JP5888041B2 - Start control device for compression self-ignition engine - Google Patents

Description

  The present invention is provided in a compression self-ignition engine that burns fuel injected from a fuel injection valve into a cylinder by self-ignition, and automatically stops the engine when a predetermined automatic stop condition is satisfied, and then Start control of a compression self-ignition engine that restarts the engine by injecting fuel from the fuel injection valve while applying a rotational force to the engine using a starter motor when the restart condition is satisfied Relates to the device.

Compressed self-ignition engines such as diesel engines are generally more widely used as in-vehicle engines in recent years because they are more thermally efficient than spark ignition engines such as gasoline engines and emit less CO ₂ I am doing.

In the compression self-ignition engine as described above, in order to further reduce CO ₂ , it is effective to employ a so-called idle stop control technology that automatically stops or restarts the engine. Various researches have also been made.

  As an example, Patent Document 1 below discloses that a diesel engine is automatically stopped when a predetermined automatic stop condition is satisfied, and then fuel injection is performed while driving a starter motor when a predetermined restart condition is satisfied. It is disclosed to restart the diesel engine.

  Specifically, in this document, when the diesel engine is automatically stopped, the stop position of the piston of the stop-time compression stroke cylinder in the compression stroke at that time is examined. Thereafter, when the engine restart condition is satisfied, it is determined whether or not the piston stop position of the compression stroke cylinder at the time of stop is within an appropriate range set relatively near the bottom dead center. The first fuel is injected into the compression stroke cylinder at the time of stop, and the engine is started by restarting combustion from the first compression which reaches the first compression top dead center as a whole (hereinafter referred to as this). (Referred to as “1 compression start”).

  On the other hand, when the piston stop position of the compression stroke at the time of stop is on the top dead center side with respect to the appropriate range, after the cylinder that was stopped in the intake stroke (intake stroke cylinder at the time of stop) shifts to the compression stroke. The first fuel is injected into the cylinder, and the engine is started by restarting combustion from the second compression that reaches the second compression top dead center as a whole (hereinafter, this is referred to as “two-compression start”). ).

JP 2009-62960 A

  According to the technique of the above-mentioned Patent Document 1, when the piston of the compression stroke cylinder at the time of stop is in an appropriate range, the engine can be restarted promptly by one compression start injecting fuel from the first compression, If the engine is off to the top dead center side, the two-compression start that injects the fuel from the second compression instead of the first compression prevents the fuel from misfiring while ensuring a certain speed. The engine can be restarted.

  Here, in the above-mentioned Patent Document 1, an appropriate range that is a piston stop position range in which one compression start is possible may naturally be different if the state of the engine at the start of restart is different. For this reason, in order to properly determine whether the engine is in the 1-compression start mode or the 2-compression start-up regardless of the state of the engine, it is necessary to always be able to accurately grasp the crank angle that can be the boundary of the appropriate range. However, since there is a restriction on the structure of a sensor (crank angle sensor) for specifying the piston stop position, it is not easy to satisfy the above requirements.

  The present invention has been made in view of the circumstances as described above, and whether or not 1 compression start is possible while variably setting the boundary of the piston stop position range in which 1 compression start is possible depending on the state of the engine. It is an object of the present invention to provide a start-up control device for a compression self-ignition engine that can always accurately determine the above.

In order to solve the above problems, the present invention is provided in a compression self-ignition engine that burns fuel injected from a fuel injection valve into a cylinder by self-ignition, and when a predetermined automatic stop condition is satisfied. When the engine is automatically stopped and then a predetermined restart condition is satisfied, the engine is restarted by injecting fuel from the fuel injection valve while applying a rotational force to the engine using a starter motor. A start-up control device for a compression self-ignition engine to be started, wherein the control means controls various devices including the fuel injection valve and the starter motor, and the engine crankshaft rotates together with a number of teeth on the outer periphery. And a crank angle sensor that outputs a pulse signal in response to passage of teeth of the crank plate, The control means specifies the piston stop position of the stop-time compression stroke cylinder that has been stopped in the compression stroke when restarting the automatically stopped engine based on the detection signal of the crank angle sensor. Depending on whether or not is at the bottom dead center side with respect to a predetermined reference stop position, the one-compression start for injecting the first fuel into the stop-time compression stroke cylinder, or the stop-time intake stroke stopped in the intake stroke One of the two compression starts for injecting the first fuel into the cylinder is performed while driving the fuel injection valve and the starter motor, and the reference stop position is a boundary between the first compression start and the second compression start. Is variably set according to the degree of progress of warm-up of the engine, and the crank plate has teeth omitted at specific locations on the outer peripheral portion thereof as a reference for cylinder discrimination. And has a missing tooth portions, no signal angular range is a crank angle corresponding to the missing teeth portion, so as not to overlap the variable range of the reference stop position changes depending on the progress of warm-up, the Mu The position of the top dead center side in the signal angle range is set to be the same as or lower than the position of the bottom dead center side in the variable range of the reference stop position, and the fuel injection valve is When the engine is restarted due to the one-compression start, at least the first fuel injection into the compression stroke cylinder at the time of stop is the main injection that causes the main combustion to reach the peak of the heat generation rate after the compression top dead center And pre-injection that causes pre-combustion to reach a peak of the heat generation rate before the start of the main injection, and the stop-time compression stroke at the time of the first compression start The amount of fuel injected into the cylinder is set to be smaller as the piston stop position of the cylinder is closer to top dead center, and the control means is configured such that the piston of the compression stroke cylinder at the time of stop is in the non-signal angle range. When the engine is restarted by the one compression start from that state, the amount of injection to the compression stroke cylinder at the time of stop is most dead in the no-signal angle range. An injection amount corresponding to the position on the point side is set (claim 1).

According to the present invention, the reference stop position for determining whether or not one-compression start is possible is variably set according to the degree of progress of warm-up of the engine. By changing the reference stop position to the top dead center side as the engine is improved, it is possible to flexibly change the piston stop position range in which one compression start is possible and to perform appropriate engine restart. In addition, since the variable range of the reference stop position that changes according to the degree of progress of warm-up does not overlap with the no-signal angle range corresponding to the tooth missing portion of the crank plate, the piston stop position of the compression stroke cylinder at the time of stop is the reference. Whether it is at the bottom dead center side or the top dead center side from the stop position can be accurately detected regardless of the degree of progress of warm-up, and based on the result, 1 compression start and 2 compression start Can be properly used.
Further, at the time of one compression start in which fuel is injected into the stop compression stroke cylinder, pre-injection is first executed, and then main injection is executed. The pre-injected fuel is combusted by self-ignition after a predetermined ignition delay (pre-combustion), and increases the in-cylinder temperature and pressure of the compression stroke cylinder at the time of stop, so when main injection is subsequently executed, The injected fuel will burn soon by self-ignition (main combustion). Thus, since the ignitability of the fuel injected by the main injection is improved by the pre-injection (pre-combustion) before that, even if the compression allowance in the stop compression stroke cylinder is not so much, the stop compression stroke cylinder Combustion at is ensured. As a result, the piston stop position range in which one compression start is possible can be expanded to the top dead center side, and the speeding up of the engine start can be promoted.
In this case, in the present invention, since the no-signal angle range is shifted to the bottom dead center side with respect to the reference stop position range, it is possible to effectively avoid the overlap between the pre-injection timing and the no-signal angle range. The timing of injection can be determined accurately.
In particular, according to the present invention, when it is expected that the piston of the compression stroke cylinder at the time of stop is stopped in any one of the no-signal angle ranges, and the engine is restarted by one compression start from that state, the compression at the time of stop is performed. Since the injection amount to the stroke cylinder is set to the injection amount corresponding to the position of the top dead center side in the no-signal angle range, excess fuel is supplied relative to the amount of air remaining in the cylinder. (That is, the air-fuel mixture becomes over-rich) can be reliably prevented, so that the amount of HC generated by combustion can be suppressed, and low emission at the time of restart can be more reliably achieved.

