JP2019203435A - Control device of engine - Google Patents

Abstract

To secure sufficient responsiveness while suppressing overshoot in feedback control of an EGR rate in any of a low load operation and a high load operation of an engine.SOLUTION: In an engine 1 including an engine main body 10, an EGR passage 66, an EGR valve 62, an intake pressure sensor 106, and an exhaust pressure sensor 118, a control device 200 is constituted to detect an EGR rate, and to control an opening of the EGR valve 62 so that a detection value of the EGR rate approaches a target EGR rate by feedback control. Further the control device 200 is constituted to determine feedback gain by using an EGR rate deviation as deviation between the detection value of the EGR rate and the target EGR rate, an intake gas amount supplied to the engine main body 10, and difference between an intake pressure and an exhaust pressure detected by the intake pressure sensor 106 and the exhaust pressure sensor 118.SELECTED DRAWING: Figure 1

Description

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

  Known feedback control methods include PID control that combines P (proportional) operation, I (integration) operation, and D (differential) operation, and PI control that combines P operation and I operation. For example, in an 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 supercharging pressure is performed by PID control.

JP 2017-198091 A

  By the way, the EGR device mounted on the engine is controlled for the purpose of improving exhaust emission, for example. The exhaust gas is recirculated by operating the EGR device, and the recirculated exhaust gas (EGR gas) is included in the intake gas, thereby lowering the combustion temperature of the engine. By doing so, generation of NOx due to combustion can be suppressed. By suppressing the generation of NOx due to combustion during engine operation, the amount of NOx in the exhaust gas is reduced.

  When the EGR device is in operation, if the amount of EGR gas is excessively larger than the amount of fresh air taken into the combustion chamber of the engine, combustion during engine operation becomes unstable. On the other hand, if the amount of EGR gas is too small relative to the amount of fresh air, the generation of NOx due to combustion during engine operation is not sufficiently suppressed. Therefore, during the operation of the EGR device, feedback control (PID control) is performed so that the EGR rate (the ratio of the EGR gas amount in the intake gas amount supplied to the engine body) becomes an appropriate value (target EGR rate). Alternatively, PI control or the like is performed.

  The feedback control of the EGR rate operates (adjusts) the opening degree (hereinafter also referred to as “EGR opening degree”) of an EGR valve provided in a return passage (a passage for returning a part of exhaust gas to the intake passage). It is done by doing. Further, the feedback control gain 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, in recent years, with the tightening of exhaust regulations, the inventors of the present application have confirmed the following new problems regarding the feedback control described above.

  Due to the strengthening of exhaust regulations, it is required to recirculate 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 exhaust gas pressure increases, so that the sensitivity of the EGR gas amount change with respect to the EGR opening change (and hence the sensitivity of the EGR rate change with respect to the EGR opening change) tends to increase. For this reason, 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 that the feedback gain is reduced to slow the opening / closing operation of the EGR valve. However, if the feedback gain is always reduced, the responsiveness of the feedback control is reduced, and the exhaust emission is likely to deteriorate due to the delay in entering the EGR gas.

  The present invention has been made to solve the above-described problems, and its purpose is to suppress overshoot in feedback control of the EGR rate in both low load operation and high load operation of the engine. It is to ensure sufficient responsiveness.

  An engine control apparatus according to the present invention includes an engine body having a combustion chamber, a reflux path, an EGR valve provided in the reflux path, a first pressure detection unit, and a second pressure detection unit. The EGR rate, which is the ratio of the EGR gas amount in the intake gas amount 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 opening degree of the valve.

  In the above-described engine, the recirculation path is a path for connecting the intake passage and the exhaust passage without passing through the engine main body to recirculate a part of the exhaust gas flowing through the exhaust passage to the intake passage. The EGR valve is configured to be able to adjust the amount of EGR gas recirculated from the exhaust passage to the intake passage. The first pressure detector is configured to detect an intake pressure that is the pressure of the intake gas sucked into the combustion chamber. The second pressure detection unit is configured to detect an exhaust pressure that is a pressure of the exhaust gas discharged from the combustion chamber. 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 an actual measurement value measured using a pressure sensor, or an engine It may be an estimated value estimated from the state or the like.

