JP2009062961A - Control device of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more surely enhance restartability of a diesel engine automatically stopped. <P>SOLUTION: A control device is provided with an operation state determination section 101 which includes at least a function of detecting fuel pressure P of a fuel supply system of the diesel engine and determines an operation state of a vehicle equipped with the diesel engine. A temperature rise control section 105 is provided for controlling a glow plug 18 of the diesel engine based on the determination of the operation state determination section 101. The temperature rise control section 105 drives the glow plug 18 when the fuel pressure P detected by the operation state determination section 101 falls below a threshold value Pth in a case that the diesel engine is automatically stopped. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for a diesel engine.

  For example, as disclosed in Patent Document 1, the engine is automatically stopped when a predetermined automatic stop condition is satisfied, and the automatic stop is automatically restarted when the predetermined restart condition is satisfied. / Restart control is being adopted for diesel engines.

When restarting a diesel engine that has been automatically stopped, it is necessary to inject fuel into a cylinder that is in the compression stroke when the diesel engine is stopped and to self-ignite the cylinder. Therefore, there is a problem that when the temperature of the diesel engine decreases during automatic stop, the startability often deteriorates. In order to solve such a problem, Patent Document 1 discloses a configuration in which supply of a large current to a glow plug attached to a diesel engine is set at the start of cranking, or a glow plug provided in a cylinder in a compression process when stopped. There is disclosed a technique for making the energization amount of the current larger than the energization amount of other glow plugs.
JP 2006-46251 A

  By the way, in general, when the diesel engine is stopped, the fuel is returned from the fuel injection valve from the viewpoint of safety and the like, and the pressure in the common rail is reduced in about 1 to 2 minutes. For this reason, after the diesel engine is automatically stopped, the startability decreases with the elapsed time. Therefore, the startability may not be sufficiently improved only by driving the glow plug based on the in-cylinder temperature. there were.

  This invention is made | formed in view of the said malfunction, and makes it the subject to provide the control apparatus of the diesel engine which can improve the restartability of the diesel engine which stopped automatically more reliably.

  In order to solve the above-described problems, the present invention automatically stops the diesel engine when a predetermined automatic stop condition is satisfied, and automatically causes the diesel engine after the automatic stop when the predetermined restart condition is satisfied. In the control device for the diesel engine to be restarted, an operation state determination unit that determines an operation state of a vehicle equipped with the diesel engine, and a fuel pressure of a fuel supply system of the diesel engine are detected and output to the operation state determination unit A fuel pressure detection means that performs the restart control of the diesel engine based on the determination of the operation state determination unit, and the in-cylinder rise of the diesel engine based on the determination of the operation state determination unit A temperature increase control unit for controlling the temperature means, and the temperature increase control unit is provided when the diesel engine is automatically stopped. Te, when the fuel pressure the fuel pressure detecting means has detected is equal to or less than a predetermined threshold value, the control apparatus for a diesel engine, characterized in that to drive the cylinder temperature increasing means. In this aspect, when the diesel engine is automatically stopped, the in-cylinder temperature raising means is driven under necessary and sufficient conditions, and the diesel engine after the automatic stop can be kept in a standby state in a restartable state. In other words, even when the fuel pressure has decreased due to the automatic stop of the diesel engine, the glow plug is operated in consideration of the decrease, so the reliability at restart is improved and the startability is more reliably ensured. Can be increased.

  In a preferred aspect, the operating state determination unit estimates an in-cylinder temperature of a cylinder to be injected with fuel, and the threshold value of the fuel pressure is determined based on the estimated in-cylinder temperature. Is. In this aspect, the threshold value of the fuel pressure is set more appropriately based on the relationship with the in-cylinder temperature, and the startability can be improved more reliably. That is, since the delay in self-ignition has a characteristic that depends on the temperature in the cylinder, by increasing the temperature in the cylinder, the shortage of fuel pressure can be compensated and the startability can be improved.

  In a preferred aspect, the operating state determination unit corrects the threshold value to a lower pressure side as the in-cylinder temperature is higher. In this aspect, the fuel pressure threshold value can be shifted to a lower pressure side as the in-cylinder temperature rises, so that the operating time and the movable frequency of the in-cylinder temperature raising means are suppressed to a necessary and sufficient level. be able to.

