JP2022167348A - Stop control device for engine - Google Patents

Abstract

To suppress generation amount of NOx while securing ignitability at restart of an automatically stopped engine.SOLUTION: A stop control device for an engine includes: a determination section determining whether an automatic stop condition is satisfied; and a control section stopping the engine in accordance with satisfaction of the automatic stop condition. The control section executes oxygen concentration adjustment control for controlling a throttle valve and an EGR valve so that oxygen concentration in an intake passage downstream of a connection part to an EGR passage becomes a predetermined target value Dx from execution of fuel cut until the engine is stopped completely. The oxygen concentration adjustment control includes: first control for causing the throttle valve to become an opened state so as to increase the oxygen concentration; and second control for closing the throttle valve when the oxygen concentration has increased to the target value.SELECTED DRAWING: Figure 5

Description

The present invention includes a cylinder, an output shaft that rotates by receiving energy of combustion in the cylinder, an intake passage through which intake air introduced into the cylinder flows, an exhaust passage through which exhaust gas discharged from the cylinder flows, and an intake air. The present invention relates to a stop control device that is applied to an engine having an EGR passage that connects the passage and an exhaust passage, and that stops the engine when a predetermined automatic stop condition is satisfied.

As an example of the stop control device, the one disclosed in Patent Document 1 below is known. The engine stop control device disclosed in Patent Document 1 includes a throttle valve provided in an intake passage, an EGR valve (EGR control valve) provided in an EGR passage, and a control unit for controlling the throttle valve and the EGR valve. Prepare. When there is a request to automatically stop the engine, the control unit stops fuel injection to the cylinder while opening the EGR valve, and closes the throttle valve and EGR valve when the engine stops due to the injection stop (fuel cut). . With such control, in Patent Document 1, EGR gas (exhaust gas) is introduced into the intake passage through the EGR passage before the engine stops, and the EGR gas is confined in the intake passage after the engine stops.

JP 2004-100497 A

According to the engine stop control device described in Patent Document 1, when the stopped engine is restarted, intake air containing EGR gas is introduced into the cylinder, thereby reducing the amount of NOx generated by combustion during restarting. The effect of being suppressed is expected. However, depending on the operating state immediately before the fuel cut is performed, it is assumed that the engine will stop with an excessive amount of EGR gas trapped in the intake passage. In such a case, the proportion of fresh air introduced into the cylinders at the time of restarting becomes too low, and there is a risk that the ignitability of the fuel cannot be ensured.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an engine stop control device capable of suppressing the amount of NOx generated while ensuring ignitability at restart. and

In order to solve the above-mentioned problems, the present invention provides a cylinder, an output shaft that receives the energy of combustion in the cylinder and rotates, an intake passage through which the intake air introduced into the cylinder flows, and an intake air that is discharged from the cylinder. A stop control device applied to an engine having an exhaust passage through which exhaust gas flows and an EGR passage connecting the intake passage and the exhaust passage, the injector supplying fuel to the cylinder and the EGR passage. An EGR valve provided to be openable and closable, a throttle valve provided to be openable and closable in an intake passage upstream of a connecting portion between the EGR passage and the intake passage, and an automatic stop condition for automatically stopping the engine. A determination unit that determines whether or not the automatic stop condition is satisfied, and a control unit that controls each part of the engine including the injector, the throttle valve, and the EGR valve, wherein the determination unit determines whether the automatic stop condition is satisfied. When it is confirmed, the control unit executes a fuel cut to stop the supply of fuel by the injector, and during a period from the execution of the fuel cut to the stop of the rotation of the output shaft, the connection unit executing oxygen concentration adjustment control for controlling the throttle valve and the EGR valve so that the oxygen concentration in the intake passage on the downstream side reaches a predetermined target value, and the oxygen concentration adjustment control increases the oxygen concentration and a second control that closes the throttle valve when the oxygen concentration reaches the target value. There is (claim 1).

According to the present invention, since the throttle valve is opened after the fuel cut (first control), fresh oxygen-rich air flows into the intake passage on the downstream side of the throttle valve, The oxygen concentration in the intake passage on the downstream side of the connecting portion with the EGR passage (hereinafter also referred to as the final intake oxygen concentration) increases. Further, since the throttle valve is closed when the final intake oxygen concentration rises to the target value (second control), the introduction of fresh air through the throttle valve is stopped. It can be maintained substantially at the target value. This means that the final intake oxygen concentration when the engine is restarted can be adjusted to a value higher than the concentration when the automatic stop condition is established and lower than the oxygen concentration contained in the atmosphere.

Here, before the automatic stop condition is satisfied, the final intake oxygen concentration is significantly lower than the atmospheric oxygen concentration due to the exhaust gas recirculation (EGR operation) through the EGR passage. Therefore, if the first control for temporarily opening the throttle valve is not performed, the engine is restarted while the final intake oxygen concentration is significantly low. There is a risk that the ignitability of the fuel at that time will be impaired. On the other hand, in the present invention, the throttle valve is opened after the fuel cut, so that the final intake oxygen concentration can be increased to ensure ignitability at restart.

However, if the final intake oxygen concentration is unreasonably increased, combustion is performed in the cylinder with an extremely small amount of EGR gas, which is an inert gas. There is a risk. In contrast, in the present invention, the throttle valve is closed when the final intake oxygen concentration reaches an appropriate concentration (target value) (second control). (In other words, the state in which EGR gas is contained in the intake air) can be maintained, and the amount of NOx produced by combustion can be effectively suppressed.

Preferably, the first control is control to open not only the throttle valve but also the EGR valve (claim 2).

According to this configuration, the inflow amount of fresh air can be reduced compared to the case where the EGR valve is not opened, and a rapid increase in the final intake oxygen concentration can be avoided. As a result, the point in time when the final intake oxygen concentration reaches the target value can be specified with high accuracy, and the accuracy of concentration adjustment can be improved.

In the above configuration, more preferably, the first control includes control for reducing the opening of the throttle valve according to a decrease in engine speed, which is the speed of the output shaft (claim 3).

According to this configuration, fluctuations in the increase rate of the final intake oxygen concentration can be suppressed while stabilizing the intake pressure. That is, when the engine speed decreases after the fuel cut, the reciprocating speed of the piston decreases, the suction force during the intake stroke decreases, and the amount of intake air into the cylinder decreases. For this reason, if the opening of the throttle valve after opening is fixed, there is a high possibility that a large amount of fresh air will be introduced into the cylinder that is out of balance with the amount of gas discharged from the cylinder. This may lead to fluctuations in the rate of increase of the final inspired oxygen concentration. On the other hand, in the configuration described above, the opening of the throttle valve is gradually reduced so as to match the engine speed that decreases after the fuel cut, so that an appropriate amount of fresh air that can be balanced with the amount of gas discharged from the cylinder is introduced. Therefore, it is possible to suppress fluctuations in the increase rate of the final intake oxygen concentration while stabilizing the intake pressure.