  The above control device includes an EGR rate deviation that is a deviation between the detected value of the EGR rate and the target EGR rate, an intake gas amount supplied to the engine body (hereinafter also simply referred to as “intake gas amount”), The feedback control gain (feedback gain) is determined using a differential pressure between the intake pressure and the exhaust pressure (hereinafter also referred to as “intake / exhaust differential pressure”).

  In the engine control apparatus described above, the feedback gain is determined based on the EGR rate deviation, so that when the EGR rate deviation is large, feedback control can be performed with a large gain in order to quickly bring the EGR rate close to the target EGR rate. When the EGR rate deviation is small, feedback control can be performed with a large gain to suppress overshoot. The deviation is a parameter indicating a deviation (degree of difference) between two values. As the deviation, a difference or a ratio can be adopted. The greater the difference (absolute value), the greater the deviation. Also, 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 with respect to the EGR opening change (hereinafter also referred to as “EGR opening sensitivity”) shows high correlation with each of the intake / exhaust differential pressure and the intake gas amount. It was. When the intake / exhaust differential pressure is large, the influence of the fluctuation of the EGR opening on the EGR gas quantity becomes large, and the EGR gas quantity tends to change greatly by the operation of the EGR opening 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 greatly due to the fluctuation of the EGR gas amount.

  The engine control apparatus can grasp the height of the EGR opening sensitivity from the intake gas amount and the intake / exhaust differential pressure, and can employ a feedback gain corresponding to the height of the EGR opening sensitivity. That is, an appropriate feedback gain should be adopted even 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 (eg, during low-load operation of the engine). Can do.

  As described above, according to the engine control apparatus of the present invention, in the EGR rate feedback control, an appropriate feedback gain is employed in both low load operation and high load operation of the engine, thereby overshooting. It is possible to ensure sufficient responsiveness while suppressing the above.

  In the engine control apparatus, the feedback control gain may be determined such that it decreases as the EGR rate deviation decreases, decreases as the intake gas amount decreases, and decreases as the intake / exhaust differential pressure increases. .

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

  The engine control device may have correspondence information (such as a map) indicating 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 correspondence information, and the fresh air amount supplied to the engine body from the obtained estimated value of the intake gas amount The EGR gas amount may be calculated by subtracting. Then, the control device may obtain the detected value of the EGR rate by dividing the EGR gas amount calculated in this way by the estimated value of the intake gas amount. According to such a configuration, the detected value of the EGR rate can be appropriately acquired with a configuration that is easy to realize in terms of cost and technology.

  The engine control device may have gain information (such as a map) indicating a relationship among an intake gas amount, an intake / exhaust differential pressure, and a gain of feedback control. For example, the control device may include a storage device that stores such gain information. The gain information is not limited to the one that defines the value of the feedback gain, but may be one that defines a correction coefficient for correcting the feedback gain. The control device may be configured to determine a gain of feedback control using a relationship defined by the gain information. The gain information indicates that the feedback control gain decreases as the intake gas amount decreases if the intake / exhaust differential pressure is the same, and the feedback control gain increases as the intake / exhaust differential pressure increases if the intake gas amount is the same. May be defined. According to such a configuration, the EGR rate can be appropriately feedback controlled.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to ensure sufficient responsiveness, suppressing an overshoot in feedback control of an EGR rate in both the low load operation and the high load operation of the engine.

1 is an overall configuration diagram of an engine control system according to an embodiment of the present invention. It is a figure which shows the element which comprises in-cylinder inhalation gas. It is a figure which shows the relationship between the EGR gas amount variation | change_quantity when the opening degree of an EGR valve is operated to the side opened only unit operation amount, and intake / exhaust differential pressure | voltage. It is a figure which shows in-cylinder inhalation gas which EGR gas increased by operation of the EGR opening degree about two examples. It is a figure which shows the tendency of the use condition of an engine in each before and after exhaust regulations are strengthened. 1 is a control block diagram showing a configuration for performing feedback control of an EGR rate in an engine control apparatus according to an embodiment of the present invention. It is a figure which shows an example of the 1st gain information used in order to determine a feedback gain. It is a figure which shows an example of the 2nd gain information used in order to determine a feedback gain.

  Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference numerals and description thereof will not be repeated.

