JP5910125B2 - Start control device for compression self-ignition engine - Google Patents

Description

  The present invention is provided in a vehicle equipped with a compression self-ignition engine that burns fuel injected into a cylinder from a fuel injection valve by self-ignition, and automatically stops the engine when a predetermined automatic stop condition is satisfied. And a start control device 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 a predetermined restart condition is established. .

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 , the engine is automatically stopped at the time of idle operation or the like, and then the engine is restarted when the vehicle is started. It is effective to adopt a so-called idle stop control technique, and various studies have been conducted on this.

  For example, in Patent Document 1 below, when a predetermined automatic stop condition is satisfied, the diesel engine is stopped, and when a predetermined restart condition is satisfied, fuel injection is performed while the starter motor is driven to restart the diesel engine. In a control device for a diesel engine to be started, it is disclosed to variably set a cylinder for injecting fuel first based on a piston stop position of a cylinder stopped in a compression stroke (compression stroke cylinder at stop).

  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 obtained, and the piston stop position is relatively close to the bottom dead center. In the case of being in the proper position, the first fuel is injected into the above-mentioned compression stroke cylinder at the time of stop so that the first compression top dead center of the engine as a whole is obtained. Combustion is resumed from the time of arrival (hereinafter referred to as “one compression start”).

  On the other hand, when the piston in the compression stroke at the time of stop is at the top dead center side from the appropriate position, the cylinder stopped in the intake stroke (intake stroke cylinder at the time of stop) shifts to the compression stroke and then the cylinder first By injecting this fuel, combustion is restarted from the time when the engine reaches the second compression top dead center (hereinafter referred to as “two-compression start”). As described above, the two-compression start in which fuel is injected into the stop intake stroke cylinder instead of the stop compression stroke cylinder is performed when the piston of the stop compression stroke cylinder is deviated from the appropriate position to the top dead center side. Because the compression allowance (stroke amount to top dead center) by the piston is small and the air in the cylinder does not sufficiently heat up, misfire may occur even if fuel is injected into the compression stroke cylinder at the time of stop. is there.

JP 2009-62960 A

  In 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 position, the engine is restarted by one compression start, so the time required for restarting the engine (the time until the engine completes explosion) ) Can be shortened, and quick startability can be secured.

  However, according to the research of the present inventor, when one compression start is performed in which the first fuel is injected into the compression stroke cylinder at the time of stop, the torque fluctuation of the engine accompanying the combustion is caused by the resonance of the power train system including the engine and the transmission. It has been found that vibrations close to the frequency may be generated. Such vibration is easy to detect even if it is very temporary.

  However, for example, when the occupant (driver) operates the accelerator and restarts the engine, it is the engine restart intended by the occupant, and the vehicle starts at the same time as the engine restarts. Such vibrations are not particularly conscious and are at a level that does not give a sense of incongruity. However, for example, when the engine is restarted due to a request on the system (decrease in battery power, etc.), it is an engine restart that is not intended by the occupant, and the engine is restarted while the vehicle is stopped. Even slight vibrations are easily detected (conscious) and give the passenger a sense of incongruity. Therefore, in such a case, it is desirable to restart the engine with as little vibration as possible.

  The present invention has been made in view of the circumstances as described above, and vibrations at the time of engine restart are made possible when there is no vehicle start request while prompt engine restart by one compression start is attempted. It is an object of the present invention to provide a start control device for a compression self-ignition engine that can be reduced to a low level.

