JP7055700B2 - Engine control - Google Patents

Description

The present invention relates to an engine control device, and more particularly to a control device for controlling an EGR valve in an engine including an EGR (Exhaust Gas Recirculation) device.

As a method of feedback control, PID control combining P (proportional) operation, I (integral) operation and D (differential) operation, and PI control combining P operation and I operation are known. For example, in the engine control device described in Japanese Patent Application Laid-Open No. 2017-198091 (Patent Document 1), feedback control of EGR rate is performed by PI control, and feedback control of boost pressure is performed by PID control.

Japanese Unexamined Patent Publication No. 2017-198091

By the way, the EGR device mounted on the engine is controlled for the purpose of improving exhaust emission, for example. By operating the EGR device to recirculate the exhaust gas and including the recirculated exhaust gas (EGR gas) in the intake gas, the combustion temperature of the engine is lowered. By doing so, it is possible to suppress the generation of NOx due to combustion. By suppressing the generation of NOx due to combustion during engine operation, the amount of NOx in the exhaust gas is reduced.

If the amount of EGR gas becomes excessively large with respect to the amount of fresh air sucked into the combustion chamber of the engine during the operation of the EGR device, the combustion during engine operation becomes unstable. On the other hand, if the amount of EGR gas is too small with respect to the amount of fresh air, the generation of NOx due to combustion during engine operation cannot be sufficiently suppressed. Therefore, while the EGR device is in operation, feedback control (PID control) is performed so that the EGR rate (the ratio of the amount of EGR gas to the amount of intake gas supplied to the engine body) becomes an appropriate value (target EGR rate). Or PI control, etc.) is performed.

The feedback control of the EGR rate operates (adjusts) the opening degree of the EGR valve (hereinafter, also referred to as "EGR opening degree") provided in the return passage (passage for returning a part of the exhaust gas to the intake passage). It is done by doing. Further, the gain of the feedback control is adjusted based on the EGR rate deviation (deviation between the current EGR rate and the target EGR rate). More specifically, when the EGR rate deviation is large, feedback control is performed with a large gain to bring the EGR rate closer to the target EGR rate quickly, and when the EGR rate deviation is small, feedback control is performed with a small gain to suppress overshoot. Is done. Hereinafter, the gain of feedback control is also referred to as “feedback gain”.

However, with the recent tightening of exhaust regulations, the inventor of the present application has confirmed new problems as described below with respect to the above feedback control.

Due to the tightening of exhaust gas regulations, it is required to recirculate the exhaust gas by the EGR device not only during low load operation of the engine but also during high load operation. During high-load operation of the engine, the sensitivity of the change in the amount of EGR gas to the change in the EGR opening degree (and by extension, the sensitivity to the change in the EGR rate to the change in the EGR opening degree) tends to be high due to the increase in the exhaust pressure. Therefore, when feedback control of the EGR rate is performed during high load operation of the engine, the EGR rate becomes excessively high due to overshoot, and the combustion of the engine (and thus the operation of the engine) tends to become unstable.

In order to suppress the excessive increase in the EGR rate as described above, it is conceivable to reduce the feedback gain to slow down the opening / closing operation of the EGR valve. However, if the feedback gain is always reduced, the responsiveness of the feedback control is lowered, and the exhaust emission is likely to be deteriorated due to the delay in entering the EGR gas.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to suppress overshoot in feedback control of the EGR rate in both low load operation and high load operation of the engine. Ensuring sufficient responsiveness.

The engine control device of the present invention is an engine control device including an engine body having a combustion chamber, a recirculation path, an EGR valve provided in the recirculation path, a first pressure detection unit, and a second pressure detection unit. Therefore, the EGR rate, which is the ratio of the amount of EGR gas to the amount of intake gas supplied to the engine body, is detected, and the EGR opening degree (EGR) is set so that the detected value of the EGR rate approaches the target EGR rate by feedback control. It is configured to operate the valve opening).

In the above engine, the return passage is a passage for connecting the intake passage and the exhaust passage without passing through the engine main body and returning a part of the exhaust gas flowing through the exhaust passage to the intake passage. The EGR valve is configured so that the amount of EGR gas returning from the exhaust passage to the intake passage can be adjusted. The first pressure detecting unit is configured to detect the intake pressure, which is the pressure of the intake gas sucked into the combustion chamber. The second pressure detecting unit is configured to detect the exhaust pressure, which is the pressure of the exhaust gas discharged from the combustion chamber. In addition, each of the detection value (intake pressure) of the first pressure detection unit and the detection value (exhaust pressure) of the second pressure detection unit may be the actual measurement value actually measured by using the pressure sensor, or the engine. It may be an estimated value estimated from the state of.

The above-mentioned control device has an EGR rate deviation, which is a deviation between the detected value of the EGR rate and the target EGR rate, and an intake gas amount supplied to the engine body (hereinafter, also simply referred to as "intake gas amount"). It is configured to determine the gain (feedback gain) of the above-mentioned feedback control by using the differential pressure of the intake pressure and the exhaust pressure (hereinafter, also referred to as “intake / exhaust differential pressure”).

In the above engine control device, by determining the feedback gain based on the EGR rate deviation, it becomes possible to perform feedback control with a large gain in order to quickly bring the EGR rate closer to the target EGR rate when the EGR rate deviation is large. When the EGR rate deviation is small, it becomes possible to perform feedback control with a large gain in order to suppress overshoot. The deviation is a parameter indicating the deviation (degree of difference) between the two values. As the deviation, a difference, a ratio, or the like can be adopted. The larger the difference (absolute value), the larger the deviation. Further, the closer the ratio is to 1, the smaller the deviation.