  FIG. 1 is an overall configuration diagram of an engine control system according to the present embodiment. Referring to FIG. 1, an engine 1 to be controlled in this engine control system is mounted on a vehicle (for example, a four-wheeled vehicle) as a power generation device for traveling, for example. In the present embodiment, the engine 1 is a common rail in-line four-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 of a cylinder layout other than in-line (for example, V type or horizontal type). Further, the number of cylinders can be arbitrarily changed.

  The engine 1 includes an engine 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. The engine 1 is controlled by the control device 200. Hereinafter, in the engine 1, for piping or the like that functions as a flow path, 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”.

  The engine body 10 includes a plurality of cylinders 12, a common rail 14, and a plurality of injectors 16. Each cylinder 12 is provided with a piston (not shown), 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 the common rail 14. The fuel stored in a 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 into the combustion chamber from each injector 16 at a predetermined timing.

  The air cleaner 20 is provided in the middle of the first intake pipe 22 so as to remove foreign matters contained in air sucked from an intake port (not shown) provided at a first end of the first intake pipe 22. 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.

  A first end of the third intake pipe 27 is connected to the intercooler 25, and a 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 the second portion of the EGR passage 66 is connected to the connection portion C <b> 1 located downstream of the intake throttle valve 26 (intake manifold 28 side). The end is connected to the third intake pipe 27.

  The intake throttle valve 26 includes a valve, a motor, an opening sensor (throttle position sensor), and the like. The flow rate of air 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 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 so as to pass through the intake throttle valve 26 and supply the fresh air amount (hereinafter simply referred to as “new air” supplied to the connection portion C1 (and hence the intake manifold 28). Can also 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. A first end of the first exhaust pipe 52 is connected to the exhaust manifold 50, and a 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.

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

  In the engine 1, the compressor 32 and the turbine 36 constitute 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. Thereby, 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 body 10 and for returning a part of the exhaust gas flowing through the exhaust manifold 50 to the third intake pipe 27. is there. The EGR valve 62 is provided in the EGR passage 66, and is configured to be able to adjust the amount of EGR gas that recirculates from the exhaust manifold 50 to the third intake pipe 27. The EGR gas is exhaust gas recirculated 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 constitute an intake passage. The exhaust manifold 50, the first exhaust pipe 52, the second exhaust pipe 54, and the third exhaust pipe 58 constitute an exhaust passage. Further, the EGR passage 66 and the bypass passage 68 constitute a reflux passage.

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

  A first end of the EGR passage 66 is connected to the exhaust manifold 50, and a second end of the EGR passage 66 is connected to the connection portion C1 of the third intake pipe 27 described above. 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.

  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 connection portions C2 and C3, respectively. A path that does not pass through the EGR cooler 64 is formed by the bypass passage 68. That is, the EGR gas supplied to the connection portion C2 reaches the connection portion C3 of the EGR passage 66 without passing through the EGR cooler 64 by passing through the bypass passage 68. The connection portion C3 includes an EGR gas cooled by the EGR cooler 64 (hereinafter also referred to as “first EGR gas”) and an EGR gas that passes through the bypass passage 68 and does not pass through the EGR cooler 64 (hereinafter referred to as “second EGR gas”). Is also provided). The first and second EGR gases merge at the connection portion C3 to become mixed EGR gas, and are supplied to the EGR valve 62. In addition, you may provide the valve for adjusting the mixing ratio of 1st EGR gas and 2nd EGR gas in the location (connection part C3) where 1st and 2nd EGR gas merges.

  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 (for example, a non-contact type 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 passage sectional area. The EGR valve 62 permits the flow of EGR gas in the open state (the state where the EGR opening is larger than 0%), and prohibits the flow of EGR gas in the closed state (the state where the EGR opening is 0%). To do. The EGR opening degree is controlled by the control device 200. The control device 200 adjusts the EGR opening, thereby passing through the EGR valve 62 and supplying the EGR gas amount (hereinafter simply referred to as “EGR gas amount”) supplied to the second end (connecting portion C1) of the EGR passage 66. 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 air temperature sensor 116. Is further provided.

