JP5842678B2 - Start control method and apparatus for compression self-ignition engine - Google Patents

Description

  The present invention sets an automatic stop condition and a restart condition for a compression self-ignition engine in which fuel injected from a fuel injection valve into a cylinder is burned by self-ignition, and the automatic stop is performed during operation of the engine. By automatically stopping the engine when a condition is satisfied, and then 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 The present invention also relates to a start control method for a compression self-ignition engine that automatically starts the engine.

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 during idle operation or the like, and then the engine is automatically started 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.

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

  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. After that, 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 in an appropriate position 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 in the compression stroke at the time of stop is on the top dead center side from the appropriate position, the cylinder that has been 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

  Here, when the engine is automatically started by the above-described 1-compression start or 2-compression start, the engine rotation speed is increased to a predetermined speed as quickly as possible so that the vehicle can be started in a short period after the start of the start. There is a need. However, if you continue to inject a large amount of fuel that suddenly increases the rotation speed, the engine rotation speed will rise more than necessary, and depending on the timing when the driver steps on the accelerator pedal, the vehicle may suddenly jump out. There is a risk that it will behave.

  On the other hand, an engine start that is started when a passenger on the vehicle performs a predetermined operation (for example, key operation or button operation) for starting the engine (hereinafter, such engine start is referred to as “forced start”). Then, unlike when the engine is automatically started as described above, it is rather preferable that the engine is blown up to some extent because the occupant can surely recognize that the engine has been started. It is said that. For this reason, if the same control as when the engine is forcibly started is also performed when the engine is automatically started, the engine blows up, and it becomes impossible to solve problems such as vehicle jump-out. That is, in order to suppress the blow-up at the time of automatic engine start, it is necessary to perform a unique fuel injection control that has never been done before.

  The present invention has been made in view of the circumstances as described above, and an object of the present invention is to automatically and quickly start an engine while suppressing engine blow-up in a compression self-ignition engine with an idling stop function. And

  In order to solve the above-described problems, the present invention sets automatic stop conditions and restart conditions for a compression self-ignition engine for vehicle use that burns fuel injected from a fuel injection valve into a cylinder by self-ignition. The engine is automatically stopped when the automatic stop condition is satisfied during the operation of the engine, and then, when the restart condition is satisfied, a rotational force is applied to the engine using a starter motor. However, it is a start-up control method for a compression self-ignition engine that automatically starts the engine by injecting fuel from the fuel injection valve, and when the stop is stopped in the compression stroke after the restart condition is satisfied The fuel injection valve from the first compression when the compression stroke cylinder reaches the compression top dead center, or from the second compression when the intake stroke cylinder at the time of stop that has stopped in the intake stroke reaches the compression top dead center. By injecting fuel and restarting combustion, fuel is injected and burned each time one of the cylinders reaches compression top dead center, and combustion is performed sequentially until the engine speed increases to a predetermined complete explosion speed. And a small amount of fuel set so that the in-cylinder equivalence ratio is smaller than that in the speed increasing process when there is no vehicle start request after the speed increasing process. Including a stabilization step that suppresses an increase in engine rotational speed by burning, and the number of combustions in the speed increasing step is a period during which the rotational speed increases in the initial stage when the engine is forcibly started. Is set to be less than the number of combustions performed during the period, and the in-cylinder equivalence ratio based on at least the first fuel injection performed after the transition to the stabilization step is set during the forced start of the engine. It is characterized in that the blow-up period is set to be larger than the equivalent ratio based on the first fuel injection to be executed after the completion Te (claim 1).

  According to the present invention, when the engine is automatically started, combustion is performed in a relatively rich environment by the number of times smaller than the number of times of combustion performed during the blow-up period at the time of forced start (increase in speed). Process), and the equivalence ratio is reduced to reduce the combustion energy unless there is a vehicle start request thereafter (stabilization process). Therefore, the engine speed is increased rapidly to force the engine to complete explosion. It is possible to suppress an excessive increase in the rotational speed that occurs during the blowing-up period at the start, and to smoothly shift the engine to the idling state. As a result, noise during automatic engine start can be reduced, and even when a vehicle start request is made immediately after the speed increasing process, the vehicle does not jump out suddenly, improving the safety and comfort of the vehicle. It can be improved effectively.

  In addition, since the equivalence ratio at the time of combustion performed in the stabilization process after the engine complete explosion is set larger than the extremely small equivalent ratio set immediately after the blow-up period at the time of forced engine start, Immediately after the rotation, the rotational speed is prevented from excessively decreasing. For this reason, it is possible to reliably avoid a situation in which the rotational speed undulates violently before the engine rotational speed is stabilized, and a smoother automatic engine start can be achieved.

  In the present invention, preferably, the equivalent ratio in the speed increasing step is set to 0.7 or more, and the equivalent ratio in the stabilization step is set to 0.1 or more and less than 0.5 (Claim 2). .

  In this way, the engine can be quickly raised to the complete explosion speed by combustion at a relatively rich equivalent ratio (0.7 or more) set during the acceleration process, and the equivalent after the complete explosion By reducing the ratio to 0.1 or more and less than 0.5, it is possible to reliably prevent the engine from being blown up, the rotational speed of which increases more than necessary.

  The equivalence ratio based on the first fuel injection executed after the blow-up period ends at the time of forced start of the engine may be set to 0 or more and 0.1 or less (Claim 3). On the other hand, in the above configuration, the equivalence ratio after the complete explosion is set to 0.1 or more and less than 0.5, so that it is possible to reliably prevent the rotational speed from excessively decreasing after the engine completes the explosion. Can do.

  The equivalence ratio during the speed increasing step may be calculated based on a theoretical air amount that does not consider air leaking from the cylinder during compression. In this case, it is preferable to set the theoretical equivalent ratio to 0.7 or more and less than 1.0.

  Thus, when the equivalence ratio is calculated based on the theoretical air amount that does not consider air leakage, the actual equivalence ratio may exceed the theoretical value due to air leakage from the cylinder. is there. However, according to the above configuration in which the equivalence ratio is less than 1.0, since an appropriate amount of fuel is supplied in consideration of air leakage, an increase in HC and CO due to excessive supply fuel can be suppressed. It is possible to effectively prevent deterioration of fuel consumption.

  When the crankshaft of the compression self-ignition engine is connected to an automatic transmission via a torque converter, the speed increasing step causes the engine to perform a total of three combustions, and the stabilization from the fourth combustion It is preferable to shift to a process (claim 5).

  In this way, in an engine for an AT vehicle equipped with an automatic transmission, combustion is performed three times with a relatively rich equivalence ratio, and the engine is properly exhausted properly. By reducing the equivalence ratio by combustion, it is possible to reliably prevent the engine from blowing up.