  In a preferred aspect, the operating state determination unit estimates the in-cylinder temperature when the in-cylinder temperature raising means is operating after the restart condition is satisfied, and the restart control unit When the restart condition is satisfied and the in-cylinder temperature exceeds a predetermined set temperature, restart is performed with the stop compression stroke cylinder in the compression stroke at the time of stop being the fuel injection target, and the cylinder When the internal temperature is equal to or lower than the set temperature and the restart condition is satisfied based on the driver's start request, the engine is immediately restarted with the stop intake stroke cylinder in the intake stroke at the time of stop as the fuel injection target When the in-cylinder temperature is equal to or lower than the set temperature and the restart condition is established based on requirements other than the driver's start request, the diesel engine is kept until the in-cylinder temperature exceeds the set temperature. of It is intended to wait for a start-up. In this aspect, when the driver requests restart, the diesel engine can be restarted quickly and reliably even when the in-cylinder temperature is low. Even if the restart condition is satisfied, if the in-cylinder temperature is low, the diesel engine is restarted in principle after waiting for the temperature in the cylinder to rise. Restart by fuel injection can be achieved. Therefore, not only can the restartability be improved, but also the starter motor drive time is shortened, the fuel consumption is improved, and the starter motor durability is longer than when restarting by injecting fuel into the intake stroke cylinder during stoppage. It is possible to improve the performance.

  In a preferred aspect, the operating state determination unit uses the time during which the temperature increase control unit is driving the in-cylinder temperature raising means as an element for estimating the in-cylinder temperature.

  As described above, according to the present invention, even when the fuel pressure is reduced due to the automatic stop of the diesel engine, the glow plug is operated in consideration of the reduction, so the reliability at the time of restart is improved. There is a remarkable effect that the startability can be improved more reliably.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a schematic configuration of a four-cycle diesel engine having an engine control apparatus according to the present invention.

  Referring to FIG. 1, engine 10 has a cylinder head 11 and a cylinder block 12. The cylinder head 11 and the cylinder block 12 are provided with four cylinders 14A to 14D. Also, a piston 16 connected to the crankshaft 15 by a connecting rod (not shown) is fitted into each cylinder 14A to 14D. A cavity 16 a that defines the combustion chamber 17 together with the cylinder head 11 is formed in the piston 16. The pistons 16 provided in the cylinders 14A to 14D are configured to move up and down with the rotation of the crankshaft 15 with a predetermined phase difference. Here, in the engine 10 that is a four-cylinder four-cycle engine, each of the cylinders 14A to 14D performs a cycle including intake, compression, expansion, and exhaust strokes with a predetermined phase difference. Crank angle in order of No. cylinder (cylinder 14A in the example shown), No. 3 cylinder (cylinder 14C in the example shown), No. 4 cylinder (cylinder 14D in the example shown), and No. 2 cylinder (cylinder 14B in the example shown) The phase difference is 180 ° (180 ° CA).

  The cylinder head 11 is provided with a glow plug 18 for each of the cylinders 14A to 14D as in-cylinder temperature raising means disposed so 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. The fuel injection valve 19 has a branch pipe 21 disposed for each of the cylinders 14A to 14D with respect to the common rail 20 that stores and distributes fuel in a high pressure state higher than the valve opening pressure (injection pressure) of the fuel injection valve 19. Are connected to each other. Each fuel injection valve 19 opens the fuel passage by electromagnetic force when energized to open the true valve of the injection nozzle by the fuel pressure P, and the high-pressure fuel supplied from the common rail 20 is supplied from the plurality of injection holes at the tip of the injection nozzle. Direct injection is supplied into the cylinders 14A to 14D toward the cavity 16a of the combustion chamber 17. In the present embodiment, the common rail 20 is provided with a fuel pressure sensor SW1 as fuel pressure detection means for detecting the fuel pressure P. The fuel injection amount of the fuel injection valve 19 is controlled by the energization time. A common rail 20 that supplies fuel to the fuel injection valve 19 is connected to a fuel supply pump 23 via a high-pressure fuel supply pipe 22.