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

  The intake pressure sensor 106 detects the pressure of the intake gas (intake pressure) 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. Note that the intake pressure sensor 106 and the exhaust pressure sensor 118 according to this embodiment correspond to examples of a “first pressure detection unit” and a “second pressure detection unit” according to the present disclosure, respectively.

  The rotational speed sensor 108 detects the rotational speed (engine rotational 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 amount of depression (accelerator opening) of an 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 device, 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 working memory and a storage for storage (ROM (Read Only Memory), rewritable nonvolatile memory, etc.). The control device 200 receives signals from various devices connected to the input port (for example, the above-described various sensors), and various devices connected to the output port based on the received signals (such as the injector 16 and the EGR device 60). To control. Various controls are executed by the CPU executing the program stored in the storage device. However, various types of control are not limited to processing by software, and can be processed by dedicated hardware (electronic circuit).

  In this embodiment, the NOx amount in the exhaust gas is reduced by operating the EGR device 60 during operation of the engine 1. However, if the amount of EGR gas is excessive with respect to the amount of fresh air during the 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 relative to the amount of fresh air, the generation of NOx due to combustion during engine operation is not sufficiently suppressed. Therefore, during the operation of the EGR device 60, feedback control is performed so that the EGR rate becomes an appropriate value (a target EGR rate described later).

  The EGR rate in the engine 1 is the ratio of the amount of EGR gas in the amount of intake gas supplied to the engine body 10 during a predetermined period. The intake gas supplied to the engine body 10 corresponds to the intake gas that is distributed to each cylinder 12 by the intake manifold 28 and is sucked into the combustion chamber of each cylinder 12, and is hereinafter also referred to as “in-cylinder intake gas”. The in-cylinder intake gas amount (intake gas amount supplied to the engine body 10) corresponds to the total intake gas amount sucked into each cylinder 12.

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

  In this embodiment, correspondence information (such as a map) indicating the relationship between the intake pressure detected by the intake pressure sensor 106 and the in-cylinder intake gas amount is obtained in advance through experiments or the like, for example, and It is stored in the storage device. The control device 200 estimates the in-cylinder intake gas amount using such correspondence information and the detection value Pb of the intake pressure sensor 106. Further, the control device 200 subtracts the amount of EGR gas by subtracting the amount of fresh air supplied to the engine body 10 (for example, the detection value FI of the air flow meter 102) from the obtained estimated value of the cylinder intake gas amount. calculate. Then, the control device 200 divides the EGR gas amount thus calculated by the estimated value of the in-cylinder intake gas amount to obtain a detection value of the EGR rate (= EGR gas amount / 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, engine speed, engine coolant 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. The control device 200 performs feedback control based on the deviation (EGR rate deviation) between the detected value of the EGR rate and the target EGR rate obtained as described above, and the detected value of the EGR rate approaches the target EGR rate. Thus, the opening degree of the EGR valve 62 is operated.

  The gain of the feedback control (feedback gain) 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. Note that the feedback gain corresponds to a generic name of a proportional gain, an integral gain, and a differential gain in PID control.

  By the way, when the engine 1 is operated at a high load, the sensitivity of the EGR gas amount change with respect to the EGR opening change (and hence the sensitivity of the EGR rate change with respect to the EGR opening change) tends to increase due to the increase in the exhaust pressure. There is. For this reason, 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 hence 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 that the feedback gain is reduced 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 reduced, and the exhaust emission is likely to deteriorate 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 detection of 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 feedback gain is configured to be determined using a differential pressure (intake and exhaust differential pressure) between the value Pb and the detected value P4 of the exhaust pressure sensor 118.

  In this embodiment, as the intake / exhaust differential pressure, a value obtained by subtracting the detected value Pb (intake pressure) of the intake pressure sensor 106 from the detected value P4 (exhaust pressure) of the exhaust pressure sensor 118 (hereinafter referred to as “intake / exhaust difference”). Pressure P4-Pb "). Since the intake pressure is higher than the exhaust pressure, the intake / exhaust differential pressure P4-Pb is 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 the EGR rate change with respect to the EGR opening change) is highly correlated with the intake / exhaust differential pressure P4-Pb and the in-cylinder intake gas amount. Hereinafter, this correlation is demonstrated using FIG.3 and FIG.4.

