JP2012012994A - Device for starting diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten an average time necessary for restarting a diesel engine.SOLUTION: When a position of a stop-time compression stroke cylinder 2C stopped at a compression stroke at an automatic stop is in a specified range R which is set at an intermediate part between an upper dead point and a lower dead point, a glow plug 31 corresponding to the stop-time compression stroke cylinder 2C is carried with electricity in advance. By injecting fuel into the stop-time compression stroke cylinder 2C from a fuel injection valve 15 while driving a starter motor 34, the diesel engine is restarted.

Description

  The present invention automatically stops a diesel engine when a predetermined automatic stop condition is satisfied, and restarts the diesel engine after the automatic stop when a predetermined restart condition is satisfied. About.

  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 CO2. It's getting on.

  In order to further reduce CO2 in the compression self-ignition engine as described above, the engine is automatically stopped during idle operation or the like, and then the engine is automatically operated when the vehicle is started. It is effective to employ a so-called idle stop control technique that restarts automatically, and various studies have been conducted on this.

  For example, in Patent Document 1 below, a diesel engine is automatically stopped when a predetermined automatic stop condition is satisfied, and when a predetermined restart condition is satisfied, fuel injection is performed while driving a starter motor to In a diesel engine control device that restarts an engine, a cylinder that first injects fuel is variably set based on a piston stop position of a compression stroke cylinder at the time of stoppage that is in a compression stroke at the time of stoppage (when the stop is completed) Is disclosed.

  Specifically, in this document, when the diesel engine is automatically stopped, the piston position of the stop-time compression stroke cylinder in the compression stroke at that time is obtained, and the piston position is determined at a predetermined appropriate position (for example, compression top dead). If it is in the proper position, the first fuel is injected into the compression stroke cylinder at the time of stop, but the upper dead than the proper position. When it is on the point side, the first fuel is injected into the intake stroke cylinder at the stop in the intake stroke cylinder at the stop.

  According to such a configuration, when the piston of the compression stroke cylinder at the time of stop is in the appropriate position, the fuel can be surely self-ignited by injecting the fuel into the compression stroke cylinder at the time of stop, and the relatively short The engine can be restarted in time. On the other hand, when the piston of the stop compression stroke cylinder is deviated from the above-mentioned proper position to the top dead center side, the compression allowance by the piston is small and the air in the cylinder is not sufficiently heated. Misfire may occur even if fuel is injected. Therefore, in such a case, by injecting the fuel not into the stop-time compression stroke cylinder but into the stop-time intake stroke cylinder, the air in the cylinder can be sufficiently compressed and the fuel can be surely self-ignited.

JP 2009-62960 A

  However, in the technique of the above-mentioned Patent Document 1, the engine can be restarted quickly when the piston of the compression stroke cylinder at the time of stop is in the proper position, but if the engine is deviated from the proper position to the top dead center side, the engine is stopped. Because fuel must be injected into the intake stroke cylinder, the fuel until the piston of the stop intake stroke cylinder reaches the compression top dead center (that is, until the engine reaches the second top dead center) There is a problem that self-ignition based on injection cannot be performed and the restart time becomes long.

  The present invention has been made in view of the above circumstances, and when restarting a diesel engine after automatic stop, a diesel engine capable of further reducing the average time required for the restart It is an object to provide a starting device.

  In order to solve the above-mentioned problem, the present invention automatically stops the diesel engine when a predetermined automatic stop condition is satisfied, and also after the automatic stop when the predetermined restart condition is satisfied. A diesel engine starter for restarting an engine, comprising: a fuel injection valve that injects fuel into each cylinder of the diesel engine; a glow plug that has a heat generating portion in the cylinder that generates heat when energized; and the diesel engine A control means for controlling various devices including a starter motor for applying a rotational force, and the control means includes a top dead center and a bottom dead center in which the piston position of the compression stroke cylinder at the stop when stopped in the compression stroke at the time of automatic stop And energizing the glow plug corresponding to the above-mentioned stop compression stroke cylinder, The diesel engine is restarted by injecting fuel from the fuel injection valve to the stop-time compression stroke cylinder while driving the starter motor when the restart condition is satisfied after (Claim 1).

  According to the present invention, it is possible to expand the range of the piston stop position at which the so-called one-compression start can be restarted by injecting fuel into the stop-time compression stroke cylinder, and shorten the average time required for engine restart. be able to.

  That is, if the piston stop position of the compression stroke cylinder at the time of stop is in a specific range that is an intermediate part between the top dead center and the bottom dead center, it is surely ensured even if fuel is injected into the compression stroke cylinder at the time of stop. It is difficult to cause self-ignition to occur, and it is necessary to inject fuel into the cylinder that reaches the compression stroke (intake stroke cylinder when stopped). However, as in the present invention, if the glow plug of the stop compression stroke cylinder is energized in advance and the inside of the cylinder is heated to a high temperature, an environment that is more likely to self-ignite is created. The fuel injected into the fuel can be surely self-ignited. As a result, the range of the piston stop position where one compression start is possible can be expanded, and a quick engine restart by one compression start can be realized at a higher frequency, so that the average time required for engine restart can be effectively reduced. It can be shortened.

  In the present invention, preferably, the specific range is set closer to the bottom dead center as the cooling water temperature of the engine is lower.

