Freezing diagnostic device for exhaust emission control system for internal combustion engine

Abstract

To more accurately diagnose a frozen state of a differential pressure detection section.SOLUTION: In an exhaust emission control system for an internal combustion engine including: a filter (7) installed in an exhaust passage (3) through which exhaust gas from the internal combustion engine (1) passes; and a differential pressure detection section (10) comprising a differential pressure detection passage (8) connected to the exhaust passage (3) and bypassing the filter (7) and a differential pressure sensor (9) installed in the differential pressure detection passage (8) to detect differential pressure between upstream side pressure and downstream side pressure of the filter (7), a freezing diagnostic device (100) that diagnoses the freezing of the differential pressure detection section (10) includes determination means (102) that determines freezing of the differential pressure detection section (10) when the differential pressure detected by the differential pressure sensor (9) falls into either of a maximum state, a minimum state or a state where no differential pressure occurs.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a freeze diagnosis device for an exhaust gas purification system of an internal combustion engine. [Background technology]

[0002] In automobiles powered by an internal combustion engine, a GPF (gasoline particulate filter) is installed in the exhaust passage through which exhaust gas from the internal combustion engine passes. In this case, in order to diagnose conditions such as clogging of the GPF, a differential pressure detection passage that bypasses the GPF may be connected to the exhaust passage, and a differential pressure sensor that detects the differential pressure between the upstream and downstream pressures of the GPF may be installed in the differential pressure detection passage. Here, because exhaust gas contains water vapor, when the outside temperature is low and the exhaust gas comes into contact with the pipes that make up the differential pressure detection passage or the differential pressure sensor, the water vapor contained in the exhaust gas is cooled, condenses, and freezes, which can block the pipes and the differential pressure sensor. In this state, the differential pressure sensor cannot measure the differential pressure correctly, and the condition of the GPF cannot be accurately diagnosed. Patent Document 1 discloses a configuration for determining whether a differential pressure detection passage is in a non-frozen state based on at least one of a parameter related to the exhaust temperature of an internal combustion engine and a parameter related to the atmospheric temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-2694 A Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, the non-frozen state of the differential pressure detection passage is estimated based on the exhaust temperature of the internal combustion engine and the atmospheric temperature, but this temperature information cannot be said to directly indicate the freezing of the differential pressure detection passage, and there is a possibility that the frozen state of the differential pressure detection passage cannot be accurately diagnosed.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to make it possible to more accurately diagnose the frozen state of a differential pressure detection unit. [Means for solving the problem]

[0006] The freeze diagnosis device for an exhaust purification system of an internal combustion engine of the present invention is provided in an exhaust purification system of an internal combustion engine which includes a filter installed in an exhaust path through which exhaust gas from the internal combustion engine passes, a differential pressure detection passage connected to the exhaust path and bypassing the filter, and a differential pressure detection unit configured with a differential pressure sensor installed in the differential pressure detection passage and detecting the differential pressure between the upstream pressure and downstream pressure of the filter.The freeze diagnosis device performs a freeze diagnosis on the differential pressure detection unit, and is characterized in that it includes a determination means for determining that the differential pressure detection unit is frozen when the differential pressure detected by the differential pressure sensor falls into any of an extremely maximum state, an extremely minimum state, and a state in which no differential pressure is generated. Effect of the Invention

