JP4341475B2 - 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, 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 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

  However, even if the restartability of the engine is increased as in the engine starter disclosed in Patent Document 1 and Patent Document 2, it cannot be said that the restartability of the engine is sufficiently high. In particular, when the engine is restarted after a specific period after the engine is automatically stopped (for example, about 5 s to 15 s after the engine is stopped), the restartability tends to decrease.

  In view of the above circumstances, the present invention provides an engine starter capable of performing a stable restart regardless of the elapsed time after the engine is automatically stopped.

According to the first aspect of the present invention, when a 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, at least the engine is stopped. In an engine starter that restarts the engine by supplying fuel to an expansion stroke cylinder that is sometimes in the expansion stroke and igniting it for combustion, a water temperature sensor for detecting the coolant temperature of the engine, and when the engine is stopped Also, an electric water pump capable of forcibly circulating engine cooling water, a radiator provided on the engine cooling water circuit to reduce the engine cooling water temperature by heat exchange, and provided on the cooling water circuit to the radiator side A thermo-valve that can be switched between a valve-opening state that guides cooling water and a valve-closing state that does not guide cooling water to the radiator side. The provided, together with the cooling water temperature in one of the engine automatic stop conditions include that the predetermined automatic stop permission temperature above the valve opening temperature of the thermo-valve in the engine operation, than the automatic stop permission temperature Is set at a high temperature, and when the engine is automatically stopped due to the establishment of the engine automatic stop condition, even if the coolant temperature of the engine is lower than the opening temperature of the thermo valve. The in- cylinder cooling mode for opening the thermo valve and operating the electric water pump is performed.

  In this specification, a cylinder in the expansion stroke while the engine is automatically stopped is referred to as an expansion stroke cylinder (similarly, a cylinder in the compression stroke is referred to as a compression stroke cylinder, 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 expansion stroke, the cylinder is referred to for convenience. Is called an expansion stroke cylinder (the same applies to the compression stroke cylinder).

  According to a second aspect of the present invention, in the engine starting device according to the first aspect, the in-cylinder cooling mode has a local maximum temperature after the engine is automatically stopped when the electric water pump is not operated. It is set to be earlier than the time point.

  According to a third aspect of the present invention, in the engine starter according to the first aspect, the start timing of the in-cylinder cooling mode is set to be within 5 seconds after the engine is automatically stopped. To do.

  According to a fourth aspect of the present invention, in the engine starter according to the first aspect, the start timing of the in-cylinder cooling mode is set so as to be when the engine automatic stop condition is satisfied. To do.

According to a fifth aspect of the present invention, there is provided the engine starting device according to any one of the first to fourth aspects, wherein the opening temperature of the thermo valve during engine operation is high in a low load region of the engine. a high temperature with respect to, and is characterized in that it is set to be a higher temperature than the automatic stop permission temperature.

According to a sixth aspect of the present invention, in the engine starter according to any one of the first to fifth aspects, the in-cylinder cooling mode is established when the restart condition is satisfied during the execution of the in-cylinder cooling mode. It is characterized by terminating.

According to a seventh aspect of the present invention, in the engine starting device according to any one of the first to sixth aspects, the radiator includes a fan that blows cooling air and operates the fan during the in-cylinder cooling mode. It is characterized by making it.

  According to the present invention, by executing the in-cylinder cooling mode, it is possible to effectively suppress a phenomenon in which restartability is reduced during a specific period after the engine is automatically stopped. Stable restart can be performed regardless of the elapsed time.

  The inventor of the present application has found that the cause of the phenomenon that the restartability is reduced when restarting after a specific period after the engine has automatically stopped (for example, about 5 to 15 seconds since the engine stopped) has been conducted through earnest research. And found that the in-cylinder temperature is rapidly increasing. That is, when the engine is stopped, the water pump that circulates the cooling water is also stopped, so that the cooling performance of the engine is lowered and the in-cylinder temperature starts to rise rapidly. Then, it reaches a peak after about 10 seconds and then gradually decreases (see FIG. 11). Since the air density decreases when the in-cylinder temperature rises, the mass of air decreases even at the same piston stop position (in-cylinder volume). Accordingly, the energy due to combustion is also reduced. In other words, if the engine is restarted during this period (about 5 s to 15 s after the engine is stopped) after the engine is stopped, the combustion energy is reduced and the restartability is lowered.

