JP2009127547A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine capable of cooling EGR gas irrespective of a flow-in route to a heat recovery apparatus. <P>SOLUTION: The control device for the internal combustion engine includes a heat exchanger. The heat exchanger includes an exhaust gas heat recovery function exchanging heat with a cooling water passage and an EGR cooler function cooling EGR gas of an EGR device. The heat exchanger includes an EGR take-out port provided at a position between cooling water passages. Since EGR gas can be cooled at the EGR take-out port, thereby, irrespective of the flow-in passage of the heat exchanger, fluctuation of EGR quantity due to temperature change of EGR gas, and stabilization of a combustion state and improvement of fuel economy can be achieved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine provided with an EGR device.

  2. Description of the Related Art Conventionally, in an internal combustion engine equipped with an exhaust gas recirculation (EGR) device that recirculates a part of exhaust gas to an intake system, a heat exchanger for recovering thermal energy from the exhaust gas is arranged. Control for passing the exhaust gas through the heat exchanger is performed by opening and closing an exhaust control valve provided on the exhaust passage.

  Note that Patent Document 1 includes a connecting pipe formed between downstream catalytic converters that joins a merging portion on an exhaust passage, and one or more exhaust control valves that control exhaust gas flowing into a heat exchanger. An exhaust emission control device is described. In addition, Patent Documents 2 to 6 describe techniques related to the present invention.

JP 2007-024022 A JP 2005-528554 A JP-A-2005-291055 JP 2006-291921 A JP 2006-299895 A JP 2006-125356 A

  However, during the state transition of the exhaust adjustment valve, that is, when it is at an intermediate position of opening and closing, the exhaust gas flows backward from the exhaust connection pipe from the heat exchanger to the exhaust passage, and is recirculated as EGR gas. There is. Since the above-mentioned connecting pipe is not in contact with cooling water, the exhaust gas in this case is recirculated without being sufficiently cooled. However, when the temperature of the EGR gas is not constant, the amount of EGR gas at the same opening degree of the EGR valve is not constant, and as a result, the combustion state of the engine may become unstable and fuel consumption may deteriorate. Patent Documents 1 to 6 do not discuss the above problems.

  The present invention has been made to solve the above-described problems, and provides a control device for an internal combustion engine capable of cooling EGR gas regardless of a path flowing into a heat recovery device. Objective.

  In one aspect of the present invention, an internal combustion engine control device having an EGR device includes an exhaust heat recovery function for exchanging heat with a cooling water passage, and an EGR cooler function for cooling EGR gas of the EGR device. And a heat exchanger having the EGR outlet provided at a position sandwiched between the cooling water passages.

  The control device for an internal combustion engine is a control device for an internal combustion engine having an EGR device that recirculates a part of exhaust gas to an intake system. The control device for an internal combustion engine includes a heat exchanger. The heat exchanger has both an exhaust heat recovery function for exchanging heat with the cooling water passage and an EGR cooler function for cooling the EGR gas of the EGR device. The heat exchanger includes an EGR extraction port provided at a position sandwiched by the cooling water passage. By doing so, the EGR gas can be cooled at the EGR extraction port regardless of the passage flowing into the heat exchanger, so that the fluctuation of the EGR due to the temperature change of the EGR gas is prevented and the combustion state is stabilized. In addition, fuel consumption can be improved.

  One aspect of the control device for an internal combustion engine is a first bypass passage for passing exhaust gas from an exhaust passage to the heat exchanger, and for passing exhaust gas from the heat exchanger to the exhaust passage. A second bypass passage, wherein the EGR outlet is connected to the first bypass passage and the second bypass passage in the heat exchanger, and the first bypass passage and the second bypass passage. It is located in the middle of the bypass passage.

  In this aspect, the control device for an internal combustion engine further includes a first bypass passage and a second bypass passage, and the EGR take-out port is formed by joining the first bypass passage and the second bypass passage substantially at an intermediate point. Is formed. With this configuration, not only the first bypass passage, but also the EGR outlet and the second bypass passage are adjacent to the cooling water passage. Therefore, even when there is an unexpected exhaust gas flow from the second bypass passage to the heat exchanger, the EGR gas can be sufficiently cooled, the fluctuation of the EGR due to the temperature change of the EGR gas is prevented, and the combustion state Stabilization and improvement of fuel consumption can be achieved. Note that the above-described intermediate point does not strictly mean the middle point, and may be located between the first bypass passage and the second bypass passage.