  An intake port 24 and an exhaust port 25 that open toward the combustion chamber 17 are provided in the upper portions of the cylinders 14A to 14D. In addition, an intake valve 26 and an exhaust valve 27 are respectively provided at a connection portion between the ports 24 and 25 and the combustion chamber 17. An intake passage 28 and an exhaust passage 29 are connected to the intake port 24 and the exhaust port 25. The downstream side of the intake passage 28 is branched into branched intake passages 28a branched for each of the cylinders 14A to 14D, and the upstream ends of the branched intake passages 28a communicate with the surge tank 28b. A common intake passage 28c is provided on the upstream side of the surge tank 28b. Although schematically shown in FIG. 1, in this common intake passage 28c, an intake shutter valve 30 capable of adjusting the amount of air flowing into each of the cylinders 14A to 14D, an air flow sensor SW2 for detecting the intake flow rate, and an intake pressure An intake pressure sensor SW3 for detecting the intake air temperature and an intake air temperature sensor SW4 for detecting the intake air temperature are provided. The intake shutter valve 30 is configured to be opened and closed by an actuator 30a. In the illustrated example, 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. The alternator 32 includes a regulator circuit 33 that adjusts the amount of power generation by adjusting the output voltage by controlling the current of a field coil (not shown), and is controlled by the engine control unit 100 that is input to the regulator circuit 33. Based on the signal, control of the power generation amount corresponding to the electric load of the vehicle, the voltage of the on-vehicle battery, and the like is executed.

  The engine 10 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. 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 fixed to a flywheel (not shown) concentrically with respect to the center of rotation. When the engine 10 is restarted using the starter motor 34, the pinion gear 34b moves to a predetermined meshing position and meshes with a ring gear 35 fixed to the flywheel. The shaft 15 is driven to rotate.

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

  The operation of the engine 10 is controlled by the engine control unit 100.

  The engine control unit 100 is composed of a CPU, a memory, a counter timer group, an interface, and a microprocessor having a bus for connecting these units. Based on detection signals from input elements such as the sensors SW1 to SW8, the engine control unit 100 And a control signal for each actuator such as the fuel injection valve 19, the starter motor 34, or the glow plug 18 is output. For example, the fuel injection amount, injection timing, and ignition timing according to the operating conditions are calculated, 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. .

  The engine control unit 100 includes a driving state determination unit 101 that determines the driving state of the vehicle, a fuel injection control unit 102 that controls fuel injection of the engine 10 based on the determination of the driving state determination unit 101, and a driving state determination unit 101. An intake air amount flow control unit 103 that adjusts the intake air flow rate flowing into the cylinder based on this determination, and a starter that drives and controls the starter motor 34 of the engine 10 when the restart condition is satisfied based on the determination of the operating state determination unit 101 The control unit 104 and the temperature increase control unit 105 that controls the glow plug 18 are logically configured.

  The operating state determination unit 101 is based on sensor signals from the fuel pressure sensor SW1, the airflow sensor SW2, the intake pressure sensor SW3, the intake temperature sensor SW4, the crank angle sensors SW5 and SW6, the water temperature sensor SW7, the accelerator opening sensor SW8, and the like. This module determines various operating conditions such as the fuel pressure P, the stop position of the piston 16, the in-cylinder temperature T of the stop-time compression stroke cylinder and the stop-time intake stroke cylinder, and whether or not the engine 10 is rotating forward. . The in-cylinder temperature T is configured to be estimated based on data stored in advance in a memory. In calculating the in-cylinder temperature T, it may be estimated from at least one of the stop position of the piston 16, the intake air temperature, the engine water temperature, and the stop time of the engine 10. In the present embodiment, the driving state determination unit 101 is input with a detection signal from a sensor (not shown) so as to be able to determine the braking state and the vehicle speed of the vehicle.

  The fuel injection control unit 102 sets the fuel injection amount and the fuel injection timing corresponding to the appropriate air-fuel ratio of the engine 10 based on the determination of the operation state determination unit 101, and drives the fuel injection valve 19 based on the setting. This is the module to control.

  The intake air amount flow control unit 103 is a module that sets an appropriate intake air flow amount of the engine 10 based on the determination of the operation state determination unit 101 and drives and controls the intake shutter valve 30 based on the setting.

  The starter control unit 104 is a module that outputs a control signal to the starter motor 34 when the engine 10 is started to drive the starter motor 34.