Further, the inventor of the present application has found that the sensitivity of the EGR rate change to the change of the EGR opening degree (hereinafter, also referred to as “EGR opening degree sensitivity”) shows a high correlation with each of the intake / exhaust differential pressure and the intake gas amount. rice field. When the intake / exhaust differential pressure is large, the influence of the fluctuation of the EGR opening degree on the EGR gas amount becomes large, and the EGR gas amount tends to change greatly by the operation of the EGR opening degree in the feedback control. Further, when the intake gas amount is small, the influence of the fluctuation of the EGR gas amount on the EGR rate becomes large, and the EGR rate tends to change significantly due to the fluctuation of the EGR gas amount.

The engine control device can grasp the high EGR opening sensitivity from the intake gas amount and the intake / exhaust differential pressure, and can adopt a feedback gain according to the high EGR opening sensitivity. That is, an appropriate feedback gain should be adopted both in a situation where the EGR opening sensitivity is high (for example, during high load operation of the engine) and in a situation where the EGR opening sensitivity is low (for example, during low load operation of the engine). Can be done.

As described above, according to the engine control device of the present invention, in the feedback control of the EGR rate, an appropriate feedback gain is adopted in both the low load operation and the high load operation of the engine to overshoot. It becomes possible to secure sufficient responsiveness while suppressing.

In the engine control device, the feedback control gain may be determined to be smaller as the EGR rate deviation is smaller, smaller as the intake gas amount is smaller, and smaller as the intake / exhaust differential pressure is larger. ..

In the feedback control of the EGR rate, the smaller the EGR rate deviation or the larger the EGR opening sensitivity, the more likely the overshoot tends to occur. Further, as the amount of intake gas decreases or the intake / exhaust differential pressure increases, the EGR opening sensitivity tends to increase. In response to these trends, the control device having the above configuration determines the feedback gain so that the feedback gain becomes small when overshoot is likely to occur. By doing so, when overshoot is unlikely to occur, the feedback gain can be increased to ensure sufficient responsiveness, while when overshoot is likely to occur, the feedback gain can be reduced to suppress overshoot. Therefore, generally, by making the gain of the feedback control variable according to the above tendency, the feedback control of the EGR rate can be suitably performed.

The engine control device may have corresponding information (map or the like) showing the relationship between the intake pressure and the intake gas amount. For example, the control device may include a storage device that stores such correspondence information. Further, the control device estimates the intake gas amount using the detection value of the first pressure detection unit and the above corresponding information, and the fresh air amount supplied to the engine body from the obtained estimation value of the intake gas amount. The amount of EGR gas may be calculated by subtracting. Then, the control device may acquire the above-mentioned detected value of the EGR rate by dividing the EGR gas amount thus calculated by the estimated value of the intake gas amount. According to such a configuration, the above-mentioned detected value of the EGR rate can be appropriately acquired by a configuration that is easy to realize in terms of cost and technology.

The engine control device may have gain information (map or the like) showing the relationship between the intake gas amount, the intake / exhaust differential pressure, and the gain of the feedback control. For example, the control device may include a storage device for storing such gain information. The gain information is not limited to the one that defines the value of the feedback gain, and may be the one that defines the correction coefficient for correcting the feedback gain. The control device may be configured to determine the gain of the feedback control using the relationships defined in the gain information above. The gain information is such that if the intake / exhaust differential pressure is the same, the feedback control gain becomes smaller as the intake gas amount decreases, and if the intake / exhaust differential pressure is the same, the feedback control gain increases as the intake / exhaust differential pressure increases. Relationship may be specified. According to such a configuration, the EGR rate can be appropriately feedback-controlled.

According to the present invention, it is possible to secure sufficient responsiveness while suppressing overshoot in the feedback control of the EGR rate in both the low load operation and the high load operation of the engine.

It is an overall block diagram of the engine control system which concerns on embodiment of this invention. It is a figure which shows the element which constitutes the inhalation gas in a cylinder. It is a figure which shows the relationship between the EGR gas amount change amount and intake / exhaust differential pressure when the opening degree of an EGR valve is operated to the side which opens by a unit operation amount. For two examples, it is a figure which shows the in-cylinder intake gas which increased the EGR gas by the operation of the EGR opening degree. It is a figure which shows the tendency of the use condition of the engine before and after the exhaust regulation is tightened. It is a control block diagram which shows the structure for performing the feedback control of the EGR rate in the control device of the engine which concerns on embodiment of this invention. It is a figure which shows an example of the 1st gain information used for determining a feedback gain. It is a figure which shows an example of the 2nd gain information used for determining a feedback gain.

Embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals and the description thereof will not be repeated.

FIG. 1 is an overall configuration diagram of an engine control system according to the present embodiment. With reference to FIG. 1, the engine 1 to be controlled in this engine control system is mounted on a vehicle (for example, a four-wheeled vehicle) as a power generator for traveling, for example. In the present embodiment, the engine 1 is a common rail type in-line 4-cylinder diesel engine, but the engine to be controlled is not limited to such a diesel engine. The engine to be controlled may be a gasoline engine or an engine having a cylinder layout other than in-line (for example, V type or horizontal type). Also, the number of cylinders can be changed arbitrarily.

The engine 1 includes an engine main body 10, an air cleaner 20, an intercooler 25, an intake throttle valve 26, an intake manifold 28, a supercharger 30, an exhaust manifold 50, and an EGR device 60. Then, the engine 1 is controlled by the control device 200. Hereinafter, in the engine 1, one end on the upstream side is referred to as a "first end" and the other end on the downstream side is referred to as a "second end" with respect to a pipe or the like that functions as a flow path in the engine 1.

The engine body 10 includes a plurality of cylinders 12, a common rail 14, and a plurality of injectors 16. A piston (not shown) is provided in each cylinder 12, and a combustion chamber is formed by the cylinder 12 and the piston. An injector 16 is provided for each cylinder 12, and each injector 16 is connected to a common rail 14. The fuel stored in the fuel tank (not shown) is pressurized to a predetermined pressure by a supply pump (not shown) and supplied to the common rail 14. The fuel supplied to the common rail 14 is injected from each injector 16 into the combustion chamber at a predetermined timing.