  In another aspect of the control device for an internal combustion engine, the first bypass passage and the second bypass passage pass through a position in the heat exchanger where heat can be exchanged with the cooling water passage. It arrange | positions so that it may do. As a result, the EGR gas can be sufficiently cooled regardless of whether the exhaust gas passes through either the first bypass passage or the second bypass passage to the heat exchanger, and the temperature of the EGR gas changes. It is possible to prevent fluctuations in the EGR amount, stabilize the combustion state, and improve fuel efficiency.

  Another aspect of the control device for an internal combustion engine further includes an exhaust gas switching valve that adjusts a flow of exhaust gas from an exhaust passage to the heat exchanger, and the exhaust gas switching valve includes the second bypass passage and the second bypass passage. The flow of the exhaust gas to the heat exchanger is adjusted by opening and closing the exhaust passage. Thereby, the flow of the exhaust gas to the heat exchanger can be appropriately adjusted by opening and closing one exhaust gas switching valve, and the control can be simplified.

  Another aspect of the control device for an internal combustion engine described above further includes failure detection means for detecting sticking of the exhaust gas switching valve, and the failure detection means determines the presence or absence of the sticking based on an EGR amount. And The failure detection means is, for example, an ECU (Electronic Control Unit), and detects a failure of the exhaust gas switching valve based on the EGR amount. The amount of EGR can be estimated from, for example, the EGR gas temperature measured by the EGR valve or the pressure in the intake passage. Thereby, it is possible to determine the failure of the exhaust gas switching valve only with the existing sensor, and it is possible to determine the failure by the device itself without relying on manual operation while preventing an increase in cost.

  In another aspect of the control apparatus for an internal combustion engine, the failure detection means alternately transmits an open signal and a close signal to the exhaust gas switching valve in a steady state, and changes the detected state value after transmission. Based on this, the presence or absence of the sticking is determined.

  In this aspect, the state value is measured while transmitting the opening / closing signal of the exhaust gas switching valve while keeping the state of the engine or the like constant. As the state value, a detection value obtained from an existing sensor such as the EGR gas temperature, the pressure in the intake passage, the temperature of the cooling water at the heat exchanger outlet, the temperature of the exhaust gas after passing through the heat exchanger, and the like is arbitrarily selected. When the variation value of the state quantity due to switching of the open / close signal is smaller than a predetermined value, it is determined that the exhaust gas switching valve is fixed. By doing in this way, failure detection with higher accuracy can be performed without increasing the cost of installing a new sensor.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[Control device for internal combustion engine]
First, the configuration of the control device for an internal combustion engine according to the present embodiment will be described. FIG. 1 is a block diagram showing an example of a schematic configuration of a control device 100 for an internal combustion engine having an engine 3 according to the present embodiment. In FIG. 1, solid arrows indicate the flow of intake and exhaust, and broken arrows indicate control signals. The control device 100 for an internal combustion engine is mounted on a vehicle and uses the output of the engine 3 as a driving power source. The control device 100 for the internal combustion engine includes the engine 3, the EGR device 5, the catalysts 30a and 30b, the exhaust gas switching valve 20, various sensors 27, 28, and 29, and the ECU 10 as components.

  The engine 3 is supplied with air (intake air) through the intake passage 2. A throttle valve 22 that adjusts the amount of inflow into the engine is disposed in the intake passage 2. Further, an exhaust passage 4 is connected to the engine 3, and exhaust gas generated by the above-described combustion is discharged from the exhaust passage 4.

  The control device 100 for an internal combustion engine includes an EGR device 5 that recirculates a part of the exhaust gas to the intake system. The EGR device 5 includes an EGR passage 6, a heat exchanger 7, and an EGR valve 9. The EGR passage 6 has one end connected to the exhaust passage 4 and the other end connected to the intake passage 2.