  The temperature increase control unit 105 is a module that drives the glow plug 18 when the engine is warmed up. In this embodiment, the glow plug 18 is also controlled based on the fuel pressure P determined from the in-cylinder temperature P.

  In the present embodiment, the fuel injection control unit 102 and the starter control unit 104 mainly function as a restart control unit for restarting the engine 10.

  Next, control examples of the automatic stop control and restart control of the engine 10 will be described.

  FIG. 2 is a flowchart centering on the automatic stop control according to the present embodiment, and FIG. 3 is a timing chart showing the transition of the engine speed Ne based on the control example of FIG.

  Referring to FIG. 2, engine control unit 100 waits for a preset automatic engine stop condition to be satisfied (step S10). Specifically, when the brake operation state continues for a predetermined time and the vehicle speed is equal to or lower than a predetermined threshold value, it is determined that the automatic stop condition of the engine 10 is satisfied.

  If it is determined in step S10 that the automatic stop condition is satisfied, engine speed adjustment control including alternator control is started (step S11). Specifically, it waits for the engine rotation speed Ne to be adjusted to a predetermined first rotation speed N1 (for example, 850 rpm) (step S12). The fuel supply from the fuel injection valve 19 is stopped at the timing t1 when the engine rotation speed Ne becomes the first rotation speed N1 (YES timing in step S12) (step S14). At this timing t1, the engine control unit 100 fully closes the intake shutter valve 30 (step S15). By this control, it is possible to increase the probability that the piston 16 stops at the proper stop position A.

  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 immediately before the engine 10 is completely stopped and the air amount in the stop compression stroke cylinder. Therefore, in order to stop the piston 16 in the proper stop position A in the diesel engine, first, the intake flow amount of the stop expansion stroke cylinder and the stop compression stroke cylinder is temporarily reduced, and then the stop compression stroke cylinder is sufficient. Therefore, it is necessary to adjust the intake air flow rate for both cylinders so that the amount of air is larger than the air amount in the expansion stroke cylinder when stopped. Therefore, in this embodiment, the intake pressure is reduced by fully closing the intake shutter valve 30 at the timing t1, and the intake flow rates of the stop expansion stroke cylinder and the stop compression stroke cylinder are reduced.

  When the fuel injection 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 kinetic energy of the crankshaft 15 and the like is generated by friction resistance. When the engine 10 is consumed by pumping work of each cylinder 14A to 14D, the engine 10 descends with undulations, and the 4-cylinder 4-cycle engine reaches about 10 compression top dead centers. Stop later. In this process, the timing at which any one of the cylinders 14A to 14D exceeds the compression top dead center coincides with the timing at which the engine speed Ne undulates.

  Therefore, in the present embodiment, after the intake shutter valve 30 is fully closed at the timing t1, the engine control unit 100 causes the engine rotation speed Ne to become lower than a predetermined second rotation speed N2 (for example, about 400 rpm). (Step S16). 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.

  If YES in step S16, engine control unit 100 opens intake shutter valve 30 (step S17). 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.

  After that, the engine control unit 100 continues the alternator control and continues to adjust the stop position of the piston 16, and waits for the engine 10 to completely stop based on the detected values of the crank angle sensors SW5 and SW6 (step S18). ). If the engine 10 has completely stopped, the engine speed adjustment control is terminated (step S19).

  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 substantially closed, a large amount of air sucked into the cylinder is compressed by the piston 16 with the bottom dead center added. On the other hand, in the expansion stroke cylinder at the time of stop, the piston 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 will be stopped on the relatively bottom dead center side by the compression reaction force in the cylinder. Therefore, the piston of the stop-time compression stroke cylinder is appropriately set by appropriately setting the second rotational speed N2 and the intake air flow amount at the timing t2 when the second rotational speed N2 is detected by experiments or the like. 16 can be stopped at a predetermined bottom dead center side stop position (in this embodiment, from 100 ° CA before compression top dead center to 120 ° CA before compression top dead center).

  When the engine 10 is completely stopped, the engine control unit 100 stores the stop position of the piston 16 determined by the operation state determination unit 101 based on detection of the crank angle sensors SW5 and SW6 (step S20).

  Next, engine restart will be described with reference to FIGS. 4 and 5. 4 and 5 are flowcharts centering on restart control according to the present embodiment.