In order to solve the above problems, the present invention is provided in a vehicle equipped with a compression self-ignition engine that burns fuel injected from a fuel injection valve into a cylinder by self-ignition, and has a predetermined automatic stop condition. By automatically stopping the engine when established, and then injecting fuel from the fuel injection valve while applying a rotational force to the engine using a starter motor when a predetermined restart condition is established, A start control device for restarting the engine, wherein a piston of a stop-time compression stroke cylinder that has stopped in a compression stroke due to the automatic stop is in a specific range set to a lower dead center side than a predetermined reference stop position. Determination means for determining whether or not the piston of the compression stroke cylinder at the time of stop is stopped in the specific range, and the engine restart condition is satisfied The case, by controlling the fuel injection valve while injecting the first fuel into the stop-state compression-stroke cylinder, such as a the first fuel injection, reaches a peak of heat release rate from the past CTDC Injection control means for executing main injection that causes main combustion and pre-injection that causes pre-combustion that reaches a peak of the heat generation rate before the start of the main injection, and the injection control means includes: If the restart condition is not based on a start request for the driver to start the vehicle, the injection amount of the first fuel injection to be performed for the stop-time compression stroke cylinder is less than the time established for the restart conditions based on the start request from the user, control to reduce the first fuel injection amount for the stop-state compression-stroke, said Mei while the same injection amount of the pre-injection A control to reduce the injection amount of injection, is characterized in that (claim 1).

  According to the present invention, when the piston of the stop-time compression stroke cylinder is stopped in a specific range relatively near the bottom dead center, the first fuel is injected into the stop-time compression stroke cylinder after the restart condition is satisfied. The engine can be restarted quickly by the compression start. However, even if the piston stop position is within a specific range, if the establishment of the restart condition is not based on a start request from the driver, the engine is restarted with the vehicle stopped. Therefore, if a normal amount of fuel is injected at the time of one compression start, the vibration at the time of restart may be clearly sensed by the occupant. Therefore, even in a situation where one compression start is performed (when the piston stop position is in a specific range), if the restart condition is not based on the start request from the driver, the compression at stop is performed. A one-compression start in a special mode in which the amount of injection into the stroke cylinder is reduced. As a result, the energy of combustion that first occurs in the engine is reduced, and the vibration frequency based on the combustion (vibration frequency due to torque fluctuation between the first combustion and the second combustion) is moved away from the resonance frequency of the powertrain system. Therefore, the magnitude of vibration transmitted to the passenger compartment can be reduced, and NVH performance (noise, vibration, and harshness reduction effect) can be improved.

Further, in the present invention, pre-injection is first executed at the time of one compression start in which the engine is restarted by fuel injection to the stop-time compression stroke cylinder, 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 (specific range) 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.

Further, in the present invention, the control for reducing the initial fuel injection amount for the compression stroke at the time of stop is performed by reducing the injection amount of the main injection while keeping the same injection amount of the pre-injection, so that it is relatively early. By making the injection amount of the pre-injection performed the same, the misfire is surely prevented, and the injection amount of the subsequent main injection is reduced, thereby reducing the torque due to the first combustion that occurs in the stop compression stroke cylinder. The vibration at the time of restart can be effectively suppressed.

  As described above, according to the start-up control device for a compression self-ignition engine according to the present invention, when the vehicle is not required to start while the engine is restarted quickly by one compression start, Vibration can be reduced as much as possible.

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 flowchart which shows the specific procedure of the automatic stop control of the said engine. It is a schematic diagram which illustrates the state of each cylinder at the time of completion | finish of the said automatic stop control. It is a flowchart which shows the specific procedure of the restart control of the said engine. It is a figure which shows the aspect of the fuel injection at the time of 1 compression start by a normal mode, and the combustion waveform based on it. It is a figure which shows the aspect of the fuel injection at the time of 1 compression start by a small injection mode, and the combustion waveform based on it. It is a figure which shows the result of having measured the torque fluctuation | variation at the time of engine restart.

(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. Therefore, for example, if the first cylinder 2A is in the expansion stroke, the third cylinder 2C, the fourth cylinder 2D, and the second cylinder 2B are in the compression stroke, the intake stroke, and the exhaust 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 lined up at a constant pitch are projected on the outer peripheral portion of the crank plate 25, and a tooth missing portion 25a (teeth) for specifying a reference position is provided in a predetermined range on the outer peripheral portion. A portion where no is present) is formed. Then, the crank plate 25 having the tooth missing portion 25a at the reference position rotates in this way, and a pulse signal based on the crank plate 25 is output from the crank angle sensor SW2, whereby the rotation angle (crank angle) of the crankshaft 7 and The rotational speed (engine rotational speed) is detected.

