Abnormality diagnosis device for gas sensor

Abstract

To provide an abnormality diagnostic device for a gas sensor capable of suppressing deterioration of diagnostic accuracy.SOLUTION: An abnormality diagnosis device for a gas sensor that diagnoses an abnormality of the gas sensor according to an output value of the gas sensor provided in an exhaust passage of an engine having a port injection valve and an in-cylinder injection valve, the abnormality diagnosis device increasing and decreasing a total fuel injection amount from the port injection valve and the in-cylinder injection valve in a predetermined cycle so that an air-fuel ratio of exhaust gas flowing through the exhaust passage increases and decreases, the abnormality diagnosis device comprising: A determination unit configured to determine whether a change rate of a ratio of an injection amount from the port injection valve to the total fuel injection amount is equal to or less than a predetermined value; SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an abnormality diagnosis device for a gas sensor. [Background technology]

[0002] There is a gas sensor abnormality diagnosis device that increases or decreases the amount of fuel injected from a fuel injection valve at a predetermined cycle so as to increase or decrease the air-fuel ratio of exhaust gas flowing through an engine's exhaust passage, and diagnoses abnormalities in the gas sensor based on the output value of a gas sensor installed in the exhaust passage (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-013792 Summary of the Invention [Problem to be solved by the invention]

[0004] Some engines are equipped with port injection valves and direct injection valves. If the ratio of the amount of fuel injected from the port injection valve to the total amount of fuel injected from the port injection valve and the direct injection valve changes significantly, the air-fuel ratio of the exhaust gas may also change significantly. Therefore, if this ratio changes significantly during the diagnosis of an abnormality in the gas sensor as described above, the diagnostic accuracy may decrease.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a gas sensor abnormality diagnostic device that suppresses a decrease in diagnostic accuracy. [Means for solving the problem]

[0006] The above object can be achieved by a gas sensor abnormality diagnosis device that increases or decreases the total fuel injection amount from the port injection valve and the in-cylinder injection valve at a predetermined cycle so as to increase or decrease the air-fuel ratio of exhaust gas flowing through the exhaust passage of an engine having the port injection valve and the in-cylinder injection valve, and diagnoses an abnormality in the gas sensor according to the output value of a gas sensor provided in the exhaust passage, the gas sensor abnormality diagnosis device comprising: a determination unit that determines whether the rate of change in the ratio of the injection amount from the port injection valve to the total fuel injection amount is equal to or less than a predetermined value; and an authorization unit that, when the determination unit makes a positive determination, authorizes the diagnosis of an abnormality in the gas sensor. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a gas sensor abnormality diagnosis device in which a decrease in diagnostic accuracy is suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic configuration diagram of an engine. [Figure 2] 4 is a flowchart illustrating an example of abnormality diagnosis control for an air-fuel ratio sensor executed by an ECU. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Engine outline] FIG. 1 is a schematic diagram of an engine 10. The engine 10 is mounted on, for example, a vehicle. The engine 10 has a cylinder block with a plurality of cylinders 11 (only one is shown in FIG. 1). A piston 12 provided in each cylinder 11 is connected to a crankshaft 13 via a connecting rod 14. The connecting rod 14 converts the reciprocating motion of the piston 12 into the rotational motion of the crankshaft 13. A cylinder head is attached to the top of the cylinder block. A combustion chamber 15 in which an ignition plug 16 is disposed is formed between the cylinder head and the upper end of the piston 12. An intake port 17 and an exhaust port 18 provided corresponding to the combustion chamber 15 are connected to an intake passage 19 and an exhaust passage 20, respectively.

[0010] A compressor 23A of the turbocharger 23 is disposed in the intake passage 19. A turbine 23B of the turbocharger 23 is disposed 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 introduced exhaust gas operates the turbine 23B, the compressor 23A on the intake passage 19 side operates in conjunction, compressing the air on the intake passage 19 side. As the air is compressed, the pressure inside the intake passage 19, i.e., the intake pressure, is increased, and this pressure efficiently fills the combustion chamber 15 with air.

[0011] The intake passage 19 is provided with 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, from the upstream side. The intake bypass passage 33 bypasses the compressor 23A. The intake bypass passage 33 is provided with an air bypass valve 34. The throttle valve 22 adjusts the intake air amount by changing its opening. The intake passage 19 branches at an intake manifold provided downstream of the throttle valve 22 in the intake direction, and is connected to each combustion chamber 15 through these branched portions. The intake passage 19 is provided with a port injection valve 24 that injects fuel toward the intake port. A direct injection valve 25 that injects fuel into the cylinder 11 is provided. The air flow meter 92, throttle opening sensor 93, and boost pressure sensor 94 will be described later.