The air cleaner 20 is provided in the middle of the first intake pipe 22 so as to remove foreign matter contained in the air sucked from the intake port (not shown) provided at the first end of the first intake pipe 22. It is composed. The second end of the first intake pipe 22 is connected to the inlet of the compressor 32 of the supercharger 30, and the first end of the second intake pipe 24 is connected to the outlet of the compressor 32. The compressor 32 supercharges the air sucked through the first intake pipe 22 and supplies it to the second intake pipe 24.

The intercooler 25 is provided in the middle of the second intake pipe 24 and is configured to cool the air flowing through the second intake pipe 24. The intercooler 25 is, for example, an air-cooled or water-cooled heat exchanger.

The first end of the third intake pipe 27 is connected to the intercooler 25, and the second end of the third intake pipe 27 is connected to the intake manifold 28. Further, an intake throttle valve 26 is provided in the middle of the third intake pipe 27, and a connection portion C1 located on the downstream side (intake manifold 28 side) of the intake throttle valve 26 is the second EGR passage 66. The end is connected to the third intake pipe 27.

The intake throttle valve 26 includes a valve, a motor, an opening degree sensor (throttle position sensor), and the like. The air flow rate supplied to the intake manifold 28 (more specifically, the amount of fresh air output from the intercooler 25 and supplied to the intake manifold 28) changes according to the opening degree of the intake throttle valve 26. The opening degree of the intake throttle valve 26 is controlled by the control device 200. The control device 200 adjusts the opening degree of the intake throttle valve 26 to pass through the intake throttle valve 26 and supply fresh air to the connection portion C1 (and by extension, the intake manifold 28) (hereinafter, simply "fresh air"). Also called "quantity") can be controlled.

The intake manifold 28 is connected to the intake port of each cylinder 12 of the engine body 10. On the other hand, the exhaust manifold 50 is connected to the exhaust port of each cylinder 12 of the engine body 10. The first end of the first exhaust pipe 52 is connected to the exhaust manifold 50, and the second end of the first exhaust pipe 52 is connected to the inlet of the turbine 36 of the supercharger 30. The exhaust gas discharged from the exhaust port of each cylinder 12 is collected in the exhaust manifold 50 and then supplied to the turbine 36 via the first exhaust pipe 52.

The first end of the second exhaust pipe 54 is connected to the outlet of the turbine 36, and the inlet of the exhaust purification device 56 is connected to the second end of the second exhaust pipe 54. Examples of the exhaust gas purification device 56 include a DPF (Diesel Particulate Filter), a NOx catalyst, and a DPNR (Diesel Particlulate-NOx Reduction). The first end of the third exhaust pipe 58 is connected to the outlet of the exhaust gas purification device 56. The exhaust gas purified by the exhaust purification device 56 passes through the third exhaust pipe 58 and is discharged to the outside of the vehicle via a muffler or the like (not shown).

In the engine 1, the compressor 32 and the turbine 36 form a supercharger 30 (for example, a variable nozzle turbo). A compressor wheel 34 is provided in the housing of the compressor 32, and a turbine wheel 38 is provided in the housing of the turbine 36. The compressor wheel 34 and the turbine wheel 38 are connected by a connecting shaft 42 and rotate integrally. As a result, the compressor wheel 34 is rotationally driven by the exhaust energy of the exhaust gas supplied to the turbine wheel 38.

The EGR device 60 includes an EGR valve 62, an EGR cooler 64, an EGR passage 66, and a bypass passage 68. The EGR passage 66 is a passage for connecting the third intake pipe 27 and the exhaust manifold 50 without passing through the engine main body 10 and returning a part of the exhaust gas flowing through the exhaust manifold 50 to the third intake pipe 27. be. Further, the EGR valve 62 is provided in the EGR passage 66, and is configured so that the amount of EGR gas recirculated from the exhaust manifold 50 to the third intake pipe 27 can be adjusted. The EGR gas is an exhaust gas that is returned to the intake side by the EGR device 60. In this embodiment, the first intake pipe 22, the second intake pipe 24, the third intake pipe 27, and the intake manifold 28 form an intake passage. Further, the exhaust manifold 50, the first exhaust pipe 52, the second exhaust pipe 54, and the third exhaust pipe 58 form an exhaust passage. Further, the EGR passage 66 and the bypass passage 68 form a return path.

The EGR device 60 is configured to return a part of the exhaust gas to the intake passage. The EGR device 60 is controlled for the purpose of improving exhaust gas, for example, and by including the exhaust gas in the intake gas, the combustion temperature of the engine body 10 can be lowered and the generation of NOx due to combustion can be suppressed. By suppressing the generation of NOx due to combustion during engine 1 operation, the amount of NOx in the exhaust gas is reduced.

The first end of the EGR passage 66 is connected to the exhaust manifold 50, and the second end of the EGR passage 66 is connected to the connection portion C1 of the third intake pipe 27 described above. Further, an EGR valve 62 is provided in the middle of the EGR passage 66. Fresh air whose flow rate is adjusted by the intake throttle valve 26 and EGR gas whose flow rate is adjusted by the EGR valve 62 are supplied to the connection portion C1 of the third intake pipe 27. The first end of the EGR passage 66 may be connected to the first exhaust pipe 52, and the second end of the EGR passage 66 may be connected to the intake manifold 28.

In the EGR passage 66, an EGR cooler 64 is provided on the upstream side (exhaust manifold 50 side) of the EGR valve 62. The EGR cooler 64 is configured to cool the EGR gas. The EGR cooler 64 is, for example, a water-cooled or air-cooled heat exchanger.