  The heat exchanger 7 functions as an EGR cooler that cools the exhaust gas that passes through the EGR passage 6 and also functions as an exhaust heat recovery device that transmits thermal energy contained in the exhaust gas to the engine coolant. That is, the heat exchanger 7 is a heat exchanger in which the functions of the EGR cooler and the exhaust heat recovery device are integrated. Specifically, the heat exchanger 7 is configured as a water-cooled type, and performs cooling using cooling water passing through the inside. That is, the heat exchanger 7 cools the exhaust gas by exchanging heat between the cooling water and the exhaust gas. The cooling water passes through the cooling water passage 8 and is circulated by a water pump (not shown).

  The EGR valve 9 is a valve for controlling the amount of exhaust gas to be recirculated (hereinafter referred to as “EGR amount”). The opening degree of the EGR valve 9 is controlled by a control signal S2 supplied from the ECU 10.

  A first catalyst 30 a and a second catalyst 30 b are disposed in the exhaust passage 4. The first catalyst 30 is a small catalyst having a small volume, and is a catalyst disposed in the exhaust passage 4 downstream of the engine 3 and upstream of the first bypass passage 15. In a preferred example, the first catalyst 30a is preferably a NOx storage reduction catalyst that stores and purifies NOx.

  The second catalyst 30b is a large-sized catalyst having a larger volume than the first catalyst 30a, and is a catalyst disposed downstream of the exhaust gas switching valve 20 in the exhaust passage 4. The second catalyst 30b is preferably a NOx storage reduction catalyst that stores and purifies NOx, similarly to the first catalyst 30a.

  The first bypass passage 15 is a passage for connecting the exhaust passage 4 and the heat exchanger 7 and flowing the exhaust gas from the exhaust passage 4 to the heat exchanger 7. The second bypass passage 16 is a passage for connecting the exhaust passage 4 and the heat exchanger 7 and allowing the exhaust gas to flow from the heat exchanger 7 to the exhaust passage 4.

  The exhaust gas switching valve 20 is a valve that adjusts the flow of exhaust gas by opening and closing the second bypass passage 16 and the exhaust passage 4. The exhaust switching valve 20 is controlled to be opened and closed by a control signal S1 supplied from the ECU 10.

  Further, the control device 100 for the internal combustion engine is provided with various sensors. Specifically, an EGR temperature sensor 27 for measuring the EGR gas temperature is provided on the EGR device 5. A water temperature sensor 28 that measures the temperature of the cooling water is provided on the cooling water passage 8 at the outlet of the heat exchanger 7. Further, a gas temperature sensor 29 for measuring the temperature of the exhaust gas flowing from the heat exchanger 7 is provided on the second bypass passage. The EGR temperature sensor 27, the water temperature sensor 28, and the gas temperature sensor 29 supply detection signals S7 to S9 corresponding to the detected temperatures to the ECU 10, respectively.

  The ECU 10 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like (not shown). The ECU 10 controls the engine 3 based on detection signals supplied from various sensors. For example, the ECU 10 determines the required torque of the engine 3 based on a detection signal supplied from an accelerator opening sensor (not shown). Then, the ECU 10 controls the engine 3 based on the determined required torque.

  Further, the ECU 10 transmits a control signal S1 to the exhaust gas switching valve 20, and determines whether the exhaust gas switching valve 20 is fixed based on information such as detection signals S7 to S9 detected after transmission. Therefore, the ECU 10 functions as a failure detection means in the present invention.

  The configuration of the control device 100 for an internal combustion engine to which the present invention is applicable is not limited to this. For example, the heat exchanger 7 may be disposed downstream of the second catalyst 30b in the exhaust passage 4. In this case, since the exhaust gas always passes through the second catalyst 30b before passing through the heat exchanger 7, the warm-up of the second catalyst 30b is performed regardless of whether or not the exhaust gas passes through the heat exchanger 7. Can be executed. In FIG. 1, the EGR gas sensor 27 is provided on the EGR passage 6. However, the EGR gas sensor 27 is not limited to this. For example, the function of the EGR gas sensor 27 may be added to the EGR valve 9.

  Next, the state of the airflow of each exhaust gas, which changes by the control of the EGR valve 9 and the exhaust gas switching valve 20 performed by the ECU 10, will be described.

