JP5771911B2 - Automatic stop / restart system for compression ignition internal combustion engine - Google Patents

Description

  The present invention relates to an automatic stop / restart system that automatically stops and restarts operation of a compression ignition internal combustion engine.

  Conventionally, an automatic stop / restart system for automatically stopping and restarting an internal combustion engine has been developed. The automatic stop / restart system automatically stops operation when a predetermined stop condition is satisfied during operation of the internal combustion engine, and then automatically restarts when a predetermined restart condition is satisfied.

  Patent Document 1 discloses an engine automatic stop control in a state in which an exhaust gas recirculation passage is opened during execution of deceleration fuel cut control for stopping fuel injection during deceleration and an intake flow rate introduced into each cylinder is reduced. Techniques for performing are described.

JP 2005-344653 A

  An object of the present invention is to provide a technique capable of suppressing the amount of NOx generated during restart in an automatic stop / restart system for a compression ignition internal combustion engine.

  In the present invention, when the operation of a compression ignition internal combustion engine (hereinafter, also simply referred to as an internal combustion engine) is automatically stopped, the burned gas existing in the cylinder and the exhaust gas existing in the exhaust passage at that time are EGR. It is introduced into the intake passage as EGR gas through the passage and recirculated.

More specifically, the automatic stop / restart system for a compression ignition internal combustion engine according to the present invention is:
Automatic stop / restart means for automatically stopping operation when a predetermined stop condition is satisfied during operation of the compression ignition internal combustion engine, and then automatically restarting when a predetermined restart condition is satisfied;
An EGR device that has an EGR passage connecting an exhaust passage and an intake passage of a compression ignition internal combustion engine, and introduces exhaust gas into the intake passage as EGR gas through the EGR passage;
When the operation of the compression ignition internal combustion engine is automatically stopped by the automatic stop / restart means, the burned gas existing in the cylinder of the compression ignition internal combustion engine and the exhaust gas existing in the exhaust passage at that time are passed through the EGR passage through the EGR passage. Automatic stop EGR control means for introducing gas into the intake passage and recirculating;
It has.

  In the present invention, when the internal combustion engine is automatically stopped, the exhaust (burned gas) existing in the cylinder or in the exhaust passage at that time is prevented from being released to the outside, and the exhaust is recirculated as EGR gas. Let According to this, when the internal combustion engine is restarted, combustion is performed in a state where more EGR gas exists in the cylinder. As a result, the amount of NOx generated at the time of restart can be suppressed.

The automatic stop / restart system according to the present invention may further include an exhaust throttle valve provided on the downstream side of the connection portion of the EGR passage in the exhaust passage. In this case, when the operation of the compression ignition internal combustion engine is automatically stopped by the automatic stop / restart means, the automatic stop EGR control means may control the exhaust throttle valve to a fully closed state. According to this, when the internal combustion engine is automatically stopped, it is possible to suppress the release of exhaust gas (burned gas) existing in the cylinder or in the exhaust passage, and to recirculate the exhaust gas as EGR gas through the EGR passage. Can do.

  The automatic stop / restart system according to the present invention may further include a throttle valve provided in an intake passage of the internal combustion engine. In this case, when the operation of the compression ignition internal combustion engine is automatically stopped by the automatic stop / restart means, the EGR control means at the time of automatic stop sets the opening of the throttle valve to the intake air necessary for combustion at the time of restart of the internal combustion engine. You may control to the minimum opening in the range which can ensure quantity. According to this, when the internal combustion engine is automatically stopped, it is possible to recirculate as much EGR gas as possible while ensuring combustion at the time of restart.

  The automatic stop / restart system according to the present invention may further include fuel injection control means for controlling fuel injection in the internal combustion engine during restart. In this case, the fuel injection control means increases the number of fuel injections compared to the normal start time when the internal combustion engine is restarted by the automatic stop / restart means after executing the EGR control by the automatic stop EGR control means. May be. According to this, the ignitability of the fuel can be improved in a situation where a large amount of EGR gas is present in the cylinder. As a result, stable combustion at the time of restart can be ensured.

