step S102, the subsequent (second) fuel injection timing for the expansion stroke cylinder 12A is calculated (step S124). This second injection timing is a timing when the in-cylinder air is compressed after the piston 13 starts moving to the top dead center side (reverse rotation of the engine), and the vaporization latent heat of the injected fuel is compressed by the compression pressure. Is effectively reduced (the piston 13 is moved as close as possible to the top dead center), and the time for the second injected fuel to evaporate by the ignition timing is set to be as long as possible. .

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

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

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

  Note that the second fuel injection to the compression stroke cylinder 12C is performed only to reduce the compression pressure in the cylinder, and ignition and combustion are not performed on this (the richer than the combustible air-fuel ratio). So self-ignition does not occur.) This incombustible fuel then reacts with oxygen stored in the catalyst 37 in the exhaust passage 22 and is rendered harmless.

  Since the second injection fuel in the compression stroke cylinder 12C does not burn as described above, the next combustion following the first combustion in the expansion stroke cylinder 12A is the intake stroke cylinder 12D (# 4 which was in the intake stroke when stopped) This is the first combustion in the cylinder, see FIG. As energy for the piston 13 of the intake stroke cylinder 12D to exceed the compression top dead center, a part of the energy of the first combustion in the expansion stroke cylinder 12A is allocated. That is, the energy of the first combustion in the expansion stroke cylinder 12A is provided both for the compression stroke cylinder 12C to exceed the compression top dead center and for the intake stroke cylinder 12D to exceed the compression top dead center.

  Therefore, for smooth start-up, it is desirable that the energy required for the intake stroke cylinder 12D to exceed the compression top dead center is small. The following steps S140 to S144 are controls for reducing the energy for exceeding the compression top dead center as much as possible when performing combustion in the next intake stroke cylinder 12D.

  First, in step S140, the in-cylinder air density is estimated, and the air amount of the intake stroke cylinder 12D is calculated from the estimated value. Next, an air-fuel ratio correction value for preventing self-ignition is calculated based on the in-cylinder temperature estimated in step S102 (step S141). That is, when self-ignition occurs, a force (reverse torque) that pushes the piston 13 back to the bottom dead center before the compression top dead center is generated by the combustion. This is undesirable because it consumes a lot of energy for exceeding the compression top dead center. Therefore, in order to suppress this reverse torque, the air-fuel ratio is corrected to the lean side so that self-ignition does not occur.

  Next, the fuel injection amount to the intake stroke cylinder 12D is calculated from the air amount of the intake stroke cylinder 12D calculated in step S140 and the air-fuel ratio considering the air-fuel ratio correction value calculated in step S141 (step S140). S142).

  Then, fuel is injected into the intake stroke cylinder 12D. This fuel injection is performed so that the compression pressure is reduced by the latent heat of vaporization (that is, the energy required for exceeding the compression top dead center is reduced). This is delayed until later (step S143). The delay amount is calculated based on the engine automatic stop period, the intake air temperature, the engine water temperature, and the like.

  Next, in order to suppress the occurrence of the reverse torque, the ignition timing is delayed after top dead center and ignited (step S144). With the above control, in the intake stroke cylinder 12D, the compression pressure is reduced to easily exceed the top dead center until the compression top dead center, and when the top dead center is passed, the torque in the forward direction is generated by the combustion energy. To come.

  After step S144, the routine may shift to normal control, but in this embodiment, further blow-up suppression control is performed. The term “air-up” as used herein means that the engine speed rapidly increases more than necessary after the initial combustion in the intake stroke cylinder 12D, and it is desirable that an acceleration shock may occur or the driver may feel uncomfortable. Absent. Ascending, since the intake pressure (pressure downstream of the throttle valve 23) during the automatic stop period is substantially atmospheric pressure, the combustion in each cylinder immediately after the start (after the initial combustion in the intake stroke cylinder 12D) This is caused by a temporary increase in energy compared to the combustion energy during normal idle operation. Therefore, in subsequent steps S145 to S158, control for suppressing this blow-up is performed.

  First, power generation by the alternator 28 is started (step S145). The target current value is set higher than usual by the power generation amount control unit 44 of the ECU 2. Since the load (engine load) of the crankshaft 3 is increased by the power generation of the alternator 28, the blow-up is suppressed.

  Next, it is determined whether or not the intake pressure detected by the intake pressure sensor 26 is higher than the intake pressure during normal idling when idling stop is not performed (step S150). If YES is determined here, it is in a state in which the engine is likely to blow up. Therefore, the opening of the throttle valve 23 is made smaller than the throttle opening during the normal idling operation (step S151), and the combustion energy is reduced. Reduce the amount generated.

  Next, it is determined whether or not the temperature of the catalyst 37 provided in the exhaust passage 22 is equal to or lower than the activation temperature (step S152). If YES is determined, the target air-fuel ratio is set to a rich air-fuel ratio satisfying λ ≦ 1. At the same time (step S153), the ignition timing is delayed after top dead center (step S154). By doing so, the temperature increase of the catalyst 37 is promoted, and the amount of combustion energy generated is suppressed by the delay of the ignition timing.