  After the engine 10 stops, the engine control unit 100 measures the stop time and integrates it (step S21). Since the temperature in the cylinder depends on the stop time of the engine 10, in the present embodiment, the engine control unit 100 is provided with data in which the relationship between the stop time and the temperature is previously mapped, and is based on the stop time. Therefore, the in-cylinder temperature is estimated.

  Next, the operating state determination unit 101 of the engine control unit 100 is based on the intake air temperature detected by the intake air temperature sensor SW4, the coolant temperature detected by the water temperature sensor SW7, the stop time of the engine 10, and the drive time of the glow plug 18. Thus, the in-cylinder temperature T of the stop-time compression stroke cylinder is calculated (step S22).

  Next, the operating state determination unit 101 sets the threshold value Pth of the fuel pressure P from the in-cylinder temperature T (step S23). Since the fuel pressure P for self-igniting the fuel mixture can be related as a function of the in-cylinder temperature T, in this embodiment, the relationship between the in-cylinder temperature T and the fuel pressure P is based on experimental values or the like. Then, the threshold value Pth is obtained from the in-cylinder temperature T by storing the data as a control map M1. Here, in the control map M1, the characteristic is set such that the higher the in-cylinder temperature T, the lower the threshold value Pth becomes.

  Next, the temperature increase control unit 105 determines whether or not the current fuel pressure P is equal to or lower than the threshold value Pth based on the value detected by the fuel pressure sensor SW1 (step S24). If the fuel pressure P is equal to or lower than the threshold value Pth, the temperature increase control unit 105 operates the glow plug 18 (step S25), and stops the glow plug 18 if the threshold value Pth is exceeded. (Step S26). The glow plug 18 controls the engine 10 to be in a standby state so that it can be restarted immediately even during automatic stop.

  After step S25 or S26, the operating state determination unit determines whether or not the restart condition is satisfied (step S27). If it is determined that the restart condition is satisfied, the control proceeds to the flow of FIG. On the other hand, when it is determined that the restart condition is not satisfied, the process returns to step S21 and the above-described control is repeated. For this reason, the threshold value Pth set in step S23 also changes as the measurement time and the in-cylinder temperature change, and the higher the in-cylinder temperature T, the more the threshold value Pth is corrected to the low pressure side. .

  Here, the restart condition according to the present embodiment includes a restart request based on the driver's intention, such as depression of the accelerator pedal 36, and a restart request based on automatic control such as a decrease in battery or air conditioning operation. include. And in this embodiment, as shown in FIG. 5, depending on the driving | running state of the engine 10, it is comprised so that restart control may be performed appropriately based on the kind of restart request | requirement.

  Referring to FIG. 5, when it is determined that the restart condition is established, operation state determination unit 101 first determines whether or not glow plug 18 is operating (step S30). If the glow plug 18 is operating, the in-cylinder temperature T is in an operating state that is considerably low. In this case, in principle, control is performed to restart the engine 10 after raising the temperature in the cylinder. The First, the stop time is integrated as in steps S20 and S21 (step S31), and the in-cylinder temperature T of the stop compression stroke cylinder is calculated (step S32).

  Next, the operating state determination unit 101 determines whether or not the in-cylinder temperature T is equal to or lower than a predetermined set temperature Tst (step S33). In the case where the in-cylinder temperature T is equal to or lower than the set temperature Tst, it is better to restart the temperature after the temperature of the cylinder in the stop compression stroke cylinder is raised by the glow plug 18 in terms of shortening the driving time of the starter motor 34, Therefore, the increase in the in-cylinder temperature T is waited.

  Here, in the present embodiment, it is determined whether or not the restart request is a request based on the driver's intention (step S34). Even if it is advantageous to wait for the increase in the in-cylinder temperature T in terms of control, it is necessary to immediately operate the engine 10 when the driver requests restart. Therefore, in the present embodiment, it is determined whether or not the restart request is related to the driver's operation, and is not related to the driver's intention (for example, an engine start request based on a low battery). If there is, the process returns to step S31 and repeats the above-described processing, and waits for the temperature inside the cylinder to rise. S35) The engine 10 is immediately restarted. In step S33, if the in-cylinder temperature T exceeds the set temperature Tst, it is considered that the temperature increase in the stop compression stroke cylinder has been completed. In this case, the glow plug 18 is stopped. (Step S39) The engine 10 is operated with the compression stroke cylinder at the time of stop as the fuel injection target (Step S40). Further, when the glow plug 18 is stopped in step S30, it is considered that the in-cylinder temperature T is sufficiently high. In this case also, the stop-time compression stroke cylinder is set as the fuel injection target (step S40). Then, the process proceeds to step S36 and thereafter, and the engine 10 is operated.