  In the present invention, preferably, the engine is automatically stopped when the engine coolant temperature is equal to or higher than a reference temperature lower than 80 ° C. (Claim 2).

  According to this configuration, the engine is automatically stopped even when the engine is not warmed up so much, and the opportunity for automatic stop increases. In this case, the reference stop position for determining whether or not one compression start is possible can vary widely depending on the degree of progress of warm-up of the engine. If the non-signal angle range does not overlap each other, whether the piston stopped at the top dead center side or the bottom dead center side from the reference stop position even though the reference stop position fluctuated widely Can be accurately detected. Therefore, according to the above configuration in which the reference temperature for automatic stop is lower than 80 ° C., it is always accurately determined whether or not one compression start is possible while increasing the chance of automatic stop of the engine and further improving fuel efficiency. can do.

  As described above, according to the start-up control device for a compression self-ignition engine of the present invention, one compression start can be performed while variably setting the boundary of the piston stop position range where one compression start is possible depending on the state of the engine. Whether it is possible or not can always be determined accurately.

It is a figure showing the whole diesel engine composition to which the starting control device concerning one embodiment of the present invention was applied. It is a figure which shows the pulse signal output from a crank angle sensor during driving | operation of an engine. It is a flowchart which shows the specific procedure of the automatic stop control which stops the said engine automatically. It is a time chart which shows the change of the various state quantities at the time of the automatic stop control of the engine. FIG. 5 is a partially enlarged view of the engine speed and crank angle waveforms in the time chart of FIG. 4 and a change in the number of a cylinder that becomes a compression stroke. FIG. 6 is a view corresponding to FIG. 5 in a case where the compression stroke cylinder at the time of stop is different. It is a flowchart which shows the specific procedure of the restart control which restarts the engine which stopped automatically. It is a flowchart which shows the procedure which determines the quantity of the fuel which should be injected into the compression stroke cylinder at the time of an engine restart by 1 compression start. It is a figure for demonstrating the reference | standard stop position which is an upper limit piston stop position in which 1 compression start is possible. It is a figure which shows the positional relationship of the variable range of the said reference | standard stop position, and the no-signal angle range corresponding to the tooth-missing part of a crankplate. It is an example of the map used in order to determine the injection quantity to the said compression stroke cylinder at the time of a stop. It is the figure which showed what timing the injected fuel combusts when fuel is injected separately into pre-injection and main injection.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing an overall configuration of a diesel engine to which a start control device according to an embodiment of the present invention is applied. The diesel engine shown in the figure is a four-cycle diesel engine mounted on a vehicle as a power source for driving driving. The engine body 1 of this engine is of a so-called in-line 4-cylinder type, and is provided on the upper surface of the cylinder block 3 having a cylinder block 3 having four cylinders 2A to 2D arranged in a line in a direction orthogonal to the paper surface. A cylinder head 4 and a piston 5 inserted in each of the cylinders 2A to 2D so as to be reciprocally slidable are provided.

  A combustion chamber 6 is formed above the piston 5, and light oil as fuel is supplied to the combustion chamber 6 by injection from a fuel injection valve 15 described later. The injected fuel (light oil) is self-ignited in the combustion chamber 6 that has been heated to a high temperature and pressure by the compression action of the piston 5 (compression self-ignition), and the piston 5 pushed down by the expansion force due to the combustion is moved vertically. It is designed to reciprocate.

  The piston 5 is connected to the crankshaft 7 via a connecting rod (not shown), and the crankshaft 7 rotates around the central axis in accordance with the reciprocating motion (vertical motion) of the piston 5. .

  Here, in the four-cycle four-cylinder diesel engine as shown in the figure, the piston 5 provided in each of the cylinders 2A to 2D moves up and down with a phase difference of 180 ° (180 ° CA) in crank angle. For this reason, the timing of combustion (fuel injection therefor) in each of the cylinders 2A to 2D is set to a timing shifted in phase by 180 ° CA. Specifically, if the cylinder numbers of the cylinders 2A, 2B, 2C, and 2D are 1, 2, 3, and 4, respectively, the first cylinder 2A → the third cylinder 2C → the fourth cylinder 2D → the second cylinder Combustion is performed in the order of 2B. For this reason, for example, if the first cylinder 2A is in the compression stroke, the third cylinder 2C, the fourth cylinder 2D, and the second cylinder 2B have an intake stroke, an exhaust stroke, and an expansion stroke, respectively.

  The cylinder head 4 is provided with an intake port 9 and an exhaust port 10 that open to the combustion chambers 6 of the cylinders 2A to 2D, and an intake valve 11 and an exhaust valve 12 that open and close the ports 9 and 10, respectively. The intake valve 11 and the exhaust valve 12 are driven to open and close in conjunction with the rotation of the crankshaft 7 by valve mechanisms 13 and 14 including a pair of camshafts and the like disposed in the cylinder head 4.

  The cylinder head 4 is provided with one fuel injection valve 15 for each of the cylinders 2A to 2D. Each fuel injection valve 15 is connected to a common rail 20 as a pressure accumulation chamber via a branch pipe 21. In the common rail 20, fuel (light oil) supplied from the fuel supply pump 23 through the fuel supply pipe 22 is stored in a high pressure state, and the fuel increased in pressure in the common rail 20 passes through the branch pipe 21 to each fuel injection valve. 15 respectively.

  The fuel injection valve 15 is of a multi-hole type having a plurality of (for example, 8 to 12) injection holes at the tip, a fuel passage communicating with each of the injection holes, and the fuel passage. And a needle-like valve element that is electromagnetically driven to open and close (both are not shown). The valve body is driven in the opening direction by electromagnetic force generated by energization, so that the fuel supplied from the common rail 20 is directly injected from the respective injection holes toward the combustion chamber 6.

  A cavity 5a is formed in the center portion of the crown surface (upper surface) of the piston 5 facing the fuel injection valve 15 so as to be recessed below other portions (peripheral edge portions of the crown surface). For this reason, when the fuel is injected from the fuel injection valve 15 with the piston 5 being near the top dead center, the fuel first enters the cavity 5a.

  Here, the engine body 1 of the present embodiment has a geometric compression ratio (ratio of the combustion chamber volume when the piston 5 is at bottom dead center and the combustion chamber volume when the piston 5 is at top dead center). Is set to 14. That is, the geometric compression ratio of a general vehicle-mounted diesel engine is often set to 18 or more, whereas in this embodiment, the geometric compression ratio is set to a considerably low value of 14. Has been.

  A water jacket (not shown) through which cooling water flows is provided inside the cylinder block 3 and the cylinder head 4, and a water temperature sensor SW1 for detecting the temperature of the cooling water in the water jacket is provided in the cylinder. It is provided in the block 3.

  The cylinder block 3 is provided with a crank angle sensor SW2 for detecting the rotation angle and rotation speed of the crankshaft 7. The crank angle sensor SW2 outputs a pulse signal according to the rotation of the crank plate 25 that rotates integrally with the crankshaft 7.

  Specifically, a large number of teeth 25a arranged at a constant pitch project from the outer periphery of the crank plate 25, and a plurality of teeth 25a are omitted from a specific reference position on the outer periphery. A portion 25b is formed. Then, the crank plate 25 having the tooth missing portion 25b at the reference position rotates in this way, and a pulse signal based on the crank plate 25 (ON / OFF signal based on the presence or absence of the tooth 25a) is output from the crank angle sensor SW2. The rotation angle (crank angle) and rotation speed (engine rotation speed) of the crankshaft 7 are detected.

