JP5109752B2 - Automatic stop device for diesel engine - Google Patents

Description

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

  Diesel engines are widely used as engines for automobiles because they have high thermal efficiency and high fuel efficiency, so they can reduce carbon dioxide emissions, which contribute to global warming, and are highly durable and reliable. It has been. In a diesel engine, air aspirated into the fuel chamber is adiabatically compressed by a piston, the temperature of the air is raised above the ignition temperature of the fuel, and the fuel is injected into the high-temperature air and burned by self-ignition. I am doing so.

On the other hand, in general, when the automobile is temporarily stopped, the engine rotates in an idling state. However, such idling reduces the fuel efficiency of the automobile and increases the carbon dioxide emission. Therefore, in recent years, the engine is automatically stopped when the vehicle is temporarily stopped or idling, and the engine is automatically restarted when the vehicle starts or when the accelerator pedal is depressed, that is, an engine that performs an idle stop. Is used. And even in diesel engines with originally high fuel efficiency and low carbon dioxide emissions, it has been proposed to perform idle stop in order to further improve fuel efficiency and reduce carbon dioxide emissions. (For example, refer to Patent Document 1).
JP 2004-176469 A (paragraph [0020], FIG. 2)

  However, when performing idling stop with a diesel engine, the temperature in the cylinder is lowered when the engine is stopped. Therefore, when the air sucked into the fuel chamber is compressed by the piston when the engine is restarted, a part of the heat of the air in the combustion chamber is obtained. There is a problem in that it is dissipated to the surroundings, and the temperature of the air in the combustion chamber does not rise sufficiently, resulting in fuel ignition failure. Therefore, for example, in the diesel engine disclosed in Patent Document 1, the combustion chamber is heated by using a glow plug at the time of idling stop to suppress a decrease in the temperature in the cylinder. However, in normal driving conditions in urban areas, idling stops are frequently performed. Therefore, if the glow plug is energized each time, the reliability or durability of the glow plug is reduced and the power consumption is greatly increased. Arise.

  The present invention has been made in order to solve the above-described conventional problems, and the engine from the idling stop state without causing problems such as a decrease in reliability or durability of the glow plug or an increase in power consumption. It is an object to be solved to provide an automatic stop device for a diesel engine that can effectively prevent fuel ignition failure during restart.

An automatic stop device for a diesel engine according to the present invention, which has been made to solve the above-described problems, automatically stops the diesel engine when a predetermined automatic stop condition is satisfied, while the diesel engine automatically stops when a predetermined restart condition is satisfied. An automatic stop / restart control means for automatically restarting the engine is provided. Here, the diesel engine includes an exhaust gas recirculation passage (EGR passage) connecting the intake passage and the exhaust passage, an exhaust gas recirculation valve (EGR valve) disposed in the exhaust gas recirculation passage, an intake passage and an exhaust gas. The recirculation state of the exhaust gas (EGR gas) is controlled via the intake shutter valve disposed in the intake passage upstream of the connection portion of the recirculation passage and the exhaust gas recirculation valve, and the engine rotational speed is set to a predetermined rotational speed. And comprehensive control means including automatic stop / restart control means for performing engine rotation speed adjustment control including waiting until the engine speed decreases . The overall control means starts the engine rotational speed adjustment control when the automatic stop condition is satisfied, when the engine rotational speed becomes the predetermined rotational speed, the fuel supply is stopped, the intake shutter valve Is fully closed and the exhaust gas recirculation valve is controlled in the valve opening direction when the engine temperature is lower than a predetermined temperature at which the engine can self-ignite .

Here, in the exhaust gas recirculation passage of the diesel engine, an exhaust gas cooling means (EGR cooler) that cools the exhaust gas, a bypass passage that bypasses the exhaust gas cooling means and distributes the exhaust gas, and an exhaust gas in the bypass passage When a switching valve capable of switching the gas flow state is provided, the comprehensive control means moves the switching valve to the side where the exhaust gas flows through the bypass passage when a predetermined bypass condition is satisfied. Preferably, the exhaust gas is operated to the side where the exhaust gas flows through the bypass passage when the automatic stop condition is satisfied.

In addition, when the diesel engine is provided with engine temperature detection means for detecting the engine temperature (or engine water temperature), the comprehensive control means detects the engine temperature detection means when the automatic stop condition is satisfied. when the engine temperature is lower than the predetermined temperature, to control the exhaust gas recirculation valve in the opening direction, preferably the exhaust gas switching valve is configured to actuate the side flowing through the bypass passage .