  After the setting up to step S35 or step S40 is completed, the starter control unit 104 drives the starter motor 34 (step S36). Next, the fuel injection control unit 102 performs fuel injection on the cylinder that is the target of fuel injection (step S37). Thereafter, control is transferred to normal operation (step S38), and the restart process is terminated.

  As described above, in the present embodiment, when the restart condition is satisfied after the engine 10 is automatically stopped, the fuel is injected into the compression stroke cylinder at the time of stop, and the starter motor 34 is driven. Is restarted. Prior to this restart, in the present embodiment, the glow plug 18 can be driven under necessary and sufficient conditions, and the engine 10 after the automatic stop can be kept on standby in a restartable state. That is, even when the fuel pressure P is decreased due to the automatic stop of the engine 10, the glow plug 18 is operated in consideration of the decrease, so that the reliability at the time of restart is improved and the engine is started more reliably. Can increase the sex.

  In the present embodiment, the operating state determination unit 101 estimates the in-cylinder temperature T of the cylinder to be injected with fuel, and the threshold Pth of the fuel pressure P is set to the estimated in-cylinder temperature T. It is determined based on this. For this reason, in this embodiment, the threshold value of the fuel pressure P is set more appropriately based on the in-cylinder temperature T, and the startability can be improved more reliably. That is, since the delay in self-ignition has a characteristic that depends on the temperature in the cylinder, by increasing the cylinder temperature T, the shortage of the fuel pressure P can be compensated and the startability can be improved.

  In the present embodiment, the operating state determination unit 101 corrects the threshold value Pth to the lower pressure side as the in-cylinder temperature T is higher. For this reason, in the present embodiment, the threshold value Pth of the fuel pressure P can be shifted to the lower pressure side as the in-cylinder temperature T rises, so that the operating time and operating frequency of the glow plug 18 are necessary and sufficient. Can be suppressed to level.

  Further, in the present embodiment, as shown in step S34 of FIG. 5, the operation state determination unit 101 estimates the in-cylinder temperature T when the glow plug 18 is operating after the restart condition is satisfied. In the fuel injection control unit 102 and the starter control unit 104 serving as a restart control unit, the restart condition is established based on the driver's start request when the in-cylinder temperature T is equal to or lower than the set temperature Tst. In this case, the restart is executed immediately with the intake stroke cylinder at the time of stop as the fuel injection target. Therefore, in this embodiment, when the driver requests restart, the engine 10 can be restarted quickly and reliably even when the in-cylinder temperature T is low.

  In the present embodiment, the fuel injection control unit 102 and the starter control unit 104 as the restart control unit set the restart condition to a condition other than the driver's start request when the in-cylinder temperature T is equal to or lower than the set temperature Tst. When established based on this, the engine 10 is kept waiting for restart until the in-cylinder temperature T exceeds the set temperature Tst. For this reason, in this embodiment, even if the restart condition is satisfied, if the in-cylinder temperature T is low, the engine 10 is restarted after the temperature rise, so the compression stroke at the time of stop is relatively high. The restart by the fuel injection to a cylinder can be aimed at. Therefore, not only can the restartability be improved, but also the starter motor 34 can be driven for a shorter period of time and fuel consumption can be improved and the starter motor 34 can be reduced as compared with the case where the restart is performed by injecting fuel into the intake stroke cylinder. The durability can be improved.

  The above-described embodiments are merely preferred specific examples of the present invention, and the present invention is not limited to the above-described embodiments.

  For example, when in-cylinder temperature T is lower than a predetermined value when fuel is injected after the restart condition is established, split injection is executed to prevent a decrease in in-cylinder temperature due to latent heat of vaporization. It may be.