  The present invention is also 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 the engine is operated when a predetermined automatic stop condition is satisfied. Start that automatically stops 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 satisfied after that. The control apparatus is a first-compression cylinder in which the compression stroke at the time of stop, which has been stopped in the compression stroke after the restart condition is satisfied, reaches the compression top dead center, or an intake stroke cylinder in the stop which has been stopped in the intake stroke The fuel is injected into the fuel injection valve from the second compression at which compression top dead center is reached, and combustion is restarted. Then, every time any cylinder reaches compression top dead center, fuel is injected and burned. In this way, the first control for sequentially performing combustion until the engine rotation speed rises to a predetermined reference speed, and the equivalence ratio in the cylinder when there is no vehicle start request after the first control. Control means for executing a second control for suppressing an increase in the engine rotation speed by injecting and burning a small amount of fuel set to be smaller than that in the speed increasing step, The number of combustions in the control No. 1 is set to be smaller than the number of combustions performed during the blow-up period, which is a period during which the rotational speed increases in the initial stage of the forced start of the engine. The in-cylinder equivalence ratio based on at least the first fuel injection executed after the transition is equivalent to the first fuel injection executed after the blow-up period ends at the forced start of the engine. It is characterized in that is set larger than (claim 6).

  According to the start-up control device for a compression self-ignition engine of the present invention, the same effects as those of the previous method invention can be obtained.

  As described above, according to the present invention, in a compression self-ignition engine with an idling stop function, the engine can be automatically started quickly and smoothly while suppressing engine blow-up.

It is a figure showing the whole diesel engine composition to which the starting control method concerning one embodiment of the present invention was applied. It is a figure which shows schematic structure of the power train system containing the said engine. It is a flowchart which shows the specific procedure of the automatic stop control which stops the said engine automatically. It is a schematic diagram which illustrates the state of each cylinder at the time of the said automatic stop control being complete | finished. It is a flowchart (the 1) which shows the specific procedure of the automatic start control which starts the said engine automatically. It is a flowchart (the 2) which shows the specific procedure of the said automatic start control. It is the figure which showed what timing the injected fuel combusts when fuel is injected separately into pre-injection and main injection. It is a figure which shows the change of the equivalence ratio in a cylinder set by each combustion time in the automatic start control of the said engine. It is a figure which shows the behavior of the engine automatically started based on the setting of the equivalence ratio of the said FIG. It is a figure which shows the example of a setting of the equivalence ratio at the time of the forced start which starts the said engine compulsorily. FIG. 11 shows the behavior of an engine that is forcibly started based on the setting of the equivalence ratio in FIG. It is a figure for demonstrating other embodiment of this invention.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing an overall configuration of a diesel engine to which a start control method 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 includes a cylinder block 3 having four cylinders 2A to 2D (see also FIG. 2 to be described later) arranged in a row in a direction orthogonal to the paper surface, and a cylinder. It has a cylinder head 4 provided on the upper surface of the block 3 and a piston 5 inserted into each of the cylinders 2A to 2D so as to be able to reciprocate.

  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. .

  FIG. 2 is a diagram simply showing a powertrain system including the engine body 1. As shown in FIG. 2, the crankshaft 7 of the engine body 1 is connected to the automatic transmission 101 via a torque converter 102. That is, the vehicle on which the diesel engine of this embodiment is mounted is an AT vehicle in which a speed change operation is automatically performed.

  The torque converter 102 includes a pump impeller that rotates integrally with the crankshaft 7 of the engine body 1, a turbine runner that is disposed opposite to the pump impeller, and a stator that is disposed between the pump impeller and the turbine runner. It has a conventionally known structure. The rotation of the pump impeller is transmitted to the turbine runner via the working fluid (ATF oil) in the torque converter 102 and finally extracted as the rotation of the input shaft 103 of the automatic transmission 101. The automatic transmission 101 is a conventionally known one that incorporates a meteor gear mechanism and a frictional engagement element (clutch or brake), and according to the vehicle speed and the like by hydraulically controlling the intermittent engagement of the frictional engagement element. Further, a desired shift speed (for example, one of 6 forward speeds or 1 reverse speed) is realized.

  Returning to FIG. 1 again, the configuration of the diesel engine of the present embodiment will be described. In the four-cycle four-cylinder diesel engine as in the present embodiment, the pistons 5 provided in the cylinders 2A to 2D move 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 in accordance with the rotation of the crank plate 25 that rotates integrally with the crankshaft 7, and based on this pulse signal, 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 outputting cylinder discrimination information. That is, the cam angle sensor SW3 outputs a pulse signal according to the passage of the teeth of the signal plate that rotates integrally with the camshaft. Based on this signal and the pulse signal from the crank angle sensor SW2, Which cylinder is in which stroke is determined.

  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. The alternator 32 has a target value of power generation (target power generation determined from the electric load of the vehicle, the remaining battery capacity, etc.). 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 includes a microprocessor including a CPU, a ROM, a RAM, and the like, and corresponds to 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 a vehicle speed sensor SW5 for detecting the traveling speed (vehicle speed) of the vehicle, an accelerator opening sensor SW6 for detecting the opening of the accelerator pedal 36 that is depressed by the driver, and a brake pedal. Brake sensor SW7 for detecting ON / OFF of 37 (presence / absence of brake), battery sensor SW8 for detecting the remaining capacity of the battery (not shown), and room temperature sensor SW9 for detecting the temperature in the vehicle compartment And are provided. The ECU 50 acquires information such as the vehicle speed, the accelerator opening, the presence / absence of the brake, the remaining battery capacity, and the vehicle interior temperature based on the input signals from the sensors SW5 to SW9.

  The ECU 50 controls each part of the engine while executing various calculations based on input signals from the sensors SW1 to SW9. That is, 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. Based on the result of the calculation and the like, the ECU 50 controls each of these devices for driving. Output a signal.

  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 having a basic function such as power generation, a so-called idle stop function also has a function of automatically stopping or starting the engine under predetermined specific conditions. For this reason, the ECU 50 includes an automatic stop control unit 51 and an automatic start control unit 52 as functional elements relating to the automatic stop or automatic start of the engine.

  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 automatic start control unit 52 determines whether or not a predetermined restart condition is satisfied after the engine is automatically stopped, and executes control for automatically starting 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. 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 air flow sensor SW4, the vehicle speed sensor SW5, the accelerator opening sensor SW6, the brake 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, vehicle speed, accelerator opening, presence of brake, 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 It is above a predetermined value (that is, warm-up has progressed to some extent), the remaining capacity of the battery is above a predetermined value, and the load on the air conditioner (the difference between the cabin temperature and the set temperature of the air conditioner) is relatively small It is determined that the automatic stop condition is satisfied when all of the plurality of requirements such as the above are met. 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.

  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. 4 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 2A stopped in the expansion stroke is referred to as “stop expansion stroke cylinder 2A”, the cylinder 2B stopped in the exhaust stroke is referred to as “stop exhaust stroke cylinder 2B”, and the cylinder stopped in the compression stroke. 2C is referred to as “stopped compression stroke cylinder 2C”, and the stopped cylinder 2D stopped in the intake stroke is referred to as “stopped intake stroke cylinder 2D”.

(4) Automatic Start Control Next, specific contents of the engine automatic start control executed by the automatic start control unit 52 of the ECU 50 will be described with reference to the flowcharts of FIGS.

