JP2020176565A - Control method and control system for engine - Google Patents

Abstract

To accurately make an abnormality determination of a differential pressure sensor and appropriately suppress deterioration of fuel economy when the differential pressure sensor is abnormal in a control method for an engine including the differential pressure sensor of an EGR valve and other methods.SOLUTION: A control method for an engine includes steps of: performing a first combustion mode of performing compression ignition combustion of an air-fuel mixture through self-ignition in the state where a gas air-fuel ratio G/F that is a ratio between total gas amount including EGR gas in a combustion chamber 17 and fuel amount is larger than a theoretical air-fuel ratio; a second combustion mode of performing spark ignition combustion of the air-fuel mixture through spark ignition; controlling a throttle valve 43 to a closed side so as to maintain a pressure difference between an upstream side and a downstream side of an EGR valve 54 to be predetermined pressure or greater during an abnormality determination of a differential pressure sensor SW15; and performing control for stopping recirculation of EGR gas and switching the first combustion mode to the second combustion mode when a determination that the differential pressure sensor SW15 has an abnormality is made.SELECTED DRAWING: Figure 8

Description

The present invention relates to an engine control method and control system including a differential pressure sensor for detecting the differential pressure between the upstream side and the downstream side of the EGR valve provided on the EGR passage.

Conventionally, an abnormality determination has been performed using a differential pressure sensor that detects the differential pressure between the upstream side and the downstream side of the EGR valve provided on the EGR passage of the engine. For example, Patent Document 1 describes an EGR passage connecting an exhaust passage and an intake passage, an EGR valve for adjusting the flow rate of EGR gas flowing through the EGR passage, and an EGR gas on the exhaust passage side and an intake passage side of the EGR valve. In a failure diagnosis device of an EGR system equipped with a differential pressure sensor that detects the differential pressure with the EGR gas, the exhaust pressure of the EGR gas on the exhaust passage side when the EGR valve is closed and detected by the differential pressure sensor. A technique for diagnosing a failure of the EGR system based on the differential pressure has been proposed.

Japanese Unexamined Patent Publication No. 2013-144961

By the way, in recent years, a technique related to compression ignition combustion has been proposed in which an air-fuel mixture in a combustion chamber is self-ignited in a state where EGR gas is introduced into an engine. In this case, EGR gas is introduced at the time of compression ignition combustion in order to form an environment (temperature of the combustion chamber of the engine, etc.) for appropriately causing compression ignition combustion. Typically, compression ignition combustion (for example, some air-fuel mixture) is carried out in a state where the gas air-fuel ratio G / F, which is the ratio of the total amount of gas in the combustion chamber containing EGR gas to the amount of fuel, is larger than the stoichiometric air-fuel ratio. Partial compression ignition combustion is performed such that after spark ignition combustion by spark ignition, the remaining air-fuel mixture is compressed ignition combustion by self-ignition). By performing such compression ignition combustion, it is possible to improve fuel efficiency and output.

On the other hand, it is important to ensure the controllability of the EGR valve in order to perform compression ignition combustion at an appropriate timing. Generally, the control of the EGR valve is performed based on the differential pressure detected by the differential pressure sensor. Therefore, in order to ensure EGR controllability, it is desirable to accurately determine the abnormality of the differential pressure sensor. Here, exhaust pulsation occurs in the exhaust system, and this exhaust pulsation is a factor that lowers the accuracy of abnormality determination of the differential pressure sensor. This is because the pressure detected by the differential pressure sensor fluctuates relatively greatly due to the exhaust pulsation, in other words, the noise corresponding to the exhaust pulsation appears in the detected value of the differential pressure sensor.

The present inventor has found that when the differential pressure between the upstream side and the downstream side of the EGR valve is large, the influence of the exhaust pulsation becomes small, and it is preferable to perform an abnormality determination of the differential pressure sensor in a state where the differential pressure is large. Thought. However, if the abnormality determination is performed only in such a state where the differential pressure is large, the execution frequency of the abnormality determination decreases. Therefore, the present inventor controls the throttle valve on the intake passage to the closed side so as to increase the differential pressure between the upstream side and the downstream side of the EGR valve when determining the abnormality of the differential pressure sensor. Thought. If the throttle valve is controlled to the closed side in this way, the fuel consumption tends to deteriorate (for example, in an engine provided with a supercharger, the fuel consumption deteriorates due to an increase in the boost pressure according to the closing amount of the throttle valve. It is considered that this deterioration in fuel efficiency can be sufficiently compensated for by the fuel efficiency improvement effect caused by the implementation of the above-mentioned compression ignition combustion. This is because if the differential pressure between the upstream side and the downstream side of the EGR valve is large, the controllability of the EGR valve is ensured, and the compression ignition combustion can be stabilized.

However, when the differential pressure sensor is abnormal, the controllability of the EGR valve using the output value of the differential pressure sensor deteriorates. At this time, in order to improve the controllability of the EGR valve, it is conceivable to further increase the differential pressure between the upstream side and the downstream side of the EGR valve, but this tends to significantly deteriorate the fuel consumption. It is considered that this deterioration in fuel efficiency cannot be sufficiently compensated by the stabilization of compression ignition combustion as described above.

Therefore, the present invention accurately determines an abnormality of the differential pressure sensor in an engine control method and control system including a differential pressure sensor that detects the differential pressure between the upstream side and the downstream side of the EGR valve, and also performs the differential pressure sensor. The purpose is to appropriately suppress the deterioration of fuel efficiency in the event of an abnormality.

In order to achieve the above object, the present invention is an engine control method, and the output of a differential pressure sensor that detects the differential pressure between the upstream side and the downstream side of the EGR valve provided on the EGR passage of the engine. By controlling the opening of the EGR valve based on the value and controlling the opening of the EGR valve, the gas air-fuel ratio G is the ratio of the total amount of gas in the combustion chamber including the EGR gas from the EGR passage to the amount of fuel. In a state where / F is larger than the theoretical air-fuel ratio, the step of executing the first combustion mode in which the air-fuel mixture in the combustion chamber of the engine is compressed and ignited by self-ignition, and the combustion of the engine instead of executing the first combustion mode. A step of executing a second combustion mode in which the air-fuel mixture in the room is spark-ignited and burned by spark ignition, a step of determining an abnormality of the differential pressure sensor based on the output value of the differential pressure sensor, and a step of determining an abnormality of the differential pressure sensor. At this time, the step of controlling the throttle valve of the engine to the closed side and the differential pressure sensor are determined to be abnormal so that the differential pressure between the upstream side and the downstream side of the EGR valve is maintained at a predetermined pressure or higher. At that time, the EGR valve is controlled to be closed to stop the recirculation of the EGR gas from the EGR passage to the intake passage of the engine, and when the first combustion mode is being executed, this first combustion mode is set. It is characterized by having a step of controlling switching to the second combustion mode.

According to the present invention configured as described above, when the abnormality determination of the differential pressure sensor is performed, the throttle valve is closed so that the differential pressure between the upstream side and the downstream side of the EGR valve is maintained at a predetermined pressure or higher. Therefore, it is possible to accurately perform the abnormality determination while ensuring the execution frequency of the abnormality determination. Further, by maintaining the differential pressure at a predetermined pressure or higher in this way, deterioration of EGR controllability due to exhaust pulsation can be suppressed, and fuel efficiency can be ensured.
Further, according to the present invention, when the differential pressure sensor is abnormal, the recirculation of the EGR gas is stopped and the gas air-fuel ratio G / F is lean (a state in which a relatively large amount of EGR gas is introduced). The first combustion mode in which the air-fuel mixture is compressed and ignited and burned by self-ignition is switched to the second combustion mode in which the air-fuel mixture is spark-ignited and burned by spark ignition. As a result, when the differential pressure sensor is abnormal, the differential pressure between the upstream side and the downstream side of the EGR valve is improved so as to improve the EGR controllability in order to maintain the implementation of the first combustion mode utilizing the EGR gas. By further increasing the value, it is possible to appropriately suppress the deterioration of fuel efficiency. That is, according to the present invention, when the differential pressure sensor is abnormal, it is possible to surely suppress the deterioration of fuel consumption due to the control to maintain the first combustion mode, and the first combustion. By switching the mode to the second combustion mode, the combustion stability of the engine can be ensured.

In the present invention, preferably, when switching from the first combustion mode to the second combustion mode, the opening / closing timing of the intake valve is set so as to delay the closing timing of the intake valve of the engine in order to reduce the effective compression ratio of the engine. It further has a step of controlling an adjustable intake valve mechanism.
According to the present invention configured as described above, when switching from the first combustion mode to the second combustion mode, the effective compression ratio of the engine can be lowered and knocking can be appropriately suppressed.

In the present invention, preferably, when the intake valve mechanism is controlled so as to delay the closing timing of the intake valve, it further includes a step of controlling the ignition timing of the engine.
In the present invention configured as described above, knocking can be suppressed more effectively when switching from the first combustion mode to the second combustion mode.

In the present invention, preferably, in the engine, the gas air-fuel ratio G / F is larger than the theoretical air-fuel ratio, and the air-fuel ratio A / F, which is the ratio of the amount of air in the combustion chamber to the amount of fuel, substantially matches the theoretical air-fuel ratio. When the first combustion mode is performed in the state and the third combustion mode in which the air-fuel ratio A / F is larger than the stoichiometric air-fuel ratio and the compression ignition combustion is performed is further provided and the differential pressure sensor is determined to be abnormal. , While prohibiting the execution of the first combustion mode, further has a step of permitting the execution of the third combustion mode.
In the present invention configured in this way, when the differential pressure sensor is determined to be abnormal, the first combustion mode is prohibited, while the air-fuel ratio is lean, and the air-fuel mixture is self-ignited. Allows a third combustion mode for compression ignition combustion. As a result, the first combustion mode using the EGR gas can be reliably prohibited in a state where the EGR controllability is not ensured due to the abnormality of the differential pressure sensor, and thus the first combustion mode is prohibited while the third combustion mode is prohibited. Since the combustion mode is permitted, it is possible to appropriately secure the improvement of fuel consumption and the reduction of NOx by the compression ignition combustion.