  The automatic stop / restart system according to the present invention may further include determination means for determining whether or not to execute EGR control by the EGR control means during automatic stop. In this case, the determination unit determines whether or not to execute the EGR control by the automatic stop EGR control unit based on at least the outside air temperature, the cooling water temperature, and the exhaust gas temperature when the predetermined stop condition is satisfied. May be. According to this, when EGR control by the EGR control means at the time of automatic stop is executed, if it can be determined that it is difficult to ensure combustion at the time of restart, the EGR control is not performed. Therefore, stable restart can be ensured.

  According to the present invention, in the automatic stop / restart system for a compression ignition internal combustion engine, the amount of NOx generated at the time of restart can be suppressed.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its intake / exhaust system. It is a flowchart which shows the control flow at the time of the automatic stop of an internal combustion engine based on an Example. It is a flowchart which shows the control flow at the time of the automatic restart of the internal combustion engine based on an Example.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<Example>
Here, a case where the present invention is applied to a diesel engine for driving a vehicle will be described as an example.

[Schematic configuration of internal combustion engine and its intake and exhaust system]
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment. The internal combustion engine 1 is a diesel engine for driving a vehicle having four cylinders 2. Each cylinder 2 is provided with a fuel injection valve 3 that directly injects fuel into the cylinder 2.

  An intake manifold 4 and an exhaust manifold 5 are connected to the internal combustion engine 1. An intake passage 6 is connected to the intake manifold 4. An exhaust passage 7 is connected to the exhaust manifold 5. In this embodiment, the intake manifold 4 and the intake passage 6 correspond to the intake passage according to the present invention, and the exhaust manifold 5 and the exhaust passage 7 correspond to the exhaust passage according to the present invention. A compressor 8 a of a turbocharger 8 is installed in the intake passage 6. A turbine 8 b of a turbocharger 8 is installed in the exhaust passage 7.

  An intercooler 10 and a throttle valve 11 are provided downstream of the compressor 8 a in the intake passage 6. The intercooler 10 cools intake air by exchanging heat between outside air and intake air. Further, the throttle valve 11 adjusts the flow rate of the intake air flowing through the intake passage 6 by changing the cross-sectional area of the intake passage 6. An air flow meter 9 is provided in the intake passage 6 upstream of the compressor 8a. The air flow meter 9 detects the intake air amount of the internal combustion engine 1.

  On the downstream side of the turbine 8b in the exhaust passage 7, an oxidation catalyst 12 and a particulate filter 13 are provided as an exhaust purification device. The catalyst provided in the exhaust passage 7 is not limited to the oxidation catalyst, and any catalyst having an exhaust purification function may be used. Further, a catalyst may be supported on the particulate filter.

  An exhaust temperature sensor 15 is provided between the oxidation catalyst 12 and the particulate filter 13 in the exhaust passage 7. An exhaust throttle valve 14 is provided downstream of the particulate filter 13 in the exhaust passage 7. The exhaust throttle valve 14 adjusts the flow rate of the exhaust gas flowing through the exhaust passage 7 by changing the cross-sectional area of the exhaust passage 7.

  The intake / exhaust system of the internal combustion engine 1 is provided with an EGR system for introducing a part of the exhaust gas flowing through the exhaust system into the intake system as EGR gas for recirculation. The EGR system according to this embodiment includes a high pressure EGR device 30 and a low pressure EGR device 34.

  The high pressure EGR device 30 includes a high pressure EGR passage 31, a high pressure EGR valve 32, and a high pressure EGR cooler 33. The high pressure EGR passage 31 has one end connected to the exhaust manifold 5 and the other end connected to the intake manifold 4. In the present embodiment, the EGR gas introduced from the exhaust manifold 5 to the intake manifold 4 through the high pressure EGR passage 31 may be referred to as high pressure EGR gas.

  The high pressure EGR valve 32 and the high pressure EGR cooler 33 are provided in the high pressure EGR passage 31. The high pressure EGR valve 32 adjusts the flow rate (high pressure EGR gas amount) of the high pressure EGR gas introduced into the intake manifold 4 by changing the flow path cross-sectional area of the high pressure EGR passage 31. The high pressure EGR cooler 33 cools the high pressure EGR gas by exchanging heat between the high pressure EGR gas flowing through the high pressure EGR passage 31 and the cooling water of the internal combustion engine 1.