  FIG. 2A shows a state in which the ECU 10 controls the EGR valve 9 and the exhaust gas switching valve 20 so that the EGR valve 9 is closed and the exhaust gas switching valve 20 closes the second bypass passage 16. That is, the state 70 is a state when the ECU 10 controls the EGR valve 9 and the exhaust gas switching valve 20 so that the exhaust gas is not recirculated by the EGR device 5 and the exhaust gas switching valve 20 is positioned on the broken line 20a. Hereinafter, the state 70 is referred to as “catalyst warm-up mode”. An arrow 80 indicates the flow of exhaust. Hereinafter, controlling the exhaust gas switching valve 20 to be positioned on the broken line 20a is simply expressed as “closing the exhaust gas switching valve 20” or “making the exhaust gas switching valve 20 closed”.

  In the catalyst warm-up mode, the exhaust gas discharged from the engine 3 does not pass through the heat exchanger 7, so that the heat of the exhaust gas is not recovered by the heat exchanger 7. Therefore, the exhaust gas follows the flow of the arrow 80 and passes through the second catalyst 30b. Thereby, the second catalyst 30b is warmed up by the exhaust gas.

  FIG. 2B shows a state in which the ECU 10 controls the EGR valve 9 and the exhaust gas switching valve 20 so as to close the EGR valve 9 and open the exhaust gas switching valve 20. Hereinafter, the state 71 is referred to as a “heat recovery mode”. An arrow 81 indicates the flow of exhaust. Hereinafter, controlling the exhaust gas switching valve 20 to be positioned on the broken line 20b is expressed as “opening the exhaust gas switching valve 20” or “opening the exhaust gas switching valve 20”.

  In the heat recovery mode, as indicated by an arrow 81, the exhaust gas discharged from the engine 3 passes through the heat exchanger 7, whereby the heat of the exhaust gas is recovered by the heat exchanger 7.

  FIG. 3A shows a state in which the ECU 10 controls the EGR valve 9 and the exhaust gas switching valve 20 so that the EGR valve 9 is opened and the exhaust gas switching valve 20 is closed. Hereinafter, the state 72 is referred to as “EGR cooler mode”. Arrows 82a and 82b indicate the flow of exhaust.

  In the EGR cooler mode, as indicated by the arrow 82a, part of the exhaust gas discharged from the engine 3 is recirculated to the intake passage 2 by the EGR device 5 again. Thereby, the negative pressure of the intake passage 2 is relatively lowered, and the fuel consumption can be improved by the reduction of the pumping loss. Further, the exhaust gas that is not recirculated by the EGR device 5 passes through the second catalyst 30b without passing through the heat recovery unit 7, as indicated by the arrow 82b. As a result, the second catalyst 30b is warmed up by the exhaust gas.

  FIG. 3B shows a state in which the ECU 10 controls the EGR valve 9 and the exhaust gas switching valve 20 so that the EGR valve 9 is opened and the exhaust gas switching valve 20 is opened. Hereinafter, the state 73 is referred to as “heat recovery / EGR cooler mode”. Arrows 83a and 83b indicate the flow of exhaust.

  In the heat recovery / EGR cooler mode, as indicated by an arrow 83a, a part of the exhaust gas discharged from the engine 3 is returned to the intake passage 2 again by the EGR device 5. Thereby, the negative pressure of the intake passage 2 is relatively lowered, and the fuel consumption can be improved by the reduction of the pumping loss. In the heat recovery / EGR cooler mode, as indicated by arrows 83a and 83b, the exhaust gas discharged from the engine 3 passes through the heat exchanger 7 so that the heat of the exhaust gas is recovered by the heat exchanger 7. Is done.

  The ECU 10 can appropriately function as the EGR cooler and the exhaust heat recovery unit by appropriately switching the exhaust state mode according to the traveling state. However, switching between the open state and the closed state of the exhaust gas switching valve 20 is not usually executed instantaneously, and it takes a certain time to complete the switching. At this time, the heat recovery unit may not properly perform the function as the EGR cooler.