(4-1) Control until Complete Explosion First, control executed after the engine restart condition is satisfied and until the engine reaches complete explosion will be described with reference to FIG. When the process shown in the flowchart of FIG. 5 starts, the automatic start 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, The 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 cabin temperature 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.

  When it is determined YES in step S11 and it is confirmed that the restart condition is satisfied, the automatic start control unit 52 performs the cylinder that has stopped in the compression stroke in accordance with the above-described automatic engine stop control (when the engine is stopped in FIG. 4). The piston stop position of the compression stroke cylinder 2C) is specified based on the crank angle sensor SW2 or the like, and the specified piston stop position is set to a specific range Rx set on the bottom dead center side with respect to the reference stop position X shown in FIG. (Step S12). In the present embodiment, the reference stop position X is set in the vicinity of an intermediate position between the top dead center and the bottom dead center, for example, any position of BTDC (before top dead center) 90 to 75 ° CA. The

  When it is determined 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 automatic start control unit 52 causes the stop-time compression stroke cylinder 2C to be dead in compression. Control is performed to start the engine by one compression start to resume combustion from the first compression that reaches the point.

  The specific procedure of the 1 compression start is as follows. First, the automatic start control unit 52 executes control for driving the starter motor 34 (step S13). As a result, the engine is forcibly rotated, and the piston 5 of the compression stroke cylinder 2C at the time of stop starts moving toward the compression top dead center. Then, based on whether or not the piston 5 of the compression stroke cylinder 2C at the time of stopping has reached a predetermined position near the top dead center, it is determined whether or not the combustion injection timing of the first compression has arrived. (Step S14).

  When it is determined YES in step S14 and it is confirmed that the fuel injection timing of the first compression has arrived, the automatic start control unit 52 shifts from the fuel injection valve 15 of the stop-time compression stroke cylinder 2C to the cylinder 2C. Control is performed to inject fuel and burn the fuel by self-ignition (step S15). The injection amount in the first compression fuel injection is set to a value such that the in-cylinder equivalence ratio φ is 0.75.

  Here, the target equivalent ratio φ when performing the first-compression fuel injection is injected from the theoretical cylinder air amount corresponding to the piston stop position of the stop-time compression stroke cylinder 2C and the fuel injection valve 15. It is a value calculated on the basis of the amount of fuel. Note that the internal air of the cylinder 2C at the time of the stop compression stroke leaks to the outside through the gap between the piston 5 and the cylinder wall surface immediately after the engine is completely stopped. Air volume decreases until atmospheric pressure is reached. Therefore, the theoretical air amount of the first compression is considered to be smaller as the piston stop position is at the top dead center. In other words, the equivalence ratio φ for the first compression is the amount of air when the internal pressure of the compression stroke cylinder 2C at the time of stoppage is reduced to the atmospheric pressure (determined in proportion to the stop position of the piston 5), and the fuel injection valve 15 The equivalent ratio determined from the fuel injection amount from As is well known, the equivalence ratio φ is 1 when a fuel that is not theoretically excessive or deficient with respect to the amount of air in the cylinder, and is a value when an amount of fuel less than that is supplied. (Conversely, the equivalent ratio φ when the fuel is excessive is more than 1).

  When the first-compression fuel injection into the stop-time compression stroke cylinder 2C is completed as described above, the automatic start control unit 52 performs the stop-time intake stroke that reaches the compression top dead center next to the stop-time compression stroke cylinder 2C. Based on the piston position of the cylinder 2D, it is determined whether or not the combustion injection timing of the second compression (the timing at which the piston 5 of the cylinder 2D reaches near the compression top dead center) has arrived (step S16).

  When it is determined YES in step S16 and it is confirmed that the fuel injection timing of the second compression has arrived, the automatic start control unit 52 has an in-cylinder equivalent ratio φ with respect to the stop-time intake stroke cylinder 2D. A control is performed to inject an amount of fuel that becomes 0.85 and burn the fuel by self-ignition (step S17).

  Here, the target equivalent ratio φ when performing the fuel injection amount of the second compression is the theoretical air amount when it is assumed that the intake stroke cylinder 2D at the time of stop is filled with the maximum amount of air, that is, the intake valve 11 is closed. The amount of air when assuming that the cylinder is filled with atmospheric air with the piston 5 in the position corresponding to the timing (near the bottom dead center), and the amount of fuel injected from the fuel injection valve 15 Is a value calculated based on This also applies to the equivalent ratio φ of the third compression described later and the equivalent ratio φ of the second to fourth compressions at the time of starting the second compression.

  When the second-compression fuel injection to the stop-time intake stroke cylinder 2D is completed as described above, the automatic start control unit 52 performs the stop-time exhaust stroke that reaches the compression top dead center next to the stop-time intake stroke cylinder 2D. Based on the piston position of the cylinder 2B, it is determined whether or not the combustion injection timing of the third compression (the timing at which the piston 5 of the cylinder 2B reaches near the compression top dead center) has arrived (step S18).

  When it is determined YES in step S18 and it is confirmed that the fuel injection timing of the third compression has arrived, the automatic start control unit 52 has the equivalent ratio φ in the cylinder with respect to the exhaust stroke cylinder 2B at the time of stop. A control is performed to inject an amount of fuel that becomes 0.9 and burn the fuel by self-ignition (step S19).

  When combustion based on three fuel injections in total is performed as described above, the engine speed increases sufficiently and reaches a complete explosion speed Nx (see FIG. 9 described later) set to about 700 to 800 rpm, for example. To do. The automatic start control unit 52 confirms that the engine rotation speed has increased above the complete explosion speed Nx (engine complete explosion) (step S30), and then performs the control (control after complete explosion) shown in FIG. ).

  Next, when it is determined NO in step S12, that is, the piston stop position of the stop-time compression stroke cylinder 2C that has stopped in the compression stroke in accordance with the automatic engine stop control is higher than the specific range Rx (FIG. 4). The control when it is off to the dead point side will be described. In this case, the automatic start control unit 52 does not start from the first compression at which the above-mentioned compression stroke cylinder 2C at the stop reaches the compression top dead center, but the intake stroke cylinder 2D at the stop when stopped at the intake stroke reaches the compression top dead center. Control is performed to start the engine by two-compression starting that restarts combustion from the second compression that greets.

  The specific procedure for the above-mentioned two-compression start is as follows. First, the automatic start control unit 52 drives the starter motor 34 to start the forced rotation of the engine (step S21), and performs fuel injection until the piston 5 of the stop-time compression stroke cylinder 2C passes the compression top dead center. It waits without performing (step S22). Then, based on the piston position of the stop-time intake stroke cylinder 2D that reaches the compression top dead center next to the stop-time compression stroke cylinder 2C, the combustion injection timing of the second compression (the piston 5 of the cylinder 2D is compressed top dead center). It is determined whether or not (timing to reach near) has come (step S23).