[0007] According to the present invention, the frozen state of the differential pressure detection unit can be diagnosed more accurately. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing a configuration example of an exhaust gas purification system for an internal combustion engine according to an embodiment; [Diagram 2] 11A and 11B are diagrams for explaining freezing of a differential pressure detection unit. [Diagram 3] 4 is a characteristic diagram showing an example of a time series change in a differential pressure DP detected by a differential pressure sensor. FIG. [Figure 4] 4 is a flowchart showing a process for diagnosing a frozen differential pressure detection unit executed by an ECU in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A freeze diagnosis device (100) for an exhaust purification system of an internal combustion engine according to one embodiment of the present invention is provided in an exhaust purification system of an internal combustion engine including a filter (7) installed in an exhaust passage (3) through which exhaust gas from an internal combustion engine (1) passes, a differential pressure detection passage (8) connected to the exhaust passage (3) and bypassing the filter (7), and a differential pressure detection unit (10) configured with a differential pressure sensor (9) installed in the differential pressure detection passage (8) and detecting the differential pressure between the upstream pressure and the downstream pressure of the filter (7). The freeze diagnosis device (100) performs a freeze diagnosis of the differential pressure detection unit (10), and includes a determination means (102) for determining that the differential pressure detection unit (10) is frozen when the differential pressure detected by the differential pressure sensor (9) corresponds to any one of an extremely maximum state, an extremely minimum state, and a state in which no differential pressure is generated. This makes it possible to more accurately diagnose the frozen state of the differential pressure detection portion (10). EXAMPLES

[0010] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows an example of the configuration of an exhaust gas purification system for an internal combustion engine according to an embodiment. An automobile is equipped with an engine 1, which is an internal combustion engine having a plurality of cylinders, and an ECU (Electronic Control Unit) 100. An intake passage 2 and an exhaust passage 3 are connected to the engine 1. A mixture of intake air and fuel supplied from an injector 4 is introduced into a combustion chamber of the engine 1 via the intake passage 2 and an intake valve (not shown). In the combustion chamber, ignition is performed by a spark plug 5, and the mixture compressed by a piston (not shown) is burned. The burnt mixture expands, pushing down a piston (not shown) and rotating a crankshaft (not shown). Exhaust gas exhausted from the engine 1 via an exhaust valve (not shown) is exhausted via the exhaust passage 3.

[0011] In the exhaust passage 3, from the upstream side, a three-way catalyst (TWC) 6 and a gasoline particulate filter (GPF) 7 are installed. The TWC 6 purifies harmful substances in the exhaust gas by oxidation and reduction. The GPF 7 captures particulate matter (PM) contained in the exhaust gas. In addition, a differential pressure detection passage 8 that bypasses the GPF 7 is connected to the exhaust path 3. A diaphragm type differential pressure sensor 9 is installed in the differential pressure detection passage 8 to detect a differential pressure DP between the upstream pressure and downstream pressure of the GPF 7. In this way, the differential pressure detection passage 8 and the differential pressure sensor 9 installed in the differential pressure detection passage 8 constitute a differential pressure detection unit 10.

[0012] The ECU 100 is responsible for engine control such as fuel injection by the injector 4, the opening and closing timing of the intake valve and exhaust valve, and the ignition timing by the spark plug 5. Note that engine control can be performed using known techniques, and detailed description thereof will be omitted here.

[0013] The ECU 100 also diagnoses the state of the GPF 7. When clogging occurs in the GPF 7 due to accumulation of PM, the differential pressure DP detected by the differential pressure sensor 9 increases due to pressure loss. When the differential pressure DP detected by the differential pressure sensor 9 becomes equal to or greater than a preset clogging determination threshold, the ECU 100 notifies the driver that clogging has occurred by turning on a warning light, for example. In the GPF, the trapped PM is burned and eliminated at the exhaust gas temperature. When the differential pressure DP detected by the differential pressure sensor 9 falls below the clogging determination threshold, the clogging is eliminated, and the warning light is turned off. When so-called loss occurs in the GPF 7 due to melting or the like of the filter material, the differential pressure DP detected by the differential pressure sensor 9 decreases. When the differential pressure DP detected by the differential pressure sensor 9 becomes equal to or less than a preset loss determination threshold, the ECU 100 notifies the driver that loss of the GPF 7 has occurred by turning on a warning light, for example.

[0014] 3 shows an example of time series change of the differential pressure DP detected by the differential pressure sensor 9. As shown in FIG. 3, a clogging determination threshold and a loss determination threshold are set, and the range between them is the range where neither clogging nor loss occurs, in other words, the normal range of the GPF 7. In this embodiment, the differential pressure DP detected by the differential pressure sensor 9 is a positive value (+ value) when the upstream pressure of the GPF 7 is greater than the downstream pressure, and is a negative value (- value) when the upstream pressure of the GPF 7 is less than the downstream pressure. Both the clogging determination threshold and the loss determination threshold are set in the positive range (+ range), and the normal range of the GPF 7 exists in the positive range.