  On the other hand, the cylinder head 4 is provided with a cam angle sensor SW3 for detecting the angle of a camshaft (not shown) for valve actuation. 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, the pulse signal output from the crank angle sensor SW2 includes a non-signal portion generated every 360 ° CA corresponding to the above-mentioned tooth missing portion 25a. Even if the angle can be known, it is not possible to recognize which cylinder is in what stroke (cylinder discrimination). 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 of the non-signal portion of the crank angle sensor SW2 (tooth missing). The cylinder discrimination is performed on the basis of the passage timing of the section 25a.

  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.

  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 SW8) 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, and a battery sensor SW8 for detecting the remaining capacity of the battery (not shown) are provided. The ECU 50 acquires information such as the accelerator opening, the presence / absence of the brake, the vehicle speed, and the remaining battery capacity based on the input signals from the sensors SW5 to SW8.

  The ECU 50 controls each part of the engine while executing various calculations based on input signals from the sensors SW1 to SW8. 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. When the process shown in the flowchart of FIG. 2 is started, the automatic stop control unit 51 executes control for reading various sensor values (step S1). Specifically, the respective detection signals are read 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, and the battery sensor SW8. Based on this signal, various information such as engine coolant temperature, crank angle, rotation speed, cylinder discrimination information, intake air flow rate, atmospheric pressure, accelerator opening, presence / absence of brake, vehicle speed, remaining battery capacity, and the like are acquired.

  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 When all of the requirements are met, such as being above a certain value (that is, the warm-up has progressed to some extent), the remaining capacity of the battery is above a certain value, the load on the air conditioner is relatively small, etc. 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.

  As in step S2, the determination of whether the automatic stop condition is satisfied takes into account not only the vehicle speed and accelerator / brake operation, but also the battery, air conditioner, and engine coolant temperature (the degree of warm-up). This is in consideration of restartability after automatic stopping. For example, when the engine is in a cold state or when the remaining capacity of the battery is extremely small, it may be difficult to restart the engine after automatically stopping the engine. Also, it is not appropriate to stop the engine when the load on the air conditioner (that is, the difference between the temperature in the passenger compartment and the set temperature of the air conditioner) is large. Due to such restrictions on the system, the automatic stop condition includes requirements such as a battery and an air conditioner.

  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).

  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, when the intake throttle valve 30 is fully closed (0%), the target injection amount, which 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 fuels The fuel cut is executed by stopping the fuel injection from the injection valve 15.

  After the fuel cut, the engine temporarily rotates due to inertia but eventually reaches a complete stop. In order to confirm that, the automatic stop control unit 51 determines whether or not the rotational speed of the engine is 0 rpm (step S5). And when it becomes YES here and it is confirmed that the engine has stopped completely, the automatic stop control part 61 returned the opening degree of the intake throttle valve 30 to the opening degree (for example, 80%) at the normal time. Above (step S6), the automatic stop control is terminated.

  FIG. 3 illustrates a state of each cylinder 2A to 2D of the engine after the automatic stop control as described above is completed. In the example of this figure, the first cylinder 2A stops in the expansion stroke, the second cylinder 2B stops in the exhaust stroke, the third cylinder 2C stops in the compression stroke, and the fourth cylinder 2D stops in the intake stroke. Yes. In the following, a cylinder stopped in the XX stroke by the automatic stop control may be referred to as a “stopped XX stroke cylinder”. For example, the cylinder 2C stopped in the compression stroke is referred to as a stop compression stroke cylinder 2C, and the stopped cylinder 2D stopped in the intake stroke is referred to as a stop intake stroke cylinder 2D.

(4) Restart Control Next, the specific content 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. As will be apparent from the description herein, in this embodiment, the restart control unit 52 of the ECU 50 functions as a determination unit that determines the position of the piston 5 of the stop-time compression stroke cylinder 2C, and the engine. It also functions as an injection control means for injecting fuel during restart.