  Further, the specific range may be set closer to the bottom dead center as the atmospheric pressure is lower (claim 3).

  Furthermore, the specific range may be set closer to the bottom dead center as the outside air temperature is lower (Claim 4).

  As shown in these configurations, when the energization of the glow plug is started from a position closer to the bottom dead center according to the environment in which the fuel is difficult to ignite, even when the external environment is severe, 1 The range where compression start is possible can be expanded, and the engine can be started quickly.

  In the present invention, preferably, the control means may increase the temperature of the heat generating portion of the glow plug to exceed a predetermined value even when the piston stop position of the stop-time compression stroke cylinder is in the specific range. Thus, energization of the glow plug is prohibited (claim 5).

  According to this configuration, since the temperature of the heat generating part of the glow plug can be prevented from rising more than necessary, the power consumed by the glow plug can be effectively suppressed, and the deterioration of fuel consumption due to the increase in power consumption can be minimized. Can be suppressed.

  As described above, according to the present invention, when the diesel engine after automatic stop is restarted, the average time required for the restart can be further shortened.

It is a figure showing the whole diesel engine composition to which the starting device concerning one embodiment of the present invention was applied. It is a time chart which shows the change of each state quantity when the above-mentioned engine stops automatically. It is a figure for demonstrating the specific range of the piston stop position of a compression stroke cylinder at the time of a stop. It is a figure for demonstrating the electricity supply form to a glow plug. It is a graph which shows the relationship between the piston stop position of the compression stroke cylinder at the time of a stop, and the restart time of an engine when a glow plug is not used. It is a graph which shows the relationship between the piston stop position of the compression stroke cylinder at the time of a stop, and the largest in-cylinder pressure when an engine is started 1 compression. FIG. 7 is a graph showing the relationship between the piston stop position and the maximum in-cylinder pressure of a compression stroke cylinder when stopped under a condition different from that in FIG. 6. It is a figure which shows the first half part of the flowchart which shows the specific content of engine automatic stop and restart control. It is a figure which shows the latter half part of the said flowchart.

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

  A combustion chamber 6 is formed above the piston 5, and fuel (light oil) injected from a fuel injection valve 15 described later is supplied to the combustion chamber 6. The injected fuel 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 reciprocates vertically. It is like that.

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

  Here, in the four-cycle four-cylinder diesel engine as shown in the figure, the piston 5 provided in each of the cylinders 2A to 2D moves up and down with a phase difference of 180 ° (180 ° CA) in crank angle. For this reason, the timing of combustion (fuel injection) 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 (see FIG. 2).

  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 close the ports 9 and 10 so that they can be opened and closed. ing. 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 via a common rail 20 as a pressure accumulation chamber and 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.

  Further, the cylinder head 4 is provided with one glow plug 31 for each of the cylinders 2A to 2D. The glow plug 31 has a heat generating portion that generates heat when energized at its tip, and the heat generating portion is provided so as to protrude into the combustion chamber 6. Then, for example, when necessary at the time of cold start or the like, the heat generating portion is energized, whereby the air in each of the cylinders 2A to 2D is heated to promote self-ignition of fuel.

  Each fuel injection valve 15 is composed of an electromagnetic needle valve in which an injection nozzle having a plurality of injection holes is provided at the tip, and a fuel passage that communicates with the injection nozzle and an electromagnetic force act in the inside thereof. It has a needle-like valve element that opens and closes the fuel passage (both are not shown). Then, 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 toward the combustion chamber 6 from each injection hole of the injection nozzle. Yes.

  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 a rotation angle and a rotation speed of the crankshaft 7. The crank angle sensor SW2 outputs a pulse signal according to the rotation of the crank plate 25 that rotates integrally with the crankshaft 7.

  Specifically, a large number of teeth lined up at a constant pitch are projected on the outer peripheral portion of the crank plate 25, and a tooth missing portion 25a (teeth) for specifying a reference position is provided in a predetermined range on the outer peripheral portion. A portion where no is present) is formed. The crank plate 25 having the tooth missing portion 25a at the reference position rotates in this way, and a pulse signal based on the crank plate 25 is output from the crank angle sensor SW2, whereby the rotation angle (crank angle) of the crankshaft 7 and The rotational speed (engine rotational speed) is detected.

  On the other hand, the cylinder head 4 is provided with a cam angle sensor SW3 for detecting the angle of a camshaft (not shown) for valve actuation. The cam angle sensor SW3 outputs a pulse signal for cylinder discrimination according to the passage of teeth of a signal plate that rotates integrally with the camshaft.

  That is, the pulse signal output from the crank angle sensor SW2 includes a no-signal portion generated every 360 ° CA corresponding to the above-mentioned tooth missing portion 25a. When the piston 5 is moving up, it is impossible to determine which cylinder corresponds to the compression stroke or the exhaust stroke. Therefore, a pulse signal is output from the cam angle sensor SW3 based on the rotation of the camshaft that rotates once every 720 ° CA, the timing at which the signal is output, and the timing of the non-signal portion of the crank angle sensor SW2 (tooth missing). The cylinder discrimination is performed on the basis of the passage timing of the section 25a.

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

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

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

  The surge tank 28b is provided with an intake pressure sensor SW4 for detecting the intake pressure, and the common passage 28c between the surge tank 28b and the intake throttle valve 30 is used for detecting the intake flow rate. Air flow sensor SW5 is provided.