[0015] Furthermore, the ECU 100 performs freezing diagnosis of a differential pressure detection section 10 constituted by a differential pressure detection passage 8 and a differential pressure sensor 9. In this embodiment, the ECU 100 functions as a freezing diagnosis device to which the present invention is applied. Fig. 1 shows the functional configuration of the ECU 100. As described above, the ECU 100 has functions other than those of the freezing diagnosis device to which the present invention is applied, but Fig. 1 shows only the functional configuration as a freezing diagnosis device.

[0016] Here, the freezing of the differential pressure detection unit 10 will be described with reference to Fig. 2. Fig. 2 is a diagram for explaining the freezing of the differential pressure detection unit 10. As shown in FIG. 2(a), when a frozen portion 201 occurs in the differential pressure detection passage 8 downstream of the GPF 7, only the pressure upstream of the GPF 7 acts on the differential pressure sensor 9, as indicated by the arrow 202. As a result, the differential pressure DP detected by the differential pressure sensor 9 reaches a maximum state. The maximum state means that the differential pressure DP detected by the differential pressure sensor 9 becomes extremely large, exceeds the normal range, and reaches a value close to the upper limit of the output range of the differential pressure sensor 9. The same applies when the differential pressure sensor 9 is frozen downstream of the GPF 7. When the differential pressure DP detected by the differential pressure sensor 9 is in a maximum state in this way, it can be determined that the differential pressure detection unit 10 downstream of the GPF 7 is frozen.

[0017] Also, as shown in FIG. 2(b), when a frozen portion 201 occurs in the differential pressure detection passage 8 upstream of the GPF 7, only the downstream pressure of the GPF 7 acts on the differential pressure sensor 9, as indicated by the arrow 203. As a result, the differential pressure DP detected by the differential pressure sensor 9 becomes extremely small. The extremely small state means that the differential pressure DP detected by the differential pressure sensor 9 is extremely small, has a large negative value with an absolute value, exceeds the normal range, and becomes a value close to the lower limit of the output range of the differential pressure sensor 9. The same applies to a state in which the upstream side of the GPF 7 in the differential pressure sensor 9 freezes. When the differential pressure DP detected by the differential pressure sensor 9 is in an extremely small state, it can be determined that the differential pressure detection unit 10 is frozen upstream of the GPF 7.

[0018] 2(c), when frozen portions 201 occur in the differential pressure detection passage 8 on the upstream and downstream sides of the GPF 7, no pressure acts on the differential pressure sensor 9, and the output of the differential pressure sensor 9 becomes 0. The same applies when the upstream and downstream sides of the GPF 7 in the differential pressure sensor 9 are frozen. In this way, when the differential pressure DP detected by the differential pressure sensor 9 is in a state where no differential pressure is occurring, it can be determined that the differential pressure detection portion 10 is frozen on the upstream and downstream sides of the GPF 7.

[0019] Returning to the explanation of FIG. 1, the ECU 100 includes an input unit 101, a freeze determination unit 102, and a notification unit 103. The input unit 101 receives an input of a differential pressure DP between the upstream pressure and the downstream pressure of the GPF 7 from the differential pressure sensor 9 .

[0020] The freezing determination unit 102 determines whether the differential pressure DP inputted by the input unit 101 corresponds to any of a maximum state, a minimum state, and a state where no differential pressure is generated, and if any of the above conditions are satisfied, it determines that the differential pressure detection unit 10 is frozen. Specifically, as shown by the characteristic line 301 in FIG. 3, the differential pressure DP is in a maximum state when it is equal to or greater than a first threshold (threshold 1) set between the clogging determination threshold and the upper limit of the output range of the differential pressure sensor 9. As shown by the characteristic line 302 in FIG. 3, the differential pressure DP is in a minimum state when it is equal to or less than a second threshold (threshold 2) set between the loss determination threshold and the lower limit of the output range of the differential pressure sensor 9. As shown by the characteristic line 303 in FIG. 3, the differential pressure DP is in a predetermined range including 0 (a range inside ±a third threshold (threshold 3)), and thus no differential pressure is generated.