  When the process shown in the flowchart of FIG. 4 starts, the restart control unit 52 determines whether or not the engine restart condition is satisfied based on various sensor values (step S11). For example, the brake pedal 37 has been released, the accelerator pedal 36 has been depressed, the engine coolant temperature has fallen below a predetermined value, the amount of decrease in the remaining battery capacity has exceeded an allowable value, 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 temperature in the passenger compartment and the set temperature of the air conditioner exceeded the allowable value), etc. When at least one of the requirements is satisfied, it is determined that the restart condition is satisfied.

  As in step S11 described above, in the determination of whether the restart condition is satisfied, not only the operation on the accelerator pedal 36 or the brake pedal 37 (that is, the operation for the driver to start the vehicle), but also the battery, air conditioner, and engine coolant temperature. The downtime is also taken into account. For example, if the remaining battery capacity is extremely low or the engine has cooled down due to the engine being stopped for a long time, it will be difficult to restart the engine. Must be restarted. Further, when the difference between the temperature in the passenger compartment and the set temperature of the air conditioner increases, the comfort is impaired, and the engine needs to be restarted in order to operate the air conditioner. Due to such restrictions on the system, the restart condition includes requirements such as a battery and an air conditioner.

  Since the engine restart condition is set as described above, the restart condition can be satisfied not only when the driver performs an accelerator / brake operation but also when there is no such operation. For this reason, the restart conditions can be classified into two types, those based on the start request from the driver and those not based on the start request. The former (restart condition based on the start request) is established by the accelerator / brake operation by the driver, and the latter (restart condition not based on the start request) is the state of the battery or air conditioner or the upper limit stop of the engine. This is established due to system constraints such as time and degree of cooling.

  When it is determined as YES in step S11 and it is confirmed that the restart condition is satisfied, the restart control unit 52 determines the cylinder stopped in the compression stroke with the above-described automatic engine stop control, that is, in FIG. The piston stop position of the indicated compression stroke cylinder 2C at the time of stop is specified based on the crank angle sensor SW2 and the cam angle sensor SW3, and the specified piston stop position is at the bottom dead center side than the preset reference stop position X. It is determined whether it is in the specific range Rx (step S12).

  When it is determined NO in Step S12 and it is confirmed that the piston 5 of the stop-time compression stroke cylinder 2C has stopped on the top dead center side with respect to the specific range Rx, the restart control unit 62 performs the intake stroke. Control is executed to restart the engine by two-compression start in which the first fuel is injected into the stopped intake stroke cylinder 2D that has been stopped (step S16). That is, the engine is driven only by driving the starter motor 34 without injecting fuel until the piston 5 of the stop compression stroke cylinder 2C exceeds the top dead center and then the stop intake stroke cylinder 2D reaches the compression stroke. Force to rotate. At that time, fuel is injected from the fuel injection valve 15 into the stop-time intake stroke cylinder 2D, and the injected fuel is self-ignited, so that the combustion is resumed from the time when the engine reaches the second compression top dead center. Restart the engine.

  On the other hand, when it is determined as YES in step S12 and it is confirmed that the piston stop position of the stop-time compression stroke cylinder 2C is within the specific range Rx, the restart control unit 52 determines that the restart condition established in step S11 is satisfied. Is determined based on the start request from the driver (step S13). That is, when the restart condition is established by the driver depressing the accelerator pedal 36 or releasing the brake pedal 37, it is determined that the driver is based on a start request from the driver, and other requirements (battery If the restart condition is satisfied due to system restrictions such as the upper limit stop time of the engine, the air conditioner, and the engine), it is determined that it is not based on the start request from the driver.

  If it is determined NO in step S13 and it is confirmed that the restart condition is satisfied based on the start request from the driver, the restart control unit 52 injects the first fuel into the stop-time compression stroke cylinder 2C. The control which restarts an engine by 1 compression start to perform is performed (step S14). That is, by driving the starter motor 34 and applying rotational force to the crankshaft 7, fuel is injected from the fuel injection valve 15 into the compression stroke cylinder 2 </ b> C at the time of stop and self-ignited, whereby the engine as a whole is first compressed. The combustion is restarted from the time when the dead point is reached, and the engine is restarted. In such an engine restart by one compression start, the time required for the engine restart compared to the two compression start (step S16) in which combustion is not restarted until the second compression top dead center is reached as a whole engine. That is, the time from the start of driving the starter motor 34 to the complete explosion of the engine (for example, the state where the rotational speed reaches 750 rpm) is shortened, and the engine can be restarted more quickly.