Therefore, when the in-cylinder cooling mode of the present invention is executed, the cooling water can be circulated to the radiator by turning on the thermo valve while the engine is stopped and operating the electric water pump (Claim 1). Cooling performance can be improved. In particular, even if the cooling water temperature does not reach the opening temperature of the thermo-valve and the idling stop is performed from the state where the thermo-valve is closed, the thermo-valve is opened along with the execution of the in-cylinder cooling mode. Therefore, an increase in the in-cylinder temperature after the engine is stopped can be reliably suppressed. Therefore, the rapid increase in the in-cylinder temperature as described above is suppressed, and a decrease in restartability can be effectively suppressed. Here, one of the engine automatic stop conditions includes that the coolant temperature is equal to or higher than a predetermined automatic stop permission temperature. By setting the automatic stop permission temperature to an appropriate temperature (for example, 60 ° C.), it is possible to reliably prevent idle stop when the combustion is unstable, such as during warm-up operation. The decrease can be suppressed.

In order to sufficiently obtain the effect of the in-cylinder cooling mode, the start time is from the time when the in-cylinder temperature reaches the maximum value after the automatic engine stop when the electric water pump is not operated (the time corresponding to 10 s in FIG. 11). It is desirable to be early (Claim 2). For example, the in-cylinder cooling mode may be started within 5 seconds after the engine is automatically stopped. Further, if it is earlier, for example, when the engine automatic stop condition is satisfied, the cooling performance is further improved and the restartability can be improved ( claim 4 ).

  Further, by executing the in-cylinder cooling mode early in this way, it is possible to increase the power consumption until the engine is stopped and to reduce the remaining battery capacity. By doing so, the power generation margin of the generator (alternator) can be increased. Increasing the power generation margin of the alternator is preferable because it makes it easier to control the alternator for load adjustment after engine startup.

When the in-cylinder cooling mode is executed, cooling of the engine is promoted. However, if too much cooling is performed, the combustion stability at the time of restarting is lowered, so that it is desirable to end at an appropriate time. The appropriate time may be set to a time when the increase in the in-cylinder temperature is at an allowable level even after the in-cylinder cooling mode is terminated (for example, in the case of the characteristic shown in FIG. 11, after 30 s to 60 s, etc.). However, when the restart condition is satisfied and the restart is started by the end time, the water pump interlocked with the engine is activated by starting the engine. Good ( Claim 6 ).

By the way, even during operation of the engine, it is important to cool the engine appropriately by circulating the cooling water appropriately. The cooling water temperature easily rises during high-load operation of the engine, and the cooling water temperature hardly rises during low-load operation. On the other hand, if the valve opening temperature at which the thermo valve is turned on is set to a high value, the frequency of circulation to the radiator decreases, so the cooling water temperature tends to rise, and if it is set to a low value, the frequency of circulation to the radiator increases. The water temperature does not rise easily. Therefore, according to claim 5 of the present invention, during a high load operation in which the cooling water temperature is likely to rise, the temperature of the thermo valve is suppressed by setting the opening temperature of the thermo valve relatively low so that the cooling water temperature does not rise easily. During low-load operation, the temperature increase can be promoted by setting the valve opening temperature of the thermo valve relatively high. By doing in this way, since the heat radiation from the radiator during low-load operation can be effectively suppressed, the fuel consumption can be further improved.

And in-cylinder cooling mode, when operating the fan for blowing cooling air to the radiator, it is possible to further improve the cooling performance of the engine (claim 7).

  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 includes 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 combustion control unit 41 of the ECU 2. The fuel corresponding to the amount of 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. 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.