In the present invention, preferably, the engine performs the third combustion mode in the low load low rotation speed region where the load is less than the predetermined load and the rotation speed is less than the predetermined rotation speed, and in the region other than the low load low rotation speed region. Performs a second combustion mode.
In the present invention configured as described above, the third combustion mode by compression ignition combustion is performed in the low load low rotation region, and the second combustion mode by spark ignition combustion is performed in the region other than the low load low rotation region. Appropriate combustion can be achieved in all operating areas of.

In the present invention, preferably, the engine includes a supercharger that supercharges the intake air supplied to the engine, a bypass passage that bypasses the supercharger and allows the intake air to flow, and a bypass provided on the bypass passage. A valve is provided, and the turbocharger has a step of setting a target boost pressure and controlling the opening degree of the bypass valve so that the target boost pressure is realized. In the control step, when the throttle valve is controlled so that the differential pressure between the upstream side and the downstream side of the EGR valve is maintained above a predetermined pressure in order to determine the abnormality of the differential pressure sensor, the throttle valve of this throttle valve The opening degree of the bypass valve is feedback-controlled based on the target supercharging pressure so as to compensate for the fluctuation of the supercharging pressure due to the control.
In the present invention configured in this way, the pressure on the upstream side of the supercharger (specifically, the pressure on the downstream side of the throttle valve and the upstream side of the supercharger, in other words, the downstream of the EGR valve that regulates the differential pressure of the EGR valve). Both the pressure on the side (pressure on the side) and the pressure on the upstream side of the turbocharger (supercharging pressure) can be appropriately set to the desired pressure.

In the present invention, preferably, the turbocharger is a mechanical turbocharger driven by an engine.
In such a supercharger, the supercharging pressure cannot be adjusted by direct control of the supercharger, but the target supercharging pressure can be appropriately achieved by controlling the bypass valve as described above. ..

In the present invention, preferably, in the step of determining the abnormality of the differential pressure sensor, the differential pressure corresponding to the output value of the differential pressure sensor and the pressure corresponding to the output value of the pressure sensor provided on the downstream side of the EGR valve are used. When the difference between the pressure difference from the pressure corresponding to the output value of the atmospheric pressure sensor and the pressure difference is equal to or more than a predetermined determination threshold value, the differential pressure sensor is determined to be abnormal.
According to the present invention configured as described above, it is possible to accurately determine the abnormality of the differential pressure sensor.

In the present invention, preferably, the higher the engine speed, the higher the step of setting the determination threshold value.
According to the present invention configured as described above, the influence of the exhaust pressure when the engine speed increases can be appropriately eliminated, and the accuracy of abnormality determination can be effectively ensured.

In the present invention, preferably, when the engine speed is equal to or higher than the predetermined rotation speed, the execution of the abnormality determination of the differential pressure sensor is prohibited, while when the engine speed is less than the predetermined rotation speed, the differential pressure sensor is prohibited. Further has a step of permitting the execution of the abnormality determination of.
According to the present invention configured in this way, the abnormality determination of the differential pressure sensor is executed only when the engine speed is less than the predetermined speed, that is, only in the low speed region, and the exhaust flow rate is large and the influence of pulsation. Since the execution of the abnormality determination is prohibited in the high rotation speed region where the value is large, the accuracy of the abnormality determination can be appropriately ensured.

In another aspect, in order to achieve the above object, the present invention is an engine control system provided on the engine and an EGR passage that recirculates the exhaust gas of the engine to an intake passage. It has an EGR valve, a differential pressure sensor that detects the differential pressure between the upstream side and the downstream side of the EGR valve, and a controller that is composed of a circuit and is configured to at least control the engine. , The controller controls the opening of the EGR valve based on the output value of the differential pressure sensor, and by controlling the opening of the EGR valve, the total amount of gas and the amount of fuel in the combustion chamber including the EGR gas from the EGR passage are combined. In a state where the gas recirculation ratio G / F, which is the ratio of Instead, the second combustion mode is executed in which the air-fuel mixture in the combustion chamber of the engine is spark-ignited and burned by spark ignition, an abnormality of the differential pressure sensor is determined based on the output value of the differential pressure sensor, and an abnormality of the differential pressure sensor is determined. The throttle valve of the engine is controlled to the closed side so that the differential pressure between the upstream side and the downstream side of the EGR valve is maintained at a predetermined pressure or higher, and the differential pressure sensor is determined to be abnormal. At that time, the EGR valve is controlled to be closed to stop the recirculation of the EGR gas from the EGR passage to the intake passage of the engine, and when the first combustion mode is being executed, this first combustion mode is set. It is configured to control switching to the second combustion mode.
Also according to the present invention configured in this way, it is possible to accurately determine the abnormality of the differential pressure sensor and appropriately suppress the deterioration of fuel consumption when the differential pressure sensor is abnormal.

According to the present invention, in the control method and control system of an engine having a differential pressure sensor that detects the differential pressure between the upstream side and the downstream side of the EGR valve, the abnormality determination of the differential pressure sensor is accurately performed and the differential pressure sensor is performed. It is possible to appropriately suppress the deterioration of fuel efficiency at the time of abnormalities.

It is a schematic block diagram of the compression ignition type engine by embodiment of this invention. It is sectional drawing of the combustion chamber of the compression ignition type engine by embodiment of this invention. It is a block diagram which shows the control system of the compression ignition type engine by embodiment of this invention. It is explanatory drawing of the operating area of the engine by embodiment of this invention. It is explanatory drawing about the relationship between the pressure ratio of the upstream side and the downstream side of an EGR valve, and a stream function value. It is explanatory drawing about the relationship between the pressure detection error by a differential pressure sensor and the flow rate estimation error. It is a flowchart which shows the control process of the throttle valve and the air bypass valve by embodiment of this invention. It is a flowchart which shows the abnormality determination process of the differential pressure sensor by embodiment of this invention. It is a map that defines the judgment threshold value to be set for the engine speed. It is a time chart which shows the result when the abnormality determination of the differential pressure sensor by embodiment of this invention is performed. It is a time chart which shows the result at the time of performing the engine control at the time of abnormality determination of the differential pressure sensor by embodiment of this invention.

Hereinafter, an engine control method and a control system according to an embodiment of the present invention will be described with reference to the accompanying drawings.

<Device configuration>
First, the engine control method and the configuration of the control system according to the embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a diagram illustrating a configuration of a compression ignition type engine according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating the configuration of the combustion chamber of the compression ignition type engine according to the embodiment of the present invention. The intake side in FIG. 1 is on the left side of the paper, and the exhaust side is on the right side of the paper. The intake side in FIG. 2 is on the right side of the paper, and the exhaust side is on the left side of the paper. FIG. 3 is a block diagram showing a control system of a compression ignition type engine according to an embodiment of the present invention.

In the present embodiment, the engine 1 is a gasoline engine that is mounted on a four-wheeled automobile and performs partial compression ignition combustion (SPark Controlled Compression Ignition: SPCCI). Specifically, the engine 1 includes a cylinder block 12 and a cylinder head 13 mounted on the cylinder block 12. A plurality of cylinders 11 are formed inside the cylinder block 12. Although only one cylinder 11 is shown in FIGS. 1 and 2, the engine 1 is a multi-cylinder engine in the present embodiment.

A piston 3 is slidably inserted in each cylinder 11. The piston 3 is connected to the crankshaft 15 via a connecting rod 14. The piston 3 partitions the combustion chamber 17 together with the cylinder 11 and the cylinder head 13. The "combustion chamber" is not limited to the meaning of the space formed when the piston 3 reaches the compression top dead center. The term "combustion chamber" may be used in a broad sense. That is, the "combustion chamber" may mean a space formed by the piston 3, the cylinder 11, and the cylinder head 13 regardless of the position of the piston 3.

As shown in FIG. 2, the upper surface of the piston 3 is a flat surface. A cavity 31 is formed on the upper surface of the piston 3. The cavity 31 is recessed from the upper surface of the piston 3. The cavity 31 has a shallow dish shape. The cavity 31 faces the injector 6, which will be described later, when the piston 3 is located near the compression top dead center.

The cavity 31 has a convex portion 31a. The convex portion 31a is provided substantially at the center of the cylinder 11. The convex portion 31a has a substantially conical shape and extends upward from the bottom of the cavity 31 along the central axis X of the cylinder 11. The upper end of the convex portion 31a is substantially the same height as the upper surface of the cavity 31. The cavity 31 also has a recessed portion 31b provided around the convex portion 31a.

As shown in FIG. 2, the lower surface of the cylinder head 13, that is, the ceiling surface of the combustion chamber 17, is composed of an inclined surface 13a and an inclined surface 13b. The inclined surface 13a has an upward slope from the intake side toward the axis X. The inclined surface 13b has an upward slope from the exhaust side toward the axis X. The ceiling surface of the combustion chamber 17 has a so-called pent roof shape.
The shape of the combustion chamber 17 is not limited to the shape illustrated in FIG. For example, the shape of the cavity 31, the shape of the upper surface of the piston 3, the shape of the ceiling surface of the combustion chamber 17, and the like can be changed as appropriate.

The geometric compression ratio of the engine 1 is set high for the purpose of improving the theoretical thermal efficiency and stabilizing the CI (Compression Ignition) combustion described later. Specifically, the geometric compression ratio of the engine 1 is 17 or more. The geometric compression ratio may be 18, for example. The geometric compression ratio may be appropriately set in the range of 17 or more and 20 or less.

The cylinder head 13 is formed with two intake ports 18 (FIG. 1) for each cylinder 11. The intake port 18 communicates with the combustion chamber 17. An intake valve 21 is provided at the intake port 18. The intake valve 21 opens and closes between the combustion chamber 17 and the intake port 18. The intake valve 21 is opened and closed at a predetermined timing by an intake VVT (Variable Valve Timing) 23 (FIG. 3), which is a variable valve mechanism. The intake VVT 23 is configured to continuously change the rotational phase of the intake camshaft within a predetermined angle range. Thereby, the valve opening timing and the valve closing timing of the intake valve 21 can be continuously changed. The intake VVT 23 is configured to be driven electrically or hydraulically.