In the above configuration, more preferably, the first control includes control for reducing the degree of opening of the EGR valve according to a decrease in the engine speed (claim 4).

In this manner, when the opening degree of the EGR valve is also gradually decreased together with the opening of the throttle valve, fluctuations in the increase rate of the final intake oxygen concentration can be sufficiently suppressed, and the final intake oxygen concentration reaches the target value. The time point reached can be specified with higher accuracy.

Preferably, the control unit closes the EGR valve at a timing later than when the oxygen concentration rises to the target value and earlier than when the output shaft stops rotating (Claim 5).

In this way, when the EGR valve is closed after the closing of the throttle valve, the intake pressure becomes excessively negative during the period from the closing of the EGR valve to the complete stop of the engine. This has the advantage of reducing the shock that may occur when the engine is completely stopped.

As described above, according to the engine stop control device of the present invention, it is possible to suppress the amount of NOx generated while ensuring ignitability at restart.

1 is a schematic system diagram showing a preferred embodiment of an engine to which a stop control device of the invention is applied; FIG. It is a functional block diagram showing a control system of the engine. 4 is a flowchart showing the first half of automatic stop control for automatically stopping the engine; 4 is a flow chart showing the second half of the automatic stop control. FIG. 5 is a time chart showing an example of temporal changes in each state quantity when the automatic stop control is executed; FIG. FIG. 6 is a time chart showing an example of temporal changes in each state quantity when automatic stop control is performed under conditions different from those in FIG. 5; FIG.

<Overall configuration of the engine>
FIG. 1 is a schematic system diagram showing a preferred embodiment of an engine to which the stop control device of the present invention is applied. The engine shown in this figure is a 4-cycle diesel engine mounted on a vehicle as a power source for running. The engine includes an engine main body 1 driven by being supplied with fuel containing light oil, an intake passage 30 through which intake air introduced into the engine main body 1 flows, and an exhaust gas through which exhaust gas discharged from the engine main body 1 flows. A passage 40, a supercharger 50 driven by exhaust gas passing through the exhaust passage 40, a high pressure EGR device 60 and a low pressure EGR device 70 for recirculating part of the exhaust gas flowing through the exhaust passage 40 to the intake passage 30. Prepare.

The engine body 1 is of an in-line multi-cylinder type having a plurality of cylinders 2 (only one of which is shown in FIG. 1) arranged in a direction perpendicular to the plane of FIG. The engine body 1 includes a cylinder block 3 in which a plurality of cylinders 2 are formed, a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to close the upper end opening of each cylinder 2, and each cylinder 2. and a plurality of pistons 5 slidably housed. In this embodiment, the side facing the cylinder head 4 from the cylinder block 3 is treated as the top, and the reverse is treated as the bottom.

A combustion chamber 6 is formed above the piston 5 of each cylinder 2 . Each combustion chamber 6 is a space defined by the lower surface of the cylinder head 4 , the side peripheral surface (cylinder liner) of the cylinder 2 , and the crown surface 5 a of the piston 5 . Fuel is supplied to the combustion chamber 6 by injection from an injector 15, which will be described later. A mixture of the supplied fuel and air is combusted in the combustion chamber 6, and the piston 5, which is pushed down by the expansion force of the combustion, reciprocates vertically.

A crankshaft 7 that is an output shaft of the engine body 1 is provided below the cylinder block 3 (below the piston 5). The crankshaft 7 is connected to the piston 5 of each cylinder 2 via a connecting rod 8 and rotates around the central axis in accordance with the reciprocating motion (vertical motion) of the piston 5 .

A crank angle sensor SN1 and a water temperature sensor SN2 are attached to the cylinder block 3 . The crank angle sensor SN1 detects the crank angle, which is the rotation angle of the crankshaft 7, and the engine speed, which is the rotation speed of the crankshaft 7. The water temperature sensor SN2 detects the temperature of cooling water flowing inside the cylinder block 3 and the cylinder head 4, that is, the engine water temperature.

An intake port 9 and an exhaust port 10 communicating with the combustion chamber 6 are formed in the cylinder head 4 for each cylinder 2 . In addition, the cylinder head 4 is equipped with a combination of an intake valve 11, an exhaust valve 12, and an injector 15 for each cylinder 2, respectively. The intake valve 11 is a valve that opens and closes the opening of the intake port 9 on the combustion chamber 6 side. The exhaust valve 12 is a valve that opens and closes the opening of the exhaust port 10 on the side of the combustion chamber 6 . The injector 15 is an injection valve that injects fuel (light oil) into the combustion chamber 6. For example, the injector 15 is attached to the cylinder head 4 so as to inject fuel from the center of the ceiling surface of the combustion chamber 6 toward the crown surface 5a of the piston 5. .

A valve mechanism 13 that drives the intake valve 11 to open and close, and a valve mechanism 14 that drives the exhaust valve 12 to open and close are assembled to the cylinder head 4 . A combination of these valve mechanisms 13 and 14 includes, for example, a pair of camshafts linked to the crankshaft 7, and drives the intake valve 11 and the exhaust valve 12 of each cylinder 2 to open and close in conjunction with the rotation of the crankshaft 7. .

The intake passage 30 is a tubular member forming a flow passage for intake air introduced into the combustion chamber 6 of each cylinder 2 . The intake passage 30 has an intake manifold 30a (including a plurality of branch pipes arranged in a direction perpendicular to the plane of FIG. 1) branched corresponding to the plurality of cylinders 2 in a downstream portion close to the engine body 1. ing. The intake manifold 30 a is connected to the cylinder head 4 so as to communicate with the intake port 9 of each cylinder 2 . A portion of the intake passage 30 other than the intake manifold 30a is a single tubular member that forms a common passage connecting to the intake manifold 30a.

An air cleaner 31 , a throttle valve 32 , an intercooler 33 , and a surge tank 34 are arranged in the intake passage 30 in this order from the upstream side. The air cleaner 31 is a filter that removes foreign matter from intake air. The throttle valve 32 is an electric butterfly valve that can adjust the flow rate of intake air flowing through the intake passage 30 . The intercooler 33 is a heat exchanger that cools the intake air compressed by the turbocharger 50 (more specifically, the compressor 51, which will be described later). The surge tank 34 is a tank that provides a space for evenly distributing intake air to each cylinder 2, and is connected to the upstream end of the intake manifold 30a.

An airflow sensor SN3 and an intake pressure sensor SN4 are arranged in the intake passage 30 . The airflow sensor SN3 is arranged in a portion downstream of the air cleaner 31 in the intake passage 30, and detects the flow rate of intake air passing through that portion, that is, the intake flow rate. The intake pressure sensor SN4 is arranged in the surge tank 34 and detects the pressure of the intake air passing through the surge tank 34, that is, the intake pressure.

