Abnormality diagnosis device for gas sensor

Abstract

The present invention addresses the problem of providing an abnormality diagnosis device for a gas sensor in which a decrease in diagnosis accuracy is suppressed. This abnormality diagnosis device for a gas sensor increases and decreases the air-fuel ratio of exhaust gas flowing through an exhaust passage of an engine having a port injection valve and an in-cylinder injection valve by increasing and decreasing the total fuel injection amount from the port injection valve and the in-cylinder injection valve at a predetermined cycle. The abnormality diagnosis device for a gas sensor is provided with: a determination unit that determines whether or not the rate of change of the ratio of the injection amount from the intake port injection valve to the total fuel injection amount is equal to or less than a predetermined value, and that diagnoses the abnormality of the gas sensor on the basis of the output value of the gas sensor provided in the exhaust passage; and a permission unit that permits the diagnosis of the abnormality of the gas sensor when the determination unit has made a positive determination.

Description

Technical Field

[0001] This invention relates to a device for diagnosing malfunctions in gas sensors. Background Technology

[0002] There is a gas sensor malfunction diagnostic device that increases or decreases the fuel injection quantity from the fuel injection valve at a predetermined cycle to increase or decrease the air-fuel ratio of the exhaust gas flowing in the exhaust passage of the engine, and diagnoses the malfunction of the gas sensor based on the output value of the gas sensor provided in the exhaust passage (see, for example, Patent Document 1).

[0003] Existing technical documents

[0004] Patent Document 1: Japanese Patent Application Publication No. 2003-013792 Summary of the Invention

[0005] The problem that the invention aims to solve

[0006] The engine has both port injection valves and in-cylinder injection valves. When the ratio of the fuel injection quantity from the port injection valves to the total fuel injection quantity from both the port injection valves and the in-cylinder injection valves changes significantly, the air-fuel ratio of the exhaust gas may also change significantly. Therefore, when such a ratio changes significantly during the diagnosis of anomalies in gas sensors as described above, the diagnostic accuracy may decrease.

[0007] Therefore, the object of the present invention is to provide an abnormality diagnostic device for a gas sensor that suppresses the decline in diagnostic accuracy.

[0008] Methods for solving problems

[0009] The aforementioned objective can be achieved by a gas sensor malfunction diagnostic device that increases or decreases the total fuel injection quantity from the intake port injection valve and the cylinder injection valve at a predetermined cycle, thereby increasing or decreasing the air-fuel ratio of the exhaust gas flowing in the exhaust passage of an engine having the intake port injection valve and the cylinder injection valve, and diagnoses malfunctions of the gas sensor based on the output value of the gas sensor provided in the exhaust passage. The gas sensor malfunction diagnostic device includes: a determination unit that determines whether the rate of change of the ratio of the injection quantity from the intake port injection valve to the total fuel injection quantity is below a predetermined value; and an approval unit that, if the determination unit makes an affirmative determination, approves the diagnosis of the gas sensor malfunction.

[0010] Invention Effects

[0011] According to the present invention, an abnormality diagnostic device for a gas sensor that suppresses the decline in diagnostic accuracy can be provided. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the engine's structure.

[0013] Figure 2 This is a flowchart illustrating the abnormal diagnostic control of the air-fuel ratio sensor performed by the ECU. Detailed Implementation

[0014] [Engine's general structure]

[0015] Figure 1 This is a schematic structural diagram of engine 10. Engine 10 is, for example, mounted in a vehicle. Engine 10 has multiple cylinders 11 in the cylinder block. Figure 1 (Only one is shown in the figure). The piston 12, located in the cylinder 11, is connected to the crankshaft 13 via the connecting rod 14. The reciprocating motion of the piston 12 is converted into the rotational motion of the crankshaft 13 by the connecting rod 14. A cylinder head is installed on the upper part of the cylinder block. A combustion chamber 15, in which a spark plug 16 is disposed, is formed between the cylinder head and the upper end of the piston 12. An intake passage 19 and an exhaust passage 20 are respectively connected to an intake port 17 and an exhaust port 18, which are provided corresponding to the combustion chamber 15.