  FIG. 2 shows a pulse signal output from the crank angle sensor SW2 during engine operation. As shown in the figure, the pulse signal from the crank angle sensor SW2 includes a non-signal portion P generated every 360 ° CA corresponding to the tooth missing portion 25b of the crank plate 25 described above. . That is, since no pulse signal is generated by the number of teeth omitted in the tooth missing portion 25b, a non-signal portion P having no signal is generated over a predetermined period. Since the number of omitted teeth in the tooth missing portion 25b is generally 5 or more, for example, if the pitch angle of the teeth 25a (the angular interval between adjacent teeth 25a) is 6 degrees, The no-signal portion P is generated at least 30 degrees in crank angle.

  The no-signal part P is generated at a frequency of once every two cycles. For example, in the case of the first cylinder 2A and the fourth cylinder 2D, the non-signal portion P is generated only when the cylinder is in the compression stroke or the exhaust stroke.

  As shown in FIG. 1, the cylinder head 4 is provided with a cam angle sensor SW3 for detecting the angle of a valve camshaft (not shown). The cam angle sensor SW3 outputs a pulse signal for cylinder discrimination according to the passage of the teeth of the signal plate that rotates together with the camshaft.

  That is, in the pulse signal output from the crank angle sensor SW2 during the operation of the engine, there is a non-signal portion (P portion in FIG. 2) every 360 ° CA corresponding to the above-mentioned tooth missing portion 25b. Although it is generated, it is not possible to recognize which cylinder is in how many strokes (cylinder discrimination) even if the crank angle can be known only by the information. Therefore, a pulse signal is output from the cam angle sensor SW3 based on the rotation of the camshaft that rotates once every 720 ° CA, the timing at which the signal is output, and the timing (tooth) of the non-signal portion P of the crank angle sensor SW2. The cylinder is determined based on the passage timing of the chipped portion 25b.

  An intake passage 28 and an exhaust passage 29 are connected to the intake port 9 and the exhaust port 10, respectively. That is, intake air (fresh air) from the outside is supplied to the combustion chamber 6 through the intake passage 28 and exhaust gas (combustion gas) generated in the combustion chamber 6 is discharged to the outside through the exhaust passage 29. It is like that.

  Of the intake passage 28, a range from the engine body 1 to the upstream side by a predetermined distance is a branch passage portion 28a branched for each of the cylinders 2A to 2D, and the upstream end of each branch passage portion 28a is a surge tank 28b. It is connected to the. A common passage portion 28c including a single passage is provided on the upstream side of the surge tank 28b.

  The common passage portion 28c is provided with an intake throttle valve 30 for adjusting the amount of air (intake flow rate) flowing into the cylinders 2A to 2D. The intake throttle valve 30 is basically fully opened during operation of the engine or maintained at a high opening degree close thereto, and is configured to be closed only when necessary, such as when the engine is stopped, to block the intake passage 28. Has been.

  An air flow sensor SW4 for detecting the intake air flow rate is provided in the common passage portion 28c between the intake throttle valve 30 and the surge tank 28b.

  An alternator 32 is connected to the crankshaft 7 via a belt or the like. This alternator 32 incorporates a regulator circuit that controls the current of a field coil (not shown) and adjusts the amount of power generation. Based on the current), the driving force is obtained from the crankshaft 7 to generate power.

  The cylinder block 3 is provided with a starter motor 34 for starting the engine. The starter motor 34 has a motor body 34a and a pinion gear 34b that is rotationally driven by the motor body 34a. The pinion gear 34b meshes with a ring gear 35 connected to one end of the crankshaft 7 so as to be detachable. When the engine is started using the starter motor 34, the pinion gear 34b moves to a predetermined meshing position and meshes with the ring gear 35, and the rotational force of the pinion gear 34b is transmitted to the ring gear 35. As a result, the crankshaft 7 is driven to rotate.

(2) Control system Each part of the engine configured as described above is centrally controlled by an ECU (engine control unit) 50. As is well known, the ECU 50 is a microprocessor including a CPU, a ROM, a RAM, and the like, and functions as a control unit according to the present invention.

  Various information is input to the ECU 50 from various sensors. That is, the ECU 50 is electrically connected to the water temperature sensor SW1, the crank angle sensor SW2, the cam angle sensor SW3, and the airflow sensor SW4 provided in each part of the engine, and input signals from these sensors SW1 to SW4. Based on the above, various information such as engine coolant temperature, crank angle, rotational speed, cylinder discrimination information, intake air flow rate, and the like are acquired.

  The ECU 50 also receives information from various sensors (SW5 to SW9) provided in the vehicle. That is, the vehicle includes an accelerator opening sensor SW5 for detecting the opening degree of the accelerator pedal 36 that is depressed by the driver, and a brake sensor for detecting ON / OFF of the brake pedal 37 (presence of braking). SW6, a vehicle speed sensor SW7 for detecting the traveling speed (vehicle speed) of the vehicle, a battery sensor SW8 for detecting the remaining capacity of the battery (not shown), and a room temperature sensor SW9 for detecting the temperature in the vehicle interior And are provided. Based on the input signals from these sensors SW5 to SW9, the ECU 50 acquires information such as the accelerator opening, the presence / absence of the brake, the vehicle speed, the remaining battery capacity, and the vehicle interior temperature.

  The ECU 50 controls each part of the engine while executing various calculations based on input signals from the sensors SW1 to SW9. Specifically, the ECU 50 is electrically connected to the fuel injection valve 15, the intake throttle valve 30, the alternator 32, and the starter motor 34. The control signal is output.

  More specific functions of the ECU 50 will be described. For example, during normal operation of the engine, the ECU 50 causes the fuel injection valve 15 to inject a required amount of fuel that is determined based on operating conditions, and the required power generation amount that is determined based on the electric load of the vehicle, the remaining battery capacity, and the like. In addition to the basic function of generating power, the engine has a function of automatically stopping or restarting the engine under a predetermined specific condition as a so-called idle stop function. For this reason, the ECU 50 includes an automatic stop control unit 51 and a restart control unit 52 as functional elements related to engine automatic stop or restart control.

  That is, the automatic stop control unit 51 determines whether or not a predetermined engine automatic stop condition is satisfied while the engine is operating, and executes control to automatically stop the engine when it is satisfied. It is.

  The restart control unit 52 determines whether or not a predetermined restart condition is satisfied after the engine is automatically stopped, and executes control to restart the engine when the restart condition is satisfied. is there.

(3) Automatic Stop Control Next, the contents of the automatic engine stop control executed by the automatic stop control unit 51 of the ECU 50 will be described with reference to the flowchart of FIG. 3 and the time chart of FIG.

  When the process shown in the flowchart of FIG. 3 is started, the automatic stop control unit 51 executes control for reading various sensor values (step S1). Specifically, the detection signals from the water temperature sensor SW1, the crank angle sensor SW2, the cam angle sensor SW3, the airflow sensor SW4, the accelerator opening sensor SW5, the brake sensor SW6, the vehicle speed sensor SW7, the battery sensor SW8, and the room temperature sensor SW9, respectively. Based on these signals, various information such as engine coolant temperature, crank angle, rotation speed, cylinder discrimination information, intake air flow rate, accelerator opening, presence / absence of brake, vehicle speed, remaining battery capacity, vehicle interior temperature, etc. To get.

  Next, the automatic stop control unit 51 determines whether or not an automatic engine stop condition is satisfied based on the information acquired in Step S1 (Step S2). For example, the vehicle is in a stopped state, the opening degree of the accelerator pedal 36 is zero (accelerator OFF), the brake pedal 37 is depressed more than a predetermined depression force (brake ON), and the engine coolant temperature is Multiple requirements such as being above a predetermined reference temperature, the remaining battery capacity being above a predetermined value, and the load of the air conditioner (the difference between the cabin temperature and the set temperature of the air conditioner) being relatively small When they are aligned, it is determined that the automatic stop condition is satisfied. As for the requirement that the vehicle is in a stopped state, it is not always necessary to make a complete stop (vehicle speed = 0 km / h), and the vehicle stops when the vehicle speed falls below a predetermined low vehicle speed (for example, 3 km / less). You may determine with being in a state. Further, the reference temperature, which is the lower limit value of the coolant temperature of the engine, is set to a value (for example, 30 ° C.) that is considerably lower than 80 ° C., which is a guideline temperature at which the engine is sufficiently warmed up. That is, in the present embodiment, the automatic engine stop is executed not only when the engine is in a warm-up state, but also when it is in a semi-warm-up state where the coolant temperature is lower than this.