The exhaust passage 40 is a tubular member forming a flow passage for exhaust gas discharged from the combustion chamber 6 of each cylinder 2 . The exhaust passage 40 has an exhaust manifold 40a (including a plurality of branch pipes arranged in a direction perpendicular to the plane of FIG. 1) branched corresponding to the plurality of cylinders 2 in an upstream portion near the engine body 1. ing. The exhaust manifold 40 a is connected to the cylinder head 4 so as to communicate with the exhaust port 10 of each cylinder 2 . A portion of the exhaust passage 40 other than the exhaust manifold 40a is a single tubular member forming a common passage connecting to the exhaust manifold 40a.

The exhaust passage 40 is provided with a catalytic device 41 that purifies the exhaust gas. The catalyst device 41 includes an oxidation catalyst 42 that oxidizes CO and HC in the exhaust gas to render them harmless, and a DPF (Diesel Particulate Filter) 43 that collects particulate matter contained in the exhaust gas. built-in.

An exhaust _O2 sensor SN5 is attached to the exhaust passage 40 . The exhaust _O2 sensor SN5 is provided in a portion between the turbine 52 and the catalyst device 41 in the exhaust passage 40, and detects the concentration of oxygen contained in the exhaust gas passing through that portion, that is, the exhaust oxygen concentration.

The supercharger 50 includes a compressor 51 arranged in the intake passage 30 , a turbine 52 arranged in the exhaust passage 40 , and a turbine shaft 53 connecting the compressor 51 and the turbine 52 .

The turbine 52 is an impeller that rotates with the energy of the exhaust gas flowing through the exhaust passage 40 . The turbine 52 is arranged in the exhaust passage 40 between the downstream end (exhaust collecting portion) of the exhaust manifold 40 a and the catalytic device 41 . Rotation of the turbine 52 is transmitted to the compressor 51 via the turbine shaft 53 .

The compressor 51 is an impeller that compresses and sends out (supercharges) intake air by rotating in conjunction with the rotation of the turbine 52 . The compressor 51 is arranged in the intake passage 30 between the air cleaner 31 and the throttle valve 32 .

The high-pressure EGR device 60 is a recirculation device for recirculating part of the relatively high-pressure exhaust gas before flowing into the turbine 52 to the intake passage 30 as EGR gas. The high-pressure EGR device 60 includes a first EGR passage 61 connecting the exhaust passage 40 and the intake passage 30 , and a first EGR valve 62 and a first EGR cooler 63 provided in the first EGR passage 61 . The first EGR valve 62 is an electrically operated valve that can adjust the flow rate of EGR gas flowing through the first EGR passage 61 . The first EGR cooler 63 is a heat exchanger that cools the EGR gas flowing through the first EGR passage 61 . The first EGR passage 61 and the first EGR valve 62 respectively correspond to the "EGR passage" and the "EGR valve" in the present invention.

A first EGR inlet portion 61a is a portion where an upstream end (exhaust passage 40 side) of the first EGR passage 61 is connected to the exhaust passage 40, and a downstream end (intake passage 30 side) of the first EGR passage 61 is intake air. A portion connected to the passage 30 is referred to as a first EGR outlet portion 61b. In this case, the first EGR inlet portion 61a is located between the turbine 52 in the exhaust passage 40 and the downstream end (exhaust collecting portion) of the exhaust manifold 40a. Also, the first EGR outlet portion 61 b is located between the throttle valve 32 and the surge tank 34 in the intake passage 30 . In other words, the first EGR passage 61 connects the exhaust passage 40 on the upstream side of the turbine 52 and the intake passage 30 on the downstream side of the throttle valve 32 to each other. The first EGR outlet portion 61b corresponds to the "connecting portion between the EGR passage and the intake passage" in the present invention.

The low-pressure EGR device 70 is a recirculation device for recirculating part of the relatively low-pressure exhaust gas after passing through the turbine 52 to the intake passage 30 as EGR gas. The low-pressure EGR device 70 includes a second EGR passage 71 connecting the exhaust passage 40 and the intake passage 30 , and a second EGR valve 72 and a second EGR cooler 73 provided in the second EGR passage 71 . The second EGR valve 72 is an electrically operated valve that can adjust the flow rate of EGR gas flowing through the second EGR passage 71 . The second EGR cooler 73 is a heat exchanger that cools the EGR gas flowing through the second EGR passage 71 .

A second EGR inlet portion 71a is a portion where an upstream end (exhaust passage 40 side) of the second EGR passage 71 is connected to the exhaust passage 40, and a downstream end (intake passage 30 side) of the second EGR passage 71 is intake air. A portion connected to the passage 30 is referred to as a second EGR outlet portion 71b. In this case, the second EGR inlet portion 71 a is located downstream of the turbine 52 and the catalyst device 41 in the exhaust passage 40 . The second EGR outlet 71b is located between the air cleaner 31 and the throttle valve 32 in the intake passage 30 (more specifically, between the air cleaner 31 and the compressor 51). In other words, the second EGR passage 71 connects the exhaust passage 40 on the downstream side of the turbine 52 and the intake passage 30 on the upstream side of the throttle valve 32 to each other.

<Control system>
FIG. 2 is a functional block diagram showing an engine control system. The ECU 100 shown in this figure is a device for comprehensively controlling the engine, and is a microcomputer including a processor (CPU) that performs various arithmetic processing, memories such as ROM and RAM, and various input/output buses. It is composed of

Information detected by each sensor of the engine is input to the ECU 100 . For example, the ECU 100 is electrically connected to the aforementioned crank angle sensor SN1, water temperature sensor SN2, airflow sensor SN3, intake pressure sensor SN4, and exhaust _O2 sensor SN5. Information detected by the sensors SN1 to SN5, that is, information such as crank angle, engine speed, engine water temperature, intake flow rate, intake pressure, exhaust oxygen concentration, etc., is sequentially input to the ECU 100. FIG.

The ECU 100 also receives information detected by various sensors provided in the vehicle. In this embodiment, the vehicle is provided with a vehicle speed sensor SN6, an accelerator sensor SN7, and a brake sensor SN8. The vehicle speed sensor SN6 is a sensor that detects the vehicle speed, which is the running speed of the vehicle. The accelerator sensor SN7 is a sensor that detects the accelerator opening, which is the opening of an accelerator pedal provided in the vehicle. It is a sensor that detects the presence or absence of operation of the brake pedal (brake operation). Information detected by each of the sensors SN6 to SN8 (information on vehicle speed, accelerator opening, and brake operation) is also sequentially input to the ECU 100. FIG.