[0016] A compressor 23A with a turbocharger 23 is installed in the intake passage 19. A turbine 23B with a turbocharger 23 is installed in the exhaust passage 20. Exhaust gas generated by combustion in the combustion chamber 15 of each cylinder is introduced into the turbine 23B of the turbocharger 23 through the exhaust manifold. When the turbine 23B operates with the introduced exhaust gas, the compressor 23A on the intake passage 19 side compresses the air on the intake passage 19 side in conjunction. By compressing the air, the pressure in the intake passage 19, i.e., the intake pressure, is increased, and air is efficiently filled into the combustion chamber 15 by this pressure.

[0017] In the intake passage 19, an air flow meter 92, an intake bypass passage 33, a boost pressure sensor 94, a throttle valve 22, and a throttle opening sensor 93 are provided from its upstream side. The intake bypass passage 33 bypasses the compressor 23A. An air bypass valve 34 is provided in the intake bypass passage 33. The throttle valve 22 adjusts the intake air volume by changing its opening. The intake passage 19 branches in the intake manifold located downstream of the throttle valve 22, and is connected to each combustion chamber 15 through this branch portion. An intake port injection valve 24 for injecting fuel into the intake port is provided in the intake passage 19. An in-cylinder injection valve 25 for injecting fuel into the cylinder 11 is provided. The air flow meter 92, the throttle opening sensor 93, and the boost pressure sensor 94 will be described later.

[0018] An exhaust bypass passage 35 bypassing the turbine 23B is provided in the exhaust passage 20. An exhaust gas pressure relief valve 36 is provided in the exhaust bypass passage 35. The exhaust gas pressure relief valve 36 regulates the boost pressure of the turbocharger 23. A catalyst 29 for purifying exhaust gas is provided downstream of the exhaust gas pressure relief valve 36. In addition, an air-fuel ratio sensor 95 is provided in the exhaust passage 20 upstream of the catalyst 29 and downstream of the exhaust bypass passage 35. The air-fuel ratio sensor 95 will be described later.

[0019] The engine 10 includes an intake valve 26 and an exhaust valve 27 that open and close the intake port 17 and exhaust port 18, which are respectively connected to the intake passage 19 and the exhaust passage 20. The intake valve 26 and the exhaust valve 27 open and close in sync with the rotation of the intake-side camshaft and the exhaust-side camshaft, which are driven and connected to the crankshaft 13. Thus, the intake valve 26 and the exhaust valve 27 are synchronized with the rotation of the crankshaft 13, that is, they are opened and closed at predetermined timings in sync with the reciprocating movement of each piston 12.

[0020] The intake variable valve timing mechanism (hereinafter referred to as intake VVT) 26a changes the opening and closing timing of the intake valve 26 by changing the phase of the rotation of the intake camshaft relative to the crankshaft 13. The exhaust variable valve timing mechanism (hereinafter referred to as exhaust VVT) 27a changes the opening and closing timing of the exhaust valve 27 by changing the phase of the rotation of the exhaust camshaft relative to the crankshaft 13. Thus, the opening periods of both the intake valve 26 and the exhaust valve 27, i.e., the valve overlap period, can be changed. The intake VVT ​​26a and exhaust VVT 27a are hydraulic, but not limited to this.

[0021] The ECU (Electronic Control Unit) 100 includes a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), and a storage device. The ECU 100 controls the engine 10 by executing programs stored in the ROM and the storage device. The ECU 100 is an example of a gas sensor anomaly diagnostic device. The ECU 100 functionally implements the determination and authorization units described later through the CPU, ROM, RAM, and storage device.