  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 vehicle-mounted 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, the regulator circuit 28a of the alternator 28, and the starter motor 39, respectively. The ECU 2 functionally includes a combustion control unit 41, a power generation amount control unit 44, a piston position detection unit 45, and an in-cylinder temperature estimation unit 46. Other elements included in the ECU 2 (electric water pump control unit 47, electric fan control unit 48, electric thermo valve control unit 49, see FIG. 3) will be described later.

  The combustion control unit 41 mainly sets a fuel injection timing, a fuel injection amount in each injection, an ignition timing, an intake air flow rate, etc., and controls combustion in each cylinder.

  Regarding the fuel injection amount and the fuel injection timing, these are set appropriately and a control signal is output 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 combustion control unit 41 also sets the divided injection timing and fuel distribution.

  With respect to the ignition timing, an appropriate ignition timing is set for each of the cylinders 12 </ b> A to 12 </ b> D, and an ignition signal is output to each ignition device 27.

  Regarding the intake flow rate, an appropriate intake flow rate is set for each of the cylinders 12A to 12D, and an opening degree signal of the throttle valve 23 corresponding to the intake flow rate is output 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 combustion control unit 41 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 restart, control is performed to increase the engine load by generating a larger amount of 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.

  FIG. 3 is a configuration diagram of a cooling system circuit of the engine of the present embodiment. The cooling water circulates on the cooling water circuit L in the direction indicated by the arrow. The cooling water circuit L mainly includes a water jacket portion L1 configured inside the engine body 1, a radiator portion L2 that performs heat exchange with the radiator 50, and a bypass portion L3 that bypasses the radiator portion L2 so as not to circulate. Consists of.

  A water pump 56 and an electric water pump 57 are provided in parallel to the upstream portion of the water jacket portion L1. These are all pumps that pump the cooling water recirculated from the radiator L2 or the bypass L3 to the water jacket L1, and at least one of them is operated to circulate the cooling water. The water pump 56 is a water pump provided in a conventional general engine, and is interlocked with the operation of the engine. That is, when the engine stops, the water pump 56 stops. On the other hand, the electric water pump 57 is an electric water pump that operates using a battery (not shown) as a power source, and can be operated even when the engine is stopped. The water jacket portion L1 is provided with a water temperature sensor 33 that detects the temperature of the cooling water.

  An electric thermo valve 53 is provided at a branch point where the water jacket portion L1 branches to the radiator portion L2 or the bypass portion L3. The electric thermo valve 53 is a thermo valve that opens and closes the passage from the water jacket portion L1 to the radiator portion L2 in accordance with the cooling water temperature. The electric thermo valve 53 of the present embodiment is electrically turned on (open) / OFF (closed) can be controlled. When the electric thermo valve 53 is ON, the flow of the cooling water is mainly the water jacket portion L1 → the radiator portion L2 → the water jacket portion L1, and when the electric thermo valve 53 is OFF, the flow of the cooling water is the water jacket portion L1 → Bypass portion L3 → water jacket portion L1.

  An electric fan 51 and a fan motor 52 for driving the electric fan 51 are provided in the vicinity of the radiator 50. The electric fan 51 blows air to the radiator 50 and promotes heat exchange between the cooling water and the external air (cooling air) in the radiator portion L2.

  The electric thermo valve 53, the electric water pump 57, and the fan motor 52 are each operated by a control signal from the ECU 2. In addition to the combustion control unit 41 and the like (see FIG. 2), the ECU 2 further includes an electric water pump control unit 47, an electric fan control unit 48, and an electric thermo valve control unit 49 as control means for the cooling system. Included.

  The electric water pump control unit 47 is based on a detection signal from the water temperature sensor 33, when the engine is stopped, the cooling water temperature is high, and the cooling water needs to be circulated (for example, a predetermined period after the engine is automatically stopped). The electric water pump 57 is activated.

  The electric fan control unit 48 operates the fan motor 52 when it is necessary to promote heat exchange in the radiator unit L2 (for example, when the coolant temperature is high).