The cylinder head 13 is also formed with two exhaust ports 19 (FIG. 1) for each cylinder 11. The exhaust port 19 communicates with the combustion chamber 17. An exhaust valve 22 is provided at the exhaust port 19. The exhaust valve 22 opens and closes between the combustion chamber 17 and the exhaust port 19. The exhaust valve 22 is opened and closed at a predetermined timing by the exhaust electric VVT 24 (FIG. 3), which is a variable valve mechanism. The exhaust VVT 24 is configured to continuously change the rotational phase of the exhaust camshaft within a predetermined angular range. Thereby, the valve opening timing and the valve closing timing of the exhaust valve 22 can be continuously changed. The exhaust VVT 24 is configured to be driven electrically or hydraulically.

Although the details will be described later, in the present embodiment, the engine 1 can adjust the length of the overlap period related to the opening of the intake valve 21 and the opening of the exhaust valve 22 by the intake VVT23 and the exhaust VVT24. .. As a result, the residual gas in the combustion chamber 17 is scavenged, and the hot burned gas is confined in the combustion chamber 17 (that is, the internal EGR (Exhaust Gas Recirculation) gas is introduced into the combustion chamber 17). be able to. It should be noted that the introduction of such an internal EGR gas is not limited to the realization by VVT.

As shown in FIG. 2, an injector 6 is attached to the cylinder head 13 for each cylinder 11. The injector 6 is configured to inject fuel directly into the combustion chamber 17. The injector 6 is arranged at a valley portion of the pent roof where the inclined surface 13a on the intake side and the inclined surface 13b on the exhaust side intersect. Further, the injector 6 is arranged so that its injection axis is along the central axis X of the cylinder 11. The injection axis of the injector 6 and the position of the convex portion 31a of the cavity 31 substantially coincide with each other. The injector 6 faces the cavity 31. The injection axis of the injector 6 does not have to coincide with the central axis X of the cylinder 11. Even in that case, it is desirable that the injection axis of the injector 6 and the position of the convex portion 31a of the cavity 31 coincide with each other.

Although detailed illustration is omitted, the injector 6 is composed of a multi-injection type fuel injection valve having a plurality of injection ports. The injector 6 injects fuel so that the fuel spray spreads radially from the center of the combustion chamber 17, as shown by an arrow in FIG.

As will be described later, the injector 6 may inject fuel at a timing when the piston 3 is located near the compression top dead center. In that case, when the injector 6 injects fuel, the fuel spray flows downward along the convex portion 31a of the cavity 31 while mixing with the fresh air, and also flows downward along the bottom surface and the peripheral side surface of the concave portion 31b. It spreads radially outward from the center of 17 and flows. After that, the air-fuel mixture reaches the opening of the cavity 31 and flows from the outer side in the radial direction toward the center of the combustion chamber 17 along the inclined surface 13a on the intake side and the inclined surface 13b on the exhaust side.
The injector 6 is not limited to the multi-injection type injector. As the injector 6, an externally open valve type injector may be adopted.

As shown in FIG. 1, a fuel supply system 61 is connected to the injector 6. The fuel supply system 61 includes a fuel tank 63 configured to store fuel, and a fuel supply path 62 that connects the fuel tank 63 and the injector 6 to each other. A fuel pump 65 and a common rail 64 are provided in the fuel supply path 62. The fuel pump 65 is configured to pump fuel to the common rail 64. In the present embodiment, the fuel pump 65 is a plunger type pump driven by the crankshaft 15. The common rail 64 is configured to store the fuel pumped from the fuel pump 65 at a high fuel pressure. When the injector 6 opens, the fuel stored in the common rail 64 is injected into the combustion chamber 17 from the injection port of the injector 6. The fuel supply system 61 is configured to be able to supply fuel having a high pressure of 30 MPa or more to the injector 6. The maximum fuel pressure of the fuel supply system 61 may be, for example, about 120 MPa. The pressure of the fuel supplied to the injector 6 may be changed according to the operating state of the engine 1. The configuration of the fuel supply system 61 is not limited to the above configuration.

A spark plug 25 is attached to the cylinder head 13 for each cylinder 11. The spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17. As shown in FIG. 2, in the present embodiment, the spark plug 25 is arranged on the intake side of the cylinder 11 with the central axis X in between. The spark plug 25 is located between the two intake ports 18. The spark plug 25 is attached to the cylinder head 13 so as to be inclined from the upper side to the lower side toward the center of the combustion chamber 17. The electrodes of the spark plug 25 face the combustion chamber 17 and are located near the ceiling surface of the combustion chamber 17.

As shown in FIG. 1, an intake passage 40 is connected to one side surface of the engine 1. The intake passage 40 communicates with the intake port 18 of each cylinder 11. The intake passage 40 is a passage through which the gas introduced into the combustion chamber 17 flows. An air cleaner 41 for filtering fresh air is disposed at the upstream end of the intake passage 40. A surge tank 42 is arranged near the downstream end of the intake passage 40. The intake passage 40 downstream of the surge tank 42 constitutes an independent passage that branches for each cylinder 11, although detailed illustration is omitted. The downstream end of the independent passage is connected to the intake port 18 of each cylinder 11.

A throttle valve 43 is provided between the air cleaner 41 and the surge tank 42 in the intake passage 40. The throttle valve 43 is configured to adjust the amount of fresh air introduced into the combustion chamber 17 by adjusting the opening degree of the valve.

In the intake passage 40, a supercharger 44 is also arranged downstream of the throttle valve 43. The supercharger 44 is configured to supercharge the gas to be introduced into the combustion chamber 17. In the present embodiment, the supercharger 44 is a mechanical supercharger driven by the engine 1. The mechanical turbocharger 44 may be, for example, a roots type. The configuration of the mechanical turbocharger 44 may be any configuration. The mechanical turbocharger 44 may be a Rishorum type or a centrifugal type.

An electromagnetic clutch 45 is interposed between the supercharger 44 and the output shaft of the engine 1. The electromagnetic clutch 45 transmits a driving force from the engine 1 to the supercharger 44 or cuts off the transmission of the driving force between the supercharger 44 and the engine 1. As will be described later, when the ECU 10 (FIG. 3) switches between the connected state and the non-connected state of the electromagnetic clutch 45, the supercharger 44 is switched on and off. That is, the engine 1 can switch between supercharging the gas introduced into the combustion chamber 17 by the supercharger 44 and not supercharging the gas introduced into the combustion chamber 17 by the supercharger 44. It is configured so that it can be done.

An intercooler 46 is arranged downstream of the supercharger 44 in the intake passage 40. The intercooler 46 is configured to cool the compressed gas in the turbocharger 44. The intercooler 46 may be configured to be water-cooled, for example.

A bypass passage 47 is connected to the intake passage 40. The bypass passage 47 connects the upstream portion of the supercharger 44 and the downstream portion of the intercooler 46 in the intake passage 40 to each other so as to bypass the supercharger 44 and the intercooler 46. An air bypass valve 48, which is a bypass control valve, is provided in the bypass passage 47. The air bypass valve 48 adjusts the flow rate of gas flowing through the bypass passage 47.

When the supercharger 44 is turned off (that is, when the electromagnetic clutch 45 is disengaged), the air bypass valve 48 is fully opened. As a result, the gas flowing through the intake passage 40 bypasses the supercharger 44 and is introduced into the combustion chamber 17 of the engine 1. The engine 1 operates in a non-supercharged state, that is, in a naturally aspirated state.
When the turbocharger 44 is turned on (that is, when the electromagnetic clutch 45 is connected), a part of the gas that has passed through the turbocharger 44 flows back to the upstream of the turbocharger through the bypass passage 47. .. Since the reverse flow rate can be adjusted by adjusting the opening degree of the air bypass valve 48, the boost pressure of the gas introduced into the combustion chamber 17 can be adjusted. In this configuration example, the supercharging system 49 is configured by the supercharger 44, the bypass passage 47, and the air bypass valve 48.

An exhaust passage 50 is connected to the other side surface of the engine 1. The exhaust passage 50 communicates with the exhaust port 19 of each cylinder 11. The exhaust passage 50 is a passage through which the exhaust gas discharged from the combustion chamber 17 flows. Although detailed illustration is omitted, the upstream portion of the exhaust passage 50 constitutes an independent passage that branches for each cylinder 11. The upstream end of the independent passage is connected to the exhaust port 19 of each cylinder 11. An exhaust gas purification system having one or more catalytic converters 51 is arranged in the exhaust passage 50. The catalyst converter 51 is configured to include a three-way catalyst. The exhaust gas purification system is not limited to the one containing only the three-way catalyst.

An EGR passage 52 constituting an external EGR system is connected between the intake passage 40 and the exhaust passage 50. The EGR passage 52 is a passage for returning a part of the burnt gas to the intake passage 40. The upstream end of the EGR passage 52 is connected to the downstream of the catalytic converter 51 in the exhaust passage 50. The downstream end of the EGR passage 52 is connected to the upstream of the turbocharger 44 in the intake passage 40.

A water-cooled EGR cooler 53 is provided in the EGR passage 52. The EGR cooler 53 is configured to cool the burnt gas. An EGR valve 54 is also provided in the EGR passage 52. The EGR valve 54 is configured to regulate the flow rate of the burnt gas flowing through the EGR passage 52. By adjusting the opening degree of the EGR valve 54, the recirculation amount of the cooled burnt gas, that is, the external EGR gas can be adjusted.

In the present embodiment, the EGR system 55 is composed of an external EGR system including an EGR passage 52 and an EGR valve 54, and an internal EGR system including the above-mentioned intake VVT23 and exhaust VVT24. ing. The EGR valve 54 also constitutes one of the state quantity setting devices.

As shown in FIG. 3, the engine 1 includes an ECU (Electronic Control Unit) 10 for operating the engine 1. The ECU 10 is a controller based on a well-known microcomputer, and includes a microprocessor 10a as a central processing unit (CPU) for executing a program, and for example, a RAM (Random Access Memory) or a ROM (Read Only). It is composed of a Memory) and includes a memory 10b for storing programs and data, an input / output bus for inputting / outputting electric signals, and the like. The ECU 10 is an example of a controller.

As shown in FIGS. 1 and 3, various sensors SW1 to SW17 are connected to the ECU 10. The sensors SW1 to SW17 output a detection signal to the ECU 10. The sensors include the following sensors.