[0021] When the freezing determination unit 102 determines that the differential pressure detection unit 10 is frozen, the notification unit 103 notifies the driver. For example, a warning light that notifies of clogging or loss of the GPF 7 is blinked. Note that the method of notification by the notification unit 103 is not limited to this, and a display unit or an audio output unit may be used. Furthermore, when the freezing determination unit 102 determines that the differential pressure detection unit 10 is frozen, the ECU 100 stops diagnosing the state (clogging, loss) of the GPF 7 until the freezing determination is released. This is because, when the differential pressure detection unit 10 is frozen, the differential pressure sensor 9 cannot correctly measure the differential pressure DP, and the state of the GPF 7 cannot be accurately diagnosed.

[0022] FIG. 4 is a flowchart showing the process of freezing diagnosis of the differential pressure detection unit 10 executed by the ECU 100. Fig. 4(a) shows a process for determining freezing of the differential pressure detection unit 10. The flowchart of Fig. 4(a) is executed, for example, during a predetermined period after the engine 1 is started. In step S1, the input unit 101 inputs the differential pressure DP between the upstream pressure and the downstream pressure of the GPF 7 from the differential pressure sensor 9.

[0023] In step S2, the freezing determination unit 102 determines whether the differential pressure DP input in step S1 is in a maximum state, that is, whether it is equal to or greater than threshold 1 set between the clogging determination threshold and the upper limit of the output range of the differential pressure sensor 9. If it is equal to or greater than threshold 1 (see characteristic line 301 in FIG. 3), the process proceeds to step S5, and if it is below threshold 1, the process proceeds to step S3. In step S3, the freezing determination unit 102 determines whether the differential pressure DP input in step S1 is in a minimum state, that is, whether it is equal to or less than threshold 2 set between the drop determination threshold and the lower limit of the output range of the differential pressure sensor 9. If it is equal to or less than threshold 2 (see characteristic line 302 in FIG. 3), the process proceeds to step S5, and if it exceeds threshold 2, the process proceeds to step S4. In step S4, the freezing determination unit 102 determines whether the differential pressure DP input in step S1 is in a state where no differential pressure is occurring, that is, whether it is within a predetermined range including 0 (a range within ±threshold value 3). If it is within the predetermined range (see characteristic line 303 in FIG. 3), the process proceeds to step S5, and if it is not within the predetermined range, the process returns to step S1.

[0024] In step S5, the freezing determination unit 102 determines whether the differential pressure DP is equal to or greater than threshold value 1, equal to or less than threshold value 2, or within a predetermined range for a predetermined period of time. If it has continued for the predetermined period of time, the process proceeds to step S6, and if it has not continued for the predetermined period of time, the process returns to step S1. In step S6, the notification unit 103 determines that the differential pressure detection unit 10 is frozen and notifies the driver. For example, a warning light notifying of clogging or loss of the GPF 7 is flashed. Also, the ECU 100 stops diagnosing the state (clogging, loss) of the GPF 7. 4(a) is executed for a predetermined period of time after the engine 1 is started, but may be executed as appropriate while the engine 1 is running. This is because the differential pressure detection passage 8 and the differential pressure sensor 9 may freeze due to wind generated while the vehicle is traveling.

[0025] Fig. 4(b) shows a process for canceling the frozen determination of the differential pressure detection unit 10. The flowchart of Fig. 4(b) is executed after it is determined in the flowchart of Fig. 4(a) that the differential pressure detection unit 10 is frozen. In step S7, the input unit 101 inputs the differential pressure DP between the upstream pressure and the downstream pressure of the GPF 7 from the differential pressure sensor 9. In step S8, the freeze determination unit 102 determines whether the differential pressure DP input in step S7 has returned to the normal range. If it has returned to the normal range, the process proceeds to step S9. If it has not returned to the normal range, the process returns to step S7. In the example of the characteristic line 301 in FIG. 3, at the timing t 1 The differential pressure DP has returned to the normal range. In step S9, the notification unit 103 determines that the differential pressure detection unit 10 is no longer frozen, releases the frozen determination, and notifies the driver. For example, the warning light that was blinked in step S6 is turned off. In addition, the ECU 100 resumes the diagnosis of the state (clogging, loss) of the GPF 7 that was stopped in step S6.