The ECU 100 controls each section of the engine while executing various determinations and calculations based on the input information from the sensors SN1 to SN8. For example, the ECU 100 is electrically connected to the injector 15, the throttle valve 32, the first EGR valve 62, and the second EGR valve 72, and outputs control signals to these devices based on the results of the above calculations. do.

The ECU 100 functionally has a determination section 101, an automatic stop control section 102, and a restart control section 103 as elements for realizing the control described above. Note that the automatic stop control unit 102 corresponds to the "control unit" in the present invention.

The automatic stop control unit 102 is a control module that automatically stops the running engine when a specific condition is established. The restart control unit 103 is a control module that restarts the engine stopped by the automatic stop control unit 102 . The determination unit 101 is a control module that performs various determinations and calculations necessary for executing control by the automatic stop control unit 102 and the restart control unit 103 .

<Automatic stop control>
Next, the details of the automatic stop control for automatically stopping the running engine will be described. 3 and 4 are flowcharts showing specific procedures of the automatic stop control. When the control according to this flowchart starts, the determination unit 101 of the ECU 100 determines whether or not a predetermined automatic stop condition is satisfied (step S1). The automatic stop condition is a condition that permits the automatic stop of the engine, and various conditions can be set depending on the type of vehicle and the like.

For example, in a vehicle whose power source for running is substantially only an engine (so-called engine vehicle), (i) the vehicle is substantially stopped, (ii) the accelerator pedal is off, ( iii) The automatic stop condition can be met when a plurality of conditions are all met, including that the brake pedal is in an ON state. In this case, determination unit 101 determines whether the vehicle speed is substantially zero based on the information input from vehicle speed sensor SN6, accelerator sensor SN7, and brake sensor SN8. It is determined whether or not there is, and whether or not the brake pedal is depressed. When all of these determinations are YES (that is, when all of the above conditions (i) to (iii) are satisfied), it is determined that the automatic stop condition is satisfied.

On the other hand, in a vehicle that also uses a motor as a power source for running, i.e., a so-called hybrid vehicle that is capable of EV running using only the motor, the driving force of the engine may not be necessary even while the vehicle is running. An automatic stop condition can be satisfied when such a situation occurs. In this case, the determination unit 101 calculates the target torque of the drive source including the engine and the motor from the vehicle speed detected by the vehicle speed sensor SN6, the accelerator opening detected by the accelerator sensor SN7, and the calculated target torque. It is determined whether engine output (positive output torque that contributes to running) is necessary from various conditions including. Then, when it is determined that the engine output is unnecessary, it is determined that the automatic stop condition is established.

The engine load is not high immediately before the automatic stop condition is established in any of the above patterns. In this state, the engine is operated with at least one of the first EGR valve 62 and the second EGR valve 72 open. That is, on the premise that the automatic stop condition is established, the engine is executing EGR that recirculates the exhaust gas from the exhaust passage 40 to the intake passage 30, and the EGR rate (the ratio of EGR gas in the intake air) is compared. high. Therefore, when the automatic stop condition is established, the oxygen concentration in the intake passage 30 is significantly higher than the oxygen concentration in the atmosphere at least in the vicinity of the engine body 1 (specifically, the portion downstream of the first EGR outlet 61b). , which is lower than the target value Dx of the oxygen concentration used in step S9, which will be described later.

If it is determined YES in step S1 and it is confirmed that the automatic stop condition is satisfied, the automatic stop control section 102 of the ECU 100 closes the throttle valve 32 (step S2). That is, the automatic stop control unit 102 drives the throttle valve 32 to close so that the opening degree of the throttle valve 32 is reduced to the equivalent of fully closed (0%). The opening degrees of the first EGR valve 62 and the second EGR valve 72 may differ depending on the operating conditions before the automatic stop condition is satisfied. (state other than fully closed), and that state is maintained in step S2. In other words, in step S2, control is executed to close the throttle valve 32 while maintaining the first EGR valve 62 in the open state.

Next, the automatic stop control unit 102 executes fuel cut to stop the fuel injection from the injector 15 of each cylinder 2 (step S3). After this fuel cut is executed, combustion in each cylinder 2 is stopped, and the engine speed gradually decreases.

Next, the determination unit 101 determines whether or not conditions for permitting oxygen concentration adjustment control are satisfied (step S4). The oxygen concentration adjustment control is performed by controlling the amount of oxygen present in the intake passage 30 (mainly the surge tank 34 and the intake manifold 30a) downstream of the first EGR outlet portion 61b, which is the connection portion between the first EGR passage 61 and the intake passage 30. This is the control for adjusting the oxygen concentration to a predetermined target value, and here refers to the control of steps S5 to S10, which will be described later. Further, the condition for permitting the oxygen concentration adjustment control is a condition that influences whether or not the oxygen concentration can be adjusted to the target value. In the following, the concentration of oxygen to be adjusted, that is, the concentration of oxygen in the intake air present in the intake passage 30 downstream of the first EGR outlet portion 61b (in other words, the concentration of EGR gas recirculated from the first EGR passage 61 Oxygen concentration in subsequent inspiration) is also referred to as "final inspiratory oxygen concentration".

Specifically, in step S4, it is determined whether or not the condition for permitting the oxygen concentration adjustment control is satisfied based on the engine coolant temperature and the atmospheric pressure. For example, the determination unit 101 determines that the first condition is that the engine water temperature detected by the water temperature sensor SN2 is equal to or higher than a predetermined threshold, and that the atmospheric pressure estimated from the detection value of the intake pressure sensor SN4 is equal to or higher than the predetermined threshold. It is determined that the permission condition is satisfied when both the second condition is satisfied. That is, the determination unit 101 permits the execution of the oxygen concentration adjustment control after step S5, which will be described later.

Conversely, if either the first or second condition is not satisfied, that is, if the engine water temperature is low or the atmospheric pressure is low, there is a possibility that the ignitability required for restarting cannot be ensured. Therefore, it is necessary to give priority to the ignitability of the fuel over the adjustment of the oxygen concentration. Therefore, in such a case, the determination unit 101 determines in step S4 that the permission condition is not satisfied, and prohibits the oxygen concentration adjustment control. In this case, the automatic stop control unit 102 executes control to stop the engine while greatly increasing the oxygen concentration (step S22). Although the details are omitted, in this step S22, the opening of the throttle valve 32 is relatively adjusted at some timing after the fuel cut so that the final intake oxygen concentration is increased to a value that can sufficiently ensure ignitability. Execute control such as increasing to a high value.

If the determination in step S4 is YES and it is confirmed that the oxygen concentration adjustment control is permitted, the automatic stop control unit 102 sets the opening degree of the throttle valve 32 and the opening degree of the first EGR valve 62 in advance. The valves 32, 62 are controlled so as to have an intermediate opening degree (step S5). An intermediate degree of opening is an degree of opening that is neither fully closed (0%) nor fully open (100%), and is an degree of opening that substantially narrows the flow path while allowing gas flow. Through the control in step S5, the throttle valve 32 changes from the fully closed state to the open state. Such opening of the throttle valve 32 has the effect of increasing the concentration of oxygen in the intake air.

