阅读说明：本技术 氧传感器的响应性诊断方法及废气净化系统 (Oxygen sensor responsiveness diagnosis method and exhaust gas purification system ) 是由 西方彰朗 村泽直人 于 2020-03-06 设计创作，主要内容包括：本公开的废气净化装置的ECU(110)具有：输入部(111),输入氧传感器(121、122)的检测结果λ1、λ2；减少/增加时间计算部(112),在LNT(101)从稀燃控制转移到浓燃控制时或从浓燃控制转移到稀燃控制时,求出λ1、λ2各自从第一值X1减少到第二值X2所需的减少时间Δt1、Δt2或从第三值X3增加到第四值X4所需的增加时间Δt3、Δt4；以及判断部(113),基于λ1的减少时间Δt1与λ2的减少时间Δt2的差|Δt1-Δt2|或λ1的增加时间Δt3与λ2的增加时间Δt4的差|Δt3-Δt4|,判断氧传感器(121、122)的响应性。(An ECU (110) of an exhaust gas purification device of the present disclosure includes: an input unit (111) for inputting the detection results (lambda 1, lambda 2) of the oxygen sensors (121, 122); a decrease/increase time calculation unit (112) that, when the LNT (101) is shifted from lean control to rich control or from rich control to lean control, determines decrease times Δ t1 and Δ t2 for λ 1 and λ 2 to decrease from the first value X1 to the second value X2 or increase times Δ t3 and Δ t4 for λ 1 and λ 2 to increase from the third value X3 to the fourth value X4, respectively; and a determination unit (113) that determines the responsiveness of the oxygen sensors (121, 122) based on the difference | Δ t1- Δ t2| between the decrease time Δ t1 of λ 1 and the decrease time Δ t2 of λ 2 or the difference | Δ t3- Δ t4| between the increase time Δ t3 of λ 1 and the increase time Δ t4 of λ 2.)

1. A responsiveness diagnostic method for an oxygen sensor, characterized by comprising the steps of:

a step of inputting a first detection result that is a detection result of a first oxygen sensor provided on an upstream side of an NOx occlusion reduction catalyst and a second detection result that is a detection result of a second oxygen sensor provided on a downstream side of the NOx occlusion reduction catalyst;

a step of obtaining a decrease time required for the first detection result and the second detection result to decrease from a first value to a second value or an increase time required for the NOx occlusion reduction catalyst to increase from a third value to a fourth value, respectively, when the NOx occlusion reduction catalyst is shifted from lean control to rich control or from rich control to lean control; and

determining the responsiveness of the first oxygen sensor and the second oxygen sensor based on a difference between the decrease time of the first detection result and the decrease time of the second detection result or a difference between the increase time of the first detection result and the increase time of the second detection result.

2. The responsiveness diagnostic method of an oxygen sensor according to claim 1,

when the difference in the decrease time or the difference in the increase time is equal to or greater than a predetermined value, it is determined that the oxygen sensor of the first oxygen sensor or the second oxygen sensor that has a longer decrease time or a longer increase time has decreased in responsiveness.

3. The responsiveness diagnostic method of an oxygen sensor according to claim 1,

in the step performed when shifting from the lean control to the rich control or from the rich control to the lean control, the step performed when shifting from the rich control to the lean control is performed with priority over the step performed when shifting from the lean control to the rich control.

4. An exhaust gas purification system, comprising:

an NOx occlusion reduction catalyst;

a first oxygen sensor provided on an upstream side of the NOx occlusion reduction catalyst;

a second oxygen sensor provided on the downstream side of the NOx occlusion reduction catalyst;

an input section that inputs a first detection result and a second detection result, the first detection result being a detection result of the first oxygen sensor, the second detection result being a detection result of the second oxygen sensor;

a decrease/increase time calculation unit that obtains a decrease time required for the first detection result and the second detection result to decrease from a first value to a second value or an increase time required for the NOx occlusion reduction catalyst to increase from a third value to a fourth value, when the NOx occlusion reduction catalyst is shifted from lean control to rich control or from rich control to lean control; and

and a determination unit configured to determine the responsiveness of the first oxygen sensor and the second oxygen sensor based on a difference between the decrease time of the first detection result and the decrease time of the second detection result or a difference between the increase time of the first detection result and the increase time of the second detection result.