In the diesel engine automatic stop device according to the present invention, the comprehensive control means that the diesel engine actually stopped after the automatic stop condition is satisfied and the exhaust gas recirculation valve is controlled in the valve opening direction. It is preferable that the exhaust gas recirculation valve is closed when the engine is detected.

According to the diesel engine automatic stop device of the present invention, when the automatic stop condition is satisfied and the engine is automatically stopped, the engine rotation speed adjustment includes waiting until the engine rotation speed is reduced to a predetermined rotation speed. When the control is started and the engine speed reaches the predetermined speed, the fuel supply is stopped, the intake shutter valve is fully closed, and the exhaust gas is discharged when the engine temperature is lower than the predetermined temperature at which the engine can self-ignite. The gas recirculation valve is controlled in the valve opening direction, high-temperature exhaust gas is introduced into the combustion chamber (inside the cylinder), and the combustion chamber or the periphery of the combustion chamber is maintained in a high-temperature state until the engine is restarted. For this reason, the temperature of the air in the combustion chamber can be raised above the self-ignition temperature of the fuel without any trouble by adiabatic compression near the top dead center of the compression stroke when the engine is restarted, and the fuel can be self-ignited effectively. . Therefore, it is possible to effectively prevent the occurrence of fuel ignition failure when the engine is restarted from the idle stop state without using a glow lamp.

  In the automatic stop device for a diesel engine according to the present invention, when the switching valve is operated to the side where the exhaust gas flows through the bypass passage when the automatic stop condition is satisfied, the exhaust gas is discharged into the combustion chamber (inside the cylinder). High-temperature exhaust gas that is not cooled by the gas cooling means is introduced, and the combustion chamber or the periphery of the combustion chamber is maintained at a higher temperature until the engine is restarted. For this reason, the temperature of the air in the combustion chamber can be further increased in the vicinity of the top dead center of the compression stroke when the engine is restarted, and it is possible to more effectively prevent the occurrence of fuel ignition failure.

  In the diesel engine automatic stop device according to the present invention, the exhaust gas recirculation valve is controlled in the valve opening direction only when the engine temperature is lower than a predetermined temperature, that is, when the engine temperature is low and the self-ignitability of the fuel is poor. When the switching valve is operated to the side where the exhaust gas circulates in the bypass passage, the fuel is prevented from being unnecessarily supplied to the combustion chamber while the self-ignition property of the fuel is good. When the self-ignition property of the fuel is poor, the self-ignition property of the fuel, and thus the restartability of the engine can be improved.

  In the automatic stop device for a diesel engine according to the present invention, after the automatic stop condition is established and the exhaust gas recirculation valve is controlled in the valve opening direction, the exhaust gas recirculation is detected when it is detected that the diesel engine has actually stopped. When the valve is closed, excessive exhaust gas is prevented from being supplied to the intake system after the engine is stopped, and engine restartability is prevented from deteriorating due to excessive exhaust gas supply. Or can be suppressed.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 shows a system configuration of a direct injection type diesel engine 10 (hereinafter referred to as “engine 10” for short) provided with an automatic stop device according to the present invention. Although the engine 10 is a four-cylinder engine, only one cylinder is shown in FIG. 1, and the other cylinders are not shown. Of course, the present invention is not limited to a four-cylinder engine, and can be applied to multi-cylinder engines other than four-cylinder engines (for example, a six-cylinder engine, an eight-cylinder engine, etc.).

  As shown in FIG. 1, the engine 10 includes a cylinder head 11 and a cylinder block 12. The first to fourth cylinders 14 </ b> A to 14 </ b> D are provided across the cylinder head 11 and the cylinder block 12. Moreover, although not shown in figure, the piston 16 connected with the crankshaft 15 by the connecting rod is inserted in each cylinder 14A-14D. A cavity 16 a that defines the combustion chamber 17 together with the cylinder head 11 is formed in the upper portion of the piston 16.

  Each piston 16 provided in each of the cylinders 14A to 14D reciprocates in the cylinder central axis direction with the rotation of the crankshaft 15 with a predetermined phase difference. In the engine 10 that is a four-cylinder four-cycle engine, each of the cylinders 14A to 14D repeats a cycle composed of intake, compression, expansion, and exhaust strokes with a predetermined phase difference. Each cycle is repeated in the order of the first cylinder 14A, the third cylinder 14C, the fourth cylinder 14D, and the second cylinder 14B with a phase difference of 180 ° (180 ° CA) in crank angle.