Specifically, in step S5, the opening degrees of the throttle valve 32 and the first EGR valve 62 are set to approximately the same value. For example, the opening degrees of the throttle valve 32 and the first EGR valve 62 can each be set to approximately 30%. The degree of opening of the second EGR valve 72 can be set to an appropriate value. For example, the degree of opening of the second EGR valve 72 can be set to a specific intermediate degree of opening determined separately from that of the throttle valve 32 and the first EGR valve 62 .

Next, the determination unit 101 determines whether or not the current oxygen concentration condition corresponds to a predetermined assumed concentration condition (step S6). Specifically, the determining unit 101 determines that the oxygen concentration condition corresponds to the assumed concentration condition when both of the following conditions (x) and (y) are satisfied.
(x) the estimated value of the final intake oxygen concentration is greater than or equal to a predetermined first threshold value D1;
(y) the detected value of the exhaust oxygen concentration is equal to or greater than a predetermined second threshold value D2;

In the above condition (x), the estimated value of the final intake oxygen concentration is the estimated value of the oxygen concentration in the intake air present at a specific location (for example, the surge tank 34) in the intake passage 30 on the downstream side of the first EGR outlet portion 61b. includes, for example, the exhaust oxygen concentration detected by the exhaust _O2 sensor SN5, and the operating history of the engine (for example, the opening degree data of the first and second EGR valves 62, 72 in the most recent specific period, etc.) Estimated by calculation from various conditions. In the above condition (y), the detected value of the exhaust oxygen concentration is the exhaust oxygen concentration detected by the exhaust _O2 sensor SN5. The first threshold value D1 used in the condition (x) is set to a value smaller than the oxygen concentration target value Dx used in step S9 described later (D1<Dx), and used in the condition (y). The second threshold D2 is set to a value smaller than the first threshold D1 (D2<D1).

If the determination in step S6 is YES and it is confirmed that the current oxygen concentration condition corresponds to the assumed concentration condition, that is, both the estimated value of the final intake oxygen concentration and the detected value of the exhaust oxygen concentration are threshold values (D1 , D2), the automatic stop control unit 102 closes the throttle valve 32 and the first EGR valve 62 so that the opening degrees of the throttle valve 32 and the first EGR valve 62 change in conjunction with the engine speed. control (step S7). Specifically, the automatic stop control unit 102 controls the valves 32 and 62 so that the opening degrees of the throttle valve 32 and the first EGR valve 62 gradually decrease in accordance with the gradual decrease in the engine speed after the fuel cut. do. If the ratio of the amount of decrease in the opening of each valve 32, 62 to the amount of decrease in the engine speed is taken as the opening degree change rate, the opening degree change rate does not cause a sudden change in the final intake oxygen concentration and can stabilize the intake pressure. It is predetermined to be an appropriate value. In this embodiment, the opening degrees of the throttle valve 32 and the first EGR valve 62 are controlled so as to decrease at the same rate of change. In other words, in step S7, the opening degrees of the throttle valve 32 and the first EGR valve 62 are gradually decreased while being maintained at approximately the same value.

On the other hand, if the determination in step S6 is NO and it is confirmed that the current oxygen concentration condition does not correspond to the assumed concentration condition, that is, if at least one of the estimated value of the final intake oxygen concentration and the detected value of the exhaust oxygen concentration is If it is confirmed that the threshold value (D1 or D2) is less than the threshold value (D1 or D2), the automatic stop control unit 102 controls the throttle valve 32 and the first EGR valve 62 so that the opening degree of the throttle valve 32 is larger than the opening degree of the first EGR valve 62. 62 (step S8). In this step S8, the opening degree of the throttle valve 32 is made larger than the opening degree of the throttle valve 32 (that is, the opening degree set in step S7) when the current oxygen concentration condition corresponds to the assumed concentration condition. , and is set to a value larger than the opening of the first EGR valve 62 . For example, if the opening degrees of the throttle valve 32 and the first EGR valve 62 are both about 30% at the start of step S7, the opening degree of the throttle valve 32 is increased to about 50% in step S8. It is possible to set the degree of opening of the first EGR valve 62 to 30% or a slightly lower value. That is, in the control of step S8 executed under the condition that the oxygen concentration is lower than assumed, the opening degree of the throttle valve 32 is increased as compared with the control of step S7 executed under the other condition. . On the other hand, the opening degree of the first EGR valve 62 is not increased, and is maintained at substantially the same opening degree (same or slightly lower opening degree).

After the control in either step S7 or S8 is started, the determination unit 101 determines whether or not the estimated value of the final intake oxygen concentration has increased to a predetermined target value Dx or higher (step S9). . The target value Dx of the final intake oxygen concentration used here is set to a value larger than the above-described first threshold value D1. It is set to a value smaller than the density.

If the determination in step S9 is YES and it is confirmed that the final intake oxygen concentration has reached or exceeded the target value Dx, the automatic stop control unit 102 closes the throttle valve 32 (step S10). That is, the automatic stop control unit 102 closes the throttle valve 32 so that the opening degree of the throttle valve 32 is reduced to the level corresponding to the fully closed position.

Next, the automatic stop control unit 102 adjusts the opening degree of the first EGR valve 62 so that the intake pressure does not fall below a predetermined reference pressure Px (see FIG. 5(d)) (step S11). The reference pressure Px used here is the pressure in the surge tank 34 detected by the intake pressure sensor SN4, that is, the reference value of the intake pressure, and is set to a value corresponding to a weak negative pressure slightly below the atmospheric pressure. be. Since the reference pressure Px is such a value (weak negative pressure), when the step S11 is started, the degree of opening of the first EGR valve 62 is increased from the degree of opening immediately before that. That is, since the introduction of new intake air is basically stopped by closing the throttle valve 32 in step S10, the opening of the first EGR valve 62 must be is increased to promote the recirculation of EGR gas through the first EGR passage 61 . Therefore, in step S11, the automatic stop control unit 102 drives the first EGR valve 62 in the opening direction, thereby adjusting the intake pressure so that it does not fall below the reference pressure Px (stays at a weak negative pressure). Specifically, the automatic stop control unit 102 determines the basic opening degree of the first EGR valve 62 from the engine speed while referring to a map or the like, and determines the determined basic opening degree using the pressure detected by the intake pressure sensor SN4. , the target opening of the first EGR valve 62 is calculated. In step S11, the opening degree of the first EGR valve 62 is controlled according to the target opening degree thus calculated so that the intake pressure in the surge tank 34 does not fall below the reference pressure Px (weak negative pressure). adjusted.