  This will be described below. FIG. 4 is a conceptual diagram of an exhaust state in the control device for an internal combustion engine according to the comparative example. In the state 74, the EGR gas recirculation control is performed, and the exhaust gas switching valve 20 is positioned at an intermediate position between the open state and the closed state indicated by the broken line 20c. That is, the state 74 indicates a state in the middle of switching between the heat recovery / EGR cooler mode and the EGR cooler mode. In the heat exchanger 7 a, the cooling water passages 8 a and 8 b are arranged so as to sandwich the first bypass passage 15 on the assumption that the exhaust gas passes from the first bypass passage 15. Thereby, the exhaust gas passing through the first bypass passage 15 can be cooled.

  However, in the state 74, the pressure loss is lower on the second bypass passage 16 side than on the first bypass passage 15 side. Accordingly, the exhaust gas has a stronger air flow indicated by the solid line arrow 84 than the air flow indicated by the broken line arrow 85. The exhaust gas that passes through the second bypass passage 16 and flows to the EGR passage 6 is not sufficiently cooled because there are few adjacent portions to the cooling passages 8a and 8b. Therefore, in the state 74, the heat exchanger 7a cannot sufficiently exhibit the function as the EGR cooler, and as a result, the fuel consumption of the engine 3 may deteriorate.

  FIG. 5 shows a conceptual diagram of the exhaust state in the control apparatus for an internal combustion engine in which the heat exchanger according to the present embodiment is installed. The heat exchanger 7 has a passage where the first bypass passage 15 and the second bypass passage 16 merge in the broken line frame 90 (hereinafter referred to as “EGR extraction port”). Further, a portion corresponding to the cooling water passage 8a in FIG. 4 branches into the cooling water passage 8ax and the cooling water passage 8ay so as to sandwich the EGR outlet. In other words, both the first bypass passage 15 and the second bypass passage 16 are adjacent to the cooling water passage in the heat exchanger 7 and pass through a position where heat can be exchanged with the cooling water passage. Has been placed.

  By configuring the cooling water passage and the EGR outlet in the heat exchanger 7 in this way, even when the exhaust gas switching valve 20 is at the position of the broken line 20c and the exhaust gas passes through the path indicated by the solid arrow 84, the first Since there are many adjacent portions of the two bypass passages 16 and the EGR outlet and the cooling water passages 8ax, 8ay, 8b, the exhaust gas can be sufficiently cooled. That is, the heat exchanger 7 can sufficiently exhibit the function of the EGR cooler regardless of the position of the exhaust gas switching valve 20. Therefore, the EGR amount at the same opening degree of the EGR valve 9 can be made constant, and the instability of the combustion state of the engine 3 and the deterioration of fuel consumption can be prevented.

[Failure detection method of exhaust gas switching valve]
Next, a failure detection method for the exhaust gas switching valve 20 performed by the ECU 10 will be described. Hereinafter, of the control signal S1 transmitted from the ECU 10 to the exhaust gas switching valve 20, a command for switching to the open state is defined as an “open signal”, and a command for switching to the closed state is defined as a “close signal”.

  If the ECU 10 does not react even if an open signal or a close signal is transmitted to the exhaust gas switching valve 20, that is, if the exhaust gas switching valve 20 is stuck due to a failure, the ECU 10 collects exhaust heat, warms up the catalyst, and recirculates EGR gas. Etc. cannot be appropriately executed. In particular, if the exhaust gas switching valve 20 is stuck in the open state, the cooling water may be overheated at the time of high output of the engine 3, and boiling of the cooling water may occur.

  Therefore, in the present embodiment, the ECU 10 has sufficiently cooled the cooling water after switching from the heat recovery / EGR cooler mode to the EGR cooler mode, that is, during the operation of the EGR, and has transmitted a close signal to the exhaust gas switching valve 20. Thereafter, a failure of the exhaust gas switching valve 20 is detected based on the measured EGR amount. The measurement of the EGR amount can be estimated using the output value of an existing sensor. For example, the EGR amount can be estimated from the EGR gas temperature measured by the EGR temperature sensor 27 and the output value of the pressure sensor on the intake passage 2 (not shown).