Further, the EGR passage 66 is connected to the bypass passage 68 on the upstream side and the downstream side of the EGR cooler 64. The first end and the second end of the bypass passage 68 are connected to the EGR passage 66 by the connecting portions C2 and C3, respectively. The bypass passage 68 forms a route that does not pass through the EGR cooler 64. That is, the EGR gas supplied to the connection portion C2 reaches the connection portion C3 of the EGR passage 66 by passing through the bypass passage 68 without passing through the EGR cooler 64. The connection portion C3 has an EGR gas cooled by the EGR cooler 64 (hereinafter, also referred to as “first EGR gas”) and an EGR gas that has passed through the bypass passage 68 and has not passed through the EGR cooler 64 (hereinafter, “second EGR gas”). ”) And is supplied. The first and second EGR gases merge at the connection portion C3 to form a mixed EGR gas, which is supplied to the EGR valve 62. A valve for adjusting the mixing ratio of the first EGR gas and the second EGR gas may be provided at a position (connecting portion C3) where the first and second EGR gases meet.

The EGR valve 62 includes a valve (for example, a butterfly valve), a motor for driving the valve (for example, a DC motor), and a sensor for detecting the valve opening degree (for example, a non-contact valve rotation angle sensor using a Hall element). Consists of including. The opening degree (EGR opening degree) of the EGR valve 62 corresponds to the cross-sectional area of the passage. The EGR valve 62 allows the flow of EGR gas in the open state (the state where the EGR opening is larger than 0%), and prohibits the flow of the EGR gas in the closed state (the state where the EGR opening is 0%). do. The EGR opening degree is controlled by the control device 200. The control device 200 adjusts the EGR opening degree to pass through the EGR valve 62 and supply the second end (connection portion C1) of the EGR passage 66 to the EGR gas amount (hereinafter, also simply referred to as “EGR gas amount”). Can be controlled.

The engine 1 includes an air flow meter 102, an intake pressure sensor 106, a rotation speed sensor 108, a water temperature sensor 110, an exhaust pressure sensor 118, an accelerator pedal position sensor 112, an atmospheric pressure sensor 114, and an outside temperature sensor 116. Further prepare.

The air flow meter 102 detects the amount of air (fresh air amount) taken in from the outside through the air cleaner 20 and supplied to the engine body 10, and outputs the detected value FI to the control device 200.

The intake pressure sensor 106 detects the pressure (intake pressure) of the intake gas supplied to the intake manifold 28, and outputs the detected value Pb to the control device 200. The exhaust pressure sensor 118 detects the pressure (exhaust pressure) of the exhaust gas discharged to the exhaust manifold 50, and outputs the detected value P4 to the control device 200. The intake pressure sensor 106 and the exhaust pressure sensor 118 according to this embodiment correspond to examples of the "first pressure detection unit" and the "second pressure detection unit" according to the present disclosure, respectively.

The rotation speed sensor 108 detects the rotation speed (engine rotation speed) of the output shaft of the engine body 10 and outputs the detected value NE to the control device 200. The water temperature sensor 110 detects the temperature of the cooling water of the engine body 10 (engine cooling water temperature), and outputs the detected value TE to the control device 200. The accelerator pedal position sensor 112 detects the depression amount (accelerator opening degree) of the accelerator pedal (not shown), and outputs the detected value AP to the control device 200. The atmospheric pressure sensor 114 detects the atmospheric pressure and outputs the detected value Pa to the control device 200. The outside air temperature sensor 116 detects the outside air temperature and outputs the detected value Ta to the control device 200.

The control device 200 includes a CPU (Central Processing Unit) as an arithmetic unit, a storage device, and input / output ports for inputting / outputting various signals (none of which are shown). The storage device includes a RAM (Random Access Memory) as a work memory and a storage (ROM (Read Only Memory), a rewritable non-volatile memory, etc.) for storage. The control device 200 receives signals from various devices connected to the input port (for example, various sensors described above), and based on the received signals, various devices connected to the output port (injector 16, EGR device 60, etc.). To control. Various controls are executed by the CPU executing the program stored in the storage device. However, various controls are not limited to software processing, but can also be processed by dedicated hardware (electronic circuit).

In this embodiment, the amount of NOx in the exhaust gas is reduced by operating the EGR device 60 while the engine 1 is in operation. However, if the amount of EGR gas becomes excessively large with respect to the amount of fresh air during operation of the engine 1, combustion in the engine body 10 becomes unstable. On the other hand, if the amount of EGR gas is too small with respect to the amount of fresh air, the generation of NOx due to combustion during engine operation cannot be sufficiently suppressed. Therefore, during the operation of the EGR device 60, feedback control is performed so that the EGR rate becomes an appropriate value (target EGR rate described later).

The EGR ratio in the engine 1 is the ratio of the amount of EGR gas to the amount of intake gas supplied to the engine main body 10 in a predetermined period. Since the intake gas supplied to the engine body 10 corresponds to the intake gas distributed to each cylinder 12 by the intake manifold 28 and sucked into the combustion chamber of each cylinder 12, it is also referred to as "in-cylinder intake gas" below. The amount of intake gas in the cylinder (the amount of intake gas supplied to the engine body 10) corresponds to the total amount of intake gas sucked into each cylinder 12.

FIG. 2 is a diagram showing elements constituting the in-cylinder intake gas. With reference to FIG. 2, the in-cylinder intake gas is composed of fresh air and EGR gas supplied to the engine body 10. The in-cylinder intake gas is fresh air output from the intercooler 25 when the EGR valve 62 is in the closed state, and is a mixed gas of fresh air and EGR gas when the EGR valve 62 is in the open state. The amount of in-cylinder intake gas is the amount of fresh air supplied from the compressor 32 to the intake manifold 28 through the intercooler 25 and the amount of EGR gas supplied from the exhaust manifold 50 to the intake manifold 28 through the EGR passage 66 and the bypass passage 68. It corresponds to the sum (= fresh air amount + EGR gas amount).