[0012] An exhaust bypass passage 35 that bypasses the turbine 23B is provided in the exhaust passage 20. A wastegate valve 36 is provided in the exhaust bypass passage 35. The wastegate valve 36 adjusts the boost pressure of the turbocharger 23. A catalyst 29 that purifies exhaust gas is provided downstream of the wastegate valve 36. In addition, an air-fuel ratio sensor 95 is provided upstream of the catalyst 29 in the exhaust passage 20 and downstream of the exhaust bypass passage 35. The air-fuel ratio sensor 95 will be described later.

[0013] The engine 10 is equipped with an intake valve 26 and an exhaust valve 27 that respectively open and close an intake port 17 and an exhaust port 18 that are connected to an intake passage 19 and an exhaust passage 20. The intake valve 26 and the exhaust valve 27 open and close in accordance with the rotation of an intake-side camshaft and an exhaust-side camshaft that are drivingly connected to the crankshaft 13. As a result, the intake valve 26 and the exhaust valve 27 are driven to open and close in synchronization with the rotation of the crankshaft 13, that is, at predetermined timing corresponding to the reciprocating movement of each piston 12.

[0014] The intake variable valve mechanism (hereinafter referred to as intake VVT) 26a changes the opening and closing timing of the intake valve 26 by changing the rotation phase of the intake camshaft relative to the crankshaft 13. The exhaust variable valve mechanism (hereinafter referred to as exhaust VVT) 27a changes the opening and closing timing of the exhaust valve 27 by changing the rotation phase of the exhaust camshaft relative to the crankshaft 13. This makes it possible to change the valve overlap period, which is the period during which both the intake valve 26 and the exhaust valve 27 are open. The intake VVT ​​26a and the exhaust VVT 27a are hydraulic, but are not limited to this.

[0015] 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 abnormality diagnosis device. The ECU 100 functionally realizes a determination unit and an authorization unit, which will be described later, by using the CPU, ROM, RAM, and storage device.

[0016] The ECU 100 controls the fuel injection amount, ignition timing, the opening of the throttle valve 22, the opening and closing timings of the intake valve 26 and the exhaust valve 27, and the openings of the air bypass valve 34 and the wastegate valve 36, etc., according to the operating state of the engine 10. The ECU 100 controls the in-cylinder injection rate, which is the ratio of the injection amount from the in-cylinder injection valve 25 to the total fuel injection amount, and the port injection rate, which is the ratio of the injection amount from the port injection valve 24 to the total fuel injection amount, according to the operating state of the engine 10. The ECU 100 controls the opening and closing timings of the intake valve 26 and the exhaust valve 27 by controlling the intake VVT ​​26a and the exhaust VVT 27a according to the operating state of the engine 10.

[0017] The ECU 100 performs predetermined calculations based on detection signals from the various sensors described above. For example, the ECU 100 calculates the engine speed based on the detection signal from the crank angle sensor 90. The ECU 100 calculates the opening degree of the accelerator pedal operated by the driver based on the detection signal from the accelerator position sensor 91. The ECU 100 calculates the intake air amount, which is the amount of air introduced into the combustion chamber 15, based on the detection signal from the air flow meter 92. The ECU 100 calculates the opening degree of the throttle valve 22 based on the detection signal from the throttle position sensor 93. The ECU 100 calculates the actual boost pressure, which is the pressure of the intake air supercharged by the compressor 23A, based on the detection signal from the boost pressure sensor 94. The ECU 100 calculates the air-fuel ratio of the exhaust gas based on the detection signal from the air-fuel ratio sensor 95. The air-fuel ratio sensor 95 is an example of a gas sensor, and an oxygen sensor that detects the oxygen concentration of the exhaust gas may be provided instead of the air-fuel ratio sensor 95.

[0018] [Air-fuel ratio sensor abnormality diagnosis] Next, an abnormality diagnosis of the air-fuel ratio sensor 95 will be described. When a predetermined condition is met, the ECU 100 executes an abnormality diagnosis of the air-fuel ratio sensor 95. In the abnormality diagnosis of the air-fuel ratio sensor 95, the total fuel injection amount from the port injection valves 24 and the in-cylinder injection valves 25 is controlled so that the air-fuel ratio of the exhaust gas increases or decreases, specifically so that the air-fuel ratio increases or decreases between a desired rich air-fuel ratio and a desired lean air-fuel ratio. Whether the air-fuel ratio sensor 95 is normal or abnormal is diagnosed based on the rate of change of the output voltage of the air-fuel ratio sensor 95 when the fuel injection amount is increased or decreased in this way.