  An alternator 32 is connected to the crankshaft 7 via a timing 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. Thus, the crankshaft 7 is driven to rotate.

(2) Control system The engine configured as described above is centrally controlled by the ECU 50 at each part. The ECU 50 is a microprocessor composed of a well-known CPU, ROM, RAM, and the like, and corresponds to the control means 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, the intake pressure sensor SW4, and the airflow sensor SW5 provided in each part of the engine. Based on the input signal from SW5, various information such as engine coolant temperature, crank angle, engine rotation speed, cylinder discrimination, intake pressure, intake flow rate, and the like are acquired.

  The ECU 50 also receives information from various sensors (SW6 to SW11) provided in the vehicle. That is, the vehicle includes an accelerator opening sensor SW6 for detecting the opening degree of the accelerator pedal 36 that is depressed by the driver, and a brake sensor for detecting ON / OFF of the brake pedal 37 (presence of braking). SW7, a vehicle speed sensor SW8 for detecting the traveling speed (vehicle speed) of the vehicle, a battery sensor SW9 for detecting the remaining capacity of the battery (not shown), an atmospheric pressure sensor SW10 for detecting atmospheric pressure, and an outside air temperature. An outside air temperature sensor SW11 for detection is provided. The ECU 50 acquires information such as the accelerator opening, the presence / absence of a brake, the vehicle speed, the remaining battery capacity, the atmospheric pressure, and the outside air temperature based on the input signals from the sensors SW6 to SW11.

  The ECU 50 controls each part of the engine while executing various calculations based on input signals from the sensors SW1 to SW11. Specifically, the ECU 50 is electrically connected to the fuel injection valve 15, the intake throttle valve 30, the glow plug 31, the alternator 32, and the starter motor 34. The control signal for driving is output to each of the above.

  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, the engine is also automatically stopped or restarted under a predetermined specific condition. For this reason, the ECU 50 includes an automatic stop control unit 51 and a restart control unit 52 as functional elements related to engine automatic stop or restart control.

  The automatic stop control unit 51 determines whether or not a predetermined engine automatic stop condition is satisfied during operation of the engine, and executes control to automatically stop the engine when it is satisfied. .

  For example, the automatic stop condition is satisfied when it is confirmed that the vehicle is in a stopped state (vehicle speed is 0 km / h) and the like, and it is confirmed that there is no problem even if the engine is stopped. Is determined. Then, the engine is stopped, for example, by stopping fuel injection from the fuel injection valve 15.

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

  For example, when the driver needs to start the engine by depressing the accelerator pedal 36 to start the vehicle, it is determined that the restart condition is satisfied. Then, the engine is restarted by, for example, restarting fuel injection from the fuel injection valve 15 while driving the starter motor 34 to apply rotational force to the crankshaft 7.

(3) Automatic Stop / Restart Control Next, the details of the engine automatic stop / restart control executed by the automatic stop control unit 51 and the restart control unit 52 of the ECU 50 will be described more specifically.

  FIG. 2 is a time chart showing changes in each state quantity when the engine automatically stops. Here, the time point when the automatic engine stop condition is satisfied is defined as t1. As shown in the figure, during the engine automatic stop control, the target generated current Ge of the alternator 32 is set to a predetermined value at a time t1 when the automatic stop condition is satisfied. Then, while maintaining this state, fuel injection from the fuel injection valve 15 is stopped (fuel cut) at the subsequent time t2. The opening degree K of the intake throttle valve 30 is maintained at the same high opening degree (for example, 80%) as in normal operation until the time point t4 when the engine is completely stopped.

  As described above, while maintaining the opening degree K of the intake throttle valve 30 at a high degree and maintaining the target generated current Ge of the alternator 32 at a constant value (that is, while applying a constant load from the alternator 32 to the engine). By executing the fuel cut, the engine speed Ne decreases in a generally similar manner while undulating. Here, the position of the valley in the waveform of the engine rotation speed Ne coincides with the timing when any of the cylinders 2A to 2D reaches the top dead center. In the illustrated engine, after the top dead center is exceeded a plurality of times after the fuel cut is executed, the last top dead center (final TDC) of all the cylinders is reached at time t3. After that, a complete stop state is reached at time t4 without exceeding the top dead center (moving temporarily in the reverse direction).

  When the automatic stop of the engine is completed as described above, the piston 5 of the cylinder (cylinder 2C in FIG. 2; hereinafter referred to as the compression stroke cylinder 2C at the time of stop) in the compression stroke at the time of stop (when the stop is completed) It is determined whether or not the vehicle is stopped within a specific range R shown in FIG. The specific range R is set at an intermediate portion between the top dead center and the bottom dead center. When it is confirmed that the piston stop position of the stop-time compression stroke cylinder 2C is within the specific range R, as shown in FIG. 4, the glow plug 31 corresponding to the stop-time compression stroke cylinder 2C is intermittently energized. The temperature of the heat generating part of the glow plug 31 is increased. The reason why the glow plug 31 is intermittently energized is to prevent the temperature of the heat generating portion from rising more than necessary and to minimize the power consumed by the glow plug 31.