In this embodiment, correspondence information (map or the like) showing the relationship between the intake pressure detected by the intake pressure sensor 106 and the in-cylinder intake gas amount is obtained in advance by, for example, an experiment or the like, and the control device 200 is used. It is stored in the storage device. The control device 200 estimates the amount of inhaled gas in the cylinder by using such correspondence information and the detected value Pb of the intake pressure sensor 106. Further, the control device 200 subtracts the fresh air amount supplied to the engine body 10 (for example, the detected value FI of the air flow meter 102) from the obtained estimated value of the in-cylinder intake gas amount to obtain the EGR gas amount. calculate. Then, the control device 200 acquires the detected value of the EGR rate (= EGR gas amount / cylinder inhaled gas amount) by dividing the EGR gas amount thus calculated by the estimated value of the in-cylinder intake gas amount. ..

The control device 200 determines the target EGR rate based on, for example, the operating state of the engine body 10 (accelerator opening degree, engine speed, engine cooling water temperature, etc.) and environmental information (atmospheric pressure, outside air temperature, etc.). A map or the like can be used to determine the target EGR rate. Then, the control device 200 performs feedback control based on the deviation (EGR rate deviation) between the detected value of the EGR rate acquired as described above and the target EGR rate, and the detected value of the EGR rate approaches the target EGR rate. The opening degree of the EGR valve 62 is operated in this manner.

The gain (feedback gain) of the feedback control is variable according to the EGR rate deviation. More specifically, when the EGR rate deviation is large, feedback control is performed with a large gain to bring the EGR rate closer to the target EGR rate quickly, and when the EGR rate deviation is small, feedback control is performed with a small gain to suppress overshoot. Is done. In PID control, the feedback gain is a general term for proportional gain, integrated gain, and differential gain.

By the way, during high load operation of the engine 1, the sensitivity of the change in the amount of EGR gas to the change in the EGR opening degree (and by extension, the sensitivity to the change in the EGR rate to the change in the EGR opening degree) tends to increase due to the increase in the exhaust pressure. There is. Therefore, when feedback control of the EGR rate is performed during high load operation of the engine 1, the EGR rate becomes excessively high due to overshoot, and the combustion of the engine 1 (and thus the operation of the engine 1) tends to become unstable. Become. In order to suppress such an excessive increase in the EGR rate, it is conceivable to reduce the feedback gain to slow down the opening / closing operation of the EGR valve 62. However, if the feedback gain is always reduced, the responsiveness of the feedback control is lowered, and the exhaust emission is likely to be deteriorated due to the delay in entering the EGR gas.

Therefore, in this embodiment, the control device 200 detects the estimated value of the in-cylinder intake gas amount and the intake pressure sensor 106 in addition to the EGR rate deviation (deviation between the detected value of the EGR rate and the target EGR rate). The differential pressure (intake / exhaust differential pressure) between the value Pb and the detected value P4 of the exhaust pressure sensor 118 is configured to determine the above feedback gain.

In this embodiment, the intake / exhaust differential pressure is obtained by subtracting the detection value Pb (intake pressure) of the intake pressure sensor 106 from the detection value P4 (exhaust pressure) of the exhaust pressure sensor 118 (hereinafter, “intake / exhaust difference”). Pressure P4-Pb ") is adopted. Since the intake pressure is higher than the exhaust pressure, the intake / exhaust differential pressure P4-Pb becomes a positive value. The absolute value of the difference between the intake pressure and the exhaust pressure may be adopted as the intake / exhaust differential pressure.

The inventor of the present application has found that the EGR opening sensitivity (sensitivity of EGR rate change with respect to EGR opening change) shows a high correlation with each of the intake / exhaust differential pressure P4-Pb and the in-cylinder intake gas amount. Hereinafter, this correlation will be described with reference to FIGS. 3 and 4.

FIG. 3 shows the relationship between the EGR gas amount change amount Δegr (hereinafter, also simply referred to as “Δegr”) when the opening degree of the EGR valve 62 is operated to the side opened by a unit operation amount, and the intake / exhaust differential pressure P4-Pb. It is a figure which shows. In FIG. 3, the magnitude of Δegr is shown with Δegr as 0 (reference) when the intake / exhaust differential pressure P4-Pb is 0.

With reference to FIG. 3, the amount of increase in EGR gas (Δegr) when the EGR opening is operated to the side opened by a certain amount increases as the intake / exhaust differential pressure P4-Pb increases. It is considered that the reason for this is that the larger the intake / exhaust differential pressure P4-Pb, the easier it is for the EGR gas to be supplied from the exhaust manifold 50 to the intake manifold 28. When the intake / exhaust differential pressure P4-Pb is large, the influence of the fluctuation of the EGR opening degree on the EGR gas amount becomes large, and the EGR gas amount tends to change greatly by the operation of the EGR opening degree in the feedback control. Therefore, even if the operation amount of the EGR opening degree (the amount of changing the EGR opening degree by the feedback control) is small, the amount of EGR gas (and thus the EGR rate) can change significantly.

FIG. 4 is a diagram showing in-cylinder intake gas to which EGR gas corresponding to Δegr is added by manipulating the EGR opening degree for two examples. In the two examples shown in FIG. 4, Δegr is the same. However, in the example on the right side, the amount of inhaled gas in the cylinder is larger than that in the example on the left side.

With reference to FIG. 4, the fluctuation amount (Δegr) of the EGR gas is the same in both the example on the left side and the example on the right side. However, from the relational expression such as "EGR rate = EGR gas amount / inhalation gas amount in the cylinder", the EGR rate changes due to the fluctuation of the EGR gas amount (more specifically, the increase of the EGR gas corresponding to Δegr). The amount is larger in the example on the left side (example in which the amount of inhaled gas in the cylinder is small) than in the example on the right side (example in which the amount of inhaled gas in the cylinder is large). When the amount of inhaled gas in the cylinder is small, the influence of the fluctuation of the EGR gas amount on the EGR rate becomes large, and the EGR rate tends to change significantly due to the fluctuation of the EGR gas amount. Therefore, even if the operation amount of the EGR opening degree (and by extension, the change amount of the EGR gas) is small, the EGR rate can change significantly.