  When performing one compression start in step S14, an appropriate amount of fuel commensurate with the amount of air present in the cylinder 2C is injected as the first fuel injection to the compression stroke cylinder 2C at the time of stop (normal mode) ). At this time, it is conceivable to complete the injection fuel to the compression stroke cylinder 2C at the time of one stop, but in the present 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 fuel by the pre-injection is used to reliably cause diffusion combustion (hereinafter referred to as “main combustion”) that occurs mainly after compression top dead center based on 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 the pre-injection as described above is executed for the compression stroke cylinder 2C 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 2C at the time of stop However, even if it approaches the top dead center side, the engine can be reliably restarted by one compression start. The reference stop position X (FIG. 3) that is the boundary of the specific range Rx 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. 3, 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, BTDC 90 to 75 ° CA. . As a result, the specific range Rx expands to the top dead center side, so that the piston 5 of the compression stroke cylinder 2C at the time of stoppage falls within the specific range Rx with a higher frequency, and an opportunity to perform a quick restart by one compression start Will 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.

  More specifically, the pre-injection in this embodiment is performed a plurality of times (before the compression top dead center) and within a crank angle range in which the injected fuel is accommodated in the cavity 5a of the piston 5 crown surface ( (For example, any number of times 2 to 5). If this is the same amount of fuel, it is possible to continuously form a rich air-fuel mixture in the cavity 5a by injecting it in multiple pre-injections rather than injecting it in one pre-injection. This is because the ignition delay can be shortened. That is, by making the pre-injection a plurality of times, the injection amount of the pre-injection per time is reduced and the penetration of the spray is weakened. As a result, the ratio of the fuel remaining in the cavity 5a increases, and as a result, the cavity 5a The air-fuel mixture becomes rich, and the ignitability can be effectively improved.

FIG. 5 is a diagram illustrating a mode of fuel injection at the time of one compression start in the normal mode performed in step S14. Here, as an example, pre-injection is executed three times. Specifically, between BTDC 18 to 10 ° 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 (BTDC 0 ° CA) (more than that for one pre-injection) (lower waveform Im). Further, the waveforms (Bp, Bm) shown in the upper part of FIG. 5 illustrate the state of combustion caused by such fuel injection as a change in the heat generation rate.

  As shown in FIG. 5, 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 (BTDC 0 ° 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). .

  Although FIG. 5 shows the injection mode when the first fuel is injected into the stop-time compression stroke cylinder 2C in order to perform the one-compression start, the compression stroke reaches after the stop-time compression stroke cylinder 2C. Also for the cylinders, the combustion control based on the pre-injection and the main injection may be executed as necessary as in FIG. When the engine is restarted, the ignitability is most severe in the combustion in the stop compression stroke cylinder 2C, which reaches the first compression top dead center (hereinafter referred to as “1 compression TDC”) as the whole engine. The cylinders 2D and 2B (see FIG. 3) reaching the third compression top dead center (hereinafter referred to as “2-compression TDC” and “3-compression TDC”) are also considered to have insufficient improvement in ignitability. is there. Therefore, from the viewpoint of reliably preventing misfire, combustion control based on pre-injection and main injection may be performed on the cylinders 2D and 2B (hereinafter referred to as “subsequent cylinders”).

  However, in the 2-compression TDC, the 3-compression TDC, etc., where the subsequent cylinders reach compression top dead center, the engine speed is faster than in the 1-compression TDC, where the compression stroke cylinder 2C when stopped reaches compression top dead center. The number of pre-injections to the subsequent cylinder is not necessarily the same as that to the compression stroke cylinder 2C at the time of stop. For example, when the number of times of pre-injection to the stop compression stroke cylinder 2C is 3, the number of times of pre-injection to the subsequent cylinders is reduced to 2 or 1 as the compression proceeds to 2 compression TDC, 3 compression TDC,. At the same time, it is conceivable to adjust the timing and injection amount of each pre-injection.