Next, the determination unit 101 determines whether or not the engine speed has decreased below a predetermined reference speed Nx (step S12). The reference speed Nx is set to a value smaller than the engine speed at the time of the fuel cut in step S3, and is set to a value that can adjust the intake pressure to a negative pressure in the future to an appropriate level. Specifically, the reference rotational speed Nx is set to a value such that the minimum value Py (see FIG. 5(d)) of the intake pressure, which is greatly reduced to negative pressure after step S13, which will be described later, falls within a predetermined target range Z. be done. The target range Z can be set to include, for example, 50 kPa, and the reference rotation speed Nx can be set to, for example, about 700 to 800 rpm.

If it is determined YES in step S12 and it is confirmed that the engine speed has become less than the reference speed Nx, the automatic stop control unit 102 closes the first EGR valve 62 (step S13). That is, the automatic stop control unit 102 closes the first EGR valve 62 so that the degree of opening of the first EGR valve 62 is reduced to the level corresponding to the fully closed position. At this point, the throttle valve 32 is already fully closed after the control in step S10. Therefore, after step S13, both the throttle valve 32 and the first EGR valve 62 are fully closed, and the intake pressure is reduced to negative pressure.

Next, the determination unit 101 determines whether or not the engine has completely stopped (step S14). That is, the determination unit 101 determines whether or not the engine speed detected by the crank angle sensor SN1 has substantially decreased to zero. ), it is determined that the engine has completely stopped.

If the determination in step S14 is YES and it is confirmed that the engine has completely stopped, the automatic stop control unit 102 opens the first EGR valve 62 to an intermediate opening degree or fully open while maintaining the throttle valve 32 in a fully closed state. Open to a near opening (step S15). This is preparatory control for restarting the engine, and is performed for the purpose of avoiding excessive cranking resistance when restarting the engine.

As can be understood from the flow of control after step S9 described above, in the engine of the present embodiment, normally, the phenomenon that the final intake oxygen concentration rises to the target value Dx or higher, and the phenomenon that the engine speed drops below the reference speed Nx A decrease phenomenon occurs in this order. However, for example, when the engine speed when the automatic stop condition (S1) is satisfied is considerably lower than expected, or when the intake oxygen concentration when the automatic stop condition is satisfied is considerably lower than expected, the former The latter phenomenon may occur before the phenomenon. Next, the content of control performed in such a special case will be described.

In order to confirm whether or not a special case as described above has occurred, the determination unit 101 further determines that the engine speed has decreased to less than the reference rotation speed Nx (step S17).

If the determination in step S17 is YES and it is confirmed that the engine speed has decreased below the reference speed Nx, that is, before the final intake oxygen concentration reaches the target value Dx or more, the engine speed reaches the reference speed. When it is confirmed that a special case has occurred in which the engine speed drops below Nx, the automatic stop control unit 102 closes both the throttle valve 32 and the first EGR valve 62 (step S18). That is, the automatic stop control unit 102 drives the throttle valve 32 and the first EGR valve 62 to close so that the respective opening degrees of the throttle valve 32 and the first EGR valve 62 decrease to correspond to full closing.

Next, the determination unit 101 determines whether or not the engine has stopped completely, that is, whether or not the engine speed has substantially decreased to zero (step S19).

If the determination in step S19 is YES and it is confirmed that the engine has completely stopped, the automatic stop control unit 102 opens the throttle valve 32 to a predetermined intermediate opening (step S20). This is preparatory control for restarting the engine, and is performed for the purpose of avoiding insufficient ignitability when restarting the engine. That is, in the above special case, the throttle valve 32 is closed before the final intake oxygen concentration reaches the target value Dx, so if the engine is restarted in this state, there is a high possibility that the necessary ignitability will not be ensured. Therefore, by opening the throttle valve 32 in advance in step S20, the ignitability at restart is ensured.

<Operation example of each part by automatic stop control>
FIG. 5 is a time chart showing an example of the change over time of each state quantity when the automatic stop control shown in FIGS. 3 and 4 is executed. Chart (b) shows the time change of the flag indicating the necessity of fuel injection from the injector 15. Chart (c) shows the time change of the engine speed. Chart (e) shows changes over time in the opening degrees of the throttle valve 32 and the first EGR valve 62, and chart (f) shows changes over time in the intake oxygen concentration in the surge tank 34 (that is, the final intake oxygen concentration). Each shows a change.

In FIG. 5, t0 is the time when the automatic stop condition (step S1 in FIG. 3) is met. In response to the establishment of the automatic stop condition at time t0, first, the opening of the throttle valve 32 is reduced to 0% (fully closed) (chart (e)). This corresponds to the control of step S2 in FIG.

At time t1, which is delayed from time t0 when the automatic stop condition is satisfied, fuel cut is executed to stop fuel injection (chart (b)). This corresponds to the control of step S3 in FIG. Furthermore, immediately after this fuel cut, the opening of the throttle valve 32 is increased from 0% to α%, and the opening of the first EGR valve 62 is similarly set to α% (chart (e)). This corresponds to the control of step S5 in FIG. α% is set to a predetermined intermediate opening degree (for example, about 30%) that is neither 0% nor 100%. As the throttle valve 32 is thus opened to the intermediate opening degree, the final intake oxygen concentration gradually increases after time t1 (chart (f)). Also, since not only the throttle valve 32 but also the first EGR valve 62 is opened, the final intake oxygen concentration does not rise so rapidly, but rises at a relatively stable rate of rise. In the example of FIG. 5, the opening degree of the first EGR valve 62 is set to a value larger than α% before time t0 when the automatic stop condition is satisfied. Therefore, along with the fuel cut, the opening of the first EGR valve 62 is reduced from the opening greater than α% to α%.

At time t2, which is delayed from fuel cut execution time t1, the engine speed actually begins to decrease (chart (c)). In response to this, the opening degrees of the throttle valve 32 and the first EGR valve 62 are gradually reduced after time t2 (chart (e)). This corresponds to the control of step S7 in FIG. Here, the fact that the control in step S7 is executed means that the determinations in steps S4 and S6 before that are both YES. In other words, the time chart of FIG. 5 shows an operation example when the condition for permitting oxygen concentration adjustment control is satisfied and the oxygen concentration condition corresponds to the assumed concentration condition. In this case, since the final inspired oxygen concentration is equal to or higher than the threshold value D1, there is no need to increase the final inspired oxygen concentration particularly quickly. Therefore, in FIG. 5, in order to moderately suppress the rate of increase in the final intake oxygen concentration, the above-described control for gradually decreasing the opening degrees of the throttle valve 32 and the first EGR valve 62 in conjunction with the engine speed after time t2 is executed. be.