  When it is determined YES in step S2 and it is confirmed that the automatic stop condition is satisfied, the automatic stop control unit 51 sets the opening degree of the intake throttle valve 30 to the normal opening degree (set during idle operation). For example, the control is performed to decrease from 80% to fully closed (0%) (step S3). In the time chart of FIG. 4, the time point when the automatic stop condition is satisfied is t1, and the time point when the opening degree of the intake throttle valve 30 starts to decrease thereafter is t2.

  Next, the automatic stop control unit 51 executes a fuel cut that stops the supply of fuel from the fuel injection valve 15 (step S4). That is, after the intake throttle valve 30 is fully closed (0%), the target injection amount that is the amount of fuel to be injected from the fuel injection valve 15 of each cylinder 2A to 2D is set to zero, and all the fuel injection valves are set. The fuel cut is executed by stopping the fuel injection from 15. In the time chart of FIG. 4, the fuel cut is executed at a time point t3 slightly after the time point when the intake throttle valve 30 is fully closed.

  After the fuel cut is executed, the engine temporarily rotates by inertia as shown in the engine speed waveform after time t3 in FIG. Specifically, the engine rotational speed drops temporarily every time one of the four cylinders 2A to 2D reaches the compression top dead center (the top dead center between the compression stroke and the expansion stroke), and the compression top dead center is reduced. After going up and down, it will gradually decrease while repeating up and down.

  The time point t4 in FIG. 4 shows the timing of the final TDC, which is the top dead center that the engine finally reaches during the stop operation. After exceeding this final TDC, the engine never reaches the top dead center (while temporarily rotating backward due to the swinging back of the piston), and finally reaches a complete stop at time t5. In FIG. 4, the cycle of each cylinder 2A to 2D when the engine is stopped (cylinder cycle after time t4 of the final TDC) is the compression stroke of the first cylinder 2A, the intake stroke of the third cylinder 2C, and the fourth cylinder 2D. Is the exhaust stroke, and the second cylinder 2B is the expansion stroke.

  After executing the fuel cut in step S4, the automatic stop control unit 51 determines whether or not the rotational speed of the engine is 0 rpm, that is, whether or not the engine is completely stopped (step S5). When it is determined YES in this case and it is confirmed that the engine is completely stopped, the automatic stop control unit 51 sets the opening of the intake throttle valve 30 to a normal opening (for example, 80%). After returning (step S6), the automatic stop control is terminated.

  5 is a partially enlarged view of the engine speed and crank angle waveforms in the time chart of FIG. 4, and also shows changes in the cylinder number (compression stroke cylinder No.) for the compression stroke. In FIG. 4, the cylinder that finally stops in the compression stroke is the first cylinder 2A. Therefore, in FIG. 5, the compression stroke cylinder no. Becomes “1” (the first cylinder 2A). The compression stroke cylinder No. before the final TDC (time t4) is also displayed. For “2” (No. 2 cylinder 2B) from the top dead center one to the last TDC before the final TDC, “4” (No. 4 from the last two TDCs to the top TDC before the last TDC. Cylinder 2D), and “3” (3rd cylinder 2C) from the top dead center three to three before the final TDC.

  As shown in FIG. 5, the crank angle waveform after the time point t4 when the first cylinder 2A is in the compression stroke (that is, the detected angle by the crank angle sensor SW2) has a large crank angle as shown by the broken circle. A part to jump occurs. In addition, when going back before time t4, it can be seen that the same phenomenon is seen every time when going back one cycle (that is, once every two cycles). This corresponds to the tooth missing portion 25b of the crank plate 25.

  That is, as described above with reference to FIG. 2, in the pulse signal from the crank angle sensor SW2, there is a non-signal portion P every 360 ° CA corresponding to the tooth missing portion 25b of the crank plate 25. Arise. Since this no-signal part P is generated when the first cylinder 2A or the fourth cylinder 2D is in the compression stroke, in FIG. 5, in FIG. 5, the last cycle after the time point t4 and its cycle A crank angle jump phenomenon (circled by a broken line) is seen in each cycle two to four before. The fine steps other than the portion showing the jump phenomenon are caused by the pitch angle of the teeth 25a formed on the crank plate 25 (the angular interval between adjacent teeth 25a). In other words, if the pitch angle of the tooth 25a is α, a pulse signal is output from the crank angle sensor SW2 for each pitch angle α (see FIG. 2), and therefore the detected angle by the crank angle sensor SW2 is also the above-mentioned value. It will be recognized step by step for each pitch angle α.

  Here, a crank angle range in which a jump phenomenon of the crank angle due to the non-signal portion P is observed is defined as a non-signal angle range H, and upper and lower limit angles are defined as V2 and V1, respectively. In the example of FIG. 5, it is apparent that the piston 5 of the first cylinder 2A in the compression stroke at the time of stoppage is stopped at the position of the angle V1. However, a pulse signal from the crank angle sensor SW2 cannot be obtained in the angles V1 to V2 (no signal angle range H), and an accurate crank angle cannot be recognized. Therefore, actually, the piston 5 of the cylinder 2A is not limited to the angle V1, but may be stopped at any position between the angles V1 and V2 (see the waveform of W indicated by the broken line). . In the present embodiment, the no-signal angle range H is set to a position that does not overlap with a later-described reference stop position X in the first half of the compression stroke.

  The above-mentioned problem that the exact piston stop position of the cylinder stopped in the compression stroke (hereinafter referred to as the compression stroke cylinder at the time of stop) is not known is also the case where the compression stroke cylinder at the stop is the fourth cylinder 2D. It occurs in the same way. This is because the non-signal portion P shown in FIG. 2 is generated not only when the first cylinder 2A but also the fourth cylinder 2D is in the compression stroke.

  On the other hand, if the compression stroke cylinder at the time of stop is the second cylinder 2B or the third cylinder 2C, the above problem does not occur. This is because the non-signal portion P does not occur when the second cylinder 2B or the third cylinder 2C is in the compression stroke, as shown in FIG.

  FIG. 6 is a view corresponding to FIG. 5 when the compression stroke cylinder at the time of stop is the third cylinder 2C. In this figure, the piston stop position (crank angle) of the third cylinder 2C is the angle V1, which means that the actual piston stop position is also the angle V1. That is, when the compression stroke cylinder at the time of stop is the third cylinder 2C (the same applies to the second cylinder 2B), the pulse signal from the crank angle sensor SW2 is obtained in the entire angle range during the compression stroke. Thus, there is no influence of the no-signal angle range H, and an accurate piston stop position can be known. Of course, more strictly speaking, the crank angle can be recognized only in a stepwise manner due to the presence of the pitch angle α of the teeth 25a in the crank plate 25. However, the non-signal angle range H (the tooth missing with a plurality of teeth 25a omitted) Compared with the case of FIG. 5 in which the crank angle cannot be recognized over a range corresponding to the portion 25b), the influence is small.

  As described above, in the present embodiment, when the first cylinder 2A or the fourth cylinder 2D stops in the compression stroke, the presence of the no-signal angle range H in which the crank angle detection angle jumps greatly. A situation may occur in which an accurate piston stop position cannot be recognized. That is, even if the piston 5 of the first cylinder 2A or the fourth cylinder 2D stops at any position in the no-signal angle range H, it is recognized only at the angle V1 that is the boundary of the no-signal angle range H. It is not possible to recognize the exact piston stop position.

  Such a problem that the piston stop position of the specific cylinder (the first cylinder 2A or the fourth cylinder 2D) may not be accurately recognized needs to be considered when the engine is restarted. The specific contents will be described in the following “(4) Restart control”.