That is, the air flow sensor SW1 which is arranged downstream of the air cleaner 41 in the intake passage 40 and detects the flow rate of fresh air flowing through the intake passage 40, the first intake air temperature sensor SW2 which detects the temperature of the fresh air, and the intake passage. The pressure of the gas that is located downstream of the connection position of the EGR passage 52 in 40 and upstream of the supercharger 44 and flows into the supercharger 44 (hereinafter, also appropriately referred to as "supercharger upstream pressure"). The first pressure sensor SW3 for detecting the temperature of the gas flowing out from the supercharger 44 is located downstream of the supercharger 44 in the intake passage 40 and upstream of the connection position of the bypass passage 47. 2 Intake temperature sensor SW4, second pressure sensor SW5, which is attached to the surge tank 42 and detects the pressure of gas downstream of the supercharger 44 (hereinafter, appropriately referred to as "supercharging pressure"), to each cylinder 11. Correspondingly, the finger pressure sensor SW6, which is attached to the cylinder head 13 and detects the pressure (in-cylinder pressure) in each combustion chamber 17, is arranged in the exhaust passage 50 and detects the temperature of the exhaust gas discharged from the combustion chamber 17. Exhaust temperature sensor SW7, linear O ₂ sensor SW8 (linear A / F sensor: LAFS) that detects the oxygen concentration in the exhaust gas discharged from the combustion chamber 17, and the output shaft located near the output shaft of the engine 1. Engine rotation speed sensor SW9 that detects the rotation speed of the engine, water temperature sensor SW10 that is attached to the engine 1 and detects the temperature of the cooling water, crank angle sensor SW11 that is attached to the engine 1 and detects the rotation angle of the crank shaft 15. , The accelerator opening sensor SW12 attached to the accelerator pedal mechanism and detecting the accelerator opening corresponding to the operation amount of the accelerator pedal, and the intake cam angle sensor SW13 attached to the engine 1 and detecting the rotation angle of the intake cam shaft. The exhaust cam angle sensor SW14, which is attached to the engine 1 and detects the rotation angle of the exhaust cam shaft, and the EGR differential pressure sensor SW15, which is arranged in the EGR passage 52 and detects the differential pressure upstream and downstream of the EGR valve 54, A fuel pressure sensor SW16 that is attached to the common rail 64 of the fuel supply system 61 and detects the pressure of the fuel supplied to the injector 6, and an atmospheric pressure sensor SW17 (typically provided in the ECU 10) that detects the atmospheric pressure. is there.

Based on these detection signals, the ECU 10 determines the operating state of the engine 1 and calculates the control amount of each device. The ECU 10 outputs a control signal related to the calculated control amount to the injector 6, the spark plug 25, the intake VVT23, the exhaust VVT24, the fuel supply system 61, the throttle valve 43, the EGR valve 54, the electromagnetic clutch 45 of the supercharger 44, and , Output to the air bypass valve 48 to control the engine 1. For example, the ECU 10 adjusts the opening degree of the air bypass valve 48 based on the front-rear differential pressure of the supercharger 44 obtained from the detection signals of the first pressure sensor SW3 and the second pressure sensor SW5 to adjust the boost pressure. adjust. Further, the ECU 10 adjusts the opening degree of the EGR valve 54 based on the front-rear differential pressure of the EGR valve 54 obtained from the detection signal of the EGR differential pressure sensor SW15 (hereinafter, also simply referred to as “differential pressure sensor SW15”). The amount of external EGR gas introduced into the combustion chamber 17 is adjusted accordingly.

<Driving area>
Next, the operating region of the engine according to the embodiment of the present invention will be described with reference to FIG. 4 (A) to 4 (C) are operation maps for explaining the difference in control according to the progress of warming up of the engine 1 and the rotation speed / load of the engine 1. In the present embodiment, when the warm-up of the engine 1 is completed (for example, when "engine water temperature ≥ 80 ° C" or "intake air temperature ≥ 50 ° C"), and when the engine 1 is warmed up halfway, it is semi-warm. During operation (for example, when "30 ° C. ≤ engine water temperature <80 ° C." and "25 ° C. ≤ intake air temperature <50 ° C.") and when engine 1 is unwarmed (for example, "engine water temperature <30 ° C.") In addition, different operation maps are prepared corresponding to the three stages of "when the intake air temperature is <25 ° C.").

First, the combustion control when the engine 1 is cold will be described with reference to FIG. 4 (A). When it is cold, relatively orthodox SI (Spark Ignition) combustion is performed in the region R1 corresponding to almost the entire operating region of the engine 1. SI combustion is a form in which the air-fuel mixture is ignited by spark ignition using a spark plug 25, and the air-fuel mixture is forcibly burned by flame propagation that expands the combustion region from the ignition point to the surroundings. The SI combustion corresponds to the "second combustion mode" of the engine 1.

In order to realize such SI combustion, the main components of the engine 1 are controlled by the ECU 10 as follows. The injector 6 injects the injection for at least a predetermined period of time that overlaps with the intake stroke. For example, the injector 6 injects fuel over a series of periods from the intake stroke to the compression stroke. Further, the spark plug 25 ignites the air-fuel mixture near the compression top dead center. For example, the spark plug 25 ignites the air-fuel mixture at a timing slightly on the advance angle side of the compression top dead center. Then, SI combustion is started triggered by this ignition, and all of the air-fuel mixture in the combustion chamber 17 is burned by flame propagation. The opening degree of the EGR valve 54 is controlled so that the air-fuel ratio A / F, which is the ratio of the amount of air and the amount of fuel in the combustion chamber 17, is substantially the stoichiometric air-fuel ratio (14.7).

Next, with reference to FIG. 4B, combustion control during semi-warming of the engine 1 will be described. At the time of semi-warm-up, SI combustion is executed in the region R2 as in the region R1 at the time of cold. On the other hand, in the region R3, partial compression ignition combustion (SPCCI combustion) in which SI combustion and CI combustion are mixed is executed. CI combustion is a form in which the air-fuel mixture is burned by self-ignition in an environment where the temperature and pressure are increased by the compression of the piston 3. In SPCCI combustion, which is a mixture of SI combustion and CI combustion, a part of the air-fuel mixture in the combustion chamber 17 is SI-combusted by spark ignition performed in an environment just before the air-fuel mixture self-ignites, and the SI combustion is performed. This is a combustion mode in which the remaining air-fuel mixture in the combustion chamber 17 is CI-combusted by self-ignition (due to further increase in temperature and pressure accompanying SI combustion).

SPCCI combustion has the property that the heat generation during CI combustion is steeper than the heat generation during SI combustion. For example, in the waveform of the heat generation rate due to SPCCI combustion, the slope of the rise at the initial stage of combustion corresponding to SI combustion becomes smaller than the slope of the rise that occurs corresponding to the subsequent CI combustion. In other words, the waveform of the heat generation rate during SPCCI combustion is the heat generation rate part formed by SI combustion with a relatively small rising slope and the heat generation formed by CI combustion with a relatively large rising slope. The portions are formed so as to be continuous in this order. Further, in response to such a tendency of the heat generation rate, in SPCCI combustion, the pressure increase rate (dp / dθ) in the combustion chamber 17 generated during SI combustion becomes smaller than that during CI combustion.

When the temperature and pressure in the combustion chamber 17 increase due to SI combustion, the unburned air-fuel mixture self-ignites and CI combustion is started. At the timing of this self-ignition (that is, the timing at which CI combustion starts), the slope of the waveform of the heat generation rate changes from small to large. That is, the waveform of the heat generation rate in SPCCI combustion has an inflection point that appears at the timing when CI combustion starts.

After the start of CI combustion, SI combustion and CI combustion are performed in parallel. Since the combustion speed of the air-fuel mixture is faster in CI combustion than in SI combustion, the heat generation rate is relatively large. However, since CI combustion is performed after the compression top dead center, the slope of the heat generation rate waveform does not become excessive. That is, when the compression top dead center is passed, the motoring pressure decreases due to the lowering of the piston 3, and as a result of suppressing the increase in the heat generation rate, it is possible to prevent the dp / dθ during CI combustion from becoming excessive. To. In this way, in SPCCI combustion, CI combustion is performed after SI combustion, so that dp / dθ, which is an index of combustion noise, is unlikely to become excessive, and simple CI combustion (when all fuels are CI-combusted). ), Combustion noise can be suppressed.

With the end of CI combustion, SPCCI combustion also ends. Since CI combustion has a faster combustion rate than SI combustion, the combustion end time can be earlier than that of simple SI combustion (when all fuels are SI-combusted). In other words, in SPCCI combustion, the combustion end time can be brought closer to the compression top dead center within the expansion stroke. As a result, in SPCCI combustion, fuel efficiency can be improved as compared with simple SI combustion.

In particular, in the region R3 shown in FIG. 4B, the air-fuel ratio in the combustion chamber 17 is set to substantially the stoichiometric air-fuel ratio (14.7), and SPCCI combustion (hereinafter, appropriately referred to as “first SPCCI combustion”). The first SPCCI combustion corresponds to the "first combustion mode" of the engine 1). In other words, in the region R3, SPCCI combustion is performed in a stoichiometric environment (λ≈1) in which the excess air ratio λ (value obtained by dividing the actual air-fuel ratio by the stoichiometric air-fuel ratio) is 1 or its vicinity.

In such a region R3, the main components of the engine 1 are controlled by the ECU 10 as follows. The injector 6 advances the injection timing of at least a part of the fuel to the intake stroke. For example, the injector 6 executes the first fuel injection during the intake stroke and the second fuel injection during the compression stroke. The spark plug 25 ignites the air-fuel mixture near the compression top dead center. For example, the spark plug 25 ignites the air-fuel mixture at a timing slightly on the advance angle side of the compression top dead center. Further, the spark plug 25 ignites the air-fuel mixture at a timing on the advance side of the SI combustion described above. Then, SPCCI combustion is started triggered by this ignition, a part of the air-fuel mixture in the combustion chamber 17 is burned by flame propagation (SI combustion), and then the remaining air-fuel mixture is burned by self-ignition (CI combustion). ..