  Generally, the pressure loss at the EGR take-out port differs between when the exhaust gas switching valve 20 is in the open state and when it is in the closed state. Even when the EGR valve 9 has the same opening, the EGR amount differs if the pressure loss at the EGR outlet is different. Therefore, first, the ECU 10 holds in advance a value of the EGR amount corresponding to the opening degree of the EGR valve 9 in the EGR cooler mode. Then, when switching from the heat recovery / EGR cooler mode to the EGR cooler mode, the EGR amount held in advance is compared with the EGR amount after switching, and if both differ by a predetermined value or more, the exhaust gas switching valve 20 It can be determined that is not operating, that is, is stuck in the open state. The failure detection method described above can be similarly applied based on the EGR amount even when switching from the EGR cooler mode to the heat recovery / EGR cooler mode.

  Thereby, since it is possible to autonomously detect a failure of the exhaust gas switching valve 20 using only existing sensors, it is possible to quickly detect the failure and prevent an increase in cost due to the installation of a new sensor.

  On the other hand, there may be a case where the difference between the EGR amount after the mode switching and the EGR amount held in advance is small and it cannot be determined that the exhaust gas switching valve 20 is fixed. In this case, the ECU 10 can cope with this by using another failure detection method for the exhaust gas switching valve 20 described below. First, the ECU 10 performs control so that the operating state of the engine 3 and the like is constant and the EGR amount is constant. Then, a close signal and an open signal are alternately transmitted to the exhaust gas switching valve 20. The output values of the detection signals of various sensors such as the EGR gas temperature, the pressure in the intake passage 4, the detection signal S8 of the water temperature sensor 28, the detection signal S9 of the gas temperature sensor 29, etc. (Hereinafter referred to as “state value”) and the amount of fluctuation is calculated. The state value does not need to use all of the exemplified detection signals, and may be limited to only existing sensors. When the above-mentioned fluctuation amount does not change by a predetermined value or more, it is determined that the exhaust gas switching valve 20 is not operating, that is, is fixed. Also by the above method, the failure of the exhaust gas switching valve 20 can be detected only with the existing sensor, and the failure can be detected autonomously without increasing the cost.

It is a figure which shows schematic structure of the control apparatus of an internal combustion engine. It is a figure which shows the flow of exhaust in the state which closed the EGR valve. It is a figure which shows the flow of exhaust in the state which opened the EGR valve. It is a figure which shows the exhaust state of the control apparatus of the internal combustion engine which concerns on a comparative example. It is a figure which shows the exhaust state of the control apparatus of the internal combustion engine which concerns on embodiment.

Explanation of symbols

3 Engine 7 Heat exchanger 9 EGR valve 10 ECU
20 Exhaust gas switching valve 100 Control device for internal combustion engine

Claims (6)

In a control device for an internal combustion engine having an EGR device,
A heat exchanger having both an exhaust heat recovery function for exchanging heat with the cooling water passage and an EGR cooler function for cooling the EGR gas of the EGR device,
The control apparatus for an internal combustion engine, wherein the heat exchanger includes an EGR extraction port provided at a position sandwiched between the cooling water passages. A first bypass passage for passing exhaust gas from the exhaust passage to the heat exchanger;
A second bypass passage for passing exhaust gas from the heat exchanger to the exhaust passage,
The EGR take-out port is connected to the first bypass passage and the second bypass passage in the heat exchanger, and is located between the first bypass passage and the second bypass passage. The control apparatus for an internal combustion engine according to claim 1.   3. The internal combustion engine according to claim 2, wherein the first bypass passage and the second bypass passage are disposed so as to pass through positions where heat can be exchanged with the cooling water passage in the heat exchanger. Engine control device. An exhaust switching valve for adjusting the flow of exhaust gas from the exhaust passage to the heat exchanger;
The internal combustion engine control according to any one of claims 1 to 3, wherein the exhaust gas switching valve adjusts the flow of exhaust gas to the heat exchanger by opening and closing the second bypass passage and the exhaust passage. apparatus. A failure detection means for detecting sticking of the exhaust gas switching valve;
The control device for an internal combustion engine according to any one of claims 1 to 4, wherein the failure detection means determines the presence or absence of the sticking based on an EGR amount.   6. The failure detection unit according to any one of claims 1 to 5, wherein the failure detection means alternately transmits an open signal and a close signal to the exhaust gas switching valve in a steady state, and determines the presence or absence of the sticking based on a fluctuation amount of a state value detected after transmission. The control device for an internal combustion engine according to any one of the preceding claims.

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