  The electric thermo valve control unit 49 turns on the electric thermo valve 53 to lower the temperature of the cooling water when the cooling water temperature is higher than a predetermined valve opening temperature. When the cooling water temperature is lower than the valve opening temperature (for example, during warm-up operation), the electric thermo valve 53 is turned OFF to prevent the cooling water temperature from being excessively lowered. The opening temperature of the electric thermo valve 53 of this embodiment is set to about 90 ° C. in the low load region of the engine and about 75 ° C. in the high load region.

The ECU 2 opens the electric thermo valve 53 and at least the electric water pump during a period including at least a predetermined period during which the engine is automatically stopped (that is, a part or all of the period during which the engine is automatically stopped, or a period including these periods) . The in-cylinder cooling mode for activating 57 is executed. The in-cylinder cooling mode will be described in detail later.

  The operation of the present embodiment having the above-described configuration will be described particularly with respect to the features of the present invention. First, during normal operation of the engine, when the coolant temperature is higher than a predetermined valve opening temperature, the electric thermo valve 53 is turned on and opened. When the electric thermo valve 53 is turned ON, the cooling water is circulated to the radiator L2, so that heat exchange with the surrounding air is performed and the temperature is lowered. Since this cooling water is recirculated to the water jacket portion L1 by the water pump 56, the engine is properly cooled and stable operation can be performed.

  When the cooling water temperature is lower than the predetermined valve opening temperature, the electric thermo valve 53 is turned off and closed. When the electric thermo valve 53 is turned OFF, the cooling water is not circulated to the radiator part L2, but is returned to the water jacket part L1 through the bypass part L3. Therefore, it is possible to suppress heat dissipation more than necessary from the radiator and improve fuel efficiency. Further, when there is a request to increase the temperature of the cooling water, such as immediately after the engine is started, the temperature increase can be promoted.

  Next, the idle stop control of this embodiment will be described below. In the idle stop control, the fuel supply is stopped to stop the engine when a predetermined engine automatic stop condition is satisfied, and the engine is restarted when the predetermined restart condition is satisfied after the engine is stopped. In the present embodiment, one of the engine automatic stop conditions is such that the coolant temperature is equal to or higher than a predetermined automatic stop permission temperature (for example, 60 ° C.). By doing so, idle stop is reliably prevented when the combustion is unstable, such as during warm-up operation, and the reduction in restartability is suppressed.

  When restarting, the combustion is first performed in the compression stroke cylinder, whereby the piston 13 is pushed down and the crankshaft 3 is slightly reversed. As a result, the piston 13 of the expansion stroke cylinder is once raised (closed to top dead center), and the air in the cylinder (which becomes the air-fuel mixture after fuel injection) is compressed and ignited and burned. ing. By this combustion, a driving torque in the normal rotation direction is applied to the crankshaft 3 to restart the engine.

  In order to properly restart the engine simply by igniting the fuel injected into a specific cylinder as described above, sufficient combustion energy is obtained by burning the air-fuel mixture in the expansion stroke cylinder. Accordingly, the cylinder that reaches the compression top dead center (in this embodiment, the compression stroke cylinder and the intake 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. 4A and 4B, since the phases of the compression stroke cylinder and the expansion stroke cylinder are shifted by 180 ° CA, 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).

  The ECU 2 performs the following control so as to stop the piston 13 within the proper stop range R. FIG. 5 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. 6 is an enlarged view after the vicinity of the time point t1 in FIG. 5. In addition to FIG. 5, a crank angle CA and a stroke transition chart of each cylinder are shown. 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). . 5 and 6 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. 6, 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 rotational speed Ne gradually decreases and eventually stops at time t5. As shown in FIGS. 5 and 6, the engine rotational 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. 6, 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. 6) has passed, no cylinder 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. 6 (for example, about K1 = 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 t3 in FIG. 6) 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 time 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. 6) that is lower (or closed) than K1. 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.

  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 cooling water temperature is equal to or higher than a predetermined automatic stop permission temperature (for example, 60 ° C.), the brake switch is kept on for a predetermined time, and the remaining battery level is equal to or higher than a preset reference value. Yes, when it is confirmed that the vehicle speed is a predetermined value (for example, 10 km / h) or less, it is determined that the automatic engine stop condition is satisfied, and one of the above requirements is not satisfied. Is determined that the automatic engine 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 in-cylinder cooling mode is executed. That is, the electric thermo valve 53 is opened (step S2) and the electric water pump 57 is driven (step S3). The electric fan 51 is also driven (step S4).