  The cylinder head 11 is provided with a glow plug 18 for each of the cylinders 14 </ b> A to 14 </ b> D arranged such that the plug tip faces the combustion chamber 17. The cylinder head 11 is provided with a fuel injection valve 19 for each of the cylinders 14A to 14D. Each fuel injection valve 19 has a branch pipe 21 disposed for each of the cylinders 14A to 14D on a common rail 20 that stores and distributes fuel in a high pressure state higher than the opening pressure (injection pressure) of the fuel injection valve 19. Connected through. Each fuel injection valve 19 is energized to open the fuel passage by electromagnetic force, so that the true valve of the injection nozzle is opened by the fuel pressure, and the high pressure fuel supplied from the common rail 20 is supplied to a plurality of injection holes at the tip of the injection nozzle. To the cavity 16a of the piston 16 directly. The common rail 20 is provided with a fuel pressure sensor SW1 for detecting the fuel pressure. The fuel injection amount of the fuel injection valve 19 is controlled by the energization time. The common rail 20 is connected to a fuel supply pump 23 through a high-pressure fuel supply pipe 22.

  The cylinder head 11 is provided with an intake port 24 and an exhaust port 25 that open toward the combustion chamber 17. An intake valve 26 and an exhaust valve 27 are disposed in the intake port 24 and the exhaust port 25, respectively. An intake passage 28 and an exhaust passage 29 are connected to the intake port 24 and the exhaust port 25, respectively. The downstream side of the intake passage 28 is branched to a branched intake passage 28a that is branched for each of the cylinders 14A to 14D. The upstream end of each branch intake passage 28a is connected to a surge tank 28b. A common intake passage 28c is provided upstream of the surge tank 28b.

  In the common intake passage 28c, an intake shutter valve 30 that can adjust the intake inflow amount to each of the cylinders 14A to 14D, an air flow sensor SW2 that detects the intake flow amount, and an intake pressure sensor SW3 that detects the intake pressure. An intake air temperature sensor SW4 for detecting the intake air temperature is provided (see FIG. 2). The intake shutter valve 30 is driven to open and close by an actuator 30a. The intake shutter valve 30 is set so that air flows even in the fully closed state.

  The engine 10 is provided with an alternator 32 connected to the crankshaft 15 by a timing belt or the like. Although not shown in detail, the alternator 32 includes a regulator circuit 33 that adjusts the amount of power generated by controlling the current of the field coil and adjusting the output voltage. The alternator 32 is configured to control the amount of power generation corresponding to the electric load of the vehicle, the voltage of the vehicle-mounted battery, and the like based on the control signal from the control unit C input to the regulator circuit 33. .

  The engine 10 is provided with a starter motor 34 for starting the engine 10. The starter motor 34 includes a motor body 34a and a pinion gear 34b. The pinion gear 34b reciprocates on the output shaft of the motor body 34a in a state where relative rotation is impossible. The crankshaft 15 is provided with a ring gear 35 coaxially fixed to a flywheel (not shown). When the engine 10 is started using the starter motor 34, the pinion gear 34b moves to a predetermined meshing position and meshes with the ring gear 35 fixed to the flywheel, so that the crankshaft 15 is rotationally driven. .

  Further, the engine 10 is provided with two crank angle sensors SW5 and SW6 for detecting the rotation angle of the crankshaft 15. The engine rotational speed Ne is detected based on a detection signal (pulse signal) output from one crank angle sensor SW5, and based on detection signals out of phase output from both crank angle sensors SW5 and SW6. Thus, the rotation angle (crank angle) of the crankshaft 15 is detected. Further, the engine 10 detects a water temperature sensor SW7 that detects the engine water temperature, an accelerator opening sensor SW8 that detects an accelerator opening corresponding to the operation amount of the accelerator pedal 36 of the vehicle, and an operation of the brake pedal 37 of the vehicle. A brake pedal sensor SW9 is provided.

  The engine 10 is provided with an EGR device 40 (exhaust gas recirculation device). The EGR device 40 includes an EGR passage 41 that recirculates EGR gas (recirculation exhaust gas) from the exhaust passage 29 to the intake passage 28 (intake system), and an EGR valve 42 provided in the middle of the EGR passage 41. The opening degree of the EGR valve 42 is controlled by a control unit C described later. Further, a water-cooled EGR cooler 43 for cooling the EGR gas is provided in the EGR passage 41 on the upstream side of the EGR valve 42 in the flow direction of the EGR gas.