(4) Restart Control Next, the specific contents of the engine restart control executed by the restart control unit 52 of the ECU 50 will be described with reference to the flowchart of FIG. When the process shown in this flowchart starts, the restart control unit 52 reads various sensor values (step S11), and determines whether or not the engine restart condition is satisfied based on the values (step S12). ). For example, the brake pedal 37 has been released, the accelerator pedal 36 has been depressed, the engine coolant temperature has fallen below the reference temperature (for example, 30 ° C.), and the amount of decrease in the remaining battery capacity has an allowable value. Exceeded, the engine stop time (elapsed time after automatic stop) exceeded the upper limit time, the necessity of air conditioner operation occurred (that is, the difference between the passenger compartment temperature and the air conditioner set temperature It is determined that the restart condition is satisfied when at least one of the requirements such as “exceeded” is satisfied.

  When it is determined as YES in Step S12 and it is confirmed that the restart condition is satisfied, the restart control unit 52 executes control for determining the reference stop position X shown in FIG. 9 (Step S13). . Here, the reference stop position X serves as a reference for determining whether the engine is restarted in the first compression start or the second compression start described later, and the engine detected by the water temperature sensor SW1. It is variably set according to the cooling water temperature (that is, according to the progress degree of warm-up). Specifically, the reference stop position X is set to the top dead center side as the cooling water temperature of the engine is high, and the reference stop position X is set to the bottom dead center side as the cooling water temperature is low.

  Next, the restart control unit 52 specifies the piston stop position of the stop-time compression stroke cylinder (the first cylinder 2A in FIG. 4) stopped in the compression stroke in accordance with the engine automatic stop control described above based on the crank angle sensor SW2. Then, it is determined whether or not the specified piston stop position is at the bottom dead center side with respect to the reference stop position X determined in step S13, that is, within the specific range Y shown in FIG. 9 (step S14).

  When it is determined NO in step S14 and it is confirmed that the piston 5 of the compression stroke cylinder at the time of stoppage is stopped at the top dead center side from the specific range Y, the restart control unit 52 stops at the intake stroke. A control is performed to restart the engine by the two-compression start in which the first fuel is injected into the stopped intake stroke cylinder (the third cylinder 2C in FIG. 4) that has been performed (step S16). That is, only the drive of the starter motor 34 is performed without injecting fuel until the piston 5 of the compression stroke cylinder at the time of stop passes the first compression point when the top dead center is reached and the intake stroke cylinder at the time of stop next reaches the compression stroke. To force the engine to rotate. At that time, the fuel is injected from the fuel injection valve 15 into the stop-time intake stroke cylinder, and the injected fuel is self-ignited, so that the combustion as a whole is restarted from the second compression which reaches the second compression top dead center. And restart the engine.

  On the other hand, if it is determined YES in step S14 and it is confirmed that the piston stop position of the compression stroke cylinder at the time of stop is on the bottom dead center side (specific range Y) from the reference stop position X, the restart control unit 52 Performs a control for restarting the engine by one compression start for injecting the first fuel into the compression stroke cylinder at the time of stop (the first cylinder 2A in FIG. 4) (step S15). That is, the starter motor 34 is driven to apply a rotational force to the crankshaft 7 and fuel is injected from the fuel injection valve 15 into the compression stroke cylinder at the time of stop to cause self-ignition, whereby the engine as a whole is first compressed top dead. Combustion is restarted from the first compression that reaches a point, and the engine is restarted.

  The engine can be restarted by one compression start as in step S15 above if the piston stop position of the stop-time compression stroke cylinder is within a specific range Y that is relatively close to the bottom dead center. This is because (the stroke amount up to the top dead center) is large, and as the piston 5 rises at the time of restarting the engine, the air in the cylinder is sufficiently compressed to increase the temperature and pressure. In the engine restart by the 1 compression start, the time required for the engine restart compared to the time of the 2 compression start (step S14) in which the combustion is not restarted until the second compression when the intake stroke cylinder at the stop reaches the compression top dead center, That is, the time from the start of driving of the starter motor 34 to the complete explosion of the engine (for example, the state where the rotational speed reaches 750 rpm) can be shortened, and the engine can be restarted more quickly.

  As described above, in the present embodiment, the one-compression start (S15) and the two-compression start are performed depending on whether or not the piston 5 of the stop-time compression stroke cylinder is stopped at the bottom dead center side from the reference stop position X. (S16) is properly used. The reference stop position X (FIG. 9), which is the piston stop position between the 1-compression start and the 2-compression start, is variably set according to the engine coolant temperature as described above. In the embodiment, the reference stop position is set so that the reference stop position X in any case is on the top dead center side (or at least the same as the upper limit angle V2 of the no-signal angle range H) above the no-signal angle range H. A variable range of the position X is set.

  FIG. 10 shows a no-signal angle range H that occurs when the first cylinder 2A or the fourth cylinder 2D is in the compression stroke, and a range that the reference stop position X can take (that is, a reference stop position that changes according to the engine coolant temperature). It is a figure which illustrates the positional relationship with X variable range) Rx. As shown in the figure, the variable range Rx of the reference stop position X is set to a position that does not overlap with the no-signal angle range H. Specifically, in the present embodiment, the position (lower limit angle) closest to the bottom dead center in the variable range Rx of the reference stop position X is set to the same V2 as the upper limit angle of the no-signal angle range H, and the reference stop position X The position (upper limit angle) closest to the top dead center in the variable range Rx is set to V3 which is shifted to the top dead center side from the angle V2.

  A preferred example will be described using specific numerical values. The no-signal angle range H may occur in a section of 42 to 72 ° CA after bottom dead center (ABDC) during the compression stroke of the cylinders 2A and 2D. At this time, the variable range Rx of the reference stop position X can be set to, for example, ABCC 72 to 102 ° CA. That is, in this example, the lower limit angle V1 of the no-signal angle range H, the upper limit angle (= the lower limit angle of the variable range Rx of the reference stop position X) V2, and the upper limit of the variable range Rx of the reference stop position X The angles V3 are ABDC 42, 72, and 102 ° CA, respectively.

  When the variable range Rx of the reference stop position X is set to ABDC 72 to 102 ° CA as in the above example, the reference stop position X is set as follows according to the cooling water temperature. That is, the reference stop position X is set to ABCC 72 ° CA (= lower limit angle V2) in a state where the cooling water temperature is lowered to a reference temperature (for example, 30 ° C.) that is a lower limit temperature at which the engine can be automatically stopped. When the cooling water temperature rises, it changes to the top dead center side, and when the cooling water temperature is sufficiently raised (for example, 80 ° C. or higher), it is set to ABDC 102 ° CA (= upper limit angle V3). The

  Next, how fuel is injected when performing one compression start in step S15 will be described. When performing a one-compression start, basically, an appropriate amount of fuel commensurate with the amount of air existing in the cylinder is used as the first fuel injection into the compression stroke cylinder at the time of stop (the first fuel injection). Be injected. At this time, it is conceivable to complete the injection fuel to the compression stroke cylinder at the time of stopping, but in this embodiment, the fuel is injected in a plurality of times. Specifically, in addition to the main injection injected near or at the compression top dead center, a pre-injection that is a preliminary injection prior to the main injection is performed. The pre-injection is executed at least once before the compression top dead center and within a crank angle range in which the injected fuel is contained in the cavity 5a of the piston 5 crown surface.

  The fuel injected by the pre-injection is used to reliably cause diffusion combustion (hereinafter, this combustion is referred to as “main combustion”) that occurs mainly after compression top dead center based on the main injection. That is, in a stage earlier than the main injection, a small amount of fuel is injected by pre-injection, and the injected fuel is burned after a predetermined ignition delay (hereinafter, this combustion is referred to as “pre-combustion”). Increase the temperature and pressure to promote the subsequent main combustion.