At time t3, which is delayed from time t2 when the engine speed starts to decrease, the final intake oxygen concentration rises to the target value Dx (chart (f)). In response to this, the opening degree of the throttle valve 32 is reduced to 0% and the opening degree of the first EGR valve 62 is increased to β% (>α%) (chart (e)). This corresponds to the control of steps S10 and S11 in FIG. By fully closing the throttle valve 32, the increase in the final intake oxygen concentration is substantially stopped, and the value is maintained near the target value Dx (chart (f)). Further, by increasing the degree of opening of the first EGR valve 62, the intake pressure is adjusted so as not to drop significantly, and is maintained at a value not lower than the reference pressure Px (chart (d)).

At time t4, which is later than time t3 when the target value Dx is achieved, the engine speed decreases to the reference speed Nx (chart (c)). In response to this, the opening degree of the first EGR valve 62 is reduced to 0% (chart (e)). This corresponds to the control of step S13 in FIG. Since both the first EGR valve 62 and the throttle valve 32 are fully closed by this control, the intake pressure drops sharply after time t4, and a relatively strong negative pressure is created in the surge tank 34 and the intake manifold 30a. pressure is generated (chart (d)). Since the generation of such negative pressure increases the pumping loss of the engine, the speed at which the engine speed decreases is accelerated compared to when the throttle valve 32 or the first EGR valve 62 is opened.

After a while from time t4 (here, just before the engine is completely stopped), the intake pressure drops to the minimum value Py and stops dropping any further. Chart (d) shows an example in which the minimum value Py of the intake pressure is appropriately within the target range Z. As shown in FIG. This means that the closing of the first EGR valve 62 triggered by the decrease to the reference engine speed Nx is executed at an appropriate timing such that the minimum value Py of the intake pressure falls within the target range Z.

At time t5 after the time t4 at which the engine speed drops to the reference speed Nx, the engine speed drops to zero and the engine comes to a complete stop. Then, at time t6 thereafter, the first EGR valve 62 is increased from 0% to γ%. This corresponds to the control of step S15 in FIG. In the example of FIG. 5, γ% is set to a high degree of opening (for example, an degree of opening close to full opening) that is greater than both α% and β% described above.

In the operation example of FIG. 5 described above, the control to open both the throttle valve 32 and the first EGR valve 62 from time t1 to time t3 corresponds to the "first control" in the present invention. do. Further, the control for closing the throttle valve 32 at time t3 corresponds to the "second control" in the present invention.

Next, an operation example when the determination in step S6 in FIG. 3 is NO, that is, when the oxygen concentration condition does not correspond to the assumed concentration condition will be described with reference to FIG. Time points t0 to t6 in the time chart of FIG. 6 have the same meanings as time points t0 to t6 in the time chart of FIG. However, in the example of FIG. 6, the final intake oxygen concentration at the fuel cut execution time t1 is lower than that in FIG. 5 and below the first threshold value D1. As a result, in the example of FIG. 6, the determination in step S6 is NO, and the control in step S8 for opening the throttle valve 32 relatively large is executed. This is the reason why the opening of the throttle valve 32 from time t1 to time t3 in FIG. 6 is larger than that in FIG. Specifically, in FIG. 6, the opening degree of the throttle valve 32 is increased from 0% to α1% after time t1, and the opening degree α1 after this increase is the first EGR valve set immediately after time t1. 62 is made larger than the opening α2%.

Opening the throttle valve 32 after time t1 as described above increases the final intake oxygen concentration at a relatively high rate of increase. As a result, the final intake oxygen concentration rises to the target value Dx at time t3, which is delayed from time t1, and the throttle valve 32 is accordingly fully closed. On the other hand, the first EGR valve 62 is once driven in the opening direction at time t3, and then fully closed at time t4.

<Effect>
As described above, in the present embodiment, fuel cut (step S3 in FIG. 3) for stopping the fuel injection from the injector 15 is executed in response to establishment of the automatic engine stop condition, and the engine is stopped from the fuel cut. The throttle valve 32 and the like are controlled so that the final intake oxygen concentration, which is the concentration of oxygen in the intake air present in the intake passage 30 on the downstream side of the first EGR outlet 61b, reaches the target value Dx until the engine is completely stopped. be. Specifically, control to open the throttle valve 32 immediately after fuel cut (step S4 in FIG. 3, etc.) and control to close the throttle valve 32 when the final intake oxygen concentration reaches the target value Dx ( Step S10) in FIG. 4 is executed. According to such a configuration, there is an advantage that the amount of NOx generated can be suppressed while ensuring ignitability when restarting the engine that has been automatically stopped.

That is, in the present embodiment, the throttle valve 32 is opened after the fuel cut, so fresh oxygen-rich air flows into the intake passage 30 on the downstream side of the throttle valve 32. Oxygen concentration rises. Further, when the final intake oxygen concentration reaches the target value Dx, the throttle valve 32 is closed (fully closed). The oxygen concentration can be substantially maintained at the target value Dx. This means that the final intake oxygen concentration when the engine is restarted can be adjusted to a value higher than the concentration when the automatic stop condition is established and lower than the oxygen concentration contained in the atmosphere.

Here, before the automatic stop condition is established, the final intake oxygen concentration is significantly lower than the oxygen concentration in the atmosphere by recirculating the exhaust gas through the EGR passages 61 and 71 (EGR operation). . Therefore, if the control for temporarily opening the throttle valve 32 was not performed, the engine would be restarted while the final intake oxygen concentration was significantly low. The ignitability of the fuel may be impaired. On the other hand, in the present embodiment, the throttle valve 32 is opened after the fuel cut, so that the final intake oxygen concentration can be increased to ensure ignitability at restart.

However, if the final intake oxygen concentration is unreasonably increased, combustion is performed in each cylinder 2 with an extremely small amount of EGR gas, which is an inert gas. may increase. In contrast, in the present embodiment, the throttle valve 32 is closed when the final intake oxygen concentration reaches an appropriate concentration (target value Dx), so the final intake oxygen concentration is lower than the atmospheric oxygen concentration. The concentration can be maintained (in other words, the state in which the EGR gas is contained in the intake air) can be maintained, and the amount of NOx produced by combustion can be effectively suppressed.

Further, in the present embodiment, when the throttle valve 32 is controlled to open immediately after fuel cut, the first EGR valve 62 is also opened (step S4 in FIG. 3). The inflow of fresh air can be reduced as compared with the case where the valve is not opened but closed, and a sudden rise in the final intake oxygen concentration can be avoided. This facilitates the estimation of the final inspired oxygen concentration, so that the point in time when the final inspired oxygen concentration reaches the target value Dx can be specified with high accuracy, and the accuracy of concentration adjustment can be improved.