  Then, control for automatically stopping the engine sequentially is executed. First, the shift range of the automatic transmission is set to neutral so as to be in a no-load state (step S5), and an EGR valve (not shown) provided in the EGR passage is closed to stop exhaust gas recirculation (step S5). S6) The target value (target speed) of the engine rotational speed Ne is set to a value N1 (for example, about 850 rpm) higher than the normal idle rotational speed (step S7). 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 S8), and the engine The ignition timing retard amount is calculated so that the rotational speed Ne becomes the target speed N1 (step S9). 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, step S5 and step S6 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. .

  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 S10), the process returns to step S8 and the control operation is repeated. Then, at the time when YES is determined in step S10 (time t1 in FIGS. 5 and 6), the throttle valve 23 is opened to a relatively large opening (about 30%) (step S11), and the alternator 28 is turned on. The power generation amount is set to 0 to stop power generation (step S12), and fuel injection is stopped (step S13).

  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 S14). Then, the throttle valve 23 is closed when it is determined YES in step S14 (time t2) (step S15). As a result, the boost pressure Bt that opens the throttle valve 23 in step S11 so as to approach the atmospheric pressure starts to decrease with a predetermined time difference according to 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 S14 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 S16). If it determines with YES here, it will control from now on so that the rotational speed Ne of an engine may fall along the preset reference line. In the present embodiment, the power generation amount of the alternator 28 is adjusted so that the top dead center rotational speed ne at the time of each compression top dead center that sequentially passes is within the appropriate rotational speed range (step S17). Specifically, when the top dead center rotational speed ne is high, the power generation amount is increased to increase the rotational resistance of the crankshaft 3, and the lowering speed of the engine rotational speed Ne is increased to increase the next top dead center rotational speed ne. Approaches the preset reference line. Conversely, when the top dead center rotational speed ne is low, the power generation amount is decreased.

  Then, each time each cylinder sequentially passes through the compression top dead center, it is determined whether or not the engine top dead center rotational speed ne is equal to or lower than a predetermined value N3 (step S18). 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 point when each cylinder sequentially passes through the compression top dead center is also detected and stored.

  If NO is determined in step S18, the control operation is repeated after returning to step S13, and YES is determined in step S18, and the engine top dead center rotational speed ne becomes equal to or lower than the predetermined value N3. When it is confirmed (time t4), it is determined that the last top dead center has been passed. Further, at this time point t4, the boost pressure Bt at the time when the compression top dead center has passed the previous time (time point t3) is read out and determined as the boost pressure Bt at the second compression top dead center from before the stop ( Step S19).

  The top dead center rotational speed ne (hereinafter referred to as final top dead center rotational speed ne1) when passing through the last compression top dead center and the boost pressure Bt (hereinafter referred to as boost pressure Bt2) at the second compression top dead center from before the stop. ), It is determined whether or not the tendency to stop near the late stage of the stroke (close to the bottom dead center in the expansion stroke cylinder 12A) is large (step S20). Specifically, 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 the first predetermined pressure P2 (for example, P2 = −200 mmHg) (vacuum side). Sometimes, the tendency to stop near the end of the stroke (the position where the piston stop position in the expansion stroke cylinder 12A is close to 120 ° CA with respect to the appropriate range R in which 100 to 120 ° CA after compression top dead center) is large. Determined.

  If it is determined NO in this step S20, 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 K of the throttle valve 23 is increased so as to be the first predetermined opening K1 set to about 40%, and the intake flow rate is increased (step S21). 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 the determination in step S19 is YES, the piston 13 is in the latter half of the stroke when 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. Accordingly, the throttle valve 23 is opened so that the opening K becomes the second predetermined opening K2 (opening close to the opening of the throttle valve 23 when the valve is closed in step S11, for example, K2 = about 5%). The opening degree K is adjusted (step S22). 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 stopped (step S23). 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 S24), the control operation is terminated.