5. An exhaust gas purification system as set forth in claim 4,

when the difference in the decrease time or the difference in the increase time is equal to or greater than a predetermined value, the determination unit determines that the oxygen sensor of the first oxygen sensor or the second oxygen sensor that has a longer decrease time or a longer increase time has decreased in responsiveness.

Technical Field

The present disclosure relates to a responsiveness diagnostic method of an oxygen sensor that monitors an air-fuel ratio of an internal combustion engine, and an exhaust gas purification system.

Background

As an exhaust gas purifying apparatus for an internal combustion engine, an NOx occlusion reduction type catalyst (Lean NOx Trap: hereinafter referred to as "LNT") is known (for example, see patent document 1). The LNT stores NOx in the exhaust gas in a lean state of the air-fuel ratio of the exhaust gas, and reacts the stored NOx with CO, HC, or the like in the exhaust gas in a rich state of the air-fuel ratio of the exhaust gas to reduce the stored NOx into harmless gas such as nitrogen gas and release the gas. LNTs are described in, for example, patent documents 1 and 2.

In the LNT, an oxygen sensor is generally provided to detect an excess air ratio (λ) of exhaust gas. The excess air ratio (λ) detected by the oxygen sensor can be obtained from λ ═ the actual air-fuel ratio of the air-fuel mixture/the theoretical air-fuel ratio. An engine control unit of an internal combustion engine controls the engine based on an air excess ratio (lambda) detected by an oxygen sensor and a target average air-fuel ratio which is a target air-fuel ratio. Incidentally, in the control of the diesel engine, engine control using the excess air ratio (λ) as an index is performed particularly at a rich air-fuel ratio (at the time of LNT reduction). For example, patent document 3 discloses control of an oxygen sensor and an engine using the oxygen sensor.

As described above, the oxygen sensor plays an important role in controlling the air-fuel ratio of the engine, and therefore, it is necessary to constantly monitor whether the response performance thereof is normal. As a method of diagnosing the response performance of the oxygen sensor, there is a method of: the change in the output value of the oxygen sensor at the time of fuel cut (Q cut) was evaluated. Specifically, the time from the fuel cut until the output value of the oxygen sensor reaches a predetermined value is measured, and it is diagnosed that the responsiveness has decreased as the time is longer.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2017-203409

Patent document 2: japanese patent laid-open publication No. 2019-007424

Patent document 3: japanese patent laid-open publication No. 2011-185097

Disclosure of Invention

Problems to be solved by the invention

However, the diagnostic method of the oxygen sensor described above is based on the basic principle of observing the responsiveness of the oxygen sensor when the oxygen concentration sharply increases due to a fuel cut. However, since the range of change in the oxygen concentration at the time of fuel cut is inherently small, it may be difficult to perform highly reliable diagnosis simply by diagnosing the responsiveness of the oxygen sensor based on the output value of the oxygen sensor at the time of fuel cut.

For example, it is assumed that the exhaust gas oxygen concentration before fuel cut is about 10%, and the exhaust gas oxygen concentration after fuel cut is about 21%. If the exhaust gas oxygen concentration is the above-assumed exhaust gas oxygen concentration, the range of variation in oxygen concentration at the time of fuel cut can be secured, and therefore there is no problem. However, the exhaust gas oxygen concentration before the fuel cut largely depends on the accelerator operation by the driver or the like. For example, if the exhaust gas oxygen concentration before the fuel cut is far below 10%, the change in the exhaust gas oxygen concentration at the time of the fuel cut is large and thus the reliability of the responsiveness diagnosis is high, but if the exhaust gas oxygen concentration before the fuel cut is far above 10%, for example, the change in the exhaust gas oxygen concentration at the time of the fuel cut is small and thus the reliability of the responsiveness diagnosis is low.