  When it is determined YES in step S23 and it is confirmed that the fuel injection timing of the second compression has arrived, the automatic start control unit 52 has an equivalent ratio φ in the cylinder with respect to the intake stroke cylinder 2D at the time of stop. A control is performed to inject an amount of fuel to be 0.75 and burn the fuel by self-ignition (step S24).

  Next, the automatic start control unit 52 determines the combustion injection timing of the third compression based on the piston position of the stop exhaust stroke cylinder 2B that reaches the compression top dead center after the stop intake stroke cylinder 2D. It is determined whether or not the timing at which the piston 5 reaches the vicinity of the compression top dead center has arrived (step S25).

  When it is determined YES in step S25 and it is confirmed that the fuel injection timing of the third compression has arrived, the automatic start control unit 52 has the equivalent ratio φ in the cylinder with respect to the exhaust stroke cylinder 2B at the time of stop. A control is performed to inject an amount of fuel to be 0.85 and burn the fuel by self-ignition (step S26).

  Next, the automatic start control unit 52 determines the combustion injection timing of the fourth compression based on the piston position of the stop expansion stroke cylinder 2A that reaches the compression top dead center next to the stop exhaust stroke cylinder 2B. It is determined whether or not the timing at which the piston 5 reaches the vicinity of the compression top dead center has arrived (step S27).

  When it is determined YES in step S27 and it is confirmed that the fuel injection timing of the fourth compression has arrived, the automatic start control unit 52 has the equivalent ratio φ in the cylinder with respect to the stop-time expansion stroke cylinder 2A. A control is performed to inject an amount of fuel such that 0.9 and burn the fuel by self-ignition (step S28).

  When combustion based on a total of three fuel injections is performed as described above, the automatic start control unit 52 waits until the engine reaches a complete explosion as in the case of the above-described single compression start (step S30). ), And shifts to the control shown in FIG. 6 (control after complete explosion).

  Here, in the engine automatic start control in the present embodiment, as shown in FIG. 5, according to the piston stop position of the stop-time compression stroke cylinder 2 </ b> C, 1-compression start (S 13-) and 2-compression start (S 21-1). ) And can be used properly for the following reasons.

  As described above, the specific range Rx (FIG. 4) in which one compression start is possible is set on the bottom dead center side with respect to a predetermined reference stop position X (for example, any position between BTDC 90 to 75 ° CA). Has been. If the piston 5 of the stop stroke cylinder 2C is stopped in such a specific range Rx near the bottom dead center, the compression allowance (stroke amount to the top dead center) by the piston 5 is relatively large. As the piston 5 rises at the time of starting, the air in the cylinder 2C is sufficiently compressed to increase in temperature and pressure. For this reason, if the first fuel at the time of automatic start is injected into the stop-time compression stroke cylinder 2C (1 compression start), this fuel will reach self-ignition relatively easily in the cylinder 2C and burn.

  On the other hand, if the piston 5 of the stop compression stroke cylinder 2C deviates from the specific range Rx to the top dead center side, the compression allowance by the piston 5 is small, and even if the piston 5 rises to the top dead center, Since the air does not sufficiently increase in temperature and pressure, misfire may occur even if fuel is injected into the compression stroke cylinder 2C at the time of stop. Therefore, in such a case, the engine is automatically started by injecting fuel into the stop-time intake stroke cylinder 2D instead of the stop-time compression stroke cylinder 2C to cause self-ignition (two compression start).

  In the above-described two-compression start, combustion based on fuel injection cannot be performed until the second compression at which the piston 5 of the intake stroke cylinder 2D at the time of stop reaches the compression top dead center, and the time required for the automatic start of the engine That is, the time from the start of driving of the starter motor 34 to the complete explosion of the engine becomes long. Therefore, when starting the engine automatically, it is preferable to start the engine by one compression start as much as possible.

  Therefore, in the present embodiment, at the time of fuel injection at the first compression in at least one compression start (fuel injection into the compression stroke cylinder 2C at the time of stop), 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 automatically started by one compression start. The reference stop position X (FIG. 4) that is the boundary of the specific range Rx is set in consideration of the improvement in ignitability by such pre-injection. In other words, 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. 4, 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, and the piston 5 of the compression stroke cylinder 2C at the time of stop fits in the specific range Rx with a higher frequency, and an opportunity to perform a quick automatic start 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 is increased. The air-fuel mixture becomes rich, and the ignitability can be effectively improved.

FIG. 7 is a diagram illustrating an example of the first-compression fuel injection (step S15) at the time of the first compression start. Here, as an example, pre-injection is executed three times. Specifically, between BTDC 18 to 10 ° CA, 2 mm ³ of fuel is injected three times as a pre-injection (lower waveform Ip), and then a relatively large amount of fuel is compressed as a main injection. Injection is performed at the dead point (BTDC 0 ° CA) (lower waveform Im). As shown in the flowchart of FIG. 5, the injection amount of the first compression (the total injection amount of pre-injection and main injection) is set to a value such that the equivalent ratio φ in the cylinder is 0.75. Therefore, the main injection amount is determined as a value obtained by subtracting the injection amount (2 × 3 = 6 mm ³ ) of the pre-injection from the injection amount corresponding to φ = 0.75.

  In the upper part of FIG. 7, the state of combustion caused by the fuel injection as described above is illustrated as a change in the heat generation rate. As can be understood from the upper waveform in FIG. 7, when three pre-injections (Ip) are executed, the pre-injection is performed after a predetermined ignition delay time has elapsed after the completion of the last pre-injection. Pre-combustion (Bp) occurs due to self-ignition of the fuel. 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 compression top dead center. As a result, main combustion (Bm) due to self-ignition of the main injected fuel continues to occur. 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. 7 shows a mode of fuel injection of the first compression (fuel injection into the compression stroke cylinder 2C at the time of stop) performed at the time of the start of 1 compression, but compression is performed after the compression stroke cylinder 2C at the time of stop. As with the first compression, it is desirable to execute combustion control based on pre-injection and main injection for the cylinders that reach the stroke (stop intake stroke 2D and stop exhaust stroke cylinder 2B). The ignitability that is most severe when the engine starts automatically 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 sufficiently improved in ignitability. Because it is considered. However, the number of pre-injections can be reduced in the second compression and the third compression in which the engine speed has increased to some extent, compared with the first compression.

  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.

(4-2) Control after Complete Explosion Next, control performed after the engine reaches a complete explosion by the control of FIG. 5 (1 compression start or 2 compression start) will be described with reference to FIG. After the engine reaches a complete explosion, the automatic start control unit 52 first determines whether or not the accelerator pedal 36 is depressed, that is, whether or not there is a request to start the vehicle (step S31).

  Here, when the restart condition established in the first step (S11) of FIG. 5 is established by depression of the accelerator pedal 36, or the accelerator pedal 36 is depressed during the control of FIG. If it is determined, the determination in step 31 is of course YES. Then, the automatic start control unit 52 shifts to normal operation, and executes control for injecting fuel from the fuel injection valve 15 in an amount corresponding to the opening of the accelerator pedal 36 (accelerator opening) (step S41). That is, as the accelerator opening is larger and the acceleration request is higher, a higher engine torque is generated by injecting a large amount of fuel into the cylinder from the fuel injection valve 15 and burning it.