The control device 200 grasps the height of the EGR opening sensitivity from the in-cylinder intake gas amount (estimated value) and the intake / exhaust differential pressure P4-Pb, and adopts a feedback gain according to the height of the EGR opening sensitivity. be able to. That is, an appropriate feedback gain is adopted both in a situation where the EGR opening sensitivity is high (for example, during high load operation of the engine 1) and in a situation where the EGR opening sensitivity is low (for example, during low load operation of the engine 1). can do. Therefore, in the feedback control of the EGR rate, the control device 200 adopts an appropriate feedback gain in both the low load operation and the high load operation of the engine 1 to suppress overshoot and have sufficient responsiveness. Can be secured.

In recent years, due to the tightening of exhaust gas regulations, it is required to recirculate the exhaust gas by the EGR device not only during the low load operation of the engine but also during the high load operation. FIG. 5 is a diagram showing trends in engine usage conditions before and after emission regulations are tightened. In the graph shown in FIG. 5, the horizontal axis indicates the intake / exhaust differential pressure P4-Pb, and the vertical axis indicates the amount of intake gas in the cylinder. In FIG. 5, the data D1 shows the data before the exhaust regulation is tightened, and the data D2 shows the data after the exhaust regulation is tightened.

As shown in the data D2 with reference to FIG. 5, by tightening the exhaust regulation, the usage area of the engine is expanded as compared with before the tightening of the exhaust regulation (data D1). The region R indicates a region in which the EGR opening sensitivity is particularly high among the regions in which the engine is used after the exhaust gas recirculation is tightened. More specifically, the EGR opening sensitivity becomes high under the condition that the amount of intake gas in the cylinder is small and the intake / exhaust differential pressure P4-Pb is high. In the region R, the in-cylinder intake gas amount is 80 g / s or more and 120 g / s or less, and the intake / exhaust differential pressure P4-Pb is 50 kPa or more and 70 kPa or less (hereinafter, also referred to as “high frequency region”). However, it is used particularly frequently.

In this embodiment, in consideration of the usage conditions (use area) of the engine after the exhaust regulation is tightened as shown in FIG. 5, the gain information (for example, described later) as described below by the control device 200 is taken into consideration. The second gain information shown in FIG. 8) is possessed, and the feedback gain is determined using the relationship defined by this gain information.

The gain information defines the relationship between the intake / exhaust differential pressure P4-Pb and the amount of in-cylinder intake gas. More specifically, if the intake / exhaust differential pressure P4-Pb is the same, the smaller the amount of in-cylinder intake gas becomes. It defines a relationship in which the feedback gain becomes smaller as the intake / exhaust differential pressure P4-Pb becomes larger when the feedback gain becomes smaller and the amount of inhaled gas in the cylinder is the same. Further, the gain information is described above in a region where the in-cylinder intake gas amount is at least 80 g / s or more and 120 g / s or less and the intake / exhaust differential pressure is 50 kPa or more and 70 kPa or less (that is, the above-mentioned high frequency region). Define the relationship.

The opening / closing speed of the EGR valve 62 (for example, the angular velocity of the valve) changes according to the feedback gain, and the higher the feedback gain, the faster the opening / closing operation of the EGR valve tends to be. By determining the feedback gain using the gain information as described above, in a situation where the EGR opening sensitivity is high (for example, during high load operation of the engine), the EGR opening sensitivity is low (for example, in the engine). The feedback gain becomes smaller than in the case of low load operation), the opening / closing operation of the EGR valve becomes slower, and an excessive increase in the EGR rate is suppressed. Further, in a situation where the EGR opening sensitivity is low, the feedback gain becomes sufficiently large to speed up the opening / closing operation of the EGR valve, and it becomes possible to secure sufficient responsiveness in the feedback control of the EGR rate.

Further, according to the gain information, the EGR rate can be appropriately feedback-controlled in the high frequency region, which is frequently used when the exhaust gas is recirculated by the EGR device 60 during high load operation of the engine 1. It will be possible.

When a plurality of gains (for example, proportional gain, integral gain, and differential gain) are used in the feedback control of the EGR rate, gain information suitable for each gain may be prepared. Further, only a specific gain (for example, a proportional gain that easily affects the opening / closing speed of the EGR valve 62) may be determined by the above gain information, and other gains may be determined by another method.

Hereinafter, the feedback control of the EGR rate executed by the control device 200 will be described. FIG. 6 is a control block diagram showing a configuration for performing feedback control of the EGR rate in the control device 200.

With reference to FIG. 6, the control device 200 includes a controller 210, an in-cylinder intake gas amount acquisition unit 220, an EGR rate acquisition unit 230, and subtraction units 240 and 250.

The in-cylinder intake gas amount acquisition unit 220 acquires the in-cylinder intake gas amount based on the detection value Pb of the intake pressure sensor 106, and outputs a signal EGin indicating the in-cylinder intake gas amount to the EGR rate acquisition unit 230 and the controller 210. Output to each.

Correspondence information (for example, a mathematical formula) indicating the relationship between the intake pressure and the amount of intake gas in the cylinder can be used to acquire the amount of intake gas in the cylinder. The in-cylinder intake gas amount acquisition unit 220 can estimate the in-cylinder intake gas amount from the detection value Pb of the intake pressure sensor 106 by referring to the corresponding information stored in the storage device of the control device 200 in advance. Correspondence information is not limited to mathematical formulas, and may be a map, a table, or a model. Further, the correspondence information may be configured by combining a plurality of maps and the like. In addition to the detection value Pb of the intake pressure sensor 106 corresponding to the boost pressure, the intake air temperature of the intake manifold 28 (for example, the intake air temperature actually measured by the temperature sensor (not shown) provided in the intake manifold 28). ) And the engine speed may be taken into consideration to determine the amount of intake gas in the cylinder.