  The reason why the glow plug 31 of the stop-time compression stroke cylinder 2C is energized as described above is to promote the self-ignition of the fuel injected into the cylinder 2C when the engine is restarted. That is, if the piston stop position of the stop-time compression stroke cylinder 2C is in the specific range R, the amount of air inside the cylinder is not so large. It is difficult to reliably ignite the fuel, and it is necessary to inject fuel into the intake stroke cylinder at the time of stop (that is, the cylinder in the intake stroke when the stop of the engine is completed; cylinder 2D in FIG. 2). However, if the glow plug 31 of the stop-time compression stroke cylinder 2C is energized in advance as described above, an environment in which self-ignition is more likely to occur as the temperature in the cylinder rises is created. The fuel can be surely self-ignited. As a result, the range of the piston stop position where the fuel can be restarted by injecting fuel into the stop compression stroke cylinder 2C can be expanded, and the time required for restart can be shortened on average.

  This point will be described in detail with reference to FIG. FIG. 5 is a graph showing the relationship between the piston stop position (horizontal axis) of the stop-time compression stroke cylinder 2C and the engine restart time (vertical axis) when no glow plug 31 is used. The restart time here refers to the time from when the starter motor 34 is started until the engine speed reaches 750 rpm. Also, the ● mark plot in the figure represents the case where the first fuel was injected into the stop compression stroke cylinder 2C and the engine was restarted, and the ◆ mark plot represents the first fuel in the stop intake stroke cylinder Represents a case where the engine is restarted by injecting fuel. The data of these plots was obtained under conditions of an engine cooling water temperature of 75 ° C., an outside air temperature of 25 ° C., and an altitude of 0 m (atmospheric pressure is standard atmospheric pressure).

  As shown in the graph of FIG. 5, under the conditions of a cooling water temperature of 75 ° C., an outside air temperature of 25 ° C., and an altitude of 0 m, the piston 5 of the stop compression stroke cylinder 2C is positioned approximately 80 ° before the crank angle from the top dead center ( The engine can be restarted by injecting the first fuel into the compression stroke cylinder 2C at the time of stop if it is further on the bottom dead center side (around BTDC 80 ° CA). That is, if the piston stop position of the stop-time compression stroke cylinder 2C is in the above range, a relatively large amount of air exists in the cylinder 2C. The air in the cylinder 2C is sufficiently compressed to increase the temperature. For this reason, even if the first fuel at the time of restart is injected into the compression stroke cylinder 2C at the time of stop, this fuel is surely self-ignited and burned in the cylinder 2C.

  Thus, if the piston stop position of the stop-time compression stroke cylinder 2C is on the bottom dead center side from near BTDC 80 ° CA, the engine can be restarted by injecting fuel into the stop-time compression stroke cylinder 2C. it can. In this case, since the fuel injection can be started when the engine reaches the first top dead center, the time required for restarting the engine is considerably short (approximately 300 to 400 msec). Hereinafter, as described above, injecting fuel into the stop-time compression stroke cylinder 2C and restarting the engine may be referred to as one-compression start.

  On the other hand, if the piston stop position of the stop-time compression stroke cylinder 2C is on the top dead center side near BTDC 80 ° CA, even if fuel is injected into the stop-time compression stroke cylinder 2C, it cannot be self-ignited. It is necessary to inject the first fuel into the intake stroke cylinder 2D at the time of stop (plotted with ◆ mark). That is, if the piston stop position of the stop-time compression stroke cylinder 2C is within the above range, only a relatively small amount of air exists in the cylinder 2C. The air in the cylinder 2C is not sufficiently compressed, and a significant increase in temperature cannot be expected. For this reason, it is necessary to restart the engine by injecting the first fuel not into the stop-time compression stroke cylinder 2C but into the stop-time intake stroke cylinder 2D that reaches the next compression stroke.

  As shown in FIG. 3, after the stop compression stroke cylinder 2C and the stop intake stroke cylinder 2D are out of phase by 180 ° CA, the piston 5 of the stop compression stroke cylinder 2C has passed the top dead center. Then, the piston 5 of the intake stroke cylinder 2D at the time of stop reaches the compression top dead center. Therefore, after waiting for the piston 5 of the intake stroke cylinder 2D at the time of stop to rise to the vicinity of the compression top dead center (that is, the engine reaches the second top dead center as a whole), the first fuel is put into the cylinder 2D. Spray. Thereby, although the time required for restarting the engine increases (approximately 400 to 500 msec), the engine can be reliably restarted. Hereinafter, the injection of fuel into the stop-time intake stroke cylinder 2D as described above to restart the engine may be referred to as a two-compression start.

  As can be understood from the above, in order to restart the engine without using the glow plug 31 under conditions of a cooling water temperature of 75 ° C., an outside air temperature of 25 ° C., and an altitude of 0 m, the piston of the stop compression stroke cylinder 2C is stopped. 1 compression start in which fuel is injected into the compression stroke cylinder 2C at the time of stop depending on whether the position is on the bottom dead center side or the top dead center side from the vicinity of BTDC 80 ° CA (boundary for BTDC 80 ° CA); The two-compression start in which fuel is injected into the intake stroke cylinder 2D at the time of stop may be properly used. Thereby, the engine can be reliably restarted regardless of the piston position when the engine is stopped.