  If pre-injection as described above is performed on the compression stroke cylinder at the time of stop, the in-cylinder temperature and pressure near the compression top dead center can be intentionally increased, so the piston stop position of the compression stroke cylinder at the time of stop is slightly Even when approaching the top dead center side, the engine can be reliably restarted by one compression start. The reference stop position X, which is the boundary of the specific range Y, is set in consideration of the improvement in ignitability by such pre-injection. That is, when there is no pre-injection, the reference stop position X must be set to the bottom dead center side than the example of FIG. 10, but the reference stop is improved by improving the ignitability by pre-injection. It becomes possible to set the position X to the top dead center side. As a result, the reference stop position X can be set to a position far away from the bottom dead center, for example, ABCC 72 to 102 ° CA. . As a result, the specific range Y expands to the top dead center side, so that the piston 5 of the compression stroke cylinder at the time of stop fits in the specific range Y at a higher frequency and there is an opportunity to perform a quick restart by one compression start. Increase. In particular, in this embodiment, since the geometric compression ratio of the engine body 1 is as low as 14 and it is difficult to ensure the ignitability of the fuel, it is possible to improve the ignitability at the start by the pre-injection. 1 It is particularly effective in increasing the chance of starting compression.

FIG. 12 is a diagram showing a mode of fuel injection at the time of one compression start performed in step S15. Here, as an example, pre-injection is executed three times. Specifically, between ABDC 162 to 170 ° CA, fuel of 2 mm ³ is injected three times as a pre-injection (lower waveform Ip), and then more than the pre-injection as the main injection (at least The fuel is injected at a compression top dead center (ABDC 180 ° CA) (more than in one pre-injection) (lower waveform Im). In addition, the waveforms (Bp, Bm) shown in the upper part of FIG. 12 illustrate the state of combustion that occurs as a result of such fuel injection as a change in the heat generation rate.

  As shown in FIG. 12, when three pre-injections (Ip) are executed, after completion of the last pre-injection, a predetermined ignition delay time elapses and pre-injection due to self-ignition of the pre-injected fuel is performed. Combustion (Bp) occurs. This pre-combustion (Bp) occurs before the compression top dead center (ABDC 180 ° CA), and then converges after reaching the peak of the heat generation rate, but the main injection (Im) starts from the vicinity of the compression top dead center. By being started, main combustion (Bm) due to self-ignition of the fuel injected by the main injection continues. This main combustion (Bm) starts combustion after a very short ignition delay (diffusion combustion) based on main injection (Im) executed in a state in which the inside of the cylinder is heated to high temperature and pressure by pre-combustion (Bp). .

  FIG. 12 shows a mode of fuel injection of the first compression (fuel injection to the stop-time compression stroke cylinder) performed at the time of starting the one-compression, but the compression stroke is performed after the stop-time compression stroke cylinder. Also for the cylinders (No. 3 Cylinder 2C and No. 4 Cylinder 2D in FIG. 4), the same combustion control based on pre-injection and main injection may be executed as necessary. The most ignitable when restarting the engine is the first compression that reaches the first compression top dead center of the engine as a whole, but at least the second and third compressions are not enough to improve the ignitability. It is possible.

  Further, the combustion control based on the pre-injection and the main injection as described above is performed not only at the time of 1 compression start in which combustion by fuel injection is resumed from the first compression but also by 2 compression in which combustion by fuel injection is resumed from the second compression. It is desirable to do the same when starting the engine by starting.

  Here, in this embodiment, when the compression stroke cylinder at the time of stop is a specific cylinder (the first cylinder 2A or the fourth cylinder 2D), as described above, the piston stop position of the cylinder cannot be accurately grasped. Cases can arise. For this reason, when the engine is restarted by the one-compression start, it is necessary to change the way of determining the amount of fuel to be injected first, depending on the number of the stop-time compression stroke cylinder. This point will be described in detail with reference to the flowchart of FIG. 8 showing a specific control procedure for one compression start.

  When the process shown in the flowchart of FIG. 8 is started, the restart control unit 52 determines whether the cylinders stopped in the compression stroke (the compression stroke cylinder at the time of stop) of the first cylinder 2A and the fourth cylinder 2D in accordance with the automatic engine stop control. It is determined whether it is any one or other cylinders (step S21). When YES is determined here (that is, when the first cylinder 2A or the fourth cylinder 2D is a stop-time compression stroke cylinder), the restart control unit 52 performs compression at the time of stop detected by the crank angle sensor SW2. It is determined whether or not the piston stop position (crank angle) of the stroke cylinder is the angle V1 shown in FIG. 5 (step S22).

  If NO is determined in any of the above steps S21 and S22, that is, whether the compression stroke cylinder at the time of stop is the second cylinder 2B or the third cylinder 2C, or the detected crank angle of the compression stroke cylinder at the time of stop is an angle If not V1, control is performed to read the injection amount corresponding to the piston stop position from a predetermined map stored in advance as the initial fuel injection amount injected into the compression stroke cylinder at the time of stop (step S24).

  FIG. 11 shows an example of a map used to determine the fuel injection amount to the compression stroke cylinder at the time of stop. As shown in this figure, the injection amount (total injection amount of the pre-injection amount and the main injection amount) to the compression stroke cylinder at the time of stop is smaller as the piston stop position of the cylinder is on the top dead center (TDC) side. Is set. It should be noted that the compression stroke at the time of the stop is a one-compression start in which fuel is injected and burned from the first compression at which the compression top dead center reaches compression top dead center, when the piston stop position of the cylinder is closer to the bottom dead center side than the reference stop position X Therefore, the injection amount data shown in FIG. 11 is set only between the bottom dead center (BDC) and the reference stop position X. And based on such map data, the injection amount to the compression stroke cylinder at the time of stop is set to decrease as it approaches the reference stop position X, and is set to increase as it moves away from the reference stop position X toward the bottom dead center side. Become.

  The fuel injection amount is set in the above manner because the closer the piston stop position is to the top dead center (or the reference stop position X), the smaller the amount of air present in the compression stroke cylinder at the time of stop. Because it becomes. That is, in the compression stroke cylinder at the time of stop, since the compressed air in the cylinder leaks to the outside from the gap between the piston 5 and the cylinder wall surface immediately after the engine is completely stopped, the pressure in the cylinder eventually becomes The air in the cylinder may decrease until atmospheric pressure is reached. Therefore, in anticipation of such an air leak after engine stop, the amount of air in the stop compression stroke cylinder is considered to be smaller as the piston stop position is at the top dead center, and an appropriate fuel injection amount is set. I am doing so.

  Further, in FIG. 11, the injection amount is set finely in a stepwise manner, which corresponds to the pitch angle of the teeth 25 a of the crank plate 25. For example, if the pitch angle is 6 degrees, the piston stop position can be recognized only in increments of 6 degrees. Accordingly, the injection amount is set stepwise in increments of 6 degrees.

  In the map of FIG. 11, not only the injection amount (total injection amount of main injection and pre-injection) but also the number of pre-injections is variably set according to the piston stop position. Is done. Specifically, the number of pre-injections is set to be larger as the piston stop position is closer to the top dead center (or the reference stop position X), and is set to be smaller as the piston is closer to the bottom dead center. For example, it is set to 3 times in the case closest to the top dead center and 1 time in the case closest to the bottom dead center.

When the fuel injection amount to the stop compression stroke cylinder and the number of pre-injections are determined based on the map of FIG. 11, the restart control unit 52 follows the determined injection amount and the number of pre-injections. Control for injecting fuel into the compression stroke cylinder at the time of stop is executed (step S25). For example, from the map of FIG. 11, it is determined that the injection amount (total injection amount) is 25 mm ³ and the number of pre-injections is three, and that the injection amount per pre-injection is 2 mm ^3. In this case, in the control in step S25, the pre-injection of the amount of 2 mm ³ is executed three times, and the main injection of the amount of 25-2 × 3 = 19 mm ³ is executed.