  The EGR device 40 is branched from the EGR passage 41 at a portion B1 (branch portion) upstream of the EGR cooler 43 as viewed in the flow direction of the EGR gas, and a portion between the EGR cooler 43 and the EGR valve 42. A bypass passage 44 is provided which is assembled with the EGR passage 41 again at B2 (aggregation portion) and flows the EGR gas by bypassing the EGR cooler 43. A switching valve 45 controlled by the control unit C is provided at a portion B2 (aggregation part) where the bypass passage 44 and the EGR passage 41 gather.

  When the switching valve 45 is turned on by the control unit C (when an ON signal is applied), it opens the bypass passage 44 and closes the EGR passage 41. In this case, the EGR gas is not cooled by the EGR cooler 43 but is supplied to the intake passage 28 through the bypass passage 44. On the other hand, when the switching valve 45 is turned off by the control unit C (when an off signal is applied), the bypass valve 44 is closed while the EGR passage 41 is opened. In this case, the EGR gas does not pass through the bypass passage 44 but is cooled by the EGR cooler 43 and supplied to the intake passage 28.

Hereinafter, the control system of the engine 10 will be described. The engine 10 is provided with a control unit C. The control unit C is a comprehensive control means for the engine 10 or its accessory devices including the “automatic stop / restart control means ” described in the section for solving the problems. Although not shown in detail, the control unit C has an input / output unit (interface) that inputs and outputs control signals, a storage unit (memory such as ROM and RAM) that stores data and control information, and various arithmetic processes. A computer including a central processing unit (CPU), a timer, a counter, a bus, and the like.

  As shown in FIG. 2, the control unit C performs various calculations based on detection signals from the input elements such as the sensors SW1 to SW9, and each of the fuel injection valve 19, the starter motor 34, the glow plug 18, and the like. A control signal is output to the actuator. For example, the fuel injection amount, injection timing, and the like are calculated according to the operating conditions, and a control signal is output to the fuel injection valve 19 and the like. Further, the target opening of the intake shutter valve 30 is calculated according to the operating conditions, and a control signal is output to the actuator 30a of the intake shutter valve 30 so that the opening of the intake shutter valve 30 becomes the target opening.

  Although not shown in detail, the control unit C is functionally or logically viewed as an operation state determination unit, a fuel injection control unit, an intake air flow rate control unit, a starter control unit, a glow plug control unit, and an EGR control unit. And so on. Note that these determination units or control units are not distinguished as hardware. Here, the driving state determination unit determines the driving state of the vehicle. The fuel injection control unit controls fuel injection of the engine 10 based on the determination of the operating state determination unit. The intake air flow rate control unit adjusts the intake air flow rate that flows into the combustion chamber 17 based on the determination by the operation state determination unit. The starter control unit drives and controls the starter motor 34 of the engine 10 when the restart condition is satisfied based on the determination of the operation state determination unit. The glow plug control unit controls the glow plug 18. The EGR control unit drives and controls the EGR device 40.

Hereinafter, functions of the determination unit or each control unit that functionally or logically configure the control unit C will be described.
(Driving judgment part)
The driving state determination unit outputs output signals from the fuel pressure sensor SW1, air flow sensor SW2, intake pressure sensor SW3, intake air temperature sensor SW4, crank angle sensors SW5 and SW6, water temperature sensor SW7, accelerator opening sensor SW8, brake pedal sensor SW9, and the like. Based on this, various operating conditions such as establishment or cancellation of the automatic stop condition or restart condition of the engine 10, fuel pressure, stop position of the piston 16, in-cylinder temperature, or whether the engine 10 is rotating forward are determined. To do.

  The operating state determination unit determines the stop position of the piston 16 when the engine 10 is automatically stopped, and sets an appropriate stop position SA at which the piston 16 should stop. Here, the appropriate stop position SA of the compression stroke cylinder at the time of stop is set by default in a range from 120 ° CA before compression top dead center to 100 ° CA before compression top dead center. As will be described later, in the engine 10, it is necessary to inject fuel into the compression stroke cylinder at the time of stop, and to drive the piston 16 by the starter motor 34 so that the fuel is self-ignited in the cylinder into which the fuel has been injected. . For this reason, it is preferable that the piston 16 is stopped on the bottom dead center side.