In the intake VVT 23 and the exhaust VVT 24, the valve timings of the intake valve 21 and the exhaust valve 22 are set to the timing for performing the internal EGR, that is, both the intake valve 21 and the exhaust valve 22 are opened across the exhaust top dead point. Set the timing so that the valve overlap period is sufficiently formed. As a result, an internal EGR that leaves burned gas in the combustion chamber 17 is realized, and the temperature of the combustion chamber 17 (initial temperature before compression) is raised. Specifically, in the region R3, the intake VVT 23 closes the intake valve 21 at a timing earlier than SI combustion, and the exhaust VVT 24 closes the exhaust valve 22 at a timing later than SI combustion. The throttle valve 43 is closed to a predetermined intermediate opening degree, and the entire air-fuel ratio A / F in the combustion chamber 17 is set to substantially the stoichiometric air-fuel ratio.

The opening degree of the EGR valve 54 is controlled so that the entire air-fuel ratio in the combustion chamber 17 becomes the target air-fuel ratio. Basically, the EGR valve 54 is left in the combustion chamber 17 by the amount of air corresponding to the target air-fuel ratio (A / F≈14.7) and the internal EGR from the total amount of gas introduced into the combustion chamber 17. The flow rate in the EGR passage 52 is adjusted so that the amount of gas excluding the amount of the burned gas to be discharged is returned from the EGR passage 52 to the combustion chamber 17 as the external EGR gas. Here, in the region R3, the air-fuel ratio (A / F) is set to substantially the stoichiometric air-fuel ratio as described above, and EGR gas (external EGR gas and internal EGR gas) is introduced into the combustion chamber 17. The gas air-fuel ratio G / F, which is the ratio of the total amount of gas in the combustion chamber 17 containing EGR gas to the amount of fuel, is lean (a value exceeding 14.7) larger than the stoichiometric air-fuel ratio, for example, 35 to 45. ).

Next, with reference to FIG. 4C, the combustion control of the engine 1 when it is warm will be described. In the warm state, SI combustion is executed in the region R4 as in the cold region R1 and the semi-warm region R2, and in the region R5, the SPCCI combustion is performed as in the semi-warm region R3. Will be executed. However, in the region R5, the gas-fuel ratio G / F is not set to lean like the region R3. On the other hand, in the region R6, unlike the region R3 and the region R5, the air-fuel ratio A / F in the combustion chamber 17 is set to a value larger than the theoretical air-fuel ratio (14.7), and SPCCI combustion (hereinafter, "second SPCCI"). It is called "combustion". This second SPCCI combustion corresponds to the "third combustion mode" of the engine 1). In other words, in the region R6, SPCCI combustion is performed in an air-fuel ratio lean environment (λ> 1) in which the excess air ratio λ is larger than 1. In one example, the excess air ratio λ is set to 2 or more.

In such a region R6, the main components of the engine 1 are controlled by the ECU 10 as follows. The injector 6 injects all or most of the fuel to be injected during one cycle during the compression stroke. For example, the injector 6 injects fuel in two steps from the middle to the latter half of the compression stroke. The spark plug 25 ignites the air-fuel mixture near the compression top dead center. For example, the spark plug 25 ignites the air-fuel mixture at a timing slightly ahead of the compression top dead center (timing on the advance side of SI combustion). Then, SPCCI combustion is started triggered by this ignition, a part of the air-fuel mixture in the combustion chamber 17 is burned by flame propagation (SI combustion), and then the remaining air-fuel mixture is burned by self-ignition (CI combustion). ..

The intake VVT 23 and the exhaust VVT 24 are the timings for performing the internal EGR for the valve timings of the intake valve 21 and the exhaust valve 22, that is, the valves in which both the intake valve 21 and the exhaust valve 22 are opened across the exhaust top dead point. Set the timing so that the overlap period is sufficiently formed. As a result, an internal EGR that leaves burned gas in the combustion chamber 17 is realized, and the temperature of the combustion chamber 17 (initial temperature before compression) is raised. Specifically, in the region R6, the intake VVT 23 closes the intake valve 21 at a timing earlier than SI combustion, and the exhaust VVT 24 closes the exhaust valve 22 at a timing later than SI combustion. The throttle valve 43 is opened to an opening degree corresponding to full opening, and the overall air-fuel ratio (A / F) in the combustion chamber 17 is set to 30 to 40.

<Abnormality judgment of differential pressure sensor>
Hereinafter, an abnormality determination method of the differential pressure sensor (EGR differential pressure sensor) SW15 according to the embodiment of the present invention and a control method of the engine 1 related to the abnormality determination will be described.

First, with reference to FIGS. 5 and 6, the basic concept of the abnormality determination method of the differential pressure sensor SW15 according to the embodiment of the present invention will be described. The horizontal axis of FIG. 5 shows the ratio (pressure ratio) of the pressure on the upstream side and the pressure on the downstream side of the EGR valve 54. The value of this pressure ratio becomes smaller as the pressure on the downstream side of the EGR valve 54 becomes lower than the pressure on the upstream side of the EGR valve 54 (that is, as the negative pressure becomes larger). Further, the vertical axis of FIG. 5 is defined according to the pressure ratio between the upstream side and the downstream side of the EGR valve 54, and the flow rate flowing through the EGR valve 54 (that is, the EGR gas recirculated from the EGR passage 52 to the intake passage 40). The value of the flow rate function, which is an index indicating the flow rate of), is shown. The flow rate flowing through the EGR valve 54 is proportional to this flow rate function. Further, in FIG. 5, the solid line shows the graph when there is no exhaust pulsation, the broken line shows the graph when there is exhaust pulsation of about ± 2.5 kPa, and the alternate long and short dash line is the graph when there is exhaust pulsation of about ± 5 kPa. Is shown.

Further, in FIG. 6, the horizontal axis shows the pressure detection error [%] by the differential pressure sensor SW15, and the vertical axis shows the error [%] when the flow rate flowing through the EGR valve 54 is estimated using the above flow rate function. (Flow rate estimation error) is shown. In FIG. 6, the solid line shows the graph when the negative pressure is 5 kPa, and the broken line shows the graph when the negative pressure is 2 kPa. The negative pressure referred to here is basically synonymous with the differential pressure between the upstream side and the downstream side of the EGR valve 54. That is, the negative pressure is the pressure at the upstream end of the EGR passage 52 (the pressure of the exhaust passage 50 on the downstream side of the catalytic converter 51, which basically corresponds to the atmospheric pressure) at the downstream end of the EGR passage 52. (It is the pressure of the intake passage 40 on the downstream side of the throttle valve 43 and on the upstream side of the supercharger 44).

As shown in FIG. 5, when the negative pressure is 2 kPa (in this case, the pressure ratio is 0.98 when the atmospheric pressure is 100 kPa), the magnitude of the influence of the exhaust pulsation on the flow rate of the EGR gas is large. Is about 40% (see arrow A1), whereas when the negative pressure is 5 kPa (in this case, the pressure ratio is 0.95 when the atmospheric pressure is 100 kPa), the flow rate of the EGR gas is increased. The magnitude of the effect of exhaust pulsation is about 8%. That is, when the negative pressure is 5 kPa, it is hardly affected by the exhaust pulsation as compared with the case where the negative pressure is 2 kPa. Further, as shown in FIG. 6, for example, when the pressure detection error by the differential pressure sensor SW15 is 1 kPa, the flow rate estimation error is about 30% when the negative pressure is 2 kPa, whereas it is negative. When the pressure is 5 kPa, the flow rate estimation error is about 10%. That is, when the negative pressure is 5 kPa, the influence of the pressure detection error on the flow rate estimation is considerably smaller than when the negative pressure is 2 kPa. This is because the larger the negative pressure, the larger the absolute value of the stream function and the gentler the slope of the stream function, so that the influence of the pressure detection error becomes smaller.

From the above, it can be said that the influence of exhaust pulsation becomes small when the differential pressure between the upstream side and the downstream side of the EGR valve 54 is relatively large, specifically, when the differential pressure is 5 kPa or more. When the influence of the exhaust pulsation is reduced in this way, the accuracy of the abnormality determination of the differential pressure sensor SW15 can be ensured. Therefore, in the present embodiment, the differential pressure between the upstream side and the downstream side of the EGR valve 54 is relatively large. Occasionally, it was decided to determine the abnormality of the differential pressure sensor SW15. Here, if the abnormality determination is performed only in the situation where the differential pressure becomes large depending on the operating state of the engine 1, the execution frequency of the abnormality determination decreases. Therefore, when determining the abnormality of the differential pressure sensor SW15, it is sufficient to generate a large differential pressure between the upstream side and the downstream side of the EGR valve 54, but if this differential pressure is made too large, fuel consumption will be reduced. It tends to get worse.

Therefore, in the present embodiment, the ECU 10 controls to generate a differential pressure of 5 kPa between the upstream side and the downstream side of the EGR valve 54 when determining the abnormality of the differential pressure sensor SW15. .. Specifically, the ECU 10 maintains at least a throttle valve in order to maintain the differential pressure between the upstream side and the downstream side of the EGR valve 54 at 5 kPa (hereinafter, such a differential pressure is appropriately referred to as a "target differential pressure"). The 43 is controlled to the closed side. Specifically, the ECU 10 refers to the pressure of the intake passage 40 on the downstream side of the throttle valve 43 and on the upstream side of the turbocharger 44, which is necessary for achieving the target differential pressure (hereinafter, appropriately “target turbocharger upstream pressure””. ) Is set, and the opening degree of the throttle valve 43 is feedback-controlled based on this target turbocharger upstream pressure.

Next, with reference to FIG. 7, the control of the throttle valve 43 and the air bypass valve 48 when determining the abnormality of the differential pressure sensor SW15 will be specifically described in the embodiment of the present invention. FIG. 7 is a flowchart showing a control process of the throttle valve 43 and the air bypass valve 48 according to the embodiment of the present invention. The process according to this flowchart is repeatedly executed by the ECU 10 at a predetermined cycle when an execution request for abnormality determination of the differential pressure sensor SW15 is issued.

First, in step S11, the ECU 10 acquires various information from the sensors SW1 to SW17 (see FIGS. 1 and 3) described above. Typically, the ECU 10 acquires the supercharger upstream pressure detected by the first pressure sensor SW3, the supercharging pressure detected by the second pressure sensor SW5, and the atmospheric pressure detected by the atmospheric pressure sensor SW17. ..