The EGR rate acquisition unit 230 acquires the EGR rate based on the signal EGin input from the in-cylinder intake gas amount acquisition unit 220 and the detection value FI of the air flow meter 102, and subtracts the signal eegr indicating the EGR rate. Output to 240. More specifically, the EGR rate acquisition unit 230 calculates the EGR gas amount by subtracting the detected value FI (fresh air amount) of the air flow meter 102 from the estimated value of the in-cylinder intake gas amount indicated by the signal EGin. do. Then, the EGR rate acquisition unit 230 acquires the EGR rate by dividing the EGR gas amount thus calculated by the estimated value of the in-cylinder intake gas amount.

The subtraction unit 240 subtracts the current EGR rate (hereinafter, also referred to as “actual EGR rate”) indicated by the signal egr from the target EGR rate indicating the target value of the EGR rate, and the calculated value (that is, the target EGR rate). And the deviation from the actual EGR rate) is output to the controller 210. The target EGR rate is generated based on, for example, the operating state of the engine body 10 (detection values AP, NE, TE), environmental information (detection values Pa, Ta), and the like.

On the other hand, the subtraction unit 250 subtracts the detection value Pb (current intake pressure) of the intake pressure sensor 106 from the detection value P4 (current exhaust pressure) of the exhaust pressure sensor 118, and the calculated value (that is, the current intake / exhaust). The differential pressure P4-Pb) is output to the controller 210.

The controller 210 is input from the signal EGin input from the in-cylinder intake gas amount acquisition unit 220, the EGR rate deviation (deviation between the target EGR rate and the actual EGR rate) input from the subtraction unit 240, and the subtraction unit 250. The feedback gain (eg, proportional gain, integrated gain, and differential gain) is determined using the intake and exhaust differential pressures P4-Pb.

The determination of the feedback gain by the controller 210 is performed with reference to the gain information (map or the like) stored in the storage device of the control device 200. The storage device of the control device 200 contains first gain information indicating the relationship between the EGR rate deviation and the feedback gain, and second gain information indicating the relationship between the in-cylinder intake gas amount, the intake / exhaust differential pressure, and the feedback gain. It is remembered. For example, the first gain information and the second gain information suitable for each gain are obtained in advance by an experiment or the like and stored in the storage device. The first gain information and the second gain information may be maps, tables, mathematical formulas, or models independently of each other. Further, each gain information may be configured by combining a plurality of maps and the like.

FIG. 7 is a diagram showing an example (map) of the first gain information. With reference to FIG. 7, the first gain information defines the value of the feedback gain corresponding to the EGR rate deviation. The first gain information defines a relationship in which the feedback gain increases as the EGR rate deviation increases.

FIG. 8 is a diagram showing an example (map) of the second gain information. With reference to FIG. 8, the second gain information defines a correction coefficient for correcting the feedback gain obtained by the first gain information. The range of the in-cylinder intake gas amount in this second gain information is a range including 80 g / s or more and 120 g / s or less (for example, 30 g / s or more and 150 g / s or less). Further, the range of the intake / exhaust differential pressure in the second gain information is a range including 50 kPa or more and 70 kPa or less (for example, 30 kPa or more and 150 kPa or less). For the second gain information, if the intake / exhaust differential pressure is the same, the correction coefficient becomes smaller as the amount of intake gas in the cylinder decreases, and if the amount of intake gas in the cylinder is the same, the correction coefficient becomes smaller as the intake / exhaust differential pressure increases. It stipulates such a relationship.

In this embodiment, the value obtained by multiplying the value of the feedback gain obtained by the first gain information by the correction coefficient obtained by the second gain information is defined as the feedback gain. In this way, the feedback gain is determined by the first gain information and the second gain information. In the second gain information, the maximum value of the correction coefficient (more specifically, the value of the correction coefficient defined in the region where the amount of inhaled gas in the cylinder is large and the intake / exhaust differential pressure is small) is, for example, 1.0. (No correction), and the minimum value of the correction coefficient (more specifically, the value of the correction coefficient defined in the region where the in-cylinder intake gas amount is small and the intake / exhaust differential pressure is large) is, for example, 0. It is 5.

The control device 200 performs feedback control of the EGR rate using the feedback gain determined as described above. More specifically, the controller 210 executes PID control (proportional integral differential control) by the feedback gain based on the EGR rate deviation input from the subtraction unit 240, so that the EGR rate deviation approaches 0. The operation amount (more specifically, the operation amount of the EGR opening degree) is calculated, and the drive signal Feedback corresponding to this operation amount is generated and output to the EGR valve 62. By driving the EGR valve 62 by this drive signal Vegr, the opening degree of the EGR valve 62 is operated so that the actual EGR rate approaches the target EGR rate.

In the feedback control of the EGR rate by the control device 200, the in-cylinder intake gas amount acquisition unit 220 acquires the in-cylinder intake gas amount, the EGR rate acquisition unit 230 acquires the EGR rate, and the subtraction unit 240 calculates the EGR rate deviation. And, the acquisition of the intake / exhaust differential pressure P4-Pb by the subtraction unit 250, the determination of the gain by the controller 210, and the calculation of the operation amount of the EGR opening degree by the controller 210 are repeatedly performed, and the EGR calculated by the controller 210 is performed repeatedly. The EGR valve 62 is driven by the drive signal Vegr generated based on the operation amount of the opening degree. As a result, the actual EGR rate is controlled so as to converge to the target EGR rate.