  On the other hand, when the piston 16 is in the vicinity of the bottom dead center, the drive time of the starter motor 34 becomes long. Therefore, in order to achieve both reliable self-ignition and shortening of the drive time of the starter motor 34, the compression is increased by default. It is set in a range from 120 ° CA before the dead center to 100 ° CA before the compression top dead center. However, when the in-cylinder temperature is high, the effective compression ratio of the stop-time compression stroke cylinder can be set small, so the appropriate stop position SA is corrected to the top dead center side by the in-cylinder temperature. The in-cylinder temperature is estimated based on data stored in advance in the memory. The driving state determination unit also determines whether the vehicle brake pedal 37 is on or off, the vehicle speed, and the like.

(Each control unit)
The fuel injection control unit sets the fuel injection amount corresponding to the appropriate air-fuel ratio of the engine 10 and the fuel injection timing based on the determination of the operating state determination unit, and based on the setting, the fuel injection valve 19 is set. Drive control. The intake air flow rate control unit sets an appropriate intake air flow rate of the engine 10 based on the determination of the operation state determination unit, and drives and controls the intake shutter valve 30 based on the setting. The starter control unit outputs a control signal to the starter motor 34 when the engine 10 is started, and drives the starter motor 34. The glow plug control unit controls the driving of the glow plug 18 during warm-up. The EGR control unit basically opens the EGR valve 42 in a predetermined partial load operation region to stabilize combustion or reduce the amount of NOx generated, and opens the EGR valve 42 during idle stop to open the combustion chamber 17. Is maintained at a high temperature to improve the restartability of the engine 10.

  Next, the automatic stop / restart control of the engine 10 according to the present invention performed by the control unit C will be described with reference to the flowcharts shown in FIGS. 3 and 4 and the time chart shown in FIG. When the automatic stop / restart control is started, it is first determined in step S1 whether an engine stop condition (automatic stop condition) is satisfied. If it is determined that the engine stop condition is not satisfied (NO), step S1 is repeatedly executed. That is, in step S1, the process waits until a preset engine automatic stop condition is satisfied. Specifically, for example, when the operating state of the brake pedal 37 continues for a predetermined time and the vehicle speed is equal to or lower than a predetermined value, it is determined that the automatic stop condition of the engine 10 is satisfied.

  If it is determined in step S1 that the engine stop condition is satisfied (YES), engine speed adjustment control including alternator control is started in step S2. Subsequently, in step S3, it is determined whether or not the engine rotational speed Ne is less than a predetermined first rotational speed N1 (for example, 850 rpm). If it is determined that the engine speed Ne is N1 or more (NO), step S3 is repeatedly executed. That is, in step S3, the process waits until the engine speed Ne drops below N1.

  On the other hand, if it is determined in step S3 that the engine speed Ne is less than N1 (YES), fuel injection by the fuel injection valve 19 is stopped (fuel cut) in step S4. That is, in FIG. 5, the fuel injection from the fuel injection valve 19 is stopped at the timing t1 when the engine rotational speed Ne becomes the first rotational speed N1. Subsequently, in step S5, the intake shutter valve 30 is closed (fully closed) almost simultaneously with the fuel cut (timing t1). By this control, it is possible to increase the probability that the piston 16 stops at an appropriate stop position SA.

  That is, the stop position of the piston 16 is substantially determined by the balance between the air amount in the stop expansion stroke cylinder and the air amount in the stop compression stroke cylinder immediately before the engine 10 is completely stopped. Therefore, in order to stop the piston 16 within the proper stop position SA in the engine 10 that is a diesel engine, first, the intake flow amount of the stop expansion stroke cylinder and the stop compression stroke cylinder is first reduced, and then the stop flow is stopped. It is necessary to adjust the air quantity for both cylinders so that sufficient air is supplied to the compression stroke cylinder and the air quantity of the expansion stroke cylinder at the time of stop is larger. Therefore, in the automatic stop / restart control, the intake shutter valve 30 is fully closed at the timing t1 to reduce the intake pressure, thereby reducing the air amount in the stop expansion stroke cylinder and the stop compression stroke cylinder. .

  When the fuel injection from the fuel injection valve 19 is stopped at the timing t1, the cylinders 14A to 14D repeat the intake, compression, expansion, and exhaust cycles with a very small intake flow amount, and the movement of the crankshaft 15 and the like. Energy is consumed by mechanical loss due to frictional resistance and pump work of each cylinder 14A-14D. As a result, the rotational speed of the engine 10 decreases while oscillating, and the four-cylinder four-cycle engine 10 stops after reaching about 10 compression top dead centers. In this process, the timing when any one of the cylinders 14A to 14D exceeds the compression top dead center coincides with the timing of the valley where the engine rotational speed Ne vibrates.