Next, in step S12, the ECU 10 obtains a target boost pressure to be set by the supercharger 44. Basically, the ECU 10 is detected by the current air amount of the engine 1, the target air amount to be supplied to the engine 1 in response to a request from the driver (accelerator pedal operation), and the second pressure sensor SW5. Set the target boost pressure based on the current boost pressure. Specifically, the ECU 10 obtains the target boost pressure required to supply the target air amount to the engine 1 from the current air amount and the current boost pressure. Further, the ECU 10 sets the target boost pressure in consideration of the current amount of EGR gas. For example, when the EGR gas amount increases, the ECU 10 is controlled to keep the air amount constant, and as a result, the boost pressure rises. Therefore, the ECU 10 adjusts the target boost pressure with respect to the target air amount accordingly. To.

Next, in step S13, the ECU 10 controls the air bypass valve 48 so as to realize the target boost pressure set in step S12. Specifically, the ECU 10 compares the current boost pressure (actual boost pressure) detected by the second pressure sensor SW5 with the target boost pressure, and the actual boost pressure matches the target boost pressure. The opening degree of the air bypass valve 48 is feedback-controlled so as to be performed.

On the other hand, in parallel with the processes of steps S12 and S13 described above, the ECU 10 performs the processes of steps S14 and S15. First, in step S14, the ECU 10 sets the turbocharger upstream pressure (target turbocharger upstream pressure) required to set the differential pressure between the upstream side and the downstream side of the EGR valve 54 to the target differential pressure (5 kPa). Ask. Specifically, the ECU 10 uses the atmospheric pressure (about 100 kpa) detected by the atmospheric pressure sensor SW17 as the pressure on the upstream side of the EGR valve 54, and supercharges the atmospheric pressure and the pressure on the downstream side of the EGR valve 54. Since the difference from the upstream pressure of the machine may be 5 kPa, the ECU 10 sets the pressure obtained by subtracting 5 kPa from the atmospheric pressure as the target upstream pressure of the supercharger.

Next, in step S15, the ECU 10 controls the throttle valve 43 so as to realize the target turbocharger upstream pressure set in step S14. Specifically, the ECU 10 compares the current turbocharger upstream pressure (actual turbocharger upstream pressure) detected by the first pressure sensor SW3 with the target turbocharger upstream pressure, and compares the actual turbocharger upstream pressure. The opening degree of the throttle valve 43 is feedback-controlled so that the pressure matches the upstream pressure of the target turbocharger.

Here, in steps S14 and S15, when the throttle valve 43 is controlled so that the target differential pressure is realized, the booster pressure upstream of the turbocharger changes, and the booster pressure downstream of the throttle valve tends to change. .. In this case, in steps S12 and S13 parallel to steps S14 and S15, the air bypass valve 48 is feedback-controlled so that the target boost pressure is realized independently of the control of the throttle valve 43. The pressure will be maintained almost constant. That is, the feedback control of the air bypass valve 48 is performed so that the fluctuation of the boost pressure due to the control of the throttle valve 43 is compensated. Typically, the ECU 10 controls the throttle valve 43 to the closed side in order to achieve a target differential pressure of 5 kPa, that is, to generate a negative pressure equivalent to 5 kPa downstream of the throttle valve 43, while this throttle. The air bypass valve 48 is controlled to the closed side so as to compensate for the decrease in air due to the control of the valve 43. In this way, the feedback control of the throttle valve 43 and the feedback control of the air bypass valve 48 are performed separately and in parallel, so that both the upstream side and the downstream side of the supercharger 44 have desired pressures (targets). Supercharger upstream pressure and target supercharging pressure) can be set appropriately.

Next, with reference to FIG. 8, the abnormality determination of the differential pressure sensor SW15 according to the embodiment of the present invention will be specifically described. FIG. 8 is a flowchart showing an abnormality determination process of the differential pressure sensor SW15 according to the embodiment of the present invention. The process related to this flowchart is repeatedly executed by the ECU 10 at a predetermined cycle in parallel with the process related to the flowchart shown in FIG. 7 when an execution request for abnormality determination of the differential pressure sensor SW15 is issued.

First, in step S21, the ECU 10 acquires various information from the sensors SW1 to SW17 (see FIGS. 1 and 3) described above. Typically, the ECU 10 has a supercharger upstream pressure detected by the first pressure sensor SW3, an engine rotation speed detected by the engine rotation speed sensor SW9, a differential pressure detected by the EGR differential pressure sensor SW15, and a large amount. The atmospheric pressure detected by the pressure sensor SW17 is acquired. In addition, the ECU 10 acquires the voltage of the battery for driving various electronic devices in the vehicle including the sensors SW1 to SW17 and the like.

In step S22, the ECU 10 determines whether or not the battery voltage acquired in step S21 is equal to or higher than a predetermined voltage. Here, in order to ensure the accuracy of the abnormality determination of the differential pressure sensor SW15, it is determined whether or not the battery voltage is stable and the differential pressure sensor SW15 is in a state where it can output a highly reliable detection signal. There is. When the battery voltage is equal to or higher than the predetermined voltage (step S22: Yes), the ECU 10 proceeds to step S23 in order to determine the abnormality of the differential pressure sensor SW15. On the other hand, when the battery voltage is less than the predetermined voltage (step S22: No), the ECU 10 exits the series of routines shown in this flowchart. In this case, the ECU 10 does not determine the abnormality of the differential pressure sensor SW15.

Next, in step S23, the ECU 10 determines whether or not the engine speed acquired in step S21 is less than the predetermined speed. In the present embodiment, the ECU 10 performs the determination as in step S23 in order to determine the abnormality of the differential pressure sensor SW15 only when the engine rotation speed is less than the predetermined rotation speed, that is, only in the low rotation speed region. .. In this embodiment, atmospheric pressure is used as the pressure on the upstream side that defines the differential pressure of the EGR valve 54, but in the low rotation region, the pressure on the upstream side of the EGR valve 54 is atmospheric pressure. This is because it exactly matches. Further, in the low rotation speed region, the influence of exhaust pulsation is relatively small. The predetermined rotation speed used in the determination in step S23, that is, the predetermined rotation speed for determining the low rotation region is set to, for example, about 2000 rpm.

As a result of step S23, when the engine speed is less than the predetermined speed (step S23: Yes), the ECU 10 proceeds to step S24 in order to determine the abnormality of the differential pressure sensor SW15. On the other hand, when the engine speed is equal to or higher than the predetermined speed (step S23: No), the ECU 10 exits the series of routines shown in this flowchart. In this case, the ECU 10 does not determine the abnormality of the differential pressure sensor SW15.

Next, in step S24, the ECU 10 sets a determination threshold value to be used in the abnormality determination of the differential pressure sensor SW15 based on the engine speed acquired in step S21. Specifically, the ECU 10 sets a determination threshold value corresponding to the current engine speed with reference to a map as shown in FIG. FIG. 9 is a map that defines a determination threshold value (vertical axis) to be set for the engine speed (horizontal axis). This determination threshold is defined by the pressure and is applied when performing an abnormality determination based on the differential pressure detected by the differential pressure sensor SW15 (specifically, when the value used for the determination becomes equal to or greater than the determination threshold). The differential pressure sensor SW15 is determined to be abnormal). As shown in FIG. 9, the higher the engine speed, the larger the set determination threshold value. This is done in order to eliminate the influence of the exhaust pressure by increasing the determination threshold value because the influence of the exhaust pressure becomes larger as the engine speed increases.

Next, in step S25, the ECU 10 first calculates the differential pressure between the upstream side and the downstream side of the EGR valve 54 (hereinafter, appropriately referred to as a “differential pressure calculated value”), and the differential pressure calculated value and the differential pressure. Whether or not the difference (absolute value is used) from the differential pressure detected by the sensor SW15 (hereinafter, appropriately referred to as “differential pressure sensor value”) is equal to or greater than the determination threshold value set in step S24. To judge. In this case, the ECU 10 obtains the differential pressure calculation value by subtracting the atmospheric pressure detected by the atmospheric pressure sensor SW17 and the supercharger upstream pressure detected by the first pressure sensor SW3.

As a result of step S25, when the difference between the differential pressure sensor value and the differential pressure calculated value is equal to or greater than the determination threshold value (step S25: Yes), the ECU 10 proceeds to step S26 and determines that the differential pressure sensor SW15 is abnormal. , Turn on the abnormality determination flag of the differential pressure sensor SW15. On the other hand, when the difference between the differential pressure sensor value and the differential pressure calculated value is less than the determination threshold value (step S25: No), the ECU 10 exits the series of routines shown in this flowchart. In this case, the ECU 10 determines that the differential pressure sensor SW15 is normal, and turns off the abnormality determination flag of the differential pressure sensor SW15.

When the difference between the differential pressure sensor value and the differential pressure calculated value is equal to or greater than the determination threshold value, it is not limited to immediately determining that the differential pressure sensor SW15 is abnormal, and the differential pressure sensor value and the differential pressure are not limited to the immediate determination. When the state in which the difference from the calculated value is equal to or greater than the determination threshold value continues for a predetermined time or longer, the differential pressure sensor SW15 may be determined to be abnormal. In this case, even if the difference between the differential pressure sensor value and the differential pressure calculated value is equal to or greater than the determination threshold value, the determination with respect to the differential pressure sensor SW15 may be waited until the state continues for a predetermined time or longer.

After the above step S26, the ECU 10 proceeds to step S27 and controls to close the EGR valve 54 (fully closed control). This is because the differential pressure sensor SW15 is abnormal, so that the EGR valve 54 cannot be appropriately controlled based on the differential pressure detected by the differential pressure sensor SW15. That is, since the EGR gas amount cannot be accurately controlled by the EGR valve 54 (that is, the EGR controllability cannot be ensured), the EGR valve 54 is closed to stop the recirculation of the EGR gas to the intake passage 40. ..

Next, in step S28, when the engine 1 is performing the first SPCCI combustion, the ECU 10 prohibits the first SPCCI combustion and controls to switch from the first SPCCI combustion to SI combustion. This is because the first SPCCI combustion is performed in a state where the EGR gas is recirculated as described above (specifically, the first SPCCI combustion is in a state where the gas air-fuel ratio G / F is lean (a relatively large amount of EGR gas is introduced). When the recirculation of the EGR gas is stopped due to the abnormality of the differential pressure sensor SW15 as described above, the first SPCCI combustion is prohibited.