Specifically, if the change in the exhaust gas oxygen concentration at the time of fuel cut is small, the time from the time of fuel cut until the output value of the oxygen sensor reaches the predetermined value does not change substantially between the case where the responsiveness of the oxygen sensor is good and the case where the responsiveness is not good.

To avoid this, it is conceivable to perform the responsiveness diagnosis only when the change in the exhaust gas oxygen concentration during the fuel cut is large, for example, only when the exhaust gas oxygen concentration before the fuel cut is far below 10%. However, in this case, the frequency of the responsive diagnosis is reduced, and as a result, the reliability of the responsive diagnosis is lowered.

An object of the present disclosure is to provide a responsiveness diagnosis method for an oxygen sensor and an exhaust gas purification system, which can improve the reliability of responsiveness diagnosis of the oxygen sensor.

Means for solving the problems

A responsiveness diagnostic method for an oxygen sensor according to an embodiment of the present disclosure includes the steps of:

a step of inputting a first detection result that is a detection result of a first oxygen sensor provided on an upstream side of an NOx occlusion reduction catalyst and a second detection result that is a detection result of a second oxygen sensor provided on a downstream side of the NOx occlusion reduction catalyst;

a step of obtaining a decrease time required for the first detection result and the second detection result to decrease from a first value to a second value or an increase time required for the NOx occlusion reduction catalyst to increase from a third value to a fourth value, respectively, when the NOx occlusion reduction catalyst is shifted from lean control to rich control or from rich control to lean control; and

determining the responsiveness of the first oxygen sensor and the second oxygen sensor based on a difference between the decrease time of the first detection result and the decrease time of the second detection result or a difference between the increase time of the first detection result and the increase time of the second detection result.

An exhaust gas purification system according to an aspect of the present disclosure includes:

an NOx occlusion reduction catalyst;

a first oxygen sensor provided on an upstream side of the NOx occlusion reduction catalyst;

a second oxygen sensor provided on the downstream side of the NOx occlusion reduction catalyst;

an input section that inputs a first detection result and a second detection result, the first detection result being a detection result of the first oxygen sensor, the second detection result being a detection result of the second oxygen sensor;

a decrease/increase time calculation unit that obtains a decrease time required for the first detection result and the second detection result to decrease from a first value to a second value or an increase time required for the NOx occlusion reduction catalyst to increase from a third value to a fourth value, when the NOx occlusion reduction catalyst is shifted from lean control to rich control or from rich control to lean control; and

and a determination unit configured to determine the responsiveness of the first oxygen sensor and the second oxygen sensor based on a difference between the decrease time of the first detection result and the decrease time of the second detection result or a difference between the increase time of the first detection result and the increase time of the second detection result.

Effects of the invention

According to the present disclosure, since the method of comparing the difference between the time required for the decrease or increase in the output value of the oxygen sensor on the upstream side and the downstream side of the NOx occlusion reduction catalyst is adopted, the reliability of the responsiveness diagnosis of the oxygen sensor can be improved.

Drawings

FIG. 1 is a diagram showing the configuration of a main part of an exhaust gas purification system to which a method for diagnosing the responsiveness of an oxygen sensor according to an embodiment is applied,

FIG. 2 is a functional block diagram of an ECU (Electronic Control Unit) for implementing the diagnosis of the responsiveness of the oxygen sensor of the embodiment,

FIG. 3 is a waveform diagram showing the detection result of the oxygen sensor at the time of rich spike (rich spike),

fig. 4 is an enlarged view of a waveform in the vicinity of a section (transition section 1) for transition from the lean control to the rich control in the waveform diagram of fig. 3,

FIG. 5 is a waveform diagram in the case where the responsiveness of one of the oxygen sensors has decreased,

fig. 6 is a flowchart showing diagnostic processing steps executed by the ECU.

Detailed Description

The embodiments will be described in detail below with reference to the drawings.