  Further, when the engine 10 is restarted by injecting fuel into the intake stroke cylinder at the time of stoppage, the degree of fresh air taken in before the piston 16 of the intake stroke cylinder at the time of stoppage enters the compression stroke is taken into consideration. Thus, it is preferable to set the in-cylinder temperature T and set the fuel injection amount and the fuel injection timing based on the in-cylinder temperature T.

  Furthermore, when the engine 10 is stopped, the necessity of driving the glow plug 18 may be determined based on the piston stop position.

  Alternatively, the cylinder to be injected may be selected based on the piston stop position.

  It goes without saying that various modifications can be made within the scope of the claims of the present invention.

1 is a schematic configuration of a four-cycle diesel engine having an engine control device according to the present invention. It is a flowchart centering on the automatic stop control which concerns on this embodiment. It is a timing chart which shows transition of engine speed based on the example of control of Drawing 2. It is a flowchart centering on restart control which concerns on this embodiment. It is a flowchart centering on restart control which concerns on this embodiment.

Explanation of symbols

10 Engine 14A Cylinder 14B Cylinder 14C Cylinder 14D Cylinder 16 Piston 17 Combustion Chamber 18 Glow Plug (an example of in-cylinder temperature raising means)
19 Fuel injection valve (an example of a fuel injection system)
20 Common rail (an example of a fuel injection system)
23 Fuel supply pump (an example of a fuel injection system)
34 starter motor 100 engine control unit 101 operating state determination unit 102 fuel injection control unit (an example of a restart control unit)
103 Intake air amount flow control unit 104 Starter control unit (an example of restart control unit)
105 Temperature rise control unit P Fuel pressure Pth threshold SW1 Fuel pressure sensor (an example of fuel pressure detection means)
SW2 Airflow sensor SW3 Intake pressure sensor SW4 Intake temperature sensor SW5, SW6 Crank angle sensor SW7 Water temperature sensor SW8 Accelerator opening sensor T In-cylinder temperature Tst Set temperature

Claims (5)

In the diesel engine control device that automatically stops the diesel engine when a predetermined automatic stop condition is satisfied, and automatically restarts the diesel engine after the automatic stop when a predetermined restart condition is satisfied,
An operation state determination unit for determining an operation state of a vehicle equipped with the diesel engine;
A fuel pressure detecting means for detecting a fuel pressure of a fuel supply system of the diesel engine and outputting the detected fuel pressure to the operating state determining unit;
Based on the determination of the operating state determination unit, a restart control unit that controls restart of the diesel engine,
A temperature rise control unit for controlling the in-cylinder temperature raising means of the diesel engine based on the determination of the operating state determination unit,
The temperature raising control unit drives the in-cylinder temperature raising means when the fuel pressure detected by the fuel pressure detecting means is not more than a predetermined threshold value when the diesel engine is automatically stopped. There is a control device for a diesel engine. The control device for a diesel engine according to claim 1,
The operating state determination unit estimates an in-cylinder temperature of a cylinder to be injected with fuel,
The control device for a diesel engine, wherein the threshold value of the fuel pressure is determined based on an estimated in-cylinder temperature. The control device for a diesel engine according to claim 2,
The control device for a diesel engine, wherein the operating state determination unit corrects the threshold value to a lower pressure side as the in-cylinder temperature is higher. The diesel engine control device according to any one of claims 1 to 3,
The operating state determination unit estimates the in-cylinder temperature when the in-cylinder temperature raising means is operating after the restart condition is established,
When the restart condition is satisfied and the in-cylinder temperature exceeds a predetermined set temperature, the restart control unit restarts the stop-time compression stroke cylinder in the compression stroke at the time of stop as a fuel injection target. When the in-cylinder temperature is equal to or lower than the set temperature and the restart condition is established based on a driver's start request, the stop-intake intake stroke cylinder that is in the intake stroke at the stop is subject to fuel injection. If the restart condition is satisfied based on requirements other than the start request of the driver when the in-cylinder temperature is equal to or lower than the set temperature, the in-cylinder temperature is set to the set temperature. The diesel engine control device waits for the restart of the diesel engine until the engine exceeds. The control device for a diesel engine according to any one of claims 1 to 4,
The operating state determination unit uses a time during which the temperature increase control unit is driving the in-cylinder temperature raising means as an element for estimating the in-cylinder temperature.

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