  However, as is apparent from the graph of FIG. 5, for example, when the piston stop position of the stop-time compression stroke cylinder 2C is in the vicinity of BTDC 80 ° CA, two-compression start (starting method of injecting fuel into the stop-time intake stroke cylinder 2D) ), The time required for restarting the engine is prolonged to a value close to 500 msec. That is, when the piston 5 of the stop-time compression stroke cylinder 2C is stopped at the intermediate portion of the piston stroke (intermediate portion between the top dead center and the bottom dead center) such as around BTDC 80 ° CA, the phase is 180 °. The piston 5 of the intake stroke cylinder 2D at the time of stop different in CA is also stopped at an intermediate portion of the piston stalk (BTDC 100 ° CA). In order to inject fuel into the stop-time intake stroke cylinder 2D in which the piston 5 is stopped at such a position, the piston 5 of the cylinder 2D once descends from the intermediate portion and then reverses to be top dead center ( It is necessary to wait until it rises near compression top dead center). For this reason, the waiting time until fuel injection is long, and accordingly, the time required for restarting the engine is prolonged.

  Therefore, in the present embodiment, even when the piston 5 of the stop-time compression stroke cylinder 2C is stopped at the above position (intermediate part of the piston stroke), the engine is injected by injecting fuel into the stop-time compression stroke cylinder 2C. In order to enable one-compression start in which the engine is restarted, the glow plug 31 of the cylinder 2C is energized in advance in the specific range R shown in FIG. Thereby, the self-ignition of the fuel injected into the compression stroke cylinder 2C at the time of stop is promoted, and the fuel is surely self-ignited even if the compression allowance in the cylinder 2C is not so large. Even if 5 stops, one compression start can be performed. Then, compared with the case of FIG. 5, the maximum value of the time required for engine restart becomes small, and the average restart time is shortened.

  FIG. 6 shows a case where one compression start is performed under the same conditions as in FIG. 5 (cooling water temperature 75 ° C., outside air temperature 25 ° C., altitude 0 m) regardless of the piston stop position of the stop compression stroke cylinder 2C. It is a graph which shows how the maximum in-cylinder pressure Pmax in 2C changes with piston stop positions. In this graph, the ▲ mark plot represents the case where one compression start was performed without using the glow plug 31 (that is, the glow plug 31 was not energized), and the ○ mark plot was used with the glow plug 31 Represents a case where one compression start is performed.

  According to FIG. 6, the maximum in-cylinder pressure Pmax (marked by a mark ▲) of the compression stroke cylinder 2C at the stop when the one-compression start is performed without using the glow plug 31 is such that the piston stop position is close to BTDC 80 ° CA. It can be seen that there is a significant drop from about 4 MPa to about 2 MPa. Such a large drop in the in-cylinder pressure represents that the fuel injected into the stop-time compression stroke cylinder 2C did not self-ignite (misfired). This is consistent with the fact that the vicinity of BTDC 80 ° CA was the limit of one compression start in the graph of FIG. In other words, there is no problem even if the glow plug 31 is not used as long as it is in the range of the bottom dead center side excluding the vicinity of BTDC 80 ° CA (for example, the range of the bottom dead center side of BTDC 82 ° CA). One compression start is possible.

  On the other hand, as shown in the plot of the circle mark, when one compression start is performed while using the glow plug 31, a certain crank angle (BTDC 74 °) even at the top dead center side from BTDC 82 ° CA. If it is up to the vicinity of CA), a relatively high value of about 4 MPa is obtained as the maximum in-cylinder pressure Pmax (see P part in the figure). This represents that the fuel injected into the cylinder 2C self-ignitions and burns due to the increase in the in-cylinder temperature of the stop-time compression stroke cylinder 2C due to the energization of the glow plug 31. Further, there is data of the maximum in-cylinder pressure Pmax that is somewhat larger (3 MPa or more) even at the top dead center side than the P part in FIG. 6, but in this range, the data that Pmax has decreased to about 2 MPa (that is, misfired). Therefore, it cannot be said that the fuel injected into the stop-time compression stroke cylinder 2C is surely self-ignited.

  From the above results, in the example of FIG. 6, the range of BTDC 74 to 82 ° CA is set as the specific range R in which one compression start using the glow plug 31 is possible. The range A1 on the bottom dead center side of the specific range R is a range in which one compression start is possible without using the glow plug 31, and the range A2 on the top dead center side of the specific range R is the glow dead center side. Since misfire occurs even if the plug 31 is used, it is in a range where two compression start is necessary.

  FIG. 7 is a graph showing the results of an experiment similar to FIG. 6 under the conditions of a cooling water temperature of 60 ° C., an outside air temperature of 25 ° C., and an altitude of 0 m. That is, the conditions in FIG. 7 are lower than the conditions in FIG. 6 (cooling water temperature 75 ° C., outside air temperature 25 ° C., altitude 0 m), and other conditions are the same.

  According to the graph of FIG. 7, the maximum in-cylinder pressure Pmax of the compression stroke cylinder 2C at the time of stop when the one-compression start is performed without using the glow plug 31 (the plot of the mark ▲) is that the piston stop position is BTDC 88 ° CA. When it is in the vicinity, it has dropped significantly (ie, misfire has occurred). In other words, there is no problem even if the glow plug 31 is not used as long as it is in the range of the bottom dead center side excluding the vicinity of BTDC 88 ° CA (for example, the range of the bottom dead center side of BTDC 90 ° CA). One compression start is possible.