  Going back, if NO is determined in step S152, the target air-fuel ratio is set to a lean air-fuel ratio satisfying λ> 1 (step S158) and combustion is performed. This lean combustion can suppress the amount of combustion energy generated while suppressing fuel consumption.

  After step S154 or step S158, the process returns to step S150, and the above control is repeated until NO is determined. If it is determined as NO in step S150, there is no longer a possibility that the engine will blow up, and the routine proceeds to normal control including the power generation amount of the alternator 28 (step S160).

  When the restart control is executed, as shown in FIGS. 13 and 14, first, the first fuel injection J3 is performed in the compression stroke cylinder 12C (# 3 cylinder), and combustion is performed by ignition (in FIG. 13). (1)) is performed. With the combustion pressure (part a in FIG. 14) due to this combustion (1), the piston 13 of the compression stroke cylinder 12C is pushed down to the bottom dead center side, and the engine is driven in the reverse direction. Here, the first fuel injection J3 of the compression stroke cylinder 12C becomes a lean air-fuel ratio (λ> 1) when the air amount is relatively large, and a stoichiometric air-fuel ratio or a rich air-fuel ratio (λ ≦ 1) when it is small. Therefore, the combustion energy is moderate enough for reversing the engine, that is, the combustion energy of the degree that the air in the expansion stroke cylinder 12A is sufficiently compressed but does not excessively reverse the compression top dead center. Can be obtained.

  The piston 13 of the expansion stroke cylinder 12A (# 1 cylinder) starts to move in the direction of the top dead center with the start of reverse rotation of the engine. Immediately thereafter, the first (previous) fuel injection J1 in the expansion stroke cylinder 12A is performed and vaporization starts.

  Then, when the piston 13 of the expansion stroke cylinder 12A moves to the top dead center side (preferably closer to the top dead center from the stroke center) and the air in the cylinder is compressed, the second (second stage) fuel injection J2 is performed. Is called. The compression pressure is reduced by the latent heat of vaporization of the injected fuel, and the piston 13 is closer to the top dead center, so the density of the compressed air (air mixture) increases (part b in FIG. 14).

  When the piston 13 of the expansion stroke cylinder 12A is sufficiently close to the top dead center, the cylinder is ignited, and the first injected fuel (J1) and the second injected fuel (J2) whose vaporization is promoted are promoted. Are combusted ((2) in FIG. 13), and the engine is driven in the forward rotation direction by the combustion pressure (c portion in FIG. 14).

  Furthermore, fuel that is richer than the combustible air-fuel ratio is injected into the compression stroke cylinder 12C at an appropriate timing (J4) ((3) in FIG. 13). The compression pressure of the compression stroke cylinder 12C is reduced by the latent heat of vaporization caused by fuel injection (part d in FIG. 14). Thereby, the first combustion energy of the expansion stroke cylinder 12A consumed to exceed the compression top dead center (the first compression top dead center from the start of the start) can be reduced.

  Furthermore, the timing of fuel injection (J5) in the intake stroke cylinder 12D, which is the next combustion cylinder, is set to an appropriate timing (for example, after the middle of the compression stroke) when the temperature in the cylinder and the compression pressure are reduced by the latent heat of vaporization of the fuel. Since it is set ((4) in FIG. 13), self-ignition in the compression stroke of the intake stroke cylinder 12D (before compression top dead center) is prevented. Further, in combination with the ignition timing of the intake stroke cylinder 12D being set after the compression top dead center, combustion before the compression top dead center is prevented (part e in FIG. 14). That is, the expansion consumed to exceed the compression top dead center (second compression top dead center from the start of starting) by reducing the compression pressure by the fuel injection (J5) and not performing the combustion before the compression top dead center. The energy of the first combustion in the stroke cylinder 12A can be reduced.

  Thus, the first compression top dead center ((3) in FIG. 13) and the second compression top dead center ((3) in FIG. 13) and the second compression top dead center ((3) in FIG. 13) by the energy of the initial combustion ((2) in FIG. 13) in the expansion stroke cylinder 12A. (4)) in FIG. 13 can be exceeded, and smooth and reliable startability can be ensured.

  After that ((5), (6)... In FIG. 13), the air-fuel ratio is made lean (λ> 1) or the ignition timing is delayed in accordance with the temperature of the catalyst 37 to prevent the blow-up. However, it shifts to normal operation.

  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 embodiment, the fuel injection for the initial combustion in the expansion stroke cylinder 12A at the restart is divided injection (J1 + J2), but this can reduce the compression pressure due to the latent heat of vaporization and ensure the vaporization performance. A timing (predetermined fuel injection timing) that can be achieved as much as possible may be determined by experiment or the like, and one fuel injection at the predetermined fuel injection timing may be performed.

  Further, the divided fuel injection performed for the first combustion of the expansion stroke cylinder 12A at the time of restart may be divided into three or more as required.