Specifically, the ECU 10 controls the intake VVT 23 so as to delay the valve closing timing of the intake valve 21 when switching from the first SPCCI combustion to SI combustion as described above. By doing so, the effective compression ratio of the engine 1 is lowered to suppress knocking. Further, in addition to controlling the intake VVT 23, the ECU 10 controls the exhaust VVT 24 so as to accelerate the closing timing of the exhaust valve 22. By doing so, the overlap period of the intake valve 21 and the exhaust valve 22 is reduced, the amount of internal EGR gas introduced into the combustion chamber 17 is reduced, and the temperature inside the cylinder is lowered, thereby further suppressing knocking. I am doing it. Further, the ECU 10 controls the spark plug 25 so as to delay the ignition timing in order to further suppress knocking.

Next, in step S29, the ECU 10 lights a warning lamp indicating that the differential pressure sensor SW15 is abnormal. After this, the ECU 10 exits the series of routines shown in this flowchart.

<Action and effect>
Next, the engine control method and the operation and effect of the control system according to the embodiment of the present invention will be described.

FIG. 10 is a time chart showing an example of the result when the abnormality determination of the differential pressure sensor SW15 according to the embodiment of the present invention is performed. 10 shows, in order from the top, the boost pressure, the opening degree of the throttle valve 43, the opening degree of the air bypass valve 48, the differential pressure sensor value of the differential pressure sensor SW15 according to the present embodiment, and the difference between the differential pressure sensor SW15 according to the comparative example. The pressure sensor value and the abnormality determination flag of the differential pressure sensor SW15 are shown. Further, in FIG. 10, regarding the opening degree of the throttle valve 43, the opening degree of the air bypass valve 48, and the abnormality determination flag of the differential pressure sensor SW15, the results according to the present embodiment are shown by solid lines, and the results according to the comparative example are shown by broken lines. ing. Note that FIG. 10 shows the results when the differential pressure sensor SW15 is actually normal in both the present embodiment and the comparative example.

In the comparative example, when the abnormality determination of the differential pressure sensor SW15 is performed, the control for positively changing the differential pressure between the upstream side and the downstream side of the EGR valve 54 is not performed, and the differential pressure is relatively small (for example, 2 kpa). Less than). On the other hand, in the present embodiment, when the abnormality determination of the differential pressure sensor SW15 is performed, the differential pressure is specifically set to 5 kPa so that the differential pressure between the upstream side and the downstream side of the EGR valve 54 is relatively large. As described above, the throttle valve 43 is controlled to be closer to the closed side than the comparative example, and the air bypass valve 48 is controlled to the closed side from the comparative example according to the control of the throttle valve 43. In the example shown in FIG. 10, the boost pressure is increased, and the throttle valve 43 is gradually controlled to the open side in both the present embodiment and the comparative example in response to the increase in the boost pressure. At the same time, the air bypass valve 48 is gradually controlled to the closing side. As the boost pressure increases in this way, the exhaust pulsation also increases.

In both the present embodiment and the comparative example, the differential pressure sensor value fluctuates under the influence of exhaust pulsation, and as the boost pressure increases, the fluctuation range of the differential pressure sensor value increases. Further, in both the present embodiment and the comparative example, the temporal average values av1 and av2 of the differential pressure sensor values are used for determining the abnormality of the differential pressure sensor SW15, not the differential pressure sensor value itself.

In the comparative example, since the differential pressure between the upstream side and the downstream side of the EGR valve 54 is relatively small, the differential pressure sensor value fluctuates in a range where the value is relatively small. Therefore, in the comparative example, as shown by the broken line in the graph of the differential pressure sensor value, the differential pressure between the upstream side and the downstream side of the EGR valve 54 may be lower than the detectable lower limit value of the differential pressure sensor SW15. Sometimes the differential pressure sensor value is fixed at the lower limit. Therefore, in the comparative example, the average value av2 of the differential pressure sensor value is raised and becomes larger than the value corresponding to the actual differential pressure. As a result, in the comparative example, at time t11, the average value av2 of the differential pressure sensor value becomes the threshold value th2 or more corresponding to the differential pressure calculated value (this threshold value th2 is the above-mentioned determination threshold value added to the differential pressure calculated value). It is a value, and the fact that the average value av2 of the differential pressure sensor value is equal to or higher than the threshold value th2 corresponds to the difference between the average value av2 and the differential pressure calculated value being equal to or higher than the judgment threshold value), and the differential pressure sensor SW15 is abnormal. The judgment flag is turned on. In this case, in the comparative example, it is erroneously determined that the differential pressure sensor SW15 is abnormal.

On the other hand, in the present embodiment, since the differential pressure between the upstream side and the downstream side of the EGR valve 54 is relatively large, the differential pressure sensor value fluctuates in a range where the value is relatively large. Therefore, in the present embodiment, unlike the comparative example, the differential pressure between the upstream side and the downstream side of the EGR valve 54 does not fall below the lower limit value that can be detected by the differential pressure sensor SW15, and the differential pressure sensor value is the lower limit value. Will always be exceeded. Therefore, in the present embodiment, unlike the comparative example, the average value av1 of the differential pressure sensor value is not raised and becomes larger than the value corresponding to the actual differential pressure. Therefore, in the present embodiment, the average value av1 of the differential pressure sensor value does not become equal to or higher than the threshold value th1 corresponding to the differential pressure calculated value (this threshold value th1 is obtained by adding the above-mentioned determination threshold value to the differential pressure calculated value). It is a value, and the fact that the average value av1 of the differential pressure sensor value is less than the threshold value th1 corresponds to the difference between the average value av1 and the differential pressure calculated value being less than the determination threshold value), and the difference pressure sensor SW15 is abnormal. The verdict flag is kept off. From this, it can be said that the differential pressure sensor SW15 can be accurately determined according to the present embodiment.

Next, FIG. 11 is a time chart showing an example of the result when the engine is controlled at the time of abnormality determination of the differential pressure sensor SW15 in the embodiment of the present invention. In FIG. 11, in order from the top, the differential pressure sensor value of the differential pressure sensor SW15, the abnormality determination flag of the differential pressure sensor SW15, the opening degree of the EGR valve 54, the combustion mode of the engine 1, and the operation of the intake VVT23 (particularly the intake by the intake VVT23). The valve closing timing of the valve 21), the operation of the exhaust VVT 24 (particularly the valve closing timing of the exhaust valve 22 by the exhaust VVT 24), and the ignition timing by the spark plug 25 are shown.

As shown in FIG. 11, at time t21, the average value av3 of the differential pressure sensor value becomes the threshold value th3 or more corresponding to the differential pressure calculated value, and the abnormality determination flag of the differential pressure sensor SW15 is turned on. At this time, the EGR valve 54 is closed so as to stop the return of the EGR gas to the intake passage 40. In addition to this, in the present embodiment, the combustion mode of the engine 1 is switched from the first SPCCI combustion to the SI combustion (in the comparative example, as shown by the broken line, the combustion mode of the engine 1 is maintained in the first SPCCI combustion. ). Further, in the present embodiment, control of the intake VVT 23 for delaying the valve closing timing of the intake valve 21 and exhaust valve 22 so as to suppress knocking of the engine 1 when switching from the first SPCCI combustion to SI combustion. The control of the exhaust VVT 24 for accelerating the valve closing timing and the control of the spark plug 25 for delaying the ignition timing are executed.

After that, at time t22, when a predetermined condition is satisfied, the combustion mode of the engine 1 is switched from SI combustion to the second SPCCI combustion. That is, in the present embodiment, at the time of abnormality determination of the differential pressure sensor SW15, the first SPCCI combustion is prohibited, but the second SPCCI combustion is permitted. For example, in a situation where combustion stability is ensured and it is determined that combustion noise does not pose a problem even if SPCCI combustion is performed (in one example, it is determined based on the in-cylinder pressure detected by the acupressure sensor SW6). The combustion mode is switched from SI combustion to the second SPCCI combustion. When the SI combustion is switched to the second SPCCI combustion in this way, the control of the intake VVT 23 for advancing the valve closing timing of the intake valve 21 and the control of the exhaust VVT 24 for delaying the valve closing timing of the exhaust valve 22 Control of the spark plug 25 for advancing the ignition timing is executed.

As described above, according to the present embodiment, when the ECU 10 determines the abnormality of the differential pressure sensor SW15, the differential pressure between the upstream side and the downstream side of the EGR valve 54 is maintained at a predetermined pressure or higher. Since the throttle valve 43 is controlled to the closed side, the abnormality determination can be performed accurately while ensuring the execution frequency of the abnormality determination. Further, by maintaining the differential pressure at a predetermined pressure or higher in this way, deterioration of EGR controllability due to exhaust pulsation can be suppressed, and fuel efficiency can be ensured.

Further, according to the present embodiment, when the differential pressure sensor SW15 is abnormal, the ECU 10 stops the recirculation of the EGR gas and the gas air-fuel ratio G / F is in a lean state (a relatively large amount of EGR gas is generated). In the introduced state), the first SPCCI combustion in which the air-fuel mixture in the combustion chamber 17 is compressed and ignited by self-ignition is switched to SI combustion in which the air-fuel mixture is spark-ignited and burned by spark ignition. As a result, when the differential pressure sensor SW15 is abnormal, the difference between the upstream side and the downstream side of the EGR valve 54 so as to improve the EGR controllability in order to maintain the execution of the first SPCCI combustion using the EGR gas. By further increasing the pressure, it is possible to appropriately suppress the deterioration of fuel efficiency. That is, according to the present embodiment, when the differential pressure sensor SW15 is abnormal, it is possible to surely suppress the deterioration of fuel consumption due to the control to maintain the first SPCCI combustion, and the first SPCCI. By switching the combustion to SI combustion, the combustion stability of the engine 1 can be ensured.

Further, according to the present embodiment, the ECU 10 controls the intake VVT 23 so as to delay the closing timing of the intake valve 21 when switching from the first SPCCI combustion to the SI combustion, so that the effective compression ratio of the engine 1 is lowered. Therefore, knocking can be appropriately suppressed.

Further, according to the present embodiment, when the ECU 10 controls the intake VVT 23 so as to delay the closing timing of the intake valve 21 as described above, the ignition timing by the spark plug 25 is retarded, so that knocking is further improved. It can be effectively suppressed.