[0022] The ECU 100 controls the fuel injection quantity, ignition timing, throttle valve 22 opening degree, intake valve 26 and exhaust valve 27 opening and closing timing, air bypass valve 34 and exhaust gas pressure relief valve 36, etc., according to the operating state of the engine 10. The ECU 100 also controls the ratio of the injection quantity from the in-cylinder injection valve 25 to the total fuel injection quantity (i.e., the in-cylinder injection rate) and the ratio of the injection quantity from the intake port injection valve 24 to the total fuel injection quantity (i.e., the intake port injection rate), according to the operating state of the engine 10. Furthermore, the ECU 100 controls the intake VVT ​​26a and exhaust VVT 27a according to the operating state of the engine 10, thereby controlling the opening and closing timing of the intake valve 26 and exhaust valve 27.

[0023] ECU 100 performs predetermined calculations based on the detection signals from the various sensors mentioned above. For example, ECU 100 calculates the engine speed based on the detection signal from crankshaft angle sensor 90. ECU 100 calculates the opening of the accelerator pedal operated by the driver based on the detection signal from accelerator opening sensor 91. ECU 100 calculates the amount of air introduced into combustion chamber 15, i.e., the intake air volume, based on the detection signal from air flow meter 92. ECU 100 calculates the opening of throttle valve 22 based on the detection signal from throttle opening sensor 93. ECU 100 calculates the pressure of the intake air after being pressurized by compressor 23A, i.e., the actual boost pressure, based on the detection signal from boost pressure sensor 94. ECU 100 calculates the air-fuel ratio of the exhaust gas based on the detection signal from air-fuel ratio sensor 95. Air-fuel ratio sensor 95 is an example of a gas sensor; an oxygen sensor that detects the oxygen concentration of the exhaust gas can also be used instead of air-fuel ratio sensor 95.

[0024] [Diagnosis of air-fuel ratio sensor malfunctions]

[0025] Next, the abnormal diagnosis of the air-fuel ratio sensor 95 will be explained. When predetermined conditions are met, the ECU 100 performs an abnormal diagnosis of the air-fuel ratio sensor 95. In the abnormal diagnosis of the air-fuel ratio sensor 95, the total fuel injection quantity from the intake port injection valve 24 and the in-cylinder injection valve 25 is controlled to increase or decrease the air-fuel ratio of the exhaust gas, specifically, between the desired rich air-fuel ratio and lean air-fuel ratio. The air-fuel ratio sensor 95 is diagnosed as normal or abnormal based on the rate of change of its output voltage when the fuel injection quantity is increased or decreased in this way.

[0026] In anomaly diagnosis, this is based on the rate of change of the output voltage of the air-fuel ratio sensor 95 per unit time during the execution of the air-fuel ratio increase / decrease control of the exhaust gas. This is because the greater the rate of change of the air-fuel ratio of the exhaust gas supplied to the air-fuel ratio sensor 95, the greater the rate of change of the output voltage of the air-fuel ratio sensor 95. For example, if the absolute value of the rate of change of the air-fuel ratio sensor 95 is above a predetermined threshold, the air-fuel ratio sensor 95 has good responsiveness and is diagnosed as normal; if it is below the threshold, the responsiveness of the air-fuel ratio sensor 95 decreases and is diagnosed as abnormal.

[0027] Next, the impact of changes in the intake port injection rate on the accuracy of anomaly diagnosis by the air-fuel ratio sensor 95 will be explained. For example, consider a scenario where the total fuel injection quantity remains constant, but the intake port injection rate decreases significantly. Here, the intake port injection quantity is incrementally corrected for the amount of fuel adhering to the intake. Considering such an incremental correction of the intake port injection quantity, it is necessary to maintain the actual amount of fuel supplied for combustion and decrease the intake port injection rate to increase the in-cylinder injection rate. However, in reality, when the rate of change in the intake port injection rate is large, the amount of fuel used for combustion also changes, and the air-fuel ratio of the exhaust gas may fluctuate significantly. Therefore, when the air-fuel ratio of the exhaust gas fluctuates significantly due to changes in the intake port injection rate during the execution of anomaly diagnosis by the air-fuel ratio sensor 95, the accuracy of the anomaly diagnosis by the air-fuel ratio sensor 95 may decrease.