[0026] As described above, instead of estimating the non-frozen state based on the exhaust temperature of the internal combustion engine or the atmospheric temperature as in Patent Document 1, the change in the differential pressure DP detected by the differential pressure sensor 9 when the differential pressure detection unit 10 freezes is captured, making it possible to more accurately diagnose the frozen state of the differential pressure detection unit 10. Furthermore, if any of the maximum state, minimum state, and no differential pressure state continues for a predetermined time, it is determined that the differential pressure detection unit 10 is frozen, thereby preventing erroneous determination that the differential pressure detection unit 10 is frozen. Depending on the situation, the differential pressure DP may fluctuate instantaneously, causing the detection of the maximum state, minimum state, or no differential pressure state, but by requiring that the state continue for a predetermined time, such instantaneous fluctuations in the differential pressure DP can be eliminated.

[0027] Although the embodiments of the present invention have been described in detail above with reference to the drawings, each embodiment merely shows a specific example of the implementation of the present invention. The technical scope of the present invention is not limited to each embodiment. Various modifications of the present invention are possible without departing from the spirit of the present invention, and these modifications are also included in the technical scope of the present invention. In this embodiment, the GPF 7 has been described as the filter of the present invention, but the present invention is not limited to this and may be applied to, for example, a DPF (diesel particulate filter). A freezing diagnosis device to which the present invention is applied is configured by a computer device equipped with, for example, a CPU, ROM, RAM, etc., and the functions of each means are realized by the CPU executing a predetermined program stored, for example, in the ROM. [Explanation of symbols]

[0028] 1: engine, 2: intake passage, 3: exhaust passage, 7: GPF, 8: differential pressure detection passage, 9: differential pressure sensor, 10: differential pressure detection unit, 100: ECU, 101: input unit, 102: freeze determination unit, 103: notification unit

Claims

1. 1. An exhaust purification system for an internal combustion engine, the system comprising: a filter disposed in an exhaust passage through which exhaust gas from the internal combustion engine passes; a differential pressure detection passage connected to the exhaust passage and bypassing the filter; and a differential pressure detection section constituted by a differential pressure sensor disposed in the differential pressure detection passage and detecting a differential pressure between an upstream pressure and a downstream pressure of the filter, the system comprising: A freeze diagnosis device for an exhaust purification system of an internal combustion engine, comprising a determination means for determining that the differential pressure detection unit is frozen when the differential pressure detected by the differential pressure sensor corresponds to any of an extremely maximum state, an extremely minimum state, and a state in which no differential pressure is occurring.

2. 2. The freeze diagnosis device for an exhaust gas purification system of an internal combustion engine according to claim 1, wherein the determination means determines that the differential pressure detection unit is frozen when any of the extremely maximum state, the extremely minimum state, and the state in which no differential pressure is generated continues for a predetermined period of time.

3. The maximum state is a state in which the differential pressure detected by the differential pressure sensor is equal to or greater than a first threshold value set between a threshold value for determining whether the filter is clogged and an upper limit of an output range of the differential pressure sensor, 3. The freeze diagnosis device for an exhaust gas purification system of an internal combustion engine as described in claim 1 or 2, characterized in that the extremely minimum state is a state in which the differential pressure detected by the differential pressure sensor is equal to or lower than a second threshold value set between a threshold value for determining whether the filter has come off and a lower limit of an output range of the differential pressure sensor.

4. 3. A freeze diagnosis device for an exhaust gas purification system of an internal combustion engine as claimed in claim 1, wherein the state in which no differential pressure is generated is a state in which the differential pressure detected by the differential pressure sensor is within a predetermined range including 0.

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