  FIG. 9 is a flowchart showing the piston stop position detection control operation shown in step S24 of FIG. 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. 10A 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. 10A, 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. 10 (b), 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 the engine is stopped, the piston stop position is obtained by examining the measured value of the CA counter (step S44), and the process returns.

  Next, the in-cylinder cooling mode will be described below. When the engine is completely stopped by the automatic stop control as described above, the water pump 56 is stopped. At this time, if the electric water pump 57 is also stopped, the in-cylinder temperatures of the cylinders 12A to 12D change as shown in the temperature characteristics of FIG. FIG. 11 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, if the circulation of the cooling water stops when the engine is completely stopped, the in-cylinder temperature starts to rise rapidly immediately after the stop. Then, it peaks at about 10 seconds after the engine stops, and gradually decreases thereafter.

  When the in-cylinder temperature is high (near the peak in FIG. 11), the in-cylinder air density is small. Therefore, if the engine is restarted at this time, the combustion energy of the engine is lowered and the restartability may be reduced. Therefore, in this embodiment, the ECU 2 executes the in-cylinder cooling mode to suppress a rapid temperature increase as shown in the temperature characteristics of FIG.

  In the in-cylinder cooling mode, the electric thermo valve 53 is opened and the electric water pump and the electric fan 51 are operated. By doing so, the cooling water can be circulated to the radiator L2 even when the engine is stopped, and the temperature rise in the cylinder can be suppressed. Moreover, since the heat exchange in the radiator L2 is promoted by the electric fan 51, the cooling effect is increased, and the in-cylinder temperature rise suppressing effect can be further enhanced.

  The start time of the in-cylinder cooling mode is set earlier than the time when the in-cylinder temperature reaches a maximum value (peak) after the engine is automatically stopped when the electric water pump is not operated (in the example of FIG. 11, about 10 s after the engine is stopped). Is effective. For example, it may be 5 s after the engine stop before the in-cylinder temperature reaches the peak or earlier, but in this embodiment, it is set to be when the engine automatic stop condition is satisfied (time t0 in FIG. 5). Yes. By setting at such an early stage, a higher cooling effect can be obtained. Moreover, the effect that the alternator power generation margin at the time of restart is increased in advance by increasing the power consumption before the engine is stopped (details will be described later).

  The in-cylinder cooling mode may be ended when the increase in the in-cylinder temperature reaches an allowable level even if this is ended. In the present embodiment, this time is set as a preset timer value (in the example of FIG. 11, 30 s to 60 s after the engine stop is appropriate). In addition, for example, it may be the time when the estimated value of the in-cylinder temperature by the in-cylinder temperature estimation unit 46 becomes a predetermined value or less. By doing so, the in-cylinder temperature is prevented from dropping more than necessary.

  When the restart condition is established during the in-cylinder cooling mode and the engine is restarted, the in-cylinder cooling mode is terminated.

  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.

  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 front stage fuel injection is performed at the beginning of the reverse rotation operation, and the rear stage fuel injection is performed during the reverse rotation operation. 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 combustion 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, the piston stop position of the expansion stroke cylinder 12A, and the in-cylinder air temperature at the start of reverse rotation (estimation). Value), 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, when the in-cylinder air temperature is relatively high, the subsequent fuel injection timing is delayed. 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 from a stopped state is performed, when a battery voltage is reduced, or when an air conditioner is activated) is satisfied ( 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.) The incombustible fuel then reacts with oxygen stored in a catalyst (not shown) provided 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. Will come to do.

  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 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. (Step S153), the ignition timing is delayed after the top dead center (Step S154). By doing so, the temperature rise of the catalyst 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).

  By executing the restart control, as shown in FIG. 15, first, the first fuel injection J3 is performed in the compression stroke cylinder 12C (# 3 cylinder), and combustion is performed by ignition. With the combustion pressure (part a in FIG. 15) due to this combustion, 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 that the density of the compressed air (air mixture) increases (part b in FIG. 15).

  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. And the engine is driven in the forward rotation direction by the combustion pressure (c portion in FIG. 15).