  On the other hand, as shown in the plot of the circle mark, when one compression start is performed while using the glow plug 31, a certain degree of crank angle (BTDC 80) even at the top dead center side from BTDC 90 ° CA. Up to around ° CA), a relatively high value of about 4 to 5 MPa is obtained as the maximum in-cylinder pressure Pmax (see part P in the figure), and the self-ignition of the fuel in the compression stroke cylinder 2C at the time of stop is achieved. It turns out that it is possible.

  From the above results, in the example of FIG. 7, the range of BTDC 80 to 90 ° CA is set as the specific range R in which one compression start using the glow plug 31 is possible. As in the case of FIG. 6, in the range A1 closer to the bottom dead center than the specific range R, one compression start can be performed without using the glow plug 31, and the top dead center side beyond the specific range R is possible. In the range A2, even if the glow plug 31 is used, 1 compression start is impossible and 2 compression start is necessary.

  As shown in FIGS. 6 and 7, the specific range R in which one compression start using the glow plug 31 is performed is variably set depending on the engine coolant temperature. That is, since the specific range R is shifted to the bottom dead center side in FIG. 7 than in FIG. 6, the specific range R is set closer to the bottom dead center as the cooling water temperature is lower. Is done. This means that the lower the coolant temperature and the closer the engine is to cold, the worse the ignitability of the fuel. Therefore, even if the piston stop position is a little closer to the bottom dead center (that is, there is some compression allowance) This is because the glow plug 31 needs to be operated.

  Although not shown, for the same reason, the specific range R is set closer to the bottom dead center as the outside air temperature is lower, and closer to the bottom dead center as the altitude is higher (that is, as the atmospheric pressure is lower). Set to range.

  Next, a specific control procedure of the ECU 50 (the automatic stop control unit 51 and the restart control unit 52) that controls the automatic engine stop / restart control as described above will be described with reference to the flowcharts of FIGS. .

  When the processing shown in the flowchart of FIG. 8 is started, the ECU 50 executes control for reading various sensor values (step S1). Specifically, the water temperature sensor SW1, the crank angle sensor SW2, the cam angle sensor SW3, the intake pressure sensor SW4, the airflow sensor SW5, the accelerator opening sensor SW6, the brake sensor SW7, the vehicle speed sensor SW8, the battery sensor SW9, and the atmospheric pressure sensor SW10. , And the ambient air temperature sensor SW11, and based on these signals, based on these signals, the engine coolant temperature, the rotational speed, the crank angle, the cylinder discrimination, the intake pressure, the intake flow rate, the accelerator opening, the presence / absence of the brake, the vehicle speed Various information such as remaining battery capacity, atmospheric pressure, and outside air temperature are acquired.

  Next, the ECU 50 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 stopped (vehicle speed = 0 km / h), the opening degree of the accelerator pedal 36 is zero (accelerator OFF), the brake pedal 37 is being operated (brake ON), and the engine is cooled. It is determined that the automatic stop condition is satisfied when a plurality of conditions such as the water temperature is equal to or higher than a predetermined value (warm state) and the remaining capacity of the battery is equal to or higher than the predetermined value. Note that the vehicle speed does not necessarily have to be a complete stop (vehicle speed = 0 km / h), and a condition of a predetermined low vehicle speed or less (eg, 5 km / h or less) may be set.

  When it is determined YES in step S2 and it is confirmed that the automatic stop condition is satisfied, the ECU 50 executes control for setting the target generated current Ge of the alternator 32 to a predetermined value (step S3). ). That is, the target generated current Ge of the alternator 32 is variably set according to conditions such as the remaining battery capacity and the electric load of the vehicle, but when the automatic stop condition is satisfied, at that time (time t1 in FIG. 2). The fixed value is not related to the above conditions.

  Next, the ECU 50 executes control to stop the supply of fuel from the fuel injection valve 15 by always keeping the fuel injection valve 15 in a closed state (step S4). In the time chart shown in FIG. 2, the fuel supply stop (fuel cut) is executed at a time t2 when a predetermined time has elapsed after the automatic stop condition is satisfied and the target generated current Ge is set to a predetermined value. .

  When the fuel cut is executed in step S4, the engine then reaches a complete stop state after exceeding the top dead center a plurality of times (that is, the rotational speed Ne becomes 0 rpm). The ECU 50 determines whether or not the engine has completely stopped by determining whether or not the rotational speed Ne = 0 rpm after the fuel cut (step S5).

  When it is determined YES in step S5 and it is confirmed that the engine has completely stopped, the ECU 50 determines the piston stop position of the stop-time compression stroke cylinder 2C based on the detection signals of the crank angle sensor SW2 and the cam angle sensor SW3. The control to acquire is executed (step S6).

  Next, the ECU 50 proceeds to the process shown in the flowchart of FIG. 9 and executes control for determining the specific range R shown in FIG. 3 (or FIG. 6, FIG. 7) (step S7). That is, based on the detection signals of the water temperature sensor SW1, the atmospheric pressure sensor SW10, and the outside air temperature sensor SW11, the engine coolant temperature, the atmospheric pressure, and the outside air temperature are acquired, and the specific range R obtained from these values is stored in advance in the map. The specific range R is determined by reading from data or the like. As described above, the specific range R is set closer to the bottom dead center as the cooling water temperature, the atmospheric pressure, or the outside air temperature is lower.