  Next, the case where YES is determined in step S22, that is, the case where the stop-time compression stroke cylinder is the first cylinder 2A or the fourth cylinder 2D and the detected crank angle of the cylinder is the angle V1 will be described. . In this case, if the map of FIG. 11 is used as it is, the fuel injection amount to the compression stroke cylinder (2A or 2D) at the time of stop is the injection amount Q1 corresponding to the angle V1, more precisely the angles V1 to (V1 + α). ) Is set to the injection amount Q1 corresponding to the section. However, when the detected crank angle is the angle V1, as indicated by the broken line waveform W in FIG. 5, the actual stop position (crank angle) of the piston 5 is not the angle V1, but the angles V1 to V2 (none). Any of the signal angle ranges H). For this reason, if the injection amount is set to Q1, when the actual piston stop position is at the top dead center side from the angle V1 + α, excess fuel is supplied with respect to the actual air amount. The air-fuel mixture may become overrich. If it does so, the quantity of HC produced by combustion will increase, and it will lead to impairing the emission nature at the time of starting.

  In order to avoid such a situation, in the next step S23, not the angle V1, but the injection amount corresponding to the section (V2-α) to V2 closer to the top dead center than this (when the angle is V1). Is set as the injection amount to the compression stroke cylinder at the time of stop. That is, the restart control unit 52, as shown by a broken line in FIG. 11, is a section in which the pitch angle α is returned from the angle V2 that is the upper limit angle (the limit value on the top dead center side) of the no-signal angle range H. That is, the injection amount Q2 corresponding to the section from the angle (V2-α) to V2 is read as the injection amount to the stop-time compression stroke cylinder. As for the number of pre-injections, the number of times when the piston stop position (crank angle) is in the section (V2-α) to V2 is read. Then, in accordance with the injection amount determined in this way and the number of pre-injections, control is performed to inject fuel into the stop-time compression stroke cylinder (step S25).

(5) Operational effects and the like As described above, in the present embodiment, in a diesel engine having a so-called idle stop function that automatically stops or restarts the engine under a predetermined condition, Adopting a characteristic configuration.

  When the restart condition is satisfied after the engine is automatically stopped, the restart control unit 52 of the ECU (engine control unit) 50 is based on the detection signal of the crank angle sensor SW2 and stopped during the compression stroke. It is checked whether or not the piston 5 of the cylinder is on the bottom dead center side (specific range Y) with respect to the predetermined reference stop position X. When the piston stop position of the stop-time compression stroke cylinder is on the bottom dead center side with respect to the reference stop position X, the engine is restarted by one-compression start in which the first fuel is injected into the stop-time compression stroke cylinder. On the other hand, if this is not the case (when the piston 5 is stopped at the top dead center side from the specific range Y), the second compression start is performed in which the first fuel is injected into the stop intake stroke cylinder that has been stopped in the intake stroke. To restart the engine.

  The reference stop position X that is the boundary between the 1-compression start and the 2-compression start is variably set according to the progress of engine warm-up (more specifically, the value of the coolant temperature). The variable range Rx (angles V2 to V3 in FIG. 10) is a non-signal generated corresponding to the tooth missing portion 25b of the crank plate 25 when a specific cylinder (the first cylinder 2A or the fourth cylinder 2D) is in the compression stroke. It is set not to overlap with the angle range H (angles V1 to V2).

  According to the above configuration, whether or not one compression start is possible while variably setting the reference stop position X, which is the boundary of the piston stop position range in which one compression start is possible, depending on the degree of progress of warm-up of the engine. There is an advantage that can always be accurately determined.

  That is, in the above embodiment, the reference stop position X for determining whether or not one compression start is possible is variably set according to the degree of progress of engine warm-up (the value of engine coolant temperature). For example, by changing the reference stop position X to the top dead center side as the warm-up progresses and the ignitability is improved, the piston stop position range (specific range Y) in which one compression start is possible is flexibly changed. And appropriate engine restart. Further, since the variable range Rx of the reference stop position X that changes according to the progress degree of warm-up does not overlap with the no-signal angle range H corresponding to the tooth missing portion 25b of the crank plate 25, the compression stroke cylinder of the stop time Whether the piston stop position is at the bottom dead center side or the top dead center side from the reference stop position X can be accurately detected regardless of the degree of progress of warm-up, and based on the result, one compression is performed. It is possible to properly use starting and two-compression starting.

  For example, if it is assumed that the variable range Rx of the reference stop position X and the no-signal angle range H overlap, when the piston stops in the overlap range, the exact piston position is not known. However, there are cases where it is necessary to select the 2-compression start. On the other hand, in the above embodiment, such a situation cannot occur, so it can always be determined accurately whether or not one compression start is possible.

  In particular, in the above-described embodiment, the reference temperature, which is the lower limit value of the cooling water temperature at which the automatic stop of the engine is permitted, is lower than 80 ° C., which is a guideline temperature at which it can be said that the warm-up has sufficiently progressed (for example, 30 ° C. ), The engine is automatically stopped even when the engine is not warmed up so much, and the opportunity for automatic stop increases. In this case, the reference stop position X for determining whether or not one compression start is possible can vary widely depending on the progress of warm-up of the engine. However, as in the above embodiment, the reference stop position X If the variable range Rx and the no-signal angle range H do not overlap with each other, the reference stop position X varies widely, but the upper dead center side or the lower dead center side than the reference stop position X. It is possible to accurately detect which of the pistons 5 has stopped. Therefore, according to the above embodiment in which the reference temperature for automatic stop is lower than 80 ° C., it is always accurately determined whether or not one compression start is possible while increasing the chance of automatic stop of the engine and further improving fuel efficiency. Judgment can be made.

  Further, in the above embodiment, as shown in FIG. 12, for example, as the fuel injection to the compression stroke cylinder at the time of one compression start, the main heat generation rate peaks after the compression top dead center is reached. Main injection (Im) that causes combustion (Bm) and pre-injection (Ip) that causes pre-combustion (Bp) that reaches the peak of the heat generation rate before the start of the main injection are executed. . According to such a configuration, it is possible to further improve the ignitability at the time of one-compression start and further accelerate the engine start.

  That is, a small amount of pre-injected fuel is burned by self-ignition after a predetermined ignition delay (pre-combustion), and the in-cylinder temperature / pressure of the compression stroke cylinder at the time of stop is increased, so that main injection is subsequently executed. When this is done, the injected fuel will soon burn by self-ignition (main combustion). In this way, since the ignitability of the main injected fuel is improved by the pre-injection (pre-combustion) before that, the compression allowance (stroke amount to the top dead center) in the compression stroke cylinder at the time of stop is so much. Even if not, combustion in the compression stroke cylinder at the time of stop is reliably performed. As a result, the piston stop position range (specific range Y) in which one compression start is possible can be expanded to the top dead center side, and the speed of engine start can be accelerated.

  In the above embodiment, as shown in FIG. 11, the number of pre-injections performed on the compression stroke cylinder at the time of one compression start is such that the closer the piston stop position of the cylinder is to the top dead center. Many are set. According to such a configuration, the injected fuel can be reliably supplied even in a situation where the increase in the in-cylinder temperature and pressure in the vicinity of the compression top dead center cannot be expected so much because the piston 5 in the compression stroke at the time of stop is close to the top dead center. Can be burned. That is, as the piston stop position is closer to the top dead center, the number of pre-injections is increased, so that the amount of injection per pre-injection is reduced and spray penetration is suppressed. As a result, a rich air-fuel mixture that is easily ignited is formed in the cylinder (inside the cavity 5a), so that the ignitability can be improved effectively, and the opportunity for starting one compression can be further increased.