  Although omitted in the above embodiment, at the time of engine restart, when a predetermined condition is satisfied (for example, when the piston stop position is not within the proper stop range R, or when the engine rotation speed is increased by a predetermined time after start-up). Control with assistance by a starter motor may be performed.

  The control for automatically stopping the engine is not limited to the above embodiment, and may be set as appropriate. However, in order to improve restartability, the stop position of the piston 13 in the expansion stroke cylinder 12A is slightly closer to the bottom dead center than the center of the stroke (in the compression stroke cylinder 12C, slightly closer to the top dead center than the center of the stroke). Control is desirable.

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 further is a time chart showing a crank angle and a stroke transition of each cylinder. It is a flowchart which shows detection control operation | movement of a piston stop position. It is explanatory drawing which shows the output signal of a crank angle signal. It is a graph which shows the relationship between the elapsed time from an engine stop, and a cylinder temperature estimated value. It is a graph which shows the relationship between the crank angle at the time of the fuel injection for the first combustion of the expansion stroke cylinder at the time of restart, and the crank angle of the piston reaching point at that time. It is a flowchart (1/3) which shows the control action at the time of engine restart. It is a flowchart (2/3) which shows the control action at the time of engine restart. It is a flowchart (3/3) 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

12A # 1 cylinder (expansion stroke cylinder)
12B # 2 cylinder (exhaust stroke cylinder)
12C # 3 cylinder (compression stroke cylinder)
12D # 4 cylinder (intake stroke cylinder)
13 piston 16 fuel injection valve 41 fuel injection control unit (fuel injection control means)
45 Piston position detector (piston position detector)
46 In-cylinder temperature estimation unit (in-cylinder temperature estimation means)
J1 First stage of split fuel injection in expansion stroke cylinder J2 Second stage of split fuel injection in expansion stroke cylinder R Appropriate stop range of piston

Claims (5)

When the predetermined engine automatic stop condition is satisfied, the fuel supply is stopped to stop the engine. When the predetermined restart condition is satisfied after the engine stop, fuel is supplied to the compression stroke cylinder in the compression stroke when the engine is stopped. Is supplied and ignited to cause combustion to temporarily operate the engine in a reverse direction, and when the engine is stopped, the compression pressure is increased by raising the piston of the expansion stroke cylinder in the expansion stroke. In the engine starting device for starting the engine by operating it in the normal rotation direction by performing combustion in
Piston position detecting means for detecting at least the piston position of the expansion stroke cylinder;
Fuel injection control means for setting a fuel injection timing for the first combustion at the time of engine restart in at least the expansion stroke cylinder,
When the piston position during engine stop in the expansion stroke cylinder is closer to the bottom dead center than the center of the stroke, the fuel injection control means determines the fuel injection timing for the first combustion in the expansion stroke cylinder of the engine. An engine starter characterized by being set to a predetermined fuel injection timing during reverse rotation and after the piston of the expansion stroke cylinder has moved closer to the top dead center than the center of the stroke. In-cylinder temperature estimating means for estimating at least the in-cylinder air temperature of the expansion stroke cylinder,
2. The engine starter according to claim 1, wherein the fuel injection control means delays the predetermined fuel injection timing when the estimated value of the in-cylinder air temperature of the expansion stroke cylinder is high compared to when the estimated value is low. When the predetermined engine automatic stop condition is satisfied, the fuel supply is stopped to stop the engine. When the predetermined restart condition is satisfied after the engine stop, fuel is supplied to the compression stroke cylinder in the compression stroke when the engine is stopped. Is supplied and ignited to cause combustion to temporarily operate the engine in a reverse direction, and when the engine is stopped, the compression pressure is increased by raising the piston of the expansion stroke cylinder in the expansion stroke. In the engine starting device for starting the engine by operating it in the normal rotation direction by performing combustion in
A fuel injection control means for setting a fuel injection timing and a fuel injection amount for the first combustion at the time of engine restart in at least the expansion stroke cylinder;
The fuel injection control means supplies fuel for the first combustion in the expansion stroke cylinder by split injection, and at least the timing of fuel injection to be performed at the end of the split injection is after the start of reverse operation of the engine. An engine starter characterized in that the engine is set to be in reverse rotation. At least piston position detecting means for detecting the piston position of the expansion stroke cylinder;
The fuel injection control means is relatively close to the top dead center when the piston position during engine stop in the expansion stroke cylinder is relatively close to the bottom dead center within a predetermined appropriate stop range suitable for restart. 4. The engine starting device according to claim 3, wherein a ratio of the subsequent injection amount in the divided injection is increased as compared with the case. In-cylinder temperature estimating means for estimating at least the in-cylinder air temperature of the expansion stroke cylinder,
5. The fuel injection control means for delaying the fuel injection timing at the latter stage of the divided injection when the estimated value of the in-cylinder air temperature of the expansion stroke cylinder is high compared to when the estimated value is low. Engine starter.

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