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

  Referring to FIG. 3, the increase amount (Δegr) of EGR gas when the EGR opening degree is manipulated to open by a certain amount increases as the intake / exhaust differential pressure P4-Pb increases. The reason for this is considered that EGR gas is more easily supplied from the exhaust manifold 50 to the intake manifold 28 as the intake / exhaust differential pressure P4-Pb increases. When the intake / exhaust differential pressure P4-Pb is large, the influence of the fluctuation of the EGR opening on the EGR gas quantity becomes large, and the EGR gas quantity tends to change greatly by the operation of the EGR opening degree in the feedback control. For this reason, even if the operation amount of the EGR opening (the amount by which the EGR opening is changed by feedback control) is small, the EGR gas amount (and thus the EGR rate) can change greatly.

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

  Referring to FIG. 4, the EGR gas fluctuation amount (Δegr) is the same in both the left example and the right example. However, from the relational expression such as “EGR rate = EGR gas amount / in-cylinder intake gas amount”, the change in the EGR rate accompanying the change in the EGR gas amount (more specifically, the increase in EGR gas corresponding to Δegr) The amount is larger in the example on the left side (example in which the cylinder intake gas amount is small) than in the example on the right side (example in which the cylinder intake gas amount is large). When the in-cylinder intake gas amount is small, the influence of the variation of the EGR gas amount on the EGR rate becomes large, and the EGR rate tends to change greatly due to the variation of the EGR gas amount. For this reason, even if the manipulated variable of the EGR opening degree (and thus the amount of change in EGR gas) is small, the EGR rate can change greatly.

  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 employs a feedback gain according to the height of the EGR opening sensitivity. be able to. That is, an appropriate feedback gain is adopted even 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 (eg, during low-load operation of the engine 1). can do. For this reason, in the feedback control of the EGR rate, the control device 200 employs an appropriate feedback gain in both the low load operation and the high load operation of the engine 1 to sufficiently respond while suppressing overshoot. Can be secured.

  In recent years, exhaust gas regulations have been strengthened, so that exhaust gas recirculation using an EGR device is required not only during low-load operation of an engine but also during high-load operation. FIG. 5 is a diagram showing the tendency of the use conditions of the engine before and after exhaust regulations are strengthened. In the graph shown in FIG. 5, the horizontal axis represents the intake / exhaust differential pressure P4-Pb, and the vertical axis represents the in-cylinder intake gas amount. In FIG. 5, data D1 indicates data before exhaust regulations are strengthened, and data D2 indicates data after exhaust regulations are strengthened.

  Referring to FIG. 5, as shown by data D <b> 2, the use range of the engine is expanded as a result of stricter exhaust regulations than before stricter exhaust regulations (data D <b> 1). A region R indicates a region where the EGR opening sensitivity is particularly high among the use region of the engine after the exhaust restriction is strengthened. More specifically, the EGR opening degree sensitivity becomes high under the condition that the in-cylinder intake gas amount is small and the intake / exhaust differential pressure P4-Pb is high. Among the regions 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”). Are used particularly frequently.

  In this embodiment, the control device 200 considers the use conditions (use region) of the engine after exhaust regulations as shown in FIG. The second gain information shown in FIG. 8 is held, 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 in-cylinder intake gas amount. More specifically, if the intake / exhaust differential pressure P4-Pb is the same, the in-cylinder intake gas amount decreases. If the feedback gain is reduced and the in-cylinder intake gas amount is the same, a relationship is defined such that the feedback gain decreases as the intake / exhaust differential pressure P4-Pb increases. The gain information includes at least the above-mentioned in the region where the in-cylinder intake gas amount is 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 high frequency region). Define the relationship.

  The opening / closing speed of the EGR valve 62 (for example, the angular speed of the valve) varies depending on the feedback gain. The higher the feedback gain, the faster the opening / closing operation of the EGR valve. 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 engine operation), the EGR opening sensitivity is low (for example, the engine The feedback gain becomes smaller than that during low-load operation, and the opening and closing operation of the EGR valve is delayed, 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 so that the opening / closing operation of the EGR valve is accelerated, and sufficient responsiveness can be ensured in the feedback control of the EGR rate.