<1> Structure of exhaust gas purification System

Fig. 1 is a diagram showing the configuration of a main part of an exhaust gas purification system 100 to which the oxygen sensor responsiveness diagnosis method of the present embodiment is applied. In the present embodiment, a mode in which the oxygen sensor responsiveness diagnosis method of the present disclosure is applied to the exhaust gas purification system 100 of the diesel engine 10 will be described as an example. However, the responsiveness diagnostic method for an oxygen sensor according to the present embodiment is not limited to being applied to the exhaust gas purification system 100 of the diesel engine 10, and may be applied to an exhaust gas purification system of a gasoline engine.

The exhaust gas purification system 100 is mounted on a vehicle such as a truck, for example, and purifies NOx in the exhaust gas of the engine 10.

The engine 10 is configured to include, for example, a combustion chamber and a fuel injection device that injects fuel into the combustion chamber. The engine 10 generates power by combusting and expanding a mixture of fuel and air in a combustion chamber. An intake pipe 20 for introducing air into the combustion chamber and an exhaust pipe 30 for discharging combusted exhaust gas discharged from the combustion chamber to the outside of the vehicle are connected to the engine 10.

The exhaust gas purification system 100 includes an LNT (Lean NOx Trap) 101, a DPF (Diesel Particulate Filter) 102, an SCR (Selective Catalytic Reduction) 103, and an ECU (Electronic Control Unit) 110. In reality, the exhaust gas purification system 100 has other configurations such as a urea water injection device, but these configurations are omitted in fig. 1.

The LNT101 adsorbs NOx in the exhaust gas in a state where the air-fuel ratio of the exhaust gas is lean. In addition, the LNT101 reacts the stored NOx with CO, HC, or the like in the exhaust gas in a state where the air-fuel ratio of the exhaust gas is rich, and reduces the NOx to harmless gas such as nitrogen gas, and releases the gas. Note that when the LNT101 approaches the saturation state, the efficiency with which NOx can be stored decreases. Therefore, the ECU110 monitors the NOx occlusion state of the LNT101, and periodically performs regeneration (also referred to as "rich spike") of the LNT 101.

The DPF102 traps particulate matter contained in the exhaust gas.

The SCR103 adsorbs ammonia obtained by hydrolyzing urea water supplied from a urea water injection device (not shown), and selectively reduces and purifies NOx from exhaust gas by the adsorbed ammonia.

The ECU110 controls the operation of the exhaust gas purification system 100. ECU110 controls injection from a fuel injection device of engine 10. Further, the ECU110 performs rich control for realizing rich spike and the like based on the information of the NOx occlusion state of the LNT 101.

The ECU110 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input port, an output port, and the like. Each function of the ECU110, which will be described later, is realized by the CPU referring to a control program and various data stored in the ROM, the RAM, and the like. However, it is needless to say that the function is not limited to the processing by software, and may be realized by a dedicated hardware circuit.

The ECU110 acquires the state of the urea solution injection device (not shown) and controls the urea solution injection device. The ECU110 acquires sensor information from an oxygen sensor 121 disposed on the upstream side of the LNT101, an oxygen sensor 122 disposed on the downstream side of the LNT101, or other sensors not shown, and detects the state of the exhaust gas flowing through the exhaust pipe 30, the state of the LNT101, the state of the DPF102, the state of the SCR103, and the like based on the sensor information.

<2> diagnosis of responsiveness of oxygen sensor of the present embodiment

The ECU110 has a function of diagnosing the response performance of the oxygen sensors 121, 122.

Fig. 2 shows a functional block diagram of the ECU110 for implementing the diagnosis of the responsiveness of the oxygen sensor according to the present embodiment. As described above, the function may be realized by software or may be realized by a dedicated hardware circuit.

Fig. 3 is a waveform diagram showing detection results λ 1, λ 2 of the oxygen sensors 121, 122 at the time of rich spike.

Fig. 4 is an enlarged view of a waveform in the vicinity of a section (transition section 1) in which the lean control is shifted to the rich control in the waveform diagram of fig. 3.

As shown in fig. 2, the ECU110 has an input section 111, a decrease/increase time calculation section 112, and a determination section 113.