  Next, the ECU 50 determines whether or not the piston stop position of the stop-time compression stroke cylinder 2C acquired in step S6 is included in the specific range R acquired in step S7 (step S8).

  When it is determined as YES in Step S8 and it is confirmed that it is within the specific range R, the ECU 50 determines whether it is possible to energize the glow plug 31 (Step S9). For example, when the remaining capacity of the battery is extremely small, it may be determined that the glow plug 31 cannot be energized because there is a risk that the battery will run up when the glow plug 31 is energized. Is determined to be energized.

  When it is determined YES in step S9 and it is confirmed that the glow plug 31 can be energized, the ECU 50 determines the temperature (heat generation temperature) of the heat generating portion of the glow plug 31 corresponding to the stop-time compression stroke cylinder 2C. It is determined whether Tg is equal to or less than a predetermined threshold Tgx (step S10). The heat generation temperature Tg can be estimated from the resistance value of the glow plug 31.

  Here, during normal operation of the engine, the glow plug 31 is not energized. For this reason, immediately after the engine is automatically stopped, the heat generation temperature Tg of the glow plug 31 is low, and the first determination in step S10 is naturally YES. Then, ECU50 performs control which starts electricity supply to the glow plug 31 of the compression stroke cylinder 2C at the time of a stop (step S11).

  On the other hand, when energization to the glow plug 31 is started and the temperature of the heat generating portion rises and Tg> Tgx is satisfied, the determination in step S10 is NO. Then, the ECU 50 executes control for stopping energization of the glow plug 31 (step S12).

  By repeating such control, the glow plug 31 is energized intermittently in the stop compression stroke cylinder 2C within a range in which the heat generation temperature Tg of the glow plug 31 does not exceed the threshold value Tgx (FIG. 4).

  While intermittently energizing the glow plug 31 as described above, the ECU 50 determines whether or not an engine restart condition is satisfied based on various sensor values (step S13). For example, the accelerator pedal 36 is depressed to start the vehicle (accelerator ON), the remaining battery capacity is reduced, the engine coolant temperature is below a predetermined value (cold state), the engine is stopped When at least one of the conditions such as the continuation time (elapsed time after automatic stop) exceeds a predetermined time is determined, it is determined that the restart condition is satisfied.

  When it is determined YES in step S13 and it is confirmed that the restart condition is satisfied, the ECU 50 controls to restart the engine by injecting the first fuel into the stop-time compression stroke cylinder 2C (one compression start). Is executed (step S14). That is, by driving the starter motor 34 and applying a rotational force to the crankshaft 7, the first fuel is injected into the compression stroke cylinder 2C at the time of stop and self-ignited so that the first top dead center of the engine as a whole is obtained. Combustion is restarted from the point of time and the engine is restarted. At this time, as described above, since the temperature in the cylinder 2C is sufficiently increased by intermittent energization of the glow plug 31 of the compression stroke cylinder 2C at the time of stop, the injected fuel is surely self-ignited and burned. .

  Next, a description will be given of the control operation when it is determined NO in step S8, that is, when the piston stop position of the stop-time compression stroke cylinder 2C is out of the specific range R. In this case, the ECU 50 determines whether the piston stop position of the stop-time compression stroke cylinder 2C is on the bottom dead center side with respect to the specific range R, that is, is included in the crank angle range A1 shown in FIG. It is determined whether or not (step S15).

  When it is determined as YES in step S15 and it is confirmed that the specific range R is closer to the bottom dead center side, the ECU 50 determines whether or not the restart condition is satisfied (step S13) (step S13). S16). Then, when it is determined as YES and it is confirmed that the restart condition is satisfied, the first fuel is injected into the stop-time compression stroke cylinder 2C while driving the starter motor 34, as in step S14. Thus, the control (1 compression start) for restarting the engine is executed (step S17). At this time, the glow plug 31 is not energized, but the in-cylinder temperature sufficiently rises due to compression from the bottom dead center side with respect to the specific range R. The fuel injected into the cylinder 2C surely ignites and burns.

  Next, a description will be given of the control operation when it is determined NO in step S15 or when it is determined NO in step S9. Note that when the determination in step S15 is NO, the piston stop position of the stop-time compression stroke cylinder 2C is higher than the specific range R, that is, the crank angle range A2 shown in FIG. 6 or FIG. In the case where the determination in step S9 is NO, the piston stop position is included in the specific range R, but the glow plug 31 cannot be energized.

  In these cases, the ECU 50 determines whether or not a restart condition is satisfied (step S18), as in step S13. If it is determined YES here and it is confirmed that the restart condition is satisfied, the engine is restarted by injecting the first fuel into the stop-time intake stroke cylinder 2D while driving the starter motor 34. Control (2 compression start) is executed (step S19). In this way, by injecting fuel into the stop intake stroke cylinder 2D instead of the stop compression stroke cylinder 2C, the time required for fuel injection becomes longer, but the fuel is injected after the air is sufficiently compressed. Therefore, the injected fuel surely ignites and burns.