  On the other hand, if it is determined NO in step S31 and it is confirmed that the accelerator is OFF (the vehicle has not been requested to start), the automatic start control unit 52 first reaches compression top dead center after the engine complete explosion. It is determined whether or not the timing for injecting fuel into the cylinder, that is, whether or not the first compression fuel injection timing after the complete explosion of the engine has arrived (step S32). In this embodiment, since the number of combustions until the engine complete explosion is three times, the first compression after the engine complete explosion is the fourth compression counted from the start of automatic start in the case of one compression start. In the case of 2 compression start, this is the fifth compression counting from the start of automatic start. Accordingly, the cylinder that injects the combustion at the first compression after the complete explosion is the expansion stroke cylinder 2A at the time of the first compression start, and the compression stroke cylinder 2C at the time of the stop at the second compression start (second order).

  When it is determined YES in step S32 and it is confirmed that the fuel injection timing of the first compression after the complete explosion has arrived, the automatic start control unit 52 determines that the cylinder (the expansion stroke cylinder at the time of stoppage at the time of one compression start). 2A, in the case of 2 compression start, control is performed to inject an amount of fuel so that the equivalent ratio φ in the cylinder becomes 0.4 and to burn the fuel by self-ignition with respect to the compression stroke cylinder 2C at the time of stop (Step S33).

  Here, the equivalence ratio φ that is set when fuel is injected into a predetermined cylinder after the complete explosion of the engine is the actual intake flow rate (intake charge amount) detected by the airflow sensor SW1 and the fuel injection valve 15 This is the equivalent ratio determined from the fuel injection amount. On the other hand, in the control before the complete explosion shown in FIG. 5, the equivalence ratio φ is obtained based on the theoretical amount of air in the cylinder without depending on the actual measurement value by the air flow sensor SW1, but this is the same as the completion of the engine. This is because the rotational speed is low before the explosion and the accurate air amount is not known even if the air flow sensor SW1 is used.

  After executing fuel injection in step S33, the automatic start control unit 52 determines whether or not the accelerator pedal 36 is depressed (step S34). If the determination is YES, the automatic start control unit 52 responds to the accelerator opening. The routine proceeds to normal operation for injecting fuel (step S41).

  On the other hand, if it is determined NO in step S34 and it is confirmed that the accelerator is OFF (the vehicle has not been requested to start), the automatic start control unit 52 determines the fuel injection timing of the second compression after the complete explosion of the engine. Is determined (step S35). In the present embodiment, the second compression after the complete explosion is the fifth compression (in the case of the first compression start) or the sixth compression (in the case of the two compression start) counted from the start of the automatic start. The cylinders to be injected are the compression stroke cylinder 2C at the time of stop when the first compression is started, and the intake stroke cylinder 2D at the time of stop when the second pressure is started (second order).

  When it is determined YES in step S35 and it is confirmed that the fuel injection timing of the second compression after the complete explosion has arrived, the automatic start control unit 52 determines the equivalent amount in the cylinder with respect to the cylinder (2C or 2D). Control is performed to inject an amount of fuel such that the ratio φ becomes 0.3 and to burn the fuel by self-ignition (step S36).

  Next, the automatic start control unit 52 determines whether or not the accelerator pedal 36 is depressed (step S37). If the determination is YES, the automatic start control unit 52 shifts to a normal operation in which fuel is injected according to the accelerator opening. (Step S41).

  On the other hand, when it is determined as NO in step S37 and it is confirmed that the accelerator is OFF (the vehicle has not been requested to start), the automatic start control unit 52 determines the fuel injection timing of the third compression after the engine is completely exploded. Is determined (step S38). In this embodiment, the third compression after the complete explosion is the sixth compression (in the case of one compression start) or the seventh compression (in the case of two compression start) counted from the start of the automatic start. The cylinders to be injected are the intake stroke cylinder 2D at the time of stop at the time of 1 compression start, and the exhaust stroke cylinder 2B at the time of stop at the time of 2 pressure start (2nd order).

  When it is determined YES in step S38 and it is confirmed that the fuel injection timing of the third compression after the complete explosion has arrived, the automatic start control unit 52 determines the equivalent amount in the cylinder with respect to the cylinder (2D or 2B). Control is performed to inject an amount of fuel such that the ratio φ becomes 0.25 and to burn the fuel by self-ignition (step S39).

  Next, the automatic start control unit 52 determines whether or not the accelerator pedal 36 is depressed (step S40). If the determination is YES, the automatic start control unit 52 shifts to a normal operation in which fuel is injected according to the accelerator opening. (Step S41).

  On the other hand, when it is determined NO in step S40 and it is confirmed that the accelerator is OFF (the vehicle is not requested to start), the automatic start control unit 52 executes control for operating the engine in the idling state ( Step S42). Specifically, the engine speed is maintained at a predetermined idling speed by injecting a small amount of fuel into the cylinder so that the equivalence ratio φ is about 0.1 to 0.2. The idling speed is set to an appropriate value near 800 rpm, for example.

  FIG. 8 is a diagram showing a change in the in-cylinder equivalence ratio set at each combustion cycle in the automatic engine start control executed based on the flowcharts of FIGS. 5 and 6 as described above. In FIG. 8, the engine restart condition is satisfied by requirements other than the accelerator ON (for example, brake OFF, engine stop time, and air conditioner requirements), and the accelerator pedal 36 is maintained for a while after the engine complete explosion. Shows the change in the equivalence ratio φ when the is not stepped on. Further, the “combustion times” shown on the horizontal axis in FIG. 8 is the case where the first combustion is the first combustion regardless of the first compression start and the second compression start. Therefore, the number of combustion times = 1, 2, 3... Is the first compression, the second compression, the third compression. It is combustion of eyes, 4 compression eyes.

  As shown in FIG. 8, in this embodiment, the first to third combustion (that is, the first to third compression combustion at the time of the first compression start, or the second to fourth compression combustion at the time of the second compression start) ), The equivalence ratio φ is gradually increased from 0.75 → 0.85 → 0.9, and after the three explosions have reached a complete explosion, the vehicle start request by the accelerator ON is made. Unless otherwise, the equivalent ratio φ is gradually decreased from 0.4 → 0.3 → 0.25, and the equivalent ratio for idling operation (φ = 0.1 to 0.2) is set from the seventh combustion. Is done.

  FIG. 9 is a diagram showing the behavior of the engine automatically started based on the setting of the equivalence ratio in FIG. Note that FIG. 9 illustrates the change over time in the rotational speed of the engine, taking as an example a one-compression start in which fuel is injected from the first compression and burned.