The input unit 111 inputs the detection result λ 1 of the oxygen sensor 121 and the detection result λ 2 of the oxygen sensor 122.

The decrease/increase time calculation unit 112 determines the decrease times Δ t1 and Δ t2 required for the detection results λ 1 and λ 2 to decrease from the first value X1 (fig. 4) to the second value X2 (fig. 4) and the increase times Δ t3 and Δ t4 required for the detection results λ 2 to increase from the third value X3 to the fourth value X4, respectively, when the LNT101 transitions from lean control to rich control (corresponding to transition interval 1 in fig. 3) or from rich control to lean control (corresponding to transition interval 2 in fig. 3).

Here, it is preferable that the above-described values X1 and X2 are values that are as far apart from each other as possible within a range in which both the detection results λ 1, λ 2 exist in the transition section 1. Likewise, it is preferable that the above-described values X3 and X4 are values that are as far apart from each other as possible within a range in which both the detection results λ 1, λ 2 in the transition section 2 exist. In the present embodiment, for example, X1 is set to 1.4, and X2 is set to 1.1.

It should be noted that, since the increase times Δ t3 and Δ t4 can be obtained in the same manner as the decrease times Δ t1 and Δ t2, only the values X1 and X2 and the decrease times Δ t1 and Δ t2 are shown in the drawing.

The determination unit 113 determines the responsiveness of the oxygen sensors 121 and 122 based on the difference | Δ t1- Δ t2| between the decrease time Δ t1 of the detection result λ 1 and the decrease time Δ t2 of the detection result λ 2, or the difference | Δ t3- Δ t4| between the increase time Δ t3 of the detection result λ 1 and the increase time Δ t4 of the detection result λ 2. The determination unit 113 outputs the determination result to, for example, a display (not shown) of the vehicle.

Fig. 6 is a flowchart showing diagnostic processing steps executed by the ECU 110.

The ECU110 determines in step S1 whether the LNT101 has shifted from the lean control to the rich control, or whether it has shifted from the rich control to the lean control. Here, the ECU110 grasps the timing at which the rich spike is performed, and therefore also grasps the timing of the transition from the lean control to the rich control and the timing of the transition from the rich control to the lean control. Incidentally, in general, the rich spike is performed several times every 30 minutes. Accordingly, the responsiveness diagnosis according to the present embodiment is also performed several times every 30 minutes. The number of times varies depending on the NOx occlusion state of LNT101, and the like.

If an affirmative decision is made in step S1, the ECU110 proceeds to step S2. In step S2, the decrease/increase time calculation unit 112 of the ECU110 calculates Δ t1 from the detection value λ 1 and Δ t2 from the detection value λ 2, as shown in fig. 4.

In the next step S3, the determination unit 113 of the ECU110 compares the difference | Δ t1- Δ t2| between the reduction time Δ t1 and the reduction time Δ t2 with a predetermined threshold Th 1. When the difference | Δ t1- Δ t2| is lower than the threshold Th1 (no in step S3), the determination unit 113 proceeds to step S4 and determines that the responsiveness of the oxygen sensors 121 and 122 is normal.

On the other hand, when the difference | Δ t1- Δ t2| is equal to or greater than the threshold Th1 (step S3: yes), the determination unit 113 proceeds to step S5. In step S5, the determination unit 113 compares the magnitudes of Δ t1 and Δ t 2. When determining that Δ t1 is greater than Δ t2 (step S5: "yes"), the determination unit 113 proceeds to step S6 and determines that the responsiveness of the oxygen sensor 121 has decreased. On the other hand, if a negative result is obtained in step S5 (step S5: NO), the determination unit 113 proceeds to step S7, and determines that the responsiveness of the oxygen sensor 122 has decreased.

Here, the case where it is determined in step S4 that the responsiveness of the oxygen sensors 121 and 122 is normal is the case where λ 1 and λ 2 as shown in fig. 4 are obtained, for example. On the other hand, the case where it is determined that the responsiveness of the oxygen sensor 122 has decreased as in step S7 is, for example, the case where λ 1 and λ 2 as shown in fig. 5 are obtained. That is, the slope of λ 2 is gentle. Although not shown, the slope of λ 1 is relatively gentle when it is determined that the responsiveness of the oxygen sensor 121 has decreased as in step S6.