  Next, in step S6, it is determined whether or not the engine water temperature (engine temperature) is lower than the reference temperature T1. The reference temperature T1 is set to a temperature at which the fuel can self-ignite, for example, 80 ° C. or 70 ° C., if the engine water temperature is equal to or higher than the reference temperature T1, without taking any special measures when the engine is restarted. Is done. If it is determined that the engine water temperature is lower than the reference temperature T1 (YES), the switching valve 45 is turned on in step S7, and then the EGR valve 42 is opened (fully opened) in step S8. At this time, the switching valve 45 opens the bypass passage 44 and closes the EGR passage 41, and the EGR gas is supplied to the intake passage 28 through the bypass passage 44 without being cooled by the EGR cooler 43. As a result, high-temperature EGR gas that is not cooled by the EGR cooler 43 is introduced into the combustion chamber 17, and the combustion chamber 17 or the surroundings of the combustion chamber is maintained in a high-temperature state until the engine restart described later is performed. Is done. Thereafter, step S9 is executed.

  On the other hand, if it is determined in step S6 that the engine water temperature is equal to or higher than the reference temperature T1 (NO), even if EGR gas is not introduced into the combustion chamber 17, at the time of engine restart, near the top dead center of the compression stroke. Since the temperature of the air in the fuel chamber 17 is predicted to be equal to or higher than the fuel self-ignition temperature, steps S7 to S8 are skipped and step S9 is executed. That is, while preventing self-ignition of the fuel from being unnecessarily supplied to the combustion chamber 17, the self-ignition of the fuel and the engine restart in a situation where the self-ignition of the fuel is poor is prevented. Can be improved.

  As described above, the intake shutter valve 30 is closed at the timing t1, and when the engine water temperature is lower than the reference temperature T1, high-temperature EGR gas is supplied into the combustion chamber 17, and then in step S9, the engine rotational speed Ne. Is less than a predetermined second rotation speed N2 (for example, about 400 rpm). If it is determined that the engine speed Ne is N2 or more (NO), this step S9 is repeatedly executed. That is, in step S9, the process waits until the engine speed Ne decreases to less than N2 (that is, timing t2 in FIG. 5). The second rotational speed N2 coincides with the timing at which the piston 16 of the stop-time compression stroke cylinder reaches the top dead center from the expansion stroke to the intake stroke.

  On the other hand, if it is determined in step S9 that the engine speed Ne is less than N2 (YES), the intake shutter valve 30 is opened in step S10. As a result of this valve opening operation, the intake valve 26 and the exhaust valve 27 are closed with a small amount of air in the stop expansion stroke cylinder and shifted to the compression stroke, whereas the intake valve 26 is opened in the stop compression stroke cylinder. As a result, a relatively large amount of fresh air is sucked into the cylinder. As a result, the amount of air in the stop compression stroke cylinder is larger than that in the stop expansion stroke cylinder.

  Next, in step S11, it is determined whether or not the engine 10 has stopped. If it is determined that the engine 10 has not stopped (NO), step S11 is repeatedly executed until the engine 10 stops. That is, as described above, the control unit C continues the alternator control and continues to adjust the stop position of the piston 16, so that the engine 10 is completely stopped based on the detected values of the crank angle sensors SW5 and SW6. stand by.

  On the other hand, if it is determined in step S11 that the engine 10 is stopped (YES), the engine speed adjustment control is ended in step S12. At the timing when the engine 10 is completely stopped, the piston 16 of the stop-time compression stroke cylinder passes through the bottom dead center of the intake stroke and shifts to the compression stroke. At this timing, since the intake valve 26 and the exhaust valve 27 are generally closed, a large amount of air sucked into the combustion chamber 17 (inside the cylinder) is compressed by the piston 16 that has passed through the bottom dead center. .

  On the other hand, in the stop-time expansion stroke cylinder, the piston 16 compressed in the cylinder having a relatively small amount of air passes through the compression top dead center and shifts to the expansion stroke. For this reason, in the compression stroke cylinder at the time of stop, it stops on the lower dead center side relatively by the compression reaction force in the cylinder. Therefore, the second rotational speed N2 and the intake air flow amount at the timing t2 in FIG. 5 in which the second rotational speed N2 is detected by experiments and the like are set in advance, so that The piston 16 of the compression stroke cylinder can be stopped at a predetermined bottom dead center side stop position (in this embodiment, 100 ° CA before compression top dead center to 120 ° CA before compression top dead center).