  In FIG. 9, the rotation of the engine by the starter motor 34 is started at time t0, and the compression top dead centers (1TDC, 2TDC) of the first compression, the second compression, and the third compression at the subsequent times t1, t2, and t3. 3TDC). In the one-compression start as shown in FIG. 9, fuel is injected from the first compression, combustion is restarted, and the engine speed is increased. Specifically, in the first compression, the second compression, and the third compression, combustion is performed at a relatively rich equivalent ratio of φ = 0.75 to 0.9 as shown in FIG. The engine rotation speed gradually increases, and reaches the complete explosion speed Nx (700 to 800 rpm) at time t4 after combustion at the third compression is performed. In the following, a process of increasing the engine rotation speed by combustion at a relatively large equivalent ratio before the engine reaches a complete explosion (before time t4) as in the combustion control at the first to third compressions. This is referred to as a “speed increasing step”.

  On the other hand, after the time point t4 when the engine has reached the complete explosion speed Nx, at the time of combustion at the fourth compression, the fifth compression, and the sixth compression (the first to third valley portions in the waveform after the time t4) In FIG. 8, the equivalence ratio φ is reduced to 0.4 to 0.25, so that an increase in the rotational speed after the complete explosion of the engine is suppressed. Specifically, the rotational speed after the complete explosion of the engine (from time t4) changes while undulating in the vicinity of the complete explosion speed Nx, and after the time t5, the idling speed (800 rpm) that is close to the complete explosion speed Nx. Near). After this time t5 (at the time of combustion after the seventh compression), the equivalence ratio φ is set to the minimum value (φ = 0.1 to 0.2) necessary to maintain the idling speed. Hereinafter, the process of reducing the equivalence ratio and suppressing the engine speed increase during the period from the complete engine explosion to the idling state (time t4 to t5) as described above is referred to as “stabilization step”. Called.

  Although FIG. 9 shows the behavior of the engine when the engine is automatically started by one compression start, the first fuel injection (combustion) is two compression when the two compression start is different from the one compression start. Eyes. That is, after the second to fourth compression, combustion is performed at φ = 0.75 to 0.9, and the rotational speed is increased. As a result, after the engine reaches a complete explosion, φ ≦ 0. The rotational speed is stabilized by the combustion at 4. For this reason, in the case of the two-compression start, the combustion control from the fourth compression corresponds to the speed increasing process, and the combustion control from the fifth compression to the seventh compression corresponds to the stabilization process.

(5) Control at Forced Start Next, engine start that is started when the engine is forcibly started, that is, when a passenger on the vehicle performs a predetermined operation for starting the engine will be described.

  When the engine is forcibly started, the engine is generally started by forcibly rotating the engine one or more times by the starter motor 34 and then performing combustion in a fuel-rich environment. As described above, the forced rotation of more than one rotation (rotation by the starter motor 34) is required until the first fuel injection (combustion). The forced engine start is that the system is once shut down and the cylinder discrimination information becomes invalid. This is because the engine rotation is performed from the state, and at least one rotation of the engine is required to newly perform cylinder discrimination.

  FIG. 10 is a diagram showing an example of setting the equivalence ratio at the time of forced start of the engine (change in equivalence ratio according to the number of combustion cycles), and FIG. 11 is an engine that is forcibly started based on the equivalence ratio setting of FIG. FIG. In the examples shown in these drawings, the starter motor 34 starts to be driven at the time point t0, and the cranking for rotating the engine only by the driving force of the starter motor 34 is continued until the first compression and the second compression are exceeded. The During this time, fuel injection is not performed and combustion does not occur, so the engine speed does not increase so much. Thereafter, when the compression top dead center (3TDC) of the third compression is reached at time t11, combustion based on fuel injection is started for the first time, and the engine speed starts to increase substantially. The fuel injection amount at this time is set to the theoretical air fuel ratio (φ = 1) or the vicinity thereof.

  After the initial combustion at the third compression, combustion in a rich environment is performed four more times. That is, in the examples of FIGS. 10 and 11, from the third compression (time t11) to the seventh compression (time t12), fuel is injected by an amount corresponding to the stoichiometric air-fuel ratio (φ = 1) or its vicinity. The control to be repeated is repeated 5 times. As a result, the engine rotation speed greatly exceeds the complete explosion speed Nx (700 to 800 rpm) at the time of automatic engine start, and finally increases to a peak speed (for example, 1000 to 1500 rpm) at time t13.

  As described above, the purpose of increasing the rotational speed more than necessary is to make sure that the occupant recognizes that the engine has started, and also for the effect on merchandise. In the following, the period (time point t0 to t13) in which the rotation speed is significantly increased by performing many combustions in the vicinity of the theoretical equivalent ratio (φ = 1) at the time of forced start of the engine is referred to as “blow-up period”. Called. It should be noted that the number of combustions in the vicinity of φ = 1 executed during this blow-up period may not be five depending on the state of the engine before the forced start, but at least the speed increase during the automatic start of the engine More than the number of times of combustion in the process (three times in this embodiment).

  After the blowing-up period ends, the equivalence ratio φ is greatly reduced. In the example of FIG. 10, the equivalence ratio φ is set to 0 to 0.1 (0 or more and 0.1 or less) at the first combustion after the end of the blow-up period (sixth combustion counted from the first combustion). In the subsequent combustion, the equivalent ratio φ is set to a small value of about 0.1 to 0.2. In particular, in the first combustion after the end of the blow-up period, the equivalence ratio φ is set to an extremely small value of 0 to 0.1 (φ = 0 means fuel cut to stop fuel injection). When the engine is forcibly started, combustion near φ = 1 is repeated many times and the rotational speed is once significantly increased. Therefore, it is not necessary to almost inject fuel immediately after the end of the period (the blow-up period). Because.

(6) Operation, etc. As described above, in the present embodiment, in the in-vehicle diesel engine having a so-called idle stop function that automatically stops or starts the engine under a predetermined condition, Such a characteristic configuration was adopted.

  When a predetermined restart condition is satisfied after the engine is automatically stopped, the automatic start control unit 52 of the ECU 50 causes the piston stop position of the stop-time compression stroke cylinder 2C that has been stopped in the compression stroke to be relatively close to bottom dead center. 1 compression start in which combustion is resumed from the first compression at which the compression stroke 2C at the time of stoppage reaches the compression top dead center according to the determination result, or Then, the two-compression start is performed in which the combustion is resumed from the second compression at which the stop-time intake stroke cylinder 2D that has stopped in the intake stroke reaches the compression top dead center.

  After the first combustion in the stop-time compression stroke 2C or the stop-time intake stroke cylinder 2D, the combustion is repeated every time one of the cylinders reaches compression top dead center, but a total of three times including the first combustion. Is burned in a relatively rich environment with an equivalent ratio φ = 0.75 to 0.9, whereby the engine speed is increased to a predetermined complete explosion speed Nx (700 to 800 rpm) ( Speed-up process). On the other hand, if there is no vehicle start request (accelerator ON) after this speed increasing step, a small amount of fuel set so that the equivalence ratio φ is smaller than that in the speed increasing step is injected. As a result, an increase in engine rotation speed is suppressed, and the rotation speed is maintained at a level close to the complete explosion speed Nx (stabilization step).