  Further, according to the gain information, it is possible to appropriately feedback control the EGR rate in the high frequency region used frequently when exhaust gas recirculation is performed by the EGR device 60 during high load operation of the engine 1. It becomes possible.

  Note that when a plurality of gains (for example, a proportional gain, an integral gain, and a 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 based on the gain information, and other gains may be determined by another method.

  Hereinafter, 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 EGR rate feedback control in control device 200.

  Referring to FIG. 6, 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 of the EGR rate acquisition unit 230 and the controller 210. Output to each.

  Corresponding information (for example, a mathematical expression) indicating the relationship between the intake pressure and the in-cylinder intake gas amount can be used to acquire the in-cylinder intake gas amount. 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 correspondence information stored in advance in the storage device of the control device 200. The correspondence information is not limited to a mathematical expression, and may be a map, a table, or a model. The correspondence information may be configured by combining a plurality of maps and the like. In addition to the detected value Pb of the intake pressure sensor 106 corresponding to the supercharging pressure, the intake air temperature of the intake manifold 28 (for example, the intake air temperature actually measured by a temperature sensor (not shown) provided in the intake manifold 28). ), And the engine speed may be taken into account to obtain the in-cylinder intake gas amount.

  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. 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 EEGin. To 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 subtracting unit 240 subtracts the current EGR rate (hereinafter, also referred to as “actual EGR rate”) indicated by the signal eegr from the target EGR rate indicating the target value of the EGR rate, and calculates the calculated value (that is, the target EGR rate). And the deviation between the actual EGR rate and the actual EGR rate). The target EGR rate is generated based on, for example, the operating state (detected values AP, NE, TE) of the engine body 10 and environmental information (detected values Pa, Ta).

  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 calculates the calculated value (that is, current intake / exhaust pressure). The differential pressure P4-Pb) is output to the controller 210.

  The controller 210 receives a signal EGin input from the in-cylinder intake gas amount acquisition unit 220, an EGR rate deviation (deviation between the target EGR rate and the actual EGR rate) input from the subtraction unit 240, and an input from the subtraction unit 250. The feedback gain (for example, proportional gain, integral gain, and differential gain) is determined using the intake / exhaust differential pressure P4-Pb.

  The determination of the feedback gain by the controller 210 is performed with reference to gain information (such as a map) stored in the storage device of the control device 200. The storage device of the control device 200 includes 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, first gain information and second gain information suitable for each gain are obtained in advance through experiments or the like and stored in the storage device. The first gain information and the second gain information may be independently a map, a table, a mathematical expression, or a model. Each gain information may be configured by combining a plurality of maps and the like.

  FIG. 7 is a diagram illustrating an example (map) of the first gain information. Referring 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 such that the feedback gain increases as the EGR rate deviation increases.

  FIG. 8 is a diagram illustrating an example (map) of the second gain information. Referring to FIG. 8, the second gain information defines a correction coefficient for correcting the feedback gain obtained from the first gain information. The range of the in-cylinder intake gas amount in the second gain information is a range including 80 g / s to 120 g / s (for example, 30 g / s to 150 g / s). In addition, the range of the intake / exhaust differential pressure in the second gain information is a range including 50 kPa to 70 kPa (for example, 30 kPa to 150 kPa). The second gain information indicates that the correction coefficient decreases as the in-cylinder intake gas amount decreases if the intake / exhaust differential pressure is the same, and the correction coefficient decreases as the intake / exhaust differential pressure increases if the in-cylinder intake gas amount is the same. This relationship is prescribed.

  In this embodiment, a value obtained by multiplying the feedback gain value obtained from the first gain information by the correction coefficient obtained from the second gain information is set as the feedback gain. Thus, 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 a region where the in-cylinder intake gas amount is large and the intake / exhaust differential pressure is small) is, for example, 1.0. 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. 5.