  Returning to FIG. 4 again, if the determination in step S13 is YES, that is, the restart condition is satisfied while the piston stop position of the compression stroke cylinder 2C is within the specific range Rx, the restart condition is satisfied. Will be described when the control is not based on the start request from the driver (that is, the restart condition is established due to system restrictions such as the upper limit stop time of the battery, the air conditioner, and the engine). In this case, the restart control unit 52 performs the one-compression start in the small injection mode in which the fuel injection amount for the stop-time compression stroke cylinder 2C is smaller than that in the normal mode (step S14) (step S15).

FIG. 6 is a diagram exemplifying a mode of fuel injection (first fuel injection into the compression stroke cylinder 2C at the time of stop) at the time of one compression start in the small injection mode. As shown in the figure, in the small injection mode, when the fuel is injected into the stop compression stroke cylinder 2C, the number of pre-injections Ip and the injection amount are made the same as in the normal mode (FIG. 5), By reducing the injection amount of the main injection Im, the total fuel injection amount is reduced. For example, if the injection amount of the main injection Im in the normal mode is 4 mm ³ , the main injection Im in the small injection mode is set to 2 mm ³ or less (0 to 2 mm ³ ). In FIG. 6, for comparison, the waveform of the fuel injection rate by main injection in the normal mode is indicated by a broken line.

  As shown in FIG. 6, in the small injection mode in which the fuel injection amount to the stop compression stroke cylinder 2C is reduced, the energy generated by the combustion in the cylinder 2C (combustion at the time of 1 compression TDC) is reduced and applied to the engine. Torque is reduced. Therefore, as compared with the normal mode of FIG. 5, the time (from 1 compression TDC to 2) until the piston 5 of the stop intake stroke cylinder 2D reaches the compression top dead center after combustion in the stop compression stroke cylinder 2C. The time until compression TDC is slightly longer. However, after the 2 compression TDC, the normal amount of fuel is injected, so that the engine speed gains momentum, and the engine reaches a complete explosion in a time not so late.

(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 causes the piston 5 of the stop-time compression stroke cylinder 2C stopped in the compression stroke to move from a predetermined reference stop position X. Is determined to be within a specific range Rx (FIG. 3 (b)) set at the bottom dead center side. If it is within the specific range Rx, the fuel injection valve 15 moves to the above-described stop-time compression stroke cylinder 2C. The engine is restarted by injecting the first fuel (one compression start). However, even in the case of one compression start, if the establishment of the restart condition is not based on the start request from the driver, that is, system constraints such as the battery, air conditioner, engine upper limit stop time, etc. When the restart condition is satisfied by the above, when the restart condition is satisfied based on the start request (accelerator / brake operation) from the driver, the injection amount of the first fuel injection performed on the compression stroke cylinder 2C at the time of stop is satisfied. Is set to be smaller than

  According to the above configuration, when the piston 5 of the stop-time compression stroke cylinder 2C is stopped in the specific range Rx relatively near the bottom dead center, after the restart condition is satisfied, the first fuel is supplied to the stop-time compression stroke cylinder 2C. The engine can be restarted quickly by one compression start injecting However, even if the piston stop position is in the specific range Rx, if the establishment of the restart condition is not based on the start request from the driver, the engine is restarted with the vehicle stopped. Therefore, if a normal amount of fuel is injected at the time of one-compression start, there is a possibility that the vibration at the time of restart is clearly perceived by the occupant. Therefore, even in a situation where one compression start is performed (when the piston stop position is in the specific range Rx), if the establishment of the restart condition is not based on the start request from the driver, A one-compression start is executed in a special mode (small injection mode) in which the amount of injection into the compression stroke cylinder 2C is reduced. Thereby, since the energy of the combustion which arises initially in an engine reduces, the vibration at the time of restart is suppressed and NVH performance (the reduction effect of noise, vibration, and harshness) can be improved.