  The number of times of combustion (3 times) executed in the speed increasing step is greater than the number of times of combustion (5 times) executed during the blow-up period, which is a period during which the rotational speed increases in the initial stage of forced engine start. Be reduced. Further, the equivalent ratio φ based on fuel injection after the transition to the stabilization process (after the complete explosion of the engine) is, for example, φ = 0.4 at the first, second, and third combustion after the complete explosion. 0.3 and 0.25, both of which are considerably smaller than the equivalent ratio (φ = 0.75 to 0.9) during the speed increasing process, but at the time of forced engine start Is set to be larger than the equivalent ratio (φ = 0 to 0.1) based on the fuel injection executed after the blow-up period ends.

  According to the configuration of the above-described embodiment, there is an advantage that the engine can be started quickly and smoothly while suppressing the blow-up when the engine is automatically started to restart the engine that has been automatically stopped. .

  That is, in the above-described embodiment, when the engine is automatically started, the equivalence ratio φ = 0.75 to 0.9 is less than the number of times of combustion (three times) performed during the blow-up period at the forced start. Because the combustion is performed in a relatively rich environment (acceleration process), and thereafter the equivalence ratio φ is reduced to reduce the combustion energy unless there is a vehicle start request (stabilization process). While the engine speed can be increased rapidly to bring the engine to a complete explosion, it is possible to suppress the excessive increase in engine speed that would occur during the forced start-up period and to smoothly shift the engine to the idling state. be able to. As a result, noise during automatic engine start can be reduced, and even if there is a vehicle start request (accelerator ON) immediately after completion of the speed increasing process, the vehicle does not jump out suddenly, and the vehicle safety And ride comfort can be improved effectively.

  Further, the equivalent ratio (φ = 0.4 to 0.25) at the time of combustion performed in the stabilization process after the complete explosion of the engine is an extremely small equivalent ratio φ set immediately after the blow-up period at the time of forced engine start. Since it is set to be larger than (= 0 to 0.1), it is possible to prevent the rotational speed from being excessively reduced immediately after the engine is completely exploded. For this reason, it is possible to reliably avoid a situation in which the rotational speed undulates violently before the engine rotational speed is stabilized, and a smoother automatic engine start can be achieved.

  Further, in the above embodiment, in the first to third combustion corresponding to the speed increasing process at the time of automatic start, the equivalent ratio φ in the cylinder (that is, the equivalent ratio of the first to third compression at the time of one compression start, or 2 (Equivalent ratio at the second to fourth compression at the time of compression start) is set to 0.75 to 0.9, while equivalent ratio φ at the time of the fourth and subsequent combustion corresponding to the stabilization process is set to less than 0.4 did. According to such a configuration, the engine can be quickly increased to the complete explosion speed by combustion at a relatively rich equivalent ratio set during the speed increasing process, and the equivalent ratio after the complete explosion is rapidly decreased. As a result, it is possible to reliably prevent the engine from being blown up when the rotational speed increases more than necessary.

  Note that the equivalent ratio (φ = 0.75 to 0.9) during the speed increasing process may be uniformly set to the theoretical equivalent ratio (φ = 1) if only the speed of starting is required. Of course this is possible. However, since the engine speed has not increased sufficiently during the speed increasing process, the air leaks outside through the gap between the piston 5 and the cylinder wall surface while the piston 5 is compressing the air. Is easy to happen. For this reason, in the cylinder in which the piston 5 reaches the compression top dead center during the speed increasing process, it is considered that the actual air amount in the cylinder is smaller than the theoretical air amount. However, in the above embodiment, as described in (4-1) above, when determining the fuel injection amount during the speed increasing process, the target equivalent ratio φ is set to the theoretical air amount (leakage during compression). Therefore, if an amount of fuel corresponding to the theoretical equivalent ratio (φ = 1) is injected, it is excessive for the actual air amount. There is a possibility that fuel will be supplied, resulting in deterioration of fuel consumption and emission.

  Therefore, in the above embodiment, the equivalent ratio φ during the speed increasing process is set to 0.75 to 0.9 on the theoretical air amount basis. As a result, an appropriate amount of fuel is supplied in consideration of air leakage during the speed-up process in which compressed air is likely to leak to the outside because the rotational speed has not increased sufficiently. It is possible to suppress the increase in HC and CO due to the above, and to effectively prevent the deterioration of fuel consumption.

  In particular, in the above embodiment, the equivalence ratio φ during the speed increasing process is gradually increased from 0.75 → 0.85 → 0.9 as the number of combustions progresses. The automatic start-up can be speeded up. That is, as the engine speed increases gradually, the amount of compressed air leaking to the outside decreases accordingly, so the upper limit equivalence ratio φ that does not cause excessive fuel is increased as the number of compressions is repeated (as combustion progresses in the order of cylinders). Should be bigger. Therefore, by gradually increasing the equivalence ratio φ in accordance with this, it is possible to effectively shorten the time required for automatic engine start (automatic start time) while preventing deterioration of emissions due to excessive fuel. it can.

  In the above embodiment, in the speed increasing process at the time of automatic engine start, the theoretical equivalent ratio φ set at the time of the first to third combustion (the equivalent ratio of the first to third compression at the time of one compression start and 2 The equivalent ratio of the second to fourth compressions at the start of compression) was gradually increased from 0.75 → 0.85 → 0.9. If it is 7 or more and less than 1.0, it can change suitably. In the above embodiment, the equivalent ratio φ (equivalent ratio at the time of the fourth to sixth combustion from the start of the automatic start) in the stabilization process after the complete explosion of the engine is 0.4 → 0.3 → 0. Although it was made to decrease gradually with .25, the equivalence ratio of each time during the stabilization step can be appropriately changed as long as it is 0.1 or more and less than 0.5. For example, when the change in the rotational speed at the time of automatic start is examined based on the actually measured value and feedback control is performed to reflect the change in the equivalent ratio setting value, the equivalent ratio in each of the above steps is the engine rotational speed. It can fluctuate within a certain range corresponding to the measured value of. However, in any case, the equivalent ratio φ in the stabilization process is still smaller than the equivalent ratio φ in the speed increasing process.

  Further, in the above embodiment, the equivalent ratio φ to be set during the speed increasing process at the time of engine automatic start is calculated based on a theoretical air amount that does not consider air leakage during compression, and the theoretical equivalent ratio is calculated. The injection amount was determined so that φ would be 0.75 to 0.9. For example, the amount of air in the cylinder during the speed increasing process due to the fact that the engine has an in-cylinder pressure sensor that detects the pressure in the cylinder. Can be detected accurately, the equivalence ratio φ may be calculated based on the accurate air amount. Since the equivalent ratio φ calculated in this way is considered to be almost the same as the actual value, it is not always necessary to make the equivalent ratio φ smaller than 1.0 (theoretical equivalent ratio) during the speed increasing step. , 1.0, or a slightly larger value can be set. Therefore, depending on how the equivalent ratio φ is obtained, the upper limit value of the equivalent ratio φ during the speed increasing step may be 1.0 or more.