  Control device 200 performs feedback control of the EGR rate using the feedback gain determined as described above. More specifically, the controller 210 executes the PID control (proportional integral derivative control) by the feedback gain based on the EGR rate deviation input from the subtracting unit 240, so that the EGR rate deviation approaches 0. An operation amount (more specifically, an operation amount of the EGR opening degree) is calculated, and a drive signal Vegr corresponding to this operation amount is generated and output to the EGR valve 62. When the EGR valve 62 is driven by the 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 cylinder intake gas amount acquisition unit 220 acquires the cylinder intake gas amount, the EGR rate acquisition unit 230 acquires the EGR rate, and the subtraction unit 240 calculates the EGR rate deviation. The subtraction unit 250 repeatedly obtains the intake / exhaust differential pressure P4-Pb, the controller 210 determines the gain, and the controller 210 calculates the operation amount of the EGR opening, and the controller 210 calculates the EGR. The EGR valve 62 is driven by the drive signal Vegr generated based on the operation amount of the opening. As a result, the actual EGR rate is controlled 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 cylinder intake gas amount is smaller, and smaller as the intake / exhaust differential pressure P4-Pb is larger. By making the feedback control gain variable in such a 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 response is secured while suppressing overshoot in the feedback control of the EGR rate. It becomes possible to do. The controller 210 may execute PI control instead of PID control.

  In the above-described 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 an optimal feedback gain in two steps (that is, obtain a provisional gain and then optimize it by correction). From the EGR rate deviation, the in-cylinder intake gas amount, and the intake / exhaust differential pressure, it is not essential. The optimum feedback gain may be directly obtained. For example, an optimum feedback gain (and a function thereof) for each condition is obtained in advance through experiments or the like, and a gain (for example, proportional) expressed as a function of EGR rate deviation, in-cylinder intake gas amount, and intake / exhaust differential pressure. EGR rate feedback control (for example, PID control or PI control) may be performed using a gain.

  In the above-described embodiment, the intake / exhaust differential pressure is obtained using the actually measured values of the intake pressure and the exhaust pressure (actually 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 of the supercharger 30 (opening of the nozzle vane constituting the variable nozzle mechanism). Further, the exhaust pressure of the exhaust manifold 50 is estimated from the exhaust pressure downstream 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). May be.

  The target 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 embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiment but by the scope of claims, 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 rail, 16 injector, 20 air cleaner, 22 first intake pipe, 24 second intake pipe, 25 intercooler, 26 intake throttle valve, 27 third intake pipe, 28 intake manifold, 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, 116Outside air 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 (4)

An engine main body having a combustion chamber; a recirculation path that connects the intake passage and the exhaust passage without passing through the engine main body, and recirculates part of the exhaust gas flowing through the exhaust passage to the intake passage; and the recirculation path And an EGR valve configured to adjust an amount of EGR gas recirculated from the exhaust passage to the intake passage, and a first pressure detection for detecting an intake pressure that is a pressure of the intake gas sucked into the combustion chamber And a second pressure detection unit that detects an exhaust pressure that is the pressure of the exhaust gas discharged from the combustion chamber,
An EGR rate that is a ratio of the EGR gas amount in the intake gas amount supplied to the engine body is detected, and the opening degree of the EGR valve is set so that the detected value of the EGR rate approaches the target EGR rate by feedback control Is configured to operate
The feedback using the EGR rate deviation which is a deviation between the detected value of the EGR rate and the target EGR rate, the amount of intake gas supplied to the engine body, and the differential pressure between the intake pressure and the exhaust pressure. An engine controller that determines the gain of control.   2. The engine control according to claim 1, wherein the feedback control gain is determined so as to decrease as the EGR rate deviation decreases, to decrease as the intake gas amount decreases, and to decrease as the differential pressure increases. apparatus.   Correspondence information indicating a relationship between the intake pressure and the intake gas amount is held, the intake gas amount is estimated using the detection value of the first pressure detection unit and the correspondence information, and the intake gas amount is estimated. The EGR gas amount is calculated by subtracting the amount of fresh air supplied to the engine body from the value, and the EGR gas amount is divided by the estimated value of the intake gas amount by dividing the calculated EGR gas amount. The engine control device according to claim 1, wherein the control device is configured to acquire a detection value. Holding gain information indicating a relationship between the intake gas amount, the differential pressure, and the gain of the feedback control, and configured to determine the gain of the feedback control using a relationship defined by the gain information;
The gain information indicates that the feedback control gain decreases as the intake gas amount decreases if the differential pressure is the same, and the feedback control gain increases as the differential pressure increases if the intake gas amount is the same. The engine control device according to any one of claims 1 to 3, wherein a relationship that decreases is defined.

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