Incidentally, in fig. 4 and the like, the detection result λ 2 of the downstream oxygen sensor 122 is slightly shifted in a delayed direction on the time axis compared with the detection result λ 1 of the upstream oxygen sensor 121 because the oxygen sensor 122 is provided on the downstream side of the oxygen sensor 121 and it takes time for the exhaust gas to move the distance.

<3> summary

As described above, according to the present embodiment, the presence or absence of an oxygen sensor whose responsiveness has decreased is compared based on the difference | Δ t1, Δ t2| (| Δ t3, Δ t4|) of the time Δ t1, Δ t2(Δ t3, Δ t4) required for the decrease or increase of the two oxygen sensors 121, 122, and when the difference is equal to or greater than the threshold Th1, it is determined that the responsiveness of the oxygen sensor whose time required for the decrease or increase is longer has decreased, whereby the reliability of the responsiveness diagnosis of the oxygen sensor can be improved.

Here, the responsiveness diagnostic method for the oxygen sensor according to the above-described embodiment is based on the assumption that there is no case where the responsiveness of both the upstream and downstream oxygen sensors of the LNT101 decreases at the same time and the degree of the decrease is the same. On such a premise, the oxygen sensor whose responsiveness has been reduced is searched for by comparing the detection results of the two oxygen sensors.

However, as is clear from fig. 3, 4, and the like, in the rich control interval, when regeneration of the LNT101 proceeds, the value of the detection result λ 2 of the downstream-side oxygen sensor 122 also decreases. That is, the value of λ 2 at the end time point becomes smaller than the value of λ 2 at the start time point of the rich control. As a result, X3 and X4 set for increasing can be set to values farther from each other than X1 and X2 set for decreasing. That is, it is possible to set (X1-X2) < (X3-X4).

In view of this, it is more preferable that the diagnosis of responsiveness using the difference described in the above-described embodiment is performed when shifting from the rich control to the lean control. Of course, the diagnosis using the differential responsiveness described in the above embodiment may be performed at either one of the two timings when the control is shifted from the lean control to the rich control and when the control is shifted from the rich control to the lean control, or at both of the two timings when the control is shifted from the lean control to the rich control and when the control is shifted from the rich control to the lean control.

Further, since the sensor characteristics of the oxygen sensors 121, 122 are different in many cases when shifting from the rich control to the lean control and when shifting from the lean control to the rich control, it is more preferable in view of this that both timings are performed when shifting from the lean control to the rich control and when shifting from the rich control to the lean control. This can further improve the diagnostic accuracy of the responsive diagnosis.

The above-described embodiments are merely specific examples for carrying out the present disclosure, and the technical scope of the present disclosure is not to be construed in a limiting manner. That is, the present disclosure can be implemented in various forms without departing from the spirit or main features thereof.

In the above-described embodiment, the case where the responsiveness diagnosis method of the oxygen sensor of the present disclosure is executed at the time of rich spike has been described, but the responsiveness diagnosis method of the oxygen sensor of the present disclosure may be executed at the time of fuel cut (Q cut), for example.

The present application claims priority based on japanese patent application No. 2019-042439 filed on 8/3/2019. The contents described in the specification and drawings of this application are all incorporated in the specification of this application.

Industrial applicability

The present disclosure is suitable as a method and an apparatus for performing a response diagnosis on an oxygen sensor provided in an exhaust gas purification system.

Description of the reference numerals

10 engines

20 air inlet pipe

30 exhaust pipe

100 exhaust gas purification system

101LNT (Lean NOx Trap)

102DPF (Diesel Particulate Filter)

103SCR (Selective Catalytic Reduction catalyst)

110: ECU (Electronic Control Unit)

111 input unit

112 decrease/increase time calculation section

113 determination unit

121. 122 oxygen sensor