  In the above embodiment, when the engine is restarted by one compression start, the amount of fuel injected into the stop compression stroke cylinder is basically determined by the top dead center (or reference stop position) of the piston 5 of the cylinder. X is set to be smaller as it stops at a position closer to X). However, when it is predicted that the piston 5 is stopped in the no-signal angle range H (angles V1 to V2) corresponding to the tooth missing portion 25b of the crank plate 25, that is, the stop compression stroke cylinder is the first. When the cylinder 2A or the fourth cylinder 2D and the detection position of the piston 5 based on the crank angle sensor SW2 is the angle V1, as shown by a broken line in FIG. Alternatively, the injection amount to 2D) is set to the injection amount Q2 corresponding to the position of the top dead center side in the no-signal angle range H (more precisely, the section between the angles V2-α to V2). According to such a configuration, it is possible to prevent an excessive amount of fuel from being supplied, and to ensure good emission characteristics at the time of restart.

  That is, when the piston 5 of the stop-time compression stroke cylinder (2A or 2D) is stopped in the no-signal angle range H, the stop position of the piston 5 cannot be accurately known by the crank angle sensor SW2. 5, the actual stop position of the piston 5 may be shifted to the top dead center side from the detection position based on the crank angle sensor SW2. In response to such a problem, in the above-described embodiment, when the piston 5 of the stop-time compression stroke cylinder (2A or 2D) is expected to stop in the no-signal angle range H, the no-signal angle range H Is set uniformly to the minimum injection amount Q2 corresponding to the position of the top dead center side (angle V2-α to V2) in the engine, so that the amount of fuel that is excessive relative to the amount of air remaining in the cylinder Is reliably prevented (that is, the air-fuel mixture becomes over-rich). As a result, the amount of HC generated by combustion can be suppressed, and the emission can be reduced more reliably at the time of restart.

  In the above embodiment, as shown in FIG. 10, the no-signal angle range H that occurs when the first cylinder 2A or the fourth cylinder 2D is in the compression stroke changes according to the degree of progress of warm-up. The position of the tooth missing portion 25b of the crank plate 25 is set so as to shift toward the bottom dead center side with respect to the variable range Rx of the stop position X. The no-signal angle range H is equal to the variable range Rx of the reference stop position X. It suffices if it exists at a position that does not overlap, and may be set at a position shifted to the top dead center side with respect to the variable range Rx, that is, one of the angle ranges Z in FIG. However, when the no-signal angle range H is set in such an angle range Z, at least one fuel injection including the pre-injection Ip and the main injection Im performed on the compression cylinder at the time of the compression start is performed. There is a possibility that it cannot be controlled accurately. That is, if the no-signal angle range H exists in the angle range Z that is relatively close to the top dead center, the timing of the pre-injection Ip executed before the compression top dead center and the no-signal angle range H overlap. There is a possibility that the timing of pre-injection cannot be determined accurately. In order to surely avoid such a situation, it is desirable to shift the no-signal angle range H to the bottom dead center side with respect to the variable range Rx of the reference stop position X as in the above-described embodiment.

  In the above embodiment, the position of the top dead center side (upper limit angle) in the no-signal angle range H and the position of the lowest dead center side (lower limit angle) in the variable range Rx of the reference stop position X are both Although the angle V2 is the same and the variable range Rx of the reference stop position X and the no-signal angle range H are continuous, of course, the upper limit angle of the no-signal angle range H and the variable range Rx are separated from each other. May be.

  In the above embodiment, the establishment of the automatic stop condition or the restart condition of the engine is determined including the requirements regarding the operation of the accelerator pedal 36 and the brake pedal 37. This is based on the AT car installed. On the other hand, when the vehicle is not an AT vehicle, that is, when the vehicle is an MT vehicle equipped with a manual transmission, requirements different from the above can be adopted. For example, regarding the automatic stop condition, a requirement that the gear stage of the manual transmission is neutral and the clutch pedal is released can be set in place of the requirement that the accelerator is OFF and the brake is ON. Regarding the restart condition, a requirement that the clutch pedal is depressed can be set instead of the requirement that the accelerator is ON or the brake is OFF.

  Moreover, in the said embodiment, although the preferable form of this invention was demonstrated taking the example of the diesel engine provided with the engine main body 1 whose geometric compression ratio is 14, the engine which can apply the structure of this invention naturally. Is not limited to a geometric compression ratio of 14. From the viewpoint of ensuring emission properties and ignitability, the diesel engine to which the present invention can be suitably applied is a diesel engine having a geometric compression ratio of 12 or more and less than 16, more preferably geometric compression. A diesel engine having a ratio of 13 to 15.

  The present invention is not limited to a diesel engine (an engine that burns light oil by self-ignition) as in the above embodiment as long as it is a compression self-ignition engine. For example, recently, an engine of a type that compresses fuel containing gasoline at a high compression ratio and self-ignites has been researched and developed, but the present invention also applies to such a compression self-ignition type gasoline engine. Such automatic stop / restart control can be suitably applied.

DESCRIPTION OF SYMBOLS 1 Engine main body 2A-2D Cylinder 5 Piston 15 Fuel injection valve 25 Crank plate 25a Tooth 25b Tooth missing part 34 Starter motor 50 ECU (control means)
SW2 Crank angle sensor X Reference stop position Rx (reference stop position) variable range H No signal angle range Ip Pre-injection Im Main injection Bp Pre-combustion Bm Main combustion

Claims (2)

Provided in a compression self-ignition engine that burns fuel injected from a fuel injection valve into a cylinder by self-ignition, and automatically stops the engine when a predetermined automatic stop condition is satisfied, and then restarts the engine A start control device for a compression self-ignition engine that restarts the engine by injecting fuel from the fuel injection valve while applying rotational force to the engine using a starter motor. ,
Control means for controlling various devices including the fuel injection valve and the starter motor;
A crank plate that rotates integrally with the crankshaft of the engine and has a large number of teeth on the outer periphery;
A crank angle sensor that outputs a pulse signal according to the passage of the teeth of the crank plate,
The control means specifies the piston stop position of the stop-time compression stroke cylinder that has been stopped in the compression stroke when restarting the automatically stopped engine based on the detection signal of the crank angle sensor, and the specified piston stop position Depending on whether or not is at the bottom dead center side with respect to a predetermined reference stop position, the one-compression start for injecting the first fuel into the stop-time compression stroke cylinder, or the stop-time intake stroke stopped in the intake stroke One of the two compression starts for injecting the first fuel into the cylinder is performed while driving the fuel injection valve and the starter motor,
The reference stop position that becomes the boundary between the 1-compression start and the 2-compression start is variably set according to the progress degree of warm-up of the engine,
The crank plate has a tooth missing portion in which teeth are omitted in order to serve as a cylinder discrimination reference at a specific portion of the outer peripheral portion, and a no-signal angle range that is a crank angle corresponding to the tooth missing portion is The position of the top dead center side in the no-signal angle range is the lowest dead center in the variable range of the reference stop position so as not to overlap with the variable range of the reference stop position that changes according to the progress degree of warm-up. It is set to the same as the position of the side or the bottom dead center side than this ,
The fuel injection valve has a main combustion that reaches the peak of the heat generation rate after passing the compression top dead center at least as the first fuel injection to the compression stroke cylinder at the time of stop when the engine is restarted by the one compression start. Is controlled to execute a main injection that causes a pre-combustion that causes a peak of the heat generation rate before the start of the main injection,
The amount of fuel injected into the stop-time compression stroke cylinder at the time of the one-compression start is set to be smaller as the piston stop position of the cylinder is closer to the top dead center,
When the engine is restarted by the one-compression start from that state, the control means is expected to stop the piston of the compression stroke cylinder at the time of stop at any one of the non-signal angle ranges. A start control device for a compression self-ignition engine, characterized in that the injection amount to the hour compression stroke cylinder is set to an injection amount corresponding to a position on the most dead center side in the non-signal angle range . The start control device for a compression self-ignition engine according to claim 1,
The above-mentioned control means permits the automatic stop of the engine when the engine coolant temperature is equal to or higher than a reference temperature lower than 80 ° C.

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