Further, according to the present embodiment, when the differential pressure sensor SW15 is determined to be abnormal, the ECU 10 prohibits the first SPCCI combustion, while the ECU 10 self-produces the air-fuel mixture in a state where the air-fuel ratio A / F is lean. The second SPCCI combustion, which is compressed ignition combustion by ignition, is permitted. As a result, in a state where EGR controllability is not ensured due to an abnormality of the differential pressure sensor SW15, the first SPCCI combustion using the EGR gas can be reliably prohibited, and thus the first SPCCI combustion is prohibited while the second SPCCI combustion is prohibited. Since the above is permitted, it is possible to appropriately secure the improvement of fuel efficiency and the reduction of NOx by SPCCI combustion.

Further, in the present embodiment, the engine 1 performs the second SPCCI combustion in the low load low rotation region and SI combustion in the region other than the low load low rotation region, so that appropriate combustion is performed in the entire operating region of the engine 1. It can be realized.

Further, according to the present embodiment, when the ECU 10 controls the throttle valve 43 so that the differential pressure is maintained at a predetermined pressure or higher in order to determine the abnormality of the differential pressure sensor SW15, the throttle valve 43 is controlled. The air bypass valve 48 is feedback-controlled based on the target boost pressure so as to compensate for the fluctuation of the boost pressure due to the above. As a result, the pressure on the upstream side of the supercharger 44 (specifically, the pressure on the downstream side of the throttle valve 43 and the upstream side of the supercharger 44, in other words, the pressure on the downstream side of the EGR valve 54 that regulates the differential pressure of the EGR valve 54). Both the pressure) and the pressure on the upstream side of the supercharger 44 (supercharging pressure) can be appropriately set to a desired pressure.

Further, in the present embodiment, a mechanical turbocharger 44 driven by the engine 1 is used. In this supercharger 44, the supercharging pressure cannot be adjusted by direct control of the supercharger 44, but the target supercharging pressure can be appropriately realized by controlling the air bypass valve 48 as described above. Can be done.

Further, according to the present embodiment, the ECU 10 is based on the differential pressure (differential pressure sensor value) detected by the differential pressure sensor SW15, the supercharger upstream pressure detected by the first pressure sensor SW3, and the atmospheric pressure sensor SW17. When the difference from the detected atmospheric pressure and the differential pressure (differential pressure calculated value) is equal to or greater than the determination threshold value, the differential pressure sensor SW15 is determined to be abnormal. As a result, the abnormality of the differential pressure sensor SW15 can be accurately determined.

Further, according to the present embodiment, the ECU 10 sets the determination threshold value to a higher value as the engine speed increases, so that the influence of the exhaust pressure when the engine speed increases is appropriately eliminated to determine the abnormality. The accuracy of can be effectively ensured.

Further, according to the present embodiment, the ECU 10 executes the abnormality determination of the differential pressure sensor SW15 only when the engine speed is less than the predetermined speed, that is, only in the low speed region, and the exhaust flow rate is large and pulsation occurs. Since the execution of the abnormality determination is prohibited in the high rotation speed region where the influence is large, the accuracy of the abnormality determination can be appropriately ensured.

<Modification example>
In the above-described embodiment, the combustion mode of the engine 1 is switched between SI combustion and SPCCI combustion (partial compression ignition combustion), but the present invention is not limited to the configuration for switching the combustion mode in this way. Not done. The present invention is also applicable to a configuration in which CI combustion is used instead of SPCCI combustion and the combustion mode of the engine 1 is switched between SI combustion and CI combustion.

In the above-described embodiment, the supercharger 44 mechanically driven by the engine 1 is provided in the intake passage 40, but instead of such a mechanical supercharger 44, an electric supercharger driven by an electric motor A turbocharger or a turbocharger driven by the energy of exhaust gas may be provided.

1 engine 6 injector 10 ECU
17 Combustion chamber 21 Intake valve 22 Exhaust valve 23 Intake VVT
24 Exhaust VVT
25 Spark plug 40 Intake passage 43 Throttle valve 44 Supercharger 48 Air bypass valve 50 Exhaust passage 52 EGR passage 54 EGR valve SW3 1st pressure sensor SW5 2nd pressure sensor SW15 EGR differential pressure sensor SW17 Atmospheric pressure sensor

Claims (11)

It ’s an engine control method.
A step of controlling the opening degree of the EGR valve based on the output value of the differential pressure sensor that detects the differential pressure between the upstream side and the downstream side of the EGR valve provided on the EGR passage of the engine.
By controlling the opening degree of the EGR valve, the gas air-fuel ratio G / F, which is the ratio of the total amount of gas in the combustion chamber including the EGR gas from the EGR passage to the amount of fuel, is larger than the theoretical air-fuel ratio. The step of executing the first combustion mode in which the air-fuel mixture in the combustion chamber of the engine is compressed, ignited and burned by self-ignition, and
Instead of executing the first combustion mode, a step of executing a second combustion mode in which the air-fuel mixture in the combustion chamber of the engine is spark-ignited and burned by spark ignition.
A step of determining an abnormality of the differential pressure sensor based on the output value of the differential pressure sensor, and
A step of controlling the throttle valve of the engine to the closed side so that the differential pressure between the upstream side and the downstream side of the EGR valve is maintained at a predetermined pressure or higher when determining an abnormality of the differential pressure sensor.
When the differential pressure sensor is determined to be abnormal, the EGR valve is controlled to be closed to stop the recirculation of the EGR gas from the EGR passage to the intake passage of the engine, and the first combustion mode. When is executed, the step of controlling to switch the first combustion mode to the second combustion mode and
A method of controlling an engine, characterized in that it has. When switching from the first combustion mode to the second combustion mode, the opening / closing timing of the intake valve can be adjusted so as to delay the closing timing of the intake valve of the engine in order to reduce the effective compression ratio of the engine. The engine control method according to claim 1, further comprising a step of controlling an intake valve mechanism. The engine control method according to claim 2, further comprising a step of controlling the ignition timing of the engine when the intake valve mechanism is controlled so as to delay the closing timing of the intake valve. The first engine is in a state where the gas air-fuel ratio G / F is larger than the theoretical air-fuel ratio and the air-fuel ratio A / F, which is the ratio of the amount of air in the combustion chamber to the amount of fuel, substantially matches the theoretical air-fuel ratio. It further has a third combustion mode in which the combustion mode is performed and the compression ignition combustion is performed in a state where the air-fuel ratio A / F is larger than the stoichiometric air-fuel ratio.
Any of claims 1 to 3, further comprising a step of prohibiting the execution of the first combustion mode and permitting the execution of the third combustion mode when the differential pressure sensor is determined to be abnormal. The engine control method described in item 1. The engine performs the third combustion mode in the low load low rotation speed region where the load is less than the predetermined load and the rotation speed is less than the predetermined rotation speed, and the third combustion mode is performed in the region other than the low load low rotation speed region. 2. The engine control method according to claim 4, wherein the combustion mode is performed. The engine is provided with a supercharger for supercharging the intake air supplied to the engine, a bypass passage for passing the intake air by bypassing the supercharger, and a bypass valve provided on the bypass passage. And
It further has a step of setting a target boost pressure by the supercharger and controlling the opening degree of the bypass valve so that the target boost pressure is realized.
In the step of controlling the bypass valve, the throttle valve is controlled so that the differential pressure between the upstream side and the downstream side of the EGR valve is maintained at the predetermined pressure or higher in order to determine the abnormality of the differential pressure sensor. At that time, the opening degree of the bypass valve is feedback-controlled based on the target boost pressure so as to compensate for the fluctuation of the boost pressure due to the control of the throttle valve.
The engine control method according to any one of claims 1 to 5. The engine control method according to claim 6, wherein the supercharger is a mechanical supercharger driven by the engine. In the step of determining the abnormality of the differential pressure sensor, the differential pressure corresponding to the output value of the differential pressure sensor, the pressure corresponding to the output value of the pressure sensor provided on the downstream side of the EGR valve, and the atmospheric pressure sensor. The method according to any one of claims 1 to 7, wherein the differential pressure sensor determines that the differential pressure sensor is abnormal when the difference between the differential pressure and the pressure corresponding to the output value is equal to or greater than a predetermined determination threshold value. How to control the engine. The engine control method according to claim 8, further comprising a step of setting the determination threshold value to a higher value as the engine speed increases. When the rotation speed of the engine is equal to or higher than the predetermined rotation speed, the execution of the abnormality determination of the differential pressure sensor is prohibited, while when the rotation speed of the engine is less than the predetermined rotation speed, the abnormality of the differential pressure sensor is prohibited. The engine control method according to any one of claims 1 to 9, further comprising a step of permitting execution of the determination. It ’s an engine control system.
With the engine
An EGR passage that recirculates the exhaust gas of the engine to the intake passage, an EGR valve provided on the EGR passage, and a differential pressure sensor that detects the differential pressure between the upstream side and the downstream side of the EGR valve.
It comprises, at least, a controller configured to control the engine, which is composed of circuits.
The controller
The opening degree of the EGR valve is controlled based on the output value of the differential pressure sensor.
By controlling the opening degree of the EGR valve, the gas air-fuel ratio G / F, which is the ratio of the total amount of gas in the combustion chamber including the EGR gas from the EGR passage to the amount of fuel, is larger than the theoretical air-fuel ratio. Execute the first combustion mode in which the air-fuel mixture in the combustion chamber of the engine is compressed, ignited and burned by self-ignition.
Instead of executing the first combustion mode, a second combustion mode in which the air-fuel mixture in the combustion chamber of the engine is spark-ignited and burned by spark ignition is executed.
Based on the output value of the differential pressure sensor, an abnormality of the differential pressure sensor is determined.
When determining an abnormality of the differential pressure sensor, the throttle valve of the engine is controlled to the closed side so that the differential pressure between the upstream side and the downstream side of the EGR valve is maintained at a predetermined pressure or higher.
When the differential pressure sensor is determined to be abnormal, the EGR valve is controlled to be closed to stop the recirculation of the EGR gas from the EGR passage to the intake passage of the engine, and the first combustion mode. Is executed, the control for switching the first combustion mode to the second combustion mode is performed.
An engine control system characterized by being configured in such a manner.

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