(4) Operational effects and the like As described above, in this embodiment, when an engine consisting of a four-cycle diesel engine is automatically stopped, the piston position of the compression stroke cylinder 2C at the time of stop is the top dead center and the bottom dead center. It is determined whether or not it is within the specific range R set in the middle of the point. If it is within the specific range R, the glow plug 31 corresponding to the stop-time compression stroke cylinder 2C is energized, Thereafter, when the restart condition is satisfied, the engine is restarted by injecting fuel from the fuel injection valve 15 into the stop-time compression stroke cylinder 2 </ b> C while driving the starter motor 34. According to such a configuration, it is possible to expand the range of the piston stop position where the so-called one-compression start can be performed by injecting fuel into the stop-time compression stroke cylinder 2C and restarting, and the average time required for engine restart There is an advantage that can be shortened.

  That is, when the piston stop position of the compression stroke cylinder 2C at the time of stop is in a specific range R corresponding to an intermediate portion between the top dead center and the bottom dead center, as shown in the plots of the ▲ marks in FIGS. Originally, even if fuel is injected into the stop-time compression stroke cylinder 2C, it is difficult to reliably ignite this, and it is necessary to inject fuel into the stop-time intake stroke cylinder 2D that reaches the next compression stroke. However, as in the above-described embodiment, if the glow plug 31 of the stop-time compression stroke cylinder 2C is energized in advance to increase the temperature inside the cylinder, an environment in which self-ignition is likely to occur is created accordingly. As shown by the circled plots in FIG. 7, the fuel injected into the stop-time compression stroke cylinder 2C can be surely self-ignited. As a result, the range of the piston stop position where one compression start is possible can be expanded, and quick engine restart by one compression start can be realized at a higher frequency, effectively reducing the average time required for restart. be able to.

  In the above embodiment, the specific range R is set closer to the bottom dead center as the engine coolant temperature, the atmospheric pressure, or the outside air temperature is lower and the ignitability of the fuel deteriorates. As described above, when the energization of the glow plug 31 is started from a position closer to the bottom dead center in accordance with an environment in which the fuel is difficult to ignite, the one-compression start is performed even when the external environment is severe. The possible range can be expanded and the engine can be started quickly.

  Further, in the above embodiment, when the glow plug 31 is energized and its heat generation temperature Tg rises to exceed the threshold value Tgx, the glow plug 31 is prohibited from energizing, as shown in FIG. The plug 31 is energized intermittently according to the degree of heat generation. According to such a configuration, since the heat generation temperature Tg of the glow plug 31 can be prevented from rising more than necessary, the power consumed by the glow plug 31 can be effectively suppressed, and the fuel consumption deteriorates due to the increase in power consumption. Can be minimized.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to the structure of the said embodiment, In the range which does not deviate from the meaning, it can change suitably.

  For example, in the above embodiment, the opening degree K of the intake throttle valve 30 is set to the same high opening degree as that during normal operation over a period from the start of the automatic engine stop control to the complete stop of the engine (time points t1 to t4 in FIG. 2). (For example, 80%) and the target generated current Ge of the alternator 32 is set to a predetermined value. During the automatic engine stop control, the opening degree K of the intake throttle valve 30 and the alternator 32 By appropriately adjusting the target power generation current Ge in accordance with the degree of decrease in the engine speed Ne, the piston stop position of the compression stroke cylinder 2C at the time of stop is set to the specific range R and its bottom dead center side (FIGS. 6 and 7). In the crank angle range A1). In this way, the piston 5 of the stop-time compression stroke cylinder 2C is less likely to stop closer to the top dead center side (crank angle range A2) than the specific range R, so the frequency at which two-compression start is required decreases. There is an advantage that the restart time of the engine is more effectively shortened.

2A to 2D cylinder 2C Stop compression stroke cylinder 15 Fuel injection valve 31 Glow plug 34 Starter motor 50 ECU (control means)
R Specific range

Claims (5)

A diesel engine starter that automatically stops a diesel engine when a predetermined automatic stop condition is satisfied, and restarts the diesel engine after the automatic stop when a predetermined restart condition is satisfied,
Controls various devices including a fuel injection valve that injects fuel into each cylinder of the diesel engine, a glow plug that has a heat generating portion that generates heat when energized, and a starter motor that applies rotational force to the diesel engine Control means to
When the piston position of the stop compression stroke cylinder stopped in the compression stroke at the time of automatic stop is in a specific range set at an intermediate portion between the top dead center and the bottom dead center, the stop compression stroke is performed. By energizing the glow plug corresponding to the cylinder and then injecting fuel from the fuel injection valve to the stop compression stroke cylinder while driving the starter motor when the restart condition is satisfied, A diesel engine starter for restarting the diesel engine. The starting device for a diesel engine according to claim 1,
The diesel engine starter characterized in that the specific range is set closer to the bottom dead center as the coolant temperature of the engine is lower. The starting device for a diesel engine according to claim 1 or 2,
The diesel engine starting device is characterized in that the specific range is set closer to the bottom dead center as the atmospheric pressure is lower. The starting device for a diesel engine according to any one of claims 1 to 3,
The starting device for a diesel engine, wherein the specific range is set to a range closer to bottom dead center as the outside air temperature is lower. In the starting device of the diesel engine of any one of Claims 1-4,
Even if the piston stop position of the compression stroke cylinder at the time of stop is within the specific range, the control means energizes the glow plug if the temperature of the heat generating part of the glow plug rises above a predetermined value. Diesel engine starter characterized by prohibiting

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