[0028] Furthermore, consider the following scenario where the intake injection rate changes significantly: When the engine 10's operating state shifts from the naturally aspirated region to the turbocharged region, the valve overlap period increases with turbocharged operation. This can sometimes lead to scavenging, where intake air is blown from the intake passage 19 through the cylinder 11 into the exhaust passage 20. Due to this scavenging, unburned fuel injected from the intake injection valve 24 may pass through the cylinder 11 and reach the catalyst 29, where it can burn. This can cause the catalyst 29 to overheat. To suppress this overheating of the catalyst 29, the intake injection rate is sometimes significantly reduced when the engine 10's operating state shifts from the naturally aspirated region to the turbocharged region. Similarly, the intake injection rate is sometimes significantly increased when the engine 10's operating state shifts from the turbocharged region to the naturally aspirated region.

[0029] Figure 2This is a flowchart illustrating the abnormal diagnosis control of the air-fuel ratio sensor 95 performed by the ECU 100. The ECU 100 determines whether the conditions for abnormal diagnosis of the air-fuel ratio sensor 95 are met (step S1). The abnormal diagnosis conditions are, for example, the engine 20 being in an idling state, the air-fuel ratio sensor 95 being in an active state, and the abnormal diagnosis not being completed after ignition is turned on. If the condition is no in step S1, this control ends. If the condition is yes in step S1, the ECU 100 determines whether the rate of change of the intake injection rate is below a predetermined value (step S2). The predetermined value is, for example, set as described above, as the minimum rate of change of the intake injection rate when the engine 10's operating state shifts from the naturally aspirated region to the boosted region or from the boosted region to the naturally aspirated region. Step S2 is an example of the processing performed by the determination unit. If the condition is no in step S2, this control ends. That is, abnormal diagnosis of the air-fuel ratio sensor 95 is not performed. If the condition is yes in step S2, the ECU 100 permits the execution of abnormal diagnosis of the air-fuel ratio sensor 95 (step S3), and performs abnormal diagnosis of the air-fuel ratio sensor 95 (step S4). Step S3 is an example of the processing performed by the permitting unit.

[0030] As described above, when the rate of change of the intake injection rate is below a predetermined value, abnormal diagnosis of the air-fuel ratio sensor 95 is permitted. Therefore, the decrease in the accuracy of abnormal diagnosis of the air-fuel ratio sensor 95 is suppressed.

[0031] The embodiments of the present invention have been described in detail above, but the present invention is not limited to these specific embodiments. Various modifications and alterations can be made within the scope of the spirit of the present invention as set forth in the claims.

[0032] Explanation of reference numerals in the attached figures

[0033] 10 Engines

[0034] 24. Inlet Injection Valve

[0035] 25-cylinder injection valve

[0036] 95 Air-fuel ratio sensor (gas sensor)

[0037] 100 ECU (Gas Sensor Abnormal Diagnosis Device, Judgment Unit, Permitting Unit).

Claims

1. A gas sensor malfunction diagnostic device, comprising increasing or decreasing the total fuel injection quantity from an intake port injection valve and a cylinder injection valve at predetermined intervals to increase or decrease the air-fuel ratio of exhaust gas flowing in the exhaust passage of an engine having said intake port injection valve and said cylinder injection valve, and diagnosing malfunctions of the gas sensor based on the output value of a gas sensor disposed in said exhaust passage. The gas sensor anomaly diagnosis device includes: The determination unit determines whether the rate of change of the ratio of the injection quantity from the intake port injection valve to the total fuel injection quantity is below a predetermined value; and The authorization department, upon receiving a positive determination from the determination department, authorizes the diagnosis of any abnormalities in the gas sensor.

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