  The low pressure EGR device 34 includes a low pressure EGR passage 35, a low pressure EGR valve 36, and a low pressure EGR cooler 37. One end of the low pressure EGR passage 35 is connected to the downstream side of the particulate filter 13 in the exhaust passage 7 and the upstream side of the exhaust throttle valve 14, and the other end thereof is connected to the downstream side of the air flow meter 9 in the intake passage 6 and the compressor 8a. It is connected upstream. In this embodiment, the EGR gas introduced from the exhaust passage 7 into the intake passage 6 through the low pressure EGR passage 31 may be referred to as low pressure EGR gas.

  The low pressure EGR valve 36 and the low pressure EGR cooler 37 are provided in the low pressure EGR passage 35. The low pressure EGR valve 36 adjusts the flow rate (low pressure EGR gas amount) of the low pressure EGR gas introduced into the intake passage 6 by changing the cross-sectional area of the low pressure EGR passage 35. The low pressure EGR cooler 37 cools the low pressure EGR gas by exchanging heat between the low pressure EGR gas flowing through the low pressure EGR passage 35 and the cooling water of the internal combustion engine 1.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 20. An air flow meter 9 and an exhaust temperature sensor 15 are electrically connected to the ECU 20. Furthermore, the coolant temperature sensor 16, the outside air temperature sensor 17, the crank position sensor 21, and the accelerator opening sensor 22 are electrically connected to the ECU 20. The cooling water temperature sensor 16 detects the temperature of the cooling water of the internal combustion engine 1. The outside air temperature sensor 17 detects the temperature of outside air. The crank position sensor 21 outputs a pulse signal corresponding to the engine speed of the internal combustion engine 1. The accelerator opening sensor 22 outputs a signal corresponding to the accelerator opening of the vehicle on which the internal combustion engine 1 is mounted. Output signals from these sensors are input to the ECU 20.

  Further, the fuel injection valve 3, the throttle valve 11, the exhaust throttle valve 14, the high-pressure EGR valve 32, and the low-pressure EGR valve 36 are electrically connected to the ECU 20. These devices are controlled by the ECU 20.

[Automatic stop / restart control]
In the internal combustion engine 1 according to this embodiment, the ECU 20 performs automatic stop / restart control. In the automatic stop / restart control, when a predetermined stop condition is satisfied during the operation of the internal combustion engine 1, the operation is automatically stopped (that is, fuel injection from the fuel injection valve 3 is stopped), and thereafter Are automatically restarted when the restart condition is satisfied (that is, fuel injection from the fuel injection valve 3 is restarted).

  Here, as a stop condition, in a vehicle equipped with the internal combustion engine 1, the shift position is the drive position, the accelerator opening is zero, the brake is depressed, and the accelerator opening is reduced during the deceleration operation. It can be exemplified that it becomes zero. In addition, examples of the restart condition include that the accelerator opening is larger than zero (that is, the accelerator pedal is depressed).

[EGR control during automatic stop]
During operation of the internal combustion engine 1, the amount of NOx produced by combustion in the internal combustion engine 1 is suppressed by recirculating EGR gas by at least one of the high pressure EGR device 30 and the low pressure EGR device 34. ing. Here, when the internal combustion engine 1 is automatically stopped, the rotation of the internal combustion engine 1 (rotation of the crankshaft) continues for a while by the inertial force even after the fuel injection from the fuel injection valve 3 is stopped. The exhaust (burned gas) existing in the cylinder 2 and the exhaust passage 7 when the engine is automatically stopped by the inertial force is discharged to the outside through the exhaust passage 7 and newly added to the cylinder 2. Introducing fresh air (air).

  Therefore, when the internal combustion engine 1 is restarted, there is almost no EGR gas in the cylinder 2. As a result, there is a risk that the amount of NOx generated in the internal combustion engine 1 increases during restart.