  After the engine 10 is completely stopped in this way, the stop position of the piston 16 determined based on the detected values of the crank angle sensors SW5 and SW6 is stored in step S13. Next, the switching valve 45 is turned off in step S14. Thereby, the switching valve 45 closes the bypass passage 44 and opens the EGR passage 41. Subsequently, in step S15, the EGR valve 42 is closed (fully closed). Thereby, it is possible to prevent the EGR gas from being excessively supplied to the intake passage 28 after the engine is stopped, and to prevent or suppress the restartability of the engine 10 from being deteriorated due to the excessive supply of exhaust gas. .

  After the engine 10 is thus stopped, the stop time is measured and integrated in step S16. Since the in-cylinder temperature (temperature in the combustion chamber 17) depends on the stop time of the engine 10, in this embodiment, the control unit C stores in advance data that maps the relationship between the stop time and the temperature. In addition, the in-cylinder temperature is estimated based on the stop time of the engine 10.

  Next, in step S17, the in-cylinder temperature is determined based on the intake air temperature detected by the intake air temperature sensor SW4, the engine water temperature detected by the water temperature sensor SW7, the stop time of the engine 10, and the drive time of the glow plug 18. Calculated. Subsequently, in step S18, a target fuel pressure is determined based on the calculated in-cylinder temperature, and an appropriate stop position SA is set based on the fuel pressure. In this embodiment, since an appropriate stop position SA is set based on the in-cylinder temperature and the target fuel pressure, a more suitable stop position determination can be performed.

  After the appropriate stop position SA is set in this way, in step S19, it is determined whether or not the piston 16 of the stop-time compression stroke cylinder is on the top dead center side with respect to the proper stop position SA. If it is determined that the piston 16 is at the top dead center side with respect to the appropriate stop position SA (YES), the glow plug 18 is turned on in step S20, and the inside of the cylinder is heated. On the other hand, when it is determined in step S19 that the piston 16 of the compression stroke cylinder at the time of stop is not on the top dead center side from the proper stop position SA (NO), that is, when the piston 16 is in the proper stop position SA. In step S21, the glow plug 18 is turned off.

  Next, in step S22, it is determined whether a restart condition for the engine 10 is satisfied. Examples of the restart condition include that the accelerator pedal 36 is depressed, and that the automatic stop condition is released after the engine 10 is stopped. Here, when it is determined that the restart condition of the engine 10 is not satisfied (NO), the process returns to step S16 and the processes of steps S16 to S22 are repeated. For this reason, the appropriate stop position SA set in step S23 also changes with changes in the measurement time and the in-cylinder temperature.

  On the other hand, if it is determined in step S22 that the restart condition of the engine 10 is satisfied (YES), the starter motor 34 is driven in step S23. Thereby, in the compression stroke cylinder at the time of stop, piston 16 moves to a top dead center, compressing the air in a cylinder. Subsequently, in step S24, it is determined whether or not the piston 16 of the stop-time compression stroke cylinder is on the top dead center side with respect to the appropriate stop position SA.

  If it is determined in step S24 that the piston 16 of the stop compression stroke cylinder is on the top dead center side with respect to the appropriate stop position SA (YES), until the stop intake stroke cylinder enters the compression stroke in step S25. After waiting, the intake stroke cylinder at the time of stop enters the compression stroke, and then fuel is injected from the fuel injection valve 19 at a predetermined timing. That is, when the piston stop position deviates from the proper stop position SA in this way, combustion in the stop-time compression stroke cylinder is stopped.

  On the other hand, if it is determined in step S24 that the piston 16 of the compression stroke cylinder at the time of stop is not at the top dead center side from the proper stop position SA (NO), that is, if the piston stop position is within the proper stop position SA. In step S26, the fuel is injected from the fuel injection valve 19 into the compression stroke cylinder at the time of stop, and the engine 10 is restarted by the combustion of the fuel in the cylinder.

  As described above, after step S25 or step S26 is executed, the engine 10 is shifted to normal operation in step S27, and the current automatic stop / restart process ends (end).

  As described above, according to the engine automatic stop device or the automatic stop / restart control according to the embodiment of the present invention, when the automatic stop condition is satisfied and the engine 10 is automatically stopped, the EGR valve 42 is in the valve opening direction. Thus, high-temperature exhaust gas is introduced into the combustion chamber 17 (inside the cylinder), and the combustion chamber 17 or the surroundings of the combustion chamber 17 is maintained in a high-temperature state until the engine is restarted. For this reason, when the engine is restarted, the temperature of the air in the combustion chamber 17 can be raised above the self-ignition temperature of the fuel without any trouble by adiabatic compression near the top dead center of the compression stroke, and the fuel can be self-ignited effectively. Can do. Therefore, without using the glow lamp 18 unnecessarily, it is possible to effectively prevent the occurrence of fuel ignition failure when the engine is restarted from the idle stop state.