  The reason why reducing the fuel injection amount at the time of starting one compression as described above leads to suppression of vibration will be described in more detail.

  The inventor of the present application measured the torque fluctuation applied to the crankshaft 7 in order to understand the vibration that occurs when the engine is restarted by one-compression start or two-compression start, and obtained the results shown in FIG. In this figure, the solid line shows the torque fluctuation at the time of one compression start (one compression start in the normal mode without reducing the fuel injection amount), and the broken line shows the torque fluctuation at the time of two compression start.

  In the 1-compression start (solid line), combustion occurs from 1-compression TDC (compression top dead center at which the engine as a whole reaches the first time) where the compression stroke cylinder 2C at the time of stop reaches the compression top dead center, and torque is generated. Combustion also occurs in 2-compression TDC, 3-compression TDC (compression top dead center at the second, third, etc. for the engine as a whole), and torque is generated each time. At this time, the vibration frequency due to torque fluctuation from 1 compression TDC to 2 compression TDC was 12.0 Hz, and the vibration frequency due to torque fluctuation from 2 compression TDC to 3 compression TDC was 19.4 Hz.

  On the other hand, in the 2-compression TDC (broken line), combustion is not performed in the 1-compression TDC in which the compression stroke 2C at the time of stop reaches the compression top dead center, and combustion is performed from the 2-compression TDC in which the intake-stroke cylinder 2D at the time of stop occurs. Therefore, only the torque from the starter motor 34 acts on the crankshaft 7 in one compression TDC, and the torque is smaller than that at the time of one compression start. As a result, the time from 1 compression TDC to 2 compression TDC is longer than that at the time of 1 compression start, and the vibration frequency from 1 compression TDC to 2 compression TDC and the vibration frequency from 2 compression TDC to 3 compression TDC are They were 5.6 Hz and 16.1 Hz, respectively.

  Here, according to the knowledge of the present inventor, the resonance frequency of the powertrain system including the engine body 1 and the transmission is about 11 Hz in a general ordinary passenger car that is commercially available. Therefore, if vibration close to the resonance frequency (about 11 Hz) is caused by torque fluctuation at the time of engine restart, power train roll resonance may occur, and a relatively large vibration may be transmitted to the passenger compartment.

  Referring to FIG. 7 based on this knowledge, in the case of 2 compression start (broken line), the vibration frequency between 1 and 2 compression TDC (5.6 Hz), the vibration frequency between 2 and 3 compression TDC (16.1 Hz). In any case, since it is far away from the resonance frequency (11 Hz) of the power train system, it is unlikely that roll resonance will occur. After 3 compression TDC, the vibration frequency due to torque fluctuation becomes higher, so there is no concern about roll resonance.

  On the other hand, in the case of 1 compression TDC (solid line), the vibration frequency between 1 and 2 compression TDC is 12.0 Hz. Since this value is close to the resonance frequency (11 Hz) of the powertrain system, roll resonance is highly likely to occur. Of course, even if roll resonance occurs, the engine restarts based on the driver's intention (accelerator operation, etc.) and the vehicle starts with the restart (that is, the restart condition is satisfied based on the start request) Vibration), vibration is not particularly noticeable, and NVH performance is hardly impaired.

  On the other hand, regardless of the driver's intention, when the engine restarts with the vehicle stopped (that is, when the restart condition is not based on the start request), even a slight vibration can be detected (consciousness). Therefore, if 1 compression start in the same normal mode as the solid line in FIG. 7 is performed, vibration of 12.0 Hz particularly between 1 and 2 compression TDC is greatly sensed and NVH performance is impaired.

  As a measure for solving such a problem, in the above embodiment, the piston stop position is in the specific range Rx, so even if one compression TDC is performed, it is not based on the start request from the driver. When the start condition is satisfied, the one-compression start in the small injection mode is executed. In the small injection mode, the initial fuel injection to the stop compression stroke cylinder 2C is set to a small amount, and the torque due to the combustion generated in the 1 compression TDC is reduced. Therefore, the time from the 1 compression TDC to the 2 compression TDC is reduced. The vibration frequency during the period can be reduced. For example, if the vibration frequency between the 1 and 2 compression TDCs is reduced from 12.0 Hz to less than 9 Hz, the distance from the resonance frequency of the powertrain system, 11 Hz, can be reliably avoided.