Therefore, in the present embodiment, when the internal combustion engine 1 is automatically stopped, the exhaust existing in the cylinder 2 or the exhaust passage 7 at the time of the automatic stop (hereinafter, the exhaust may be referred to as residual exhaust). ) Is introduced into the intake manifold 4 and the intake passage 6 as EGR gas through the high-pressure EGR passage 31 and the low-pressure EGR passage 35 and is recirculated to execute EGR control.

The automatic stop EGR control is realized by fully closing the exhaust throttle valve 14 and controlling the throttle valve 11 in the valve closing direction when the internal combustion engine 1 is automatically stopped. By making the exhaust throttle valve 14 fully closed, it is possible to suppress the release of residual exhaust to the outside, and the residual exhaust is introduced into the intake passage 6 as EGR gas through the high pressure EGR passage 31 and the low pressure EGR passage 35. can do. The EGR gas introduced into the intake passage 6 circulates through the exhaust passage 7, the EGR passages 31 and 35, the intake passage 6, and the like while the rotation by the inertial force of the internal combustion engine 1 continues.

  At this time, by reducing the opening of the throttle valve 11, the amount of intake air can be reduced, so that more EGR gas can be introduced into the intake manifold 4 through the high-pressure EGR passage 31. However, if the amount of air supplied into the cylinder 2 becomes excessively small, combustion in the cylinder 2 may become difficult when the internal combustion engine 1 is automatically restarted. Therefore, the opening degree of the throttle valve 11 is controlled to the minimum opening degree within a range where the intake air amount necessary for combustion at the time of restarting the internal combustion engine 1 can be secured. Thus, more EGR gas can be recirculated through the high-pressure EGR passage 31 while ensuring combustion at the time of restart.

  By executing such EGR control during automatic stop, more EGR gas exists in the cylinder 2 when the internal combustion engine 1 is restarted. Further, since the internal combustion engine 1 is restarted in a state where the EGR gas is present in the high pressure EGR passage 31, the low pressure EGR passage 35, the intake passage 6, and the intake manifold 4, the EGR gas is Immediately supplied into the cylinder 2. Therefore, at the time of restart, combustion can be performed in a situation where a large amount of EGR gas is present, and thus the amount of NOx produced can be suppressed.

[Control flow during automatic stop]
Hereinafter, the control flow at the time of the automatic stop of the internal combustion engine in the present embodiment will be described based on the flowchart shown in FIG. This flow is stored in advance in the ECU 20 and is repeatedly executed by the ECU 20 at predetermined intervals during the operation of the internal combustion engine 1.

  In this flow, first, in step S101, it is determined whether or not a stop condition is satisfied. If it is determined that the stop condition is satisfied, then in step S102, the fuel injection from the fuel injection valve 3 is stopped. That is, the operation of the internal combustion engine 1 is automatically stopped.

  Next, in step S103, it is determined whether or not the above-described conditions for executing the automatic stop EGR control are satisfied. Here, it is determined whether or not the condition is satisfied based on the outside air temperature, the cooling water temperature, and the exhaust gas temperature.

  The lower the outside air temperature or the cooling water temperature, the more difficult the fuel is ignited in the cylinder 2 at the time of restart. Therefore, if the automatic stop EGR control is executed when the outside air temperature or the cooling water temperature is low, it becomes difficult to ensure combustion at the time of restart. Therefore, in step S103, when the outside air temperature detected by the outside air temperature sensor 17 is lower than a predetermined lower limit temperature, or when the cooling water temperature detected by the cooling water temperature sensor 16 is lower than a predetermined lower limit water temperature, automatic stop is performed. It is determined that the condition for executing the hour EGR control is not satisfied. The lower limit temperature and the lower limit water temperature are determined in advance based on experiments and the like, and are stored in the ECU 20.

Further, when the operation of the internal combustion engine 1 is automatically stopped, the temperature of the oxidation catalyst 12 may increase due to a decrease in the amount of heat taken away by the exhaust. At this time, fresh air having a low temperature is transferred to the internal combustion engine 1.
And if it supplies to this oxidation catalyst 12 through an exhaust passage, the temperature rise can be suppressed. However, when the EGR gas having a high temperature circulates and the EGR gas is supplied to the oxidation catalyst 12, the oxidation catalyst 12 may be overheated. Therefore, in step S103, when the temperature of the oxidation catalyst 12 estimated based on the detection value of the exhaust gas temperature sensor 15 has an upper limit tendency, it is determined that the condition for executing the automatic stop EGR control is not satisfied.