1 is a schematic diagram showing a system configuration of a diesel engine according to an embodiment of the present invention. It is a block diagram which shows the structure of the control system of the engine shown in FIG. FIG. 3 is a part (first stage) of a flowchart showing a control procedure of automatic stop / restart control of the engine shown in FIG. 1. FIG. 2 is a part (second stage) of a flowchart showing a control procedure of automatic stop / restart control of the engine shown in FIG. 1. FIG. 5 is a timing chart showing changes in engine rotation speed when the automatic stop / restart control shown in FIGS. 3 and 4 is performed. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Diesel engine (engine), 11 Cylinder head, 12 Cylinder block, 14A-14D 1st-4th cylinder, 15 Crankshaft, 16 Piston, 16a Cavity, 17 Combustion chamber, 18 Glow plug, 19 Fuel injection valve, 20 Common rail , 21 Branch pipe, 22 High pressure fuel supply pipe, 23 Fuel supply pump, 24 Intake port, 25 Exhaust port, 26 Intake valve, 27 Exhaust valve, 28 Intake passage, 28a Branch intake passage, 28b Surge tank, 28c Common intake passage, 30 Intake shutter valve, 30a Actuator, 32 Alternator, 33 Regulator circuit, 34 Starter motor, 34a Motor body, 34b Pinion gear, 35 Ring gear, 36 Accelerator pedal, 37 Brake pedal, 40 EGR device, 4 EGR passage, 42 EGR valve, 43 EGR cooler, 44 bypass passage, 45 switching valve, C control unit, SW1 fuel pressure sensor, SW2 airflow sensor SW3 intake pressure sensor, SW4 intake temperature sensor, SW5 crank angle sensor, SW6 crank angle sensor, SW7 Water temperature sensor, SW8 accelerator opening sensor, SW9 Brake pedal sensor.

Claims (4)

Diesel engine having automatic stop / restart control means for automatically stopping the diesel engine when a predetermined automatic stop condition is satisfied, and automatically restarting the diesel engine when the predetermined restart condition is satisfied In the automatic stop device of
An exhaust gas recirculation passage connecting the intake passage and the exhaust passage;
An exhaust gas recirculation valve disposed in the exhaust gas recirculation passage;
An intake shutter valve disposed in the intake passage on the upstream side of a connection portion between the intake passage and the exhaust gas recirculation passage;
The automatic stop / restart control means for controlling engine rotation speed adjustment including controlling the exhaust gas recirculation state via the exhaust gas recirculation valve and waiting until the engine rotation speed decreases to a predetermined rotation speed. And comprehensive control means including
The overall control means, the automatic stop condition starts the engine rotational speed adjustment control when satisfied, when the engine rotational speed becomes the predetermined rotational speed, the fuel supply is stopped, the intake shutter valve The diesel engine automatic stop device is configured to control the exhaust gas recirculation valve in the valve opening direction when the engine temperature is lower than a predetermined temperature at which the engine can self-ignite. . The exhaust gas recirculation passage can be switched to an exhaust gas cooling means for cooling the exhaust gas, a bypass passage for bypassing the exhaust gas cooling means and flowing the exhaust gas, and a flow state of the exhaust gas in the bypass passage. Switching valve is provided,
The comprehensive control means operates the switching valve to the side where the exhaust gas flows through the bypass passage when a predetermined bypass condition is satisfied, and the exhaust gas is operated when the automatic stop condition is satisfied. 2. The automatic stop device for a diesel engine according to claim 1, wherein the automatic stop device is configured to be operated to a side where the bypass passage is circulated. Engine temperature detecting means for detecting the engine temperature is provided,
The overall control means, when the automatic stop condition is satisfied, when the engine temperature detected by the engine temperature detecting means is lower than the predetermined temperature, control in the valve opening direction to the exhaust gas recirculation valve In addition, the automatic stop device for a diesel engine according to claim 2, wherein the switching valve is configured to operate the exhaust gas to the side where the exhaust gas flows through the bypass passage. The comprehensive control means is configured to detect the exhaust gas recirculation when it is detected that the diesel engine has actually stopped after the automatic stop condition is satisfied and the exhaust gas recirculation valve is controlled to open. The automatic stop control device for a diesel engine according to claim 1, wherein the valve is configured to close the valve.

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