  In the above embodiment, as shown in FIG. 5, for example, as the fuel injection at the time of one compression start, main combustion (Bm) that reaches the peak of the heat generation rate after the compression top dead center is caused. The main injection (Im) and the pre-injection (Ip) for causing the pre-combustion (Bp) to reach 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 combusted by self-ignition after a predetermined ignition delay (pre-combustion), and raises the in-cylinder temperature and pressure of the stop compression stroke cylinder 2C. When executed, the injected fuel will soon burn by self-ignition (main combustion). As described above, the ignitability of the fuel injected by the main injection is improved by the pre-injection (pre-combustion) before that, so that the compression allowance (stroke amount to the top dead center) in the compression stroke cylinder 2C at the time of stop is much Even if not, combustion in the compression stroke cylinder 2C at the time of stop is reliably performed. As a result, the piston stop position range (specific range Rx) in which one compression start is possible can be expanded to the top dead center side, and speeding up of the engine start can be promoted.

  In the above embodiment, since the establishment of the restart condition is not based on the start request, when one compression start in the small injection mode is performed, as shown in FIG. 6, the injection amount of the pre-injection The amount of main injection was reduced while keeping the same. According to such a configuration, the compression amount at the time of stoppage is reduced by reducing the injection amount of the main injection performed thereafter, while reliably preventing misfire by making the injection amount of the pre-injection performed relatively early the same. Torque due to the first combustion generated in the stroke cylinder 2C can be reduced, and vibration during restart can be effectively suppressed.

  In the above embodiment, whether or not the automatic stop condition or restart condition of the engine is satisfied is determined including the requirements related to 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.

  Further, in the above embodiment, at the time of one compression start in the small injection mode, only the injection amount of the main injection Im to the stop compression stroke cylinder 2C is reduced to make the injection amount of the pre-injection Ip the same. As long as the total injection amount to the compression stroke cylinder 2C can be reduced and misfire can be avoided, any injection mode may be used. For example, the injection amounts of both the pre-injection Ip and the main injection Im May be reduced.

  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 34 Starter motor 52 Restart control part (determination means, injection control means)
X Reference stop position Rx Specific range Ip Pre-injection Im Main injection Bp Pre-combustion Ip Main combustion

Claims (1)

Provided in a vehicle equipped with a compression self-ignition engine that burns fuel injected from the fuel injection valve into the cylinder by self-ignition, and automatically stops the engine when a predetermined automatic stop condition is satisfied, and then When the restart condition is satisfied, a start control device that restarts the engine by injecting fuel from the fuel injection valve while applying a rotational force to the engine using a starter motor,
Determination means for determining whether or not the piston of the compression stroke cylinder at the time of stop that has been stopped in the compression stroke due to the automatic stop is in a specific range set on the bottom dead center side with respect to a predetermined reference stop position;
When it is determined that the piston of the stop compression stroke cylinder has stopped in the specific range and the engine restart condition is satisfied, the fuel injection valve is controlled to supply the first fuel to the stop compression stroke cylinder. As the first fuel injection, the main injection that causes the main combustion to reach the peak of the heat generation rate after passing the compression top dead center, and the heat generation rate before the start of the main injection Injection control means for performing pre-injection that causes pre-combustion to reach a peak ,
The injection control means performs the first fuel injection to be performed on the stop-time compression stroke cylinder when the establishment of the restart condition is not based on a start request for the driver to start the vehicle. Reduce the injection amount compared to when the restart condition is established based on the start request from the driver ,
The compression self-ignition engine characterized in that the control for reducing the initial fuel injection amount for the stop-time compression stroke is control for reducing the injection amount of the main injection while keeping the same injection amount of the pre-injection. Start control device.

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