  The method for determining whether or not the condition for executing the EGR control at the time of automatic stop is satisfied is not limited to the above. A condition that should be prioritized over the suppression of the NOx generation amount at the time of restart may be determined in advance, and the determination may be performed based on the condition. If an affirmative determination is made in step S103, the process of step S104 is performed next. If a negative determination is made, execution of this flow is terminated.

  In step S104, the high pressure EGR valve 32 and the low pressure EGR valve 36 are controlled to be fully opened. Next, in step S105, the exhaust throttle valve 14 is controlled to be fully closed.

  Next, in step S106, the throttle valve 11 is controlled in the valve closing direction. Next, in step S107, it is determined whether or not the intake air amount Ga detected by the air flow meter 9 has decreased to the lower limit value Gamin of the intake air amount necessary for combustion when the internal combustion engine 1 is restarted. . When it is determined that the intake air amount Ga does not decrease to the lower limit value Gamin, the process of step S106 is executed again, and the opening degree of the throttle valve 11 is further reduced. If it is determined in step S107 that the intake air amount Ga has decreased to the lower limit value Gamin, the execution of this routine is terminated.

  In the above flow, instead of steps S106 and S107, the opening degree of the throttle valve 11 is calculated so that the intake air amount becomes the lower limit value Gamin necessary for combustion when the internal combustion engine 1 is restarted. The throttle valve 11 may be closed to the same degree.

[Fuel injection control at restart]
As described above, when the EGR control at the time of automatic stop is executed, the amount of EGR gas in the cylinder 2 at the time of restart increases. Thereby, although the production amount of NOx can be suppressed, the ignitability of the fuel is lowered. As a result, if stable combustion becomes difficult, there is a risk that the fuel consumption will increase and the exhaust properties will deteriorate until the start is completed. In addition, since the ignition delay period becomes longer, the combustion noise may be deteriorated.

  Therefore, in the present embodiment, when the EGR control at the time of automatic stop is executed, when the internal combustion engine 1 is restarted thereafter, the number of fuel injections from the fuel injection valve 3 is increased as compared with the normal start. According to this, the ignitability of the fuel can be improved in a situation where a large amount of EGR gas is present in the cylinder 2. As a result, stable combustion at the time of restart can be ensured, and deterioration of combustion noise can be suppressed.

[Control flow during automatic restart]
Hereinafter, the control flow at the time of automatic restart of the internal combustion engine in the present embodiment will be described based on the flowchart shown in FIG. This flow is stored in advance in the ECU 20, and is repeatedly executed by the ECU 20 at predetermined intervals after the internal combustion engine 1 is automatically stopped.

  In this flow, first, in step S201, it is determined whether or not a restart condition is satisfied. If it is determined that the restart condition is satisfied, it is then determined in step S202 whether or not the exhaust throttle valve 14 is fully closed.

If it is determined in S202 that the exhaust throttle valve 14 is in the fully closed state, it can be determined that the automatic stop EGR control has been executed during the automatic stop. In this case, in step S203, the number of fuel injections from the fuel injection valve 3 per combustion cycle is set to the target number nt_egr at the time of restart after the EGR control at the time of automatic stop. On the other hand, if it is determined in S202 that the exhaust throttle valve 14 is open, it can be determined that the automatic stop EGR control is not executed during the automatic stop. In this case, in step S204, the number of fuel injections from the fuel injection valve 3 per combustion cycle is set to the target number nt_normal at the time of normal restart. The target number of times nt_egr at the time of restart after the EGR control at the time of automatic stop and the target number of times nt_normal at the time of normal restart are determined in advance based on experiments and the like, and nt_egr is larger than nt_normal.

  When the number of times of fuel injection from the fuel injection valve 3 per combustion cycle is set in step S203 or S205, next, fuel injection from the fuel injection valve 3 is executed in step S204. That is, the internal combustion engine 1 is automatically restarted.