Further, in the present embodiment, the opening degrees of the throttle valve 32 and the first EGR valve 62, which are opened after the fuel cut, are gradually decreased in conjunction with the engine speed after the fuel cut (step S7), it is possible to suppress fluctuations in the increase rate of the final intake oxygen concentration while stabilizing the intake pressure. That is, when the engine speed decreases after the fuel cut, the reciprocating speed of the piston 5 decreases, the suction force during the intake stroke decreases, and the intake air amount to each cylinder 2 decreases. Therefore, if the opening degree of the throttle valve 32 after opening is fixed, there is a high possibility that a large amount of fresh air that is out of balance with the amount of gas discharged from each cylinder 2 will be introduced into each cylinder 2. This may lead to an increase in air pressure and fluctuations in the rate of increase in the final inspiratory oxygen concentration. In contrast, in the present embodiment, the opening of the throttle valve 32 is gradually reduced so as to match the engine speed that decreases after the fuel cut. In this way, it is possible to stabilize the inspiratory pressure and suppress fluctuations in the rate of increase of the final inspiratory oxygen concentration. Furthermore, since the opening degree of the first EGR valve 62 is also gradually reduced together with the throttle valve 32, fluctuations in the increase rate of the final intake oxygen concentration can be sufficiently suppressed, and the final intake oxygen concentration reaches the target value Dx. Time points can be specified more accurately.

Further, in this embodiment, when the final intake oxygen concentration reaches the target value Dx, the throttle valve 32 is closed as described above, while the opening degree of the first EGR valve 62 is controlled to increase. (Step S11 in FIG. 4). After that, the first EGR valve 62 is kept open for a while and then closed when the engine speed becomes less than the reference speed Nx (step S13 in FIG. 4). In this manner, when the first EGR valve 62 is closed with a delay from the closing of the throttle valve 32, the intake pressure becomes excessive during the period from the closing of the first EGR valve 62 to the complete stop of the engine. Negative pressure can be prevented. For example, it is possible to prevent the minimum value Py of the intake pressure shown in the chart (d) of FIG. If the minimum value Py of the intake pressure falls below the target range Z, that is, if the intake pressure drops to an excessively strong negative pressure, the engine rotation speed decreases excessively, resulting in the engine completely stopping. Occasional shocks (shocks transmitted to the vehicle body due to reaction to sudden stops) are likely to increase, and the occupants may feel uncomfortable. On the other hand, in the present embodiment, the closing timing of the first EGR valve 62 is relatively delayed (later than the closing timing of the throttle valve 32), so the amount of decrease in intake pressure can be kept within an appropriate range. , the shock when the engine is stopped can be reduced.

Also, depending on the engine, stop position control may be performed to adjust the stop position of the piston 5 of each cylinder 2 to a position that is advantageous for restarting. In such an engine, when the control of relatively delaying the closing of the first EGR valve 62 is employed as in the present embodiment, the speed of decrease in the engine speed can be adjusted within an appropriate range. It is possible to prevent the accuracy of the stop position control of 5 from being lowered, and to improve the restartability of the engine.

<Modification>
In the above-described embodiment, the oxygen concentration in the intake air present in the intake passage 30 on the downstream side of the first EGR outlet portion 61b (the oxygen concentration in the intake air after the EGR gas is recirculated from the first EGR passage 61) is the final intake air Although the oxygen concentration is estimated by calculation and the throttle valve 32 is closed when the estimated final intake oxygen concentration reaches the target value Dx, the final intake oxygen concentration may be directly detected by a sensor. For example, a sensor capable of detecting the oxygen concentration may be attached to the surge tank 34 to detect the final intake oxygen concentration.

In the above embodiment, in addition to the high-pressure EGR device 60 including the first EGR passage 61 connecting the exhaust passage 40 upstream of the turbine 52 and the intake passage 30 downstream of the throttle valve 32, Although the engine is provided with the low-pressure EGR device 70 including the second EGR passage 71 that connects the exhaust passage 40 on the downstream side and the intake passage 30 on the upstream side of the throttle valve 32, the low-pressure EGR device 70 is not essential and is omitted. You may

In the above embodiment, an example in which the present invention is applied to a diesel engine that burns fuel containing light oil by pressure ignition is described, but an engine to which the present invention can be applied recirculates exhaust gas from the exhaust passage to the intake passage. The present invention may be applied to any engine other than a diesel engine as long as the engine is capable of EGR operation. For example, it is possible to apply the present invention to a gasoline engine capable of combusting gasoline-containing fuel by spark ignition and having an EGR device.

1: Engine body 2: Cylinder 7: Crankshaft (output shaft)
15: Injector 30: Intake passage 32: Throttle valve 40: Exhaust passage 61: First EGR passage (EGR passage)
61b: First EGR outlet (connection between EGR passage and intake passage)
62: 1st EGR valve (EGR valve)
101: Determination unit 102: Automatic stop control unit (control unit)

Claims (5)

A cylinder, an output shaft that rotates with the energy of combustion in the cylinder, an intake passage through which the intake air introduced into the cylinder flows, an exhaust passage through which the exhaust gas discharged from the cylinder flows, an intake passage and an exhaust passage. A stop control device applied to an engine comprising an EGR passage connecting the
an injector that supplies fuel to the cylinder;
an EGR valve provided in the EGR passage so as to be openable and closable;
a throttle valve provided in an intake passage on the upstream side of a connecting portion between the EGR passage and the intake passage so as to be openable and closable;
a determination unit that determines whether an automatic stop condition for automatically stopping the engine is satisfied;
a control unit that controls each part of the engine including the injector, the throttle valve, and the EGR valve;
When the judgment unit confirms that the automatic stop condition is satisfied, the control unit executes a fuel cut to stop the supply of fuel by the injector, and after the fuel cut is executed, the output shaft until the rotation of the engine stops, oxygen concentration adjustment control is executed to control the throttle valve and the EGR valve so that the concentration of oxygen in the intake passage on the downstream side of the connecting portion reaches a predetermined target value. ,
The oxygen concentration adjustment control includes a first control that opens the throttle valve so that the oxygen concentration rises, and a second control that closes the throttle valve when the oxygen concentration rises to the target value. An engine stop control device comprising: In the engine stop control device according to claim 1,
The engine stop control device, wherein the first control is a control to open not only the throttle valve but also the EGR valve. In the engine stop control device according to claim 2,
The engine stop control device, wherein the first control includes control for reducing the opening of the throttle valve in response to a decrease in engine speed, which is the speed of the output shaft. In the engine stop control device according to claim 3,
The engine stop control device, wherein the first control includes control for reducing the degree of opening of the EGR valve in accordance with a decrease in the engine speed. In the engine stop control device according to any one of claims 1 to 4,
The engine stop control device, wherein the control unit closes the EGR valve at a timing later than a point in time when the oxygen concentration rises to the target value and earlier than a timing at which the rotation of the output shaft is stopped.

Images