  Furthermore, fuel that is richer than the combustible air-fuel ratio is injected into the compression stroke cylinder 12C at an appropriate timing (J4), so that the compression stroke cylinder 12C is not combusted, but the compression stroke is caused by the latent heat of vaporization caused by the fuel injection. The compression pressure of the cylinder 12C is reduced (d portion in FIG. 15). 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. Therefore, 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. 15). 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 energy of the first combustion in the expansion stroke cylinder 12A can exceed the first compression top dead center and the second compression top dead center after the start of restart, and a smooth and reliable startability can be ensured. .

  Thereafter, the air-fuel ratio is made lean (λ> 1) or the ignition timing is delayed in accordance with the temperature of the catalyst to shift to normal operation while preventing blow-up.

  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 restart by only the combustion of the present embodiment, the engine is once reversed, but it is not always necessary to do so, and the engine may be operated in the normal rotation direction from the beginning.

  In the above embodiment, the fuel injection for the initial combustion in the expansion stroke cylinder 12A at the time of restart is divided injection (J1 + J2). However, 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.

  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 the restartability, the stop position of the piston 13 in the expansion stroke cylinder 12A is slightly closer to the bottom dead center than the stroke center (in the compression stroke cylinder 12C, slightly closer to the top dead center than the stroke center). 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 a cooling system circuit block diagram 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. 6 is a partially enlarged view of FIG. 5, and is a time chart showing a crank angle and a stroke transition of each cylinder. It is the first half part of the flowchart which shows the engine automatic stop operation. It is the latter half part of the flowchart which shows the engine automatic stop operation | movement. 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 graph which shows the relationship between the elapsed time from an engine stop, and a cylinder temperature estimated value. 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 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)
33 Water temperature sensor 50 Radiator 51 Electric fan (fan)
53 Electric Thermo Valve (Thermo Valve)
57 Electric water pump L Cooling water circuit

Claims (7)

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 stop, at least the expansion stroke cylinder in the expansion stroke when the engine is stopped In an engine starter that supplies fuel and ignites and restarts the engine by burning,
A water temperature sensor for detecting the engine coolant temperature,
An electric water pump capable of forcibly circulating engine cooling water even when the engine is stopped;
A radiator provided on the engine coolant circuit for reducing the engine coolant temperature by heat exchange;
A thermo valve provided on the cooling water circuit and capable of switching between a valve opening state for guiding cooling water to the radiator side and a valve closing state for not guiding cooling water to the radiator side;
One of the engine automatic stop conditions includes that the coolant temperature is equal to or higher than a predetermined automatic stop permission temperature,
The opening temperature of the thermo valve during engine operation is set to be higher than the automatic stop permission temperature,
When the engine is automatically stopped due to the establishment of the engine automatic stop condition, the thermo valve is opened and the electric motor is operated even when the coolant temperature of the engine is lower than the opening temperature of the thermo valve. An engine starter characterized in that an in-cylinder cooling mode for operating a water pump is executed.   2. The start timing of the in-cylinder cooling mode is set so as to be earlier than the time when the in-cylinder temperature reaches a maximum value after the engine is automatically stopped when the electric water pump is not operated. Engine starter.   2. The engine starting device according to claim 1, wherein the start timing of the in-cylinder cooling mode is set to be within 5 seconds after the engine is automatically stopped.   2. The engine starter according to claim 1, wherein the start timing of the in-cylinder cooling mode is set so as to be when the engine automatic stop condition is satisfied. Opening temperature of the thermo-valve in the engine operation, in the low load region of the engine is hot relative to the high load region, and the feature that it is set to be a higher temperature than the automatic stop permission temperature The engine starting device according to any one of claims 1 to 4. The engine starter according to any one of claims 1 to 5, wherein when the restart condition is satisfied during execution of the in-cylinder cooling mode, the in-cylinder cooling mode is terminated. The radiator is equipped with a fan that sends cooling air,
  The engine starter according to any one of claims 1 to 6, wherein the fan is operated during the in-cylinder cooling mode.

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