  Further, in the above embodiment, the equivalence ratio (φ = 0.4, 0.3, 0.25) set during the stabilization process at the time of automatic engine start is the blowing-up period at the forced engine start. Is larger than the equivalent ratio (φ = 0 to 0.1) based on the fuel injected at the first time after the end of the process, but at least after the transition to the stabilization process, the equivalent ratio at the first time is As long as it is larger than the equivalence ratio immediately after the end of the blowing-up period, the equivalence ratio for the second and subsequent times after the transition to the stabilization process is not necessarily limited thereto.

  In the above embodiment, the number of combustions required to increase the rotational speed to the complete explosion speed Nx at the time of automatic engine start (the number of combustions performed during the acceleration process) is three times. The number of combustions up to can be naturally changed if the setting method of the equivalence ratio φ and the engine specifications are different. However, from the viewpoint of suppressing an excessive increase in rotational speed (engine blow-up), the above-mentioned number of combustions (the number of combustions until the complete explosion at the automatic start) is at least the blow-up period at the forced engine start. It is set to be less than the number of combustion times.

  In the above embodiment, the preferred embodiment of the present invention has been described by taking the AT vehicle in which the crankshaft 7 of the engine body 1 is connected to the automatic transmission 101 via the torque converter 102 as an example. Can be applied not only to AT cars but also to MT cars in which the crankshaft 7 is connected to a manual transmission via a clutch. However, in the case of an MT vehicle, a flywheel having a relatively large mass is attached to one end of the crankshaft 7, so that the speed at which the rotational speed increases when the engine starts due to the inertia of the flywheel is Slightly slower. For this reason, in the speed increasing process at the time of automatic start, the number of combustions required to increase the rotation speed to the complete explosion speed Nx is compared with the number of combustions (three times) in the above embodiment based on the AT vehicle. Become more.

  FIG. 12 is a diagram illustrating how the equivalence ratio φ is set when the engine is automatically started when the vehicle on which the diesel engine is mounted is an MT vehicle. As shown in the figure, in the case of an MT vehicle, the number of combustions in the speed increasing process in which the engine speed is increased by combustion at a relatively large equivalent ratio (φ = 0.75 to 0.9 in the example) is It has been set to 5 times, and since the 6th combustion after that, it has shifted to a stabilization process for reducing the equivalent ratio φ to less than 0.5.

  Thus, in the case of the MT vehicle, the number of times of combustion during the speed increasing process is set to 5 times, which is larger than that in the case of the AT vehicle (3 times). However, in the MT vehicle, the number of combustion during the blow-up period at the forced start of the engine is also increased (for example, 7 times) in the case of the AT vehicle (e.g., 7 times), so during the speed increasing process at the automatic start The tendency that the number of combustions is smaller than the number of combustions during the blow-up period at the forced start is the same for both the AT and MT cars.

  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 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 / start control can be suitably applied.

DESCRIPTION OF SYMBOLS 1 Engine main body 2A-2D Cylinder 5 Piston 7 Crankshaft 15 Fuel injection valve 34 Starter motor 50 ECU (control means)
101 Automatic transmission 102 Torque converter Nx Complete explosion speed

Claims (6)

An automatic stop condition and a restart condition are set for an in-vehicle compression self-ignition engine that burns fuel injected from the fuel injection valve into the cylinder by self-ignition, and the automatic stop condition is set during operation of the engine. By automatically stopping the engine when the above is satisfied, and then injecting fuel from the fuel injection valve while applying rotational force to the engine using the starter motor when the restart condition is satisfied, A start control method for a compression self-ignition engine for automatically starting the engine,
After the restart condition is satisfied, the compression stroke cylinder at the time of stop that has been stopped in the compression stroke reaches the compression top dead center, or the intake stroke cylinder at the time of stop that has been stopped in the intake stroke reaches the compression top dead center. The fuel is injected into the fuel injection valve from the second compression that is greeted, and combustion is resumed. Thereafter, the fuel is injected and burned every time one of the cylinders reaches compression top dead center. A speed increasing process that sequentially burns until the explosion speed increases,
By injecting and burning a small amount of fuel set so that the equivalence ratio in the cylinder becomes smaller than that in the speed increasing process when there is no vehicle start request after the speed increasing process, Including a stabilization process for suppressing an increase in rotational speed,
The number of combustions in the speed increasing step is set to be less than the number of combustions performed during the blow-up period, which is the period during which the rotational speed increases in the initial stage of forced engine start,
The in-cylinder equivalence ratio based on at least the first fuel injection executed after the transition to the stabilization step is based on the first fuel injection executed after the blow-up period ends at the time of forced start of the engine. A starting control method for a compression self-ignition engine, wherein the starting ratio is set to be larger than an equivalence ratio. In the starting control method of the compression self-ignition engine according to claim 1,
Start of a compression self-ignition engine characterized in that the equivalence ratio in the speed increasing step is set to 0.7 or more, and the equivalence ratio in the stabilization step is set to 0.1 or more and less than 0.5. Control method. In the starting control method of the compression self-ignition engine according to claim 2,
A starting control for a compression self-ignition engine, characterized in that an equivalence ratio based on the first fuel injection that is executed after completion of the blow-up period at the time of forced start of the engine is set to 0 or more and 0.1 or less. Method. The start-up control method for a compression self-ignition engine according to claim 2 or 3,
The equivalence ratio in the speed increasing step is calculated based on a theoretical air amount that does not take into account air leaking out of the cylinder during compression, and the theoretical equivalence ratio is 0.7 or more and less than 1.0. A starting control method for a compression self-ignition engine, characterized in that In the starting control method of the compression self-ignition type engine according to any one of claims 2 to 4,
The compression self-ignition engine has a crankshaft connected to an automatic transmission via a torque converter,
A start control method for a compression self-ignition engine, characterized in that in the speed increasing step, combustion is performed a total of three times in the entire engine, and the routine proceeds from the fourth time combustion to the stabilization step. 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, A start control device that automatically starts 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 satisfied,
After the restart condition is satisfied, the compression stroke cylinder at the time of stop that has been stopped in the compression stroke reaches the compression top dead center, or the intake stroke cylinder at the time of stop that has been stopped in the intake stroke reaches the compression top dead center. The fuel is injected into the fuel injection valve from the second compression that is greeted and combustion is resumed. Then, every time any cylinder reaches compression top dead center, the fuel is injected and burned, so that the engine rotational speed becomes a predetermined standard. A first control for sequentially burning until the speed is increased;
After the first control, when there is no vehicle start request, by injecting and burning a small amount of fuel set so that the equivalent ratio in the cylinder becomes smaller than that in the speed increasing step, Control means for executing second control for suppressing an increase in engine rotation speed;
The number of combustions in the first control is set to be smaller than the number of combustions performed during the blow-up period, which is a period during which the rotational speed increases in the initial stage of forced engine start,
The in-cylinder equivalence ratio based on at least the first fuel injection executed after the shift to the second control is the same as the first fuel injection executed after the blow-up period ends at the forced start of the engine. A starting control device for a compression self-ignition engine, wherein the starting control device is set to be larger than an equivalent ratio based thereon.

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