  Note that after the start of fuel injection, the opening of the exhaust throttle valve 14, the throttle valve 11, and the EGR valves 32 and 36 are controlled as usual.

  If the period from when the operation of the internal combustion engine 1 is automatically stopped to when it is restarted is short, the temperature drop in the cylinder 2 is small, so that the fuel is more easily ignited than when the period is long. Therefore, at the time of restart, the number of fuel injections and / or the amount of fuel injection may be corrected based on the elapsed time from the time when the automatic stop was performed. In this case, the number of fuel injections and / or the amount of fuel injection is reduced as the elapsed time from the point of automatic stop is shorter.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 6 ... Intake passage 7 ... Exhaust passage 11 ... Throttle valve 14 ... Exhaust throttle valve 15 ... Exhaust temperature sensor 16 ... Cooling water temperature sensor 17 ... Outside air temperature sensor 20・ ECU
30 ・ ・ High pressure EGR device 31 ・ ・ High pressure EGR passage 32 ・ ・ High pressure EGR valve 34 ・ ・ Low pressure EGR device 35 ・ ・ Low pressure EGR passage 36 ・ ・ Low pressure EGR valve

Claims (5)

Automatic stop / restart means for automatically stopping operation when a predetermined stop condition is satisfied during operation of the compression ignition internal combustion engine, and then automatically restarting when a predetermined restart condition is satisfied;
An EGR device that has an EGR passage connecting an exhaust passage and an intake passage of a compression ignition internal combustion engine, and introduces exhaust gas into the intake passage as EGR gas through the EGR passage;
When the operation of the compression ignition internal combustion engine is automatically stopped by the automatic stop / restart means, the burned gas existing in the cylinder of the compression ignition internal combustion engine and the exhaust gas existing in the exhaust passage at that time are passed through the EGR passage through the EGR passage. Automatic stop EGR control means for introducing gas into the intake passage and recirculating;
In the case where the compression ignition internal combustion engine is restarted by the automatic stop restarting means after the EGR control by the EGR control means at the time of automatic stop is executed, the number of times of fuel injection is determined by the automatic stop restarting means. It said fuel injection control means to increase compared to the normal restart to restart the compression ignition internal combustion engine by without the automatic stop and restart means performing EGR control by the automatic stop EGR control means when the operation is automatically stopped When,
An automatic stop / restart system for a compression ignition internal combustion engine.   When the fuel injection control means restarts the compression ignition internal combustion engine by the automatic stop / restart means after the EGR control by the EGR control means at the time of automatic stop is executed, the number of fuel injections is compared with that at the time of normal restart. 2. The compression ignition internal combustion engine according to claim 1, wherein the increase in the number of times of fuel injection with respect to the normal restart is reduced as the elapsed time from the automatic stop to the automatic restart of the operation of the compression ignition internal combustion engine is shorter. Automatic stop restart system. An exhaust throttle valve provided on the downstream side of the connection portion of the EGR passage in the exhaust passage;
The compression ignition according to claim 1 or 2 , wherein when the operation of the compression ignition internal combustion engine is automatically stopped by the automatic stop / restart means, the EGR control means at the time of automatic stop controls the exhaust throttle valve to a fully closed state. Automatic stop / restart system for internal combustion engines. A throttle valve provided in an intake passage of the compression ignition internal combustion engine;
When the operation of the compression ignition internal combustion engine is automatically stopped by the automatic stop / restart means, the automatic stop EGR control means determines the degree of opening of the throttle valve for combustion at the time of restart of the compression ignition internal combustion engine. The automatic stop / restart system for a compression ignition internal combustion engine according to any one of claims 1 to 3, wherein the opening is controlled to a minimum opening within a range in which an intake air amount can be secured. And a discriminating unit that discriminates whether or not to execute the EGR control by the EGR control unit at the time of automatic stop based on at least the outside air temperature, the cooling water temperature, and the exhaust gas temperature when the predetermined stop condition is satisfied. An automatic stop / restart system for a compression ignition internal combustion engine according to any one of claims 1 to 4 .

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