In the feedback control of the EGR rate, the feedback gain is determined to be smaller as the EGR rate deviation is smaller, smaller as the in-cylinder intake gas amount is smaller, and smaller as the intake / exhaust differential pressure P4-Pb is larger. By making the gain of the feedback control variable in this tendency, the feedback control of the EGR rate can be suitably performed (see FIGS. 3 and 4). Further, according to the first gain information (FIG. 7) and the second gain information (FIG. 8), even in the region R in FIG. 5, sufficient responsiveness is ensured while suppressing overshoot in the feedback control of the EGR rate. It will be possible to do. The controller 210 may execute PI control instead of PID control.

In the above embodiment, a map (first gain information) that defines the value of the feedback gain and a map (second gain information) that defines the correction coefficient are used. However, it is not essential to obtain the optimum feedback gain in two steps (that is, to obtain a temporary gain and then optimize it by correction), and it is necessary to obtain the EGR rate deviation, the amount of intake gas in the cylinder, and the intake / exhaust differential pressure. The optimum feedback gain may be obtained directly. For example, the optimum feedback gain (and its function) for each condition is obtained in advance by experiments, etc., and the gain expressed as a function of the EGR rate deviation, the in-cylinder intake gas amount, and the intake / exhaust differential pressure (for example, proportional). (Gain) may be used to perform feedback control of the EGR rate (for example, PID control or PI control).

In the above embodiment, the intake / exhaust differential pressure is obtained by using the measured values of the intake pressure and the exhaust pressure (measured values by the intake pressure sensor 106 and the exhaust pressure sensor 118). However, the present invention is not limited to this, and an estimated value estimated from the state of the engine 1 or the like may be used as at least one of the intake pressure and the exhaust pressure. For example, the exhaust pressure of the exhaust manifold 50 may be estimated from the engine speed, the engine load (fuel injection amount), and the VN opening degree of the turbocharger 30 (the opening degree of the nozzle vane constituting the variable nozzle mechanism). Further, the exhaust pressure of the exhaust manifold 50 is estimated from the exhaust pressure on the downstream side of the exhaust manifold 50 (for example, the exhaust pressure measured by a pressure sensor (not shown) provided near the inlet of the exhaust purification device 56). You may.

The object to which the engine control device of the present invention is applied is not limited to a vehicle, but is arbitrary. The application target may be, for example, other vehicles (ships, airplanes, etc.).

The embodiments disclosed this time should be considered to be exemplary and not restrictive in all respects. The scope of the present invention is shown by the scope of claims rather than the description of the embodiments described above, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 engine, 10 engine body, 12 cylinders, 14 common rails, 16 injectors, 20 air cleaners, 22 first intake pipes, 24 second intake pipes, 25 intercoolers, 26 intake throttle valves, 27 third intake pipes, 28 intake manifolds, 30 turbocharger, 32 compressor, 34 compressor wheel, 36 turbine, 38 turbine wheel, 42 connecting shaft, 50 exhaust manifold, 52 first exhaust pipe, 54 second exhaust pipe, 56 exhaust purification device, 58 third exhaust pipe, 60 EGR device, 62 EGR valve, 64 EGR cooler, 66 EGR passage, 68 bypass passage, 102 air flow meter, 106 intake pressure sensor, 108 rotation speed sensor, 110 water temperature sensor, 112 accelerator pedal position sensor, 114 atmospheric pressure sensor, 116 Outside temperature sensor, 118 exhaust pressure sensor, 200 control device, 210 controller, 220 in-cylinder intake gas amount acquisition unit, 230 EGR rate acquisition unit, 240, 250 subtraction unit.

Claims (3)

An engine main body having a combustion chamber, a recirculation path connecting an intake passage and an exhaust passage without passing through the engine main body, and returning a part of exhaust gas flowing through the exhaust passage to the intake passage, and a recirculation path. An EGR valve that is provided in the above and is configured to be able to adjust the amount of EGR gas that returns from the exhaust passage to the intake passage, and a first pressure detection that detects the intake pressure that is the pressure of the intake gas that is sucked into the combustion chamber. An engine control device including a unit and a second pressure detecting unit that detects an exhaust pressure, which is the pressure of the exhaust gas discharged from the combustion chamber.
The control device of the engine detects the EGR rate, which is the ratio of the EGR gas amount to the intake gas amount supplied to the engine body, and the detected value of the EGR rate approaches the target EGR rate by feedback control. It is configured to operate the opening degree of the EGR valve.
The control device of the engine has an EGR rate deviation which is a deviation between the detected value of the EGR rate and the target EGR rate, an intake gas amount supplied to the engine main body, and a differential pressure between the intake pressure and the exhaust pressure. To determine the gain of the feedback control ,
The engine control device determines that the gain of the feedback control becomes smaller as the EGR rate deviation becomes smaller, becomes smaller as the intake gas amount becomes smaller, and becomes smaller as the differential pressure becomes larger . It possesses correspondence information indicating the relationship between the intake pressure and the intake gas amount, estimates the intake gas amount using the detection value of the first pressure detection unit and the correspondence information, and estimates the intake gas amount. The EGR gas amount is calculated by subtracting the fresh air amount supplied to the engine body from the value, and the calculated EGR gas amount is divided by the estimated value of the intake gas amount to obtain the EGR rate. The engine control device according to claim 1 , which is configured to acquire a detected value. It has gain information indicating the relationship between the intake gas amount, the differential pressure, and the gain of the feedback control, and is configured to determine the gain of the feedback control using the relationship defined by the gain information.
As for the gain information, if the differential pressure is the same, the smaller the amount of the intake gas, the smaller the gain of the feedback control, and if the amount of the intake gas is the same, the larger the differential pressure, the greater the gain of the feedback control. The engine control device according to claim 1 or 2 , which defines a relationship that makes the relationship smaller.

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