[0019] The abnormality diagnosis is thus performed based on the rate of change of the output voltage of the air-fuel ratio sensor 95 per unit time while control is being executed to increase or decrease the air-fuel ratio of the exhaust gas. This is because the rate of change of the output voltage of the air-fuel ratio sensor 95 increases as the rate of change of the air-fuel ratio of the exhaust gas supplied to the air-fuel ratio sensor 95 increases. For example, if the absolute value of the rate of change of the air-fuel ratio sensor 95 is equal to or greater than a predetermined threshold, the responsiveness of the air-fuel ratio sensor 95 is deemed to be good and the air-fuel ratio sensor 95 is diagnosed as normal, whereas if it is less than the threshold, the responsiveness of the air-fuel ratio sensor 95 is deemed to have decreased and the air-fuel ratio sensor 95 is diagnosed as abnormal.

[0020] Next, we will explain how changes in the port injection rate affect the accuracy of abnormality diagnosis of the air-fuel ratio sensor 95. For example, assume that the port injection rate significantly decreases even when the total fuel injection amount remains constant. Here, the port injection amount is increased by a correction amount corresponding to the amount of fuel deposited in the intake port. Taking this increase correction amount into account, it is necessary to decrease the port injection rate and increase the in-cylinder injection rate while maintaining the actual amount of fuel used for combustion. However, in reality, if the rate of change in the port injection rate is large, the amount of fuel used for combustion also changes, which could cause the air-fuel ratio of the exhaust gas to fluctuate significantly. Therefore, if the air-fuel ratio of the exhaust gas fluctuates significantly due to a change in the port injection rate while an abnormality diagnosis of the air-fuel ratio sensor 95 is being performed, the accuracy of the abnormality diagnosis of the air-fuel ratio sensor 95 could be reduced.

[0021] The port injection rate may change significantly in the following cases, for example: When the operating state of the engine 10 transitions from the naturally aspirated region to the supercharging region, the valve overlap period increases in response to the supercharging operation. This may result in scavenging, where intake air flows from the intake passage 19 through the cylinder 11 and into the exhaust passage 20. Scavenging may cause unburned fuel injected from the port injection valve 24 to pass through the cylinder 11 and reach the catalyst 29, where it may be burned. This may result in an overheating of the catalyst 29. To prevent such an overheating of the catalyst 29, the port injection rate may be significantly reduced when the operating state of the engine 10 transitions from the naturally aspirated region to the supercharging region. Similarly, the port injection rate may be significantly increased when the operating state of the engine 10 transitions from the supercharging region to the naturally aspirated region.

[0022] FIG. 2 is a flowchart illustrating an example of abnormality diagnosis control of the air-fuel ratio sensor 95 executed by the ECU 100. The ECU 100 determines whether or not a condition for abnormality diagnosis of the air-fuel ratio sensor 95 is met (step S1). The condition for abnormality diagnosis is, for example, when the engine 20 is in an idling state, the air-fuel ratio sensor 95 is in an activated state, and abnormality diagnosis has not been completed after the ignition is turned on. If the answer is No in step S1, this control ends. If the answer is Yes in step S1, the ECU 100 determines whether or not the rate of change of the port injection rate is equal to or less than a predetermined value (step S2). The predetermined value is set to, for example, the minimum value of the rate of change of the port injection rate when the operating state of the engine 10 transitions from the naturally aspirated region to the supercharged region, or from the supercharged region to the naturally aspirated region, as described above. Step S2 is an example of processing executed by the determination unit. If the answer is No in step S2, this control ends. That is, abnormality diagnosis of the air-fuel ratio sensor 95 is not executed. If the result of step S2 is Yes, the ECU 100 permits execution of abnormality diagnosis of the air-fuel ratio sensor 95 (step S3) and executes abnormality diagnosis of the air-fuel ratio sensor 95 (step S4). Step S3 is an example of processing executed by the permission unit.

[0023] As described above, when the rate of change of the port injection rate is equal to or less than a predetermined value, the abnormality diagnosis of the air-fuel ratio sensor 95 is permitted. Therefore, a decrease in the accuracy of the abnormality diagnosis of the air-fuel ratio sensor 95 is suppressed.

[0024] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0025] 10 Engine 24-port injection valve 25 In-cylinder injection valve 95 Air-fuel ratio sensor (gas sensor) 100 ECU (gas sensor abnormality diagnosis device, judgment unit, permission unit)

Claims

[Claim 1] 1. A gas sensor abnormality diagnosis device for an engine having a port injection valve and a direct injection valve, wherein a total fuel injection amount from the port injection valve and the direct injection valve is increased or decreased at a predetermined cycle so as to increase or decrease an air-fuel ratio of exhaust gas flowing through the exhaust passage, and the gas sensor abnormality diagnosis device diagnoses an abnormality in the gas sensor according to an output value of the gas sensor provided in the exhaust passage, a determination unit that determines whether a rate of change in a ratio of the injection amount from the port injection valve to the total fuel injection amount is equal to or less than a predetermined value; a permission unit that permits diagnosis of an abnormality of the gas sensor when the determination unit makes a positive determination; A gas sensor abnormality diagnosis device comprising:

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